Objectives: To demonstrate nocturnal polyuria objectively and to assess the role of atrial natriuretic peptide (ANP) in healthy elderly males with and without nocturnal polyuria (NP).
Patients and methods: 31 healthy elderly men known to have NP (passing more than 33% of their 24-hour urine output during an 8-hour period overnight) and 12 controls without NP were invited to take part in the study. Blood and urine samples were collected at 4-hourly intervals in order to measure urine output, serum and urine electrolytes and osmolality as well as serum cortisol, renin, aldosterone, arginine vasopressin (AVP) and ANP.
Results: 26 men with NP and 8 controls agreed to take part in the study. Subjects with NP were found to have a diuresis and natriuresis as well as a significant increase in ANP overnight compared to the control group. There was no difference in the other parameters between the 3 groups, with the exception of aldosterone and AVP.
Conclusions: This study has shown a group of subjects with increased natriuresis and diuresis overnight, associated with an increase in ANP. It is possible that subclinical cardiac failure causes an increase in ANP therefore causing nocturnal urinary symptoms and this theory needs further exploration.