Endocrine Abstracts

In most countries in the world, an increasing number of people suffer from the metabolic syndrome, normally defined as obesity, high blood sugar, high blood fats and high blood pressure. The new understanding that adult humans possess active brown adipose tissue has led to hope that a (re)activation of this tissue (browning) may be helpful in ameliorating the metabolic syndrome. Brown adipose tissue has the ability to combust (extra) food intake in a direct way, due to the unique presence in this tissue of the UnCoupling-Protein-1 (UCP1). Thus, if activated – normally through the release of norepinephrine from the sympathetic nervous system – the tissue will burn away food energy, leaving only heat, water and CO₂. Thus, it protects against the development of obesity. When the tissue is chronically activated, the stored lipid reserves in the tissue will not suffice for continued heat production, and the tissue will take up large amounts of sugar from the circulation, through a unique adrenergic mechanism, leading to lowering of blood sugar levels through a large glucose disposal. It will similarly activate the synthesis of lipoprotein lipase, leading in parallel to a large increase in lipid uptake from the circulation, diminishing blood triglyceride levels. During prolonged stimulation, the constant burning of food in the tissue will lead to the mobilization of the body’s lipid reserves (the white adipose tissue) that will be broken down and the released fatty acids will be transported to the brown adipose tissue for combustion, i.e. the brown adipose tissue is slimming (and all these effects together will likely also result in lowering of blood pressure). Although the acute activity of the tissue is determined by norepinephrine, it would seem that sex hormones (positively) and glucocorticoids (negatively) can affect the tissue. The tendency to a worsening of the metabolic syndrome with age could then partly be explained by a diminished sex hormone stimulation and an unaltered but increasingly dominating negative effect of glucocorticoids, together leading to brown adipose tissue inactivity, and thus to obesity.