Increase in Serum FSH Following Unilateral Ovariectomy in the Rat

Abstract

It has been suggested that increased gonadotrophin secretion follows unilateral ovarian removal and leads, a priori, to the compensatory hypertrophy of the remaining ovary. Recent studies have failed to substantiate this increase, possibly because the techniques employed were insufficiently sensitive to determine subtle alterations in gonadotrophin levels. A modification of the Steelman-Pohley bioassay for FSH was utilized in a study of serum and pituitary FSH in unilaterally ovariectomized rats. In a number of experiments, FSH was observed to increase in the pooled serum of adult, albino females of a Wistar strain that had been operated four days previously. This increase was followed by a gradual decrease, with serum FSH values returning to preoperative levels at 20–24 days, at which time rapid hypertrophy of the remaining ovary had ceased. Pituitary FSH decreased in the 24 hr following ovarian removal and remained depressed until the first detectable increase in weight of the remaining ovary at 4 days. Estradiol or progesterone blocked the compensatory hypertrophy of the remaining ovary and the concomitant increase in serum FSH. These results confirm the suspected rise in serum gonadotrophins following unilateral ovarian removal. It is postulated that the increase in serum FSH following unilateral ovariectomy results from a decrease in circulating ovarian hormones which partially releases the hypothalamico-hypophysial system from feedback inhibition. As the remaining ovary hypertrophies and is stimulated to secrete these hormones, the level of inhibition is restored and serum FSH returns to preoperative levels. Our hypothesis is that an increase in FSH secretion is an important component in the mechanism of compensatory hypertrophy. {Endocrinology 84: 369, 1969)