triiodothyronine--reverse and Obesity

Serum thyroid hormone concentrations and their metabolic fate are within the normal range limits in obese subjects. Also serum TSH concentrations and its response to TRH are normal, suggesting that tissue availability of thyroid hormones is normally preserved in these subjects. In contrast, during caloric restriction serum T3 concentrations decrease as a consequence of its reduced production rate from peripheral deiodination of T4. Opposite, serum rT3 concentrations markedly increase as a result of its decreased metabolic clearance rate. During caloric overfeeding serum T3 concentration increase whereas serum rT3 concentrations decrease. In this condition the production rate of T3 increases. During caloric restriction and overfeeding serum T4 concentrations and its production and degradation are not modified.

Topics: Energy Intake; Humans; Obesity; Thyroid Hormones; Thyrotropin; Thyrotropin-Releasing Hormone; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

In a study of the mechanism of adaptation to protein deficiency, 10 moderately obese women underwent a 3-wk fast followed by random allocation to a 1-wk refeeding regimen providing 80 g carbohydrate or protein. Protein metabolism was studied by means of nitrogen (N) balance, urinary 3-methylhistidine excretion, and postabsorptive plasma leucine flux using L-[1-13C]leucine infusions. After the 3-wk fast, plasma leucine flux and 3-methylhistidine excretion both decreased by 31% from control diet values (P less than 0.01), and N balance was -5.9 g/day. After protein refeeding, N balance was positive (+1.7 g/day, P less than 0.05) whereas leucine flux was unchanged from prolonged fasting values. After carbohydrate refeeding, N balance improved to -3.1 g N/day, whereas leucine flux decreased by a further 18% (P less than 0.05). Protein and carbohydrate refeeding were associated with further 23 and 31% reductions of 3-methylhistidine excretion compared with prolonged fasting (P less than 0.05). The results support the hypothesis that improved efficiency of protein retention in starvation is intimately associated with a decreased rate of protein turnover.

Topics: 3-Hydroxybutyric Acid; Blood Glucose; Carbon Isotopes; Diet, Reducing; Dietary Carbohydrates; Dietary Proteins; Energy Intake; Fasting; Fatty Acids, Nonesterified; Female; Humans; Hydroxybutyrates; Insulin; Isotope Labeling; Leucine; Nitrogen; Obesity; Proteins; Random Allocation; Thyroxine; Triiodothyronine, Reverse

We measured the effects of iopanoic acid on thyroid hormone metabolism in obese men during severe calorie restriction to study the nutrition regulation of thyroid hormone metabolism. Eight morbidly obese men received a weight-maintenance diet followed by 6 wk of 600 kcal/d. During underfeeding, patients received iopanoic acid or placebo for 2-wk periods in a double-blind crossover fashion. Underfeeding alone (UF) produced a 28.3% decline in the serum triiodothyronine (T3) concentration, and iopanoic acid plus underfeeding (IOP) produced a 49.5% decline in T3 concentration from baseline. Serum reverse T3 concentrations increased 289% during IOP compared with UF alone (p less than 0.001). Serum TSH concentration was unchanged by underfeeding but increased twofold during IOP treatment. Thyroid hormone kinetics demonstrated a decrease in T3 production during IOP compared with UF. These findings suggest that calorie restriction regulates T3 production by modulating only type I 5'-deiodinase activity.

Topics: Adult; Diet, Reducing; Double-Blind Method; Energy Intake; Humans; Iopanoic Acid; Kinetics; Male; Obesity; Thyroid Gland; Thyroid Hormones; Thyrotropin; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Serum T4, 3,5,3'triiodothyronine (T3), 3,3',5'-triiodothyronine (reverse T3, rT3), 3,3'-diiodothyronine (3,3'-T2), 3',5'-diiodothyronine (3',5'-T2) and thyrotrophin (TSH) levels were studied in nineteen obese patients before and 6, 12, and 18, months after a jejuno-ileal bypass. Before surgery, the obese patients had increased serum T3 levels compared with a group of lean, matched controls (median: 1.94 nmol/l v. 1.44 nmol/l, P less than 0.01). Serum T3 decreased to normal (1.64 nmol/l) 18 months after surgery. A slight decrease was also observed in serum 3,3'-T2 levels, whereas progressive reductions in serum concentrations of rT3 and 3',5'T2 occurred. Eighteen months postoperatively the serum levels of rT3 and 3',5'-T2 had decreased from 0.676 nmol/l to 0.430 nmol/l (P less than 0.02) and 55.2 pmol/l to 40.0 pmol/l (P less than 0.01), respectively, and the values at 18 months were also reduced compared with the control group [0.722 nmol rT3/1 (P less than 0.01), 51.4 pmol 3',5'-T2/1 (P less than 0.01)]. concomitant with the decrease in serum level of the iodothyronines, serum TSH concentrations increased from 0 Micro U/ml to 0.9 microu/ml (P less than 0.01).

Topics: Adult; Diiodothyronines; Female; Humans; Ileum; Jejunum; Male; Middle Aged; Obesity; Thyronines; Thyrotropin; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Twenty obese patients were treated as out-patients with a 3.35 MJ (800 Kcal) per day diet, and, by the double-blind method, ten of the patients were prescribed 40 micrograms of triiodothyronine (T3) daily and the other ten placebo. Body weight and serum thyroxine (T4), T3 and reverse T3 (rT3) concentrations were measured before treatment, then monthly over 6 months. No significant difference in mean weight loss was found between the patients receiving T3 and those on placebo. Serum T3 concentration decreased slightly in patients on placebo and increased in those on T3 but these changes were not statistically significant. However, patients on T3 maintained a significantly higher concentration of T3 in serum than those on placebo. Mean serum T4 and rT3 concentrations remained essentially unchanged in the patients on placebo, whereas both decreased significantly in patients receiving T3. We conclude that changes in serum T3 during dietary treatment of obesity are of minor significance in limiting the expected weight loss in the patients.

