Interrelationships between pituitary hormones as assessed from 24-h serum concentrations in healthy older subjects.

Hormones of the hypothalamic-pituitary-target gland axes are mostly investigated separately, while the interplay between hormones might be as important as each separate hormonal axis.Our aim is to determine the interrelationships between GH, TSH, ACTH, and cortisol in healthy older individuals.We made use of 24-h hormone serum concentrations assessed with intervals of 10 min from 38 healthy older individuals with a mean age (SD) of 65.1 (5.1) years from the Leiden Longevity Study. Cross-correlation analyses were performed to assess the relative strength between two 24-h hormone serum concentration series for all possible time shifts. Cross-approximate entropy was used to assess pattern synchronicity between two 24-h hormone serum concentration series.Within an interlinked hormonal axis, ACTH and cortisol were positively correlated with a mean (95% CI) correlation coefficient of 0.78 (0.74 - 0.81) with cortisol following ACTH concentrations with a delay of 10 min. Between different hormonal axes, we observed a negative correlation coefficient between cortisol and TSH of -0.30 (-0.36 - -0.25) with TSH following cortisol concentrations with a delay of 170 min. Furthermore, a positive mean (95% CI) correlation coefficient of 0.29 (0.22 - 0.37) was found between TSH and GH concentrations without any delay. Moreover, cross-ApEn analyses showed that GH and cortisol exhibit synchronous serum concentration patterns.This study demonstrates that interrelations between hormones from interlinked as well as different hypothalamic-pituitary-target gland axes are observed in healthy older individuals. More research is needed to determine the biological meaning and clinical consequences of these observations.