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The influence of antiplatelet drugs on platelet survival after aortic damage or implantation of a dacron arterial prothesis
RESEARCH 15; 181-189 Printed Press Ltd.1979.
THROMBOSIS Pergamon
in Great Britain
THE INFLUENCE OF ANTIPLATELET DRUGS ON PLATELET SURVIVAL AFTER AORTIC DAMAGE OR IMPLANTATION OF A DACRON ARTERIAL PROTHESIS
Alan R.Wilkinson, Department
Robert
J. Hawker
and Linda M. Hawker
of Surgery, University of Birmingham, Birmingham B15 2TH,England
Edgbaston
(Received 8.1.1979; in revised form 19.2.1979. Accepted by Editor A. L. Bloom)
ABSTRACT The effect of antiplatelet drugs on platelet survival,as measured by Indium-111 labelled platelets, was studied in two groups of surgically treated animals. In the dog, platelet survival and loss were measured following surgery and implantation of a dacron arterial prosthesis. These same parameters were measured after aortic damage in the Animals treated with the antiplatelet drugs, sulphrat. inpyrazone and ticlopidine were compared with controls. In the dog the sulphinpyrazone treated animals had a significantly increased platelet survival and decreased platelet loss following surgery (PcO.05). In the rat, both ticlopidine and sulphinpyrazone showed significantly increased platelet survival and decreased loss of platelets following surgery when compared with controls (P( 0.001). Rats receiving sulphinpyrazone showed significantly increased platelet survival and decreased loss (P
aspects
is effective thrombosis
in preventing
(1) whilst
complications
drugs have been studied
of vascular
disease.
synthetic
dipyridamole
after mitral
in several
Sulphinpyrazone
arteriovenous (Persantin)
valve replacement 181
(Anturan)
shunt
reduces exnbolic (2). Prevention of
182
ANTI-PLATELET DRUGS
Vo1.15,No.1/2
transient ischaemia has also been described using sulphinpyrazone (31, although the Canadian Cooperative Study Group did not show any benefit with this drug (4). The recent report of the Anturan re-infarction trial research group also showed significant benefit from ingestion of sulphinpyrazone when compared with placebo (5).
Recently antiplatelet drugs have been
administered to patients with peripheral vascular disease in an effort to improve the long-term patency of small diameter synthetic arterial prostheses.
As yet the usefulness of this app-
roach is not proven and awaits the results of controlled clinical trials. A correlationhasbeen reported between platelet survival and thrombotic complications following valve replacement (6) or prosthesis implantation (7).
We have measured
platelet survival after aortic resection and implantation of a dacron graft in dogs and after experimental aortic damage in rats. These animal models have been used to assess the potential usefulness of two antiplatelet drugs, sulphinpyrazone and ticlopidine. Sulphinpyrazone has variable effects on platelet aggregation in different species (8,9,10), but has been shown in clinical practice to be effective in preventing thromboembolism Ticlopidine is a new and potent inhibitor of platelet (1,3,5). aggregation in vivo in experimental animals (11) and ex vivo in man (12). MATERIALS AND METHODS Platelet Labelling Platelets were labelled with Ill-Indium-oxine as Blood (22.5 ml) was collected by previously described (13). clean venepuncture from the jugular vein of the dog or by cannulation of the aorta of two donor rats using 3.8% trisodium citrate as anticoagulant (1:9). Platelets were separated by centrifugation using 100 ng/ml Prostaglandin El. (PGEl) to inhibit platelet aggregation (13). The platelet pellet was resuspended to one half the original volume of PRP using Ringer citrate dextrose (306 m.osmol, pH 7.0) containing PGEl and lllIn-oxine was then added. After incubating for 7.5 minutes at 37OC, platelet poor plasma containing PGEl was added, to restore the original volume and the sample centrifuged. The resulting
ANTI-PLATELET
Vo1.15,No.1/2
platelet
pellet
(obtained
was resuspended
by centrifugation
platelet
measured
platelet
from platelets activity
in the cells
vivo elution
was not measured
less
labelling
procedure
and
Experimental
was
Method
anaesthesia
diameter idine
of the labelled
in the rat.
the
aggregation
considered
and replaced
was
knitted
rats
with
second daily.
