Proceedings of The Physiological Society
University College Dublin (2009) Proc Physiol Soc 15, C30
Role of thiazide-sensitive sodium transporter in the development of angiotensin II dependent hypertension.
A. Ashek1, J. J. Mullins1, M. A. Bailey1
1. Molecular Physiology,CVS, University of Edinburgh, Edinburgh, United Kingdom.
Inappropriate modulation of the renin angiotensin system (RAS) can lead to deranged blood pressure homeostasis. To identify important mechanisms underlying the development of angiotensin II dependent hypertension, we inserted the mouse Ren2 gene into the Fischer rat genome under the control of an inducible Cyp1a1 promoter (1). Induction of the transgene causes an increase in blood pressure, associated with a reduction in urinary sodium excretion (2). The aim of this investigation was to establish the contribution of renal sodium handling to the development of hypertension in the Cyp1a1 Ren2 transgenic rat. Expression of the Ren2 transgene was induced by daily gavage of indole 3 carbinol (I3C) at the dose of 100mg/kg Bwt for either 1 or 3 days (with a non-induced group as control), after which rats were anesthetized (Inactin, 120mg/kg, IP) and prepared for renal clearance experiments as described (2). A urine collection was made to establish baseline sodium excretion, renal blood flow and glomerular filtration rate. In the same rats, hydrochlorothiaxzide (2mg/Kg Bwt/h) was administered to inhibit NCC and a second urine collection made. At the end of the experiment, a 1ml blood sample was taken and rats killed by an overdose of Inactin. In a separate cohort of rats, HCTZ was chronically administered via osmotic minipump (4mg/d; 50% DMSO in saline), implanted under halothane anaesthesia. Baseline Systolic blood pressure (SBP) was obtained using tail cuff before any induction of the Ren2 transgene and then SBP was measured during the 3 days of induction by I3C daily gavage. Statistical comparisons were made by using one-way ANOVA (Tukey posthoc test). BP in the non-induced Ren2 transgenic rats was (125±4.8 mmHg; n=6). Induction of Ren2 expression for either 1 (146.9±2.2 mmHg; n=9) or 3 (171.5±5 mmHg; n=6) days caused a significant increase in BP. Neither glomerular filtration rate nor renal blood flow was affected by transgene induction. Excretion of sodium was significantly lower in the 1 day induced group compared to the non-induced group (0.5±0.1 vs. 0.95±0.16 µmol/min, p<0.05). A further incremental drop in sodium excretion was found after three days of induction (0.36±0.09 vs. 0.95±0.16 µmol/min, p<0.05). Acute injection of HCTZ caused a significant natriuresis in all three groups of rats: the net effect of thiazide on sodium excretion was greater in the 1 day (10.8±1.5 µmol/min, NS) and 3 day (12.9±1.4 µmol/min, p<0.05) group than in the non-induced controls (7.2±0.84 µmol/min). Chronic administration of HCTZ significantly blunted the hypertensive response to transgene induction (145.1±4.1 mmHg; n=6). These data suggest that thiazide-sensitive sodium transport contributes to the development of angiotensin II dependent hypertension.
Where applicable, experiments conform with Society ethical requirements