Abstract
Very large concentrations of atropine sulfate, but not atropine methyl bromide, excite powerful rhythmic contractions of esophageal circular smooth muscle from the opossum. The response is dose-related, reversible by washing and not subject to tachyphylaxis and persists during a long period of exposure. Mean geometric threshold concentration for l-hyoscyamine, 4.59 x 10-5 g/ml (as the base), is significantly lower than that for racemic atropine sulfate, 3.22 x 10-4 g/ml (as the base). The response to atropine is not affected by nicotine, hexamethonium, tolazoline, dehydroergotamine, propranolol, d-tubocurarine, tripelennamine, methysergide and tetrodotoxin, or by local anesthetics except at very high concentrations. It persists during histamine tachyphylaxis. The results indicate that the esophageal response reflects a direct action of atropine on muscle.
Footnotes
- Received April 24, 1968.
- Accepted June 3, 1968.
- © 1968 by the Williams & Wilkins Co.
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