Alterations in Aldosterone Biosynthesis and Secretion in Long-Term Experiments and Diseases

Abstract

Restriction of sodium intake or loss of body sodium by diuresis, sweating, peritoneal dialysis or sequestration of saliva are very potent stimuli of aldosterone secretion. In reverse, increased sodium intake or parenteral administration of sodium result in diminished aldosterone production. This close correlation between sodium balance and aldosterone secretion was first observed in man (Luetscher and Axelrad, 1954) and has since been found in a great number of different animal species including the toad (Crabbe, 1963) the bullfrog (Ulick and Feinholtz, 1968), the rat (Singer and Stackdunne, 1955), the rabbit (Blair-West et al., 1968), the dog (Rosnagle and Farrell, 1956), the sheep (Blair-West et al., 1963), the opossum (Johnston et al., 1965b) the wombat and the kangaroo (Coghlan and Scoggins, 1967). Since sodium retention is the primary biological effect of aldosterone, the physiological importance of the adaptation of aldosterone secretion to alterations in sodium balance is obvious. However, the physiological and biochemical mechanisms involved in this regulation are only partially known in spite of extensive studies carried out in this field by a great number of investigators. The present state of ignorance and controversy is most likely due to the great complexity which appears to pertain to all parts of a possible control system: stimuli, receptors, afferent signals, control organs, efferent signals and response of the adrenal cortex. The physiological strains induced by sodium depletion are numerous including at various stages decreased extracellular fluid volume, decreased total and circulating plasma volume, decreased arterial blood pressure, decreased arterial blood flow, potassium retention and alterations of electrolyte concentrations in the extra- and intracellular fluids. It is difficult to evaluate the relative importance of all these different parameters of sodium loss in eliciting increases in aldosterone production. Perhaps, the diversity of physiological effects of sodium deficiency may explain the diversity of morphological and functional changes it induces in the adrenal cortex, which will be briefly reviewed in the following paragraphs.