PMID: 41191Sep 1, 1979

Demonstration of alpha-adrenoceptors in the rabbit heart by [3H]-dihydroergocryptine binding

Naunyn-Schmiedeberg's Archives of Pharmacology
H J Schümann, O E Brodde


For direct identification of alpha-adrenoceptors in a membrane fraction of the rabbit heart the potent alpha-adrenoceptor antagonist [3H]-dihydroergocryptine ([3H]-DHE) was used. 1. The binding of [3H]-DHE was saturable with 80 fmol of [3H]-DHE bound/mg protein and of high affinity with an equilibrium dissociation constant (KD) of 11.5 nM. Binding of [3H]-DHE (6 nM) was rapid (t 1/2 = 2 min) and readily reversible. From the ratio of the rate constants for forward (K1 = 1.97 X 10(7) M-1 min-1) and reverse (K2 = 0.206 min-1) reactions a KD-value of 10 nM was calculated, which is in good agreement with that obtained by equilibrium studies. 2. Adrenergic agonists compete for [3H]-DHE binding in an order to potency: (-)adrenaline greater than (-)phenyleprine greater than (-)isoprenaline and adrenergic antagonists in the order: phentolamine greater than yohimbine greater than (-)propranolol. Binding is stereospecific as indicated by the greater potency of (-)adrenaline than (+/-)adrenaline in displacing [3H]-DHE from the binding sites. 3. For comparison the binding of the potent beta-adrenoceptor antagonist (-)[3H]-dihydroalprenolol ((-)[3H]-DHA) was measured in the same membrane fraction. The number and affinity of beta-adrenoceptor...Continue Reading


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May 5, 1978·Naunyn-Schmiedeberg's Archives of Pharmacology·J Wagner, O E Brodde
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Related Concepts

Adrenergic alpha-Agonists
Adrenergic alpha-Antagonists
Ergot Alkaloids, Hydrogenated
Tissue Membrane
Norepinephrine Receptors
Beta-adrenergic receptor

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