Topics: Adult; Body Weight; Diet, Reducing; Female; Humans; Male; Middle Aged; Obesity; Thyroid Hormones; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Serum levels of thyroxine (T4), 3,3',5-triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3) and thyrotrophin, and T3-uptake were measured in 13 morbidly obese patients preoperatively and during the first five months after jejunoileal bypass surgery, in which period the patients lost 20% in body weight. They were randomized to a ratio of 3:1 or 1:3 between the jejunal and ileal segment included in the bypass, but the results in the two groups did not differ significantly. T4 level showed a slight decrease during the five months after surgery. T3 level was reduced to 82% of the preoperative value within the first month of surgery, and was stable thereafter. rT3 level was unaffected by surgery, as was the level of thyrotrophin. T3-uptake increased slightly after surgery. These findings are compatible with caloric restriction with low carbohydrate intake, and suggests that disruption of the enterohepatic circulation of iodothyronines is without clinical importance.

Topics: Adult; Female; Humans; Ileum; Jejunum; Male; Obesity; Thyrotropin; Thyroxine; Time Factors; Triiodothyronine; Triiodothyronine, Reverse

The interactions of catecholamine and thyroid hormones in determining changes in metabolic rate were assessed in obese patients given propranolol, both on weight maintenance diet and during semistarvation. Propranolol reduced the resting metabolic rate by 8.6% on a weight maintenance diet but had no effect during energy restriction. Since propranolol led to a similar fall in triiodothyronine (T3) and an increase in reverse T3 on both diets, the early fall in RMR on semi-starvation may depend on catecholamine-mediated mechanisms. Beta-adrenergic blockade might promote energy retention on a normal energy intake but should not reduce the efficacy of slimming diets.

Topics: Adrenergic beta-Antagonists; Adult; Basal Metabolism; Catecholamines; Diet, Reducing; Female; Humans; Middle Aged; Obesity; Propranolol; Thyroid Gland; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Obese persons generally regain lost weight, suggesting that adaptive metabolic changes favor return to a preset weight.. Our objective was to determine whether adaptive changes in resting metabolic rate (RMR) and thyroid hormones occur in weight-reduced persons, predisposing them to long-term weight gain.. Twenty-four overweight, postmenopausal women were studied at a clinical research center in four 10-d study phases: the overweight state (phase 1, energy balance; phase 2, 3350 kJ/d) and after reduction to a normal-weight state (phase 3, 3350 kJ/d; phase 4, energy balance). Weight-reduced women were matched with 24 never-overweight control subjects. After each study phase, assessments included RMR (by indirect calorimetry), body composition (by hydrostatic weighing), serum triiodothyronine (T(3)), and reverse T(3) (rT(3)). Body weight was measured 4 y later, without intervention.. Body composition-adjusted RMR and T(3):rT(3) fell during acute (phase 2) and chronic (phase 3) energy restriction (P: < 0.01), but returned to baseline in the normal-weight, energy-balanced state (phase 4; mean weight loss: 12.9 +/- 2.0 kg). RMR among weight-reduced women (4771 +/- 414 kJ/d) was not significantly different from that in control subjects (4955 +/- 414 kJ/d; P: = 0.14), and lower RMR did not predict greater 4-y weight regain (r = 0.27, NS).. Energy restriction produces a transient hypothyroid-hypometabolic state that normalizes on return to energy-balanced conditions. Failure to establish energy balance after weight loss gives the misleading impression that weight-reduced persons are energy conservative and predisposed to weight regain. Our findings do not provide evidence in support of adaptive metabolic changes as an explanation for the tendency of weight-reduced persons to regain weight.

Topics: Aged; Basal Metabolism; Body Composition; Body Mass Index; Calorimetry, Indirect; Diet, Reducing; Energy Intake; Female; Humans; Kinetics; Middle Aged; Models, Biological; Obesity; Postmenopause; Triiodothyronine; Triiodothyronine, Reverse; Weight Gain; Weight Loss

In a first experiment, serum thyroxine (T4), 3,5,3'-triiodothyronine (T3) and thyrotrophin (TSH) concentrations as well as thyroid gland T4 and T3 contents were measured in developing lean and obese Zucker male and female rats of 4-16 weeks of age. The rats were bred in our laboratory and always treated in sex-matched pairs of one lean and one obese rat from the same litter. Serum T4 was not different in any phenotype/sex group at 4 weeks. In male rats, it became progressively lower (27 and 37% at 12 and 16 weeks respectively) in obese than in lean rats. In females, similar levels of serum T4 were maintained in both obese and lean developing rats. Serum T3 was similar in obese and lean male 4-week-old rats whereas it was lower (28%) in obese than in lean females. It became progressively lower (39 and 49% at 12 and 16 weeks respectively) in obese than in lean developing male rats. In females, lower levels of serum T3 were maintained (25 and 43% at 12 and 16 weeks respectively) in obese than in lean rats. Serum TSH was not different in any phenotype/sex group at 4 weeks. It rose in both obese and lean male rats with age, but became progressively lower (33 and 23% at 12 and 16 weeks respectively) in obese compared with lean rats. In females, similar levels of serum TSH were maintained in both obese and lean developing rats. Thyroid gland weight was not different in any phenotype/sex group at 4 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Female; Male; Obesity; Radioimmunoassay; Rats; Rats, Mutant Strains; Sex Factors; Thyroid Gland; Thyroid Hormones; Thyrotropin; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Triiodothyronine (T3) kinetic studies were performed on ten clinically non-fasting euthyroid obese individuals and on eight normal subjects. Kinetic analysis was carried out according to a three-pool model whose basic approach involved the acquisition of data from both vascular and extravascular sources. The former were represented by the plasma disappearance curves of iv injected radiolabeled T3. The latter included fecal and urinary losses and liver, kidney and thigh uptake. A detailed comparison of the T3 kinetics of obese and normal individuals did not uncover many differences between these two groups in the way the hormone is distributed, metabolized and excreted. The mean value for the plasma equivalent distribution volume of T3(VD3) in obese individuals (27.05 L) was not significantly different from that in controls (24.60 L) nor were significant differences observed between the mean value for the plasma appearance rate of the hormone (PAR3) in obese subjects (29.80 micrograms/day) and that in controls (30.05 micrograms/day). The mean value for the size of the slow pool (Qc), including fatty tissue as well as skeletal muscle, was unchanged in obese individuals when compared with controls, although in the obese subjects the mean value for the mass of fatty tissue was about 5 times greater. In addition, in obese individuals, the mean value for the fractional rate transfer from plasma to the slow pool (Kca), which was 9.06 day-1, did not significantly differ from that in controls (9.22 day-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adolescent; Adult; Feces; Female; Humans; Kidney; Liver; Male; Middle Aged; Models, Biological; Muscles; Obesity; Thyrotropin; Thyrotropin-Releasing Hormone; Thyroxine; Tissue Distribution; Triiodothyronine; Triiodothyronine, Reverse

