Effects of extracellular calcium and of calcium antagonists on the contractile responses of isolated human pial and mesenteric arteries.
In isolated human pial arteries (diameter 0.4-0.5 mm), contractions were produced by potassium, noradrenaline, serotonin, and prostaglandin F2 alpha. For comparison, experiments were also performed on human mesenteric arteries. Threshold concentration for potassium-induced contraction in pial arteries was about 10 mM; in mesenteric arteries it was 3-5 mM higher. In pial arteries the calcium antagonists nifedipine and nimodipine caused an almost complete relaxation of contractions induced by potassium at drug concentrations relaxing prostaglandin F2 alpha-contracted vessels to only about 60%. Both nifedipine and nimodipine effectively inhibited contraction elicited by noradrenaline and serotonin in pial arteries. Nifedipine had a higher potency for relaxing cerebral than mesenteric arteries contracted by potassium (p less than 0.001). No such difference was demonstrated for nimodipine. In pial arteries pretreated in a calcium-free medium for 30 min, potassium depolarisation elicited contractions reaching a maximum amplitude of about 40% of that evoked in normal Krebs solution. Both nifedipine and nimodipine effectively inhibited contractions induced by calcium in pial arteries pretreated in a calcium-free medium and depolarised by potassium. The results suggest that potassium, amines, and prostaglandin F2 alpha activate isolated pial and mesenteric arteries by different calcium-dependent mechanisms and confirm the potent relaxant effects of nifedipine and nimodipine in these vessels.
D002118:Calcium / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015237:Dinoprost; D006801:Humans; D008638:Mesenteric Arteries / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D009539:Nicotinic Acids / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D009553:Nimodipine; D009638:Norepinephrine / Q000494:pharmacology; D010841:Pia Mater / Q000098:blood supply; D011188:Potassium / Q000494:pharmacology; D011460:Prostaglandins F / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology
D002121:Calcium Channel Blockers; D009539:Nicotinic Acids; D011460:Prostaglandins F; D012701:Serotonin; D009553:Nimodipine; D015237:Dinoprost; D009543:Nifedipine; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine