ADRENOCEPTOR BLOCKING EFFECTS OF AROTINOLOL, A NEW COMBINED ALPHA-ADRENOCEPTOR AND BETA-ADRENOCEPTOR BLOCKING-AGENT

  • 1 January 1984
    • journal article
    • research article
    • Vol. 271  (2) , 249-262
Abstract
In isolated tissues and anesthetized animals, .beta.- and .alpha.-adrenoceptor blocking properties of arotinolol were studied in comparison with other typical adrenoceptor antagonists. The following order of .beta.-adrenoceptor blocking activities were obtained in isolated tissues: arotinolol = pindolol > propranolol = oxprenolol = alprenolol .gtoreq. labetalol for .beta.1-adrenoceptors (guinea pig right atrium) and pindolol = oxprenolol = arotinolol > propranolol > labetalol for .beta.2-adrenoceptors (guinea pig trachea). In anesthetized cats, arotinolol was .apprx. 9 and 25 times more potent than propranolol, and .apprx. 30 and 100 times more potent than labetalol in blocking .beta.1- and .beta.2- adrenoceptors. Arotinolol showed a competitive antagonistic effect on phenylephrine-induced contraction of isolated rat aortic strips. The relative order of .alpha.1-adrenoceptor blocking potencies was as follows: prazosin > phentolamine > labetalol > arotinolal = yohimbine. Presynaptic .alpha.2-adrenoceptor blocking action of arotinolol was also assessed in isolated rat vas deferens and was revealed to be a much weaker presynaptic .alpha.2-adrenoceptor antagonist. In anesthetized rats arotinolol was 4-5 times less potent than labetalol and .apprx. 26 times less potent than phentolamine in blocking .alpha.1-adrenoceptors. Arotinolol exhibited a selectivity for .alpha.1-adrenoceptors over presynaptic .alpha.2-adrenoceptors. [This study has applications to the treatment of hypertension.].