Contribution of central amiloride-sensitive transport systems to the development of hypertension in spontaneously hypertensive rats

Contribution of central nitric oxide to the regulation of blood pressure and sodium balance in DOCA-salt hypertension

We examined whether central nitric oxide is involved in blood pressure (BP) regulation in deoxycorticosterone acetate (DOCA)-salt hypertension. DOCA-salt rats were intracerebroventricularly infused (ICV) NG-monomethyl L-arginine (L-NMMA) for 4 weeks at either low (0.08 mg/kg/d; n = 8) or high (0.16 mg/kg/d; n = 8) dose. Saline ICV (n = 9) and intraperitoneal infused L-NMMA (low, n = 6; high dose, n = 6) were served as controls. Also, L-NMMA ICV (low, n = 6; high dose, n = 6) was conducted in normal rats. At week 3 and after, DOCA-salt with low L-NMMA ICV showed a higher BP than saline ICV (at week 4: 167.4 +/- 3.6 vs. 150.3 +/- 3.9 mm Hg, P < 0.01); this difference of BP was cancelled after ganglionic block. High L-NMMA ICV did not affect the trend of BP; however, it caused a reduced amount of saline drinking and a less estimated sodium retention than saline or low L-NMMA ICV (for 3 wk; 47.5 +/- 1.1 vs. 66.0 +/- 3.7 and 61.7 +/- 2.5 mmol, P < 0.01). In normal rats, high, but not low, L-NMMA ICV elevated BP with no effect on drinking behavior. Intraperitoneal infused L-NMMA did not affect the development of hypertension and/or sodium balance. These data suggested that, in DOCA-salt, central nitric oxide is involved in BP regulation through the dual action on sympathetic nervous activity and sodium balance.

Enhanced central hypertonic saline-induced activation of angiotensin II-sensitive neurons in the anterior hypothalamic area of spontaneously hypertensive and Dahl S rats

High dietary salt intake activates the brain renin-angiotensin system in spontaneously hypertensive rats (SHR) and Dahl S rats, resulting in sympathetic hyperactivity and hypertension. Increases of sodium concentration in cerebrospinal fluid (CSF) and/or enhanced responses to CSF sodium are considered to be involved in the high dietary salt-induced activation of central nervous system pathways in those rats. Previously we have demonstrated that intracerebroventricular injection of hypertonic saline increases the neural activity of angiotensin II-sensitive neurons trans-synaptically via endogenous angiotensins in the anterior hypothalamic area (AHA) of rats. In the present study, we examined whether the AHA angiotensin II-sensitive neuron response to hypertonic saline would differ in SHR and Dahl S rats from those of their controls. Male 15- to 16-week-old SHR and age-matched Wistar Kyoto rats (WKY), Dahl S rats and Dahl R rats and Wistar rats were anesthetized and artificially ventilated. Extracellular potentials were recorded from single neurons in the AHA. Intracerebroventricular injection of hypertonic saline increased the firing rate of AHA angiotensin II-sensitive neurons. The threshold sodium concentration for the central sodium-induced increase of neural firing was lower in SHR than those of WKY, Dahl S rats, Dahl R rats and Wistar rats. The increase in neural firing induced by hypertonic saline (250 mM) was greater in SHR than those of other four kinds of rats. Similarly, the threshold sodium concentration was lower in Dahl S rats than those of WKY, Dahl R rats and Wistar rats and the increase in neural firing induced by hypertonic saline (250 mM) was greater in Dahl S rats than those of WKY, Dahl R rats and Wistar rats. In SHR, intracerebroventricular injection of the amiloride-sensitive sodium channel blocker benzamil abolished the hypertonic saline (250 mM)-induced increase in neural firing, but the sodium channel blocker itself did not affect the basal firing of these neurons. These findings indicate that central sodium-induced activation of AHA angiotensin II-sensitive neurons is enhanced in SHR and Dahl S rats.