Total Thyroxine Concentrations Research Articles

Total thyroxine, triiodothyronine, and thyrotropin concentrations during acute nonthyroidal illness and recovery in dogs.

Acute illness can result in changes in serum total thyroxine (tT4), total triiodothyronine (tT3), and thyrotropin (TSH) concentrations in euthyroid dogs defined as nonthyroidal illness syndrome, but longitudinal evaluation of these hormones during the recovery phase is lacking. To longitudinally evaluate serum tT4, tT3, and TSH concentrations during the acute phase and recovery from acute illness in dogs. Nineteen euthyroid client-owned dogs hospitalized for acute illness at a veterinary teaching hospital. Prospective longitudinal study. Serum tT4, tT3, and TSH concentrations were measured at the admission (T0), at last day of hospitalization (T1), and during the recovery phase at 3, 7, 14, and 21 days after the discharge (T2, T3, T4, and T5), respectively. tT4 and tT3 were below the reference interval (RI) at T0 in 3 (16%) and 18 (95%) dogs, respectively; tT4 normalized in all dogs early in the recovery phase, while low tT3 persisted at the end of the study in 16 (83%) dogs. Median TSH concentrations were increased at T5 compared with T1 (0.19 ng/mL [range 0.03-0.65] vs 0.11 ng/mL [range (0.05-0.26)], mean difference = 0.09 ng/mL; P = .03). Five (26%) dogs had TSH above the RI at least at 1 time point during the recovery phase. None of the dogs had concurrent low tT4 and high TSH during the study. In euthyroid dogs acute illness can interfere with evaluation of thyroid function up to 21 days during the recovery phase. Thyroid testing should be avoided or postponed in these dogs.

Calculation of reference intervals for indicators of thyroid hormones and cortisol in horses

The article discusses the results of calculating reference intervals for thyroid hor mones and cortisol in adult horses. The study included the results of a laboratory study of the concentrations of total triiodothyronine, total and free thyroxine and cortisol from 50 horses aged 3 to 29 years, including 17 mares, 13 stallions and 20 geldings. All animals underwent an extensive biochemical blood test, the results of which revealed no pathological changes.To calculate the normative limits of fluctuations for each hormone, calculations were carried out using the Tukey method, which is used to determine the reference limits in the case of a small number of variants in the group and the absence of a normal distribution. Microsoft Excel was used for calculations. The conducted studies made it possible to clarify the reference intervals for thyroid hormones and cortisol in horses, which were: total triiodothyronine (T3) - 1.13-4.04 nmol/l, total thyroxine (T4) - 20.97-57.42 nmol/l, free thyroxine (fT4) 7.38-23.07 pmol/l, cortisol – 39.42-227.02 nmol/l. The results obtained can be recommended for use not only for the clinical and biochemical laboratory of St. Petersburg State University of Medicine, but also for all veterinary laboratories using diagnostic test systems for enzyme immunoassay of Vital Development Corporation.

Long-term dietary exposure to the non-steroidal anti-inflammatory drugs diclofenac and ibuprofen can affect the physiology of common carp (Cyprinus carpio) on multiple levels, even at “environmentally relevant” concentrations

The aim of the study was to evaluate the effects of emerging environmental contaminants, the non-steroidal anti-inflammatory drugs (NSAIDs) diclofenac (DCF) and ibuprofen (IBP), on physiological functions in juvenile common carp (Cyprinus carpio). Fish were exposed for 6 weeks, and for the first time, NSAIDs were administered through diet. Either substance was tested at two concentrations, 20 or 2000 μg/kg, resulting in four different treatments (DCF 20, DCF 2000, IBP 20, IBP 2000). The effects on haematological and biochemical profiles, the biomarkers of oxidative stress, and endocrine disruption were studied, and changes in RNA transcription were also monitored to obtain a comprehensive picture of toxicity. Fish exposure to high concentrations of NSAIDs (DCF 2000, IBP 2000) elicited numerous statistically significant changes (p < 0.05) in the endpoints investigated, with DCF being almost always more efficient than IBP. Compared to control fish, a decrease in total leukocyte count attributed to relative lymphopenia was observed. Plasma concentrations of total proteins, ammonia, and thyroxine, and enzyme activities of alanine aminotransferase (ALT), aspartate aminotransferase, and alkaline phosphatase (ALP) were significantly elevated in either group, as were the activities of certain hepatic antioxidant enzymes (superoxide dismutase, glutathione-S-transferase) in the DCF 2000 group. The transcriptomic profile of selected genes in the tissues of exposed fish was affected as well. Significant changes in plasma total proteins, ammonia, ALT, and ALP, as well as in the transcription of genes related to thyroid function and the antioxidant defense of the organism, were found even in fish exposed to the lower DCF concentration (DCF 20). As it was chosen to match DCF concentrations commonly detected in aquatic invertebrates (i.e., the potential feed source of fish), it can be considered “environmentally relevant”. Future research is necessary to shed more light on the dietary NSAID toxicity to fish.

