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Effect of specific thromboxane-synthetase inhibition on thromboxane and prostaglandin synthesis in stable angina induced by exercise test
THROMBOSIS RESEARCH 37; 259-266, 1985 0049-3848/85 $3.00 + .OO Printed in the USA. Copyright (c) 1985 Pergamon Press Ltd. All rights reserved.
EFFECT OF SPECIFIC THROMBOXANE-SYNTHETASE INHIBITION ON THROMBOXANE AND PROSTAGLANDIN SYNTHESIS IN STABLE ANGINA INDUCED BY EXERCISE TEST
Mogensen,
F., Knudsen, J.B., Rasmussen, V., Kjdller, E., Gormsen, J. 2nd Medical Department and Coagulation Laboratory Municipal Hospital, Copenhagen, Denmark. (Received 14.3.1984; Accepted in revised form 6.11.1984 by Edit& T. Astrup)
ABSTRACT 14 patients with effort induced angina pectoris were treated with a specific TxB inhibitor Dazoxiben or verapamil for two weeks wit 2 a wash-out period of 14 days between the two regimens. A sub-maximal bicycle test was performed before treatment and at the end of each treatment period. The bicycle test induced a significant increase in serum TxB in patients without treatment and during verapami-2.therapy. This increase was significantly inhibited by Dazoxiben treatment. No alterations in plasma TxB or 6-keto-PGF,o were observed on either regimen. Dizoxiben had no clinical effect, while verapamil caused a highly significant prolongation of exercise time.
INTRODUCTION The discovery of the potent vaso-active prostaglandins, prostacyclin (PG12) and thromboxane A (TxA 1 has evoked speculations about the role of these poten $ pros zaglandins in ischemit heart disease, especially in stable and unstable angina pectoris (1). These naturally occurring products of arachidonic acid have opposing effects on vascular tone and platelet behavior. It has been suggested that the PGI /TxA, ratio may play an important role in the regulation of nor 4 al coronary blood flow (2 , 3). Increased platelet reactivity and TxA production in conjunction with decreased PGI production fro & endothelial cells of atherosclerotic vesse 3s (4) may be related to the risk Key words: Effort angina, Dazoxiben, exercise test. 259
verapamil,
thromboxane
B2,
9AZOXIBENEFFECT IN EFFORT ANGINA
Vo1.37, No.2
factors of coronary heart disease as well as to the hemodynamic changes observed during angina1 attacks. Pharmacologically TXA~ production can be inhibited by Dazoxiben which is an orally active specific thromboxane A synthetase inhibitor (5).Dazoxiben decreased the TxA ion capacity of platelets in healthy volunteers an patients with ischemic heart disease by 75-86% (6). By diversion of accumulated endoperoxides from platelets to endothelial cells, the prostacyclin synthetase of these cells may increase the prostacyclin production leading to a beneficial change in the PGI /TxA ratio (7). TO test the biochemical and clinical effects 8f spgcific TxA synthetase inhibition in angina pectoris, patients with stab ze angina were selected and exposed to a standard exercise test. The TxA inhibitor Dazoxiben (Pfizer) was compared with a clin+gT 11y egfective , Knoll). drug, the calcium antagonist verapamil (Isoptin Plasma and serum values of TxB (a stable metabolite of TxA 1 and 6-keto-PGF (a stable metgbolite of PGI 1 were measures in peripheral bled@ immediately before and afte ? each exercise test. Physical capacity and ECG were compared in order to detect the clinical effect of the pharmacological intervention.
MATERIAL
AND METHODS
Patient selection. 14 patients, 11 males and 3 females, mean age of 59 years (50 to 70) with effort-induced angina pectoris and ECG changes indicating ischemia were selected for the study. Five patients had a MI more than three months before entering the study, one had diabetes mellitus and two were previously treated with betablocking agents. Written informed consent was obtained from the participants. Patients in treatment with betablockers or anticoagulants, women of fertile age, patients with arterial hypertension (diastolic pressure >lOO mm Hg), interindications of immittent claudication, bronchitis, asthma, paired liver or kidney function, hematological disorderg, bleeding time (a.m.Duke) > 5 min. or platelet count < 100x10 /l or allergic reactions were excluded from the study. Anti-angina1 medication was restricted to nitroglycerine ad libitum. ASA and non-steroid anti-inflammatory drugs were prohibited. Paracetamol was allowed at a maximum dosage of 1 g t.i.d. Protocol. After an entry period of one week in which sublingual nitroglycerine was the only anti-angina1 therapy, patients were treated with verapamil 120 mg t.i.d. for two weeks and after a drug-free wash-out period of two weeks, Dazoxiben 100 mg t.i.d. for further two weeks. The sequence of therapy was randomly selected. At the beginning and the end of each regimen, a submaximal bicycle exercise test was performed using low increments of 49.2 watts every 4 minutes until the patient claimed unable to continue. Prior to each test a 12-lead ECG was recorded in the recumbent position. Resting heart rate (HR) and blood pressure (BP) were measured after five minutes at rest on the bicycle. Blood samples were taken for analysis of content of TxB in serum and plasma and determination of p ?ateand 6-keto-PGF let aggregatio dl" During exercise a 6-lead ECG was continuously recorded. The appearance time of ischemic changes in the ECG,
Vo1.37, No.2
BAZOXIBENEFFECT IN EFFORT ANGIIIA
261
the time of onset of chest pain and the total duration of exercise were recorded. Immediately after cessation of exercise, BP was measured and blood samples were taken for analysis of the abovementioned parameters. For statistical analysis the Wilcoxon rank sum test of paired samples was applied. Serum TxB sim;asurpments. 5 ml of blood were drawn by veinminimum stasis into glass vials and incubated for puncture 1 hour at 36 C according to Patron0 et al. (8). TxB2 was measured by radioimmunoassay based on the double antibody procedure described by Parry (5). Normal range established in 30 healthy volunteers is SO-150 pg/l. Cross reactivity with other prostaglandins is low. Plasma TxB2 measurements. 5 ml of venous blood was drawn in precooled plastic vials containing 100 ~1 of a solution containing EDTA(69 g/l) and indometacine (18 g/l). The samples were kept on ice for 20 minutes and centrifuged at 3000 G (4 C/20 min.). The plasma was immediately remoged after centrifugation and stored in plastic vials at - 60 C until measurement. measurements. 6-keto-PGF was measured in blood for plasma TxB measurem&t. Plasma 6-keto-PGF was measured by radioimmuno 2 ssay using double antibody tech%que described by Parry (5). Normal levels in volunteers were < 0.04 14/l. Platelet aggregation. Platelet aggregation was measured in a Paton double channel aggregometer determining the threshold concentration of epinephrine. The threshold concentration was defined as the lowest concentration of the aggregation inducer which when added to platelet-rich plasma produced a positive response of no less than 80% of that given by a platelet-poor plasma. Epinephrine (Gauche, Rhdne Poulenc, Paris, France) was used in final concentrations of 0.01 - 0.05 - 0.10 and 1.00 mg/l plasma.
EXPERIMENTAL Clinical results. 14 patients entered the study, one patient randomized to Dazoxiben as first drug, had a myocardial infarction, another withdrew due to moving abroad. 12 patients completed the study. Verapamil treatment caused a marked prolongation of mean exercise time compared to pre-treatment value (fig. 1). No similar prolongation of exercise time occurred during Dazoxiben treatment. Chest pain during verapamil therapy appeared later in 7 patients, at the same time in one and not at all in 4 patients. Dazoxiben did not influence either exercise time or appearance of chest pain in any of the patients. Resting heart rate was not significantly affected neither by verapamil nor by Dazoxiben. Resting blood pressure was significantly reduced during the verapamil therapy compared to baseline values. During treatment with Dazoxiben blood pressure was unaffected. No differences were found between the two baseline
262
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Vo1.37,No.2
values obtained immediately before each treatment
period (table 1). Verapamil caused a marked reduction of the post-exercise mean value of systolic and diastolic blood pressure compared to the pre-treatment baseline values, but no reduction of maximal heart rate (table 1). Dazoxiben caused no changes of heart rate and blood pressure at rest or after exercise compared to pre-treatment values. No withdrawal symptoms or side effects appeared in either regimens and no arrhythmias were observed during the exercise tests. Laboratory results. In the two exercise tests performed before levels were significantly treatment ,_the pre-exercise serum TxB elevated (X = 243 f 24.8 ug/l) compar 2 d with normal range. In 7 out of 12 patients epinephrine enhanced the platelet aggregability (threshold concentration of 0.05 mg/l epinephrine). Plasma were within normal range. concentrations of TxB and 6-keto-PGF levkys in serum of TxB were During treatment the &e-exercise significantly reduced by Dazoxiben to 76 i 15.1 ug/l (p<*O.Ol), but unaffected by verapamil (X = 283 2 31 ug/l) (fig. 2). In 6-keto-PGF,cor plasma no changes in pre-exercise levels of TxB eatment with in aggregation threshold were recorded during t 8' Dazoxiben or verapamil. In the two exercise tests performed before treatment a sig(X = 369 2 38.5 pg/l) was renificant increase in serum TxB corded (p< 0.01). During treat & ent with Dagoxiben post-exercise values of serum TxB remained suppressed (X = 81.5 2 16.5 pg/l) (fig. 2),whereas duging verapamil therapy no depressing effect on post-exercise serum TxB2 values (2 = 346 Z! 41 pg/l) was recorded.
