LEPTIN CORTICOTROPIN-RELEASING HORMONE (CRH), AND NEUROPEPTIDE-Y (NPY) IN FREE-RANGING PREGNANT BATS

Leptin, the product of the obese gene first identified in mice, restor es fertility in obese mice, and accelerates puberty in mice. We hypoth esized that leptin's putative role in reproduction may extend to pregn ancy and lactation. Leptin levels were determined in Myotis lucifugus, the little brown bat, a free-ranging mammal with a seasonal breeding cycle. The present study shows that plasma levels of leptin progressiv ely rise during pregnancy, supporting a potential role for leptin in t he maintenancy of pregnancy. In contrast, leptin was significantly low er during lactation, a time when most mammals, including bats, demonst rate reduced fertility. In addition to its possible roles in reproduct ion, leptin appears important in regulation of energy balance. M. luci fugus spontaneously fasts for up to 16 h each day during the active se ason, which allowed us to test the hypothesis that acute fasting was a ssociated with decreased leptin. Leptin was significantly lower in fas ted (lactating) bats, compared to those that recently returned from ni ghtly foraging. Although postprandial lactating bats had a significant ly higher fat index than fasted bats, plasma leptin and body fat were not significantly correlated, and were only weakly correlated (r(2) = 0.26) when both pregnant and lactating females were included in the an alysis. Similar changes during pregnancy, lactation, and the daily fee ding cycle were observed in the hypothalamic neuropeptide, corticotrop in-releasing hormone (CRH), which is believed to play an important rol e in energy balance and reproduction. By contrast, neuropeptide Y (NPY ) increased during pregnancy but did not change during fasting. These results suggest that leptin's putative role in reproduction may extend to pregnancy and lactation, and that spontaneous, acute fasting resul ts in decreased circulating levels of leptin in M. lucifugus.