title: Acute and chronic regulation of alpha 2-adrenoceptor number and function in man.
abstract: Agonist regulation of platelet alpha 2-adrenoceptors was examined in human volunteers after acute elevations of adrenoceptor agonist and during chronic elevation of plasma catecholamines in two patients with phaeochromocytoma. Platelet alpha 2-adrenoceptor number was measured by radioligand binding [( 3H]yohimbine) and alpha 2-adrenoceptor function measured by turbidimetric platelet aggregation. Short term infusion of adrenoceptor agonists with alpha 2 activity caused reductions in the platelet response to adrenaline in vitro; conversely an increase in activity was observed postoperatively in two patients after removal of phaeochromocytoma. The changes in platelet response were not accompanied by changes in alpha 2-adrenoceptor number. It is proposed that a process of receptor inactivation occurs during desensitization and this is responsible for the dynamic regulation of platelet responses.
authors.forename: C R
authors.initials: CR
authors.lastname: Jones
authors.forename: C A
authors.initials: CA
authors.lastname: Hamilton
authors.forename: K F
authors.initials: KF
authors.lastname: Whyte
authors.forename: H L
authors.initials: HL
authors.lastname: Elliott
authors.forename: J L
authors.initials: JL
authors.lastname: Reid
mesh_terms: D000293:Adolescent; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000368:Aged; D001792:Blood Platelets / Q000187:drug effects* / Q000502:physiology; D004837:Epinephrine / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D009638:Norepinephrine / Q000097:blood; D010673:Pheochromocytoma / Q000503:physiopathology*; D010974:Platelet Aggregation / Q000187:drug effects; D011869:Radioligand Assay; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*
chemical_list: D000316:Adrenergic alpha-Agonists; D011942:Receptors, Adrenergic, alpha; D009638:Norepinephrine; D004837:Epinephrine