FIG. 1 Effect on maximal exercise duration of verapamil (left) and Dazoxiben (middle section). Comparison of baseline values of the individual patients before treatment with verapamil and Dazoxi< 0.01. ben (right section). Mean f: S.E.M. +-+
Vo1.37, No.2
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263
TABLE 1. Effects of Dazoxiben and Verapamil on Exercise Tolerance, Resting and Exercise Heart Rate, Blood Pressure, and Exercise Duration until Pain. Mean 2 standard deviation. n.s. = not significant. Baseline values before verapamil
Verapamil therapy 360 mg/day
Baseline Dazoxiben thevalues rapy 300 before Dazoxibenmg/day
Resting results Heart rate (HR)beats/min. 84214 n.s. 78213 Systolic BP 138216 ~0.05 128215 mm Hg Diastolic BP mm Hg 882 7 pco.01 78+12
85+10 n.s. 89+14 149220 n.s.145222 90210 n.s. 88212
Exercise results Exercise duration until pain sec. Total exercise duration sec. Peak HR beats/min. Peak syst. BP mm Hg Peak diast. BP mm Hg
490?130n.s.503?142 146215 n.s.151?19 177219 n.s.173+22 88211 n.s. 86211
3,00+75p
144216 n.s. 139217 174225 p
87+, 9pCO.01 75+11
FIG. 2 Effect on TxB levels in serum of submaximal exercise test in patients with'stable angina pectoris without treatment (left), during Dazoxiben (middle) and verapamil therapy (right). TxB concentrations in pg/l. Mean f S.E.M. are indicated by dottea lines and brackets in the figure.
264
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DISCUSSION Prostacyclin mainly produced by endothelial cells and thromboxane A2 produced by platelets are naturally occurring potent antagonizing prostaglandin derivatives endogenously produced from arachidonic acid located in the cell membranes. The vasodilatory and platelet inhibitory effect of prostacyclin in conjunction with the vasoconstrictive and platelet activating effect of TxB has led to the suggestion that the balance between these tw i; potent but shortlived prostaglandins plays a major role in the regulation of vascular tone, as well as in pathological conditions involving vasoconstriction, local ischemia, and platelet aggregation formation and platelet deposition. It has been shown in man that increased TxA production in the myocardial circulation is related to atgacks of unstable angina pectoris (3). A fivefold increase in the difference between thromboxane levels in aorta and the coronary sinus has been recorded in spontaneously occurring angina. A logical approach seems thus to be a specific inhibition of the thromboxane synthesizing capacity, i.e. an inhibition of thromboxane synthetase in platelets. According to present knowledge this should lead to a reduction in platelet plasma thromboxane levels and an inhibition of increased thromboxane production in pathological conditions involving platelet activation. It has further been suggested by Needleman et al. (7) that inhibition of platelet thromboxane synthetase would lead to an accumulation of endoperoxides in platelets which can be diverted to endothelial cells and function as a substrate for the prostacyclin synthetase thus leading to an increased prostacyclin production. In order to test the hypothesis of the importance of the prostaglandins in angina pectoris we have treated patients with stable angina with a specific thromboxane synthetase inhibitor, Dazoxiben, comparing the clinical and biochemical reaction to a standardized physical stress test with the responses in the same patient on non-angina therapy and on therapy with a known antianginal drug, the calciumantagonist verapamil. During exercise a significant increase in serum TxB but not in plasma TxB2 was demonstrated in the non-treatmen $ and verapamil treatment periods. The increase in serum TxB abolished by Dazoxiben treatment, but the plasma TxB 2 4aZs were normal and unaffected by this treatment. This 1 st observation was also made by Reuben et al. (9). The plasma TxB2 in the levels reflect the actual circulating levels of TxB patient's plasma at the time when the samples were 2 rawn. The serum TxB values represent the maximal TxB2 production capacity of t4 e patient's platelets, when gxposed to thrombin during clotting in the test tube at 37 C for 60 minutes. The effects on platelets of the standardized physiological stress of the ergometer-cycle test is an increase in their maximal This TxB2 synthesizing capacity when exposed to thrombin. increase in TxB2 synthesizing capacity may be secondary to an increase in platelet reactivity induced by the increased me-
