Truncated gamma-glutamyl carboxylase in rambouillet sheep.

A flock of Rambouillet sheep was examined because of increased lamb mortality due to ineffective hemostasis at parturition. Decreased activities of coagulation factors II, VII, IX, and X, and severely reduced hepatic gamma-glutamyl carboxylase activity with adequate vitamin K 2,3 epoxide reductase activity was determined.(1,)(21) Parenteral vitamin K(1) supplementation did not improve vitamin K-dependent coagulation factor activities in 3 affected lambs. Affected lamb gamma-glutamyl carboxylase deoxyribonucleic acid was sequenced, and 4 single nucleotide polymorphisms (SNPs 2-5) of the gamma-glutamyl carboxylase gene were identified. Single nucleotide polymorphism-4 results in an arginine to stop codon (UGA) substitution, which prematurely terminates the peptide at residue 686 (R686Stop). This genotype (GATT/GATT) has a strong association with the coagulopathy observed in clinically affected lambs, P < 0.001. The frequency of SNP-3 in exon 11 (R486H) within the MARC 1.1 database is high in the US sheep population overall. Gamma-glutamyl carboxylase activity in hepatic microsomes from a SNP-3 homozygous lamb lacking the SNP-4 mutation (GACC/GACC) was similar to control sheep homozygous for arginine at 486 and also lacking SNP-4 (TGCC/TGCC), indicating that the R486H does not measurably impact gamma-glutamyl carboxylase activity. The remaining two SNPs (2 and 5) are located within non-coding intron sequences. These 4 SNPs allowed for determining the genotype associated with the observed fatal coagulopathy. Screening for the premature truncation (SNP-4) based on the presence of a Bbv I restriction site in clinically normal lambs but not in the homozygous affected lambs allows for detection of the heterozygous state (GATT/GACC), because carrier animals are clinically normal.

The monitoring of heparin administration by screening tests in experimental dogs.

The objective of this study was to investigate the relationship between different screening tests of haemostasis and amidolytic plasma activities of unfractionated (standard) heparin in dogs. Different doses of intravenous (i.v.) [25, 50 or 100 IU Kg(-1)bodyweight (BW)] and subcutaneous (s.c.) heparin (250, 500 and 750 IU kg(-1)) were given to groups each of five clinically healthy adult beagles. Measurements of heparin activity with a factor Xa-dependent chromogenic substrate, activated partial thromboplastin time (APTT) (two different reagents), thrombin time (TT, two different thrombin activities in the reagent: 3 and 6 IU ml(-1)) and the reaction time of the resonance thrombogram (RTG -r) with two different measuring devices were performed at different times. The relationship between ratio values (actual/baseline values) of the coagulation tests and heparin activity was analysed based on regression analysis and correlation coefficient. The greatest alterations were seen for the TT([3 IU ml(-1)])and the RTG -r which were near or exceeded the upper limit of measuring range, if 25 IU kg(-1)BW heparin were given i.v. at heparin plasma levels of 0.54 +/- 0.13 IU ml(-1). These results show, that only APTT and TT measured with high thrombin activity assay appear suitable for guiding high dose heparin therapy in dogs. Averaged alterations of APTT ratio in canine plasma were less than those observed in people for similar plasma heparin levels, indicating that the guideline extrapolated from people for monitoring high dose heparin therapy using APTT may not be valid for use in dogs. After coagulation times had been converted into ratio values, based on regression analysis and Wilcoxon's test, differences of heparin sensitivity were found not only for TT measured with different thrombin activities but also for different APTT reagents (P < 0.001). The correlation between amidylotic antifactor Xa activity and ratio of coagulation times was only moderate and found to be lower for RTG -r (instrument 1: r(s)= 0.711; instrument 2: r(s)= 0.573) than for the other coagulation tests (r(s)= 0.822 to r(s)= 0.890). This indicates a considerable variability of the ratio values of the screening tests at defined heparin plasma activities. These results show, that blood coagulation tests in general are little or unsuitable for heparin antifactor-Xa activity control.

The effect of administration of a single dose of T-2 toxin on blood coagulation in the rabbit.

The single intravenous administration of T-2 toxin to rabbits at a dosage of 0.5 mg per kg body weight produced an alteration in several blood coagulation parameters. The activities of factors VII, VIII, IX, X and XI were decreased by approximately 40% six hours after T-2 toxin administration. Plasma fibrinogen concentration became elevated within 24 hours after T-2 toxin exposure. Circulating platelet numbers were unaffected by T-2 toxin administration. The similarity of coagulation parameter changes induced by T-2 toxin in animals receiving daily subcutaneous injections of vitamin K (0.5 mg per kg body weight) and those in nonvitamin K supplemented animals suggests that T-2 toxin does not function as a vitamin K antagonist.