Salt appetite during the early phase of renal hypertension in rats

In male Sprague-Dawley rats the left renal artery was constricted by a 0.2mm silver clip while the contralateral kidney was left untouched. 10 days after clipping the animals were offered, in addition to water, 0.9% saline as drinking fluid for 6 days. Hypertensive animals drank twice as much saline as did control rats throughout the period of observation. In the hypertensive animals, 24-hrs saline intake during the first day of the self-selection study was quantitatively related to the actual height of blood pressure and to the preceding blood pressure increase. After 6 days on the self-selection regimen, plasma angiotensin II concentrations in the hypertensive rats were elevated by 50% when compared with control rats. On the basis of these and previously reported findings (i.e. an increased activity of the renin-angiotensin-aldosterone system and sodium retention) it is suggested: a) despite sodium retention salt appetite is enhanced, indicating a disordered regulation of sodium balance during the early phase of renal hypertension in rats; b) elevated plasma concentrations of angiotensin II and aldosterone could have enhanced salt appetite; c) despite greater salt intake than in control rats the activity of the renin-angiotensin system remains elevated in renal hypertensive rats, thereby possibly inducing a sustained high saline intake.