Selected aspects of the pathophysiology of metabolic acidosis in diabetes mellitus.

Metabolic acidosis with a normal anion gap results from either bicarbonate loss or a urine acidification defect. The bicarbonate loss may be via the gastrointestinal tract or the urine, or may be indirect due to excretion of the sodium and potassium as opposed to the ammonium salts of ketone body anions. Defects in urine acidification in the diabetic have several etiologies: first, hydrogen ion secretion may be decreased because of an intrinsic defect in the hydrogen ion pump (i.e., diseases of the renal medulla); second, there may be a failure to augment hydrogen ion secretion by a favorable electrical gradient (e.g., reduced mineralocorticoids); and third, there may be a failure to generate a favorable chemical gradient to augment hydrogen ion secretion (e.g., reduced urine ammonia). Reduced levels of aldosterone associated with hyporeninemia has been termed type IV RTA, and these patients have specific therapeutic needs.