â-adrenergic antagonists influence abdominal aorta contractility by mechanisms not involving â-adrenergic receptors. Folia Biologica (Kraków) 62: 243-250. â-adrenergic receptors (â-AR) are widely distributed in the cardiovascular system, where they considerably contribute to the control of its functions. â-blockers are commonly used in the treatment of disorders of the circulatory system. They act primarily by inhibiting cardiac â-receptors. However, there are also reports of pleiotropic action

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... of â-blockers as well as of new compounds created to study â 3 adrenergic receptors. The study aimed to investigate additional mechanisms of action of â-AR inhibitors in the rabbit abdominal aorta with emphasis on their action on á-adrenergic receptors and calcium influx. Responses to propranolol, betaxolol, metoprolol and SR59230A were evaluated in phenylephrine and PGF 2alpha precontracted aortic rings. The effect of propranolol on the phenylephrine concentration-contraction curve was examined. Propranolol ($10 FM) and SR59230A ($0.1 FM) induced relaxations in phenylephrine-precontracted rings, while betaxolol and metoprolol had little effect. The â-AR inhibitors produced further contraction of tissues preincubated with PGF 2alpha , excluding SR59230A, which after initial contraction, elicited marked relaxation at a concentration above 1 ìM. 100 FM of propranolol caused a significant rightward shift of the concentration-contraction curve to phenylephrine with no reduction in the maximum response. Incubation of aortic rings in phentolamine reduced the maximal contraction to propranolol; verapamil pretreatment by contrast enhanced contractile response. In conclusion, SR59230A and propranolol most probably act as á 1 -AR competitive antagonists in the presence of phenylephrine in rabbit abdominal aortic rings. After á-ARs blockade, propranolol exerts a weak relaxing activity connected with Ca 2+ channel inactivation. SR59230A at a high concentration acts on the rabbit aorta by an additional mechanism needing further investigation.