The suppressive effect of the maternal pituitary on relaxin secretion during the second half of pregnancy in rats does not require the presence of the nonluteal ovarian tissue.

This study was conducted to determine whether the suppressive effect of the maternal pituitary on relaxin secretion, luteal growth, and progesterone secretion during the second half of pregnancy in rats (Golos and Sherwood, 1984) requires the presence of the nonluteal ovary. At proestrus, rats received unilateral follicular autotransplants to the kidney capsule. These developed into ectopic corpora lutea (eCL) which maintained pregnancy following removal of the in situ ovary on Day 13 of pregnancy. On Day 8, the conceptus number was left unchanged (eCL-5C) or adjusted to 2 (eCL-2C). Serum relaxin levels, eCL relaxin levels, and eCL weights were significantly lower in eCL-2C rats than in eCL-5C rats from Day 12 through Day 20. Following hypophysectomy on Day 13, serum relaxin levels increased significantly in both groups. Mean luteal weights also increased following hypophysectomy of eCL-2C rats. Although not statistically significant, serum progesterone levels tended to be higher in eCL-5C rats than in eCL-2C rats from Day 12 until Day 18; serum progesterone levels tended to increase following hypophysectomy regardless of conceptus number. It is concluded that the presence of the non-luteal components of the ovary are not required for the suppressive effect of the maternal pituitary on relaxin secretion and luteal growth during the second half of pregnancy.