DECREASED RENAL HEMODYNAMIC-RESPONSE TO INHIBITION OF NITRIC-OXIDE SYNTHASE IN SUBTOTALLY NEPHRECTOMIZED RATS

To assess the renal haemodynamic response to manipulations of the nitr ic oxide (NO) system, we examined subtotally nephrectomized (SNX) rats and control rats (CON) 28 days after their operation. Bolus infusions of the NO synthase inhibitor N-G-nitro-L-arginine (L-NA) were given i ntravenously at doses of 2 mg/kg and 10 mg/kg. Blood pressure was meas ured intra-arterially, glomerular filtration rate was measured by inul in clearance and fractional changes in renal blood flow(RBF) were dete rmined. by a Doppler flow probe. Both doses of L-NA caused a similar a nd dose-dependent increase in mean blood pressure in both SNX and CON rats. In contrast, the decrease in RBF and the increase in the renovas cular resistance index (RVRI) was less in SNX rats as compared to CON rats (RBF = -70.1 +/- 2.2% of baseline vs -52.7 +/- 5.2%, P < 0.01; RV RI = +177 +/- 9% of baseline vs +243 +/- 24%, P < 0.05). These changes were not affected by autonomic blockade (hexamethonium), or by blocka de of the angiotensin II receptor (Losartan). The exogenous NO donor s odium nitroprusside (0.5 and 1.5 mu g . kg(-1). min(-1)) lowered mean blood pressure to a similar degree in SNX and CON rats; in contrast, R VRI decreased less in SNX rats (86.9 +/- 9.2% of baseline) than in CON rats (68.2 +/- 4.6%, P < 0.05). We conclude that the reaction of the renal vasculature to manipulations of the NO system is altered in the SNX rats. The data suggest that in the remnant kidney, renovascular re sistance is less dependent on endogenous NO and the vascular bed is le ss sensitive to exogenous NO.