Mean T4 Levels Research Articles

CLINICAL STUDY OF AUTONOMOUSLY FUNCTIONING THYROID NODULES (AFTN)

Twenty six cases of autonomously functioning thyroid nodule (AFTN), including 9 cases with toxic symptoms (toxic group) and 17 without toxic symptoms (non-toxic group), were experienced and their clinical and pathological characteristics were examined. AFTN existed in 2.9% of all thyroid tumors, and occurred predominatly in females (1:7.7). Mean time to admission of toxic group was significantly longer than that of non-toxic group (p<0.05). Mean tumor size of toxic group was significantly larger than that of non-toxic group (p<0.05). Mean T3 level in toxic group was higher than cut-off value (1.8 ng/ml), mean T3 and T3/T4 ratio in toxic group being significantly higher than those in non-toxic group (p<0.01, p<0.05). Histopathologically, almost two thirds of AFTNs in either group were adenomatous goiters, and about one third of their were adenomas. Three out of 26 cases of AFTN simultaneously associated with a thyroid cancer. Two of the three cases had a non-functioning papillary carcinoma and one, a functioning follicular carcinoma.

Monitoring thyroxine treatment during pregnancy.

Data were analyzed from 77 pregnancies in 65 hypothyroid women treated with levothyroxine (T4) to determine (a) how often, how severely, and when serum thyrotropin (TSH) and free T4 concentrations become abnormal during pregnancy in women taking constant T4 doses and (b) how much to increase T4 doses to normalize elevated serum TSH levels. Group I consisted of 36 women with previous thyroid ablation. Group II consisted of 29 women with Hashimoto's thyroiditis. Serum TSH levels rose above normal (greater than 4 microU/mL) during pregnancy more often in Group I (76%) than in Group II (47%) during treatment with constant T4 doses, and mean serum free T4 levels decreased significantly in both groups, by 47% in Group I and by 35% in Group II, compared to preconception values. Serum TSH concentrations rose above 20 microU/mL in 22% of the women, and serum free T4 concentrations fell below normal in 13%. Elevated serum TSH levels usually were detected by the first TSH test during pregnancy, as early as 4 weeks gestation. Of those women tested after an initial normal serum TSH value during pregnancy, 30% had an elevated serum TSH concentration later in the pregnancy. Of 12 women followed through two pregnancies, 10 had elevated serum TSH values in both pregnancies, 1 had normal serum TSH values in both, and 1 had discordant serum TSH values.(ABSTRACT TRUNCATED AT 250 WORDS)

The Incidence of Clinical Thyroid Dysfunction in an Unselected Group of Pregnant and Post Partum Women

This study has examined the incidence of thyroid dysfunction during pregnancy and up to six months post partum in 65 women attending an antenatal clinic in the West of Scotland. Five were found to be positive for thyroid antibodies at presentation and in these the antibody titre fluctuated during pregnancy and in the post partum period. One patient developed thyroglobulin antibodies post partum. Mean total T3 and total T4 levels rose during pregnancy but had normalised by six weeks post partum. The changes in FT4 and TBG levels observed during pregnancy did not normalise until after six weeks post partum. Only one patient developed any biochemical evidence of thyrotoxicosis post partum and this was not found to be associated with the presence of thyroid antibodies. No patient showed any evidence of hypothyroidism.

Metabolite and hormonal profiles in heat stroke patients at Mecca Pilgrimage

Sera obtained during the Hajj seasons of 1985, 1986, 1987 and 1988 from 125 heat stroke patients were collected and subjected to chemical analysis which included determination of glucose, lactate, cholesterol, and triglycerides, as well as assay of T3, T4, TSH and cortisol. Hyperglycaemia and lactic acidaemia were found to be the most frequent metabolic abnormalities. The changes in cholesterol did not exhibit a specific pattern. Triglycerides were significantly elevated in only 6% of patients. Cortisol levels were very significantly elevated in precooled patients. Although the mean T3 levels remained within the normal range, the mean concentration on admission was significantly higher than the post-cooling mean. TSH and T4 levels did not show significant changes.

