Influence of drugs on thyroid function in dogs

Clinical hypothyroidism in a cat associated with sulfonamide administration for the management of intracranial nocardiosis

A 2-year-old cat was referred for suspected generalised seizure activity and reclusive behaviour, with a history of non-resolving facial abscess. Magnetic resonance imaging (MRI) revealed a contrast enhancing lesion occupying the left calvarium and adjacent peripheral tissues. The intracranial lesion was causing significant mass effect, with oedema and transtentorial herniation. Nocardia nova was isolated from the lesion and identified by DNA sequencing. Treatment consisted of debridement via craniotomy and ventral bulla osteotomy, and combination antibiotic therapy with clarithromycin, amoxycillin and trimethoprim-sulfonamide (sulfadoxine parenterally, then sulfadiazine orally). After several weeks of antibiotic therapy, the cat developed weakness, bicavitary effusion, myxoedema, non-regenerative anaemia and azotaemia. Total thyroxine (TT4) was below the detectable limit and canine thyroid stimulating hormone (cTSH) assay was markedly elevated at 7.53 ng/mL (reference interval 0.15-0.3 ng/mL). Discontinuation of sulfonamides and administration of levothyroxine resulted in resolution of clinical signs. The cat was subsequently able to discontinue levothyroxine, with recovery of euthyroid state. To the authors' knowledge, this is the first report of clinical hypothyroidism in a cat treated with sulfonamide antibiotics and may influence antimicrobial selection and monitoring during therapy. This report also described the management of an atypical presentation of nocardiosis with intracranial extension.

[Impact of hypothyroidism on bitch fertility and neonatal mortality and morbidity - a review of the literature]

There are a few studies and case reports that postulate a connection between hypothyroidism and reproductive disorders in bitches and an increased neonatal mortality and morbidity in puppies. Other studies, however, cannot demonstrate a connection between hypothyroidism and reproductive disorders in bitches. In this work, the relevant literature is to be checked for its evidence. The connection between hypothyroidism and reproductive disorders in the bitch, puppy mortality and neonatal morbidity to hypothyroidism will be analyzed based on a literature review. For this purpose, the available German and international "English-language" literature from 1986 to January 2023 was analyzed. It turns out that only a small amount of literature contains high levels of scientific evidence, as it mostly consists of case reports and expert opinions. In some case reports a connection between estrous abnormalities, galactorrhoea and infertility and the presence of hypothyroidism could be seen, but in experimental studies and according to the opinion of other authors the connection between hypothyroidism and reproductive disorders does not exist. A negative influence of hypothyroidism on the birth process could not be clearly proven. In an experimental study, although the duration and intensity of uterine contractions were longer and weaker in animals with hypothyroidism, the interval between pup births was not affected. Only in the area of neonatal mortality and morbidity a connection with the hypothyroidism of the dam could be demonstrated. The puppies of affected bitches showed a lower birth weight and were weaker than puppies of euthyroid bitches. The importance of hypothyroidism for fertility in the bitch has not yet been documented in the literature, but this endocrinopathy seems to have an influence on neonatal vitality.

Clinical and magnetic resonance imaging findings in a French bulldog puppy with genetically confirmed congenital hypothyroidism

A 7-month-old male French bulldog was referred for abnormal mentation and gait. Physical examination revealed a dome shaped calvarium and persistent bregmatic fontanelle. Neurological examination revealed proprioceptive ataxia, pelvic limb paraparesis and strabismus with moderate ventriculomegaly, thinning of the cerebral parenchyma, and widened cerebral sulci on magnetic resonance imaging. Masses were identified in the region of the thyroid, which appeared heterogeneous and hyperintense in T1-weighted and T2-weighted compared with the adjacent muscle signal masses were identified. Radiological diagnosis was hydrocephalus "ex vacuo" and goiter. Blood test revealed abnormally low total thyroxine (TT4), free thyroxine (FT4), and normal thyrotropin concentration. A diagnosis of congenital hypothyroidism was confirmed by positive genetic test for thyroid peroxidase mutation. Thyroxine supplementation treatment rapidly improved clinical signs.

Assessment of the likelihood of hypothyroidism in dogs diagnosed with and treated for hypothyroidism at primary care practices: 102 cases (2016-2021)

BACKGROUND

There is a possibility that an incorrect diagnosis of hypothyroidism could be made in euthyroid dogs, and the prevalence of hypothyroidism in the dog population remains unknown.

OBJECTIVES

To retrospectively assess the percentage of dogs diagnosed with, and treated for, hypothyroidism at first opinion practice which are likely to be hypothyroid and require levothyroxine supplementation.

ANIMALS

One hundred two client-owned dogs were included in this study.

MATERIALS AND METHODS

The computerized databases of 7 first opinion practices were searched to identify dogs treated with levothyroxine supplementation. Three European College of Veterinary Internal Medicine-Companian Animals (ECVIM-CA) diplomates independently assigned 1 of 4 clinical assessments to each case as follows: confirmed or likely hypothyroid, hypothyroidism suspected but not confirmed, hypothyroidism considered unlikely, and no reason to suspect hypothyroidism. They commented as to whether or not they thought levothyroxine supplementation was appropriate.

RESULTS

The clinical assessments of "confirmed or likely hypothyroid"; "Hypothyroidism suspected but not confirmed"; "Hypothyroidism considered unlikely"; and "No reason to suspect hypothyroidism" was assigned respectively by Clinician 1 to 38.2%, 5.9%, 3.9%, and 52% of cases, by Clinician 2 to 48%, 22.6%, 22.6%, 6.9% of cases, and by Clinician 3 to 55.9%, 11.8%, 13.7% and 18.6%. Clinician 1, Clinician 2, and Clinician 3 considered levothyroxine supplementation not indicated in 58.8%, 52.9%, and 45.1% of cases, respectively.

CONCLUSION

These results support the concern that hypothyroidism might be overly and incorrectly diagnosed in first opinion practice, and that thyroid function testing should be performed only in those dogs with a high pretest probability of the disease.

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

BACKGROUND

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.

HYPOTHESIS

Estrous stage may influence thyroid function in German Shepherd dogs.

METHODS

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.

ANIMALS

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.

RESULTS

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.

CONCLUSIONS

Different stages of estrus can influence the measurement of TT4 in female dogs.

Thyroid function tests during nonthyroidal illness syndrome and recovery in acutely ill dogs

BACKGROUND

Nonthyroidal illness syndrome (NTIS) can result in thyroid function test alterations that mimic hypothyroidism. The duration of NTIS-induced changes in dogs is not well-described.

OBJECTIVES

Document alterations in thyroid function tests during NTIS and recovery, and the time necessary for their resolution.

ANIMALS

From 103 dogs sampled, 25 euthyroid dogs with acute, resolvable illness having a low serum total thyroxine (TT4) concentration on admission were analyzed.

