Influence of calcium intake on calcitriol levels in idiopathic hypercalciuria in children

Effects of thiazide on the expression of TRPV5, calbindin-D28K, and sodium transporters in hypercalciuric rats

TRPV5 is believed to play an important role in the regulation of urinary calcium excretion. We assessed the effects of hydrochlorothiazide (HCTZ) on the expression of TRPV5, calbindin-D(28K), and several sodium transporters in hypercalciuric rats. Sprague-Dawley rats were divided into 4 groups; control, HCTZ, high salt, and high salt with HCTZ group in experiment 1; control, HCTZ, high calcium (Ca), and high Ca with HCTZ group in experiment 2. To quantitate the expression of TRPV5, calbindin-D(28K), and sodium transporters, western blotting was performed. In both experiments, HCTZ significantly decreased urinary calcium excretion. TRPV5 protein abundance decreased in all hypercalciuric rats, and restored by HCTZ in both high salt with HCTZ and high Ca with HCTZ group. Calbindin-D(28K) protein abundance increased in the high salt and high salt with HCTZ groups, but did not differ among groups in experiment 2. Protein abundance of NHE3 and NKCC2 decreased in all hypercalciuric rats, and were restored by HCTZ in only high Ca-induced hypercalciuric rats. In summary, protein abundance of TRPV5, NHE3, and NKCC2 decreased in all hypercalciuric rats. The hypocalciuric effect of HCTZ is associated with increased protein abundance of TRPV5 in high salt or calcium diet-induced hypercalciuric rats.

Urinary excretion of endothelin-1 in children with absorptive idiopathic hypercalciuria

Urinary excretion of endothelin-1 (ET-1) and plasma ET-1 were measured in 21 children with absorptive idiopathic hypercalciuria (AIH) and 22 controls. The absorptive type of idiopathic hypercalciuria was determined by a calcium loading test. Daily urinary excretion of ET-1 and urinary ET-1/creatinine ratio were significantly increased ( P=0.005 and P=0.007, respectively) in patients with AIH (9274+/-6444 pg/24 h and 14.04+/-9.52 pg/mg, respectively) compared with controls (4699+/-2120 pg/24 h and 7.36+/-4.71 pg/mg, respectively). Plasma ET-1 levels were significantly lower in patients with AIH (0.84+/-0.64 pg/ml) than in controls (1.54+/-0.54 pg/ml, P=0.0001). In conclusion, patients with AIH had increased urinary ET-1 excretion and decreased plasma ET-1 levels. This is most likely due to the decreased reabsorption of ET-1 in the renal tubule and increased renal production.

[Hypercalciuria: etiologies and treatment]

Hypercalciuria is a rare biological symptom with multiple possible etiologies in children. Normal calcium excretion rate in children is defined as lower than 4 mg/kg per day, significantly higher values being observed in infants. When using urinary calcium: creatinine ratio, normal values are below 0.22 mg/mg in children, and below 0.6 to 0.8 mg/mg in infants. In our experience half patients with hypercalciuria have idiopathic hypercalciuria. Idiopathic hypercalciuria can be hereditary with a dominant autosomal mode of inheritance. Its pathophysiology is unclear, increased calcium intestinal absorption and impaired renal tubular calcium reabsorption being the two main underlying anomalies. Patients with hypercalciuria should be informed about the risk of urolithiasis and its possible prevention by a high water intake. In those patients with nephrocalcinosis or recurrent episodes of lithiasis, hydrochlorothiazide can be effective in reducing hypercalciuria. However, adverse effects of hydrochlorothiazide on serum lipids have been recently reported and make this treatment questionable in the long term.