Renal water channel expression in newborns: measurement of urinary excretion of aquaporin-2.
Aquaporin-2 (AQP-2) encodes the vasopressin-regulated "water channels" of the renal collecting duct and is excreted in human urine. We measured urinary excretion of AQP-2 by radioimmunoassay in 15 term and 10 preterm infants on day 1 and day 4 of life to determine the molecular basis of water balance during the newborn period. AQP-2 was detectable in the urine of term and preterm newborns, but AQP-2 excretion was severalfold less than the reported level in normal adults. Urinary excretion of AQP-2 significantly decreased postnatally, in parallel with a reduction in urine osmolality and arginine vasopressin (AVP) excretion. Urinary AQP-2 correlated positively and significantly with urine osmolality on days 1 and 4 and with AVP on day 1 in both groups. No significant differences were detected in AQP-2 levels between term and preterm newborns. Our findings suggest that vasopressin-regulated water channels are expressed in the renal collecting duct of both term and preterm newborns, although to a lesser extent as compared with adults, and these channels encoded by AQP-2 contribute to the urine concentrating power of the newborn kidney.
Tsukahara
H
H
Department of Pediatrics, Fukui Medical School, Japan.
Hata
I
I
Sekine
K
K
Miura
M
M
Kotsuji
F
F
Mayumi
M
M
D000118:Acetylglucosaminidase / Q000652:urine; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins / Q000378:metabolism* / Q000652:urine; D001127:Arginine Vasopressin / Q000652:urine; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D007668:Kidney / Q000378:metabolism*; D008297:Male; D009994:Osmolar Concentration; D001613:beta 2-Microglobulin / Q000652:urine
C496023:AQP2 protein, human; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D001613:beta 2-Microglobulin; D001127:Arginine Vasopressin; D000118:Acetylglucosaminidase