Studies on the Metabolism of Catecholamines

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Abstract
Administered H3-epinephrine and H3-nor-epinephrine are rapidly and selectively taken up by heart muscle and retained for many hours. The uptake and retention of circulating H3-norepinephrine by the heart is greater than that of H3-epinephrine. Two minutes after the administration of H3-catecholamines large amounts of metanephrine and normetanephrine are found in the heart indicating rapid O-methylation of these hormones during the period of their inactivation. H3-epinephrine is more readily O-methylated than H3-norepinephrine. Enzyme inhibition studies indicate that catechol-O-methyl transferase is the enzyme mainly concerned with the metabolism of catecholamines in the heart. Reserpine, cholorpromazine, imipramine, amphetamine, cocaine, and phenoxybenzamine markedly inhibit the uptake of circulating H3-norepinephrine by the heart.