PMID: 6109014Oct 1, 1980Paper

Characterization of alpha-1 adrenergic receptors in the heart using [3H]WB4101: effect of 6-hydroxydopamine treatment

The Journal of Pharmacology and Experimental Therapeutics
S YamadaW R Roeske

Abstract

To identify and characterize the cardiac alpha-adrenoceptors, a radioreceptor binding assay using the potent alpha adrenergic antagonist, [3H]WB4101 was performed in rat hearts. Specific [3H]WB4101 binding to rat left ventricular homogenates was saturable, reversible and of high affinity (Kd = 0.18 nM) with a Bmax of 2.57 fmol/mg of tissue (27.7 fmol/mg of protein). Adrenergic agonists competed for specific [3H]WB4101 binding in the order: (-)-epinephrine > (-)-norepinephrine greater than (-)-isoproterenol. Stereospecificity of the [3H]WB4101 binding sites was also demonstrated with (-)-epinephrine, (Ki = 90) nM being 270 times as potent as (+)-epinephrine, (K1 = 24 microM). Adrenergic antagonists competed for the binding in the order: WB4101 = prazosin greater than yohimbine greater than (-)-propranolol. WB4101 and prazosin exhibited a markedly greater (2000 times) affinity for [3H]WB4101 binding sites than yohimbine. The affinities (pKi) of alpha agonists and antagonists for [3H]WB4101 binding sites in the rat heart closely correlated with their pharmacological potencies in the heart. Scatchard analysis for [3H]WB4101 binding, performed in five regions from control and 6-hydroxydopamine-treated rat hearts, revealed specific [...Continue Reading

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