Influence of extracellular calcium and calcium antagonists on contractions induced by potassium and prostaglandin F_2α in isolated cerebral and mesenteric arteries of the cat

Abstract

1The effects of a number of calcium antagonists (diltiazem, nifedipine, nimodipine and verapamil) have been studied on feline isolated pial arteries contracted by potassium (127 mM) or prostaglandin F2X (PGF2,,, 2.5 riM) and mesenteric arteries contracted by potassium (127 mM). 2 Withdrawal of Ca2+ from the extracellular medium for 30 min reduced the contractile response to potassium in cerebral vessels by 92% and in mesenteric vessels by 96%. Subsequent addition of Ca2+ caused reproducible contractions which were inhibited by both nifedipine and nimodipine. 3 The four calcium antagonists relaxed the isolated middle cerebral artery contracted either by potassium or PGF2,,, and mesenteric arteries contracted by potassium, in the following order of potency: nimodipine > nifedipine > verapamil > diltiazem. 4 Nimodipine was more potent than nifedipine in cerebral arteries, and more potent in cerebral than in mesenteric arteries. Otherwise, the potassium-contracted cerebral and mesenteric vessels showed no major differences in sensitivity to calcium antagonists.

In vitro effects of calcium entry blockers, chlorpromazine and fenoterol upon human pregnant myometrium contractility

“…The order ofpotency of nifedipine and verapamil against K+-induced contractions found in this study is consistent with other reports on voltage-operated channels (Cauvin et al, 1983). Studies with isolated arteries indicate that nifedipine is approximately a hundred fold more Fleckenstein-Grun, 1980;Fanta & Drazen, 1983;Andersson et al, 1983). Our data, however, do not permit us to determine whether these drugs shared a common mechanism of action in pregnant human myometrium, but do indicate that calcium influx is necessary for the development ofK+ -induced contractions and to a lesser extent for spontaneous contractions.…”

A comparison of several calcium antagonists on uterine, vascular and cardiac muscles from the rat

“…This rank order (or nifedipine > verapamil > diltiazem) has also been found against K+-evoked spasms ofcerebral and mesenteric arteries of the cat (Andersson et al, 1983) and coronary arteries of the pig (Fleckenstein & Fleckenstein-Grun, 1980). These data provide no support for the idea that these three compounds interact at different sites in these tissues.…”

Effects of five different organic calcium antagonists on guinea‐pig isolated trachea

“…The rank order seems to be different in other experimental models, verapamil, for instance, being more active than diltiazem in cat cerebral and mesenteric arteries (Andersson et al, 1983).…”