Predicting soil pH changes in response to application of urea and sheep urine.

Volatilization of NH3 following urea application or livestock urine deposition can result in significant loss of N to the environment. Urea hydrolysis to NH4 + results in an increase in pH, which in turn promotes transformation of NH4 + to NH3 . Accurately predicting changes in soil pH following urea (or urine) application will allow successful simulation of NH3 volatilization. The magnitude of the pH change depends on the soil's pH buffering capacity (pHBC). However, as actual pHBC values are not generally available, pHBC proxies (e.g., cation exchange capacity) have been used in modeling studies. In a 34-d laboratory incubation study, we measured soil pH and mineral N (NH4 + and NO3 - ) following a large application of urea (800 mg N kg-1 soil) to four soils with a range of pHBC values. In a second incubation, pH changes and mineral N dynamics were monitored in soil treated with sheep urine (773 mg N kg-1 soil) in the absence and presence of the nitrification inhibitor dicyandiamide. In both incubations, pH changes associated with urea hydrolysis and subsequent nitrification of NH4 + were predicted well using measured pHBC data. Our results confirmed that pHBC is base-type dependent (values greater when measured using KOH than NH4 OH). Soil pHBC is easily measured, and the use of a measured value (determined using NH4 OH) can improve model simulations of pH in the field and, potentially, lead to improved estimates of NH3 loss from animal-deposited urine patches and urea-treated soil.

Short-term biological variation of serum thyroid hormones concentrations in clinically healthy cats.

Thyroid disease is common in cats, but little is known about the biologic variability of serum thyroid hormone concentrations and its impact on diagnostic utility in either healthy cats or cats with thyroid disease. The purpose of this study was to determine the biological variation, index of individuality, and reference change values for thyroid hormones and thyroid-stimulating hormone (TSH) in clinically healthy cats. Serum samples for analysis of total thyroxine (T4), triiodothyronine (T3), free T4 by dialysis, and TSH were obtained weekly for 6 wk from 10 healthy cats, then frozen until single-batch analyzed. Data were evaluated for outliers, and we determined the CV within individual cats (CVI) and between individual cats (CVG) for each hormone and the variation between duplicates or analytical variation (CVA). The index of individuality and reference change values for each hormone were then calculated. Serum concentrations of total T4, free T4, T3, and TSH all showed greater variation between cats (CVG) than within cats (CVI). Total and free T4 had an intermediate index of individuality (1.1 and 1.2, respectively), suggesting that these hormones would be best evaluated by a combination of their population-based reference intervals and reference change values. Serum TSH concentrations had high index of individuality (1.8), suggesting this hormone would be best evaluated with reference change values rather than the population-based reference interval. Total T3 also had a high calculated index of individuality (1.8); however, T3 had high ratio of analytical variation (CVA) to within cat variation (CVI), so RCV could not be accurately calculated. This study demonstrates that clinically normal cats show considerable interindividual biological variation in serum thyroid hormone and TSH concentrations, whereas the intraindividual variability in hormone concentrations is much narrower. This suggests that for all serum thyroid hormones, but especially serum TSH and T3 concentrations, comparing individual cat's hormone results to a population-based reference interval may be misleading, especially in those with early or subclinical thyroid disease. Clinicians might improve the diagnosis of feline thyroid disease by establishing baseline concentrations of T4, free T4, T3, and TSH for individual cats (ideally when healthy) and applying reference change values to subsequent measurements.

Evaluation of Serum Symmetric Dimethylarginine Concentration as a Marker for Masked Chronic Kidney Disease in Cats With Hyperthyroidism.

