Renotropic stimulation in rat kidney cell culture

A circulating renotropic factor specific for renal cells has been described in rats. The addition of sera obtained from unilaterally nephrectomized (uni) rats 24h after operation compared to sham-operated (sham) rats augments 3H-thymidine incorporation into the DNA of incubating kidney slices approximately 10%-30%. Attempting to amplify the sensitivity of the assay for this renotropic agent, we replaced slices with primary rat kidney cultures. The assay system was based on one previously used for rabbits. The cultured cells were synchronized in their growth phase by a period of protein-free starvation. Compared to sera from sham rats, sera from uni rats showed significant stimulation of thymidine incorporation into DNA, 35.5% +/- 9.3 (SEM), p less than .0001, at 16 h; 63.3% +/- 10.0 (SEM), p less than .001, at 24 h; and 19.5% +/- 6.5 (SEM), p less than .01, at 48 h post operation. Accordingly, the maximal stimulation at 24 h was greater than that previously found using the kidney slice assay. Measurable renotropic activity occurred earlier and over a shorter duration than in rabbits. Stimulation was similar when a D-valine medium, relatively specific for renal epithelial cells, replaced DME medium. We conclude that growth synchronized, primary rat renal cells in culture verify the presence of a circulating renotropin arising 24 h post uni.