RELAXATION OF ISOLATED HUMAN MYOMETRIAL MUSCLE BY BETA(2)-ADRENERGIC RECEPTORS BUT NOT BETA(1)-ADRENERGIC RECEPTORS

OBJECTIVE: Human myometrium contains both beta(1)-adrenergic and beta( 2)-adrenergic receptors. This study was designed to assess the importa nce of each beta-adrenergic receptor subtype in relaxation of human my ometrial muscle strips. STUDY DESIGN: Radioligand binding studies were used to establish the presence of each beta-adrenergic receptor subty pe, whereas highly selective beta(1)-antagonists and beta(2)-antagonis ts were used to assess the contribution of beta-adrenergic receptor su btypes to myometrial relaxation after exposure to (-)-isoproterenol. R ESULTS: Membranes prepared from myometrium contained 82% +/- 4% beta(2 )-adrenergic receptors. After contraction produced by exposure to pota ssium chloride (35 mmol/L), isoproterenol produced relaxation with hal f maximal effect at 0.02 mu mol/L and a maximal relaxation of 52% +/- 3%. beta(1)-Antagonist CGP-20712A had no significant effect, whereas b eta(2)-antagonist ICI-118551 produced a characteristic rightward shift of the isoproterenol concentration-relaxation relationship. CONCLUSIO NS: Although both beta(1)-adrenergic receptors and beta(2)-adrenergic receptors are present in human myometrial tissue at term, relaxation b y nonselective beta-agonist isoproterenol is mediated exclusively by b eta(2)-adrenergic receptors.