Urinary aquaporin-2 excretion during early human development

Abstract

This study was undertaken to assess one of the determinants of kidney concentrating capacity, aquaporin-2 (AQP2), in order to understand the physiopathology of water balance in newborn babies. Urinary AQP2 excretion has been shown to be proportional to AQP2 level in the apical plasma membrane of the kidney collecting ducts and has been suggested as a marker of vasopressin (AVP) action. Urinary AQP2 excretion in the early postnatal period and at 3 weeks of age was measured in 123 neonates admitted during a 6-month period to the neonatal intensive care unit of the Children's Hospital of Toulouse, France. Clinical and biochemical data were collected for each child. During the first days after birth, higher urinary AQP2 was observed in boys than in girls (P=0.01) and positively correlated with urinary sodium/potassium (Na/K) ratio (r=0.33, P=0.01). When the babies had reached 3 weeks of age, urinary AQP2 was proportional to the gestational age at birth (r=0.33, P=0.0068) and daily weight gain (r=0.36, P=0.003). It did not correlate with urinary osmolality, which was overall very low in all babies. Urinary AQP2 was decreased in conditions of impaired renal function (r=-0.42, P=0.0005) and acidosis (P=0.03). Prenatal corticosteroid treatment had no significant impact on urinary AQP2 level. Our data show that urinary AQP2 correlates with the overall maturity of tubular function in human neonates. In babies at this early age, urinary AQP2 cannot serve as a direct marker of the renal action of AVP but reflects AQP2 expression level associated with different physiopathological conditions.

The renal adverse effects of ibuprofen are not mediated by AQP2 water channels

“…In a human study involving newborn preterm and term infants, Nyul et al detected no relationship between AQP2 excretion and urine osmolality [11]. Previous data published by our group [12] also suggest that AQP2 excretion may not be used as a direct marker of the renal AVP activity and of the capacity to concentrate urine in preterm newborns during the early postnatal adaptation to extra-uterine life.…”

“…The level of AQP2 in the urine was measured by dotimmunoblotting, as previously described [12]. A 100-to 300-μL urine sample was applied to a nitrocellulose membrane (pore size 0.45 μm, Trans-Blot Transfer Medium; Bio-Rad, Hercules, CA) using a Bio-Dot microfiltration apparatus (Bio-Rad).…”

“…The role of aquaporin (AQP) water channels in the postnatal adaptation of water homeostasis has been extensively studied [10][11][12][13]. AQP2, which is the target of vasopressin (AVP), is located in the apical cell membranes of the collecting duct principal cells [14], where AVP induces the translocation of AQP2 from the intracellular stores to the apical membrane, leading to a dramatic increase in water reabsorption in the collecting duct [15].…”

New Insights into the Diagnosis and Management of Pregnancy-Related Diabetes Insipidus

“…Aquaporin-2 metabolism in the fetus and neonate is not fully understood. Researches in both preterm and at term infants suggested that in early postnatal life aquaporin-2 urinary levels cannot serve as a marker of AVP renal action and renal capacity to concentrate urine (Nyul et al, 2002;Zelenina et al, 2006) although opposing results were reported (Iacobelli et al, 2006). Nevertheless, in the same studies urinary aquaporin-2 concentrations correlated adequately with the overall maturity of tubular renal function and decreased in conditions of impaired kidney activity.…”

Early urinary angiotensinogen excretion in critically ill neonates

“…The measurements were repeated on eight 'standard' samples that were run with each set of patient samples to confirm the reliability of the results. 26 The final angiotensinogen concentration was expressed in micrograms per gram of urinary creatinine (µg/g uCr).…”