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Function of Pituitary-Thyroid Axis in Copper-Deficient Rats^1,2,

Department of Nutrition and Food Science, University of Arizona, Tucson, AZ 85721

Thirty male weanling Sprague-Dawley rats were fed either a copper-deficient diet (0.85 mg Cu/kg) or a copper-adequate diet (8 mg Cu/kg). After 7 weeks, the rats were fasted for 12 hours, and injected intravenously with thyrotropin-releasing hormone (TRH, 30 ng/100 g body weight). Six rats from each treatment were killed at 0, 0.5, 1, 2 and 4 hours after TRH injection. Sera obtained at 0, 0.5 and 1 hour, and at 0, 2 and 4 hours were used for the radioimmunoassay of thyroid-stimulating hormone (TSH) and thyroxine (T₄), respectively. Reduction in liver copper content confirmed that the rats fed the test diet were copper-deficient. Serum TSH levels appeared to have peaked at 30 minutes but declined to a level higher than basal at 1 hour. No difference in TSH response was observed between the 2 treatments. Serum T₄ response to TRH was reduced in the copper-deficient as compared to the adequate rats at all time intervals. After 2 hours a slight elevation was observed in the controls, but marked elevations in T₄ were observed in both treatments at 4 hours. This reduction in T₄ levels could be due to an impaired T₄ synthesis or release in copper-deficient rats.

KEY WORDS: • copper deficiency • thyroid-stimulating hormone • thyroxine

¹ Aided by funds from the American Heart Association and by Biomedical Research Support Grant S07 RR07002 awarded by the National Institutes of Health.

² Published as article number 3584 of the Arizona Agricultural Experiment Station.

³ To whom reprint requests and correspondence should be sent: Dept. of Nutrition and Food Science, 309 Agricultural Sciences Building, University of Arizona, Tucson, AZ 85721.

Manuscript received 17 March 1982.