Vo1.37,No.2
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chanical forces on circulating cells in peripheral blood during periods of elevated cardiac output and blood pressure. The plasma levels of TxB2 was not elevated by the standard physical or other biochemical stress test indicating that no thrombin 9%~ production inducers were present in the patient's circulat$on at the time of experiment to challenge the increased TxB synthesizing capacity of platelets. The results of the pregent study indicate that the standardized physical stress test in stable angina pectoris does not produce a state Of platelet activation involving significant TxB2 generation. This is in contrast to findings in unstable angina (3). synthetase inhibition is thus an inappropriSpecific TxB ate approach to $he pathophysiological mechanism and hence without clinical effect as demonstrated in this study. The synthesis induced by thrombin. in the serum inhibition of TxB samples reflects & erely the biochemical activity of the drug, while the lack of consistent effects on platelet aggregation formed from the reflects the opposing effect of accumulated endoperoxides during TX During specific thromboxane clinical or electrocardiographical parameter indicated improved physical performance of the patient. In contrast, verapamil caused a highly significant prolongation of exercise time. This indicates that the participating patients responded adequately to antianginal therapy and that the physical strain during the exercise tests was sufficient to induce myocardial ischemia (10). We conclude, that specific TxA2 synthetase inhibition with Dazoxiben in patients with stable angina pectoris is capable of reducing the serum levels of TXB significantly, but has no effect on plasma TxB plasma 6-kets-PGF and on clinical and 1 parameters in exe 1e* cise tests. electrocardiographic 2'
REFERENCES 1. HIRSCH, P.D., CAMBELL, W.B., WILLERSON, I-T., and HELLIS, P.L. Prostaglandins and ischemic heart disease. Am J Med 71, 1009-1021, 1981. 2. MONCADA, S. and VANE, J.R. Arachidonic acid metabolites and the interactions between platelets and blood-vessel walls. N Engl J Med 300, 1142-1147, 1979. 3. LEWY, R.I., WEINER, L., WALMSKY, P., LEFER, A.N., SILVER, M.J. and SMITH, J.B. Thromboxane release during pacing induced angina pectoris: Possible vasoconstrictor influence on the coronary vasculature. Circulation 61, 1165-1171, 1980. 4. D'ANGELO, V., VILLA, S., MYSLIWIEC, M., DONATI, M.B. and DE GAETANO, G. Defective fibrinolytic and prostacyclin-like activity in human atheromatous plaques. Thromb Haemostas 2, 535-536, 1978.
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EFFECT
IN EFFORT ANGINA
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5.
PARRY, M.J. Effects of thromboxane synthetase inhibition on arachidonate metabolism and platelet behaviour. Br J Clin Pharmac 15, 235-295, 1983.
6.
TYLER, H-M., SAXTON, C.A.P.D. and PARRY, M.J. Administration a selective inhibitor of thromboxto man of UK 37.248-01, ane synthetase. Lancet l_, 629-632, 1981.
7.
NEEDLEMAN, P., WYCHE, A. and RAZ, A. Platelet and blood vessel arachidonate metabolism and interactions. J Clin Invest 12, 345-349, 1979.
8.
PATRONO, C., CIABBATONI, G. and PINCA, E. Low dose aspirin and inhibition of thromboxane B production in healthy subjects. Thromb Res 17, 317-326, 1980.
9.
REUBEN, S.R., KUAN, P., CAIRNS, J. and GYDE, O.H. Effects of Dazoxiben on exercise performance in chronic stable angina. Br J Clin Pharmac 15, suppl.: Dazoxiben - clinical prospects for a thromboxane synthetase inhibitor, 83 S 86
S,
1983.
IO.
PINE, M.B., CITRON, P.D., BAILLY, D-J., BUTMAN, S., PLASENCIA, G.O., LANDA, D.W. and WONG, R.K. Verapamil versus placebo in relieving stable angina pectoris. Circulation 65, 17-22, 1982.
11.
