title: Effects of microsomal enzyme inducers on thyroid-follicular cell proliferation, hyperplasia, and hypertrophy.
abstract: The microsomal enzyme inducer (MEI), phenobarbital (PB), has been proposed to promote thyroid tumors by increasing the biotransformation and elimination of T(4), resulting in an increase in serum thyroid-stimulating hormone (TSH). In turn, TSH stimulates thyroid gland function, growth, and ultimately neoplasia. The dose-dependent effects of MEI on thyroid-follicular cell proliferation, a measure of thyroid gland growth, has not been reported. In the present study, it was hypothesized that MEIs that increase TSH would stimulate thyroid-follicular cell proliferation and the total number of thyroid-follicular cells. Male Sprague-Dawley rats were fed either a basal diet or a diet containing PB (at 300, 600, 1200, or 2400 ppm), pregnenolone-16alpha-carbonitrile (PCN) (at 200, 400, 800, or 1600 ppm), 3-methylcholanthrene (3MC) (at 50, 100, 200, or 400 ppm), or Aroclor 1254 (PCB) (at 25, 50, 100, or 200 ppm) for 7 days. PB and PCN increased TSH 65% and 95%, respectively, whereas 3MC and PCB did not appreciably affect TSH. PB and PCN increased thyroid-follicular cell proliferation 625% and 1200%, respectively, whereas 3MC and PCB did not have a consistent or appreciable effect. The total number of thyroid-follicular cells was not significantly increased by MEI treatment. In conclusion, small increases in TSH by PB and PCN produced large increases in thyroid-follicular cell proliferation, which did not result in a comparable increase in the total number of thyroid-follicular cells. Furthermore, MEI that did not increase TSH did not consistently or appreciably increase thyroid-follicular cell proliferation or cell number.
authors.affiliation: Department of Pharmacology, University of Kansas Medical Center, Kansas City, Kansas, 66160-7140, USA.
authors.forename: A
authors.initials: A
authors.lastname: Hood
authors.forename: R
authors.initials: R
authors.lastname: Hashmi
authors.forename: C D
authors.initials: CD
authors.lastname: Klaassen
mesh_terms: D000818:Animals; D002452:Cell Count; D002455:Cell Division / Q000187:drug effects; D020111:Chlorodiphenyl (54% Chlorine) / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006965:Hyperplasia; D006984:Hypertrophy; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology; D009929:Organ Size; D010634:Phenobarbital / Q000494:pharmacology*; D011285:Pregnenolone Carbonitrile / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013961:Thyroid Gland / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
chemical_list: D014284:Triiodothyronine; D020111:Chlorodiphenyl (54% Chlorine); D011285:Pregnenolone Carbonitrile; D008748:Methylcholanthrene; D013972:Thyrotropin; D013974:Thyroxine; D010634:Phenobarbital