The first Sadoul Lecture in

Eur Respir
1989, 2, 107-115
INTRODUCTION
The first Sadoul Lecture
K. B. Saunders*
The first Sadoul Lecture was given by J. G.
Widdicombe at the Athens Congress of our Society in
June, 1988. It forms an appropriate foil to the Cournand
Lecture which is reserved for younger investigators (less
than 40 yrs old) and commemorates a distinguished
French scientist who worked for much of his life in the
United States. This new lecture commemorates another
French scientist, Paul Sadoul, a founder member of this
Society and long-time editor of the Bulletin Europeen de
Physiopathologic Respiratoire, predecessor of this
Journal.
An invitation to give the Sadoul Lecture is intended to
honour senior European scientists with a world-wide
reputation. There could hardly be a more appropriate
choice than John Widdicombe to give the first lecture.
Educated at Oxford and Saint Bartholomew's Hospital,
London, he is also a Fellow of the Royal College of
Physicians of London, a rare honour for a non-practising
•St Geo~ge's Hospital Medical School, Cranmer Terrace, London SW17
ORE.
medical doctor. A series of prizes and titled lectureships
in Europe have decorated his career, in particular he was
an invited guest and lecturer at the Centennial Meeting
of the American Physiological Society, 1987.
His research interests have spanned the entire range of
respiratory physiology - gas exchange, mechanics, respiratory and cardiovascular reflexes, chemical control of
breathing, and so on. More recent interests have focussed
on airway secretions, bronchial circulation, and that
somewhat neglected respiratory organ, the nose. In a long
Executive Committee meeting in 1987, the one decision
reached immediately, unanimously, and "magna cum
laude", was the recommendation that J. G. Widdicombe
be asked to give the first Sadoul Lecture. The masterly
result is printed in this issue.
John Widdicombe is an honorary member of the
European Society for Clinical Respiratory Physiology.
Throughout the years he has contributed greatly to our
Society. He was our treasurer for six years. His judgement was highly valued in the Executive Committee and
on the scientific committee of many of our meetings.
SADOUL LECTURE
Airway mucus
J.G. Widdicombe
Airway mucus. J.G. Widdicombe.
ABSTRACT: Airway surface liquid (ASL), a mixture of perlclllary nuld
and submucosal gland secretions, was collected from the ferret Isolated
trachea in vitro. The trachea was closed, without possibility of evaporation. The collected ASL was hyperosmolar (310-350 mosmol·kg· 1) compared with Krebs-Henselelt solution (280 mosmol·kg'1). Compared with
surrounding Krebs-Henselelt solution, the ASL had higher sodium and
chloride contents, and considerably higher potassium and calcium contents. Tbe ASL was acid (pH about 7.00) compared with Krebs-Henseleit
solution (pH 7.40). Applying methacholine and salbutamol to the preparation significantly changed most of the electrolyte concentrations, and
reduced pH. The pH was not significantly changed by bubb1lng the
surrounding buffer with 0-20% C02 , with corresponding buffer changes
in pH of 6.95-8.05. Adding labelled albumin to the external buffer
resulted In lumenal concentrations that, in the presence of salbutamol,
were higher than outside. This and other evidence suggested that albumin
could be actively secreted into the lumen, a process enhanced by salbutamol. Thus ASL Is byperosmolar, of d.ifferent electrolyte composition from
interstitial fluid, and of low pH which Is homeostatically regulated. The
epithelium can actively secrete albumin into the lumen.
Eur Respir J., 1989. 2. 107-115.
Dept of Physiology, St George's Hospital Medical School, London SW17 ORE, UK.
Keywords: Acidity; albumen; mucus; osmolality;
trachea.
Received: July, 1988.
108
J.G. WIDDlCOMBE
Preface
In this ftrst Paul Sadoul lecture, the Society honours
Dr Sadoul and acknowledges his great contributions to
SEPCR, and to European and international respiratory
medical science. There is no space to detail the wealth of
his contributions to medical literature, or to list the very
many young doctors and scientist he has led into important and distinguished careers. He has received many
personal honours, titles and distinctions, but as a Society
we take especial pride in the fact that he is our Honorary
President.
In more general terms his contributions to respiratory
medicine are unique. For over forty years he built the
Department of Physiopathologic Respiratoire at the
University of Nancy into a world centre of excellence in
respiratory medicine, as can be vouched for by the
innumerable scientific visitors to his department from
all over the world. He was the founder in 1965 of the
Bulletin Europ&m de Physiopathologic Respiratoire and
for twenty years was its Editor-in-Chief and its inspiration.
In 1966, he was a eo-founder of our Society, and has
been a continuous source of strength for its growth and
development He encouraged it to bring together respiratory scientists from all over Europe, and in particular the
contributions of those from Eastern Europe have depended
greatly on his vision and enthusiasm. While he would be
the ftrst to acknowledge that many others have played an
active role in this task, he provided the foundation and
established the harmonious and fruitful international
collaboration that has been of high significance in the
progress of respiratory medicine.
