A comparison of the effects of angiotensin II and Bay K 8644 on responses to noradrenaline mediated via postjunctional α₁‐and α₂‐adrenoceptors in rabbit isolated blood vessels

Postjunctional α‐adrenoceptors in the rabbit isolated distal saphenous artery: indirect sensitivity to prazosin of responses to noradrenaline mediated via postjunctional α2‐adrenoceptors

“…This is apparent since NA can clearly sustain a response alone after isolation of postjunctional OC2-adrenoceptors (Daly et al, 1988a), contrasting with the distal saphenous artery, where responses are wholly dependent on the presence of a stimulatory agent. Again in this preparation, the facilitatory action of AII on postjunctional a2-adrenoceptor-mediated responses is apparent only if al-adrenoceptors are blocked by prazosin or phenozybenzamine (Dunn et al, 1991). An even more subtle interaction between al-and X2-adrenoceptors has been demonstrated in the cat nictitating membrane (Shepperson, 1984) and rat isolated tail artery (Xiao & Rand, 1989 Since the original demonstration of postjunctional a2-adrenoceptors in the pithed rat (Drew & Whiting, 1979;Docherty et al, 1979), identification of this subtype in isolated vascular preparations, both responding to NA and resistant to prazosin or a suitable xl-adrenoceptor antagonist, has proved very difficult.…”

“…Secondly, responses to NA in the rabbit femoral artery were shown to be prazosin-sensitive, rauwolscine-resistant, and therefore by definition a,-adrenoceptor-mediated (Purdy & Weber, 1988 (Furchgott, 1972). This irreversible antagonist possesses selectivity for vascular a,-adrenoceptors (Constantine et al, 1982;Dunn et al, 1991), and a concentration that eliminates any 'receptor-reserve' (viewed as a reduction in the maximum response) will inevitably alter the relative contribution of al-and X2-adrenoceptors to the observed response before and after inactivation. Hence, one of the underlying assumptions for the use of phenoxybenzamine in the quantitative analysis of the interaction between agonist and a-adrenoceptor (see: Besse & Furchgott, 1976) cannot be guaranteed in vascular smooth muscle.…”

“…The observations parallel results obtained in the rat tail artery, in which the lower third of the CCRC to NA is slightly 'resistant' to prazosin over a limited prazosin concentration range (Rajanayagam & Medgett, 1987) and in which postjunctional a2-adrenoceptor-mediated contractile responses have subsequently been demonstrated (Templeton et al, 1989). Furthermore, All also reduces the potency of prazosin on responses to both B-HT 920 and NA in the rabbit lateral saphenous vein, another preparation in which postjunctional a2-adrenoceptors have been clearly shown (Schumman & Lues, 1983;Daly et al, 1988a;Dunn et al, 1991). The introduction of a prazosinresistant component of responses to NA, therefore, strongly indicates the presence of both postjunctional al-and 0x2-adrenoceptors in the distal saphenous artery.…”

Fluorescent ligand binding reveals heterogeneous distribution of adrenoceptors and ‘cannabinoid‐like’ receptors in small arteries

“…, 2005). Functional interactions between angiotensin and noradrenaline have long been recognized (Dunn et al. , 1991), and more recently we have shown a functional interaction between anandamide (endogenous cannabinoid) and noradrenaline (Daly et al.…”

Influences of the endothelium and hypoxia on α1‐ and α2‐adrenoceptor‐mediated responses in the rabbit isolated pulmonary artery

“…For example, in the rat tail artery, when vascular tone is raised with vasopressin, endothelin-1 or 5-hydroxytryptamine, a previously quiescent a2-adrenoceptor population is 'uncovered' (Templeton et al, 1989;MacLean & McGrath, 1990). The presence of angiotensin II selectively facilitates responses mediated via postjunctional M2-adrenoceptors in the saphenous artery and ear vein of the rabbit (Dunn et al, 1991a). In addition, inhibition of neuronal uptake will reveal aX2-adrenoceptor-mediated nerve responses in the rat tail artery (Papanicolaou & Medgett, 1986).…”