Circadian urinary excretory patterns in an Antarctic environment.

Thirteen 24 h urine collections were made by each of the four members of an expedition to Cape Hallett, northern Victoria Land, Antarctica, during five weeks of the 1982/3 summer. Each collection period was divided into the wake (0700 h-2200 h), and the sleep (2200 h-0700 h) times. Three control collections were made in Christchurch prior to the journey to Antarctica. The mean urine volume increased by 500 ml/24 h; the sodium excretion by 50 mmol/24 h. The 24 h potassium, urea, and creatinine excretions showed no significant changes. Daily excretion patterns of water, sodium, potassium, urea and creatinine were observed by comparing the 9 h overnight excretions with the 24 h excretions. Circadian excretion patterns of the pre-Antarctic control period were preserved over the five weeks of continuous daylight. By comparing the 9 h with the same day 24 h results, the ability to predict a 24 h value from the 9 h excretion was tested. Such predictions were shown to be unreliable. Predictions from 9 h sodium creatinine ratios, potassium creatinine ratios, and urea creatinine ratios were no better.