In an attempt to explain reverse T3 changes during protein supplemented semistarvation, reverse T3 (rT3) and T3 changes have been evaluated in regard of bw changes and changes of nutrient combustion. Significant (p less than 0.001) bw and body mass decrease was characterized by a significant (p less than 0.01) increase in rT3 levels, whereas no significant decrease of T3 could be found. During semistarvation carbohydrate combustion decreased from 34 to 13% where lipid combustion rate increased from 51 to 72%. No correlation could be found between delta rT3 and changes in bw, BMR or oxygen consumption. A significant correlation (p less than 0.005) exists between delta rT3 and delta % lipid combustion, while a negative correlation (p less than 0.02) was present between delta rT3 and delta % protein combustion. No correlation exists between delta rT3 and carbohydrate combustion. Although no definite clue could be found for the rT3 increase during semistarvation, a combined effect of lipolysis and lean mass preservation is suggested.

Topics: Adult; Calorimetry; Creatinine; Diet; Dietary Carbohydrates; Dietary Fats; Dietary Proteins; Female; Humans; Male; Middle Aged; Nitrogen; Obesity; Oxidation-Reduction; Thyroid Function Tests; Triiodothyronine; Triiodothyronine, Reverse

Successive determinations of serum total (T4) and free (FT4) thyroxine, total (T3) and free (FT3) 3,5,3'-triiodothyronine and total 3,3',5'-triiodothyronine (rT3) concentrations were performed by radioimmunoassay in 17 moderately obese women during a 6-week slimming cure. The 2.09 MJ/d (500 kcal/d) diet (50 per cent protein, 25 per cent carbohydrate and 25 per cent lipid) was given as three daily meals of general foods. During the cure, the body mass index (BMI) decreased by about 10 per cent, with a gradual decrease in the rate of weight loss. Moreover, the patients with the highest basal overweight had the largest subsequent weight loss. A decrease of about 15 per cent in serum T4 was observed from the second week to the end of the diet period. Inversely, serum FT4 increased transiently on day 3, then returned to the baseline. The fall in serum T3 and FT3 was obvious on day 3 and an approximate 20 per cent decrease in the two hormonal forms remained from the second to the last week of diet. Serum rT3 increased by 30 per cent during the first week, then returned to the baseline on the third week. The largest decreases in serum T4, T3 and FT3 observed during the cure occurred in the patients with the highest corresponding basal values. These findings suggest that (i) the rapid changes of the serum thyroid hormone concentrations observed during the slimming cure may be an adaptive mechanism against a further weight loss, and (ii) these changes would be related to the initial state of the thyroid hormone metabolism.

Topics: Adolescent; Adult; Body Constitution; Diet, Reducing; Female; Humans; Obesity; Thyroid Hormones; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Changes in thyroid hormone metabolism in the low-3,5,3'-triiodothyronine (T3) syndrome cannot be fully explained in all conditions by a decrease in 5'-deiodinase activity. Recent observations showed that in rat hepatocytes iodothyronines are taken up by an active transport mechanism. To investigate whether regulation, i.e., inhibition of active transmembraneous transport for iodothyronines in humans may contribute to the generation of the low-T3 syndrome, tracer thyroxine (T4) and T3 kinetic studies were performed in 10 obese subjects before and after 7 days on a 240 kcal diet. Kinetics analyses were performed according to a three-pool model of distribution and metabolism for both T4 and T3. For T4 kinetics, during caloric deprivation serum total T4 and plasma pool did not change and production rate and metabolic clearance rate (MCR) were significantly lower. Despite a significantly higher serum free T4, the mass transfer rate to the rapidly equilibrating pool (REP) and the slowly equilibrating pool (SEP) diminished significantly, leading to smaller tissue pools. For T3 kinetics, both serum total T3, free T3, plasma pool, and production rate diminished significantly, while MCR remained unchanged. Mass transfer rates to the REP and the SEP were lowered by approximately 50%, leading to smaller tissue pools. These changes cannot be fully explained by a similar decrease of serum free T3 (only 25%), indicating a diminished transport efficiency for T3. In conclusion, during caloric restriction, transport of T4 and T3 into tissues is diminished, and this phenomenon is much more pronounced for T4 than for T3.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adult; Diet, Reducing; Energy Intake; Female; Humans; Iodide Peroxidase; Iodine Radioisotopes; Kinetics; Male; Obesity; Syndrome; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Seventeen subjects, including 12 mildly obese women, were investigated to determine the presence of a diurnal variation in serum T3 levels. A subset of 8 subjects was studied after fasting for 6 days, while another subset of 5 subjects was studied 2 days after receiving 3 mg T4, orally, to suppress TSH secretion. To negate the influence of hemoconcentration produced by ambulation, serum T3 to T4 ratios (nanograms per microgram) rather than total T3 values were used for analysis. A synchronous diurnal rhythm for mean serum T3 to T4 ratios and TSH values was found, with mean nighttime increases of 7.8% and 49.5%, respectively. The timing of the T3 to T4 and TSH nocturnal peaks for individual subjects, however, were not correlated, suggesting that T3 to T4 ratios changes were not caused by TSH stimulation of thyroid T3 release. During fasting, the diurnal rhythm of serum T3 to T4 was obliterated within 24 h of beginning the fast, although TSH rhythmicity persisted. After the 3-mg oral T4 dose, serum TSH became undetectable, while the diurnal serum T3 to T4 ratio changes persisted. In contrast, there was no detectable diurnal rhythmicity of serum T3 to T4 ratios during either the control or fasting period. We conclude that the diurnal rhythm of serum T3 is not TSH dependent, but, rather, is influenced by some as yet unidentified dietary signal, which alters the efficiency of the peripheral tissue T4 to T3 conversion.

