Behavior in the Rat of a Transport-specific, Bicyclic Amino Acid

A model amino acid, 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid, highly specific to the Na+-independent transport agency for neutral amino acids with large apolar side chains, has been shown to be excreted slowly by the intact rat, to be metabolized to a very small extent if at all, and to be accumulated by tissues, especially by pancreas. One of the two isomeric forms of this substance was retained in the rat longer than the other, although both were taken up by tissues, and both presumably were resorbed from the glomerular filtrate. When 5 to 10 mmoles per kg of body weight were injected intraperitoneally, the urinary excretion of several ordinary amino acids was increased. In addition, the plasma levels of several amino acids were decreased, although that of phenylalanine may have increased. These effects appeared to be at least as severe in adrenalectomized rats, which were easily prostrated by 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid administration. The injections were found to lower the blood glucose, the effect being especially strong in animals first treated with tolbutamide. The effect was more prolonged than that of leucine. This behavior leads us to propose that the stimulation of insulin secretion may be triggered by binding at strategically situated transport receptor sites. The uptake of 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid by the isolated, intact rat diaphragm was, however, not stimulated by insulin.