The scientific achievements of the Department of
Physiopathologic Respiratoire at Nancy, with Paul Sadoul
as its Chairman, are manifold; they include extensive
developments of bronchial provocation tests, ergospirometry, cardiac catheterization and gasometric analyses. At a
more basic scientific level the Nancy school established
studies on mucus and mucociliary transport, which are
being continued in a distinguished manner by Dr Edith
Puchelle in Reims. Because of this last-mentioned activity of the Nancy department, I hope it will be thought
appropriate if I devote the scientific part of this lecture
to some studies on mucus.
Introduction
Research on respiratory tract mucus has developed
rapidly in the past twenty years, and now many teams
throughout the world are conducting sophisticated studies on, for example, mucoglycoprotein biochemistry,
mucus rheology and biochemistry including enzymology.
Modem techniques such as cell culture and the use of
monoclonal antibodies are rapidly being applied to
airway secretory tissues. However, in spite of all this
flourishing research, we are still regrettably ignorant about
some of the basic properties of airway secretions. Indeed
it could be said that mucus is one of the main mysteries
of respiratory disease.
We have no baseline for the study of tracheobronchial
mucus in man, since resting output in health is small and
has never been measured accurately [1, 2]. The chemical
composition of this resting output is very uncertain and
published values are very variable. The distinction between periciliary fluid, presumably controlled mainly by
ion-pumping mechanisms in the epithelium, and the
submucosal gland secretions is unclear. The use of terms
such as "sol" and "gel" is imprecise and hides our ignorance as to the differences between the two phases and
how they may interact, chemically and physically. The
balance of the beneficial and the harmful properties of
mucus in disease is a matter of dispute; for example in
therapy we often do not know whether to increase or
decrease the output of mucus, or how to change its
physicochemical properties.
One of the major problems in studying mucus, certainly from man, is the great difficulty in collecting it
pure and unadulterated in disease; the secretion in health
is probably so small that analysis is almost impossible.
Most studies have been on sputum, which must nearly
always be contaminated by saliva. Bronchial washings
may be distorted by the effects of the washing medium,
as I will discuss later. Aspiration of respiratory tract
mucus implies that either a pathological process is present or that the secretion is induced by the presence of an
endobronchial tube and suction catheter. Bronchoalveolar lavage (BAL) inevitably contains mainly alveolar
fluids in a large volume of washing.
Table I lists some of the constituents of airway sutface
liquid (ASL). In most of this presentation I shall not
distinguish between gland secretions and periciliary fluid,
since the chemical distinction between the two is unclear
except possibly in the concentrations of mucoglycoproteins. Most items on the list in table 1 could be subdivided twenty times or more and each subdivision might
justify a lengthy discussion. However, I will limit my
presentation to the most simple constituents of mucus,
about which perhaps we know least: water, electrolytes
and albumin.
Table 1. - Some constituents of
airway liquid
Wa!i!r
Electrolytes
Glycopro!i!ins
Immunoglobulins
Albumin
Lipids
Enzymes
Anti-enzymes
Anti-bac!J!rials
Cell products
Mediators
Most categories can be extensively
subdivided.
Methods
A few years ago we developed a simple method for
collecting unadulterated mucus from the trachea of the
ferret in vitro [3-5] (fig. 1). The whole trachea, from
larynx to carina, is removed from a ferret and placed
inverted in an organ bath. "Pure" ASL, including
AIRWAY MUCUS
secreted mucus, is carried down the trachea by gravity
and mucociliary transport, and collected in a fine catheter for subsequent chemical analysis. The external
bathing medium of the organ bath is normally KrebsHenseleit solution, the composition of which is shown in
table 2. The trachea can be connected to a pressure
109
Side View
To Pressure Transducer
Electrode
Trachea
Catheter
Top View
Krebs-Henselelt
Cannula
Electrode
Fig. 2. -The arrangement of the ion-selective and potential difference
electrodes in the collecting cannula. One electrode was used for
reference and the others for pH and Ca++ estimations.
Fig. 1. - Diagram of the ferret whole tracheal in vitro preparation. The
trachea is placed laryngeal end down in the organ bath, surrounded by
Krebs-Henseleit solution, and mucus is collected into a catheter inserted into the lower tracheal cannula.
Table 2. - Electrolyte concentrations of ferret airway
surface liquid (ASL) compared with other appropriate
liquids
Ferret
trachea
pH
ea
ea++
Na
K
et·
He03 •
Refs
7.08
3.1
2.7
172
9.1
129
13*
[5, 7, 8,)
Dog
trachea
7.90
6.9
158
28.9
134
37*
(10]
Ferret
plasma
7.38
3.2
1.8
139
5.4
105
24
Krebs-Henseleit
solution
7.40
2.4
146
5.9
126
25
[12-14)
All values arc means, and are in mmoH 1 except for pH. Values
are for total molecular concentrations, except for ea••, CI· and
pH. *: calculated value.
recorder with a closed system, to indicate changes in
smooth muscle tone [6]. A valuable development of this
method is to insert catheter-tip electrodes into the lower
cannula from which the mucus is collected [7, 8] (fig. 2);
these electrodes can monitor transmucosal potential difference, pH and various cation concentrations, especially
ea++.