BERTELk, V. FALANGA, A., TOMASIAK, M., CHIABRANDO, C., CERLETTI, C. and DE GAETANO, G. Pharmacological inhibition of thromboxane synthetase and platelet aggregation: Modulatory role of cyclooxygenase products. Blood 63, 1460-1466, 1984.
EFFECT OF SPECIFIC THROMBOXANE-SYNTHETASE INHIBITION ON THROMBOXANE AND PROSTAGLANDIN SYNTHESIS IN STABLE ANGINA INDUCED BY EXERCISE TEST
Mogensen,
F., Knudsen, J.B., Rasmussen, V., Kjdller, E., Gormsen, J. 2nd Medical Department and Coagulation Laboratory Municipal Hospital, Copenhagen, Denmark. (Received 14.3.1984; Accepted in revised form 6.11.1984 by Edit& T. Astrup)
ABSTRACT 14 patients with effort induced angina pectoris were treated with a specific TxB inhibitor Dazoxiben or verapamil for two weeks wit 2 a wash-out period of 14 days between the two regimens. A sub-maximal bicycle test was performed before treatment and at the end of each treatment period. The bicycle test induced a significant increase in serum TxB in patients without treatment and during verapami-2.therapy. This increase was significantly inhibited by Dazoxiben treatment. No alterations in plasma TxB or 6-keto-PGF,o were observed on either regimen. Dizoxiben had no clinical effect, while verapamil caused a highly significant prolongation of exercise time.
INTRODUCTION The discovery of the potent vaso-active prostaglandins, prostacyclin (PG12) and thromboxane A (TxA 1 has evoked speculations about the role of these poten $ pros zaglandins in ischemit heart disease, especially in stable and unstable angina pectoris (1). These naturally occurring products of arachidonic acid have opposing effects on vascular tone and platelet behavior. It has been suggested that the PGI /TxA, ratio may play an important role in the regulation of nor 4 al coronary blood flow (2 , 3). Increased platelet reactivity and TxA production in conjunction with decreased PGI production fro & endothelial cells of atherosclerotic vesse 3s (4) may be related to the risk Key words: Effort angina, Dazoxiben, exercise test. 259
verapamil,
thromboxane
B2,
9AZOXIBENEFFECT IN EFFORT ANGINA
Vo1.37, No.2
factors of coronary heart disease as well as to the hemodynamic changes observed during angina1 attacks. Pharmacologically TXA~ production can be inhibited by Dazoxiben which is an orally active specific thromboxane A synthetase inhibitor (5).Dazoxiben decreased the TxA ion capacity of platelets in healthy volunteers an patients with ischemic heart disease by 75-86% (6). By diversion of accumulated endoperoxides from platelets to endothelial cells, the prostacyclin synthetase of these cells may increase the prostacyclin production leading to a beneficial change in the PGI /TxA ratio (7). TO test the biochemical and clinical effects 8f spgcific TxA synthetase inhibition in angina pectoris, patients with stab ze angina were selected and exposed to a standard exercise test. The TxA inhibitor Dazoxiben (Pfizer) was compared with a clin+gT 11y egfective , Knoll). drug, the calcium antagonist verapamil (Isoptin Plasma and serum values of TxB (a stable metabolite of TxA 1 and 6-keto-PGF (a stable metgbolite of PGI 1 were measures in peripheral bled@ immediately before and afte ? each exercise test. Physical capacity and ECG were compared in order to detect the clinical effect of the pharmacological intervention.
