Ontogeny of thyroid tissue and tissue thyroid hormone clearance in rainbow trout embryos reared at two temperatures

摘要

The development of the thyroid tissue and clearance of thyroid hormones was studied in rainbow trout embryos reared at 8.5 and 5.5deg C. The pattern of whole body thyroid hormone clearance did not appear to be related to rearing temperature. Thyroid follicles appeared at different times in embryos reared at the 2 temperatures, but these differences could not be predicted based on the temperature. These results suggest that the development of the thyroid tissue and the clearance of yolk hormones are not directly related to rearing temperature. Immunohistochemical staining of the thyroid tissue indicated 2 phases of thyroid activity, 1 associated with hormonogenesis and the other a later phase of hormone release. There was no increase in whole body thyroid hormone level associated with the time of appearance of colloid in the follicles. It seemed likely that the extraction method used did not remove thyroid hormone associated with colloidal thyroglobulin in the follicles. There was also evidence of sporadic increases in 'whole body' thyroid hormone content, after the development of phase 2 thyroid follicles which might indicate pulsatile release of thyroxine and triiodothyronine.