METHODS

Prospective observational study. Serum TT4 concentration was measured in 103 dogs within 4 hours of admission. If below the reference interval (RI), subsequent serum samples were obtained every 24 hours from admission until discharge (acute phase) and at 2 weeks and 4 weeks after discharge (recovery phase). Serum samples were submitted for batch measurement of serum TT4, free thyroxine (fT4), total 3,5,3'-triiodothyronine (TT3), and thyroid-stimulating hormone (TSH) concentrations.

RESULTS

In the cohort of dogs analyzed, serum TT4, TT3, and fT4 concentrations were below the RI in 100%, 80%, and 16% at admission; 20%, 80%, and 0% at discharge; 4%, 8%, and 0% at 2 weeks; and 0%, 0%, and 0% at 4 weeks, respectively. Serum TSH concentration was within the RI in 100% at admission and discharge, and above the RI in 4% and 12% at 2 weeks and 4 weeks, respectively.

CONCLUSIONS AND CLINICAL IMPORTANCE

Naturally occurring NTIS in dogs induces alterations in thyroid function tests during acute illness and recovery. Measurement of serum TT4 concentration 2 to 4 weeks after discharge or serum fT4 concentration by ED during illness is recommended for accurate assessment of thyroid function in acutely ill dogs.

Changes of the salivary and serum proteome in canine hypothyroidism

In this study, changes in salivary and serum proteome of dogs with hypothyroidism were studied using tandem mass tags (TMT) labelling and liquid chromatography-mass spectrometry (LC-MS/MS). Saliva and serum proteome from 10 dogs with hypothyroidism were compared with 10 healthy dogs. In saliva, a total of seven proteins showed significant changes between the two groups, being six downregulated and one upregulated, meanwhile, in serum, a total of six proteins showed significant changes, being five downregulated and one upregulated. The altered proteins reflected metabolic and immunologic changes, as well as, skin and coagulation alterations, and these proteins were not affected by gender. One of the proteins that were downregulated in saliva, lactate dehydrognease (LDH), was measured by a spectrophotometric assay in saliva samples from 42 dogs with hypothyroidism, 42 dogs with non-thyroid diseases and 46 healthy dogs. The activity of LDH was lower in the saliva of hypothyroid dogs when compared to non-thyroid diseased dogs and healthy controls. This study indicates that canine hypothyroidism can produce changes in the proteome of saliva and serum. These two sample types showed different variations in their proteins reflecting physiopathological changes that occur in this disease, mainly related to the immune system, metabolism, skin and coagulation. In addition, some of the proteins identified in this study, specially LDH in saliva, should be further explored as potential biomarkers of canine hypothyroidism.

Influence of medications on thyroid function in dogs: An update

Erroneous thyroid function test results can occur because of drugs that alter thyroid hormone physiology in one or more aspects, including synthesis, secretion, distribution, and metabolism. Research since publication of the last review in the Journal of Veterinary Internal Medicine (JVIM) 20 years ago has evaluated the effects of amiodarone, zonisamide, inhalant anesthetics, clomipramine, trilostane, and toceranib on thyroid function tests in the dog. In addition, recent work on the effects of glucocorticoids, sulfonamides, phenobarbital, and nonsteroidal anti-inflammatory drugs will be reviewed. Awareness of these effects is necessary to avoid misdiagnosis of hypothyroidism and unnecessary treatment.

2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines

Canine and feline endocrinopathies reflect an endocrine gland disease or dysfunction with resulting hormonal abnormali ties that can variably affect the patient's wellbeing, quality of life, and life expectancy. These guidelines provide consensus recommendations for diagnosis and treatment of four canine and feline endocrinopathies commonly encountered in clini cal practice: canine hypothyroidism, canine hypercortisolism (Cushing's syndrome), canine hypoadrenocorticism (Addi son's disease), and feline hyperthyroidism. To aid the general practitioner in navigating these common diseases, a stepwise diagnosis and treatment algorithm and relevant background information is provided for managing each of these diseases. The guidelines also describe, in lesser detail, the diagnosis and treatment of three relatively less common endo crinopathies of cats: feline hyperaldosteronism, feline hypothyroidism, and feline hyperadrenocorticism. Additionally, the guidelines present tips on effective veterinary team utilization and client communication when discussing endocrine cases.

Assessment of Sex, Age, and Metabolism Relationships to Serum Thyroid Concentrations in Retired Alaskan Husky Sled Dogs

Sled dogs are purpose-bred dogs selected for endurance work. Prior studies in racing dogs showed that serum thyroid parameters (total T4, free T4, and T3) are lower than the reference range in approximately 25% of dogs. Whether this is related to training, breeding, or body condition remains unclear. We hypothesized that retired sled dogs of normal body condition (9–13 years old) would have predominantly normal serum thyroid parameters and that serum thyroid status would be correlated to energy consumption based on metabolic body weight. Eighty-six sled dogs who were deemed healthy on physical exam, not on confounding medications, and without a prior diagnosis of hypothyroidism were included. All dogs' mean body condition scores were 5.1 ± 0.4 and body weight 24.5 ± 4.2 kg at fasting blood collection with stable dietary intake for 3 months before sampling. The total T4, free T4, and T3 serum concentrations were 23.4 ± 9.1 nmol/L, 9.53 ± 4.3 pmol/L, and 0.93 ± 0.39 nmol/L, respectively, with 38% lower than the reference range for total T4, 45% for free T4, and 37% for T3. All dogs were negative for thyroglobulin antibody, and TSH results were within normal ranges. Pearson's correlates based on kilocalories consumed on a metabolic body weight basis for total T4 (R = 0.14), free T4 (R = 0.01) and T3 (R = 0.23) showed poor correlation. No differences were observed between thyroid hormones and age, breed, or sex. Inactive, retired sled dogs can be misdiagnosed with hypothyroidism; therefore, our data suggests that misdiagnosis of hypothyroidism can occur and that the racing Alaskan sled dog has a unique reference range that should be considered when assessing serum thyroid status.

Simultaneous analysis of 6 inorganic anions in urine by double-suppress ion exchange chromatography

This study is aimed to establish a simple, rapid, and accurate ion chromatography approach for simultaneous detection of 6 inorganic anions in urine. Various performance parameters affecting the determination of anions were optimized, including the selection of sample protein precipitation agent, eluent, and flow rate. The final eluent was 3.6 mmol/L sodium carbonate and 12% isopropanol with a flow rate of 0.6 mL/min. Acetonitrile was used for pretreatment to precipitate proteins, and the volume ratio of urine to acetonitrile was 1:4. The correlation coefficient of the target anion calibration curve ranged from 0.9973 to 0.9999. The limit of detection ranged from 1.50 to 12.0 μg/L, and the method detection limit ranged from 15.0 to 120 μg/L. The standard recovery rate for low, medium, and high concentrations ranged from 90 to 110%. The inter-day and intra-day relative standard deviations were < 5%. The method has high accuracy and good reproducibility, and is suitable for the separation and determination of anions in urine. This article is protected by copyright. All rights reserved.

