Leptin stimulates basal and GHRH-induced GH release from cultured rat anterior pituitary cells in vitro.

Leptin, the product of ob gene, is secreted from adipocytes and appears to regulate food intake and energy expenditure through its receptor in the hypothalamus. In addition, leptin is reported to modulate pituitary hormones including LH, FSH and ACTH, probably via the hypothalamus. In obesity, growth hormone (GH) secretion is impaired, while serum leptin levels are elevated. To investigate the possibility that leptin serves as a metabolic signal that influences GH secretion from the pituitary, we studied the effect of leptin on GH secretion from primary monolayer cultures of rat anterior pituitary cells. Twenty micrograms/ml leptin increased GH secretion, but did not increase GH release at a physiological concentration up to 200 ng/ml. However, 200 ng/ml leptin stimulated GH release in the presence of GH-releasing hormone (GHRH) ranging from 10(-8) to 10(-7) M. Twenty ng/ml leptin tended to increase 10(-7) M GHRH-induced GH release, whereas 20 ng/ml leptin did not increase either 10(-9) or 10(-8) M GHRH-induced GH release. This result suggests that leptin has a direct effect on the pituitary to enhance GHRH-induced GH secretion.