Effects of aging on in-vivo synthesis of skeletal muscle myosin
heavy chain and sarcoplasmic protein in humans.
Balagopal, P., Olav E. Rooyackers, Deborah B. Adey, Philip A. Ades,
and K. Sreekumaran Nair.
Endocrine Research Unit, Mayo Clinic and Foundation, Rochester, MN
55905, USA and Department of Medicine, University of Vermont,
Burlington, VT 05405, USA
APStracts 4:0152E, 1997.
Adecline in muscle mass and contractile function are prominent
features of the sarcopenia of old age. Since myosin heavy chain is an
important contractile protein, it was hypothesized that synthesis of
this protein decreases in sarcopenia. The fractional synthesis rate
of myosin heavy chain was measured simultaneously with those of mixed
muscle and sarcoplasmic proteins from the increment of [13C]leucine
in these proteins purified from serial needle biopsy samples taken
from 24 subjects (age: from 20 to 92 years) during a primed
continuous infusion of L[1-13C]leucine. A decline in synthesis rate
of mixed muscle protein (p<0.01) and whole body protein (p<0.01)
was observed from young to middle age with no further change with
advancing age. An age related decline of myosin heavy chain synthesis
rate was also observed (p<0.01); with progressive decline occuring
from young through middle to old age. However, sarcoplasmic protein
synthesis did not decline with age. Myosin heavy chain synthesis rate
was correlated with measures of muscle strength (p<0.05),
circulating IGF-1 (p<0.01) and DHEA-S (p<0.05) in men and women
and free testosterone levels in men (p<0.01). A decline in the
synthesis rate of myosin heavy chain implies a decreased ability to
remodel this important muscle contractile protein and likely
contribute to the declining muscle mass and contractile function in
the elderly.
Received 11 March 1997; accepted in final form 3 July 1997.
APS Manuscript Number E105-7.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 24 July 1997