Changes in the Hormone Content of Swine Pituitaries during the Estrual Cycle

Abstract

Assay of individual pituitaries from 33 female swine killed on almost every day of the 21-day estrual cycle showed that the gonadotrophic hormone was lowest during the two days of heat, remained low after ovulation until the eighth day of the cycle when it increased suddenly and remained high until the 20th day. There is complete correspondence between the rise or fall in gonadotrophic hormone in the pituitary and the rise or fall in the number but not the size of follicles. The follicular phase, as judged by uterine histology, begins on the 14th day of the cycle which coincides with the increase in follicle size and is independent of the increase in follicle number. A very high positive association was found between the day of the cycle and the gonadotrophic potency (r=0.62, p=0.01) and between the gonadotrophic potency and the number and size of follicles in the ovaries (r=0.69, p=0.01). These correlations and other considerations lead to the conclusion that so far as the gonadotrophic hormone is concerned the bio-assay of the pituitary actually reflects the rate at which this hormone is being secreted. There is an increase in the amount of thyrotrophic hormone secreted during the cycle (r=0.42, p=0.02), a questionable association between this hormone and the rate of secretion of gonadotrophic hormone (r=0.33, p=0.06) and no association between the thyrotrophic hormone and the events in the ovaries (r=0.21, ns.). There is no change in the weight of the pituitary during the cycle and no association between its weights and the rate of hormone secretion. Copyright © . .