CHRONIC MEDIAN EMINENCE LESIONS AND OVARIECTOMY: EFFECTS ON FOLLICLE-STIMULATING HORMONE SECRETION IN THE RAT

SUMMARY Pituitary and serum follicle-stimulating hormone (FSH) concentrations were determined by the Steelman—Pohley ovarian augmentation bioassay method in normal adult rats and in rats subjected to ovariectomy and/or electrolytic lesioning of the tuberal hypothalamus 10, 30 or 90 days previously. Ovariectomy resulted in a rapid, significant increase in FSH concentration of the adenohypophysis. Pituitary FSH concentrations were increased sixfold 10 and 30 days after ovariectomy and by 90 days were increased by 700%. (Hormone stores in the adenohypophysis increased correspondingly.) Serum FSH levels in ovariectomized rats also increased but at a slower rate. Ten days after ovariectomy, serum FSH levels were still normal. Thirty and ninety days postoperatively, serum FSH titres were doubled and quintupled, respectively. Chronic median eminence lesions eventually caused obesity, a marked atrophy of the reproductive system and significant increase in the FSH concentration of the adenohypophysis. Follicle-stimulating hormone was not detected in the sera of rats with short-term lesions but serum hormone levels were in the normal range 30 and 90 days after the lesions were made. Complete destruction of the median eminence in ovariectomized rats was associated with further increase in pituitary FSH concentration and content. Ninety days after simultaneous lesioning and ovariectomy, FSH concentration of the adenohypophysis was almost twice that of the ovariectomized control and the hormone content was about 14 times that in the normal pituitary. In contrast, the raised FSH serum levels observed after long-term ovariectomy were significantly reduced (50%). It is concluded that chronic median eminence lesions which induce obesity and ovarian atrophy in rats differentially affect synthesis and release of FSH by the adenohypophysis.