A. Sandra et al., INFUSED IGF-I IGFBP-3 COMPLEX CAUSES GLOMERULAR LOCALIZATION OF IGF-IIN THE RAT-KIDNEY/, American journal of physiology: endocrinology and metabolism, 38(1), 1998, pp. 32-37
Insulin-like growth factor I(IGF-I) increases renal blood flow, glomer
ular filtration rate (GFR), and proximal tubule reabsorption of phosph
ate in humans and rodents. The biological effects of ICF-I are likely
to be influenced by cellular localization of IGF-I within the kidney.
We therefore tested whether the renal localization of infused IGF-I co
uld be altered if given with selected IGF-binding proteins (IGFBPs). R
ats were treated with intravenous injections of I-125-labeled IGF-I,I-
125-IGFBP-3, or I-125-IGFBP-4 alone or with complexes of I-125-IGF-I a
nd IGFBP-3 or IGFBP-3. The cellular localization of IGF and the IGFBP
within the kidney was then determined. I-125-IGF-I, I-125-IGFBP-4, and
I-125-IGF-I/IGFBP-4 complexes were found almost exclusively in vacuol
ar structures (endosomes) of proximal renal tubules. In contrast, abou
t one-third of renal I-125-IGFBP-3 and I-125-IGF-I/IGFBP-3 was localiz
ed to glomeruli. When I-125-IGF-I was given alone, 3% was found in glo
meruli and 89% in proximal tubules. When given as I-125-IGF-I/IGFBP-3,
29% was in glomeruli and 65% in proximal tubules. We conclude that th
e cellular localization of IGF-I within the kidney can be directed to
glomerular elements if the IGF-I is given with IGFBP-3.