| Abstract: | Electrical ventricular fibrillation threshold (VFT) was determined, using programmed isolated stimuli on the left-ventricular apex, in male Wistar rats at different times after 10 hours' immobilization stress (IS). The VFT decrease reached a maximum of 48% 12 hours after IS. Cardiac sensitivity to the inhibiting vagal influence was increased considerably at the same time. The adaptation to short episodes of IS over 6 days, intermittent exposure to high-altitude hypoxia (5 hours daily at a 5000 m "altitude" for 40 days) and the antioxidant ionol (50 mg/kg) prevented IS-induced fibrillation threshold decrease. In cases of coronary arterial ligation in waking animals, the antioxidant ionol reduced fourfold the mortality associated with ventricular fibrillation and raised the spontaneous defibrillation rate from 28% to 72%. Possible mechanisms of these phenomena are discussed. |
