Compensatory kidney collagen growth vs. age in uni-nephrectomized rats

Kidney collagen content, wet and dry weights, were measured in male Wistar rats unilaterally nephrectomized (NX) at ages ranging from 3-52 weeks. The compensatory responses in the contralateral kidney were assessed at eight (NX + 8) and 16 (NX + 16) weeks post-operatively; the (NX) values were compared with those from sham-operated controls at the same age and post-operative time. Both (NX) and sham (S) values were contrasted to the normal kidney growth parameters of unoperated control (C) rats. Kidney wet weight in the (NX) group was greater than that in either (S) or (C) and the major part of the compensatory growth occurred in the (NX + 8) period. In younger rats (12 weeks at NX), the dry weight response was like that of net weight, but in older animals the dry weight compensation had a generally slower onset. The compensatory growth of collagen in younger (NX) rats was greater than that seen in (S), and (S) was the same as (C). In older rats, (NX) and (S) collagen were not different, but both were much higher than (C). The finding that older animals, unlike young ones, increase their kidney collagen in response to surgery, with or without a loss of renal tissue, points to a nonspecific stimulus for collagen growth and suggests that, in older rats, the turnover equilibrium of collagen is shifted toward synthesis under such conditions.