 BackResearch Article ScienceAsia 10 (1984): 089-099 |doi: 10.2306/scienceasia1513-1874.1984.10.089
DIFFERENCE BETWEEN PATTERNS OF MELATONIN UPTAKE IN RAT BRAIN AFTER THE MORNING AND THE AFTERNOON MELATONIN ADMINISTRATION
B. WITHYACHUMNARNKUL and W.K. TRAKULRUNGSIABSTRACT: 3H-Melatonin uptake was determined in the brain of rats infused with 3H-melatonin into the right common carotid artery. When the infusion was performed in the morning (4 h after onset of light), 3H-melatonin. uptake in the hypothalamus was higher than that in the cerebrum, the cerebellum, and the midbrain. In contrast, when the infusion was performed in the afternoon (3 h before onset of darkness), the uptake in the hypothalamus was equal to that found in the morning but the uptake in all other regions increased significantly comparable to that in the hypothalamus. The uptake in the interior pituitary and the pineal gland was lower than that in the brain. Total radioactivity in serum of the mornining and the afternoon rats were comparable, whereas melatonin radioactivity in serum of the afternoon rats was significantly higher than that of the morning rats. These data suggest that melatonin may act primarily in the hypothalamus but the action has to be facilitated by melatonin interaction to other brain regions which occurs only during the late light phase. The increased melatonin binding in the brain may retard the rate of melatonin degradation in the liver. Department of Anatomy, Faculty of Science Mahidol University, Rama 6 Rd., Bangkok 10400, Thailand. Received 23 March 1984
|
