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Suppressed urinary excretion of aquaporin-2 in an infant with primary polydipsia
T Matsumoto1, M Takeya, S Takuwa
1Department of Pediatrics and Child Health, Kurume University, School of Medicine, Fukuoka, Japan.
Insights
Severe overhydration in a child with primary polydipsia was linked to reduced antidiuretic hormone (ADH) secretion. The water channel protein (aquaporin-2) remained functional, indicating polydipsia caused the ADH and aquaporin-2 suppression.
Area of Science:
- Pediatric Endocrinology
- Nephrology
- Water Balance Physiology
Background:
- Primary polydipsia is characterized by excessive water intake, potentially leading to water intoxication.
- Antidiuretic hormone (ADH) plays a crucial role in regulating water reabsorption in the kidneys.
- Aquaporin-2 (AQP2) is a water channel protein regulated by ADH, essential for concentrating urine.
Observation:
- An 18-month-old Japanese girl presented with severe overhydration.
- Basal secretion of ADH was found to be decreased in the patient.
- Urinary excretion of aquaporin-2 was suppressed under basal conditions.
Findings:
- Despite suppressed basal levels, the aquaporin-2 response to ADH was preserved, suggesting the water channel's integrity.
- The findings indicate that the primary issue was excessive water intake (polydipsia) rather than a defect in the water channels themselves.
- Reduced ADH secretion and suppressed aquaporin-2 excretion were consequences of the severe overhydration.
Implications:
- This case highlights that severe overhydration from primary polydipsia can suppress the body's natural water-regulating mechanisms, including ADH secretion and AQP2 expression.
- Understanding this interplay is vital for diagnosing and managing pediatric patients with excessive thirst and water intake.
- The preserved AQP2 response suggests potential for recovery of normal water balance once polydipsia is addressed.
Abstract:
We observed severe overhydration in an 18-month-old Japanese girl with primary polydipsia. The secretion of antidiuretic hormone (ADH) was decreased, and urinary excretion of aquaporin-2, a vasopressin-sensitive water channel protein, was suppressed under basal conditions, but the response of aquaporin-2 to ADH was essentially preserved. These findings suggest that the water channel itself was intact and that overhydration resulting from polydipsia was responsible for the decreased ADH secretion and suppression of the water channel protein.