[Catecholamines, nitrogen oxide, and resistivity to stressor lesions: effect of adaptation to hypoxia]

Pronouncement of stress-induced disturbance of searching behaviour (using "open field" test) and stomach ulceration were compared for the first time with activity of the catecholamine system in hypothalamus and striatum and also with activity of the stress-limiting system of nitric oxide (NO) in the rats of two strains August and Wistar, which differ in their resistance against stress-induced cardiovascular disorders. The effect of prior adaptation to hypobaric hypoxia on these disorders was also studied. August rats appeared to be more resistant than Wistar rats against stress-induced disturbance of the searching behaviour and stomach ulceration. Results of measuring the content of catecholamines in brain structures and the content of NO stable metabolites nitrate/nitrite in plasma suggested that these differences could be due to the stress activation of the nigro-striatal dopaminergic system in August rats, which was not observed in Wistar rats, and also to the higher production of NO in August than in Wistar rats. Adaptation to hypoxia considerably restricted these stress disorders in rats of both strains. Importantly, the protective effects were associated with activation of the nigro-striatal dopaminergic system in all the animals. In the result, adapted Wistar rats, as distinct from non-adapted Wistar rats, displayed a stress activation of this system. The protective effects of adaptation were also accompanied by an increased NO synthesis. Taken together, the data suggest an important role of the responsiveness of the brain dopaminergic system and NO system in the mechanism of resistance against stress-induced disturbances.