rT3 Concentrations Research Articles

EFFECTS OF THREE-DAY ORAL CHOLECYSTOGRAPHY ON SERUM IODOTHYRONINES AND TSH CONCENTRATIONS: COMPARISON OF THE EFFECTS AMONG SOME CHOLECYSTOGRAPHIC AGENTS AND THE EFFECTS OF IOPANOIC ACID ON THE PITUITARY-THYROID AXIS

The effects of repeated doses of oral cholecystographic agents on serum thyroxine (T4), 3,3',5-triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3) and thyrotrophin (TSH) concentrations were studied in 37 euthyroid male subjects. Iobenzamic acid, tyropanoic acid, iopanoic acid, and ipodate sodium, in a dosage of 3 g for 3 days, respectively, induced a significant decrease in serum T3 and an increase in rT3 within 24 h after the initial dose, followed by an increase in TSH and a slight increase in T4. The extent of the changes in rT3 varied between the agents, ipodate causing the greatest change, but without any relation to the changes in T3 or T4. Responses of serum T4, T3, rT3 and TSH concentrations to exogenous thyrotrophin-releasing hormone (TRH) and bovine TSH were also studied before and after 3-day doses of iopanoic acid. In 11 subjects given iopanoic acid, the response to TSH to TRH (500 micrograms, iv) was increased but the T3 response was unchanged. A dose of TSH (10 U.S.P. units, im) caused a significant increase in serum T3 and a decrease in TSH concentrations in 5 subjects both before and after cholecystography. It is thus suggested that in euthyroid subjects given multiple doses of oral cholecystographic agents, (1) the primary and consistent events are the reciprocal changes of serum T3 and RT3, although the extent of the changes is not coordinately reciprocal; (2) the responsiveness of the pituitary thyrotrophs and thyroid to TRH is preserved; and (3) the high basal and TRH-induced TSH in the serum may be ascribed to the decrease in the serum T3 concentration.

Serum 3,5,3'-triiodothyronine and 3,3',5'-triiodothyronine concentrations during acute heat load.

To determine the changes in thyroid hormone metabolism during short periods of exposure to heat, 30 euthyroid healthy male volunteers (aged 23--40 yr) were placed in a climatic chamber for 2 h (35 C, 50% relative humidity). The subjects were at complete rest during the first hour and performed light work (40 watts) during the second hour. Blood samples for T4, T3 and rT3 were drawn at 0, 60, and 120 min. Rectal temperature and heart rate were monitored continuously. No significant changes in T4, T3, rT3, rectal temperature, or heart rate were observed after the first hour (basal levels, 8.5 +/- 0.3 microgram/dl, 160 +/- 5 ng/dl, 14.5 +/- 2.5 ng/dl, 37.2 +/- 0.1 C, and 78 +/- 8 beats/min, respectively; mean +/- SEM). During the second hour, a significant rise in body temperature was recorded (38.5 +/- 0.1 C), accompanied by a significant decrease in mean serum T3 concentration and a rise in mean serum rT3 concentration, T4 concentration remained unchanged. Our findings suggest that, parallel to the elevation in body temperature, there is a shift in the conversion of T4 to the noncalorigenic rT3 metabolite rather than to T3.

Comparison of T4, T3, RT3 and TSH concentrations in cord blood and serum of infants up to 3 months of age

T4, T3, TSH and rT3 concentrations were measured by radio immunoassay in cord and postnatal (8–94 days of age) serum samples from randomly selected normal newborn infants (Group I). T4 and TSH levels also were determined in cord and postnatal sera from an additional group of apparently healthy infants 8–260 days of age, whose cord serum T4 levels were in the upper or lower 10% of the normal range of values (Group II). Postnatal T4, T3 and TSH concentrations were stable over this age range; there were no significant differences between male and female infant samples. However, there was a significant decrease in serum rT3 concentrations from 8 to 50 days of age. For the Group I infants, there were significant positive correlations between cord serum T4 and postnatal serum T4 levels, cord serum TSH and postnatal serum TSH levels, and cord serum rT3 and postnatal serum rT3 concentrations. For Group II infants, a significant positive correlation was found for cord T4-postnatal T4 serum concentrations.

Plasma triiodothyronines in fetal sheep: effects of illness and thyroidectomy.

