Cold exposure inhibits leptin secretion in vitro by a direct and non-specific action on adipose tissue

Objective: Leptin secretion is reduced by low temperatures in experimental animals, and this effect has been explained as an adaptive mechanism to col d environments. This study investigated the in vitro effects of cold exposu re on human white adipose tissue. Design: To understand whether the low temperature action is a direct or a m ediated effect, leptin secretion was assessed in vitro in human omental adi pose tissue incubated at varied temperatures, from 38 donors. As an interna l control, the effect of reduced temperatures on in vitro GH secretion by G H3 cells was assessed, Methods: Measurement of hormones secretion was carried out with an RIA, whi le human ob gene mRNA expression was assessed with reverse transcription PC R. Results: Compared with the standard temperature of 37 degrees C. leptin secretion by human adipose tissue was significantly (P<0.05) reduced when t he incubations were carried out at 34.5 degrees C (41% inhibition), and 32 degrees C (68% inhibition), with no parallel changes in the ob mRNA express ion. At these reduced temperatures, glucocorticoid-mediated leptin secretio n was well preserved, When the effect of reduced temperatures was assessed on in vitro GH secretion, a superimposable reduction was observed. Conclusions: These results indicate: (i) that low temperatures reduce lepti n secretion by acting directly on the adipose tissue and (ii) that the simi lar reduction in a hormone unrelated to energy metabolism, such as GH, sugg ests that the observed reduction is a mechanical perturbation of leptin sec retion, which may be devoid of physiological implications.