DIVERGENT REGULATION OF VASCULAR ENDOTHELIAL GROWTH-FACTOR AND OF ERYTHROPOIETIN GENE-EXPRESSION IN-VIVO

There is accumulating evidence from in vitro experiments that the gene expression of the vascular endothelial growth factor (VEGF) is, like that of the erythropoietin (EPO) gene, regulated by the oxygen tension and by divalent cations such as cobalt. Since the information about t he regulation of VEGF gene expression in vivo is rather scarce, this s tudy aimed to examine the influence of hypoxia and of cobalt on VEGF g ene expression in different rat organs and to compare it with that on EPO gene expression. To this end male Sprague-Dawley rats were exposed to carbon monoride (0.1% CO), hypoxia (8% O-2) or to cobalt chloride (12 and 60 mg/kg s.c.) for 6 h. mRNA levels for VEGF- 188, -164, and - 120 amino acid isoforms in lungs, hearts, kidneys and livers were semi quantitated by RNase protection. For these organs we found a rank orde r of VEGF mRNA abundance of lung >> heart > kidney = liver. EPO mRNA l evels were semiquantitated in kidneys and livers. Hypoxia, CO and coba lt increased EPO mRNA levels 60-fold, 140-fold and 5-fold, respectivel y, in the kidneys, and 11-fold, 11-fold and 3-fold, respectively, in t he livers. None of these manoeuvres caused significant changes of VEGF mRNA in lung, heart or kidneys. Only in the livers did hypoxia lead t o a significant (50%) increase of VEGF mRNA. These findings suggest th at, in contrast to the in vitro situation, the expression of the VEGF gene in normal rat tissues is rather insensitive to hypoxia. In conseq uence, the in vivo regulation of the VEGF and the EPO genes appear to differ substantially, suggesting that the regulation of the VEGF and E PO genes may not follow the same essential mechanisms in vivo.