β3 adrenergic receptor activation relaxes human corpus cavernosum and penile artery through a hydrogen sulfide/cGMP-dependent mechanism
Erectile function is a widely accepted indicator of systemic endothelial activity since from a clinical standpoint erectile dysfunction (ED) often precedes cardiovascular events. Recently it has been described a potential role for β3 adrenoceptor in cardiovascular diseases emphasizing a possible development of new drugs. β3 adrenoceptor stimulation relaxes human corpus cavernosum (HCC) strips in cyclic guanosine monophosphate (cGMP)-dependent and endothelium/nitric oxide (NO)-independent manner. Hydrogen sulfide (H2S), along with NO, is another gaseous molecule involved in cardiovascular system and as a consequence also in penile erection. Cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE), the enzymes mainly responsible for H2S biosynthesis, are constitutively expressed in HCC. CSE rather than CBS is more abundant in human penile tissue. Herein we investigated the involvement of H2S pathway in β3 adrenoceptor-induced relaxation in HCC and penile artery. Penile artery expresses both CSE and β3 adrenoceptor. BRL37344, a β3 selective agonist, relaxed HCC strips and penile artery rings and this effect was significantly reduced by CSE inhibition. Incubation of HCC and penile artery homogenate with BRL37344 significantly increased H2S production. This effect was significantly reduced by the inhibition of either CSE or β3 adrenoceptor. Finally, the BRL37344-induced increase in cGMP was reduced by CSE inhibition in both tissues. Thus, BRL37344-induced relaxation in HCC and penile artery occurs in a H2S/cGMP-dependent manner.
In conclusion, β3/H2S/cGMP pathway can act as an alternative to NO. Since about 15% of patients do not respond to phosphodiesterase-5 inhibitors, β3 agonists could represent a therapeutic alternative or a useful adjuvant therapy to treat these patients.