Concentrations of seven iodothyronine metabolites in brain regions and the liver of the adult rat.
The concentrations of the iodothyronine metabolites T(4), T(3), 3,5-diiodothyronine (3,5-T(2)), 3,3'-diiodothyronine (3,3'-T(2)), reverse T(3) (rT(3)), 3,3'-T(2) sulfate (3,3'T(2)S), and T(3) sulfate (T(3)S) were measured in 12 regions of the brain, the pituitary gland, and liver in adult male rats. Quantification of iodothyronine was performed by RIA following a newly developed method of purification and separation by HPLC. 3,5-T(2), 3,3'-T(2), rT(3) and T(2)S were detectable in the low femtomolar range (20-200 fmol/g) in most areas of the rat brain. T(3)S was detectable only in the hypothalamus. The concentrations of T(3) and T(4) were approximately 20- to 60-fold higher, ranging between 1 and 6 pmol/g. There was a significant negative correlation between the activities of inner-ring deiodinase and T(3) concentrations across brain areas. In the liver, 3,5-T(2), rT(3), and T(3)S were measurable in the low femtomolar range, whereas 3,3'-T(2) and 3,3'T(2)S were not detectable. 3,5-T(2) and 3,3'-T(2) were not detectable in mitochondrial fractions of the brain regions. Tissue concentrations of 3,5-T(2) exhibited a circadian variation closely parallel to those of T(3) in the brain regions and liver. T(3) was not a substrate for outer-ring deiodination under different experimental conditions; thus, it remains unclear which substrate(s) and enzyme(s) are involved in the production of 3,5-T(2). These results indicate that five iodothyronine metabolites other than T(3) and T(4) are detectable in the low femtomolar range in the rat brain and/or liver. The physiological implications of this finding are discussed.
Pinna
Graziano
G
Department of Radiology and Nuclear Medicine (Radiochemistry), Universitätsklinikum Benjamin-Franklin, Free University of Berlin, Hindenburgdamm 30, 12200 Berlin, Germany.
Brödel
Oliver
O
Visser
Theo
T
Jeitner
Andreas
A
Grau
Hannah
H
Eravci
Murat
M
Meinhold
Harald
H
Baumgartner
Andreas
A
D000818:Animals; D001923:Brain Chemistry / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid; D002940:Circadian Rhythm / Q000502:physiology; D007453:Iodide Peroxidase / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D010902:Pituitary Gland / Q000378:metabolism; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000493:pharmacokinetics / Q000494:pharmacology; D013347:Subcellular Fractions / Q000378:metabolism; D013963:Thyroid Hormones / Q000378:metabolism* / Q000493:pharmacokinetics; D013974:Thyroxine / Q000378:metabolism; D014018:Tissue Distribution; D014284:Triiodothyronine / Q000378:metabolism
D011994:Recombinant Proteins; D013963:Thyroid Hormones; D014284:Triiodothyronine; D007453:Iodide Peroxidase; D013974:Thyroxine