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Effect of non-carbonic acid loading on renal oxalate excretion: a randomized placebo-controlled trial in healthy subjects and recurrent calcium oxalate stone formers

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Effect of non-carbonic acid loading on renal oxalate excretion: a randomized placebo-controlled trial in healthy subjects and recurrent calcium oxalate stone formers.

Frederikke Eichner Christiansen, Susanne Sloth Osther, Helene Jung, Kim Hovgaard Andreassen and Palle Jörn Sloth Osther.

Urological Research Center (URC),Department of Urology, Lillebaelt Hospital,University of Southern Denmark, Fredericia, Denmark

INTRODUCTION

Clinical data on the effects of protein loads on renal oxalate excretion are conflicting. One of the main metabolic consequences of protein ingestion is an increased endogeneous production of non-carbonic acid.

AIM OF STUDY

The aim of the present study was to analyse the effect of acid loading on renal oxalate excretion in recurrent idiopathic calcium oxalate (CaOx) stone formers and healthy controls.

 

METHODS

5 h NH4Cl-loading studies: Placebo-controlled Cross-over Studies

• Renal excretion rates of Oxalate • AP(CaOx)

RESULTS

Randomized Placebo Controlled Acid Loading Studies

Acid loading studie: There was no difference in the rate of renal oxalate excretion between the stone formers and the controls during the placebo study (i.e. during fasting). During loading with 1.9 mmol NH4Cl/kg renal oxalate excretion rose slightly, but significantly, in both stone formers and controls (p<0.01). Following administration of 3.8 NH4Cl/kg renal oxalate excretion remained in the same order of magnitude in the controls, whereas it tended to increase further in the stone formers. There were, however, no statistically differences in renal oxalate excretion between the stone formers and the controls (Figure 1: nOx(U)=rate of renal oxalate excretion, shaded area 95% CI for healthy subjects)

CONCLUSIONS

•The rate of renal oxalate excretion in fasting urine seems to be of the same order of magnitude in healthy subjects and CaOx stone formers.
•Acid loading causes increased renal oxalate excretion with no obvious differences between CaOx stone formers and matched controls.
•The conflicting data in the literature on the effect of dietary protein on renal oxalate excretion may be explained by differences in the rate of endogeneous acid production resulting from different diets.
•The significantly higher AP(CaOx during acid loading in stone formers compared to controls in this study could not be attributed to higher oxalate excretion rates.