Figure 328

Approach to hyperkalemia: low aldosterone with normal to increased plasma renin. Heparin impairs aldosterone synthesis by inhibiting the enzyme 18-hydroxylase. Despite its frequent use, heparin is rarely associated with overt hyperkalemia; this suggests that other mechanisms (eg, reduced renal potassium secretion) must be present simultaneously for hyperkalemia to manifest itself. Both angiotensin-converting enzyme inhibitors and the angiotensin type 1 receptor blockers (ATi) receptor blockers interfere with adrenal aldosterone synthesis. Generalized impairment of adrenal cortical function manifested by combined glucocor-ticoid and mineralocorticoid deficiencies are seen in Addison's disease and in defects of aldosterone biosynthesis.

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Impai red renal m ratio n o f pobsiu m h

Normal to increased fJasma aldosterone

to aldosterone)

Dec reas-ed bjt'jla r K+ sac istio n

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Tia mterene

Spi ro nölacto ne

Ti metho pn m

Pen bmidi fie teeudo hypo aldosteronism ty pe I

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