Nov 1, 1988

Alpha 1-adrenoceptors of rat myocardium: comparison of agonist binding and positive inotropic response

Naunyn-Schmiedeberg's Archives of Pharmacology
G GrossC Rugevics

Abstract

Binding of agonists to alpha 1-adrenoceptors labelled by 3H-prazosin was investigated in membranes of rat myocardium and compared to the inotropic response elicited by alpha 1-adrenoceptor activation on isolated right ventricles. 1. At 30 degrees C the full agonists, adrenaline and phenylephrine, displaced 3H-prazosin with a shallow inhibition curve. The data are compatible with the assumption that 32% of the binding sites were in a state of high affinity for the agonist adrenaline (KI 85 nmol/l) and 68% in a low affinity state (KI 1738 nmol/l). GTP transformed all binding sites into the low affinity form suggesting that at least some of the cardiac alpha 1-adrenoceptors are coupled to N-proteins. 2. At 0 degree C most of the binding sites (86%) were in a state of high affinity for agonists (KI for adrenaline: 91 nmol/l). 3. For several partial agonists and antagonists (cirazoline, methoxamine, indanidine (Sgd 101-75), oxymetazoline and phentolamine) no such distinct temperature- and GTP-shifts could be demonstrated suggesting a different kind of interaction with alpha 1-binding sites. 4. When temperature was changed during incubation with adrenaline, a rise of temperature (from 0 degrees C to 30 degrees C) converted high affin...Continue Reading

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Mentioned in this Paper

Myocardial Contraction
Tissue Membrane
Phenoxybenzamine Hydrochloride
Oxymetazoline
Right Ventricular Structure
August Rats
Methoxamine
Myocardium
Adrenergic alpha-Agonists
Adrenergic alpha-Antagonists

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