The effect of amino acids on intestinal smooth muscle related to their content in blood and tissue.

The concentration of amino acids in the blood of the guinea pig is about 0.1 mM, while the intracellular concentration in the gastrointestinal smooth muscle cells is about ten times higher. Most amino acids, applied exogenously to isolated smooth muscles, exert effects in concentrations resembling their intracellular concentration. The results show that the inhibiting amino acids do not function as a neurotransmitter in the non-adrenergic inhibitory nervous system. The effective amino acids may possess modifying properties with respect to the contractile state of the muscle.