Iodoprotein and iodoamino acid distribution in pig thyroid tissues at different periods of development.

A biochemical study of the thyroid tissue in pigs at various stages of development was undertaken. The iodine and protein concentrations, and the iodoamino acid content of thyroglobulin (TG) were determined. Expressed as mu 127I/100 mg wet tissue, the mean iodine content of pig fetus is 66.4, 89.2 in the piglet and 168 in the adult pig. TG accounts for 95% of total proteins; its content increases with age. Mean iodine content of TG is 0.70 mug 127I/100 microgram in the fetus, 0.78 in the piglet and 0.97 in the adult pig. The average number of molecules of thyroxine residues is 1.6 in the fetus, 2.2 in the piglet and 3.5 in the adult. Average triiodothyronine residues are lower around birth than in the adult. At all stages of development, synthesis of thyroxine is less effective in the pig than in the human, relative to the iodine content of TG. In contrast to the human, iodinated compounds are not found at a very low level near birth, but TG and iodine content regularly increase.