CIRCADIAN RHYTHMS OF CREATININE AND ELECTROLYTE EXCRETION IN HEALTHY PREGNANT WOMEN

Cireadian rhythms of urine flow, creatinine, sodium, chloride, potassium, and osmolar excretion were studied in 11 healthy pregnant women. The effects of posture and activity were tested by studying subjects in bed in lateral recumbency, ambulant while normally active, and while awake and upright all night. On recumbency days all measured rhythms were constant from subject to subject with daytime peaks as in nonpregnant individuals. On activity days, however, rhythms of volume and sodium excretion varied: 2 had diurnal peaks of both urine flow and sodium excretion; nocturnal peaks of flow alone occurred in 5; and nocturnal peak of sodium excretion alone in 1 and of both flow and sodium excretion in 3 subjects. These nocturnal peaks did not appear when the same subjects were recumbent all day, nor most of the time in 2 subjects kept awake and upright all night, suggesting that posture plays a major role in their production. © 1969.