Types of Adrenoreceptors Mediating Responses of Rabbit Gastric Muscularis Mucosae

This study investigated adrenoreceptor-mediated responses of muscularis mucosae from the fundic and antral ends of the rabbit gastric corpus. Norepinephrine-induced fundic muscularis mucosae contractions were enhanced by propranolol and converted to relaxations by phentolamine. Methoxamine, but not clonidine, elicited large fundic contractions. Fundic muscle responded to low isoproterenol concentrations with atenolol- and butoxamine-resistant relaxations, and to high concentrations with atenolol-sensitive contractions. Norepinephrine evoked propranolol-resistant relaxations of antral muscularis mucosae that were enhanced by phentolamine. Methoxamine and clonidine elicited small antral contractions. Lower concentrations of isoproterenol caused atenolol-resistant antral relaxations that were enhanced by butoxamine; higher concentrations produced weak excitation. Fundic and antral relaxations to isoproterenol were abolished by cyanopindolol. Fundic muscularis mucosae possesses excitatory ₁-, ₁- and inhibitory ₃-adrenoreceptors. Excitatory ₂- and inhibitory ₃-adrenoreceptors predominate in the antral region. The heterogeneous adrenoreceptor-mediated responses of the gastric muscularis mucosae suggest that adrenergic modulation of its motor activity is unlikely to be linked to acid secretion.