T3-hyperthyroidism caused by enhanced and shifted T4-conversion.
Radioactivities of endogenously labelled thyroid hormones following in vivo application of 131 I and extraction from serial blood samples, show that T4 secretion is enhanced in T3-hyperthyroidism as it is in T4-T3-hyperthyroidism. In an extreme case of T3-hyperthyroidism with serum concentrations (SC) of T3 nearly equal to T4 (1000 ng/dl and 1800 ng/dl, respectively) tracer studies revealed a very short half life of T4 when compared to T3 (21.8 and 20.2 hrs., respectively). In 110 cases with both types of hyperthyroidism, regression analysis showed that T3/T4 ratio as an indicator of T4 conversion, as well as T3/rT3 ratio as an indicator of the direction of the conversion, are related to T4SC (r = -0.84 and -0.72, respectively, p less than 0.001). T3-hyperthyroidism is described by high values of these ratios. For the definition of T3-hyperthyroidism it is suggested that both T4 and rT3SC are within the normal range (T4 less than or equal to 11.5 micrograms/dl, rT3 less than or equal to 43.0 ng/dl) and according to this definition, T3/rT3 is higher than in T4-T3-hyperthyroidism and in an undefined group (24.8 +/- 4.5 vs. 6.3 +/- 0.4 or 7.5 +/- 0.4, respectively). By means of the ratios the undefined group may be allocated to T4-T3-hyperthyroidism. The T3/rT3 ratio is value of greater than 10 has a frequency of 88% in thus defined T3-hyperthyroidism and a ratio of less than or equal to 10 is found in 90% of the other cases.(ABSTRACT TRUNCATED AT 250 WORDS)
D006098:Granulocytes / Q000378:metabolism; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood / Q000209:etiology*; D007457:Iodine Radioisotopes; D007700:Kinetics; D013347:Subcellular Fractions / Q000378:metabolism; D013974:Thyroxine / Q000097:blood / Q000378:metabolism*; D014284:Triiodothyronine / Q000097:blood / Q000502:physiology*; D014285:Triiodothyronine, Reverse / Q000097:blood
D007457:Iodine Radioisotopes; D014284:Triiodothyronine; D014285:Triiodothyronine, Reverse; D013974:Thyroxine