Norvaline Reduces Blood Pressure and Induces Diuresis in Rats with Inherited Stress-Induced Arterial Hypertension

Abstract

Growing evidence suggests that increased arginase activity affects vital bioprocesses in various systems and universally mediates the pathogenesis of numerous metabolic diseases. The adverse effects of arginase are associated with a severe decline in L-arginine bioavailability, which leads to nitric oxide synthase substrate insufficiency, uncoupling, and, eventually, superoxide anion generation and substantial reduction of nitric oxide (NO) synthesis. In cooperation, it contributes to chronic oxidative stress and endothelial dysfunction, which might lead to hypertension and atherosclerosis. Recent preclinical investigations point arginase as a promising therapeutic target in ameliorating metabolic and vascular dysfunctions. In the present study, adult rats with inherited stress-induced arterial hypertension (ISIAH) were used as a model of hypertension. Wistar rats served as normotensive controls. Experimental animals were intraperitoneally administered for seven days with nonproteinogenic amino acid L-norvaline (30 mg/kg/day), which is a potent arginase inhibitor, or with the vehicle. Blood pressure (BP), body weight, and diuresis were monitored. The changes in blood and urine levels of creatinine, urea, and NO metabolites were analyzed. We observed a significant decline in BP and induced diuresis in ISIAH rats following the treatment. The same procedure did not affect the BP of control animals. Remarkably, the treatment had no influence upon glomerular filtration rate in two experimental groups, just like the daily excretion of creatinine and urea. Conversely, NO metabolite levels were amplified in normotonic but not in hypertensive rats following the treatment. The data indicate that L-norvaline is a potential antihypertensive agent and deserves to be clinically investigated. Moreover, we suggest that changes in blood and urine are causally related to the effect of L-norvaline upon BP regulation.

Figure 1

Metabolic fates of arginine in the mammalian cells. (a) Arginine is a mutual substrate for arginase and NOS, which are in equilibrium in physiologic conditions. Regularly coupled eNOS utilizes O₂ and arginine to produce NO and citrulline. Arginase, in turn, converts arginine into ornithine and urea. (b) eNOS is uncoupled by substrate deficiency to produce superoxide anion rather than NO, which further diminishes NO availability.

Figure 2

The experimental design.

Figure 3

Effects of L-norvaline treatment on the systolic blood pressure (BP). (a) The mean basal levels of systolic BP measured in two experimental rat strains before treatment on day 0. Unpaired t-test. Floating bars (min to max with line at mean). (b) The mean systolic BP on day 7. Two-way ANOVA test, ^∗∗∗p < 0.001. Data presented as mean ± SEM.

Figure 4

Effects of L-norvaline on fluid homeostasis. Mean water intake (a), mean urine output (b), and mean urine/water ratio (c). Water restriction was initiated immediately after dosing. Data presented as mean ± SEM. Two-way ANOVA test. Significant difference is indicated as ^∗∗p < 0.01 and ^∗p < 0.05.

Figure 5

Effects of L-norvaline treatment on the levels of NO derivatives in the plasma and urine (7th experimental day). The mean concentrations of (a) plasma NO metabolites and (b) urine NO metabolites. Two-way ANOVA test; ^∗∗p < 0.01; data presented as mean ± SEM.