Purpose: We investigated the circadian rhythm of solute excretion and regulating hormones as well as blood pressure in patients with monosymptomatic nocturnal enuresis.
Materials and methods: We included 15 patients with a mean age +/- SE of 13.4 +/- 0.9 years who had monosymptomatic nocturnal enuresis with at least 3 wet nights weekly and a control group of 10 healthy children with a similar age and sex distribution. During inpatient circadian studies urine was collected during 6 periods and blood was drawn at 7 time points during 24 hours. Heart rate and blood pressure was recorded with an ambulatory blood pressure monitor every 30 to 60 minutes.
Results: The total patient group excreted a significantly larger nocturnal urine volume than controls (p <0.01). Five patients had marked nocturnal polyuria (nocturnal urine volume greater than the mean in the control group +2 SD), whereas urine output in the remaining patients without polyuria were similar to controls. Nocturnal polyuria was caused mainly by increased nocturnal solute excretion, especially Na. Serum aldosterone and plasma angiotensin II showed a marked circadian rhythm in normal children with a nocturnal increase concomitant with a significant decrease in mean arterial blood pressure during sleep. In contrast, the group of patients with nocturnal polyuria showed a lack of circadian rhythm in all excretion variables as well as an attenuated rhythm in plasma angiotensin II and mean arterial blood pressure. Interestingly this group had normal circadian rhythms of the circadian rhythm markers plasma cortisol and heart rate.
Conclusions: The study suggests that an abnormally large nocturnal excretion of Na caused by selectively attenuated circadian rhythms of Na regulating hormones might be an important pathogenic factor in monosymptomatic nocturnal enuresis.