Effect of general anaesthetics and organic solvents on alpha 1-adrenoceptors in the myometrium.

The alpha 1 selective radioligand 3H-prazosin was used to assay alpha 1 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 alpha 1 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 greater than carbon tetrachloride greater than dichloromethane. The depression of 3H-prazosin binding seemed to be induced on the alpha 1 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 alpha 1 receptor. The ability of the general anaesthetics and organic solvents to inhibit contractions elicited by alpha 1 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 greater than or equal to halothane=chloroform greater than trichloroethylene greater than dichloromethane. The mechanism of action for alpha 1 receptor and myometrial depression is discussed.