RESUMO
BACKGROUND AND OBJECTIVES: Bariatric surgery (BS) may be associated with increased oxalate excretion and a higher risk of nephrolithiasis. This study aimed to investigate urinary abnormalities and responses to an acute oxalate load as an indirect assessment of the intestinal absorption of oxalate in this population. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Twenty-four-hour urine specimens were collected from 61 patients a median of 48 months after BS (post-BS) as well as from 30 morbidly obese (MO) participants; dietary information was obtained through 24-hour food recalls. An oral oxalate load test (OLT), consisting of 2-hour urine samples after overnight fasting and 2, 4, and 6 hours after consuming 375 mg of oxalate (spinach juice), was performed on 21 MO and 22 post-BS patients 12 months after BS. Ten post-BS patients also underwent OLT before surgery (pre-BS). RESULTS: There was a higher percentage of low urinary volume (<1.5 L/d) in post-BS versus MO (P<0.001). Hypocitraturia and hyperoxaluria (P=0.13 and P=0.36, respectively) were more frequent in BS versus MO patients. The OLT showed intragroup (P<0.001 for all periods versus baseline) and intergroup differences (P<0.001 for post-BS versus MO; P=0.03 for post-BS versus pre-BS). The total mean increment in oxaluria after 6 hours of load, expressed as area under the curve, was higher in both post-BS versus MO and in post-BS versus pre-BS participants (P<0.001 for both). CONCLUSIONS: The mean oxaluric response to an oxalate load is markedly elevated in post-bariatric surgery patients, suggesting that increased intestinal absorption of dietary oxalate is a predisposing mechanism for enteric hyperoxaluria.
Assuntos
Cirurgia Bariátrica/efeitos adversos , Hiperoxalúria/urina , Obesidade Mórbida/urina , Oxalatos/urina , Adulto , Análise de Variância , Cálcio/urina , Distribuição de Qui-Quadrado , Citratos/urina , Creatinina/urina , Feminino , Humanos , Hiperoxalúria/etiologia , Absorção Intestinal , Magnésio/urina , Masculino , Pessoa de Meia-Idade , Oxalatos/administração & dosagem , Oxalatos/farmacocinética , Oxalobacter formigenes , Estatísticas não Paramétricas , Ureia/urina , Ácido Úrico/urina , Urina/microbiologiaRESUMO
OBJECTIVE: To investigate the oxalate intake and the effect of an oxalate load on urinary oxalate excretion in calcium stone-forming (CSF) patients. DESIGN: Prospective study. SETTING: University-affiliated outpatient Renal Lithiasis Unit. PATIENTS AND CONTROLS: Seventy (70) CSF and 41 healthy subjects (HS) collected a 24-hour urine sample and were submitted to a 3-day dietary record to determine mean oxalate (Ox), calcium (Ca) and vitamin C intake. Fifty-eight (58) CSF patients were randomly selected to receive milk (N = 28) or dark (N = 30) chocolate as an oxalate load. INTERVENTION: Administration of either milk (94 mg Ox + 430 mg Ca) or dark chocolate (94 mg Ox + 26 mg Ca) for 3 days. A 24-hour urine sample was obtained before and after the load to determine calcium, oxalate, sodium, potassium, urea, and creatinine. MAIN OUTCOME MEASURE: Oxalate intake and excretion. RESULTS: CSF patients presented mean Ox intake of 98 +/- 137 mg/d, similar to that of HS (108 +/- 139 mg/d). Mean Ox and vitamin C intake was directly correlated with Ox excretion only in CSF. The consumption of dark chocolate induced a significant increase in mean urinary Ox (36 +/- 14 versus 30 +/- 10 mg/24 hr) not observed in the milk chocolate group. Thus, a 2-fold increase in Ox intake in this population of CSF patients produced a significant 20% increase in oxaluria, not observed when Ca was consumed simultaneously. CONCLUSION: The present study suggests that even small increases in Ox intake affect oxalate excretion and the mitigation of urinary oxalate increase by Ca consumption reinforces that Ca and Ox intakes for CSF patients should be in balance. Further studies are necessary to assess whether or not a 20% increase in oxaluria will lead to a higher risk of stone formation.
Assuntos
Cálcio/farmacologia , Hiperoxalúria/epidemiologia , Cálculos Renais/etiologia , Oxalatos/administração & dosagem , Oxalatos/urina , Adulto , Animais , Ácido Ascórbico/administração & dosagem , Cacau/química , Cálcio da Dieta/administração & dosagem , Registros de Dieta , Feminino , Humanos , Hiperoxalúria/etiologia , Cálculos Renais/prevenção & controle , Masculino , Leite/química , Oxalatos/farmacocinéticaRESUMO
Oxalic acid is an end product of metabolism, and no significant degradation of oxalate occurs in mammals. The sole route of oxalate excretion is believed to be via the kidney. The extrarenal clearance of oxalate in control rats (N = 16) and in 5/6 nephrectomized rats (N = 25) with renal insufficiency was investigated. [14C]oxalic acid, approximately 2 microCi/day, was infused sc by a mini osmotic pump over 4 days. Excretion of 14C was measured in urine, in feces, and in expired CO2. The 14C content of kidney, heart, liver, muscle and bone was also determined at the time the animals were killed. Plasma oxalate was determined by an enzymatic method and by an isotopic dilution procedure. Creatinine clearance in the controls was 1.82 +/- 0.1 mL/min (mean +/- SE) compared with 0.31 +/- 0.04 mL/min (P < 0.0005) in the nephrectomized rats. Plasma oxalate was 5.6 +/- 0.6 mumol/L in controls and 27.0 +/- 3.9 (mean +/- SE; N = 24) in nephrectomized animals (P < 0.0005). The total 14C recovered in urine, feces, and CO2 combined was similar in both groups. The 14C excreted in the feces over the 4-day period was 27.8 +/- 1.5% (of the 14C recovered) in rats with renal failure and 6.5 +/- 0.5% in controls (P < 0.0005). Percent fecal 14C excretion in nephrectomized rats was inversely correlated with creatinine clearance (r = 0.80; P < 0.0001) and directly correlated with plasma oxalate (r = 0.66; P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)