Cocaine may piggyback on sperm into egg.

Tiny specks of cocaine can attach to specific sites on human sperm, according to a newly reported laboratory experiment. The finding suggests that the dangerous drug could piggback its way into a new embryo by hitching a ride on the fertilizing sperm, perhaps harming the embryo's development.

"This is the first time I know of that a substance that causes abnormalities in offspring has been shown to bind to sperm," says the study's leader, Ricardo A. Yazigi of Temple University School of Medicine in Philadelphia. The new data might also explain some animal and human studies showing developmental or neurological problems among the offspring of males exposed to drugs, alcohol or other environmental toxicants, such as lead, he adds.

Yazigi, who conducted the experiment while at Washington University School of Medicine in St. Louis, studied samples from non-drug-using donors to the university's sperm bank. He and his colleagues added increasingly larger amounts of radioactively labeled cocaine to the samples, and filtered them onto disks that the researchers could wash and analyze using a type of Geiger counter.

The samples initially became more and more radioactive as the researchers added in more cocaine. But after the cocaine reached a certain level, the radioactivity of the samples stabilized. This suggests that each sperm cell has a finite number of specific sites for binding cocaine, Yazigi says. His team also found that samples treated with a mixture of labeled and unlabeled cocaine were less radioactive than those treated with only labeled cocaine, further indicating that both compounds compete for a limited number of sites.

Cocaine levels normally found in the semen of cocaine-abusers did not kill the sampled sperm cells or slow their movement, the researchers report in the Oct. 9 JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION.

Yazigi acknowledges that no human studies have linked cocaine use by fathers with birth defects or developmental problems, although some have found that newborns whose fathers drank excessively weighed less a birth than did infants of men who did not consume alcohol. But he notes that other researchers have shown that some offspring of male rats given cocaine cannot perform basic tasks, such as successfully navigating a maze to find food.

Yazigi speculates that no one has observed the effects of paternal cocaine abuse in humans because it may cause "very subtle defects," such as learning disabilities and memory problems. In contrast, cocaine abuse by the mother may cause more severe disabilities, such as low birthweight, because the unborn child is exposed to the drug throughout pregnancy (SN: 9/7/91, p.152).

Yazigi's team made "a very interesting finding," says behavioral neuroscientist David F. Wozniak at Washington University. "People have been sort of skeptical of the effects of paternal drug use," he says, "but the evidence is mounting that there should be further studies."