Action of leptin on GTH cells in Podarcis sicula pituitary gland

Leptin, the protein product of the ob gene, is a hormone synthesized by adipocytes that signals available energy reserves to the brain. It has an important role in the regulation of appetite and metabolism but this hormone has also pleiotropic actions in development and physiology. Some of the major actions of leptin uncovered in recent years include the promotion of linear growth through its influence on energy balance and the stimulation of secretion of pituitary growth hormone. Leptin seems to be a phylogenetically preserved protein and in non mammalian vertebrates it has been found in all major taxa (Paolucci M., 2010). In the present work we have analysed the action of leptin on the GTH cells of the lizard Podarcis sicula. The study was performed on five groups of female lizards by the intraperitoneal injection of recombinant human leptin for three consecutive days at four different concentrations. As control, one group of lizards were treated with an injection of physiological solution. Sections of 5um of the pituitary glands enclosed in paraffin were processed by histological and immunohistochemical stains. GTH cells were revealed by ABC technique using the antisera anti-human LH and anti-human FSH at working dilution of 1:100. At low doses of leptin, GTH cells showed a decrease in immunoreactivity. This evidence shows an activating action of leptin on the secretory activity of these cells. At high doses instead GTH cells appeared markedly immunoreactive and numerous. The action of the leptin on GTH cells in P. sicula appears similar to that already reported in mammals.