Obesidad y excreción urinaria de sodio en niños y adolescentes / Obesity and urinary sodium excretion in children and adolescents

Background: Qbesity is a disease characterized by an abnormal accumulation body fat that results in neuroen-docrine changes that alter the homeostasis of sodium, producing an increased risk of hypertension in adulthood. objective: To evaluate the effect of obesity on urinary sodium excretion in children and adolescents. subjects and Methods: 266 male and female children in the age group of 5-15 years were studied: 154 obese (OB) with > 95th percentile of BMI, and 112 normal-weight patients (C) with percentile 5-85 of BMI, from the outpatient service of the Children Hospital, Posadas, Misiones, Argentina during the years 2008 -2009. The determinations of serum sodium (Na s) and 24-hour urine (Na ur) were performed using Ion Selective Electrode. The fractional excretion of sodium (FENa percent) was calculated. results: Na ur values (mEq/kg/day) and FENa percent reported significantly lower differences in the obese group compared to controls: OB Na ur 2.23 vs C Na ur 3.40 (p < 0.0001); OB FENa percent 0.59 vs C FENa percent 0.71 (p = 0.001). Conclusion: Results obtained in the present study showed that obese children have a significantly decreased urinary sodium excretion compared to normal weight children. This difference could be caused by renal retention of this ion.

Introducción: La obesidad es una enfermedad caracterizada por el aumento de grasa corporal, que genera modificaciones neuroendocrinas involucrando alteraciones en la homeostasis del sodio, que podrían generar hipertensión arterial en la adultez. Objetivo: Evaluar el efecto de la obesidad sobre la excreción urinaria de sodio en niños y adolescentes. Pacientes y Método: Se estudiaron 266 niños de ambos sexos, entre 5 y 15 años: 154 obesos (OB) definidos como IMC percentil > 95, y 112 normopeso (C), IMC percentil 5-85, provenientes del Servicio de Consultorio Externo del Hospital de Pediatría-Posadas, Misiones, Argentina, durante los años 2008-2009. Las determinaciones de sodio en suero (Na s) y orina de 24 h (Na ur) se realizaron con electrodo ion selectivo. Se calculó la excreción fraccional de sodio (EFNa por ciento). Resultados: Los valores de Naur (mEq/ kg/día) y la EFNa por ciento significativamente menores en el grupo de obesos con respecto a los controles: Na ur QB 2,23 vs Na ur C 3,40 (p < 0,0001); EFNa por ciento OB 0,59 vs EFNa por ciento C 0,71 (p = 0,001). Conclusión: En el presente estudio los resultados mostraron que los niños y adolescentes obesos presentan una disminución significativa de la excreción urinaria de sodio respecto de los niños normopeso. Dicha diferencia podría estar generada por la retención renal de dicho ion.

The Role of Aldosterone on the Development of Renal Tubular Reabsorption in Low Birth Weight Infants

PURPOSE: To determine the postnatal changes in aldosterone action on the renal tubular reabsorption in low birth weight(LBW) infants, we assessed the relation of the aldosterone concentrations to renal parameters during the first 10 days of life. METHODS: Twenty LBW infants were evaluated and their gestational ages ranged from 32.4 to 39.3 weeks and their birth weights ranged from 1,440 to 2,500 g. Estimated glomerular filtration rate, fractional excretion of sodium(FENa) and potassium(FEK), and plasma aldosterone concentrations were analyzed according to the postnatal age and the conceptional age(CA). RESULTS: Glomerular functions were improved after birth and were correlated with CA. FENa and FEK decreased after birth and correlated with CA. Plasma aldosterone concentrations increased to 318.6 +/- 147.2 ng/dL at 48 hours and then decreased to 162.0 +/- 72.2 ng/dL at 10 days after birth. Plasma aldosterone concentrations of infants less than 38th week of CA were higher than that of infants more than 38th week. There was a significant negative correlation coefficient between plasma aldosterone concentrations and FENa in infants more than 34th week of CA, but not in that of less than 34th week. CONCLUSIONS: LBW infants have higher plasma aldosterone concentrations, but a poor correlation between plasma aldosterone concentration and urinary sodium excretion for the first few days of life and in lower chronologic aged infants. These results show that the renal tubule reabsorption of sodium is less responsive to plasma aldosterone in these infants and, therefore, the careful management of fluid and electrolyte balance is mandatory.