Objective: Leptin is predominantly secreted by adipocytes and plays a central role in the regulation of energy homeostasis and food intake. . It is proposed that leptin provides information to the brain that there are enough energy stores for reproductive functions, thus becomes an important factor for determination of the start of puberty. Day length (DL) affects leptin secretion by modulating melatonin secretion and this secretion subsequently affects leptin-regulated physiological functions. The aim of this study was to investigate the effect of long DL induced serum leptin level cahnges on onset of puberty in female rats fed by high-fat.

Material and Methods: Wistar type female rats were fed by pellets containing 45%, 10% or 2.4% (control) fat. The groups were divided into two groups according to exposing either to 12-h light/dark or 18-h light/6-h dark cycles. Female rats were stopped milk feding at day 21 and body weight, daily food intake and vaginal opening were controlled daily after day 26. The animals were decapitated when the estrus period was detected by vaginal smear. Serum leptin and estrodiol levels were determined by ELISA method.

Results: Puberty onset was earlier in rats fed by very high fat diet (45%). Serum leptin levels were found to be significantly higher (P<0.05) in the groups fed by diets with 45% and 10% fat compared to the rats fed by diet with control. Serum leptin levels also increased significantly in rats exposed to long term light (18 h day light/ 6 h night), whereas puberty onset was delayed in all three groups.

Conclusion: Time of exposure to light independent from the metabolic state affects leprtin release and onset of puberty in female rats.