Determinants of intrarenal oxygenation. II. Hemodynamic effects.

To study hemodynamic effects on intrarenal oxygenation, O2 microelectrodes were inserted into rat kidneys. In a previous study [M. Brezis, Y. Agmon, and F. H. Epstein. Am. J. Physiol. 267 (Renal Fluid Electrolyte Physiol. 36): F1059-F1062, 1994], we showed that tubular metabolism is a major determinant of intrarenal oxygenation, in part responsible for medullary hypoxia observed under basal conditions. Acute hypotension (by controlled hemorrhage, aortic ligation, or nitroprusside infusion) paradoxically increased medullary PO2 (from 21 +/- 2 to 39 +/- 2 mmHg, P < 0.001) while decreasing cortical PO2 (from 46 +/- 2 to 32 +/- 3 mmHg, P < 0.001), abolishing corticomedullary gradients of oxygen. Laser-Doppler studies indicated that, while cortical blood flow was reduced during hypotension, medullary blood flow was unchanged or increased. The increase in medullary PO2 induced by hypotension was abolished by prior administration of furosemide, suggesting that during hypotension, reduced glomerular filtration rate (GFR), distal delivery, and reabsorption result in decreased oxygen utilization. Acute infusions of atriopeptin III (0.1-1 microgram.kg-1.min-1) decreased both cortical PO2 (from 61 +/- 2 to 55 +/- 2 mmHg, P < 0.001) and medullary PO2 (from 15 +/- 1 to 7 +/- 1 mmHg, P < 0.001), consistent with atriopeptin-induced increases in GFR and tubular reabsorptive work. These data suggest that medullary oxygen availability increases during renal hypoperfusion and may decrease during renal vasodilation.