Archives Internationales de Physiologie, de Biochimie et de Biophysique, 1992, 100, 241 -246
24 1
Requ le 10 juillet 1991.
Cholinergic mechanisms and bronchoconstriction in guinea-pigs. BY
R. MARCELLE (Institut Leon Fredericq, Physiologie, Universite de Liege, Belgique)
Archives of Physiology and Biochemistry Downloaded from informahealthcare.com by Nyu Medical Center on 01/07/15 For personal use only.
(3 figures)
Seventy-four guinea-pigs have been actively sensitized against ovalbumin. The effects of bilateral cervical vagotomy and of cholinergic efferent blockade on the bronchoconstriction induced by inhaled acetylcholine, histamine or antigen have been quantified. Animals were curarized then tested during controlled ventilation to ensure constant conditions throughout the whole experiment by suppressing the postvagotomy apneusis. Bronchial sensitivity was estimated by calculating the bronchoconstrictor dose-threshold provoking respiratory asynchronism. Corresponding variation of total lung resistance and dynamic compliance were also measured as indices of bronchial reactivity. The data obtained in 27 guinea-pigs indicated that the vagi section produced no significant effect on the direct bronchial response to histamine (P>0.5), to acetylcholine (P>O.l) or t o antigen (P>O.5). In 47 guinea-pigs, atropine at doses 5 and 10 times higher than the acetylcholine blocking one did not alter the direct bronchial response to histamine ( P > 0.5). Higher doses induced a progressive decrease in bronchial sensitivity to antigen (.05 > P > .01) which could be related to the repetitive administration of the antigen. According to the present results, peripheral cholinergic mechanisms play no significant role in guinea-pigs neither in histamine nor in anaphylactic bronchoconstriction. Curarization has no influence on resting bronchial tone.
Introduction
According to DALE (1914, in BROWN, 1937), acetylcholine (ACh) is the only one known neurotransmetter released at motor vagal nerve endings. It induces bronchial smooth muscle constriction by a specific stimulation of muscarinic receptors, properly blocked by atropine (JAMMES, 1989; HARF, 1990). Such a response seems to implicate the parasympathetic system in the regulation of tracheobronchial smooth muscle tone (WIDDICOMBE,1963; NADEL, 1973). Moreover it has been suggested that an autonomic imbalance favoring cholinergic activity to the airways is also implicated, at least for a part, in the asthmatic attack (NADEL, 1973; CROPP, 1975). Accordingly, atropine derivatives have been proposed as spasmolytic drugs, as a rational alternative to sympathomimetic ones in the asthmatic patients (CHAMBERLAINet al., 1962; Yu et af., 1972; GOLD, 1973). Nevertheless, up to now none of the studjes performed in experimental asthma demontrates clearly that the efferent vagal nerves take a chief part in the antigen-induced bronchospasm mechanisms, notably MILLS& WIDDICOMBE, 1970; JOINERet al., 1974; MICHOUDet al., 1976; COTTON et al., 1977; DRAZENei al., 1978; WASSERMAN & GRIFFIN,1979; HIRSHMAN & DOWNES,1981;ADVENIER ei al., 1982 (see details in discussion).
Some years ago, we have observed in a large number of guinea-pigs that active sensitization against ovalbumin enhanced bronchial sensitivity to ACh as well as to others bronchoconstrictors : histamine (H), serotonine (5HT), bradykinine (B). This indicates that a non specific hyperactivity of bronchial smooth muscles to these agents has been induced. (MARCELLE & LAURENT,1973). In the present study, effects of vagotomy and of vagal efferent blockade by atropine on the bronchial response of actively sensitized guinea-pigs to inhaled ACh, H and antigen are tested in order to assess the role of cholinergic peripheral mechanisms in mediating antigen-induced bronchoconstriction as well as bronchial aspecific hyperreactivity linked with active sensitization. Methods and Materials Seventy four guinea-pigs (Hartley strain) of either sex, weighing 300 to 550 g. were used. 1. Sensitizing procedure. - On day 0, the guineapigs were injected intraperitoneally and subcutaneously with 200 mg of purified ovalbumin (OA), dissolved in 1 ml of 0,9% NaCl solution. On day 15, animals were subcutaneously injected with the same dose of OA precipitated by 50 mg ZnCI2
242
R . MARCELLE
B
Archives of Physiology and Biochemistry Downloaded from informahealthcare.com by Nyu Medical Center on 01/07/15 For personal use only.
