Decreased Triiodothyronine Binding to the Hepatic Nuclear Thyroid Hormone Receptor in the Diabetic Mouse

<p>The diabetic C57BL/KsJ-<em>db m</em> mouse has abnormal thyroid hormone levels and indications of thyroid hormone resistance. To investigate the basis of these abnormalities, the hepatic nuclear thyroid hormone receptor was extracted with 0.4 M KCl, 1.1 mM MgCl₂, 20 mM Tris/HCl, pH 7.9 from hepatocyte nuclei of normal C57BL/KsJ, heterozygous C57BL/KsJ-<em>db</em> <em>m (db/m)</em>, and diabetic C57BL/KsJ-<em>db m</em> (<em>db/db</em>) mice. Normal and heterozygous mice were grouped together as the controls. Triiodothyronine (T₃) binding studies at 4°C using nitrocellulose filtration to separate free T₃ from receptor bound T₃ demonstrated an apparent dissociation constant of (1.3 ± 0.8) x 10^-10 M for controls which was significantly less than that of (8.7 ± 10.4) x 10^-10 M for diabetic mice (p < 0.01, one tailed <em>t</em>-test). However, the maximum binding capacity were not significantly different at (4.6 ± 3.3) x 10^-13 moles/mg DNA for controls and (3.2 ± 4.6) x 10^-13moles/mg DNA for diabetic mice. Triiodothyronine-receptor dissociation rates also demonstrated a significantly greater dissociation of the diabetic T₃-receptor complex (p < 0.05, one-tailed <em>t</em>-test). The half-life for dissociation was 101 ± 22 hours for controls versus 70 ± 21 hours for diabetics. Although equilibrium binding conditions were not achieved, the use of Scatchard analysis to compare the controls and diabetics is justified by the similar conclusion from dissociation experiments that T₃ binding is significantly decreased in the diabetic mouse. Triiodothyronine was found to interact freely with the receptor, binding 98 ± 2% of that predicted to be bound if T₃ were free in solution, even though 70 ± 2% of the T₃ is initially adsorbed to the glassware. However, adsorption to glassware did explain the negative values for specific binding above 10^-6 M T₃ as calculated from the difference between total and nonspecific binding. Isoelectric focusing and sedimentation velocity of the receptor preparation did not demonstrate any differences between control and diabetic mice. Comparison of the level of saturation of the nuclear T₃ receptor in the diabetic mouse to other obese syndromes suggests that the decreased T₃ binding reported here has a significant impact on the obesity of the diabetic mouse.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Biochemistry

Year

1988

Author dc:creator

• DeWind, Thomas J.

Contributors dc:contributor

• George M. Lessard
• R. Bruce Wilcox
• E. Clifford Herrmann
• Lamont Murdoch
• Richard Fehn
• Terry D. Shultz

• Animal Experimentation and Research
• Biochemistry
• Biostatistics
• Endocrinology, Diabetes, and Metabolism
• Hormones, Hormone Substitutes, and Hormone Antagonists
• Laboratory and Basic Science Research
• Triiodothyronine; Receptors, Thyroid Hormone; Binding Sites; Thyroid Hormones

Statement dc:rights

• This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Language dc:language

English

Repository record dc:identifier

https://scholarsrepository.llu.edu/etd/1510

OAI identifier oai:identifier

oai:scholarsrepository.llu.edu:etd-2286