Topics: Adult; Circadian Rhythm; Fasting; Female; Humans; Male; Obesity; Reference Values; Thyrotropin; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Anorexia nervosa is accompanied by increased serum reverse triiodothyronine levels and decreased serum triiodothyronine levels. We observed 28 women undergoing gastric plication for morbid obesity and found serum reverse triiodothyronine levels to be significantly decreased (p = 0.018) from a preoperative mean (+/- SD) of 0.30 (+/- 0.17) to 0.21 (+/- 0.06) ng/ml after weight loss. As all of our subjects were on semistarvation diets and had a significant weight loss (p less than 0.001), the observed decrease in reverse triiodothyronine rather than increase (as reported in anorexia nervosa) suggests factors other than weight loss or a semistarvation diet are important in the reverse triiodothyronine increase observed in anorexia nervosa.

Topics: Adult; Body Weight; Female; Humans; Obesity; Serum Albumin; Stomach; Thyroxine; Thyroxine-Binding Proteins; Triiodothyronine; Triiodothyronine, Reverse

Effects of high fat diet (HFD)-induced obesity and moderate aging on iodothyronine kinetics were studied in young adult (3 month old) chow-fed male rats and two groups of older 9- to 11-month-old) male rats, one on chow and the other on HFD. Labeled T4, T3, and rT3 were each injected via an intraatrial double lumen catheter in unanesthetized rats. Serial blood samples were collected according to optimally designed schedules, and labeled iodothyronines in serum were quantified with three different Sephadex gel chromatographic systems. Comprehensive kinetic analyses indicated the following. Several T4 metabolic indices were markedly different between the two older groups (chow vs. HFD), most notable, increased plasma T4 clearance rate (0.098 vs. 0.15 ml/min), decreased plasma T4 concentration (23 vs. 15 ng/ml), and a plasma T4 fractional turnover rate 2 times greater (0.10 vs. 0.19/min), all in the HFD group. There was also a high negative correlation between T4 concentration and body weight (r = 0.77), but not with age. However, the three groups manifested no significant differences in T4 secretion rates (2.0 vs. 2.2 vs. 2.3 ng/min) or whole body pool sizes (2.1 vs. 2.3 vs. 2.4 micrograms). Accounting for metabolic body size, there still were no differences in T4 secretion rate or pool sizes. For T3, we found an almost 3-fold increase in T3 whole body production rates, and a greater than 2-fold increase (from about 25% to 60%) in the percentage of T4 converted to T3 in both older groups relative to that in the young rats. There were almost no significant differences in T3 kinetics between older HFD and older chow-fed groups, and differences in rT3 kinetics among the three groups revealed no clear pattern. Our results suggest that age-related correlations in T4 concentration are a consequence of body weight differences, not age as such. However, the metabolic fate of T4 changes with age, with more than twice as much converted to T3 in older animals. Constancy of T4 production rate and total pool size in young and older animals, independent of body weight, together with the apparent increase in T4 conversion to T3 suggest that the metabolic needs of the animal are being met by regulation of T3 production from T4 conversion, not by regulation of T4 production as such.

Topics: Aging; Animals; Body Weight; Dietary Fats; Kinetics; Male; Obesity; Rats; Rats, Inbred Strains; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

The relationship between the changes in serum thyroid hormone levels and nitrogen economy during caloric deprivation were investigated in ten obese men during a 40 d, 400 kcal protein-supplemented weight-reducing diet. This regimen induced increases in the serum levels of total T4, free T4 and total rT3, and decreases of total T3, while serum TSH remained unchanged. There were progressive decreases in total body weight and urinary losses of total nitrogen and 3-methylhistidine, with the early negative nitrogen balance gradually returning towards basal values during the 40 days. Subjects with the largest weight loss had the most increase in the serum levels of total T4 and free T4 index and the greatest decrease in T3. The magnitude of the increase of the nitrogen balance from its nadir was correlated with the extent of the reduction of T3 and increase of T3 uptake ratio and free T4 levels. The decrease in the urinary excretion of 3-methylhistidine correlated with the increase in free T4 and rT3 levels. Nadir serum transferrin values were directly related to peak rT3 values, and the lowest albumin concentrations occurred in subjects with the highest total T4 and free T4 index values. Further, the maximum changes in the serum thyroid hormone levels preceded those of the nutritional parameters. These relationships suggest that: (1) increases in serum rT3 and free T4 and reductions in T3 concentrations during protein supplemented weight reduction may facilitate conservation of visceral protein and reduce muscle protein turnover; and (2) the variation in the magnitude of these changes may account for the heterogeneity of nitrogen economy.

Topics: Adult; Diet, Reducing; Dietary Proteins; Energy Intake; Humans; Male; Methylhistidines; Middle Aged; Nitrogen; Obesity; Proteins; Thyroid Hormones; Thyrotropin; Thyroxine; Time Factors; Triiodothyronine; Triiodothyronine, Reverse

Topics: Adult; Female; Humans; Male; Obesity; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Serum total thyroxine (T4), 3,5,3'-triiodo-L-thyronine (T3), 3,3',5'-triiodo-L-thyronine (reverse T3 or rT3) and free thyroxine (FT4), free 3,5,3'-triiodo-L-thyronine (FT3) concentrations were measured by radioimmunoassay in 52 moderately obese patients and 32 age-matched control subjects with constant body weight and no dietary restriction. The comparisons of iodothyronine concentrations in the obese and control subjects gave the following results: serum T4 and FT4 concentrations were not different in the two samples (mean +/- s.e. T4: 105.8 +/- 3.0 vs 109.4 +/- 4.0 nmol/l, FT4: 10.9 +/- 0.4 vs 10.8 +/- 0.8 pmol/l). A slight but non-significant decrease in serum rT3 concentrations was observed in the obese patients (0.29 +/- 0.02 vs 0.32 +/- 0.02 nmol/l). A slight (10 per cent) but highly significant (P less than 0.01) decrease was observed in the obese patients for serum T3 (2.20 +/- 0.06 vs 2.44 +/- 0.05 nmol/l) and FT3 (6.0 +/- 0.2 vs 6.9 +/- 0.2 pmol/l). Serum FT4 and T4 on the one hand and serum FT3 and T3 on the other were positively correlated both in the obese and control subjects. No correlation was found between serum T3 and weight expressed as body mass index. The results suggest that the most important factor responsible for the decrease in the serum total and free T3 concentrations is the nutrient intake.

