Circadian Variation of Cyclic AMP in the Rat Pineal Gland

Abstract: This study was carried out to investigate circadian variation of cyclic AMP contents in the rat pineal glands, using the high-energy microwave radiation technique. The pattern of cyclic AMP concentration in the pineal gland showed a distinct circadian variation, with the maximum level at 0200 and the lowest at 1400. The administration of propranolol completely blocked the dark-induced increase in the pineal cyclic AMP level at 0200, and the administration of isoproterenol induced a threefold, rapid increase in the cyclic AMP level at 1400, although it did not change the level at 0200.