CENTRAL INTERACTION BETWEEN ATRIAL-NATRIURETIC-PEPTIDE AND ANGIOTENSIN-II IN THE CONTROL OF SODIUM-INTAKE AND EXCRETION IN FEMALE RATS

We investigated the effects of estrogen on sodium intake and excretion induced by angiotensin II (ANG II), atrial natriuretic peptide (ANP) or ANG II plus ANP injected into the median preoptic nucleus (MnPO). F emale Holtzman rats weighing 250-300 g were used. Sodium ingestion and excretion 120 min after the injection of 0.5 mu l of 0.15 M NaCl into the MnPO were 0.3 +/- 0.1 ml (N = 12) and 29 +/- 7 mu Eq in intact ra ts, 0.5 +/- 0.2 ml (N = 10) and 27 +/- 6 mu Eq in ovariectomized rats, and 0.2 +/- 0.08 (N = 11) and 38 +/- 8 mu Eq in estrogen-treated ovar iectomized (50 mu g/day for 21 days) rats, respectively. ANG II (21 mu M) injection in intact, ovariectomized, and estrogen-treated ovariect omized rats increased sodium intake (3.8 +/- 0.4, 1.8 +/- 0.3 and 1.2 +/- 0.2 ml/120 min, respectively) (N = 11) and increased sodium excret ion (166 +/- 18, 82 +/- 22 and 86 +/- 12 mu Eq/120 min, respectively) (N = 11). ANP (65 mu M) injection in intact (N = 11), ovariectomized(N = 10)and estrogen-treated ovariectomized (N = 10) rats increased sodi um intake (1.4 +/- 0.2, 1.8 +/- 0.3, and 1.7 +/- 0.3 ml/120 min, respe ctively) and sodium excretion (178 +/- 19, 187 +/- 9, and 232 +/- 29 m u Eq/120 min, respectively). Concomitant injection of ANG II and ANP i nto the MnPO of intact (N = 12), ovariectomized (N = 10) and estrogent reated ovariectomized (N = 10) rats caused smaller effects than those produced by each peptide given alone: 1.3 +/- 0.2, 0.9 +/- 0.2 and 0.3 +/- 0.1 ml/120 min for sodium intake, respectively, and 86 +/- 9, 58 +/- 7, and 22 +/- 4 mu Eq/120 min for sodium excretion, respectively. Taken together, these results demonstrate that there is an antagonisti c interaction of ANP and ANG II on sodium intake and excretion, and th at reproductive hormones affect this interaction.