Inhibitory effect of leptin on growth hormone secretion of GH3 cells: Involvement of cell proliferation, apoptosis and intracellular free Ca super(2+)

Recent studies have identified leptin and leptin receptors in the pituitary of different species, which suggest that there may be endocrine and paracrine regulatory roles between leptin-producing cells and cells with leptin receptor in pituitary, including growth and secretion of GH cells. The aim of this study was to investigate the effects of leptin on growth hormone (GH) secretion of GH3 cell. GH3 cells were cultured and treated with leptin. Cell proliferation was evaluated by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay, distribution of cell cycle and rate of apoptosis determined by flow cytometry and fluorescence microscopy, and intracellular free Ca super(2+) levels ([Ca super(2+)] sub(i)) of single GH3 cells measured by a laser scanning confocal microscope. Leptin (10 super(-9)-10 super(-7) mol/L) at 1 day or longer of treatment inhibited the basal growth hormone secretion of GH3 cells (P < 0.05), but had no significant effect on short-term treatment. Leptin inhibited cell proliferation, reduced the proportion of cells in DNA synthesis period (S phase) to inhibit DNA synthesis of GH3 cells, and accelerated cell apoptosis of GH3 cells. Furthermore, the level of [Ca super(2+)] sub(i) of single GH3 cell was found to decrease immediately upon the addition of leptin (10 super(-8) mol/L). Leptin inhibits the basal GH secretion of GH3 cells, which may be due to the inhibition of proliferation, DNA synthesis and advanced apoptosis of GH3 cell. The inhibition of leptin on GH synthesis and secretion may be related to intracellular free Ca super(2+) level.