Relaxation of isolated human myometrial muscle by beta2-adrenergic receptors but not beta1-adrenergic receptors.
OBJECTIVE
Human myometrium contains both beta1-adrenergic and beta2-adrenergic receptors. This study was designed to assess the importance of each beta-adrenergic receptor subtype in relaxation of human myometrial muscle strips.


METHODS
Radioligand binding studies were used to establish the presence of each beta-adrenergic receptor subtype, whereas highly selective beta1-antagonists and beta2-antagonists were used to assess the contribution of beta-adrenergic receptor subtypes to myometrial relaxation after exposure to (-)-isoproterenol.


RESULTS
Membranes prepared from myometrium contained 82% +/- 4% beta2-adrenergic receptors. After contraction produced by exposure to potassium chloride (35 mmol/L), isoproterenol produced relaxation with half maximal effect at 0.02 micromol/L and a maximal relaxation of 52% +/- 3%. Beta1-antagonist CGP-20712A had no significant effect, whereas beta2-antagonist ICI-118551 produced a characteristic rightward shift of the isoproterenol concentration-relaxation relationship.


CONCLUSIONS
Although both beta1-adrenergic receptors and beta2-adrenergic receptors are present in human myometrial tissue at term, relaxation by nonselective beta-agonist isoproterenol is mediated exclusively by beta2-adrenergic receptors.
Liu
Y L
YL
Department of Pharmacology, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, USA.
Nwosu
U C
UC
Rice
P J
PJ
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D005260:Female; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009126:Muscle Relaxation / Q000502:physiology*; D009215:Myometrium / Q000187:drug effects / Q000502:physiology*; D011189:Potassium Chloride / Q000494:pharmacology; D011412:Propanolamines / Q000494:pharmacology; D011869:Radioligand Assay; D018342:Receptors, Adrenergic, beta-1 / Q000502:physiology*; D018343:Receptors, Adrenergic, beta-2 / Q000502:physiology*
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D007093:Imidazoles; D011412:Propanolamines; D018342:Receptors, Adrenergic, beta-1; D018343:Receptors, Adrenergic, beta-2; C026777:ICI 118551; D011189:Potassium Chloride; C049763:CGP 20712A; D007545:Isoproterenol