The effectiveness within the cells themselves of thyroid hormone, and we're now talking about liothyronine (T3), in raising the metabolic activity of the cell, is governed by substances which switch the process on, or switch it off. The alpha-adrenergic receptors are one such, and the enzyme phosphodiesterase is another. But of crucial importance are the GI proteins, of which for thyroid receptors there are four, two to switch on and two to switch off. The chief and most important switcher off is the one called Gq/11.
The object of the Gq/11 especially is to inhibit or slow down the activity of T3 in stimulating cellular metabolism. If blood thyroid hormones are low, this is picked up by the hypothalamus and it responds by producing TRH, which now is passed to the pituitary to stimulate it to produce more TSH. TSH stimulates the thyroid toproduceT4 & T3, but the T3 stimulates the production of Gq/11, which reduces the activity of T3 in the cell until blood levels have normalised. This is all very well and good unless there is, for some reason, an abnormal and exaggerated over-activity of Gq/11. This, it turns out, can happen under the influence of fluoride compounds, and silica, beryllium and aluminium; the result is that the metabolic activity of the cell is wrongly reduced.
It gets worse.
Some fluoride compounds actually prevent the TRH - from the hypothalamus - binding to the pituitary cells which make the TSH. Consequently, the circulating TSH drops even though (due to low thyroid levels) it should be high. This of course means the TSH blood test may be quite wrong. So we have two really awful problems to worry about. One is that the Gq/11 proteins in our modern polluted environment may overwork and shut down thyroid activity -thus reducing metabolism - and the other is that if this does happen, blood tests may not show it, especially the widely used TSH test.
Unfortunately, we cannot even leave it there. We noted that these Gq/11 proteins are over-activated by the presence of fluoride, and that
fluoride can also work to reduce TSH output; but fluoride has not finished its evil work yet. Fluoride can actually diplace the iodine in thyroid compounds, which means those with fluoride in their makeup don't work, although blood tests will show no sign of this, since being halogens
the chemical respons is the same. And if that wasn't enough, the conversion of T4 -> T3 can also be interfered with. What happens here is that the 5'-deiodinase enzymes are targeted and reverse T3 is manufactured at the expense of normal T3, which as you will recall is biologically inactive, promoting a hypothyroid state.
Source: Your Thyroid and How to Keep it Healthy: The Great Thyroid Scandal and How to Survive it by Barry Durrant-Peatfield MD