Litchfield WR, Silva P, Dluhy RG
Renal potassium excretion is normal in glucocorticoid
remediable aldosteronism
11th Scientific Meeting, American Society of Hypertension
Am J Hypert
(Apr) 9:126A 1996
Glucocorticoid-remediable aldosteronism (GRA) is a genetic disorder in which
the enzyme responsible
of synthesizing aldosterone from corticosterone (aldosterone synthase) is
incorrectly linked up to a
regulatory portion of the previous enzyme in the aldo cascade (11-beta-
hydroxylase). The latter is
regulated by ACTH, whereas aldosterone synthase is not. As a result,
aldosterone synthesis, which
normally occurrs only in the zona glomerulosa, now occurs in the zona
fasciculata, and is regulated
by ACTH in patients with the disorder. Patients with GRA are often
normokalemic (about 50% of
cases), for reasons which are unknown. Thus they may present as essential
hypertension, although
frequently hypokalemia is unmasked when such patients are given thiazides. A
genetic test for the
disorder is now available (Jamieson et al, Arch Dis Child, 71:40,
1994), and treatment is to give
low doses of dexamethasone which reduces ACTH release and often corrects the
hypertension.
In this abstract, Litchfield and colleagues explore why the majority of such
patients are
normokalemic despite high levels of aldosterone. One idea has been, that
such patients have a
defect in K excretion. Litchfield et al studied 8 normokalemic GRA patients
and 8 normal controls.
With the patients on a 150 mM sodium and 100 mM potassium diet, K excretion
was challenged by
alternately giving either 50 mM KCl po or two days of fludrocortisone, 0.2 mg
q 12 h. Saline was
infused at 85 ml/h for 6 hours after each K stimulus, to assure adequate
distal sodium delivery.
Urine K and TTKG (transtubular potassium gradient) were measured.
Normally, the TTKG, which adjusts urine potassium for the amount water
extracted in the collecting
tubule by factoring using the urine/plasma osmolality, is about 9, and should
increase to above 11
with a K load. The urinary K excretion as well as TTKG were similar in both
groups, and the TTKG
was 11 or higher in the GRA patients. The conclusion of the study was, that
urinary K excretion is
not impaired in patients with GRA.
(John T. Daugirdas, M.D., University of Illinois at Chicago)
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11th Scientific Meeting, American Society of Hypertension
H: Special problems :
Endocrine hypertension