Association of recessive c.430G>A (p.(Gly144Arg)) thyroid peroxidase variant with primary congenital hypothyroidism in cats

BACKGROUND

Primary congenital hypothyroidism (CH) is a rare endocrine disorder in cats with a largely unknown genetic cause.

OBJECTIVES

Describe the clinical presentation of CH in 11 affected cats and identify the causal genetic variant.

ANIMALS

Eleven CH-cats from 10 unrelated families, 11 CH-free family members, 21 unrelated CH-free cats, and 155 unrelated nondiagnosed cats from different breeds.

METHODS

Case control study of CH-cats and their siblings (2019-2021). Diagnosis was based on low to low-normal serum thyroxine (T4) concentrations, high thyroid-stimulating hormone (TSH) concentrations and clinical signs compatible with CH. We identified the causal variant using Sanger sequencing, genotyping via PCR-RFLP and variant interpretation using ACMG/AMP guidelines.

RESULTS

All CH-cats (5 weeks-8 years) had disproportionate dwarfism. A goiter was not palpable in all. Thyroid scintigraphy with radiopertechnetate showed abnormally high uptake by thyroid glands, whereas scintigraphy with radioiodine showed abnormally low uptake, compatible with a defect in iodine organification by thyroid peroxidase (TPO). All cases were homozygous for TPO variant XM_006930524.4:c.430G>A(p.(Gly144Arg)), while none of the CH-free cats were. All sampled parents were heterozygous for this recessive variant. This variant was found in 15 cat breeds with an estimated allele frequency of 9%.

CONCLUSIONS AND CLINICAL IMPORTANCE

Disproportionate dwarfism, abnormally high TSH and abnormally low to low-normal T4 concentrations are diagnostic for CH in cats. All cases had dyshormonogenesis demonstrated by thyroid scintigraphy. This novel TPO missense variant (not described in humans) causes CH in cats and awareness of it can assist in diagnosis and breeding.

Nonclinical Safety Profile of Sotorasib, a KRASG12C-Specific Covalent Inhibitor for the Treatment of KRAS p.G12C-Mutated Cancer

Sotorasib is a first-in-class KRAS^G12C covalent inhibitor in clinical development for the treatment of tumors with the KRAS p.G12C mutation. A comprehensive nonclinical safety assessment package, including secondary/safety pharmacology and toxicology studies, was conducted to support the marketing application for sotorasib. Sotorasib was negative in a battery of genotoxicity assays and negative in an in vitro phototoxicity assay. Based on in vitro assays, sotorasib had no off-target effects against various receptors, enzymes (including numerous kinases), ion channels, or transporters. Consistent with the tumor-specific target distribution (ie, KRAS^G12C), there were no primary pharmacology-related on-target effects identified. The kidney was identified as a target organ in the rat but not the dog. Renal toxicity in the rat was characterized by tubular degeneration and necrosis restricted to a specific region suggesting that the toxicity was attributed to the local formation of a putative toxic reactive metabolite. In the 3-month dog study, adaptive changes of hepatocellular hypertrophy due to drug metabolizing enzyme induction were observed in the liver that was associated with secondary effects in the pituitary and thyroid gland. Sotorasib was not teratogenic and had no direct effect on embryo-fetal development in the rat or rabbit. Human, dog, and rat circulating metabolites, M24, M10, and M18, raised no clinically relevant safety concerns based on the general toxicology studies, primary/secondary pharmacology screening, an in vitro human ether-à-go-go-related gene assay, or mutagenicity assessment. Overall, the results of the nonclinical safety program support a high benefit/risk ratio of sotorasib for the treatment of patients with KRAS p.G12C-mutated tumors.

Prognostic value of serum total thyroxine concentration at admission to an intensive care unit for critically ill dogs

OBJECTIVE

To determine whether serum total thyroxine (TT4) concentration at admission to an intensive care unit (ICU) was associated with mortality rate and duration of hospitalization for critically ill dogs.

ANIMALS

166 client-owned dogs that were hospitalized in the ICU of a private veterinary practice from January 2013 through December 2016 and for which serum TT4 concentration had been measured at admission.

PROCEDURES

Medical records were reviewed to collect data regarding patient signalment, concurrent illnesses, medications, reason for hospitalization, outcome (death, euthanasia, or survival to hospital discharge), duration of hospitalization, and initial serum TT4 concentration.

RESULTS

Mean age of the 166 dogs was 8.6 years (range, 1 to 16 years). Overall mortality rate was 15.7%, with 26 dogs failing to survive to hospital discharge. Of these 26 dogs, 7 died and 19 were euthanized. No significant association was identified between serum TT4 concentration at admission and survival to discharge (yes or no) or duration of hospitalization. Age was significantly associated with survival to discharge, with older dogs less likely to survive than younger dogs. Duration of hospitalization was also associated with survival to discharge, with longer hospital stays associated with a lower likelihood of survival to discharge.

CONCLUSIONS AND CLINICAL RELEVANCE

Findings suggested that serum TT4 concentration at admission to an ICU had no prognostic value in this population of critically ill dogs.

A review of species differences in the control of, and response to, chemical-induced thyroid hormone perturbations leading to thyroid cancer

This review summarises the current state of knowledge regarding the physiology and control of production of thyroid hormones, the effects of chemicals in perturbing their synthesis and release that result in thyroid cancer. It does not consider the potential neurodevelopmental consequences of low thyroid hormones. There are a number of known molecular initiating events (MIEs) that affect thyroid hormone synthesis in mammals and many chemicals are able to activate multiple MIEs simultaneously. AOP analysis of chemical-induced thyroid cancer in rodents has defined the key events that predispose to the development of rodent cancer and many of these will operate in humans under appropriate conditions, if they were exposed to high enough concentrations of the affecting chemicals. There are conditions however that, at the very least, would indicate significant quantitative differences in the sensitivity of humans to these effects, with rodents being considerably more sensitive to thyroid effects by virtue of differences in the biology, transport and control of thyroid hormones in these species as opposed to humans where turnover is appreciably lower and where serum transport of T4/T3 is different to that operating in rodents. There is heated debate around claimed qualitative differences between the rodent and human thyroid physiology, and significant reservations, both scientific and regulatory, still exist in terms of the potential neurodevelopmental consequences of low thyroid hormone levels at critical windows of time. In contrast, the situation for the chemical induction of thyroid cancer, through effects on thyroid hormone production and release, is less ambiguous with both theoretical, and actual data, showing clear dose-related thresholds for the key events predisposing to chemically induced thyroid cancer in rodents. In addition, qualitative differences in transport, and quantitative differences in half life, catabolism and turnover of thyroid hormones, exist that would not operate under normal situations in humans.

