No abstract

The effects of feeding a heat treated rapeseed meal, which has goitrogenic properties, on the concentrations of plasma pituitary and thyroid gland hormones was investigated in broiler cockerels of between 3 and 10 weeks of age. For purposes of comparison, two other groups were included in the study; one was fed the goitrogen, methimazole, and the other a normal control diet. The hormones measured were thyroxine (T4), triiodothyronine (T3), growth hormone (GH), prolactin, and luteinizing hormone (LH). In birds fed methimazole the thyroid glands were greatly enlarged, the concentrations of plasma T4 and T3 were depressed and the concentrations of growth hormone, prolactin, and LH were elevated. The high level of plasma LH in the birds fed methimazole was not due to the absence of sufficient concentrations of plasma testosterone to exert a negative feedback effect. Although the inclusion of rapeseed meal in the diet caused the thyroid glands to enlarge, the concentrations of all the hormones studied, with the exception of T3, were similar to those in the control birds. However, there was a tendency, which was more pronounced in birds of between 3 and 5 weeks of age, for rapeseed meal to depress the concentrations of plasma T4, GH, and LH and to increase the concentration of plasma prolactin. The most significant observation was that between 3 and 5 weeks of age the inclusion of rapeseed meal in the diet significantly (P less than .001) depressed the concentration of plasma T3.

Normal fed and 2 days fasted Warren chickens were injected intravenously with 100 micrograms of ovine growth hormone (GH) and ovine prolactin and plasma concentrations of thyroid hormones were assayed prior and up to 2 h after injection. Fasting alone decreases T3, but increases T4. An injection of GH resulted in increases of plasma T3 concentrations in two fasting experiments by 40% (after 3/4 h) and 104% (after 1 h). In normal fed animals no increase is observed in the first experiment, whereas a 35% increase occurs in the second one. An injection of 100 micrograms prolactin does not influence T3 in normal fed or fasting animals. Both GH and prolactin, however, may decrease plasma concentrations of T4. In a separate experiment 50 micrograms and 200 micrograms of GH raised the decreased T3 levels after fasting by 39% and 60% respectively 1 h after injection and by 24 and 61% respectively in normal fed chicken, whereas prolactin was ineffective in this regard. Using Hisex chickens, the influence of an injection of 100 micrograms GH on plasma concentrations of thyroid hormones could be confirmed. At the same time GH increases the liver 5'-monodeiodinase activity by 330% after 1 h and by 147% after 2 h. The peroxidase activity is not influenced in normal fed chickens, but GH decreases this activity in food deprived animals after 1 h and 2 h. It is concluded that ovine GH, but not prolactin, stimulates the peripheral conversion of T4 into T3 in both normal fed and food deprived chicken and that this effect is dose dependent.

Cells binding anti-bovine TASH beta serum were found exclusively in the rostral lobe of the adenohypophysis of the drake using the peroxidase-antiperoxidase complex unlabelled antibody method. The specificity of the binding of the anti-serum to TSH cells was established by relating the morphology and relative abundance of immunochemically stained cells to the TSH content of the adenohypophysis after experimentally altering the activity of the pituitary-thyroid axis. The TSH activity of the adenohypophysis was assessed indirectly, by the weight of the thyroid glands, and directly, by bioassay. As determined by bioassay, the TSH content of the rostral lobe of the adenohypophysis was much greater than that of the caudal lobe. Compared with control drakes, immunochemically stained cells in birds fed a goitrogen, methimazole, seemed to be enlarged and were closer together, while the stained cells in drakes injected with thyroxine were shrunken and less intensely stained. The TSH content of the adenohypophysis was increased in drakes fed methimazole. Castration did not alter the TSH content of the adenohypophysis or change the morphology of immunochemically stained cells. These observations suggest that in the drake: 1) anti-bovine TSH beta serum binds specifically to TSH cells; 2) the TSH cells occur in the rostral and not in the caudal lobe of the adenohypophysis; and 3) the activity of TSH cells is not inhibited by the feedback effects of gonadal steroids.