The following is from a discussion between members of About.com Thyroid UK Forum and Dr. Barry Durrant-Peatfield regarding the contention as to whether T1, T2 and calcitonin are present in desiccated porcine thyroid
Dr. Peatfield:
The way it works is this. Within the thyroid gland there is a matrix of a complex protein called thyroglobulin. Within this matrix, under the influence of TSH, the presence of thyroid peroxidase (TPO) and hydrogen peroxide (H2O2) the precursor amino acids diiodotyrosine (DIT) and monoiodotyrosine (MIT) are coupled together; the separate rings are joined and form monoiodothyronine and diiodothyronine.
So first of all, T0 doesn't mean anything. It has got no iodine in it and therefore does not count as a thyroid hormone. Once the rings are coupled together, their chemistry is determined by the number and position of iodine atoms on each ring. Monoiodothyronine (T1) has one ring with one iodine atom and the other ring with none. Diiodothyronine (T2) has an iodine atom on each ring. Triiodothyronine (T3) has two atoms on one ring and one on the other; if it has one atom on the first ring and two on the other (not quite the same) itis the isomer (RT3). With two iodine atoms on each ring it is tetraiodothyronine (T4).
This is released into the bloodstream and in the tissues of the body, under the action of one of the three deiodinase enzymes is changed back into T3 (or RT3) to be used by the tissues.
So the contention that the thyroid does not make T2 or T1 within itself is wrong. These are part of the build-up stage (to T4) so Armour is bound to contain them. T1 and T2 appear in the tissues again as T4 is deiodinated to either T3 or RT3 and then T2 and T1 as further breakdown products to be recycled in the liver to iodine and tyrosine. In this connection, in a most recent letter from the manufacturers of Armour (Forest) they say that there is likely to be small amounts of T1 and T2 in Armour, but because the two have not been considered of sufficient importance the actual amounts are not required to be measured.
The "different kinds" of T2, while theoretically possible, have not to my present knowledge been identified. As in my book, it is noted that T2 is indeed believed to have other uses in the body, in the brain and in adipose tissue for example. Both T4 and T3 are broken down in due course by the tissues. T4 has a half-life of perhaps 21 days and T3 about 8 hours, so they all disappear eventually.
To summarise, the thyroid involved does make T1 and T2 as part of the building-up process; it may indeed reappear as part of the recycling process. And I confirm that calcitonin is made in the thyroid (with trace amounts elsewhere) not the parathyroids. Armour will contain T1, T2, T3 and T4. T2 has other effects and its inclusion in Armour may well be of clinical benefit. I also agree that these things are not matters of belief but matters of fact.
References:
Durrant-Peatfield Barry, The Great Thyroid Scandal and How to Survive
It, pp
24-26, Barons Down Publishing, 2003
Griffin James & Ojeda Sergio R, Text Book of Endocrine Physiology,
pp 303-306,
Oxford University Press, 2000