Topics: Adolescent; Adult; Body Weight; Female; Humans; Male; Middle Aged; Obesity; Thyroid Hormones; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Topics: Acclimatization; Disease; Fasting; Female; Fetus; Humans; Infant, Newborn; Kinetics; Obesity; Pregnancy; Receptors, Cell Surface; Receptors, Thyroid Hormone; Starvation; Temperature; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Fasting and hypocaloric diets are known to induce a reduction of triiodothyronine (T3) and to increase reverse triiodothyronine (rT3) in normal and obese subjects. The effect of 8-day fasting was evaluated on T3, thyroxine (T4), free T4, rT3, TSH, immunoreactive insulin (IRI), thyroxine binding globulin (TBG) and glycemia in 21 obese subjects (5 males, 16 females) grouped according to the average starting blood glucose concentration in: group I, diabetic obese subjects (9 patients); group II, non diabetic obese subjects (12 patients). All patients had no history of recent weight loss due to dietetic therapy or drugs. Blood samples were drawn in the morning at 0, 2, 4, 6, 8 days after total caloric deprivation and 2 days after refeeding. A superimposable variation of weight and glucose concentration were seen in both groups. In addition, no difference was observed in ketone body excretion, SH, TBG, T4, free T4. In group II a significant decrease of IRI was observed during diet (p less than 0.05); T3 decreased (p less than 0.01) and rT3 increased (p less than 0.01) significantly. No variations in T3 and rT3 values were observed in group I. These results are consistent with a possible role of glucose metabolism in the genesis of the low T3 syndrome.

Topics: Adult; Diabetes Mellitus; Fasting; Female; Humans; Insulin; Male; Middle Aged; Obesity; Thyroglobulin; Thyroid Hormones; Thyrotropin; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Thyroid hormones were measured before, during and after acute exercise (60 min) or physical training (3 months) in obese women. Thyroid stimulating hormone concentration increased during acute work and decreased immediately after. No changes were seen during the two following days. An increase was seen after ten days as well as after three months of physical training. Thyroxine concentrations showed no changes. 3,5,3'-Triiodothyronine decreased slightly immediately after acute exercise, and after three months of physical training, 3,3',5'-triiodothyronine (reverse triiodothyronine) increased slowly during and after acute exercise. A negative correlation was found between changes in fasting insulin and thyroxine and a positive correlation between changes in blood pressure and triiodothyronine after training. Lack of agreement in previous reports is probably due to methodological differences such as methods more or less susceptible to fatty acid interference, and thyroid hormones changing differently during acute work and before and after physical training. The duration of the study may also be of importance, even 3 months possibly being too short for attaining equilibrium in thyroid homeostasis.

Topics: Exercise Test; Exercise Therapy; Female; Humans; Middle Aged; Obesity; Physical Education and Training; Thyroid Hormones; Thyrotropin; Thyroxine; Thyroxine-Binding Proteins; Triiodothyronine; Triiodothyronine, Reverse

This study describes the existence of a peripheral tissue mechanism for maintaining serum T3 concentrations in states of T4 deficiency or excess in man. Serum T3 and T4 levels were determined in 242 primary hypothyroid subjects who had been maintained on varying doses of oral T4 therapy. Subjects treated with sub-maintenance T4 doses were supplemented by additional oral T3 therapy to maintain eumetabolic status as assessed by suppression of serum TSH values. This T3 supplementation was withdrawn 4-5 days prior to study in order to obviate any influence on serum T3 indices. Serum total T3/T4 ratio values in this study population were observed to progressively decline fivefold in a curvilinear manner as serum T4 concentrations rose from less than 0.5 to 20 micrograms/dl (total serum T3/T4 ratio fell from approximately 50 to 10, ng T3/ng T4 X 10(3)). This phenomenon is presumably the result of an altered T4 to T3 conversion by peripheral tissue 5'-deiodinase systems. A similar alteration of T4 to rT3 conversion with changing serum T4 levels does not appear to occur since serum rT3/T4 ratios did not vary in a separate study population over a serum T4 concentration span from 4-16 micrograms/dl. The mechanism by which this autoregulatory control of T4 to T3 conversion occurs is unknown. However, it would appear physiologically to complement the pituitary-thyroid autoregulatory system by acting to defend and maintain serum T3 concentrations in states of T4 deficiency and excess.

Topics: Female; Humans; Hypothyroidism; Middle Aged; Obesity; Radioimmunoassay; Thyrotropin; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

The direct effects of L-T3 (triiodothyronine) on glucose utilization, 2-deoxyglucose uptake and O2 consumption were evaluated in vitro in isolated adipocytes from 6-week-old obese and nonobese Zucker rats. Adipocytes treated for 30 min with L-T3 had a 20-25% decrease in glucose conversion to CO2, fatty acids and glyceride-glycerol and uptake of 2-deoxyglucose. Incubation of adipocytes with either D-T3 or rT3 (reverse T3) did not decrease utilization of glucose. T3 also decreased the insulin-stimulated fatty acid synthesis from glucose in both obese and nonobese adipocytes. Adipocyte O2 consumption was decreased by T3 in media that contained glucose but not in media that contained either acetate or no exogenous substrate. These data indicate that T3 has a direct, immediate and specific action on adipocyte glucose utilization and may act to modulate adipose lipogenesis and lipolysis.

Topics: Adipose Tissue; Animals; Deoxyglucose; Epididymis; Glucose; Male; Obesity; Oxygen Consumption; Rats; Rats, Zucker; Thinness; Triiodothyronine; Triiodothyronine, Reverse

Severe calorie restriction for treating the obese reduces serum triiodothyronine (T3) and energy expenditure, and may be counterproductive. In order to avoid severe calorie deficiency, we measured the individual minimum energy requirements (threshold, T) in 17 obese females and fed each on a sub-threshold diet, comprising the maximum number of calories commensurate with weight loss (T-200 cals). Mean T-200 was 1318 +/- 96 cals, but the mean weight loss after 16 weeks on a sub-threshold diet (STD) was identical (17 kg) to that obtained by 22 age-matched female controls on a classical diet of 659 +/- 59 cals, exactly half the intake. Weight loss on the classical diet was initially rapid but decelerated sharply after 8 weeks, while on the sub-threshold diet the rate of loss remained constant throughout. In a second study, thyroid hormone measurements were performed three times weekly in 27 obese females during the 4 week period required to establish T. The mean weight loss was 4.02 +/- 0.3 kg, but T3 levels varied minimally and very transiently. STD produces short-term results similar to those obtained by severe calorie deprivation, but is more acceptable to the patient. It appears not to provoke the fat-saving reflexes provoked by the classical, low-calorie diet.

