Changes in Aerobic and Anaerobic Metabolism in Rat Cardiac and Skeletal Muscles after Total or Partial Dietary Restrictions

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Abstract
This study examined the effects of acute dietary restriction on aerobic and anaerobic metabolic capacity of skeletal and cardiac muscles. Male weanling Sprague-Dawley rats were fed a 28% casein diet to a body weight of 100 g. The control group was killed at 100 g and the experimental groups were starved to 70 g body weight by either 4-day total restriction (TR) or 9-day partial restriction (PR). The heart, soleus, extensor digitorum longus (EDL), biceps brachii, psoas and red and white portions of the gastrocnemius (GR and GW) were assayed for oxygen uptake and succinic dehydrogenase (SDH) and pyruvate kinase (PK) activity. Cytochrome c was also measured in the gastrocnemius and psoas. The decrease in muscle weight was similar to the 30% decrease in body weight with the exception of the soleus which decreased by only 10% due to either TR or PR. PK, an estimate of anaerobic capacity, appeared to increase per unit weight in all tissues after both TR and PR; however, total muscle PK remained unchanged. Total cytochrome c and SDH activity, estimates of aerobic capacity, decreased in all muscles after either treatment. The largest decreases in SDH were 38% in the soleus and 51% in the heart after TR and 50% in the GR and 48% in the GW after PR. Oxygen uptake increased in the soleus (20%) and heart (70%) but decreased in all other skeletal muscles with the greatest effect after PR (50%). This study has shown that there is a decrease in aerobic capacity during acute starvation and that total muscle anaerobic metabolic capacity remains near normal.