The Role of Renal “Work” in Compensatory Kidney Growth

In a series of studies designed to test the role of renal “work” in compensatory kidney growth we examined the relationship between absolute sodium reabsorption—which constitutes the bulk of renal energy expenditure, and growth of the remaining kidney at various intervals after contralateral nephrectomy. The increase in weight of the remaining kidney preceded the rise in sodium reabsorption and these two processes took place at different rates between 24 hours and 21 days after uninephrectomy. Absolute sodium reabsorption did not change during the first hours after contralateral nephrectomy, at a time when biochemical alterations are known to occur. The rate of [(14)C] choline incorporation into renal phospholipid, an early biochemical indicator of compensatory kidney growth, increased significantly one hour after contralateral nephrectomy but remained unchanged after sham-nephrectomy, regardless of the magnitude or direction of the concomitant change in absolute sodium reabsorption (“kidney work”). These results indicate that renal work expended in the reabsorption of glomerular filtrate is neither the initiating, nor the primary controlling factor, of the compensatory kidney growth that follows unilateral nephrectomy.