1. A pharmacological study of the pre- and postjunctional muscarinic receptors of the isolated rat vas deferens was carried out using more selective agonists and antagonists. 2. The prejunctional receptor was characterized on electrically stimulated preparations, while the postjunctional receptor was studied on vasa deferentia without stimulation. 3. The results indicate that atropine exhibited a similar affinity for the two populations of muscarinic receptor subtypes of this tissue. 4. 4-DAMP was able to differentiate with high affinity a subtype located at postjunctional level which had pharmacological similarities with the M3-ACh subtype and with low affinity a subtype located at prejunctional level. 5. The selective M1-ACh agonist McN-A-343 was not able to activate the postjunctional receptor, but showed a similar affinity to ACh for the prejunctional one. 6. At present, the prejunctional receptor can be considered as an atypical M1-ACh subtype based on the results obtained with the selective drugs available.
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