BACKGROUND: Hyperthyroidism can complicate (mask) the diagnosis of chronic kidney disease (CKD) because it increases glomerular filtration rate and decreases body muscle mass, both of which can lower serum creatinine concentrations. Currently, there is no clinical test that can reliably predict which hyperthyroid cats have concurrent azotemic CKD that will become apparent after treatment of the hyperthyroidism. OBJECTIVES: To investigate serum symmetric dimethylarginine (SDMA) concentration as a potential marker of masked azotemia in untreated hyperthyroid cats. ANIMALS: Two hundred and sixty-two hyperthyroid cats and 206 aged-matched, clinically normal cats. METHODS: Prospective study. We measured creatinine, urea nitrogen, SDMA, T4 , and TSH concentrations before and 1, 3, and 6 months after treatment with radioiodine (131 I) and classified 131 I-treated cats as azotemic or nonazotemic based on persistent, post-treatment creatinine concentrations >2.1 mg/dL. Groups were compared via nonparametric tests, and diagnostic accuracy was determined by receiver operating characteristic analysis and logistic regression. RESULTS: No hyperthyroid cats were azotemic before treatment, but 42 (16%) became azotemic when rechecked at 4-8 months (median, 6 months) after 131 I treatment; of these, 14 had high SDMA concentrations before treatment. As a diagnostic test for pre-azotemic (masked) CKD in untreated hyperthyroid cats, SDMA showed a sensitivity of 33.3% and specificity of 97.7%. CONCLUSIONS AND CLINICAL IMPORTANCE: Finding a high serum SDMA concentration in a hyperthyroid cat can help predict development of azotemia after treatment. The test has high diagnostic test specificity (few false-positive results) but relatively low sensitivity (fails to predict azotemia in most hyperthyroid cats).

Serum thyroxine and thyroid-stimulating hormone concentration in hyperthyroid cats that develop azotaemia after radioiodine therapy.

OBJECTIVES: The objectives of this study were to determine which serum thyroid hormone test best identifies iatrogenic hypothyroidism in cats that develop azotaemia after radioiodine treatment and to determine which thyroid test best differentiates these azotaemic, hypothyroid cats from azotaemic, radioiodine-treated euthyroid cats, as well as from azotaemic cats with chronic kidney disease and no history of thyroid disease. MATERIALS AND METHODS: A total of 42 hyperthyroid cats that developed azotaemia (serum creatinine ê220 µmol/L) after radioiodine treatment had serum concentrations of thyroxine and free thyroxine by dialysis and thyroid--stimulating hormone measured at 3, 6 and 12 months. Iatrogenic hypothyroidism was confirmed (n=28) or excluded (n=14) on the basis of thyroid scintigraphy. A total of 14 cats with chronic kidney disease and 166 clinically normal cats underwent similar serum thyroid testing and scintigraphy. RESULTS: Concentrations of thyroxine and free thyroxine were lower and thyroid-stimulating hormone higher in hypothyroid cats than in all three groups of euthyroid cats (P<0·0001). Of the hypothyroid cats, thyroxine and free thyroxine concentrations were low in 15 (53·6%) and seven (25%), respectively. Low serum thyroxine and free thyroxine concentrations were also detected in seven (50%) and two (14·3%) of the cats with chronic kidney disease. Thyroid-stimulating hormone concentrations were elevated in all hypothyroid cats but remained within the reference interval in all three groups of euthyroid cats. Serum thyroid--stimulating hormone had a higher test sensitivity and specificity than either thyroxine or free thyroxine concentration. CLINICAL SIGNIFICANCE: The finding of high serum thyroid-stimulating hormone concentrations best identifies feline iatrogenic hypothyroidism and differentiates it from non-thyroidal illness syndrome in cats that develop azotaemia after treatment.

Thyroid Cysts in Cats: A Retrospective Study of 40 Cases.

BACKGROUND: Thyroid cysts are rare in cats and poorly documented. OBJECTIVES: To report distinguishing clinical features and treatment responses of cats with thyroid cysts. ANIMALS: Forty client-owned cats. METHODS: Retrospective review of medical records for cats with thyroid cysts confirmed by scintigraphy, ultrasound, magnetic resonance imaging, or necropsy at 4 referral centers between 2005 and 2016. Signalment, clinical findings, diagnostic testing, treatment, and outcome were recorded. RESULTS: Cats ranged in age from 8 to 20 years with no apparent breed or sex predilection. 37 of 40 (93%) cats were hyperthyroid (duration, 1-96 months). Clinical findings included palpable neck mass (40/40, 100%), weight loss (15/40, 38%), dysphagia (8/40, 20%), decreased appetite (5/40, 13%), and dyspnea (4/40, 10%). Cysts were classified as small (≤8 cm3 ) in 16 (40%) and large (>8 cm3 ) in 24 (60%) cats. Of 25 cats treated with radioiodine, hyperthyroidism resolved in 23 (92%), whereas thyroid cysts resolved in 12 (50%). Radioiodine treatment resolved small cysts in 8 of 13 (62%) cats and large cysts in 4 of 11 (36%) cats. Eight cats, including 2 euthyroid cats, underwent thyroid-cystectomy; 3 with bilateral thyroid involvement were euthanized postoperatively for hypocalcemia. Excised cystic thyroid masses were identified as cystadenoma (4) and carcinoma (4). CONCLUSIONS AND CLINICAL IMPORTANCE: Thyroid cysts are encountered in hyperthyroid and euthyroid cats with benign and malignant thyroid tumors. Radioiodine treatment alone inconsistently resolved thyroid cysts. Thyroid-cystectomy could be considered in cats with unilateral thyroid disease or when symptomatic cysts persist despite successful radioiodine treatment of hyperthyroidism.

