Sex difference in sensitivity to exogenous oxytocin in different models of sodium appetite in the rat.

Brain oxytocin (OT) has been suggested to be involved in the inhibition of sodium appetite in the rat. Sodium depleted male rats showed no decrease in sodium intake after they were given a pulse intracerebroventricular (pICV) injection of either OT (1 microgram/microliter) or the selective OT agonist Tyr4-Gly7OT (1 microgram/microliter). Administration of the OT selective antagonists, d(CH2)5Tyr(Me)-[Orn8]vasotocin and Compound VI [d(CH2)5,Tyr(Me)2,Thr4,Tyr-NH2(9)]OVT (1 microgram/microliter), did not further increase their sodium intake. On the other hand, sodium appetite of sodium depleted female rats were inhibited by the same dose of pICV OT but not by the selective agonist Tyr4-Gly7 OT (1 microgram/microliter). The reduction od sodium appetite in female rats may have been in part due to the competitive behavior of grooming that followed the OT injection. Nevertheless, the OT inhibition in females of the need-free sodium intake and of the sodium appetite that occurs after furosemide but not in adrenalectomized or DOCA treated rats, argue for a mechanism independent from angiotensin or aldosterone alone related sodium appetite and the mechanism involved in the suppression of these salt intakes remain to be clarified.