Rabbits may be the last animals that come to mind when it comes to sexual dysfunction, but if they ever need help in that area, they have it now -- and humans could be next.
Using tissue engineering techniques, researchers at the Institute for Regenerative Medicine at Wake Forest University Baptist Medical Center in Winston-Salem, N.C. constructed a fully functional rabbit penis that enabled the animals to mate and produce offspring. The process could someday allow normal penile function in men with damaged erectile tissue.
"The major challenge is that the penis is a solid organ," said Dr. Anthony Atala, director of the Institute for Regenerative Medicine at Wake Forest. "With this project, it was also a challenge to determine the ideal mix of smooth muscle and endothelial cells that would allow for normal function."
The research, which resulted in the most functional erectile tissue replacement reported to date, was published today in online early edition of the Proceedings of the National Academy of Sciences.
On a collagen scaffold, which provided the organ structure, Atala and his group grew smooth muscle and endothelial cells, the same cells that make up blood vessels, harvested from rabbit erectile tissue.
The scaffold and cells were implanted into 12 rabbits, where the tissue continued to develop.
But part of what makes erectile tissue so complex is the structure, a honeycomblike arrangement with spaces between the cells that fill with blood upon erection. In the rabbits, engineering the proper cellular configuration, along with having sufficient blood flow, allowed normal sexual function.
"This tissue has a unique structure, which the [scaffold] allowed us to replicate," Atala said.
Earlier research by Atala's group replacing portions of the erectile tissue returned about 50 percent of normal erectile function but the researchers hoped to improve upon those results.
And even in rabbits, lacking proper sexual function may make it difficult to try and mate.
The study showed that rabbits with bioengineered organs attempted to copulate with a female within one minute of introduction, whereas the control rabbits, who either had scaffold implants with no erectile tissue or no implants at all, made no such attempts.
However, Dr. Atala said it would be difficult to measure whether there is a cognitive component regarding the drive to mate and if it could be linked to functional erectile tissue.
And sexual function is complex, said Dr. Paul Turek, director of the Turek Clinic, a San Francisco-based male reproductive health clinic, involving anatomy, physiology, hormones, nerves and emotions.
"This [research] does not solve sexual function," he said. "It [could] solve problems of faulty sexual anatomy."
However, such advances are not the answer for infertility. Rather, regenerated, individualized and functional erectile tissue has more potential to help those born with dysfunctional erectile tissue, who have suffered trauma, have penile cancer and, in some cases, those with erectile dysfunction.
"If you lack erections, it's difficult to reproduce the old-fashioned way, but it's still possible," said Dr. Michael O'Leary, senior urologic surgeon at Brigham and Women's Hospital in Boston, Mass. "This particular technology is trying to treat erectile dysfunctions."
According to the Massachusetts Male Aging Study, a two-year survey of 1,290 men between the ages of 40 and 70, self-reported incidence of erectile dysfunction, ranging from mild to severe, occurred in 52 percent of respondents.
While there are plenty of treatments for older men who lose normal erectile function, including medications and prosthetic implants, men who are born with a defective organ -- one that is very small or nonexistent, for example -- have few options.
"Particularly for patients who have congenital abnormalities, that is those who are born with conditions that render them with a dysfunctional organ, there's almost nothing to offer them," Dr. O'Leary said.