It will be apparent that the main defect in this method
is that the trachea is in vitro, although it can be modified
to allow in vivo studies. All the results to be present here
concern the in vitro trachea, with its vascular supply
inactive.
Airway surface liquid osmolality
There have been a number of indications that ASL is
normally hypcrosmol compared wilh interstitial nuid or
plasma [5, 9, 10]. Most o f lhese results have been interpreted ralher cautiously in view of the possibility lhat
there might be evaporation from lhe ASL resulting in an
increase in osmolality; this has certainly been shown to
occur [9, 10]. However, with our preparation there is no
possibility of evaporation, and lhe collected Ouid, whether
resting secretion or weakly stimulated by secretagogucs,
is indeed hyperosmol [N. Robinson, H. Kyle, S. Wcbbcr,
A. Price, J. G. Widdicombe, unpublished results]. We
found values in the range 310-350 mosmol·kg-1, and these
compare closely with those of BoucHER et al. [10] for
dog trachea, who give a value of 330±15 (mean±SEM),
and of MAN et al. [9] also with dog trachea, who found
a value of 339±18 mosmol·kg·1 • For man, MATIHEws et
al. [11] found an osmolality of 359±56 mosmol·kg- 1• By
comparison, ferret plasma has an osmolality of about
277±8 mosmol·kg·1 [12], and the Krebs-Henseleit buffer
solution used in our experiments an osmolality of about
280 mosmoJ.kg·•. Human and dog plasma osmolalities
are close to 280 mosmol·kg-1 [10, 11].
110
J.G. WIDDICOMBE
Airway surface liquid electrolyte composition
The reason for the hyperosmolality is seen when the
electrolyte composition of the fluid is studied. Table 2
compares results by BoucHER et al. [10] for the dog with
our results from the ferret, and they are very similar.
Typical values for plasma or interstitial fluid for the ferret
[12-14] are also given, and for Krebs-Henseleit buffer
solution. For simplicity only mean values are given;
standard errors can be found in the published work. The
main features are that sodium and chloride concentrations are considerably higher in ASL than in plasma,
accounting for the hyperosmolality. However, other
features are also striking. For example the pH is consistently less in the ASL, and corresponds to H• concentration of 96 nmoJ./·1 compared to 40 nmoJ./·1 for plasma.
The Ca++ and total calcium are higher than both plasma
and Krebs-Henseleit values, the former being almost
double the plasma value. Potassium is also far higher in
concentration, although values were very variable. The
methods used (except for Ca++) have measured total
elemental contents rather than ionized values, so there
could be some distortion by cations bound to mucoglycoprotein. However, estimates of protein-bound
cations suggest that this would only lead to a small error
[9], and this view is supported by the osmolality measurements. Comparison between results for dog and ferret
tracheal ASL indicates that the dog has far higher calcium, potassium and bicarbonate values, and correspondingly higher pH. Some of these differences could be
because of very different methods of collecting ASL in
the two species. It is interesting that NIELSON [15] has
found that rabbit alveolar liquid subphase has a high
potassium concentration, although this liquid is isotonic
with serum.
There are several points of significance in these results. One is that the use of "physiological saline" (i.e.
9 g·/·1 NaCl solution) for BAL and bronchial washings
introduces a "non-physiological" liquid, both in terms of
osmolality and individual ion contents. In this sense
physiological saline is pathological. Whether the differences in ion contents would make any appreciable
difference to the results of lavage and washings is uncertain, but at least this is a potential problem. Even if physiological saline were replaced by phosphate-buffered
saline (PBS) or a solution such as Krebs-Henseleit
buffer, this would not solve the problem, since these
solutions are isotonic but their ion concentrations are
different from those of ASL especially in relation to
potassium and Ca++. The last two are known to be especially active on cell function.
The results also raise the question as to what is the
optimum or most natural medium for cell culture. Most
cell culture mediums have osmolalities and electrolyte
concentrations as dose as possible to those in plasma,
but at least the apical ends of the airway epithelial cells
seem in life to be exposed to media of quite different
composition. Apart from the epithelial cells, washing out
cells from the airway lumen with physiologicai saline or
even PBS is to expose them suddenly to a chemical
environment to which they are not accustomed. Again,
one cannot say whether this makes any difference to
their function.
A final aspect of these results is the question of what
happens when evaporation of water from ASL is allowed
to occur. This is a possible component of the mechanisms that are activated in exercise or cold air-induced
asthma, where hypcrosmolality of ASL may be a trigger
[16, 17). The values in table 2 suggest that the normal
baseline of osmolality is higher than for tissue fluid.
