Adiposity associated rise in leptin impairs ovarian activity during winter dormancy in Vespertilionid bat, Scotophilus heathi

Abstract

The aim of the study was to evaluate the seasonal variation in serum leptin levels in a natural population of the female bat,Scotophilus heathiand their relationship to the changes in the body mass, serum insulin level, and ovarian activity. Circulating leptin level varied significantly over the season and correlated positively with the changes in body mass, and circulating insulin and androstenedione (A4) levels. Circulating leptin concentrations showed two peaks; one coincides with the maximum fat accumulation prior to winter dormancy, whereas the second shorter peak coincides with late pregnancy. Thein vivostudy inS. heathishowed that the increased circulating leptin level during winter dormancy coincides with the decreased expression of ovarian steroidogenic acute regulatory (StAR) protein, and low circulating estradiol (E2) level. At the same time, increased circulating leptin level coincides with increased expression of ovarian insulin receptor and high circulating A4 level. The low circulating leptin level during preovulatory period coincides with the increase in StAR protein but decrease in insulin receptor protein. Thein vitrostudy confirmed thein vivoobservations of inhibitory effect of leptin on LH induced StAR expression and E2production, whereas the stimulatory effect of leptin (high dose) on LH induced expression of insulin receptor protein and A4 production. However, pharmacological dose of leptin produced inhibitory effect on the expression of insulin receptor protein. The results of the present study thus suggest that high circulating leptin level during winter dormancy promotes adiposity and impairs ovarian activity by suppressing StAR-mediated E2production as well as by enhancing insulin receptor-mediated A4 synthesis thereby contributing anovulatory condition of delayed ovulation inS. heathi.