Role of norepinephrine & angiotensin II in the neural control of renal sodium & water handling in spontaneously hypertensive rats.

Background & objectives: A wealth of information concerning the essential role of renal sympathetic nerve activity (RSNA) in the regulation of renal function and mean arterial blood pressure homeostasis has been established. However, many important parameters with which RSNA interacts are yet to be explicitly characterized. Therefore, the present study aimed to investigate the impact of acute renal denervation (ARD) on sodium and water excretory responses to intravenous (iv) infusions of either norepinephrine (NE) or angiotensin II (Ang II) in anaesthetized spontaneously hypertensive rats (SHR). Methods: Anaesthetized SHR were acutely denervated and a continuous iv infusion of NE (200 ng/min/kg) or Ang II (50 ng/min/kg) was instigated for 1 h. Three 20-min urine clearances were subsequently collected to measure urine flow rate (UV) and absolute sodium excretion (UNaV). Results: Higher UV and UNaV (P<0.05) were observed in denervated control SHR as compared to innervated counterparts. The administration of NE or Ang II to innervated SHR produced lower UV and UNaV (P<0.05 vs. innervated control SHR). Lower diuresis/natriuresis response to ARD was observed in NE-treated SHR compared to denervated control SHR (P<0.05). Salt and water excretions in denervated NE-treated SHR, however, were significantly higher (P<0.05) relative to the excretion levels in control denervated SHR. Conversely, there was a higher (all P<0.05) diuresis/natriuresis response to ARD when Ang II was administered to SHR compared to denervated control or innervated Ang II-treated SHR. Interpretation & conclusions: NE retains its characteristic antidiuretic/antinatriuretic action following ARD in SHR. Typical action of Ang II on salt and water excretions necessitates the presence of an intact renal innervation. Ang II is likely to facilitate the release of NE from renal sympathetic nerve terminals through a presynaptic site of action. Moreover, there is a lack of an immediate enhancement in the renal sensitivity to the actions of NE and Ang II following ARD in a rat model of essential hypertension.

Cardiovascular activity of the n-butanol fraction of the methanol extract of Loranthus ferrugineus Roxb

We investigated the vascular responses and the blood pressure reducing effects of different fractions obtained from the methanol extract of Loranthus ferrugineus Roxb. (F. Loranthaceae). By means of solvent-solvent extraction, L. ferrugineus methanol extract (LFME) was successively fractionated with chloroform, ethyl acetate and n-butanol. The ability of these LFME fractions to relax vascular smooth muscle against phenylephrine (PE)- and KCl-induced contractions in isolated rat aortic rings was determined. In another set of experiments, LFME fractions were tested for blood pressure lowering activity in anesthetized adult male Sprague-Dawley rats (250-300 g, 14-18 weeks). The n-butanol fraction of LFME (NBF-LFME) produced a significant concentration-dependent inhibition of PE- and KCl-induced aortic ring contractions compared to other fractions. Moreover, NBF-LFME had a significantly higher relaxant effect against PE- than against high K+-induced contractions. In anesthetized Sprague-Dawley rats, NBF-LFME significantly lowered blood pressure in a dose-dependent manner and with a relatively longer duration of action compared to the other fractions. HPLC, UV and IR spectra suggested the presence of terpenoid constituents in both LFME and NBF-LFME. Accordingly, we conclude that NBF-LFME is the most potent fraction producing a concentration-dependent relaxation in vascular smooth muscle in vitro and a dose-dependent blood pressure lowering activity in vivo. The cardiovascular effects of NBF-LFME are most likely attributable to its terpenoid content.