91色情片

A MOTHER鈥橲 diet in the first few days after conception could determine the
health of her unborn child for life, say British researchers.

An embryo sets its growth rate according to its environment鈥攁 process
known as programming. If a mother is malnourished, for instance, the embryo
grows more slowly, which leads to low birthweight. Babies that are born small
are more susceptible to diabetes, high blood pressure and strokes in later
life.

Now a team led by Tom Fleming of the University of Southampton suggests that
programming may take place in the four or five days following fertilisation,
before the embryo even implants in the womb.

After allowing female rats to mate, the researchers fed them a low-protein
diet for the following four and a quarter days鈥攖he window between
fertilisation and implantation. The rats ate a normal diet for the rest of their
pregnancies.

The female pups of these mothers were born small, but then put on an
unusually fast growth spurt before settling down to a normal weight. Males were
born normal-sized, but had an abnormal pattern of growth. They also had high
blood pressure, shrunken livers and enlarged kidneys.

It鈥檚 not clear why the defects occur. When the team took early embryos from
mother rats on the restricted diet and counted their cells, they found that
these embryos had fewer cells than expected because they had gone through fewer
divisions.

One possible explanation is that an embryo鈥檚 nutritional environment affects
how its genes are expressed. Fleming says the findings could explain the
abnormal development of sheep and cattle grown from cloned
embryos鈥攕o-called 鈥渓arge offspring鈥� or 鈥渄opey calf鈥� syndrome
(New Scientist, 23 January 1999, p 15).

Ian Wilmut of the Roslin Institute near Edinburgh agrees that is a
possibility and says that human embryos could also be sensitive to this effect.
鈥淎ll of these observations should make people who are carrying out IVF, and who
are thinking of changing their protocols, think more cautiously,鈥� he says.