TESTOSTERONE AND HYPOTHALAMIC VASOPRESSIN EXPRESSION IN THE HYPONATREMIC RAT

The level of serum osmolality is known to influence the expression of the arginine vasopressin (AVP) gene in the rat hypothalamus. Accumulat ion of AVP messenger ribonucleic acid (mRNA) is enhanced by sustained hypernatremia and diminished by sustained hyponatremia. We recently re ported that gonadal steroid hormones modify the accumulation of hypoth alamic AVP mRNA during sustained hypernatremia (12). Gonadectomized (g dx) hypernatremic male rats failed to increase AVP mRNA abundance, and testosterone (T) restored the response. Therefore, we questioned whet her the decreased accumulation of AVP mRNA in experimentally-induced h yponatremic male rats is influenced, in part, by circulating concentra tions of T, and determined if AVP mRNA accumulation would differ in th e hypothalamus of gdx vs intact hyponatremic animals. Decreased accumu lation of AVP mRNA was found in both intact and gdx hyponatremic anima ls compared to normonatremic animals. The level of AVP mRNA accumulati on was not correlated with serum T concentrations. We conclude that di minished AVP in the hypothalamus of hyponatremic male rats occurs inde pendent of circulating T concentrations.