ABT-866, a novel alpha(1A)-adrenoceptor agonist with antagonist properties at the alpha(1B)- and alpha(1D)-adrenoceptor subtypes

N-[3-(1H-Imidazol-4-ylmethyl)phenyl]ethanesulfonamide, maleate (ABT-866) is a novel alpha(1)-adrenoceptor agent with mixed pharmacological properties in vitro. Compared to phenylephrine, ABT-866 demonstrates intrinsic activity at the alpha(1A)-adrenoceptor subtype present in the rabbit urethra (pD(2) = 6.22, with 80% of the phenylephrine response), reduced intrinsic activity at the alpha(1B)-adrenoceptor subtype in the rat spleen (pD(2)= 6.16, with 11% of the phenylephrine response), and no intrinsic activity at the rat aorta alpha(1D)-adrenoceptor subtype. ABT-866 also demonstrated antagonism at the rat spleen alpha(1B)-adrenoceptor (pA(2) = 5.39 +/- 0.08, slope = 1.20 +/- 0.12), and the rat aorta alpha(1D)-adrenoceptor (pA(2)= 6.18 +/- 0.09, slope = 0.96 +/- 0.13). This is in contrast to the weak non-selective activity seen with the alpha(1)-adrenoceptor agonist, phenylpropanolamine (2-amino-1-phenyl-1-propanol hydrochloride), and the alpha(1A/D)-adrenoceptor selective agonist 1-(2',5'-dimethoxyphenyl)-2-aminoethanol hydrochloride (ST-1059), the active metabolite of midodrine, that has been used clinically for the treatment of stress urinary incontinence. This study identifies a unique agent that may prove to be a valuable in vivo tool in testing the hypothesis that the alpha(1A)-adrenoceptor can be stimulated to contract the smooth muscle present in the urethra without evoking blood pressure elevations presumably caused by alpha(1B)- and alpha(1D)-adrenoceptor subtype involvements in the vasculature.