[Changes in the sympathetic-adrenal system during stress in rats with high and low resistance to acute hypoxia]

Quantitative luminescent microscopy was used to examine the sympathetic system of cardiac ventricles (SSCV) and the adrenal medulla (AM) of adult Wistar male rats high-resistant (HRH) and low-resistant (LRH) to acute hypoxia and exposed norepinephrine (NE) stress. The relative area of fluorescence adrenergic terminals (RAFAT) of the ventricles and AM catecholamine levels (CL) were shown to be equal in control HRH and LRH rats. The LRH rats displayed a two-phase SSCV response in the first 6 hours of NE stress. Their RAFAT rose an hour later and their RAFAT in the basal zone of the left ventricle insignificantly exceeded that of HRH rats, RAFAT in the latter being unchanged by that time. At hour 6, the heart RAFAT decreased as compared to 1-hour and control levels in LRH and HRH rats and became equal in the two groups. The AM CL in LRH and HRH rats remained unaltered within the whole period of the examination. Despite the profound differences in the resistance of HRH and LRH rats to hypoxia, the responsiveness of their sympathoadrenal system (SAS) to stress is rather homogeneous. With stress, the sympathetic link of SAS is more labile than the adrenal one.