β2-Adrenergic Receptor Characteristics in Sleep Apnea Patients

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Abstract
This study examined the relationship between sleep apnea and β2 -adrenergic receptor characteristics. Using standard polysomnography, individuals were classified as either apneic (n = 15) or mild to nonapneic (n = 15) according to their respiratory disturbance index (RDI). Subjects were similar in terms of sodium excretion and blood pressure. Apneic subjects showed a decrease in β2-adrenergic receptor sensitivity (p = 0.01) [as determined by isoproterenol-stimulated cyclic adenosine 5’-monophosphate (AMP) production in lymphocytes] and an increased binding affinity to the β receptor antagonist [125I]iodopindolol (p < 0.001). β receptor density was also diminished in apneics, but not significantly (p = 0.08). Forskolin-stimulated cyclic AMP was not significantly different between the groups, indicating a similarity in postreceptor Gs-adenylate cyclase activation. Across all subjects, RDI was negatively correlated with β receptor sensitivity (r = –0.35, p = 0.05) and Kd (r = –0.54, p < 0.01) and positively correlated with systolic blood pressure (r = 0.37, p < 0.05). The findings indicate that sleep apnea is associated with a diminished β2-adrenergic receptor function but no change in postreceptor components and suggest a mechanism for the high comorbidity between sleep apnea and hypertension.

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