Renal Regulation of Fluid, Electrolyte, and Acid-Base Homeostasis in the Salt-Losing Syndrome of Congenital Adrenal Hyperplasia (SL-CAH)* ECF Volume: A Compensating Factor in Aldosterone Deficiency

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Abstract
Two patients (A and B) aged 12 and 13 1/2 yr with the salt-losing variety of congenital adrenal hyperplasia, who were apparently equilibrated on glucocorticosteroid supplementation alone, underwent sequential clearance studies establishing renal contribution to Na and acid-base balance before and after reinstitution of mineralocorticosteroid therapy. Since therapy induced an increase of plasma volume, the same studies were also performed during acute isotonic volume expansion before therapy. During control studies plasma volume was very low in patient A and normal for height in patient B. Patient A exhibited a fractional Na excretion of 2.1% despite a plasma Na of 127 mEq/1. Renal acid-base equilibrium was at 18.3 mmol bicarbonate/l plasma. The only pathologic finding in patient B was a renal acid-base equilibrium at 21.5 mmol bicarbonate/l plasma. In patient B isotonic saline infusion (3.5 ml/min per m2) induced an increase of plasma volume to slightly above normal for height and simultaneously the fractional Na excretion increased to 2.3%. The renal acid-base equilibrium decreased as compared with control by 1 mmol/l. Treatment with 200 .mu.g of 9.alpha.-fluorohydrocortisone [9.alpha.F] in patient A increased plasma volume to slightly below normal for height, increased plasma Na concentration to 135 mEq/l, and increased the renal acid-base equilibrium to 21.5 mmol bicarbonate/l plasma. Treatment with 400 .mu.g of 9.alpha.F increased plasma volume to normal in patient A, and to above normal for height in patient B. Plasma Na concentrations were 140 and 144 mEq/l, the fractional Na excretion 2.3 and 2.2%. Renal acid-base equilibrium at 24.3 and 24.5 mmol bicarbonate/l plasma. The extent of the mineralocorticosteroid effect was dose-dependent. After treatment with 400 .mu.g/day of 9.alpha.F the so-called escape phenomenon was observed. In the absence of mineralocorticosteroid substitution, volume might be the main regulatory factor of Na and acid-base balance, whereas during substitution its regulatory effect recedes. Mineral-corticosteroid substitution should never be discontinued in patients with salt-losing variety of congenital adrenal hyperplasia but careful individual dose finding must be performed.