Session 26 : pharmacologie broncho-pulmonaire

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Session 26 : pharmacologie broncho-pulmonaire

261

EFFECTS OF GENISTEIN, A TYROSINE KINASE INHIBITOR, ON THE GUINEA PIG ISOLATED TRACHEA.

E. Corompt, F. Caron, G. Bessard and Ph. Devillier

Laboratoire de Pharmacologie, Faculté de Médecine de Grenoble, Domaine de la Merci, 38 706 La Tronche Cedex, France

Smooth muscle contains high levels of tyrosine kinase activity and tyrosine kinase pathways influence force development by acting on mechanisms which regulate both intracellular free calcium level and the effects of calcium on the contractile apparatus. In order to characterize the in vitro effects of tyrosine kinase inhibition on airway smooth muscle, we have compared the effects of genistein and its inactive analog daidzein on the guinea pig trachea (GPT).

Genistein (10-5 M to 10-4 M) inhibited the contractions of GPT induced by KCI and CaC12 whereas daidzein (up to 10-4 M) was devoid of inhibitory effect on KCI-induced contraction. In addition, genistein induced the relaxation of GPT pre contracted with acetylcholine (pD2 = 4.8

± 0.1). However, daidzein also exerted a relaxant effect with a similar potency but a weaker efficacy. The relaxant effect of genistein was not inhibited by potassium channel blockers or potentiated by phosphodiesterase inhibitors (rolipram, zaprinast). In contrast, genistein (10-4 M) potentiated the relaxant responses to isoprenaline and forskolin but did not alter the relaxation induced by sodium nitroprusside. Similarly, daidzein (10-4 M) potentiated the relaxant responses to isoprenaline and forskolin but was devoid of effect on the relaxation induced by sodium nitroprusside. These results suggest that genistein and daidzein potentiate the AMPc-dependent pathway of relaxation by inhibiting the activity of the relevant phosphodiesterases.

In conclusion, genistein induced a potent inhibition of the GPT contraction induced by KCI and CaCl2 probably by inhibition of the tyrosine kinases. However, genistein is not a specific inhibitor of these kinases since, as its inactive analog on the tyrosine kinases, it also exerted an inhibitory effect on the AMPc-specific phosphodiesterases which contributes to explain its relaxant activity on the GPT.

262

INTERACTIONS BETWEEN C-FIBERS, CHOLINERGIC FIBERS AND MAST CELLS IN TRACHEALLY PERFUSED RABBIT LUNGS

A. Nemmar, A. Delaunois, P. Gustin

Dpt. de Pharmacologie, Pharmacothérapie et Toxicologie, Fac. Méd.Vét., Université de Lidge, Bd. de Colonster Bat 41, B-4(XN) Liège, Belgique.

Biochemical and pharmacological mechanisms involved in the interactions between C fibers, cholinergic fibers and mast cells were investigated in tracheally perfused rabbit lungs. The amounts of SP and histamine released in lungs superfusates were measured by radioimmunoassay (RIA) after capsaicin and carbachol administration. Capsaicin (10-4M) induced a simultaneous increase in SP and histamine release in lung effluents. The release of both mediators was prevented by pretreating the lungs with the NK1 antagonist SR 140333 (10-7M) and atropine (10-6M). Carbachol (l0-4M) also caused an increase in SP and histamine release. SR 140333 (10-7M) prevented the release of SP but not that of histamine. Exogenous SP induced an increase in histamine release, this latter being significantly greater in lungs perfused with neutral endopeptidase (NEP) inhibitor, thiorphan (10-5M). We conclude that capsaicin can induce the release of SP from C fibers with subsequent release of histamine by activation of NR1 receptors present on mast cells. Owing to the blokade of capsaicine-induced SP release by SR 140333 and atropine, we conclude that SP can also cause the release of acetylcholine (Ach) by activation of NK1 receptors present on cholinergic fihers. Like capsaicin, carbachol induced the release of SP from C fibers by activating muscarinic receptors with subsequent release of histamine from mast cells. In addition, carbachol can produce the release of histamine by a direct stimulation of mast cells.

Work supported by FNRS (Fond National de la Recherche Scientifique) and FSR (Fonds Spéciaux de la Recherche, Université de Liège).

263

EFFECTS OF OZONE ON THE MECHANICAL PROPERTlES AND HEMODYNAMICS OF ISOLATED PERFUSED RABBIT LUNGS

A. Delaunois, P. Segura*, M. Vargas*, L, Montano*, P. Gustin

Dpt. de Pharmacologie-Toxicologie, Fac. Méd.Vét.9 Université de Liège, Bd. de Colonster Bat 41, B-4000 Liège, Belgique.

*: Opt of Research in Asthma INER, Calz. de Tlalpan, 4502, Mexico D.F., Mexico.

The effects of rabbit exposure to ozone (O3) (0.4 ppm for 4 hours) on pulmonary mechanics and hemodynamics have been investigated on the isolated perfused lung model. Tracheal pressure, airflow and tidal volume were measured in order to calculate lung resistance (RL) and dynamic compliance (Cdyn). Using arterial/venous/double occlusions the total pressure gradient (

D Pt) was partitioned into four components (arterial, pre-, postcapillary and venous). Dose-response curves to acetylcholine (ACh), substance P (SP) and histamine were constructed in lungs isolated from rabbits immediately or 48h after air or O3 exposure. O3 induced a significant increase in the baseline value of D Pt and partly inhibited the ACh-, SP- and histamine-induced decreases in Cdyn and increases in RL. Immediately after exposure, O3 did not significantly modify the ACh-, SP- and histamine-induced vasoconstriction. Forty-eight hours alter exposure, O3 induced a contractile response to ACh and SP in the arterial segment, but decreased the response to histamine. It was concluded that O3 can induce direct vasoconstriction. Directly but also 48h after exposure, O3 can inhibit the ACh-, SP- and histamine-induced changes in lung mechanical properties. Ozone can also induce some changes in the intensity and in the location of the vascular responses to ACh-, SP and histamine.

264

COMPARED EFFECTS OF ISOPRENALINE, SALBUTAMOL AND SR 59104A ON POTASSIUM CHANNELS IN HYPOXIC PULMONARY VASOCONSTRICTION

JP Dumas1, F. Goirand1, M.Bardoul1,2, M Dumas1, L. Rochette1, C Advenier2, JF Giudicelli3

Lab. Physiopathol. Pharmacol. Cardiovasc., Fac. Médecine 21000 Dijon (1) Lab.Pharmacol. Fac. Médecine Paris-Ouest 75006 Paris (2) and Paris-Sud 94276 Le Kremlin Bicêtre Cedex (3), France.

This study investigated in isolated perfused rat lungs the antagonist effects of a non selective (isoprenaline ) and of selective

b 2-(salbutamol) and b 3-(SR 59104A) adrenoceptor agonists vs the hypoxic pulmonary pressor response (HPR). Glibenclamide (GLI 10-6 M), charybdotoxin (CHTX 10-7 M) and apamine (APA 5.10-8 M) were used to block KATP, high conductance KCa and low conductance KCa (SKCa) channels respectively. GLI, CHTX and APA did not enhance significantly the baseline pressure in normoxia. Hypoxic ventilation (5%CO2-95%N2) produced a significant pressor response (+3.92 ± 0.07 mmHg, P