Genetic risk factors for insidious equine recurrent uveitis in Appaloosa horses.

Appaloosa horses are predisposed to equine recurrent uveitis (ERU), an immune-mediated disease characterized by recurring inflammation of the uveal tract in the eye, which is the leading cause of blindness in horses. Nine genetic markers from the ECA1 region responsible for the spotted coat color of Appaloosa horses, and 13 microsatellites spanning the equine major histocompatibility complex (ELA) on ECA20, were evaluated for association with ERU in a group of 53 Appaloosa ERU cases and 43 healthy Appaloosa controls. Three markers were significantly associated (corrected P-value <0.05): a SNP within intron 11 of the TRPM1 gene on ECA1, an ELA class I microsatellite located near the boundary of the ELA class III and class II regions and an ELA class II microsatellite located in intron 1 of the DRA gene. Association between these three genetic markers and the ERU phenotype was confirmed in a second population of 24 insidious ERU Appaloosa cases and 16 Appaloosa controls. The relative odds of being an ERU case for each allele of these three markers were estimated by fitting a logistic mixed model with each of the associated markers independently and with all three markers simultaneously. The risk model using these markers classified ~80% of ERU cases and 75% of controls in the second population as moderate or high risk, and low risk respectively. Future studies to refine the associations at ECA1 and ELA loci and identify functional variants could uncover alleles conferring susceptibility to ERU in Appaloosa horses.

A locus-wide approach to assessing variation in the avian MHC: the B-locus of the wild turkey.

Studies of major histocompatibility complex (MHC) diversity in non-model vertebrates typically focus on structure and sequence variation in the antigen-presenting loci: the highly variable and polymorphic class I and class IIB genes. Although these studies provide estimates of the number of genes and alleles/locus, they often overlook variation in functionally related and co-inherited genes important in the immune response. This study utilizes the sequence of the MHC B-locus derived from a commercial turkey to investigate MHC variation in wild birds. Sequences were obtained for nine interspersed MHC amplicons (non-class I/II) from each of 40 birds representing 3 subspecies of wild turkey (Meleagris gallopavo). Analysis of aligned sequences identified 238 single-nucleotide variants approximately one-third of which had minor allele frequencies >0.2 in the sampled birds. PHASE analysis identified 70 prospective MHC haplotypes in the wild turkeys, whereas a combined analysis with commercial birds identified almost 100 haplotypes in the species. Denaturing gradient gel electrophoresis (DGGE) of the class IIB loci was used to test the efficacy of single-nucleotide polymorphism (SNP) haplotyping to capture locus-wide variation. Diversity in SNP haplotypes and haplotype sharing among individuals was directly reflected in the DGGE patterns. Utilization of a reference haplotype to sequence interspersed regions of the MHC has significant advantages over other methods of surveying diversity while identifying high-frequency SNPs for genotyping. SNP haplotyping provides a means to identify both divergent haplotypes and homozygous individuals for assessment of immunological variation in wild and domestic populations.

Mapping of genes expressed in activated porcine Peyer's patch.

To determine the chromosomal locations for genes expressed in porcine Peyer's patches, polymerase chain reaction-based mapping of expressed sequence tags (ESTs) isolated from a porcine Peyer's patch-specific cDNA library was performed across a 6500-rad swine radiation hybrid panel. A total of 116 ESTs were mapped with LOD scores >6.0, and another 11 ESTs had LOD scores between 5.0 and 6.0. Of these 127 ESTs, 63% matched known genes (

Amiodarone, thyroid hormone indexes, and altered thyroid function: long-term serial effects in patients with cardiac arrhythmias.

Amiodarone, a drug that has electrophysiologic actions resembling those of hypothyroidism, increases serum levels of T4 and reverse T3 (rT3) and decreases T3. The drug's long-term effects on thyroid function are poorly defined. Serial thyroid hormone indexes in 76 patients given amiodarone for 6 to 32 months (mean +/- standard deviation 16 +/- 7) for arrhythmias were determined serially. Over this period, 68 patients (89%) remained euthyroid; hypothyroidism developed in 6 (8%) and hyperthyroidism developed in 2 (3%). In patients who remained euthyroid, thyroid hormone alterations attained steady-state values at 3 months: T4 increased 42% (p less than 0.01), rT3 increased 172% (p less than 0.01) and T3 decreased 16% (p less than 0.05), without significant effect on thyroid stimulating hormone. For the euthyroid patients, the 90% tolerance limits (95% confidence) over the follow-up period for T4 was 5 to 19 micrograms/dl (normal 4 to 12), for T3 36 to 163 ng/dl (normal 60 to 160), for rT3 22 to 131 ng/dl (normal 15 to 50) and for thyroid stimulating hormone 0 to 14 microU/ml (normal 1 to 6). The changes in hormone indexes in hyperthyroid or hypothyroid patients were unrelated to the cumulative dose or duration of drug therapy. The most reliable diagnostic indexes for amiodarone-induced altered thyroid state were: thyroid stimulating hormone level over 20 microU for hypothyroidism and T4 over 20 ng/dl or high T3 over 200 ng/dl for hyperthyroidism. All levels were within the 90% tolerance limits derived for these hormones from patients remaining euthyroid on amiodarone long-term.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetic significance of serum reverse T3 levels during amiodarone treatment: a potential method for monitoring chronic drug therapy.

