Myometrial tissue rings from postpartum rats (24 h after delivery) were studied in vitro by electric field stimulation, and the α1/β2-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 β2-agonists (terbutaline and fenoterol) and α-antagonists (phentolamine, urapidil and yohimbine) in a concentration-dependent manner. Their effects were not altered by the adrenergic neuron-blocking agent bretylium. The α-antagonists (except phentolamine) elicited the same maximal inhibition as the β2-agonists. Receptor assays revealed that the α1/β2 ratio was about 2 in the measured uteri. It was concluded that the inhibitory effects of α-antagonists and β2-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 α-receptors. It is believed that this is the first functional proof of the existence of non-synaptic α1-adrenoceptors in smooth muscle.
- Electric field stimulation
- Non-synaptic regulation
- Receptor density
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Pharmacology, Toxicology and Pharmaceutics(all)