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Tubular reabsorption rates as related to elevated glomerular filtration in diabetic children
J Ditzel1, J Brøchner-Mortensen
1Department of Medicine, Aalborg Regional Hospital, Denmark.
Insights
Diabetic children show increased renal tubular reabsorption of sodium, glucose, and calcium, but impaired phosphate handling. This suggests altered tubulo-glomerular balance in pediatric type 1 diabetes.
Area of Science:
- Nephrology
- Pediatric Endocrinology
- Diabetology
Background:
- Type 1 diabetes can affect kidney function.
- Understanding renal tubular reabsorption and tubulo-glomerular balance is crucial in diabetic children.
Purpose of the Study:
- To investigate renal tubular reabsorption and tubulo-glomerular balance in ambulatory children with type 1 diabetes.
- To compare kidney function parameters between diabetic children and healthy controls.
Main Methods:
- Measured glomerular filtration rate (GFR) and tubular reabsorption rates of sodium, glucose, calcium, and phosphate in fasting diabetic and healthy children.
- Analyzed tubulo-glomerular balance by correlating reabsorption rates with GFR.
Main Results:
- Diabetic children had significantly higher GFR than healthy controls.
- Increased tubular reabsorption rates for sodium, glucose, and calcium were observed in diabetic children.
- Phosphate reabsorption was not enhanced, and the renal threshold for phosphate was suppressed in diabetic children, correlating inversely with glucose reabsorption.
Conclusions:
- Pediatric type 1 diabetes is associated with altered renal tubular handling of electrolytes and glucose.
- The maximal reabsorption of phosphate relative to GFR is reduced in diabetic children, indicating impaired tubulo-glomerular balance.
Abstract:
To study renal tubular reabsorption and tubulo-glomerular balance in diabetic children, glomerular filtration rate (GFR) and tubular reabsorption rates of sodium, glucose, ultrafilterable calcium, and phosphate were measured during fasting in 26 ambulatory type I (insulin-dependent) diabetic children without clinical signs of microangiopathy (age 7-14 yr; duration of diabetes 3-14 yr). Similar measurements were made in 28 healthy school children (age 8-14 yr). Mean GFR in the diabetic children was significantly higher than in the normal children (138 versus 109 ml/min/1.73 m2, P less than 0.01). Mean tubular reabsorption rates of sodium, glucose, and calcium were significantly increased in the diabetic subjects (P less than 0.001). In contrast, tubular reabsorption rate of phosphate in the diabetic subjects was not enhanced. The renal threshold concentration of phosphate (TmPO4/GFR) was suppressed in the diabetic compared with the healthy subjects (1.23 versus 1.73 mmol/L, P less than 0.001). TmPO4/GFR was unrelated to circulating parathyroid and growth hormone concentrations but correlated inversely with the reabsorption rate of glucose (r = -0.53, P less than 0.01). Sodium reabsorption was closely correlated to GFR in both diabetic (r = 0.99, P less than 0.0001) and healthy subjects (r = 1.00, P less than 0.0001), and both groups showed identical regression lines. The tubular glucose reabsorption rate was independent of GFR in the diabetics. Tubular calcium and phosphate reabsorptions correlated equally well with sodium reabsorption and with GFR in the diabetic and healthy subjects (P less than 0.001). The maximal reabsorption of phosphate relative to GFR was lowered in the diabetic children.(ABSTRACT TRUNCATED AT 250 WORDS)