Effects of Lithium on the .BETA.-Adrenergic Receptor-Adenylate Cyclase System in Rat Cerebral Cortical Membranes.

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The effects of lithium on the β-adrenoceptor-adenylate cyclase system in cerebral cortical membranes of rats were investigated. Lithium chloride inhibited adenylate cyclase activity in a concentration-dependent manner in vitro. However, relatively high concentrations of lithium were needed for this inhibition; and at 1 mM, no significant reduction in adenylate cyclase activity was seen under any condition. Administration of lithium carbonate for 21 days decreased the maximum number of [<SUP>3</SUP>H]dihydroalprenolol binding sites without changing the apparent dissociation constant. Activation of adenylate cyclase by (-)-isoproterenol in the presence of 1 μM guanyl-5'-ylimidodiphosphate (Gpp(NH)p) was significantly attenuated in lithiumtreated rats compared with the controls. Lithium treatment reduced the Gpp(NH)pstimulated adenylate cyclase activity in the presence of 10 μM (-)-isoproterenol, but not in the absence of this β-adrenergic receptor agonist. Basal activity or adenylate cyclase activity stimulated by forskolin or manganese was not affected, whereas the activity stimulated by sodium fluoride was significantly attenuated by long-term lithium treatment. These results indicate that chronic lithium treatment induces subsensitivity in the β-adrenoceptor-adenylate cyclase system, for which down-regulation of β-adrenergic receptors is chiefly responsible.
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