Hyperkalemia with mild ECF volume contraction: studies to provide a possible physiologic interpretation.

A 30-y-old female presented with a history of hypertension and a modest degree of hyperkalemia. There was a mild degree of contraction of her ECF volume on clinical examination, with elevated levels of renin and aldosterone in plasma. No causes for secondary hypertension were found. Laboratory investigations revealed a slightly reduced glomerular filtration rate (GFR) and a subnormal kaliuretic response to exogenous mineralocorticoids. When a further degree of ECF volume contraction was induced, she was unable to conserve Na+ and Cl- appropriately. Moreover, expansion of the ECF volume led to a significant suppression of the levels of both renin and aldosterone in plasma. We speculate that these findings could be explained by a diminished net rate of reabsorption of Na+ in the cortical collecting duct. Such a reduction could lead to a diminished generation of an electrical gradient to favour the net secretion of K+ and lead to hyperkalemia with renal salt wasting. The resultant contraction of the extracellular fluid volume with the release of renin and aldosterone (and probably other vasoactive hormones) might have predisposed her to hypertension. This hypothesis was supported by the finding that NaCl supplements led to a significant drop in her blood pressure. This case could represent a new syndrome of hyperkalemia and "salt sensitive" hypertension.