Serum-free thyroxine concentrations, measured by chemiluminescence assay before and after thyrotropin administration in healthy dogs, hypothyroid dogs, and euthyroid dogs with dermathopathies.

The purpose of this study was to determine the usefulness of free thyroxine (FT4) measured by chemiluminescence in evaluating thyroid function in dogs. Total thyroxine (TT4) concentration measured by radioimmunoassay (RIA) and FT4 measured by chemiluminescence were evaluated in 30 healthy dogs, 60 euthyroid dogs with concurrent dermatopathies, and 30 hypothyroid dogs before and after intravenous stimulation with 1 or 2 IU of thyrotropin (TSH). Median basal TT4 and median TT4 concentrations at 4 h post-TSH administration were not significantly different (P < 0.0001) between healthy dogs and euthyroid dogs with dermatopathies, but were significantly higher than those in hypothyroid dogs. In healthy dogs, the median TT4 concentrations at 4 and 6 h post-TSH administration were not significantly different. Median basal FT4 and median FT4 concentrations at 4 h post-TSH administration in healthy dogs were significantly lower (P < 0.0001) than those in euthyroid dogs with dermatopathies, but significantly higher than the same parameters in hypothyroid dogs. There was a significant difference between the median FT4 concentrations at 4 h post-TSH administration and median basal FT4 concentrations for healthy dogs and euthyroid dogs with dermatopathies, but not for hypothyroid dogs. Lastly, in healthy dogs, median FT4 concentrations at 4 and 6 h post-TSH administration were not significantly different. Free thyroxine measured by chemiluminescence was highly correlated (P < 0.0001; Spearman r = 0.91) with FT4 measured by the reference method for free hormone analysis, namely, equilibrium dialysis, when sera from 56 dogs were used.     

Evaluation of recombinant human thyroid-stimulating hormone to test thyroid function in dogs suspected of having hypothyroidism

OBJECTIVE: To evaluate the use of recombinant human (rh) thyroid-stimulating hormone (TSH) in dogs with suspected hypothyroidism. ANIMALS: 64 dogs with clinical signs of hypothyroidism. PROCEDURES: Dogs received rhTSH (75 microg/dog, IV) at a dose independent of their body weight. Blood samples were taken before and 6 hours after rhTSH administration for determination of total serum thyroxine (T(4)) concentration. Dogs were placed into 1 of 3 groups as follows: those with normal (ie, poststimulation values indicative of euthyroidism), unchanged (ie, poststimulation values indicative of hypothyroidism; no thyroid gland stimulation), or intermediate (ie, poststimulation values between unchanged and normal values) post-TSH T(4) concentrations. Serum canine TSH (cTSH) concentration was determined in prestimulation serum (ie, before TSH administration). RESULTS: 14, 35, and 15 dogs had unchanged, normal, and intermediate post-TSH T(4) concentrations, respectively. Basal T(4) and post-TSH T(4) concentrations were significantly different among groups. On the basis of basal serum T(4) and cTSH concentrations alone, 1 euthyroid (normal post-TSH T(4), low basal T(4), and high cTSH concentrations) and 1 hypothyroid dog (unchanged post-TSH T(4) concentration and low to with-in reference range T(4) and cTSH concentrations) would have been misinterpreted as hypothyroid and euthyroid, respectively. Nine of the 15 dogs with intermediate post-TSHT(4) concentrations had received medication known to affect thyroid function prior to the test, and 2 of them had severe nonthyroidal disease. CONCLUSIONS AND CLINICAL RELEVANCE: The TSH-stimulation test with rhTSH is a valuable diagnostic tool to assess thyroid function in selected dogs in which a diagnosis of hypothyroidism cannot be based on basal T(4) and cTSH concentrations alone.     

