The Concentration and Significance of the Butanol-Extractable I131 of Serum in Patients with Diverse States of Thyroidal Function

Abstract

Thyroxine, if not truly the active thyroid hormone ( 1, 2) is clearly the principal iodine-containing compound released by the thyroid gland, and ordinarily comprises the largest fraction of the plasma's protein-bound iodine (3-6). Many investigators have, therefore, attempted to assess thyroidal function by measuring the concentration of protein-bound I'll (PB1181) in the plasma following the administration of radioactive iodine (7-11). The PBI111 (12), or even the total radioactivity in the plasma (13, 14), determined several days after the administration of the tracer, reflects the radioactivity of circulating thyroxine, except in patients who have received large doses of 1181 (15).It has been shown that the hormonal iodine which is extractable from serum with butanol and not re-extractable with alkali (hereafter referred to as the butanol-extractable iodine) is composed largely of thyroxine. Its concentration in serum differs significantly from that of the protein-bound iodine (16).The present communication reports the results in 109 patients with varying states of thyroidal function in whom the plasma's concentration of radioactive butanol-extractable iodine was determined both one and three days after the administration of 181. From a correlation of these results with measurements of the amount of 11l8 accumulated by the thyroid gland, an estimate of both the amount and the rate of turnover of glandular hormone has been made.

Clinical and Physiological Observations in a Patient With an Idiopathic Decrease in the Thyroxine-Binding Globulin of Plasma*

“…These were analyzed for their concentration of I". Aliquots of urine were also subjected to a butanol extraction procedure, similar to that described for serum (10), and the proportion of total urinary I" present as butanol-extractable I" was determined. The several functions calculated and their derivations are described in the Appendix.…”

Simultaneous Estimation of Rates of Thyroxine Degradation and Thyroid Hormone Synthesis1

“…

Implicit in many studies of thyroidal function is the assumption that the rates of synthesis and degradation of thyroid hormone are equal (1)(2)(3)(4) (1,(4)(5)(6). This pool is capable of maintaining, at least for a time, constancy of SPI, despite marked discrepancies between rates of hormonal production and degradation (7).

A method has been devised for simultaneous estimation of the rate of degradation of thyroxine within the body and the rate of iodination of organic moieties within the thyroid gland.4 The equivalence of these two functions has been assessed in patients with diverse thyroidal states.

…”

“…Implicit in many studies of thyroidal function is the assumption that the rates of synthesis and degradation of thyroid hormone are equal (1)(2)(3)(4) (1,(4)(5)(6). This pool is capable of maintaining, at least for a time, constancy of SPI, despite marked discrepancies between rates of hormonal production and degradation (7).…”

“…Yet (1,(4)(5)(6). This pool is capable of maintaining, at least for a time, constancy of SPI, despite marked discrepancies between rates of hormonal production and degradation (7).…”

Diagnostic Procedures in Thyroid Disease

“…They are convenient in requiring only one sample which can easily be measured in a distant laboratory, but have little other advantage over the types of test based on uptake measurements. The results may be expressed either simply as a concentration of P.B.131I (Goodwin et al, 1951;Ingbar et al, 1954) as a 'conversion-ratio,' the ratio of the P.B.131I to iodide-131I in the plasma (Sheline et al, 1951), or possibly more sensitively as a ratio of P.B.131I to salivary iodide (Thode et al, 1954). This last procedure takes advantage of the fact that the iodide of the plasma is concentrated into the saliva, normally about thirty-fold; but this is not so important since the really critical measurement of this test is that of the plasma P.B.'11I.…”