[Studies on circadian rhythm and the feedback mechanism of hormone secretion from the hypothalamic-pituitary-adrenal system --pertaining to the circadian variation of feedback sensitivity in the hypothalamic-pituitary axis-- (author's transl)].

In order to investigate the relationship if any between the circadian rhythm of the hypothalamic-pituitary-adrenal system and of feedback sensitivity in the hypothalamic-pituitary axis, temporal changes of serum corticoid level and of ACTH responsiveness to metyrapone were studied in 5 controls, 4 patients with loss of consciousness due to central nervous system diseases (Group A), 2 blind subjects (Group B) and 2 patients with psychiatric disorders accompanied with sleep-wake cycle disturbance (Group C). Two patients in Group A with normal circadian rhythm of serum corticoid levels exhibited abnormal rhythm in ACTH responsiveness to metyrapone. In contrast, 2 other patients in Group A with normal rhythm in ACTH responsiveness to metyrapone exhibited abnormal circadian rhythms of serum corticoid levels. In spite of the disturbed circadian rhythm of serum corticoid levels, 2 patients in Group B showed normal rhythm in ACTH responsiveness to metyrapone. Two patients in Group C exhibited abnormalities in both circadian changes. It was concluded that there might be different control mechanisms between the circadian rhythmicity of the hypothalamic-pituitary-adrenal system and of the feedback sensitivity.