The effects of isoproterenol on taurine concentration in the rat heart

Administration of the beta-agonist isoproterenol to rats caused a sharp increase in the influx rate of taurine into the heart, but had no effect on the rate of biosynthesis of taurine in the heart. Influx rates of other amino acids were also stimulated, the distribution ratios, (dpm/g heart)/(dpm/ml plasma), of beta-amino acids being 3--4 times higher than alpha-amino acids. The doses of isoproterenol employed induced cardiac hypertrophy, but the stimulation of taurine influx appeared to be an independent phenomenon, in that near maximum stimulation of influx was achieved prior to stimulation of ornithine decarboxylase activity. Reserpine treatment also produced stimulation of taurine influx with no effect on biosynthesis. These results indicate a close connection between increased sympathomimetic activity and increased influx of amino acids.