Under pressure

26 March 2009

Putting on weight generally leads to a rise in blood pressure. Now, a study of a particular group of obese individuals has shown that this association is controlled by the melanocortin system in the brain.

Dr Sadaf Farooqi and colleagues at the University of Cambridge found that people with an inherited form of obesity, caused by mutations in the MC4R gene, have lower blood pressure than other obese people.

Conversely, when the researchers stimulated the melanocortin 4 receptors (which are produced by the MC4R gene) of obese people without MC4R mutations, blood pressure increased. The melanocortin 4 receptor is found in the brain and is involved in the control of weight and appetite; mutations in the MC4R gene are present in up to 6 per cent of obese individuals and lead to problems controlling weight.

“We’ve now shown that the link between gaining weight and increased blood pressure is through the melanocortin system,” says Dr Farooqi. “What happens in the brain is likely to be key to understanding obesity and its associated complications.”

Many obese people are susceptible to diabetes, and raised insulin levels had previously been associated with raised blood pressure. However, this study found that insulin levels did not explain the association between blood pressure and obesity.

Reference

Greenfield JR et al. Modulation of blood pressure by central melanocortinergic pathways. N Engl J Med 2009;360(1):44-52.