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.
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C Menendez, R Baldelli, JP Camina, B Escudero, R Peino, C Dieguez, and FF Casanueva
V Pineiro, X Casabiell, R Peino, M Lage, JP Camina, C Menendez, J Baltar, C Dieguez, and F Casanueva
Leptin, the product of the Ob gene, is a polypeptide hormone expressed in adipocytes which acts as a signalling factor from the adipose tissue to the central nervous system, regulating food intake and energy expenditure. It has been reported that circulating leptin levels are higher in women than in men, even after correction for body fat. This gender-based difference may be conditioned by differences in the levels of androgenic hormones. To explore this possibility, a systematic in vitro study with organ cultures from human omental adipose tissue, either stimulated or not with androgens (1 microM), was undertaken in samples obtained from surgery on 44 non-obese donors (21 women and 23 men). The assay was standardized in periods of 24 h, ending at 96 h, with no apparent tissue damage. Leptin results are expressed as the mean+/-s.e.m. of the integrated secretion into the medium, expressed as ng leptin/g tissue per 48 h. Spontaneous leptin secretion in samples from female donors (4149+/-301) was significantly higher (P<0.01) than that from male donors (2456+/-428). Testosterone did not exert any significant effect on in vitro leptin secretion in either gender (4856+/-366 in women, 3322+/-505 in men). Coincubation of adipose tissue with dihydrotestosterone (DHT) induced a significant (P<0.05) leptin decrease in samples taken from women (3119+/-322) but not in those taken from men (2042+/-430). Stanozolol, a non-aromatizable androgen, decreased (P<0.05) leptin secretion in female samples (2809+/-383) but not in male (1553+/-671). Dehydroepiandrosterone sulphate (DHEA-S) induced a significant (P<0.01) leptin decrease in female samples (2996+/-473), with no modifications in samples derived from males (1596+/-528). Exposure to androstenedione also resulted in a significant reduction (P<0.01) of leptin secretion in samples taken from women (2231+/-264), with no effect on male adipose tissue (1605+/-544). In conclusion, DHT, stanozolol, DHEA-S and androstenedione induced a significant inhibition of in vitro leptin secretion in samples from female donors, without affecting the secretion in samples from men. Testosterone was devoid of activity in either gender.