Diurnal variation of plasma atrial natriuretic peptide in normals and patients with enuresis nocturna

Abstract

The circadian variation of plasma atrial natriuretic peptide (ANP) in relation to urinary excretion of sodium (U_Na) and potassium (U_K) as well as clearance of creatinine (C_crea) was assessed in 15 juvenile patients with enuresis nocturna and compared with 11 age-, sex-, and weight-matched normal subjects. Normal juveniles showed a highly significant diurnal variation (p<0.001) of plasma ANP with diurnal peak levels at midnight (0000 hours) and minimum levels at 0400 hours. Enuretic patients showed a similar diurnal rhythmicity with normal levels during day and night. In normals both U_Na and U_K showed significant diurnal rhythmicity with a marked reduction from daytime to night-time. Although the total diurnal excretions of U_Na and U_K were similar to normals, patients with enuresis showed abnormal diurnal variation in both U_Na (p<0.05) and U_K (p<0.01). The abnormal circadian rhythm of U_Na and U_K in enuretics seemed to be caused by abnormal tubular handling as similar abnormalities were found in the fractional excretions and as the circadian variation of C_crea was normal. Especially during the first hours of sleep (2200 hours to 0000 hours), the patients showed polyuria (230±138 ml vs 116±58 ml, p<0.01), natriuresis (20.9±16.3 mmol 1⁻¹ vs 10.7±6.8 mmol 1⁻¹, p<0.01), and kaliuresis (7.3±6.3 mmol 1⁻¹ vs 3.7±2.3 mmol 1⁻¹, p<0.05), despite normal levels of plasma ANP. In conclusion, the study describes the diurnal variation of plasma ANP in relation to urinary excretion of sodium and potassium in a juvenile normal population. Patients with nocturnal enuresis show abnormal diurnal rhythmicity in the urinary excretion of sodium and potassium that is not correlated to the plasma levels of ANP.

Key Words:

• circadian rhythm
• normohydration
• potassium
• sodium
• urinary excretion