Role of Leptin on Growth Hormone and Prolactin Secretion by Bovine Pituitary Explants

Leptin is an important hormone regulating nutritional status in humans and animals. Its most relevant activity is at the hypothalamic level, where it modulates food behavior, thermogenesis, and secretion of several pituitary hormones. The exact mechanisms underlying these processes are unclear. The purpose of this study was to verify whether leptin could modulate growth hormone (GH) and prolactin (PRL) secretion acting directly on bovine pituitary cells. Adenohypophyseal explants were cultured with different concentrations of leptin (50, 250, and 500 ng/mL); GH and PRL concentrations in culture media were determined by RIA. On tissues treated with 250 ng/mL of leptin, GH and PRL mRNA, as well as protein content, were estimated by reverse transcription-PCR and Western immunoblotting, respectively. Concentrations of GH in culture media containing 250 and 500 ng/mL of leptin were significantly higher than in controls: 1,063.5 ± 141.2 (mean ± SEM) and 1,018.8 ± 88.4 vs. 748.9 ± 74.0 ng/mg of tissue, respectively, after 1 h of treatment. Prolactin concentrations were significantly higher in culture media containing 50, 250, and 500 ng/mL of leptin than in controls after 2 h of treatment (547.1 ± 50.3, 547.5 ± 58.8, and 577.0 ± 63.7 vs. 406.8 ± 43.9 ng/mg of tissue, respectively). Tissues cultured with 250 ng/mL of leptin had significantly higher GH mRNA and lower GH protein content than controls (389.7 ± 17.9 vs. 289.7 ± 16.7; 1,601.5 ± 90.1 vs. 2,212.7 ± 55.6 arbitrary units, respectively) after 5 h of treatment. In contrast, no significant differences were found for PRL mRNA and protein content, possibly because of a delay in the leptin stimulation of PRL secretion. The results suggest that GH and PRL secretion in bovine pituitary explants can be directly regulated by leptin.