Intrarenal oxygen tension measured by a modified Clark electrode at normal and low blood pressure and after injection of x-ray contrast media

 The oxygen tension (pO2) in the rat kidney was studied using a Clark microelectrode with a guard cathode behind the sensing cathode. The mean (± SEM) outer tip diameter of the electrodes used was 5.5 ± 1.9 μm. The zero-pO2 current amounted to 12.5 ± 0.9 pA at 37°C; at air saturation it was 252 ± 22.9 pA. Rats with a systolic blood pressure (BP) above 80 mmHg (where 1 mmHg = 133 Pa) showed an average pO2 in the cortex of 45 ± 2 mmHg and in the outer medulla of 31 ±1 mmHg. In rats with a BP below 80 mmHg a paradoxically high outer medullary pO2 of 40 ± 4 mmHg was found, while the pO2 in the cortex was 27 ± 4 mmHg. Changes in pO2 were also noted in the renal cortex and outer medulla after intravenous injections of the x-ray contrast medium diatrizoate (370 mg iodine/ml). In rats with normal BP, injection of diatrizoate caused a slight fall in pO2 in the renal cortex, from 42 ± 4 to 38 ±4 mmHg. In the medulla pO2 decreased significantly from 34 ± 6 to 20 ±4 mmHg. Ringer’s solution did not induce any changes.