The pharmacological properties of
SGB-1534, 3-[2-[4-[(o-methoxyphenyl)-1-piperazinyl]ethyl]-2,4(1H,3H)-
quinazolinedione monohydrochloride, a selective alpha 1-adrenoceptor antagonist, compared with
prazosin,
phentolamine and
yohimbine, were examined in contractile responses of isolated canine mesenteric arteries and veins and femoral arteries and veins to exogenous
noradrenaline. The arteries and veins concentration-dependently contracted when exposed to
noradrenaline. The sensitivity to
noradrenaline, when compared in terms of pD2 values, was significantly higher in the veins than in the arteries.
Phentolamine and
yohimbine were competitive antagonists against
noradrenaline in the arteries and the veins.
SGB-1534 and
prazosin caused a parallel shift to the right of the concentration-response curves for
noradrenaline only in the arteries: the two antagonists were less effective in the veins than in the arteries when low concentrations of
noradrenaline were applied. The pharmacological characteristics of
SGB-1534 resemble those of
prazosin. The pA2 values for
SGB-1534 against
noradrenaline in the arteries were much higher than those for
prazosin,
phentolamine and
yohimbine. The result indicates that
SGB-1534 may predominantly act upon arterial resistance vessels rather than the venous side, resulting in potent
hypotension.