The pathologic response of the liver and thyroid of the rat to potassium prorenoate (SC-23992)

A 3-month dose range finding study in preparation for a 2-yr carcinogenicity study of potassium prorenoate (SC-23992), a steroid with an antihypertensive profile, is reported. The drug was administered by gavage once daily at doses of 10, 30, and 100 mg/kg/day to Charles River CD rats. Treatment was terminated at 13 weeks and 10 randomly selected animals from each treatment group were killed and necropsied. The remaining 10 animals in each dose group, including controls, were maintained for an additional 4 weeks, in order to investigate reversibility of changes, and then were killed and necropsied. Dose-related increases in thyroid-stimulating hormone (TSH) levels were observed in treated animals of both sexes during the dosing period and the changes were statistically significant and correlated with an increased thyroid weight in females at 13 weeks. Dose-related morphologic changes in the thyroid, observed by light and electron microscopy, were compatible with the effects of TSH stimulation. Liver weights, which increased, were dose-related. In females the increase was statistically significant at the high dose at 2, 4, and 13 weeks. In males it was significant at the high dose at 13 weeks. Microsomal enzyme levels were increased in a time- and dose-related manner with higher values in females than in males. The pattern of enzyme induction was of the type exemplified by pregnenolone- 16-alpha-carbonitrile. Morphologic changes in the liver showed centrilobular hepatocyte enlargement with smooth endoplasmic reticulum membrane proliferation confirmed by electron microscopy. All positive findings returned to normal after the 4-week treatment-free period. The relationship between the thyroid stimulation to liver enzyme induction is of interest. Evidence is presented here that in the presence of SC-23992, TSH stimulation and liver enzyme induction occurred. The possibility that the liver metabolism stimulates the thyroid T3, T4 elimination with secondary TSH activity is a possible explanation, but on the basis of existing information, direct action by SC-23992 on the thyroid cannot be excluded.