BINDING OF [3H]‐PRAZOSIN AND [3H]‐DIHYDROERGOCRYPTINE TO RAT CARDIAC α‐ADRENOCEPTORS

Abstract

1 [³H]-prazosin binds specifically to a single class of α-adrenoceptors in rat cardiac membranes (K_D25°C = 0.2 nM). 2 That these receptors are of the α₁-type was indicated by competition studies, i.e. α₁-antagonists such as prazosin and (2-(2, 6-dimethoxyphenoxyethyl) aminomethyl-1, 4-benzodioxane (WB 4101) were more potent than the α₂-antagonists, yohimbine and piperoxan in inhibiting [³H]-prazosin binding. 3 A comparative study of [³H]-prazosin binding and [³H]-dihydroergocryptine binding to cardiac membranes showed that both [³H]-prazosin and [³H]-dihydroergocryptine (at low concentrations) bind to α₁-adrenoceptors, while [³H]-dihydroergocryptine (at higher concentrations) also binds to another class of sites.