Effects of chronic ethanol ingestion on mouse brain beta-adrenergic receptors (BAR) and adenylate cyclase

Previous work showed that chronic ethanol ingestion by C57BL mice resulted in reduced stimulation of cerebral cortical adenylate cyclase (AC) activity by isoproterenol (ISO) and guanine nucleotides (GN). To investigate the mechanism of this change we have assessed the effect of chronic ethanol ingestion on agonist and antagonist binding to BAR in cerebral cortex (mainly beta 1-AR) and cerebellum (mainly beta 2-AR). C57BL mice were fed ethanol in a liquid diet for seven days and were withdrawn for various intervals. Agonist (ISO) binding data were best fit by a two-site model (high and low affinity states) in cortical membranes of control mice. GN induced conversion to a one site model (low affinity state). At the time of withdrawal, ISO binding data in cortical membranes were best fit by a one-site model even in the absence of GN. Antagonist binding was not affected. These results resemble those seen after heterologous desensitization, indicating "uncoupling" of receptor and AC. Control cerebellar ISO binding data were similar to cortical data. Chronic ethanol ingestion, however, did not produce data fit by a one site model in cerebellum. The affinity for ISO of the high affinity state of the BAR was significantly decreased at the time of withdrawal. ISO-stimulated AC-activity in cerebellar membranes was not affected by chronic ethanol ingestion, indicating that, in contrast to cerebral cortex, the cerebellar BAR was not uncoupled from AC.