Efficacy of Low-dose (2 millicurie) versus Standard-dose (4 millicurie) Radioiodine Treatment for Cats with Mild-to-Moderate Hyperthyroidism.

BACKGROUND: Radioiodine (131 I) is effective treatment for hyperthyroidism in cats, but optimal dose to restore euthyroidism without inducing hypothyroidism is unclear. Treatment-induced hypothyroidism can lead to azotemia and reduced duration of survival. OBJECTIVE: To compare efficacy and short-term outcomes of low-dose 131 I versus higher, standard-dose 131 I as treatment for hyperthyroidism. ANIMALS: A total of 189 client-owned cats undergoing 131 I treatment for mild-to-moderate hyperthyroidism (serum T4 ≥ 4.0 µg/dL and <13.0 µg/dL). METHODS: Prospective, nonrandomized, cohort study comparing treatment with either low-dose (2 mCi, n = 150) or standard-dose (4 mCi, n = 39) 131 I. Serum T4 , thyroid-stimulating hormone (TSH), and creatinine concentrations were measured after 1, 3, and 6 months to determine persistent hyperthyroidism, overt hypothyroidism (low T4 , high TSH), subclinical hypothyroidism (normal T4 , high TSH), and azotemia. RESULTS: There was no significant difference in prevalence of cats with persistent hyperthyroidism between standard- and low-dose treatment groups at 3 (0% versus 5.3%; P = .34) and 6 (0% versus 3.3%; P = .51) months. Overt (18% versus 1%; P = .0005) or subclinical (46% versus 21%; P = .004) hypothyroidism was more common in cats at 6 months after standard-dose 131 I. No difference in incidence of azotemia existed between groups, but cats treated with standard-dose 131 I had higher creatinine concentrations (P < .05) and higher percent rises in creatinine (P < .0001). CONCLUSIONS AND CLINICAL IMPORTANCE: Low-dose 131 I is safe and effective for cats with mild-to-moderate hyperthyroidism, as evidenced by a cure rate of >95% with reduced frequency of iatrogenic hypothyroidism and azotemia.

Evaluation of Body Weight, Body Condition, and Muscle Condition in Cats with Hyperthyroidism.

BACKGROUND: The contribution of fat loss versus muscle wasting to the loss of body weight seen in hyperthyroid cats is unknown. OBJECTIVES: To investigate body weight, body condition score (BCS), and muscle condition score (MCS) in hyperthyroid cats. ANIMALS: Four hundred sixty-two cats with untreated hyperthyroidism, 117 of which were reevaluated after treatment. METHODS: Prospective cross-sectional and before-after studies. Untreated hyperthyroid cats had body composition evaluated (body weight, BCS, and MCS). A subset of these cats were reevaluated 3-12 months after treatment when euthyroid. RESULTS: Pretreatment body weight (median, 4.36 kg; IQR, 3.5 to 5.2 kg) was lower than premorbid weight (5.45 kg; IQR, 4.6 to 6.4 kg, P < .0001) recorded 1-2 years before diagnosis. 154 (35.3%) cats were thin or emaciated; 357 (77.3%) had loss of muscle mass. Cats showed increases in body weight (median, 4.1 kg to 5.0 kg), BCS (median, 3/5 to 3.5/5), and MCS (2/3 to 3/3) after treatment (P < .001), but mild-to-moderate muscle wasting persisted in 45% of treated cats. CONCLUSIONS AND CLINICAL IMPORTANCE: Most hyperthyroid cats lose body weight but maintain an ideal or overweight BCS, with only a third being underweight. As in human hyperthyroid patients, this weight loss is associated with muscle wasting, which affects >75% of hyperthyroid cats. Successful treatment leads to weight gain and increase of BCS in most cats, but almost half fail to regain normal muscle mass.

