Polynocturia in chronic kidney disease is related to natriuresis rather than to water diuresis.
BACKGROUND
Nocturnal polyuria has been well known in renal insufficiency. Recently, we found that as renal function deteriorated in chronic kidney disease (CKD), natriuresis was enhanced during the night with nocturnal blood pressure elevation. In the present study, we investigated whether nocturnal polyuria in CKD was due to the inability to concentrate urine, as previously proposed, or based on osmotic diuresis mainly by natriuresis.


METHODS
In 27 CKD patients, circadian rhythms of urinary sodium, potassium, urea and osmolar excretion rates (U(Na)V, U(K)V, U(urea)V, U(osm)V) as well as of urinary volume (V) and free-water clearance (C(H(2)O)) were estimated during both daytime (6:00 to 21:00) and nighttime (21:00 to 6:00). Then, the night/day ratios of these parameters were analysed in relation to creatinine clearance (C(cr)) as a marker of glomerular filtration rate.


RESULTS
C(cr) had significantly negative relationships with night/day ratios of V (R = -0.69; P < 0.0001), U(osm)V (R = -0.54; P = 0.004) and U(Na)V (R = -0.63; P = 0.0005), but no correlation with night/day ratios of C(H(2)O) (R = -0.33; P = 0.1), U(K)V (R = -0.29; P = 0.1) or U(urea)V (R = -0.31; P = 0.1). Linear and multiple regression analysis identified nocturnal natriuresis rather than urea excretion as an independent determinant of nocturia.


CONCLUSIONS
As renal function deteriorated, nocturnal polyuria was seen, being consistent with classical recognition. Furthermore, this increase in nocturnal urine volume seemed related to osmotic diuresis mainly by natriuresis rather than to water diuresis or urea excretion.
Fukuda
Michio
M
Department of Internal Medicine and Pathophysiology, Nagoya City University Graduate School of Medical Sciences, Mizuho-ku, Nagoya 467-8601, Japan. momoca@sage.ocn.ne.jp
Motokawa
Masahiro
M
Miyagi
Sota
S
Sengo
Kinya
K
Muramatsu
Wataru
W
Kato
Nobuo
N
Usami
Takeshi
T
Yoshida
Atsuhiro
A
Kimura
Genjiro
G
D001794:Blood Pressure / Q000502:physiology; D002908:Chronic Disease; D002940:Circadian Rhythm / Q000502:physiology; D003404:Creatinine / Q000097:blood; D018450:Disease Progression; D004231:Diuresis / Q000502:physiology*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007674:Kidney Diseases / Q000150:complications* / Q000503:physiopathology / Q000652:urine; D008297:Male; D008875:Middle Aged; D009318:Natriuresis / Q000502:physiology*; D053158:Nocturia / Q000209:etiology / Q000503:physiopathology*; D009994:Osmolar Concentration; D011188:Potassium / Q000652:urine; D011507:Proteinuria / Q000453:epidemiology / Q000209:etiology; D014508:Urea / Q000652:urine
D014508:Urea; D003404:Creatinine; D011188:Potassium