Effects of low oxygen and of carbon monoxide on the renal circulation in unanesthetized rabbits.

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The effects of breathing 9.6% O 2 in N 2 and of breathing 0.1% to 0.2% CO in air on the renal blood flow (RBF), glomerular filtration rate (GFR) and renal PAH extraction ratio were studied in the unanesthetized rabbit in relation to changes in cardiac output, heart rate, blood pressure and ventilation. All experiments were carried out during moderate water and mannitol diuresis. The RBF and GFR were reduced in both types of hypoxia but this effect was produced by different mechanisms. With low O 2 mixtures reduction in RBF and GFR occurred mainly as a result of nervous vasoconstriction acting on the afferent arteriole. The arterial chemoreceptors played a part in the production of vasoconstriction. With carbon monoxide, reduction in RBF and GFR occurred mainly as a result of passive reduction in blood pressure, and only slight transient nervous vasoconstriction could be demonstrated in the early period of exposure to this gas. The results suggest that differences in arterial oxygen pressure (Pa o o2 ) were of major importance in accounting for the differences in renal circulatory effects of low O 2 mixtures and CO in the rabbit.