Effect of modifying O2diffusivity and delivery on glomerular and tubular function in hypoxic perfused kidney

Is O2 diffusivity within renal capillaries rate limiting for O2 delivery to hypoxic renal tubules? Equations based on diffusion theory and developed here predict that soluble hemoglobin (Hb) increases O2 diffusivity by a factor of 1 + [442 Hb%/(P50 + P O 2 )], where P50 is the partial pressure of O2 at which the Hb is half saturated. To examine the effect of P50 and Hb concentrations on renal function, we perfused isolated rat kidneys with Hb-P35(P50 = 35 mmHg) and Hb-P11(P50 = 11 mmHg). Venous P O 2 was lower with Hb-P11 (10 ± 1 vs 16 ± 1 mmHg with arterial P O 2 = 35 mmHg and 28 ± 2 vs. 40 ± 2 mmHg with arterial P O 2 =140 mmHg;P < 0.001). Perfusate P50 did not influence vascular resistance, glomerular filtration rate, O2 consumption, Na reabsorption, protein excretion, or free water clearance. Percent glucose and phosphate excretion were lower with Hb-P11 than with Hb-P35(P < 0.001). Urine glucose was 0.17 mmol/l with Hb-P11 and 0.77 mmol/l with Hb-P35(P < 0.001). Hb-P35 (2%) doubled O2 delivery and lo...