THE RENIN SYSTEM AND ATRIAL NATRIURETIC HORMONE IN CONGESTIVE HEART FAILURE

The renin angiotensin system is activated in the majority of patients with chronic congestive heart failure of moderate to severe symptomology. Renin release may result from one of several different stimuli: renal tubular sodium delivery and sensing by the macula densa, sympathetic nervous system activity, and baroreceptor to changes in renal blood flow. Difficulties arise with an analysis of renin angiotensin system activity due to the necessity for diuretic therapy in the majority of these patients. Despite the presence of diuretic therapy, however, there is a wide range of renin angiotensin system activity. In evaluating this activity the administration of a converting enzyme inhibitor will block the contribution of angiotensin mediated vasoconstriction, thereby confirming the importance of the renin angiotensin system activity as a mediator of the long-term consequences of heart failure In situations of low plasma renin activity, vasoconstriction is mediated by an alternate mechanism. The mechanisms of this non-renin mediated vasoconstriction are less apparent, but may include calcium mediated vasoconstriction, and the effects of increased cytosolic content. This low renin group of patients appear to be very sensitive to reversal of vasoconstriction by calcium channel antagonists, especially when converting enzyme inhibitors are ineffective. In an analysis of the factors that may result in renin release, tubular delivery of sodium to the macula densa may emerge as the most important regulator of renin release. In milder forms of heart failure, or in the absence of diuretic therapy, the renin angiotensin system does not show the degree of activation that occurs in the more severe form of heart failure when diuretics are given. From a theroretical standpoint, endogenous atrial natriuretic factor may emerge as an important regular of sodium and water excretion, acting either independently, or as a regulator of the renin angiotensin system, It will therefore be necessary to evaluate the impact of atrial natriuretic factor in patients with congestive heart failure particularly in relation to the renin angiotensin system.