Bombesin-induced contractions of guinea pig lung strips are modulated by endogenous nitric oxide.

We have investigated the effects of a nitric oxide (NO) biosynthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) on the bombesin-evoked contraction of guinea pig parenchymal lung strips. The bombesin-induced contractions of lung strips were significantly increased after L-NAME (300 micro)) pre-treatment. The maximal response was increased (P < 0.01) by 37% after L-NAME treatment when compared with the control group. The pD2 value was not influenced by L-NAME pre-treatment. The enhancement of the bombesin-induced contraction caused by L-NAME was reversed by addition of an excess of the NO precursor L-arginine (600 microM) but not by the addition of its inactive enantiomer D-arginine (600 microM). Like L-NAME, methylene blue (1 microM), an agent that inhibits the soluble guanylyl cyclase activated by NO, significantly increased (P < 0.01) the maximal contraction induced by bombesin (183 +/- 16 mg) when compared with the control group (141 +/- 15 mg). When tested against other agonist-induced contractions, L-NAME did not change the responsiveness of parenchymal lung strips to bradykinin or carbachol but significantly increased lung contraction induced by histamine. NO synthesis inhibition resulted in a pronounced increase in the bombesin-induced contraction of guinea-pig lung strips. Our results suggest that bombesin contributes to NO synthesis and release which then acts to reduce the contraction of the lungstrip in response to bombesin.

Endopeptidase 24.15 modulates bradykinin-induced contraction in guinea-pig trachea.

Guinea-pig tracheal strips were contracted with cumulative concentrations of bradykinin or substance P in the presence of thiorphan, an inhibitor of endopeptidase 24.11 and of angiotensin-converting enzyme, or in the presence of N-[1-(R,S)-carboxy-3-phenylpropyl]Ala-Ala-Phe-para-aminobenzoate (cFP-AAF-pAB), a selective inhibitor of endopeptidase 24.15. The concentration-effect curve of bradykinin was shifted to the left in the presence of each inhibitor whereas the curve of substance P was sensitive to thiorphan but not to cFP-AAF-pAB. These results show that endopeptidase 24.15 may modulate the contractile effect of bradykinin but not that of substance P in the guinea-pig trachea.

Characterization of muscarinic receptors in human, guinea pig and rat lung.

Muscarinic receptor subtypes in human, guinea pig and rat lung tissue were characterized by radioligand binding, and functional studies were carried out on guinea pig and rat tissues. Control binding experiments were performed with membranes from human tissues rich in M1 (hippocampus), M2 (pons-medulla) and M3 (salivary gland) receptor subtypes. Competitive binding experiments with atropine and 4-diphenylacetoxy-N-methylpiperidine methobromide did not reveal any tissue selectivity of these ligands. Pirenzepine, a selective M1 antagonist with 11-2[[2-[(diethylamino)methyl]-1-piperidinyl] acetyl]-5, 11-dihydro-6H-pyrido[2,3-b] [1,4]-benzodiazepine-6-one (AF-DX116), a selective M2 antagonist, made it possible to characterize muscarinic subtypes. In hearts from the three species, the low affinity for pirenzepine and the high affinity for AF-DX116 were related to M2 receptors. In rat lung, the high affinity for AF-DX116 and the intermediate affinity for pirenzepine indicate M2 and M3 subtypes. Guinea pig and human lung tissues contain 48 and 67%, respectively, of muscarinic binding sites with high affinity for pirenzepine (M1). The second muscarinic receptor population in human lung might be classified as M3 in view of the cardioselectivity of AF-DX116, but the occurrence of M2 cardiac-type receptors could not be excluded. In guinea pig lung, both M2 and M3 subtypes might occur in addition to M1 receptors. Muscarinic stimulation led to the contraction of guinea pig and rat lung strips but did not significantly affect human lung strips. We suggest that presynaptic M2-muscarinic receptors modulated the M3-induced contraction in the guinea pig lung smooth muscle.

Role of cyclic AMP- and cyclic GMP-phosphodiesterases in the control of cyclic nucleotide levels and smooth muscle tone in rat isolated aorta. A study with selective inhibitors.

