Dietary Selenium Status and Plasma Thyroid Hormones in Chicks

Transcription

1 by The Humana Press Inc. All rights of any nature whatsoever reserved /86/ $02.00 Dietary Selenium Status and Plasma Thyroid Hormones in Chicks L. S. JENSEN,* G. L. COLNAGO, K. TAKAHASHI, AND Y. AKIBA Department of Poultry Science, University of Georgia, Athens, Georgia Received September 13, 1985; Accepted November 25, 1985 ABSTRACT Experiments were conducted to study the effect of marginal levels of selenium and vitamin E on plasma thyroid hormones of meattype chicks. Plasma thyroxine (T4) was significantly increased when a semipurified diet was supplemented with either selenium or vitamin E. Triiodothyronine (T3) was also significantly increased by vitamin E and in one experiment with selenium supplementation. No significant increase in these hormones was observed in birds fed a corn-soybean-meal diet supplemented with these nutrients. Plasma corticosterone level was reduced and weight of the bursa of Fabricius increased by selenium or vitamin E supplementation. These nutrients may be necessary for providing the optimum thyroid conditions for activity of thyroid peroxidase. Index Entries: Selenium; vitamin E; plasma thyroid hormones; thyroxine; triiodothyronine; plasma corticosterone, and selenium-vitamin E deficiency; selenium-vitamin E deficiency, and bursa of Fabricius weight. INTRODUCTION Thyroid function of domestic animals is known to be altered by many environmental factors. Total caloric deprivation is associated with *Author to whom all correspondence and reprint requests should be addressed. Biological Trace Element Research ] ] Vol. 1 O, 1986

2 12 Jensen et al a decrease in triiodothyronine (T3) production and serum T3 concentration in man and rats (1-3). The mechanism of this fall in serum T3 seems to be impaired peripheral 5'-deiodination of thyroxine (T4), since liver homogenates from rats fasted for 2-3 d have shown impaired T 4 to T 3 conversion in vitro (4-5). In chickens, short periods of fasting reduced serum T3 concentration and increased serum T 4 (6). Thyroidal activity in rats (3) and laying hens (7) is influenced by dietary composition. Specific nutrient effects on thyroidal activity have also been studied. Vitamin-A-deficient rats had increased plasma T3, T4, and free thyroxine index (8). Plasma T 4 concentration and free T 4 increased in goats fed diets deficient in cobalt and vitamin B12 for 23 wk (9). Chicks fed diets deficient in aromatic amino acids, lysine, or valine had reduced thyroidal activity, but the deficiency had to be very severe (10,11). In rats, magnesium or potassium deficiency reduced thyroidal activity (12). Copper, iron, or zinc deficiency also resulted in decreased blood T 3 and/or T 4 in rats (13-16). Calves given selenium (Se) subcutaneously or vitamin E intramuscularly had increased T4 levels in the peripheral blood 48 h after dosage (17). In view of these results, the present studies were undertaken to determine if marginal dietary levels of Se and/or vitamin E would affect plasma thyroid hormones in the chick. METHODS Day-old male broiler chicks of the Hubbard or Arbor Acre strains, obtained from a commercial hatchery, were housed in electrically heated battery brooders under constant illumination, with feed and water supplied ad libitum. The composition of the basal diets, which contained no supplementary Se, vitamin E, or antioxidants, is shown in Table 1. Calculated vitamin E levels for the corn-soybean and semipurified diets were 14.5 and 2.5 IU/kg, respectively. Actual Se levels for the two diets were and mg/kg, respectively. Sodium selenite served as the source of supplemental Se and all-rac-ec-tocopheryl acetate as the source of vitamin E. Diets were analyzed for their Se content by the method of Wetter and Ullrey (18). Four groups of 10 chicks/group were used for each treatment in Expts. 1, 3, and 4 and eight groups of 10 chicks in Expt. 5. Twelve birds/ treatment were used in Expt. 2. Body weight and feed intake data were based on pen averages in all experiments, except Expt. 2, in which body weight was a mean of individual chicks, and feed intake was not measured. At 21 d of age, blood samples were taken by heart puncture, using a heparinized syringe from 10 chicks/treatment in Expts. 1 and 2 and eight chicks/treatment in Expts. 3, 4, and 5. Plasma samples were stored at -40~ until assayed for hormones. In Expts. 2, 3, and 4, chickens were killed by cervical dislocation after blood collection and the bursa of Fabricius was removed and weighed. Biological Trace Element Research Vol. 1 O, 1986

