Differentiation and Cell Kinetics of Mammary Gland in Pubescent Virgin Rats Treated with Bromocriptine

Sprague-Dawley female rats were orally administered 10 mg/kg of Bromocriptine (CB) daily between 31 to 51 days of age. In metaand di-estrus rats with regular sex cycles, serum prolactin (PRL) was elevated for 3 days and peaked at 2 days (96. 6 ± 9. 82 ng/ml) after the termination of subchronic treatment, compared with those (2. 1 ± 0. 29 ng/ml) at the termination. Untreated, ovariectomized, and ovariectomized and CB-treated rats were used as controls, and mammary gland development was observed in relation to the serum PRL fluctuation in such regularly sex-cycling metaand di-estrus rats. Compared with untreated controls, the mammary gland exhibited significantly predominant terminal ducts (TD) with an accompanying decrease in alveolar buds (AB) in nearly normal-sized parenchyma at the termination of subchronic treatment with CB. It also exhibited a marked predominance of lobules (Lob) and AB with fewer TD in larger parenchyma 3 and 6 days after the termination. Immunohistochemically, there were fewer bromodeobxyuridine (BrdU) -labeled glandular cells in terminal end buds (TEB) and TD at termination, and more in ducts and AB 3 days after termnation, compared with untreated controls. Therefore, the development of the mammary glands is retarded in rats with low serum PRL levels, and a rebound increase in PRL levels accelerated the development.