Characterization of dog platelet alpha-adrenergic receptor: lack of in vivo down regulation by adrenergic agonist treatments.
The dog platelet alpha-adrenergic receptor was characterized using [3H]clonidine and [3H]yohimbine. The binding of both radioligands was rapid and reversible at 25 degrees C; saturation and kinetic experiments revealed a single population of binding sites. The number of [3H]yohimbine sites was 2-3-fold higher than the number of [3H]clonidine sites as reported in other tissues containing alpha2-adrenoceptors. The various alpha-agonists and antagonists displaced [3H]clonidine and [3H]yohimbine with an order of potency indicating alpha2-adrenoceptor specificity. Neither (-)adrenaline nor clonidine infusions (0.5 micrograms/min/kg during 3 hr) modified the number of [3H]yohimbine and [3H]clonidine sites or the affinity of the ligands for the alpha2-sites of the dog platelet. Oral administration of clonidine (3 X 150 micrograms/day) did not alter the binding parameters of either ligand.
Villeneuve
A
A
Berlan
M
M
Lafontan
M
M
Montastruc
J L
JL
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003000:Clonidine / Q000097:blood; D004285:Dogs; D005260:Female; D007700:Kinetics; D008297:Male; D010974:Platelet Aggregation / Q000187:drug effects; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000378:metabolism*; D015016:Yohimbine / Q000097:blood
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D000244:Adenosine Diphosphate; D003000:Clonidine