Response of the Rabbit Coronary Arteries to Autonomic Agents

Abstract

The right or left coronary arteries were constricted by cholinergic agents and dilated by adrenergic agents. The receptors mediating cholinergic responses are muscarinic. Comparison with the ear artery indicates that the adrenergic receptors mediating dilatation in the coronary artery resemble β₁ rather than β₂. However, the ratios of the dilator potencies of noradrenaline, adrenaline and isoprenaline on the coronary artery were 1:0.23:2.6 compared with ratios of their positive inotropic potencies of 1:1.1:33 on the rabbit papillary muscle. The markedly smaller relative potency of noradrenaline on the papillary muscle may be due to uptake₁, since the potentiating effect of cocaine on noradrenaline on this tissue was approximately 12-fold, but was negligible on the coronary artery. The contribution of uptake₂ is unclear, since histochemical observations indicated selective accumulation of noradrenaline in the wall of the artery, whereas the dilator responses were not appreciably altered by uptake₂ inhibitors.

Effects of Uptake Inhibitors on Responses of Sheep Coronary Arteries to Catecholamines and Sympathetic Nerve Stimulation

“…Phenoxybenzamine could not be tested at an effective concentration for inhibition of neuronal (or extraneuronal) uptake since it markedly reduced responses to the spasmogen, acetylcholine. The present results support observations on cattle, rabbit and pig coronary arteries that cocaine does not alter responses to noradrenaline (Nishioka, 1971;Kalsner, 1974;De La Lande et al, 1974). Sensitization of tissues to noradrenaline by neuronal uptake inhibitors seems to be inversely related to the size of the neuroeffector junction (Verity, 1971).…”

“…Coronary arteries receive a rich supply of sympathetic nerves which terminate at the adventitial-medial border (De la Lande, Harvey & Holt, 1974;Denn & Stone, 1976). The nerve terminals are separated from vascular smooth muscle cells by a large synaptic cleft reported as being between 40 and 700 nm wide (Lever, Mumtazuddin & Irvine, 1965;Malor, Griffin & Taylor, 1973).…”

“…The nerve terminals are separated from vascular smooth muscle cells by a large synaptic cleft reported as being between 40 and 700 nm wide (Lever, Mumtazuddin & Irvine, 1965;Malor, Griffin & Taylor, 1973). In addition to the potential neuronal uptake sites for catecholamines, fluorescence histochemistry indicates the presence of extraneuronal uptake and connective tissue binding sites (Clarke, Jones & Linley, 1969;Gillespie & Muir, 1970;De la Lande et al, 1974). Both neuronal and extra-neuronal uptake of catecholamines have been demonstrated in isolated kitten coronary arteries by the use of radioactively labelled noradrenaline and isoprenaline respectively.…”

“…Potentiation of amine responses have been observed in coronary arteries of cattle (Kaisner, 1974;Kalsner, Frew & Smith, 1975) but not in those from rabbits and cats (De la Lande et al, 1974;.…”

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

“…Also, the f-adrenoceptor type in some blood vessels has subsequently been classified as l, viz. in the coronary blood vessels (Baron, Speden & Bohr, 1972;de la Lande, Harvey & Holt, 1974) and in some cerebral blood vessels (Edvinsson & Owman, 1974). These, and most other studies which have attempted to classify vascular P-adrenoceptors, have used relative potency values of selective agonists or selective antagonists.…”