Effect of leptin on LH levels and hypothalamic release of GnRH. Its relationship with the hypothalamic neurotransmitter amino acids system in adult male rats

The objective of the present paper was to determine the effect of leptin on the reproductive axis in adult male rats, as well as the hypothalamic mechanisms involved in this effect. For this purpose, we studied the in vivo effect of leptin in adult male rats on serum LH levels, and the in vitro effect on hypothalamic GnRH and amino acid neurotrasmitter release. For in vivo experiments, animals were injected i.p. with leptin at a dose of 30, 100 and 300 µg/kg. In the in vitro experiments, hypothalamic samples were incubated for 60 min in Earle's medium with leptin: 10− 9, 10− 10 and 10− 12 M for GnRH determination, and 10− 10 M for amino acids evaluation. Finally, we studied the effect of the lowest effective leptin dose on plasma LH levels in peripubertal male rats to compare the effect between this group and adults. Leptin induces significant decreases of serum LH levels with the different studied doses (p < 0.01 vs. control) in adult male rats, while in peripubertal male rats, it induced a significant (...