The neuroendocrine systems which are most profoundly affected by heart failure are:
Renin-aldosterone system:
- the renin-aldosterone system is inactive or only slightly activated in untreated heart failure
- diuretics greatly stimulate renin production
- angiotensin II increases peripheral vascoconstriction and hence the afterload on the heart
- angiotensin II causes constriction of the efferent arteriole in the kidney:
- in the normal kidney this may maintain the glomerular filtration rate in the face of reduced arterial blood pressure
- in a kidney which is already dependent on angiotensin II e.g. in renal artery stenosis, further angiotensin II may cause reduced renal function
- angiotensin II may be directly toxic to myocytes
Autonomic nervous system:
- the sympathetic system is activated
- the parasympathic tone is reduced
- there is no good explanation for these changes
- increased sympathetic activity may be detected by analysing heart rate variability
- increased sympathetic activity is associated with fatal arrhythmias