PROGESTERONE ADMINISTRATION TO OVARIECTOMIZED RATS REDUCES WATER AND SALT INTAKE INDUCED BY CENTRAL ADMINISTRATION OF ANGIOTENSIN-II

We tested the effects of estradiol, progesterone and testosterone on w ater and salt intake induced by angiotensin II (ANG II) injected into the third ventricle of female Holtzman rats weighing 250-300 g. The wa ter and salt ingestion observed after 120 min in the control experimen ts (injection of 0.5 mu l of 0.15 M NaCl into the third ventricle) was 1.6 +/- 0.3 ml (N = 10) and 0.3 +/- 0.1 ml (N = 8) in intact rats, re spectively, and 1.4 +/- 0.3 ml (N = 10) and 0.2 +/- 0.1 (N = 8) in ova riectomized rats, respectively. ANG II injected in intact rats (4, 6, 12, 25, and 50 ng, icv, in 0.5 mu l saline) induced an increase in wat er intake (4.3 +/- 0.6, 5.4 +/- 0.7. 7.8 +/- 0.8, 10.4 +/- 1.2, 11.2 /- 1.4 ml/120 min, respectively) (N = 43). The same doses of icv ANG I I in intact rats increased the 3% NaCl intake (0.9 +/- 0.2; 1.4 +/- 0. 3, 2.3 +/- 0.4, 2.2 +/- 0.3. and 2.5 +/- 0.4 ml/120 min, respectively) (N = 42). When administered to ovariectomized rats ANG II induced com parable amounts of water intake (4.0 +/- 0.5, 4.8 +/- 0.6, 6.9 +/- 0.7 . 9.6 +/- 0.8, and 10.9 +/- 1.2 ml/120 min, respectively) (N = 43) but there was a significant decrease of 3% NaCl solution ingestion (0.3 /- 0.1, 0.4 +/- 0.1, 0.8 +/- 0.2, 0.7 +/- 0.2, and 0.6 +/- 0.2 ml/120 min, respectively) (N = 44). Estrogen (50 mu g), progesterone (25 ng), and testosterone (300 mu g) were injected daily into ovariectomized r ats for 21 days. Treatment with estrogen decreased the water intake an d abolished the saline ingestion induced by icy injection of ANG II (1 2 ng (2.8 +/- 1.2 and 0.3 +/- 0.1 ml/120 min, respectively) (N = 8). T reatment with progesterone also reduced the water intake (3.3 +/- 0.6 ml/120 min) (N = 8) and abolished the ANG II-induced saline ingestion (0.4 +/- 0.1 ml/120 min) (N = 8), but these effects were not observed with testosterone (6.4 +/- 0.8 and 2.2 +/- 0.3 ml/120 min, respectivel y) (N = 8). These results indicate that ANG II induces a greater incre ase in sodium intake in intact female rats than in ovariectomized rats and that estrogen and progesterone impair water and sodium intake in ovariectomized rats.