In vitro effect of nifedipine on KCl and 5-hydroxytryptamine-induced contractions of the sheep coronary, cerebral and pulmonary arteries.

The aim of the present study was to compare the sensitivity to nifedipine of contraction, obtained with 5-hydroxytryptamine (5-HT) and high K+, of arteries from three vascular territories (coronary, cerebral and pulmonary), selecting arteries of equivalent diameter (0.4-0.8 mm). In the coronary and middle cerebral arteries, contraction produced by KCl was abolished by nifedipine 10(-7) M. However, in the pulmonary artery 39 +/- 2% (n = 5) of the KCl contraction remained in the presence of nifedipine 10(-6) M and a similar sized contraction remained in the presence of Ni2+ 10 mM, La3+ 1 mM or Ca(2+)-free conditions. Nifedipine caused less inhibition of 5-HT than of KCl in all three arteries. In the coronary and middle cerebral arteries 5-HT was inhibited to 55 +/- 9% and to 55 +/- 4% and in the pulmonary artery to 78 +/- 3% (n = 6) by nifedipine 10(-6) M. In conclusion, a comparison of coronary, cerebral and pulmonary arteries, of comparable size and from the same species, has shown that there is diversity in the sensitivity of 5-HT-induced contraction to inhibition by nifedipine. Moreover, the KCl-induced contraction in the sheep pulmonary artery is mediated, in part, by a mechanism independent of Ca2+ influx.