Failure to demonstrate decreased beta-adrenergic receptor concentration or decreased agonist efficacy in term or...

Iodine 125-labeled iodocyanopindolol, a radioactive beta-adrenergic antagonist, bound to particulate preparations of pregnant human myometrium in a manner compatible with binding to the beta-adrenergic receptor. Studies with a specific beta 2-antagonist, IPS 339, indicated that 72% of receptors present were of the beta 2-subtype. Quantitative studies of beta-receptor concentrations in myometrium from women at term indicated no change in receptor concentration during labor. Similarly, there was no difference in beta-receptor concentration in myometrium from women in labor or before labor between 28 and 34 weeks of gestation. Concentrations of the beta-receptor were not different at any stage of gestation assayed. Isoproterenol competition for iodocyanopindolol binding was used to examine efficacy of receptor agonist interactions in myometrium from women at term, in labor, or before labor and from women in preterm labor. There was no difference in high-affinity binding, an index of efficacy, in any of the groups examined.