AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 1 266-R271, Copyright © 1995 by American Physiological Society
Presence of insulin-like growth factor I but absence of the binding proteins in the bile of rats
W. Kong, A. F. Philipps, B. Dvorak, G. G. Anderson, M. Lake and O. Koldovsky
Department of Pediatrics, Steele Memorial Children's Research Center, Furrow Research Laboratory, University of Arizona College of Medicine, Tucson 85724.
Whereas insulin-like growth factor I (IGF-I) has been found in various body
fluids from different species, the presence or absence of IGF and
associated binding proteins (IGFBPs) in bile has not been clearly defined.
Bile concentration of IGF-I was measured in this study and found to be
highest in the neonate and lowest in adult rats [133 +/- 15.9, 79.4 +/-
10.5, 45.3 +/- 12.7 ng/ml (mean +/- SE) in 12-day-old, 33-day-old, and
adult rats, respectively]. When bile delivery rates of IGF-I (i.e., the
product of IGF-I concentration in bile and the biliary flow rate) were
calculated, IGF-I delivery was highest in weanling rats (469 pg.h-1.g body
wt-1). When expressed as amount of IGF-I in bile delivered per day,
however, delivery rates rose from 0.2 micrograms/day in the suckling and
remained constant at 1.6-1.7 micrograms/day in both weanling and adult
animals. Bile samples exposed to a placental membrane IGF receptor
preparation showed significant dose-dependent inhibition of binding of
native IGF-I. Because no IGF binding proteins were identified by Western
ligand blot or by Sephadex gel chromatography, the results suggest the
presence of biologically significant quantities of bioactive IGF-I in bile.
We speculate that IGF-I in bile may play an important role in the growth of
the gastrointestinal tract, both in the suckling as well as later in life.