A
ml 51 TIDAL VOLUME
lsec. .
FIG.1. Occlusion tracings, from left to right, of the trachealpressure, the airflow and the tidal volume, continuously recorded during controlled ventilation in an actively sensitized guinea-pig inhaling a 5% aerosolized antigen solution. From the start, the figure shows the transition from normal conditions to bronchoconstriction. On the left side (normal), airway occlusions performed by the interrupter induce rectangular tracheal pressure waves (details in A). They correspond to an instantaneous pressure equilibration between alveoli and trachea, measuring the actual dynamic component of the transthoracopulmonary pressure. On the right side, total tracheal pressure variations are increasing when airflow and tidal volume remain unmodified. Simultaneously, tracheal pressure waves induced by the airway occlusions show an incurved profile (details in B). Through narrowed bronchi, pressure equilibration between alveoli and trachea is no more instantaneous but is slowing down and progressive. Such modifications from A to B in the continuous tracheal pressure tracings indicate the onset of the bronchoconstriction. The corresponding inhaled dose is the threshold dose.
to ensure a progressive resorption of the antigen during at least the 7 days preceding the experiment (COLLIER & JAMES, 1967). 2. Ventilatory measurements. - The animals were lightly anesthetized with a low dose of pentobarbitone (Nembutal :20 mg/kg ip), preserving spontaneous ventilation. Local anesthesia (xylocaine 1070) allowed the tracheotomy, the dissection and the catherization of the oesophagus with a 2 mm catheter, filled with water. A tracheal canula was connected to an airflow interrupter (MARCELLE, 1967) extended by a pneumotachograph (Fleisch type no 000) connected to a differential pressure transducer (Efema, EMT 32) measuring airflow (V). A pressure transducer (Efema, EMT 31) filled with distilled water, was connected to the oesophagal catheter to record intrathoracic pressure (PIT). A third pressure transducer (Elema, EMT 31) connected to a small tubing inserted between the endotracheal tube and the interrupter measured the intratracheal pressure (PT). During spontaneous ventilation, transpulmonary pressure (PTP) was obtained by electrical subtraction of the output signals of the intratracheal pressure transducer (PT) from these of the intrathoracic one
(PIT). Tidal volume (Vt) was determined as the electrical integral of airflow (Elema integrator). Output signals representing PT, PTP, V and Vt were simultaneously recorded on a Mingograph polygraph model 42. Flow resistance (FR) and dynamic lung compliance (C Dyn) were calculated. During controlled ventilation managed by a Braun type constant respirator, total lung resistance (RL) and dynamic compliance (C Dyn) were determined from the transthoracopulmonary pressure variations measured at tracheal tubing. Dynamic and elastic components were respectively reported to corresponding values of V and Vt. Throughout the entire experiment the blood pressure was recorded from a catheter inserted in the right carotid artery. Repetitive interruptions of the airflow were used to distinguish between actual elastic and dynamic components of the tracheal pressure, in spontaneous as well as in controlled ventilation (OTIS& PROCTOR, 1947; MARCELLE, 1967; GOTTFRIED et af., 1984).
3. Protocol. - Respiratory measurements were performed in supine position firstly during spontaneous respiration and secondly during controlled ventilation. This latter was performed on curarised animals
243
CHOLINERGIC MECHANISMS AND BRONCHO-CONSTRICTION
(Pancuronium :1 ml/ip) t o ensure muscle relaxation and constant conditions by suppressing the postvagotomy apneusis. Agonists or antagonists dissolved in 9% or 1 % NaCl solutions, were nebulized (Mistogen) and inhaled during continuous registration of Vt in order to calculate the dose (Q) which has been administered,
Archives of Physiology and Biochemistry Downloaded from informahealthcare.com by Nyu Medical Center on 01/07/15 For personal use only.
