ALTHOUGH the clinical importance of the adrenal cortex in the regulation of electrolyte balance had long been realized (1), it was not until the early 1950s that the major regulatory steroid, aldosterone, was isolated and identified by Simpson et al. (2). Simpson and Tait used a sensitive mineralocorticoid bioassay based on changes of urinary 24Na/42K ratios in adrenalectomized rats to help isolate aldosterone (3). Aldosterone is still the most potent mineralocorticoid known: 30–50 times more potent than deoxycorticosterone and at least a thousand times more active than the glucocorticoids, cortisol and corticosterone. Aldosterone's greater potency is balanced by a reduced secretory rate compared with most other adrenal steroids (4, 5). Its synthesis, exclusively by the zona glomerulosa of the adrenal cortex, is responsive to dietary sodium and potassium manipulations and more acutely to ACTH, plasma potassium concentrations, and the renin-angiotensin system (5, 6). Many of the initial investigations were...

The Metabolism and Mechanism of Action of Aldosterone

Chapter 8 – BIOLOGICAL ACTIONS OF STEROID HORMONES IN NONMAMMALIAN VERTEBRATES

CONTENTS PAGE Introduction 333 Oestradiol receptors of the female reproductive tract 333 Progesterone receptors of the female reproductive tract 340 Androgen receptors of the male reproductive tract 342 Gonadal steroid receptors of the brain and adenohypophysis 343 Corticosteroid receptors 349 Other aspects 351 Conclusion 351 Appendix 353 References 353 INTRODUCTION It is believed that in target tissues steroid hormones are bound by cytoplasmic receptors* of high affinity and specificity; that the steroid receptor complex moves to the nucleus where physiological changes are initiated via a modification of genetic expression. The aim of this review is to examine the evidence for the receptor concept, its generality and physiological significance. Aspects which have already been reviewed extensively will be treated summarily. The effects of steroids on nucleic acid and protein synthesis will, for the most part, be ignored. The reader is referred to the papers of Bruchovsky & Wilson (1968a), Neal (1970), Hamilton (1971), and Mueller (1971) for further information. An early step may be the synthesis of a new mRNA species, the translation of which into protein could be a prerequisite of an increase in rRNA synthesis (Knowler & Smellie, 1971; Baulieu, Alberga, Raynaud-Jammet & Wira, 1972).

R.S. Snart

Papers

Binding of aldosterone in the toad bladder