3 Selenium and Thyroid Hormones 13 Ingredients TABLE 1 Composition of Basal Diets (%) Diet Corn-Soybean (CS) SemiPurified (SP) Glucose (cerelose) Isolated soy protein Torula yeast Yellow corn Soybean meal (49% protein) Poultry fat Dicalcium phosphate Limestone Cellulose Potassium carbonate Salt Magnesium sulfate H D,L-Methionine Choline chloride (50%) Vitamin mixture" Trace-mineral mixture h Calculated analysis ~ Crude protein (%) ME (kcal/kg) Calcium (%) Phosphorus, available (%) Vitamin E (IU/kg) Selenium (actual analysis) (mg/kg) ~Supplying per kg of feed: vitamin A, 11,000 IU; vitamin D3, 1100 ICU.; menadione sodium bisulfite, 1.1 ing; riboflavin, 4.4 mg; Ca pantothenate, 12.0 mg; nicotinic acid, 44.0 mg; choline chloride, 220 mg; pyridoxine HCI, 2.2 rag; folic acid, 0.55 rag; D-biotin, 0.11 mg; thiamine mononitrate, 2.2 mg; vitamin Bl2, 6.6 ~g. ~Supplying mg/kg of feed: manganese, 60; zinc, 50; iron, 30; copper, 5; iodine, ~Scott, M. L., Nesheim, M. C., and Young, R. J. Nutrition of The Chicken. Ithaca, NY (1982). Plasma T 3 and T4 were determined by radioimmunoassay, using commercial radioimmunoassay kits (Gammacoat [125I]thyroxine and [125I]triiodothyronine radioimmunoassay kits, Clinical Assays, Cambridge, MA). The use of these kits for chicken T 3 and T4 has been validated (7). Plasma corticosterone was determined by radioimmunoassay (19). The data generated by these studies were analyzed using the General Linear Models procedure of the Statistical Analysis System (20) in conjunction with the Duncan separation of mean options to locate significant (P < 0.05) differences among means. Biological Trace Element Research VoL 10, 1986

4 14 Jensen et al. RESULTS The results of these experiments (Tables 2-5) show that feeding diets marginal in Se and vitamin E to chicks reduced plasma T4 concentration. Supplementation of the semipurified diet with 0.1 mg or more Se/kg in all five experiments and with vitamin E in Expt. 4 significantly increased plasma T4 level. A significant increase in plasma T3 was also observed when vitamin E in Expt. 4 and Se in Expt. 5 were added to the semipurified diet (Tables 4,5). Selenium supplementation of a cornsoybean diet did not significantly affect plasma T4 levels (Tables 3,4) and significantly reduced T3 level in one experiment (Table 4). In Expt. 2, Se supplementation of the semipurified diet significantly reduced plasma corticosterone (Table 2). Selenium or vitamin E supplementation of the semipurified diet also appeared to reduce plasma corticosterone level in Expt. 4 (Table 4), but the differences were not statistically significant (P > 0.05). A significant interaction between supplements and type of diet on plasma corticosterone level was observed, however. Supplementation of the semipurified diet with 0.1 ppm of Se significantly increased weight of the bursa of Fabricius in two experiments (Tables 2,3). In Exp. 4 (Table 4), Se or vitamin E supplementation TABLE 2 Effect of Selenium Supplementation of a Semipurified Diet on Plasma Thyroid Hormones and Other Parameters in Chicks ~ Experiment No. Added Se (mg/kg) Parameter Analyzed dietary Se, mg/kg Body wt gain, g + SEM 507 _+ 20 a 513 _+_ 11 a a 445 _+ 20 b Feed intake, g + SEM a 781 +_ 18 a Bursal wt, rag/100 g '~ 252 _+ 11 b BW ~ Plasma T3 ng/ml a a + SEM ~ Plasma T4 ng/ml ~ b ~ b + SEM 3 Plasma corticosterone, a b ng/ml _+ SEM ~ ~Values within a row and experiment without a common letter are significantly different (P < 0.05). 2The basal diet contained a calculated level of 2.5 IU vitamin E/kg. 3Mean of 10 birds/treatment. 2 Biological Trace Element Research VoL 10, 1986