Although evaporation in hyperpnoea-induced asthma
would certainly lead to an increase in osmolality [9, 10),
the relative values of the various ionic contents of the
ASL in this condition are not known.
In theory it might be possible to make up a solution of
composition similar to that of ASL shown in table 2, and
to use this for lavage and washings. However, if this is
done another prob1em is introduced. This is that the
compositions shown in table 2 are not constant. As
shown in table 3, when various pharmacological mediators known to change mucus secretion or epithelial ion
transport systems or both are added to the preparation,
the composition of the collected ASL changes. These are
to some extent due to dilution of the ASL with submucosal gland secretions, but they probably also include
changes in ion transport by the epithelial cells [18, 19].
The direction of changes may be different for different
med-iators, seen for example on comparing methacholine
with salbutamol (table 3).
Table 3.- Changes in electrolyte composition of ferret airway surface liquid
(ASL) due to methacholine and salbutamol.
pH
Ca
Ca..
Na
K
Cl·
Methacholine
Salbutamol
-0.11*
-1.18*
-0.80*
-17.8*
+3.2
-20.4*
-0.058*
+().87*
+0.20
-8.5
+2.8*
+9.6
All values are means, and in mmoH 1
except pH. Values are for total molecular
concentrations, except for pH, Ca+> and CI·
*p<O.OS by Student's t test.
Table 3 raises the question as to the relative contribution of submucosal gland and epithelial secretions. As
mentioned already, there is no clear answer to this question. However, QUINTON [20] has shown that the secretion from cat submucosal glands is close in electrolyte
concentrations to those for plasma and interstitial fluid,
except that the calcium concentration is lower and the
sulphur concentration higher in the gland secretions. If
these results apply to other species it is a reasonable
hypothesis that the main determinants of ASL electrolyte
composition are the secretory mechanisms in the epithelial cell layer, and that submucosal gland secretion acts
mainly by diluting the ASL, thus bringing its composition closer to that of interstitial fluid.
AIRWAY MUCUS
The general conclusion must be that there is no such
thing as a "normal electrolyte" composition of ASL in
physiological conditions. Furthermore, the results tabulated apply only to the ferret and dog, and there is some
evidence that the values in man may be quite different
[21]. An additional complication is that all the results
given apply to healthy tissue; in diseases, such as those
which damage or destroy the airway epithelium and/or
the submucosal glands, the composition of ASL may be
quite different from that described. There seems to be
little experimental evidence on this particular point. A
fmal consideration is that the data given are deficient in
some important respects, such as the concentrations of
magnesium and phosphate ions that might have important physiological actions.
111
X
a.
Airway surface liquid acidity
6
0
As shown in table 2, ASL is slightly acid compared
to plasma in the ferret. The same was found to be true
for man by BoucHER et al. [21], who obtained a figure of
6.88±0.08. Other published values for pH of ASL vary
widely, possibly because of different methods and species used [7, 22, 23]. This acidity is unlikely to be due
to abnormal carbon dioxide concentrations. The intraluminal CO~ tension is on average lower than that in tissue
fluid, and would make the ASL more alkaline; this is
because of the presence of environmental air in the
respiratory tract after each inspiration.
A possibility is that the mucoglycoproteins in the ASL
and gland secretions might have an abnormal buffering
action maintaining the pH lower than for tissue fluid.
They are on balance anionic and their isoelectric point
might be expected to lie on the acid side of the pH range.
The influence of mucoglycoproteins can be tested by
comparing the buffer curves for Krebs-Henseleit solution with those for secreted mucus [H. Kyle, J. Ward,
J.G. Widdicombe, unpublished results]. Using mucus
collected from the ferret trachea in vitro, it was found
to have a very similar COjpH relationship to KrebsHenseleit solution (fig. 3). The curve was displaced
downwards but not by more than 0.2 units at a C02 concentration of 5.0%. Thus the buffering properties of
secreted mucoglycoproteins cannot account for the low
pH of ASL (the curves in figure 3 are not strictly buffer
curves but COjpH curves; a detailed analysis of the
buffering properties of respiratory tract mucus has been
made by HOLMA [22]).
When the C02 content of the Krebs-Hcnseleit solution surrounding the trachea in the organ bath was changed
from 0-20%, while ASL pH was measured with a
catheter-tip electrode, we were surprised to find there
was no significant change in ASL pH, and it remained
on average close to 6.9 units. This is shown in figure
4, and figure 5 shows the same results expressed as the
pH of the Krebs-Henseleit buffer compared with that of
the mucus. A similar result was obtained by NIELSoN et
al. [24) with alveolar liquid subphase. The pH was acid
(6.92±0.01) and remained constant over an external pH
range of 7.7-7.50, shifting only slightly at more extreme
external values.
