Melatonin prevents X-ray irradiation induced oxidative damagein peripheral blood and spleen of the seasonally breeding rodent, Funambulus pennanti during reproductively active phase. 
Biological effects of X-ray irradiation and protection by melatonin on the immune status of a tropical rodent, Funambulus pennanti, was examined by estimating oxidative damage of peripheral blood and spleen and protection by melatonin treatment.  Seventy squirrels were divided into 4 sets of 25, 25, 10 and 10 having subdivisions into a total of eight groups.  Squirrels of set 1 (groups A and B) received only normal saline, set 2 (groups C and D) received 25 microg/100 g body weight (bwt) melatonin and set 3 (groups E and F) received 25 microg/100 g bwt vitamin E for four weeks.  Groups G and H of set 4 received high doses of melatonin (0.5 mg/100 g bwt) 30 min prior to and 30 min after X-ray irradiation, respectively, and were sacrificed 1 h after irradiation.  Groups B and D were sacrificed after 4 h, 24 h, 48 h and 72 h of irradiation for total leukocyte count (TLC) in peripheral blood, percent apoptotic cells and lipid peroxidation (LPO) in spleen while group F was sacrificed after 4 h of irradiation to measure LPO.  Pre-melatonin treatment (25 microg/100 g bwt) restored TLC, percent apoptotic cells and LPO levels of X-ray exposed squirrels.  High dose pre-melatonin treatment (0.5 mg/100 g bwt) restored the above conditions significantly while post treatment did not.  Vitamin E reduced elevated LPO level in irradiated tissue, but the effect of melatonin was more potent.  Melatonin administration prior to X-ray irradiation prevented radiation-induced oxidative damage during the reproductively active phase of the seasonally breeding rodent suggesting a high protective role of melatonin following X-ray irradiation.