group
surgery.
was also measured In 3 of these
on two occasions
in
animals
for assessment
in Rats rats were
anaesthetised
A segment forceps
ticlopidine
(n=14) were
The remaining
dogs matched
of the method.
coarse
(n=17) received
Beagle
The
the study.
survival
was measured
on halothane.
then crushed
under
Sulphinpyrazone
of the study.
no treatment.
platelet
of the reproducibility
maintained
greater
the
to 8 dogs for two
the study.
used throughout
dogs not undergoing
Male Wistar
response
twice daily to 8 dogs for 2 days
received
In addition,
Method
that the
(USC1 Ltd). Ticlop-
orally
and for the remainder
for age and sex were
Experimental
In
than 75%, the
rich plasma,
dacron
administered
orally
was given
survival
platelets.
a 2.5 cm length of 5 mm
with
(60 mg/kg)
6 control
of radio-
aorta was resected
and throughout
platelet
of isotope
satisfactory.
days pre-operatively
6 animals
was compared
Provided
was greater
with platelet
ultra-lightweight
remaining
was
in Dogs
(50 mg/kg/day)
pre-operatively
of
of a 5 ml sample of blood with-
In 20 dogs the infrarenal general
platelets
In vivo elution
by the platelets
than 3%
by the platelets
in the dog by measurement
re-injection
than 70% of that achieved
after removal
to 2.2 x 10a5M adenosine
labelled
and plasma
after
of isotope
elution
response
rich plasma.
was measured
drawn one hour
uptake
of isotope
of the resuspended
control
poor plasma
blood
.
of uptake
and the aggregation
diphosphate with
183
in platelet
of titrated
PRP)
rich plasma, The amount
DRUGS
with ether and
of the infrarenal
for 30 seconds. (50 mg/kg)
daily,
given sulphinpyrazone
animals
(n=14) received
aorta was
One group of and the
(60 mg/kg) normal
twice
saline
184
ANTI-PLATELET DRUGS
Vo1.15,No.1/2
(0.5 ml/day) this dose being given once daily to half of the animals and twice daily to the remainder.
The administration of drugs or placebo was performed via a nasogastric tube under light ether anesthesia.
All drugs and placebo were given for two days pre-operatively and throughout the study. Platelet survival was also measured in a further 6 rats not undergoing surgery. Measurement of Platelet Survival For measurement of platelet survival in the dog, 5 ml of blood was withdrawn post-operatively and then daily for 7 days. In the rat, 0.2 ml of blood was withdrawn from the tail vein under ether anesthesia daily for 5 days after operation. The radio-activity in each sample was measured in a Well Crystal detector (NaI) linked to a counter (J & P Engineering Ltd., MS310), the accumulated samples for each animal being counted on the last day of study. Calculation of Results For each animal the radio-activity in the daily sample was expressed as a percentage of the first post-operative sample (i.e. one hour in the dog and one day in the rat). The platelet survival was calculated by a least squares linear regression plot The intercept,a,
of percentage circulating with time (Fig.1). 100
PLATELET SURVIVAL
1
I
survival calculated from a/t
FIG.1 An example of platelet survival in a ticlopidine treated dog following insertion of a dacron graft.
ANTI-PLATELET DRUGS
Vo1.15,No.1/2
185
with the ordinate is an expression of the initial loss of platelets following surgery. Survival was estimated by equating the slope b,with the calculated value of a. Results of the three groups of rats and dogs that had undergone surgery were compared using an unpaired Student's t test. RESULTS The repeated estimations of platelet survival parameters in three control dogs (Table 1) indicated good reproducibility of the method. The mean (,+SD) platelet survival in six dogs not undergoing surgery was 7.03 + 0.28 days with a calculated initial loss of 5.03 + 2.833 and a daily loss of 13.53 + 0.79%.
