THE CHARACTERISTICS OF [3H]‐CLONIDINE BINDING TO ANα‐ADRENOCEPTOR IN MEMBRANES FROM GUINEA‐PIG KIDNEY

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Abstract
1 [3H]-clonidine binds to membranes prepared from guinea-pig kidney. 2 At 25°C the binding is rapid and saturable. 3 Scatchard analysis of the binding data showed that the Kd for [3H]-clonidine binding in kidney membranes is 8.54 nM and the density of binding sites 12.5 pmol/g wet wt. tissue. 4 Hill plots of the binding data showed that there were no cooperative site interactions associated with binding. 5 [3H]-clonidine binding could be displaced by drugs, the most potent being drugs with a high affinity for the α-adrenoceptor. The neuroleptic drugs (+)-butaclamol, ds-clopenthixol and ds-flupen-thixol at high concentration also displaced [3H]-clonidine binding. 6 Drugs acting as agonists or antagonists of β-adrenoceptors, histamine receptors, acetylcholine receptors as well as prostaglandins E1 E2, Flα and F2α, angiotensin II, arginine vasopressin, naloxone, nalorphine and pargyline had little effect on binding. 7 It is likely that the binding site labelled by [3H]-clonidine in guinea-pig kidney membranes is an α-adrenoceptor similar in some pharmacological aspects to an a2-adrenoceptor.