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A method for free thyroxine estimation in serum, using labelled thyroxine and Sephadex G-25 has been developed. The experiment has been carried out by incubating labelled thyroxine with serum samples and separating the free thyroxine from bound protein in the serum by gel filtration after complete equilibrium between exogenous and endogenous thyroxine. Factors affecting the free thyroxine ratio such as volume of serum used, concentration of labelled thyroxine, time and temperature of incubation were studied and the optimum conditions for the test were selected. The sensitivity of the technique was determined by carrying out twelve estimations of the free thyroxine ratio on samples of pooled normal serum, pooled hypothyroid serum, and pooled hyperthyroid semm. In addition free thyroxine ratio leas determined for 23 hypothyroidisms, 99 euthyroid patients, 40 untreated thyrotoxicosis and 50 normal serum samples. A good correlation with the thyroid status of the patients (as determined) clinically and with ra...

SUMMARY The effective thyroxine ratio (ETR), a single test of thyroid function which has a highly significant linear correlation with serum free thyroxine (T4) concentration, was assessed for its effectiveness in distinguishing the euthyroid state in subjects with abnormalities of T4-binding proteins. In patients with low activity of T4-binding proteins, the diagnostic accuracy of the ETR (80±5%) is superior to that of the free T4 index (62±5%) and free T4 concentration (67%). In patients with elevated T4-binding proteins the diagnostic accuracy of ETR was even higher at 93±5% and again better than the free T4 index (83%) and the free T4 concentration (91%).

In 9 euthyroid obese volunteers, 4 weeks of total caloric deprivation resulted in striking decreases in both total and free triiodothyronine (T3) concentrations in serum together with a slight increase in free thyroxine (T4) concentration. These changes were not associated with alterations in the basal serum TSH concentration or in the TSH or T3 responses to exogenous TRH. It is suggested that the decrease in serum T3 concentration that occurs during starvation results from decreased peripheral conversion of T4 to T3 and may explain, at least partially, the decreased serum T3 seen in clinical states associated with inanition.

The rate of appearance of labeled thyroxine (T4) and albumin in lymph from various areas after simultaneous i.v. injection of the labeled substances in conscious ambulatory sheep has been used to estimate the relative rates of transcapillary movement of stable T4 and albumin. Labeled T4 appeared in hepatic lymph at the same rate as albumin. In intestinal and leg lymph, labeled T4 appeared eight and four times as rapidly as albumin indicating that T4 crosses capillaries in these areas independently of and much more rapidly than albumin and other proteins having similar distribution kinetics. The lymph:plasma ratios for all the T4-binding proteins including albumin were very similar in any one area showing that the relative fractional rates of transcapillary movement of these proteins were very similar. Therefore in extrahepatic areas, transcapillary movement of T4 in the protein-bound form was quantitatively much less important than in the free form. The findings support earlier views, recently questioned, that free T4 is of considerable physiological significance.

A method of measuring free thyroxine (T4) is described which uses the property of Sephadex to bind T4. If 500 mg Sephadex G-25, 40 μI of serum in 4 ml physiological buffer, and 125I-T4 are mixed for 10 min at 37 C in a test tube, the unbound or free 125I-T4 in the aqueous phase is 12% of the 125I-T4 bound to Sephadex. This fraction depends specifically on the low affinity but high capacity of Sephadex for T4, and is unaffected by the amount of T4 or protein in the system although the amount of protein-bound 125I-T4 in the aqueous phase may change markedly. Since Sephadex-bound 125I-T4 is readily measured, the amount of free 125I-T4, and the fraction, free/total 125I-T4 in the dilute serum which forms the aqueous phase in the system are readily calculated. This “free T4 fraction” is related to the in vivo free T4 fraction only if the ratio, total T4: T4 binding protein is the same in this aqueous phase as it is in undiluted serum. These conditions are obtainable by experimental design or calculati...

SummaryThe correlation between the suppression of thyroidal uptake of radioactive iodide and the serum percent free thyroxine (PFT) in rats with hormone-secreting pituitary tumors was studied. Thyr...

