Thyroid Hormone Secretion Rate Research Articles

Comparison of thyroid function in different emotional states of drug-na\xefve patients with bipolar disorder

BackgroundPrevious studies have shown that bipolar disorder is closely related to thyroid dysfunction. Psychiatric drugs have a large or small effect on thyroid function, and thyroid hormone levels can also affect the effect of drug treatment. Therefore, the purpose of this study is assessment the thyroid function of drug-naive bipolar disorder across different mood states, with the expectation of providing support for treatment options.MethodsThe present study is a cross-sectional study. Patients diagnosed with bipolar disorder according to the International Classification of Diseases diagnostic Criteria, Edition 10 (ICD 10) and who had never received medication were included in the study. The Montgomery Depression Scale (MADRS) was used to assess depressive symptoms and the Young Mania Rating Scale (YMRS) for manic symptoms. Thyroid function indicators include thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), total triiodothyronine (TT3), free thyroxine (FT4), and total thyroxine (TT4). Levels of TSH, TT4, FT4, TT3, and FT3 were measured within 48 h of hospitalization, between 06:00 and 08:00.ResultsThe data analysis finally covered the data of 291 subjects (136 in a bipolar manic group, 128 in a bipolar depressive group, and 27 in a bipolar mixed group), including 140 males and 151 females, with an average age of 27.38 ± 8.01. There was no significant difference in age, sex, marital status, work status, family history, and course of illness among the manic group, depressive group, and mixed group. The level of FT3, the rate of thyroid hormone increased secretion, and the total abnormality rate of thyroid hormone secretion in the manic group were significantly higher than those in the depressive group.ConclusionThese findings indicate that thyroid functions were significantly different between depressive and manic episodes in BD patients. In clinical practice, it is necessary to take into account the differences in thyroid hormone levels in patients with BD across different emotional states in choosing drug.

Effects of substances on plants' active compounds on changes in the hormone levels of the pituitary–Thyroid axis in hyperthyroidism and hypothyroidism

The roles of thyroid glands in different functions of the body have been well explained such that hypothyroidism and hyperthyroidism can impair the metabolism and normal functions of the body's tissues. Recently, using medicinal plants and their active compounds in treating diseases has attracted attention, and the people's tendency to use these compounds, which are considered to be low risk and to cause no side effect, is increasing. Because changes in the levels of thyroid hormones have considerable effects on body physiology and play a substantial role in the pathogenesis of different diseases, it is necessary to conduct further studies on hyperthyroidism and hypothyroidism and also the effects of plants and their compounds on thyroid hormone secretion rates. This review was conducted to present the information on thyroid hormones, as metabolism-regulating agents, and their association with different diseases as well as the effects of plant-based active compounds on changes in the hormone levels of the pituitary–thyroid axis in hyperthyroidism and hypothyroidism. Results indicated that disrupted serum levels of the thyroid hormones lead to increased incidence of cardiovascular disease, diabetes, depression, menstrual disorders, and kidney disease. The most important effective compounds on these hormones include flavonoids, coumarins, alkaloids, minerals, essential oil components, such as terpinene, gamma-terpinene, and limonene, and antioxidant compounds that directly influence thyroid and change serum levels of the thyroid hormones through inhibiting thyroid peroxidase. Other mechanisms of change in thyroid hormone levels by plant-based compounds are related to decrease in lipoxygenase activity and increase in the activities of catalase and dismutase. It can therefore be argued that using medicinal plants and their compounds can be a novel and efficient approach to develop drugs for thyroid diseases.

