Regional blood flow responses to acute ANG II infusion: Effects of nitric oxide synthase inhibition

We hypothesized that nitric oxide (NO) opposes regional vasoconstriction ca used by acute angiotensin II (ANG II) infusion in conscious rats. Mean arte rial pressure (MAP), blood flow, and vascular conductance (regional blood f low/ MAP: ml/min/100 g/mm Hg) were measured and/or calculated before and at 2 min of ANG II infusion (0.05 or 1 mu g/kg/min, i.a.) in the absence and presence of NO synthase (NOS) inhibition [N-G-nitro-L-arginine methyl eater (L-NAME), 0.25 or 1 mg/kg, i.a.]. ANG II reduced stomach and hindlimb cond uctance only after NOS inhibition. For example, whereas 0.05 mu g/kg/min AN G II did not attenuate conductance in the stomach (i.e., 1.04 +/- 0.08 to 0 .93 +/- 0.12 ml/min/100 g/mm Hg), this variable was reduced (i.e., 0.57 +/- 0.14 to 0.34 +/- 0.05 ml/min/ 100 g/mm Hg; p < 0.05) when ANG II was infus ed after 0.25 mg/kg L-NAME. In addition, whereas hindlimb conductance was s imilar before and after administering 1 mu g/kg/min ANG II (i.e., 0.13 +/- 0.01 and 0.09 +/- 0.02, respectively), this variable was reduced (i.e., 0.0 7 +/- 0.01 and 0.02 +/- 0.00, respectively; p < 0.05) when ANG II was infus ed after 1 mg/kg L-NAME. These findings indicate that NO opposes ANG II-ind uced vasoconstriction in the stomach and hindlimb. In contrast, whereas bot h doses of ANG II decreased (p < 0.05) vascular conductance in the kidneys and small and large intestine regardless of whether NOS inhibition was pres ent, absolute vascular conductance was lower (p < 0.05) after L-NAME. For e xample, 1 mu g/kg ANG II reduced renal conductance from 3.34 +/- 0.31 to 1. 22 +/- 0.14 (p < 0.05). After 1 mg/kg L-NAME, renal conductance decreased f rom 1.39 +/- 0.18 to 0.72 +/- 0.16 (p < 0.05) during ANG II administration. Therefore the constrictor effects of NOS inhibition and ANG Ii are additiv e in these circulations. Taken together, our results indicate that the abil ity of NO to oppose ANG II-induced constriction is not homogeneous among re gional circulations.