Aims: 

Melatonin is synthesized in a series of organs and tissues besides the pineal gland. However, its intracellular distribution, regulation and functions are unclear. The aim of this study was to analyze the subcellular distribution of melatonin in rat liver and brain, and its relation with pineal melatonin.

Methods: 

Male Wistar rats (3 mo. age) were housed in a 12:12 h light:dark cycle. Animals were sacrificed at 08h, 12h, 16h, 20h, 00h, 02h, 04h and 06h, and nuclei, membrane, mitochondria and cytosol were isolated from livers and brains by differential centrifugation. Melatonin concentration in these compartments was measured by HPLC with fluorescence detection.

Results: 

In liver, the highest concentration of melatonin was found in membranes following by mitochondria, nuclei and cytosol, respectively. In brain, the highest melatonin concentration was detected in mitochondria, following by membranes, nuclei, and cytosol, respectively. Tissue melatonin leves were significantly higher than those in plasma, and they did not show a circadian rhythm.

Conclusions: 

Liver and brain contain melatonin, with a different pattern of subcellular distribution, probably reflecting the oxidative stress status of each compartiment. Tissue levels of the indoleamine are higher than pineal levels and they do not follow a typical circadian rhythm.

Supported by grants: RD06/0013/0008 and P07-CTS-03135