Identification, functional analysis, prevalence and treatment of monocarboxylate transporter 8 (MCT8) mutations in a cohort of adult patients with mental retardation

Monocarboxylate transporter 8 (MCT8) is an essential thyroid hormone (TH) transporter as humans with MCT8 mutations have severe neurological and endocrine abnormalities. The objectives are (i) to identify novel MCT8 mutations and (ii) to assess their functional relevance; (iii) to describe the effects of block-and-replace treatment in an MCT8 patient. The TOP-R study is a cross-sectional nation-wide multicentre study. Subjects with unexplained mental retardation (MR) were screened for MCT8 mutations. We identified three mutations: p.F501del (previously described), p.L492P and p.T162T. The F501del and L492P mutants, but not the T162T mutant, showed diminished T3, T4 and rT3 transport in transfected cells. TH transport in T162T fibroblasts was also not affected. One patient was treated with block-and-replace therapy to normalize serum TH levels. The results indicated a slow onset of the decrease in serum T4 and T3 by successive treatment with methimazole and PTU, and eventually their complete normalization by administration of LT4 with PTU but not with methimazole. The frequency of MCT8 mutations in males with X-linked MR approximately 3·9%. We identified several MCT8 mutations in a cohort of subjects with unexplained MR. We demonstrated the pathogenicity of two missense mutations. The synonymous variant did not affect TH transport. Block-and-replace therapy of one patient reversed the TH abnormalities. Our data suggest a decreased TH secretion rate and an increased T4 to T3 conversion by the type I deiodinase in patients with MCT8 mutations. Our study indicates that MCT8 mutations are a relatively frequent cause of X-linked MR.

The Relationship between Thyrotropin Receptor Antibody Levels and Intrathyroid Vascularity in Patients with Graves’ Disease

Thyroid stimulating hormone receptor antibodies (TSHRAbs) are specific autoantibodies of Graves' disease (GD). They activate adenylate cyclase, induce thyroid growth, and cause an increased rate of thyroid hormone production and secretion. TSHRAbs levels are decreased by treatment and may predict recurrence when they persist. Theoretically, TSHRAbs levels should be related to intrathyroid vascularity (ITV) due to the autoimmunity and inflammation. We aimed to analyze the relationship between TSHRAbs represented by thyrotropin-binding inhibitory immunoglobulin (TBII) levels and ITV measured by thyroid duplex sonography (TDS). 56 GD patients were prospectively recruited. ITV, measured using TDS, was defined as follows: (average color-flow area in the right and left sides of the thyroid/total thyroid area in transverse view)×100. The average TBII level was 47.1% and average ITV was 27.24. ITV positively and significantly correlated with TBII (p<0.001). TSHRAbs show significant correlation with ITV. This may help doctors to estimate thyroid autoimmune activity when they performing sonography at clinics.

2010 The studies of calbindin-, parvalbumin- and calretinin-positive neurons in the olfactory bulb of the insectvore, suncus murinus

A mean thyroid hormone secretion rate (TSR) of 1.61 μg/100 g body wt/day was determined for 26 Asian musk shrews (Suncus murinus) born and raised in captivity. Young females had statistically higher TSR's (1.90 ± 0.17 μg) than old males but the biological significance of this is unknown. The mean TSR of the entire group is not excessive for mammals in this weight class (mean 32.2 g) and is actually less than that of the Missouri Valley mole.The mean t12 of l-T4 in young males and females (15.19 ± 0.98 hr) is significantly shorter than in old males (20.38 ± 0.46 hr) when Tapazole is administered to prevent 131I recycling. An overall mean t12 of 18.08 ± 0.28 hr for 17 shrews does not indicate inordinate thyroid activity when compared with the t12 of laboratory rodents.These data indicate that the thyroid activity, and presumably, the overall metabolic rate of this tropically distributed insectivore species does not justify placing Suncus murinus in a metabolically peculiar category.

Free and Total Thyroid Hormones in Serum of Holstein Cows

Basic parameters are reported for free thyroxine and triiodothyronine in blood serum of dairy cattle. Free thyroxine ranged from a low of 1.47 ng/dl in the summer to 1.86 ng/dl in the spring and from 1.37 ng/dl in early lactation to 1.85 ng/dl in midlactation. The average free triiodothyronine went from a low of 2.98 pg/ml in winter to a high of 6.23 pg/ml in the fall and from 3.45 pg/ml in early lactation to 5.37 pg/ml in midlactation. The free fraction of the serum compared with the total fraction averaged .0267% for thyroxine and .291% for triiodothyronine. Free and total thyroxine were high in fall, low in winter, and intermediate in spring and summer. Free and total triiodothyronine showed a similar pattern with a greater magnitude in the variations. Even though the thyroid hormone secretion rate was higher in winter (earlier studies), increased tissue utilization kept serum concentrations low. Free and total thyroxine and triiodothyronine were low in early lactation due to high demands from peak milk production. Stage of lactation had a much greater influence on changes in serum thyroid hormones than did season.