Serum total thyroxine and thyroid stimulating hormone concentrations in dogs with behavior problems

The aim of this case controlled study was to determine whether dogs with behavioral problems have evidence of abnormal thyroid function on routine screening tests for hypothyroidism. The hypothesis of the study was that thyroid function, as assessed by serum total thyroxine (TT4) and serum thyroid stimulating hormone (thyrotropin) (TSH) concentrations, is normal in most dogs with behavioral problems. Concentrations of TT4 and TSH in 39 dogs with behavior problems presenting to a veterinary behavior referral clinic (abnormal behavior group), were compared with TT4 and TSH concentrations in 39 healthy control dogs without behavior problems presenting to 5 community veterinary practices (control group). Dogs in the control group were matched for age and breed with the abnormal behavior group. Dogs with behavioral problems had higher TT4 concentrations than dogs without behavioral problems (t-test: t = 2.77, N = 39, P = 0.009), however none of the TT4 values were outside the reference range. There was no significant difference in TSH concentration between the 2 groups. Two dogs with behavior problems and 1 dog without behavior problems had results suggestive of hypothyroidism. All other dogs were considered to be euthyroid. There was no evidence to support a diagnosis of hypothyroidism in the majority of dogs with behavior problems in this study. The higher concentration of TT4 in dogs with behavior problems suggests, however, that alteration in thyroid hormone production or metabolism may occur in some dogs with behavior problems. Further studies that include additional indicators of thyroid status such as serum total triiodothyronine, serum, free thyroxine, and anti-thyroid antibody concentrations are necessary to further evaluate the significance of this finding.     

Comparison of colloid,thyroid follicular epithelium,and thyroid hormone concentrations in healthy and severely sick dogs

OBJECTIVES: To compare serum concentrations of total thyroxine (TT4), free thyroxine (fT4), and thyroid-stimulating hormone (TSH), as well as measures of thyroid follicular colloid and epithelium, between groups of healthy dogs and severely sick dogs. DESIGN: Cross-sectional study. ANIMALS: 61 healthy dogs and 66 severely sick dogs. PROCEDURE: Serum samples were obtained before euthanasia, and both thyroid lobes were removed immediately after euthanasia. Morphometric analyses were performed on each lobe, and serum TT4, fT4, and TSH concentrations were measured. RESULTS: In the sick group, serum TT4 and fT4 concentrations were less than reference range values in 39 (59%) and 21 (32%) dogs, respectively; only 5 (8%) dogs had high TSH concentrations. Mean serum TT4 and fT4 concentrations were significantly lower in the sick group, compared with the healthy group. In the healthy group, a significant negative correlation was found between volume percentage of colloid and TT4 or fT4 concentrations, and a significant positive correlation was found between volume percentage of follicular epithelium and TT4 or fT4 concentrations. A significant negative correlation was observed between volume percentages of colloid and follicular epithelium in both groups. CONCLUSIONS AND CLINICAL RELEVANCE: TT4 and fT4 concentrations are frequently less than reference range values in severely sick dogs. Therefore, thyroid status should not be evaluated during severe illness. The absence of any significant differences in mean volume percentages of follicular epithelium between healthy and severely sick dogs suggests that these 2 groups had similar potential for synthesizing and secreting thyroid hormones.     

Evaluation of serum free thyroxine and thyrotropin concentrations in the diagnosis of canine hypothyroidism

