Purpose: In adults and adolescents the transition from day to night is followed by a pronounced decrease in diuresis, as well as reduction in the amount of osmotically active substances excreted. We investigate the circadian variations in urine production in healthy children 3 to 14 years old.
Materials and methods: A total of 92 children completed urine collections in 2 consecutive days to be analyzed for electrolytes, urea, creatinine, osmolality, vasopressin and prostaglandin E2.
Results: We found a marked reduction in urine output during the night (43.41 +/- 18.53 to 25.69 +/- 12.71 ml per hour) accompanied by a decrease in the amount of electrolytes excreted (sodium 4.44 +/- 2.09 to 2.66 +/- 1.55 mmol per hour and potassium 2.38 +/-0.96 to 0.90 +/- 0.54 mmol per hour). Age and gender did not influence the observed circadian rhythm in the quantity and quality of urine production. Urinary excretion of vasopressin did not seem to reflect the circadian variations previously described for the plasma levels of the hormone. Prostaglandin E2 showed a clear circadian variation with a 30% decrease at night (32.2 +/- 19.0 to 22.0 +/- 12.6 ng/mmol creatinine).
Conclusions: Healthy children exhibit pronounced circadian variations in the amount and composition of urine output with a decrease in nocturnal diuresis and excretion of osmotically active solutes. In the age range of 3 to 14 years neither age nor gender seems to affect this rhythm. Vasopressin-to-prostaglandin E2 excretion ratio appears to be of importance for regulation of urine production.