Effect of catabolic hormone infusion on organ amino acid uptake

Elevated plasma levels of the so-called catabolic hormones (glucocorticoid, epinephrine, glucagon) have been observed in severely injured patients, and infusion of these hormones to normal subjects has reportedly simulated several metabolic aberrations characteristic of severe trauma and sepsis. We recently reported that amino acid uptake was reduced in soleus muscle, heart, and diaphragm, and increased in the liver, of septic rats. The purpose of the present study was to investigate organ amino acid uptake in nonseptic rats infused with catabolic hormones. Central venous catheters were placed in male Sprague-Dawley rats (100-150 g) and after 24 hr hormones (glucagon 5 micrograms/kg/hr, epinephrine 6 micrograms/kg/hr, corticosterone 4.2 mg/kg/hr) or vehicle (saline, ascorbic acid 1 mg/ml, albumin 3 mg/ml) was infused for 72 hr. Animals were housed in metabolic cages and allowed food and water ad lib. One hour prior to sacrifice, alpha-[3H]aminoisobutyric acid (AIB) (2.5 microCi), a nonmetabolized amino acid analog mainly transported by system-A, was injected intravenously. Animals were killed and organs were removed, weighed, and dissolved in tissue solubilizer for measurement of radioactivity. AIB uptake was significantly elevated in all organs of catabolic hormone-infused animals studied. The results suggest that catabolic hormones may be involved in the pathogenesis of increased amino acid uptake in the liver during sepsis. Inhibited amino acid uptake in skeletal muscle during sepsis, however, is probably not primarily mediated by catabolic hormones.