Melatonin and glucose metabolism.

Abstract

Melatonin (N-acetyl-5-methoxytryptamine) is a neurohormone secreted from the pineal gland during the night and is known as a synchronizer of the circadian rhythm. It is a hormone that has been present not only in vertebrates but all kinds of living organisms. Recently, several reports showed that the hormone plays very important roles such as energy metabolism and glucose metabolism, in particular. It has been reported that in animal models of type 2 diabetes, melatonin ameliorates glucose homeostasis by improving insulin action in muscles and adipose tissues. We demonstrated that melatonin treatment increased glucose uptake in a dose-dependent manner in a primary culture of goldfish brain cells using insulin-free medium. These findings suggest that nocturnal melatonin increases glucose uptake in the brain via insulin independent action. To the best of our knowledge, this study is the first to demonstrate that nocturnal melatonin directly regulates glucose uptake in place of insulin in a vertebrate species. In this paper, we introduce new findings concerning glucose metabolism by melatonin on mammals, and consider a role of melatonin in aspect of the evolution of glucose metabolism.