LAUSR

Sildenafil is well known selective phosphodiesterase-5 (PDE-5) enzyme inhibitor that is used extensively in erectile dysfunction in males. The effect of sildenafil is mediated through raising the tissue level of the second messenger cyclic guanosine monophosphate (cGMP) leading to relaxation of smooth muscle [1] through reduction of intracellular [Ca2+] and downregulation of contractile apparatus [2]. The reduction of intracellular [Ca2+] is through inhibition of Ca2+ influx [3] and decreasing Ca2+ release from the endoplasmic reticulum by blocking Ca2+ channels [4]. PDE-5 is found in high concentrations in the corpus cavernosum and in pulmonary artery smooth muscle, and therefore its inhibition leads to an increase in penile blood flow and a decrease in pulmonary vascular resistance [5]. Levels of cGMP in smooth muscle is also increased by nitric oxide (NO), which is formed from l-arginine through the actions of different types of NO synthase. NO acts a vasodilator, neurotransmitter and inflammatory mediator in human airways [6]. It relaxes tracheal smooth muscle [7] and decreases methacholine-induced bronchoconstriction in experimental animals [8]. Turner et al. [9] presented supporting evidence for a role of NO in airway dilatation by demonstrating that an NO-donating compound potentiates the effects of a β2-adrenoceptor agonist. Can sildenafil be used to treat asthma? http://ow.ly/13Y830bgExG