Maternal leptin is elevated during pregnancy in sheep.

Area of Science:

• Reproductive Physiology
• Endocrinology
• Animal Science

Background:

• Maternal plasma leptin increases during pregnancy in many species.
• The drivers of this elevation, whether adiposity or energy balance, remain unclear.

Purpose of the Study:

• To investigate the regulation of maternal plasma leptin during the pregnancy-lactation cycle in sheep.
• To determine if changes in adiposity or energy balance influence leptin levels.
• To assess the role of insulin sensitivity in pregnancy-induced leptin changes.

Main Methods:

• Karakul ewes were fed to maintain energy equilibrium throughout the pregnancy-lactation cycle.
• Blood samples were collected at pre-breeding, mid-pregnancy, late-pregnancy, and early lactation.
• Maternal plasma leptin, insulin, NEFA, and glucose concentrations were measured.
• Leptin gene expression in white adipose tissue (WAT) was analyzed.
• Insulin tolerance tests were conducted.

Main Results:

• Maternal body weight increased only in late pregnancy due to conceptus weight.
• Plasma insulin, NEFA, and glucose remained stable, indicating stable energy balance.
• Maternal plasma leptin concentration significantly increased from pre-breeding to mid-pregnancy and then declined.
• Leptin gene expression in WAT showed a similar pattern, increasing by mid-pregnancy and returning to baseline by lactation.
• Insulin sensitivity decreased from pre-breeding to lactation but did not correlate with leptin levels or WAT leptin mRNA.

Conclusions:

• Pregnancy stimulates leptin synthesis in sheep, independent of changes in adiposity or energy balance.
• The observed increase in leptin during pregnancy is not mediated by altered insulin sensitivity.