Plasma 3,5,3'-triiodothyronine (T3) and 3,3',5'-triiodothyronine concentrations were measured in fetal sheep prior to death in utero and after thyroidectomy. In six fetal sheep who subsequently died in utero, plasma rT3 concentrations were elevated in all for 2 to 13 days prior to death. There were no consistent changes in plasma T4 concentrations. In two thyroidectomized fetal sheep, plasma T4 and rT3 concentrations fell to low levels. Plasma T3 concentrations remained low and there was no increase in plasma T3 in the last week prior to parturition like that which occurs in normal fetal sheep. Parturition was preceded by the normal increase in fetal plasma cortisol concentrations and occurred at the normal time. These data indicate that plasma rT3 concentrations are increased as a result of illness in fetal sheep and that such measurements may be useful as an indicator of fetal distress. The normal increase in plasma T3 late in gestation is not necessary for the late gestational cortisol surge or for normal parturition.

Oscillations in Reverse Triiodothyronine Levels in Serum of Healthy Infants Aged 0 to 130 Hours*

rT3 was measured by RIA in sera from 273 normal healthy infants between 0--130 h of age. The curve for the mean rT3 level plotted against age was polyexponential in shape and showed superimposed oscillations with a period of about 16 h, similar to the curves for T4, T3, and TSH previously found for the same group of subjects (J Clin Endocrinol Metab 47: 61, 1978). The ratio of concentrations of rT3 to T4 remained approximately constant, with a mean value of 0.016 over the age range of 3--130 h. These observations suggest that the variations in rT3 levels in newborn serum during the first few days of life are largely accountable by variations in T4 substrate concentrations.

Effect of Carbohydrate and Noncarbohydrate Sources of Calories on Plasma 3,5,3′-Triiodothyronine Concentrations in Man*

ABSTRACT To evaluate the effect of changes in dietary carbohydrate (CHO) and excessive caloric consumption on circulating thyroid hormone levels, six normal weight subjects were fed five separate diets: three isocaloric diets with 20%, 40%, or 80% CHO and two hypercaloric (+2000 calories) diets with 20% or 40% CHO for 5 days each as outpatients. T4, T3, and rT3 concentrations were measured in plasma samples collected on the morning of the sixth day. At least 1 week of the subjects' usual diets intervened between each experimental diet. Mean T4 and rT3 levels were similar after all diets. Pair-wise comparisons among all five diets revealed significantly (P < 0.005) increased T3 concentrations after both hypercaloric diets compared to the iso-20 and iso-40 diets, and after the iso-80 compared to the iso-20 diet. A multiple regression analysis of the data revealed the highest correlation of T3 levels with total calories (r = 0.68; P < 0.001) rather than with the intake of CHO (r = 0.46; P < 0.025), fat (r = ...

Amniotic fluid concentrations of 3,3',5'-tri-iodothyronine (reverse T3), 3,3'-di-iodothyronine, 3,5,3'-tri-iodothyronine (T3) and thyroxine (T4) in normal and complicated pregnancy.

Amniotic fluid concentrations of 3,3',5'-tri-iodothyronine (rT3), 3,3'-Di-iodothyronine (3,3'-T2), 3,5,3'-tri-iodothyronine (T3) and T4 were studied in 384 women during normal and complicated pregnancy. An inverse correlation was observed between decreasing rT3 and increasing 3,3'-T2 concentrations in amniotic fluid with gestational age. The mean rT3 level in normal pregnancy was 2.81 nmol/1 at 12-20 weeks and decreased significantly to 1.06 nmol/1 at 36-42 weeks of gestation. The mean 3,3'-T2 concentration was 49.1 pmol/1 at12-20 weeks increasing to 119 pmol/1 at 36-42 weeks. The mean T4 value of 3.83 nmol/1 at 12-20 weeks was about half that of later periods. The T3 concentration in a random sample of 45 amniotic fluids ranged from less than 28 to 370 pmol/1 (mean 102 pmol/1). The mean rT3, 3,3'-T2 and T4 values measured in patients with intra-uterine malnutrition, gestation diabetes, tocolysis, placental insufficiency and rhesus incompatibility at 31-40 weeks of gestation were not significantly different from those in uncomplicated pregnancy. Significantly decreased rT3 and T4 concentrations were found in toxaemia. From the results obtained in complicated pregnancy it may be concluded that measurements of iodothyronines, especially rT3, in amniotic fluid have insignificant diagnostic value in the recognition of intra-uterine lesions with the probable exception of fetal hypothyroidism. The analysis of the dependence of iodothyronine concentrations on the gestational age showed a maximum of rT3 and T4 levels between 20 and 30 weeks of pregnancy. This marked rise of iodothyronine concentrations in amniotic fluid at mid-gestation may be due to the onsetting maturation of the hypothalamic-pituitary-thyroid control system of the fetus.

