title: Norepinephrine-induced down regulation of alpha 1 adrenergic receptors in cultured rabbit aorta smooth muscle cells.
abstract: Drug-induced refractoriness of alpha-adrenergic receptor-mediated vasoconstriction may be a clinically important phenomenon. We have investigated the possible molecular mechanisms underlying this phenomenon in cultured vascular smooth muscle cells derived from the rabbit aorta. alpha 1-Adrenergic receptors were identified in membranes prepared from these cells by [125I]HEAT binding. The radioligand bound to a high affinity site (Kd = 140 pM) in a saturable fashion (202 fmol/mg protein). Adrenergic agonists and antagonists competed for binding of [125I]HEAT with the expected order of potency for an alpha 1-receptor, (-)epinephrine greater than or equal to (-) norepinephrine greater than (+)epinephrine greater than isoproterenol and prazosin greater than phentolamine greater than yohimbine. Exposure of cells for 26 hours to 10 microM norepinephrine resulted in a 70% decrease in the number of alpha 1-receptors as measured by [125I]HEAT binding without any significant change in the affinity of the receptor for the ligand. When the alpha-receptors were blocked with 10 microM phentolamine the loss of receptors induced by norepinephrine was completely prevented. Similar down-regulation of the [125I]HEAT binding sites was observed when the alpha 1-agonist phenylephrine was used instead of norepinephrine. It is concluded that alpha-agonists induce down-regulation of aortic smooth muscle alpha 1-receptors. This reduction of alpha-receptors could be important in the mechanisms by which vascular smooth muscle develops refractoriness to alpha-adrenergic stimulation.
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D001665:Binding Sites / Q000187:drug effects; D002478:Cells, Cultured; D007457:Iodine Radioisotopes; D008024:Ligands; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology*; D010627:Phenethylamines / Q000494:pharmacology; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D044024:Tetralones; D014661:Vasoconstriction / Q000187:drug effects
chemical_list: D000317:Adrenergic alpha-Antagonists; D007457:Iodine Radioisotopes; D008024:Ligands; D010627:Phenethylamines; D011942:Receptors, Adrenergic, alpha; D044024:Tetralones; C010652:BE 2254; D009638:Norepinephrine