Concentrations of leptin in the serum of pregnant, lactating, and cycling rats and of leptin messenger ribonucleic acid in rat placental tissue.

Leptin concentrations were measured in the serum of cycling, pregnant, and lactating Sprague-Dawley rats. Serum leptin concentrations did not vary significantly during the estrous cycle. In contrast, as gestation advanced, serum leptin concentrations increased significantly, p < 0.0001. Following delivery, leptin concentrations declined and remained stable during lactation. Leptin messenger ribonucleic acid (mRNA) was identified in the visceral adipose tissue and placenta of rats sacrificed on days 14 and 21 of pregnancy. The relative abundance of placental leptin mRNA increased approximately 4 to 5 fold from day 14 to 21 of gestation. The pattern of elevated leptin concentrations in the serum of late pregnant rats is similar to that reported in pregnant women, therefore the rat may be a useful model for the study of leptin during pregnancy. The increase in leptin in the serum of late pregnant rats, as well as an increase in placental mRNA, raises the possibility that leptin may serve a physiological role for the late parturient rat and/or its young.