| Modification Notes |
Melatonin (Mel), a hormone secreted by the pineal gland, is expressed at night in response to the circadian clock (1,2). Melatonin is thought to be involved in regulating reproductive physiological development and the progression of sexual maturation, and it is also thought to play a role in tumorigenesis (1,3). The melatonin receptors, MEL-1A-R and MEL-1B-R, are members of the super-family of guanine nucleotide-binding regulatory protein (G protein)-coupled receptors (4,5). Signaling through the melatonin receptors inhibits adenylate cyclase and stimulates phospholipase Cb upon activation of pertussis toxin (PTX)-sensitive G proteins (4,5). MEL-1A-R may be involved in pacing the biological clock (5). However, both MEL-1A-R and MEL-1B-R are implicated in controlling cellular growth in response to melatonin (6,7). |