According to a 2003 study by German and American scientists, a component of the Lily of the Valley scent known as Bourgeonal
alters the calcium balance of human sperm and attracts the sperm. The
“Lily of the Valley phenomenon”—also the title of a book about
smelling—was born as a result of this discovery that sperm act as
swimming olfactory cells which follow a “scent trail” laid by the egg.
However, a detailed explanation for the Lily of the Valley phenomenon
remained elusive as neither Bourgeonal
nor other scents could be identified in the female sex organ.
Scientists from the caesar research centre in Bonn, an Institute of the
Max Planck Society, have now discovered that sperm do not function like
olfactory cells—a finding that casts doubt on the assumption that scents
play a role in fertilisation.
have a long journey ahead in their quest for the egg cell or ovum, and
just a few of the million sperm reach their destination. The ovum
supports the sperm in their quest by transmitting “chemical signposts”,
known as attractants. Researchers first discovered this ingenious system
in sea urchins and found out that attractants control the swimming
movement of the sperm by altering their calcium balance. The attraction
of the sperm to the egg is referred to as “chemotaxis”. Unlike in sea
urchins, which release sperm and eggs into the seawater, the conditions
in the narrow human fallopian tube are very difficult to emulate in
to another model, the female sex hormone progesterone—which is formed
by cumulus cells near the ovum—attracts the sperm. CatSper (cation channels of sperm)
ion channels are responsible for the effect of the progesterone. The
CatSper channels, which are found only in sperm, play an indispensable
role in reproduction: men who carry a gene defect for CatSper are
infertile. In a 2011 study, which was seen as a sensational
breakthrough, scientists from the caesar
research centre succeeded in showing that progesterone opens the
CatSper channels directly and calcium flows through the channels into
the sperm cell.
their current study, the Bonn researchers demonstrate, in cooperation
with scientists from the Forschungszentrum Jülich, that the Lily of the
Valley scent imitates the effect of progesterone on sperm: Bourgeonal
opens the CatSper channels directly—that is without deviation via
olfactory receptors and complex biochemical signalling pathways as found
in olfactory cells. However, the scents only work at concentrations
over 1,000 times higher than progesterone. Therefore, scents only work
if overdosed. The “Lily of the Valley phenomenon” is a laboratory
artefact: sperm do not have an olfactory signalling pathway.
findings provide important new insights for the sperm researchers. Why
are the CatSper channels so unselective, and even react to menthol if
the concentration is high enough? This “promiscuous” characteristic is
probably crucial for reproduction. Using different “chemical signposts”,
the sperm must repeatedly reassure themselves on their difficult
journey to the ovum that they are still on the right track. With the
help of the CatSper channels as versatile and highly perceptive sensors,
sperm can “read” the chemical milieu in the fallopian tube and find the
ovum in this way. The Bonn-based researchers are now concentrating on
identifying other attractants in the fallopian tube in addition to
progesterone. One thing is clear at this stage: it is very unlikely that
these are scents.
new insights are also significant in medical terms. If the scientists
succeed in disrupting the effect of female factors on the CatSper
channels, it could lead to the development of an innovative
contraceptive: the pill for men. However, such a development is still a
very long way off.