AJP - Endocrinology and Metabolism, Vol 262, Issue 3 E289-E294, Copyright © 1992 by American Physiological Society
Muscle phosphorus energy state in very-low-birth-weight infants: effect of exercise
L. A. Bertocci, C. E. Mize and R. Uauy
Rogers Magnetic Resonance Center, Department of Radiology, University of Texas Southwestern Medical Center, Dallas 75235-9085.
Skeletal muscle hypotonia is a hallmark clinical finding in
very-low-birth-weight (VLBW) human infants. Although the biochemical basis
for this phenomenon is not completely understood, one hypothesis is that
the phosphorylation potential is abnormally low in the skeletal muscle of
these infants. Therefore, we used 31P-nuclear magnetic resonance (NMR)
spectroscopy to measure phosphorus metabolites in the skeletal muscle of
VLBW infants during rest and during reflex-induced muscle contractions.
Compared with healthy larger infants or to adults, the total phosphorus NMR
signal is lower in VLBW infants. In VLBW infants during rest,
[PCr]/([PCr]+[Pi]), where PCr is phosphocreatine and brackets denote
concentration, was 89% and [ATP]/[ADP][Pi] was 59% of that found in larger
infants (P less than 0.05). During reflex-induced isometric contractions in
VLBW infants, [PCr]/([PCr]+[Pi]) declined by 24% and [ATP]/[ADP][Pi]
declined by 35% (P less than 0.05 vs. rest). In all conditions, muscle pH
remained 7.1. Overall, the differences in skeletal muscle energy state
during rest and the corresponding changes in concentration of high-energy
phosphates during mild exercise suggest a very limited energy reserve in
the hypotonic muscle of VLBW infants.
