Some 40 years ago, researchers at the University of Missouri were searching for an alternative to the condom — a cheap, trustworthy and reversible form of male birth control.
For their first study, published in 1975, they strapped anesthetized rats, face-down, to a plexiglass platform with a cut-out cup full of water for their dangling scrota. The scientists then exposed the animals’ testicles to a variety of things.
Heat, for example, can kill sperm (which is thought to explain why the testes hang outside of the body). So some of the animals got a 140-degree Fahrenheit water bath for 15 minutes. Others received a dose of infrared radiation, or short blasts of microwaves or ultrasound. After treatment, the animals had constant access to females until they impregnated them.
Rats given the hot water bath didn’t conceive for 35 days. Infrared radiation doubled that sterile window, to 75 days. Sometimes microwave treatment worked, sometimes it didn’t. The best protocol, by far, was ultrasound, which the researchers transmitted through the water cup. One 5-minute exposure to these high-frequency sound waves led to seven months of sterility. Histology studies of the tissue confirmed that the animals showed a big loss of developing sperm at two months post-ultrasound, but were back to normal by 10 months.
Over the next two years, the scientists, led by Mostofa Fahim, observed the sperm-killing (and painless, by the way) effects of ultrasound in cats, dogs, monkeys and men. So why aren’t $1,100 ultrasound machines sitting in sock drawers across America? According to reporting by Willie Jones, of IEEE Spectrum, a more high-powered researcher couldn’t replicate Fahim’s results. The work was forgotten for decades.
Fahim died in 1995, and most of the equipment he used is no longer sold. But in the past few years, three independent teams have painstakingly tweaked Fahim’s methods — using newer ultrasound machines, and changing the frequency, power and duration of the sound waves — to good effect in several animal models. Preliminary data from monkey and dog experiments was presented at a contraception conference in October (the same meeting where I learned about another decades-old male contraceptive). And just last week, a study came out confirming ultrasound’s effectiveness in rats.
No one knows exactly why ultrasound causes sterility. It probably has to do with the heat produced when tissue absorbs the high-pressure sound waves. But something else is going on, too: In Fahim’s rat study, the tissue temperature after ultrasound was only 100 degrees, far lower than the 140-degree water bath. Fahim hypothesized that the ultrasound affected the ion exchange in fluid of different areas of the testes, leading to conditions that prevented sperm development.
The researchers who carried out the new rat study did not observe the animals long enough to see if, as Fahim reported, ultrasound’s effects are reversible — a key factor, of course, in whether this technology will ever be able to usurp the condom.