AJP - Renal Physiology, Vol 259, Issue 3 474-F479, Copyright © 1990 by American Physiological Society
Growth hormone stimulates IGF I gene expression in isolated rat renal collecting duct
S. A. Rogers, S. B. Miller and M. R. Hammerman
Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
To determine whether growth hormone (GH) directly stimulates insulin-like
growth factor I (IGF I) gene expression in renal collecting duct, plasma
membranes prepared from collecting ducts isolated from rat kidney, and
collecting ducts themselves were incubated in presence and absence of GH.
GH enhanced phospholipase C activity in collecting duct plasma membranes
establishing the potential for GH-signal transduction. Inclusion of GH in
suspensions of collecting ducts increased production of immunoreactive IGF
I in a time-dependent and concentration-dependent manner. Production was
stimulated significantly by addition of 10(-10), 10(-8), or 10(-6) M GH to
suspensions for 2 h. IGF I produced in isolated collecting ducts was
released into the suspending media. Levels of IGF I mRNA in collecting
ducts were increased 2.8-fold after incubation with 10(-6) M GH in vitro.
IGF I of collecting duct origin was indistinguishable from recombinant
human IGF I in terms of its size and receptor-binding characteristics. Our
findings demonstrate a direct action of GH to enhance collecting duct IGF I
gene expression in vitro. Such enhancement is likely to reflect the
mechanism by which GH stimulates renal IGF I production in intact kidney.
