Studies on YM-12617: a selective and potent antagonist of postsynaptic alpha 1-adrenoceptors

YM-12617, 5-[2-[[2-(2-ethoxyphenoxy)ethyl]-amino]propyl]-2 -methoxybenzenesulfonamide HCl is a structurally new type of extremely potent alpha 1-adrenoceptor antagonist. Its alpha-adrenoceptor blocking properties have been compared with those of prazosin, phentolamine and yohimbine using both pharmacological and 3H-ligand binding techniques in vitro and in vivo. In the isolated rabbit aorta, a tissue known to contain mainly alpha 1-adrenoceptors at postjunctional sites, YM-12617 competitively antagonized noradrenaline-induced contraction with a pA2 value of 10.11. Although YM-12617 was also a competitive antagonist toward clonidine at prejunctional alpha 2-adrenoceptors in the isolated rat vas deferens, its affinity for these receptors (pA2 = 6.41) was 5,000 times lower than that displayed for the postjunctional alpha 1-adrenoceptors in the isolated rabbit aorta. YM-12617 displaced both 3H-WB 4101 and 3H-clonidine binding to rat brain membranes; however, the affinity of YM-12617 for alpha 1-adrenoceptors (pKi = 9.64) was 3800 times higher than that for alpha 2-adrenoceptors (pKi = 6.06). Based on pA2 values obtained in the isolated tissues and pKi values in the binding assays, YM-12617 was 2-18, 36-117 and 1,740-5,750 times more potent than prazosin, phentolamine and yohimbine in antagonizing alpha 1-adrenoceptors, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)