Resume Filtration through dextran gel (Sephadex) was applied to the analysis of iodocompounds of serum and thyroid gland. With the proposed technique it is possible to separate iodide, iodotyrosines and iodothyronines. In the case of serum, inorganic iodide, thyroxine bound to proteins and free thyroxine can be identified in one single operation, without pre-treatment of the serum. The presence of abnormal compounds in serum (iodotyrosines, iodinated peptides) can be detected and their amount determined in the same operation. The method was applied to the quantitative determination of the distribution of the radioactivity in the iodo-compounds of serum after administration of small doses (50–80 μC) of Na 131 I to humans. The reproducibility is excellent. The separation of iodo-amino acids of the thyroid was also successfully carried out. This separation can be either analytical or preparative. The advantages and the possibilities of the method are discussed.

When diphenylhydantoin is added to serum in vitro the free thyroxine fraction increases. The apparent magnitude of this effect is diminished by diluting serum prior to analysis. In contrast to the in vitro effect of diphenylhydantoin, there was no significant difference in the free thyroxine fraction of undiluted serum obtained from diphenylhydantoin treated and control patients. Administration of diphenylhydantoin to normal subjects also failed to increase the free thyroxine fraction. Because of a decrease in total hormonal iodine concentration in the serum, the free thyroxine concentration in diphenylhydantoin treated patients and experimental subjects was lower than in their respective controls. Electrophoretic analysis of serum from diphenylhydantoin treated patients showed that a decreased fraction of total serum thyroxine was bound to thyroxine binding globulin. Since free thyroxine concentration was depressed despite the competitive effects of diphenylhydantoin, it appears that the mainten...

SummaryImplantation of rats with growth hormone- and prolactin-secreting pituitary tumors cause weight reduction of the host's pituitary gland. This change was accompanied by a decrease in the pituitary content of TSH and a fall in 131I uptake by the thyroid gland in rats with prolactin- and growth hormone-secreting pituitary tumor MtTW5. These results correlated well with the finding that the proportion of organified iodine and the intrathyroid to serum iodine ratio, in the presence of high concentrations of stable iodine, were higher in the tumor bearing rats. The amount of circulating free thyroxine was measured and found to be slightly lower in tumor-bearing rats. It is suggested that the pituitary tumor hormones have a direct suppressive effect on the host's pituitary gland production of TSH and thus indirectly decrease thyroid function.

The mechanism by which salicylate depresses thyroid function has been investigated in normal rats. Bio-assay of TSH in the plasma of rats was carried out using a modification of the McKenzie mouse procedure. It was demonstrated that the administration of salicylate, 2,4-dinitrophenol and γ-resorcylate (2,6-dihydroxybenzoate) significantly depressed circulating TSH in association with a significant depression in plasma PBI. There was no effect of p-hydroxybenzoate on plasma TSH or plasma PBI. Previous suggestions that the hypermetabolism induced by salicylate and 2,4-dinitrophenol was responsible for the depression in thyroid function may now be excluded, since γ-resorcylate lacks this effect. Using the dialysis procedure of Christensen for the determination of free thyroxine, it has been demonstrated that the in vitro addition of salicylate and γ-resorcylate to rat serum increased the rate of dialysis of radiothyroxine; p-hydroxybenzoate produced a smaller effect. Circulating free thyroxine was elevated a...

It has been investigated whether radioactive contaminants in commercial [ 125 I]thyroxine charges altered the results of free thyroxine estimations in human serum by means of equilibrium dialysis and subsequent MgCl 2 precipitation. By means of paper chromatography, between 4.6 and 11.8% di-iodo- and triiodothyronine and 3–19% ( R )-tri-iodothyronine could be demonstrated as contaminants. Dialysis for purification decreased the contamination, at the same time increasing the thyroxine content (85–95%). The iodothyronines investigated here were precipitable with MgCl 2 showing a ratio of 1:2:4 (T 2 :T 3 :T 4 ), whereas iodotyrosines and iodide did not precipitate. The amount of contaminating iodine compounds increased with the length of time after the synthesis of [ 125 I]thyroxine. By purification dialysis the mean value of free thyroxine was significantly decreased by 0.004%; therefore, a routine predialysis is recommended when free thyroxine is estimated by equilibrium dialysis and MgCl 2 precipitation. In euthyroidism ( n :49) free thyroxine (AFT 4 ; ng%) was 2.16 ± 0.48, in hyperthyroidism ( n :35) 12.30 ± 6.64 and in hypothyroidism ( n :7 0.38 ± 0.26.

