Iodoaminoacids in normal and iodine-deficient rat thyroids: comparison between 125I and 127I distribution.

Abstract

Rats on normal and low-iodine diet (LID) were sacrificed 72 hr after 125I injection. 125I distribution in thyroid hydrolysates was determined by paper chromatography and 127I distribution by gas chromatography by means of the N,O-dipivalyl methyl esters. Amounts of all 127iodoamino acids were very much lower in LID glands. 125I-3,3′,5′T3 (T3′) was found in LID glands only, but 127I-T′3 was found in both normal and LID glands. 125I-MIT/DIT and 125I-T3/T4 ratios were markedly increased in LID glands as was the 127I-MIT/DIT ratio, but 127I-T3/T4 ratio was increased by only a small factor, compared to the increase in the other ratios. 127I-T3 values then remained below T4 values in LID glands. Specific activity (SA) per iodine atom of MIT or DIT was within the same range in normal glands, but was greater than that of T3 and T4. In LID glands all SA were very much larger. Again, SA of MIT or DIT was within the same range, which was very close to that of T3; SA of T4 was lower, on the contrary. Preferential syn...