Testosterone-Dependent Effects of Galanin on Pituitary Luteinizing Hormone

Galanin is a 29-amino-acid peptide that colocalizes with GnRH in hypothalamic neurons. High concentrations of galanin are present in portal vessel blood of both male and female rats, and galanin receptors are present on gonadotropes in both sex-es. Results from studies of female rats indicate that galanin acts at the level of the pituitary to directly stimulate LH secretion and also to enhance GnRH-stimulated LH secretion. The effects of galanin on pituitary LH secretion in male rats are relatively uncharacterized; thus, the present in vivo study was conducted 1) to examine the ability of galanin to affect basal or GnRH-stimulated LH secretion in male rats and 2) to determine wheth-er the effects of galanin on LH secretion in male rats are tes-tosterone-dependent. All three doses of galanin used (1, 5, and 10 mg/pulse) significantly enhanced GnRH-stimulated LH secre-tion in intact male rats. Only the highest dose of galanin directly stimulated LH secretion (without GnRH coadministration) in in-tact males. Galanin did not directly stimulate LH secretion or enhance GnRH-stimulated LH secretion in castrated male rats. In fact, the highest dose of galanin inhibited GnRH-stimulated LH secretion in castrated males. Upon testosterone replace-ment, the ability of galanin to directly stimulate LH secretion and to enhance GnRH-stimulated LH secretion was restored in castrated males. These results suggest a role for galanin in the regulation of LH release in male rats and demonstrate that tes-tosterone upregulates the ability of the pituitary to respond to the stimulatory effects of galanin. galanin, gonadotropin-releasing hormone, luteinizing hormone, male reproductive tract, pituitar