title: Relationship of thyroid status to growth hormone and insulin-like growth factor-I (IGF-I) in plasma and IGF-I mRNA in liver and skeletal muscle of cattle.
abstract: Steers were made hyperthyroid or hypothyroid to study the effects of physiological alterations in thyroid hormone status on plasma growth hormone (GH) profiles, plasma insulin-like growth factor-I (IGF-I) concentrations, and relative abundance of IGF-I mRNA in skeletal muscle and liver. Eighteen yearling crossbred steers (360 to 420 kg) were randomly allotted to hyperthyroid (subcutaneous injection 0.6 microgram/kg BW L-thyroxine for 10 d), hypothyroid (oral thiouracil; 0.25% diet plus 12.5 g capsule/d for 17 d), or control (subcutaneous injection 0.9% NaCl) treatment groups. Blood samples were taken for measurement of GH, IGF-I, thyroxine (T4) and triiodothyronine (T3) by RIA. Samples of liver and skeletal muscle were taken by biopsy for measurement of IGF-I mRNA by solution hybridization. Steers receiving thiouracil had 57 and 53% (P less than .05) lower T4 and T3, respectively, than control steers (84.1 and 1.7 ng/ml). The hyperthyroid steers had 228 and 65% greater (P less than .05) T4 and T3 than control steers. Neither increased nor decreased thyroid status had any significant effects on plasma GH profiles, liver IGF-I mRNA, or plasma concentration of IGF-I. There was no effect of thyroid hormone alteration on skeletal muscle IGF-I mRNA concentrations. The results of this study suggest that short-term changes in thyroid status of cattle had no major impact on the GH-IGF-I axis or skeletal muscle IGF-I mRNA.
authors.affiliation: Department of Animal Science, Iowa State University, Ames 50011.
authors.forename: K
authors.initials: K
authors.lastname: Hannon
authors.forename: A
authors.initials: A
authors.lastname: Trenkle
mesh_terms: D000818:Animals; D002417:Cattle / Q000254:growth & development* / Q000378:metabolism; D013006:Growth Hormone / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000032:analysis* / Q000235:genetics; D008099:Liver / Q000737:chemistry; D008297:Male; D009132:Muscles / Q000737:chemistry; D009693:Nucleic Acid Hybridization; D012333:RNA, Messenger / Q000032:analysis; D011897:Random Allocation; D013889:Thiouracil / Q000494:pharmacology; D013961:Thyroid Gland / Q000502:physiology*; D013963:Thyroid Hormones / Q000097:blood; D013974:Thyroxine / Q000494:pharmacology
chemical_list: D012333:RNA, Messenger; D013963:Thyroid Hormones; D013889:Thiouracil; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D013974:Thyroxine