% C02
Fig. 3. - A combined graph of the changes in Krebs-Hcnseleit pH
(•> and in mucus pH without a trachea present <•> due to changes
in percentage eo. in the gaseous phase. Values are means±SBM.
arc calculated ignoring the fact that pH is a logarithmic value
SllM$
7· 4
7· 2
:X:
c. 7·0
Ill
I
j
()
j
::;
6·8
I
+
6·6
0
5
10
15
20
25
% C0 2
Fig. 4. - Measurement of mucus pH with change in percentage C01
in the submucosal bathing medium for the isolated ferret trachea. Values
are mean±sBM. SBM are calculated ignoring the fact that pH is a logarithmic value.
These results indicate not only that the pH of the ASL
is lower than that of interstitial fluid, but also that it is
maintained constant over a wide range of changes in external pH. This is presumably due to a homoeostatic
mechanism regulating the pH in the periciliary fluid
secretions of HCO;JH• by the epithelial cells. The changes
in gland secretion due to phannacological agents (table
3) alter the pH slightly but significantly, but in all instances tested it remains well below values for plasma.
Species differences are uncertain. As mentioned,
BoucHER et al. [21] found a pH value of 6.88±0.08 for
healthy man. A comprehensive study in man by
J.G. WIDDICOMBE
112
et al. [23, 25) gave mean values from 6.73±0.56
(sEM) for rabbit. For the rat, tracheal pH is in the range
7.40-7.57 [26). Although the most careful studies directly on tracheal mucus show an acid ASL for several
species including man, other observations show a wide
range of values; this may sometimes be explained by
differences in experimental methods.
GUERRIN
H
1·1
:r
c.
1·0
"'
::1
<>
::1
:!:
11•8
t
+
I "
&·6
7·3
7·5
7·9
8 ·1
Krebs-Henseleit pH
homeostasis are altered by disease, as seems very likely,
this could have important implications in the behaviour
of secreted enzymes and lumenal cells, and even of the
activity of inhaled aerosolized drugs.
Albumin secretion
We used the ferret in vitro tracheal model to see whether
drugs like histamine change the epithelial permeability
to macromolecules such as albumin [30-32; A. Price, S.
Webber, J.G. Widdicombe, unpublished results]. To
do this, fluorescent-labelled albumin was put in the
surrounding Krebs-Henseleit buffer and its output and
concentration in the ASL were measured. Similar experiments were done with dextran of similar molecular weight
to albumin (70,000 Da) and also of a lower molecular
weight dextran (9,000 Da).
We were surprised to find that in resting secretions the
concentration and output of albumin was very considerably higher than that of both dextrans (fig. 6). Since we
presumed that the dextrans were entering the tracheal
lumen by passive transudation, this seemed strong evidence that the albumin was being actively secreted.
Fig. 5. -Measurement of mucus pH with change in Krebs-Henseleit
pH in the submucosal bathing medium for the isolated ferret trachea.
Same values as in figure 4 (means±sEM). SEMs are calculated ignoring
the fact that pH is a logarithmic value.
0.2
i:
The details of the mechanisms maintaining ASL pH
constant and somewhat acid (compared to interstitial fluid)
have not been analysed. Presumably the homeostasis of
resting ASL pH is primarily a function of epithelial
secretions, but changes induced by pharmacological
agents could be due either to epithelial or submucosal
gland activities. Epithelial secretory function has been
measured primarily with Ussing chambers, and controlled
and maintained environmental pH [18, 19]. The pH of
"pure" gland secretions does not seem to have been
measured, nor have the bicarbonate concentrations that
might give an indication of pH. It is not clear what, if
any, functional advantage derives from pH acidity and
homeostasis. pH affects both mucus rheology and ciliary
beat frequency, but the values needed to achieve this are
far more extreme that those quoted here [22, 23). Therefore, any effects on these variables must be small. Another
possibility, that seems more likely, is that the pH of ASL
would affect the activity of the many enzymes and antienzymes present in the liquid. To give one example,
deoxyribonucleases are inactive at pH 7.0 but active at
pH 5.0 [27). The value and constancy of pH might be
important factors in determining the effectiveness of this
and other enzymes. Cellular function in the airway lumen
is also affected by pH; mast cell degranulation has an
optimum at pH 6.8-7.3 [28]. We need to know far more
about the optimal pH values for lumenal enzymic and
cellular functions. As for the electrolyte concentrations
described earlier, the effect of mucosal disease conditions on ASL pH has not been much studied, although
pH seems to decrease in asthma [29). If pH and its
~
:;.
"g.
.Albumin
a.
c
.!!
WAloextren
~(MW 70,000)
c
D
"'"'
'5
3
'§
0
c
I!
8c
"'
"c
x
0
'D
0
c
o.xtran
(MW 9,000)
0.1
E
I!
x
"'
'D
"
.D
<(
c
E
"
.D
<(
0
Fig. 6. - The output and conce:ntralion of albumin (filled bars), dcxtran -70,000 (hatched bars) and dextran-9,000 (empty bars) in control
periods when mucus volwne output had not been stimulated by drugs.
Results are the means of ~ detenninations with SEMS shown by
venical lines. . .: p<O.Ol for dextrans compared to albumin.
