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 baseline 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 (10⁻¹⁰M to 10⁻⁶M), 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. (Aging Clin. Exp. Res. 5: 349-356, 1993)