Inhibited amino acid uptake in skeletal muscle during starvation

Amino acid uptake in skeletal muscle is reduced during different catabolic conditions such as sepsis, endotoxic shock, and uremia. The present study was designed to determine the effect of another catabolic condition, starvation, on amino acid transport in skeletal muscle. Male Sprague-Dawley rats (40-60 g) were starved for 24, 48, or 72 hr and soleus (SOL) muscles were removed intact and incubated for 2 hr in a medium consisting of Krebs-Henseleit bicarbonate buffer (pH 7.4) with glucose (5 mM), [¹⁴C]-inulin, and [³H]-α-aminoisobutyric acid (AIB). Amino acid uptake was determined from intracellular to extracellular ratio of AIB following incubation. AIB uptake was significantly reduced after 24 hr of starvation and remained low with further fasting. After 72 hr the AIB distribution ratio was approximately 50% of initial value. Amino acid uptake returned to normal within 24 hr after refeeding of animals that had been starved for 72 hr. Plasma (0.25 ml) from starved rats, added to the incubation medium (2.75 ml) of muscles from nonfasted rats, significantly inhibited AIB uptake. The present results suggest that amino acid uptake in skeletal muscle is progressively reduced during starvation, an effect that may be mediated by a circulating factor(s) present in blood.