Evaluation of Serum Thyroid-Stimulating Hormone Concentration as a Diagnostic Test for Hyperthyroidism in Cats.

BACKGROUND: In humans, measurement of serum thyroid-stimulating hormone (TSH) concentration is commonly used as a first-line discriminatory test of thyroid function. Recent reports indicate that canine TSH (cTSH) assays can be used to measure feline TSH and results can help diagnose or exclude hyperthyroidism. OBJECTIVES: To investigate the usefulness of cTSH measurements as a diagnostic test for cats with hyperthyroidism. ANIMALS: Nine hundred and seventeen cats with untreated hyperthyroidism, 32 euthyroid cats suspected of having hyperthyroidism, and 131 clinically normal cats. METHODS: Prospective study. Cats referred to the Animal Endocrine Clinic for suspected hyperthyroidism were evaluated with serum T4, T3, free T4 (fT4), and TSH concentrations. Thyroid scintigraphy was used as the gold standard to confirm or exclude hyperthyroidism. RESULTS: Median serum TSH concentration in the hyperthyroid cats (<0.03 ng/mL) was significantly (P < .001) lower than concentrations in clinically normal cats (0.05 ng/mL) or euthyroid cats with suspected thyroid disease (0.06 ng/mL). Only 18 (2.0%) hyperthyroid cats had measurable TSH concentrations (≥0.03 ng/mL), whereas 114 (69.9%) of the 163 euthyroid cats had detectable concentrations. Combining serum TSH with T4 or fT4 concentrations lowered the test sensitivity of TSH from 98.0 to 97.0%, but markedly increased overall test specificity (from 69.9 to 98.8%). CONCLUSIONS AND CLINICAL IMPORTANCE: Serum TSH concentrations are suppressed in 98% of hyperthyroid cats, but concentrations are measurable in a few cats with mild-to-moderate hyperthyroidism. Measurement of serum TSH represents a highly sensitive but poorly specific test for diagnosis of hyperthyroidism and is best measured in combination with T4 and fT4.

Clinical features and treatment outcomes of 41 dogs with sublingual ectopic thyroid neoplasia.

BACKGROUND: Thyroid neoplasia is common in dogs, but there are few reports of dogs with ectopic, sublingual thyroid tumors. OBJECTIVES: To describe clinical features and outcomes of dogs with ectopic, sublingual thyroid neoplasia. ANIMALS: Five hundred and forty-four dogs with thyroid neoplasia. METHODS: This retrospective study reviewed the medical records of dogs referred for thyroid neoplasia between 1995 and 2013. Data extracted included signalment, extent of thyroid disease (eutopic or ectopic; metastasis), serum thyroxine (T4) concentration, treatment, and survival. RESULTS: Of 544 dogs with thyroid neoplasia, 41 (7.5%) dogs had ectopic sublingual thyroid tumors. The clinical features of these 41 dogs were similar to the cohort group of 503 dogs with eutopic or ectopic mediastinal thyroid tumors, but dogs with sublingual tumors were younger and less likely to have metastatic disease (15% versus 30%, P < .05). Of the 41 dogs, 28 received treatment: 21 with surgery (which included partial hyoidectomy in 13), 7 with radioiodine alone, and 13 with surgery followed by administration of radioiodine. Overall median survival was 562 days (range, 1-1,850 days). CONCLUSIONS AND CLINICAL IMPORTANCE: When compared with eutopic thyroid carcinomas, ectopic sublingual thyroid tumors generally have a less aggressive biologic behavior. Many dogs have prolonged survival, even without treatment, although death because of local tumor invasiveness or metastasis can develop in some dogs. Surgical thyroidectomy, including partial hyoidectomy, is generally effective for control of local disease. Administration of radioiodine, alone or in combination with surgical treatment, is recommended for multifocal disease or metastasis.

New parameters controlling the effect of temperature on enzyme activity.

