A new study shows that melatonin, a hormone available without prescription, has broader effects in the brain than once thought. In experiments on the Japanese quail, the researchers found that melatonin switches on a recently discovered hormone called gonadotropin inhibitory hormone (GnIH), which has been found to have the opposite effect to the key hormone priming the body for sex gonadotropin releasing hormone (GnRH). In birds, switching off GnRH causes the gonads testes and ovary to shrink as part of the birds' yearly cycle.
Though the role of melatonin is likely to be more complex in humans, the fact that the hormone has such a big effect on birds suggests it could have significant though unnoticed effects in humans, said George E. Bentley, an assistant professor of integrative biology at UC Berkeley. In humans, GnRH one of various short protein or peptide hormones referred to as neuropeptides brings on puberty.
"This is quite exciting in terms of potential effects of melatonin on the reproductive axis, that is, the link between the brain, the pituitary gland and the gonads," said Bentley, who is finishing post-doctoral work at the University of Washington, Seattle, before a planned move this summer to UC Berkeley. "Melatonin has not been considered to have an effect on any neuropeptide in the brain of any vertebrate. If melatonin can do this on one neuropeptide system, it has the potential to do it on any other neuropeptide system."
Bentley noted that melatonin could have good as well as bad effects, but that the current lack of knowledge of the hormone's function in the human brain is troubling.
"It really amazes me that melatonin is available in any pharmacy," Bentley said. "It is a powerfu
Contact: Robert Sanders
University of California - Berkeley