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| - Downregulation of β-adrenergic receptors by low density lipoproteins and its prevention by β-adrenergic receptor antagonists
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| - Abstract. Objective: Vasodilation by β-adrenergic receptors of smooth muscle cells appears to be impaired early after the onset of hypercholesteremia. The aim of this study was to analyze the modulation of β-adrenergic receptor density and adenylyl cyclase activity in the presence of moderately elevated concentrations of LDL. The effects of β1- and β2-adrenergic receptor antagonists on LDL-induced receptor changes were studied. Methods and results: Media explants of porcine coronary arteries were incubated with moderately elevated LDL concentrations (0.7-3.9 mmol/l). The density of β-adrenergic receptors was determined in plasma membranes using the radioligand [125I]iodocyanopindolol. LDL (3.9 mmol/l) resulted in a decrease of β-adrenergic receptor density (control 137±5 vs. 89±7 fmol/mg protein, P<0.01). After removal of LDL and cultivation for an additional 3 days β-adrenergic receptors increased to 129±5 fmol/mg. In the presence of the β1- or β2-adrenergic receptor antagonists the LDL-mediated decrease was inhibited. Addition of metoprolol after 3 days of LDL incubation caused a restoration of receptor density. The basal, isoproterenol- and forskolin-stimulated adenylyl cyclase activities were increased after LDL incubation by 180, 110 or 80%, respectively. Conclusion: Moderately elevated LDL levels decreased β-adrenergic receptor density while adenylyl cyclase activity was simultaneously increased. β1- or β2-adrenergic receptor antagonists prevented this receptor decrease and might preserve the β-adrenergic receptor density in the presence of moderately elevated LDL levels.
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