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

Purpose 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. Methods 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). Results 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. Conclusions 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.

Automated summary

This study investigated the role of the placenta in regulating maternal serum leptin levels in pregnant rats. The results showed that the number of fetal-placental implants impacted maternal serum leptin levels, with lower implant numbers associated with higher leptin levels. Additionally, progesterone appears to suppress maternal serum leptin levels.