London: Scientists claim to have made a step closer to developing an entirely new form of contraception for men after finding that a dose of ultrasound to the testicles helps stop the production of sperm in rats.
In their study, published in the journal Reproductive Biology and Endocrinology, researchers at the University of North Carolina found that sound waves could be used to reduce sperm counts to levels that would cause infertility in humans.
Although the findings are "promising", far more tests are required before it could be used in humans, they said. "Further studies are required to determine how long the contraceptive effect lasts and if it is safe to use multiple times," lead researcher Dr James Tsuruta was quoted as saying by the BBC News.
The concept was first proposed in the 1970s, but is now being pursued by the North Carolina team who won a grant from the Bill & Melinda Gates Foundation. They found that two, 15-minute doses "significantly reduced" the number of sperm-producing cells and sperm levels.
The sperm count in rats dropped to below 10 million sperm per millilitre. It was most effective when delivered two days apart and through warm salt water.
In humans, the researchers said men were considered to be "sub-fertile" when sperm counts dropped below 15 million sperm per millilitre.
Dr Tsuruta said they need to ensure that the ultrasound produces a reversible effect, contraception not sterilisation, as well as investigate whether there would be cumulative
damage from repeated doses.
Dr Allan Pacey, a professor in andrology at University of Sheffield, said: "It`s a nice idea, but a lot more work is needed."
He said that it was likely that there would be recovery of sperm production, but the "sperm might be damaged and any baby might be damaged" when sperm production resumed.
"The last thing we want is a lingering damage to sperm," he said.