This conclusion was confirmed when the effects of
various pharmacological agents were tested on albumin
and dextran transports across the mucosa. As shown in
figure 7, methacholine, phenylephrine, salbutamol and
histamine all increased the outputs of albumin into the
lumen. The first two agents are powerful stimulants of
submucosal glands, and concentrations of albumin significantly decreased, presumably because of dilution
by gland secretion. However, salbutamol, which causes
very little increase in gland secretion, actually increased
AIRWAY MUCUS
the concentration of albumin; indeed the concentration
became higher than that of the external medium
(4 J..Lg·J..Ll·1), strongly suggesting stimulation of an active
transport system so that it built up a positive gradient of
albumin being greater in the airway lumen.
Methacholine Phenylephrine Salbutamol
When the same experiment was done with dextran70,000, no increase in output of this substance was
obtained with any of the mediators, although the concentrations of dextran-70,000 significantly decreased with
methacholine and phenylephrine, presumably because of
dilution with glandular mucus (fig. 8). This supports the
view that the changes in albumin output and concentration are due to active mechanisms in the airway epithelium. With dextran-9,000, similar results were obtained
although some increases in output were observed [30-32)
(not illustrated).
We therefore conclude that albumin can be actively
secreted into the airway lumen, a conclusion reinforced
by experiments showing that the increase in output due
to methacholine is almost entirely inhibited by cooling
the preparation to 4 ·c. The results suggest strongly that
this secretory process is in the epithelium rather than the
submucosal glands, and that the transport can be very
strongly stimulated by salbutamol and to a lesser extent
by methacholine. Albumin has been detected in the ASL
in many in vivo studies (e.g. [9-11]), but the natural
concentrations cannot be directly related to the results
with our in vitro model, nor is the concentration in
interstitial fluid in the mucosa known.
The ability of alveolar and airway epithelium to transport albumin actively has been previously described.
The bullfrog epithelium can actively transport albumin
from lumen to interstitium [33] and the dog bronchial
epithelium can do the same [34]. Our results suggest that
the ferret trachea can actively transport albumin in the
opposite direction, from interstitium to lumen. The transport could be bidirectional with the balance of directions
depending on experimental circumstances. Suspensions
of serous cells from submucosal glands of the cow can
secrete and probably synthesize albumin [35]; however,
Histamine
0
Conlrol
2.
**
i:
e
~
:;
g.
1.0
;;;)
0
Fig. 7.- The effect of drugs on the concentration and output of bovine
serum albumin from the ferret trachea. Empty bars denote control
periods and hatched bars drug-induced periods. Results are the means
of 4-{) determinations with SI!Ms shown by vertical lines. The interrupted line on the lower histogram represents the albumin concentration in the organ-bath buffer. H:p<O.Ol; *:p<0.05 for response to
drug compared to control.
Histamine
Salbutamol
Phenylephrine
Methacholine
113
0
Control
~
·ei::
Drug
i:n
1.0
;:!.
0
0
0
:;
Q
ci :;
,...
0
~
~
z
<
a:
1X
w
c
3.
i:n
4 .0
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
::1.
c:
.2
~
c
Cl>
u
c:
0
()
Fig. 8. - The effect of drugs on the concentration and ouput of dextran-70,000 from the ferret trachea. Empty bars denote control periods and
hatched bars drug-induced periods. Results are the means of 4-{) determinations with SEMS shown by vertical lines. The interrupted line represents
the dextran concentration in the organ-bath buffer. . .p<O.Ol for response to drug compared to control.
J.G. WIDDICOMBE
114
our results with our ferret model suggest that such a
process is not appreciably important compared with the
epithelial transport mechanism.
The physiological and pathological significance of
albumin secretion depends on what role albumin may
have in the airway lumen. Albumin can change the
rheology of mucus [36, 37]. It can also be a carrier of
substances such as lipids [38]. It inactivates surfactant
and materials such as leukotrienes [39-40}. It is a scavenger for free radicals which play a part in some diseases
of the airways [41]. Which of these functions may be
important in health and disease we cannot say.
Another aspect of the results with albumin is that it
may be an imprecise marker for transudation if the
proportion of active secretion compared to transudation
is significant. Clearly much more research needs to be
done on the role of lumenal albumin and the control of
its secretion and transudation.
Conclusions
I have described some relatively simple experiments
on the composition of respiratory tract fluid in an unsophisticated model. The results suggest that some of the
most basic properties of respiratory tract fluid, whether
it is coming across the epithelium or being secreted by
submucosal glands, need considerable further study.
Whether the changes in osmolality, electrolyte composition and albumin content of the ASL exert significant
effects in health and disease also requires further research,
but at this stage of our knowledge they are clearly of
potential importance.
Acknowledgements:
I am grateful to Drs N.
Robinson, H. Kyle, S. Webber and Ms A. Price for
pennission to include unpublished results of some of
their research. I am also grateful to them for valuable
discussions.
