Blasting a man's testicles with sound waves could cut his sperm production and may be used in the future as a male contraceptive treatment, a new study has found.
Scientists at the University of North Carolina tested doses of ultrasound waves on rats and found they “significantly reduced” the number of sperm-producing cells and sperm levels.
The equivalent outcome would result in reversible infertility in humans but far more tests are required before it could be made available as a male contraceptive treatment.
Study leader Dr James Tsuruta, from the University said: "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.
"Further studies are required to determine how long the contraceptive effect lasts and if it is safe to use multiple times."
The treatment was most effective when the rats were given two 15-minute doses delivered two days apart through warm salt water, with the testes at a temperature of 37C.
Following the treatment, the sperm count of the rats dropped to below 10m sperm per millilitre. As men are considered to be “sub-fertile” when their sperm count falls below 15m sperm per millilitre, the experiment may offer a promising future for male contraception.
Dr Tsuruta's team found that rotating a three megahertz high frequency ultrasound beam around rats' testes wiped out the germ cells that produce sperm.
The ultrasound method of sperm reduction was first trialled in the 1970s. Several prostate cancer patients who were due to have their testicles removed underwent the treatment, which resulted in a "dramatic loss of germ cells".
"These men reported that the procedure was pain-free, only creating a gentle feeling of warmth," the authors said in the journal Reproductive Biology and Endocrinology.
The scientists wrote: "The non-invasive nature of ultrasound and its efficacy in reducingsperm count make therapeutic ultrasound a promising candidate for a male contraceptive.
"Our results clearly show that therapeutic ultrasound treatment depleted developing germ cells from the testis and subsequently decreased the size of sperm reserves."