[Longitudinal study on circadian rhythms of plasma hormone levels during Japanese Antarctic Research Expedition].

Circadian rhythms of plasma cortisol, aldosterone and testosterone levels were studied longitudinally in a member of the 21st Japanese Antarctic Research Expedition during periods of one year both in Antarctica and in Hokkaido, Japan. Results were as follows. Plasma cortisol, aldosterone and testosterone levels of man both in Antarctica and in Hokkaido showed average patterns of rhythmicity which were similar to respective Aschoff's standard curves with an exception of testosterone rhythm pattern in Hokkaido. Monthly mean plasma cortisol level diminished markedly in June, the month of darkness throughout the day, but normal circadian rhythm of cortisol level was maintained even during this period. However in Japan the seasonal fluctuation of monthly mean plasma cortisol level was small and had no correlation with the environmental temperature and solar rhythm. Monthly mean plasma aldosterone level increased markedly in July, dark winter month and also in December, the month of midnight sun in Antarctica. In Japan also the same kind of seasonal fluctuation which showed peaks in winter and summer was observed. Monthly mean plasma testosterone level increased markedly in June, the month of darkness in Antarctica. However little seasonal fluctuation was observed in Japan. These findings suggest that social factors rather than light-dark cycle act as a Zeitgeber effective for the maintenance of circadian rhythms of human circulating hormone levels.