Effect of tri-iodothyronine replacement on the metabolic and pituitary responses to starvation.

To determine the implication of decreased T3 production during fasting, seven normal men were fasted for 80 hours on two occasions; they received 5 microgram of T3 every three hours durnig the second fast. The mean serum T3 concentration declined during the control fast from 120 to 73 ng per deciliter (P less than 0.01), but remained slightly above base-line values during the T3 fast. Mean serum T4 concentrations did not change, and mean serum rT3 concentrations increased, during both fasts. The peak serum TSH increment after TRH was 11.1 micromicron per milliliter before fasting, 8.9 (not significant) after the control fast and 2.2 (P less than 0.01) after the T3 fast. Urea excretion was 9.1 per cent higher during the T3 fast; there were no differences in the changes in blood glucose, plasma fatty acids or other substrates during the two fasts. Pretreatment with potassium iodide lowered serum T4 concentrations and increased the serum TSH response to TRH after fasting. We conclude that the decrease in serum T3 concentrations during fasting spares muscle protein. Fasting is accompanied by a lower set point of TSH secretion, which remains sensitive to changes in serum thyroid hormone concentrations.

Amniotic Fluid 3,3′- and 3f,5′-Diiodothyronine in Fetal Hypothyroidism in Sheep*

ABSTRACT. The concentration of rT3 in human amniotic fluid (AF) at term is higher than in maternal serum and about 50%that of fetal serum. On the other hand, rT3 concentrations in sheep AF are very low (< 10–20 ng/dl) compared to both maternal (24–85 n/gl) and fetal (400–740 ng/dl) sera. This finding led us to consider the possibility that rT3 in sheep may normally be metabolized to 3,3′-diiodothyronine (3,3′-T2) and/or 3′,5′-T2 and that measurement of T2S in AF may be useful in recognition of fetal hypothyroidism. The concentrations of T2s were measured by specific RIAs in maternal sera and term AF and sera from normal and previously thyroidectomized neonatal (10–60 min of age) sheep; thyroidectomy was performed surgically in utero at 50–93 days gestation (term in sheep is about 145 days). The mean (±SE) serum 3,3′-T2 concentration of 15 ± 12 ng/dl in 3hypothyroid neonates was significantly lower than the corresponding value of 98 ± 7.4 ng/dl in 10 normal neonates (P < 0.001) and lower (borderline) than that of 24 ± 2.4 ng/dl in 9 maternal specimens (0.05 ≶ P < 0.1). Serum 3′,5′-T2 concentrations were undetectable (<1.5 ng/dl) in hypothyroid neonates; the corresponding mean values were 14 ± 1.8 ng/dl in normal neonates and 10 ± 0.6 ng/dl in maternal specimens. The concentrations of 3,3′-T2 [7.5 ± 1.4 (n = 3) vs. 25 ± 1.9 (n = 10) ng/dl; p < 0.001] and 3′,5′-T2 [4.9 ± 1.1 (n = 4) vs. 14 ± 1.3 (n = 9) ng/dl; P < 0.001] in AF of pregnancies with hypothyroid fetuses were also clearly less than those in normal pregnancies. The various data suggest that 1) 3,3′-T2 and 3′,5′-T2 are normally clearly detectable in sheep AF at a time when rT3 (or T3) is very low or undetectable and 2) low AF 3,3′-T2 and 3′,5′-T2 are reliable indicators of fetal hypothyroidism. By inference, AF rT3 may be useful in antenatal diagnosis of hypothyroidism in species (e.g. man) where it is normally present in easily measureable concentrations.

Reverse tri-iodothyronine to tri-iodothyronine ratio and gestational age

The biologic significance of reverse tri-iodothyronine is not yet identified. Cord blood values reflect the fetal thyroid state, with rT3 excess and tri-iodothyronine deficiency. In an attempt to correlate thyroid function and gestational age, T3 and rT3 concentrations were measured by radioimmunoassay on 64 cord blood samples. Infant gestational ages ranged from 29 to 42 weeks; birth weights from 650 to 3,870 gm. The results show a significant positive correlation between gestational age and T3 and a significant negative correlation between gestational age and rT3. The rT3/T3 offers the best correlation.

