Studies on synergism between glucose and amino acids with respect to insulin release in vitro

The mutual enhancement of the effect of insulin release by glucose and amino acids is not clearly understood. Present in vitro studies with isolated rat islets were undertaken to elaborate the role of amino acids on insulin release, particularly their interaction with glucose as well as among each other, which has been reported to lead to synergism in the human subjects. In the presence of 8.3 mM glucose, both arginine, as well as, leucine potentiated the effect of glucose which increased progressively with the increasing concentrations of the amino acid. This effect of arginine was not synergistic in nature because arginine did not stimulate insulin release in the absence of glucose. The effect of glucose and leucine was found to be additive and not synergistic. No synergism was exhibited by any of the amino acid pairs tested in the present study. Thus both phenylalanine and lysine did not potentiate the effect of either arginine or leucine. Arginine showed a mild, but significant potentiating effect on leucine-stimulated insulin release. It is suggested that synergism between glucose and amino acids and between certain amino acid pairs reported in man may not be due to the direct effects of these stimuli on the beta cells, but some other factors in vivo may be involved.