title: Prolonged activation of alpha 1 adrenoceptors induces down-regulation of protein kinase C in vascular smooth muscle.
abstract: Sustained exposure of vascular smooth muscle to catecholamines results in desensitization of alpha 1-adrenoreceptor-mediated vascular smooth muscle contraction. The present study was designed to determine the effects of prolonged exposure of blood vessels to catecholamines on protein kinase C (PKC) activity. Incubation of rat aortic smooth muscle with 10 microM norepinephrine (NE) for 4 h resulted in a threefold decrease in sensitivity of the contractile response of rat aortic smooth muscle to the phorbol ester 4 beta-phorbol 12,13-dibutyrate (PDBu); this loss in sensitivity was dependent on the presence of endothelium. NE induced a 45% decrease in enzymatic activity of the soluble and particulate forms of PKC. With [3H]PDBu used to label phorbol ester receptor binding sites in the aorta, there was a 34% decrease in [3H]PDBu binding sites in NE-treated blood vessels without change in binding affinity for the ligand. To determine whether this loss in enzymatic activity and [3H]PDBu binding resulted from a decrease in the quantity of the enzyme, Western blot analyses were performed using a monoclonal antibody (MoAb) against PKC. This approach confirmed the presence of an 80-Kd immunoreactive PKC in the soluble fraction of rat aortic smooth muscle and demonstrated a 44% decrease in the amount of PKC in blood vessels after sustained exposure to catecholamines. Our results demonstrate that prolonged activation of alpha-adrenoceptors in blood vessels leads to down-regulation of PKC which may contribute to desensitization of contraction mediated by vasoconstrictors.
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D001667:Binding, Competitive / Q000187:drug effects; D015153:Blotting, Western; D015536:Down-Regulation / Q000187:drug effects*; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009124:Muscle Proteins / Q000096:biosynthesis; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000201:enzymology*; D009638:Norepinephrine / Q000494:pharmacology; D015240:Phorbol 12,13-Dibutyrate / Q000378:metabolism / Q000494:pharmacology; D010703:Phorbol Esters / Q000378:metabolism; D011493:Protein Kinase C / Q000096:biosynthesis*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects* / Q000502:physiology
chemical_list: D009124:Muscle Proteins; D010703:Phorbol Esters; D011942:Receptors, Adrenergic, alpha; D015240:Phorbol 12,13-Dibutyrate; D011493:Protein Kinase C; D009638:Norepinephrine