In the din of the Levothyrox affair, one should not forget that the thyroid has physiological variations in its activity. Researchers now have a better understanding of the influence that these seasonal variations have on seasonal variations in human mood, metabolism and sexuality.
The way thyroid hormones work is part of the reason for the seasonal changes in mood, metabolism, and sexuality that affect humans. Co-authors Tomoya Nakayama and Takashi Yoshimura of a Nagoya University study, analyzed the relationship between the length of daylight, the secretion of the hormone (TSH) that stimulates the thyroid from the base of the brain (pituitary gland) and the activity of the ovaries and testes in mammals.
They were interested in different comparative studies in various mammals, in which it appears that molecules such as TSH have been conserved through evolution.
This work may help shed light on the mechanisms underlying the symptoms of seasonal depression, weight gain, and sexuality in humans.
TSH is the hormone of spring
Through a series of very detailed studies, Dr. Yoshimura’s group discovered that the T3 produced in a region of the base of the brain, the mid-basal hypothalamus, regulates the secretion of the hormone that stimulates the secretion of sex hormones (GnRH) on a seasonal basis.
” The increase in triiodothyronine (T3) depends on the differential expression and activity of deiodinase type 2 ”, comments Peter A. Kopp, professor of medicine, and professor at Northwestern University. ” The most interesting thing is that the expression of deiodinase type 2 is regulated by the TSH secreted by pars tuberalis. ” However, the TSH secreted by this source differs in its mode of glycosylation and it does not stimulate the thyroid TSH receptor in the same way as the TSH which is secreted by another region (the pars distalis) and does not act in the same way for the usual feedback: this ultimately allows an increase in general activity.
These studies therefore reveal the existence of another form of TSH, the secretion of which is only seasonal and which would act as a spring hormone.
These seasonal variations in the regulation of TSH account for the seasonal variations found in metabolic activity, mood and sexuality in humans.
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