Abstract
Cystamine has been reported to be taken up and metabolized to taurine by the rat lung slices. The objectives of the present study were to compare the uptake and metabolism of cystamine and taurine in isolated perfused lungs of rats and rabbits and examine the action of glutathione (GSH) on these processes. The uptake and metabolism of [ 14C]cystamine and [ 14C]taurine were studied at 20 μM concentrations each in isolated, ventilated, perfused rat and rabbit lungs. In some experiments, 1 μM GSH was included in the perfusate prior to the addition of cystamine. The perfusate and lung homogenate samples were analyzed for cystamine and its metabolites. [ 14C]cystamine uptake with and without GSH was 13 and 14% in rat lungs and 37 and 32% in rabbit lungs. [ 14C]taurine uptake was 10% in rat and 37% in rabbit lungs. The levels of radiolabeled cystamine and its metabolites were (nmol/g lung): 20.0 ± 10.0 and 11.5 ± 7.0 cystamine, 4.7 ± 0.5 and 3.2 ± 0.5 hypotaurine and 56.0 ± 16.0 and 49.4 ± 6.0 taurine, for rat and rabbit lungs, respectively, when perfused without GSH; and 18.0 ± 1.0 and 2.5 ± 0.5 cystamine, 6.6 ± 0.5 and 18 ± 10 hypotaurine and 60.0 ± 12.0 and 33.6 ± 9.0 taurine, when perfused with GSH, for rats and rabbit lungs, respectively. Taurine did not undergo any further metabolism in either of the lungs. These studies show that cystamine is taken up and metabolized to taurine via hypotaurine by both rat and rabbit lungs in a manner similar to that seen in rat lung slices. However, rat lungs have much greater capacity to metabolize cystamine to taurine than rabbit. Inclusion of GSH did not significantly alter the ability of lungs to sequester cystamine from the perfusate but the metabolism of hypotaurine to taurine was markedly decreased in rabbit lungs. Taurine was not metabolized any further. It is concluded that rat and rabbit lungs take up cystamine from the systemic circulation, metabolize it via hypotaurine to taurine, and effuse most of the latter in to the circulation.
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