Prostaglandins involved in contractions by angiotensin II and bradykinin of isolated dog sphincter pupillae

Abstract

1 The dog isolated sphincter pupillae contracted in response to acetylcholine, angiotensin II (AII), bradykinin, prostaglandins F_2α, D₂, E₂ and I₂, and thionate thromboxane A₂ (sTXA₂) in a concentration-dependent manner. 2 AII-induced contractions were suppressed by treatment with saralasin, indomethacin, aspirin and diphloretin phosphate (DPP), a prostaglandin receptor antagonist. Contractions induced by bradykinin were also attenuated by indomethacin, aspirin and DPP. The amount of prostaglandin F_2α (PGF_2α) in the bathing media was increased approximately 41% following stimulation of the preparations by bradykinin. 3 The potency of contractile responses was in the order of PGF_2α > PGD₂ = sTXA₂ > PGE₂ > arachidonic acid > PGI₂. Contractions induced by PGF_2α were not significantly affected by treatment with indomethacin and ONO3708, an antagonist of the vasoconstrictor effect of prostaglandins, but appreciably attenuated by DPP. Arachidonic acid-induced contractions were inhibited by indomethacin. 4 Contractions of dog iris sphincter muscle in response to AII and bradykinin may be mediated via substances synthesized by cyclo-oxygenase from arachidonic acid. The distribution and nature of the prostaglandin receptors appear to differ markedly in iris sphincter and vascular smooth muscles.