Stimulation effect of galanin-like peptide (GALP) on luteinizing hormone-releasing hormone-mediated luteinizing hormone (LH) secretion in male rats

Galanin-like peptide (GALP) is a recently isolated hypothalamic peptide whi ch has sequence homology to galanin and binds to galanin receptors with hig h affinity. It has been shown that GALP neurons are localized in the arcuat e nucleus and that GALP-immunoreactive fibers are in close apposition with LHRH neurons in the medial preoptic area (MPA). In the present study, we fo und that intracerebroventricular (icv) administration of GALP increased the plasma LH level but did not change the levels of other hormones. Concomita ntly, accumulation of c-Fos protein was dramatically increased in the nucle i of LHRH-positive cells in the MPA by icv GALP administration. Furthermore , the GALP-induced plasma LH response was completely abolished by pretreatm ent with Cetrorelix, a LHRH receptor antagonist. On the other hand, GALP di d not affect the release of LH, FSH, TSH, ACTH, GH or PRL directly from dis persed rat pituitary cells in vitro. These results strongly suggest a role for GALP in the control of gonadotropin secretion through a hypothalamic me chanism involving the release of LHRH.