Effects of ouabain on smooth muscle of the corpus cavernosum.

The effect of ouabain, an inhibitor of the membrane Na+/K+ ATPase, on smooth muscle of the corpus cavernosum was investigated. In an in vivo study using dogs, the intracorporeal pressures (ICPs) were measured before and during electrical stimulation of the cavernous nerve, and during nerve stimulation following intracorporeal injection of ouabain (1 x 10(-7) M). There was a significant drop of ICP following intracorporeal injection of ouabain (P < 0.001). In the in vitro study, ouabain increased the basal tone of the isolated cavernosal strip from the rabbit. When the strip was pretreated with tetrodotoxin (5 x 10(-7) M), phentolamine (1 x 10(-5) M), propranolol (1 x 10(-5) M) and atropine (1 x 10(-5) M), ouabain was still capable of contraction of the strip. The ouabain partly inhibited the relaxation effect of acetylcholine (1 x 10(-6) M), VIP (vasoactive intestinal polypeptide: 1 x 10(-8) M) and 2-chloro-adenosine (1 x 10(-6) M). The ouabain acts directly on the smooth muscle of the corpus cavernosum, increases its basal tone and diminishes the relaxation effect of acetylcholine, VIP and adenosine.