Regulation of nephron acidification by corticosteroids

The Role of the Endocrine System in the Regulation of Acid-Base Balance by the Kidney and the Progression of Chronic Kidney Disease

Systemic acid-base status is primarily determined by the interplay of net acid production (NEAP) arising from metabolism of ingested food stuffs, buffering of NEAP in tissues, generation of bicarbonate by the kidney, and capture of any bicarbonate filtered by the kidney. In chronic kidney disease (CKD), acid retention may occur when dietary acid production is not balanced by bicarbonate generation by the diseased kidney. Hormones including aldosterone, angiotensin II, endothelin, PTH, glucocorticoids, insulin, thyroid hormone, and growth hormone can affect acid-base balance in different ways. The levels of some hormones such as aldosterone, angiotensin II and endothelin are increased with acid accumulation and contribute to an adaptive increase in renal acid excretion and bicarbonate generation. However, the persistent elevated levels of these hormones can damage the kidney and accelerate progression of CKD. Measures to slow the progression of CKD have included administration of medications which inhibit the production or action of deleterious hormones. However, since metabolic acidosis accompanying CKD stimulates the secretion of several of these hormones, treatment of CKD should also include administration of base to correct the metabolic acidosis.

Adrenal 11-beta hydroxysteroid dehydrogenase activity in response to stress

This work studied the effect of stresses produced by simulated gavage or gavage with 200 mmol/L HCl two hours before adrenal extraction, on the activities of the 11beta-hydroxysteroid dehydrogenase 1 and 11beta-hydroxysteroid dehydrogenase 2 isoforms present in the rat adrenal gland. These activities were determined on immediately prepared adrenal microsomes following incubations with 3H-corticosterone and NAD+ or NADP+. 11-dehydrocorticosterone was measured as an end-product by TLC, and controls were adrenal microsomes from rats kept under basal (unstressed) conditions. 11beta-hydroxysteroid dehydrogenase 1 activity, but not 11beta-hydroxysteroid dehydrogenase 2 activity, was increased under both stress-conditions. Homeostatically, the stimulation of 11beta-hydroxysteroid dehydrogenase 1 activity would increase the supply of glucocorticoids. These, in turn, would activate the enzyme phenylethanolamine N-methyl transferase, thereby improving the synthesis of epinephrine as part of the stress-response.

Recurrent calcium nephrolithiasis associated with primary aldosteronism

Typical manifestations of hyperaldosteronism include salt retention, hypokalemia, and metabolic alkalosis. However, a consequence infrequently recognized and described is hypocitraturia. In combination with hypercalciuria, aldosterone-induced hypocitraturia can trigger calcium nephrolithiasis. The authors report a case of an individual with primary hyperaldosteronism from an adrenal adenoma that resulted in hypocitraturia. The patient had severe recurrent renal calcium calculi that corrected with adrenalectomy. The clinical physiology of renal calcium and citrate handling in hyperaldosteronism is reviewed.

Dose-dependence of the effects of corticosterone and the non-glucocorticoid, 18-hydroxycorticosterone, on the brush-border Na+/K+ exchanger

Up to now, only glucocorticoids were thought to act on the renal proximal Na+/H+ exchanger. Using fluorimetric techniques we studied the kinetics of Na+/H+ exchange in brush border vesicles from ADX rats treated with increasing doses of corticosterone (B) and 18-hydroxycorticosterone (18OHB). Significant linear correlations were obtained when the Vmax of each treatment were plotted against log doses. 18OHB exhibits a slightly higher sensitivity than B and log-dose responses were steeper for 18OHB than for B treated rats. Differences between both treatments were highly significant at the 4.8 microg/100 g level, corresponding to the physiological blood level of 18OHB. Physiological doses of both steroids elicited equal Na+/H+ exchange-responses. 18OHB is not a glucocorticoid since even 88 microg/100 g did not promote hepatic glycogen deposition while the same dose of B increases glycogen deposits 3.5-fold. These results demonstrate the importance of the Na+/H+ exchanger as a mediator between corticoid action and H+ transport and that of the non-glucocorticoid 18OHB in this process.