Relationship between ovarian steroids, gonadotrophins and relaxin during the menstrual cycle.

The circulating levels of relaxin have been measured and their relationship with the plasma levels of oestradiol (E 2 ), progesterone, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) have been investigated during the normal menstrual cycle. In addition, the effect of human chorionic gonadotrophin (hCG) on plasma relaxin levels has been studied. In the first part of the study, blood samples were obtained on days 5, 10 and 1 5 of the follicular phase and on alternate days from the day of the LH surge (detected in early-morning urine and confirmed by circulating levels of LH) until day 6 of the following follicular phase in nine normally cycling female volunteers