Defective thyroidal iodine concentration in protein-calorie malnutrition.

Although protein-calorie malnutrition (PCM) is known to result in various abnormalities of thyroid function, the exact relationship between the two is not clearly understood. Therefore, the thyroid function of 10 men, 13-55 yr of age, with severe PCM was studied in a clinical research ward before and 3-4 months after protein-calorie repletion. Before repletion, all subjects had low serum T4 (mean +/- SEM, 5.1 +/- 0.5 micrograms/dl) and T3 (74 +/- 6 ng/dl) concentrations. Eight subjects were chemically euthyroid, and their free T4 (1.5 +/- 0.1 ng/dl) and serum TSH (2.9 +/- 1.4 microU/ml) values were normal. Two subjects were chemically hypothyroid, with low free T4 values and high serum TSH values. After repletion, the 8 euthyroid subjects had significant increases in serum T4 (P less than 0.01) and T3 (P less than 0.005), but TSH did not change. Serum T4 and T3 were still lower (P less than 0.05-0.001) and TSH higher (P less than 0.01) than in 28 normal men of comparable age coming from the same area. After repletion, values remained unchanged in the 2 hypothyroid subjects, except for moderate increases in serum T3 and slight decreases in TSH. In all PCM subjects, values of thyroidal exchangeable iodine (23.1 +/- 7 vs. 42.9 +/- 8 mg; P less than 0.02), estimated thyroidal I per g wet wt (1.05 +/- 0.3 vs. 1.99 +/- 0.36 mg; P less than 0.02), and thyroidal iodide clearance (13.8 +/- 1.6 vs. 19.4 +/- 1.3 ml/min; P less than 0.002) were lower before repletion than after; the protein-bound 131I level (72 h; 0.27% vs. 0.08 dose/liter; P less than 0.05) was higher, but thyroid hormone secretion rates (200 +/- 49 vs. 153 +/- 25 micrograms/day) were not significantly different. Thyroid iodide clearance was lower even though plasma inorganic iodine (6.3 +/- vs. 12.5 +/- 3 micrograms/liter; P less than 0.05) and daily urinary iodine excretion (158 +/- 43 vs. 395 +/- 62 micrograms; P less than 0.01) were lower before than after repletion. In 2 PCM euthyroid subjects, baseline thyroid 131I uptake was lower before than after repletion, and the magnitude of the increase after TSH (10 U, im) stimulation was greater when the malnourished state improved. TSH increased concentrations of serum T4 and T3 both before and after protein repletion. After repletion, one hypothyroid patient failed to respond to TSH; the other had a small increase in 131I uptake but not in serum T4 or T3. The results indicate defective thyroid iodine concentration in human PCM, but adequate hormone secretion. This situation leads to depletion of thyroid iodine stores. This alteration, if extreme, might result in hypothyroidism. Adequate protein-calorie intake tends to reverse these abnormalities.

Thyroid blood flow rate in man. Electromagnetic flowmetry during operation in euthyroid normal gland, nontoxic goiter, and hyperthyroidism.