(a) The thyroxine-binding proteins were investigated in 23 cases of untreated thyrotoxicosis and 16 cases of untreated hypothyroidism, employing reverse flow paper electrophoresis with the glycine acetate system at pH 8.6 in the Durrum type cell. (b) In active thyrotoxicosis, all sera exhibited diminished thyroxine-binding prealbumin (TBPA) capacities. however, 17 of the 23 sera also had diminished thryroxine-binding alpha globulin (TBG) capacities, as well as markedly elevated free thyroxine fractions. In contrast, six thyrotoxic sera had normal TBG capacities and normal or slightly elevated free thyroxine fractions. (c) In hypothyroidism, the TBPA capacities showed no consistent deviation from the normal range. 11 of the 16 sera had elevated TBG capacities as well as markedly diminished free thyroxine fractions. In contrast, five hypothyroid sera had normal TBG capacities and normal or nearly normal free thyroxine fractions. (d) In thyrotoxicosis and hypothyroidism, the inverse correlation between free thyroxine fraction and TBG was much closer than that with TBPA. When diagnostic categories were considered separately, only TBG bore a significant inverse relation to the free thyroxine fraction. It is therefore suggested that in thyroid diseases TBG may sometimes play a more important role than TBPA in determining the free thyroxine fraction. (e) The demonstrated variations in the binding proteins were considered sufficient to explain the abnormalities of the free thyroxine fractions in thyroid disease.

A critical assessment is made of the separation of thyroxine, free and bound to plasma proteins, and of iodide by means of gel filtration on Sephadex. The following sources of error are discussed: (I) Spontaneous degradation of thyroxine to iodide. (2) The effect of the shape and size of the column on the relative proportions of the separated substances. (3) The effect of the adsorption of free thyroxine on the Sephadex material. The ways by which thyroxine is eluted from the column are also discussed and the error for the method is determined.

To study thyroid-pituitary interrelationships in man, serial measurements of plasma thyrotropin (TSH), protein-bound iodine (PBI) and free thyroxine have been made in hypothyroid patients during therapy with L-thyroxine. In each patient, PBI and free thyroxine concentrations increased progressively during therapy. Conversely, initially elevated plasma TSH concentrations fell, ultimately becoming undetectable in all. Thus, a curvilinear relationship was found relating plasma TSH to both PBI and free thyroxine. At concentrations of free thyroxine below the normal, plasma TSH rises rapidly with small decrements in circulating thyroid hormone. Above this point, relatively smaller reductions in plasma TSH accompany similar increments in total or free thyroxine levels. The secretion of pituitary TSH appears to be finely regulated over a wide range of plasma thyroid hormone concentrations.

Twelve apparently euthyroid patients from Goiaz, Brazil, with the neurological form of endemic cretinism manifested by mental retardation, short stature, upper-motor-neurone disease, deaf-mutism, and multinodular goitre were studied. Although standard thyroid-function studies were normal, subtle evidence of thyroid dysfunction was uncovered. Three of the twelve had total and free thyroxine levels slightly below normal; six had raised basal thyrotrophin levels; five had an increased thyrotrophin response to thyrotrophin-releasing hormone (T.R.H.); and six had a diminished thyroidal response to T.R.H. In contrast, pituitary response to gonadotrophin-releasing hormone was normal. The demonstration that cretins previously thought to be euthyroid do indeed have evidence of thyroidal failure supports the view that these patients were hypothyroid during a critical stage of embryogenesis, resulting in irreversible neurological damage.

Res-O-Mat ETRは血中FT4の新しい指標として開発された甲状腺機能検査法である。原理的には血中T4測定に応用されるCPBAと131I-T3uptake testの原理を同一検査中に行なうのを特徴とする。本検査法に影響を及ぼす因子のうち抽出上澄み液とマイクロピペット中の血清量の比率が重要である。本法は規定の条件に従えばかなり再現性が良いことが確かめられた。臨床成績ではETR値は甲状腺機能異常者と正常者の間に重なりが少なく妊婦は全例正常値を示した。ETR値はTriosorb値およびRes-O-Mat T4値と直線的な相関を示した (γ=0.86, 0.90) 。しかしT7値とは直線的な比例関係 (γ=0.70) ではなく, T7値の平方根と良い相関を示した (γ=0.95) 。