The association between dyslipidaemia in the first trimester and adverse pregnancy outcomes in pregnant women with subclinical hypothyroidism: a cohort study

BackgroundSubclinical hypothyroidism (SCH) is linked to dyslipidaemia and adverse pregnancy outcomes. However, the impact of dyslipidaemia on the outcome of pregnancy in SCH is unclear.MethodsWe enrolled 36,256 pregnant women and evaluated their pregnancy outcomes. The following data was gathered during the first trimester (≤ 13+ 6 weeks of gestation): total cholesterol (TC), low-density lipoprotein (LDL-C), triglyceride (TG), high-density lipoprotein (HDL-C), free thyroxine (FT4) and thyroid-stimulating hormone (TSH) concentrations. The reference ranges for lipids were estimated to range from the 5th to the 95th percentile. Logistic regression assessed the relationships between dyslipidaemia and adverse pregnancy outcomes, including abortion, preeclampsia/eclampsia, low birth weight, foetal growth restriction, premature rupture of foetal membranes, gestational hypertension, preterm birth, macrosomia and gestational diabetes mellitus (GDM). Additionally, the best thresholds for predicting adverse pregnancy outcomes based on TSH, FT4, and lipid levels were determined using receiver operating characteristic curves.ResultsIn the first trimester, LDL-C > 3.24 mmol/L, TG > 1.92 mmol/L, HDL-C < 1.06 mmol/L, and TC > 5.39 mmol/L were used to define dyslipidaemia. In this cohort, 952 (3.56%) patients were diagnosed with SCH, and those who had dyslipidaemia in the first trimester had higher incidences of gestational hypertension (6.59% vs. 3.25%), preeclampsia/eclampsia (7.14% vs. 3.12%), GDM (22.53% vs. 13.77%), and low birth weight (4.95% vs. 2.08%) than did those without dyslipidaemia. However, after adjusting for prepregnancy body mass index (pre-BMI), dyslipidaemia was no longer related to these risks. Furthermore, elevated TG dyslipidaemia in SCH patients was connected to an enhanced potential of gestational hypertension (odds ratio [OR]: 2.687, 95% confidence interval [CI]: 1.074 ~ 6.722), and elevated LDL-C dyslipidaemia correlated with increased preeclampsia/eclampsia risk (OR: 3.172, 95% CI: 1.204 ~ 8.355) after accounting for age, smoking status, alcohol use, pre-BMI, and levothyroxine use. Additionally, the combination of TC, TG, LDL-C, pre-BMI, and TSH exhibited enhanced predictive capabilities for gestational hypertension, preeclampsia/eclampsia, and GDM. Values of 0.767, 0.704, and 0.706 were obtained from the area under the curve.ConclusionsAmong pregnant women with SCH, dyslipidaemia in early pregnancy was related to elevated risks of adverse pregnancy consequences. The combined consideration of age, pre-BMI, TSH, and lipid levels in the first trimester could be beneficial for monitoring patients and implementing interventions to reduce adverse pregnancy outcomes.

Indicators of lipid metabolism and their relationship with the thyroid status during the dry and post-calving periods in cows with different fertility

