Studies of the congenitally goitrous sheep. Composition and metabolism of goitrous thyroid tissue.

1. Normal and congenitally goitrous thyroid tissue was examined to identify the defective mechanism in the goitrous glands. 2. The uptake of [(131)I]iodide from the blood stream into the goitrous glands (average 74.9%) was significantly greater than normal (average 43.5%; P < 0.005), as was the rate of [(131)I]iodide release (goitrous t((1/2)) average 72.3hr., normal t((1/2)) average 198.7hr.; P0.025). 3. The l-[(131)I]-iodotyrosine-deiodinase activity was significantly (P0.02) greater than normal in goitrous-thyroid slices. 4. The 0.9%-sodium chloride-soluble proteins of [(131)I]-iodide-labelled thyroid glands were fractionated with ammonium sulphate: 68.7+/-4.0% of the total radioactivity appeared in the 35-45%-saturation precipitate from normal gland extracts, but less than 20% of the total radioactivity was in in this fraction from goitre extracts. 5. Ultracentrifugal analysis of 0.9%-sodium chloride-soluble proteins of goitrous glands showed no protein of S(20,w) 19-20s (thyroglobulin) even when the animals had previously received 0.1-2.0mg. of l-thyroxine/day intramuscularly for 40 days. The major proteins of goitrous glands had S(20,w) 3.2-7.6s. 6. The incorporation in incubated slices of [(14)C]proline and [(14)C]leucine into soluble proteins precipitated by 35-42%-saturated ammonium sulphate was markedly lower in goitrous tissue. 7. It was concluded that the goitrous tissue exhibited defective biosynthesis of thyroglobulin.