Thyroid hormone binding in early pregnancy and the risk of spontaneous abortion

Serum thyroxine (T4), free thyroxine (FT4) and thyroxine binding globulin (TBG) were measured at 6, 8, 10, 12, 14 and 16 weeks menstrual age (MA) in 32 pregnant females, who had been selected for a high risk of spontaneous abortion on account of previous abortion (18 cases) or ovulation induction (14 cases). Eight of these subjects experienced a spontaneous abortion occurring between 8 and 20 weeks. The other women, who carried to term, served as controls. In the abortion group, mean pre-abortion TBG and T4 levels were lower than in the control group from the 6th week on. In spite of this, the way T4 changes with TBG was very similar in both groups. No detectable change or difference with respect to control values were observed for FT4. These observations are taken as evidence against impaired maternal thyroid function playing a role in the unsuccessful outcome of pregnancy. Decreased TBG was detected on the average at 5.2 (range 0–13) weeks before abortion. Diagnostic sensitivity and positive predictive value were estimated as about 70 and 80%, respectively, for the high-risk group, indicating that serum TBG might only play a minor role as a predictor of the outcome of pregnancy.

Thyroid hormone periodicity in healthy adult geldings.

Serum samples were collected from 10 healthy geldings every 4 h for three consecutive days and the triiodothyronine (T3) and thyroxine (T4) concentrations determined by radioimmunoassay. There were significant differences in the hormone concentrations related to time. The mean (+/- sd) T3 concentration peaked around 08.00 h at a level (54.06 +/- 14.02 ng/dl) significantly (P less than .001) higher than the lowest concentration (38.71 +/- 10.81 ng/dl) around midnight. Although the highest mean T3 level was 08.00 h, this value was not significantly different from the noon and 16.00 h levels. Likewise, the mean T3 level at midnight was not significantly different from the 20.00 h and 04.00 h levels, resulting in a plateau from 08.00 h to 16.00 h and a trough from 20.00 h to 04.00 h. The mean (+/- sd) T4 concentration peaked around 16.00 h at a level (2.43 +/- .81 micrograms/dl) significantly (P less than .01) higher than the lowest concentration (1.79 +/- .63 micrograms/dl) around 04.00 h.

Promotive effect of 4,4′-methylenebis( N,N-dimethyl)benzenamine on N-bis(2-hydroxypropyl)nitrosamine-induced thyroid tumors in Wistar rats

The promotive effect of 4,4′-methylenebis( N,N-dimethyl)benzenamine (MDBA) on 2-stage thyroid tumorigenesis induced by N-bis(2-hydroxypropyl)nitrosamine (DHPN) in Wistar male rats was investigated. Animals were given i.p. injections of DHPN, and then a basal diet containing 0.0375% MDBA for 19 weeks. In addition, localization of the thyroid-stimulating hormone (TSH) in the pituitary gland was investigated. Levels of TSH and T4 in serum were measured by radioimmunoassay (RIA). The addition of MDBA to the diet significantly increased the incidence and numbers of preneoplastic lesion (focal hyperplasia), adenoma and carcinoma of the thyroid. TSH was usually localized in the thyroidectomy-cell in the anterior lobe of the pituitary gland, and the number of TSH-positive cells increased in the group treated with MDBA. Mean circulating levels of TSH were elevated in all MDBA-treated groups, and mean T4 levels in groups treated with MDBA were significantly lower different ( P < 0.05) than those in control groups.

Suppressed plasma prolactin response to thyrotropin-releasing hormone in hyperthyroidism reproduced by thyroxine but not by triiodothyronine administration to normal subjects

In 10 hyperthyroid women studied in the follicular phase of the menstrual cycle, basal plasma PRL was normal, but PRL release after TRH was significantly suppressed compared with that in 11 control women. The suppressed PRL response to TRH was not explained by changes in serum estradiol or sex hormone-binding globulin. It recovered after treatment of hyperthyroidism. When normal women were treated with T4 (0.5 mg daily for 6 to 10 days), their mean serum free T4 level increased to about 70% of that in the hyperthyroid patients, whereas their serum free T3 levels increased to a lesser degree. During T4 administration, these women had PRL changes similar to those of the hyperthyroid patients. When the normal women took T3 (60-120 micrograms for 6 to 8 days), their serum free T3 increased to almost the level of the hyperthyroid patients, but the TRH stimulated PRL release remained close to the control level. The PRL increase after dopaminergic blockade with metoclopramide was significantly suppressed in hyperthyroid patients, and they had no PRL response to TRH after pretreatment with metoclopramide. In conclusion, the PRL changes in hyperthyroidism were reproduced by administration of T4, but not by administration of T3 to healthy women. The site of action is suggested to be pituitary, but additional hypothalamic effects cannot be excluded.

