Pharmacology of penile erection
by
Andersson KE.
Department of Clinical Pharmacology,
Lund University Hospital,
S-22185 Lund, Sweden.
Karl-Erik.Andersson@klinfarm.lu.se
Pharmacol Rev 2001 Sep;53(3):417-50
ABSTRACT
Erection is basically a spinal reflex that can be
initiated by recruitment of penile afferents, but also by visual,
olfactory, and imaginary stimuli. The reflex involves both autonomic and
somatic efferents and is modulated by supraspinal influences. Several
central transmitters involved in the erectile control have been
identified. Dopamine, acetylcholine, nitric oxide (NO), and peptides, such
as oxytocin and adrenocorticotropic/alpha-melanocyte-stimulating hormone,
seem to have a facilitatory role, whereas serotonin may be either
facilitatory or inhibitory, and enkephalins are inhibitory. Peripherally,
the balance between contractant and relaxant factors controls the degree
of contraction of the smooth muscle of the corpora cavernosa and
determines the functional state of the penis. Noradrenaline contracts both
corpus cavernosum and penile vessels via stimulation of
alpha(1)-adrenoceptors. Neurogenic NO is considered the most important
factor for relaxation of penile vessels and corpus cavernosum. The role of
other mediators released from nerves or endothelium has not been
definitely established. Erectile dysfunction (ED) may be due to inability
of penile smooth muscles to relax. This inability can have multiple
causes. However, patients with ED respond well to the pharmacological
treatments that are currently available. The drugs used are able to
substitute, partially or completely, the malfunctioning endogenous
mechanisms that control penile erection. Most drugs have a direct action
on penile tissue facilitating penile smooth muscle relaxation, including
prostaglandin E(1), NO donors, phosphodiesterase inhibitors, and alpha-adrenoceptor
antagonists. Dopamine receptors in central nervous centers participating
in the initiation of erection have been targeted for the treatment of ED.
Apomorphine, administered sublingually, is the first of such drugs
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