Responses of isolated dog arteries to amrinone

Helically-cut strips of dog cerebral, coronary, mesenteric, renal and femoral arteries contracted with prostaglandin (PG) F2 alpha or K+ responded to amrinone (10(-5) to 10(-4) mol X litre-1) with relaxation, which was not influenced by treatment with propranolol, atropine, cimetidine, aminophylline or aspirin. The contractile response of mesenteric arteries to transmural electrical stimulation (2, 5 and 20 Hz) and noradrenaline was attenuated by amrinone (3 X 10(-5) and 10(-4) mol X litre-1); the attenuation of the response to nerve stimulation and noradrenaline did not significantly differ. Ca2+-induced contractions in mesenteric arteries exposed to Ca2+-free media and depolarised by excess K+ were inhibited by amrinone, and the inhibition could not be reversed by the addition of excess Ca2+. Treatment with amrinone potentiated the relaxant responses of mesenteric arteries to adenosine but did not alter the response to isoprenaline. Amrinone in concentrations sufficient to produce moderate and marked relaxation did not significantly alter the content of cyclic AMP in mesenteric arteries. Attenuation by amrinone of the contractile response to transmural stimulation, noradrenaline and Ca2+ and the relaxation of a variety of arteries induced by amrinone may not be due to interference with the transmembrane influx of Ca2+ and intracellular accumulation of cyclic AMP but to a nonspecific action on arterial smooth muscle. Amrinone appears to increase the metabolic vasodilatation by potentiating the vasodilator action of adenosine.