Thyroid Hormone and Thyrotropin Responses to Parturition in Premature Infants With and Without the Respiratory Distress Syndrome

Serum thyroxine (T4), triiodothyronine (T3), reverse triiodothyronine (rT3), thyrotropin (TSH), and thyroxine-binding globulin (TBG) concentrations were measured in well full-term infants (group 1), well premature infants (group 2), and premature infants with the respiratory distress syndrome (group 3). Samples were collected at birth and at 2, 12, and 24 hours after delivery. Significant increases in mean serum TSH concentrations occurred in all three groups two hours after delivery, but the two-hour levels measured in groups 2 and 3 were less than those in group 1 infants. Serum T4 concentrations increased significantly after delivery in groups 1 and 2 but not in group 3 newborns; mean TBG concentrations did not vary significantly in any of the groups. Serum T4, concentrations increased significantly at two hours in all three groups but were significantly depressed at 12 and 24 hours in group 3 infants. Mean serum rT3, concentrations decreased after birth in group 2 and 3 in contrast to group 1 newborns; the mean value increased significantly between 2 and 24 hours in group 3 infants. The pattern of decreasing senrum T3 and increasing rT3 concentrations in group 3 infants between 2 and 24 hours resembles the pattern of change in triiodothyronines in ill adult patients, which suggests that these variations are due primarily to illness and not to prematurity.

Metabolic Clearance and Production Rates of 3′,5′-Diiodothyronine and 3,3′-Diiodothyronine in Man*

Abstract MCRs and production rates (PRs) of 3′,5′-diiodothyronine (3′,5′-T2), 3,3′-diiodothyronine (3,3′-T2), and rT3 were determined in seven, five, and four normal subjects, respectively. The constant infusion technique was used to measure the MCR; the PR was calculated as the product of MCR and the concentration of iodothyronine as measured by RIA. The results of measurements of MCR and PR were adjusted to 70 kg BW. In the case of 3′,5′-T2, the serum concentration (mean ± SE) was 6.5 ± 0.4 ng/100 ml, the MCR was 159 ± 21 liters/day, and the PR was 10.9 ± 1.5 μg/day. The serum concentration of 3,3′-T2 was 4.0 ± 0.6 ng/100 ml, while its MCR was 560 ± 59 liters/day and the PR was 23 ± 4.5 μg/day. The serum concentration of rT3 was 39 ± 8.7 ng/100 ml, MCR was 131 ± 27 liters/day, and the PR was 44.8 ± 6.5 μg/day. Additionally, serum concentrations of 3′,5′-T2 and 3,3′-T2 were measured before and after oral administration of 300 μg L-rT3 to normal subjects. Serum 3′,5′-T2 levels increased maximally at 1 h t...

Free T4, free T3 and free reverse T3 in dialysates of serum. The influence of electrolytes and pH with special reference to the physiological range.

The influence of electrolyte composition and pH of buffer on free T4, free rT3, and free T3 concentrations in serum dialysates has been evaluated, using an equilibrium dialysis method with subsequent direct radioimmunoassay estimations of the dialysate. Cl-, HCO3- and H+ were found to be the important ions which at concentrations similar to those occurring in vivo decreased the protein binding of all three hormones in serum, T3 being much less sensitive to these changes than T4 and rT3. The possible influence of pathological concentrations of electrolytes in serum on estimated free thyroid hormone concentrations is discussed. Because the effect of in vivo changes in serum Cl-, HCO3- and H+ on free thyroid hormone concentrations to a certain extent tend to counteract each other, it is concluded that electrolyte and pH disturbances only to a minor extent can affect measurements on free T4, free rT3 and free T3 concentrations in serum obtained by an equilibrium dialysis method.

Alterations in circulating thyroid hormones and thyrotropin after complete thyroidectomy.

Changes in serum TSH, T4, T3, and rT3 concentrations after complete thyroidectomy were observed in 21 euthyroid patients with thyroid carcinoma. Serum TSH levels rose progressively during the 4 weeks of observation and a significant increase was noticed as early as 54 h after thyroidectomy. Serum T4 and T3 concentrations decreased significantly 42 and 6 h, respectively, after thyroidectomy. However, serum rT3 levels increased significantly within 18 h and reached maximum levels 30 h after thyroidectomy. The rates of decrease of serum T4 and T3 concentrations were constant between the 6–28 days after thyroidectomy (t)/2, 16.3 and 22.3 days, respectively), and the decrease rate of serum rT3 levels was similar to that of serum T4 after the day 18 (t1/2, 16.6 days). An initial sharp decrease in serum T3 and a sharp increase in serum rT3 concentrations without a significant change in serum T4 concentrations seems to be due to inhibition of outer ring monodeiodination in postsurgical states. When a significant ...