Long term treatment of Graves' disease with iopanoic acid (Telepaque).

To investigate the long term utility of the cholecystographic contrast agent iopanoic acid (Telepaque) for treatment of Graves' hyperthyroidism, we studied 40 patients treated with 500 mg, orally, daily for 1-12 months. We measured thyroid size; body weight; serum T3, T4, and free T4 concentrations; and antithyroglobulin and antimicrosomal antibody levels at monthly intervals. Based on the effects of the therapy, the patients were divided into 3 groups: 6 patients had excellent responses with return of serum thyroid hormone levels to normal (group A); 12 patients had fair responses, but 1 thyroid hormone test remained elevated (group B); and 22 patients had minimal benefit (group C) with only slight clinical improvement and transient reduction of serum T3 concentration. Mean serum T3 levels decreased significantly after 1 month of therapy in all 3 groups and became normal in groups A and B, but the reduction in group C was not sustained. Mean serum T4 and free T4 levels remained above normal during the course of therapy in groups B and C. Sixty-eight percent of patients in group C had large goiters compared with 33% of group A and 25% of group B, and those in group C tended to have more severe biochemical hyperthyroidism initially. There were no significant changes in antibody titers during therapy. These data indicate that iopanoic acid is not effective therapy for many hyperthyroid patients.

Plasma thyroxine and cortisol under basal conditions and during cold stress in the aging dog.

The effects of aging on plasma concentration of thyroxine (T4) and cortisol and on responses of these hormones to low ambient temperatures were determined in the dog. Female beagle dogs were divided into three age groups: old, adult, and puppies. The mean (+/- SD) ages were 11.4 +/- 0.2 years, 3.0 +/- 0.4 years, and 7.6 +/- 0.2 weeks, respectively. All dogs came from a genetically homogeneous colony and were free from any disease. The adult and old dogs were used during anestrus. Based on four daily blood samples, the mean (+/- SE) T4 level in the old dogs (2.8 +/- 0.1 microgram/dl) was significantly (P less than 0.001) lower than that in the adults (4.2 +/- 0.2 micrograms/dl) and puppies (4.4 +/- 0.2 micrograms/dl). By contrast, mean plasma cortisol levels in the old dogs (21.1 +/- 3.1 ng/ml) and adults (15.4 +/- 2.4 ng/ml) were significantly higher than those in the puppies (7.2 +/- 1.1 ng/ml). No significant changes in plasma T4 and cortisol occurred in any of the three age groups at 22 degrees C or during exposure to 10 or 4 degrees C. Exposure to -5 degrees C, however, produced significant increases in T4 (greater than 130% by 5 hr) and cortisol (greater than 280% by 1 hr) in adult dogs. This temperature produced only a modest increase in T4 (70% by 3.5 hr) and no change in cortisol in the old dogs. The puppies showed no change in T4 and cortisol during exposure to -5 degrees C. The results demonstrate that with advancing age, plasma T4 and cortisol concentrations change in opposite directions, thus supporting the hypothesis of a negative relationship between these two hormones. These results also show that the responses of these hormones to the stress of cold decline during aging and are not yet developed in the very young.

Conversion of thyroxine to 3,5,3'-triiodothyronine in several rat tissues in vivo: the effect of hypothyroidism.

