Adrenoceptor profile of blood vessels in the knee joint of the rabbit.

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1. An in vitro preparation of the rabbit knee joint, perfused with oxygenated Locke solution, was used to assess the nature of adrenoceptors within articular blood vessels. 2. Dose/response relationships were obtained to intra-arterial injection of alpha- and beta-adrenoceptor agonists. 3. Adrenaline and noradrenaline produced a similar pattern of increasing constriction of articular vessels with increasing dose of drug. 4. The alpha 1-agonist, phenylephrine, also produced dose-dependent constrictor responses, but the alpha 2-agonist; clonidine, had no effect. The alpha 2-agonist UK-14304 did, however, produce modest vasoconstriction which was not greatly altered by the alpha 1-blocker prazosin. The constrictor effect of noradrenaline was abolished by both the alpha 1,2-blocker phenoxybenzamine and by prazosin but not by the alpha 2-blocker rauwalscine. 5. The beta-adrenoceptor agonist, isoprenaline, had little effect at a dose of 10(-6) M or lower, but gave rise to a constrictor effect at higher concentrations. This response was blocked by phenoxybenzamine but not by the beta 1,2-blocker propranolol, suggesting that the constrictor effect was mediated via alpha-adrenoceptors. 6. The results suggest that alpha 1- and alpha 2-adrenoceptors are present within articular blood vessels, but that beta-receptors are absent. The effects of noradrenaline appear to be mediated principally via alpha 1-adrenoceptors.

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