according t o the formula : Q
=
v x c ~
Pg
1.34 where V is the total ventilation performed throughout the inhalation of the aerosol; C, the concentration of the agent in pg/ml, 1.34 is an approximate characteristic of the nebulizor representing the volume of air (in liter) dispersing 1 ml of the solution. Inhalation of the agonists was stopped as soon as a bronchial response occurs. The latter is indicated by the appearance of a respiratory asynchronism, as revealed by an increase of the tracheal pressure (PT) variations associated with an incurved profile of the tracheal pressure waves observed during the interruptions of the airflow. This configuration contrasts with the rectangular profile of the same waves in normal conditions as shown in Figure 1 (OTISet al., 1956; PETIT & MARCELLE,1964). The dose inhaled at that time represents the threshold bronchoactive dose. It is an index of bronchial sensitivity. The lower the dose, the higher the sensitivity. 4. Drugs. - The following drugs were used : ovalbumin (Calbiochem); pentobarbitone (NembutalCeva); xylocaine dihydrochloride (Astra); acetylcholine chloride (Fluka); pancuronii bromidum; histamine dihydrochloride (Calbiochem).
5 . Statistics. - The results were expressed as mean f SEM. Difference were tested for non paired values
by a Student's t test. P i s considered as significant when 0.5). After vagotomy the bronchial response to ACh at the delay corresponding to the installation of the respiratory asynchronism did not vary as far as RL and C Dyn variations were concerned (P>O.5). The mean dose of inhaled ACh was somewhat higher but the difference was not statistically significant ( P > 0.1). Vagotomy exerted no appreciable effect on the antigeninduced bronchoconstriction : the mean inhaled dose of ovalbumin corresponding to respiratory asynchronism threshold, to increase in RL and to decrease in C Dyn did not show any significant difference (P>0.5) in comparison with the mean dose of antigen active in control conditions. 3. Effects of graded doses of atropine.
In 47 guinea-pigs, 3 doses of atropine were tested, as calculated afterwards : 824 pg (SD : k 165); 4235 pg (SD : k316) and 9041 pg (SD : k384). They corresponded to the inhalation of the 1% aerosol during 2 min, and of the I % aerosol during 1 min and 2 min respectively. Figure 3 shows that bronchial responses to a 16 fold higher dose of ACh had fallen to zero from the smallest atropine dose (824 pg f 165). Even the highest atropine dose (9041 pg k 384) did not exert any appreciable effect on H-induced bronchospasm (P>O.5). The bronchial reactivity to the antigen was somewhat decreased. After the lowest dose of atropine, antigen inhalation was increased from 1400 to 2100 pg. After the two higher doses of atropine, a proportional increase of the ovalbumin inhaled dose, respectively 2400 pg and 3600 pg, was necessary in order to get a comparable bronchial response. The decrease of the bronchial sensitivity to the antigen with increasing doses of atropine is statistically significant (respectively : P = 0.03; P = 0.05; P = 0.01).
244
R. MARCELLE
Archives of Physiology and Biochemistry Downloaded from informahealthcare.com by Nyu Medical Center on 01/07/15 For personal use only.
Histamine H
Acetylcholine E4
I
Ovalbumine
Ed
I
ml .cm H,O-' FIG. 2 . Bronchial responses in 27 actively sensitized guinea-pigs before (A) and after (B) vagofomy. Open columns show mean increase in RL and decrease in C Dyn successively induced by histamine, acetylcholine and ovalbumin, before (A) and after (B) vagotomy. Striped columns indicate mean inhaled doses of these 3 agents in the two conditions (A and B). Vertical lines represent s.e.m. Statistical evaluation of the results shows that vagotomy does not reduce the bronchial sensitivity to pharmacological and anaphylactic stimulations in actively sensitized guinea-pigs ( P > 1).