TABLE 1 Results of Repeated Studies in 3 Dogs Dog
Platelet Survival
Calculated % Platelets circulating at a time zero
% Loss per day
A
7.40 7.22
92.13 101.49
B
6.77 7.09
96.47
14.25
101.90
14.36
91.34 91.93
13.50
C
6.77 6.77
12.44 14.06
13.58
TABLE 2 Comparison of Platelet Survival and Loss Following Surgery in Dogs (Mean 2 S.D.) Group Graft - no drug Graft + Ticlop. Graft + Sulphin
Number
Platelet Survival (days)
6
6.03 2 1.04
8 8
6.46 _+0.59 6.58 ,+0.76
Loss Following Surgery (100-a) 34.27 ,+ 11.00 29.20 t 14.21 18.73 ,+ 12.29
186
ANTI-PLATELET
DRUGS
Vo1.15,No.1/2
Table 2 compares these survival parameters in animals undergoing implantation of a dacron graft, with and without treatment with antiplatelet drugs. Sulphinpyrazone significantly (P
increased platelet survival and decreased platelet loss following surgery. The effects of ticlopidine were not significantly different from the no treatment group. In the aortic damage model in rats, both ticlopidine and sulphinpyrazone significantly increased platelet survival (P
Number
Platelet Survival (days)
Loss Followinq Surgery %
Operation no drug
16
2.89 t 0.22
52.35 f 5.38
Operation + ticlop.
17
3.17 2 0.04
35.82 + 4.59
Operation + sulphin.
14
3.39 ,+0.09
22.13 f 3.52
Platelet survival in the rats receiving sulphinpyrazone was significantly greater (PxO.001) and the percentage loss following surgery was significantly lower (P(O.001) when compared with ticlopidine treated animals. Platelet survival in the 7 rats not undergoing surgery was 3.87 + 0.12 days with a calculated initial loss of platelets of 3.68 f 3.3% and 24.81 2 0.33% removed from circulation per day. DISCUSSION Improvements in long term patency of small diameter synthetic arterial prostheses has been approached by modification in the design and texture of the graft material (14,15,16) and also by the use of oral anticoagulants (17,181. The latter did
Vo1.15,No.1/2
ANTI-PLATELET DRUGS
not however, result In any measurable benefit to the patient (19). with the evidence that antiplatelet drugs reduce thromboembolism in patients with different types of arterial disease, the role of such drugs in preventing or lowering the rate of thrombotic occlusion of synthetic arterial prostheses warrants further investigation. In the present study, measurements of platelet survival have been used to evaluate sulphinpyrazone, which has been clinically assessed in thromboembolic complications, and ticlopidine which is a new drug exhibiting marked effects on platelet
aggregation in ex vivo studies in man and animals. The dosage regimes for the dogs and rats were derived
from preliminary experiments in an attempt to parallel observations with therapeutic levels in man. At the doses used,plasma levels of sulphinpyrazone and the reduced ex-viva aggregation responses
to ADP produced by ticlopidine, were similar to those
seen clinically. The high uptake of Ill-Indium-oxine by platelets has enabled.platelet survival to be measured accurately over a 5 day period, despite the 2.8 days half-life of the isotope. Platelet survival using Ill-Indium-oxine is best described by a linear plot (13). In unoperated dogs and rats, the calculated amount of isotope initially circulating approximates to 100% indicating rapid equilibrium of platelets between spleen and circulation. The observed loss of platelets after surgery probably represents deposition of platelets on the graft surface or site of aortic damage and within the wound. The significant reduction in this loss of platelets in rats treated with sulphinpyrazone or ticlopidine, and in dogs treated with sulphinpyrazone, suggests that these drugs may reduce the early post-operative deposition of platelets at sites of vascular damage, and in the case Of sulphinpyrazone on artificial surfaces. Similarly, the significant lengthening of platelet survival in the treated rats and sulphinpyrazone treated dogs implies a continued protection from thrombogenic activation at the site of aortic damage or on a graft surface. Finally, damage to the rat infrarenal aorta, with subsequent measurement of platelet survival is a useful and
ANTI-PLATELET DRUGS
188
Vol.l5,No.1/2
inexpensive method for comparison of different antiplatelet drugs. From these studies both sulphinpyrazone and ticlopidine merit evaluation as potential agents for reducing the risk of thrombotic occlusion in patients with peripheral vascular disease and also in patients with synthetic arterial prostheses. The authors wish to acknowledge the help of Ciba-Geigy and I.C.I. in providing sulphinpyrazone and ticlopidine respectively for use in this study. REFERENCES 1.
KAEGI, A., PINEO, G.F., SHIMIZU, A., TRIVEDI, H.,HIRSCH,J., and GENT, M. Arterio-venous shunt thrombosis: Prevention by sulphinpyrazone. New Engl.J.Med. 290, 304,1974.
2.
SULLIVAN, J.M., HARKEN, D.E., GORLIN, R. Pharmacologic control of thromboembolic complications of cardiac valve replacement. New Engl.J.Med. 279, 576, 1968.
3.
EVANS, G. Effect of drugs that suppress platelet surface interaction on incidence of amaurosis fugax and transient cerebral ischaemia. Surgical Forum, 23, 239, 1972.
4.
CANADIAN COOPERATIVE STUDY GROUP. A randomised trial of aspirin and sulphinpyrazone in threatened stroke. New Engl. J.Med. 299, 53, 1978.
5.
ANTURAN REINFARCTION TRIAL RESEARCH GROUP. Sulphinpyrazone in the prevention of cardiac death after myocardial infarction. New Engl. J.Med. 298, 289, 1978.
6.
WEILY, H.S., STEELE, P.P., DAVIES, H., PAPPAS, G. and GENTON, E. Platelet survival in patients with substitute heart valves. New Engl. J. Med. 290, 534, 1974.
7.
HARKER, L.A., SLICHTER, S.J., SAUVAGE, L-R. Platelet consumption by arterial prostheses: The effects of endothelialisation and pharmacologic inhibition of platelet function. Ann. Surq. 186, 594, 1977.
8.
PACKHAM, M.A., MUSTARD, J.F. The effect of pyrazole compounds on thrombin-induced platelet aggregation. Proc. Soc.Exp.Biol.Med. 130, 72, 1969.
9.
PACKHAM, M.A., WARRIOR, E.S., GLYNN, M.F., SENYI, A.S. and MUSTARD, J.F. Alteration of the response of platelets to surface stimuli by pyrazole compounds. J.Exp.Med. 126, 173. 1967.
10.
WEILY, H.S., GENTON, E. Altered platelet function in patients with prosthetic mitral valves. Effects Of SUlfinpyrazone therapy. Circulation, 42, 967, 1970.
Vo1.15,No.1/2
ANTI-PLATELET DRUGS
189
11. MAFFRAND, J.P., ELOY, F. Synth&e de thi&opyridines et de furopyridines d'int$r%t thgrapeutique. Eur.J. Med. Chem. 9, 483, 1974. 12. THEBAULT, J.J., BLATRIX, C.E., BLANCHARD, J.F., PANAK, E.A. Effects of ticlopidine, a new platelet aggregation inhibitor in man. Clinical Pharmacology and Therapeutics, 18,485,1975. 13. WILKINSON, A.R., HAWKER, R.J., HAWKER, L.M. Ill-Indium labelled canine platelets. Thromb.Res. 13, 175, 1978. 14. MATSUMOTO, H., HASEGAWA, T., FUSE, K., YAMAMOTO, M., SAIGUSA, M., A new vascular prosthesis for a small calibre artery. Surgery, 74, 519, 1973. 15. SAUVAGE., L.R., BERGER, K., NAKAGAWA, Y., WOOD, S.J., MANSFIELD, P.B. An external velour surface for porous arterial prostheses. Surgery, 70, 940, 1971. 16. WESOLOWSKI, S.A., FRIES, C.C., KARLSON, K.E., DEBAKEY, M., SAWYER, P.N. Porosity: primary determinant of ultimate fate of synthetic vascular grafts. Surgery, 50, 91, 1961. 17. BADDELEY, R-M., LAWSON, L.J., ASHTON, F. SLANEY, G. Evaluation of autogenous vein bypass grafts for femoropopliteal arterial occlusion. Brit. Med. J. 2, 410, 1967. 18. ROB, C.C. Place of direct surgery in treatment of obliterative arterial disease. Brit. Med. J. 2, 1027, 1956. 19. BADDELEY, R.M., ASHTON, F., SLANEY, G., BARNES, A.D. Late results of autogenous vein bypass grafts in femoro-popliteal arterial occlusion. Brit. Med. J. 1, 653, 1970.
THROMBOSIS Pergamon
in Great Britain
THE INFLUENCE OF ANTIPLATELET DRUGS ON PLATELET SURVIVAL AFTER AORTIC DAMAGE OR IMPLANTATION OF A DACRON ARTERIAL PROTHESIS
Alan R.Wilkinson, Department
Robert
J. Hawker
and Linda M. Hawker
of Surgery, University of Birmingham, Birmingham B15 2TH,England
Edgbaston
(Received 8.1.1979; in revised form 19.2.1979. Accepted by Editor A. L. Bloom)
ABSTRACT The effect of antiplatelet drugs on platelet survival,as measured by Indium-111 labelled platelets, was studied in two groups of surgically treated animals. In the dog, platelet survival and loss were measured following surgery and implantation of a dacron arterial prosthesis. These same parameters were measured after aortic damage in the Animals treated with the antiplatelet drugs, sulphrat. inpyrazone and ticlopidine were compared with controls. In the dog the sulphinpyrazone treated animals had a significantly increased platelet survival and decreased platelet loss following surgery (PcO.05). In the rat, both ticlopidine and sulphinpyrazone showed significantly increased platelet survival and decreased loss of platelets following surgery when compared with controls (P( 0.001). Rats receiving sulphinpyrazone showed significantly increased platelet survival and decreased loss (P
aspects
is effective thrombosis
in preventing
(1) whilst
complications
drugs have been studied
of vascular
disease.
synthetic
dipyridamole
after mitral
in several
Sulphinpyrazone
arteriovenous (Persantin)
valve replacement 181
(Anturan)
shunt
reduces exnbolic (2). Prevention of
182
ANTI-PLATELET DRUGS
Vo1.15,No.1/2
transient ischaemia has also been described using sulphinpyrazone (31, although the Canadian Cooperative Study Group did not show any benefit with this drug (4). The recent report of the Anturan re-infarction trial research group also showed significant benefit from ingestion of sulphinpyrazone when compared with placebo (5).
Recently antiplatelet drugs have been
administered to patients with peripheral vascular disease in an effort to improve the long-term patency of small diameter synthetic arterial prostheses.
As yet the usefulness of this app-
roach is not proven and awaits the results of controlled clinical trials. A correlationhasbeen reported between platelet survival and thrombotic complications following valve replacement (6) or prosthesis implantation (7).
We have measured
platelet survival after aortic resection and implantation of a dacron graft in dogs and after experimental aortic damage in rats. These animal models have been used to assess the potential usefulness of two antiplatelet drugs, sulphinpyrazone and ticlopidine. Sulphinpyrazone has variable effects on platelet aggregation in different species (8,9,10), but has been shown in clinical practice to be effective in preventing thromboembolism Ticlopidine is a new and potent inhibitor of platelet (1,3,5). aggregation in vivo in experimental animals (11) and ex vivo in man (12). MATERIALS AND METHODS Platelet Labelling Platelets were labelled with Ill-Indium-oxine as Blood (22.5 ml) was collected by previously described (13). clean venepuncture from the jugular vein of the dog or by cannulation of the aorta of two donor rats using 3.8% trisodium citrate as anticoagulant (1:9). Platelets were separated by centrifugation using 100 ng/ml Prostaglandin El. (PGEl) to inhibit platelet aggregation (13). The platelet pellet was resuspended to one half the original volume of PRP using Ringer citrate dextrose (306 m.osmol, pH 7.0) containing PGEl and lllIn-oxine was then added. After incubating for 7.5 minutes at 37OC, platelet poor plasma containing PGEl was added, to restore the original volume and the sample centrifuged. The resulting
ANTI-PLATELET
Vo1.15,No.1/2
platelet
pellet
(obtained
was resuspended
by centrifugation
platelet
measured
platelet
from platelets activity
in the cells
vivo elution
was not measured
less
labelling
procedure
and
Experimental
was
Method
anaesthesia
diameter idine
of the labelled
in the rat.
the
aggregation
considered
and replaced
was
knitted
rats
with
second daily.
group
surgery.
was also measured In 3 of these
on two occasions
in
animals
for assessment
in Rats rats were
anaesthetised
A segment forceps
ticlopidine
(n=14) were
The remaining
dogs matched
of the method.
coarse
(n=17) received
Beagle
The
the study.
survival
was measured
on halothane.
then crushed
under
Sulphinpyrazone
of the study.
no treatment.
platelet
of the reproducibility
maintained
greater
the
to 8 dogs for two
the study.
used throughout
dogs not undergoing
Male Wistar
response
twice daily to 8 dogs for 2 days
received
In addition,
Method
that the
(USC1 Ltd). Ticlop-
orally
and for the remainder
for age and sex were
Experimental
In
than 75%, the
rich plasma,
dacron
administered
orally
was given
survival
platelets.
a 2.5 cm length of 5 mm
with
(60 mg/kg)
6 control
of radio-
aorta was resected
and throughout
platelet
of isotope
satisfactory.
days pre-operatively
6 animals
was compared
Provided
was greater
with platelet
ultra-lightweight
remaining
was
in Dogs
(50 mg/kg/day)
pre-operatively
of
of a 5 ml sample of blood with-
In 20 dogs the infrarenal general
platelets
In vivo elution
by the platelets
than 3%
by the platelets
in the dog by measurement
re-injection
than 70% of that achieved
after removal
to 2.2 x 10a5M adenosine
labelled
and plasma
after
of isotope
elution
response
rich plasma.
was measured
drawn one hour
uptake
of isotope
of the resuspended
control
poor plasma
blood
.
of uptake
and the aggregation
diphosphate with
183
in platelet
of titrated
PRP)
rich plasma, The amount
DRUGS
with ether and
of the infrarenal
for 30 seconds. (50 mg/kg)
daily,
given sulphinpyrazone
animals
(n=14) received
aorta was
One group of and the
(60 mg/kg) normal
twice
saline
184
ANTI-PLATELET DRUGS
Vo1.15,No.1/2
(0.5 ml/day) this dose being given once daily to half of the animals and twice daily to the remainder.
The administration of drugs or placebo was performed via a nasogastric tube under light ether anesthesia.
All drugs and placebo were given for two days pre-operatively and throughout the study. Platelet survival was also measured in a further 6 rats not undergoing surgery. Measurement of Platelet Survival For measurement of platelet survival in the dog, 5 ml of blood was withdrawn post-operatively and then daily for 7 days. In the rat, 0.2 ml of blood was withdrawn from the tail vein under ether anesthesia daily for 5 days after operation. The radio-activity in each sample was measured in a Well Crystal detector (NaI) linked to a counter (J & P Engineering Ltd., MS310), the accumulated samples for each animal being counted on the last day of study. Calculation of Results For each animal the radio-activity in the daily sample was expressed as a percentage of the first post-operative sample (i.e. one hour in the dog and one day in the rat). The platelet survival was calculated by a least squares linear regression plot The intercept,a,
of percentage circulating with time (Fig.1). 100
PLATELET SURVIVAL
1
I
survival calculated from a/t
FIG.1 An example of platelet survival in a ticlopidine treated dog following insertion of a dacron graft.
ANTI-PLATELET DRUGS
Vo1.15,No.1/2
185
with the ordinate is an expression of the initial loss of platelets following surgery. Survival was estimated by equating the slope b,with the calculated value of a. Results of the three groups of rats and dogs that had undergone surgery were compared using an unpaired Student's t test. RESULTS The repeated estimations of platelet survival parameters in three control dogs (Table 1) indicated good reproducibility of the method. The mean (,+SD) platelet survival in six dogs not undergoing surgery was 7.03 + 0.28 days with a calculated initial loss of 5.03 + 2.833 and a daily loss of 13.53 + 0.79%.
TABLE 1 Results of Repeated Studies in 3 Dogs Dog
Platelet Survival
Calculated % Platelets circulating at a time zero
% Loss per day
A
7.40 7.22
92.13 101.49
B
6.77 7.09
96.47
14.25
101.90
14.36
91.34 91.93
13.50
C
6.77 6.77
12.44 14.06
13.58
TABLE 2 Comparison of Platelet Survival and Loss Following Surgery in Dogs (Mean 2 S.D.) Group Graft - no drug Graft + Ticlop. Graft + Sulphin
Number
Platelet Survival (days)
6
6.03 2 1.04
8 8
6.46 _+0.59 6.58 ,+0.76
Loss Following Surgery (100-a) 34.27 ,+ 11.00 29.20 t 14.21 18.73 ,+ 12.29
186
ANTI-PLATELET
DRUGS
Vo1.15,No.1/2
Table 2 compares these survival parameters in animals undergoing implantation of a dacron graft, with and without treatment with antiplatelet drugs. Sulphinpyrazone significantly (P
increased platelet survival and decreased platelet loss following surgery. The effects of ticlopidine were not significantly different from the no treatment group. In the aortic damage model in rats, both ticlopidine and sulphinpyrazone significantly increased platelet survival (P
Number
Platelet Survival (days)
Loss Followinq Surgery %
Operation no drug
16
2.89 t 0.22
52.35 f 5.38
Operation + ticlop.
17
3.17 2 0.04
35.82 + 4.59
Operation + sulphin.
14
3.39 ,+0.09
22.13 f 3.52
Platelet survival in the rats receiving sulphinpyrazone was significantly greater (PxO.001) and the percentage loss following surgery was significantly lower (P(O.001) when compared with ticlopidine treated animals. Platelet survival in the 7 rats not undergoing surgery was 3.87 + 0.12 days with a calculated initial loss of platelets of 3.68 f 3.3% and 24.81 2 0.33% removed from circulation per day. DISCUSSION Improvements in long term patency of small diameter synthetic arterial prostheses has been approached by modification in the design and texture of the graft material (14,15,16) and also by the use of oral anticoagulants (17,181. The latter did
Vo1.15,No.1/2
ANTI-PLATELET DRUGS
not however, result In any measurable benefit to the patient (19). with the evidence that antiplatelet drugs reduce thromboembolism in patients with different types of arterial disease, the role of such drugs in preventing or lowering the rate of thrombotic occlusion of synthetic arterial prostheses warrants further investigation. In the present study, measurements of platelet survival have been used to evaluate sulphinpyrazone, which has been clinically assessed in thromboembolic complications, and ticlopidine which is a new drug exhibiting marked effects on platelet
aggregation in ex vivo studies in man and animals. The dosage regimes for the dogs and rats were derived
from preliminary experiments in an attempt to parallel observations with therapeutic levels in man. At the doses used,plasma levels of sulphinpyrazone and the reduced ex-viva aggregation responses
to ADP produced by ticlopidine, were similar to those
seen clinically. The high uptake of Ill-Indium-oxine by platelets has enabled.platelet survival to be measured accurately over a 5 day period, despite the 2.8 days half-life of the isotope. Platelet survival using Ill-Indium-oxine is best described by a linear plot (13). In unoperated dogs and rats, the calculated amount of isotope initially circulating approximates to 100% indicating rapid equilibrium of platelets between spleen and circulation. The observed loss of platelets after surgery probably represents deposition of platelets on the graft surface or site of aortic damage and within the wound. The significant reduction in this loss of platelets in rats treated with sulphinpyrazone or ticlopidine, and in dogs treated with sulphinpyrazone, suggests that these drugs may reduce the early post-operative deposition of platelets at sites of vascular damage, and in the case Of sulphinpyrazone on artificial surfaces. Similarly, the significant lengthening of platelet survival in the treated rats and sulphinpyrazone treated dogs implies a continued protection from thrombogenic activation at the site of aortic damage or on a graft surface. Finally, damage to the rat infrarenal aorta, with subsequent measurement of platelet survival is a useful and
ANTI-PLATELET DRUGS
188
Vol.l5,No.1/2
inexpensive method for comparison of different antiplatelet drugs. From these studies both sulphinpyrazone and ticlopidine merit evaluation as potential agents for reducing the risk of thrombotic occlusion in patients with peripheral vascular disease and also in patients with synthetic arterial prostheses. The authors wish to acknowledge the help of Ciba-Geigy and I.C.I. in providing sulphinpyrazone and ticlopidine respectively for use in this study. REFERENCES 1.
KAEGI, A., PINEO, G.F., SHIMIZU, A., TRIVEDI, H.,HIRSCH,J., and GENT, M. Arterio-venous shunt thrombosis: Prevention by sulphinpyrazone. New Engl.J.Med. 290, 304,1974.
2.
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