Human thyroid blood flow rate (TBF) was measured during operations by electromagnetic flowmetry in 75 euthyroid patients with normal thyroid tissue, nodular goiter, or solitary adenoma, and in 22 hyperthyroid patients with diffuse or nodular goiter. Blood flow rate was measured in one to four of the thyroid arteries. No difference in blood flow rate was seen between the left and right lobes. The slight difference found between the inferior and superior arteries was not significant. In each subject, total TBF was calculated as 4 times the mean of the recorded blood flow in the single arteries. The total TBF was 31 (9-109) ml/min (inner 95 percentile range) in euthyroid patients, similar in all 3 groups. This is less than in most earlier reports. The relative TBF was 1.2 (0.4-3.8) ml/min/g thyroid tissue in normal thyroid tissue and 0.6 (0.1-3.7) ml/min/g in nontoxic nodular goiter (p less than 0.01). Patients with hyperthyroidism had a higher total TBF 54 (15-197) ml/Min (p less than 0.001), despite preoperative treatment giving euthyroidism, Similar TBF rates were found in 3 hyperthyroid patients given propranolol preoperatively. Electromagnetic flowmetry is applicable to study thyroid blood flow rate. Human TBF shows considerable interindividual variations, which must be kept in mind when studying directly the rate of thyroid hormone secretion from arteriovenous gradients.

A reappraisal of the goitre-prevention assay: Determination of the thyroid secretion rate in the Japanese quail and the relative potencies of T 3 and T 4 in preventing goitrogenesis

This reappraisal shows that the goitre-prevention assay (GPA) is as effective as radiometric techniques for estimating thyroid hormone secretion rates (TSR) in quails ( Coturnix coturnix japonica) and can be used where cost or facilities preclude the use of radioisotopes. A simple modification of GPA results analysis is described which enables calculation of confidence limits of the estimated TSR. Birds were injected subcutaneously twice daily for 20 days with 0.5 ml 0.9% (w/v) NaCl/100 g body wt/day alone (controls) or containing a fixed dose of goitrogen (10 mg 6- n-2-propylthiouracil (PTU)/100 g body wt/day) combined with one of several doses (1.4, 2.1, 2.8, 3.5 μg/100 g body wt/day) of either l-triiodothyronine (T 3) or l-thyroxine (T 4). Thyroid weights (per 100 g body wt) were measured after decapitation on the 21st day. The goitre-preventive doses of T 3 or T 4 (referred to as TRSs) were estimated as the y-intercepts from linear regressions of T 3 or T 4 doses on the differences between the mean thyroid weight of control birds and thyroid weights of PTU-treated birds; TRSs ± 95% confidence limits were 1.81 ± 0.15 (df = 14) for T 3 and 1.67 ± 0.13 (14) μg/100 g body wt/day for T 4.

Acclimation of mousedeer ( Tragulus javanicus) to hot temperature: Changes in thyroid activity

Abstract o 1. Thyroid hormone concentrations and secretion rate of Tragulus javanicus exposed to 27 and 33°C were measured. 2. Serum levels of T3 and T4 were 0.47±0.06 ng/ml (mean±SEM) and 36.2±2.3 ng/ml ( N =8) respectively. The values were lower at 33°C. 3. Thyroid secretion rate was also decreased by the higher ambient temperature.

Thyroid and testicular hormone responses to graded and prolonged exercise in man.

Eight men were studied during graded (47, 77 and 100% of maximal oxygen uptake) and prolonged (76%) exhaustive treadmill running. Plasma catecholamine levels increased progressively with intensity and duration of exercise. Serum concentrations of thyroid-stimulating hormone (TSH) increased with increasing work loads and were 107 (58--243)% (P less than 0.001) above resting values after maximal work. Thyroxine, triiodothyronine and luteinizing hormone in serum never changed significantly. While a small increase in testosterone concentrations (13 [1--24]%) after maximal exercise probably could be explained by changes in plasma volume, a definite increase (31 [14--56]%) occurred after 40 min of prolonged exercise. During continued exercise testosterone concentrations then gradually declined. Testicular stimulation by the increased catecholamine concentrations possible contributed to the rise in testosterone concentrations, but no evidence was found for a direct catecholamine induced increase in the activity of the thyroid gland. The exercise induced increase in TSH levels possibly explians the increased thyroid hormone secretion rate, which previously has been found in individuals participating in physical training programs.

Thyroid hormone secretion rates in growing and mature goats.

