EFFECTS OF AGE AND SEX ON BASAL AND DOPAMINE-INHIBITED IN-VITRO PROLACTIN-RELEASE, AND DOPAMINE-RECEPTOR BINDING, BY THE RAT ADENOHYPOPHYSIS

We measured basal and dopamine-inhibited pituitary cell prolactin (PRL) release in vitro, and dopamine receptor binding in pituitary homogenates, from intact male and female Wistar rats of varying ages. During 48-72 hours in culture, the base-line secretion rate of PRL from pituitary cells of old (24 months) male rats was less than one-half that from cells of mature (6 months) male rats, whereas the corresponding basal secretion rate of PRL from cells of old female rats was nearly 3-fold greater than that from cells of mature female rats (p<0.001). After in vitro exposure to various concentrations of dopamine (10(-10)M to 10(-6)M), PRL secretion decreased from pituitary cells of both mature and old rats (p<0.001). However, repeated measures analysis of variance revealed an age-related, dose-dependent decrease in the magnitude of dopamine-inhibited PRL release from cells of both male and female rats (p<0.001). Dopamine receptor number did not differ with age (3-25 months), but was 2 to 3-fold greater in female than in male rats (p<0.01). Receptor affinity was decreased with age only in female rats, and was greater in female than in male rats (p<0.05). These data suggest that the decrease in dopamine-inhibited PRL release from pituitary cells of old male and female rats is not due to altered Pituitary dopamine receptor binding, despite certain sex differences.