Circadian and circannual rhythms in results of functional tests in endocrinology

: Basic aspects of the temporal organization of endocrine circadian systems are summarized. Emphasis is given to the concept of chronesthesy (rythmic changes in the susceptibility of target biosystems) and that of chronokinetics (rhythmic changes in the metabolic fate of hormones and other agents). These complementary concepts are needed for the understanding of circadian and/or circannual changes in results of a test. The following substances used either for stimulation or suppression tests were investigated: metyrapone, ACTH, corticosteroids (e.g. dexamethasone), TRH, HCG, glucose, insulin. The subject's synchronization, the time (clock hour in the 24 hours scale, month in the yearly scale) appears to be at least as important as conventional factors such as subject's sex, age, nutritional state when performing a test and interpreting the results.