The local conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) has been recognized as a source of T3 at various sites in euthyroid rats. The present study was designed to evaluate the effect of hypothyroidism on the source and quantity of T3 at several of these sites (liver, cerebral cortex (Cx), thymus, testis, brown adipose tissue). For this purpose intact euthyroid rats and radiothyroidectomized (RTx) rats received a continuous iv infusion of [125I]T4 and [131I]T3 until isotopic equilibrium was attained. In addition to the labelled iodothyronines, RTx rats received a continuous iv infusion of 0.75 microgram T4/day, in order to maintain a defined hypothyroid state. At the end of the infusion period the animals were bled and perfused, and homogenates of the various organs were prepared. The mean plasma T4 and T3 levels in T4-maintained RTx rats, as measured by RIA, were 1.5 micrograms/dl and 15 ng/dl (euthyroid values: 5.2 micrograms/dl and 48 ng/dl, respectively). The plasma and tissue homogenates were processed for thin layer chromatography and the [125I]T4, [125I]T3 and [131I]T3 levels determined. From these data the concentrations of T4, total T3 and T3 derived from local T4 to T3 conversion (LcT3(T4)) in tissue could be calculated. The relative mean contribution of LcT3(T4) to the total T3 in Cx (75%), thymus (31%), testis (43%) and brown adipose tissue (65%) from hypothyroid rats was higher than that determined for euthyroid animals (66%, 19%, 29% and 27%, respectively). The reverse was found for the liver (15% vs 39%).(ABSTRACT TRUNCATED AT 250 WORDS)

Prolactin levels in hypothyroid and euthyroid infants during the first week of life.

A radioimmunoassay (RIA) procedure was devised for the estimation of PRL in eluates of dried whole blood from filter paper. Levels of PRL were measured in newborn blood obtained during the first week of life from 530 infants of normal birthweight (greater than 2500 g) with normal T4 values, 114 infants of normal birthweight with low T4 values (T4 less than 6.0 micrograms/dl), 47 infants with congenital hypothyroidism, 57 infants of low birthweight (less than 2500 g) with normal T4 values, and 114 infants of low birthweight with low T4 values. Examination of PRL concentrations among comparably aged infants from the various groups revealed that the mean PRL values of the hypothyroid group were consistently greater than those of any of the other groups of infants regardless of the mean T4 levels. With the exception of the hypothyroid infants, the groups with both the lowest mean T4 concentrations and mean body weights also had the lowest mean PRL values.

新生児,乳児期における甲状腺機能に関する研究

Serum TSH, T4, T3 rT3 and resin T3 uptake (RT3U) were daily or monthly measured in 71 full-term neonates and 146 healthy infants, to study the changes of these thyroid hormones levels in relation to the development during infancy.Serum TSH levels at the first day of life were very high and the geometric mean was 18.8 μU/ml. Following an abrupt fall at the second day (a mean of 7.7 μU/ml), the level decreased gradually to a mean of 3.4 μU/ml at the third week, which was not significantly different from the values in children aged 1 to 5 years.Serum T4 and T7 (T4 x RT3U) values remained high during the first 5 days of life (16.1-18.9 μg/dl for T4 and 5.2-6.4 for T7) as compared with the levels in cord blood. The levels decreased to values similar to those seen in children aged 1 to 5 years by the third week of life (10.8 μg/dl for T4 and 2.9 for T7). Serum T3 levels in the first 2 days of life were high as compared with those of cord blood. Following a transient fall until the age of 4 days, the level again increased slowly and reached the maximum mean level of 208 ng/dl at 3 months. The mean T3 levels between 3 and 21 days of life (113-155 ng/dl) were lower than those in children aged 1 to 5 years (169 ng/dl), but the levels in infants aged 3 to 6 months (190-208 ng/dl) were higher than those in children aged 1 to 5 years. On the other hand, serum rT3 levels were remarkably high in cord blood (184 ng/dl) and remained high during the first 5 days of life (158-231 ng/dl). An abrupt fall occurred at the second week (a mean of 70 ng/dl), and thereafter the levels decreased slowly to a mean of 26 ng/dl by the age of 7 to 8 months, a value similar to that seen in children aged 1 to 5 years.The difference in the T3/T4 ratio from that in children aged 1 to 5 years had become insignificant by the age of 22 to 28 days, while the differences in the rT3/T4 and T3/rT3 ratios had become insignificant by the age of 7 to 8 months.These results suggested that the varying maturation of the conversion mechanism of T4 to T3 in the peripheral tissues in developing infants together with the neonatal surge of TSH secretion may be responsible for these extraordinary changes of serum thyroid hormones during infancy, especially in the neonatal period. The present study also demonstrated that the maturation of the conversion mechanism has completed by the age of 7 to 8 months.

