DEMONSTRATION OF BOTH β₁‐ AND β₂‐ADRENOCEPTORS MEDIATING RELAXATION OF ISOLATED RING PREPARATIONS OF RAT PULMONARY ARTERY

Abstract

1 Cumulative concentration-response (relaxation) curves to three I-adrenoceptor agonists, fenoterol (p2-selective), isoprenaline (non-selective) and noradrenaline (pl-selective) were obtained on isolated ring preparations of rat pulmonary artery contracted with 15 mM KCI. a-Adrenoceptors and neuronal and extraneuronal uptakes were blocked with phenoxybenzamine.The agonist concentration-response curves were reproducible.2 Responses to each of the three agonists could be blocked by the f-adrenoceptor antagonists atenolol (PI-selective) or ICI 118,551 (132-selective) confirming the presence of P-adrenoceptors.3 The relative potencies of the agonists were isoprenaline: fenoterol: noradrenaline = 100: 38:1.4. This indicated that the predominant 3-adrenoceptor type was 02.4 Schild plots were obtained for atenolol and ICI 118,551 using the three different agonists. For each antagonist the location of the Schild plot varied depending on which agonist was used. This indicated that the 3-adrenoceptor population mediating relaxation responses to P-adrenoceptor agonists was not homogeneous. 5 Atenolol was most potent when noradrenaline was the agonist and ICI 118,551 was most potent when fenoterol was the agonist. 6 It is concluded that isolated pulmonary artery ring preparations of the rat contain a mixed population of Pl-and P2-adrenoceptors both mediating relaxation.

Thyroxine treatment of aged or young rats demonstrates that vascular responses mediated by β‐adrenoceptor subtypes can be differentially regulated

“…Isolated single ring preparations of pulmonary artery or aorta were set up for recording changes in tension in the circular muscle as described by O'Donnell & Wanstall (1981a). A resting tension of 1 g was maintained throughout the experiments, and tissues were allowed to equilibrate for at least 1 h before concentration-response curves were started.…”

The classification of β‐adrenoceptors in isolated ring preparations of canine coronary arteries

“…In the present study, isolated ring preparations of three of the larger coronary arteries from dog, i.e. left circumflex artery, one of its ventricular branches and the septal branch of the left coronary artery, have been examined to see whether relaxant responses might be mediated by both 13l-and 12-adrenoceptors, as has been described for other blood vessels (Cohen & Wiley, 1978;O'Donnell & Wanstall, 1981a;1984). The method used has been described by O'Donnell & Wanstall (1981b).…”

Blood pressure reflexes following activation of capsaicin‐sensitive afferent neurones in the biliopancreatic duct of rats

“…Both subtypes often, but not always, mediate the same physiologic response. Thus, both PI and P2 receptors in blood vessels of the rat can mediate vasodilatation (Cohen & Wiley, 1978;O'Donnell & Wanstall, 1981).…”