Thyroid biochemistry

A number of articles within the last two years has reviewed the various aspects of the biochemistry of the thyroid gland (Roche and Michel, 1951 Means, 1951 Albert, 1952 Gross and Pitt-Rivers, 1952c). It might therefore be thought that yet another review of this subject would be redundant nevertheless, certain recent findings justify some discussion of the subject. In the present article, only brief mention will be made of those aspects of thyroid biochemistry which have been comprehensively discussed by other authors, and emphasis will he laid on experimental work which has not yet been reviewed. 

The iodination of tyrosine itself in the thyroid probably requires no enzymic catalysis substitution of iodine in the phenolic nucleus of tyrosine is a reaction which takes place rapidly at the pH of body tissues, and it seems an unnecessary elaboration to assume enzymic intervention. Substitution occurs in two stages, giving monoiodotyrosine and diiodotyrosine. Monoiodotyrosine was first detected in the thyroid by Fink and Fink (1948), and since then its presence has been confirmed by many other workers. Monoiodotyrosine is physiologically inactive and was at first regarded merely as the precursor of diiodot3rrosine it may, however, have a more important place in thyroid biochemistry this will be discussed later. 

Recent Advances in the Biochemistry of Thyroid Regulation Robert D. Leeper... 

I Thyroid disorders Brain biochemistry in disease... 

While this pattern of biochemistry does not exclude transient relapse of Graves hyperthyroidism (despite the finding of negative TSH receptor antibodies), or a transient thyroiditis, the authors speculated that indinavir (prescribed in this patient together with stavudine and lamivudine) had inhibited the glucuronidation of thyroxine and hence caused a rise in serum thyroid hormone concentrations. 

McNabb, R.A. and Pickford, G.E. (1970). Thyroid function in male killifish, Fundulus heteroclitus, adapted to high and low temperatures and to fresh water and sea water. Comparative Biochemistry and Physiology 33,783-792. 

Parker, S.J. and Specker, J.L. (1990). Salinity and temperature effects on whole-animal thyroid hormone levels in larval and juvenile striped bass, Morone saxatilis. Fish Physiology and Biochemistry 8,507-514. 

There are many reviews available on the biochemistry of thyroid hormones27-30 including the excellent review by Doonan in this Series1. Biosynthesis and metabolism of thyroid hormones will be reviewed briefly in this chapter. Attention will be given to recent developments relating to the mechanisms responsible for the physiological responses to thyroid hormones. 

The thyroid-pituitary-hypothalamus axis controls thyroid hormone homeostasis. Thyrotropin-releasing hormone (TRH), released from the hypothalamus, stimulates the synthesis and release of thyroid-stimulating hormone (thyrotropin, TSH) from the anterior pituitary. TSH increases the release of thyroid hormones by several mechanisms, including stimulation of the I pump. While lower than normal levels of T3 and T4 cause an exaggerated response of the pituitary to TRH, released thyroid hormones, in feedback control, blunt the stimulating action of TRH on the pituitary. For further discussion of TSH and TRH biochemistry, see, for example, the review by Kannan48. 

Lee SS and McCormickDB (1985) Thyroid hormone regulation of flavocoenzymebiosyn-thesis. Archives of Biochemistry and Biophysics 237,197-201. 

I25j 59.41 d 7 (35, 179) Biochemistry (thyroid) Diagnosis (thrombosis, kidney function)... 

Ismail AAA, Walker PL, Barth JH, Lewandowski KC, lones R, Burr WA. Wrong biochemistry results two case reports and observational study in 5310 patients on potentially misleading thyroid-stimulating hormone and gonadotropin immunoassay results. Clin Chem 2002 48 2023-9. 

Numerous methods have been developed for assessing the concentrations of FT4 and FT3 in serum. These methods include direct assays that currently serve as reference methods and indirect assays that are more widely available for general laboratory use. The following section describes the principles of these methods and offers some guidelines for their use. The theoretical basis, analytical validity, and clinical utility of these methods have been discussed. Special reports from the Nomenclature Committee of the American Thyroid Association, the National Academy of Clinical Biochemistry, and the NCCLS also review some of the issues and concerns regarding free thyroid hormone measurements. 

Note The National Academy of Clinical Biochemistry practice guidehnes for the use of thyroid tests for the diagnosis and monitormg of thyroid disease was published in Thyroid 2003 13 1 126 and is also available on the NACB web site www.nacb.org. 

Sawin CT, ed. Laboratory support for the diagnosis and monitoring of thyroid disease. Washington, DC National Academy of Clinicai Biochemistry, standards of laboratory practice monograph, 1996. 

M-J. Tsai and B. W. O Malley Molecular mechanisms and action of steroid/thyroid receptor superfamily members. Annual Review of Biochemistry 63, A5 (1994). 

Barrett EJ. The thyroid gland. In Boron WF, Boulpaep EL. Medical Physiology A Cellular and Molecular Approach. Philadelphia, PA W.B. Saunders, 2003. Litwack G, Schmidt TJ. Biochemistry of hormones I polypeptide hormones. In Devlin TM, ed. Textbook of Biochemistry with Clinical Correlations, 5th ed. New York Wiley-Liss, 2002. 

Marimuthu, A. et al. (2002) Design of thyroid hormone receptor antagonists from first principles. Journal of Steroid Biochemistry and Molecular Biology, 83, 59-73. 

Advances in the knowledge of thyroid physiology and biochemistry have been so rapid and numerous in the past half decade that no single chapter could cover the field. The author must therefore apologize for obvious gaps in the discussion which follows. The topics to be discussed This work was supported in part by NCI grant CA 08748. 

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