References
1. Phipps RJ. -The airway mucociliary system. In: Respiratory physiology ill. International review of Physiology, vol 23,
J.G. Widdicombe ed., University Park Press, Baltimore, 1981,
pp. 213-250.
2. Marin MG. - Pharmacology of airway secretion.
'Pharmaco/ Rev, 1986, 38, 273- 289.
3. Robinson NP, Widdicombe JG, Xie CC. - In. vitro collection of mucus from the ferret trachea. 1 Physiol, 1983, 340,
7P--8P.
4. Kyle H, Robinson NP, Widdicombe JG. - Mucus secretion by tracheas of ferret and dog. Eur 1 Respir Dis, 1987, 70,
14-22.
5. Robinson NP. - Mucus secretion by the tracheobronchial
tree of manunals. PhD Thesis, University of London, 1984.
6. Kyle H, Widdicombe JG, Wilffert B. - Comparison of
mucus flow rate, radiolabelled glycoprotein output and smooth
muscle contraction in the ferret trachea in vitro. Br 1 Pharmacol, 1988, 94, 293-298.
1. Kyle H. -The control and composition of mucus secre-
tion in the ferret trachea. PhD Thesis, University of London,
1987.
8. Kyle H, Robinson NP, Ward JPT, Widdicombe JG. Measurement of mucus [H+] and other ionic concentrations in
the isolated trachea of the ferret. 1 Physio/, 1987, 387, 15P.
9. Man SFP, Adams ill GK, Proctor DF. - Effects of temperature, humidity, and mode of breathing on canine airway
secretions. 1 Appl Physiol, 1979, 46, 205-210.
10. Boucher RC, Stutts MJ, Bromberg PA, Gatzy IT. Regional differences in airway surface liquid composition. J
Appl Physiol, 1981, 50, 613-620.
11. Matthews LW, Spector S, Lemm J, Potter J. - Studies on
pulmonary secretions. 1. The overall chemical composition of
pulmonary secretions from patients with cystic fibrosis, bronchiectasis and latyngectomy. Am Rev Respir Dis, 1963, 88,
199-204.
12. Mangos JA, Boyd RL, Loughlin GM, Cockrell A, Fucci
LR. - Secretion of monovalent ions and water in ferret
salivary glands: a micropuncture study. 1 Denl Res, 1981, 60,
733-737.
13. Thomton PC, Wright PA, Sacra PJ, Goodier TEW.- The
ferret. Mustela putorius furo, as a new species in toxicology.
Lab Animals, 1979, 13, 119-124.
14. Mangos JA, Boyd RL, Loughlin GM, Cockrell A, Fucci
R. - Handling of calcium by the ferret submandibular gland.
1 Denl Res, 1981, 60, 91- 95.
15. Nielson DW. - Electrolyte composition of pulmonary
alveolar subphase in anesthetized rabbits. J Appl Physiol, 1986,
60, 972r-979.
16. McFadden ER Jr.- Respiratory heat and water exchange:
physiological and clinical implications. 1 Appl Physiol, 1983,
54, 331-336.
17. Hahn A, Anderson SD, Morton AR, Black JL, Fitch KD.
- A reinterpretation of the effect of temperature and water
content of the inspired air in exercise-induced asthma. Am Rev
Respir Dis, 1984, 130,575-579.
18. Al·Bazzaz FJ. - Regulation of salt and water transport
across airway mucosa. In: Clinics in chest medicine, vol 7,
J.H. Widdicombe ed., W.B. Saunders Co, Philadelphia, 1986,
pp. 259-272.
19. Nadel JA, Widdicombe JH, Peatfield AC. - Regulation of
airway secretions, ion transport and water movement. In:
Handbook of physiology, Section 3 The respiratory system, vol
I. A.P. Fishman, A.B. Fisher eds, American Physiological
Society, Bethesda. 1985, pp. 419-446.
20. Quintan PM. - Composition and control of secretions
from tracheal bronchial submucosal glands. Nature, 1979, 279,
551- 552.
21. Mentz WM. Knowles MR, Brown JB, Gatzy IT, Boucher
RC. - Measurement of airway surface liquid (ASL) composition of normal human subjects. Am Rev Respir Dis, 1984, 129,
315A.
22. Holma B. -Influence of buffer capacity and pH-dependent rheological properties of respiratory mucus on health
effects due to acidic pollution. Science of Total Environmenl,
1985, 41, 101-123.
23. Guerrin F, Voisin C, Macquet V, Robin H, Lequien P. Apport de la pH metrie bronchique in situ. In: Chronic inflammation of the bronchi. Prog Respir Res, 1971, 6, 372-383.
24. Nielson Dw, Goerke J, Clements JA. - Alveolar subphase
pH in the lungs of anesthetized rabbits. Proc Nat/ Acad Sci
USA, 1981, 78, 7119-1123.
25. Guerrin F, Robin H, Lambert P, Kine A. - pH metric
bronchique in situ. Effects de l'hypoxie-hypercapnie. J Physiol Paris, 1969, 61, 305-306.
