Melatonin Effects on Metabolism Independent of Gonad Function

Abstract

We previously demonstrated that daily melatonin administration to middle-aged rats, restoring nocturnal plasma melatonin to young adult levels, decreased body weight and suppressed visceral fat and plasma leptin. In some species, metabolic and some neuronal responses to melatonin are mediated or dependent at least in part on gonadal steroid levels. Thus, melatonin-induced changes in gonadal steroid secretion may have mediated the aging-dependent melatonin-induced metabolic responses in our previous studies. To address this issue, melatonin (0.4 micro g/mL) or vehicle (0.01% ethanol) was administered for 10 wk in the drinking water of both castrate and sham-operated Sprague-Dawley male rats, starting 1 mo after surgery at 9 mo of age. Melatonin treatment decreased (p < 0.05) body weight in sham-operated rats by 7 +/- 2% relative to control (n = 7/treatment), comparable to our previous results; melatonin likewise decreased (p < 0.05) body weight in castrate rats by 6 +/- 2% relative to control (n = 7/treatment). Melatonin treatment also decreased both intraabdominal fat and plasma leptin levels in both intact and castrate rats, with no significant differences of percentage suppression in the intact versus castrate rats. These results demonstrate that suppression of body weight, visceral adiposity, and plasma leptin levels by daily melatonin administration to middle-aged rats was independent of gonadal function.

Melatonin reduces body weight in goldfish (Carassius auratus): effects on metabolic resources and some feeding regulators

“…administration in goldfish, supporting the previously suggested role of this molecule as a signal of nutritional status in the regulation of energetic homeostasis in fish [19,20]. Our data are in agreement with a number of studies performed in mammals [8][9][10][11][12] and in juvenile rainbow trout [24]. In the latter study, melatonin implants reduced growth rate under different photoperiod regimes during a prolonged treatment period (5 months), suggesting that melatoninÕs actions on energy homeostasis are sustained in chronic treatments, without developing a tolerance response.…”

“…These metabolic actions of melatonin could be mediated by other hormones clearly involved in the metabolism regulation. It is known the inhibitory effect of melatonin on insulin levels [11] and the increase in glucagon and growth hormone by melatonin, which would contribute to preservation of glycemia and the increased utilization of lipids [25], in accordance with present data in goldfish.…”

Diurnal rhythm in endogenous glucose production is a major contributor to fasting hyperglycaemia in type 2 diabetes. Suprachiasmatic deficit or limit cycle behaviour?

“…4), raising the possibility that, unlike the case in rodents, the SCN may be involved in suppressing a cyclic nocturnal increase in EGP, which is then unmasked in diabetes. Parenthetically, the decrease of melatonin itself in diabetes may contribute to the metabolic syndrome, since its administration in rats decreased body weight and suppressed visceral fat and plasma leptin [35].…”

Melatonin counteracts changes in hypothalamic gene expression of signals regulating feeding behavior in high-fat fed rats

“…In the rat, the responses have been conflicting, including reduction, increase or no effect on food consumption [9,10]. A decrease in fat mass and body weight has been reported in rats [10][11][12][13], whereas melatonin increases fat mass in gray mouse lemurs [14], Syrian hamster [3], raccoon dog [15] and garden dormouse [16].…”