Age-related vasopressin changes in rat plasma and the hypothalamo-hypophyseal system

Immunoreactive vasopressin (VP) weas measured in the plasma, neurohypophysis (NH) and hypothalamus (HT) of young (3 months), adult (12 months), and old (30 months) Sprague-Dawley male rats, both intact and anesthetized with halothane. VP content in the HT of the old rats was about half that of young and adult rats. Total VP content in the NH increased with age, reflecting large glandular size in the old rats. However, VP content was similar in all three groups, when expressed per mg of wet tissue. Plasma VP concentration was undetectable in the old intact rats and it rose to the levels of intact young or adult rats during halothane anesthesia. The anesthesia-related increase in plasma VP concentration was statistically significant in young but not in adult rats. These results suggest that in the intact rats during aging: (1) the synthesis of VP in the HT may be reduced; (2) the storage of VP in the NH is not impaired; and (3) the undetectable plasma VP concentration may reflect either reduced VP release or increased degradation.