Topics: Adult; Body Weight; Diet, Reducing; Energy Intake; Energy Metabolism; Female; Humans; Obesity; Thyroid Hormones; Thyrotropin; Thyroxine; Thyroxine-Binding Proteins; Triiodothyronine; Triiodothyronine, Reverse

We studied plasma concentrations of TSH (basal and after TRH), thyroxine (T4), 3,5,3'-triiodothyronine (T3), 3,3',5'-triiodothyronine (reverse T3; rT3), free T4 and free T3 in thirty obese subjects, twenty patients with anorexia nervosa, fifteen malnourished subjects and twenty normal weight subjects. Total serum T4 values were similar for the four groups of subjects while serum free T4 values were slightly increased in anorexia nervosa and normal in the other groups. Serum total and free T3 levels were both significantly decreased in anorexia nervosa and malnutrition, and within normal limits in obesity. The mean serum rT3 level was increased in anorexia nervosa and malnutrition while was reduced in obesity. A delay in peak response of TSH to TRH stimulation (30' rather than 20') was noted in anorexia and malnourished patients. The results suggest that these alterations of serum iodothyronines are due to a different peripheral conversion of T4 to T3 according to nutritional status.

Topics: Adolescent; Adult; Anorexia Nervosa; Female; Humans; Male; Middle Aged; Nutrition Disorders; Obesity; Thyroid Hormones; Thyrotropin; Thyrotropin-Releasing Hormone; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

The thyroid function was explored by comparing serum total and free iodothyronine levels in young male genetically obese Zucker rats and in their lean littermates, aged from 6 to 8 weeks old. Total and free thyroxine (T4) and 3,5,3'triiodothyronine (T3) levels were significantly decreased in obese rat serum while total 3,3',5'-triiodothyronine (rT3) remained constant. Radioactive T4 half life is slower in the plasma of obese rats. Peripheral synthesis of T3 from deiodination of T4 is also decreased in obese rat liver homogenate. These modifications produce changes in liver mitochondria oxidative phosphorylation and in marker enzyme activity, which are usually associated with hypothyroidism and hypothalamic disturbances. Genetic obesity probably involves activation of peripheral deiodination of T4 to rT3 which induces biochemical and metabolic changes.

Topics: Animals; Kinetics; Male; Mitochondria, Liver; Obesity; Oxidative Phosphorylation; Rats; Rats, Mutant Strains; Thyroid Gland; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Topics: Animals; Body Weight; Energy Intake; Energy Metabolism; Humans; Obesity; Physical Exertion; Rats; Rest; Sodium-Potassium-Exchanging ATPase; Thyroid Hormones; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Serum levels of T4, T3, rT3, RT3U and TSH were estimated in 12 obese women in the course of a 14-day fasting. Seven of these patients were treated with T3 in a daily dose of 60--80 micrograms. Fasting led to a small increase of serum T4, while fasting combined with T3 administration was accompanied by a small decrease of serum T4. Serum T3 decreased in the course of the first 2 days of fasting to 40--50% of initial values and remained at this low level up to the 15th day of fasting. In the T3 treated group a prompt increase of serum T3 was recorded (+80%), followed by a steady decrease, reaching the control values on day 15, in spite of a continuous T3 administration. Serum rT3 in the untreated fasting group steadily increased up to the 12th day (+43%) and then dropped below the control value (-28%). In the treated group after a non-significant increase (+22%), a decrease of serum rT3 was also observed (-42%). Fasting was accompanied by a tendency to increased serum RT3U values, in the T3 treated group no change occurred. TSH in the untreated fasting women remained practically unchanged while T3 administration was accompanied by a tendency to a transient decrease. The heart rate showed a non-significant tendency to increase in the T3 treated group and the last week of fasting was also accompanied in several patients by a larger weight loss. These results suggest that in addition to an enhanced synthesis of rT3 to the detriment of a decreased production of T3 from T4, an increased catabolism of administered T3 and of endogenous rT3 is involved in a strict calorie restriction. An abortive T3-TRH-TSH feed-back may also operate in these conditions.

Topics: Adult; Body Weight; Fasting; Female; Heart Rate; Humans; Obesity; Thyrotropin; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

The serum concentrations of thyroxine (T4), 3,5,3'-triiodothyronine (T3) and 3,3'5'-triiodothyronine (reverse T3) in 10 massively obese women were studied before and at intervals for one year after jejuno-ileal bypass operation. A significant rise in T3 (P less than 0.01) over the immediately preoperative value, a significant fall in rT3 (P less than 0.01) but no significant change in T4 was found during the post-recovery follow-up period. It is concluded that maintaining a relatively high T3 level following jejuno-ileal bypass surgery may contribute to the substantial weight reduction achieved by patients after this operation.

Topics: Adult; Female; Humans; Ileum; Jejunum; Middle Aged; Obesity; Thyroid Hormones; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Previous observations that acute total fasting decreases serum T3 and increase rT3 has prompted the following study. 17 obese women were placed on a 1000 kcal/day weight-reducing diet, and body weight (BW), serum T4, RT3U, T3, rT3, TSH and the Achilles tendon reflex (ATR) were estimated before and after each month for 3 consecutive months of the diet. The results showed a consistent decrease in serum T3, and inconsistent increase in rT3, a consistent prolongation of the ATR and a levelling-off of the BW loss after the second month of the diet. At 3 months there was a negative correlation between the decrease in BW and the increase in ATR, i.e. the more abnormal the ATR became, the less weight the patient lost. It is concluded: 1) Even a moderate hypocaloric diet in ambulatory patients induces a disturbance in the peripheral conversion of T4 to T3 and a secondary state of metabolic insufficiency. 2). This insufficiency is probable related to the observed tendency of the BW loss to level off after two months. 3) A controlled trial of physiologic doses of T3, such as 40 mu g/day, seems indicated, as opposed to pharmacologic dosed of T3 used by previous investigators.

