Increase In Thyroid Research Articles

N-Carbamylglutamate in ovo feeding improves carcass yield, muscle fiber development, and meat quality in broiler chickens.

Insufficient endogenous nutrients in the broiler embryo can lead to muscle gluconeogenesis, which ultimately affects the post-hatching performance of chicks. This study investigated the effects of in ovo feeding (IOF) of N-carbamylglutamate (NCG) on the growth hormones, carcass yield, and meat quality in broilers. Fertile eggs from a 30-week-old Ross 308 breeder flock were divided into three treatment groups: NC (non-injection), SC (100 μL saline-injection), and NCG (2 mg NCG injection). Each group had six replicates, with 70 eggs per replicate during incubation. Injections were administered on the 17.5th day of embryonic development. After hatching, 270 chicks were selected for 42-day rearing for further sampling. Chicks in the NCG group had significantly higher body weight (BW) and average daily gain (ADG) at the growing phase, increased growth and testosterone hormone in both feeding phases (21 and 42 days), and improved average daily gain (ADG) and food conversion ratio (FCR) in both grower and entire feeding phases (P < 0.05). Triiodothyronine (T3) and tetraiodothyronine (T4) levels, carcass yield, dressing, drum weight, breast muscle weight, drumstick weights, thighs, pectoralis major, and their part percentage of carcass were improved in the NCG group (P < 0.05), these effects were varied along feeding phases. Moreover, IOF of the NCG also improved pectoralis breast muscle color values at 24 h post mortem (P < 0.05). These results suggest that NCG injection at the late embryonic age of broiler enhances growth performance and meat quality throughout the lifespan and this can probably be attributed to an increase in thyroid and testosterone hormones, indicating potential involvement in metabolic and nutrient partitioning pathway regulation. © 2024 Society of Chemical Industry.

Combined damage to the pancreas and thyroid glands in children with obesity and metabolic syndrome

There is a functional relationship between the thyroid (thyroid) and pancreatic (pancreatic) glands and a high frequency of combined lesions of these organs. The purpose of the study: to assess the morphofunctional state of the pancreas and thyroid in obese children complicated by metabolic syndrome.Materials and methods. 483 children with various forms and degrees of obesity aged from 6 to 15 years were examined. Group I — 237 children with obesity complicated by MS, group II — 246 children with obesity without signs of MS. A complex of clinical, laboratory and instrumental examination methods was carried out according to standard and author’s methods. Results. The majority of children of both groups have various changes in the structure of the pancreas. The postprandial reaction in group I was lower than in group II, and in 17% of children in group I it was less than 5%. A tendency to increase the level of glucose, insulin and the index НОМА was established as the postprandial reaction of the pancreas decreased. Changes in the lipid spectrum of the blood were revealed depending on the postprandial reaction of the pancreas. Regardless of the group, the thyroid volume and thyroid hormone levels in most children corresponded to the normative values. Diff use increase in thyroid was detected in 11% of group I children and 4% of group II children. The data indicating the relationship of structural and functional disorders of the pancreas and thyroid gland were obtained. In children with increased thyroid volume, the size of the pancreatic head on an empty stomach was significantly higher than in children with normal thyroid sizes. With a change in the thyroid gland, more pronounced violations of the functional activity of the pancreas were recorded.Conclusions. In the absolute majority of obese children, regardless of the presence of MS, various structural changes of the pancreas are detected. The most pronounced disorders of the functional state of the pancreas are diagnosed in children with obesity complicated by MS. In 17% of children with MS, there is a significant decrease (less than 5%) of the postprandial reaction of the pancreas, indicating a decrease in adaptive capabilities and the development of a chronic inflammatory process in the pancreas. With a decrease in the postprandial reaction of the pancreas, more pronounced disorders of the carbohydrate and lipid spectrum of the blood serum are noted. Diff use increase in thyroid in children with MS was recorded 2.5 times more often. A tendency to the formation of dysthyroidism with a multidirectional change in the levels of thyroid and thyroid- stimulating hormones has been established. In children with increased thyroid volume, the size of the pancreatic head on an empty stomach was significantly higher than in children with normal thyroid sizes. At the same time, more pronounced violations of the functional activity of the pancreas were recorded in the form of a decrease in the postprandial reaction.

