Pulsatile release and circadian rhythms of thyrotropin and prolactin in children with growth hormone deficiency

Yin and Yang: Why did evolution implement and preserve the circadian rhythmicity?

Yin and Yang concept emphasizes the reciprocal and interrelated nature; neither is sufficient, both are needed to sustain the overall balance of the living system. Changing the balance, by implementing deficiency or excess of one of them, upsets the equilibrium (homeostasis) of the whole system.

PURPOSE

In this opinion article intermittent exposure is presented as the stimulus for development and evolutionary conservation of circadian rhythm, an endogenous, entrainable oscillation of approximately 24 h, to counteract/balance the cells' natural tendency to attenuate their response during long-term exposure to different endogenous substances.

RESULTS

The concept of Yin and Yang duality is an allegory on which the avoidance of attenuation of the cells' responses hypothesis is presented as an explanation for the circadian rhythmicity, which is integrated in all human cells, with the exception of stem and cancer cells.

CONCLUSIONS

We hypothesize, that circadian rhythmicity has evolved, during evolution, into a mechanism that prevents disruption of the organism's negative-feedback-loop homeostasis.

Thyrotropin secretion patterns in health and disease

Thyroid hormones are extremely important for metabolism, development, and growth during the lifetime. The hypothalamo-pituitary-thyroid axis is precisely regulated for these purposes. Much of our knowledge of this hormonal axis is derived from experiments in animals and mutations in man. This review examines the hypothalamo-pituitary-thyroid axis particularly in relation to the regulated 24-hour serum TSH concentration profiles in physiological and pathophysiological conditions, including obesity, primary hypothyroidism, pituitary diseases, psychiatric disorders, and selected neurological diseases. Diurnal TSH rhythms can be analyzed with novel and precise techniques, eg, operator-independent deconvolution and approximate entropy. These approaches provide indirect insight in the regulatory components in pathophysiological conditions.

TSH secretory pattern and thyroid function in children with growth hormone neurosecretory dysfunction

We evaluated the TSH secretory pattern and free T4 in 10 prepubertal children with short stature, normal response to GH provocative tests, and reduced GH integrated concentration (IC-GH) (GH neurosecretory dysfunction). Although their nadir TSH, peak TSH, TSH surge, and free T4 were lower than those of 12 children with short stature and normal IC-GH, none of the differences reached statistical significance. Thus, our results suggest that children with low IC-GH (GH neurosecretory dysfunction) exhibit a TSH secretory pattern and thyroid function similar to those with normal IC-GH.