Pre-contrast CT attenuation of the thyroid gland is lower in brachycephalic dogs versus non-brachycephalic dogs

Computed tomography has been used in human medicine to evaluate the thyroid gland functional status by means of Hounsfield units (HU). Studies describing attenuation value abnormalities, other than those in thyroid neoplasia, lack in veterinary medicine. The authors have observed a subjective reduction in thyroid attenuation in some patients undergoing CT for reasons other than thyroid disease. This finding has been identified more frequently in brachycephalic breeds compared to non-brachycephalic breeds. In order to determine the thyroid gland attenuation variability on CT, a retrospective and prospective, analytical, cross-sectional study was performed. The thyroid attenuation values of 65 client-owned dogs were assessed using a 16-slice helical CT scanner. Differences in attenuation between brachycephalic and non-brachycephalic dogs were estimated by Welch's t-test. Serum TT4 and TSH levels were available in 26 patients. Statistically significant differences were observed in the pre-contrast attenuation value ranges between brachycephalic and non-brachycephalic dogs (P = .04). The pre-contrast attenuation value range for the brachycephalic group was 69.1-108 HU while being 75.8-121 HU for the non-brachycephalic group. No significant correlation was found between thyroid attenuation and serum thyroid hormone levels in our population (P > .6). All patients with hypoattenuating thyroid were brachycephalic and reported euthyroid. In conclusion, brachycephalic dogs seem to have a pre-contrast attenuation thyroid gland range lower than non-brachycephalic dogs. The present study contributes to the veterinary literature by providing a new thyroid attenuation value range for brachycephalic breeds. Additionally, hypoattenuating thyroid glands may be found in dogs with normal TT4 and TSH values.

Serum thyroxine and thyrotropin concentrations decrease with severity of nonthyroidal illness in cats and predict 30-day survival outcome

Background

In cats, nonthyroidal illness affects serum thyroid hormone concentrations. Serum thyroxine (T₄) and triiodothyronine (T₃) concentrations commonly decrease, whereas free T₄ (fT₄) concentrations vary unpredictably. Limited information exists regarding effects on serum thyrotropin (thyroid‐stimulating hormone [TSH]) concentrations in cats with nonthyroidal illness syndrome (NTIS).

Objectives

To characterize alterations in thyroid function that develop in cats with NTIS and to correlate these alterations with severity and outcome of the nonthyroidal illness.

Animals

Two hundred and twenty‐two cats with NTIS and 380 clinically normal cats of similar age and sex.

Methods

Prospective, cross‐sectional study. All cats had serum T₄, T₃, free T₄, and TSH concentrations measured. Cats were grouped based on illness severity and 30‐day survival.

Results

Cats with NTIS had lower serum T₄ and T₃ concentrations than did normal cats (P < .001). Serum fT₄ and TSH concentrations did not differ between groups. Serum T₄, T₃, and fT₄ concentrations progressively decreased with increasing disease severity (P < .001). The 56 cats that died had lower T₄, T₃, and TSH concentrations than did the 166 survivors, with no difference in fT₄ concentration. Multivariable logistic regression modeling indicated that serum T₄ and TSH concentrations both predicted survival (P < .02).

Conclusions and Clinical Importance

Cats with NTIS commonly develop low serum T₄, T₃, and TSH concentrations, the prevalence and extent of which increases with disease severity. Clinicians should consider evaluating thyroid function in cats with severe NTIS, because doing so could help determine probability of successful treatment responses before investing considerable time, effort, and finances in addressing the underlying disease.

Effects of PCB exposure on serum thyroid hormone levels in dogs and cats

Polychlorinated biphenyls (PCBs) and their hydroxylated metabolites (OH-PCBs) might disrupt thyroid function. However, there is no clear evidence of PCB exposure disrupting thyroid hormone (TH) homeostasis in dogs and cats. The present study conducted in vivo experiments to evaluate the effects of a mixture of 12 PCB congeners (CB18, 28, 70, 77, 99, 101, 118, 138, 153, 180, 187 and 202, each congener 0.5 mg/kg BW, i.p. administration) on serum TH levels in male dogs (Canis lupus familiaris) and male cats (Felis silvestris catus). In PCB-exposed dogs, the time courses of higher-chlorinated PCBs and L-thyroxine (T4)-like OH-PCBs (4-OH-CB107 and 4-OH-CB202) concentrations were unchanged or tended to increase, whereas those of lower-chlorinated PCBs and OH-PCBs tended to decrease after 24 h. In PCB-exposed cats, concentrations of PCBs increased until 6 h and then remained unchanged. The levels of lower-chlorinated OH-PCBs including 4'-OH-CB18 increased until 96 h and then decreased. In PCB-exposed dogs, free T4 concentrations were higher than those in the control group at 48 and 96 h after PCB administration and positively correlated with the levels of T4-like OH-PCBs, suggesting competitive binding of T4 and T4-like OH-PCBs to a TH transporter, transthyretin. Serum levels of total T4 and total 3,3',5-triiodo-L-thyronine (T3) in PCB-exposed dogs were lower than in the control group at 24 and 48 h and negatively correlated with PCB concentrations, implying that PCB exposure enhanced TH excretion by increasing TH uptake and TH conjugation enzyme activities in the dog liver. In contrast, no obvious changes in TH levels were observed in PCB-exposed cats. This could be explained by the lower levels of T4-like OH-PCBs and lower hepatic conjugation enzyme activities in cats compared with dogs. Different effects on serum TH levels in PCB-exposed dogs and cats are likely to be attributable to species-specific PCB and TH metabolism.

Cortisol, progesterone, 17α-hydroxyprogesterone, and TSH responses in dogs injected with low-dose lipopolysaccharide

Background

Stress and diseases such as endotoxemia induce cortisol synthesis through a complex biosynthetic pathway involving intermediates (progesterone, and 17α-hydroxyprogesterone (17α-OHP)) and suppression of the hypothalamus-pituitary-thyroid axis.

Objective

To measure plasma concentrations of cortisol, progesterone, 17α-OHP, and thyroid stimulating hormone (TSH) in dogs experimentally injected with intravenous low-dose lipopolysaccharide (LPS). Our hypothesis was that LPS treatment would elicit a significant increase in cortisol and its precursors, and a significant decrease in TSH concentration.

Methods

Hormone measurements were performed on blood samples left over from a previous investigation (2011) on the effect of low-dose LPS on hematological measurands. Five sexually intact female dogs, none in estrous at the time of the study, were administered saline treatment two weeks prior to LPS treatment. LPS was administered intravenously at a dose of 0.1 µg/kg. Blood was collected before (baseline, time -24 hours) and 3-, 6- and 24-hours post-injection. Mixed model analysis for repeated measures was used, with both treatment and time as the repeated factors. Ranked transformation were applied when diagnostic analysis exhibited violation of normality and equal variance assumptions. Post hoc multiple comparisons were performed with Tukey’s adjustment. Statistical significance was defined as p < 0.05.

Results

Significant differences relative to baseline values were detected following both treatments. Compared to baseline, dogs had significantly higher cortisol and 17α-OHP at 3-hours, and significantly lower TSH at 3- and 6-hours following LPS treatment. Dogs had significantly lower TSH at 6- and 24- following saline treatment. Though not statistically significant, the trend in progesterone concentrations was similar to cortisol and 17α-OHP, with an increase at 3-hours post-injection followed by a decrease close to baseline following both LPS and saline. Cortisol and 17α-OHP concentrations were higher after LPS treatment than after saline treatment at 3- and 6-hours post-injection, but differences were not statistically significant, and no significant differences between treatments were detected for any other hormone or timepoint.

