It has been suggested that insulin-like growth factor-1 (IGF-1) may play a
role in early compensatory renal growth. Since IGF-1 action is influenced b
y IGF binding proteins (IGFBP), this study was conducted to characterize th
e changes in gene expression not only of IGF-1 and its receptor, but also o
f IGFBP in the hypertrophying kidney of adult and weanling rats 1 wk after
removal of the other kidney. At this time, there were distinct age-dependen
t changes in the renal IGF-1 axis. In the mature kidney, IGF-1 mRNA levels
fell without a change in kidney IGF-1 peptide content. Likewise, although I
GFBP-2, -3, and -5 mRNA levels fell, membrane-associated IGFBP did not chan
ge. IGF-1 receptor mRNA levels and IGF-1 receptor number both fell. In the
weanling kidneys, IGF-1 mRNA and peptide levels and IGF-1 receptor binding
were unaltered. However, IGFBP-3, -4, and -5 mRNA levels were increased, as
were plasma membrane-associated IGFBP. Although these changes in the intra
renal IGF-1 axis were distinct, it is difficult to conceive how in either t
he mature or immature rat they could contribute to the ongoing compensatory
renal growth that occurs 1 wk after loss of kidney mass unless IGF-1 were
acting in a synergistic manner with other growth promoters.