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.
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects* / Q000502:physiology; D003994:Bucladesine / Q000494:pharmacology*; D002118:Calcium / Q000037:antagonists & inhibitors / Q000502:physiology*; D003864:Depression, Chemical; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009467:Neuromuscular Depolarizing Agents / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010208:Papaverine / Q000494:pharmacology*; D051381:Rats; D013268:Stimulation, Chemical
D009467:Neuromuscular Depolarizing Agents; D003994:Bucladesine; D010208:Papaverine; D002118:Calcium; D009638:Norepinephrine