Presence of triiodothyronine, no detectable thyroxine and reverse triiodothyronine in human milk.

Thyroxine (T4), triiodothyronine (T3) and reverse triodothyronine (rT3) concentrations in human milk were measured by radioimmunoassay in 114 samples obtained from 1 week to 8 months postpartum. Several assay systems applied for the determination of serum thyroid hormone concentration were proved to be unsuitable for human milk, and the method of separating free and antibody-bound hormone by polyethylene glycol was also inappropriate for milk specimens, which tended to give a falsely high value. The binding of finity of T4 to milk was lower than that to serum protein, on which 8-anilino-1-naphthalene sulfonic acid showed no remarkable effect. In spite of the high sensitivity of 100 pg/tub in T4 assay system, no immunoassayable T4 was detected in all samples with or without ethanol extraction and trypsin hydrolysates of milk. In contrast, T3 was present in a measurable amount in most of the samples, the mean +/- SD value of which was 10 +/- 9 ng/100 ml, and those in colostrum were significantly higher than those in matured milk (P less than 0.01), whereas rT3 was not detectable in 76 samples tested. These results indicate that permeability of thyroid hormones through the mammary gland is different between T4 and T3 as well as in placental transport, and human milk can not be a source of thyroxine supply for the breast-fed infant.

Effects of dexamethasone on plasma hormone levels and milk production in the lactating cows with or without concomitant administration of thyrotropin releasing hormone, thyroxine, growth hormone, and prolactin.

We studied the effects of the administration of dexamethasone (DX) with or without thyrotropin releasing hormone (TRH), thyroxine (T4), growth hormone (GH), and prolactin (PRL) on the plasma 3, 5, 3'-triiodothyronine (T3), 3, 3', 5'-triiodothyronine (rT3), T4, thyrotropin (TSH), GH, PRL, insulin, and milk production in36 normal lactating cows. A single subcutaneous injection of 10mg DX resulted in 21% reduction in milk production on the following day. While plasma rT3level increased 1.4 fold, plasma T3 concentration reduced by 52% 24hr after DX injection (p<0.001). Reduction in plasma TSH and T4 levels was small and no significant depression of plasma GH and PRL was detected. A prompt and prolonged increase in plasma insulin concentration was observed. Simultaneous injections of 10mg DX with 2mg TRH followed by an additional injection of the same dose of TRH5hr later, resulted in no depression of milk production. Plasma T3, insulin, GH, and PRL levels 5hr after the first hormone injection was significantly elevated. Plasma T4and rT3 concentrations 24hr after the injection increased 1.78 and 3.2 fold, respectively (p<0.001), but the levels of T3, GH, and PRL returned to their pre-treatment levels. The mean plasma GH level significantly increased. In the control cows, neither plasma hormone levels nor milk production significantly changed. The injection of 10mg T4 or 20mg GH twice a day with an administration of 10mg DX reduced the milk production by less than 9% on the following day. On the other hand, no preventive effect of concomitant administration of PRL (54mg×2) with 10mg DX on depression in milk production was detected. Plasma T3 level 24hr after the simultaneous administration of DX with T4 was 1.65times as high as the pre-injection level and the level continued for several days. However, plasma T3 reduced by 40% 24hr after the administration of either DX+GH or DX+PRL. The preventive effect of TRH on the depression of milk production caused by DX might be partly derived from a synergistic action of the enhanced circulating levels of thyroid hormones and GH. A possibility of additional favourable TRH actions on lactation other than through adenohypophysis also exists.

Effects of Dexamethasone on Fetal and Maternal Thyroxine, Triiodothyronine, Reverse Triiodothyronine, and Thyrotropin Levels

