Circulating leptin during ovine pregnancy in relation to maternal nutrition, body composition and pregnancy outcome

This study examined the pattern of circulating leptin in age-matched sheep during adolescent pregnancy, and its relationship with maternal dietary int ake, body composition and tissue expression of the leptin gene. Overfeeding the adolescent pregnant ewe results in rapid maternal growth at the expens e of the placenta, leading to growth restriction in the fetus, compared wit h normal fed controls. Our results demonstrate that, in the adolescent ewe, overfeeding throughout pregnancy was associated with higher maternal leptin concentrations, when compared with moderately fed controls (P < 0.05), with no peak in circulati ng leptin towards the end of pregnancy. There was a close correlation betwe en indices of body composition and circulating leptin levels at day 104 of gestation and at term (P < 0.03). Further, when the dietary intake was swit ched from moderate to high, or high to moderate, at day 50 of gestation, ci rculating leptin levels changed rapidly. in parallel with the changes in di etary intake. Leptin mRNA levels and leptin protein in perirenal adipose ti ssue samples, taken at day 128 of gestation, were higher in overfed darns ( P < 0.04), suggesting that adipose tissue was the source of the increase in circulating leptin in the overnourished ewes. Leptin protein was also dete cted in placenta but leptin gene expression was negligible, However. leptin receptor gene expression was detected in the ovine placenta, suggesting th at the placenta is a target organ for leptin. A negative association existe d between maternal circulating leptin and fetal birth weight, placental/cot yledon weight and cotyledon number. In conclusion, in this particular ovine model, hyperleptinaemia was not obs erved during late pregnancy. Instead, circulating leptin concentrations ref lected increased levels of leptin secretion by adipose tissue primarily as a result of the increase in body fat deposition, due to overfeeding, Howeve r. there appears to be a direct effect of overfeeding, particularly in the short term. In the nutritional switch-over study, circulating leptin concen trations changed within 48 h of the change in dietary intake. The presence of leptin protein and leptin receptor gene expression in the placenta sugge sts that leptin could be involved in nutrient partitioning during placental and/or fetal development.