Veterinarians use flumequine (FLU) widely but its toxicological effects are still unclear. FLU doses of 53, 200, or 750 mg/kg were administered orally for six weeks to pubertal male rats for evaluation of their toxicity. Weight gain was poorer after seven days of exposure to FLU 750, but relative weights of the brain, adrenal and thyroid glands, and testes were notably higher. Haematological and lipid profile parameters, cardiac markers, and inorganic phosphate significantly increased in the FLU 750 group. Blood glucose, oestradiol and serum concentrations of immunoglobulins G (IgG) and E (IgE) significantly decreased after treatment. The levels of interleukins 10 (IL-10) and 6 (IL-6) fell significantly in the FLU 200 and FLU 750 groups. Cytochrome P450, family 1, subfamily A, polypeptide 1 (CYP1A1) and cyclooxygenase-2 (Cox-2) expression amplified after treatment. Serum levels of free triiodothyronine (fT3) and free thyroxine (fT4) reduced in the FLU 200 and FLU 750 groups without changes in total T3 or T4 level. All doses of FLU significantly depressed concentrations of thyroid-stimulating hormone (TSH) and testosterone. Histopathology of thyroid glands from rats treated with FLU 750 showed degeneration and depletion of thyroid follicular epithelial cells. Expression of 8-hydroxydeoxyguanosine (8-OHdG) was increased in a dose-dependent manner in the brain, but decreased in the testes. Expression of CYP1A1 increased in the adrenal and pituitary glands. The results of this study suggest that the toxicity of FLU in rats is an effect of its disruptive influence on the pituitary-thyroid hormonal system and on the dysfunction of the immune system.

Objective-To establish a sensitive test for the detection of autoantibodies against thyroid peroxidase (TPO) in canine serum samples. Sample Population-365 serum samples from dogs with hypothyroidism as determined on the basis of serum concentrations of total and free triiodothyronine (T3), total and free thyroxine (T4), and thyroid-stimulating hormone, of which 195 (53%) had positive results for at least 1 of 3 thyroid autoantibodies (against thyroglobulin Tg, T4, or T3) and serum samples from 28 healthy dogs (control samples). Procedure-TPO was purified from canine thyroid glands by extraction with detergents, ultracentrifugation, and precipitation with ammonium sulfate. Screening for anti-TPO autoantibodies in canine sera was performed by use of an immunoblot assay. Thyroid extract containing TPO was separated electrophoretically, blotted, and probed with canine sera. Alkaline phosphatase-conjugated rabbit anti-dog IgG was used for detection of bound antibodies. Results-TPO bands were observed at 110, 100, and 40 kd. Anti-TPO autoantibodies against the 40-kd fragment were detected in 33 (17%) sera of dogs with positive results for anti-Tg, anti-T4, or anti-T3 autoantibodies but not in sera of hypothyroid dogs without these autoantibodies or in sera of healthy dogs. Conclusions and Clinical Relevance-The immunoblot assay was a sensitive and specific method for the detection of autoantibodies because it also provided information about the antigen. Anti-TPO autoantibodies were clearly detected in a fraction of hypothyroid dogs. The value of anti-TPO autoantibodies for use in early diagnosis of animals with thyroid gland diseases should be evaluated in additional studies.

Twelve mature (5 sexually intact males, 4 castrated males, and 3 females) mixed-breed dogs were surgically thyroidectomized and used in a Latin-square design pharmacokinetic study of orally administered L-thyroxine. The dogs were treated with 44, 22, and 11 Kg of L-thyroxine/kg as a single morning dose or in divided doses, morning and evening. Serum concentration of thyroxine (T4) was evaluated to determine a number of pharmacokinetic variables for comparison. Mean steady-state concentrations (C(SS)) were determined from the area under the curve. Variables were analyzed for comparisons between dosages by use of ANOVA. Concentration at steady state was highest for dogs of the 44-micrograms/kg of body weight once-daily group and was lowest for dogs of the group given 11 micrograms/kg in 2 daily doses. Single daily administration resulted in higher C(SS), except at the 22-micrograms/kg/d dosage. Clearance was faster for the 22- and 44-micrograms/kg/d dosages than for the 11-micrograms/kg/d dosage. The half-life (t(1/2)) and mean residence time (MRT) also were shorter for the 44-micrograms/kg/d dosage, possibly indicating more rapid elimination of the drug at higher doses and dose-dependent kinetics. Perhaps, as the dogs' metabolism increased with higher iodothyronine concentrations, hormone degradation was accelerated. Interval (divided vs single dose) caused some expected changes: maximal concentration was higher and minimal concentration was lower when single administration was used. These undulations resulted in iodothyronine concentrations above the physiologic range for a number of hours, whereas concentration closer to physiologic ranges was achieved by use of divided doses. Delayed absorption (lag time) was seen in 37 of the 72 data sets, but was generally short, about 0.25 hour. Mean time to maximal concentration was 3 to 4 hours. At the higher dosages, serum total T4 concentration was high normal or above normal during most of the time after L-thyroxine administration, but serum concentration of total 3,5,3'-triiodothyronine did not remain within the normal range until the 44-micrograms/kg/d dosage was used. The customary dosage of 22 micrograms/kg/d (0.1 mg/10 lb/d) may not be adequate for most dogs. Pharmacokinetic variables appear to be highly dependent on the individual dog. Those with rapid absorption and higher concentration tended to have these characteristics at each dosage in this study. The pharmacokinetic variables, therefore, appear to be highly individualized, and dosages recommended for treatment of hypothyroidism should be considered to be only a starting point for the average dog. To avoid underdosing or overdosing, monitoring of treatment to adjust dose for individual dog kinetic variables seems to be imperative.