Canine thyroid-stimulating hormone (cTSH), total thyroxine (T4) and free T4 by equilibrium dialysis (fT4d) were measured in serum samples from 107 dogs with clinical signs suggestive of hypothyroidism in which the diagnosis was either confirmed (n = 30) or excluded (n = 77) by exogenous TSH response testing. Median serum total T4 and fT4d concentrations were significantly lower and cTSH significantly higher (P < 0.001) in hypothyroid compared with euthyroid dogs. Differential positive rate analysis determined optimal cut-off values of less than 14.9 nmol/litre (total T4), less than 5.42 pmol/litre (fT4d), greater than 0.68 ng/ml (cTSH), less than 17.3 (T4 to cTSH ratio), and less than 7.5 (fT4d to cTSH ratio) for hypothyroidism. These had a sensitivity and specificity of 100 and 75.3 per cent, 80 and 93.5 per cent, 86.7 and 81.8 per cent, 86.7 and 92.2 per cent, and 80 and 97.4 per cent, respectively, for diagnosing hypothyroidism. Corresponding areas under the receiver operating characteristic curves were 0.92, 0.93, 0.87, 0.93 and 0.93. Unexpectedly low cTSH values in hypothyroid dogs may have resulted from concurrent non-thyroidal illness. Unexpectedly high serum cTSH values in the euthyroid dogs might have resulted from recovery from illness or concurrent potentiated sulphonamide therapy. Measurement of endogenous cTSH concentration is a valuable diagnostic tool for canine hypothyroidism if used in association with assessment of T4. Estimation of fT4d added only limited additional information over total T4 measurement.     

Effects of administration of a low dose of frozen thyrotropin on serum total thyroxine concentrations in clinically normal dogs.

Thyroid function was evaluated in 18 healthy dogs by thyrotropin (TSH) stimulation. Two dose regimens were used in each dog: 0.1 IU/kg body weight of freshly reconstituted lyophilized TSH and 1 IU/dog of previously frozen and stored TSH (up to 200 days), both given intravenously. Blood samples were collected prior to and at four and six hours after TSH administration. Serum was evaluated for total thyroxine concentrations by radioimmunoassay. All dogs were classified as euthyroid on the basis of response to 0.1 IU/kg body weight of freshly reconstituted TSH at four and six hours. The 1 IU dose of TSH, previously frozen for up to 200 days, induced increases in serum total thyroxine concentration over baseline at four and six hours that were not significantly different from those resulting from the use of the higher dose of fresh TSH. In all test groups, there were no statistically significant differences between total thyroxine concentrations at four and six hours post-TSH administration. It was concluded that an adequate TSH response can be achieved with the use of 1 IU of TSH/dog for clinically normal dogs between 29.0 kg and 41.6 kg body weight, even if this TSH has been frozen at -20 degrees C for up to 200 days. Further, blood collection can be performed at any time between four and six hours. Similar studies are needed to evaluate this new protocol in hypothyroid dogs and euthyroid dogs suffering nonthyroidal systemic diseases.     

Effects of moderate to severe osteoarthritis on canine thyroid function

Several nonthyroidal illnesses in euthyroid dogs can affect the results of thyroid function testing, making interpretation of the results more difficult with an increased risk of overdiagnosing hypothyroidism. The purpose of this study was to evaluate the effect of chronic, moderate to severe, osteoarthritis on canine thyroid function. Ninety-six, healthy, client-owned dogs, 65 of which were suffering from moderate to severe osteoarthritis and 31 euthyroid dogs without any physical evidence of osteoarthritis, were used in this study. Blood samples were collected to evaluate serum basal total thyroxine (TT4), free thyroxine (FT4), and thyrotropin (TSHc) concentrations. Basal serum TT4 concentration was not affected by osteoarthritis in dogs. Mild, but statistically significant, differences were noticed in FT4 and TSHc concentrations among the 2 groups. However, this had limited clinical relevance, since virtually all values were within their reference range, and no dogs would have been misdiagnosed as hypothyroid. Therefore, based on the results of our study, osteoarthritis does not need to be considered a factor influencing thyroid function evaluation in dogs.     