Plasma concentrations of thyroid hormones in dogs: influence of sampling hour, breed and age.

Thyroxine (T4) and triiodothyronine (T3) plasma concentrations have been determined during 24-hr sampling periods in six mongrels (age 12-36 months), six beagles (age 35-37 months), three labradors (age 3.5 months) and three beagles (age 5 months). The mean T4 levels of the labradors were significantly lower than the values found for mongrels or older beagles (P less than 0.05), whereas T3 was higher in the 5 month old beagles compared to the mongrels (P less than 0.001), young beagles (P less than 0.05) or labradors (P less than 0.01). Circadian and ultradian rhythmicities have been evaluated by cosinor and Fourier analysis. Mongrels and older beagles did have a 12-hr rhythmicity in plasma T4 (P less than 0.05), whereas 5 month old beagles had a circadian one (P less than 0.01). A 12-hr rhythmicity was also found for T3 in the older Beagles (P less than 0.05). However, Fourier analysis indicated that the daily variation in T4 and T3 plasma levels was inadequately mathematically described by single sinusoidal rhythm and that more harmonic components are to be taken into account. The obtained data during a 24-hr period indicate that T4 and T3 concentrations in plasma may vary according to breed, age and sampling hour.

Thyroid hormone abnormalities at diagnosis of insulin-dependent diabetes mellitus in children

Comprehensive evaluation of thyroid hormone indices was performed in 58 children with insulin-dependent diabetes mellitus (IDDM) at the time of diagnosis and prior to insulin therapy. Two patients were found to have primary hypothyroidism, with markedly elevated TSH and very low T4, free T4, T3, and reverse T3 concentrations. The remaining 56 patients had the transient alterations in thyroid hormone indices that are characteristic of "euthyroid sick" or "low T3" syndrome. Mean TSH and reverse T3 values were significantly higher and the mean T3, T4, and free T4 levels were significantly lower than those observed in the control population. Ten of the diabetic patients had elevated TSH concentrations and normal or low free T4 values; eight had normal TSH levels and low T4 and free T4 values. The remainder of the group had thyroid indices compatible with abnormal peripheral metabolism of thyroid hormones. Elevated titers of antimicrosomal antibodies were found in 16% of the children with IDDM. We conclude that abnormal peripheral metabolism and altered hypothalamic-pituitary function are responsible for the transient changes in thyroid hormone indices in patients with untreated IDDM. The most reliable indicators of concomitant primary hypothyroidism in untreated IDDM are markedly elevated TSH and low reverse T3 values.

The influence of partial food deprivation on the quantity and source of triiodothyronine in several tissues of athyreotic thyroxine-maintained rats.

In the present study the influence of partial food deprivation (PFD) on the quantity and source of T3 [i.e. T3 derived from local T4 to T3 conversion (Lc T3 (T4] vs. plasma-derived T3] in several rat tissues was investigated. Two groups of athyroid rats on a synthetic diet received a continuous iv infusion consisting of T4 (1.0 microgram/100 g BW X day), [125I]T4, and [131I]T3 over a prolonged period. For one group of rats the daily food intake was restricted by one third to maintain constant BW during the infusion period. At isotopic equilibrium the mean plasma T3, T4, and TSH levels for control-fed rats were: 38 ng/dl, 5.1 micrograms/dl, and 470 ng/ml, respectively. The values for rats on PFD were T3: 22 ng/dl, T4: 4.8 micrograms/dl, TSH: less than 70 ng/ml. The [125I]T3 and [131I]T3 contents of whole homogenates from liver, kidney, thigh muscle, cerebral cortex, cerebellum, and anterior pituitary gland as well as the subcellular fractions from liver, kidney (nuclei, mitochondria, microsomes, and cytosol), and anterior pituitary gland (nuclei) were determined (after extraction in ethanol) by thin layer chromatography. The contribution of Lc T3(T4) and the total T3 levels in these tissue preparations could then be calculated. In the cerebral cortex, cerebellum, and anterior pituitary gland of PFD rats plasma-derived T3 as well as Lc T3(T4) was decreased. The total T3 level in the liver did not change under PFD, owing to an increase in Lc T3(T4). It is possible that the release of hepatic Lc T3(T4) into the blood stream was reduced. In neither group was there appreciable Lc T3(T4) in muscle. In contrast to the other tissues investigated, the [131I]T3 tissue-plasma ratio for muscle had increased under PFD, suggesting a higher uptake of T3. As a consequence, the T3 levels in the muscles of PFD rats did not differ from those in normally fed animals. For both groups of rats the contribution of Lc T3(T4) in hepatic nuclei was far lower than that found for the other hepatic cellular fractions. This would suggest that the hepatic nucleus preferentially takes up plasma-derived T3. In both control-fed and PFD rats the bulk of renal T3 appeared to be exchangeable with plasma T3. Hence the T3 levels in renal nuclei were reduced under PFD. The nuclear T3 levels in the anterior pituitaries from PFD rats were markedly decreased. Therefore it is likely that other factors determine TSH secretion under PFD.