Prednisone was given orally to 12 dogs daily for 35 days at an anti-inflammatory dosage (1.1 mg/kg of body weight in divided dose, q 12 h) to study its effect on thyroxine (T4) and triiodothyronine (T3) metabolism. Six of these dogs were surgically thyroidectomized (THX-Pred) and maintained in euthyroid status by daily SC injections of T4 to study peripheral metabolism while receiving prednisone; 6 dogs with intact thyroid gland (Pred) were given prednisone; and 6 additional dogs were given gelatin capsule vehicle as a control group (Ctrl). Baseline T4 concentration after 4 weeks of treatment was not significantly different in dogs of the THX-Pred or Pred group (mean +/- SEM, 2.58 +/- 0.28 or 3.38 +/- 0.58 microgram/dl, respectively) vs dogs of the Ctrl group (2.12 +/- 0.30 microgram/dl). A supranormal response of T4 to thyrotropin was observed in dogs of the Pred group, but the T4 response to thyrotropin-releasing hormone was normal. Baseline T3 concentration in dogs of both steroid-treated groups was significantly (P < 0.05) lower after 2 and 4 weeks of prednisone administration vs pretreatment values, but normalized 2 weeks after prednisone was stopped. Free T3 (FT3) and T4 (FT4) fractions and absolute FT3 and FT, concentrations were not altered by prednisone administration. Reverse T3 (rT3) concentration in vehicle-treated Ctrl dogs (26.6 +/- 3.5 ng/dl) was not different from rT3 concentration in dogs of the THX-Pred (25.7 +/- 4.3 ng/dl) and Pred (28.9 +/- 3.8 ng/dl) groups after 4 weeks of medication. These data indicate that daily oral administration of such anti-inflammatory dose of prednisone for 1 month reduces baseline serum T3 concentration, does not alter serum T4 concentration, and enhances thyroidal sensitivity to thyrotropin.

The influence of triiodothyronine (5 microgram/kg of body weight, SC, q 12 h for 7 days) on antipyrine (AP, 25 mg/kg, IV) plasma elimination and urinary metabolite excretion was studied in castrated male dwarf goats. After triiodothyronine treatment, a significant increase in AP elimination was found. However, the observed changes in clearances for production of AP metabolites (nor-AP, 3-hydroxy-methyl-AP; 4-hydroxy-AP, and 4,4'-dihydroxy-AP) do not suggest a clear selectivity of triiodothyronine toward any of the metabolic pathways of AP.

Assays were developed to detect and measure antibodies (AA) to thyroglobulin (Tg) and to the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). An ELISA to detect AA to Tg was developed, using purified canine Tg as the antigen and goat anti-canine IgG conjugated with alkaline phosphatase as the second antibody. A highly charged agarose electrophoresis assay was used for determination of AA to T4 and T3. Sera from dogs (n = 119) with clinical signs consistent with hypothyroidism were tested for AA to Tg, T4, and T3. Autoantibodies to at least 1 of the 3 thyroid antigens were detected in 58 of the 119 (48.7%) sera tested. Autoantibodies to Tg were detected more frequently in samples with low serum concentrations of thyroid hormones than in samples with normal concentrations. The presence of AA to T4, T3, or both was not significantly associated with low thyroid hormone concentrations, but this lack of association may have been attributable to binding of AA in the measurement of thyroid hormones by radioimmunoassay.

