Abstract
Estradiol and progesterone may play a role in controlling leptin secretion by utilizing their receptors in adipocytes and the genomic mechanisms of the leptin gene. This study was conducted to evaluate the effects of exogenous sex steroids on the blood leptin concentrations in ewes in the non-breeding season. Multiparous ewes were fed to maintenance level for their live weights. Blood samples were collected at 12-h intervals from Days -3 to -1 to determine the basal leptin levels (pre-injection period). From Day 0 to Day 5 (injection period), blood sampling continued at 12-h intervals, and the ewes were injected intramuscularly at 24-h intervals with oil, 50 mg progesterone in oil, 1 mg of estradiol in oil, or both steroids in oil. Leptin was measured using a sensitive and specific radioimmunoassay based on recombinant bovine leptin. Overall, plasma concentrations of leptin were not affected by any of the steroid treatments, and there were no differences in the value of leptin between the pre-injection and injection periods among the 4 groups. Therefore, the exogenous estrogen and progesterone used in this study do not have a strong effect on the blood leptin concentrations of ewes in the non-breeding season.
