Nephron pO(2) and renal oxygen usage in the hypertensive rat kidney

Background. The kidney has a high rate of oxygen usage (Q(o2)) that is closely dependent on tubular Na+ transport (T-Na) However, little is known concerning the regulation of the cortical partial pressure of oxygen (pO(2)). Methods. First, the pO(2) was measured in the outer cortical proximal (PT) and distal tubules (DT), efferent arterioles (EA), and superficial (SC) and deep cortical (DC) tissues in normotensive Wister Kyoto (WKY) and spontaneously hypertensive rats (SHRs) using an ultramicrocoaxial O-2 electrode. We next assessed the determinants of Q(o2) and tubular reabsorption of sodium (T-Na) for whether they could account for any differences in renal cortical pO(2) in SHRs. Results. The pO(2) in the EA was reduced 40 to 50% compared with arterial values but was similar in the two strains (WKY rats 45 +/- 2 vs. SHRs 41 +/- 1 mm Hg, P = NS). The pO(2)-value in the PT, DT, and SC did not differ within strains. All were significantly (P < 0.001) lower in SHRs (for example, pO(2) in PT of WKY rats 39 +/- 1 vs. SHRs, 30 +/- 1 mm Hg). The pO(2) in the renal vein was above that at any site in the EA or the cortex, implying a precapillary shunting of O-2 from the artery to vein. SHRs had reduced renal blood flow (RBF) leading to a reduced (P < 0.05) rate of O-2 delivery (WKY rats 42 +/- 6 vs. SHRs 30 +/- 1 mu mol . min(-1) . g(-1)) and a reduced glomerular filtration rate, leading to a lower (P < 0.001), T-Na (WKYs 115 +/- 9 vs. SHRs 66 +/- 8 mol . min(-1) . g(-1)). However, despite the 43% reduction in T-Na, the renal O-2 usage was not significantly different between strains (WKY rats 7.6 +/- 0.8 vs. SHRs 9.0 +/- 1.0 mu mol . min(-1) . g(-1)). Therefore, the SHRs had a sharp reduction (P < 0.001) in the O-2 efficiency for Na+ reabsorption (T-Na/Q(o2); WKY rats 15.1 +/- 1.6 vs. SHRs 7.3 +/- 1.0 mol(-1)). Conclusions. A precapillary O-2 Shunt reduces the pO(2) of cortical nephrons. The pO(2) is reduced further in SHRs because of less efficient O-2 usage for Na+ transport.