Three isoforms of cyclic nucleotide phosphodiesterase (PDE) have been recently isolated from aortic tissue and two of them specifically hydrolyzed adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3':5'-cyclic monophosphate (cGMP), respectively (Lugnier et al., Biochem. Pharmac. 35, 1743, 1986). The role of these forms in controlling cyclic nucleotide levels and smooth muscle tone was investigated by the use of PDE inhibitors. The effects of selective inhibitors of the two forms specifically hydrolyzing cAMP or cGMP (cAMP-PDE and cGMP-PDE, respectively) were compared to those of non-selective inhibitors of the three aortic PDE forms, including the calmodulin-sensitive one (CaM-PDE). Relaxation responses and accumulation of tissue cAMP and cGMP induced by these drugs were studied in precontracted rat isolated aorta, and compared to the effects of isoprenaline and forskolin (stimulants of adenylate cyclase) or sodium nitroprusside (SNP) and sodium azide (stimulants of guanylate cyclase). The eight PDE inhibitors tested all relaxed aorta with potencies that correlated with their potencies as inhibitors of cAMP-PDE, but not of cGMP-PDE. At a concentration producing half-maximal relaxation, all PDE inhibitors induced a moderate but significant accumulation of cAMP, which was comparable to the accumulation of cAMP elicited by half-maximally relaxing concentrations of adenylate cyclase stimulating agents. At this concentration, some PDE inhibitors (M&B 22,948, dipyridamole and to a lesser extent, trequinsin) also induced a significant increase in cGMP levels, of the same order of magnitude as that caused by agents stimulating guanylate cyclase. However, the cGMP-increasing effect of these inhibitors was dissociated from their relaxing effect. In particular, the relaxing concentrations of M&B 22,948 (a selective inhibitor of cGMP-PDE) were clearly higher than the cGMP-increasing concentrations of the compound. At a concentration at which they elicited 10% relaxation by themselves, the selective cAMP-PDE inhibitor, rolipram, as well as the mixed inhibitor of cAMP- and cGMP-PDE, AAL 05 (a cilostamide analogue) enhanced both the cAMP-increasing and the relaxing effect of isoprenaline. Under the same conditions, no clear enhancement of the relaxation induced by SNP was observed. Only M&B 22,948 showed a slight potentiating effect on SNP-induced relaxation, but this effect was limited to low concentrations of SNP (less than 10 nM).(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of papaverine on cyclic nucleotide levels in the isolated rat aorta.

An increase in cAMP but no significant modification in cGMP content could be demonstrated in rat aorta strips after applying papaverine in concentrations which reduced contractile responses. Accumulation of cAMP was induced in noradrenaline-stimulated on K+-depolarized strips, under omission of external Ca2+. Thus the elevation of cAMP level preceded the reduction of contraction subsequently elicited by readdition of Ca2+. The effects could not be dissociated under the experimental conditions used here.

Papaverine, cyclic AMP and the dependence of the rat aorta on extracellular calcium.

The spasmolytic effects of papaverine and dibutyryl cyclic AMP (db-cAMP) were compared on isometric contractile responses induced by addition of increasing amounts of external calcium to K+-depolarized or noradrenaline-stimulated rat aorta strips. Papaverine at a concentration active on depolarized strips (3 times 10(-5) moles/1) reduced the maximal contraction (Emax) elicited by Ca2+ in these preparations, while db-cAMP did not. Contrary to what was observed on depolarized aortae, the degree of inhibition of noradrenaline-stimulated strips did not decrease with increasing extracellular calcium concentration (Ca)e. Both db-cAMP and papaverine at a concentration which did not depress Emax (5 times 10(-6) moles/1) potentiated the relaxing effect of high (Ca)e on contractions elicited by noradrenaline. In conclusion, cyclic AMP is probably implicated in the mode of action of papaverine on the noradrenaline-stimulated rat aorta. At a concentration active on depolarized strips, papaverine is also able to impair contractility directly.