Atypical -Adrenergic Receptors in Rat Liver: Evidence for Transient Expression During Aging

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Abstract
This study was designed to determine whether functional β3-adrenergic receptors exist in the rat liver and whether there are alterations in the β3-adrenergic response with age in a manner similar to that which occurs for β2-adrenergic receptors. The β3 stimulation of adenylyl cyclase activity was assessed using the novel β3-specific agonist, CGP-12177A. Adenylyl cyclase activation by CGP-12177A was seen only in the adults. Isoproterenol-stimulated adenylyl cyclase activity was high in the neonates, declined by 45% in the adults, and was high again in the senescent rats. ICI 118551, a β2-selective antagonist, attenuated the isoproterenol-stimulated activity by two-thirds but had no effect on the CGP-12177a-stimulated activity. These data demonstrated the presence of the β3-adrenergic receptor in the rat liver, although only at the adult stage of development. In addition, these data confirm earlier findings that (32-adrenergic activation of adenylyl cyclase is biphasic with age and indicate that the emergence of the β3-stimulated activity coincides with the attenuation of β2-stimulated activity

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