The study,
which scrutinized the details of rabbit reproduction, found
that rabbit sperm wriggle toward warmth. But a researcher
in human reproduction who was not involved in the research
cautioned that the study's results might not apply to human
beings.
Rabbit reproductive anatomy is somewhat different
from that of human beings, Dr. Carmen Williams, an assistant
professor at the Center for Research on Reproduction and
Women's Health at the University of Pennsylvania, said in
an interview with Reuters Health.
Researchers have wondered
for a long time how it is that sperm find their way from
the uterus up the fallopian tubes to the egg, according to
the study's lead author, Dr. Michael Eisenbach.
" One
of the puzzles in mammalian fertilization is how sperm
cells navigate within the female genital tract toward the
egg,"
Eisenbach
and his colleagues note in their report. The authors point
out that the egg sends out a chemical message, but that can
only be sensed when the sperm are relatively close to the
egg.
" Another potential cue for sperm guidance," according
to the report, "is the ovulation-dependent temperature
difference within the female genital tract." In the
new study, Eisenbach and his colleagues measured temperature
at several spots in the rabbits' reproductive organs just
after the animals ovulated. They found that the temperature
at the site where eggs would normally be fertilized is
approximately 2 degrees Celsius warmer than other spots
along the path
that sperm must traverse to meet up with an egg.
To check
to see if this was the cue being used by rabbit sperm, the
researchers ran a test in the lab. They designed a device
that had two dishes connected by a narrow bridge. In one
part of the experiment, the researchers kept the temperature
in the dishes the same. For comparison, in a second experiment,
the researchers made the temperature in one dish 2 degrees
Celsius warmer than the other.
Eisenbach and his colleagues
found that the sperm were more likely to move from dish to
dish if they were put in the cooler dish and allowed to navigate
their way to the warmer one. While the results are interesting,
they may not apply to human sperm, according to Williams,
the University of Pennsylvania expert.
She pointed out that
studies in pigs have shown that there is no temperature difference
after ovulation. No one knows whether such a temperature
difference exists in the human reproductive system after
ovulation, Williams said.
Reuters
Health,· SOURCE: Nature Medicine 2003;9.
Infertility