Role of nitric oxide in the diuresis and natriuresis occurring in patients with obstructive sleep apnoea syndrome.

OBJECTIVE To determine whether nitric oxide (NO) has any role in the diuresis and natriuresis observed in patients with obstructive sleep apnoea syndrome (OSAS). METHODS We measured 12-hour urine volume in the day and in the night in patients with OSAS (n=20) and determined the concentrations of urinary sodium and nitrate. The frequency of urination in the night was also noted. The measurements were done again after two nights of continuous positive airway pressure (CPAP) therapy and after putting the patients on oral anti-oxidant treatment (vitamin C-100 mg BD and vitamin E-400 IU BD) for 45 days. Ten healthy normal subjects underwent the same protocol except the CPAP therapy. RESULTS In patients with OSAS, the night urine volume and sodium concentration were similar and the nitrate levels were higher compared to those in the day. After CPAP therapy, while the urine volume and sodium concentration decreased, the nitrate level became similar to that in the day. Such effects were not observed after anti-oxidant treatment. The frequency of urination was decreased in both the instances. The effects observed after CPAP therapy were similar to those observed in control subjects with or without anti-oxidant treatment. CONCLUSION Renal NO promotes diuresis and natriuresis in patients with OSAS.