Discussion The role played by the autonomic nervous system in bronchial hyperreactivity associated with the active sensitization in guinea-pigs remains controversial. The orthosympathetic nervous control system appears partially inhibited so that bronchial hyperreactivity can be related in part to such an inhibition of local beta receptors activity. As TOWNLEY (1965) and FINKEand MIDDLETON (1968) have suggested, adjusted administrations of propranolol increase bronchial reactivity of guinea-pigs to several bronchoconstrictors in the same range as the et al., active sensitization to ovalbumine. (MARCELLE 1973; MARCELLE, 1976). The role of the parasympathetic nervous system in the different mechanisms involved in the antigeninduced bronchoconstriction remains unclear. MILLS and WIDDICOMBE (1 970) found that vagotomy reduces by 75% the decrease in total lung conductance due to anaphylaxis in 5 guinea-pigs. On the contrary, during the anaphylaxis bronchoconstriction in the same et al. (1978) observed an increase in species, DRAZEN trapped gas volume, but it was not affected by vagotomy. In the same way, in 5 sensitized dogs, COTTON et al. (1977) found no appreciable effect of vagotomy on the bronchoconstriction induced by the antigen inhalation. On the other hand, results obtained with the use of
peripheral antagonists are not steady enough to assess the role played by cholinergic mechanisms in the experimental anaphylactic bronchoconstriction. For exet al. (1976) found that atropine (0.2 ample, MICHOUD mg/kg IP) completely protects only 2 of 5 guinea-pigs tested with antigen. WASSERMAN and GRIFFIN(1979) observed a significant protection against the dyspnea induced by aerosolized antigen in nonanaesthetized guinea-pigs only at high atropine dose (5 mg/kg IP). ADVENIERet al. (1982) on anaphylactic inducedand bronchoconstriction in guinea-pigs and HIRSMAN DOWNES(1981) on Basenji-Greyhoud dog model of asthma noticed a very slight effect of atropine at doses blocking totally exogenous cholinergic bronchial responses. Similar findings were already reported by JOINER et al. (1974) in isolated tracheal smooth muscle of sensitized guinea-pigs which appeared completely protected by atropine against ACh spastic activity but not against antigen-induced contraction. Our results concern curarized guinea-pigs tested during controlled ventilation to ensure comparable conditions in pulmonary mechanics measurements following vagotomy. In control conditions neither curarization nor controlled ventilation significantly altered mechanical properties of the lungs. The data obtained with this procedure in a large number of actively sensitized guinea-pigs indicate that in the same animal, vagotomy is unable to lessen the sensitivity or reactivity to bronchoconstrictor drugs as well as to antigen-induced bronchoconstriction.
CHOLINERGIC MECHANISMS AND
Atropine sulf. mg' 0 Gulnea pigs n : L7
0.82 t .I6
L 23 :.32
28
2L
--
____
Archives of Physiology and Biochemistry Downloaded from informahealthcare.com by Nyu Medical Center on 01/07/15 For personal use only.
2.
24 1
Requ le 10 juillet 1991.
Cholinergic mechanisms and bronchoconstriction in guinea-pigs. BY
R. MARCELLE (Institut Leon Fredericq, Physiologie, Universite de Liege, Belgique)
Archives of Physiology and Biochemistry Downloaded from informahealthcare.com by Nyu Medical Center on 01/07/15 For personal use only.
(3 figures)
Seventy-four guinea-pigs have been actively sensitized against ovalbumin. The effects of bilateral cervical vagotomy and of cholinergic efferent blockade on the bronchoconstriction induced by inhaled acetylcholine, histamine or antigen have been quantified. Animals were curarized then tested during controlled ventilation to ensure constant conditions throughout the whole experiment by suppressing the postvagotomy apneusis. Bronchial sensitivity was estimated by calculating the bronchoconstrictor dose-threshold provoking respiratory asynchronism. Corresponding variation of total lung resistance and dynamic compliance were also measured as indices of bronchial reactivity. The data obtained in 27 guinea-pigs indicated that the vagi section produced no significant effect on the direct bronchial response to histamine (P>0.5), to acetylcholine (P>O.l) or t o antigen (P>O.5). In 47 guinea-pigs, atropine at doses 5 and 10 times higher than the acetylcholine blocking one did not alter the direct bronchial response to histamine ( P > 0.5). Higher doses induced a progressive decrease in bronchial sensitivity to antigen (.05 > P > .01) which could be related to the repetitive administration of the antigen. According to the present results, peripheral cholinergic mechanisms play no significant role in guinea-pigs neither in histamine nor in anaphylactic bronchoconstriction. Curarization has no influence on resting bronchial tone.
