Abstract
The extensive use by Tainter and others of the cocaine sensitization-desensitization phenomena in studies of the circulatory actions of sympathomimetic compounds, made it desirable to determine whether the same phenomena could be elicited with intestinal muscle. Some data were available in papers by Tainter and Chang 1 and Thienes and Hockett. 2 In no case, however, had the study of excised intestine been sufficiently extensive to indicate the range of spontaneous variation in the responses to successive administrations of the amines. We, therefore, investigated the influence of cocaine upon the responses of excised rabbit duodenum to epinephrine, tyramine, ephedrine and barium, controlling the results by observations of the responses to repeated applications of the same drug in the absence of cocaine. The changes in tonus, amplitude, and rhythmic activity were correlated as much as possible.
The tissues were fresh and active, the majority being taken from recently killed rabbits. Some tissues, however, were kept on ice for 24 hours; this procedure has been found by Burn and Tainter 3 to increase the augmentor action of tyramine. The Magnus technic with longitudinal strips and Tyrode's solution were used. The pH of the bath was 7.6, and was not altered by the aeration, nor by the drugs added. A given amount of the drug was put in the organ-bath, and, after the response had been recorded, was washed out with fresh Tyrode. Before the next application, time was allowed for complete recovery of the tissue to its initial activity. A second application of the same amount of the drug was then made, and the 2 responses were compared. In the cocaine experiments the required amounts of cocaine to give concentrations between 1:15,000 and 1:2,500,000 were added to the bath before the second application of the drug being studied, so that the second response was obtained in the presence of the cocaine.
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