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Division of Pulmonary/Critical Care Medicine, Cedars-Sinai Medical Center, Burns and Allen Research Institute, University of California Los Angeles School of Medicine, Los Angeles, California 90048
Received 23 May 1996; accepted in final form 2 November 1996.
Lewis, Michael I., Thomas J. LoRusso, and Mario Fournier.
Effect of insulin-like growth factor I and/or growth
hormone on diaphragm of malnourished adolescent rats.
J. Appl. Physiol. 82(4):
1064-1070, 1997.
Young growing animals appear to have
significantly reduced "nutritional reserve" to short periods of
unstressed starvation compared with adults, with resultant growth
arrest and/or 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 h) 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
(Ctr); 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 subcutaneously implanted osmotic minipump (200 µg/day), whereas GH was administered twice daily by a subcutaneous injection (250 µg every 12 h). 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 was
quantified by using a computer-based image-processing system. Total
serum IGF-I concentrations were significantly reduced in ND and ND/GH
animals, compared with Ctr, 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 among the groups. In ND animals, there was a significant
reduction in the CSA of types I, IIa, IIx, and IIc Dia fibers compared
with Ctr. 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.
nutritional deprivation; diaphragm fiber cross-sectional area; diaphragm contractility and fatigue
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