IMMATURE RENAL TUBULES ARE RESISTANT TO PROLONGED ANOXIA

Very few data are available regarding the decreased susceptibility of the developing kidney to anoxia. Therefore, the purpose of this study was to develop an experimental system that would allow comparison of a n anoxic insult in immature and mature proximal tubule segments and to investigate the hypothesis that the developing kidney is resistant to anoxia as compared with the mature kidney. Suspensions of proximal tu bules from immature (age 8-10 d) and mature (8-10 wk) rats were obtain ed. The purity of the tubule suspension from the immature rats was doc umented by villin staining. A common buffer solution was developed to compare results from the immature and mature tubules. To study the res ponse of the tubules to anoxia, we subjected the tubule suspension fro m both the immature and mature rats to 15, 30, 45, and 60 min of anoxi a. Lactate dehydrogenase release was measured to assess plasma membran e damage, and ATP levels were determined as an index of cellular energ y. After a short anoxic insult (15 or 30 min), the percentage of lacta te dehydrogenase release was not significantly different from mature t ubules. After prolonged anoxia (45 and 60 min) lactate dehydrogenase r elease continued to increase, whereas membrane integrity stabilized in the immature tubules. ATP levels decreased in both immature and matur e tubules after anoxia, but the decline of ATP was greater in the matu re tubules, with a plateau at 20% of basal ATP levels as compared with 40% in the immature tubules. Therefore, the developing kidney is resi stant to prolonged anoxia.