Serum and renal IGF-I levels after uninephrectomy in the rat

The hypertrophy of the remaining kidney following uninephrectomy (UNx) has been related to an increase in renal insulin growth factor-I (IGF-I) content. However, while the increase in renal IGF-I lasts for only days after UNx, renal hypertrophy continues for months. In the present study we investigated whether IGF-I also plays a role in the late post uninephrectomy growth of the remaining kidney. Renal IGF-I in the remnant kidney was greater than that of control kidneys (78.3±17.3 vs 56.0±14.0 pmol g^-1; p<0.05) 3 days after UNx, tended to remain higher 30 days after UNx (83.8±23.6 vs 57.3±14.5 pmol g^-1; p=0.07), but was similar to that of the control kidney when examined 60 days after UNx (66.6±15.6 vs. 70.4±6.7 pmol g^-1). Serum IGF-I in uninephrectomized rats was similar to that of controls 3 days after UNx, started to increase above the control level at day 10 after UNx and remained higher 30 and 60 days after UNx (75.9±6.9 vs. 48.7±7.3 nmol l^-1 at 30 days, and 81.2±13.7 vs 52.9±11.0 nmol l^-1 at day 60, p<0.05 for both). The kidney weight of uninephrectomized rats was higher by 21% than that of controls 3 days after UNx, by 45% 30 days after UNx and by 63% 60 days after UNx (p<0.05 for all three observations). At the end of the study, the glomerular volume of uninephrectomized rats was higher by 36% than that of the controls (p<0.05). We suggest that in the rat, while the initial post uninephrectomy hypertrophy of the remnant kidney is associated with and most probably mediated by an increase in renal IGF-I, the hypertrophy that persists in later post UNx periods is associated with and may be mediated by an increase in serum IGF-I.