Glucagon-Like Peptide-1 Receptor Agonists and Thyroid Disorders

GLP-1 hormone secreted by L cells of intestine increases the glucose mediated insulin release, delay the gastric emptying and increases satiety by central mechanisms. Thus, a potential candidate for treatment of type 2 diabetes mellitus. Various GLP-1receptor analogues with longer half-life were introduced for the benefit of type 2 diabetes management. But animal studies of liraglutide showed increased incidence of thyroid cancers especially C cell hyperplasia in mice. This led to the safety concern of GLP-1RAs in terms of thyroid cancers. But further investigation showed that risk of thyroid cancers in humans is not significant as the receptor mapping in in vitro studies showed that in thyroid glands of humans and primates GLP-1 receptors were not expressed. Considering the safety, the drug was labelled as a contraindication for patients with MEN 2 syndrome or family history of Medullary thyroid cancer. Data from phase 3 trials of all the GLP-1RAs did not show any significant increase in thyroid cancer or any cancer with GLP-1 usage. Meta-analysis of the trials also showed no significant increase in thyroid or any other cancer in comparison to comparators. But two observational studies showed the increase in incidence of thyroid cancers among patients on GLP-RAs, but the studies showed limitations like study design limitation, unaccounted biases, over reporting etc. Surveillance data and review of all available data shows that there is no significant increase in risk of any thyroid disorder and treatment decision to be on risk benefit basis.

Effect of a bradykinin potentiating factor separated from honey bee venom on thyroid gland and testis in hypothyroid white rats

BackgroundAnimal venoms have been known as a source of drugs beneficial to human health. Accordingly, this study was designed to determine the effect of bradykinin potentiating factor (BPF) separated from honey bee venom, Apis mellifera on histological structure, thyroid and male sex hormones of the thyroid gland and testis in a model of hypothyroid male white rats induced by carbimazole.ResultsThis study includes male rats divided into 6 main and sub-groups (10 rats in each group). Control group, carbimazole group, levothyroxine group, BPF group, carbimazole group treated with levothyroxine and carbimazole group treated with BPF. At the end of experiments (60 days) rats were sacrificed and dissected; the blood was collected for determination of thyroid and male sex hormones. Also, the thyroid gland and testis were taken to histological study. The results indicated that, carbimazole group showed a highly significant decrease in thyroid hormones (T4, T3, Ft4 and Ft3) and male sex hormones (LH, FSH and testosterone), but a significant increase in TSH compared to control group. The results revealed that, treated groups with levothyroxine or BPF have significant increase in thyroid and male sex hormones and significant decreasein TSH. A significant improvement was detected in co-treated groups (hypothyroid groups) with levothyroxine or (BPF). Also, the present study showed a histopathological change in thyroid gland and testis of hypothyroid male rats.ConclusionTreated hypothyroid rats with levothyroxine as a drug and BPF as a natural product showed an improvement of these complications induced by carbimazole in thyroid gland and testis. Therefore, BPF may be benefical in treatment of hypothyroidism.

Effect of sleeve gastrectomy on thyroid-stimulating hormone levels in morbidly obese patients with normal thyroid function.

There are many studies, which demonstrate that morbid obesity is associated with an increase in Thyroid Stimulating Hormone (TSH) levels. However, the effect of Laparoscopic Sleeve Gastrectomy (LSG) procedure on postoperative TSH levels is not clear. This study aims to evaluate the effect of weight loss after LSG procedure on TSH levels in euthyroid patients with morbid obesity. 159 Euthyroid patients who applied for an LSG procedure (93.7% female, with a mean age of 34.18±10.01 years, BMI 43.2±6.82 kg/m2) were retrospectively analyzed for the study. The parameters used in the analysis were their serum free T3 levels (fT3), free T4 levels (fT4), and TSH levels preoperatively and at 6 months after surgery. The postoperative correlation between TSH and BMI (Body Mass Index), % EWL (Percent Excess Weight Loss), and % TWL (Total Weight Loss) levels were evaluated. Mean BMI change from 43.2±6.82 kg/m2 to 30.48±5.63 kg/m2 (p<0.001), 6 months after LSG, was associated with a mean reduction in the TSH from 2.27±1.09 µU/dL to 1.61±0.99 µU/dL; p<0.001). Serum fT3 levels (3.23±0.42 ng/dL at baseline and 3.21±0.48 ng/dL at 6 months after surgery; p=0.409) remained steady. Serum fT4 levels (1.21±0.18 µU/dL at baseline and 1.43±0.20 µU/dL at 6 months after LSG; p<0.001) increased. Change in TSH was significantly correlated with change in BMI at 6 months after surgery (r=0.200, p=0.015). However, the decrease in TSH following LSG procedure did not correlate with % EWL (r=-0.114, p=0.159) and % TWL (r=-0.100, p=0.209). After the LSG procedure, there was a significant decrease in TSH levels and a significant increase in fT4 levels, but no change was seen in fT3 levels. While this decrease in TSH levels showed a positive correlation with BMI, no statistically significant correlation was found with % EWL and % TWL.

