The costo-uterine muscle of the rat contains a homogeneous population of beta-adrenoceptors.
The effects of two selective beta-adrenoceptor antagonists on the inhibitory responses to some sympathomimetic amines of electrically-stimulated preparations of costo-uterine muscle, taken from virgin rats, have been examined quantitatively. pA2 values for the antagonist, atenolol (beta 1-selective) and ICI 118,551 (beta 2-selective) were obtained using as agonists, fenoterol (beta 2-selective agonist) and noradrenaline (alpha- and beta-adrenoceptor agonist, beta 1-selective); and in addition, with ICI 118,551 only, isoprenaline (beta-agonist, non-selective) and adrenaline (alpha- and beta-adrenoceptor agonist, beta 2-selective). Catecholamine uptake mechanisms and alpha-adrenoceptors were not blocked in any of these experiments. Atenolol competitively antagonized the effects of fenoterol and noradrenaline to a similar extent, the pA2 values being 5.4 and 5.7, respectively. ICI 118,551 competitively antagonized the effects of fenoterol, isoprenaline, adrenaline and noradrenaline to a similar extent; pA2 values ranged from 8.7 with noradrenaline to 9.1 with isoprenaline. These results extend our previous observations which indicated that the adrenoceptors mediating inhibition of electrically-evoked contractions of costo-uterine muscle of the virgin rat are homogeneous and of the beta 2-subtype. The potency of the beta 1-selective agonist RO 363 in producing inhibition of electrically-evoked contractions of this tissue was also examined. RO 363 was 200 times less potent than isoprenaline but was a full agonist. This indicates that there is efficient coupling between beta 2-adrenoceptor activation and tissue response in this non-innervated preparation.
Hartley
M L
ML
Pennefather
J N
JN
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001262:Atenolol / Q000494:pharmacology; D002396:Catechols; D004558:Electric Stimulation; D004837:Epinephrine / Q000037:antagonists & inhibitors; D005260:Female; D005280:Fenoterol / Q000037:antagonists & inhibitors; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000037:antagonists & inhibitors; D009130:Muscle, Smooth / Q000378:metabolism*; D009638:Norepinephrine / Q000037:antagonists & inhibitors; D011412:Propanolamines / Q000494:pharmacology; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D014599:Uterus / Q000378:metabolism*
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D002396:Catechols; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; D005280:Fenoterol; C026777:ICI 118551; D001262:Atenolol; C018420:Ro 363; D007545:Isoproterenol; D009638:Norepinephrine; D004837:Epinephrine