In black-and-white cows with reduced fertility, during the dry and early post-calving periods, changes in the functioning of the thyroid system are observed, which differ from those in individuals with high fertility. Such changes may lead to a lack of energy sources during the critical transition period.Purpose: To study the dynamics of changes in the lipid content before and after calving and its association with the content of thyroid hormones in the blood of black-and-white cows with various fertility.Materials and methods. Black-and-white cows of lactation 2-4 were used in the study. The animals were bled 6, 4 and 2 weeks before calving and 1, 3, 7 and 13 weeks after calving. In blood serum samples, the content of lipids was determined using a biochemical analyzer, as well as thyroid hormones and progesterone using ELISA. Cows were inseminated after treatment according to the Ovsynch protocol, and pregnancy was assessed on Day 33 based on ultrasound examination and progesterone levels in the blood.Results. The cows were divided into two groups: I – pregnant individuals (n=17) and II – individuals that remained infertile (n=12). The milk productivity of animals and their BCS before and after calving were similar in the compared groups. Thirteen weeks after calving, the cholesterol content in the blood of cows of group II was 1.2 times lower (p&lt;0.05) compared to this content in animals of group I. At the same time, 6 weeks before calving, the concentration of phospholipids in the blood of individuals of group II was 1.3 times higher than that of individuals of group I (p&lt;0.05). In addition, 3 weeks after calving, the level of triglycerides in cows of group I was 1.2 times higher (p&lt;0.05) than that in animals of group II. During the postpartum period, the blood levels of cholesterol and triglycerides in animals of group I positively correlated with the content of total thyroxine, whereas such a correlation was not detected in group II.Conclusions. Thus, the metabolic state of cows with higher fertility was characterized by an increased supply of lipid energy sources during the post-calving period compared to animals with low fertility. At the same time, the reduced content of triglycerides at the early stage of lactation in the blood of cows that remained infertile points to their increased accumulation by the liver. A positive relationship between the concentration of total thyroxine in the blood and the concentration of triglycerides and cholesterol, revealed during the post-calving period in cows with high fertility, suggests the participation of the thyroid hormone in maintaining the reproductive function of these animals by modulating lipid metabolism.

Development and internal validation of diagnostic prediction models using machine-learning algorithms in dogs with hypothyroidism.

Hypothyroidism can be easily misdiagnosed in dogs, and prediction models can support clinical decision-making, avoiding unnecessary testing and treatment. The aim of this study is to develop and internally validate diagnostic prediction models for hypothyroidism in dogs by applying machine-learning algorithms. A single-institutional cross-sectional study was designed searching the electronic database of a Veterinary Teaching Hospital for dogs tested for hypothyroidism. Hypothyroidism was diagnosed based on suggestive clinical signs and thyroid function tests. Dogs were excluded if medical records were incomplete or a definitive diagnosis was lacking. Predictors identified after data processing were dermatological signs, alopecia, lethargy, hematocrit, serum concentrations of cholesterol, creatinine, total thyroxine (tT4), and thyrotropin (cTSH). Four models were created by combining clinical signs and clinicopathological variables expressed as quantitative (models 1 and 2) and qualitative variables (models 3 and 4). Models 2 and 4 included tT4 and cTSH, models 1 and 3 did not. Six different algorithms were applied to each model. Internal validation was performed using a 10-fold cross-validation. Apparent performance was evaluated by calculating the area under the receiver operating characteristic curve (AUROC). Eighty-two hypothyroid and 233 euthyroid client-owned dogs were included. The best performing algorithms were naive Bayes in model 1 (AUROC = 0.85; 95% confidence interval [CI] = 0.83-0.86) and in model 2 (AUROC = 0.98; 95% CI = 0.97-0.99), logistic regression in model 3 (AUROC = 0.88; 95% CI = 0.86-0.89), and random forest in model 4 (AUROC = 0.99; 95% CI = 0.98-0.99). Positive predictive value was 0.76, 0.84, 0.93, and 0.97 in model 1, 2, 3, and 4, respectively. Negative predictive value was 0.89, 0.89, 0.99, and 0.99 in model 1, 2, 3, and 4, respectively. Machine learning-based prediction models were accurate in predicting and quantifying the likelihood of hypothyroidism in dogs based on internal validation performed in a single-institution, but external validation is required to support the clinical applicability of these models.

Relationship between thyroid function and sex hormones in female German shepherd dogs.

Several variables influence the serum concentration of thyroid hormones in dogs, including breed, age, drugs, and concurrent diseases. However, data regarding the interaction between thyroid function and the estrous stage of female dogs are limited. Estrous stage may influence thyroid function in German Shepherd dogs. Longitudinal, observational, non-randomized cohort study. The dogs were monitored during the complete estrous cycle, and different stages were determined by vaginal cytology. Two blood samples were collected at the beginning and end of each stage to analyze the following: total thyroxine (TT4), free thyroxine (fT4), total triiodothyronine (TT3), free triiodothyronine (fT3), canine thyrotropin (cTSH), progesterone, 17-β-estradiol, triglycerides, and cholesterol concentrations. Hematological and biochemical evaluations were performed at the beginning and end of the study period. Seventeen German Shepherds were included, of which 7 were bred during the study period. One dog was excluded for estrus interruption and another for suspected hypothyroidism. Serum concentrations of T4, fT4, and fT3 were negatively correlated with age. Total thyroxine demonstrated significant changes in serum concentrations between estrous stages, with higher concentrations in estrus and diestrus. Total thyroxine concentrations were positively correlated with progesterone concentrations and negatively correlated with 17-β-estradiol concentrations. Free thyroxine did not show significant variations but was positively correlated with progesterone concentrations. Canine TSH concentrations were positively correlated with 17-β-estradiol concentrations. No significant differences in thyroid hormones and cTSH concentrations were observed between diestrus during pregnancy and pseudopregnancy. Different stages of estrus can influence the measurement of TT4 in female dogs.

