Abstract
In helically-cut strips of isolated rabbit aorta, the contractile response to noradrenaline was competitively antagonized by ifenprodil in concentrations ranging from 10-8 to 2 × 10-5 M ; the pA2 value of this agent (7.45) was approx. the same as that of phentolamine (7.64). The addition of ifenprodil at 10-6 to 10-4 M attenuated the contractile response to histamine and serotonin and at 2 × 10-5 to 5 × 10-4 M also attenuated the response to Ba++ and K+. Contractions induced by angiotensin II were inhibited only at the highest concentration used (5 × 10-4M). In rabbit aorta contracted with Ba++, ifenprodil (5 × 10-6 to 10-4 M) caused a dose-related relaxation ; the potency was approx. 1/6.7 that of papaverine. In helically-cut strips of isolated canine cerebral, superior mesenteric, renal and femoral arteries contracted with K+, ifenprodil (5 × 10-6 to 5 × 10-4M) also caused a dosedependent relaxation. The relaxation observed in cerebral and renal arterial strips was greater than that in mesenteric and femoral arteries. The rate and contractility of isolated rabbit atria decreased with application of ifenprodil in a dose-dependent manner. The addition of ifenprodil produced an increase in the contractility of isolated rabbit ileum and uterus and a relaxation of isolated guinea pig tracheal strips. It may be concluded that ifenprodil possesses an alpha adrenergic blocking property in association with a nonspecific, papaverine-like vasodilating action, which appears to be greater in cerebral and renal arteries than in the other arteries studied.
