Female rats that are exposed to PCBs in the womb are reluctant to mate as adults. This raises the possibility that similar chemical contaminants can cause low sex drives in women.
PCBs are a group of stable chemical additives once widely used in the production of pesticides, lubricants and plastics. Their use was banned in many countries after it became clear that some PCBs mimic hormones. But there is strong evidence that PCBs are still widespread in the environment. The food crisis that struck Belgium in June was partly caused by PCB contamination of poultry and dairy produce.
Zoologists Yu-Wen Chung and Lynwood Clemens of Michigan State University in East Lansing tested the effects on rats of two commercial PCBs, Aroclor 1221 and 1254. A1221 is known to mimic oestrogen and A1254 is thought to reduce dopamine levels in the brain.
They injected 40 pregnant rats with either pure sesame oil or a mixture of oil and the PCBs, first on day 14 of gestation, then on the day of the pup's birth and again 10 days later while the pups were suckling. Two months later, Chung and Clemens looked at the sexual behaviour of the female offspring.
"Female rats normally adopt a stereotypical posture when copulating, raising their back and hindquarters to help the male mate," says Chung. But rats exposed to A1221 did not indulge in this sexual come-on nearly as often as rats exposed to A1254 or those that had not been exposed to either PCB.
A second test paired female and large male rats in a cage with two compartments. If the females didn't feel like mating, they could escape into the second chamber through a hole too small for the larger frustrated males to follow.
It turned out that females exposed to A1221 left the males more often and took longer to return after each copulation attempt by the males (Bulletin of Environmental Contamination and Toxicology, vol 62, p 664). "We found that females stayed away from the males for longer," says Chung.
Chung suspects that during a crucial phase of development, the oestrogen-mimicking A1221 "defeminises" the rat fetuses. She says that women's sex drives could also be affected by PCB exposure in the womb. "It's possible," she says. "Pregnancy is the critical period."
A study presented in June to the Endocrine Society in San Diego found detectable levels of PCBs in the amniotic fluid of pregnant women in Los Angeles. No one yet knows whether these levels have any influence on fetal development.
"It's hard to judge whether these doses really mimic what humans are exposed to," adds Paul Stewart, a psychologist who is researching the effects of PCBs on rats' behaviour at the State University of New York in Oswego. He points out that PCBs are normally found in humans at much lower levels than those used in Chung's experiments. He also questions whether PCBs were lowering the rats' overall levels of activity rather than just their sex drive.
Author: Matt Walker
New Scientist issue 7th August 99
PLEASE MENTION NEW SCIENTIST IF YOU USE THIS ARTICLE - THANKYOU