THYROIDECTOMY DOES NOT ALTER HYPOTHALAMIC OXYTOCIN AND VASOPRESSIN EXPRESSION IN CHRONICALLY HYPERNATREMIC RATS

Sustained hyperosmolality increases the levels of hypothalamic oxytoci n (OT) and arginine vasopressin (AVP) messenger ribonucleic acids (mRN As). Gonadectomy is known to abolish this response (12,18). In this st udy we investigated whether thyroidectomy would alter OT and AVP mRNA levels in the hypothalamic paraventricular nucleus (PVN) of the hypero smotically stimulated rat. Male Sprague-Dawley rats underwent thyroide ctomy (hypothyroid) or sham thyroidectomy (euthyroid) at 7 weeks of ag e. Three weeks later hypothyroid and euthyroid animals were administer ed 2% NaCl (6-11 days) or tap water and sacrificed at the end of the e xperiment. Northern blot hybridization was used to assess size and lev els of hypothalamic OT and AVP mRNAs. Hypothyroid rats had significant ly lower levels of serum thyroxine (T-4) than their euthyroid cohorts (P < 0.0001). Both the euthyroid and the hypothyroid animals receiving 2% NaCl developed hypernatremia and increased the levels and the size of OT and AVP mRNAs compared to their tap water cohorts. We conclude that in contrast to gonadectomy, thyroidectomy does not alter the leve l of OT and AVP mRNAs in the hypothalamus of chronically hypernatremic male rats.