Thyroid hormone dysfunction during pregnancy: A review

Thyroid dysfunctions such as hypothyroidism, thyrotoxicosis and thyroid nodules may develop during pregnancy leading to abortion, placental abruptions, preeclampsia, preterm delivery and reduced intellectual function in the offspring. Epidemiological data have shown the significant role of maternal thyroid hormone in fetal neurologic development and maternal health. It has been suggested that the deleterious effects of thyroid dysfunction can also extend beyond pregnancy and delivery to affect neuro-intellectual development in the early life of the child. Pregnancy poses an important challenge to the maternal thyroid gland as hormone requirements are increased during gestation as a result of an increase in thyroid- binding globulin, the stimulatory effect of HCG on TSH receptors, and increased peripheral thyroid hormone requirements. Maternal thyroid dysfunction is associated with increased risk for early abortion, preterm delivery, neonatal morbidity and other obstetrical complications. Early diagnosis for thyroid dysfunction of pregnant women and treatment of thyroid dysfunction during pregnancy is important and cost effective to avoid both fetal and maternal complications secondary to thyroid dysfunction. Therefore the aim of this review was to assess the thyroid function changes occurring during pregnancy, the different disorders with their maternal and fetal implications, the laboratory diagnosis and the best ways of management of these conditions.

Rats with altered behaviour following nerve injury show evidence of centrally altered thyroid regulation.

The co-morbidity of mood disturbance, in a proportion of patients, is now described across a wide range of chronic disease states. Similarly, a 'Low Thyroid Syndrome' is also reported in a proportion of individuals with chronic diseases. Here, we report on central changes in an animal model of inflammatory stress in which altered social behaviour, representing social disability, persists in a sub-group of rats following injury. We showed in an earlier study that rats with social disability following injury have significantly decreased peripheral thyroid hormones, with no increase in Thyroid Stimulating Hormone (TSH). Only rats identified by behavioural change showed changes in hypothalamic gene expression. In whole hypothalamus extracted RNA, relative expression of mRNA for Thyrotrophin-releasing hormone (TRH) was significantly down-regulated in disabled rats (p=0.039) and deiodinase 3 up-regulated (p=0.006) compared to controls. Specifically in the paraventricular nucleus (PVN), numbers of immunoreactive cells for deiodinase 3-like and thyroid hormone receptor beta-like proteins were decreased in the sub-group with disability compared to the control group (p=0.031 and p=0.011 respectively). In rats with behavioural change post-injury, down-regulation of TRH provides an explanation for the failure of the hypothalamo-pituitary-thyroid (HPT) axis to respond to the post-injury decrease in thyroxine. Decreased local expression of deiodinase 3 protein, resulting in a local increase in T3, offers an explanation for down regulation of TRH in the hypophysiotrophic TRH neurons. It is possible that, in a sub-group of animals identified behaviourally, a mechanism resulting in hypothalamic down-regulation of the HPT axis persists following inflammatory injury.

HYPERPLASTIC THYROID G1AND

Aim and Objective: The study was conducted to see the vascular and follicular changes induced by dexamethasone (syntheticcorticosteroid) during involution of hyperplastic thyroid gland in albino rats. Study Design: A comparative histological study done in PostGraduate Medical Institute Lahore in 1998 Procedure: 54 adult rats were taken and divided at random into two control groups having 27 ratsand experimental groups containing 27 rats. Control group was given normal diet along with 2 microgram of Potassium iodide intraperitonealyfor 21 days while experimental groups further subdivided into group A having 3 rats and group B and C containing 12 rats each. All theexperimental groups were treated with Thiourea for 21 days. Group A was sacrificed on day 22 after withdrawal of thiourea. Group B was givenPotassium iodide intraperitonealy after stoppage of TU on day 21 and were sacrificed on days 22,26,30 and 50 in 4 sub groups (B1-B4) tostudy the involution process. Group C was injected dexamethasone from 22 to 50 days after withdrawal of TU and sacrificed on same daysin 4 subgroups (C1-C4) as sub groups B. Results: The results of experimental group. A showed increase in thyroid and relative tissue weight.Histologically this group exhibited significant increase in stromal congestion with tall follicular cells lining the small sized follicles having scantycolloid. The results of experimental groups B and C demonstrated increase in thyroid and relative tissue weight but microscopically subgroupsB revealed early and complete involution whereas subgroups C showed significantly persistent hyperplastic changes in the form of stromalcongestion, vessels wall remained well defined and tall follicular cells lining small empty follicles. Conclusion: It was concluded thatdexamehasone did retain hyperplastic changes during involution evident by stromal congestion and small sized regular follicle lined by tallfollicular cells, so it should be carefully used in thyroid diseases.

