A sex difference in the rat pituitary FSH response to unilateral gonadectomy as revealed in plasma radioimmunoassays.

Abstract

Prepubertal and adult female and male rats were unilaterally gonadectomized and killed 6 days later to determine the degree of compensatory ovarian (COH) or testicular (CTH) hypertrophy. External jugular vein blood was drawn, under light ether anesthesia at different times after surgery, for radioimmunoassay of FSH and LEI. Unilateral orchidectomy was followed by a clear-cut CTH and by sharp increases in blood FSH concentration 2 days after the operation, values which remained at a high level in adults but continued to rise in immature animals. Blood LH levels in adult males did not change significantly. Testosterone propionate inhibited CTH and the rise in plasma FSH. In adult female rats unilateral ovariectomy on the first day of diestrus was followed by a transient sharp rise in blood FSH, values that returned to initial levels by 36 hr post-surgery and thereafter fluctuated about these levels. Estradiol berizoate treatment, starting after the rise in FSH, inhibited COH, but blood FSH and LH levels paralleled those in oil-treated controls. Similar effects were observed in immature females (25 or 30 days of age). Thus a marked sex difference exists in radioimmunoassayable FSH responses to unilateral castration and treatment with sex steroids, whereas the “internal bioassay” responses (gonadal weight) are very similar in the two sexes. It is proposed that certain endocrinological conditions may alter not only the secretion rate of pituitary FSH but also the qualitative nature of the released hormone. (Endocrinology94: 475, 1974)