Relationship between progesterone secretion and peripheral plasma levels of luteinizing hormone during pregnancy and postpartum period in hamsters.

Abstract

Levels of progesterone in the ovarian vein blood and luteinizing hormone (LH) in the peripheral plasma were measured by respective radioimmunoassays throughout pregnancy and postpartum period in hamsters. The secretion of progesterone or LH showed no significant fluctuations prior to or in association with implantation on Days 3 and 4 of pregnancy. During the second half of gestation, ovarian output of progesterone doubled (4.8 µg/hr/ovary) and the concentration of LH declined to values significantly (p < 0.01) less than those found during the early pregnancy or the diestrous phase of the cycle. During the postpartum period progesterone secretion dropped below values found on Day 1 of pregnancy (2.4 µg/hr/ovary) and LH levels rose severalfold over those found in the prepartum animals (Days 9–16, p < 0.01). The stimulus provided by suckling failed to reduce high LH values (145 ng/ml) to levels present in the second half of pregnancy (12 ng/ml). In general, a negative relationship was observed between the ovarian secretion of progesterone and circulating levels of LH both during pregnancy and the postpartum period.