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Effects of Thyroid Hormone on the Insulin Receptor in Rat Liver Membranes^*

Clinical Investigation Department, Kyle Metabolic Unit, Walter Reed Army Medical Center, Washington, D.C. 20012
Department of Medicine, The Uniformed Services University of the Health Sciences, Bethesda, Maryland 20014
the Diabetes Branch, National Institute of Arthritis, Diabetes, and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20205

Address requests for reprints to: Kenneth D. Burman, M.D., Ward 47, Kyle Metabolic Unit, Clinical Investigation Department, Walter Reed Army Medical Center, Washington, D.C. 20012.

Abstract

Although many studies have investigated the complex interrelationships between thyroid hormone levels and insulin-glucose secretion and action, there is at present a lack of information concerning the effects of various thyroid hormone levels on insulin receptors. In the present study, rat liver membranes were prepared from control, hyperthyroid [10 µg L-T₄ (T₄)/100 g BW for 14 days], and hypothyroid rats and the binding characteristics of [¹²⁵I]iodoinsulin to these membranes were studied. In addition, serum T₃, T₄, glucose, and insulin levels were measured. The mean (±SD) serum T₄ and T₃ levels were higher (P < 0.05) in the T₄-injected rats than in the hypothyroid rats (T₄, 9.1 ± 0.6 vs. 1.7 ± 0.4µg/dl; T₃, 144 ± 18 vs. 30 ± 16 ng/dl). When compared to controls, glucose levels were higher in the hypothyroid rats (116 ± 1 vs. 141± 14 mg/dl; P< 0.05) and were statistically unaltered in thyrotoxicosis. Plasma insulin levels were increased in hypothyroidism (6.5± 0.8 vs. 10.8 ± 2.9 µU/ml; P < 0.05) and decreased in thyrotoxicosis (7.5 ± 0.5 vs. 28.3 ± 15 µU/ml; P < 0.05). Despite these alterations, membrane binding and the derived Scatchard plots were not significantly different in the hyperthyroid or hypothyroid groups.

In summary, the present studies indicate that plasma membrane insulin receptor number and affinity are unaltered regardless of the thyroid state of the rat.

Footnotes

^* The opinions or assertions contained herein are the private views of the authors and are not to be construed as offical or reflecting the views of the Department of the Army or the Department of Defense.

Received October 9, 1981.