The positive inotropic and chronotropic actions of some amino acids and their effects in mobilizing noradrenaline.

The effects of methionine, cysteine and serine on the rate and strength of contractions of isolated Langendorff preparations of perfused dog heart and on spontaneous release of catecholamine (CA) from these hearts were investigated. These neutral amino acids increased the amplitude of ventricular contractions. Methionine and cysteine also stimulated the ventricular rate. They induced release of noradrenaline (NA) from the isolated heart. Their inotropic and chronotropic effects were significantly inhibited by pretreatment of the heart with propranolol.