Modulation of melatonin secretion by acetyl-L-carnitine in adult and old rats.

Modification of melatonin synthesis and release by acetyl-L-carnitine (ALC) was studied in adult (2 month old) and old (24-month-old) male Sprague Dawley rats. When ALC was injected at 1500 into adult rats at doses of 10, 30, or 90 mg/kg, there was a remarkable increase in their pineal and serum melatonin 1 hr later. However, using the same experimental protocol acute ALC administration in old rats did not modify pineal and serum melatonin levels. ALC administered in the same dose range induced a significant increase in pineal and serum melatonin in adult rats treated at 0100 h following exposure of 30 min to bright, white light to suppress endogenous melatonin. In the same conditions, in old rats, only the higher dose (90 mg/kg) caused any noteworthy increase in melatonin pineal content while lower doses were uneffective both on serum and pineal melatonin levels. It is known that ALC affects fatty acid transport in the cells, modulates CoA, modifies neuronal transmission and reduces lipofuscin accumulation which is related to lipid peroxidation. The action of ALC on melatonin synthesis could be the result of a modulation of the neuronal transmission related to circadian pineal endocrine activity. Moreover, since both ALC and melatonin exert remarkable scavenger activity, it is possible to suppose that ALC effects in reversing certain aging processing may be due to its ability to promote melatonin production.