THE CHANGES IN PINEAL N-ACETYLTRANSFERASE ACTIVITY, PINEAL AND SERUM MELATONIN CONCENTRATION IN RATS AFTER IRRADIATION OF THE HEAD

Male Wister rats adapted to a light/dark cycle (LD) 12:12 h were expos ed in the darkness to a single dose of 14.35 Gy gamma rays on the head with the body shielded. Irradiated and sham-irradiated rats were kept again in the 12 h LD cycle with a free access to food and water till the analysis performed in the darkness. Pineal N-acetyltransferase act ivity and melatonin content, the serum concentration of the melatonin, corticosterone, thyrotropin and thyroid hormones were determined. N-a cetyltransferase activity was lower 2-24 h after irradiation non-signi ficantly whereas between 3-10 days it did not differ from the controls . Radiation decreased the pineal melatonin content and its serum conce ntration 2 h after exposure and increased them significantly 1-3 days after irradiation. No changes in melatonin levels were found on postir radiation days 5-10. The corticosterone concentration was increased 2 h after exposure only. Local head irradiation changed neither thyrotro pin nor thyroid hormone levels.