We studied the antiarrhythmic effects of amiodarone, 600-1400 mg/day, in 18 patients with refractory arrhythmias, and related to drug efficacy and side effects to serum levels of T4, reverse T3 (rT3) and the QTc interval. In the 11 patients with ventricular arrhythmias, premature complexes were reduced by 90-98%, and complex ectopy and runs of ventricular tachycardia were abolished; in the seven patients with paroxysmal atrial flutter, there were no recurrences on stable drug therapy. The QTc lengthened by 11.6% (p less than 0.01), T4 increased by 31.6-63.3% (p less than 0.001) and rT3 increased by 82.9-176.8% (p less than 0.001) as a function of dose and duration of amiodarone therapy. A close correlation was found between rT3 (normal up to 50 ng/dl) and drug efficacy and some of the drug side effects; arrhythmia suppression occurred at levels of 55-100 ng/dl, and some of the known side effects at levels of 100-110 ng/dl. When amiodarone was stopped in nine patients, the changes in QTc, T4 and rT3 regressed toward normal and arrhythmia recurred in eight 2-20 weeks (mean 7.4 weeks) and when rT3 levels fell below 55 ng/dl; arrhythmia resuppression was achieved 3-28 days (mean 11 days) after resumption of amiodarone therapy. The indirect therapeutic half-life of amiodarone in seven patients, computed from the semilogarithmic plots of plasma rT3 after cessation of amiodarone therapy, ranged from 25 to 55 days (mean 35 days). The data suggest that rT3 levels may be useful in monitoring the efficacy and certain side effects of amiodarone.

Amiodarone kinetics after oral doses.

Amiodarone serum kinetics after single oral doses and after long-term therapy were investigated in patients with ventricular tachyarrhythmias. When amiodarone was given as a single oral dose (1400 to 1800 mg, n = 6), serum levels of amiodarone and its metabolite, measured by high-performance liquid chromatography, correlated (r = 0.69, P less than 0.01). Peak concentrations (amiodarone, 3 to 14 microgram/ml; metabolite, 0.7 microgram/ml) were attained in 4.9 +/- 1.2 hr. Using computer fits to the data, amiodarone mean elimination rate constant and half-life (t 1/2 e) were 0.128 +/- 0.063 hr-1 and 7.2 +/- 5.0 hr. In 12 patients given a mean dose of 1327 +/- 338 mg/day of amiodarone for 4.1 +/- 2.3 wk, mean serum amiodarone level was 3.84 +/- 2.92 microgram/ml (range 0.92 to 11.99); in three patients simultaneous determination of concentrations of amiodarone and its metabolite revealed that concentration of the latter was about 50% of that of the parent drug during long-term therapy. In four patients on maintenance therapy (400 to 800 mg/day, serum level 1.08 +/- 1.3 microgram/ml) drug was discontinued and serum amiodarone levels were determined serially. Serum drug disappearance followed a single exponential function with an elimination rate constant of 0.030 +/- 0.012 day-1 and t 1/2 e of 29 +/- 19 days. Our kinetic data are consistent with the long therapeutic amiodarone t 1/2 noted in the treatment of cardiac arrhythmias.

Hyperthyroxinemia with bradycardia and normal thyrotropin secretion after chronic amiodarone administration.

Pituitary-thyroid function was tested in 15 euthyroid patients before, during, and after long term oral treatment with amiodarone (2-n-butyl-3,4'-diethylaminoethoxy-3',5'-diiodobenzoylbenzofurane; 600-1200 mg daily), an iodine-containing potent antiarrhythmic drug. The drug caused increases in serum total T4, free T4, and rT3, with a concomitant decrease in T3. Baseline serum TSH was significantly higher after 1 week of drug treatment and returned to normal levels after 12 weeks of treatment. All patients receiving amiodarone had a slowing of their heart rate (P less than 0.01), and heart rate gradually increased 6 weeks after drug withdrawal, concurrent with the slow fall in T4 and rT3 levels. Amiodarone did not cross-react in the iodothyronine RIAs. The results suggest that amiodarone inhibits the peripheral conversion of T4 to T3 and may block the metabolic action of thyroid hormone in man.

Comparative beta-blocking potencies of acebutolol and propranolol relative to plasma drug levels.

In a double-blind placebo cross-over study, the beta-blocking potencies of acebutolol and propranolol were compared in ten healthy subjects under steady-state conditions of oral drug administration. Beta-adrenergic blockade, determined by the degree of attenuation of tachycardia induced by standardized multistage treadmill exercise, was correlated with dose as well as with the plasma levels of the two beta antagonists. On a weight-for-weight basis, propranolol was about 4 times as potent as acebutolol in inhibiting exercise-induced tachycardia and in reducing the heart rate times systolic blood pressure product due to exercise. A weak correlation was demonstrated between the degree of beta blockade and plasma concentrations of propranolol (r = 0.381, p less than 0.01) or acebutolol (r = 0.333, p less than 0.001), there being up to 20-24 fold interindividual variation in plasma level for a given dose of each compound. Plasma acebutolol levels were associated with at least twofold greater levels of its acetyl homologue metabolite. A positive linear correlation was found between percentage beta blockade and the corresponding doses of propranolol (r = 0.503, p less than 0.001) and of acebutolol (r = 0.574, p less than 0.001). Our overall data provide little support for the use of plasma levels of acebutolol and propranolol as a guide to beta-blocking therapy with these compounds.