Development of salt-sensitive hypertension in a sensory denervated model: the underlying mechanisms.

We use a novel salt-sensitive hypertensive model recently developed in our laboratory. This model shows that neonatal degeneration of capsaicin-sensitive sensory nerves renders a rat responsive to a salt load with a significant rise in blood pressure (BP). To test the hypothesis that development of salt-sensitive hypertension in sensory denervated rats is mediated by abnormal regulation of both circulating and tissue renin-angiotensin systems (RAS), neonatal Wistar rats were given capsaicin, 50 mg/kg s.c., on the first and second days of life. Control rats were treated with vehicle solution. After the weaning period, male rats were divided into four groups and subjected to the following treatments for three weeks: control + high sodium diet (4%, CON-HS), capsaicin pretreatment + normal sodium diet (0.5%, CAP-NS), capsaicin pretreatment + high sodium diet (CAP-HS), and capsaicin pretreatment + high sodium diet + candesartan cilexetil (10 mg/kg/per day, CAP-HS-CAN). Radioimmunoassay shows that plasma renin activity (ng/ml/hr, PRA) was higher in CAP-NS (2.58±0.17) than in CON-HS (0.14±0.03) and CAP-HS (0.74±0.15), and it was higher in CAP-HS than in CON-HS (p<0.05). Western blot analysis shows that expression of the angiotensin II (Ang II) type 1 (AT1) receptor in both the renal cortex and outer medulla was higher in CAP-HS than in CON-HS and CAP-NS rats (p<0.05). Expression of the Ang II type 2 (AT2) receptor in the renal cortex was higher in both CAP-HS and CAP-NS than in CON-HS rats (p<0.05), but there was no difference in AT2-receptor expression in the renal medulla between CAP-HS, CAP-NS, and CON-HS rats. Likewise, there was no difference in AT1-receptor expression in mesenteric resistance arteries between CAP-HS, CAP-NS, and CON-HS rats. In contrast, mesenteric AT2-receptor expression was lower in CAP-HS than in CAP-NS and CON-HS rats (p<0.05). Tail-cuff systolic BP (mmHg) shows that blockade of the AT1-receptor with candesartan prevents the development of hypertension in CAP-HS rats (by the end of the experiment, CON-HS, 122±3; CAP-NS, 118±10; CAP-HS, 169±9; CAP-HS-CAN, 129±2, p<0.05). Thus, both circulating and tissue RAS in sensory-denervated rats are abnormally regulated in response to a high-salt intake, which may contribute to increased salt sensitivity and account for the effectiveness of candesartan in lowering BP in this model.