The effect of chronic exposure to 3.5 ppm NO2 on hormone levels and organ weights in rats.

Male Wistar rats were exposed continuously for 1 or 2 months to 3.5 ppm NO2. Levels of histamine and serotonin in lung, noradrenaline in hypothalamus, corticosterone and thyroxine in serum and catecholamines in the adrenals were estimated. No significant changes were observed in lung histamine and serotonin, serum corticosterone, or adrenal catecholamine levels; or in the weights of lung, spleen, adrenal glands, hypothalamus, liver and the whole body. The only significant change was a decrease in the concentration of hypothalamic noradrenaline after 2 months of exposure. The results suggest that prolonged exposure to 3.5 ppm NO2 does not result in changes in hormone levels, organ and body weights, and therefore does not precipitate pulmonary defensive reactions or non-specific stress response.