Phosphodiesterase 5 - the enzyme inhibited by sildenafil
by
Sandberg M, Natarajan V
Institutt for medisinsk biokjemi Universitetet i Oslo.
Tidsskr Nor Laegeforen 1999 Mar 10; 119(7):945-9
ABSTRACT
Phosphodiesterases are enzymes that catalyze the degradation of the cyclic
nucleotides, cyclic AMP and cyclic GMP, to the corresponding 5' nucleotide
monophosphates. Ten different phosphodiesterase families have been described to
date. These enzymes exist as homodimers and there is structural similarity
between the different families. However, they differ in several respects like
selectivity for cyclic nucleotides, sensitivity for inhibitors and activators,
physiological roles and tissue distribution. Interest in these enzymes has
increased tremendously, both within the medical community and in the general
public as a consequence of sildenafil (Viagra), the medication recently
introduced for the treatment of erectile dysfunction. Sildenafil mediates its
effects by inhibiting phosphodiesterase 5. Some biochemical and molecular
biological aspects of this enzyme are presented here. To achieve satisfactory
erection, normal penile innervation is required. Nitrogen monoxide, the
transmitter substance in these nerves, activates guanylyl cyclase, thereby
increasing cyclic GMP production. The increased levels of cyclic GMP cause
relaxation of smooth muscles in penile vessels and this leads to an erection.
Erection is dependent on elevated levels of cyclic GMP and sildenafil mediates
its effects by inhibiting the degradation of cyclic GMP. Other functions that
are mediated by the phosphodiesterases explain visual disturbances, flushing and
decreased blood pressure that are some of the side effects seen with sildenafil
treatment. Furthermore, the potentially fatal consequence of combining
sildenafil and nitrovasodilators is discussed.
SSRIs
Viagra
Vardenafil
Yohimbine
Erotomania
Phentolamine
SSRIs and sex
Coolidge effect
Viagra for women
Phosphodiesterase 4A/4B
Drugs to promote female sexual desire
Is sildenafil (Viagra) an antidepressant?
Sildenafil (Viagra) and erectile dysfunction
PDE 5 inhibitors: vardenafil, tadalafil and sildenafil
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