PITUITARY-THYROID AXIS FUNCTION IN THE LOW BIRTH WEIGHT INFANT (LBW) WITH INTRACRANIAL HEMORRHAGE (IC)

The incidence of hypothyroxinemia low serum thyroxine(T4) and normal serum thyroid stimulating hormone (TSH) levels in the LBW with an IC is significantly greater than in the LBW without IC. The significance of this observation is not clear. The purpose of the study was to assess pituitary-thyroid axis function in the LBW with IC by examining the pituitary and thyroid gland response to thyrotropin releasing hormone(TRH).Twenty-four LBW weighing < 2.0 kg were screened for IC by ultrasonography between days 1 and 7 of life. On day 3, samples were drawn for serum T4 and TSH levels immediately prior to and 30 and 180 minutes after 20 μg/kg TRH IV.Six LBW were identified as having IC. Compared to the LBW without IC, the mean birth weights, 1 and 5 minute Apgar scores and incidence of RDS were similar in both groups. The mean ± SEM gestational age was significantly lower in the LBW with IC (29.5 ± 0.8 vs. 31.2 ± 0.3 weeks, p<0.025). The mean baseline serum TSH and T4 levels were similar in both groups. The mean serum T4 level was significantly greater at 30 and 180 minutes in the LBW without IC. The mean serum TSH level at 180 minutes remained significantly higher in the LBW with IC (51.4 ± 13.1 vs. 21.9 ± 4.0 μu/ml, p<0.01). Conclusion: 1) In response to TRH at 3 days, the mean serum TSH level at 180 minutes in the LBW with IC remains significantly elevated. This response is similar to that seen in patients with hypothalamic hypothyroidism.

Similar effects of thionamide drugs and perchlorate on thyroid-stimulating immunoglobulins in Graves' disease: evidence against an immunosuppressive action of thionamide drugs.

Previous studies have shown that serum titers of thyroid-specific antibodies such as thyroid-stimulating immunoglobulins (TSI), TSH-displacing antibodies (TDA), or microsomal antibodies (MAb) decrease in patients with Graves' disease during therapy with thionamide drugs (TD). In keeping with some in vitro results it was postulated that TD have an immunosuppressive action which may be partly responsible for the beneficial effects. To further elucidate this theory, we compared the changes in TSI during treatment with TD such as methimazole (MMI) and propylthiouracil (PTU) as well as with perchlorate (PC), an unrelated compound with a different mode of therapeutic action. Of 69 patients with hyperthyroidism due to Graves' disease, serum from 62 (90%) was positive for TSI, as measured by cAMP accumulation in a thyroid tissue culture assay. Six patients had to be excluded due to noncompliance. Of the remaining 56 patients, those 41 subjects (73%) with good control of the disease were followed up to 24 months during dose-adjusted antithyroid treatment. All patients with an uncomplicated course of treatment had a decline in the initially increased TSI values on either drug regimen. Five of 10 patients receiving PTU and 8 of 13 patients receiving MMI reached normal TSI levels; so did 11 of 18 patients receiving PC. There was no individual correlation between TSI decrease and drug dosages or the serum T4 and T3 levels. In all 3 groups, however, a decrease in mean T4 and T3 levels preceded the fall in TSI. By grouping the patients according to whether they had more than a 20% decrease in the initial TSI values after either 2 months or more than 4 months of treatment, it could be shown that the late responders had significantly higher T4 and T3 levels after 2 months of treatment. The similar patterns of change in TSI during treatment with TD and PC are strong evidence against an immunosuppressive effect of TD. If any direct interference occurs, a toxic effect on intrathyroidal lymphocytes by intrathyroidal drug accumulation could be the cause of the disappearance of TSI with both drug types. On the other hand, the data provide indirect evidence for the theory that the restoration of the euthyroid state is the cause of decreasing TSI levels and normalization of the immune regulation in many patients during treatment with antithyroid drugs.

