THE EFFECT OF ALDOSTERONE ON ELECTROLYTES IN MUSCLE, KIDNEY CORTEX, AND SERUM

Aldosterone: Renal Action and Physiological Effects

Aldosterone exerts profound effects on renal and cardiovascular physiology. In the kidney, aldosterone acts to preserve electrolyte and acid-base balance in response to changes in dietary sodium (Na+ ) or potassium (K+ ) intake. These physiological actions, principally through activation of mineralocorticoid receptors (MRs), have important effects particularly in patients with renal and cardiovascular disease as demonstrated by multiple clinical trials. Multiple factors, be they genetic, humoral, dietary, or otherwise, can play a role in influencing the rate of aldosterone synthesis and secretion from the adrenal cortex. Normally, aldosterone secretion and action respond to dietary Na+ intake. In the kidney, the distal nephron and collecting duct are the main targets of aldosterone and MR action, which stimulates Na+ absorption in part via the epithelial Na+ channel (ENaC), the principal channel responsible for the fine-tuning of Na+ balance. Our understanding of the regulatory factors that allow aldosterone, via multiple signaling pathways, to function properly clearly implicates this hormone as central to many pathophysiological effects that become dysfunctional in disease states. Numerous pathologies that affect blood pressure (BP), electrolyte balance, and overall cardiovascular health are due to abnormal secretion of aldosterone, mutations in MR, ENaC, or effectors and modulators of their action. Study of the mechanisms of these pathologies has allowed researchers and clinicians to create novel dietary and pharmacological targets to improve human health. This article covers the regulation of aldosterone synthesis and secretion, receptors, effector molecules, and signaling pathways that modulate its action in the kidney. We also consider the role of aldosterone in disease and the benefit of mineralocorticoid antagonists. © 2023 American Physiological Society. Compr Physiol 13:4409-4491, 2023.

Distribution of 14 elements in various rat tissues following hypophysectomy, thyroparathyroidectomy, adrenalectomy, and castration

The tissue distribution of 14 elements was simultaneously determined in rats 28 d after hypophysectomy (HPY), thyroparathyroidectomy (TPTY), adrenalectomy (ADY), and castration (CTN). The elements Na, K, Ca, Mg, Fe, S, P, Rb, Sr, Mn, Cu, and Zn were investigated in whole blood, plasma, brain, liver, kidney, heart, skeletal muscle, and bone. Additionally Mo was determined in kidney and liver. The following results were obtained: 1) With regard to hormone deficiency: HPY induced the most noticeable variations on all the elements tested owing probably to the direct and indirect effects of adenohypophyseal hormones. ADY led to the expected modification of Na and K but also to a Sr accumulation and a Rb depletion. TPTY induced a sharp decrease in plasma and tissues Ca, an increase in plasma P, but did not disturb the two elements in bone. An increase of Rb in many tissues and of Fe in heart, kidney, and liver were also observed. CTN had little consequences except in bone whose Cu and Fe contents were increased; 2) With regard to element variations: K, Mg, and S underwent little change. Discriminations were revealed between elements such as K and Rb, Ca and Sr, Ca and Mg, and Cu and Zn. The changes of Rb and Sr were consistent with regulatory mechanisms. The accumulation of Fe and Cu in tissues such as liver after HPY, TPTY, and ADY, suggest that the hormonal deficiencies could worsen the hemochromatosis and Wilson's disease; 3) With regard to plasma and tissues: No correlation appeared in element levels between plasma and other tissues. Brain was the least affected and liver, kidney and bone the most.

Effects of adrenalectomy and of adrenal hormones on the tissue distribution of 14 elements in the rat

The effects of adrenalectomy (ADY) and of replacement therapy using a mineralocorticoid, deoxycorticosterone (DOC) and a glucocorticoid, dexamethasone (DEX) on the tissue distribution of elements in the rat, were studied under semichronic conditions. The elements Na, K, Ca, Mg, Fe, S, P, Rb, Sr, Mn, Cu, and Zn were determined in whole blood, plasma, brain, liver, kidney, heart, skeletal muscle, spleen, thymus, and bone. Additionally, Mo was determined in kidney and liver and Ba in bone. ADY modified concentrations of all elements tested. Small changes were observed for K, Mg, Ca, S, and P, whereas much larger changes were noted for Na, Rb, and Sr. Cu, Zn, and Fe were mainly modified in liver and kidney, organs involved in storage and/or elimination. The consequences of ADY were corrected fairly well by DEX for Mg, Mn, Ca, Cu, and Mo; by DOC for Na and K, and by the two corticoids for Zn, Fe, Sr, and Rb. This study revealed that corticoids, mainly glucocorticoids, play an important role in the plasma and tissue balance of elements. It is suggested that these results may have a pathological and clinical significance.

Effect of insulinopenia and adrenal hormone deficiency on acute potassium tolerance

The ability to dispose of an acute intravenous potassium load was examined in glucocorticoid-replaced adrenalectomized rats and in rats made insulinopenic with somatostatin. Adrenalectomy resulted in a significantly greater rise in plasma potassium concentration compared with controls (1.46 +/- 0.11 vs. 0.92 +/- 0.05 mEq/liter, P less than 0.001) despite the excretion of an identical percentage (47%) of the administered potassium load in 2 hours. Somatostatin-induced insulinopenia (insulin levels decreased from 37 +/- 5 to 20 +/- 3 microU/ml) was also associated with a significantly greater increment in plasma potassium controls, despite the excretion of a similar amount (39%) of the administered potassium load. In animals with combined adrenal and insulin deficiency, the rise in plasma potassium concentration occurred earlier and remained elevated for a more prolonged period of time compared with animals with either adrenalectomy or insulinopenia alone. Conclusion. During acute potassium loading in the rat, insulin and adrenal hormones play an important role in maintaining normal potassium homeostasis, primarily by enhancing potassium uptake by external tissues.

Kinetics of sodium in rabbit arterial wall: inability of aldosterone to alter extra to intracellular distribution

Transport rate constants (kij) describing the kinetics of Na exchanges in isolated rabbit aorta wall were determined by a previously established method involving the use of 22Na as a tracer and digital computer simulation without recourse to ancillary chemical measurements of extracellular space. A three compartment model consisting of (i) extracellular, (ii) intracellular and (iii) subcellular spaces (compartments) was found to describe adequately the kinetics of 22Na. Normative values for intercompartmental kij and extra to intracellular Na ratio were established. It appears that the Na extracellular space in rabbit arterial wall is larger than that in dog or rat arterial wall. Surprisingly, at variance with several tissues of different species (dog, rat, mouse and human tissues), aldosterone did not influence the extra to intracellular distribution of Na. The findings are interpreted in the light of results obtained previously by other workers using entirely unrelated methodologies and suggest that species difference is an important factor to consider when studying effects of aldosterone on tissue electrolyte distribution in the rabbit.