?Sperm may hold the secret to new methods of birth control. Rather than focusing on preventing release of an egg from the ovary or on barrier techniques that keep the egg from meeting the sperm, new birth control techniques may prevent sperm from becoming activated so that they can move through the female reproductive tract. Preventing sperm from entering the egg once they reach it may also form the basis of future birth control methods.
One promising idea to prevent fertilization centers on the hormone progesterone. Scientists from the University of California, San Francisco have discovered that sperm only become mobile and capable of fertilizing an egg when exposed to the hormone progesterone. After ovulation, the leftover remnant of the follicle that originally contained the egg, called the corpus luteum, produces progesterone. Progesterone helps prepare the uterine lining for implantation.
But progesterone found in the woman's reproductive tract may also prepare sperm for fertilizing an egg by activating gated channels on sperm formed by proteins called CatSpers. When exposure to progesterone open the channels, calcium ions can enter the sperm. Calcium ions then activate the biochemical reactions that start moving sperm toward their goal--the egg.
In other cells in the body, progesterone has a much slower effect, taking hours to switch on genes. In sperm, progesterone's effects occur much more quickly. Blocking the CatSper channels through ingestion of medications with this effect may cause infertility, Dr. Yuriy Kirichok of UCSF states. This effect may occur in some people taking certain beta-channel blockers to treat heart disease.
Researchers from the Imperial College of London are studying the effects a of sugar molecule called SLeX, which allows sperm to stick to the egg so the sperm can penetrate the egg's outer layer. Finding ways to block this action may also have practical applications for new types of birth control.