Topics: Achilles Tendon; Adolescent; Adult; Body Weight; Female; Humans; Kinetics; Middle Aged; Obesity; Reflex, Stretch; Triiodothyronine; Triiodothyronine, Reverse

TSH responses to 4-hr continuous TRH infusions of approximately 0.8 microgram/min were assessed during feeding (1500 Kcal), fasting, and refeeding (1500 Kcal) intervals in 9 euthyroid obese subjects. The total area under the TSH response curve was 1854 +/- 322 muU/ml . 4-hr during feeding, decreased to 1359 +/- 199 muU/ml . 4-hr (p less than 0.01) on the 10th day of fasting, and remained low, being 1405 +/- 185 muU/ml . 4-hr, despite refeeding a 1500 Kcal diet (40% carbohydrate, 40% fat, 20% protein) for 5 days. Baseline serum T3 concentrations were 167 +/- 11 ng/dl during feeding, 86 +/- 8 ng/dl during fasting, and 119 +/- 12 ng/dl during refeeding. The observed decreases in TSH release appeared to correlate with decreased biologic action on the thyroid gland since the net rise in T3 during the infusion was less in fasting and refeeding than in the control (fed) period. Basal serum rT3 levels were 42 +/- 5 ng/dl during feeding, rose as expected to 56 +/- 5 ng/dl during fasting (p less than 0.005), and were completely restored to normal during refeeding (36 +/- 5 ng/dl). These data suggest that: (1) TSH responsiveness to prolonged TRH infusion is diminished during fasting and does not return to control (fed) values despite 5 days of refeeding a 1500 Kcal diet; (2) net T3 increases observed during the TRH infusion are greater in the fed period than in the fasting or refeeding periods; and (3) 5 days of refeeding a 1500 Kcal diet (40% carbohydrate, 40% fat, 20% protein) did not return the T3 to its original fed value whereas rT3 was completely restored to control values. Lastly, since the TSH response was lower both during the early and late phases of the infusion, the decrease in delta TSH to a bolus of TRH during fasting appears to represent one manifestation of a more general suppression of TSH neogenesis associated with caloric deprivation.

Topics: Adult; Fasting; Female; Humans; Infusions, Parenteral; Male; Obesity; Thyrotropin; Thyrotropin-Releasing Hormone; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

In ten obese euthyroid subjects the concentration of thyroxine (T4), tri-iodothyronine (T3) and reverse T3 (rT3) were assayed in serum and of T4 and T3 in urine before and after 2 weeks of 2.1 MJ (500 Kcal) per day diet. Mean serum T4 was unchanged, while T3 decreased and rT3 increased. Urinary excretion of both T4 and T3 decreased after diet. In six subjects the concentrations of serum thyroxine binding globulin (TBG), thyroxine binding prealbumin (TBPA) and albumin were measured before and after diet. Free T4 and T3 were calculated using a formula based on measured concentration of hormones and their binding proteins. Calorie restriction resulted in a significant decrease in TBG and a greater decrease in TBPA, while albumin was unchanged. Calculation of free hormones showed a fall in absolute free T3 and rise in percentage free T3, but a rise in both absolute and per cent free T4. Our data indicate a selective effect of calorie restriction on the concentrations of TBPA and to a lesser extent TBG and confirm previous reports of altered peripheral monodeiodination of T4. Decreased urinary excretion of T4, despite a calculated increase of free T4 in serum, suggests intrarenal metabolic adjustment, the mechanism of which awaits elucidation.

Topics: Adolescent; Adult; Body Weight; Diet, Reducing; Female; Humans; Male; Middle Aged; Obesity; Serum Albumin; Thyroxine; Thyroxine-Binding Proteins; Triiodothyronine; Triiodothyronine, Reverse

TSH response to TRH stimulation was studied in 40 non-obese control females and in 40 obese female subjects 40-148 per cent in excess of their ideal weight prior to receiving dietary advice. One patient was found to be hypothyroid and was excluded from further study. There was no significant difference between the basal serum TSH concentration in the subjects and controls. Obese subjects however had significantly greater serum TSH concentrations at 20 and 60 min following TRH stimulation. The implciations of these findings are at present unexplained.

Topics: Adult; Aged; Female; Humans; Middle Aged; Obesity; Thyroglobulin; Thyroid Gland; Thyrotropin; Thyrotropin-Releasing Hormone; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Starvation is accomplished by significant changes in the hypothalamic-pituitary-thyroid axis and in peripheral thyroid hormone metabolism. Less well studied, however, are the effects on thyroid hormone economy produced by hypocaloric feeding. We explored these changes in obese patients fed 200, 400, or 600 cal/day of either carbohydrate of protein for 28 days. T4' T3' reverse T3 and the TSH response to TRH were measured at frequent intervals. Each patient demonstrated a transient rise in reverse T3 and a fall in T2 that returned to near basal levels by the end of the study period. The TSH response to TRH on the other hand, declined to approximately 50% of control values and remained at that level throughout the course of study, regardless of the type of substrate or calorie level chosen. The results indicated that hypocaloric feeding is associated with changes in thyroid hormone economy similar to those in starvation and that peripheral (changes in T3 and rT3) and central (TRH response) events are controlled by separate mechanisms.

Topics: Diet; Dietary Carbohydrates; Dietary Proteins; Energy Intake; Humans; Kinetics; Obesity; Thyroid Hormones; Thyrotropin; Thyrotropin-Releasing Hormone; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

To investigate the effect of nutrition on catecholamine metabolism, four subjects were initially energy-restricted for three weeks and then refed a high-carbohydrate diet, salt intake being kept constant. Energy restriction was associated with a reduction in plasma noradrenaline, urinary excretion of 4-hydroxy 3-methoxymandelic acid (HMMA), serum triiodothyronine (T3), systolic and diastolic pressures, pulse and resting metabolic rate (RMR). Within 72 hours of refeeding there was a significant increase in the urinary excretion of HMMA, serum T3, blood pressure, pulse and the RMR. Thus catecholamine metabolism is affected both in semistarvation and during the first few days of refeeding.

