快猫短视频

TOXIC chemicals in exhaust fumes and cigarette smoke can bring on the
menopause. Research published this week shows that polycyclic aromatic
hydrocarbons, or PAHs, trigger the death of egg cells in women鈥檚 ovaries.

Tens of thousands of tonnes of these PAHs, which also cause cancer, are
released into the air each year
(快猫短视频, 10 April 1999, p 14).
鈥淭he fact that these chemicals, which are ubiquitous in the environment, have
these effects is worrying,鈥� says David Ozonoff of the Department of
Environmental Health at Boston University in Massachusetts.

Smoking can trigger an early menopause, and researchers have long pointed the
finger of suspicion at PAHs in cigarette smoke. To see whether the chemicals
really do affect fertility, Jonathan Tilly and his colleagues at the
Massachusetts General Hospital in Boston exposed mouse ovaries growing in
culture to one PAH compound. They found that the eggs began to die off after a
few days.

The compound binds to a specific receptor on the outside of ovarian cells,
the team found. This sends a signal that activates a gene called Bax,
the key gene controlling ovarian cell suicide. Bax triggers a cascade
of events that causes the cells to die.

Would the compound have the same effect on human tissue? Tilly鈥檚 team grafted
human ovarian tissue under the skin of mice, and gave the rodents an injection
of the PAH. Within a few days, egg cells in the human tissue had begun to switch
on Bax and die. According to Tilly, the amount of PAH injected into the
mice was equivalent to what a person would be exposed to smoking a pack of
cigarettes a day for a few years.

The risk to non-smokers isn鈥檛 clear. Tilly says that it is hard to determine
an average person鈥檚 exposure to PAHs because the concentrations of the chemicals
in the environment vary from place to place. Workers exposed to these compounds
on a daily basis鈥攊n road and roof tarring, coal burning and coke
manufacturing, for instance鈥攔un the biggest risk, he says.

However, it may be possible to protect women at risk. Tilly is now trying to
find ways to prevent egg loss by preventing the receptors from binding to
PAHs.

Until now, the effect of PAHs on female fertility has been hard to assess
because we can鈥檛 be sure that test results from mice apply to humans. But Tilly
says that his mice with human ovarian tissue should make it easier to test how
toxic chemicals and even experimental drugs affect female reproduction.