Background: Many studies have focused on leptin, the product of the LEP (ob) gene, searching for a possible link between energy balance and reproduction.

Objective: Investigating the effect of daily leptin injection on prepubertal female rats and the possible mechanisms by which leptin can affect reproductive axis.

Materials and method: This study was applied on eighty female albino rats weaned after 21 days. They were divided into two equal groups, group I (GI, control) was injected with saline 5uL/g and group II (GII) injected with leptin in a dose of 5µg/g. The injection was daily, intraperitoneally (i.p.), during the light cycle from 21 days age till one day before sacrification. The animals were assessed daily for body weight and vaginal opening (VO). At 28, 32, 38 and 42 days of age, 10 rats from each group were anesthetized and dissected. Blood was collected from the heart of each dissected animal for E2 and LH assay. The right ovaries were dissected and fixed in Bouin’s solution and stained with Hx & E for histological examination.

Results: Daily i.p. leptin injection (5ug/g) resulted in a statistically significant decrease in body weight, a statistically significant earlier occurrence of VO, a statistically significant increase in serum estradiol (E2) levels, and early appearance of LH surge in GII as compared with GI. Also, there was a statistically significant increase in the mean numbers of primary, growing and mature follicles and corpora lutea with earlier occurrence of ovulation in GII when compared with GI.

Conclusion: Daily i.p. injection of leptin 5ug/g BW to prepubertal female albino rats led to statistically significant decreased body weight and earlier onset of puberty and its manifestation in treated group. Leptin may act on the reproductive axis both centrally and peripherally. Leptin could be a possible link between the body fat and timing of puberty.