Biomaterial Database

Effects of microsomal enzyme inducers on thyroid follicular cell proliferation and thyroid hormone metabolism. 2001

C D Klaassen, and A M Hood

Department of Pharmacology, Toxicology and Therapeutics, University of Kansas Medical Center, Kansas City 66160-7140, USA.

The effects of microsomal enzyme inducers on thyroid hormone homeostasis and the thyroid gland are of concern. We have investigated the effects of microsomal enzyme inducers on thyroid follicular cell proliferation and thyroid hormone metabolism in rats. We have shown that small increases in serum TSH can result in large increases in thyroid follicular cell proliferation. Furthermore, only those microsomal enzyme inducers that increase serum TSH--that is, phenobarbital (PB) and pregnenolone-16alpha-carbonitrile (PCN)-increase thyroid follicular cell proliferation, whereas those microsomal enzyme inducers that do not increase serum TSH--that is, 3-methylcholanthrene (3MC) and Aroclor 1254 (PCB)-do not increase thyroid follicular cell proliferation. Deiodination does not appear to be the reason why serum T3 concentrations are maintained in microsomal enzyme inducer-treated rats. We have also shown that those microsomal enzyme inducers that increase serum TSH increase T3 UDP-glucuronosyltransferase (UGT) activity, whereas those microsomal enzyme inducers that do not increase serum TSH do not increase T3 UGT activity. This finding suggests that induction of T3 glucuronidation, rather than T4 glucuronidation, mediates increases in serum TSH of microsomal enzyme inducer treated rats.

UI	MeSH Term	Description	Entries
D008861	Microsomes	Artifactual vesicles formed from the endoplasmic reticulum when cells are disrupted. They are isolated by differential centrifugation and are composed of three structural features: rough vesicles, smooth vesicles, and ribosomes. Numerous enzyme activities are associated with the microsomal fraction. (Glick, Glossary of Biochemistry and Molecular Biology, 1990; from Rieger et al., Glossary of Genetics: Classical and Molecular, 5th ed)	Microsome
D002455	Cell Division	The fission of a CELL. It includes CYTOKINESIS, when the CYTOPLASM of a cell is divided, and CELL NUCLEUS DIVISION.	M Phase,Cell Division Phase,Cell Divisions,Division Phase, Cell,Division, Cell,Divisions, Cell,M Phases,Phase, Cell Division,Phase, M,Phases, M
D004790	Enzyme Induction	An increase in the rate of synthesis of an enzyme due to the presence of an inducer which acts to derepress the gene responsible for enzyme synthesis.	Induction, Enzyme
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D013961	Thyroid Gland	A highly vascularized endocrine gland consisting of two lobes joined by a thin band of tissue with one lobe on each side of the TRACHEA. It secretes THYROID HORMONES from the follicular cells and CALCITONIN from the parafollicular cells thereby regulating METABOLISM and CALCIUM level in blood, respectively.	Thyroid,Gland, Thyroid,Glands, Thyroid,Thyroid Glands,Thyroids
D013963	Thyroid Hormones	Natural hormones secreted by the THYROID GLAND, such as THYROXINE, and their synthetic analogs.	Thyroid Hormone,Hormone, Thyroid,Hormones, Thyroid
D051381	Rats	The common name for the genus Rattus.	Rattus,Rats, Laboratory,Rats, Norway,Rattus norvegicus,Laboratory Rat,Laboratory Rats,Norway Rat,Norway Rats,Rat,Rat, Laboratory,Rat, Norway,norvegicus, Rattus