SERUM MELATONIN, CORTICOSTERONE AND THYROID-HORMONES IN IRRADIATED RATS - EFFECT OF EXPOSURE DURING VARIOUS TIMES OF DAY AND OF LIGHT REGIMEN

Time of day and lighting regimen could modify the results of experimen ts, analyzing the effect of various stimuli. Male Wistar rats adapted to an artificial light/dark regimen (LD) 12:12 h (light 07-19 h) were whole-body irradiated with 14.4 Gy of gamma rays. The experiment was d ivided into three parts: A) rats irradiated in the dark and placed in the LD regimen, B) rats irradiated in the light and housed in the LD r egimen, C) rats irradiated in the dark and kept in the constant dark. Examinations were performed in the dark, 6 h to 4 day after exposure e xcept the 24 h interval in B group. Serum concentrations of melatonin (Mel), thyrotropin (TSH), thyroxine (T-4), 3,5,3'-triiodothyronine (T- 3) and corticosterone (CS) were determined. Irradiation enhanced the c oncentrations of Mel within days 3-4 in;he animals of groups A, B and of TSH on day 4 postexposure in group C only. Radiation decreased the levels of T-4 and T-3 6 h and 72 h in group C, in group A at 72 h, in group B at 24 h postexposure. CS level was increased 6 h to 60 h after irradiation In all groups. Lethal whole-body gamma irradiation of rat s changed the hormone levels with unsubstantionally influence of the t ime of day when the exposure were done and lighting regimen used.