Kidney cell proliferation after unilateral nephrectomy as related to age.

The effect of unilateral nephrectomy on the number of cortical kidney cells undergoing DNA synthesis and mitosis was meas ured by tritiated thymidine autoradiography in both weanling and adult rats. Among the unoperated control animals, the weanling rat group showed a base line labeling index of 0.59%, and the adult animals, one of 0.11%. The response to unilateral nephrectomy resulted in a peak value of 3.6% in the weanling animals and 1.2% in the adult animals, both occurring at 36 hr. Mitotic indices were 0.056% in the weanling control animals and 0.0062 % in the adults, with a peak of 0.30% and 0.088%, respectively, at 36 hr. Separate counts of tubule and stromal cells in the cortex revealed that the maximum increase in % labeled cells occurred later in the stromal cells than in the tubule cells, the stromal cells not reaching a maximum until 57 hr after nephrectomy. The findings indicate that, although the relative proliferative activity is much lower in adult animals, a similar response, qualitatively, is ob tained in both groups after unilateral nephrectomy.