Neuro-endocrine correlations of hypothalamic-pituitary-thyroid axis in healthy humans.

Sep 2, 2011Journal of biological regulators and homeostatic agents

Links between hormone levels in the brain and thyroid system in healthy people

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Abstract

Blood samples from ten healthy males revealed clear circadian rhythms for melatonin and TSH secretion.

Melatonin, cortisol, TRH, TSH, and FT4 levels were measured every four hours over a 24-hour period.
Cortisol showed a negative correlation with FT4 during the active phase of the day.
TSH positively correlated with TRH and negatively with FT4 in both activity and resting phases.
During the resting phase, TRH positively correlated with FT4, while melatonin negatively correlated with FT4.
Cortisol was positively correlated with FT4 during the resting phase.
The hypothalamic-pituitary-thyroid axis function may be influenced by the circadian patterns of cortisol and melatonin secretion.

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Neuro-endocrine hormone secretion is characterized by circadian rhythmicity. Melatonin, GRH and GH are secreted during the night, CRH and ACTH secretion peak in the morning, determining the circadian rhythm of cortisol secretion, TRH and TSH show circadian variations with higher levels at night. Thyroxine levels do not change with clear circadian rhythmicity. In this paper we have considered a possible influence of cortisol and melatonin on hypothalamic-pituitary-thyroid axis function in humans. Melatonin, cortisol, TRH, TSH and FT4 serum levels were determined in blood samples obtained every four hours for 24 hours from ten healthy males, aged 36-51 years. We correlated hormone serum levels at each sampling time and evaluated the presence of circadian rhythmicity of hormone secretion. In the activity phase (06:00 h-10:00 h-14:00 h) cortisol correlated negatively with FT4, TSH correlated positively with TRH, TRH correlated positively with FT4 and melatonin correlated positively with TSH. In the resting phase (18:00 h-22:00 h-02:00 h) TRH correlated positively with FT4, melatonin correlated negatively with FT4, TSH correlated negatively with FT4, cortisol correlated positively with FT4 and TSH correlated positively with TRH. A clear circadian rhythm was validated for the time-qualified changes of melatonin and TSH secretion (with acrophase during the night), for cortisol serum levels (with acrophase in the morning), but not for TRH and FT4 serum level changes. In conclusion, the hypothalamic-pituitary-thyroid axis function may be modulated by cortisol and melatonin serum levels and by their circadian rhythmicity of variation.

Neuro-endocrine correlations of hypothalamic-pituitary-thyroid axis in healthy humans.

Abstract

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