Central angiotensin converting enzyme blockade and salt preference in renovascular hypertensive rats

Previous studies have shown that the spontaneously hypertensive rat (SHR) has a preference for 0.9% NaCl solution over water as a drinking fluid. This preference was decreased by chronic treatment of SHR with intracerebroventricular captopril (an angiotensin converting enzyme inhibitor). Although other strains of rats were compared to SHR, no studies, that we are aware of, have been reported in renal hypertensive rats. Wistar-Kyoto rats were sham operated or had a silver clip (i.d., 0.20 mm) placed on the left renal artery to produce renovascular hypertension. Three weeks later the rats were operated upon again to implant osmotic minipumps to deliver captopril or saline either into the right lateral brain ventricle (i.c.v.) or into the peritoneal cavity (i.p.). The rats had a choice of 0.9% NaCl or tap water during the study. Blood pressures were measured by a tail plysmographic method in the conscious rats. The rats that became hypertensive showed a marked preference for saline. Treatment with captopril i.p. (24 mumol/kg/day) stimulated preference for saline but i.c.v. treatment (24 mumol/kg/day) decreased the preference for saline despite reductions in blood pressure in both groups of renal hypertensive rats. These changes were not seen in renal hypertensive rats infused with saline. The results suggest that captopril's antihypertensive effect in this model of renal hypertension may be independent of the effects of the drug on preference to drink saline.