Characteristics of adrenoceptors in the human radial artery: Clinical implications

Objectives: The radial artery has been suggested to be spastic. Endogenous and exogenous catecholamines and the use of beta-blockers may be related to radial artery spasm, but the characteristics of adrenoceptors in this artery are unknown. This study was designed to characterize the alpha- and beta-adrenoceptor in the human radial artery, Methods: Ring segments of the radial artery (n = 59) taken from patients undergoing coronary artery bypass grafting were studied in organ chambers. alpha-Adrenoceptor agonists (norepinephrine, methoxamine, and UK14304) and antagonists (phentolamine hydrochloride [INN: phentolamine], prazosin, and yohimbine) were used to characterize the alpha-adrenoceptor. beta-Adrenoceptor function was studied in U46619-precontracted rings in response to isoproterenol (INN: isoprenaline). Results: Norepinephrine induced 6.9 +/- 0.6 gm (80.6% +/- 6.8% of the contraction by 100 mmol/L KCI), and this was almost fully inhibited by phentolamine hydrochloride (10 mu mol/L, p < 0.0001). The contraction force induced by methoxamine (2.9 +/- 0.8 gm) was abolished by 0.5 mu mol/L prazosin (p = 0.017), The contraction force induced by UK14304 (1.7 +/- 0.4 gm) was abolished by 1 mu mol/L yohimbine, In contrast to the porcine coronary artery used as the control (fully relaxed to isoproterenol), radial artery rings did not have significant relaxation (1.1% +/- 0.8%). Conclusions: The human radial artery is an alpha-adrenoceptor-dominant artery with little beta-adrenoceptor function. The use of beta-blockers will not likely evoke the spasm of the radial artery. Furthermore, the radial artery has a dominant alpha(1)-adrenoceptor function, but the postjunctional alpha(2)-adrenoceptor is also functional. Circulating catecholamines will mainly contract the human radial artery by activation of the alpha(1)-adrenoceptors and to a lesser extent also by alpha(2)-adrenoceptors.