Modern ultrasound equipment could be used as a male contraceptive, University of North Carolina School of Medicine researchers say.
While ultrasound’s contraceptive potential was first reported nearly 40 years ago, it's never been commercially exploited - and, now, the equipment used at the time is outdated and no longer available.
But the Department of Pediatrics team says it's now established that the modern ultrasound equipment usually used for physical therapy can indeed be used as a male contraceptive.
By rotating high frequency (3MHz) ultrasound around the testes, they were able to cause uniform depletion of germ cells throughout the testes. The best results were seen using two sessions consisting of 15 minutes ultrasound, two days apart, they say.
Saline was used to provide conduction between the ultrasound transducer and skin, and the testes were warmed to 37 degrees centigrade. And, says the team, this reduced sperm to a Sperm Count Index of zero - three million motile sperm per cauda epididymis, where sperm is stored.
The World Health Organization has defined low sperm concentration as less than 15 million sperm per ml.
"Unlike humans, rats remain fertile even with extremely low sperm counts. However, our non-invasive ultrasound treatment reduced sperm reserves in rats far below levels normally seen in fertile men (95 percent of fertile men have more than 39 million sperm in their ejaculate)," says the department's James Tsuruta.
"However, further studies are required to determine how long the contraceptive effect lasts and if it is safe to use multiple times."