Sildenfail is a vasoactive agent used to treat Erectile Dysfunction and reduce symptoms in patients with pulmonary arterial hypertension. Sildenafil citrate, a specific phosphodiesterase-5 inhibitor, is increasingly used for pulmonary hypertension in pregnancy. Sildenafil is also emerging as a potential candidate for the treatment of intra-uterine growth retardation and for premature labor. Its effects in the feto-placental circulation are not known.
Sildenafil elevates levels of the second messenger, cGMP, by inhibiting its breakdown via phosphodiesterase type 5 (PDE5). PDE5 is found in particularly high concentrations in the corpus cavernosum, erectile tissue of the penis. It is also found in the retina and vascular endothelium. The vasodilatory effects of sildenafil also help reduce symptoms of PAH.
Sildenafil inhibits PDE5 in these tissues as well, which is the cause of several side effects which are believed to be due to Viagra. There are 7 types of phosphodiesterases (or isozymes). They catalyse the same reaction, but the isozymes show show different behaviour when subjected to physical biochemical techniques.
Those 7 types of PDE are summerised in the table below. The Km values are equivalent to measurements of the tightness of binding (or affinity) of enzyme (PDE) to substrate (cGMP). The smaller the Km value, the more tightly the substrate binds to the enzyme.
Common side effects of Sildenafil include facial flushing, headaches, stomach pain, nasal congestion, nausea, diarrhea, and an inability to differentiate between the colors green and blue. Loss of hearing, ringing in the ears and dizziness may occur. Sildenafil is an active ingredient of different medications, for example Apcalis Oral Jelly 20mg, Vigora, Kamagra etc.
Sildenafil is also emerging as a potential candidate for the treatment of intra-uterine growth retardation and for premature labor. Sildenafil has also been proposed as a potential therapeutic strategy to maintain placental function in pre-eclampsia.
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