Two patients (A and B) aged 12 and 13½ years with the salt-losing variety of congenital adrenal hyperplasia, who were apparently equilibrated on glu-cocorticosteroid supplementation alone, underwent sequential clearance studies establishing renal contribution to sodium 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. 1) During control studies plasma volume was very low in patient A and normal for height in patient B. Patient A exhibited a fractional sodium excretion of 2.1% despite a plasma sodium of 127 mEq/1. Renal acid-base equilibrium was at 18.3 mmol bicarbonate per liter plasma. The only pathologic finding in patient B was a renal acid-base equilibrium at 21.5 mmol bicarbonate per liter plasma. 2) In patient B isotonic saline infusion (3.5 ml/min/m2) induce d an increase of plasma volume to slightly above normal for height and simultaneously the fractional sodium excretion increased to 2.3%.The renal acid-base equilibrium decreased as compared with control by 1 mmol/1. 3) Treatment with 200 μg of 9α-fluorohydrocortisone in patient A increased plasma volume to slightly below normal for height, increased plasma sodium concentration to 135 mEq/1, and increased the renal acid-base equilibrium to 21.5 mmol bicarbonate per liter plasma. Treatment with 400 μg of 9α-fluorohydrocortisone increased plasma volume to normal in patient A, and to above normal for height in patient B. Plasma sodium concentrations were 140 and 144 mEq/1, the fractional sodium excretion 2.3 and 2.2%. Renal acid-base equilibrium at 24.3 and 24.5 mmol bicarbonate per liter plasma. 4) The extent of the mineralocorticosteroid effect was dose-dependent. After treatment with 400 μg/day of 9α-fluorohydrocortisone the so-called “escape phenomenon” was observed. It is concluded that in the absence of mineralocorti-costeroid substitution, volume might be the main regulatory factor of sodium and acid-base balance, whereas during substitution its regulatory effect recedes. It is suggested that, in contrast to general practice, mineral-ocorticosteroid substitution should never be discontinued in patients with salt-losing variety of congenital adrenal hyperplasia. However, careful individual dose finding must be performed.
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Oetliker et al. (1978) studied this question.