Abstract
Adrenergic receptors in muscularis mucosa from the body of the rat esophagus have been examined using adrenergic agonists and competitive antagonists. Neither isoproterenol nor phenylephrine produced contraction of the tissue. After contraction of the tissue with carbachol, both adrenergic agonists produced dose-dependent relaxation. Isoproterenol was approximately 1000 times more potent than phenylephrine and only the former agonist relaxed the tissue to base-line levels. Cocaine potentiated (0.65 log unit) the effects of phenylephrine; tropolone did not significantly alter the effects of isoproterenol. Phentolamine did not antagonize the relaxation produced by either agonist. Propranolol blocked effects of both agonists to a similar degree although it was approximately 1000 times less potent than in other tissues. Sotalol and practolol were not potent antagonists of the responses. The potency differences between enantiomers of isoproterenol and trimetoquinol were (in log units) 2.53 and 1.66, respectively. These values are similar to those previously reported in guinea-pig atria and trachea and suggest a similarity of receptor sites for these agonists in the three tissues. The results indicate that alpha adrenergic receptors are not present in rat esophageal muscularis mucosa and that relaxation in response to adrenergic agonists is due to activation of beta adrenergic receptors. Resistance to beta receptor antagonists need not invoke a postulate of different beta receptor types.
Footnotes
- Received September 5, 1973.
- Accepted January 17, 1974.
- © 1974 by The Williams & Wilkins Co.
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