Clinical and biochemical alterations associated with excess calcitonin in a dog with medullary thyroid carcinoma

AbstractWe present a 10‐year‐old mongrel dog with progressive weight loss, polyuria and polydipsia. Physical examination revealed poor body condition, systemic hypertension (on average 165 mmHg) and a cervical mass that was confirmed by ultrasound in the right thyroid lobe (diameter 4.0 cm). Blood biochemistry on two different days revealed a low ionised calcium concentration (1.1 and 0.81 mmol/L; reference range: 1.1–1.3 mmol/L) associated with an elevated plasma calcitonin concentration in the same sample (44.8 and 49 pg/mL; reference range: &lt;2 pg/mL). A low urine specific gravity (1.012) was also found. Total thyroxine concentration was low, corresponding to euthyroid sick syndrome. Hypercalcitoninemia, hypocalcaemia and clinical signs resolved after an uncomplicated right thyroidectomy. Positive staining of the neoplasm for calcitonin on immunohistochemistry confirmed a medullary thyroid carcinoma. This is the first report describing the clinical signs and biochemical alterations associated with excess calcitonin in a dog with medullary thyroid carcinoma confirmed by immunohistochemistry.

Effects of genetic selection for fast growth on the development of wooden breast myopathy in broilers

ABSTRACT 1. This study investigated the physiological and molecular mechanisms leading to wooden breast (WB) by comparing growth parameters, oxygen consumption rate, thyroid hormone and gene expression patterns in fast- versus slow-growing broiler lines (Cobb500 and L1986, respectively). 2. WB was observed in Cobb500 broilers only and was first diagnosed on d 21 post-hatch. Compared to the slow-growing L1986, Cobb500 showed a significantly higher growth rate, relative breast weight, breast thickness, meat pH and water-retention capacity (drip loss). Correspondingly, there was significantly lower relative heart weight, relative right ventricular weight, triiodothyronine and thyroxine concentrations and oxygen consumption rate. 3. Compared to No-WB Cobb500, the WB-affected samples exhibited higher relative breast weight, breast thickness and drip loss and lower plasma total thyroxine (T4) concentrations. 4. Selection for fast growth was associated with differential expression of genes involved in hypoxia (PLOD2), energy metabolism (FABP3, FABP4, CD36, and LPL), endoplasmic reticulum stress, muscle regeneration (CSRP3) and fibre-type switching (ANKRD1). WB-affected samples exhibited an upregulation of CSRP3, PLOD2 and ANKRD1, while CD36 was downregulated. Taken together, selection for fast growth and muscle gain is not matched by adequate cardiac and metabolic support systems.

Dietary hyperthyroidism in a dog with epileptic seizures

This report discusses a case of suspected dietary hyperthyroidism in a 2-year-old male crossbreed dog. The dog presented with a history of tonic-clonic seizures, seen over the previous 6 months, and was refractory to increasing doses of phenobarbitone. Serum total thyroxine concentrations were persistently elevated on repeated sampling; the rest of the investigations were normal. The initial diet – a raw food diet – was tested and found to contain detectable levels of total thyroxine. Dietary hyperthyroidism was therefore proposed as a potential cause of seizures in this case.

