The hunt for an effective, reversible, and socially acceptable male birth control continues. The newest target: The smooth muscle that makes up the tubes connecting the testes to the urethra. This needs to contract in order for sperm to reach their final destination. Now, scientists have shown that you can make mice sterile by eliminating their ability to contract that muscle. The result: A mouse with a dry ejaculation but which is still "pelvis thrusting with appropriate vigor and frequency".
This is a long way from becoming reversible treatment for human gentlemen, though. Right now, probably the most promising male birth control is RISUG, in which a clear polymer gel is injected into the vas deferens. The gel doesn't block the tube up completely, but it does seem to prevent sperm from successfully reaching the urethra and being capable of fertilizing an egg. RISUG is in Phase III clinical trials in India, but, even then, there are still safety questions about it and, so far, it's only been proven to be reversible in tests on non-human primates.
The latest prospect in male contraception: blasting your reproductive organs with ultrasound to halt sperm production. Experiments on rats using the technique dropped sperm counts to 10m sperm per milliliter; under 15m sperm per milliliter is considered infertile in humans.
The results were published in the journal of Reproductive Biology and Edocrinology. Andrologists warn that much more work is needed to rule out the possibility of damaged, rather than dead sperm. From the BBC:
Lead researcher Dr James Tsuruta said: "Further studies are required to determine how long the contraceptive effect lasts and if it is safe to use multiple times." The team needs 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, senior lecturer in andrology at the 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.
In the meantime, I understand that blasting Nickelback is also an effective contraceptive.