Hypocalciuria in patients with Gitelman syndrome: role of blood volume.
BACKGROUND
Hypocalciuria is common in patients with Gitelman syndrome (GS), and its cause primarily is enhanced renal reabsorption of calcium in the proximal tubule in response to hypovolemia, judged by recent studies in animals.


METHODS
Uncontrolled trial in cases and controls to evaluate the effect of acute reexpansion of extracellular fluid volume (ECFV) on urine calcium excretion in patients with GS.


METHODS
8 patients with GS and 8 sex- and age-matched healthy control subjects (CSs) were enrolled in an academic medical center.


METHODS
ECFV expansion with isotonic saline at 1 L/h for 3 hours.


METHODS
Urinary calcium excretion was measured hourly for 6 hours, and subsequent 18-hour urine was analyzed as a single collection; hormones and electrolytes were measured.


RESULTS
Patients with GS had hypokalemia, metabolic alkalosis, hypomagnesemia, severe hypocalciuria (urine calcium-creatinine ratio, 0.006 +/- 0.002 versus 0.08 +/- 0.02 mg/mg [0.02 +/- 0.01 versus 0.22 +/- 0.05 mmol/mmol]; P < 0.005), and a mild degree of ECFV contraction. Sodium excretion and creatinine clearance rates were similar to those in CSs. In patients with GS, saline infusion increased ECFV, which caused a significantly greater sodium excretion rate, but there was only a small increase in calcium excretion rate, in both the first 6 hours (0.04 +/- 0.02 mg/min [1.0 +/- 0.6 micromol/min]) and subsequent 18-hour period (0.02 +/- 0.01 mg/min [0.4 +/- 0.2 micromol/min]), as in CSs. Notwithstanding, their calcium excretion rate was still much less than that in CSs before volume repletion (0.13 +/- 0.04 mg/min [3.2 +/- 1.0 micromol/min]).


CONCLUSIONS
Patients with GS did not become euvolemic on a long-term sodium chloride supplementation because they excreted sodium chloride so rapidly.


CONCLUSIONS
Hypovolemia is not the sole cause of hypocalciuria in patients with GS.
Cheng
Chih-Jen
CJ
Department of Medicine, Division of Nephrology, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan.
Shiang
Jen-Chuan
JC
Hsu
Yu-Juei
YJ
Yang
Sung-Sen
SS
Lin
Shih-Hua
SH
D000293:Adolescent; D000328:Adult; D001810:Blood Volume / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000652:urine*; D045604:Extracellular Fluid / Q000187:drug effects / Q000502:physiology; D005260:Female; D053579:Gitelman Syndrome / Q000188:drug therapy / Q000503:physiopathology* / Q000652:urine*; D006801:Humans; D006996:Hypocalcemia / Q000188:drug therapy / Q000503:physiopathology* / Q000652:urine*; D007008:Hypokalemia / Q000188:drug therapy / Q000503:physiopathology / Q000652:urine; D020896:Hypovolemia / Q000188:drug therapy / Q000503:physiopathology / Q000652:urine; D008297:Male; D008875:Middle Aged; D012965:Sodium Chloride / Q000008:administration & dosage
D012965:Sodium Chloride; D002118:Calcium