Hypertension, or high blood pressure, tops the list of chronic health conditions. It affects about one-third of the world's population, including nearly 44 percent of German citizens. If the pressure in the blood vessels is too high, the body's organs – mainly the brain, the heart, and the blood vessels – suffer as a result. The consequences go beyond an increased risk of developing serious cardiovascular diseases like strokes or heart attacks. In a healthy body, the heart, brain, and blood vessels also play a key role in regulating blood pressure. If they are damaged by persistently high blood pressure, this regulatory ability is lost – creating a vicious circle.
To lower blood pressure, patients should make changes to their lifestyle, such as eating a well-balanced, low-salt diet, exercising regularly, and stopping smoking. Some drugs, like beta blockers and ACE inhibitors, can also help: "Conventional medications can lower blood pressure, but they fail to achieve the desired protective effect on the organs in a large portion of patients," says Dr. Suphansa Sawamiphak, who heads the Cardiovascular-Hematopoietic Interaction Lab at the Max Delbrück Center. This is particularly evident, she says, in the brain, where hypertension causes tiny blood vessels to become permeable, or eventually die off, adding: "This means there must be other control centers in the overall process that we can't target with conventional therapeutic agents."
Researchers have known for some time that components of the immune system may play a role here. Inflammatory responses in the body contribute to high blood pressure and have harmful effects on organs, but it is not yet known exactly how this occurs.
Immune cells damage blood vessels in the zebrafish brain
So Sawamiphak and her team at the Max Delbrück Center and collaborators working in Italy and Switzerland, studied larval zebrafish to shed more light on the underlying biological mechanisms. "This is an excellent model system for investigating many questions, since it is easy to manipulate the organisms by changing the environment," explains the biologist, adding: "Because young zebrafish are transparent, we can literally see how this affects the living fish."
To analyze the role of the immune system in hypertension, the research team raised zebrafish larvae in water with low ion concentration. This creates an ion imbalance in their bodies that is comparable to excessive salt consumption in humans, thus leading to high blood pressure. The team then examined how this affects the blood vessels in the brain.
