Role of leptin in seasonal adiposity associated changes in testicular activity of vespertilionid bat, Scotophilus heathi

The aim of this study was to investigate changes in circulating level of leptin in natural population of male bat, Scotophilus heathi in relation to seasonal changes in body mass, adipose tissue mass and testicular activity. The peak serum leptin level coincided with the period of maximum body mass due to heavy accumulation of adipose tissue. The in vivo study showed both inhibitory and stimulatory effects on testicular activity depending on circulating level of leptin. Moderate increase in circulating concentration of leptin coincided with the stimulatory effect on testicular activity in October, whereas peak circulating concentration of leptin coincided with suppressed testicular activity in December. Immunohistochemical and Western blot analysis confirmed expression of leptin receptors (Ob-R) in the testis, particularly in Leydig cells during different reproductive stages suggesting the direct action of leptin in regulation of testicular steroidogenesis. The in vitro study confirmed the in vivo observations of inhibitory effect of leptin on testosterone production through dose-dependent StAR expression in the testis. This study further showed that the leptin affects testicular activity through STAT3 mediated regulation of StAR expression. Thus, increased adiposity associated rise in circulating leptin level during winter dormancy impairs testicular activity by suppressing StAR mediated testosterone production in S. heathi. These results are suggestive of a link between the adipocyte derived leptin and testicular function.