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

Abstract

OBJECTIVE: Leptin secretion is reduced by low temperatures in experimental animals, and this effect has been explained as an adaptive mechanism to cold environments. This study investigated the in vitro effects of cold exposure on human white adipose tissue. DESIGN: To understand whether the low temperature action is a direct or a mediated effect, leptin secretion was assessed in vitro in human omental adipose tissue incubated at varied temperatures, from 38 donors. As an internal control, the effect of reduced temperatures on in vitro GH secretion by GH3 cells was assessed. METHODS: Measurement of hormones secretion was carried out with an RIA, while human ob gene mRNA expression was assessed with reverse transcription PCR. RESULTS: Compared with the standard temperature of 37 degrees C, leptin secretion by human adipose tissue was significantly (P<0.05) reduced when the 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 expression. At these reduced temperatures, glucocorticoid-mediated leptin secretion 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 leptin secretion by acting directly on the adipose tissue and (ii) that the similar reduction in a hormone unrelated to energy metabolism, such as GH, suggests that the observed reduction is a mechanical perturbation of leptin secretion, which may be devoid of physiological implications.