Changes in leptin levels during lactation: Implications for lactational hyperphagia and anovulation

In these studies we investigated the time course of changes in circulating leptin levels in lactating rats and the dependence of these changes on the energetic cost of lactation and evaluated the contribution of changes in le ptin levels to lactational hyperphagia and infertility. In the first experi ment, plasma leptin levels were measured on Days 5, 10, 15, 20, and 25 post partum in freefeeding lactating rats and age-matched virgin females. Retrop eritoneal and parametrial fat pads weights were obtained from the same fema les. In the second experiment the same measures, together with plasma insul in and prolactin levels, were taken on Days 15 and 20 postpartum from galac tophore-cut and sham-operated females. In Experiments 3 and 4, the effects of exogenous leptin administration, either subcutaneously (sc) or intracere broventricularly (icv), on lactational anovulation, maternal food intake, a nd dam and litter weights were examined. Circulating leptin levels decrease d in lactating rats. Leptin levels were highly positively correlated with f at pad weight. Eliminating the energetic costs of lactation by preventing m ilk delivery induced dramatic increases in plasma leptin and insulin levels and also increased adiposity. Exogenous leptin administration did not affe ct length of lactational anovulation but reduced food intake, maternal body weight, and litter weight gain when given centrally and maternal body weig ht when given systemically. Together, these data show that the energetic co sts of lactation are associated with a fall in circulating leptin levels bu t that these do not make a major contribution to the suppression of reprodu ction in lactating rats; however, they may be permissive to the hyperphagia of lactation. (C) 2000 Academic Press.