Pharmacological effects of urotensins. I. Regional vascular effects of urotensins I and II in the rat.

The effects of urotensins I and II were studied on blood space and inulin space (with 51Cr-labelled erythrocytes and 14C inulin) in organs obtained from rats anaesthetized with pentobarbital. The findings were matched with the effects of urotensins on blood pressure and on perfusion pressure in the isolated perfused rat hind limb (skeletal muscle), intestine, kidney, and lung. Blood space was greatly increased by urotensin I (50 mU/100 g body wt iv) in skeletal muscle, intestine (ileum), ear, renal cortex, medulla and papilla and in adrenal gland, but was decreased in liver and spleen. Blood space changes in these organs run in parallel with the blood-pressure-lowering effect of I. After urotensin II, no significant changes were observed in the above organs, with the exception of the renal cortex where an increase in blood space occurred. Urotensin I caused an increase in inulin space in skeletal muscle, intestine, diaphragm and adrenal, but mobilized extracellular fluid from liver, lung, spleen and ear. In the kidney, urotensin I increased the tissue/plasma inulin ratio in renal cortex, medulla and papilla, indicating water reabsorption. It is concluded that the blood-pressure-lowering effect of urotensin I in the rat is due to a potent vasodilatatory action, mainly exerted in skeletal muscle, mesenteric region, skin and kidney.