Tri-iodothyronine and thyroxine in human milk.

The concentration of tri-iodothyronine (T3) and thyroxine (T4) in human milk was determined by radioimmunoassay (RIA). The analysis of T3 was performed on unextracted milk and on ethanol extracts of defatted milk. Analysis of unextracted milk was complicated by artifacts. Reliable and reproducible results were achieved only with the milk extracts. In 10 colostral milk samples the mean T3 levels +/- SD were 0.80 +/- 0.52 nmol/l before feeding (early milk) and 0.93 +/- 0.62 after feeding (hind milk). The T3 concentration in colostrum did not change significantly during the feeding to the infant. In 12 mature milk samples collected between infant feedings, the mean T3 +/- SD was 1.19 +/- 0.42 nmol/l. T4 was not detected in any of the samples analysed (detection limit 3 nmol/l).

Different rates of thyrotropin suppression after total body scan in patients with thyroid cancer: effect of regular doses of thyroxine and triiodothyronine.

The relative rates of T4 and T3 in inducing TSH suppression when therapy is re-started after Total Body Scan (TBS), in patients with differentiated thyroid cancer, were evaluated in two groups of 9 patients, each. The doses adopted were those usually considered to be TSH suppressive in chronic administration (T4 = 3.4 ± 0.3 µg/day/kg bw; T3 = 1.1 ± 0.04 µg/day/kg bw). At time 0, TSH levels were elevated in all patients, ranging from 58 to 147 µU/ml; T3 and T4 were below the limit of detectability. After the beginning of the therapy decrease of TSH levels and inhibition of TSH response to TRH was very gradual. It was slower in patients on T4: at day 14 basal TSH level was 23.6 ± 26.7 µU/ml (mean ± SD) and 30 min after 200 µg TRH iv mean TSH level was 99 ± 40 µU/ml; at day 30 mean basal TSH was 1.5 ± 1.2 µU/ml and, after TRH, 5.8 ± 6.9 µU/ml, than in patients on T3: at day 14 mean basal TSH level was 1.8 ± 1.0 µU/ml and after TRH 10 ± 13.9 µU/ml; at day 30 mean basal TSH was 1.0 ± 0.5 µU/ml and after TRH was 2.7 ± 1.4 µU/ml. In patients taking T3, serum levels of T3 rose to normal limits very quickly (at day 3 mean serum T3 level was 159 ± 30 ng/100 ml) and afterwards remained slightly above normal range (at day 7 it was 213 ± 41 ng/100 ml). In patients taking T4, the rise of serum levels of both T3 and T4 was much slower and gradual: at day 3 mean T3 level was 53 ± 15 ng/100 ml; at day 7 it was 99 ± 25 ng/100 ml; at day 14 it was 144 ± 26 ng/100ml; at day 3 mean T4 levels was 2.0 ± 0.6 µg/100ml; at day 7 it was 6.6 ± 1.5 µg/100 ml; at day 14 it was 9.9 ± 1.9 µg/100 ml. These data show that T4 in the usual suppressive dose is not suitable to achieve TSH suppression as quickly as would be necessary in patients with differentiated thyroid cancer when therapy is re-started after TBS. Treatment with T3, 1.1 µg/day/kg bw, induces TSH suppression more quickly. Therefore, it seems advisable in such patients to start suppressive treatment with T3 and to shift to T4 after a month, in order to avoid any unnecessary stimulation by TSH of eventual residual tumor.