Effects of leptin on basal and GHRH-stimulated GH secretion from the bovine adenohypophysis are dependent upon nutritional status

We have shown recently that leptin modulates at least two aspects of anterior pituitary LH release in ruminants: basal and GnRH-mediated release. To test the hypothesis that leptin directly affects basal and GHRH-mediated GH secretion from the adenohypophysis, we examined the effects of various doses of recombinant ovine leptin (oleptin) on perifused adenohypophyseal (AP) explants and compared responses of tIssues from control and fasted cows. Ten mature, ovariectomized and estradiol-implanted cows were assigned to one of two dietary groups: (1) normal-fed (n=5) and (2) fasted for 72 h (n=5). At the end of the fasting period, cows were euthanized and pituitaries were collected. Adenohypophyseal explants were perifused for a total of 6.5 h, including a 2-h treatment at 2.5 h with Krebs-Ringer bicarbonate buffer containing 0, 5, 10, 50, or 100 ng/ml oleptin, and a challenge with GHRH at 4.5 h. All doses of oleptin greater than 5 ng/ml decreased (P