Improvement of Goiter Volume Reduction after 0.3 mg Recombinant Human Thyrotropin-Stimulated Radioiodine Therapy in Patients with a Very Large Goiter: A Double-Blinded, Randomized Trial

The effect of (131)I therapy amplification by recombinant human (rh) TSH prestimulation in very large goiters has not been evaluated in a double-blinded, placebo-controlled study. Twenty-nine patients (22 females; age range 37-87 yr) with a large multinodular goiter (median 160 ml, range 99-440 ml) were randomized to receive placebo (n = 15) or 0.3 mg rhTSH (n = 14) 24 h before (131)I administration. Goiter volume was monitored by magnetic resonance imaging. On average, the goiter volume was unchanged 1 wk after therapy in both groups, but the largest deviations from baseline were observed in the rhTSH group. After 12 months the median goiter volume was reduced from 170 to 121 ml in the placebo group and from 151 to 72 ml in the rhTSH group, respectively (within group: P = 0.001; between group: P = 0.019). This corresponds to reductions of 34.1 +/- 3.2 and 53.3 +/- 3.3%, respectively (between group: P < 0.001). In the placebo group, the goiter reduction correlated positively with the retained thyroid (131)I dose, whereas such a relationship was absent in the rhTSH group. Adverse effects, mainly related to thyroid pain and cervical compression, were more frequent in the rhTSH group. At 12 months, goiter-related complaints were significantly reduced in both groups without any between-group difference. One and three patients in the placebo and the rhTSH group, respectively, developed hypothyroidism. rhTSH-stimulated (131)I therapy improves the reduction of very large goiters by more than 50%, compared with (131)I therapy alone, but at the expense of more adverse effects after therapy. Our data suggest that rhTSH stimulation may work through mechanisms that go beyond the increase in thyroid (131)I uptake.

Mechanism of Thiazopyr-Induced Effects on Thyroid Hormone Homeostasis in Male Sprague–Dawley Rats

Chronic administration of thiazopyr in the diet at dose levels of 1000 and 3000 ppm, but not 100 ppm, has demonstrated an increase in thyroid follicular cell tumors in male Sprague–Dawley rats. In the studies reported here we have evaluated the mechanism of thiazopyr-induced thyroid tumors by studying the effect of thiazopyr on a number of endpoints that indicate hypothalamic–pituitary–thyroid homeostasis. At a dose level of 3000 ppm, thiazopyr caused a marked depression in circulating levels of T4as soon as 7 days after commencement of treatment. Concurrent with this decrease in T4was an increase in TSH levels, an increase in thyroid and liver weights, a three- to sixfold increase in hepatic T4-uridine diphosphate glucuronosyl transferase (UDPGT) activity, and increases in thyroid follicular cell hypertrophy and hyperplasia. Dose-related changes associated with thiazopyr treatment were significant increases in liver weight, thyroid weight, and hepatic T4-UDPGT activity at high doses. Increased levels of serum TSH, T3, and rT3, decreased levels of T4, and an increased incidence of thyroid follicular cell hypertrophy and hyperplasia were observed 56 days after the initiation of 3000 ppm thiazopyr. All the changes, except thyroid weight, were partially or completely reversible upon removal of thiazopyr from the diet. Increased thyroid T4elimination, primarily via increased hepatic conjugation by T4-UDPGT, resulting in decreased serum T4, appeared to be responsible for the increased TSH levels. The sustained increase in TSH by thiazopyr appears responsible for the stimulation of the thyroid follicular cells resulting in follicular cell hypertrophy, hyperplasia, and ultimately neoplasia. In summary, evidence is presented for a hormonally mediated, threshold-dependent process for the development of thyroid follicular cell tumors from high-dose thiazopyr administration in male rats. This mechanism is not considered to be relevant to humans, since the thyroid of humans is much less sensitive to this pathogenic phenomenon than rodents.

