PERFUSATE CYTOCHROME-C REDUCTION IN ISOLATED RABBIT LUNGS

The reduction of ferricytochrome c within the perfusate in isolated lung perfusion systems has been demonstrated previously. We carried out the present study 1) to determine what reducing agents might be responsible for this reduction and 2) to determine whether the cytochrome c (cyto c) reduction within the recirculating perfusion system can be accounted for by relatively stable reducing agents released into the perfusate or whether some of the reduction is dependent on short-lived agents and/or proximity to the source of the agents within the lungs. Experiments were carried out with the use of isolated rabbit lungs perfused for 1 h in a recirculating system. In one group of experiments, ferricytochrome c was included in the recirculating perfusion system. In another group, the cyto c was added to produce the same concentration in samples after they were removed from a cyto c-free recirculating system. The recirculating cyto c was reduced at a rate of approximately 1.76-mu-mol/h, and approximately 22% was inhibitable by superoxide dismutase. Most of the rest could be inhibited by ascorbate oxidase within the recirculating perfusate. When the ferricytochrome c was added to the samples removed from the cyto c-free perfusion system, virtually the entire cyto c reducing capacity was inhibitable by ascorbate oxidase. Although reduced glutathione did accumulate in the recirculating perfusate, the quantity was not sufficient to have an important role in the cyto c reduction. We conclude that most of the cyto c reducing capacity within the lung perfusate could be accounted for by ascorbate released from the lungs. There was a smaller superoxide dismutase-inhibitable fraction that was short lived, suggesting that superoxide released from the lungs within the vascular bed may have been a contributing factor.