Equilibrium dialysis of thyroxine (T4) in diluted serum at low temperature gives consistent and reproducible values for the dialyzable fraction (DF) of this hormone. The quantity of serum required for the determination is minimized by dilution, which is technically advantageous. Variations caused by temperature, dialysis time, dilution of serum, buffer system, and stability of 125I-T4 could be controlled by parallel use of a normal reference serum in each experiment. The reference serum was assigned a DF value of 0.04%, which was corrected by a factor derived from the ratio of assigned DF to the observed DF calculated from the experimental data for this reference serum. This correction factor permits the observed DF results for concurrent unknown samples to be related to the values for the DF of the normal reference serum. The free thyroxine concentration is calculated from the product of the DF and the total serum thyroxine concentration as determined by competitive binding analysis. The method is convenient for use in clinical laboratories, and data for free thyroxine obtained from patients with metabolic thyroid disorders are diagnostically discriminatory.

Adjusted total thyroxine (T4-Adj), also known as free thyroxine index, is the product of total serum thyroxine (Total T4) and T3 resin uptake ratio (T3 ratio). It was measured in 93 subjects comprising 6 groups with differing thyro-metabolic states. T4-Adj was found to have a highly significant positive correlation with a conventional method for measurement of free thyroxine (free T4) in all patients studied. T4-Adj is a relatively inexpensive determination which corrects for alterations in thyroxine binding proteins and is not influenced by iodine contamination.

Heparin elevates free and total thyroxine in patients with acute myocardial infarction. In 13 patients given heparin as a single bolus the mean free thyroxine rose from 2.4 to 12.4 ng/100 ml (p=0.1 to .001); the mean total thyroxine rose from 7.3 to 8.7 /μg/100 ml (p =0.2 to 0.1). Twelve patients given heparin infusion also demonstrated a rise in free thyroxine but for longer lengths of time. In both groups the rise in free thyroxine was chiefly from a rise in free thyroxine fractions. Acute myocardial infarction, per se, caused no change in free or total thyroxine in 7 patients, nor did warfarin sodium affect these values in 6 patients studied. The demonstration of a rise in total and free thyroxine in 3 athyreotic individuals on replacement therapy with l-thyroxine makes it unlikely that thyroid gland is necessary for this change. It is probable that heparin in some way modifies the thyroxine binding and causes a temporary transfer from its extravascular stores into the intravascular compartmen...

The ratio of free to protein-bound thyroxine (FTF) in human serum was measured by ultrafiltration of serum to which 131I-thyroxine was added. The tracer was purified by preliminary dialysis in the presence of serum protein. This resulted in a lower estimate of FTF(.026 ±.004% SD) and free thyroxine (2.1 ±O.4 × 1O−3 μg/100 ml) than has been reported previously in undiluted serum. The difference between these values and those reported by others appears to be due to the removal of contaminants during the preliminary dialysis. Ten-fold dilution of serum resulted in no significant change in free thyroxine concentration. This was consistent with mathematical analysis of the dilution effect. Thyroxine binding was markedly temperature sensitive. Free thyroxine concentration increased significantly within the temperature range seen in febrile patients.

It is often difficult to assess the thyroid status of a patient by using only a PBI determination. Measurement of thyroxine-iodine, free thyroxine, thyroid-binding proteins, or total T4-binding proteins gives the physician additional parameters for an accurate evaluation of thyroid function.

Thyroxine (T4) binding by 3 protein carriers (TBG, TBPA and albumin) was assessed in sera from various thyroid states using reverse flow paper electrophoresis, with which in normal serum 76% of endogenous T4 was bound to TBG, 15 % to TBPA and 9 % to albumin despite maximal TBG and TBPA capacities, consistent with previous reports. The percentage of endogenous T4 bound to TBG was increased to 87% in hypothyroidism and 88% in pregnancy, while it was decreased to 42 % in hyperthyroidism and 62 % in patients treated with anabolic steroids. Our results indicate that, in the above conditions, the role of TBG in T4 transport is even more important than has been previously recognized. On the basis of the newly estimated distribution of endogenous T4, the following relationship was established between free TBG capacity and triiodothyronine (T3) resin uptake (TRU): free TBG capacity (μg/100 ml) =5.02/ TRU(%/100)–4.98. Further, association constants of TBG and TBPA for T4, and free T4 concentrations were ca...