Introduction
According to DALE (1914, in BROWN, 1937), acetylcholine (ACh) is the only one known neurotransmetter released at motor vagal nerve endings. It induces bronchial smooth muscle constriction by a specific stimulation of muscarinic receptors, properly blocked by atropine (JAMMES, 1989; HARF, 1990). Such a response seems to implicate the parasympathetic system in the regulation of tracheobronchial smooth muscle tone (WIDDICOMBE,1963; NADEL, 1973). Moreover it has been suggested that an autonomic imbalance favoring cholinergic activity to the airways is also implicated, at least for a part, in the asthmatic attack (NADEL, 1973; CROPP, 1975). Accordingly, atropine derivatives have been proposed as spasmolytic drugs, as a rational alternative to sympathomimetic ones in the asthmatic patients (CHAMBERLAINet al., 1962; Yu et af., 1972; GOLD, 1973). Nevertheless, up to now none of the studjes performed in experimental asthma demontrates clearly that the efferent vagal nerves take a chief part in the antigen-induced bronchospasm mechanisms, notably MILLS& WIDDICOMBE, 1970; JOINERet al., 1974; MICHOUDet al., 1976; COTTON et al., 1977; DRAZENei al., 1978; WASSERMAN & GRIFFIN,1979; HIRSHMAN & DOWNES,1981;ADVENIER ei al., 1982 (see details in discussion).
Some years ago, we have observed in a large number of guinea-pigs that active sensitization against ovalbumin enhanced bronchial sensitivity to ACh as well as to others bronchoconstrictors : histamine (H), serotonine (5HT), bradykinine (B). This indicates that a non specific hyperactivity of bronchial smooth muscles to these agents has been induced. (MARCELLE & LAURENT,1973). In the present study, effects of vagotomy and of vagal efferent blockade by atropine on the bronchial response of actively sensitized guinea-pigs to inhaled ACh, H and antigen are tested in order to assess the role of cholinergic peripheral mechanisms in mediating antigen-induced bronchoconstriction as well as bronchial aspecific hyperreactivity linked with active sensitization. Methods and Materials Seventy four guinea-pigs (Hartley strain) of either sex, weighing 300 to 550 g. were used. 1. Sensitizing procedure. - On day 0, the guineapigs were injected intraperitoneally and subcutaneously with 200 mg of purified ovalbumin (OA), dissolved in 1 ml of 0,9% NaCl solution. On day 15, animals were subcutaneously injected with the same dose of OA precipitated by 50 mg ZnCI2
242
R . MARCELLE
B
Archives of Physiology and Biochemistry Downloaded from informahealthcare.com by Nyu Medical Center on 01/07/15 For personal use only.
A
ml 51 TIDAL VOLUME
lsec. .
FIG.1. Occlusion tracings, from left to right, of the trachealpressure, the airflow and the tidal volume, continuously recorded during controlled ventilation in an actively sensitized guinea-pig inhaling a 5% aerosolized antigen solution. From the start, the figure shows the transition from normal conditions to bronchoconstriction. On the left side (normal), airway occlusions performed by the interrupter induce rectangular tracheal pressure waves (details in A). They correspond to an instantaneous pressure equilibration between alveoli and trachea, measuring the actual dynamic component of the transthoracopulmonary pressure. On the right side, total tracheal pressure variations are increasing when airflow and tidal volume remain unmodified. Simultaneously, tracheal pressure waves induced by the airway occlusions show an incurved profile (details in B). Through narrowed bronchi, pressure equilibration between alveoli and trachea is no more instantaneous but is slowing down and progressive. Such modifications from A to B in the continuous tracheal pressure tracings indicate the onset of the bronchoconstriction. The corresponding inhaled dose is the threshold dose.
