Serotonin Induces a Biphasic Response in Rabbit Cavernosal Smooth Muscle: Relevance to the Erectile Process

Introduction: Serotonin (5-hydroxytryptamine; 5-HT) can cause contraction in cavernosal smooth muscle. We further evaluated this effect of 5-HT. Methods: Organ bath studies were used. Results: 5-HT induced a sustained contraction occasionally accompanied by a transient relaxation (in 30% of rabbit cavernosal tissues) that preceded the contraction. Ondansetron and Y-25130 (both 5-HT 3 receptor antagonists) but not SB-269970 (a 5-HT 7 receptor antagonist) significantly inhibited or abolished this transient relaxation. Doxazosin (dox, an α 1 -receptor antagonist) and ketanserin (ketan, a 5-HT 2A receptor antagonist) significantly inhibited or abolished the sustained contraction. The effects of dox on 5-HT-mediated contraction were concentration-dependent. Conclusions: Our findings further confirm that the peripheral serotonergic pathway may play a part in the erectile process via 5-HT 2A receptor-mediated contractile and 5-HT 3 receptor-mediated relaxant activities. Our results also support the findings of human studies, which suggest that both ketan and dox may exert beneficial effects on the erectile process.