Oxygen tension correlates with regional blood flow in obstructed rat kidney

As renal tissue oxygen tension (Po-2) is determined by the balance between oxygen supply and consumption, direct tissue Po-2 measurements are essential when evaluating the presence of hypoxia. The present study aimed at evaluating invasively and continuously the renal medullary and cortical tissue Po-2 by novel fibre-optic probes in rats subjected to acute unilateral ureteral obstruction (AUUO). In parallel, regional blood flow measurements were obtained by MRI to investigate the relationship between regional blood flow and tissue oxygen tension. The abundance of transport proteins was determined by immunoblotting. In the obstructed kidney, AUUO caused a prompt decrease in medullary tissue Po-2 to 60% of baseline level whereas cortical tissue Po-2 was unchanged. By contrast, tissue Po-2 slightly increased in the non-obstructed kidney. These changes developed during the first 30 min after AUUO and persisted for the 3 h observation period. Medullary blood flow declined 1.5-2 h after induction of AUUO to 61% of baseline level in the obstructed kidney. By contrast, cortical blood flow increased to 108% of baseline level in the non-obstructed kidney. Finally, the abundance of phosphorylated aquaporin 2 decreased significantly in the obstructed kidney medulla, but increased in the obstructed kidney cortex. The Na+/K+-ATPase abundance increased in the obstructed kidney medulla whereas the Na+/K+/2Cl(-) co-transporter abundance remained unchanged in the obstructed kidney. In conclusion, measurements of regional blood flow reflect tissue Po-2 changes during AUUO suggesting that reduced regional blood flow is a predictor of local hypoxia. Furthermore, the abundance of major transport protein is independent of tissue Po-2.