Serum total thyroxine, total triiodothyronine, free thyroxine, and thyrotropin concentrations in dogs with nonthyroidal disease

OBJECTIVE: To determine whether nonthyroidal disease of various causes and severity is associated with abnormalities in baseline serum concentrations of total thyroxine (T4), triiodothyronine (T3), free T4, or thyrotropin (thyroid-stimulating hormone [TSH]) in dogs believed to be euthyroid. DESIGN: Case-control study. ANIMALS: 223 dogs with confirmed nonthyroidal diseases and presumptive normal thyroid function, and 150 clinically normal dogs. PROCEDURE: Serum total T4, total T3, free T4, and TSH concentrations were measured in dogs with confirmed nonthyroidal disease. Reference ranges for hormone concentrations were established on the basis of results from 150 clinically normal dogs. RESULTS: In dogs with nonthyroidal disease, median serum concentrations of total T4, total T3, and free T4 were significantly lower than those in clinically normal dogs. Median serum TSH concentration in sick dogs was significantly greater than that of clinically normal dogs. When stratified by severity of disease (ie, mild, moderate, and severe), dogs with severe disease had low serum concentrations of total T4, total T3, or free T4 more commonly than did dogs with mild disease. In contrast, serum TSH concentrations were more likely to remain within the reference range regardless of severity of disease. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that serum total T4, free T4, and total T3 concentrations may be low (ie, in the hypothyroid range) in dogs with moderate to severe nonthyroidal disease. Serum TSH concentrations are more likely to remain within the reference range in sick dogs.     

Serum concentrations of thyroxine, 3,5,3'-triiodothyronine, thyrotropin, and prolactin in dogs before and after thyrotropin-releasing hormone administration

Serum concentrations of thyrotropin (TSH), prolactin, thyroxine, and 3,5,3'-triiodothyronine in 15 euthyroid dogs and 5 thyroidectomized and propylthiouracil-treated dogs after thyrotropin-releasing hormone (TRH) administration were measured. Although thyroidectomized and propylthiouracil-treated dogs had higher (P less than 0.01) base-line concentrations of TSH in serum than did euthyroid dogs, concentrations of TSH after TRH administration varied at 7.5, 15, and 30 minutes with 14 of 45 samples obtained from healthy dogs having lower TSH concentrations than before TRH challenge. Similarly, concentrations of 3,5,3'-triiodothyronine in the serum of euthyroid dogs 4 hours after TRH administration were similar (P less than 0.05) to concentrations before TRH challenge. Although the mean concentration of thyroxine in serum was elevated (P less than 0.05) 4 hours after administration of TRH to euthyroid animals, as compared with base-line levels, the individual response was variable with concentrations not changing or decreasing in 4 dogs. Therefore, the TRH challenge test as performed in the current investigation was of limited value in evaluating canine pituitary gland function. Although mean concentrations of TSH in serum were higher (P less than 0.05) in euthyroid dogs after TRH administration, the response was too variable among individual animals for accurate evaluation of pituitary gland function. Concentrations of prolactin in the sera of dogs after TRH administration, confirmed previous reports that exogenously administered TRH results in prolactin release from the canine pituitary and indicated that the TRH used was biologically potent.     

Autoantibodies against thyroid hormones and their influence on thyroxine determination with chemiluminescence immunoassay in dogs

Autoantibodies against thyroxin (T4AA) and triiodothyronine (T3AA) are present in dogs with autoimmune thyroiditis and have been reported to interfere with immunoassays. The objectives of this study were to determine the frequency of autoantibodies and to determine whether interference occurs by T4AA, using a non-immunological method (high performance liquid chromatography, HPLC) for thyroxin (T4) measurement. Based on clinical symptoms, T4 and thyroid stimulating hormone (TSH) concentration, 1,339 dogs were divided into six groups: Group 1: hypothyroid (n = 149); Group 2: subclinical thyroiditis (n = 110); Group 3: suspicious for non thyroidal illness (n = 691); Group 4: biochemical euthyroid (n = 138); Group 5: hypothyroid dogs under substitution therapy (n = 141); Group 6: healthy dogs (n = 110). The incidence of T4AA and T3AA, determined using radiometric assay, was low (0.5% and 3.8%) and higher in hypothyroid dogs compared to dogs suspicious for hypothyroidism (Group 2-4) (p<0.05). T4AA was not detected in dogs with normal T4 and elevated TSH. T4 concentrations of T4AA positive samples determined using HPLC were comparable to results obtained by chemiluminescence immunoassay. These findings indicate that the probability of interference of T4AA leading to falsely elevated T4 concentration in the T4 assay seems to be low.     