Comparative assessment of the functional state of the thyroid gland and the adrenal cortex in cats of different ages

The study of the secretory activity of the endocrine glands is one of the main methods for assessing their functional state and the health of animals in general. In the experiment, we studied the activity of thyroid and corticosteroid hormones in 20 healthy cats aged 1 to 14 years of different breeds and sexes. In the blood serum of the experimental animals, the concentration of total and free thyroxine, total and free triiodothyronine, adrenocorticotropic hormone and cortisol was determined by the enzyme immunoassay. The results of the study showed that the concentration of thyroid and corticosteroid hormones in the blood serum of cats differs markedly depending on age. the functional activity of the adrenal cortex is maximal in cats aged 5 months to 1 year (first group). Thus, in comparison with this group, the level of ACTH in the blood serum of cats of the second group (1-3 years old) significantly decreased by 15.8% (p≤0.05), the third (3-6 years old) and the fourth (animals over 6 years old). ) by 37.7 and 22.1%, respectively (p≤0.01). Also revealed a significant decrease in the concentration of cortisol in animals in the third and fourth groups by 22.1 and 26.8%, respectively, compared with the first group (p≤0.01). The least functional activity of the thyroid gland and adrenal cortex is observed in cats aged 6 years and older. The greatest functional activity of the adrenal cortex is observed in cats aged from 5 months to 1 year. The data obtained make it possible to more effectively detect disorders in the functioning of the thyroid and adrenal glands in animals, taking into account age-related changes.

Mediation by Thyroid Hormone in the Relationships Between Gestational Exposure to Methylmercury and Birth Size

Our previous studies have linked gestational methylmercury exposure, originating from seafood, to changes in maternal thyroid hormones and infant birth size in a Swedish birth cohort. Herein we aimed to determine associations between maternal thyroid hormones and infant birth size and elucidate if maternal hormones could mediate the relationship between methylmercury and lower birth size. In 515 women, without known thyroid disease, we assessed metal exposure by erythrocyte mercury concentrations (mainly methylmercury, reflecting exposure over the past months) in early third trimester measured with inductively coupled plasma-mass spectrometry. Plasma concentrations of total and free thyroxine (tT4 and fT4) and triiodothyronine (tT3 and fT3), and thyroid-stimulating hormone (TSH) were measured at an accredited clinical laboratory. In multivariable-adjusted linear regression models, maternal tT3 (per 1 nmol/L increase) was positively associated with birth weight (B: 125 g; 95% CI 36, 214) and length (B: 0.59 cm; 95% CI 0.21, 0.97). Maternal fT4 was inversely associated with birth weight (B: − 33 g; 95% CI − 57, − 9.5), driven by obese women (n = 76). Causal mediation analyses suggested that a doubling of erythrocyte mercury (> 1 µg/kg; n = 374) was associated with a mean tT3-mediated decrease in birth weight of 11 g (95% CI − 25, − 1.6) and in birth length of 0.1 cm (95% CI − 0.12, − 0.01), both equivalent to about 12% of the total effect. To conclude, tT3 was positively associated with infant birth size. Reduced tT3 levels appeared to mediate a minor part of the inverse association between methylmercury exposure and birth size.

Fecal microbiota and inflammatory and antioxidant status of obese and lean dogs, and the effect of caloric restriction.

Obesity is the most common nutritional disease in dogs, and is generally managed by caloric restriction. Gut microbiota alteration could represent a predisposing factor for obesity development, which has been associated with a low-grade inflammatory condition and an impaired antioxidant status. Besides, weight loss has been shown to influence the gut microbiota composition and reduce the inflammatory response and oxidative stress. However, these insights in canine obesity have not been fully elucidated. The aim of this study was to assess the differences in serum and inflammatory parameters, antioxidant status, fecal microbiota and bacterial metabolites in 16 obese and 15 lean client-owned dogs and how these parameters in obese may be influenced by caloric restriction. First, for 30 days, all dogs received a high-protein, high-fiber diet in amounts to maintain their body weight; later, obese dogs were fed for 180 days the same diet in restricted amounts to promote weight loss. Before the introduction of the experimental diet (T0), small differences in fecal microbial populations were detected between obese and lean dogs, but bacterial diversity and main bacterial metabolites did not differ. The fecal Dysbiosis Index (DI) was within the reference range (< 0) in most of dogs of both groups. Compared to lean dogs, obese dogs showed higher serum concentrations of acute-phase proteins, total thyroxine (TT4), and antioxidant capacity. Compared to T0, dietary treatment affected the fecal microbiota of obese dogs, decreasing the abundance of Firmicutes and increasing Bacteroides spp. However, these changes did not significantly affect the DI. The caloric restriction failed to exert significative changes on a large scale on bacterial populations. Consequently, the DI, bacterial diversity indices and metabolites were unaffected in obese dogs. Caloric restriction was not associated with a reduction of inflammatory markers or an improvement of the antioxidant status, while an increase of TT4 has been observed. In summary, the present results underline that canine obesity is associated with chronic inflammation. This study highlights that changes on fecal microbiota of obese dogs induced by the characteristics of the diet should be differentiated from those that are the consequence of the reduced energy intake.

