Different vascular responses to subpressor angiotensin II administration in the mesenteric and renal circulation of rats.

Administered in small doses, angiotensin II (ANG II) potentiates its own pressor responses (autopotentiation). In the present study, we investigated whether potentiation of vasoconstrictor responses in the mesenteric and renal circulation accounted for the autopotentiation of pressor responses. Male Sprague-Dawley rats, 350 to 400 g, were infused with 200 ng/kg/min ANG II intraperitoneally for 7 to 10 days. Control rats were fitted with an osmotic minipump containing vehicle only. Vascular responses to ANG II, norepinephrine (NE), arginine vasopressin (AVP) and nerve stimulation were measured in the mesenteric and renal circulation of rats. In ANG II-treated rats: 1) tail systolic BP was 4 mm Hg higher than in controls (P = NS); 2) mesenteric vascular responses to ANG II (P < .002) and nerve stimulation (P = .03) were increased, and those to NE and AVP were unchanged; and 3) renal vascular responses to nerve stimulation were reduced (P < .02), and those to ANG II, NE, and AVP were unchanged. Thus, we demonstrated autopotentiation of vascular responses to ANG II in the mesenteric, but not the renal circulation. An interaction between ANG II and sympathetic activity may explain these differences in regional vascular responses. Regional hemodynamic measurements may provide important clues to pathogenetic mechanisms in hypertension.