Objective and study design: Leptin is a circulating hormone secreted by adipose tissue and a few other tissues. It has recently been demonstrated that leptin and leptin receptors are expressed in normal and adenomatous pituitary cells. The aim of this study was to investigate the effect of recombinant human leptin on GH release from adenomatous GH-secreting cells in culture. Specimens were obtained from 10 patients with acromegaly who had undergone selective transsphenoidal adenomectomy. Cells (2 x 10(5)/well) preincubated for 24 h with leptin (10(-10)-10(-8) m) or control medium were exposed to GHRH for 2 h. The GH released into the medium was measured before and after GHRH incubation. The expression of leptin receptor isoforms was evaluated by reverse-transcriptase polymerase chain reaction (RT-PCR) in cells obtained from five adenomas.
Results: After the first incubation, there was a slight dose-dependent leptin-induced decrease in GH released into the medium. A significant increase in GH release after GHRH was noted from cells previously exposed to leptin in comparison with cells incubated with medium alone. Expression of leptin receptors was found in two out of five GH-secreting adenomas evaluated.
Conclusions: Our data confirm that some, but not all, GH-secreting adenomas express leptin receptors. Leptin seems to exert both a slight inhibitory effect on spontaneous GH secretion and a stimulatory effect on GHRH-stimulated GH secretion from GH-secreting adenomatous tissue.