WE HAVE previously shown that synthetic thyroxine, when admin' istered by mouth in single doses of from 10 to ioo mg., does not producea definite increase in basal metabolism in patients with myxedema. When administered into the duodenum in single doses of from 10 to 50 mg., it is likewise without demonstrable effect (1). On the other hand, thyroxine does produce a clear-cut calorigenic response when administered as the monosodium salt and a still greater effect when given in an alkaline solution (2). In the course of observations on the maintenance dose of monosodium thyroxine (3), thyroxine as the free amino acid was accidentally substituted and it appeared to possess slight activity. It,therefore, seemed desirable to determine more precisely the effect of thyroxine given orally as the fre eamino acid, by administering large daily doses for a comparativelylong period.

In 6 castrated patients with the complete testicular feminization syndrome, values for total and free thyroxine (T4) concentration in serum, as well as the T4-binding capacities of thyroxine binding globulin (TBG) and thyroxine binding prealbumin (TBPA), were within normal limits. As expected, patients with TFS responded to 0.02 mg ethinyl estradiol daily with increases in both the T4-binding capacity of TBG and the concentration of serum T4 and a decrease in the proportion of free T4. The magnitude of the responses was similar to that obtained in 3 normal patients given the same dose of ethinyl estradiol. In a normal patient receiving ethinyl estradiol, norethandrolone (40 mg daily) produced the expected decrease in TBG and total T4 concentration and increase in the percentage of free T4. In contrast, in 4 patients with TFS receiving ethinyl estradiol, norethandrolone did not influence TBG, total serum T4 concentration, or the proportion of free T4. A similar lack of effect of norethandrolone on TBG was ...

A dialysis method for determining "free" thyroxine in diluted serum is presented. The effect of a number of variables (pH, incubation time and temperature, buffer composition and concentration, protein concentration, and specimen dilution) was studied, and pertinent data are presented. Within-run precision (95% confidence limits) was ±10.6%; between-run precision was ±14.2%. Specimens from 84 healthy subjects were analyzed, and normal ranges are presented. The method has been used for five years, and has been found to be simple and suited to simultaneous analysis of large numbers of specimens.

The intrathyroidal fate of labeled free thyroxine (T 4 ) and triiodothyronine (T 3 ) was studied with the single pass in situ perfusion of the rat thyroid gland. 131 I-T 4 or 131 I-T 3 were added to the entering perfusate. Both iodoamino acids entered the thyroid tissue equally and were partially deiodinated therein; T 4 to a greater extent than T 3 . Both methimazole-blocked glands and glands in which organic binding of iodine was permitted deiodinated these iodothyronines. Free labeled T 3 was found in some of the methimazoleblocked glands perfused with T 4 . The use of separate labels, 125 I for newly entering iodide and 131 I for thyroxine and triiodothyronine, allowed comparison of the intrathyroidal fate of newly entering iodide and iodide derived by deiodination of iodothyronines. Iodide from either source was utilized equally in the synthesis of iodotyrosines. It is concluded that iodothyronines can be deiodinated within the thyroid and that the intrathyroidal iodide originating from iodothyronines is utilized for synthesis of new iodoamino acids or can be secreted in the same manner as newly entering iodide. Some of the free T 3 in the thyroid gland may originate from free T 4 .

The relationship between free thyroxine concentration and thyroxine turnover was studied during thyroid suppression with triiodothyronine. Although there was some increase in the proportion of serum thyroxine bound to thyroxine-binding globulin, the ratio of ultrafilterable to protein-bound hormone was not significantly affected. The fractional disappearance rate of thyroxine increased from an average control value of 11.47%/day to 14.72%/day. Because of contraction of the thyroxine distribution space the clearance of thyroxine was less markedly affected, increasing from 1.37 to 1.56 liters/day. Since the ratio of thyroxine turnover to free thyroxine concentration, i.e., the free thyroxine clearance, increased proportionately (4.79-5.55 liters × 103/day) we conclude that triiodothyronine stimulates thyroxine clearance by a mechanism that is independent of effects on free thyroxine concentration.

