GONADOTROPIC ACTION OF PITUITARIES FROM PREGNANT COWS

Abstract

Implantation of acetone dried pituitary powder into rats and inj. of aq. suspensions of the powder into chicks stimulate the gonads sufficiently to permit the quantitative assay of individual pituitaries of cattle. A steady and significant decrease in gonadotrophic activity of glands from cows takes place from early to late pregnancy. This decrease may be explained by the assumption that placental estrogen either inhibits the formation of gonadotrophic hormones in the pituitary or causes an increased rate of excretion of the hormone by the gland. The avg. decline in follicular development of cows during pregnancy favors the first alternative. Indicative of the rate of decrease from early to late pregnancy are the regression coefficients. For each cm. increase in fetus length, there is an avg. decrease in test gonad-wt. of .13 mg. for rats and .22 mg. for chicks on the 25 mg. dosage and .49 mg. for rats on the 50 mg. dosage. These regression coefficients are highly significant. Correlations between pituitary-wt. and fetus-length were not significant, thus failing to indicate an increase in the pituitary wt. during pregnancy. Pituitaries from cows carrying [female] fetuses are on the avg. richer in gonadotrophic hormone than those from cows carrying [male] fetuses. This difference is not statistically significant. Test rats show predominant luteinization in their ovaries when implanted with pituitary powder from cows in early pregnancy. In the latter part of pregnancy follicular stimulation is prevalent. This difference in response may be due to a "dosage effect" or to a change in the proportion between two gonadotrophic hormones in early and late pregnancy.