Published online 10 November 2009 | Nature | doi:10.1038/news.2009.1075

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Complete replacement of erectile tubes makes rabbits rampant again.

Scientists bioengineered working erectile tissue for New Zealand White rabbits. Nigel Cattlin/Getty

Researchers have successfully constructed functional erectile tissue that, when grafted onto rabbits who had their penises surgically removed, enables them to both copulate with and impregnate females.

The research team, at the Wake Forest Institute for Regenerative Medicine in Winston-Salem, North Carolina, says it is the most complete functional replacement of erectile tissue reported to date and raises real hopes for future therapy in humans.

The penis shaft, explains Anthony Atala, director of the institute and lead author of the study, basically consists of three tubes: a central tube comprising the urethra through which urine and semen travel, and two cylinders of erectile tissue on either side known as the corpus cavernosa.

Atala is a leading expert in organ replacement, and has previously conducted pioneering work on the bladder in humans (see 'Scientists grow bladder replacement in lab'). Atala and his colleagues report the successful replacement of these tubes of erectile tissue in Proceedings of the National Academy of Sciences USA1.

"We've already shown we can form urethra," says Atala. "This actually shows we can replace entire penile areas."

Fully functional

The team's previous attempts to replace segments of corporal penis tissue had limited success. Only around a third of tissue was replaced and the rabbits were unable to muster a full erection because blood pressure in the grafted tissue reached only half that required. However, the latest technique avoids both of these problems.

"We take a small piece of tissue from the patient, and from that we grow the cells outside the body and then put them right back into the patient," says Atala. "We've now been able to achieve full function."

“This actually shows we can replace entire penile areas.” Anthony Atala

Wake Forest Institute for Regenerative Medicine

The team used rabbit donor corpora cavernosa, which were stripped of their cells leaving just a collagen matrix as a 'scaffold'. This was then seeded with muscle and skin cells from the rabbits' own penises, and the cells were grown on the scaffold. These replacement corpora were implanted into male New Zealand White rabbits that had had their penises surgically removed.

The rabbits with artificially engineered penises were later allowed access to females and their amorousness was assessed at one, three and six months after implantation. All of the rabbits attempted intercourse within a minute of being placed together with a female.

Swabs of female rabbits showed the presence of sperm in 8 out of 12 females, and four of them were impregnated. "These bioengineered corpora were functional in terms of normal erections, adequate copulation, ejaculation, and impregnation," write the team in their paper.

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Similar techniques have been used to regenerate other organs. Although this research has only been done in rabbits, human therapy is the ultimate goal and the research shows "considerable potential", says Atala. Several patients could stand to benefit, including those with congenital abnormalities of the penis, traumatic injury or penile cancer. Some patients with severe erectile dysfunction could also potentially benefit.

Currently, artificial prostheses are used to replace erectile tissue in humans but these do not restore normal function.

Drogo Montague, director of the Center for Genitourinary Reconstruction in the Glickman Urological and Kidney Institute at the Cleveland Clinic in Ohio, adds that the technique might also eventually prove useful in "niche cases where erectile tissue has been damaged and replaced by scarring. This occurs after removal of infected penile prostheses and in [some] men with erectile dysfunction," he says.