Discussion and conclusion

Cortisol and its adrenal precursors are released in the bloodstream following a low dose of LPS, while TSH appears to decrease. Similar changes occurred following saline treatment, suggesting that even routine handling and saline injection in conditioned dogs can elicit alterations in the internal equilibrium with subsequent modification of both hypothalamus-pituitary-adrenal and thyroid axes. Changes to adrenal and thyroid hormone concentrations must be interpreted in light of clinical information. Further studies are needed to elucidate mechanisms of adrenal steroidal hormone synthesis and secretion in response to various stressful stimuli in both neutered and intact animals.

Risk factors for low plasma thyroxine and high plasma thyroid-stimulating hormone concentrations in dogs with non-thyroidal diseases

The aim of the current study was to identify independent risk factors for thyroid axis alterations in dogs with non-thyroidal diseases. In this retrospective cross-sectional study, data and plasma samples from 207 dogs with non-thyroidal diseases was used. The involvement of various factors (disease severity, sex, age, breed, category and duration of disease, and medication) in the alteration of plasma thyroxine (T4) or thyroid-stimulation hormone (TSH) concentrations was analyzed using multivariate logistic regression. Among the 207 dogs analyzed, 99 (47.8%) had low plasma T4 concentrations, while 45 (21.7%) had high TSH concentrations. Intact male sex [odds ratio (OR), 3.25; 1.67-6.35; P<0.001], Labrador Retrievers (OR, 18.70; 2.32-151.00; P=0.006), moderate (OR, 2.39; 1.21-4.74; P=0.012) and severe diseases (OR, 6.84; 2.27-20.70; P<0.001) were associated with increased risk for low plasma T4 concentrations. Meanwhile, intact male (OR, 3.93; 1.51-10.30; P=0.005), spayed female (OR, 4.22; 1.59-11.20; P=0.004), older age (OR, 2.73; 1.28-5.84; P=0.009), and Miniature Dachshunds (OR, 5.39; 2.38-12.20; P<0.001) had increased risk for high plasma TSH concentrations. Disease severity had been determined as an independent risk factor for canine NTIS. In addition, sex, age and breed were also associated with thyroid axis alterations in dogs with non-thyroidal diseases.

Behavior in dogs with spontaneous hypothyroidism during treatment with levothyroxine

Background

Thyroid hormone supplementation anecdotally has been described as a valid treatment option for dogs with aggression‐related problems. However, prospective, controlled, and blinded trials evaluating behavior and neurohormonal status in hypothyroid dogs during treatment with levothyroxine are lacking.

Objective

Levothyroxine supplementation will have a significant influence on the behavior and neurohormonal status of dogs with spontaneous hypothyroidism.

Animals

Twenty client‐owned dogs diagnosed with spontaneous hypothyroidism.

Methods

This prospective study was to evaluate the behavior of dogs, which was screened at initial presentation, and after 6 weeks, and 6 months of treatment with levothyroxine (starting dosage 10 μg/kg PO q12h) using the standardized Canine Behavioral Assessment and Research Questionnaire (C‐BARQ). At each time period, circulating serotonin and prolactin (PRL) concentrations were evaluated using a commercially validated ELISA kit and heterologous radioimmunoassay, respectively.

Results

After 6 weeks of thyroid hormone supplementation, C‐BARQ scores demonstrated a significant increase in activity of hypothyroid dogs (P < .01). No significant change in any of the behavioral signs was observed after 6 months of treatment. No significant difference in circulating concentrations of serotonin (P > .99 and P = .46) and PRL (P = .99 and P = .37) were noted between the 6‐week and 6‐month periods compared with baseline.

Conclusions and Clinical Importance

The results of this study indicate increased activity of hypothyroid dogs after 6 weeks of thyroid hormone supplementation. None of the hypothyroid dogs in this cohort showed a significant change in any of the evaluated behavioral signs and neurohormonal status after 6 months of thyroid hormone supplementation.

Spontaneous primary hypothyroidism in 7 adult cats

BACKGROUND

Naturally occurring hypothyroidism in adult cats is rare, with only 4 cases reported.

OBJECTIVES

To describe the historical, clinical, laboratory, and scintigraphic features of adult cats with spontaneous hypothyroidism.

ANIMALS

Seven adult cats referred for suspected hypothyroidism.

METHODS

Prospective case series. We collected data on cats' signalment, clinical signs, results of physical examination, routine laboratory and thyroid hormone testing, and thyroid imaging (thyroid scintigraphy or ultrasound). We subsequently treated cats with levothyroxine and evaluated their response to treatment.

RESULTS

Cats ranged from 3.5 to 11 years, with no apparent breed predilection; 6/7 cats were male. Only 2/7 cats were initially tested because of signs of hypothyroidism (hair-coat changes, lethargy, obesity); others were tested for routine thyroid monitoring or palpable thyroid nodules. Four were azotemic (serum creatinine, 2.2-3.4 mg/dL). Six of the cats had low serum thyroxine (T4 ) and free T4 (fT4 ) concentrations, whereas all 7 cats had high thyroid-stimulating hormone (TSH) concentrations. In 6/7 cats, thyroid scintigraphy revealed bilateral goiter with intense radionuclide uptake; imaging showed no visible thyroid tissue in the other. After levothyroxine treatment, serum concentrations of T4 and fT4 increased and TSH fell; high serum creatinine normalized in azotemic cats; and repeat imaging showed reduction in goiter size.

CONCLUSIONS AND CLINICAL IMPORTANCE

Primary hypothyroidism develops in adult cats, with a higher prevalence than previously thought. Most cats appear to develop a goitrous form of hypothyroidism associated with thyroid hyperplasia, whereas thyroid atrophy appears to be less common. With levothyroxine replacement, clinical and laboratory abnormalities improve or resolve.

Use of basal and TRH-stimulated plasma growth hormone concentrations to differentiate between primary hypothyroidism and nonthyroidal illness in dogs

BACKGROUND

A low plasma total thyroxine (TT₄ ) concentration in combination with a plasma TSH concentration within reference range does not distinguish between hypothyroidism and nonthyroidal illness (NTI) in dogs. Hypothyroidism is associated with TSH-releasing hormone (TRH)-induced increased release of growth hormone (GH).

HYPOTHESIS

Basal and TRH-induced plasma GH concentrations can be used to distinguish hypothyroid dogs from NTI dogs.

ANIMALS

Twenty-one dogs with signs consistent with hypothyroidism, a low plasma TT₄ concentration, and a plasma TSH concentration within reference interval.

METHODS

Case control study. Thyroid scintigraphy was performed to classify dogs as having hypothyroidism or NTI. All dogs underwent a TRH stimulation test with measurement of plasma concentrations of GH and TSH before and 30 and 45 minutes after IV administration of TRH.