to ensure a progressive resorption of the antigen during at least the 7 days preceding the experiment (COLLIER & JAMES, 1967). 2. Ventilatory measurements. - The animals were lightly anesthetized with a low dose of pentobarbitone (Nembutal :20 mg/kg ip), preserving spontaneous ventilation. Local anesthesia (xylocaine 1070) allowed the tracheotomy, the dissection and the catherization of the oesophagus with a 2 mm catheter, filled with water. A tracheal canula was connected to an airflow interrupter (MARCELLE, 1967) extended by a pneumotachograph (Fleisch type no 000) connected to a differential pressure transducer (Efema, EMT 32) measuring airflow (V). A pressure transducer (Efema, EMT 31) filled with distilled water, was connected to the oesophagal catheter to record intrathoracic pressure (PIT). A third pressure transducer (Elema, EMT 31) connected to a small tubing inserted between the endotracheal tube and the interrupter measured the intratracheal pressure (PT). During spontaneous ventilation, transpulmonary pressure (PTP) was obtained by electrical subtraction of the output signals of the intratracheal pressure transducer (PT) from these of the intrathoracic one
(PIT). Tidal volume (Vt) was determined as the electrical integral of airflow (Elema integrator). Output signals representing PT, PTP, V and Vt were simultaneously recorded on a Mingograph polygraph model 42. Flow resistance (FR) and dynamic lung compliance (C Dyn) were calculated. During controlled ventilation managed by a Braun type constant respirator, total lung resistance (RL) and dynamic compliance (C Dyn) were determined from the transthoracopulmonary pressure variations measured at tracheal tubing. Dynamic and elastic components were respectively reported to corresponding values of V and Vt. Throughout the entire experiment the blood pressure was recorded from a catheter inserted in the right carotid artery. Repetitive interruptions of the airflow were used to distinguish between actual elastic and dynamic components of the tracheal pressure, in spontaneous as well as in controlled ventilation (OTIS& PROCTOR, 1947; MARCELLE, 1967; GOTTFRIED et af., 1984).
3. Protocol. - Respiratory measurements were performed in supine position firstly during spontaneous respiration and secondly during controlled ventilation. This latter was performed on curarised animals
243
CHOLINERGIC MECHANISMS AND BRONCHO-CONSTRICTION
(Pancuronium :1 ml/ip) t o ensure muscle relaxation and constant conditions by suppressing the postvagotomy apneusis. Agonists or antagonists dissolved in 9% or 1 % NaCl solutions, were nebulized (Mistogen) and inhaled during continuous registration of Vt in order to calculate the dose (Q) which has been administered,
Archives of Physiology and Biochemistry Downloaded from informahealthcare.com by Nyu Medical Center on 01/07/15 For personal use only.
according t o the formula : Q
=
v x c ~
Pg
1.34 where V is the total ventilation performed throughout the inhalation of the aerosol; C, the concentration of the agent in pg/ml, 1.34 is an approximate characteristic of the nebulizor representing the volume of air (in liter) dispersing 1 ml of the solution. Inhalation of the agonists was stopped as soon as a bronchial response occurs. The latter is indicated by the appearance of a respiratory asynchronism, as revealed by an increase of the tracheal pressure (PT) variations associated with an incurved profile of the tracheal pressure waves observed during the interruptions of the airflow. This configuration contrasts with the rectangular profile of the same waves in normal conditions as shown in Figure 1 (OTISet al., 1956; PETIT & MARCELLE,1964). The dose inhaled at that time represents the threshold bronchoactive dose. It is an index of bronchial sensitivity. The lower the dose, the higher the sensitivity. 4. Drugs. - The following drugs were used : ovalbumin (Calbiochem); pentobarbitone (NembutalCeva); xylocaine dihydrochloride (Astra); acetylcholine chloride (Fluka); pancuronii bromidum; histamine dihydrochloride (Calbiochem).
5 . Statistics. - The results were expressed as mean f SEM. Difference were tested for non paired values
by a Student's t test. P i s considered as significant when 0.5). After vagotomy the bronchial response to ACh at the delay corresponding to the installation of the respiratory asynchronism did not vary as far as RL and C Dyn variations were concerned (P>O.5). The mean dose of inhaled ACh was somewhat higher but the difference was not statistically significant ( P > 0.1). Vagotomy exerted no appreciable effect on the antigeninduced bronchoconstriction : the mean inhaled dose of ovalbumin corresponding to respiratory asynchronism threshold, to increase in RL and to decrease in C Dyn did not show any significant difference (P>0.5) in comparison with the mean dose of antigen active in control conditions. 3. Effects of graded doses of atropine.
In 47 guinea-pigs, 3 doses of atropine were tested, as calculated afterwards : 824 pg (SD : k 165); 4235 pg (SD : k316) and 9041 pg (SD : k384). They corresponded to the inhalation of the 1% aerosol during 2 min, and of the I % aerosol during 1 min and 2 min respectively. Figure 3 shows that bronchial responses to a 16 fold higher dose of ACh had fallen to zero from the smallest atropine dose (824 pg f 165). Even the highest atropine dose (9041 pg k 384) did not exert any appreciable effect on H-induced bronchospasm (P>O.5). The bronchial reactivity to the antigen was somewhat decreased. After the lowest dose of atropine, antigen inhalation was increased from 1400 to 2100 pg. After the two higher doses of atropine, a proportional increase of the ovalbumin inhaled dose, respectively 2400 pg and 3600 pg, was necessary in order to get a comparable bronchial response. The decrease of the bronchial sensitivity to the antigen with increasing doses of atropine is statistically significant (respectively : P = 0.03; P = 0.05; P = 0.01).
