Alpha amino isobutyric acid transport in adipose tissue

Abstract

Epididymal fat was incubated in the presence of the nonutilizable amino acid, [alpha]-amino isobutyric acid (AIB)-I-C14 or sucrose-U-C14 and the distribution of the label in the tissue was measured. From the sucrose space, it was found that 75-80% of the tissue water was extracellular under the conditions of the present experiments and that AD3 was concentrated 6- to 10-fold in the intracellular water. This concentrative process was subject to saturation and was inhibited by anoxia and metabolic poisons. Na was required. The uptake of AIB was markedly inhibited by the neutral amino acids, L-leucine and glycine, only slightly inhibited by L-glutamic acid, and unaffected by L-lysine. Similar concentrative processes were also active in vivo. One hour after intravenous administration, AIB was concentrated 13-fold in the intracellular water of adipose tissue and 2- to 3-fold in the intracellular water of diaphragm muscle. Hypophysectomy, adrenalectomy, or alloxan diabetes did not reduce the uptake of AIB in adipose tissue, and, conversely insulin and growth hormone did not increase it. The data failed to support the hypothesis that insulin and growth hormone accelerate the transport of amino acids in adipose tissue.