Effect of Hypothyroidism and Hyperthyroidism on Tissue Thyroid Hormone Concentrations in Rat.
OBJECTIVE
The present study was aimed at determining the effects of experimental hypothyroidism and hyperthyroidism on tissue thyroid hormones by a mass spectrometry-based technique.


METHODS
Rats were subjected to propylthiouracil treatment or administration of exogenous triiodothyronine (T3) or thyroxine (T4). Tissue T3 and T4 were measured by liquid chromatography tandem mass spectrometry in the heart, liver, kidney, visceral and subcutaneous adipose tissue, and brain.


RESULTS
Baseline tissue T3 and T4 concentrations ranged from 0.2 to 20 pmol ∙ g(-1) and from 3 to 125 pmol ∙ g(-1), respectively, with the highest values in the liver and kidney, and the lowest values in the adipose tissue. The T3/T4 ratio (expressed as a percentage) was in the 7-20% range in all tissues except the brain, where it averaged 75%. In hypothyroidism, tissue T3 was more severely reduced than serum free T3, averaging 1-6% of the baseline versus 30% of the baseline. The extent of tissue T3 reduction, expressed as percentage of the baseline, was not homogeneous (p < 0.001), with liver = kidney > brain > heart > adipose tissue. The tissue T3/T4 ratio significantly increased in all organs except the kidney, averaging 330% in the brain and 50-90% in the other tissues. By contrast, exogenous T3 and T4 administration produced similar increases in serum free T3 and in tissue T3, and the relative changes were not significantly different between different tissues.


CONCLUSIONS
While the response to increased thyroid hormones availability was similar in all tissues, decreased thyroid hormone availability induced compensatory responses, leading to a significant mismatch between changes in serum and in specific tissues.
Departments of Pathology, University of Pisa, Pisa, Italy.
Riccardo
R
Donzelli
Clinical and Experimental Medicine, University of Pisa, Pisa, Italy.
Daria
D
Colligiani
CNR Institute of Clinical Physiology, Pisa, Italy.
Claudia
C
Kusmic
Departments of Pathology, University of Pisa, Pisa, Italy.
Martina
M
Sabatini
Departments of Pathology, University of Pisa, Pisa, Italy.
Leonardo
L
Lorenzini
Departments of Pathology, University of Pisa, Pisa, Italy; Scuola Superiore Sant'Anna, Pisa, Italy.
Alice
A
Accorroni
Clinical and Experimental Medicine, University of Pisa, Pisa, Italy.
Monica
M
Nannipieri
Departments of Pathology, University of Pisa, Pisa, Italy.
Alessandro
A
Saba
CNR Institute of Clinical Physiology, Pisa, Italy.
Giorgio
G
Iervasi
Departments of Pathology, University of Pisa, Pisa, Italy.
Riccardo
R
Zucchi
Deiodinases; Hypothyroidism; Mass spectrometry; Tissue thyroid hormones