CARDIAC WEIGHT IN HYPERTENSION INDUCED BY NITRIC-OXIDE SYNTHASE BLOCKADE

Wistar rats given a nitric oxide synthase inhibitor, N(G)-nitro-L-arginine-methyl ester (L-NAME), for 4 weeks develop time- and dose-dependent hypertension without cardiac hypertrophy. This initial study of the relation between left ventricular weight and L-NAME-induced hypertension has now been extended by giving 50 mg/kg per day L-NAME to Wistar rats (n=30) for 8 weeks and comparing results with those from control rats (n = 10) and two-kidney, one clip rats (n = 14). Although L-NAME rats and two-kidney, one clip rats had increased systolic blood pressures during the last 3 weeks of the experiment (202 +/- 24 and 224 +/- 16 mmHg, respectively), the ratio of left ventricular weight to body weight of L-NAME rats (2.12 +/- 0.32 mg/g) was not statistically different from that of control rats (1.93 +/- 0.13 mg/g), whereas that of two-kidney, one clip rats was increased (2.85 +/- 0.20 mg/g). The plasma renin activity of L-NAME rats was not significantly different from that of control rats. Two L-NAME rat subgroups were defined according to the presence of left ventricular hypertrophy (ratio of left ventricular weight to body weight > 2.19 mg/g, control mean + 2 SD) (6 of 25) or its absence (19 of 25). Systolic blood pressure, plasma renin activity, and cardiac angiotensin converting enzyme activity of L-NAME rats with left ventricular hypertrophy were significantly higher than those of the subgroup without. In a multiple regression analysis using the ratio of left ventricular weight to body weight as an independent variable and three dependent variables (L-NAME administration, plasma renin activity, and systolic blood pressure), we found that all of these three variables contributed to left ventricular weight independently of each other. Thus, even if the degree of left ventricular hypertrophy evolves in parallel with the duration and magnitude of a chronic rise in blood pressure, other factors, such as the renin-angiotensin system and nitric oxide production, influence this relation.