THE EARLY RESPONSE OF PINEAL N-ACETYLTRANSFERASE ACTIVITY, MELATONIN AND CATECHOLAMINE LEVELS IN RATS IRRADIATED WITH GAMMA-RAYS

Male Wistar rats adapted to an artificial light-dark regimen (12 h lig ht : 12 h darkness) were whole-body irradiated with a dose of 14.35 Gy of gamma rays. Irradiation, sham-irradiation and decapitation 30, 60 and 120 min after the exposure were performed between 2000 h and 0100 h in the darkness. The serotonin N-acetyltransferase activity (NAT), t he concentration of melatonin, dopamine, norepinephrine and epinephrin e were measured in the pineal gland. The serum levels of melatonin and corticosterone were also determined. lonizing radiation did not chang e the activity of the key enzyme of melatonin synthesis, NAT, but decr eased the concentration of pineal melatonin. The concentration of pine al dopamine and norepinephrine decreased 30 and 120 min after exposure , while the concentration of epinephrine was elevated 30 min after irr adiation, though later it was markedly decreased. The serum melatonin level was not changed, but an increase in corticosterone level was obs erved. In the early period after the exposure, a decrease in pineal me latonin occurred, accompanied by a decrease in pineal catecholamines. On the contrary, in the phase of developed radiation injury the signs of increased melatonin synthesis were observed on days 3 and 4 after t he exposure (Kassayova et al. 1993a). The underlying mechanisms requir e further research.