Apparent digestibility of high-fat rapeseed press cake in growing pigs and effects on feed intake, growth and weight of thyroid and liver

Rapeseed from a winter variety of Brassica napus was pressed through a screw press. The press cake (321 g crude protein, 180 g crude fat, 102 g crude fibre, glucosinolates at 18 mmol kg −1 DM (dry matter)) was tested either untreated or soaked (11 water kg −1 rapeseed press cake) and dried at 60°C. Press cake contained 28% more glucosinolates than the corresponding seed. Moist heat treatment caused a reduction of glucosinolate content to 0.3 mmol kg −1 press cake DM. Glucosinolate degradation products were not detectable (less than 0.1 mmol kg −1 DM). In a digestibility experiment consisting of two periods in a 2 × 4 crossover design four pigs received barley or diets with rapeseed press cake 500 g kg −1 as a replacement for barley. The digestibility of all measured parameters except fat was lower in the rapeseed press cake than in barley (%): crude protein 68.5 vs. 77.8, crude fat 78.4 vs. 46.4, crude fibre 14.7 vs. 42.2, N-free extract 83.8 vs. 92.4, organic matter 70.0 vs. 84.7. The differences were all significant ( P < 0.05). A metabolizable energy (ME) of rapeseed press cake of 14.1 MJ kg −1 DM was calculated, and this value was similar to that calculated for barley (14.6 MJ ME kg −1 DM). In a further 16 week experiment with four groups of ten pigs, diets with 0, 50 g, 100 g or 150 g rapeseed press cake per kilogram were tested. In a final experiment the highest rapeseed press cake level (150 g kg −1 diet) was also treated with moisture and heat. There was no significant effect of dietary level or treatment of rapeseed press cake on performance criteria. There was a trend ( P < 0.1) for daily weight gain to decrease with increasing press cake level. The dietary rapeseed press cake level caused a significant increase in thyroid and liver weights. In the group with untreated press cake at 150 g kg −1 diet the thyroid weight was trebled and the liver weight increased by 20%. Treatment significantly lowered the weight of organs. The weight of the thyroid, as well as of the liver, was significantly higher in this group with moist-heat treated rapeseed press cake at 150 g kg −1 than in animals of the glucosinolate-free control group.

Effect of Graded Levels of Parathyroid Extract and Calciferol Upon Thyroid Hormone Secretion Rate (TSR) in Normal Female Rats

SummaryThe effect of graded doses of parathyroid extract and calciferol upon thyroxine secretion rate (TSR) of normal female rats was studied with the aid of radioactive iodine 131I. Administration of 20, 30, and 40 USP units of PTE/100 g of body wt/day for 14 days induced a significant (p<.025) increase in TSR of 25.4, 35.6, and 54.1%, respectively, over their own controls associated with slight increase in body weight. Administration of calciferol (Vit. D2) in doses of 0.1, 0.15, and 0.2 mg/100 g of body wt induced a nonsignificant reduction in TSR of the first two groups (groups IV and V) but a significant 26.7% (p<.05) increase in TSR above their own control in group VI associated with loss of body weight of 14.2% when 0.2 mg calciferol/100 g of body wt was given daily for the same period. A nonsignificant increase in weight of ovaries, uteri, and a decrease of thymus glands with significant increase in thyroid and adrenal weights was noticed in the group treated with 0.2 mg of calciferol/100 g of bod...

EFFECT OF HYPERTONIC SODIUM NITRATE SOLUTIONS ON BLOOD PRESSURE OF RATS.

SummaryAdministration of NaNO3 solution to rats as their sole drinking fluid is accompanied by a significant elevation of systolic blood pressure. The threshold concentration for elevation of blood pressure lies between 0.15 and 0.175 m. Both concentration of NaNO3 solution and duration of treatment appear to be important factors in elevating blood pressure. Administration of NaNO3 is also accompanied by an increase in thyroid to body weight ratio.