RESULTS

Eleven of the dogs were classified as hypothyroid and 10 as having NTI. Basal plasma GH concentration in the hypothyroid dogs (3.2 μg/l; range, 2.0 to 12.5 μg/l) was significantly higher (p<0.001) than that in the NTI dogs (.73 μg/l; range, .45 to 2.3 μg/l), with minimal overlap, and increased (p=.009) after TRH administration in hypothyroid dogs, whereas it did not change in NTI dogs. At T=45, plasma GH concentrations in hypothyroid dogs and NTI dogs did not overlap. The plasma TSH concentration did not change significantly after TRH administration in hypothyroid dogs, whereas it increased (p<.001) in NTI dogs. At T=45, there was no overlap in percentage TSH increase from baseline between hypothyroid dogs.

CONCLUSIONS AND CLINICAL IMPORTANCE

Measurement of basal plasma GH concentration and concentrations of GH and TSH after TRH stimulation can distinguish between hypothyroidism and NTI in dogs.

Effects of Prolonged Treatment With Co-trimoxazole on the Thyroid Gland, Liver, and Epididymal Sperm Reserve in Dogs

Co-trimoxazole is an antimicrobial drug gotten from potentiation of sulfamethoxazole with trimethoprim. It is widely used for the treatment of bacterial and protozoan infections in humans. It is also used in veterinary clinics against susceptible microorganisms, but thyroid dysfunction has raised concern especially in dogs. This study aimed to determine the effects of prolonged treatment with co-trimoxazole in euthyroid dogs. Dogs were given co-trimoxazole at 30, 60, and 120 mg/kg body weight at 12-hour intervals for 21 days. Standard procedures were used to assay total T4 and T3, thyrotropin, testosterone, aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase in serum. The thyroid gland and testes were weighed. In addition, thyroid and liver were examined histologically. Epididymal sperm count was also performed. Co-trimoxazole caused dose-dependent depression of serum thyroxine levels with severe colloid depletion, intrafollicular hemorrhage, hyperplasia, and hypertrophy of the follicular cells. The liver showed vacuolar hepatopathy. Epididymal sperm count was low in the 120 mg/kg-treated group. The study revealed that thyroid hemorrhage and lowered epididymal sperm reserve were new findings in co-trimoxazole toxicity in dogs.

Effects of Toceranib Phosphate on the Hypothalamic-Pituitary-Thyroid Axis in Tumor-Bearing Dogs

Background

Thyroid dysfunction is associated with the use of tyrosine kinase inhibitors (TKI) in people.

Hypothesis/Objectives

To determine whether dysfunction in the hypothalamic‐pituitary‐thyroid axis occurs in dogs receiving the TKI, toceranib phosphate.

Animals

Forty‐three client‐owned dogs with cancer.

Methods

Prospective, observational study. Concentrations of total thyroxine (TT4), free thyroxine (FT4), total triiodothyronine (TT3), and thyroid‐stimulating hormone (TSH) were evaluated on day 0, 30, and 90. Dogs also were evaluated for the presence of thyroglobulin autoantibodies.

Results

The proportion of dogs with low TT4, low FT4, low TT3, high TSH, or primary hypothyroidism (increased TSH and decreased TT4, FT4 or both) did not change over 90 days. Hormone concentrations remained within laboratory reference intervals, but FT4 (P = 0.0032) and TSH (P < 0.0001) changed over time. Mean FT4 was 1.22 ng/dL (95% confidence interval [CI], 1.10–1.34) on day 0 and 1.00 ng/dL (95% CI, 0.86–1.16) on day 90. Mean TSH was 0.17 ng/mL (95% CI, 0.13–0.23) on day 0 and 0.34 ng/mL (95% CI, 0.24–0.48) on day 90. Furthermore, TT4/TT3 ratio also changed over time (P = 0.0086). Mean TT4/TT3 ratio was 2.57 (95% CI, 2.26–2.88) on day 0 and 2.02 on day 90 (95% CI, 1.61–2.44). Thyroglobulin autoantibodies were not detected in any dog.

Conclusions and Clinical Importance

Toceranib phosphate can disrupt the hypothalamic‐pituitary‐thyroid axis in dogs. Periodic evaluation of TT4, FT4, TT3, and TSH should be carried out in dogs receiving long‐term treatment with this medication.

Effects of Levothyroxine Administration and Withdrawal on the Hypothalamic-Pituitary-Thyroid Axis in Euthyroid Dogs

Background

Chronic supplementation can suppress the hypothalamic‐pituitary‐thyroid axis (HPTA) and make it difficult to assess thyroid function after withdrawal of levothyroxine.

Objectives

To determine whether the HPTA is suppressed after levothyroxine administration in euthyroid dogs and the time required for resolution of any suppression.

Animals

Twenty‐eight healthy euthyroid dogs.

Methods

A prospective, randomized study administering levothyroxine to euthyroid dogs for 8 weeks (group 1) or 16 weeks (group 2). Serum concentrations of total thyroxine (T₄), free thyroxine (fT₄) by equilibrium dialysis, thyroid stimulating hormone; thyrotropin (TSH), and 3,5,3′‐triiodothyronine (T₃) were measured every 4 weeks during supplementation and for 16 weeks after levothyroxine was discontinued.

Results

Mean serum concentrations of T₄ and fT₄ were significantly higher (P < .0001) and TSH was lower (P < .0001) in all dogs during levothyroxine administration compared to baseline. Mean serum concentrations of T₄, fT_4, and TSH in both groups, beginning 1 week after levothyroxine was discontinued, were significantly different (P < .01) compared to values during levothyroxine administration but not compared to baseline values (P > .3).

Conclusions and Clinical Importance

Assessing thyroid function tests 1 week after cessation of levothyroxine at 26 μg/kg once a day for up to 16 weeks will provide an accurate assessment of thyroid function in healthy euthyroid dogs.

Molecular Genetic Characterization of Thyroid Dyshormonogenesis in a French Bulldog

Background

A case of congenital hypothyroidism with goiter (CHG) in a juvenile French bulldog was identified and hypothesized to be caused by dyshormonogenesis of genetic etiology.

Objectives

To describe case management, unusual phenotypic aspects, and a CHG‐causing mutation in a French bulldog.

Animals

Thyroid tissue and blood from a CHG‐affected French bulldog and 4 normal control dogs and buccal brush samples of 125 French bulldogs were studied.

Methods

Standard clinical assessment and laboratory tests were applied. Thyroid peroxidase (TPO) iodide oxidation activity was measured in vitro, and TPO protein was assessed on Western blots. Thyroid peroxidase exons and flanking splice sites were amplified from genomic DNA and sequenced. Thyroid peroxidase cDNA was amplified from thyroid RNA and sequenced.

