Presence of renotrophic factor in plasma of unilaterally nephrectomized rats.

1. Renal cortical slices cut in two halves were incubated separately in culture medium. One half slice was used as control while the other half was treated experimentally. After incubation, their dry weights and/or their protein content were estimated. 2. Addition to half cortical slices of 30 micrograms mg-1 of freeze-dried plasma from rats killed 24 hr after unilateral nephrectomy resulted in an increase of dry weight or protein content of the order of some 10% after 4-8 hr incubation. 3. The effect of freeze-dried plasma from rats killed 24 hr after unilateral nephrectomy was specific to the renal cortex. When added to half slices from either the renal medulla or the liver there were no changes in their dry weight. 4. Addition of 30 micrograms mg-1 of freeze-dried plasma from rats killed 24 hr after bilateral nephrectomy had no significant effect on the dry weight of half cortical slices incubated for various periods of time, from 4 to 48 hr. 5. The renotrophic activity of plasma from unilaterally nephrectomized rats, killed 24 hr after the operation, appears to be metabolized or destroyed by incubation with cortical slices in 4 hr. 6. Freeze-dried plasma from normal unilaterally nephrectomized rats produced an increase dry weight when incubated for 4 hr with half cortical slices from early (3 days) hypophysectomized rats. When incubated with half cortical slices from late (23 days) hypophysectomized rats, the increase in dry weight was about 2 times as great as that observed with cortical slices from normal animals. 7. The possible reason for the production of renotrophic activity in plasma of unilaterally nephrectomized rats, and for its absence in plasma of anephric animals, is discussed.