The concentrations of T4, T3, rT3, and TSH were measured at term pregnancy in maternal and umbilical plasma and in amniotic fluid of 11 normal patients who received 8-16 mg dexamethasone 3-48 h before elective cesarean section and of 10 control patients who received no dexamethasone. The mean (+/- SE) concentrations of T4 (micrograms per dl) in maternal and umbilical plasma of dexamethasone-treated patients (12.5 +/- 0.9 and 13.0 +/- 0.9) were not significantly different (P less than 0.05) from those of the control patients (13.9 +/- 1.5 and 10.4 +/- 0.6, respectively). The mean (+/- SE) maternal plasma concentrations of T3 and rT3 (nanograms per dl) of dexamethasone-treated patients (204 +/- 6 and 82 +/- 11) were not significantly different (P less than 0.05) from those of the control patients (201 +/- 26 and 72 +/- 6, respectively). However, the mean (+/- SE) concentrations of T3 and rT3 (nanograms per dl) in umbilical plasma of dexamethasone-treated patients (106 +/- 13 and 360 +/- 35) were 3- and 2-fold and significantly higher (P less than 0.05) than those of the control group (39 +/- 6 and 195 +/- 19, respectively). No significant differences (P less than 0.05) were observed between the mean concentrations of TSH (microunits per ml) in maternal and umbilical plasma of dexamethasone-treated patients (2.5 +/- 0.5 and 3.0 +/- 1.0) and those of the control group (2.8 +/- 0.5 and 6.9 +/- 2.7, respectively). Under the conditions studied, no differences in the mean concentrations of amniotic fluid T4, T3, rT3, or TSH were observed between the two groups of patients (P less than 0.05). The increase of T3 and rT3 levels in umbilical plasma after dexamethasone administration indicates alteration in fetal thyroid economy.

Correlation of reverse-T3 and 3,3'-T2 (T2') plasma concentrations under physiological and experimental conditions in man.

T2' plasma levels are measured under different conditions and correlated to the repective rT3 concentrations. Specific RIAs for T2' and rT3 are used. Pharmacological doses of T3 cause an increase of plasma T2'; if T3 or T4 doses are administered to an athyroid patient which cause a similar level of plasma T3 the increase of T2' is much larger during T4 treatment. Cord blood levels of T2' are 2--3-fold higher than in normal adults whereas rT3 concentrations are about 10 times higher than normal. After birth rT3 and T2' levels decrease in about a parallel manner. After a bolus iv injection of 500 microgram rT3, T2' starts to increase as early as 2 min after injection. PTU in therapeutic doses causes a rapid increase of plasma rT3 with a maximum 4 h after ingestion. A dose of 150 mg PTU causes a maximum of about 100% above baseline. T2' also increases but to a lesser degree (about 50% above baseline). We conclude that rT3 is a most important precursor of T2' whereas T3 contributes only to a minor degree to the total T2' production under physiological conditions.

The Effect of Repeated Administration of Ipodate (Oragrafin) in Hyperthyroidism*

This report describes the effect of administration of repeated doses of ipodate (Oragrafin; 3 g orally every third day for five doses) in six hyperthyroid patients. Baseline serum concentrations of immunoassayable T3, rT3, and T4, were 926 +/- 206 ng/100 ml, 165 +/- 31 ng/100 ml and 21 +/- 2.7 micrograms/100 ml (mean +/- SEM), respectively. Within 24 h after the first dose of ipodate, serum T3 fell by 54% and it remained between 66-77% below baseline until the third day after the fifth dose; subsequently, there was a gradual recovery from the effect of ipodate. Serum T4 also decreased after ipodate administration; it was 23-31% lower than baseline from the second day after the third dose to the sixth day after the fifth dose. Serum rT3 increased after each dose of ipodate; peak values of 97%-203% above baseline value were observed at 24-48 h after each dose. There was a subjective improvement in clinical symptoms of hyperthyroidism in all cases. Resting pulse rate and pulse pressure dropped significantly (P less than 0.02) by the ninth day of study and remained so thereafter. Body weight increased significantly by the ninth day of the study. The various data suggest that ipodate may serve as a useful adjunct in the early treatment of hyperthyroidism.

Effect of Intraamniotic Fluid Thyroxine Injection on Fetal Serum and Amniotic Fluid Iodothyronine Concentrations*

Seven hundred micrograms of T4 were injected into the amniotic cavity 24 h before delivery of five pregnant women scheduled for elective cesarean section at term. T4, T3, and rT3 concentrations were measured by RIA in amniotic fluid obtained at the time of the injection and in amniotic fluid and cord serum samples collected at delivery. Iodothyronine concentrations also were determined on cord samples from 24 full term control infants. The geometric mean serum T4 concentration in the experimental infants was 27.2 micrograms/dl, almost 3 times that of the control population (10.3 micrograms/dl); serum rT3 concentrations were markedly elevated to a mean of 657 ng/dl, compared to 254 ng/dl in control infants. The mean serum T3 concentration was slightly but significantly increased to 61.3 ng/dl (control, 48.3 ng/dl; P less than 0.02). Amniotic fluid T4, T3, and rT3 concentrations all increased significantly. T4 injection into the amniotic fluid is an effective method of increasing fetal serum T4 concentrations. The preferential pathway of monodeiodination of the injected T4 in the human fetus is to rT3 rather than T3.