26. Gatto LA. - pH of mucus in rat trachea. J Appl Physiol,
1981, 50, 1224-1226.
AIRWAY MUCUS
27. Potter J, Mathews LW, Spector S, Lemm J.- Studies on
pulmonary secretions: osmolality and ionic environment of
pulmonary secretions from patients with cystic fibrosis, bronchiectasis and laryngectomy. Am Rev Respir Dis, 1967, 96,
83-89.
28. Diamant B. - Histamine release elicited by extracts of
Ascaris suis- influence of oxygen lack and glucose. Acta Physiol
Scan.d, 1961, 52, 8-22.
29. Ryley HC, Brogan TD. - Variation in the composition of
sputum in chronic chest disease. Br J Exp Pathol, 1968, 49,
635-633.
30. Webber SE, Widdicombe JG. - The transport of albumin
across the ferret in vitro whole trachea. J Physiol. 1989, 408,
457-472.
31. Webber SE, Widdicombe JG. - Albumin and dextran
transport across the ferret in-vitro whole trachea. FASEB J,
1988, 2, A707.
32. Price AM, Webber SE, Widdicombe JG. - The effect of
salbutamol on mucus secretion and albumin transport across
the ferret trachea in vitro. Eur Respir J, 1988, (in press).
33. Kuang-Jin K, Lebon TR, Shinbane JS, Crandall ED. Asymmetric ( 14C] albumin transport across bullfrog alveolar
epithelium. J Appl Physiol, 1985, 59, 1290-1297.
34. Johnson LG, Cheng PW, Boucher RC. - Active transcellular albumin absorption by canine broncmal epithelium (CBE).
Am Rev Respir Dis, 1988, 137 (suppl.), 221.
35. Jacquot J, Benali R, Somerhoff CP. Finkbeiner WE,
Goldstein G, Puchelle E, Basbaum CP. - Identification of
albumin-like protein released by cultured bovine tracheal
serous cells. Am Rev Respir Dis, 1988, 137 (Suppl.), 11.
36. List SJ, Findlay BP, Forstner GG, Forstncr JF. - Enhancement of the viscosity of mucin by serum albumin. Biochem J,
1975, 175, 565-571.
37. Boat TP, Cheng PW. -Biochemistry of airway mucus
secretions. Fed Proc, 1980, 39, 3067- 3074.
38. Bohney JP, Feldhoff RC. - Nonenzymatic glycation of
human albumin: effects of free fatty acids on the kinetics of
aldimine and ketoarnine formation. FASEB J, 1988, 2, A1023.
115
39. Holm BA, Enhorning G, Natter R. -The inhibition of
surfactant by plasma-derived proteins. Abstract, Eric K
Fernstrom Symposium, June 1-4, 1988, Lung, Sweden.
40. Lamm WJE, Selfe S, Albert RK. - Pharmacological and
pulmonary physiologic effects of leukotriene binding to albumin.
Am Rev Respir Dis, 1988, 137, (Suppl.), 398.
41. Halliwell B. - Albumin - an important extracellular
antioxidant? Biochem Pharmacal, 1988, 37, 568-571.
Le mucus des voies airiennes. J. Widdicombe.
RESUME: Le liquide de surface des voies aeriennes (ASL),
constirue d'une mixture du liquide periciliaire et de la secretion
des glandes sous-muqueuses, a etc prelevc in vitro au niveau
d'une trachee isolee de furet. La trachee etait fermee, sans
possibilitc d'evaporation. Le ASL s'avere hyperosmolaire
(310-350 mosmol·kg- 1) par comparaison avec la solution de
Krebs-Henseleit environnante (280 mosmol·kg-1). Le contenu
de l'ASL en sodium et en chlorure est plus eleve que celui du
Krebs-Henseleit; le contenu en potassium et en calcium est
nettement plus eleve. Le ASL est acide (pH±7.00) par comparaison avec la solution Krebs-Henseleit (pH 7.40). L'application de metacholine et de salbutamol ala preparation a modifie
de faycon significative la plupart des concentrations electrolytiques et a reduit le pH. Le pH n'a pas ete modifie sensiblement en faisant passer des bulles de C02 de 0 a 20% dans le
tampon environnant, les modifications de pH du tampon s'etalant entre 6.95 et 8.05. L'addition d'albumine marquee au tampon
extcrne a cntraine des concentrations intra-luminales qui, en
presence de salbutamol, etaient plus clevees qu'a l'exterieur.
Cette observation et d'autres suggerent que l'albumine pourrait
etre secretee activement dans la lumicre et que le processus
serait accentue par le salbutamol. ASL est done hypcrosmolaire, a une composition electrolytique differente de celle du
liquide interstiticl, et a un pH bas avec regulation homeostatique. L'epithelium pourrait secreter activement l'albumine dans
la lumiere.
Eur Respir J .. 1989, 2, 107- 115.