Serum thyroid hormone concentrations and thyrotropin responsiveness in dogs with generalized dermatologic disease.

Fifty-eight dogs with generalized dermatologic disease that had not been given glucocorticoids systemically or topically within 6 weeks of entering the study were evaluated for thyroid function by use of the thyrotropin-response test. Dogs were classified as euthyroid or hypothyroid on the basis of test results and response to thyroid hormone replacement therapy. Baseline serum thyroxine (T4), free T4 (fT4), and triiodothyronine (T3) concentrations were evaluated in the 58 dogs. Serum T4, fT4, and T3 concentrations were evaluated in 200 healthy dogs to establish normal values. Hormone concentrations were considered low if they were less than the mean -2 SD of the values for control dogs. Specificity of T4 and fT4 concentrations was 100% in predicting hypothyroidism; none of the euthyroid dogs with generalized skin disease had baseline serum T4 or fT4 concentration in the low range. Sensitivity was better for fT4 (89%) than for T4 (44%) concentration. Significant difference was not observed in serum T4 and fT4 concentrations between euthyroid dogs with generalized skin disease and healthy control dogs without skin disease. Serum T3 concentration was not accurate in predicting thyroid function; most of the euthyroid and hypothyroid dogs with skin disease had serum T3 concentration within the normal range.     

Serial thyroid hormone concentrations in healthy euthyroid dogs, dogs with hypothyroidism, and euthyroid dogs with atopic dermatitis.

Serum thyroxine (T4) and 3,5,3'-triiodothyronine (T3) concentrations were determined every 3 h for 12 h beginning at 8 a.m. in 20 healthy euthyroid dogs, 19 dogs with hypothyroidism, and 18 euthyroid dogs with atopic dermatitis. Status of thyroid function was based on history, physical findings, results of thyrotropin response testing, and requirement for thyroid hormone replacement therapy. Mean serum T4 and T3 concentrations did not vary significantly between blood samplings within each of the three groups of dogs. Between groups of dogs, mean serum T4 concentration was significantly (P less than 0.05) higher at each blood sampling time in healthy euthyroid dogs and euthyroid dogs with atopic dermatitis when compared to dogs with hypothyroidism. There was no significant difference in mean serum T4 concentration at any blood sampling time between healthy euthyroid dogs and euthyroid dogs with atopic dermatitis or in mean serum T3 concentrations at any blood sampling time between any of the three groups of dogs. Random fluctuation in serum T4 and T3 concentrations was found in dogs in all three groups. Random fluctuations were more common with serum T3 versus T4 concentrations. Consequently, sensitivity (0.88 versus 0.52), specificity (0.73 versus 0.45), predictive value for a positive test (0.75 versus 0.32), predictive value for a negative test (0.87 versus 0.65), and accuracy (0.80 versus 0.47) were better for serum T4 concentration than serum T3 concentration, respectively, when all blood samples were analysed. Measurement of serum T4 concentration was more accurate than serum T3 concentration in assessing the status of thyroid gland function.     

Evaluation of thyroid function in obese dogs and in dogs undergoing a weight loss protocol

