Abstract
All of the common antibiotics examined with the exception of sodium penicillin exert a negative inotropic effect upon the isolated dog heart. On a molar basis chloramphenicol is the most potent, followed in order by chlortetracycline, oxytetracycline and tetracycline, streptomycin and dihydrostreptomycin, and finally potassium penicillin.
Actions previously attributed to penicillin represent potassium ion intoxication.
The tetracyclines appear to act by forming insoluble salts with calcium ion.
Chloramphenicol is the most potent cardiac depressant of the substances studied, and its actions on the preparation are practically indistinguishable from the actions of pentobarbital.
Large doses of streptomycin and dihydrostreptomycin are required to produce a negative inotropic action. The mechanism of their action is unknown.
A technique is outlined for "titrating" calcium salts against a failure-producing agent to identify substances which produce a negative inotropic effect by binding calcium ion.
Footnotes
- Received January 5, 1956.
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