Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: MONDAY, April 1, 1991 TAG: 9104010211
SECTION: NATIONAL/INTERNATIONAL PAGE: A-6 EDITION: EVENING
SOURCE: The Washington Post
DATELINE: LENGTH: Medium
Researchers in the United States and Israel are to report today that a still-unidentified constituent in the fluid that surrounds a mature egg signals the sperm, and that the presence of this attractant may be crucial for fertility.
The scientists say that if they can learn exactly what the attractant is, they might be able to help women who are infertile for lack of it. Also, for birth-control purposes, it might be possible to produce an antibody to counteract the attractant.
In the laboratory, a tiny drop of the mysterious fluid acts like a powerful beacon, according to the scientists. The sperm turn their heads and start swimming vigorously toward the fluid, which is secreted by the follicle that produces an egg during ovulation.
The studies, published in today's issue of the Proceedings of the National Academy of Sciences, are the first to show that immediately after ovulation, eggs can communicate with sperm.
While such communication has long been suspected, this is the first time researchers have identified the medium that shuttles messages between the egg and sperm as they move toward their rendezvous in the Fallopian tube.
"There is a lot more work to be done. But this is the first example that in humans, the egg and sperm are really exchanging information before fertilization," said David Garbers of the Howard Hughes Medical Institute at the University of Texas in Dallas, who performed the studies with Michael Eisenbach and colleagues at the Weizmann Institute in Israel.
"It is potentially a very exciting finding," said Gregory Kopf, a research scientist at the University of Pennsylvania School of Medicine. "This may be the first step in understanding the communication that occurs between egg and sperm prior to fertilization."
The research may help solve one of the big puzzles of human and animal reproduction: Why do males produce and deliver so many sperm, when only a few arrive at the site of fertilization? In other words, why are many called, but so few allowed into the arena where all the action takes place?
A healthy male ejaculation delivers, on average, about 280 million spermatozoa to a female. But scientists have long been perplexed that out of millions of sperm, only a few hundred spermatozoa reach the area of interest, a region called the ampulla, which is in the upstream stretch of the Fallopian tube.
Researchers such as James Overstreet of the University of California at Davis have found that sperm may collect in reservoirs in females, including humans. In these holding areas, the sperm may sit relatively immobile for hours. Garbers and his colleagues believe that the follicular fluid may act as a stimulus to get the resting sperm swimming.
Moreover, some researchers speculate the attractant may communicate selectively - attracting the highly mobile and vigorous sperm, but not the older or younger sperm, which would have more trouble fertilizing the egg.
In the experiments to be reported today, the scientists worked with women in Israel who were undergoing in vitro fertilization. In the procedure, a physician collected eggs and follicular fluid from the woman. The eggs were fertilized and returned to the woman, but the follicular fluids were used for the experiments.
In the laboratory studies, the scientists observed that a minute drop of follicular fluid would attract sperm, which would swim across a permeable membrane to reach the fluid. The researchers also tracked sperm, which swim at incredible rates, as they oriented toward the follicular fluid and swam to it.
by CNB