Mammalian platelet adrenoceptors

• Published in: British journal of pharmacology Vol. 81; no. 1; pp. 91 - 102
• Main Authors: Kerry, R., Scrutton, M.C., Wallis, R.B.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.01.1984; Nature Publishing; Nature Publishing Group
• Subjects: adrenaline; aggregation; alpha -adrenergic; Animals; Biological and medical sciences; Blood Platelets - drug effects; Blood Platelets - metabolism; Blood. Blood coagulation. Reticuloendothelial system; Guinea Pigs; In Vitro Techniques; Iodocyanopindolol; Kinetics; Mammalia; Medical sciences; Pharmacology. Drug treatments; Pindolol - analogs & derivatives; Pindolol - pharmacology; Platelet Aggregation - drug effects; platelets; Rabbits; Rats; Receptors, Adrenergic - drug effects; Receptors, Adrenergic, alpha - metabolism; Receptors, Adrenergic, beta - drug effects; Species Specificity; Yohimbine - pharmacology; Adrenergic receptor; Platelet
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/j.1476-5381.1984.tb10748.x

1 Mammalian platelets vary widely in their responses to catecholamines in part because these agonists can act via excitatory α‐ and inhibitory β‐adrenoceptors. In the absence of antagonists, adrenaline enhances the response of rabbit platelets to an excitatory agonist, e.g. adenosine‐5′‐O‐(1‐thiodiphosphate) (ADP‐α‐s) acting at another receptor, but has no effect on the response of rat or guinea pig platelets to such an agonist. In the presence of a β‐adrenoceptor antagonist, adrenaline enhances the response of rat, but not guinea‐pig platelets to ADP‐α‐S and the extent of the enhanced effect on rabbit platelets is increased. In the presence of an α‐adrenoceptor antagonist, adrenaline inhibits the response of rabbit and rat platelets to ADP‐α‐S but has no such effect on the response of guinea‐pig platelets. 2 Studies using selective agonists and antagonists demonstrate that the excitatory response of rat platelets to adrenaline is mediated by an α2‐adrenoceptor, and the inhibitory response of rabbit platelets to adrenaline by a β2‐adrenoceptor as is the case in other species which have been examined. 3 The mean α2‐adrenoceptor density on human, rabbit, rat and guinea‐pig platelets as assessed using [3H]‐yohimbine as radioligand is obtained as 258, 270, 42 and < 10 receptors per platelet. 4 The mean β2‐adrenoceptor density on human, rabbit, rat and guinea‐pig platelets as assessed using (‐)‐[125I]‐iodocyanopindolol is obtained as 66, 14, 41 and < 5 receptors per platelet. 5 The nature of the effect of adrenaline on the response of mammalian platelets to other excitatory agonists, e.g. ADP‐α‐S, appears therefore to be largely determined by the absolute number of α2‐adrenoceptors and by the relative content of α2‐ and β2‐adrenoceptors on these cells for the species which have been examined in this analysis.