Results

At 9 months of age, the affected dog had signs of cretinism, but near‐normal skeletal maturation. The enlarged thyroid glands exhibited noninflammatory fibrosis and aberrant follicular organization. Thyroid peroxidase activity and immunocrossreactive protein were undetectable. There was a T>C mutation of the intron 12 splice donor consensus that caused abnormally spliced mRNA, consistent with absent TPO function. The mutant allele was not observed in 125 clinically normal French bulldogs.

Conclusions

Presumptive CHG in a French bulldog with unusual clinical presentation is described. Genetic etiology was confirmed by identifying the underlying TPO mutation.

International Veterinary Epilepsy Task Force consensus proposal: medical treatment of canine epilepsy in Europe

In Europe, the number of antiepileptic drugs (AEDs) licensed for dogs has grown considerably over the last years. Nevertheless, the same questions remain, which include, 1) when to start treatment, 2) which drug is best used initially, 3) which adjunctive AED can be advised if treatment with the initial drug is unsatisfactory, and 4) when treatment changes should be considered. In this consensus proposal, an overview is given on the aim of AED treatment, when to start long-term treatment in canine epilepsy and which veterinary AEDs are currently in use for dogs. The consensus proposal for drug treatment protocols, 1) is based on current published evidence-based literature, 2) considers the current legal framework of the cascade regulation for the prescription of veterinary drugs in Europe, and 3) reflects the authors' experience. With this paper it is aimed to provide a consensus for the management of canine idiopathic epilepsy. Furthermore, for the management of structural epilepsy AEDs are inevitable in addition to treating the underlying cause, if possible.

The role of hypothyroidism in the etiology and progression of dilated cardiomyopathy in Doberman Pinschers

BACKGROUND

Hypothyroidism and dilated cardiomyopathy (DCM) are both common diseases in Doberman Pinschers. A possible influence of hypothyroidism on the etiology and progression of DCM is controversial.

OBJECTIVES

Evaluation of the role of hypothyroidism in etiology and progression of DCM.

ANIMALS

A total of 175 Doberman Pinschers.

METHODS

In this longitudinal prospective study, echocardiography and 24-hour ambulatory ECG recordings were performed in all dogs as screening tests for DCM. Total thyroxine (TT4 ) and thyroid ultrasonography served as initial screening tests for hypothyroidism and low TT4 values were followed up by a thyroid stimulating hormone (TSH) test or free total thyroxine (fT4 )/cTSH measurements. Additionally, a follow-up study of dogs affected by both DCM and hypothyroidism under optimal treatment for hypothyroidism was conducted.

RESULTS

A total of 107 dogs were healthy, 45 dogs had DCM, 11 hypothyroidism, and 12 dogs had both DCM and hypothyroidism. TT4 values as well as the thyroid volumes were equivalent in the healthy dogs and in those with DCM. Neither ventricular premature complexes nor echocardiographic parameters differed between healthy and hypothyroid dogs. Dogs with DCM had a 2.26-fold (CI0.95 = 1.1-4.8) higher risk of also being affected by hypothyroidism. Despite optimal thyroid treatment of dogs with hypothyroidism and DCM, there was a progression of the heart disease.

CONCLUSIONS AND CLINICAL IMPORTANCE

This study did not confirm a role of hypothyroidism in the etiology or progression of DCM. Treatment of hypothyroidism did not improve the clinical outcome.

Pharmacokinetics of total thyroxine after repeated oral administration of levothyroxine solution and its clinical efficacy in hypothyroid dogs

Background

Oral levothyroxine (l‐T₄) supplementation is commonly used to treat hypothyroid dogs.

Objectives

Investigate the plasma profile and pharmacokinetics of total thyroxine (tT₄) after PO administration of a l‐T₄ solution and its clinical efficacy in hypothyroid dogs.

Animals

Ten dogs with naturally occurring hypothyroidism.

Methods

After hypothyroidism diagnosis and supplementation with l‐T₄ solution PO q24h at 20 μg/kg BW for minimum 4 weeks, the plasma profile and pharmacokinetics of tT₄ were determined over 34 hours and the clinical condition of the dogs was evaluated.

Results

Before dosing for pharmacokinetic evaluation, mean tT₄ concentration was 23 ± 9 nmol/L. l‐T₄ was absorbed rapidly (t_max, 5 hours), reaching a mean maximal tT₄ concentration of 56 ± 11 nmol/L. The apparent terminal half‐life was 11.8 hours. Clinical signs of hypothyroidism improved or resolved in all dogs after 4 weeks of treatment. The dosage of 20 μg/kg PO q24h was judged appropriate in 5 dogs, and 4 dogs required slight increases (9–16%). Twice daily treatment, with a 30% increase in dosage, was necessary for 1 dog.

Conclusions and Clinical Importance

The pharmacokinetics of l‐T₄ in hypothyroid dogs was similar to that reported in healthy euthyroid dogs. Clinical and hormonal responses to l‐T₄ solution were rapid in all dogs. The starting dosage of 20 μg/kg PO q24h was suitable for maintenance supplementation in 50% of the dogs, minor dosage modification was required in 4 other dogs, and treatment q12h was required in 1 dog.

Effects of Lersivirine on Canine and Rodent Thyroid Function

Lersivirine is a nonnucleoside reverse transcriptase inhibitor (NNRTI) being developed for the treatment of HIV-1 infection. Like other NNRTIs, lersivirine is a potent enzyme inducer in rodents capable of inducing a number of hepatic enzymes including those involved in its own metabolism. Preclinically lersivirine has been associated with hepatocellular hypertrophy and thyroid gland follicular cell hypertrophy in rats, mice, and dogs. In rodents, we show that development of thyroid hypertrophy is related to the classic mechanism, namely increased thyroxine (T4) clearance secondary to induction of uridine-diphosphoglucuronosyltransferase (UDPGT) in the liver and a resulting increase in thyroid-stimulating hormone. Similarly, lersivirine-exposed dogs exhibit a significant increase in hepatic UDPGT enzyme activity along with increased T4 clearance although clear effects on serum thyroid hormone levels were less apparent. These effects on thyroid hormonal clearance in the dog suggest that thyroid gland hypertrophy in this species is due to the same mechanism shown to occur in rodents although, as expected, dogs better adapt to these effects and therefore maintain relatively normal thyroid hormonal balance. It is also notable that the minimal thyroid follicular hypertrophy that occurs in dogs does not progress as is seen in rodents. As is the case with rodents, these adaptive changes in the dog are not considered indicative of a human health risk.