Dairy goats of four major breeds were used to determine the relationship between thyroid hormone secretion rate (TSR) and body weight. Goats ranged from 2 weeks to 6 years of age and 3 kg to 95 kg body weight. Twenty females were subjected to a total of 105 TSR determinations, while 14 males had 39 determinations. TSR was run every 3 months. TSR (mg/day) was related to body weight (kg) and the 3 primary measures used to calculate TSR (concentration in body pool, size of pool in liters, and rate of disposal of thyroxine from the body pool). Correlation coefficients were: thyroxine concentration and pool size, .038; thyroxine concentration and disposal rate, —.40; thyroxine concentration and TSR, .53; pool size and disposal rate, —.41; pool size and TSR, .72; and disposal rate and TSR, —.26. Age and TSR had a R2value of .35, while for body weight and TSR it was .53. When body weight and TSR were expressed as logarithms to comply with the mathematical expression Y = aXb, the R2 value was increased to .64. Pooling linear and quadratic effects of the logarithmic data resulted in R2 of .65, indicating no significant quadratic effect. A prediction equation developed for all 144 determinations was the following: Y (TSR, mg/day) = .010 × (body weight, kg).69. In other words, for every unit increase in body weight, there was a .69 unit increase in TSR. Prediction equation for 39 determinations on males was Y = .013 × .63 with R2 of .64, while it was Y = .010 X .70 for 105 tests in females with R2 of .63.

Relation of thyroid hormone secretion rate (TSR) in rats and fowl to hormone content of their thyroid glands

By the determination of thyroid hormone secretion rate (TSR), the amount of l-thyroxine ( l-T 4) secreted each 24 hr has been estimated. An attempt has been made in this study to determine by bioassay the relation of the daily TSR to the amount of stored hormone (thyroglobulin) in the thyroid of the rat and chicken in terms of l-T 4 equivalents. The individual TSR of 28 rats and 36 chickens was determined. Two animals having the same TSR were grouped as the donor and recipient of the thyroid homogenate. To bioassay the l-T 4 equivalents of donor thyroids, recipient rats and chickens were injected with graded levels of the thyroid homogenate until release of thyroidal 131I was blocked according to the technique used in the estimation of TSR. Mean l-T 4 equivalents in the thyroids of donor rats and chickens were 13.9 and 154.4 μg with a daily secretion of 3.58 and 27.98 μg, respectively. The amount of l-T 4 equivalent in the thyroid homogenate was 3.82 ± 0.35 times the daily TSR in rats and 5.56 ± 0.23 times in chickens ( P < 0.001). The data suggest that in rats and chickens there is a significant difference in the magnitude of bioassayable l-T 4 equivalents stored in the thyroid in terms of daily TSR.

Sympathetic innervation of the mouse thyroid and its significance in thyroid hormone secretion.

Studies were performed in mice to investigate the sympathetic innervation of the thyroid and to evaluate its role in the regulation of thyroid hormone secretion. Fluorescence histochemistry and electron microscopic autoradiography were used to study the distribution of adrenergic fibers and terminals in the thyroid and their relation to follicle cells and vessels. Bilateral surgical sympathectomy was performed by extirpation of the superior cervical ganglia, and pharmacological sympathectomy by iv injections of 6-hydroxydopamine. The secretion of thyroid hormone was estimated by daily measurements of the blood radioiodine (BRI) levels. Sympathetic, adrenergic nerve fibers were numerous in the mouse thyroid, and were mainly found in 2 locations: in relation to arterioles, and in interfollicular spaces. The terminals of the latter group had a very close relation to follicles and often were in direct contact with them, only the follicular basement membrane separating the adrenergic terminal and the follicle cell. In addition, interfollicular terminals often had a close relation to capillaries. It is concluded that in mice there is a morphological basis for a direct, nonvascular influence of the sympathetic nervous system on thyroid follicle cells. In addition, sympathetic stimuli may influence thyroid blood flow by effects on both arterioles and capillaries. Both pharmacological and surgical sympathectomy elicited a reduction in BRI levels that persisted for 1 or 2 days, presumably as a reflection of decreased thyroid hormone secretion. In view of this finding, and since a previous study has shown that unilateral sympathetic stimulation causes a large increase in BRI levels, preceded by formation of colloid droplets in the portions of the thyroid supplied by the stimulated nerve, it is suggested that the sympathetic innervation of the thyroid serves as a means for effecting prompt, short-term alterations in the rate of thyroid hormone secretion. (Endocrinology94: 959, 1974)

