Changes in Desoxyribose Nucleic Acid per Nucleus in Renal Compensatory Hypertrophy in the Rat

The mitotic activity of the compensatory hypertrophic kidney has been studied by several investigators (8, 12, 14). In general, the mitotic activity in the cortex, outer medulla, and inner medulla of the rat was largely restricted to the second day after nephrectomy. A second increase was noted in the outer medulla on the seventh day (8). Under normal interphase conditions, the D N A content per nucleus is constant in the somatic cells of different tissues of the same species and there is a direct relation between its quanti ty and the degree of chromosome ploidy (2). However, in regenerating rat liver, an increased amount of D N A per nucleus has been noted by chemical methods (16, 17) and by cytophotometry (4). A similar tendency was noted in the compensatory hypertrophic kidney, by chemical methods (9) and by cytophotometry (3). These increases were ascribed to increases in D N A during mitotic act ivi ty (15) and/or polyploidy (4). No work has been reported on the possible occurrence of polyploid nuclei in the compensatory hypertrophic kidney following uninephrectomy. In regenerating rat liver the ratio of polyploid to diploid nuclei increases (1, 4, 5). I t occurred to us that the observed increase in D N A content per nucleus in the compensatory hypertrophic kidney might also be due, in part, to the occurrence of polyploid cells even if polyploidy does not exist in the normal kidney. The present investigation was undertaken to determine the distribution pattern of D N A per nucleus during its increase in the compensatory hypertrophic kidney on various days following unilateral nephrectomy, using a cytophotometric method.