5 Selenium and Thyroid Hormones 15 TABLE 3 Effect of Se Supplementation of Semipurified and Corn-Soy Diets on Plasma Thyroid Hormones and Other Parameters in Chicks (Expt. 3) 1 Se added to diets, ppm Parameter Semipurified diet Analyzed dietary Se, mg/kg-' Body wt gain, g.+ SEM Feed intake, g _+ SEM Bursal wt, rag/100 g BW.+ SEM ~ Plasma T3, ng/ml _+ SEM 3 Plasma T4, ng/ml _+ SEM 3 Corn-Soybean diet Analyzed dietary Se, mg/kg z Body wt gain, g + SEM Feed intake, g _+ SEM Bursal wt, rag/100 g BW + SEM ~ Plasma T4, ng/ml.+ SEM _+ 15 b 460 _+ 7 b a 644 _+ 14 b 641 _+ 8 b 176 _ 20 ~ b a'b 1.56_ ~ "~ a b b a 525 _+ 5 a a 672 _+ 21 ~ b 711 _+ 19 a'b ~' a 329 _ 31 a a ~ 22.4_+0.9 ~ ~Values within a row without a common letter are significantly different (P < 0.05). ~The semipurified diet contained a calculated level of 2.5 and the corn-soybean diet 14.5 Iu vitamin E/kg. ~Mean of eight birds/treatment. increased mean bursa weight by 27 and 24%, respectively, but the differences failed to be significant (P < 0.05). No effect of either Se or vitamin E supplementation of the corn-soybean diet on bursa weight was observed. DISCUSSION The reduction in plasma T4 concentration in chicks fed diets marginal in Se and vitamin E follows the same pattern observed in the deficiency of copper, iron, zinc, and magnesium in rats and some amino acids in chicks (10-16). It is contrary, however, to the increase in T4 levels observed in vitamin A deficiency in rats and in cobalt-bla-deficient goats (8,9). Thyroid hormone levels of chicks fed the corn-soybean diet were not significantly increased by Se or vitamin E supplementation, even though Se levels of the basal diet were not greatly different from those of the semipurified diet. The natural vitamin E present in corn and soybean meal probably accounts for this observation. Exudative diathesis was observed in a few of the chicks fed the semipurified diet, but not in chicks fed the corn-soybean diet. The variation in growth rate among experiments in chicks fed similar diets is probably a result of the variation in chick source. Chicks were obtained from a Biological Trace Element Research Vol. I0, 1986

