Browning of white adipose tissue by melatonin

There are two distinct types of adipose tissue which have different functions within the body, white (WAT) and brown (BAT). Browning of WAT occurs with increases in the WAT sympathetic nervous system (SNS) drive. In this regard we previously reported that melatonin (MEL) stimulation of MEL receptor 1A (MEL1a) within the SNS outflow to the WAT might be implicated in a naturally-occurring reversal of obesity (by ~30% of total body fat). Therefore, in this study we tested the hypothesis that MEL causes browning of WAT through the stimulation of SNS drive to WAT. This was done by comparing specific browning and lipolytic markers in WAT following 10 weeks of MEL treatment, short day housing (SD), and long day housing with saline injections (LD+VEH). Browning effects of a 5 day treatment of a β3-adrenergeric (β3AR), CL 316, 243, were also measured. We found that CL 316, 243, MEL treatment, and SD housing had increased expressions of browning markers within WAT and lipolytic activity in MEL treated animals was increased in specific WAT. INDEX WORDS: Brown adipose tissue, Lipolysis, obesity, UCP1, PGC-1α BROWNING OF WHITE ADIPOSE TISSUE BY MELATONIN