Effect of insulin-like growth factor-i and/or growth hormone on the
diaphragm of malnourished adolescent rats.
Lewis, Michael I., Thomas J. Lorusso, Mario Fournier.
Division of Pulmonary/Critical Care Medicine, Cedars-Sinai Medical
Center, Burns & Allen Research Institute, UCLA School of
Medicine, Los Angeles, CA
APStracts 3:0562A, 1996.
Young growing animals appear to have significantly reduced
`nutritional reserve' to short periods of unstressed starvation
compared to adults, with resultant growth arrest/atrophy of diaphragm
(DIA) muscle fibers. The aim of this study was to assess in an
adolescent rat model of acute nutritional deprivation (ND; 72 hours),
the impact of insulin-like growth factor-I (IGF-I ), with or without
added growth hormone (GH), on the cross-sectional areas (CSA) of
individual DIA muscle fibers. Five groups were studied: 1) Control
(CTL); 2) ND; 3) ND given IGF-I (ND/IGF-I); 4) ND given GH (ND/GH);
and 5) ND given a combination of IGF-I and GH (ND/IGF-I/GH). IGF-I
was given by a SC implanted osmotic mini pump (200 [mu]g/d), while GH
was administered twice daily by SC injection (250 [mu] q12 hours).
Isometric contractile and fatigue properties of the DIA were
determined in vitro. Forces were normalized for muscle CSA (i.e.,
specific force). DIA fiber type proportions were determined
histochemically and fiber CSA quantified using a computer-based image
processing system. Total serum IGF-I concentrations were
significantly reduced in ND and ND/GH animals compared to CTL, and
elevated in the groups receiving IGF-I. The provision of growth
factors did not alter the contractile or fatigue properties of ND
animals. DIA fiber type proportions were similar between the groups.
In ND animals, there was a significant reduction in the CSA of types
I, IIa, IIx, IIc DIA fibers compared to CTL. The administration of
IGF-I alone or in combination with GH to ND animals significantly
diminished the reduction in DIA fiber size. GH alone had no effect on
DIA fiber size in ND animals. We conclude that with acute ND, the
peripheral resistance to the action of GH appears to be `bypassed' by
the administration of IGF-I alone or in combination with GH.
Received 23 May 1996; accepted in final form 2 November 1996.
APS Manuscript Number A493-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996