Effects of irradiation on the sensitivity of melatonin release to norepinephrine in cultured pineal bodies of rats

We measured levels of basal and norepinephrine (NE) -induced melatonin rele ase in cultured pineal bodies of rats just after and 2 days after irradiati on (20 or 200 Gy) or sham-irradiation. On the day of irradiation, basal and NE-induced melatonin release were not affected by irradiation. Two days af ter irradiation, basal melatonin levels in both irradiated groups were sign ificantly lower than those in control group, whereas NE-induced melatonin l evels in the irradiated groups were higher than those in the control group. These results suggested that irradiation decreases basal melatonin synthes is in pineal glands but that melatonin response to NE is increased after ir radiation. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.