Ghrelin is a novel growth hormone (GH) releaser acylated peptide that has recently been purified from stomach, and which potently binds to the GH secretagogue receptor. Ghrelin releases GH in vitro and in vivo in animal models, however its actions, potency and specificity in humans are unknown. In the present study, 12 healthy subjects were studied: 6 underwent four tests with ghrelin administered i.v. at the dose of 0 (placebo), 0.25, 0.5 and 1 mg/kg which corresponds to 0, 18, 37 and 75 mg total dose. A further 6 volunteers underwent two tests on different days with ghrelin at the dose of 3.3 or 6.6 mg/kg which corresponds to 250 mg and 500 mg total dose.Ghrelin-mediated GH secretion showed a dose±response curve, in which 1mg/kg was the minimally effective dose in some individuals, but not as a group. On the contrary, the total doses of 250 mg and 500 mg elicited a powerful GH secretion, with a mean peak of 69X8^9X2 mgal and 90X9^16X9 mgal respectively, and areas under the curve of 4435^608 and 6125^1008 mgal per 120 min respectively. All of them statistically significant vs placebo and vs the 1 mg/kg dose.Ghrelin administration also elicited a relevant dose±response mediated prolactin secretion suggesting no specificity of its actions. No relevant side effects were observed with ghrelin apart from a hyperhydrosis episode in two individuals tested with the higher ghrelin doses.In conclusion, ghrelin is a potent releaser of GH in normal individuals, with a dose±response pattern of operation. No saturating dose was observed.

Leptin is a circulating hormone secreted by adipose tissue which acts as a signal to the central nervous system where it regulates energy homeostasis and neuroendocrine processes. Although leptin modulates the secretion of several pituitary hormones, no information is available regarding a direct action of pituitary products on leptin release. However, it has been pointed out that leptin and TSH have a coordinated pulsatility in plasma. In order to test a direct action of TSH on in vitro leptin secretion, a systematic study of organ cultures of human omental adipose tissue was performed in samples obtained at surgery from 34 patients of both sexes during elective abdominal surgery. TSH powerfully stimulated leptin secretion by human adipose tissue in vitro. In contrast, prolactin, ACTH, FSH and LH were devoid of action. These results suggest that leptin and the thyroid axis maintain a complex and dual relationship and open the possibility that plasmatic changes in TSH may contribute to the regulation of leptin pulses.

Leptin, the product of the ob gene, is secreted into the circulation by white adipose tissue; its major role being to participate in the regulation of energy homeostasis. Plasma leptin levels are mainly determined by the relative adiposity of the subject; however, the great dispersion of values for any given body mass index and the noteworthy gender-based differences indicate that other factors are operating.Steroid hormones actively participate in the regulation of leptin secretion; however, non-steroid nuclear hormones have either not been studied or have provided contradictory results. In order to understand the role of hormones of the non-steroid superfamily such as 3,5,3 -tri-iodothyronine (T 3 ), vitamin D 3 and retinoic acid (RA) in the control of leptin secretion, in the present work doses of 10 9

In neonates both nutrients and regulatory factors are transferred from the mother to the suckling infant via milk. In the present work, it has been shown that human milk contains immunoreactive leptin which is identical to intact human leptin by criteria of charge, size, immunorecognition and SDS-PAGE mobility. In experimental animals it was demonstrated that leptin is transferred from the circulation to mothers' milk, then to the infant's stomach and afterwards to infant blood. Maternal leptin in milk may play a regulatory role in the suckling infant.