Renal hydroxybutyrate and acetoacetate reabsorption and utilization in the rat

Is the renal conservation of ketones effected through saturable transport systems? Does the renal reabsorption of ketoacids limit their utilization? The reabsorptive transport (T) and metabolic utilization (Q) of D-3-hydroxybutyrate (HB) and acetoacetate (AA) in the kidney were measured in anesthetized rats by use of clearance and arteriovenous extraction determinations. THB and TAA increased in proportion with increasing HB and AA filtered loads. Fractional THB decreases from 0.97 to 0.72 upon increases in the plasma HB. Fractional TAA also decreases from 0.89 to 0.73, at a constant filtered AA load, when the filtered HB load increased. Thus both saturable and nonsaturable components effect the reabsorption of HB and AA. Renal QHB increased from 0.4 to 4 mumol X g-1 X min-1 on increase in the plasma HB. THB always exceeded the simultaneously measured QHB. However, QHB was significantly correlated with THB, suggesting that QHB may be limited by delivery of HB to the renal cells through reabsorptive pathways. There was no net renal conversion of HB and AA. Both HB and AA were utilized by the kidney. Thus, utilized ketoacids must have entered pathways for complete oxidation or for synthesis (lipid?) in the kidney.