Desiccated thyroid glands (thyroideum siccum) are the dried thyroids of various domestic animals, and are required by the Pharmacopoeia to contain between 0.17 and 0.23 per cent. of iodine. They are administered in tablet or capsule form; dose, 1 to 5 grains (0.06-0.3 gm.) one to three times a day. The commercial article regularly contains iodine, and yields by special treatment various principles, such as thyroiodin and thyreoglobulin. Kendall has isolated a number of chemical principles, each of which has a special physiologic activity. The alpha-iodine compound most closely represents thyroid activity.

Iodine Content

Most thyroid glands contain iodine. In the dried glands of adult human beings Vincent found 0.3 to 0.9 per cent.; in the dried glands of seven dogs Seidell obtained 0.036 to 0.271 per cent.; and in ten sheep's thyroids dried, Simpson and Hunter obtained 0.048 to 0.383 per cent. But in the thyroids of many children and those of certain individuals of various species, as the ox, horse, pig, sheep, etc., iodine has been present in mere traces or totally absent. Yet these animals seem to get along as well as those with iodine-containing thyroids, and cannot be distinguished from them; and after thyroidectomy they show just as severe symptoms as those with even a high percentage of iodine in their thyroids. It is evident, therefore, as Vincent says, that thyroid gland free from iodine seems to meet the needs of the body apparently as well as that containing iodine.

But the experiments of Baumann, Roos, Hunt, and many others point out the ability of the gland to take iodine given by mouth into organic combination, and Hunt and Seidell have shown that there is a parallelism between the iodine content of thyroid and its physiologic activity. In their experiments, 46 dogs were used. On two successive days, 1.5 to 2 gm. of potassium iodide, or 1 to 1.3 gm. of iodoform (Chi3), were administered by mouth, and on the third day the dog was killed. The thyroids of the iodoform dogs averaged 0.3 per cent. of iodine, and of the iodide dogs, 0.148 per cent.; while those of the controls ranged between 0.106 and 0.129 per cent. These thyroids were then tested on rats and mice, and were found to decrease the resistance of rats and mice to poisoning by morphine and of rats to poisoning by acetonitril, practically in proportion to the percentage of iodine present.

From the many experiments with thyroid the numeric indicator of the activity of the preparation would seem to be the percentage of iodine. And this has led to the belief, on the part of some investigators, that commercial thyroid is merely a special form in which iodine may be administered in organic combination. That this is true in some cases is indicated by the resemblance of the effects to those of other iodine preparations; but in thyroid absence, as in myxedema or cretinism or after thyroidectomy, no other iodine preparation is of any avail.

Pharmacology

Protein Metabolism

Roos (1899) found that thyroid rich in iodine caused a marked increase in nitrogen excretion; that thyroid poor in iodine caused scarcely any increase, and that iodine-free thyroid had no effect at all on the nitrogen. Oswald found the same to be true of thyreoglobulin, the presence or absence of iodine determining the increase or otherwise of nitrogen metabolism. Schondroff, after a series of experiments of long duration, came to the same conclusion. In 4 patients with dementia praecox, Ross noted an increased output of total nitrogen, creatinin, and indolacetic acid. It may therefore be taken as established that commercial thyroid, which regularly contains iodine, increases protein loss.

Fat Metabolism

As long ago as 1894 thyroid was recommended in obesity. Stuve, in tests with healthy men, found the consumption of oxygen increased about 20 per cent., and Thiele and Nehring obtained similar results. In myxedema Magnus-Levy recorded an increase of 80 per cent. These figures indicate a loss of fat out of proportion to the loss of protein. Marine and Williams (1908) found in a dog that in eighteen days 11 gm. of dried sheep's thyroid containing 0.0292 per cent. of iodine caused no loss of weight; while in another dog, in the same time, 11 gm. of a preparation containing 0.1092 per cent. of iodine caused a loss in weight of 454 gm. There are many clinical reports pointing to the value of thyroid in obesity, but it must be remembered that, with the reduction of fat, there is also excessive protein destruction, and this is a serious feature in any reduction cure.

Bone

Many surgeons have attested to the power of thyroid to promote union in delayed fractures, and Bircher (1910) has found that it promotes the growth of bone in normal animals.

Relation To Adrenals

Cretins have large adrenals (Carlson), and Cannon has shown that thyroid activity may be, at least in some measure, dependent upon the epinephrine supply. Cannon has further shown that thyreoglobulin or stimulation of the thyroid gland augments the activity of the adrenals.

Toxicology

An intravenous dose causes a slowing of the pulse and a fall in blood-pressure. As this is prevented by atropine or by cutting the vagi, it must be due to stimulation of the vagus center.

When the drug is given in full dosage for long periods to dogs, cats, horses, sheep, etc., and especially when given to monkeys and man, it produces a regular group of effects. There are anemia, emaciation and muscular weakness, excessive sweating, a tendency to fever, headache, nervousness, tremor of face and limbs, various pains and tingling or pricking sensations or paralyses, increased heart-rate, and sometimes exophthalmos and dilatation of the pupil. Similar effects are to be seen in exophthalmic goiter, and some of them suggest stimulation of the sympathetic nervous system. In monkeys Edmunds found that death occurred from asthenia.

Therapeutics

(1) In Myxedema And Cretinism

In these conditions the effects are most striking. In myxedema the mentality and the physical characteristics are restored; in cretinism the patient may be changed from a maldeveloped and • hopelessly idiotic child to a well-developed and more intelligent one. Complete change to normal is not obtained.

(2) After Thyroidectomy - to prevent the usual train of symptoms. It is effective if the parathyroids have not been removed.

(3) In Hypothyroidism, as after some partial thyroidectomies, and in the late stages of exophthalmic goiter where reversion to colloid has taken place. It is believed that there are many cases of hypothyroidism, with ill-defined symptoms, in which thyroid may be of benefit; but the distinguishing features of this condition have not been satisfactorily determined.

(4) In Colloid Goiter. (5) In Obesity. (6) In Rheumatoid Arthritis. (7) In Infantile Wasting. (8) In Osteomalacia, Rickets, and Delayed Union of Fractures.

It is contraindicated in the hyperplasia stage of exophthalmic goiter, as it increases the symptoms. (For recent reviews on thyroid, see books on Internal Secretions by Swale Vincent and Biedl.)

Antithyroid Preparations

There are several preparations on the market designed to overcome thyroid hyperactivity. The best known are:

Beebe's serum, a serum obtained from animals after inoculation with the proteins from human thyroids.

Antithyroidin (Moebius) the blood-serum obtained from sheep whose thyroid glands had been removed at least six weeks before. It is preserved with 0.5 per cent. of phenol, and is given by mouth in dose of 8 to 15 minims (0.5-1 c.c.) three times a day.

Thyreoidectin, consisting of gelatin capsules each containing 5 grains (0.3 gm.) of a powder prepared from the dried blood of thyroidectomized animals. Dose, one or two capsules three times a day.

Any therapeutic value from these preparations is very doubtful.