Edited by Marino Macchio
Why do we drink little at night?
Water? No thanks. The interaction of three specific groups of nerve cells, present in the hypothalamus, prevents the dehydration of our body during sleep.
The answer comes from the University: "McGill University Health Center" in Montreal. Recently, some scientists have described the changes our body has made to prevent dehydration during sleep.
There is an antidiuretic hormone (vasopressin) that controls fluid retention in our body. This hormone is secreted by the cells of the hypothalamus, which in turn are activated by a group of nerve cells called osmosensitive cells that can detect concentrations of water in the blood. In conditions of dehydration, the electrical activity of these cells is amplified so as to stimulate the production of vasopressin by the hypothalamus. Thanks to the formation of more concentrated urine, vasopressin determines the recovery of body fluids. Thus, there is a proportional relationship between osmolarity, or the concentration of solutes in the plasma, and vasopressin secretion. In the hypothalamus, besides the osmosensitive cells, there is also a suprachiasmatic nucleus; it is a group of cells that regulates the daily rhythms of our body. By studying the connection between these three cell groups, two Canadian scientists Eric Trudel and Charles Borque discovered that during sleep the connection between osmosensitive cells and those that secrete vasopressin is strengthened. In this way even the slightest water deficiency can cause a huge release of the hormone. Furthermore, the activity of the suprachiasmatic nucleus is also reduced. Subsequently the two researchers of the McGill University Health Center artificially stimulated the activity of the suprachiasmatic nucleus and observed a consequent weakening of the connection between osmosensitive cells and cells that secrete vasopressin. It follows, and the results suggest it, that the suprachiasmatic nucleus acts as a brake, inhibiting the secretion of vasopressin by the hypothalamus. During the day it is sufficient to drink some liquid to remedy the low concentration of water; on the contrary, when we sleep, the activity of the suprachiasmatic nucleus is reduced, thus allowing a greater release of vasopressin than that recorded during the day. As a consequence there is a greater retention of liquids. The study of these two scientists was published in "Nature Neuroscience".
