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Saturday, 1 February, 2003, 01:20 GMT
Sperm act like guided missiles
Sperm are attracted by heat
Sperm have a lot in common with military missiles, a study suggests.

Researchers in Israel have found that sperm use heat sensors to find their target, namely the female egg.

They act in much the same way as guided missiles, which use heat to pinpoint a plane's engine.

The sperm are guided by temperature

Prof Michael Eisenbach
Scientists believe the finding could help them to improve IVF treatments for couples who have difficulty conceiving.

Professor Michael Eisenbach and colleagues at the Weizmann Institute based their findings on laboratory tests.

Lab tests

They constructed a mock reproductive shaft comprising a sperm storage area, a fertilisation area and a tube in between.

After passing the uterus, sperm cells enter the fallopian tubes. Once inside a tube, they attach themselves to the tube's wall and pause for "storage", during which they go through a maturation process. This prepares them for penetrating the egg.

A sperm cell that has completed this maturation detaches itself from the wall and leaves the storage site.

If ovulation has taken place and an egg is released, the mature sperm embarks on a long journey through the tube to the site of potential fertilisation.

As part of the study, the storage area was heated to a temperature of 37 degrees Celsius while the fertilisation area was slightly warmer at 39 degrees.

They tested the behaviour of rabbit sperm in this system and found that the sperm were sensitive to heat and move quickly to the warmer fertilisation area.

When the scientists gradually reduced the difference in temperature, they found that even a half degree difference was enough to attract the sperm.

Their study also revealed that only mature sperm - those most likely to penetrate and fertilise the egg - are heat sensitive.

"Apparently, the sperm are guided by temperature when they travel through most of the fallopian tube and navigate by tuning into the egg's chemical call when they get close to the fertilisation site."

The findings were replicated in a further study carried out in collaboration with researchers at Bar-llan University using human sperm.

See also:

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