AJP - Regulatory, Integrative and Comparative Physiology, Vol 260, Issue 6 1137-R1144, Copyright © 1991 by American Physiological Society

ARTICLES

Free-running rhythms of melatonin, cortisol, electrolytes, and sleep in humans in Antarctica

D. J. Kennaway and C. F. Van Dorp
Department of Obstetrics and Gynaecology, University of Adelaide, South Australia.

The geographic isolation and the prolonged absence of sunlight during winter make Antarctica an interesting environment for studying circadian rhythms. This study explored the effects of wintering on sleep, hormonal, and electrolyte rhythms in four human subjects living in a small Antarctic base. Up to the last sunset sleep, 6-sulfatoxymelatonin, cortisol, sodium, and potassium rhythms were synchronized within clock time. During the 126 days of winter, when there was no sunlight, the circadian rhythms of all measures free ran in each individual. For example, the free-running periods for the cortisol excretory rhythm were 24 h 29 min, 24 h 45 min, 25 h 7 min, and 25 h 14 min for subjects C, J, K, and G, respectively. The period lengths of C, J, and K were significantly different, whereas there was no significant difference between K and G. The phase relationships between each rhythm remained constant in three out of the four subjects. Total daily output and rhythm amplitude for 6-sulfatoxymelatonin, potassium, and sodium remained constant during the entrained and free-running stages of the study. Significant changes in total daily cortisol excretion were observed during the year with one subject producing less and two subjects more while the rhythms were free running. When the sun reappeared during spring, all rhythms again synchronized and entrained to the daylight. These results show that 1) circadian rhythms can free run, even when the subjects have knowledge of time; and 2) within a small communal group, individuals can maintain unique free-running periods.

This article has been cited by other articles:

				S. Yoneyama, S. Hashimoto, and K. Honma Seasonal changes of human circadian rhythms in Antarctica Am J Physiol Regulatory Integrative Comp Physiol, October 1, 1999; 277(4): R1091 - R1097. [Abstract] [Full Text] [PDF]

				J. K. Wyatt, A. R.-D. Cecco, C. A. Czeisler, and D.-J. Dijk Circadian temperature and melatonin rhythms, sleep, and neurobehavioral function in humans living on a 20-h day Am J Physiol Regulatory Integrative Comp Physiol, October 1, 1999; 277(4): R1152 - R1163. [Abstract] [Full Text] [PDF]