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 (pO(2)) 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 mu m. The zero-pO(2) current amounted to 12.5 +/- 0.9 pA at 37 degrees 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 pO(2) 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 pO(2) of 40 +/- 4 mmHg was found, while the pO(2) in the cortex was 27 +/- 4 mmHg. Changes in pO(2) 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 pO(2) in the renal cortex, from 42 +/- 4 to 38 +/-4 mmHg. In the medulla pO(2) decreased significantly from 34 +/- 6 to 20 +/-4 mmHg. Ringer's solution did not induce any changes.