Obesity and weight loss have been shown to alter thyroid hormone homeostasis in humans. In dogs, obesity is the most common nutritional problem encountered and weight loss is the cornerstone of its treatment. Therefore, it is important to clarify how obesity and weight loss can affect thyroid function test results in that species. The objectives of this study were to compare thyroid function in obese dogs and in lean dogs and to explore the effects of caloric restriction and weight loss on thyroid hormone serum concentrations in obese dogs. In the first experiment, 12 healthy lean beagles and 12 obese beagles were compared. Thyroid function was evaluated by measuring serum concentrations of total thyroxine (TT4), free thyroxine (FT4), total triiodothyronine (TT3), thyrotropin (TSH), and reverse triiodothyronine (rT3) as well as a TSH stimulation test using 75 microg i.v. of recombinant human TSH. In the second experiment, eight obese beagles were fed an energy-restricted diet [average 63% maintenance energy requirement (MER)] until optimal weight was obtained. Blood samples for determination of TT4, FT4, TT3, TSH and rT3, were taken at the start and then weekly during weight loss. Only TT3 and TT4 serum concentrations were significantly higher in obese dogs as compared to lean dogs. In the second experiment, weight loss resulted in a significant decrease in TT3 and TSH serum concentrations. Thus obesity and energy restriction significantly alter thyroid homeostasis in dogs, but the observed changes are unlikely to affect interpretation of thyroid function test results in clinics.     

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.     

Thyroid-Stimulating Hormone Stimulation Tests in Cardiomyopathic Doberman Pinschers: A Retrospective Study

Thyroid-stimulating hormone (TSH) response tests were performed in 152 Doberman Pinschers. Seventy-nine dogs had cardiomyopathy (46 were in congestive heart failure [CHF] and 33 were not in CHF). Seventy-three dogs were presented for noncardiac problems (15 with skin disease, 21 with neurologic disease, 20 with internal medicine disorders, and 17 with other problems), although some may have had cardiomyopathy. The TSH response test results in the cardiomyopathic group were interpreted as normal or euthyroid-sick in 45 (57%) dogs, abnormal in 23 (29%) dogs, and equivocal in 11 (14%) dogs. The prevalence of hypothyroidism in the CHF and non-CHF cardiomyopathy groups was not different. Among the dogs presented for noncardiac problems, 27 (37%) were assessed as normal or euthyroid-sick, 29 (40%) as hypothyroid, and 17 (23%) as equivocal. No significant differences were found in the prevalence of hypothyroid test results among the subgroups of these dogs. The prevalence of hypothyroidism was not higher in the cardiomyopathic group compared to the other group, and 63 and 49% of cardiomyopathic dogs with or without CHF, respectively, tested as either euthyroid or euthyroid-sick.     

Thyroid sonography as an effective tool to discriminate between euthyroid sick and hypothyroid dogs

The diagnosis of canine hypothyroidism and its differentiation from euthyroid sick syndrome still is a major diagnostic challenge. In this study, ultrasonography was shown to be an effective tool for the investigation of thyroid gland diseases. Healthy control dogs (n = 87), dogs with euthyroid sick syndrome (n = 26), thyroglobulin autoantibody-positive (TgAA-positive, n = 30) hypothyroid dogs, and TgAA-negative (n = 23) hypothyroid dogs were examined by thyroid ultrasonography. Maximal cross sectional area (MCSA), thyroid volume, and echogenicity were measured. Statistical analysis identified highly significant (P < .001) differences between euthyroid and hypothyroid dogs both in thyroid volume and in MCSA, whereas no significant differences in thyroid size were detected between healthy euthyroid dogs and dogs with euthyroid sick syndrome. In euthyroid and euthyroid sick dogs, parenchymal echotexture was homogeneous and hyperechoic, whereas relative thyroid echogenicity of both TgAA-positive and TgAA-negative hypothyroid dogs was significantly lower (P < .001). When using arbitrarily chosen cutoff values for relative thyroid volume, MCSA, and echogenicity, thyroid volume especially was found to have highly specific predictive value for canine hypothyroidism. In summary, the data reveal that thyroid sonography is an effective ancillary diagnostic tool to differentiate between canine hypothyroidism and euthyroid sick syndrome.     

