Increased insulin-like growth factor-II tissue concentrations during compensatory kidney growth in infantile rats

Insulin-like growth factor (IGF)-I and IGF-II serum and kidney tissue concentrations were measured in compensatory kidney growth in infantile and adult rats. We hypothesized that the known switch from IGF-II in fetal life to IGF-I in adult life may be responsible for the different modes of compensatory kidney growth, which are mainly characterized by hyperplasia in infantile rats and hypertrophy in adult rats. While IGF-I serum concentrations increased with age in infantile rats, kidney tissue concentrations of IGF-I showed a similar increase in both age groups after uninephrectomy. In adult rats, serum and kidney tissue concentrations of IGF-II were unchanged by uninephrectomy. In infantile rats, however, a significant increase in both serum and kidney concentrations of IGF-II was observed with a maximum at day 5 after uninephrectomy. To investigate if compensatory kidney growth is dependent on hyperperfusion of the remnant kidney, the left renal artery was clipped in infantile rats. The clipped kidney showed growth retardation despite normal kidney tissue concentrations of IGF-I and IGF-II. The contralateral kidney was enlarged and IGF-II kidney concentrations were elevated. However, animals with one clipped kidney and nephrectomy of the contralateral kidney showed compensatory kidney growth of the clipped kidney combined with increased IGF-II kidney tissue concentrations. We conclude that IGF-II mainly promotes compensatory kidney growth in infantile rats by hyperplasia. Hyperperfusion of the remnant kidney seems to be unnecessary for initiation of compensatory kidney growth.