Tadalafil, pharmacologically is a type 5 phosphodiesterase inhibitor (PDE-5): managing to relax smooth muscle, it causes blood vessels to dilate; this leads to a greater flow of blood into the corpus cavernosum of the penis causing an erection or a decrease in pressure resistance within the pulmonary vessels.
Tadalafil is a selective and reversible inhibitor of specific cyclic guanosine monophosphate (cGMP) type 5 phosphodiesterase (PDE5). When sexual stimulation determines the local release of nitric oxide, the inhibition of PDE5 by tadalafil causes an increase in cGMP levels in the corpus cavernosum. This determines the relaxation of smooth muscles and the flow of blood into the penis tissue, causing an erection.
An erection during sexual stimulation is caused by an increase in blood flow within the corpus cavernosum of the penis. This mechanism is mediated by the release of nitric oxide (NO) from the nerve terminals of the endothelial cells, which stimulates the synthesis of cyclic GMP in smooth muscle cells which, in turn, causes their relaxation and therefore an increase in blood flow.
Type 5 phosphodiesterase (PDE5) inhibitors, as tadalafil but also sildenafil and verdenafil, enhance the process by increasing the amount of cyclic GMP present in the tissues.