Urinary nitrite excretion and urinary variables in patients with primary nocturnal frequency of micturition: effects of indomethacin suppositories

Urinary nitrite excretion was measured in patients with primary nocturnal frequency of micturition (PNFM) and in normal individuals. Effects of indomethacin suppository on urine volume and other urinary variables were evaluated. The study comprised seven patients with PNFM and seven healthy control (age range 30–45 years). Nitrite was assayed in spot morning urine samples; urine volume, urine osmolality and electrolytes, serum osmolality and electrolytes and functional bladder capacity (FBC) were assayed. Both groups were then given 100 mg of indomethacin suppository daily for a maximum of 10 days and urinary variables were re-evaluated during day 10. Results showed that urinary nitrite excretion of patients with PNFM was greater than that of the normal subjects (230±62 umol/l vs. 42±30 umol/l, P<0.05). The mean (SD) 24 h urine volume and osmolality, the night urine volume and osmolality, serum osmolality, FBC, creatinine clearance, fractional excretion of sodium (FENa), fractional excretion of potassium (FEK), and urinary excretion of glucose and potassium were lower in patients with PNFM as compared with normal individuals, although not statistically significantly so, except for FBC that was significantly lower in the patients. Urinary excretion of sodium, calcium, chloride, phosphorus, magnesium, day-night urinary volume ratio, spot morning osmolality, nocturnal index, and nocturnal polyuria index were higher in patients with PNFM. Indomethacin decreased the 24 h urinary volume by 21%, creatinine clearance by 12%, osmolar clearance by 14% and urinary protein excretion by 38% in the patients. These variables decreased by 26, 45, 17 and 12% respectively in the healthy subjects, whereas 24 h urinary protein excretion increased mildly by 9%. Indomethacin increased day-night urinary volume ratio by 73% in the healthy subjects. It might be concluded that urinary nitrite excretion, urinary excretion of sodium, chloride, phosphorus, calcium, and magnesium increased and FBC decreased in patients with PNFM; Indomethacin decreased urinary volume, FENa, FEK, osmolar clearance, and free water clearance in the healthy subjects and the patients. These might explain the mechanism of action of indomethacin to reduce frequency of voiding. The possible interaction of prostaglandin and NO in the pathogenesis of PNFM is discussed.