MODIFICATIONS IN OVARIAN AND PITUITARY FUNCTION IN THE HYSTERECTOMIZED PREGNANT HAMSTER

Abstract

SUMMARY When hamsters were hysterectomized on day 1 of pregnancy, ovulation occurred 17 days later. On day 12 of this prolonged pseudopregnancy, plasma levels of progesterone were approximately half of those of intact animals on the same day of pregnancy. The concentration of follicle-stimulating hormone in the pituitary of the hysterectomized animals was only half that of the pregnant group, but luteinizing hormone concentrations were similar. The massive proliferation of antral follicles characteristic of pregnant hamsters on day 12 was not found in the hysterectomized animals; injection of 20 i.u. human chorionic gonadotrophin (HCG) on day 12 resulted in the ovulation of 31 and 6 ova respectively, but priming the hysterectomized hamsters with pregnant mare serum gonadotrophin (before HCG) resulted in superovulation. After hysterectomy on day 9 of pregnancy, by day 12 there was a rapid decline in luteal activity as shown histologically by the onset of structural luteolysis and a concomitant fall in luteal weight, and luteal and plasma levels of progesterone. These effects were partially or completely reversed by daily injection of 1 mg prolactin on days 9–11. The results indicate that hysterectomy before the establishment of the placenta results in the sustained release by the pituitary of prolactin and gonadotrophins, but most likely at lower levels than in pregnant animals. However, hysterectomy on day 9 abruptly removes the placental source of a prolactin-like hormone and the pituitary cannot respond in time to prevent luteolysis.