Use of recombinant human thyroid-stimulating hormone for thyrotropin stimulation test in euthyroid dogs

The purpose of this study was to evaluate the effects of the recombinant human thyroid-stimulating hormone (rhTSH) on serum total thyroxine (TT4) concentration in euthyroid dogs. Six healthy beagle dogs were used in each of the 3 phases of this study. Phase I: thyroid-stimulating hormone response tests were performed by using a total dose of 25 micrograms, 50 micrograms, and 100 micrograms of rhTSH, administered intravenously. Phases II and III: thyroid-stimulating hormone response tests were performed by using 50 micrograms of rhTSH administered by intramuscular and subcutaneous routes, respectively. In each phase and following all the administered doses of rhTSH, an increase in the serum TT4 concentration was noted, although it was not always significant. For phase I, there was a significant increase in serum TT4 concentrations. Based on this study, 50 micrograms was judged to be the optimal intravenous dose of rhTSH. For phases II and III, there was no significant increase in serum TT4 after the administration of rhTSH. Results of this study suggest that rhTSH could be a good substitute for bovine TSH, when used by the intravenous route, for the TSH stimulation test in dogs. Further studies are required to confirm its clinical usefulness.     

Short-term influence of prednisone and phenobarbital on thyroid function in euthyroid dogs.

The short-term effects of prednisone and phenobarbital on serum total thyroxine (tT4), free thyroxine (fT4), and thyroid stimulating hormone (TSH) were evaluated in euthyroid dogs. Twenty-six beagles were randomly divided into 3 groups receiving, respectively, a placebo, prednisone (1.2 to 2 mg/kg body weight, per os, every 12 hours for 3 weeks), or phenobarbital (1.8 to 3 mg/kg body weight for 1 week, then 2.7 to 4.5 mg/kg body weight, per os, every 12 hours for 2 weeks). Blood samples taken over a 6-week period were assayed for serum tT4, fT4, and TSH. Phenobarbital therapy in our study did not affect serum tT4, fT4, or TSH concentrations. Prednisone therapy, however, significantly decreased serum tT4 and fT4, but did not affect serum TSH concentrations.     

Canine serum thyroglobulin autoantibodies in health, hypothyroidism and non-thyroidal illness

Thyroglobulin autoantibody (TGAA) was measured in serum from dogs with hypothyroidism (n = 42), non-thyroidal illness (NTI) (n = 77) and clinically healthy dogs (n = 70) using a commercially available enzyme immunoassay kit. Precision studies were consistent with good intra-assay and inter-assay repeatability. TGAA positive results occurred in 15 of the 42 (36 per cent) hypothyroid and four healthy dogs of the remaining 147 animals resulting in a lower incidence of false positive results than obtained with previous TGAA assays. The presence of TGAA was not influenced by age, sex, neutering or pedigree status. Of the four apparently healthy TGAA -positive dogs, two had additional clinicopathological evidence of hypothyroidism. TGAA was positive in 43 per cent of hypothyroid dogs with unexpectedly normal serum c TSH concentrations and was particularly useful in the classification of these cases.     

Effect of 131I-induced hypothyroidism on indices of reproductive function in adult male dogs

Hypothyroidism has been cited as a cause of infertility, abnormal semen quality, and poor libido in people and animals. The purpose of this study was to evaluate the effect of hypothyroidism on variables indicative of reproductive function in adult male dogs. Nine normal dogs were randomly assigned to 2 groups. Hypothyroidism was induced with 131I in 6 dogs. Three dogs remained untreated, normal, and euthyroid. Thyroid hormone concentrations, body weight, clinical signs, and reproductive function were determined for each dog every 3 months for 2 years. Reproductive function was assessed by determining daily sperm output, total scrotal width, spermatozoal motility and morphology, libido, and serum testosterone and luteinizing hormone concentration responses to exogenous gonadotropin-releasing hormone. The 131I-treated dogs developed clinical and laboratory signs of hypothyroidism. In the hypothyroid dogs, serum concentrations of thyroid hormones were consistently below the reference range and were significantly lower than that in the euthyroid dogs. There was no difference in reproductive function between the hypothyroid and euthyroid dogs. The results of this study show that 131I-induced hypothyroidism does not affect indices of reproductive function in adult male dogs.