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. Accumulation of AVP messenger ribonucleic acid (mRNA) is enhanced by sustained hypernatremia and diminished by sustained hyponatremia. We recently reported that gonadal steroid hormones modify the accumulation of hypothalamic AVP mRNA during sustained hypernatremia (12). Gonadectomized (gdx) hypernatremic male rats failed to increase AVP mRNA abundance, and testosterone (T) restored the response. Therefore, we questioned whether the decreased accumulation of AVP mRNA in experimentally-induced hyponatremic male rats is influenced, in part, by circulating concentrations of T, and determined if AVP mRNA accumulation would differ in the hypothalamus of gdx vs intact hyponatremic animals. Decreased accumulation of AVP mRNA was found in both intact and gdx hyponatremic animals compared to normonatremic animals. The level of AVP mRNA accumulation was not correlated with serum T concentrations. We conclude that diminished AVP in the hypothalamus of hyponatremic male rats occurs independent of circulating T concentrations.