Lack of agonistic activity in McN‐A343 may be circumstantial

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Abstract
1. In Tyrode (Ca++ 1.80 mM) or Krebs (Ca++ 3.36 mM) solution, McN-A343 evoked a dose-dependent contractile response in the naive guinea-pig ileum in the dose range 0.40-40 microM, or bladder in the dose range 0.8-200 microM. 2. After two full cycles of carbachol or bethanechol administration in Tyrode solution, neither preparation responded to McN-A343 for 45 to 60 min. The response in Krebs solution, however, was almost unaltered at 15-30 min. The rate of recovery of the contractile response appears to depend on the calcium content of the medium used. 3. A previous report that McN-A343 failed to evoke a contractile response in the guinea-pig ileum or bladder must be reconsidered in the light of the present findings.