Abstract
1. The effects of strychnine sulphate solution (0.001 and 0.0001 per cent) upon irritability, latent period, phases of contraction, auriculo-ventricular interval, and heart rate were studied on thirteen perfused frog hearts.
2. In general, these properties were influenced in the same direction by both concentrations of the drug, the major effects occurring more frequently with the stronger solution.
3. When irritability, as measured directly by threshold of response to artificial stimulation, was affected by either concentration of strychnine, it was depressed. This occurred in the majority of instances for auricle and in every instance for ventricle with the 0.001 per cent solution; a similar effect was noted in about half the cases with the weaker drug solution. With increasing drug dosage, irritability was the first property measurably and consistently affected.
4. With one exception, the latent period of auricle and ventricle was either prolonged by strychnine, or was not significantly altered.
5. No consistent effect on contraction phase, relaxation phase, or diastolic pause was noted with either concentration of the drug.
6. The auriculo-ventricular interval was either prolonged or not significantly changed.
7. Heart rate was decreased in the majority of instances by the 0.001 per cent solution; increase occurred once. With the weaker solution, decrease and increase of rate occurred with equal frequency, but 45 per cent of the applications produced no consistent alteration.
8. The results show that strychnine depresses the fundamental properties of frog heart, even in threshold doses.
Footnotes
- Received July 10, 1937.
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