GONADAL-STEROID MODULATION OF OXYTOCIN AND VASOPRESSIN GENE-EXPRESSION IN THE HYPOTHALAMUS OF THE OSMOTICALLY STIMULATED RAT

We investigated the modulatory role of gonadal steroids on the express ion of oxytocin (OT) and vasopressin (AVP) cytoplasmic mRNAs in the pa raventricular nucleus and supraoptic nucleus of the osmotically stimul ated rat. We chronically administered an oral salt load (2% sodium chl oride solution for 5 days) to intact and gonadectomized female and mal e Sprague-Dawley rats and measured serum sodium, body weight, pituitar y content of OT and AVP immunoreactivities, and size and abundance of hypothalamic cytoplasmic OT and AVP mRNA transcripts. Intact and gonad ectomized rats that were administered an osmotic challenge developed c omparable degrees of hypernatremia and loss of body weight as well as depletion of posterior pituitary stores of OT and AVP. Hyperosmolality induced elongation of the OT and AVP transcripts in intact and gonade ctomized animals, but only intact rats had enhanced hypothalamic cytop lasmic OT and AVP mRNA concentrations to this stimulus. Replacement wi th gonadal steroids restored the up-regulation in OT and AVP gene expr ession in gonadectomized animals rendered hyperosmolar. The findings s upport a modulatory role for gonadal steroids in hypothalamic OT and A VP gene expression during osmotic stimulation.