Perfusion pressure and volume status determine the microvascular response of the rat kidney to NG-monomethyl-L-arginine.

This study investigated the role of volume status and perfusion pressure on the hemodynamic response of cortical and medullary renal capillaries to systemic inhibition of nitric oxide. NG-Monomethyl-L-arginine (L-NMMA) was infused intravenously (15-mg/kg bolus and 500-micrograms.min-1.kg-1 infusion), and blood flow in cortical capillaries (QCC) and in descending (QDVR) and ascending vasa recta (QAVR) was measured by fluorescence videomicroscopy in euvolemic and volume-expanded anesthetized Munich-Wistar rats. L-NMMA in euvolemic rats decreased vasa recta blood flow (delta QDVR, 3.97 +/- 0.80 nL/min [P < .01]; delta QAVR, 1.90 +/- 0.39 nL/min [P < .01]; n = 6) and QCC (delta QCC, 0.57 +/- 0.15 nL/min [P < .01]; n = 7) despite increases in renal perfusion pressure (RPP). Fractional excretion of sodium (FENa) remained unchanged. In volume-expanded rats, L-NMMA decreased vasa recta blood flow when RPP increased (delta QDVR, 1.42 +/- 0.79 nL/min [P = .05]; delta QAVR, 1.95 +/- 0.34 nL/min [P < .001]; n = 9) or was held constant by partial aortic occlusion (delta QDVR, 1.19 +/- 0.45 nL/min [P < .05]; delta QAVR, 1.44 +/- 0.40 nL/min [P < .01]; n = 8). QCC was unchanged by L-NMMA when RPP increased (delta QCC, 0.27 +/- 0.20 nL/min; n = 8) but decreased significantly by 0.61 +/- 0.11 nL/min (P < .01, n = 8) when increases in RPP were prevented. FENa increased when RPP increased (delta FENa, 2.47 +/- 0.51%; P < .001) and was held constant (delta FENa, 2.64 +/- 0.46%; P < .001).(ABSTRACT TRUNCATED AT 250 WORDS)