Synthesis of metabolism-resistant substrates for the transport system for cationic amino acids; their stimulation of the release of insulin and glucagon, and of the urinary loss of amino acids related to cystinuria

Abstract

Several amino acids have been synthesized as model transport substrates building on the piperidine and cyclohexane rings. Only when the distal N atom is part of an unambiguously cationic structure are these compounds transported predominantly by the cationic amino acid system. These amino acids in labeled form are excreted rather slowly in unmodified state, very little 14CO 2 being released. Those which are unambiguously cationic (including also homoarginine) led to a greatly increased excretion of arginine, lysine, ornithine and citrulline. Those which might be expected to act as lysine analogs had little effect on the excretion of the basic amino acids, although the excretion of citrulline and the sum of glutamine plus asparagine was accelerated. Certain of the analogs intensified the excretion of citrulline in dissociation from effects on resorption of the basic amino acids, also in dissociation from effects on cystine resorption. These results indicate citrulline resorption does not occur principally by the same agency serving for the basic amino acids, nor by the agency serving for cystine, despite the observed interactions for resorption. The injection of either of three transport analogs for arginine into the rat leads to early increases in the circulating levels of immunologically reactive insulin and glucagon.