Nitric oxide synthase blockade and body fluid volumes.

The influence of chronic nitric oxide synthase inhibition with N G-nitro-L-arginine methyl ester (L-NAME) on body fluid distribution was studied in male Wistar rats weighing 260-340 g. Extracellular, interstitial and intracellular spaces, as well as plasma volume were measured after a three-week treatment with L-NAME (approximately 70 mg/kg per 24 h in drinking water). An increase in extracellular space (16.1 +/- 1.1 vs 13.7 +/- 0.6 ml/100 g in control group, N = 12, P<0.01), interstitial space (14.0 +/- 0.9 vs 9.7 +/- 0.6 ml/100 g in control group, P<0.001) and total water (68.7 +/- 3.9 vs 59.0 +/- 2.9 ml/100 g, P<0.001) was observed in the L-NAME group (N = 8). Plasma volume was lower in L-NAME-treated rats (2.8 +/- 0.2 ml/100 g) than in the control group (3.6 +/- 0.1 ml/100 g, P<0.001). Blood volume was also lower in L-NAME-treated rats (5.2 +/- 0.3 ml/100 g) than in the control group (7.2 +/- 0.3 ml/100 g, P<0.001). The increase in total ratio of kidney wet weight to body weight in the L-NAME group (903 +/- 31 vs 773 +/- 45 mg/100 g in control group, P<0.01) but not in total kidney water suggests that this experimental hypertension occurs with an increase in renal mass. The fact that the heart weight to body weight ratio and the total heart water remained constant indicates that, despite the presence of high blood pressure, no modification in cardiac mass occurred. These data show that L-NAME-induced hypertension causes alterations in body fluid distribution and in renal mass.