Testosterone makes a contribution to nitric oxide formation. Nitric oxide, released from penile nerves stimulates guanylate cyclase which catalyzes the transformation of guanosine-5-triphosphate into 3′,5′-cyclic, guanosine monophosphate (cyclic GMP). Gyclic GMP causes vasodilatation and hence erection formation (Morelli et al 2005). The breakdown of cyclic GMP to GMP is mediated by the enzyme, phosphodiesterase type-5, the inhibitors of which (eg, sildenafil citrate) enhance erection formation and maintanence (Carson and Lue 2005).
The sex hormone testosterone is far more than just the stuff of the alpha male's swagger. Though it plays a more significant role in the life of the biological male, it is actually present in both sexes to some degree. Despite popular perceptions that testosterone primarily controls aggression and sex drive—although it does play a role in both of those things—research has shown that individual levels of testosterone are also correlated with our language skills and cognitive abilities. Testosterone occurs in the body naturally, but can be administered as a medication, too: its most common uses are in the treatment of hypogonadism and breast cancer, as well as in hormone therapy for transgender men.