Renal substrate utilization in normal and acidotic rats.

Renal arteriovenous (A-V) concentration differences of the major potential respiratory substrates were measured in whole blood of control, NH4Cl-acidotic and diabetic ketoacidotic (DKA) rats. Net renal substrate extractions were calculated from A-V differences and renal blood flows. In fed control rats lactate accounted for 78% of the total substrate extracted. Small amounts (10-12%) of citrate and the ketone bodies 3-hydroxybutyrate and acetoacetate were also extracted. There was no significant extraction of either free fatty acids, glucose, glutamine, or pyruvate. In NH4Cl-acidotic rats lactate extraction was lower (40%) than in controls, but glutamine extraction increased (28%). The amount of extra glutamine extracted approximated the fall in lactate extraction. In DKA rats, ketone bodies accounted for the major portion of the extracted substrates (56%) but a significant part of the net extraction was due to urinary excretion of these compounds. Glutamine extraction represented 23% of the total. Lactate extraction was low (14%) in DKA rats, probably as a result of the low arterial lactate concentration. In vitro studies done on renal cortical slices suggest that each of the three major substrates extracted by the kidneys of normal, NH4Cl, and DKA rats could serve as major respiratory fuels.