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eof [soylentnews.org] writes:

The Los Angeles Times has a story about potential birth control drugs for men [latimes.com]. The drugs, cyclosporine A (CsA) and FK506, are currently in use with transplant patients to reduce the possibility of rejection. They act by inhibiting an enzyme, calcineurin, one version of which is found only in sperm. Scientists studied 'knockout mice' that do not produce the proteins necessary for the enzyme, and compared them to regular mice.

The knockout mice still had sex with female mice, but the females didn’t become pregnant.

[...]The sperm were unable to fertilize an egg as long as the egg was covered by its usual layer of cumulus cells.

[...]The knockout sperm were able to move at the about same velocity as the regular sperm, the researchers found. However, the knockout sperm were deficient at something called “hyperactivation.” This is a particular type of movement that requires the sperm’s whip-like tail to beat back and forth with extra force.

[...]They determined that the tails of the knockout sperm moved with the same “beat frequencies” as regular sperm. The problem was that the part of the sperm that connects the head to the tail was too rigid. That made the entire sperm cell too inflexible to move with enough force to penetrate the [membrane that surrounds the egg].

When researchers gave the immunosuppressants to regular mice, they found they had no effect on mature sperm cells, but worked better on developing sperm.

Regular male mice that got either CsA or FK506 for two weeks became infertile, because the middle part of their sperm was rigid. Further tests showed that it took only four days for FK506 to render the mice infertile, and five days for CsA to do the same.

When the mice stopped taking the drugs, their fertility returned after one week.

The research appears in Science. [sciencemag.org]

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