Thyroid Hormone Secretion Rates in Growing Jersey Cattle

Thyroid hormone secretion rates were determined in growing Jersey cattle ranging in age from 1 wk to 3 vr. The secretion method was radioactive thyroxine pool-turnover with samples taken every 12 to 72h. Seventy individual determinations were made in 14 females and 6 males with no difference between sexes. Change in logarithm of rate of secretion (mg) versus logarithm of body weight (kg) was expressed by the equation Y = aXb or In Y = a + b In X, where Y was thyroid hormone secretion rate. When all 70 determinations were included, the linear expression was In secretion rate (mg) = −3.05 + .403 In body weight (kg) or Y = .0475 X.403. Analysis of variance indicated that the linear equation accounted for 35% of the variation of Y and the quadratic effect accounted for an additional 15%. When the data were analyzed within-animal, the linear effect accounted for 19% of the variation and the quadratic effect for 26%. Calves had higher rates than older animals per unit body weight. When individual determinations of animals 0 to 3 mo of age were excluded, the relation of secretion of body weight was Y = .0142 X.686. When animals from 0 to 6 mo were excluded, the linear expression was Y = .0052 X.811.

Thyroid hormone secretion rate in the lactating rat.

Summary. Thyroid secretion rate (TSR) was determined in lactating and non-lactating rats by the thyroxine substitution and `direct output' methods. In lactating rats, apparent TSR as determined by the substitution method was significantly greater than that of controls when dietary iodine was deficient. By the direct output method, TSR was significantly reduced even when dietary iodine was adequate. It is concluded that the substitution method measures the physiological demand for thyroid hormone, which is greater during lactation, but represents true TSR only if iodine supplies are adequate. Results obtained by the direct output method show the actual TSR to be significantly reduced both during lactation and when dietary iodine is limited. Mean thyroid acinar cell height significantly increased as thyroidal iodine was depleted. It is concluded that, during lactation, TSH was elevated but iodine was insufficient to support the demand for thyroid hormone. The low serum T4 level observed in lactating rats, as determined by a competitive binding method, supports these conclusions. Analysis of the methods of computation of TSR by direct output showed that (1) as thyroidal iodine supplies were depleted, thyroidal iodide accumulation became more efficient, (2) the iodine-deficient thyroid recycled a greater percentage of the available iodine, (3) thyroidal 131I uptake was reduced in lactating rats, (4) total thyroidal iodine was inversely correlated to its release rate (K4) from the thyroid, and (5) thyroidal iodine, and not K4, was the major factor influencing TSR under these experimental conditions.

Effect of melatonin upon thyroid hormone secretion rate in female hamsters and male rats.

ABSTRACT Thyroid hormone secretion rate (TSR) of female golden hamsters and male Sprague-Dawley-Rolfsmeyer rats at 25 days of age were estimated as 0.75 μg L-T4/100 g body weight and 1.41 μg L-T4/100 g body weight respectively. The mean TSR of control group of both hamster and male rat reduced at 55 days (0.60 and 1.20 μg L-T4/100 g body weight, respectively) gives further evidence of aging. In hamsters, melatonin treatment at higher levels had no greater depressing effect upon TSR than the lower level, but had greater effect on food consumption. However, in male rats, melatonin depressed TSR at the higher level only. It seems that hamster is more sensitive to melatonin than rats. Thus the lower level exerts a maximum effect whereas in the rat, higher levels are required for maximum effect.

Iodide and thyroxine metabolism in the brook trout, Salvelinus fontinalis (Mitchill), during sustained exercise.

