THE EFFECTS AND MOLAR POTENCY OF ILOPROST, U46619 AND SODIUM-NITROPRUSSIDE ON CAPSULAR AND VASCULAR SMOOTH-MUSCLE OF THE ISOLATED-PERFUSED CANINE SPLEEN

The isolated canine spleen was perfused at constant flow with continuo us recording of splenic arterial perfusion pressure (SAPP) and spleen weight, Intra-arterial injections of the thromboxane A(2) (TXA(2)) mim etic U46619 caused dose-related increases in splenic arterial perfusio n pressure (SAPP) of short duration (ED(50) 0.31 nmol). There were ver y small changes in spleen weight accompanying any of the vasoconstrict or responses to U46619. The stable analogue of prostacyclin, iloprost, caused dose-dependent reductions in SAPP (ED(50) 1.3 nmol) indicating vasodilatation. There were no changes in spleen weight to any doses o f iloprost indicating a lack of action on capsular smooth muscle. Simi larly, the nitric oxide (NO) mimetic sodium nitroprusside caused dose- related reductions in SAPP of short duration (ED(50) 5.8 nmol). No cha nges in spleen weight accompanied splenic vasodilator responses to any dose of sodium nitroprusside (SNP). The results indicate the potentia l actions and intrinsic potency of three endogenous vasoactive substan ces and provide information about their relative roles in the control of the splenic microcirculation in situations when they are released.