A comparison of the temporal effects of estradiol and diethylstilbestrol on pituitary content of DNA, prolactin mRNA and prolactin and on serum prolactin levels in ovariectomized Holtzman rats.

Ovariectomized Holtzman rats implanted with Silastic capsules of estradiol-17 beta (E2) or diethylstilbestrol (DES) were decapitated at intervals between 4 hours and 10 days of steroid treatment and the anterior pituitaries were collected and analyzed for DNA, prolactin mRNA, and prolactin content. Serum prolactin was also determined. Untreated ovariectomized rats decapitated at 10 days after ovariectomy served as controls. Pituitary DNA levels were not consistently affected by either steroid until 10 days of treatment when levels approximately doubled. In contrast both steroids increased prolactin mRNA and pituitary and serum prolactin levels within 4-8 hours of treatment. Prolactin mRNA levels increased throughout the 10 day period. Pituitary prolactin levels paralleled mRNA levels until day 7 then decreased significantly (P < 0.05) at day 10. Serum prolactin levels increased at 4 and 8 hours, decreased slightly at 24 hours only to increase dramatically at 48 hours. Then at 4 and 7 days of treatment serum levels decreased to the levels seen at 24 hours, followed by a significant (P < 0.05) increase at day 10. Both steroids were equipotent in their effects on serum prolactin; however, DES was significantly (P < 0.05) more potent in increasing pituitary prolactin content than was E2; whereas, E2 was more potent in increasing prolactin mRNA and pituitary DNA. It is concluded that both natural and synthetic estrogens have rapid and sustained, although not equivalent, actions on the levels of prolactin mRNA in the rat. Further, pituitary DNA and pituitary and serum prolactin do not consistently follow the temporal pattern of change seen for prolactin gene expression.