The sin of gluttony is born in the intestines
Pyotr Smirnov, "Newspaper.Ru»The problem of overeating and obesity does not give rest to scientists.
Perhaps, for many of them, it has already become a "matter of honor", because the fundamental works published monthly have not brought relief to the army of the obese and simply dissatisfied with their figure, which is growing by the minute. In the latest issue of the journal Cell Metabolism, several works devoted to this issue were published at once. According to the authors, all of them can have practical application.
Saima Malik and her colleagues from McGill University in Montreal, Canada proved that the hormone ghrelin is involved in the preparation of the nervous system for the perception of food images, and even detailed the brain regions responsible for these processes (Saima Malik et al., Ghrelin Modulates Brain Activity in Areas that Control Appetitive Behavior // Cell Metabolism, Vol 7, 400-409, 07 May 2008).
Ghrelin is synthesized by the intestinal wall and released into the blood, from where it enters the brain. In experiments on various animals, it has been repeatedly shown that it causes hunger and stimulates the absorption of food. The same effect was demonstrated on people who were not restricted in choosing food from the buffet.
However, the mechanism of action of this hormone remained very poorly researched, and this prevented the creation of drugs for those who want to lose weight, and vice versa – for those who need extra kilograms.
Malik proved that ghrelin is a kind of gluttony hormone: it is responsible for overeating, acting within the framework of a system aimed at satisfying desires.
Scientists conditionally divided all cases of food intake into 2 groups: the first is homeostatic, aimed at maintaining the physiological needs of the body, the second is hedonistic – for pleasure. Of course, it is impossible to divide absolutely all meals into these two categories – hunger can be satisfied with very tasty food. However, Malik believes that it is the second group that makes the main contribution to excess calories, first consumed and then stored by our body in the form of fat. In this "hedonic" system, visual and olfactory signals play a major role, and, as scientists have shown, hormones multiply their effect.
The scientists evaluated the brain's work using the already classic method of functional magnetic resonance imaging, which evaluates the activity of various brain regions by the intensity of blood flow in them. The demonstration of "appetizing pictures" together with the introduction of ghrelin caused significantly greater activity of neurons not only in the visual region, but also in the "pleasure region" – the so-called mesolimbic system.
However, the most important mechanism of ghrelin action could not be identified again. Probably, it simply does not exist: receptors for this hormone are located not only in the dopaminergic system responsible for receiving pleasure, but also in other parts of the brain – the arc nucleus and the amygdala. In addition, its administration increases the concentration of other hormones – prolactin, cortisol and growth hormone, which independently act on metabolism.
Due to the specific location of ghrelin receptors in neurons - they are more common on the presynaptic membrane – scientists have concluded that it does not play the role of an "activator", but a modulator, that is, it amplifies other signals, but does not independently lead to the formation of urges to refresh.
So if problems with appetite are caused by disturbances in the work of the ghrelin system, it is quite simple to cope with them: you just need not to look at the food.
Anthony Means and his colleagues from the British Durham and Australian Melbourne went a little further and proposed a drug-based method to block one of the ways of action of the "gluttony hormone". (Kristin A. Anderson et al., Hypothalamic CaMKK2 Contributes to the Regulation of Energy Balance // Cell Metabolism, Vol 7, 377-388, 07 May 2008.) If we consider that pills have always been more popular than appeals to willpower, then their work will probably find more responses in the hearts of those interested in the problem of weight loss.
Scientists have found that part of the effect of ghrelin and leptin – another "appetite hormone" secreted, however, not by the intestines, but by fat cells – is mediated in the brain through the enzyme CaMKK2. The full picture turned out to be something like this: an empty intestine secretes ghrelin, which is released into the blood and enters the hypothalamus of the brain. There ghrelin activates CaMKK2, which, in turn, leads to an increase in the formation of neuropeptide Y, which directly stimulates appetite.
To test the theory, it was enough to inhibit the work of CaMKK2 and observe the effect.
The results did not upset the scientists: during 6 days of therapy, the mice of the experimental group ate much less food and as a result not only did not gain, but even lost weight compared to the control group.
Moreover, mice whose CaMKK2 formation was turned off genetically even turned out to be resistant to the development of type 2 diabetes.
If overeating and subsequent obesity usually makes the body insensitive to insulin, then this did not happen in CaMKK2-deficient mice even after six months of a super-fat diet.
Inhibition of CaMKK2 in the brain even slowed down the deposition of fat droplets in the liver and skeletal muscles, characteristic of diabetics. And although scientists could not explain the mechanism of this phenomenon, it is it that can help in the fight against severe complications of overeating.
Since the epidemic of obesity is not to blame for the unsatisfied needs of the body, namely appetite, the clarification of the physiological mechanisms of the latter should sooner or later lead to the creation of drugs for excess weight. Until they are created, it is better not to look at extra food, and even better – to lead an active lifestyle in which the body can put all the calories consumed into action.
Portal "Eternal youth" http://vechnayamolodost.ru08.05.2008