METABOLISM OF 7-H3-EPINEPHRINE-d-BITARTRATE IN NORMAL YOUNG MEN

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Abstract
An average of 92.6% (SD = [plus or minus] 7.7) of the infused radioactivity was excreted in the urine within 54 hours. The tritium-labeled metabolites were isolated, and gave the following percentages (mean [plus or minus] SD) of total radioactivity in the urine; unchanged epinephrine 6.8 [plus or minus] 1.5, free metanephrine 5.2 [plus or minus] 1.1, metanephrine glucuronide 6.0 [plus or minus] 1.5, metanephrine sulfate 29.5 [plus or minus] 9.0, 3-methoxy-4-hydroxyphenylglycol (MHPG) 7.1 [plus or minus] 1.4, free 3,4-dihydroxy-mandelic acid (DHMA) 0.7 [plus or minus] 0.3, and conjugated DHMA 0.9 [plus or minus] 0.4. The isolated metabolites averaged 97% (SE = [plus or minus] 3.8) of the total urinary radioactivity. In this study the infused H3-epinephrine is almost completely accounted for in terms of known urinary metabolites. The findings support the thesis that O-methylation followed by deamination is the major route of metabolic inactivation of circulating epinephrine.