Seasonal Expression Of Leptin And Adiponectin In The Oviduct Of The Chinese Brown Frog (Rana Dybowskii)

The Chinese brown frog (Rana dybowskii) is a special amphibian with one unique physiological phenomenon, which is that its oviduct expands prior to hibernation, instead of during the breeding period. Leptin is a pleiotropic protein hormone mainly secreted by white adipocytes that plays a role in the regulation of body weight and food intake. Adiponectin is a kind of endogenous bioactive proteins mainly secreted by adipose tissue. Adiponectin could activates fatty acid and glucose metabolism, balances the insulin sensivity. The objective of this study was to investigate the seasonal change of oviduct of the Rana dybowskii in reproduction period and pre-hibernation, and the role of leptin and adiponectin in this oviductal hypertrophy during pre-hibernation.There were significant variations in oviductal weight and size, with values much lower in the breeding period than in pre-hibernation. Histological observations of oviduct tissues were performed in Rana dybowskii. The oviduct mainly comprises mucous epithelium and secretory glands. Besides, more ciliated mucous epithelium found in breeding period, and the secretory gland boundary is clearer in breeding period. However, the secretory gland is bigger in pre-hibernation.PCNA and PPARy2 were observed in gland and epithelial cells in both periods. The protein level of PPARy2 was higher in pre-hibernation as compared to the breeding period. However the protein level of PCNA showed no significant difference. Leptin was immunolocalized in epithelial cells in both periods, whereas leptin receptor was detected only in gland cells. Consistently, the protein levels of leptin and leptin receptor were higher in pre-hibernation as compared to the breeding period. ELISA and RT-PCR results were coincident with the western blotting. Immunolocalization of adiponectin and adiponectin receptorl were executed in oviduct of Rana dybowskii between reproduction and pre-hibernation season. Compare with that in pre-hibernation season, the immunoreactivity of adiponectin and AdipoRl in reproduction season is stronger.These results suggest that the oviduct of Rana dybowskii during pre-hibernation might contain the processes of cell proliferation and differentiation, the expression of leptin and adiponectin have significant negative correlation. They may play an important autocrine or paracrine role in oviducal cells proliferation and differentiation of Rana dybowskii.