244
R. MARCELLE
Archives of Physiology and Biochemistry Downloaded from informahealthcare.com by Nyu Medical Center on 01/07/15 For personal use only.
Histamine H
Acetylcholine E4
I
Ovalbumine
Ed
I
ml .cm H,O-' FIG. 2 . Bronchial responses in 27 actively sensitized guinea-pigs before (A) and after (B) vagofomy. Open columns show mean increase in RL and decrease in C Dyn successively induced by histamine, acetylcholine and ovalbumin, before (A) and after (B) vagotomy. Striped columns indicate mean inhaled doses of these 3 agents in the two conditions (A and B). Vertical lines represent s.e.m. Statistical evaluation of the results shows that vagotomy does not reduce the bronchial sensitivity to pharmacological and anaphylactic stimulations in actively sensitized guinea-pigs ( P > 1).
Discussion The role played by the autonomic nervous system in bronchial hyperreactivity associated with the active sensitization in guinea-pigs remains controversial. The orthosympathetic nervous control system appears partially inhibited so that bronchial hyperreactivity can be related in part to such an inhibition of local beta receptors activity. As TOWNLEY (1965) and FINKEand MIDDLETON (1968) have suggested, adjusted administrations of propranolol increase bronchial reactivity of guinea-pigs to several bronchoconstrictors in the same range as the et al., active sensitization to ovalbumine. (MARCELLE 1973; MARCELLE, 1976). The role of the parasympathetic nervous system in the different mechanisms involved in the antigeninduced bronchoconstriction remains unclear. MILLS and WIDDICOMBE (1 970) found that vagotomy reduces by 75% the decrease in total lung conductance due to anaphylaxis in 5 guinea-pigs. On the contrary, during the anaphylaxis bronchoconstriction in the same et al. (1978) observed an increase in species, DRAZEN trapped gas volume, but it was not affected by vagotomy. In the same way, in 5 sensitized dogs, COTTON et al. (1977) found no appreciable effect of vagotomy on the bronchoconstriction induced by the antigen inhalation. On the other hand, results obtained with the use of
peripheral antagonists are not steady enough to assess the role played by cholinergic mechanisms in the experimental anaphylactic bronchoconstriction. For exet al. (1976) found that atropine (0.2 ample, MICHOUD mg/kg IP) completely protects only 2 of 5 guinea-pigs tested with antigen. WASSERMAN and GRIFFIN(1979) observed a significant protection against the dyspnea induced by aerosolized antigen in nonanaesthetized guinea-pigs only at high atropine dose (5 mg/kg IP). ADVENIERet al. (1982) on anaphylactic inducedand bronchoconstriction in guinea-pigs and HIRSMAN DOWNES(1981) on Basenji-Greyhoud dog model of asthma noticed a very slight effect of atropine at doses blocking totally exogenous cholinergic bronchial responses. Similar findings were already reported by JOINER et al. (1974) in isolated tracheal smooth muscle of sensitized guinea-pigs which appeared completely protected by atropine against ACh spastic activity but not against antigen-induced contraction. Our results concern curarized guinea-pigs tested during controlled ventilation to ensure comparable conditions in pulmonary mechanics measurements following vagotomy. In control conditions neither curarization nor controlled ventilation significantly altered mechanical properties of the lungs. The data obtained with this procedure in a large number of actively sensitized guinea-pigs indicate that in the same animal, vagotomy is unable to lessen the sensitivity or reactivity to bronchoconstrictor drugs as well as to antigen-induced bronchoconstriction.
CHOLINERGIC MECHANISMS AND
Atropine sulf. mg' 0 Gulnea pigs n : L7
0.82 t .I6
L 23 :.32
28
2L
--
____
Archives of Physiology and Biochemistry Downloaded from informahealthcare.com by Nyu Medical Center on 01/07/15 For personal use only.
2.
