Effects of naproxen on the hypobaric hypoxia-induced immune changes in male rats
A model has been presented for the role of the kidney in the physiologic and pathophysiologic control of erythropoiesis. It is postulated that an oxygen deficit created by anemia or hypobaric hypoxia results in the release of prostacyclin and its metabolite 6-keto PGE1, and the release of PGE2 with ischemic hypoxia. Prostacyclin, 6-keto-PGE1, or PGE2 activation of adenylate cyclase, an increase in cyclic AMP, activation of a protein kinase and the phosphorylation of hydrolases, which have been released from lysosomes by hypoxia, lead to increased biosynthesis of erythropoietin (Ep). The mechanism of labilization of lysosomes and the release of hydrolases from these cell organelles is postulated to be related to increases in cyclic GMP levels in a renal cell. An Ep-producing human renal carcinoma cell line grown in tissue culture has been demonstrated to produce significant amounts of PGE2. Meclofenamate, an inhibitor of prostaglandins synthesis, was found to inhibit in vitro production of PGE2, Ep, and dome formation in these renal carcinoma cells, giving support to our hypothesis that pathophysiologic production of Ep tumor cells depends upon prostaglandins production. An Ep-producing clone from this renal carcinoma cell line has been developed that contains low electron density (LED) cells after the cells reach confluency, which show a cytoplasm, with abundant and widely dilated endoplasmic reticulum, an oval nucleus, dispersed chromatin, and prominent nucleoli. These are the cells responsible for dome formation and Ep production. Non-EP-producing clones have also been produced from this renal carcinoma cell line, which did not produce domes even at high cell density and had a distinctly different cell type than the Ep-producing clone. Thus, it is postulated that prostacyclin (PGI2) and its metabolite 6-keto PGE1 play a significant role in hypoxic hypoxia stimulation of Ep production and PGE2 is involved in ischemic hypoxia and renal carcinoma cell production of Ep. A modulating effect of PGE2 and PGD2, the two primary bone marrow prostaglandins, has been proposed in Ep stimulation of the erythroid progenitor cell compartment (CFU-E and BFU-E).