The relaxing activity of iloprost and prostaglandin E2 in the isolated various smooth muscle strips of the rabbit.

The effects of iloprost (ZK 36 374), a stable analogue of prostacyclin, and prostaglandin E2 (PGE2) were studied on isolated spirally cut strips of rabbit aorta, celiac, mesenteric and renal arteries continuously superfused in cascade. Iloprost and PGE2 elicited a concentration-dependent relaxation of phenylephrine-contracted celiac and mesenteric strips having equal affinities as verified by identical pD2 values. Iloprost also produced a concentration-dependent relaxation in precontracted renal artery strips at relatively higher concentrations but had little relaxing action on precontracted aortic strips. Contrary, PGE2 induced a concentration-dependent relaxing effect on precontracted aortic strips without producing an appreciable action on renal artery strips. Acetylsalicylic acid (ASA) when added to the superfusion medium elicited an increase in basal tonicity of celiac and mesenteric strips without altering the basal tonicity of renal artery and aortic strips. Iloprost at very low concentrations (10(-10)-10(-9) mol/l) produced a complete recovery in increased tonicity of both strips while at the same concentrations PGE2 had little effect. These results indicate that endogenous PGI2 may have an important role in the regulation of vascular tonicity in celiac and mesenteric arteries.