Iodide and thyroxine metabolism were followed in exercised and non-exercised starved trout.Radioiodide (125I) parameters suggested a slight increase in thyroid activity (% dose in thyroid, thyroid/serum ratio (T/S), and conversion ratio (CR)) and an increase in extrathyroidal 125I excretion resulting from exercise.The generally high and variable serum 127I levels increased up to 496 μg% during the experiments, being consistently higher in exercised fish. Individual variations in serum 127I were related in many instances to radioiodide parameters (I125I, T/S, CR) and to a limited extent to % thyroid. This demonstrates the uncertainty of radioiodide measurements when the specific activity of circulating 125I changes and the need for assessing 127I levels in radioiodide studies.Tissue uptake of radioactivity and serum loss of protein-bound radioactivity following radiothyroxine intraperitoneal injection, as well as serum stable thyronine levels, suggested both increased biliary loss of thyroid hormones and a higher thyroid hormone secretion rate as the result of exercise.

Secretion Rates of Thyroxine and Triiodothyronine in Dairy Cattle

Thyroid hormone secretion rates (TSR) were determined in 7 lactating dairy cows by the substitution method (suppression of thyroidal 131I release) and averaged .21mg L-thyroxine (L-T4) equivalents per 45.4kg body weight per day. In the same animals, TSR for thyroxine (T4SR) and for triiodothyronine (T3SR) were determined separately by the radioiodine labelled hormone pool turnover method. Pool sizes in the 7 cows were 36.9 liters (8.27% of body size) for L-T4 and 107.1 liters (22.1% of body size) for l-triiodothyronine (L-T3) when no goitrogen was given but were increased to 56.0 liters (12.2% of body size) for L-T4 and 201.0 liters (41.5% of body size) for L-T3 when the goitrogen methimazole (tapazole) was given orally at 4g per 454kg body weight per day (P<.05). Turnover rates as half-lives in days were 1.29 and .79 for L-T4 and L-T3 in the absence of goitrogen and 1.59 and 1.02 with goitrogen. Concentration of L-T4 in the plasma pool was 7.49μg per 100ml without the goitrogen and 6.18μg per 100ml with it while the concentration of L-T3 in the plasma pool, measured in the absence of goitrogen treatment only, was .149μg per 100ml. Mean T4SR in the 7 cows was .143mg per 45.4kg body weight per day without a goitrogen and .148mg in the presence of the goitrogen; T3SR was .0139mg without methimazole and .0193 with it. If L-T3 is 2.1 times as effective as L-T4 in suppressing 131I release by the thyroid, the combined TSR of L-T3 and L-T4 without a goitrogen would be .172mg of L-T4 equivalents per 45.4kg body weight per day and .189mg with the goitrogen. On this basis the substitution method overestimates TSR in cattle by 12 to 22%. Correlation coefficients for TSR with milk production were positive but low and nonsignificant, varying from .64 to zero and being .30 in 39 comparisons.

Effect of decreased dietary protein on the rate of thyroid hormone secretion and food consumption in rats.

SUMMARY One hundred and twenty albino female rats (Sprague-Dawley-Rolfsmeyer) were divided into five equal groups. Rates of thyroxine secretion (TSR) and food consumption were determined during the control period, and 10 and 25 days after initiation of dietary treatment. Animals in each group served as their own controls for the following modifications of their diet: (1) protein-free diet, (2) 5% protein (casein) diet, (3) 10% protein diet, (4) 15% protein diet, and (5) 20% protein diet. Purina lab chow (23·4% protein) and the 20% casein diet served as control diets. The TSR, the body weight and amount of food consumed were depressed significantly in the group fed on a protein-free diet for 10 and 25 days. The group fed 5% protein diet had a non-significant decrease in TSR as compared with the controls. Similarly, TSR was not reduced by 10, 15 or 20% protein diets. Food consumption decreased significantly in the groups fed a 5, 10 and 15% protein diet, but not in the group on 20% casein. Body weight decreased significantly in the groups on a protein-free diet and on a 5% protein diet. It would appear from these results that protein content of the diet does not become a limiting factor for TSR until it is lower than 5%. It is suggested that the calorie intake plays a more important role in regard to TSR than a low protein content of the food.