“Internal” Feedback Mechanism: Response of Pituitary FSH and of Stalk-Median Eminence Follicle Stimulating Hormone-Releasing Factor to Median Eminence Implants of FSH1

Abstract

In order to determine whether or not FSH exerts an "internal" feedback effect on its respective hypothalamic activator, 50-day-old female rats received implants of FSH into the median eminence (ME) area. The animals were sacrificed at 58-60 days of age and SME-FSH-RF and pituitary FSH1 were determined according to a modification of the David method, and according to the HCG [human chorionic gonadotropin] augmentation method of Steelman and Pohley, respectively. For 3 separate but identical experiments, there was a consistent and conspicuous depression of SME-FSH-RF and of pituitary FSH content of the ME +FSH animals, when compared to either their normal or sham-implanted controls. ME implants of LH or bilateral amygdalar implants of FSH were ineffective. The minimum average per cent depression of SME-FSH-RF of ME+FSH rats was approximately 46%; that of hypophysial FSH, 42%. Histologically, the ovaries revealed corpora lutea, indicative of ovulation; few mature follicles accompanied by many degenerate and primordial follicles were also present. The results demonstrate that the implanted FSH can lead to a partial inhibition of FSH secretion, via a direct negative feedback action on the hypothalamic FSH-RF mechanism. A possible parallelism between depression of SME-FSH-RF and of pituitary FSH is also observed. The present results, combined with those of other experiments, strongly suggest the participation of the pituitary gland in the regulation of its neural controller.