Association of SNP localized near &lt;i&gt;DIO2&lt;/i&gt; gene with hormonal profiles of the thyroid axis and fertility indicators in black-and-white cows

Thyroid hormones can affect the reproductive function of cows through the regulation of various metabolic pathways. The activity of the thyroid system is under the control of three types of deiodinases (DIO). In cattle, there are several genetic variants for the DIO1 and DIO3 genes, but there is no information on the polymorphism of the DIO2 gene.Purpose: to conduct a search for genetic variants for SNPs in the DIO2 gene and in nearby regions and investigate their association with prepartum and postpartum thyroid profiles and reproductive performance in dairy cows.Materials and methods. Black-and-white cows of calving 2-4 were used in the experiments. Before calving and after calving, blood was taken from the animals to determine the concentration of hormones by ELISA. The assessment of the luteal activity of the ovaries was performed on the basis of an ultrasound study and the content of progesterone in the blood. Genotyping was performed on 48 samples of cow DNA using a Bovine GGP 150K biochip.Results. No SNPs present on the Bovine GGP 150K chip were found within the target gene. The SNP Bovine- HD1000026761, localized upstream of the DIO2 gene, was selected for research, with a frequency of genotypes being 45.83% (AA), 47.92% (AG), and 6.25% (GG). In cows with the AA and AG genotypes, a decrease of 1.4 times (p&lt;0.01) in the blood concentration of total thyroxine (T4) 2 weeks before calving, compared with that for 4 weeks, and its further decrease by 1.5 -1.9 times (p&lt;0.001-p&lt;0.05) by the 1st week of lactation were found. From the 6th to the 2nd week before parturition, this indicator was 1.5–1.6 times higher (p&lt;0.001–p&lt;0.05) in individuals with the AG genotype than in ones with the AA genotype. In animals with the AG genotype, a decrease in the blood concentration of reverse T3 (1.4 times, p&lt;0.05) between the 4th week before calving and the 1st week of lactation was revealed. At the same time, this concentration was relatively constant in the animals of the other two groups. Furthermore, in animals with the AG genotype, the content of rT3 in the blood was 1.3 times lower than in animals with the AA genotype from the 3rd to the 7th week of lactation. In cows with a heterozygous genotype, the T4/T3 ratio increased 2.1 times (p&lt;0.001) between the 2nd week before calving and the 1st week after calving, and then decreased 2.2 times (p&lt;0.001) to the 3rd week. After 1 week of lactation, this ratio was 1.9 times higher (p&lt;0.001) than in animals with the AA genotype. Meanwhile, the frequency of occurrence of individuals with the shortest period of recovery of the ovarian function and open days period was the lowest in the group with the AA genotype.Conclusions. The data obtained indicate that the SNP BovineHD1000026761, located upstream of the DIO2 gene, is associated with long-term changes in thyroid hormone levels in the prepartum and postpartum periods.

Hyperthyroid cats and their kidneys: a literature review.

Hyperthyroidism and chronic kidney disease (CKD) are common diseases of geriatric cats, and often occur concurrently. Thus, a thorough understanding of the influence of thyroid function on renal function is of significant value for all feline practitioners. Among other effects, hyperthyroidism causes protein catabolism and increases renal blood flow and glomerular filtration rate (GFR). These effects render traditional renal markers insensitive for the detection of CKD in cats with uncontrolled hyperthyroidism. Furthermore, the development of iatrogenic hypothyroidism with over treatment of hyperthyroidism can be detrimental to renal function and may negatively affect long‐term survival. This review discusses important diagnostic considerations of feline hyperthyroidism, as well as key treatment modalities, with an emphasis on the use of radioiodine and the importance of post treatment monitoring of thyroid and renal parameters. In Australia, a common curative treatment for cats with benign hyperthyroidism (i.e. thyroid hyperplasia or adenoma) is a fixed dose of orally administered radioiodine, regardless of the serum total thyroxine concentration at the time of diagnosis. This review discusses the long term outcomes of this standard of care in comparison with current, relevant research literature from around the world. Finally, this review explores the use of symmetric dimethylarginine (SDMA) in assessing renal function before and after treatment in hyperthyroid cats. SDMA correlates well with GFR and creatinine in non‐hyperthyroid cats, but our understanding of its performance in hyperthyroid cats remains in its infancy.

