London: In a remarkable research
discovery, clues about how the human gut helps regulate our
appetite have come from a most unusual source fruit fly
faeces.
Scientists at the University of Cambridge are using
the fruit fly to help understand aspects of human metabolism,
including why pregnant women suffer from bloating and
constipation, and even the link between a low calorie diet and
longevity.
Although scientists have known for some time that
there are as many as 500 million nerve cells in our gut, the
sheer complexity that this presents means that little is known
about the different types of nerve cell and their functions, a
university release said.
Researchers led by Dr Irene Miguel-Aliaga, with
funding from the Wellcome Trust and the Biotechnology and
Biological Sciences Research Council, have used the fruit fly,
Drosophila melanogaster, to investigate the function of these
intestinal neurons.
The fly has simpler versions of our nervous and
digestive systems, which lend it to genetic manipulation.
Their findings are published today in `Cell
Metabolism` journal.
"We reasoned that what comes out of the gut may be
able to tell us about what is going on inside," explains Dr
Miguel-Aliaga.
"So, we devised a method to extract information about
several metabolic features from the flies` faecal deposits -
which are actually rather pretty and don`t smell bad. Then we
turned specific neurons on and off and examined what came
out."
Dr Miguel-Aliaga and colleagues found that these
intestinal neurons have very important and specialised
functions, such as regulating appetite or adjusting intestinal
water balance during reproduction.
Female flies in their reproductive stage get
constipated - their gut emptying rate is reduced even though
they are eating more food; at the same time, they retain more
water and the contents of their intestines become more
concentrated. The researchers showed that these intestinal changes
are triggered by the sex peptide, a hormone that males inject
into the female during copulation, which activates of a small
group of gut neurons.
This shares the same function as the sex hormones
found in humans, such as progesterone, oxytocin and oestrogen.
"Humans and fruit flies reproduce in very different
ways, yet the associated symptoms of constipation and bloating
and their cause - a reproductive hormone - are the same,"
explains Dr Miguel-Aliaga.
"This suggests that this mechanism has been conserved
through evolution. These intestinal changes may provide a
benefit at a time of high nutritional demand by maximising
nutrient absorption."
The research also provides tantalising clues about the
link between calorie intake and longevity.
Intestinal changes, which help maximise nutrient
absorption, would likely be active all the time, as they would
provide a selective advantage when food is scarce.
However, in flies - and possibly in humans - this may
come at a cost: a shorter lifespan.
It has been known for some time that when female flies
mate and receive the sex peptide, this shortens their
lifespan; however, this is not caused entirely by their
increased food intake or because they are laying many eggs,
the two most obvious effects of this sex peptide.
The explanation, argue the researchers, may lie in the
intestinal changes triggered by the sex peptide that lead to
constipation and water retention.
"A mechanism that maximises nutrient absorption by
slowing the passage of food through the intestine is fine when
food is scarce or during reproduction," says Dr Miguel-Aliaga,
"but when we are eating a normal diet, constipation may lead
to the build up of waste products produced during internal
metabolism."
Similarly, it could lead to changes in the composition
of the gut bacteria, which are essential to regulating
metabolism.
"Our research suggests that in addition to paying
attention to what we eat, which has been the focus of
longevity research, we may also have to consider what our body
does with the food and what goes on in our guts," said Dr
Miguel-Aliaga.
PTI
