OR I GI N A L A R T I CLE Changes in the Sensitivity of Gonadotrophin Axis to Leptin During Sexual Maturation in Female Rats

OBJECTIVES: The aim of the present paper was to determine the sensitivity of the GnRH-LH axis to leptin administration during sexual maturation in female rats. METHODS: For this purpose the hypothalamic concentration of GnRH, the pituit ary content and the plasmatic levels of LH were determined in prepubertal (15 days of age) and peripubertal female rats (30 days of age), treated with leptin at a dose of 30 µg/kg. i.p. in a single injection, 90 min before sacrifi ce. RESULTS: The results indicate that leptin signifi cantly increased the GnRH concentration at 15 days of age (p <0.01). At 30 days of age the hormone did not signifi cantly modify the hypothalamic GnRH content. Leptin increased the pituitary LH levels, both in prepubertal and peripubertal rats. Nevertheless, while the increase at 15 days of age was around 180%, in peripubertal rats it was about 51,2 %. In spite that leptin signifi cantly increased LH plasmatic levels at both ages (p < 0.01 ), in rats of 15 days of age leptin increased LH in about 244%, at 30 days of age this increase was only about 102%. CONCLUSION: These results clearly demonstrated that leptin has stimulatory effect on gonadotrophin axis been higher in prepubertal than in peripubertal rats. On these basis, and on the results of previous papers, (in which it has been demonstrated that the hypothalamic control of gonadotrophins by neurotransmitters and neuromodulators also showed qualitative and quantitative changes during sexual maturation), it is proposed that these differences are connected with the maturation of the neuroendocrine mechanisms involved in the regulatory action of leptin on the gonadotrophins axis.