Gonadotropin profile in experimentally induced hypothyroid and hyperthyroid cyclic female rats

The current study examined the association of thyroid disorders with reproductive dysfunction by determining its effect on gonadotropin secretion in cyclic female rats. Sixty cyclic females were assigned to three groups (20 each) and supplemented, for 30 days plus two consequent estrous cycles, with drinking water (control), methimazole in drinking water (0.02% w/v) (hypothyroid group), and thyroxine in drinking water (0.002% w/v) and gastric gavage of 200 μg/kg body weight (hyperthyroid group). At late proestrus, ten females from each group (for each cycle) were anesthetized and dissected. Blood samples were obtained to assess thyroid-stimulating hormone, free and total triiodothyronine, free and total thyroxin, follicle-stimulating hormone, luteinizing hormone, and prolactin concentrations. Ovarian and pituitary tissue samples were obtained for molecular analysis of ovarian thyroid receptor genes and pituitary TSH, FSHβ, and LHβ genes. In comparison with control, the Hypo group revealed increased serum concentrations of TSH and PRL and the expression levels of pituitary TSH and ovarian TRsTRs genes and significant decrease of FT3, TT3, FT4, TT4, FSH, and LHLH concentrations and the expression levels of pituitary FSHβ and LHβ genes. In contrast, the Hyper group showed increased serum FT3, TT3, FT4, TT4, and LHLH concentrations and the expression levels of pituitary LHβ and ovarian TRsTRs genes and decreased serum TSH FSH and PRL concentrations and pituitary FSHβ and TSH gene expression levels. It is concluded that thyroid dysfunction is associated with altered serum gonadotropin secretion and reproductive failure.

Association between Maternal Thyroxine and Risk of Fetal Congenital Heart Defects: A Hospital-Based Cohort Study.

Background Evidence for the association between maternal thyroxine concentration and the risk of fetal congenital heart defects (CHDs) is absent. We aimed to study the association of maternal free and total thyroxine (FT4 and TT4) concentrations and the free-to-total thyroxine proportion (FTT4P, %) with the risk of CHD. Methods The study was a hospital-based cohort study of 52,047 women who received a universal thyroid function test between 2012 and 2016. CHD was screened by ultrasound between 20 and 24 weeks of gestation or diagnosed until the 42nd day of birth. Adjusted odds ratios (ORs) of fetal CHD were estimated for maternal FT4 and TT4 concentrations or the FTT4P by multivariate logistic regression. Results A total of 41,647 women with singleton pregnancies were included for the analysis and 215 CHD cases were detected. The FT4 concentration was significantly associated with a higher risk of CHDs (OR, 1.04, 95% confidence interval (CI): 1.01 to 1.07). Each 1% higher FTT4P was related to a 1.41-fold (95% CI: 0.27 to 3.59) higher risk of CHDs. The association became stronger for women with a thyroid function test performed between 12 and 18 weeks of gestation (OR = 1.05 (95% CI: 1.01 to 1.09) for the FT4 concentration and 3.32 (95% CI: 1.43 to 7.73) for the FTT4P). Conclusions A higher FT4 concentration or FTT4P, measured between 12 and 18 weeks of gestation, was associated with an increased risk of CHDs. These findings may provide new insights into the mechanisms of CHDs and evidence for clinical decisions related to thyroid function tests.

Association of phthalate exposure with thyroid function during pregnancy.

The extent of thyroid disruptive effects of phthalates during pregnancy remains unclear. To investigate the association of maternal urinary phthalates with markers of the thyroid system during early pregnancy. Urinary concentrations of phthalate metabolites and serum concentrations of thyroid stimulating hormone (TSH), free and total thyroxine (FT4 and TT4) and free and total triiodothyronine (FT3 and TT3) were measured in pregnant women in early pregnancy in the Swedish Environmental Longitudinal, Mother and child, Asthma and allergy study (2007-ongoing), a population-based prospective cohort. In the 1,996 included women, higher di-ethyl-hexyl phthalate (DEHP) metabolites were associated with a lower FT4 (β [SE] for the molar sum: -0.13 [0.06], P=0.03) and a higher TSH/FT4 ratio (0.003 [0.001], P=0.03). Higher concentrations of di-iso-nonyl phthalate (DINP) metabolites were associated with a lower TT4 (β [SE] for the molar sum: 0.93 [0.44], P=0.03) as well as with lower TT4/FT4 and TT4/TT3 ratios. Higher metabolites of both dibutyl and butyl-benzyl phthalate (DBP and BBzP) were associated with lower T4/T3 ratio (free and total) and higher FT4/TT4 and FT3/TT3 ratios. A higher diisononyl cyclohexane dicarboxylate (DINCH) metabolite concentration was associated with a higher TT3. These results translate results from experimental studies suggesting that exposure to phthalates may interfere with the thyroid system during pregnancy. This is also true for compounds that have been introduced to replace known disruptive phthalates. Further experimental studies should take into account the human evidence to better investigate the potential underlying mechanisms of thyroid disruption by phthalates.

