Decremental vasopressin release after repeated stimulation of superfused neurohypophyses of Fisher 344 rats of different ages.

We studied the effect of aging on the decline in vasopressin (VP) release from the rat neurohypophyses (NH) as evoked by repeated stimuli with high K+ (56 mM) Locke's solution in vitro. Isolated NHs, without pars intermedia, of 2-, 12- and 30-month-old male Fisher 344 rats arbitrarily labeled as young, adult, and old were individually superfused with synthetic medium TC 199. Following the initial traumatic release, the glands were stimulated three times for 10 min each with recovery periods of 35 min between stimulations. VP was measured by radioimmunoassay. Expressed per mg NH, basal VP release in the old rats, and stimulated VP release in both the adult and old rats, was decreased. The gradual decline (slope) of VP release following subsequent stimuli with high K+ was proportional, however, in all age groups. Thus, decreasing response of VP release to repeated stimulation is a function of the initial response but is not age related. These findings suggest that only some components of the chain of events involved in the release mechanisms are impaired in aging animals, whereas others may remain unaffected.