CHANGES WITH AGE OF MAMMARY-GLANDS IN MALE AND FEMALE SOFT-FURRED RAT, MILLARDIA-MELTADA, IN RELATION TO PROLACTIN AND TESTOSTERONE

The soft-furred rat, millardia (Millardia meltada), is characterized b y the development of androgen-dependent mammary tumours only in males. The age-related changes of the activities of thymidylate synthetase ( TS) and thymidine kinase (TK), which contribute to DNA synthesis throu gh de novo and salvage pathways, respectively, and structure in the ma mmary glands were studied in both males and females of this species be tween 5-28 months of age. While TK activity had no relation to age, TS activity decreased with age in males. In the females, TK activity inc reased with age, but not TS activity. These enzyme activities were gen erally higher in females than in males. The mammary glands of both sex es consisted of fine ducts with small end-buds and the glands of males contained mostly black pigments at any age examined. In either males or females, serum levels of prolactin and testosterone related little with age, DNA synthesizing enzyme activities or structure of the mamma ry glands. Furthermore, elevation by pituitary grafting of circulating prolactin affected neither DNA synthesizing enzyme activities nor str ucture of mammary glands in both sexes. The histological structures of adrenal, testis, ovary, ventral prostate and uterus of millardia were essentially similar to those of mice or rats.