Arising from careful measurements of the thermal behaviour of enzymes, a new model, the Equilibrium Model, has been developed to explain more fully the effects of temperature on enzymes. The model describes the effect of temperature on enzyme activity in terms of a rapidly reversible active-inactive (but not denatured) transition, revealing an additional and reversible mechanism for enzyme activity loss in addition to irreversible thermal inactivation at high temperatures. Two new thermal parameters, T(eq) and DeltaH(eq), describe the active-inactive transition, and enable a complete description of the effect of temperature on enzyme activity. We describe here the Model and its fit to experimental data, methods for the determination of the Equilibrium Model parameters, and the implications of the Model for the environmental adaptation and evolution of enzymes, and for biotechnology.

Control of bacterial pathogens during processing of cold-smoked and dried salmon strips.

Microbiological and chemical changes were determined during the smoking and drying of salmon strips processed at 29 to 31 degrees C for 4 days at a facility in Alaska in 1993. During the process, Staphylococcus aureus populations increased to more than 10(5) CFU/g after 2 to 3 days of processing. Subsequent laboratory studies showed that a pellicle (dried skinlike surface) formed rapidly on the strips when there was rapid air circulation in the smokehouse and that bacteria embedded in or under the pellicle were able to grow even when heavy smoke deposition occurred. Under these conditions, an inoculum of 26 CFU/g of S. aureus increased to 10(5) CFU/g after 3 days of processing. Elimination of preprocess drying and reduction in air flow during smoking resulted in smoke deposition before pellicle formation and enabled the product to reach levels of water-phase salt and water activity that inhibit the growth of S. aureus and Listeria monocytogenes. In 1994, these modifications were then applied during processing at an Alaskan facility, and S. aureus could not be detected in the finished product. L. monocytogenes was detected in the raw product area, on the processing tables, and on the raw salmon strips, but it was not detected in the finished product when the smoke was applied before pellicle formation.

Competitive inhibition between different Clostridium botulinum types and strains.

Mixtures of proteolytic and nonproteolytic strains of toxigenic Clostridium botulinum types A, B, and F; nonproteolytic types B, E, and F; Clostridium sporogenes; and nontoxic E-like organisms resembling nonproteolytic C. botulinum were tested against each other for the purpose of selecting a mixture of compatible C. botulinum strains for inoculated pack studies on the basis of their sensitivity to bacteriophages and bacteriocin-like agents. All of the proteolytic strains produced bacteriocin-like agents that were inhibitory to three or more of the other proteolytic types and C. sporogenes. When selected strains of proteolytic types A and B were grown together, type A cultures produced neurotoxin, but type B toxin production was inhibited. Nonproteolytic strains of C. botulinum also produced bacteriocin-like agents against each other. Of these, type E strain EF4 produced bacteriocin-like agents against both proteolytic and nonproteolytic types of C. botulinum and C. sporogenes. EF4, however, was not inhibitory to the nontoxigenic E-like strains. When EF4 was grown with type A strain 62A, it had an inhibitory effect on type A toxin production. Strain 62A inactivated the type E toxin of EF4 after 7 to 21 days at 30 degrees C. On the basis of the production of these bacteriocin-like agents by different strains of C. botulinum and their potential effect on neurotoxin production, it is very important that compatible strains are used in mixtures for inoculated pack studies to determine the safety of a food process or product.

Uptake of erythromycin by first-feeding sockeye salmon, Oncorhynchus nerka (Walbaum), fed live or freeze-dried enriched adult Artemia or medicated pellets.

The potential to use adult Artemia to deliver erythromycin to first-feeding sockeye salmon, Oncorhynchus nerka (Walbaum), was investigated in three trials. In the first trial, first-feeding sockeye were fed live erythromycin enriched adult Artemia or pellets containing equal amounts of erythromycin for 35 days. At the end of the trial, tissue erythromycin concentration of the fish fed the live Artemia was significantly greater (P < 0.05, 25.52 +/- 1.29 microg mL(-1); mean +/- SEM), than the tissue concentration of the fish fed the pellets (0.72 +/- 0.01 microg mL(-1)). In the second trial, first-feeding sockeye were fed either live or freeze-dried bioencapsulated erythromycin (adult Artemia) or pellets containing erythromycin daily for 21 days. Mean daily erythromycin concentration in fish fed the freeze-dried Artemia, live Artemia, or pellets did not differ significantly. In the third trial, apparent erythromycin digestibility was determined. Significantly more (P < 0.05) erythromycin was retained by juvenile sockeye fed freeze-dried bioencapsulated erythromycin (98.3 +/- 1.0%) compared with medicated pellets (89.2 +/- 1.7%). Uptake of bioencapsulated erythromycin from adult Artemia (live or freeze-dried) appears to be greater than uptake from pellets. Freeze-dried and live Artemia were equally effective at delivery suggesting enriched freeze-dried adult Artemia could be produced into a highly palatable, consistent, off-the-shelf product.

