INCREASED PLASMA OSMOLALITY STIMULATES PERIPHERAL AND CENTRAL VASOPRESSIN RELEASE IN MALE AND FEMALE RATS

It has been demonstrated that the neurohypophysial hormones can be rel eased intrahypothalamically by the paraventricular (PVN) and supraopti c nuclei. The present experiments were undertaken to determine whether a physiological stimulus for vasopressin release, increased plasma os molality, will stimulate the release of vasopressin by the PVN into th e surrounding interstitial fluid, and whether the responses are affect ed by gender. Intravenous infusion of 2.5 M NaCl for 60 min (0.1 ml.kg (-1).min(-1)) in conscious rats resulted in an increased vasopressin c oncentration in the dialysate from a microdialysis probe adjacent to t he PVN. This response was greater in nonestrous females than in males. On the other hand, the rise in the plasma vasopressin concentration w as greater in males than in nonestrous females. Mean arterial blood pr essure increased and heart rate decreased, but these responses were no t affected by gender. The role of centrally released vasopressin in th e control of the peripheral release of vasopressin is conjectural, but both responses may be modulated by the gonadal steroid hormones.