The physical and psychological triggers underlying penile erection are fairly obvious. What happens at the physiological level, however, has proved harder to discern. To that end, study results published today in the Proceedings of the National Academy of Sciences will no doubt prove insightful. According to the report, the same chemical compound that causes an erection also maintains it over time. The findings could aid efforts to develop treatments for erectile dysfunction.

Building on previous work indicating that the release of the neurotransmitter nitric oxide from nerve endings in the penis produces erection, a team of Johns Hopkins University researchers led by Arthur Burnett focused on the role of the compound over time. Their research on rats and mice indicates that nitric oxide released at the onset of erection dilates the blood vessels, which enables blood to flow to the penis. That increased blood flow, the team discovered, slightly stresses the blood vessel wall, which prompts the release of more nitric oxide from the cells lining that wall, relaxing more tissue and allowing more blood to enter. The process repeats, sustaining erection.

The investigators conclude that drugs that prevent the inhibition of nitric oxide production might alleviate impotence. "The physiology of erection is like driving a car," Burnett remarks. "You can't just turn the key and expect to go anywhere. You also need to hit and hold the accelerator."