THE EFFECT OF THYROTROPHIC HORMONE ON THE PLASMA THYROID HORMONES IN MAN

SUMMARY The effect of thyrotrophic hormone administration on the plasma pattern of the iodine‐containing amino acids has been studied in 11 normal and 12 thyrotoxic subjects. The method employed a paper chromatographic separation of the individual iodinated compounds in plasma extracts prepared with an anion exchange resin. The iodine‐containing amino acids were then located by chemical staining by means of the ceric sulphate‐arsenious acid reaction. Parallel chemical and radioactive studies were carried out in eight of the thyrotoxic subjects after I 131 therapy. In the normal subjects, the intramuscular administration of thyrotrophic hormone (TSH ; hog origin), 30 U.S.P. units, was followed by the appearance of diiodotyrosine (DIT) and increased amounts of the iodothyronines, particularly triiodothyronine (T3) in the plasma. In hyperthyroid subjects TSH administration was followed by increases in the iodothyronine fraction. In most cases DIT was present before TSH administration, and the increases in DIT after TSH administration were smaller than those seen in normal subjects. Similar results were obtained in the parallel radioactive studies. The pattern of iodine‐containing amino acids previously described in hyperthyroidism has been reproduced in normal subjects by the administration of TSH. The association of the presence of DIT with increased amounts of T3 under conditions of thyroid over‐activity suggests that these two phenomena may be related. It is suggested that the release of DIT from the gland under these conditions may indicate a biosynthetic mechanism for the production of greater amounts of the more rapidly acting T3.