Leptin stimulates GnRHr expression in wild-type pituitaries in vitro. (A) Dispersed pituitary cells from male mice were stimulated with 1, 10, or 100 nM leptin. All concentrations of leptin stimulated an increase in the percentages of living pituitary cells that bound 1 nM biotinylated GnRH. (B) All concentrations of leptin stimulated a substantial increase in cells dual-labeled for bio-GnRH and LH. Stimulation with 100 nM resulted in the highest percentages of dual-labeled cells (compared with 1 and 10 nM, P < 0.005). (C) All concentrations of leptin stimulated an increase in the percentage of living diestrous female pituitary cells that bound biotinylated GnRH when compared with vehicle, with 1 nM being significantly lower than 10 nM (P < 0.05) and 100 nM (P < 0.005). (D) Both 10 and 100 nM leptin stimulated an increase in the percentage of diestrous pituitary cells dual labeled for LH and bio-GnRH, and 100 nM stimulated significantly more dual-labeled cells than 1 nM (P < 0.0001) and 10 nM (P < 0.005). *P < 0.05; **P < 0.005; ***P < 0.0005; ****P < 0.0001.