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Doxazosin and Serotonin (5-HT) Receptor (1A, 2A, and 4) Antagonists Inhibit 5-HT-Mediated Human Cavernosal Contraction

DAVID H. W. LAU^*,,,

CECIL S. THOMPSON^,

FAIZ H. MUMTAZ^,

DIMITRI P. MIKHAILIDIS^,

From the ^* Department of Urology, the Department of Clinical Biochemistry, and the Department of Surgery, Royal Free Hospital and University College Medical School, University College London, United Kingdom; the Department of Urology, Chase Farm Hospital, Enfield, United Kingdom; and the ^|| Department of Urology, Charing Cross Hospital, London, United Kingdom.

Correspondence to: D. P. Mikhailidis MD, FRCP, FRCPath, Academic Head of Department, Department of Clinical Biochemistry, Royal Free Hospital, Pond Street, London NW3 2QG, United Kingdom (e-mail: mikhailidis{at}aol.com).

Penile erection results from the balance between relaxation and contractile mechanisms of the corpus cavernosum. Only a few studies suggest a role for endogenous contractile agents such as 5-hydroxytryptamine (5-HT). Our aim was to confirm the possible role of 5-HT in human erection. The effect of 5-HT on human cavernosal tissues, as well as those of doxazosin (shown previously to have 5-HT inhibitory action), ketanserin (5-HT (2A) receptor antagonist), NAN-190 (5-HT (1A) receptor antagonist), and SB 203186 (5-HT (4) receptor antagonist) on 5-HT-mediated effects, were assessed using the organ bath technique, including electrical field stimulation study (EFS). Results are presented as median (mg/mg = mg contraction/mg of tissue). Consistent 5-HT-mediated (10^–3 M) contractions were demonstrated (n = 18; 63 mg/mg). These contractions were inhibited with ketanserin by 90% (n = 8), NAN-190 by 68% (n = 12), and SB 203186 by 55% (n = 12). Doxazosin showed a similar 5-HT inhibitory action in a concentration-dependent manner (10^–4 M; 94% reduction; n = 8, 10^–6 M; 68.3% reduction; n = 8). Our EFS studies indicated the presence of neuronally derived 5-HT and that a majority of the nonnoradrenogenic contraction (54%) was mediated via 5-HT(2A) receptors. These findings suggest that 5-HT may play a role in the human detumescence process via 5-HT(1A), 5-HT(2A), and 5-HT(4) receptors. Neuronally released 5-HT is probably an important contractile neurotransmitter in the erectile process. Doxazosin, ketanserin, and 5-HT(1A) and 5-HT(4) receptor antagonists may be useful as part of combination therapy used to treat erectile dysfunction.

     Key words: 5-hydroxytryptamine, erectile dysfunction, corpus cavernosum, cavernosal tone

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