Relation of nocturnal polyuria of the elderly to essential hypertension

Nocturnal polyuria is common in the elderly. In this condition the normal circadian rhythm of urine production is reversed so that urine flow is higher at night than during the day. Elderly men with nocturnal polyuria are commonly referred for prostate surgery, which, not surprisingly, fails to relieve their symptoms. Compared with controls, patients with nocturnal polyuria have higher nocturnal sodium excretion but not higher nocturnal free-water clearance. Similar results have been obtained in children with nocturnal enuresis. Use of vasopressin analogues to induce water retention in elderly patients with nocturnal polyuria is illogical and potentially hazardous; nocturia can be more safely alleviated by diuretic therapy. Nocturnal polyuria in the elderly is associated with hypertension: this is consistent with studies in younger age groups that show that essential hypertension is associated with nocturia and with increased night/day ratios for sodium excretion. We propose that nocturnal polyuria and essential hypertension share some of the same pathophysiological determinants. Specifically, we suggest that a defect in the nitric-oxide pathway may lead to resetting of the pressure-natriuresis relation in the kidney, sodium retention, and compensatory nocturnal natriuresis. This suggestion is consistent with evidence that ageing and essential hypertension are both associated with defects in the nitric-oxide pathway. Our hypothesis has obvious therapeutic implications. More generally, studying the pathogenesis of nocturnal polyuria in the elderly may advance our understanding of the pathogenesis of essential hypertension.