Aldosterone: Physiological and pathophysiological variations in man

Abstract

By virtue of its profound effects on sodium and potassium metabolism, changes in which have general repercussions in all tissues, aldosterone performs an important role in the normal physiology and pathophysiology of man. There is an abundance of circumstantial evidence, much of which is presented in the present paper, that the renin-angiotensin system exerts a major influence on aldosterone secretion in man. Moreover, the study of the patient described in the last section, in whom very low plasma aldosterone levels were associated with low levels of renin and angiotensin in the absence of any other detectable abnormality in adrenocortical control, and in whom plasma aldosterone levels could be corrected solely by angiotensin 11 infusion, provides more direct evidence of this relationship. The assumption of the importance of the renin-angiotensin system in this respect, and also the relatively recent possibility of measuring accurately the several components of this system, has allowed an understanding of the aetiology of many types of hypertensive and circulatory disease. It must, however, be emphasised that much has still to be learned of the nature of adrenal aberrations leading to abnormal control of electrolyte metabolism and arterial blood pressure. For example, detailed studies of non-aldosterone hypermineralocorticoidism are extremely few, partly due to the lack of suitable analytical techniques for many of the steroids which may be implicated, and possibly also to the apparent rarity of patients suffering from these conditions. Again, the aetiology of hyperaldosteronism associated with low plasma renin in which only adrenocortical hyperplasia or micronodular hyperplasia is found at surgery also raises the possibility of the existence of some as yet unknown adrenocortical trophic substance. Perhaps a final understanding of the control of electrolyte metabolism, blood pressure and the status of aldosterone will be obtained only when simultaneous study of metabolic, endocrine and cardiovascular changes becomes possible. The use of computer-assisted systems analysis such as has been developed by Guyton and his colleagues ( Guyton and Coleman, 1969 ), may be a first step in this direction.