Evidence of non-synaptic regulation of postpartum uterine contractility in the rat.
Myometrial tissue rings from postpartum rats (24 h after delivery) were studied in vitro by electric field stimulation, and the alpha1/beta2-adrenoceptor ratio was determined by a radioligand binding technique. Pregnancy-denervated uterine rings were stimulated by long-duration pulses (100 ms). The contractions were inhibited by beta2-agonists (terbutaline and fenoterol) and alpha-antagonists (phentolamine, urapidil and yohimbine) in a concentration-dependent manner. Their effects were not altered by the adrenergic neuron-blocking agent bretylium. The alpha-antagonists (except phentolamine) elicited the same maximal inhibition as the beta2-agonists. Receptor assays revealed that the alpha1/beta2 ratio was about 2 in the measured uteri. It was concluded that the inhibitory effects of alpha-antagonists and beta2-agonists are mediated via non-synaptic adrenoceptors of the denervated postpartum rat uterus. The same inhibitory activity could be explained by the greater amount of alpha-receptors. It is believed that this is the first functional proof of the existence of non-synaptic alpha1-adrenoceptors in smooth muscle.
Gáspár
R
R
Department of Pharmacodynamics, Albert Szent-Györgyi Medical University, Szeged, Hungary.
Márki
A
A
Zupkó
I
I
Falkay
G
G
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D004558:Electric Stimulation; D005260:Female; D005280:Fenoterol / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009215:Myometrium / Q000502:physiology / Q000648:ultrastructure; D049590:Postpartum Period / Q000502:physiology*; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D018340:Receptors, Adrenergic, alpha-1 / Q000502:physiology; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure; D013726:Terbutaline / Q000494:pharmacology; D014590:Uterine Contraction / Q000502:physiology*; D014599:Uterus / Q000502:physiology / Q000648:ultrastructure*
D000318:Adrenergic beta-Agonists; D011942:Receptors, Adrenergic, alpha; D018340:Receptors, Adrenergic, alpha-1; D011943:Receptors, Adrenergic, beta; D005280:Fenoterol; D013726:Terbutaline