Effect of chronic sodium cyanate administration on O2 transport and uptake in hypoxic and normoxic exercise

Abstract

Systemic O2 transport during maximal exercise at different inspired [Formula: see text]([Formula: see text]) values was studied in sodium cyanate-treated (CY) and nontreated (NT) rats. CY rats exhibited increased O2affinity of Hb (exercise O2half-saturation pressure of Hb = 27.5 vs. 42.5 Torr), elevated blood Hb concentration, pulmonary hypertension, blunted hypoxic pulmonary vasoconstriction, and normal ventilatory response to exercise. Maximal rate of convective O2 transport was higher and tissue O2extraction was lower in CY than in NT rats. The relative magnitude of these opposing changes, which determined the net effect of cyanate on maximal O2 uptake (V˙o 2 max), varied at different [Formula: see text]:V˙o 2 max(ml ⋅ min−1 ⋅ kg−1) was lower in normoxia (72.8 ± 1.9 vs. 81.1 ± 1.2), the same at 70 Torr [Formula: see text] (55.4 ± 1.4 vs. 54.1 ± 1.4), and higher at 55 Torr[Formula: see text] (48 ± 0.7 vs. 40.4 ± 1.9) in CY than in NT rats. The beneficial effect of cyanate on V˙o 2 max at 55 Torr [Formula: see text] disappeared when Hb concentration was lowered to normal. It is concluded that the effect of cyanate on V˙o 2 maxdepends on the relative changes in blood O2 convection and tissue O2 extraction, which vary at different [Formula: see text]. Although uptake of O2 by the blood in the lungs is enhanced by cyanate, its release at the tissues is limited, probably because of a reduction in the capillary-to-tissue[Formula: see text] diffusion gradient secondary to the increased O2 affinity of Hb.