Introduction. Age‐associated erectile dysfunction (ED) involves a decrease in nitric oxide (NO) availability and impaired relaxation. PnTx2‐6, a toxin from the Phoneutria nigriventer spider, has been demonstrated to improve erectile function via NO/cyclic guanosine monophosphate (cGMP) pathway. This spider's venom is characterized by several symptoms, including erection. PnTx2‐6 has been implicated in this phenomenon. Animal venoms have been postulated as potential drugs to treat ED.

Aim. PnTx2‐6 toxin improves erectile function in aged rats via NO/cGMP. We investigated the effect of PnTx2‐6 in the erectile function of aged rats.

Main Outcome Measures. ED was evaluated through changes in intracavernosal pressure/mean arterial pressure ratio during electrical field stimulation (EFS) of the pelvic ganglion of aged and adult rats (70 vs. 14 weeks). In functional studies, EFS‐induced relaxation of corpus cavernosum (CC) strips were performed with or without PnTx2‐6 (10‐8M).

Results. The decrease in erectile function associated with age was partially restored 15–20 minutes after injection of PnTx2‐6 and further improved by sildenafil. PnTx2‐6 enhanced EFS‐induced relaxation, as well as cGMP levels in CC, from young and aged rats. Relaxation due to PnTx2‐6 was further increased after 30 minutes incubation with Y‐27632, a Rho‐kinase inhibitor (10‐6 M), in aging CC. Nitric oxide synthase (NOS) activity in aged and young cavernosal tissue was increased by incubation with PnTx2‐6 (10 minutes). However, this toxin did not modify NOS expression.

Conclusion. PnTx2‐6 improves penile relaxation in aged rats, via increased NOS activity and NO release, resulting in enhanced cGMP levels. Nunes KP, Toque HA, Borges MH, Richardson M, Webb RC, and de Lima ME. Erectile function is improved in aged rats by PnTx2‐6, a toxin from Phoneutria nigriventer spider venom. J Sex Med **;**:**–**.