Drinking behaviour in rats treated with isoprenaline, angiotensin II or angiotensin antagonists

Abstract

SUMMARY1. Isoprenaline hydrochloride injected subcutaneously in rats given a choice test of 1-8 % NaCi and water, first induced saline intake which started immediately and was almost concluded in 15 min, followed by a copious water intake. When either saline or water were given in a separate test, saline intake surpassed the water intake in the first 15 min.2. The delay of 15, 30 or 60 min after injection of isoprenaline, 100 jug/kg, before drinking was allowed, significantly reduced saline intake but did not modify the amount of water subsequently drunk.3. Isoprenaline caused a sudden drop in arterial blood pressure, the extent and duration depending on the dose. The time of maximum drop 3-4 min after injection coincided with the time the rat drank salt.4. Isoprenaline-induced saline drinking was significantly reduced after bilateral nephrectomy but water intake was unaffected.5. The beta-adrenoceptor blocking agent, propranolol, inhibited isoprenalineinduced NaCl and water intake, while the alpha-adrenoceptor antagonist phenoxybenzamine abolished isoprenaline-induced NaCl intake and enhanced water intake.6. Saralasin acetate (P-1 13), a competitive inhibitor of angiotensin II, given into the third brain ventricle, prevented the isoprenaline-induced NaCl and water intake as well as angiotensin II-induced drinking. The angiotensin converting enzyme inhibitor SQ-20881 reduced the isoprenaline-induced NaCl and water intake.7. In conclusion, hypotension might be a component of salt drinking evoked by isoprenaline although the dipsogenic action of beta-stimulation is mainly due to endogenous renin-angiotensin activation.

Repeated administration of angiotensin II reduces its dipsogenic effect without affecting saline intake

“…We believe this is unlikely, however, especially because of our previous findings that showed only a slight difference in time between water and 1.5% NaCl intakes (no more than 5 min) after injection of Ang II (Daniels et al 2009). It is also notable that after isoprenaline injection, the dipsogenic effects of which require intact AT 1 receptors in the SFO (Krause et al 2008), delaying access to fluid attenuated saline intake, but had no effect on water intake (Chiaraviglio, 1979). Thus, it seems that any delayed response would be more likely to mask desensitization of water intake than of saline intake.…”