Influence of extracellular calcium and calcium antagonists on contractions induced by potassium and prostaglandin F2 alpha in isolated cerebral and mesenteric arteries of the cat.

1 The 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 F2 alpha (PGF2 alpha, 2.5 microM) 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 alpha, and mesenteric arteries contracted by potassium, in the following order of potency: nimodipine greater than nifedipine greater than verapamil greater than 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.