Effects of changes in pO2, pCO2 and pH on the total vascular resistance of perfused cat kidneys.

1. The effects of change in arterial P(O2), P(CO2) and pH on the total vascular resistance (RVR) of the perfused cat kidney have been separately measured and expressed as +/- percentage deviations from control values.2. Control levels in arterial blood were pH 7.38, P(-) (O2) 160 mm Hg, in equilibrium with 5% CO(2).3. Increase in P(O2) alone, in excess of 220 mm Hg, raised RVR reversibly reading 108% control levels at a P(O2) 280 mm Hg (P = < 0.001).4. High levels of P(O2) favoured the onset of ;outflow block', which was characterized by irreversible increase in RVR accompanied by rise in plasma filtration fraction (F.F.) and in the extraction ratio for p-aminohippuric acid (PAH extraction).5. Reduction in P(O2) to 80 mm Hg decreased RVR by 4% (P = < 0.001).6. RVR was not significantly affected by pH changes within the range 7.25-7.45. Lowering arterial pH to 7.15 raised RVR by 4% (P = < 0.001) reversibly. Increase in arterial pH to 7.56 raised RVR by 6% (P = < 0.001) reversibly.7. Changes in arterial P(CO2) produced large inverse reversible changes in RVR. Halving P(CO2) raised RVR by 18%; doubling P(CO2) decreased RVR by 25%.8. Changes in RVR caused by alteration of arterial pH or P(CO2) were not accompanied by changes either in F.F. or in PAH extraction.