SINGLE-DOSE IMIPRAMINE REDUCES NOCTURNAL URINE OUTPUT IN PATIENTS WITH NOCTURNAL ENURESIS AND NOCTURNAL POLYURIA

Purpose: We investigated the effect of imipramine on nocturnal urine o utput in patients with nocturnal enuresis. Materials and Methods: Ther e were 15 monosymptomatic enuretic patients 15 to 37 years and 8 contr ol subjects 25 to 32 years old. We measured nocturnal urine output, ur ine osmolality, creatinine clearance, osmolal clearance, free mater cl earance, excretion of solutes, fractional excretion of sodium, fractio nal excretion of potassium and plasma vasopressin with and without sin gle oral dose of imipramine (1 mg./kg. of body weight) taken at 8 p.m. Results: Baseline studies showed significantly larger and less concen trated nocturnal urine among enuretics compared with controls. We obse rved a marked antidiuretic effect of imipramine in 6 enuretics with se vere nocturnal polyuria. The imipramine induced decrease in urine outp ut was accompanied by reduced osmolal clearance. Approximately a third of the observed decrease in solute excretion was attributed to lower excretion of sodium and potassium. The remaining two-thirds were most likely caused by an increased tubular reabsorption of urea, which may be secondary to a sympathomimetic effect of imipramine tubules, possib ly because of altered adrenal medullary function with an increase in p roximal tubular sodium and water reabsorption. The resultant lower tub ular flow rate facilitates tubular reabsorption of urea in the distal part of the nephron. Conclusions: Imipramine has a vasopressin indepen dent antidiuretic effect if nocturnal polyuria is present. The antidiu retic effect of imipramine can be attributed primarily to increased al pha-adrenergic stimulation in the proximal tubules with a secondary in creased urea and water reabsorption more distally in the nephron.