Total and dialyzable thyroxine in cerebrospinal fluid and in serum were measured in 33 euthyroid patients with various neurological disorders and in 2 hypo-and 2 hyperthyroid patients. Total and dialyzable thyroxine in cerebrospinal fluid were found to be influenced by the protein concentration in cerebrospinal fluid and by the thyroid parameters in serum. Mean values for free thyroxine in the whole material were found to be almost identical in serum and in cerebrospinal fluid, suggesting a free passive passage of thyroxine through the blood-cerebrospinal fluid barrier. The total binding capacity of thyroxine was found to be higher in cerebrospinal fluid than in serum samples diluted to the same protein concentration as in cerebrospinal fluid, probably due to a higher concentration of prealbumin in cerebrospinal fluid.

放射化分析法を用いて正常者および種々甲状腺機能疾患患者の血中遊離型thyroxine (free T4) を直接測定した。試料血清をphosphate buffered salineに対し平衡透析を行ない, 透析外液をイオン交換樹脂columnを通すことによりfreeT4を分離し, それを原子炉中にて4×1012n/cm2・secの熱中性子束で60分間照射を行ない, 得た128Iは1) 酸灰化と蒸留, 2) 四塩化炭素抽出, 3) 硝酸銀による沈殿により分離した。この方法で無機ヨウ素, iodotyrosineおよび128I以外の核種はほとんど除去し得た。本法による測定値は甲状腺機能亢進症では従来のtracer法による値とほぼ等しい値が得られたが, 正常者および甲状腺機能低下症ではtracer法によるものよりかなり高値が得られ, その理由について考察を加えた。

When non-athletic young men commenced taking daily muscular exercise (running) peripheral degradation of thyroxine increased after a latent period, reaching 40% above resting level after 6 days. Athletes in moderately severe training had a thyroxine degradation/secretion rate 75% above that of resting, nonathletes. This fell significantly after 3 days' rest. PBI and free thyroxine levels were not significantly changed, the increase being primarily due to increased peripheral deiodination of thyroxine, which is believed to be due to repeated muscular exercise per se.

An approach to the comparison of the affinity of thyroxine-binding-globulin (TBG) in normal and hyperthyroid sera was described. The method was based on the measurement of free thyroxine fraction (FT4F) of sera at a fixed level of thyroxine (T4) and TBG-capacity. In normal and hyperthyroid sera, the concentration of T4 was measured with Murphy's method and TBG-capacity with reverse-flow paper electrophhoresis. The TBG-capacity was brought to a fixed level by diluting the sera to be tested with TBGdeficient serum. T4 was added to the sera at a final concentration of 50μg/100ml. FT4F in sera pretreated as described above was measured with a modification of Sterling's Mgprecipitation method employing barbital buffer, minimizing the effect of TBPA on FT4F.Thus, FT4F of normal and hyperthyroid sera was compared at essentially the same concentration of T4 and TBG-capacity. Therefore, the difference of FT4F must reflect the affinity of T4-TBG binding. With the method described, TBG-affinity of 6 hyperthyroid sera was compared with that of age-sex matched normal subjects. No significant difference of TBG-affinity was detected.

Studies were conducted concerning the relation between TT4 and AFT4 in a family with TBG deficiency, consisting of 8 affected and 16 unaffected members, and in a group of 48 normals. A highly significant positive relationship between these 2 parameters was found within the family, as well as within the group of normals. Subjects with TBG deficiency had low TT4 and lowered AFT4 levels. From additional studies it appeared that there existed no relationship between AFT4 and T4 disposal in 20 euthyroid controls, including 2 subjects with TBG deficiency and 2 females with TBG elevation due to oral contraceptives. It is concluded that in these circumstances AFT4 was not a clear determinant in the absolute peripheral T4 turnover.

Free thyroxine levels and thyroxine binding proteins have been studied in male adolescents and compared to the values observed in other groups of subjects. Free T4 concentration is decreased in adolescents as compared to adults, and particularly in the late stage of sexual maturation. TBPA maximal binding capacity and the blood concentration of TBPA are reduced at the beginning of puberty.

A study of the thyroid-pituitary interrelationships in normal healthy subjects is carried out by measurements of plasma thyrotrophin (TSH), by a radioimmunoassay, protein bound iodine (PBI) and free thyroxine (T4). It has been found that: – PBI and TSH significantly increase with age, which probably results from a peripheral hypometabolism, in spite of a normal free T4 concentration; – there are circadian variations of free T4 accompanied by a non significant inverse relationship of the plasma TSH level; – no important changes occur during the normal menstrual cycles but there is a significant increase in both PBI and TSH during pregnancy. The secretion of pituitary TSH seems to be finely regulated not only by the free plasma thyroxine concentration but also by the rate of metabolism of the thyroid hormones in the cell.