A thyroid peroxidase (TPO) mutation in dogs reveals a canid-specific gene structure

Congenital hypothyroidism with goiter (CHG) occurring as an autosomal recessive disorder is typically due to a defect of thyroid hormone synthesis (aka dyshormonogenesis). Thyroid peroxidase (TPO) is a multifunctional, heme-containing enzyme whose activity is required, and several inactivating TPO mutations causing CHG in humans and dogs have been described. Recently, two half-sib Spanish water dog (SWD) pups were diagnosed with CHG based on clinical signs, endocrine testing, and thyroid histology. TPO enzyme activity was absent, and immuno-cross-reactive TPO was undetectable in affected-dog thyroid tissue. A single guanosine insertion was observed in the first exon of the affected-dog TPO cDNA at a site not previously thought to be within the coding sequence. The insertion allele segregated with the deduced disease allele in the SWD breed and was not observed in unrelated dogs of various breeds. Comparison of the insertion site (an 8-nt poly-G tract) with the orthologous sequences of other mammalian reference genomes revealed that the octa-G tract obliterated the intron 1 splice acceptor site and the exon 2 translation initiation codon found at that position in other species. An in-frame ATG in strong Kozak consensus context was observed in the normal dog sequence 12 codons 5' of the usual mammalian start site, suggesting that dogs have lost the noncoding exon 1 demonstrated in human and mouse. A survey of TPO sequences in other carnivore species indicates that the poly-G tract necessitating an alternative translation initiation site is a canid-specific feature.

Recombinant human thyrotropin in veterinary medicine: current use and future perspectives

Recombinant human thyrotropin (rhTSH) was developed after bovine thyrotropin (bTSH) was no longer commercially available. It was approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMEA) as an aid to diagnostic follow-up of differentiated thyroid carcinoma in humans and for thyroid remnant ablation with radioiodine. In addition, rhTSH is used in human medicine to evaluate thyroid reserve capacity and to enhance radioiodine uptake in patients with metastatic thyroid cancer and multinodular goiter. Likewise, rhTSH has been used in veterinary medicine over the last decade. The most important veterinary use of rhTSH is thyroidal functional reserve testing for the diagnosis of canine hypothyroidism. Recent pilot studies performed at Ghent University in Belgium have investigated the use of rhTSH to optimize radioiodine treatment of canine thyroid carcinoma and feline hyperthyroidism. Radioiodine treatment optimization may allow a decreased therapeutic dosage of radioiodine and thus may improve radioprotection. This review outlines the current uses of rhTSH in human and veterinary medicine, emphasizing research performed in dogs and cats, as well as potential future applications.

Serum transthyretin concentration is decreased in dogs with nonthyroidal illness

BACKGROUND

Hypothyroidism in dogs is often difficult to diagnose owing to nonspecific clinical signs and laboratory test results that can be mimicked by nonthyroidal illness (NTI). Thyroxine (T4) circulates in blood mainly bound to T4-binding globulin and, to a lesser degree, transthyretin (TTR) and albumin. The concentration of total T4 depends on the concentrations of these binding proteins.

OBJECTIVES

We hypothesized that dogs with NTI and decreased serum total T4 concentrations would have decreased serum TTR concentrations. The objective of the study was to measure and compare serum TTR concentrations in healthy dogs, in dogs with NTI and low serum T4 concentrations, and in dogs with hypothyroidism.

METHODS

Assignment of dogs to 3 groups was based on physical examination and serum concentrations of T4 and TSH (mean ± SD): for healthy dogs (n = 13), T4 was 24.8 ± 3.6 nmol/L and TSH was 0.15 ± 0.08 μg/L; for dogs with NTI and low T4 (n = 20), T4 was 3.2 ± 3.0 nmol/L and TSH was 0.18 ± 0.13 μg/L; and for hypothyroid dogs (n = 19), T4 was 5.3 ± 4.3 nmol/L and TSH was 2.33 ± 1.90 μg/L). TTR concentrations in serum were determined semiquantitatively using western blot analysis.

RESULTS

Serum TTR concentration (mean ± SD) was decreased in the dogs with NTI (24.8 ± 7.9 mg/L) compared with that of hypothyroid dogs (41.1 ± 21.4 mg/L, P = .0035). Differences were not found between TTR concentrations in clinically healthy dogs (33.3 ± 10.1 mg/L) and hypothyroid dogs or dogs with NTI.

CONCLUSIONS

Serum TTR concentrations were significantly decreased in dogs with NTI and low T4 compared with concentrations in hypothyroid dogs. Additional studies should be done to determine if TTR concentrations can discriminate between dogs with NTI and low T4 and dogs with primary hypothyroidism.

Canine hypothyroidism: a review of aetiology and diagnosis

Hypothyroidism is recognised as an important endocrine disorder of dogs, and a frequent differential for numerous presenting complaints. Its diagnosis has never been straight forward as results suggestive of hypothyroidism can occur for a variety of reasons in dogs with normal thyroid function (euthyroid). As a consequence, the accurate investigation of hypothyroidism has been hindered by the potential inclusion of a number of cases not truly hypothyroid. In recent years, the development of newer diagnostic tests, e.g. free thyroxine, canine thyroid stimulating hormone, thyroglobulin autoantibodies, has significantly improved our ability to reliably differentiate hypothyroidism from other clinically similar disorders. This has led to a marked increase in our knowledge of the phenotypic, genotypic and aetiological aspects of this disorder in dogs.

Comparison of thyroid analytes in dogs aggressive to familiar people and in non-aggressive dogs

A cross-sectional study was performed in order to examine the association between canine aggression to familiar people and serum concentrations of total thyroxine (TT4), free thyroxine (fT4), thyroxine autoantibodies (T4AA), total triiodothyronine (TT3), free triiodothyronine (fT3), triiodothyronine autoantibodies (T3AA), thyroid stimulating hormone (TSH), and thyroglobulin autoantibodies (TgAA). The subjects were 31 dogs historically aggressive to familiar people and 31 dogs with no history of aggression. Behavioral evaluation and physical examination were completed for each dog in addition to a complete blood count, serum chemistry panel, TT4, fT4 by equilibrium dialysis, TT3, fT3, TgAA, T3AA, and T4AA. Significant differences were found between the two groups with respect to only T4AA, which was increased in the aggressive group, but the concentrations for both groups were within the normal reference range. There were no differences between the two groups in the thyroid analytes most commonly measured by veterinary practitioners evaluating thyroid function in dogs. The results of this study revealed no significant difference between aggressive and non-aggressive dogs in the thyroid concentrations most commonly used to diagnose canine hypothyroidism.

Alterations in thyroid hormone status in Greenland sledge dogs exposed to whale blubber contaminated with organohalogen compounds

As a model of high trophic level carnivores, sledge dogs were fed from 2 to 18 months of age with minke whale blubber containing organohalogen compounds (OHC) corresponding to 128 μg PCB/day. Controls were fed uncontaminated porcine fat. Thyroid hormone levels were assessed in 7 exposed and 7 control sister bitches (sampled at age 6-18 months) and 4 exposed and 4 control pups, fed the same diet as their mothers (sampled age 3-12 months). Lower free and total T3 and T4 were seen in exposed vs. control bitches beyond 10 months of age, and total T3 was lower through 3-12 months of age in exposed pups. A negative correlation with thyroid gland weight was significant for ΣDDT, as was a positive association with total T3 for dieldrin. This study therefore supports observational data that OHCs may adversely affect thyroid functions, and it suggests that OHC exposure duration of 10 months or more may be required for current OHC contamination levels to result in detectable adverse effects on thyroid hormone dynamics.