Unhealthy eating habits and high blood pressure are a prevalent problem in society today. For example, high dietary salt (sodium) intake is linked with high blood pressure (hypertension). However, it is not well understood how high levels of salt in our body can translate to high blood pressure. Researchers attempted to investigate mechanisms in the brain that may provide more insight into how elevated salt in our diet can affect our blood pressure. Researchers found prior research which suggested that higher levels of a hormone (bodily regulatory chemicals) called vasopressin were capable of increasing blood pressure. Vasopressin is a hormone responsible for the regulation of how much urine we expel, how much water we retain and how much salt is in our bodies. Moreover, vasopressin has very potent vasoconstriction (narrowing of blood vessels) properties. A narrowing of the blood vessel increases blood pressure. Thus, altering a hormone responsible for salt regulation and blood pressure can have significant effects; this provided incentive to examine any alterations in vasopressin due to diet.
A number of processes occur in our body to maintain a healthy blood pressure. For instance, if we eat a salty meal, the level of sodium in our blood stream increases. To compensate for the increase in salt in our blood we receive a load of vasopressin from magnocellular neurosecretory cells (MNC). These cells are neuroendocrine cells in the hypothalamus; here, they release hormones which regulate crucial functions like body temperature, sex drive, thirst, hunger, arousal, etc. As stated above, an increase of vasopressin can lead to an increase in high blood pressure. Fortunately, the increase of vasopressin from the salty meal is limited or else our heart would explode. Located on the walls of our blood vessels contain baroreceptors (BR). These receptors sense any change in blood pressure and send a message back to the hypothalamus saying, “okay, that’s enough, slow the release of vasopressin because the blood pressure is getting too high”. The MNCs receive this message from BR and release an inhibitory output called GABA. GABA is a chemical in our brain largely responsible to control brain activity and excitation. GABA’s main function is to inhibit connections in our brain or slow them down. Therefore, a message is sent back to the MNCs to turn off the tap that pours out vasopressin. This step by step mechanism is what occurs in a normal scenario to keep us healthy; however, researchers found that chronic high salt intake may change this process causing problems.
Results discovered that Chloride (Cl-) ion channels located on GABA receptors tend to collapse or become inactive given a repeated sodium environment. Chloride channels are responsible for whether the GABA brain cell translates information (fires) onward or not. In addition, high salt levels have been shown to stimulate an increase of proteins in our brain which causes Cl- damage. Researchers found if you impair this channel it leads to less GABA release and BR signalling to inhibit MNCs from releasing additional vasopressin. Interestingly, the reduction in GABA cell firings, allows more stimulation of vasopressin neurons in the MNC. In turn, less GABA release means the message to turn off vasopressin release was absent. This causes an elevation in blood pressure.
To clarify, mice that were given high amounts of salt showed less inhibiting output when compared to mice who did not receive high intakes of salt. In other words, the message saying “okay, that’s enough, slow the release of vasopressin because the blood pressure is getting too high” was disrupted in salt loaded mice. This alteration causes the inhibition of an inhibitory output, thus allowing excitation of vasopressin neurons. Explaining this reaction is synonymous with multiplying two negative numbers and receiving a positive outcome.
To conclude, high salt intake is normally managed well by the production of GABA on vasopressin releasing cells. Researchers discovered that this process becomes altered given chronic salty environments such as poor diet. The high prevalence of salt stimulates brain proteins which can destroy chloride ion channels. The inactive chloride channels cause less GABA release to stop vasopressin. More vasopressin leads to elevated blood pressure. These findings are very important because it shows the significant impact our diet has on our brain and more importantly our overall health.
Choe, Katrina Y,. Han, Su Y,.Cunningham, J Thomas, and Bourque, Charles W. (2015). High Salt Intake Increases Blood Pressure via BDNF-Mediated Downregulation of KCC2 and Impaired Baroreflex Inhibition of Vasopressin Neurons. Cell: Neuron, Vol 85, 549-560.