Maternal serum leptin in the pregnant rat: fetal-placental implantation number and progesterone.

Abstract

This study was designed to determine whether there is a role of the placenta in the regulation of maternal serum leptin levels in the pregnant rat. We have adjusted the number of fetal-placental implants on day 9 in the pregnant rat by aspirating fetal-placental units to adjust the number to 1-2, 4-5 per rat or >10 in controls. Serum levels of leptin and progesterone were determined by radioimmunoassay. A separate group of pregnant rats were ovariectomized and maintained with progesterone silastic capsules (10, 20 or 40 mm). In the pregnant rats with varied fetal-placental implant numbers, the maternal serum leptin were greatest in the group with the smallest number (1-2) of implants; intermediate in the midgroup (4-5 implants); and lowest in the group with a full complement of implantations (>10) (p < 0.001). Serum progesterone levels are lowest in the 1-2 implantation group. In the ovariectomized rats there was a stepwise decline in serum leptin (p < 0.05) as the dose of progesterone increased (p < 0.01). Both of these studies suggest that progesterone suppressed maternal serum leptin levels. Increasing placental mass is not associated with increasing maternal serum leptin levels in the pregnant rat; the contrary condition is observed with the least placental implants having the highest leptin levels. Progesterone seems to suppress serum leptin levels in several physiological models.