title: Stimulation of thyroid function by several pituitary hormones results in an increase in plasma thyroxine and reverse triiodothyronine in tilapia (Tilapia nilotica).
abstract: In this study, intravenous injection of several doses of porcine follicle stimulating hormone (pFSH: 0.002, 0.01, 0.05, and 0.5 micrograms/g body wt), bovine TSH (bTSH: 0.5 micrograms/g body wt), and ovine growth hormone (oGH: 0.04, 0.02, and 0.4 microgram/g body wt) stimulated an increase in plasma thyroxine (T4) and reverse triiodothyronine (rT3) in tilapia. This effect occurred in a dose-dependent manner. pFSH was the most potent in stimulating thyroid function. The dose of 0.002 microgram pFSH/g body wt increased plasma levels of T4 over control levels (2.59 +/- 0.16 ng/ml) about 2.5-fold within 4 hr, whereas a concentration of 0.5 micrograms/g body wt caused a great and prolonged increase of T4 and rT3 levels. Control levels (2.59 +/- 0.16 ng/ml for T4 and 40.37 +/- 8.60 pg/ml for rT3) were increased 19- and 22-fold respectively, over 24 hr. An increase of T4 and rT3 levels occurred also after injection of total hypophyseal extract and Con A II glycoprotein fraction of a tilapia pituitary homogenate, whereas the protein fraction failed to alter plasma concentrations of T4 and rT3. rT3 levels were also significantly increased at 2 hr, but not at 1 hr, after injection of T4. Basal T3 levels (1.90 +/- 0.22 ng/ml) were reduced by half over 24 hr in all experiments. These results suggest the existence, in tilapia, of a 5-D pathway deiodination of T4 which is pituitary independent. Stimulation of T4 release is always followed by an increase in plasma rT3 levels.
authors: Laboratory of Comparative Endocrinology, Zoological Institute, K.U.L., Leuven, Belgium.
authors: N
authors: N
authors: Byamungu
authors: S
authors: S
authors: Corneillie
authors: K
authors: K
authors: Mol
authors: V
authors: V
authors: Darras
authors: E R
authors: ER
authors: Kühn
mesh_terms: D000818:Animals; D003208:Concanavalin A / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D005399:Fishes / Q000097:blood / Q000502:physiology*; D005640:Follicle Stimulating Hormone / Q000494:pharmacology*; D013006:Growth Hormone / Q000494:pharmacology*; D008297:Male; D010902:Pituitary Gland / Q000502:physiology; D013961:Thyroid Gland / Q000187:drug effects / Q000502:physiology*; D013972:Thyrotropin / Q000494:pharmacology*; D013974:Thyroxine / Q000097:blood*; D014020:Tissue Extracts / Q000502:physiology; D014284:Triiodothyronine / Q000097:blood*
chemical_list: D014020:Tissue Extracts; D014284:Triiodothyronine; D003208:Concanavalin A; D005640:Follicle Stimulating Hormone; D013972:Thyrotropin; D013006:Growth Hormone; D013974:Thyroxine