Age-related differences in the incorporation of 3H-arginine into vasopressin in Fischer 344 rats.

ABSTRACT

We studied the effect of aging on the incorporation of 3H-arginine into vasopressin (VP) molecule in the hypothalamus (HT) and the rate of its transport into the neurohypophysis (NH) of male Fischer 344 rats of different ages 2-3 months (young, n = 28), 11-13 months (adult, n = 30) and 30 months (old, n = 27). 3H-arginine was injected in a single dose through a permanent cannula into the lateral ventricle of an awake animal. The rats were decapitated 1, 6, and 24 h after the injection. VP was extracted from individual HTs and NHs (without pars intermedia), purified in a chromatography column and determined by RIA. Hypothalamus One hour after the injection the 3H-activity was highest in the young, lower in the adult and lowest in the old rats, whereas the specific activity (cpm/pg VP) was similar in all age groups, reflecting endogenous VP content to be highest in the young, lower in the adult and lowest in the old rats. In the young rats both activities decreased 6 and 24 h after the injection. The adult rats also exhibited declining activities, whereas in the old rats the activities remained unchanged from 1 to 24 h after the injection. Neurohypophysis One hour after the injection of radioactive label 3H-activity and specific activity were significantly lower in the NH of the old than in those of young and adult rats. The activities increased 6 h after the injection in all age groups with the lowest values in the old rats. After 6 h, both activities in the old rats reached only the 1-h values of the young and adult rats suggesting a delay of at least 6 h in the axonal transport of newly synthetized VP in aged rats. Twenty-four hours after the injection both activities increased in all age groups exhibiting no difference among the age groups, indicating a decreased release of the newly synthetized VP from the NH of aged rats. These data demonstrate an age-related decrease in the rate of incorporation of 3H-arginine into VP, in the rate of its axonal transport and in the release of newly synthetized VP from the NH of Fischer 344 rats.