Abstract
The inotropic response to norepinephrine by segments of electrically driven rabbit atria was increased in the presence of 2 x 10-4 M to 1 x 10-4 M theophylline. This potentiation, calculated as the ratio of concentrations of norepinephrine inducing the same response, amounted to about 3-fold at 2 x 10-4 M and about 8-fold at 1 x 10-3 M theophylline. Aminophylline gave qualitatively and quantitatively similar results, but caffeine was less effective. The inotropic effects of tyramine also were potentiated by theophylline. Cocaine, in the presence of theophylline, potentiated the effects of norepinephrine while antagonizing those of tyramine. These data are considered to be consistent with the hypothesis that adenosine 3',5'-phosphate is a mediator of the inotropic actions of sympathomimetic amines, and that theophylline potentiates these actions by inhibiting cyclic 3',5'-nucleotide phospho-diesterase.
Footnotes
- Received September 26, 1962.
- Accepted December 19, 1962.
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