Alpha- and Beta-Adrenergic Receptors in Isolated Rabbit Uterine Membranes: Study of Receptor Alterations by Pregnancy

Abstract

The response of the rabbit uterus to exogenous catecholamines or to hypogastric nerve stimulation is changed during pregnancy. To investigate this phenomenon, the alpha-adrenergic antagonist [3H] dihydroergocryptine ([3H] DHE) and the beta-adrenergic antagonist (-)-[3H]dihydroalprenolol ((-)-[3H]DHA) were used to estimate directly the number and affinity of .alpha.- and .beta.-adrenergic receptors in uterine membranes from control and pregnant rabbits. Binding of [3H] DHE and (-)-[3H]DHA was rapid, saturable and displayed the specificity and affinity expected from the .alpha.- and .beta.-adrenergic receptors. Interactions of agonists and antagonists with the binding sites showed stereoselectivity; the (-)isomers of all agents tested being more potent than their respective (+)-isomers. The number of specific binding sites for [3H]DHE was reduced during the 2nd wk of gestation, but progressively returned to normal level thereafter. The number of available (-)-[3H]DHA binding sites declined by 55% at the end of gestation. The binding affinity of the remaining sites was not changed. The relative dominance of estrogen and progesterone affects the density of alpha- and beta-adrenoceptors in the rabbit uterus.