Control of nonproteolytic Clostridium botulinum types B and E in crab analogs by combinations of heat pasteurization and water phase salt.

Water phase sodium chloride (WPS) levels of 1.8 to 3.0% in combination with heat pasteurization for 15 min at temperatures of 75, 80, 85, and 90 degrees C were evaluated as methods for the inactivation or inhibition of nonproteolytic, psychrotrophic Clostridium botulinum types B and E in crab analogs (imitation crab legs) subsequently stored at 10 and 25 degrees C. Samples inoculated with 10(2) type B or E spores per g prior to pasteurization remained nontoxic for 120 days at 10 degrees C and for 15 days at 25 degrees C. With 10(4) type E spores per g and 80 degrees C pasteurization, > or = 2.4 and 2.7% WPS was required for inhibition at 10 and 25 degrees C storage, respectively. Pasteurization at 85 degrees C decreased the inhibitory level of WPS to 2.1% at 10 degrees C and to 2.4% at 25 degrees C. When the inoculum was 10(4) type B spores per g, samples with 2.7% WPS were toxic after 80 days of storage at 10 degrees C. Samples inoculated with 10(3) type B spores per g and processed at 85 degrees C remained nontoxic for 15 days at 25 degrees C with a WPS of > or = 2.4%. When pasteurization was carried out before inoculation and packaging, 1.8% WPS prevented toxin production by 10(2) and 10(4) type E spores per g for 30 days at 10 degrees C, and this time period increased as the WPS concentrations increased. Three percent WPS prevented toxin production by 10(4) type E spores per g in vacuum-packaged analogs stored 110 days at 10 degrees C. Pasteurization processes used in these experiments, however, do not inactivate the heat-resistant proteolytic types of Clostridium botulinum. Therefore, the most important factor controlling the growth of this bacterium is continuous refrigeration below 3.0 degrees C or frozen storage of the finished product.

Medical treatment of canine pituitary-dependent hyperadrenocorticism (Cushing's disease).

Pituitary-dependent hyperadrenocorticism (Cushing's disease) is a relatively common endocrine disorder of middle- to old-age dogs. Three treatments commonly used in the management of pituitary-dependent Cushing's disease in dogs include mitotane, ketoconazole, and L-deprenyl. These medications are associated with the potential of different side effects and expense, but all can produce satisfactory results in dogs with this disease. The choice of treatment for a given dog depends on the severity of the dog's disease, as well as clinician and client preferences. This article reviews the indications and adverse effects associated with each of these three drugs, as well as the treatment protocols commonly used in treating dogs with hyperadrenocorticism.

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.

Measurement of serum concentrations of free thyroxine, total thyroxine, and total triiodothyronine in cats with hyperthyroidism and cats with nonthyroidal disease.

OBJECTIVE: To determine the usefulness of measuring serum free thyroxine (T4) concentration as a diagnostic test for hyperthyroidism in cats, and to determine the influence of nonthyroidal disease on free T4 concentration in cats without hyperthyroidism. DESIGN: Prospective case series. ANIMALS: 917 cats with untreated hyperthyroidism, 221 cats with nonthyroidal disease, and 172 clinically normal cats. PROCEDURE: Serum free T4, total T4, and total triiodothyronine (T3) concentrations were measured in cats with untreated hyperthyroidism and cats with nonthyroidal disease. Serum total T4 and T3 concentrations were determined by use of radioimmunoassay, and free T4 concentration was measured by use of direct equilibrium dialysis. Reference ranges for hormone concentrations were established on the basis of results from the 172 clinically normal cats. RESULTS: Sensitivity of serum free T4 concentration as a diagnostic test for hyperthyroidism was significantly higher than the test sensitivity of either total T4 or T3 concentration. Of the 221 cats with nonthyroidal disease, 14 had a high free T4 concentration (ie, false-positive result). Therefore, calculated specificity of measuring serum free T4 concentration as a diagnostic test for hyperthyroidism was significantly lower than test specificity of measuring either the total T4 or T3 concentration. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that determination of free T4 concentration is useful in the diagnosis of hyperthyroidism, especially in cats in which hyperthyroidism is suspected but total T4 and T3 concentrations are within reference ranges. However, because some cats with nonthyroidal disease have high serum free T4 concentrations, hyperthyroidism should not be diagnosed solely on the finding of high free T4 concentration.

