Effect of General Anaesthetics and Organic Solvents on α1-Adrenoceptors in the Myometrium

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Abstract
The α1 selective radioligand 3H–prazosin was used to assay α1 receptors in membranes prepared from the rabbit myometrium. 3H–Prazosin was found to bind to a single high affinity site in these membranes which was the presumed α1 receptor. A series of general anaesthetics and organic solvents were tested for their ability to inhibit 3H–prazosin binding. The order of potency of the tested agents to inhibit the binding was: chloroform = halothane = trichloroethylene > carbon tetrachloride > dichloromethane. The depression of 3H–prazosin binding seemed to be induced on the α1 receptor since non–specific radioligand binding was not affected as revealed by a saturation experiment with 3H–prazosin where halothane was used as inhibiting agent. Computer analysis of the latter experiment also showed that halothane depressed mainly the affinity of 3H–prazosin for the α1 receptor. The ability of the general anaesthetics and organic solvents to inhibit contractions elicited by α1 stimulation with phenylephrine in the rabbit uterus was also investigated. In these tests the order of potency for the inhibition of the contractile response was: carbon tetrachloride ≥ halothane = chloroform > trichloroethylene > dichloromethane. The mechanism of action for α1 receptor and myometrial depression is discussed