Seasonal variations in markers of stress and oxidative stress in rats.

High ambient temperature has been reported to increase oxidative stress by increasing lipid peroxidation and decreasing antioxidant defence in transition dairy cows. It is also known to cause an increase in plasma cortisol levels in goats, European hedgehog and human volunteers. High levels of glucocorticoids have been reported to decrease blood glutathione and erythrocyte superoxide dismutase activity in rats. Although institutional animal houses in research laboratories of developed countries maintain animals in air-conditioned rooms at constant temperature, the same is not true of animal houses in the developing countries especially those belonging to smaller institutions and this could affect the results of the experiments being conducted on these animals. The present research study was done to assess the effects of seasonal variations on the status of erythrocyte oxidative damage, antioxidant defence and plasma cortisol levels in adult female Wistar rats. Rats were kept in their home cages and were left in non-air-conditioned procedure rooms in two different seasons, Hot season (March-May) and Cool season (June to September). Erythrocyte Thiobarbituric acid reactive substances and plasma cortisol levels were significantly increased in rats exposed to high ambient temperature and humidity of the hot season as compared to the rats of the cool season. Erythrocyte reduced glutathione levels, erythrocyte glutathione peroxidase and superoxide dismutase activities were significantly decreased in the hot season group of rats. The results of our experiments showed that exposure of adult female Wistar rats to high ambient temperature and humidity of the hot season increases neuroendocrine stress, oxidative stress and decreases antioxidant defence in them.