Simultaneous perfusion of rat isolated superior mesenteric arterial and venous beds: comparison of their vasoconstrictor and vasodilator responses to agonists

1. A new isolated perfused preparation is described that allows a direct comparison to be made of the responses of the perfused arterial and retrogradely perfused venous circulations of the rat superior mesenteric vascular bed. 2. In experiments comparing the responses of the intact arterially perfused mesentery and small intestine to those of the same preparation following removal of the intestine and division of the circulations, the increases in perfusion pressure produced by arginine-vasopressin (30 pmol) and noradrenaline (1 nmol) were retained by the arterial circulation and those induced by angiotensin II (30 pmol) by the venous circulation. Endothelin-1 (30 pmol) constricted both portions of the vasculature but the prolonged nature of its response was associated with only the venous vessels. 3. In the simultaneously perfused arterial and venous preparation arginine vasopressin (3-100 pmol) was a selective constrictor of the arterial circulation and angiotensin II (3-100 pmol) of the venous circulation. In addition, noradrenaline (0.3-10 nmol), 5-hydroxytryptamine (0.3-10 nmol) and KCl (1-60 micromol) were more active as constrictors of the arterial than the venous vessels, and U46619 (10-300 pmol) a more active constrictor of the venous than the arterial vessels. Endothelin-1 (3-100 pmol) constricted both the arterial and venous portions of the vasculature but was significantly longer acting as a venoconstrictor than an arterioconstrictor. 4. Angiotensin I (300 pmol) caused constrictions of the venous circulation which were dependent upon the presence of angiotensin converting enzyme for captopril (10 microM) abolished constrictions caused by angiotensin I but not by angiotensin II.(ABSTRACT TRUNCATED AT 250 WORDS)