Thyroid hormones secretion

The class III cytokine receptor family includes two TNE receptors, the low affinity NGE receptor and 7-ceU surface recognition sites that appear to play a role in proliferation, apoptosis, and immunodeficiency. TNE-a (- 17, 000 protein) is produced by astrocytes and microglia and can induce fever, induce slow-wave sleep, reduce feeding, stimulate prostaglandin synthesis, stimulate corticotrophin-releasing factor and prolactin secretion, and reduce thyroid hormone secretion. TNE-a stimulates IL-1 release, is cytotoxic to oligodendrocytes, and reduces myelination this has been impHcated in multiple sclerosis and encephalomyelitis. Astrocyte TNE-a receptors mediate effects on IL-6 expression and augment astrocytic expression of MHC in response to other stimulants such as lEN-y. 

Drugs can affect thyroid function in a number of ways.41 Effects of drugs on thyroid hormone protein binding, LT4 absorption, and metabolism have been discussed previously. Several commonly used medications can alter thyroid hormone secretion. 

Hyperthyroidism is a fairly common complaint which may occur at any age, but affects mainly females. There are several causes of increased thyroid hormone secretion but only rarely is the condition due to non-thyroidal (e.g. pituitary) illness. 

This disease is characterized by a decrease or lack of endogenic thyroid hormone secretion. When originating in childhood, it can be clinically described as cretinism (infantile hypothyroidism), and in adults as myxedema (adult hypothyroidism), which is expressed in a loss of mental or physical ability to work, suppression of metabolic processes in the body, and edema. Since thyroid function cannot be restored, the clinical effect is only visible when using thyroid hormones. Using thyroid hormones in hypothyroidism is a replacement therapy that does not correct the disease itself. 

In some cases it is recommended to take radioactive iodine drugs such as iodotop (NaT ). It accumulates in the thyroid gland along with L-thyroxine and L-triiodothyronin, where radioactive decay takes place—weak 8-radiation destroys thyroid gland follicle cells, which leads to a gradual decline in thyroid hormone secretion. 

The secretion of thyroid hormones starts with endocy-tosis of the modified thyroglobulin, followed by fusion of the endocytotic vesicles with lysosomes. The lysosomal enzymes then degrade the thyroglobulin, liberating triiodothyronine and thyroxine into the circulation. Only about five molecules of T3 and T4 are generated from each molecule of thyroglobulin. Thyroid hormone secretion is stimulated by thyrotropin (TSH), a pituitary hormone that activates adenylate cyclase in its target cells. 

The transplacental passage of maternal iodothyronines is quantitatively modest, although it might be sufficient to ensure adequate fetal development. Maternal thyroid hormone secretion is markedly increased during pregnancy (by 25-50%) thyroid therapy should therefore be carefully adjusted during pregnancy (58). 

Some goitrous patients have autonomous thyroid hormone secretion, which is still within the reference range, but they become hyperthyroid even with relatively small amounts of exogenous thyroid hormones, since the latter accumulate with the endogenous autonomous thyroid secretion. 

Feek CM, Sawers JS, Brown NS, Seth J, Irvine WJ, Toft AD. Influence of thyroid status on dopaminergic inhibition of thyrotropin and prolactin secretion evidence for an additional feedback mechanism in the control of thyroid hormone secretion. J Clin Endocrinol Metab 1980 51(3) 585-9. 

The general conclusion would thus be that the timing of the appearence of different groups of enzymes is attributable to the sequential appearance of different endocrine factors in the circulation. However, the emergence of the last, the late suckling cluster of enzymes, cannot be attributed to a new hormone, but to the secondary quantitative increase (following an early postnatal ebb) in glucocorticoid and thyroid hormone secretion(13,14). Why did these enzymes fail to respond to the first, prenatal and much more impressive rise in these secretions that occurred prenatally ... 

They are now many modifications of different sensitivity and limit of detection (Utiger 1979, Spencer 2004). In the endocrine safety pharmacology in rats and dogs, the TRH test injection with measurement of the serum TSH response is an established tool for assessment of changes at the level of thyroid hormone secretion, with consecutive modification of the pituitary TSH and prolactin response. 

Perry WF (1951) A method for measuring thyroid hormone secretion in the rat with its application to the bioassay of thyroid extracts. Endocrinology 48 643-650 Reineke EP, Turner CW (1950) Thyroidal substances. In Em-mens CW (ed) Hormone Assay, Chapter XIX. Academic Press Inc., New York, pp 489-511 Turner CW, Premachandra BN (1962) Thyroidal substances. In Dorfman RI (ed) Methods in Hormone Research, Vol II, Chapter 10. Academic Press, New York and London, pp 385-411... 

Q3 The following diagram shows the control of thyroid hormone secretion ... 

Q10 Many endocrine secretions are controlled by negative feedback systems. When the thyroid is stimulated and thyroid hormone concentration increases, it inhibits production of TSH to reduce further stimulation of the gland. As thyroid hormone secretion then diminishes, the negative feedback on the anterior pituitary is reduced and TSH secretion increases again. Basically, in... 

It would appear that there is a sudden increase in thyroid activity in terms of available or free hormone and an alteration in thyroxine-binding protein which starts probably during surgery and anesthesia and is associated with an increased peripheral utilization of thyroid hormone. Although changes in protein-bound iodine (FBI) and TSH concentrations are not necessarily related to secretion rates, the exact extent of any increase in secretion of thyroid hormone secretion remains uncertain. 

Excessive ingestion in humans can result in iodide goiter resulting from inhibition of the thyroid gland. The resulting lack of thyroid hormone secretion causes compensatory increase in thyrotropin secretion and... 

Sefkow, A.J., J.J. Distefano, III, B.A. Himick, S.B. Brown and J.G. Eales. Kinetic analysis of thyroid hormone secretion and interconversion in the 5-day fasted rainbow trout, Oncorhynchus mykiss. Gen. Comp. Endocrinol. 101 123-138, 1996. 

Schematic representation of the major steps in the regulation of thyroid hormone secretions and metabolism at five levels, namely, brain, hypothalamus, pituitary thyrotropes, thyroid, and peripheral tissues.

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