In the intact organism, while the kidney is only ∼1% of total body weight, it utilizes approximately 10% of the whole body O₂consumption (Q-O₂). Because there is a linear relationship between change in Na+ reabsorption and suprabasal renal O₂consumption, the high suprabasal renal Q-O₂has been attributed principally to the energy requirements for reabsorption of the filtered load of Na⁺[1–3]. The basal metabolism is the energy which is required for the maintenance of the renal tissue integrity and turnover of its constituents without measurable external (net transport or net synthetic) work being done. However, there is now considerable evidence that there are other suprabasal functions of the kidney which change in parallel with Na⁺reabsorption and which require an energy input separate from that used for Na⁺transport.

Thus, while there is little doubt that the rate of glomerular filtration initiates and determines the major portion of the renal suprabasal QO₂, this paper focuses on two questions: (1) Is the renal suprabasal O₂uptake related only to Na+ reabsorption? (2) Is the suprabasal O₂uptake also related to other renal functions which are proportional similarly to the rate of glomerular filtration and which also contribute to the regulation of the volume and composition of the body fluids?