The renin-angiotensin-aldosterone system (RAAS)

The renin-angiotensin-aldosterone system (RAAS) is a signaling pathway responsible for regulating the body's blood pressure.

Stimulated by low blood pressure or certain nerve impulses (e.g. in stressful situations), the kidneys release an enzyme called renin. This triggers a signal transduction pathway: renin splits the protein angiotensinogen, producing angiotensin I. This is converted by another enzyme, the angiotensin-converting enzyme (ACE), into angiotensin II.

Angiotensin II not only causes blood vessels to narrow (vasoconstriction), it also simultaneously stimulates the secretion of the water-retaining hormone vasopressin (also called AVP) in the pituitary gland (hypophysis) as well as the release of adrenaline, noradrenaline and aldosterone in the adrenal gland.

Whereas adrenaline and noradrenaline enhance vasoconstriction, aldosterone influences the filtration function of the kidneys. The kidneys retain more sodium and water in the body and excrete more potassium. The vasopressin from the pituitary gland prevents the excretion of water without affecting the electrolytes sodium and potassium.

In this way, the overall volume of blood in the body is increased: more blood is pumped through constricted arteries, which increases the pressure exerted on the artery walls – the blood pressure.

Angiotensin, aldosterone and vasopressin can also have a direct effect on the heart. Particularly in certain remodeling processes, for example after a heart attack, these hormones are involved in the abnormal enlargement of the heart or development of scar tissue, which can ultimately lead to heart failure.

Several cardiovascular therapies – e.g. for high blood pressure – target the renin-angiotensin-aldosterone system. For example, diuretics increase the discharge of water and thus reduce the volume of blood; ACE inhibitors block the enzyme that is needed for the formation of angiotensin II – thus interrupting the signaling pathway.

Bayer is also engaged in research on the renin-angiotensin-aldosterone system (RAAS) and on vasopressin receptors.

The complex interplay of the renin-angiotensin-aldosteron-system: