SENSITIVITY OF DIFFERENT THROMBOPLASTIN REAGENTS TO FACTOR VII DEFICIENCY IN THE BLOOD OF BEAGLE DOGS

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1 Laboratory Animals (1970) 4, SENSITIVITY OF DIFFERENT THROMBOPLASTIN REAGENTS TO FACTOR VII DEFICIENCY IN THE BLOOD OF BEAGLE DOGS by D. E. HALL Biological Research Department, BDH (Research) Ltd, Borough Road, Godalming, Surrey SUMMARY Differences in prothrombin time using various sources of tissue extract have been investigated in normal and factor VII-deficient beagles homozygous for the defect. All the tissue extracts tested gave a prolonged prothrombin time with factor VII-deficient plasma but the degree of difference from normal varied according to the source of the extract. Recommendations are made for screening dogs for the defect. Since the discovery that occasional beagle dogs purchased from commercial breeders showed a deficiency of factor VII in the plasma (Capel-Edwards & Hall, 1968), it has been the practice in this laboratory to screen all incoming beagles for the defect. The homozygous condition can be detected by the lengthened I-stage prothrombin time, using both rabbit- and dog-brain tissue extract (thromboplastin), and also 'Thrombotest', in which ox brain provides the thromboplastin. The source of thromboplastin is known to influence the prothrombin time of normal dog plasma (Didisheim, Hattori & Lewis, 1959; Belleville, Thouverez, Mikaeloff & Descotes, ] 966), and species specificity in the reaction between. factor VII and brain thromboplastin has been demonstrated (Stormoken, 1957). In the case of canine factor VII, human-brain thromboplastin appears especially sensitive to variations in activity (Stormoken, 1957), and the results obtained in factor Vll-deficient beagles by Garner, Hermoso-Perez & Conning (1967) confirm this. Rabbit-brain thromboplastin gives much faster prothrombin times with normal dog plasma than either canine-brain extract or 'Thrombotest', and the difference between the times for normal and homozygous factor VII-deficient beagle plasmas is small (Capel-Edwards & Hall, 1968). The difference is of the same magnitude as that seen between normal adults and newborn dogs deficient in clotting factors of the prothrombin complex, when rabbit brain is the source of thromboplastin (Quick, 1946; Hathaway, Hathaway & Belhasen, 1964).

2 56 D. E. HALL Some commercially-available samples of rabbit-brain thromboplastin have, however, been reported as being insensitive to the reduction of factor VII in human subjects receiving coumarin anticoagulants (Poller, 1964, 1967), and variations due to techniques are considerable (Biggs & Denson, 1966; Denson, 1966). Since it is common practice in many laboratories to purchase prepared rabbit-brain thromboplastin for carrying out prothrombin time estimations, it was thought of value to investigate the ability of a number of samples available from different manufacturers in the United Kingdom to detect the difference in time between plasma from normal beagles and that from animals known to be homozygous for the defect with less than 1 per cent factor VII activity (R. Garner, 1969, personal communication). The 2 commerciallyavailable ox-brain based reagents, several dog-brain preparations made in this laboratory and a widely used standard human extract were also investigated (Table 1). Table 1. Thromboplastins used. Rabbit Ox Dog Human Dade Activated phenolised suspension of rabbit-brain thromboplastin: Dade Reagents Inc., Miami, Florida, U.S.A. (supplied by A. R. Horwell Ltd, 2 Grangeway, London, N.W.6). Diagen Dried rabbit-brain thromboplastin: Diagnostic Reagents Ltd, Thame, Oxfordshire. Difco Bacto thromboplastin extract: Difco Laboratories, Detroit, Michigan, U.S.A. (supplied by Baird & Tatlock Ltd, Chadwell Heath, Romford, Essex). Hyland Dried rabbit-brain and lung thromboplastin: Hyland Division of Travenol Laboratories Inc., Los Angeles, California, U.S.A. (supplied by Baxter-Hyland Laboratories, Thetford, Norfolk). Ortho Rabbit-brain thromboplastin: Ortho Diagnostics Ltd, High Wycombe, Buckinghamshire. Simplastin General Diagnostics Department, William R. Warner & Co. Ltd, Eastleigh, Hampshire. Stayne Dried thromboplastin extract: Stayne Laboratories Ltd, High Wycombe, Buckinghamshire. Thrombotest Nygaard & Co., A/s Oslo, Norway (supplied by A. R. Horwell Ltd, 2 Grangeway, London, N.W.6). '2-7-10' Diagnostic Reagents Ltd, Thame, Oxfordshire. Dog brain Acetone and saline extracts of dog-brain taken from freswy-killed beagle and prepared according to the method of Biggs & Macfarlane (1962) Manchester Comparative Reagent (phenolised suspension).

3 FACTOR VII DEFICIENCY IN BEAGLES 57 METHODS Methods were basically as described by Capel-Edwards & Hall (1968), except that for each commercial thromboplastin the manufacturer's instructions were fully adhered to. The human-brain reagent was used in accordance with the instructions supplied by the National Thromboplastin Centre. RESULTS AND DISCUSSION The results in Table 2 show that all the thromboplastin reagents gave a prolonged prothrombin time with plasma from beagles homozygous for factor VB deficiency but, as expected, both these results and the normal times varied from batch to batch. From the data it is clear that human, ox and dog brain (in that order) show the greatest sensitivity to the defect. There was less difference between normal and factor VII-deficient times when rabbit brain was used. Using careful, consistent technique, rabbit-brain reagents detected the deficiency of factor VII; practice shows that there is a real danger that variables inherent in manual methods may reduce the differences still further and so mask the prolongation of the prothrombin time. Table 2. One-stage prothrombin times of normal and factor VII-deficient beagles using different thromboplastin extracts. Times in seconds, each result being the mean of 2 or more determinations. Thromboplastin* Beagle 202 Beagle 114 Beagle 174 (normal) Batch Rabbit brain: Dade Diagen ll Difco Hyland Ortho Simplastin Stayne Ox brain: Thrombotest t t t '2-7-10' 18.4 ] Dog brain (BDH): acetone extract saline extract Human brain See Table 1. tfibrometer method: all other results by manual technique.

4 58 D. E. HALL In my own laboratory, over 180 parallel determinations of 'Thrombotest', rabbit-brain and dog-brain prothrombin time determinations have been carried out on normal dogs with a remarkable uniformity of result (Table 3). The same uniformity has been obtained with these 3 tests on all occasions when the factor Vll-deficient beagle blood and plasma have been tested. The principal sources of variation have been due to the effects of different technicians reading endpoints, or the substitution of an automatic clot-timer ('Fibrometer', Beckton Dickinson Ltd, Baltimore, Maryland, U.S.A.) for performing the tests. It is our standard practice to employ 'Thrombotest' alone for preliminary screening and, where a time of 25 seconds or longer is recorded, to perform the I-stage prothrombin time and a factor VII assay with rabbit and dog brain, using known factor VB-deficient blood or plasma as positive controls or substrate. Suitable control material can be obtained by treatment of a normal dog with 'Dindevan' (Capel-Edwards & Hall, 1968) or 'Warfarin' (Gaston & Spivack, 1968). The 'Thrombotest' is preferred as the preliminary screening method since reconstitution of a standardised commercial reagent is all that is required, and the test utilises citrated blood, avoiding the need for preparing plasma. The use of 9.5 X 63.5 mm disposable polystyrene tubes ('LP/3', Luckham Ltd, Labro Works, Burgess Hill, Sussex) obviates the need for, and gives identical results to, specially cleaned glass tubes. Table 3. Normal I-stage prothrombin times (manual) for beagles (seconds) Mean Thrombotest 21.4 Rabbit brain (Dade) 8.1 Dog brain 13.7 Standard deviation ±2.24 ±O.19 ±2.76 Number of dogs ACKNOWLEDGEMENTS The skilled assistance of Miss Angela Sansom and Mrs Janet Yalden is gratefully acknowledged. The human brain extract was supplied as a gift through the courtesy of Dr L. Poller, Consultant Haematologist, Withington Hospital, Manchester, 20. REFERENCES Belleville, J., Thouverez, J. P., Mikaeloff, P. & Descotes, J. (1966). Etude des principaux tests de l'hemostase chez Ie chien normal. Pathologie et biologie 14, 41. Biggs, R. & Macfarlane, R. G. (1962). Human blood coagulation and its disorders, p Oxford: Blackwell.

5 FACTOR VII DEFIClENCY IN BEAGLES 59 Biggs, R. & Denson, K. W. E. (1966). Second report on the standardisation of the one-stage prothrombin time for the control of anticoagulant therapy. Thrombosis et diathesis haemorrhagica Suppl. 20, 345. Capel-Edwards, K. & Hall, D. E. (1968). Factor VII deficiency in the beagle dog. Laboratory Animals 2, 105. Denson, K. W. E. (1966). Criteria for a standard thromboplastin preparation. Thrombosis et diathesis haemorrhagica Suppl. 20, 363. Didisheim, P., Hattori, K. & Lewis, J. H. (1959). Hematological and coagulation studies in various animal species. Journal of Laboratory and Clinical Medicine 53, 866. Garner, R., Hermoso-Perez, C. & Conning, D. M. (1967). Factor VII deficiency in beagle dog plasma and its use in the assay of human factor VB. Nature, London 216, Gaston, L. W. & Spivack, A. R. (1968). Preparation of canine factor VIl deficient substrate plasma. Journal of Laboratory and Clinical Medicine 72, 548. Hathaway, W. E., Hathaway, H. S. & Belhasen, L. (1964). Coagulation factors in newborn animals. Journal of Laboratory and Clinical Medicine 63, 784. Poller, L. (1964). The effect of the use of different tissue extracts on one-stage prothrombin times. Acta haematologica 32, 292. Poller, L. (1967). A national standard for anticoagulant therapy. Lancet ,491. Quick, A. J. (1946). Experimentally induced changes in the prothrombin level of the blood: Ill. Journal of Biological Chemistry 164, 371. Stormoken, H. (1957). Species differences of clotting factors in ox, dog, horse and man. Thromboplastin and proconvertin. Acta physiologica scandinavica 41, 301.

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