Role of leptin in modulating the hypothalamic–pituitary axis and luteinizing hormone secretion in the prepuberal gilt

Three experiments (EXP) were conducted to test the hypothesis that leptin modulates LH, GnRH, and neuropeptide Y (NPY) secretion. In EXP I, prepuberal gilts received intracerebroventricular (i.c.v.) leptin injections and blood samples were collected. In EXP II, anterior pituitary cells from prepuberal gilts in primary culture were challenged with 10 −14, 10 −13, 10 −12, 10 −11, 10 −10, 10 −9, 10 −8, 10 −7, or 10 −6 M leptin individually or in combinations with 10 −10, 10 −9, and 10 −8 M GnRH. In EXP III, hypothalamic–preoptic area (HYP-POA) explants were placed in perfusion system and exposed to 0 ( n=5), 10 −12 M ( n=4), 10 −10 M ( n=4), 10 −8 M ( n=4), or 10 −6 M ( n=5) human recombinant leptin (LEP) for 30 min. In EXP I, serum LH concentrations were unaffected by leptin treatment. In EXP II, all doses of leptin increased LH secretion except for 10 −12 and 10 −7 M. Only 10 −7, or 10 −13 M leptin in combination with 10 −8 or 10 −9 M GnRH, respectively, suppressed LH secretion. In EXP III, prior to leptin, media GnRH concentrations were similar across treatments. Media GnRH concentrations increased after 10 −12, 10 −10, and 10 −8 M leptin compared to control. Leptin treatment failed to influence NPY secretion across treatments. These results indicate that components of the neuroendocrine axis that regulate GnRH and LH secretion are functional and leptin sensitive before the onset of puberty. Other neural peptides in addition to NPY may mediate the acute effects of leptin on the GnRH-LH system and lastly, the inability of i.c.v. leptin treatment to increase LH secretion may in part be related to stage of sexual maturation and associated change in negative feedback action of estradiol on LH secretion.