The repeated administration of 3-methylcholanthrene to adolescent rats resulted in (a) a profound, incomplete, and selective depression of certain hypophyseal functions; (b) decreased growth of transplanted mammary tumors; and (c) a retardation of body growth. Only the last mentioned effect was reversed by forced feeding.

The retarded rate of body growth induced by 3-methylcholanthrene was prevented by the concurrent administration of dihydrotestosterone or progesterone, or by ovariectomy; rats so treated became overweight despite the injection of 3-methylcholanthrene. Phenolic estrogens intensified the retardation of body growth induced by 3-methylcholanthrene and emaciation resulted.

The administration of 3-methylcholanthrene resulted in decreased gonadotrophin production by the pituitary and the ovaries were more drastically affected by the depression of pituitary activity than the adrenals were. The compound exerted differential effects on the pituitary glands of males and females respectively. Hormonal functions of both ovary and testis were decreased in rats treated with 3-methylcholanthrene but, whilst ovarian weight was much reduced, the size of the testis was not decreased and the germinal epithelium of the male was little affected by the treatment in most instances. There was a considerable reduction of the content of alkaline phosphatase in the breast of intact rats treated with 3-methylcholanthrene but atrophy of the mammary epithelium did not occur and hyperplasia of the mammary tree was often observed.

The administration of 3-methylcholanthrene considerably slowed the growth of transplanted mammary tumors characterized by high dependence on hormones and the concurrent administration of gonadotrophin restored the growth rate of the tumors.

The administration of 3-methylcholanthrene or androstan-17ß-ol-3-one was only moderately effective in controlling the growth of transplanted mammary tumors characterized by low hormonal dependence; the combined administration of these compounds was highly efficacious in retarding the growth of these refractory tumors.

3-Methylcholanthrene partially retarded the growth of mammary fibroadenomas in hypophysectomized rats.

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