Abstract
Insulin-like growth factors (IGFs) are bound by several IGF-binding proteins
(IGFBPs) that appear to regulate IGF transportation, receptor binding and
action. In adult human serum, most of IGFs are bound in a 150 kDa complex which
could not cross the capillary wall. We measured IGF-I and IGFBPs in chyle by
radioimmunoassay and western ligand blot. The concentration of IGF-I in chyle
was only 15% of the corresponding serum level and most of IGF-I was found in 50
kDa complex. The IGFBPs profile in chyle, especially IGFBP-3, was different from
that of serum. The concentration of IGFBP-3 in chyle was much less than in serum
and the size of glycosylated IGFBP-3 was different from that of serum. However,
the size and relative amount of IGFBP-1 and -2 in chyle were similar to serum.
This finding indicates that IGF-I and IGFBPs in chyle to a large extent
originate in the vascular system and only the 50 kDa complex can cross the
capillary barrier.