6 1 6 Jensen et al. TABLE 4 Effect of Se and Vitamin E Supplementation on Plasma Thyroid Hormones and Other Parameters in Chicks (Expt. 4) I Supplement to diet Vitamin E, Parameter None Se, 0.1 ppm 50 IU/kg Semipurified diet Analyzed dietary Se, mg/kg 2 Body wt gain, g + SEM Feed intake, g -+ SEM Bursal wt, mg/100 g BW +-- SEM ~ Plasma T3, ng/ml +_ SEM ~ Plasma T4, ng/ml +_ SEM 3 Corticosterone, ng/mu Corn-Soybean diet Analyzed dietary Se, mg/kg 2 Body wt gain, g + SEM Feed intake, g -+ SEM Bursal wt, mg/100 g BW + SEM ~ Plasma T3, ng/ml _ SEM ~ Plasma T4, ng/ml + SEM' Corticosterone, ng/ml " " ~ " a ~ " " a a a'b b " b b " ~ " a a " a a a a " a " b a'b a'b b a a a ~ IValues within a row without a common letter are significantly different (P < 0.05). 2The semipurified diet contained a calculated level of 2.5 and the corn-soybean diet 14.5 IU vitamin E/kg. 3Mean of eight birds/treatment. commercial hatchery so that the age of the breeder hens and vitamin E and Se reserves in the chicks could result in variation in response to the experimental chick diets. Fasting or food deprivation has been shown to affect thyroid function (1,2,5,6). It is possible that a severe deficiency of a nutrient is fol- TABLE 5 Effect of Selenium Added to a Semipurified Diet on Plasma Thyroid Hormones in Chicks (Expt. 5) ''2 Added Se, mg/kg Parameter Body wt, g +-- SEM Plasma T3, ng/ml _+ SEM a Plasma T4, ng/ml +- SEM ~ a a a b b b b b b 'Values within a row without a common letter are significantly different (P < 0.05). rl~he semipurified diet contained a calculated level of 2.5 IU vitamin E/kg. 'Mean of eight birds/treatment. Biological Trace Element Research VoL 10, 1986

7 Selenium and Thyroid Hormones 17 lowed by a reduction in food intake, consequently masking the specific nutrient effect on thyroid function. The effect of Se on plasma T4 appeared to be independent of its effect on growth rate and feed intake. The Se effect on plasma T4 was observed in all five experiments, but no significant effect of Se on body weight and feed intake was observed in two experiments (Tables 2,4). Furthermore, fasting increased rather than reduced serum T4 in chicks (6). A severe nutrient deficiency may also indirectly affect the thyroid function by putting the animal under a stress situation that will result in elevated plasma corticosterone. There is an inverse relationship between plasma corticosterone and thyroid hormones in chickens (21). We found that Se-vitamin E deficiency elevated plasma corticosterone and reduced plasma T4. Thus, it is possible that the Se, or vitamin E effect on thyroid function is an indirect one via corticosterone. An essential condition for thyroid hormone production is the oxidation of iodide into elementary iodine, catalyzed by peroxidases. In vitro studies have shown that several peroxidases may oxidize iodide to iodine (22). Thus, it seems possible that Se, through the Se-dependent enzyme glutathione peroxidase, may also be involved in iodide oxidation. Reduced glutathione is a potent inhibitor of iodination of bovine serum albumin by thyroid peroxidase (22). Thus, in a deficiency of Se resulting in lower glutathione peroxidase activity, an increase in the level of reduced glutathione in the thyroid gland could inhibit thyroglobulin iodination and, consequently, the synthesis of thyroid hormones. Confirming a previous report (23), we also observed a reduced weight of bursa of Fabricius in chickens fed an Se--vitamin E-deficient diet. Corticosterone administration inhibits bursa of Fabricius growth in chickens (24). Therefore, the increase in plasma corticosterone in the Se-vitamin E-deficient chicks may explain the reduced bursa weight. It may also be an explanation for the immune depression observed in chicks fed Se-vitamin E-deficient diets (25). ACKNOWLEDGMENT Supported by State and Hatch Funds allocated to the Georgia Agricultural Experiment Stations of the University of Georgia. REFERENCES 1. T. J. Merimee and E. S. Fineberg, Metabolism 25, 79 (1976). 2. G. E. Shambaugh and J. F. Wilber, Endocrinology 94, 1145 (1974). 3. A. R. Glass, R. Mellitt, K. D. Burman, L. Wartofsky, and R. S. Swerdloff, Endocrinology 102, 1925 (1978). 4. M. M. Kaplan and R. D. Utiger, J. Clin. Invest. 61, 459 (1978). 5. P. W. Nathanielsz, ]. Physiol. 206, 701 (1970). 6. J. D. May, Gen. Comp. Endocr. 34, 323 (1978). Biological Trace Element Research Vol. 1 O, 1986

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