THE UPTAKE AND METABOLISM OF CYSTAMINE AND TAURINE BY ISOLATED-PERFUSED RAT AND RABBIT LUNGS

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 co mpare the uptake acid metabolism of cystamine and taurine in isolated perfused lungs of rats and rabbits and examine the action of glutathio ne (GSH) on these processes. The uptake and metabolism of [C-14]cystam ine and [C-14]taurine were studied at 20 mu M concentrations each in i solated, ventilated, perfused rat and rabbit lungs. In some experiment s, 1 mu M GSH was included in the perfusate prior to the addition of c ystamine. The perfusate and lung homogenate samples were analyzed for cystamine and its metabolites. [C-14]cystamine uptake with and without GSH was 13 and 14% in rat lungs and 37 and 32% in rabbit lungs. [C-14 ]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 hypotau rine and 56.0 +/- 16.0 and 49.4 +/- 6.0 taurine, for rat and rabbit lu ngs, 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 r abbit lungs, respectively. Taurine did not undergo any further metabol ism 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, ra t 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. Taur ine was not metabolized any further. It is concluded that rat and rabb it lungs take up cystamine from the systemic circulation, metabolize i t via hypotaurine to taurine, and effuse most of the latter in to the circulation.