Changes in Thyroid I131 Release Rate during Growth in Holstein, Brown Swiss, and Jersey Calves at Constant Environmental Temperatures of 50 and 80° F1,2

Summary Studies on the effect of age and temperature on thyroid I 131 release rate on growing calves were conducted under the controlled environmental conditions of the Missouri Climatic Laboratory. At both temperatures and for all calves, thyroid I 131 activity increased with age, whereas thyroid I 131 activity per unit weight decreased with age. Although all calves showed the same trends, breed differences in the latter relationship were highly significant, Jerseys having the highest ratios, followed by Brown Swiss and Holsteins. The thyroid I 131 release rate of Jersey calves was approximately twice as great as the rate for Holstein and Brown Swiss, throughout this growth study; however, only the breed-age interaction was significant. Thyroid activity per unit weight was higher at 80° F. than at 50° F., with highly significant breed differences occurring, and varied significantly as a function of the interaction between temperature and age. Thyroid I 131 activity per unit surface area showed no effect of temperature alone, but did increase slightly with increments in both age and temperature. Breed differences were significant in the ratio of thyroid I 131 activity to surface area. The exponents ( b values) of the parabolic equation expressing the relationship of thyroid I 131 activity to body weight proved to be significantly higher at 80 than at 50° F. There were significant breed differences in percentage increase in thyroid I 131 activity per 1% increase in body weight, the Jerseys' rate being higher than those of the Brown Swiss or Holsteins.

FURTHER STUDIES ON THYROID - ADRENAL - ASCORBIC ACID RELATIONS IN ANIMALS EXPOSED TO COLD

The effect of ascorbate administration on resistance to cold and thyroid function was studied in adrenalectomized rats receiving various amounts of cortisone and/or DCA; in thyroidectomized rats given different doses of of thyroxine, the effect of ascorbate administration was evaluated on both resistance to cold and adrenal function.In adrenalectomized rats given large doses of cortisone (2.5 mgm.) and exposed to cold, the administration of either ascorbate (150 mgm.) or DCA (2.5 mgm.) enhances the survival, reduces the extent of thymolysis, and decreases the activation of the thyroid. In adrenalectomized rats receiving no cortisone or DCA or low doses (0.4 and 0.1 mgm.) of these hormones, ascorbate administration (150 mgm.) still retains some of its beneficial effects on resistance to cold (better growth and survival); when low doses of DCA (0.1 mgm.) are given without cortisone, ascorbate administration seems to have a deleterious effect on the growth and survival during exposure to cold, with a greater increase in thyroid activity.In thyroidectomized rats exposed to cold, ascorbate administration (150 mgm.) has no effect in the absence of thyroxine, but increases the efficiency of low doses (3 μgm.) of thyroxine, preventing at the same time some of the typical signs of an alarm reaction: thymolysis and adrenal enlargement.These results are interpreted as showing that the role of the cortical hormones in resistance to cold might be limited to a "conditioning" action and that the beneficial effects of ascorbate administration would be mediated through the thyroid hormones.

FURTHER STUDIES ON THYROID - ADRENAL - ASCORBIC ACID RELATIONS IN ANIMALS EXPOSED TO COLD

The effect of ascorbate administration on resistance to cold and thyroid function was studied in adrenalectomized rats receiving various amounts of cortisone and/or DCA; in thyroidectomized rats given different doses of of thyroxine, the effect of ascorbate administration was evaluated on both resistance to cold and adrenal function.In adrenalectomized rats given large doses of cortisone (2.5 mgm.) and exposed to cold, the administration of either ascorbate (150 mgm.) or DCA (2.5 mgm.) enhances the survival, reduces the extent of thymolysis, and decreases the activation of the thyroid. In adrenalectomized rats receiving no cortisone or DCA or low doses (0.4 and 0.1 mgm.) of these hormones, ascorbate administration (150 mgm.) still retains some of its beneficial effects on resistance to cold (better growth and survival); when low doses of DCA (0.1 mgm.) are given without cortisone, ascorbate administration seems to have a deleterious effect on the growth and survival during exposure to cold, with a greater increase in thyroid activity.In thyroidectomized rats exposed to cold, ascorbate administration (150 mgm.) has no effect in the absence of thyroxine, but increases the efficiency of low doses (3 μgm.) of thyroxine, preventing at the same time some of the typical signs of an alarm reaction: thymolysis and adrenal enlargement.These results are interpreted as showing that the role of the cortical hormones in resistance to cold might be limited to a "conditioning" action and that the beneficial effects of ascorbate administration would be mediated through the thyroid hormones.