Abstract
Numerous reports, including those presented at last year's Symposium on Tracer Applications of Tritium, have emphasized the advantages of using tritium labeling in studies of the metabolism of biologically important compounds. One particular advantage is that it is possible to prepare tritium-labeled compounds with high specific activity. In addition, the low-energy radiation which is given off by tritium allows the use in humans of much larger amounts of radioactivity than is the case with other radioactive elements, such as C14 • By taking advantage of these two factors, it has been possi ble to study the metabolism of dl-epinephrine in man at a nearly physiological dose level of this compound. Previous studies by Axelrod in vitro and in vivo [1, 2,3] have shown that 3-0-methyla tion is an important step in the inactivation and metabolism of epinephrine in rats. However, these studies were done with un labeled epinephrine and very large doses were given (correspond ing to 1.4 g in a 70-kgman). dl-Epinephrine-7 _H3 D-bitartrate was prepared for us (specific activity 267 /lcjmg)t; with this tritium labeled compound it was possible to repeat the work on the me tabolism of epinephrine in rats using much smaller doses. Fol lowing the studies on the rats, the metabolism of epinephrine in humans was investigated. dl-Epinephrine-7 _H3 D-bitartrate (1 mg) was administered Lv. in isotonic saline to each of six human males over a period of about 45 min [4]. The urine was collected for 48 hr, and the radioactivity in the individual urine specimens and in the total was determined using a modification of the method of Okita [5]. One-tenth milliliter portions of the urine, or 4-ml por tions of the isoamyl alcohol extracts were added to 4 ml of ethanol
Published Version
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