Sonicating sperm - the future of male contraception

The ideal male contraceptive would be inexpensive, reliable, and reversible. It would need to be long acting but have few side effects. New research published in BioMed Central's open access journal Reproductive Biology and Endocrinology used commercially available therapeutic ultrasound equipment to reduce sperm counts of male rats to levels which would result in infertility in humans.

Ultrasound's potential as a male contraceptive was first reported nearly 40 years ago. However the equipment used is now outdated and no longer available. Researchers from the Department of Pediatrics at the University of North Carolina School of Medicine used these experiments as a starting point to see if modern ultrasound equipment usually used for physical therapy could be used as a male contraceptive.

The team led by James Tsuruta found that 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. Saline was used to provide conduction between the ultrasound transducer and skin, and the testes were warmed to 37 degrees centigrade. Together this reduced sperm to a Sperm Count Index of zero (3 million motile sperm per cauda epididymis).

The World Health Organization has defined oligospermia (low sperm concentration) as less than 15 million sperm per ml. Dr Tsuruta explained, "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% of fertile men have more than 39 million sperm in their ejaculate). However further studies are required to determine how long the contraceptive effect lasts and if it is safe to use multiple times."

New research on rats indicates that currently available ultrasound machinery could be used to kill off sperm-growing cells, technology that could render males infertile.

"Our noninvasive ultrasound treatment reduced sperm reserves in rats far below levels normally seen in fertile men," study researcher James Tsuruta, of the University of North Carolina at Chapel Hill, said in a statement.

Male birth control for humans is still far from ready for prime time, though, Tsuruta said. "Further studies are required to determine how long the contraceptive effect lasts and if it is safe to use multiple times." Further work is also needed to figure out what specific settings work best on humans.

Sonic testes

The researchers used commercially available ultrasound equipment, which is used in physical therapy. They isolated the specific power, frequencies and temperatures needed to lower rat sperm count.

The idea was first suggested in 1970 by Mostafa Fahim, a researcher at the University of Missouri-Columbia, who published several studies of ultrasound treatments that killed germ cells and caused infertility, even testing the theory in humans. The machinery Fahim used is no longer available, so the researchers had to start over with commercially available ultrasound equipment and see what would have a similar effect to what was observed historically.