Aldosterone: History and Introduction

1.1.1

Activity of Amorphous Fraction

The first serious attempts to isolate the compound reasonable for maintaining the life of adrenalectomized animals started round about 1935 following the preparation of biologically active extracts of compounds from adrenal medulla. Several researchers developed the earlier extraction methods, and this was one of the factors vital to the eventual success in isolating relatively large amounts of aldosterone in 1953 by Reichstein. It was realized that the life maintenance tests for adrenalectomized animals under slight stress conditions favored mineralocorticoids, such as deoxycorticosterone, but under severe stress (e.g., under cold conditions) favored glucocorticoids, such as cortisol. The Ingle work test used by Kendall’s group measured chronic muscle fatigue and favored glucocorticoids. On the other hand, the Everse and de Fremery assay used by Reichstein measured the immediate response of muscle and favored mineralocorticoids. This division of corticosteroids into these classifications was arbitrary. However, as a result of the application of these tests, many corticosteroids, both “glucocorticoid” and “mineralocorticoids” were crystallized and identified, particularly by both Kendall-Mason and Reichstein before 1940.

It was realized that the amorphous fraction, remaining after the crystallization of these steroids, contained considerable mineralocorticoid activity. Kuizenga concluded that the active component in the mineralocorticoid assays was not due to the most active known mineralocorticoid, deoxycorticosterone. From the properties of the compound responsible for most of the biological activity in these early studies, it seems clear that nearly all the early investigators had preparations containing substantial amounts of aldosterone. Crystalline aldosterone was actually not obtained until 1953. The serious search for this type of active compounds in adrenal extracts started after 18 years. This delay was partially because the World War II intervened and research activity in the adrenal field was made efforts to the possible use of glucocorticoids to reduce pilot fatigue. Immediately after the war came the success of the glucocorticoids in treating certain disease such as rheumatoid arthritis and the award of the Nobel Prize for this work to the clinician Hench and the adrenal pioneers, Reichstein and Kendall.

1.1.2

Loss of Faith in Significance of the Amorphous Fraction

By the use of large amounts of steroids, such as cortisone, in clinical treatment, it was emerged that these glucocorticoids had effects on electrolyte metabolism as undesirable side effects. It was also realized that cortisol was secreted in amounts similar to those used in therapy from the content of adrenal venous blood in animals and from the quantity of appropriate urinary metabolites. Therefore, influential groups, such as those of Albright and Bartter, and Conn, proposed that cortisol was the “single” adrenal hormone, which could control both carbohydrate and electrolyte metabolisms. Furthermore, Bush who had paper chromatographed extracts originally stated that “I had almost convinced myself to join the ‘Unitarians’.” Nevertheless, it should be emphasized that such “Unitarian” views of those workers were reasonably based on the evidence available at that time. On the other hand, the existence of aldosterone was not certainly accepted smoothly. However, Ulick demonstrated that cortisol can be a ubiquitous single adrenal hormone when there is excessive systemic or local production of cortisol, as in Cushing’s syndrome. Even in normal subjects, cortisol contributes appreciably to the total mineralocorticoid activity.

But, there is an important difference in the physiological role of aldosterone and cortisol. The secretion of aldosterone is controlled by factors such as intake of electrolytes. Cortisol is obviously part of a different, mainly adrenocorticotropic hormone–based system. Although, Ulick and Beck pointed out that cortisol production might increase in aldosterone deficiency and in normal subjects on a low salt intake, the physiological significance of this observation is not yet clear. In physiological situations, it is now recognized that the aldosterone is the dominant hormone as regarding to the effects on electrolyte metabolism. However, this was certainly not the view of most workers in this field around about 1950 at least as regarding to the role of active compound in the amorphous fraction.

Apart from the views of Albright and Conn, there was a widely accepted opinion that the amorphous fraction could be because of several compounds acting synergistically. There was no evidence for the actual secretion of a single active compound. In addition, several groups, including Kendall and Reichstein, had failed to isolate an appropriate active compound. The Kendall group used mild method, the Ingle work test that was not sensitive to mineralocorticoids, such as aldosterone. On the other hand, Reichstein group used the Everse and de Fremery assay in which aldosterone is strongly active. Unfortunately, Reichstein also used alumina columns for isolating steroids. It was necessary first to acetylate steroids with an α-ketol side chain to prevent their destruction. At that time, all the known 21 acetyl derivatives of steroids were found to be nearly as biologically active as the corresponding free compound, so this phenomenon was not usually a problem. But, under the same conditions of acetylation, 18,21-diacetate of aldosterone was formed, and this is relatively inactive in the usual bioassays. This unexpected phenomenon markedly delayed the isolation of the hormone by Reichstein.