To elucidate whether heart function and endocrine levels of arginine vasopressin (AVP) or solute diuresis is associated with the nocturnal voided volume, and whether the urinary AVP could be a parameter for screening for nocturnal polyuria caused by AVP insufficiency.

A total of 50 patients were enrolled in this study. The blood and urine samples were obtained every 6 hours at 6 pm, 12 am, 6 am, and 12 pm. Atrial natriuretic peptide and brain natriuretic peptide were measured at admission. All voided urine samples were collected every 6 hours for examination. The evaluation items were AVP, osmolarity, sodium, potassium, chloride, and creatinine in blood and urine.

The patients were classified into a group with nocturnal polyuria (n = 21) and a group without nocturnal polyuria (n = 25). There was no significant difference in atrial natriuretic peptide, brain natriuretic peptide, electrolytes in blood and urine, and plasma AVP of each sample between the two groups, but urinary AVP/urinary creatinine and urine osmolarity at 12 am and 6 am in the group with nocturnal polyuria were significantly lower than those in the group without nocturnal polyuria. The nocturnal voided volume correlated with urinary AVP/urinary creatinine level in the urine samples obtained at 12 am and 6 am.

The present data have demonstrated that the significant decrease in urinary AVP/urinary creatinine level at 6 am may contribute to the increased nocturnal voided volume followed by nocturia and that the circadian rhythm disorder of AVP can be predicted by a noninvasive test measuring urinary AVP/urinary creatinine in the urine voided early in the morning.