title: Interaction of opioid drugs with human platelet alpha 2-adrenoceptors.
abstract: Morphine, naltrexone and naloxone inhibited the binding of [3H]clonidine to the alpha 2-adrenoceptors in human platelet membranes, provided that Mg2+ was present in the medium. In the presence of 5'-guanylyl imidophosphate (Gpp(NH)p) or in the absence of Mg2+ morphine did not modify the binding of [3H]clonidine. Neither [D-Ala2,N-MePhe4,Gly5-ol]enkephalin (DAGO), nor [D-Pen2,D-Pen5]enkephalin (DPDPE), nor dynorphin-(1-17) affected the [3H]clonidine binding. The presence of 1 mM naloxone did not alter the affinity of either [3H]clonidine or [3H]yohimbine, but reduced the number of binding sites of [3H]clonidine, having no effect on [3H]yohimbine. Naloxone inhibited the binding of adrenaline to high- but not low-affinity sites. It is concluded that morphine and semisynthetic antagonist derivatives interact with alpha 2-adrenoceptors only in the high-affinity state.
authors.affiliation: Departamento de Neuroquimica, Facultad de Medicina, Universidad de Alicante, Spain.
authors.forename: J J
authors.initials: JJ
authors.lastname: Ballesta
authors.forename: A
authors.initials: A
authors.lastname: Orts
mesh_terms: D000328:Adult; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D003000:Clonidine / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D009294:Narcotics / Q000494:pharmacology*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects* / Q000378:metabolism; D014316:Tritium
chemical_list: D009294:Narcotics; D011942:Receptors, Adrenergic, alpha; D014316:Tritium; D003000:Clonidine