Newborn foals of mares grazing on Acremonium coenophialum-infected fescue pasture throughout gestation or from gestation day 300 to parturition had increased gestation duration and decreased serum triiodothyronine concentration. Pregnant mares were allotted to 4 treatments: grazing continuously on endophyte-free (E-) fescue, grazing continuously on endophyte-infected (E+) fescue, grazing on E+ fescue from gestation day 300 to parturition, and grazing on E+ fescue from conception to gestation day 300. Morphometric studies indicated that foals born to mares exposed to endophyte late in gestation had large, distended thyroid follicles lined by flat cuboidal epithelial cells. Mean triiodothyronine concentration in foals exposed to endophyte (395.2 ng/dl) was decreased (P < 0.01), compared with mean values in control foals (778.0 ng/dl). Thyroxine and reverse triiodothyronine concentrations were not significantly different among groups. Foal organ weight as a percentage of foal body weight was not significantly different among experimental groups.

A bolus dose of methimazole (MMI) was administered IV over 1 minute to 5 healthy adult dogs at a dosage (40 mg/kg of body weight) known to impart protection against cisplatin-induced renal disease. Blood and urine samples for pharmacokinetic analysis were collected over a 24-hour period. Physical examination, CBC, determination of serum thyroid hormone concentrations, and serum biochemistry analysis were performed over a 10-day period to evaluate short-term toxicoses. At this dosage, MMI appears to be safe and well tolerated in dogs; only 1 of the 5 dogs had mild and transient increases in serum activity of hepatic enzymes. In addition, MMI did not alter serum thyroid hormone concentrations. Half-life of 8.82 hours and mean residence time of 12.18 hours were determined for MMI. Renal clearance of native MMI, along with sulfate and glucuronide conjugates, represented only 20% of total systemic clearance. Results of this study provide further information concerning clinical use of MMI in dogs and may contribute to better understanding of the mechanism of MMI protection against chemically induced nephrotoxicosis.

The objectives of this experiment were to determine serum concentrations of triiodothyronine (T3), thyroxine (T4), and free thyroxine (fT4) at rest, following thyroid-stimulating hormone (TSH) administration, and following phenylbutazone administration in healthy horses. This was done to determine which available laboratory test can best be used for diagnosis of hypothyroid conditions in horses. Serum T3, T4, and fT4 concentrations in serum samples obtained before and after TSH stimulation and following phenylbutazone administration for 7 days were determined. Baseline values ranged from 0.21 to 0.80 ng of T3/ml, 6.2 to 25.1 ng of T4/ml, and 0.07 to 0.47 ng of fT3/dl. After 5 IU of TSH was administered IV, serum T3 values increased to 6 times baseline values in 2 hours. Thyroxine values increased to 3 times baseline values at 4 hours and remained high at 6 hours. Free T4 values increased to 4 times baseline values at 4 hours and remained high at 6 hours. Administration of 4.4 mg of phenylbutazone/kg, every 12 hours for 7 days significantly decreased T4 and fT4 values, but did not significantly affect serum T3 concentrations, It was concluded that a TSH stimulation test should be performed when hypothyroidism is suspected. Measurement of serum fT4 concentrations, by the single-stage radioimmunoassay, does not provide any additional information about thyroid gland function over that gained by measuring T4 concentrations. Phenylbutazone given at a dosage of 4.4 mg/kg every 24 hours, for 7 days did significantly decrease resting T4 and fT4 concentrations, but did not significantly affect T3 concentrations in horses.

Serum triiodothyronine autoantibody (T3 AA), triiodothyronine (T3), and thyroxine (T4) concentrations were determined in 45 canine sera containing substantial amounts of thyroglobulin autoantibodies (Tg AA); sera also were assayed to investigate the ability of free T3 to inhibit Tg AA binding to canine Tg. Serum T3 AA concentrations defined 2 groups of sera; 28 sera had low T3 AA concentration (less than or equal to 20 ng/ml) and 17 sera had high T3 AA concentration (greater than or equal to 250 ng/ml). Direct linear correlation between T3 AA concentration and apparent serum T3 concentration was observed (r = 0.75). Serum with low T3 AA concentration had apparent T3 concentration that was significantly (P < 0.01) lower than that in serum with high T3 AA concentration. Mean serum T4 concentration was not significantly different between serum with low or high T3 AA concentration. Mean Tg AA activity was significantly (P < 0.05) lower in serum with low T3 AA concentration than in serum with high T3 AA concentration. Addition of free T3 to serum significantly (P < 0.05) decreased detectable activity of Tg AA in both groups of sera. However, significant difference in magnitude of the reduction was not observed between sera with low or high T3 AA concentration. Results indicate that a fraction of Tg AA recognizes T3-containing epitopes in Tg. Increased prevalence of T3 AA for serum with high Tg AA activity indicates that T3 AA may be another valid indicator of lymphocytic thyroiditis. These antibodies may be generated against the hormonogenic epitopes of Tg.