Alpha 2-adrenoceptors in the guinea-pig uterus: heterogeneity in the circular and longitudinal smooth muscle layers.
Homogenate binding and functional studies have been undertaken to investigate the role of alpha 2-adrenoceptors on the circular and longitudinal myometrial layers of the dioestrous guinea-pig uterus. Each myometrial layer contained a single population of [3H]rauwolscine binding sites (KD values approximately 3 nM) for which yohimbine exhibited a higher affinity than prazosin, and xylazine a higher affinity than phenylephrine, indicating the presence of alpha 2-adrenoceptor binding sites. In circular myometrium, xylazine enhanced contractile responses, was more potent than either noradrenaline or phenylephrine in inhibiting forskolin-stimulated accumulation of cyclic AMP, and reduced the inhibitory effect of forskolin on phenylephrine-induced phosphatidyl inositol hydrolysis. In longitudinal myometrium xylazine enhanced contractile responses to phenylephrine but did not inhibit forskolin-stimulated accumulation of cyclic AMP. We conclude that alpha 2-adrenoceptor binding sites are present in both uterine layers and mediate uterine contractility possibly through different mechanisms.
Haynes
J M
JM
Department of Pharmacology, Monash University, Clayton, Victoria, Australia.
Adams
G D
GD
Pennefather
J N
JN
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D009215:Myometrium / Q000187:drug effects / Q000378:metabolism; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects / Q000378:metabolism; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000378:metabolism*; D014590:Uterine Contraction / Q000187:drug effects; D014599:Uterus / Q000187:drug effects / Q000378:metabolism*; D015016:Yohimbine / Q000037:antagonists & inhibitors / Q000493:pharmacokinetics
D000316:Adrenergic alpha-Agonists; D007295:Inositol Phosphates; D018340:Receptors, Adrenergic, alpha-1; D018341:Receptors, Adrenergic, alpha-2; D005576:Colforsin; D015016:Yohimbine; D000242:Cyclic AMP