Topics: Adult; Blood Pressure; Catecholamines; Female; Food; Humans; Middle Aged; Norepinephrine; Obesity; Pulse; Starvation; Thyroid Gland; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse; Vanilmandelic Acid

The effects of total fasting for 31 +/- 10 days followed by re-alimentation with an 800 calorie diet on thyroid function, i.e. T4,T3,rT3,RT3U (resin T3 uptake), and TSH, and on TBG levels in serum were studied sequentially in obese hospitalized patients (N=18). Additionally, cortisol, growth hormone, prolactin, parathyrin and free fatty acids were followed as hormonal and metabolic parameters, respectively. Further, CBG, transferrin, alpha 2-haptoglobin and complement C'3 were measured as representatives of other serum proteins. Results before fasting: T4, T3, TBG, cortisol, CBG, alpha 2-haptoglobin and complement C'3 of the obese patients were elevated when compared with healthy normal weight controls, whereas rT3, T4/TBG ratio, T3/TBG ratio, TSH, coritsol/cbg ratio, growth hormone, prolactin, parathyrin and transferrin of the obese group were normal. RT3U and fT4 index were decreased in the obese patients. Results during fasting: Significant decreases were observed during fasting for the following parameters -- T3, TBG, T3/TBG ratio, transferrin, alpha 2-haptoglobin complement C'3. rT3, T4/TBG ratio, RT3U, fT4 index and FFA increased. T4, tsh response to TRH stimulation, cortisol, CBG, cortisol/cbg ratio, parathyrin, growth hormone and prolactin did not change. Results during re-alimentation: T3, TBG, T3/TBG ratio, TSH response to TRH, transferrin, alpha 2-haptoglobin and complement C'3 increased. Conversely, fT3, RT3U, FFA, cortisol and cortisol/cbg ratio decreased whereas the other parameters did not change.. 1) There is no evidence for primary hypothyroidism in obese patients during prolonged fasting and re-alimentation. 2) The rapid decrease of T3 and increase of RT3U after initiation of fasting are not fully explained by the observed slower decreases in TBG. 3) The alterations of T3, rT3 and RT3U resemble in their kinetics the changes in FFA levels. 4) Fasting reduced the levels of only certain serum proteins, interestingly TBG, transferrin, alpha 2-haptoglobin and complement C'3, all of which, except transferrin, are elevated in obesity. 5) The magnitude of the observed decreases does not suggest any clinically relevant deficiencies in serum proteins. 6) Re-alimentation reverses rapidly all observed changes.

Topics: Adult; Complement C3; Fasting; Fatty Acids, Nonesterified; Female; Growth Hormone; Haptoglobins; Humans; Hydrocortisone; Male; Middle Aged; Obesity; Parathyroid Hormone; Prolactin; Protein Binding; Thyrotropin; Thyrotropin-Releasing Hormone; Thyroxine; Thyroxine-Binding Proteins; Transcortin; Transferrin; Triiodothyronine; Triiodothyronine, Reverse

Topics: Adult; Female; Humans; Obesity; Thyroid Hormones; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Since recent studies have indicated that measurement in urine of the amino acid, 3-methylhistidine, accurately reflects the extent of muscle catabolism, and because it has been suggested that thyroid hormones may influence muscle breakdown, especially during fasting, the effect of T3 and reverse T3 (rT3) administration on the excretion of 3-methylhistidine was examined in obese subjects during fasting. The mean (+/- SE) 3-methylhistidine excretion in patients fed an egg protein diet (devoid of meat protein) was 256 +/- 35 mumoles/day and decreased to 190 +/- 14 mumoles/day during fasting. T3 administration (100 microgram/day x 5 days) increased 3-methylhistidine excretion to 304 +/- 37 mumoles/day during its ingestion and to 485 +/- 46 mumoles/day in the T3 posttreatment interval. T3 doses of 10 microgram every 4 hr (q4h) for the first 6 days of fasting also appeared capable of increasing 3-mehis excretion whereas 5 microgram T3 q4h administered during the first 6 days of fasting did not increase 3-mehis excretion. Reverse T3 administration (80 microgram q6h) during fasting was associated with a mean 3-methylhistidine of 130 +/- 13 mumoles/day, a value no higher than in patients fasted alone. These observations suggest that: (1) skeletal muscle catabolism decreases during fasting: and (2) pathophysiologic doses of T3 (60 microgram/day or more), but not reverse T3, enhance muscle catabolism during fasting.

Topics: Adult; Fasting; Female; Histidine; Humans; Male; Methylhistidines; Middle Aged; Muscle Proteins; Muscles; Obesity; Triiodothyronine; Triiodothyronine, Reverse

As first described in serious systemic illnesses isolated decreased T3 plasma concentration was related to impaired peripheral conversion of T4, to T3 with preferential production of reverse T3 (rT3). A "low T3 syndrome" was seen in 47 out of 109 patients with extra-thyroidal diseases. Metabolic state, TSH and TSH responses to TRH were normal despite of low T3 concentration. Euthyroidism seems mainly due to T4 itself in these patients.

Topics: Aged; Anorexia Nervosa; Diet, Reducing; Humans; Hypothyroidism; Kidney Diseases; Liver Cirrhosis; Neoplasms; Obesity; Thyroid Function Tests; Thyrotropin; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

The effect of starvation on the peripheral metabolism of rT3 was evaluated in four obese euthyroid patients. During starvation, the serum rT3 concentration increased by 69% while the MCR of rT3 decreased in all four patients from control values of 96 +/- 23 (mean +/- SD) to 68 +/- 17 liters/70 kg . day, resulting in a slight increase in the mean production rate of rT3. These findings are in contrast to the marked decrease in T3 production rate associated with fasting, indicating that inner and outer ring deiodination of T4 can be varied independently.

Topics: Female; Humans; Metabolic Clearance Rate; Obesity; Radioimmunoassay; Starvation; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Six obese subjects were studied over a period of 12 weeks whilst on a 1260 kJ (300 kcal) formula diet. Weight loss was initially rapid, but later slowed markedly despite good patient compliance. The basal metabolic rate (BMR) fell in all patients during the study. Plasma triiodothyronine fell in all patients, whilst the plasma half-life of thyroxine increased. Plasma thyroxine, reverse triiodothyronine (reverse T3) and the serum prolactin and thyrotropin response to thyroliberin all showed no significant change.

Topics: Adult; Basal Metabolism; Diet, Reducing; Female; Half-Life; Humans; Middle Aged; Obesity; Thyrotropin; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Topics: Adult; Dietary Carbohydrates; Dietary Proteins; Energy Metabolism; Humans; Obesity; Thyroid Hormones; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse