The effect of age and lung pathology on cytochrome a,a3 redox levels in rat cerebral cortex.

The steady-state reduction/oxidation (redox) ratio of cytochrome a,a3 in the non-stressed or 'resting' cerebral cortex was compared in 'healthy' mature and aged rats and in animals with varying degrees of lung pathology present. By using noninvasive dual wavelength spectrophotometry, cytochrome a,a3 was found to be approximately 30% reduced under 'resting' conditions in both mature and 'aged' brain. Although no significant age-related or strain differences were apparent, the 'resting' redox level of cytochrome a,a3 was markedly affected by the presence of lung pathology. The redox ratio was lower in animals where lung lesion involvement was not extensive, and higher (indicative or cellular hypoxia) in animals having both extensive acute and chronic lung pathology. These studies demonstate that, regardless of age or lung pathology, the cortical cytochrome a,a3 redox state is labile to changes in the amount of inspired oxygen, a condition differing from that of isolated mitochondria. These results indicate that dysfunction of the mitochondrial respiratory chain is not a direct or primary consequence of chronlogical aging in the 'resting' brain.