Long term toxicological studies on the progestin STS 557

Growth-stimulating effect of dienogest, a synthetic steroid, on rodent, canine, and primate mammary glands

We observed hyperplasia of the mammary gland in female beagle dogs, but not in female rats and monkeys, in 91-day toxicity studies on dienogest. In order to elucidate a possible mechanism for its development and to account for this species difference, we determined the plasma level of growth hormone (GH) in dogs, rats, and monkeys treated orally with dienogest for 91 days. As a result, dogs with mammary hyperplasia showed a prominent, dose-dependent increase in their GH level; and, contrarily, rats and monkeys without the hyperplasia of this organ failed to show any such increase. These results were supported by evidence from immunohistochemical and morphometric analysis of the pituitary gland. In addition, dienogest and medroxyprogesterone acetate (MPA) stimulated the growth of canine mammary epithelial cells in the presence of estradiol in vitro, but had no effect on rat and human mammary epithelial cells incubated under the same conditions. In conclusion, dienogest with progestational activity caused proliferation of the mammary gland in beagle dogs by increasing the secretion of GH, as do other progestational compounds. This change may be partially dependent on the direct effect of the drug.

Effects of STS 557 on semen and sperm functions in bonnet monkey (Macaca radiata)--a preliminary report

Intramuscular administration of STS 557 (17 alpha C-cyanomethyl-17 beta-hydroxy-estra-4,9(10)-diene-3-one) at a daily dose of 12 mg/monkey for 8 weeks induced severe oligospermia to complete azoospermia by the 9th week of initiation of treatment with concomitant decrease in the serum level of testosterone. The sperm motility was reduced from the 3rd week of treatment. Complete recovery was observed by the 14th week after withdrawal of treatment. STS 557 may have the potentiality to be used as a chemical contraceptive in the male.