Abstract
A procedure has been described for the biosynthesis of radioactive digitoxin from Digitalis purpurea L. plants grown in an atmosphere of radioactive CO2. Employing the growing chamber described, it was possible to administer as much as 4.2 mc. of C14 to each plant without causing any noticeable inhibition in growth rate when compared to control plants grown simultaneously in a second chamber under similar conditions, but without the labeled CO2. However, histological studies of radioactive plant leaves (Beal, 1949) indicate that C14 does cause injury to the plant leaves. It is believed that larger amounts of C14 can be administered to the plants although this has not yet been attempted.
An extraction procedure for the labeled drug utilizing chemical and chromatographic methods has also been described. The yield of non-crystalline digitoxin was approximately 0.06 per cent: after crystallization the yield was reduced to approximately 0.04 per cent. Depending upon the amount of C14 administered, the specific activity of the labeled glycoside ranged from 0.26 to 0.54 µc. per milligram. This range of specific activity was found to be sufficient for biological tracer studies.
Using the radioactive method of assay and adding non-labeled carrier digitoxin to the biological sample, it is possible to isolate and detect as little as 0.02 microgram of radioactive digitoxin (original sp. activity—0.537 µc./mgm.) per 100 ml. of human urine.
Identification tests performed on the radioactive drug indicated that the isolated compound was digitoxin of high purity.
Footnotes
- Received October 10, 1953.
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