Neurohormonal consequences of diuretics in different cardiovascular syndromes.

Diuretics have long been used to lower blood pressure in hypertensive patients or to control body fluid and electrolyte homeostasis in diseases such as congestive heart failure, chronic renal failure or cirrhosis. The initial response to diuretics is a negative sodium and fluid balance. The diuretic-induced loss of salt and water activates several hormonal systems such as vasopressin, the renin-angiotensin-aldosterone system or the sympathetic nervous system which tend to compensate for the changes in sodium and water balance. This neurohormonal response may have important clinical implications. Thus, the activation of the renin-angiotensin-aldosterone cascade appears to be partially responsible for the flat dose-blood pressure response curve of thiazides in hypertensive patients. It may also be responsible for the difference between responders and non-responders to diuretic therapy and for the development of side-effects such as hypokalaemia, metabolic alkalosis or hyponatraemia. There are several ways to prevent the undesirable consequences of the neurohormonal responses to diuretics. The first is to use low doses of these agents. It is also possible to combine them with agents that block the activity of the renin-angiotensin-aldosterone system such as ACE inhibitors or in combination with drugs that reduce aldosterone secretion such as calcium antagonists. The development of drugs able to enhance urinary sodium excretion and to reduce simultaneously the activity of the renin-angiotensin-aldosterone system may offer a new interesting alternative. This might perhaps be achieved in the future with the administration of neutral endopeptidase inhibitors which interfere with the enzymatic degradation of atrial natriuretic peptide.