INTRODUCTION AND OBJECTIVES: Several conditions with night-time polyuria such as enuresis and nocturia have directed the attention to the regulation of the circadian rhythm in urine production. In adults gender differences has been observed. The aim of this study was to investigate the influence of gender and puberty stage on circadian urine production and levels of antidiuretic hormone (AVP) in healthy children.

METHODS: Thirty-nine healthy volunteers (9 pre-puberty boys, 10 pre-puberty girls, 10 mid-puberty boys and 10 mid-puberty girls) were included. All underwent a 24-hours circadian in-patient study under standardized conditions regarding diet and fluid intake. Blood samples were drawn every four hours for measurements of plasma AVP and the urine was fractionally collected for measurements of aquaporin 2 (AQP2) and prostaglandin 2 (PGE2).

RESULTS: We found a marked night-time decrease in diuresis (from 1.69 ± 0.08 to 0.86 ± 0.06 ml/kg/h, p<0.001) caused by a significant night-time increase in solute-free water reabsorption (TcH2O) concurrent with a significant decrease in osmole excretion. Plasma AVP also expressed a circadian rhythm (p< 0.01) with a night-time increase and peak levels at midnight (0.49 ± 0.05 pg/ml). No difference in circadian plasma AVP rhythm between males and females (p=0.564) or puberty stages (p=0.728) was found. Increasing levels of plasma AVP were associated with increase in TcH2O (r = 0.941 [0.454 – 1.427], p < 0.001) with significantly higher night-time TcH2O in pre-puberty children. This concurred with increased night-time urinary AQP2 excretion in pre-puberty children. Urinary PGE2 exhibited circadian rhythm but no effect of sex or puberty stage.

CONCLUSIONS: This study demonstrates a circadian rhythm in diuresis and solute-free water reabsorption in healthy children, at least in part attributable to increasing night-time levels of plasma AVP. No effect of sex or puberty stage on the circadian rhythm of plasma AVP was found, though night-time solute-free water reabsorption was higher and AQP2 excretion more pronounced in pre-puberty children suggesting higher pre-puberty renal AVP sensitivity.

Source of Funding: Institute of Clinical Medicine Aarhus University, Statens forskningsråd for sundhed og sygdom