Beta cell and insulin antibodies in treated and untreated diabetic cats.

Beta cell and insulin antibodies are involved in the pathogenesis of diabetes in human patients. Beta cell antibodies have also been found in about 50% of newly diagnosed diabetic dogs. This study's objective was to examine these antibodies' role in feline diabetes. The serum of 26 newly diagnosed untreated diabetic cats, 29 cats on insulin therapy, 30 cats with diseases other than diabetes, and 30 healthy cats was examined for beta cell and insulin antibodies. For beta cell antibody testing, purified beta cells from a radiation-induced transplantable rat insulinoma were used. Serum from cats in which anti-beta cell antibodies were induced by injecting a purified beta cell suspension subcutaneously was used as a positive control. Following incubation with test sera, fluorescein-labeled anti-cat immunoglobulins were used to visualize binding between the beta cells and cat gamma globulins. Each serum was tested on two different tumor preparations. For the detection of insulin antibodies, a charcoal separation method was used. It was found that none of the healthy cats, none of the newly diagnosed, untreated diabetic cats and none of the cats with diseases other than diabetes had antibodies against beta cells or against endogenous insulin. Four diabetic cats (14%) that had been treated with different insulin preparations had insulin antibodies. It is concluded that immune-mediated processes are not causing diabetes in the cat. Further studies are needed to evaluate if antibodies directed against exogenous insulin alter the response of diabetic cats to insulin.

Natural killer cells and mast cells from gp49B null mutant mice are functional.

Immune responses are controlled by a combination of positive and negative cellular signals. Effector cells in the immune system express inhibitory receptors that serve to limit effector cell expansion and to protect the host from autoreactivity. gp49B is a receptor of unknown function that is expressed on activated mast cells and natural killer (NK) cells and whose cytoplasmic tail endows it with inhibitory potential. To gain insight into the function of gp49B in mice, we disrupted the gp49B gene by homologous recombination. gp49B(0) mice were born at expected ratios, were healthy and fertile, and displayed normal long-term survival rates. gp49B(0) mice showed no defect in NK or mast cell development. Furthermore, NK and mast cells from the gp49B(0) mice showed activation properties in vitro similar to those of cells isolated from wild-type mice. Therefore, gp49B is not critical for the development, expansion, and maturation of mast cells and NK cells in vivo. The healthy status of gp49B(0) mice makes them suitable for testing the role of gp49B in immune responses to infectious agents.

Prevalence of ocular abnormalities in cats with hyperthyroidism.

The purpose of this study was to investigate the occurrence of ocular abnormalities in hyperthyroid cats. One hundred hyperthyroid cats and 30 clinically normal, geriatric cats were studied. In both groups, ophthalmic examination was performed by use of slit-lamp biomicroscopy and indirect ophthalmoscopy after application of 1% tropicamide to dilate the pupil. Ocular abnormalities were common in both the hyperthyroid and euthyroid cats. Approximately 75% of all eyes were affected with 1 or more abnormalities, and the range of abnormalities involved all structures of the eye. Significant differences between the euthyroid and hyperthyroid cats were found in the prevalence of prominent suture lines, nonpigmented deposits on the posterior lens capsule, hyperreflective ring around the optic nerve, and hyperpigmentation of the area centralis, but all of these abnormalities were more common in the euthyroid cats than in the cats with hyperthyroidism. Active retinal lesions were only observed in 3 hyperthyroid cats (3%). The results of this study indicate that hyperthyroidism does not seem to be a frequent cause of abnormalities in the eyes of cats.