The electrophoretic migration of free thyroxine has been studied and compared with the behavior of thyroxine in the presence of serum. It has been found that the inherent mobility of thyroxine probably is faster than that of human albumin and possibly is faster than that of prealbumin. However, in certain electrophoretic systems an artifact is produced by adsorption of thyroxine to the supporting medium, thus retarding its true migration. The free thyroxine, however, appears in a discrete zone as a result of chromatography during electrophoretic migration. When added to serum in which thyroxine-binding proteins are weak or lacking, some thyroxine may migrate electrophoretically as the unbound hormone. Confusion between bound and unbound thyroxine in serum may be clarified by using different techniques of electrophoresis.

Bei 21 Patienten mit einer diffusen dekompensierten Hyperthyreose wurden vor und unter Therapie mit Methylmercaptoimidazol das proteingebundene Jod127 und das freie Thyroxin neben dem proteingebundenen Jod131 (nur vor Therapie) und dem Grundumsatz gemessen. Aus den Einzelwerten im Therapieverlauf wurden die Halbwertszeiten des proteingebundenen Jod127 und des freien Thyroxins bestimmt. Nach statistischen Kriterien erwiesen sich proteingebundenes Jod127 und freies Thyroxin in ihrer Beziehung zur Grundumsatzhohe und in der Abhangigkeit ihrer Halbwertszeiten vom intrathyreoidalen Jodumsatz als homologe Parameter. Die Halbwertszeit des freien Thyroxins ist jedoch kurzer als die des gesamten Thyroxins. Der grosere Gradient des Abfalls des freien Thyroxins ist im wesentlichen durch eine Zunahme der Gesamtbindungsvalenz der Transportproteine unter Therapie bedingt.

Chromatographic analysis of 9 lots of commercially prepared 131I-thyroxine indicated the presence of significant amounts of contaminating 131I-labeled 3,5,3′-triiodothyronine (average 3.7%) and 3,3′5′-triiodothyronine (average 5.4%). Since these iodothyronines are much less strongly bound to serum proteins than thyroxine, they would be expected to make a disproportionately high contribution to the radioactivity in the dialysate of dialysis systems used for measuring the free thyroxine concentration in serum. This expectation was experimentally confirmed. Direct chromatographic analysis of the dialysate demonstrated that a substantial proportion of the radioactivity was derived from the contaminating iodothyronines. Purification of 131I-thyroxine by paper chromatography, thinlayer chromatography, or preparative dialysis resulted in a 25% reduction in the dialyzable fraction as determined in the dialysis system employing diluted serum. Commercial preparations of 125I-labeled thyroxine were found to...

Serial measurements of the serum concentrations (as maximum binding capacities) of thyroxine binding prealbumin (TBPA), thyroxine binding globulin (TBG), PBI, free T4 (FT4), and percent free T4 (% FT4) were made before, during and after experimental infections (typhoid fever, tularemia and malaria) in 15 human subjects. In addition, the rate of disappearance of 125I-T4 from the circulation was determined. TBPA decreased during illness, but large initial decreases were dissociated in time from changes of FT4 and % FT4. Occasional but significant changes of TBG and PBI were unrelated to changes of TBPA and % FT4. PBI often dropped after the onset of illness, followed by a rebound which exceeded control values. These alterations of PBI alone resulted in significant FT4 changes in six cases. In two cases (malaria and shigeliosis) % FT3 changes paralleled changes of % FT4. In five subjects (two with typhoid fever and three with tularemia) increases of FT4 were not associated with any change in the rat...

