Thyroid hormones species differences

Such observations as these should inject caution into those who speak glibly about what metabolism is like in the mammalian organism. Furthermore, if differences such as these exist among different species of higher mammals, it lends credence to the idea that, within the human species, quantitative differences of a similar nature may exist. Because of differences in enzyme systems and the extent to which different metabolic pathways are utilized in different individuals, it is not at all unreasonable to conclude that different individuals probably have fundamental needs for quite different levels of the thyroid hormone. 

Affinity labelling of thyroid hormones to nuclear receptors indicated the presence of an abundant 47000 Da component and a less abundant 57000 Da species [40], Micrococcal nuclease also excises the two receptor forms. It is yet not clear whether these two forms are products of different genes or if the 57 000 Da form is converted or processed to the 47 000 Da species. 

DNP had partial effects (W2). Injection of mammalian TRF into tadpoles did not elicit a metamorphic response (E7). Since thyroid hormone causes metamorphosis in the tadpole, this study indicates species specificity or a different neurophypophyseal relationship in the tadpole. 

A calorigenic action of thyroid hormones can also be demonstrated in tissues excised from animals with experimentally induced hyperthyroidism. In 1924, Rohrer demonstrated increased oxygen consumption in liver, kidney, and muscle isolated from mice which had been made hyperthyroid with desiccated thyroid. Most subsequent experiments have been performed with tissue sUces excised from other species, especially the rat. Differences in the metabolic responses of various tissues to thyroid stimulation have been ob.served, depending upon the species studied and the thyroid preparations used these differences will be discussed in the subsequent section. In contrast to the response of isolated tissues to thyroid hor-... 

An alternative therapeutic approach to osteoporosis is through the use of calcitonin (798), a peptide hormone containing 32 amino acids (the sequence is species dependent) secreted by the thyroid gland, which stimulates the production of new bone. Synthetic calcitonins corresponding to human, eel, and salmon variants, and natural calcitonin extracted from pig thyroid, are all used in medicine - they have slightly different efficacies, side effects, and tolerance levels (799). 

Calcitonin (ihyrocalcilonin) is a 32-amino-acid polypeptide hormone secreted by parafollicular cells of the thyroid glands in response lo hypocalcemia. The entire 32-residue peplide appears to be required for activity, bccau.se smaller fragments are totally inactive. Common structural features of calcitonin isolated fntm different species are a COOH-lerminal prolinamide. a disulfide bond between residues I... 

Peptide hormones are produced by the endocrine glands (pituitary, thyroid, pineal, adrenal, and pancreas) or by various organs such as the kidney, stomach, intestine, placenta, or liver (Table 3.4). Peptide hormones can have complex, convoluted structures with hundreds of amino acids. Figure 3.2 illustrates the chemical structure of human insulin and its three-dimensional shape. Insulin is made of two amino acid sequences. The A-Chain has 21-amino acids, and the B-Chain has 30-amino acids. The chains are linked together through the sulfur atoms of cysteine (Cys). Peptide hormones are generally different for every species, but they may have similarities [11]. Human insulin is identical to pig insulin, except that the last amino acid of the B-Chain for the pig is alanine (Ala) instead of threonine (Thr) (lUPAC and lUBMB) [9] and [11]. 

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