Bt. Ameredes et al., Growth hormone improves body mass recovery with refeeding after chronic undernutrition-induced muscle atrophy in aging male rats, J NUTR, 129(12), 1999, pp. 2264-2270
The effects of growth hormone (GH) administration and refeeding after chron
ic undernutrition (UN) were investigated in Fischer 344 male rats aging int
o senescence (24.5 mo of age) during UN initiated at 12.5 mo of age that pr
oduced muscle atrophy and a 50% decrease in body mass. Muscle mass, protein
, myosin heavy-chain (MHC) composition and circulating testosterone levels
were measured and compared to controls with free access to food. Within 9 w
k, refeeding + GH restored body mass to control levels, whereas it was stil
l decreased with refeeding alone. By 24.5 mo of age, refeeding alone restor
ed body mass, while addition of GH resulted in overshoot. UN uniformly decr
eased mass of the gastrocnemius, extensor digitorum longus, soleus and diap
hragm muscles to 50-60% of controls. Refeeding and refeeding + GH restored
these losses with some overshoot of gastrocnemius muscle suggesting hypertr
ophy. UN move than doubled slow Type I MHC composition and approximately ha
lved fast Type IIB and IIX MHC in the deep gastrocnemius muscle while it in
creased Type IIA MHC in the diaphragm. Refeeding and refeeding + GH reverse
d these shifts. MHC shifts in the extensor digitorum longus and soleus musc
les were not statistically significant, whereas UN increased fast Type IIA
MHC followed by decrease with refeeding + GH. UN decreased testosterone lev
els to nearly zero followed by restoration with refeeding and refeeding + G
H. We conclude that the phenotype of mixed-MHC muscles such as the gastrocn
emius and diaphragm are most affected by chronic UN, which is reversible wi
th refeeding and refeeding + GH. These alterations were associated with cha
nges in circulating testosterone, which may be a key regulatory element in
these processes.