The Effect of Melatonin on the Ovaries 47

Melatonin is a very small molecule whose effects can be both detrimental and beneficial to the ovaries depending on its concentration. Too much of anything is usually not good and so is the case with melatonin. Very high doses can be damaging, but in the right amount melatonin may be able to combat various diseases and increase the chances for fertility in women. THE PRODUCTION OF MELATONIN Melatonin is an indoleamine which is produced in the pineal gland. It was first isolated from bovine pineal gland in 1958 and is currently classified as a hormone. This seemingly ambiguous hormone is found in many places in the human body and has many functions. As more research is done on melatonin, more of its importance is being uncovered. Melatonin is synthesized and released in accordance with how much light reaches the eye. When light enters the eye, the ganglion cells, which contain the photopigment melanopsin, send retinal photic signals to the suprachiasmatic nucleus (SCN) through the monosynaptic retinohypothalamic tract. The ganglion cells which contain melanopsin are sensitive to light with relatively short wavelengths (484 nm) (Macchi and Bruce 2004). There are constant rates of production of melatonin at night, but during daylight hours synthesis is suppressed by light (Macchi and Bruce 2004). The mechanism which causes the light induced suppression and dark induced release of melatonin is due to norepinephrine. Norepinephrine is the input to the pineal gland, and melatonin is the output. During the day, the retinal photoreceptors are hyperpolarized, inhibiting the release of norepinephrine and thus inhibiting the release of melatonin. Conversely, the lack of light at night causes the photoreceptors to release norepinephrine, thereby activating the enzyme Nacetyltransferase which regulates melatonin synthesis (Brzezinski 1997). In addition, melatonin concentrations are affected by exercise and changing posture. During night hours, concentrations of melatonin in the Figure 1: Tryptophan to Melatonin. Source: Macchi and Bruce 2004