As men age they experience a fall in the level of circulating androgens in their body. Low androgen levels could also be linked to other factors such the hair loss treatment finasteride (propecia) which blocks conversion of testosterone to the DHT which has a greater affinity for the androgen receptor.
This can lead to difficulties achieving or maintaining an erection and evidence suggests it may ultimately lead to changes in the structure of the penis.
There is a large body of scientific evidence which shows that androgens are important for maintaining the function and structure of penile nerves, blood vessels, muscle, connective tissue matrix, and the tunica albuginea.
Androgens are known to act on nerves which control erectile function. Studies on castrated animals have shown deterioration of cavernosal and dorsal nerves which was reversed by testosterone replacement restoring erectile capacity.
Low levels of androgens are also known to damage the lining of blood vessels in the penis inhibiting their ability to produce nitric oxide (NO) which is a substance which plays an important role in producing erections. The erectile dysfunction drug Viagra works by increasing NO levels.
Similar studies have also shown that androgens maintain penile smooth muscle content. Loss of smooth muscle due to androgen deprivation caused lower intracavernosal pressure, in other words lower blood pressure inside the penis and weaker softer erections. Similar changes to penile muscle have been seen in humans suffering from erectile dysfunction with the severity of their symptoms correlating with the degree of muscle loss. Worryingly the smooth muscle in the corpora cavernosa (the vascular inner part of the penis that fills with blood during erection) seems to be replaced by connective tissue which leads to fibrosis. This would prevent the normal expansion of the penis during erection leading to a diminished erect penis size.
A similar process occurs in the tunica albuginea which is an elastic outer layer surrounding the corpora cavernosa. This layer is normally rich in elastic fibres which allow it to expand easily when the inner corpora cavernosa blows up like a balloon as it becomes engorged with blood during erection. However in castrated animals the elastic fibres have been seen to be replaced with inelastic collagen. So again the penis is unable to expand normally.
While it is known that androgen replacement therapy such as testosterone injections and gels like Testim® and Androgel® can improve symptoms of erectile dysfunction an as yet unexplored avenue of research is the use of testosterone gel applied directly to the penis. This could produce higher local concentrations of androgens in the tissues most affected and help to reverse the structural penile changes.
This could even be of some benefit to individuals suffering erectile problems due to finasteride use. Although DHT has higher affinity for the androgen receptor and not all of the testosterone would be converted to DHT, testosterone still has action at the androgen receptor and the high local concentrations delivered by direct application could be enough to substitute for the loss of DHT.
Such studies have not yet been carried out however, so the benefits of this theoretical treatment are not currently known. However clearly more research needs to be carried out.
Traish AM. Androgens play a pivotal role in maintaining penile tissue architecture and erection: a review. J Androl. 2009 Jul-Aug;30(4):363-9 Click here to read study