Action of papaverine and verapamil on norepinephrine and calcium evoked contraction of vascular and non vascular smooth muscle.
On isolated rat vas deferens both papaverine and verapamil show a non competitive antagonism against norepinephrine and a competitive antagonism against Ca2+. Verapamil is nearly 100 times more active than papaverine. On the main pulmonary artery and on the thoracic aorta of the rabbit, verapamil shows a competitive antagonism against both norepinephrine and Ca2+ but it is more effective (almost 100 times) against Ca2+ than norepinephrine. Papaverine also shows a competitive antagonism against norepinephrine but a non competitive antagonism against Ca2+. The contrasting results obtained on rat vas deferens and rabbit vessels might be due to: 1) mechanism(s) of action of the agonist; 2) properties of the biological object as far concerns receptor activation and mechanism(s) of excitation-contraction coupling; 3) mechanism(s) of action of spasmolytic drugs. All these factors act in a cooperative way in determining the quality and the quantity of the observed responses.
D000818:Animals; D002118:Calcium / Q000037:antagonists & inhibitors*; D005260:Female; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009638:Norepinephrine / Q000037:antagonists & inhibitors*; D010208:Papaverine / Q000494:pharmacology*; D011817:Rabbits; D014700:Verapamil / Q000494:pharmacology*
D014700:Verapamil; D010208:Papaverine; D002118:Calcium; D009638:Norepinephrine