Effects of Ca antagonists on the contractile responses to vasoactive agents in isolated canine saphenous veins and superior mesenteric arteries.

Abstract

Effects of Ca antagonists, diltiazem, verapamil and nicardipine, on contractile responses to norepinephrine (NE), KCl and transmural nerve stimulation (TNS) in canine saphenous veins and superior mesenteric arteries were studied. Helical strips were suspended in an organ bath containing Krebs-bicarbonate solution (37°C) for isometric recording. Diltiazem, verapamil and nicardipine noncompetitively inhibited NE- and KCl-induced contractions both in veins and arteries in a dose-related manner. Generally, pD¿ values for the drugs were significantly greater in arteries than in veins. The drugs also noncompetitively inhibited TNS-induced contraction in a dose-dependent manner. There was no significant difference between veins and arteries in pD¿ values for the drugs except nicardipine. Phentolamine competitively inhibited NE-induced contraction and noncompetitively inhibited KCl- and TNS-induced contractions. The inhibitory effect of phentolamine on KCl-induced contraction in veins was significantly greater than that in arteries, while no significant difference between veins and arteries in the inhibitory effect of the drug on NE- and TNS-induced contractions was observed. These results suggest that exogenous NE- and KCl-induced contractions in mesenteric arteries may depend more on the influx of extracelullar Ca2+ than in saphenous veins, since inhibitory effects of Ca antagonists on these agonists-induced contractions were stronger in mesenteric arteries than in saphenous veins.