The thyroidal response to chronic goitrogenic stimulation and the persistence of effects of early goitrogenic stimulation

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Abstract
The effects of overstimulation of the thyroid gland induced by the feeding of rapeseed meal or thiouracil during the growing period persisted for as long as 75 wk after withdrawal of the source of goitrogen from the diet. Thyroid weight, thyroid I content and radioiodine uptake were all increased in birds [White Leghorn pullets] which had received goitrogen during the growing period. Follicle diameter was greater and the height of epithelial cells was lower than in control birds. The thyroid changes in these birds were deduced to be compensatory because production characteristics were normal, and distribution of a dose of radioiodine into thyronines (T3 + T4 [triiodothyronine and thyroxine, respectively]) was similar in the birds which had received goitrogen during the growing period and in the control birds. Birds which were being fed rapeseed meal at the time the thyroid glands were examined showed effects which varied in magnitude according to the length of time over which rapeseed meal had been fed. Thyroid weight, follicle diameter, amount of epithelial tissue present and the total amount of I in the thyroid glands increased, whereas coupling efficiency (radioiodine-labeled T3 + T4)/(monoiodotyrosine/diiodotyrosine) declined with time.

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