Estimations of the maximum thyroxine binding capacity of thyroxine-binding globulin (TBG) and of the free thyroxine fraction were undertaken in 12 patients with hyperlipoproteinemia, comprising 9 males and 3 females, who were receiving the hypocholesterolemic drug clofibrate (Atromid S). All patients were placed on an isocaloric diet for 3 months, which commenced 1 month prior to the initiation of 2 monthly periods of study. In one period patients received clofibrate and in the other a placebo of identical appearance. The periods were randomly distributed among the patients a double blind study. Determinations of the thyroxine-binding capacity of TBG and the percentage free thyroxine were carried out twice during each of the 2 periods. The results show a significant (paired t-test, p

Thyroxine transport and turnover were investigated in a series of patients with major nonthyroidal illnesses, mainly advanced malignancies. Measurements were made of the thyroxine binding capacities of TBPA and TBG, free thyroxine fractions and free thyroxine iodine concentrations in all sera. Diminution of both TBPA and TBG binding capacities and elevations of free thyroxine fractions and free thyroxine iodine concentrations were observed, especially during the advanced or terminal phases of the disease. In such patients, the biological half-time of thyroxine turnover was significantly shorter than in the “hospital controls.” The free thyroxine fraction bore a more significant inverse relation to the binding capacity of TBG than to that of TBPA. In the present group of sera, therefore, it was evident that TBG was the more important determinant. Furthermore, the free thyroxine fraction bore a significant inverse relation to the biological half-time. This finding is compatible with previous eviden...

The absorption of labelled thyroxine and its glucuronide conjugate from loops of small intestine has been studied in rats. Free thyroxine was found to be more readily absorbed than its conjugate, suggesting that formation of the conjugate by the liver facilitates excretion of the hormone. No difference was found between the rate of absorption of these materials from loops prepared in cold-acclimated rats and from those prepared in warm-acclimated rats. Labelled D-thyroxine added to bile was found to be absorbed as readily as added L-thyroxine.

The free thyroxine concentration in serum can be considered to be directly proportional to the product of the dialyzable fraction (DF) as determined by equilibrium dialysis and the total concentration of thyroxine based on the serum PBI value. Previous studies from this laboratory have indicated that the DF is increased in sera of patients with a variety of nonthyroidal diseases as a result of a decrease in the concentration of thyroxine-binding prealbumin (TBPA). These observations have been extended. The relationship between TBPA and DF has been examined from both an experimental and theoretical point of view. Of 36 patients with nonthyroidal disease and an increased DF, 16 had elevated free thyroxine concentrations as well. Chromatographic studies suggested that the elevated levels of free thyroxine are not due to a systematic increase in a nonthyroxine component of the serum PBI value in such patients. Twenty patients with elevated DF values had normal concentrations of free thyroxine,presumably becau...

SUMMARY The level of “free thyroxine” is currently considered to be the major determinant of thyroid status. It depends on the total thyroxine concentration in plasma and upon the unsaturated capacity of the plasma proteins for thyroxine. These can now be determined by a variety of different techniques which do not require the administration of radioactivity to the patient and which are unaffected by the presence of excess iodide. Since many of these procedures have been shown to be precise, yet simple to perform, these in vitro tests of thyroid function are proving of increasing value to the clinician for the confirmation of the clinical diagnosis of thyroid disease.

A new method is described for measuring free thyroxine in serum, in which co-current dialysis is used to simplify and speed the determination. The patient's serum is mixed with 125I-labeled thyroxine and buffer (28 ml of serum per deciliter) and co-currently dialyzed for 15 min against a mixture of pooled serum (8 ml/dl) in buffer. After dialysis, the free thyroxine of the patient's serum, which is now bound to the protein of the recipient stream (pooled serum), is precipitated with trichloroacetic acid. The radioactivity of this precipitate and of an undialyzed serum aliquot is measured, to obtain the total count. Use of pooled serum and trichloroacetic acid eliminates the need for the amounts of carrier thyroxine required in most other methods. The procedure is both simple and rapid (3 to 4 samples/unit/h). The values for free thyroxine correlate well with those obtained by the method of Lee and Pileggi [Clin. Chem. 17, 166 (1971)] and by others participating in the proficiency program of the College of American Pathologists.

SOME patients with hepatic cirrhosis show values for standard thyroid-function tests consistant with hypothyroidism.1 , 2 Whether these patients are actually myxedematous or whether these laboratory values reflect some biochemical aberration connected with disturbed liver function has not been established. Hypothermia, bizarre behavior and slow or absent deep tendon reflexes3 , 4 are several of the similarities between profound myxedema and hepatic precoma. Since metabolic status appears to be more closely related to the concentration of free serum thyroxine than to the concentration of bound hormone5 this study was undertaken to determine the free serum thyroxine in cirrhotic patients with either normal or abnormally . . .