Hormonal influences on the estradiol-induced and age-related increases of pituitary dopamine in C57BL/6J mice. Effects of gonadal steroids, gender, and prolactin.

Estradiol (E2) produces many-fold increases in the dopamine (DA) content of the anterior pituitary and also plays a role in the age-related increase in pituitary DA in female C57BL/6J mice. These studies address the following questions: (1) What are the time and dose characteristics of the E2-induced increase in pituitary DA and can other gonadal steroids - such as progesterone (P) and 5 alpha-dihydrotestosterone - also influence pituitary DA? (2) Is the age-related increase in pituitary DA due entirely to an increase in the E2:P ratio seen in aging female mice, or can extra-ovarian factors also play a role? (3) Is the E2-induced (and therefore possibly the age-related) increase in pituitary DA secondary to an E2-induced increase in serum prolactin? In ovariectomized (OVX) mice, E2 implants increased pituitary DA in a time- and dose-dependent fashion. P implants administered to OVX mice simultaneously with E2 antagonized the E2-induced increase in pituitary DA. Daily injections of 5 alpha-dihydrotestosterone given in conjunction with E2 implants had no effect on basal or E2-increased pituitary DA in OVX mice. Thus, E2 is the only gonadal steroid examined which increases anterior pituitary DA. In intact aging mice, P attenuates the age-related increase in pituitary DA, supporting the hypothesis that the increased ratio of E2:P secreted by the ovaries of aging female mice is responsible for the age-related increase in pituitary DA. However, at advanced ages, intact male mice also showed modest increases in anterior pituitary DA.(ABSTRACT TRUNCATED AT 250 WORDS)