Radioactive iodine dose and survival in cats with hyperthyroidism (2015-2020).

Radioactive iodine (131I) is the preferred treatment for feline hyperthyroidism but neither the optimal 131I dose nor consistent predictors of post-treatment azotaemia have been determined. The aims of the study were to evaluate the relationships between: (1) 131I dose and survival; and (2) pretreatment and post-treatment serum creatinine concentration. Medical records of hyperthyroid cats treated with 131I at a single referral hospital were reviewed. Information regarding signalment, body weight, pretreatment and post-treatment serum total thyroxine concentration (TT4), serum creatinine concentration, 131I dose and survival were determined. Multivariable Cox proportional hazards analysis was used to identify variables associated with survival. Multivariable linear regression analysis was used to identify variables associated with post-treatment serum creatinine concentration. One hundred and ninety-eight (79 male, 119 female) cats were treated for hyperthyroidism with 131I (median dose 138 MBq; interquartile range 92-168). Median survival time was 1153 days (range 16-1871). Post-treatment serum creatinine (P <0.001) and age (P = 0.049) were significantly associated with survival. Every 10 µmol/l increase in post-treatment serum creatinine concentration and every year increase in age was associated with a 1.07-fold (confidence interval [CI] 1.04-1.11) and 1.17-fold (CI 1.00-1.37) increase in the daily hazard of death, respectively. Pretreatment serum creatinine concentration was directly, and post-treatment serum TT4 concentration was inversely, associated with post-treatment serum creatinine concentration. Every 1 μmol/l increase in pretreatment serum creatinine concentration was associated with an increase in post-treatment serum creatinine concentration of 0.7 μmol/l (SE 0.17; P <0.001). Conversely, every 1 nmol/l decrease in post-treatment serum TT4 concentration was associated with a 1.2 μmol/l (SE 0.61; P <0.001) increase in post-treatment serum creatinine concentration. Post-treatment serum TT4 concentration was associated with post-treatment azotaemia, which was associated with survival. Although 131I dose was not directly associated with survival, dosing strategies that minimise post-treatment hypothyroidism and azotaemia could improve patient survival.

Thyroid-Related Hormone Levels in Clinical Patients With Moderately Severe-to-Profound Sudden Sensorineural Hearing Loss: A Prospective Study.

Objectives: Sudden sensorineural hearing loss (SSNHL) is a common otological emergency, causing a measure of hearing loss and affecting the quality of life. This study aims to investigate the association of thyroid-related hormone levels with moderately severe-to-profound SSNHL.Methods: The study included 70 patients with moderately severe-to-profound SSNHL and 100 age- and sex-matched healthy controls. Peripheral venous blood samples were taken from the participants, and their thyroid-related hormone levels were measured at admission and 1 week after treatment.Results: In moderately severe-to-profound SSNaHL patients, the concentrations of total triiodothyronine (TT3), total thyroxine (TT4), free triiodothyronine (FT3), and thyroid-stimulating hormone (TSH) (all P < 0.05) were significantly lower than in the control group. The TT3, TT4, FT3, and TSH levels were significantly higher in the effective group than in the ineffective group (all P < 0.05). Linear correlation analysis revealed that TSH level (R = 0.707, P < 0.05) elevation after treatment successfully predicted a favorable outcome of hearing recovery. Logistic regression analyses suggested low FT3 and TSH levels to be independent occurrence predictors, while the increase of TSH level may be an independent favorable outcome predictor.Conclusions: The results suggest that low FT3 and TSH levels are risk factors for moderately severe-to-profound SSNHL. By discovering the positive association between TSH elevation and hearing recovery, along with the potential novel predictors of FT3 and TSH, our study may contribute valuable insights to the research and treatment of moderately severe-to-profound SSNHL.