Growth hormone restores aged diaphragmmyosin composition and
performanceafter chronic undernutrition.
Ameredes, Bill T., Jon F. Watchko, Monica J. Daood, J. Fernando Rosas,
Michael P. Donahoe and Robert M. Rogers.
1Department of Cell Biology and Physiology; 2Magee Womens Research
Institute; 3Children's Hospital of Pittsburgh; and 4Division of
Pulmonary, Allergy, and Critical Care Medicine; University of
Pittsburgh School of Medicine, Pittsburgh, PA 15261
APStracts 6:0262A, 1999.
The effects of growth hormone (GH) on diaphragm muscle myosin heavy
chain (MHC)composition and mechanical performance were investigated
in Fischer 344 male rats aged tosenescence (24.5 mo. of age). Chronic
undernutrition (UN), refeeding (RF), and RF+GH werecompared to ad lib
feeding, using a model of UN that produced a 50% decrease in
bodyweight over a 12 mo. period. The effect of aging was assessed by
comparing MHCcomposition of ad lib-fed rats at 12 and 24.5 mo. of
age. At senescence, significant decreasesin slow Type I ( 23%) and
fast Type IIA ( 31%) MHC had occurred with aging. Conversely,UN over
this aging period increased Type I (32-73%) and IIA (22-23%) MHC, and
decreasedfast Type IIB (32-54%) and IIX (30-31%) MHC. RF and RF+GH
reversed these shifts backtoward control values. At senescence,
maximal specific force, maximal velocity, and specificpower capacity
were not different across treatment groups. During repetitive
isotonic contractiontrials, the UN diaphragms maintained power
production over time (54% of initial power at 60s), whereas
diaphragms of ad lib-fed rats fell to 0% (p<0.05). In comparison
with UN,respective RF and RF+GH diaphragms produced 23% (n.s.) and
11% (p<0.05) of initial power,suggesting that RF+GH treatment
restored performance characteristics after UN. We concludethat RF+GH
can reverse alterations in MHC composition and mechanical performance
producedby chronic UN in the aged rat diaphragm.
Received 7 December 1998; accepted in final form 9 June 1999.
APS Manuscript Number A1109-8.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 22 June 1999