The efficacy of DDAVP is related to the circadian rhythm of urine output in patients with persisting nocturnal enuresis

OBJECTIVE Desmopressin may be a useful treatment in some, but not all, pati ents with nocturnal enuresis, We have evaluated a relation between nocturna l urine output in patients with primary monosymptomatic nocturnal enuresis and the treatment response to synthetic vasopressin, DESIGN Adolescent or adult enuretics and normal subjects were enrolled in t he study and admitted to hospital for a 24 hour investigation of the diurna l variation in urine output, plasma vasopressin (AVP) and plasma atrial nat riuretic peptide (ANP). The enuretics were characterized prior to investiga tion as either 1-desamino-8-D-arginine vasopressin (DDAVP) responders or no n-responders. During admission the fluid intake was restricted to 25 ml/kg per day. PATIENTS Twenty-four patients (15-37 years) with primary monosymptomatic no cturnal enuresis and 9 normal subjects (24-31 years). MEASUREMENTS Circulating levels of AVP, ANP, plasma electrolytes and plasma osmolality were measured (1400, 2000, 2300, 0200, 0500 and 0800 hours) tog ether with urine volume, urine osmolality and urine electrolytes during day time and nighttime. Tubular reabsorptive capacity for water, osmoles and cr eatinine were assessed as well as urinary and fractional excretion rates of sodium and potassium. RESULTS Controls and DDAVP non-responders had a significant decrease in uri ne output at night concomitant with a significant plasma AVP amplitude in p eak/nadir values although both groups lacked a significant nocturnal increa se in AVP. In,contrast, in DDAVP responders there was no circadian variatio n in urine output and thus a nocturnal polyuria together with no oscillatio n in plasma AVP. The DDAVP responding group had a nocturnal urine productio n significantly larger than the two other groups. However, the mean 24 hour AVP levels were similar in all groups, The excessive urine production at n ight in DDAVP responders was accompanied by nocturnal natriuresis due to an increased fractional excretion of sodium. In contrast, nocturnal antidiure sis in controls and DDAVP non-responding enuretics coincided with diminishe d sodium excretion, Average ANP levels were elevated in both enuretic group s compared to normals, whereas a circadian variation was detected only in t he latter. CONCLUSION It is concluded that DDAVP responsiveness is linked to the noctu rnal urine production and that no pathophysiological role can be ascribed t o AVP or ANP in DDAVP refractory adolescent and adult enuretics, Moreover, it is suggested that an abnormal tubular handling of sodium may contribute to the nocturnal polyuria seen in DDAVP responders.