INDUCTION OF A MIDCYCLE‐LIKE PEAK OF LUTEINIZING HORMONE IN YOUNG WOMEN BY EXOGENOUS OESTRADIOL‐17β

Summary Oestradiol‐17 β , given intramuscularly in a dose of 1 mg., was found to increase the serum level of luteinizing hormone (LH) but not of follicle stimulating hormone (FSH) in eight women 48 to 72 hours after the administration. This increase of LH was preceded by a decrease in the serum levels of both FSH and LH. When 5 or 10 mg. of progesterone was administered five days after the injection of oestradiol‐17 β , a second increase of LH was observed in two of four women. These results suggest that changes in the ovarian secretion of both oestradiol‐17 β and progesterone may be of importance for the appearance of the midcycle surge of LH in women.