Abstract
Thyroidectomy decreases glycolytic and gluconeogenic enzyme activities in rat liver (1, 2). On the other hand, thyroxine increases hepatic phosphoenolpyruvate carboxykinase (3) and gluconeogenesis (4) in the rat. It is also known that human and rat jejunal glycolytic enzymes are influenced by dietary carbohydrates (5). In order to determine the effect of thyroid hormone on human intestinal enzymes, we studied four normal young men and three hypothyroid male patients who were given triiodothyronine together with different types of carbohydrate diets.
Materials and methods. Four normal young men∗, ages 19-22, served as the control group. They were housed on a metabolic ward and fed diets containing 3000 calories as shown in Table I. During fasting, only calorie-free liquids were allowed. The carbohydrate-free diet was a part liquid, part solid formula containing 70% of calories as fat (corn oil) and 30% as protein (sodium caseinate) together with meat and eggs. The glucose and fructose diets consisted of 50% of calories as the sugar, 30% as fat, and 20% as protein, together with a standard mineral supplement. Nonavitamins,∗∗ one capsule, were given daily including the fasting periods. Periods 1 through 4 included no added thyroid hormone. Periods 5 through 8 included triiodothyronine (T3, Cytomel) 100 μg orally every 8 hr. Symptoms of hyperthyroidism occurred in three of the four subjects, including variable tachycardia, loose stools, and irritability. Jejunal biopsies were obtained after overnight fasting at the end of each dietary period, using the Crosby-Kugler intestinal biopsy capsule. The tissue thus obtained was prepared as described previously (5) and the activities of glycolytic enzymes were determined spectrophotometrically: Pyruvate kinase (PK) (6), fructose-1-phosphate aldolase (F1PA), and fructose-1,6-diphosphate aldolase (FDPA) (7) and the gluconeogenic enzyme, fructose diphosphatase (FDPase) (8).
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