Relaxant effect of prostaglandin E1 on the isolated intestine of the toad (bufo melanostictus)

Abstract

The pharmacological actions of prostaglandins E1, F1α, E2 and A1 were studied on the longitudinal and circular muscles of the isolated small intestine of the toad. Prostaglandin E1 caused relaxation, whereas prostaglandin A1 was inactive and prostaglandins F1α and E2 caused contractions. Other substances which relaxed the toad intestine were adrenaline, noradrenaline and isoprenaline. On a molar basis, prostaglandin E1 was seven times less potent than isoprenaline, but it was three times more potent than adrenaline and seventeen times more potent than noradrenaline. Phentolamine and propranolol blocked the relaxant effects of catecholamines in concentrations which did not alter the relaxant effect of prostaglandin E1. The results suggested that prostaglandin E1 acted directly on the intestinal smooth muscle of the toad rather than by the local release of catecholamines. © 1970 Birkhäuser-Verlag.