MATERIAL
AND METHODS
Patient selection. 14 patients, 11 males and 3 females, mean age of 59 years (50 to 70) with effort-induced angina pectoris and ECG changes indicating ischemia were selected for the study. Five patients had a MI more than three months before entering the study, one had diabetes mellitus and two were previously treated with betablocking agents. Written informed consent was obtained from the participants. Patients in treatment with betablockers or anticoagulants, women of fertile age, patients with arterial hypertension (diastolic pressure >lOO mm Hg), interindications of immittent claudication, bronchitis, asthma, paired liver or kidney function, hematological disorderg, bleeding time (a.m.Duke) > 5 min. or platelet count < 100x10 /l or allergic reactions were excluded from the study. Anti-angina1 medication was restricted to nitroglycerine ad libitum. ASA and non-steroid anti-inflammatory drugs were prohibited. Paracetamol was allowed at a maximum dosage of 1 g t.i.d. Protocol. After an entry period of one week in which sublingual nitroglycerine was the only anti-angina1 therapy, patients were treated with verapamil 120 mg t.i.d. for two weeks and after a drug-free wash-out period of two weeks, Dazoxiben 100 mg t.i.d. for further two weeks. The sequence of therapy was randomly selected. At the beginning and the end of each regimen, a submaximal bicycle exercise test was performed using low increments of 49.2 watts every 4 minutes until the patient claimed unable to continue. Prior to each test a 12-lead ECG was recorded in the recumbent position. Resting heart rate (HR) and blood pressure (BP) were measured after five minutes at rest on the bicycle. Blood samples were taken for analysis of content of TxB in serum and plasma and determination of p ?ateand 6-keto-PGF let aggregatio dl" During exercise a 6-lead ECG was continuously recorded. The appearance time of ischemic changes in the ECG,
Vo1.37, No.2
BAZOXIBENEFFECT IN EFFORT ANGIIIA
261
the time of onset of chest pain and the total duration of exercise were recorded. Immediately after cessation of exercise, BP was measured and blood samples were taken for analysis of the abovementioned parameters. For statistical analysis the Wilcoxon rank sum test of paired samples was applied. Serum TxB sim;asurpments. 5 ml of blood were drawn by veinminimum stasis into glass vials and incubated for puncture 1 hour at 36 C according to Patron0 et al. (8). TxB2 was measured by radioimmunoassay based on the double antibody procedure described by Parry (5). Normal range established in 30 healthy volunteers is SO-150 pg/l. Cross reactivity with other prostaglandins is low. Plasma TxB2 measurements. 5 ml of venous blood was drawn in precooled plastic vials containing 100 ~1 of a solution containing EDTA(69 g/l) and indometacine (18 g/l). The samples were kept on ice for 20 minutes and centrifuged at 3000 G (4 C/20 min.). The plasma was immediately remoged after centrifugation and stored in plastic vials at - 60 C until measurement. measurements. 6-keto-PGF was measured in blood for plasma TxB measurem&t. Plasma 6-keto-PGF was measured by radioimmuno 2 ssay using double antibody tech%que described by Parry (5). Normal levels in volunteers were < 0.04 14/l. Platelet aggregation. Platelet aggregation was measured in a Paton double channel aggregometer determining the threshold concentration of epinephrine. The threshold concentration was defined as the lowest concentration of the aggregation inducer which when added to platelet-rich plasma produced a positive response of no less than 80% of that given by a platelet-poor plasma. Epinephrine (Gauche, Rhdne Poulenc, Paris, France) was used in final concentrations of 0.01 - 0.05 - 0.10 and 1.00 mg/l plasma.
EXPERIMENTAL Clinical results. 14 patients entered the study, one patient randomized to Dazoxiben as first drug, had a myocardial infarction, another withdrew due to moving abroad. 12 patients completed the study. Verapamil treatment caused a marked prolongation of mean exercise time compared to pre-treatment value (fig. 1). No similar prolongation of exercise time occurred during Dazoxiben treatment. Chest pain during verapamil therapy appeared later in 7 patients, at the same time in one and not at all in 4 patients. Dazoxiben did not influence either exercise time or appearance of chest pain in any of the patients. Resting heart rate was not significantly affected neither by verapamil nor by Dazoxiben. Resting blood pressure was significantly reduced during the verapamil therapy compared to baseline values. During treatment with Dazoxiben blood pressure was unaffected. No differences were found between the two baseline
262
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values obtained immediately before each treatment
period (table 1). Verapamil caused a marked reduction of the post-exercise mean value of systolic and diastolic blood pressure compared to the pre-treatment baseline values, but no reduction of maximal heart rate (table 1). Dazoxiben caused no changes of heart rate and blood pressure at rest or after exercise compared to pre-treatment values. No withdrawal symptoms or side effects appeared in either regimens and no arrhythmias were observed during the exercise tests. Laboratory results. In the two exercise tests performed before levels were significantly treatment ,_the pre-exercise serum TxB elevated (X = 243 f 24.8 ug/l) compar 2 d with normal range. In 7 out of 12 patients epinephrine enhanced the platelet aggregability (threshold concentration of 0.05 mg/l epinephrine). Plasma were within normal range. concentrations of TxB and 6-keto-PGF levkys in serum of TxB were During treatment the &e-exercise significantly reduced by Dazoxiben to 76 i 15.1 ug/l (p<*O.Ol), but unaffected by verapamil (X = 283 2 31 ug/l) (fig. 2). In 6-keto-PGF,cor plasma no changes in pre-exercise levels of TxB eatment with in aggregation threshold were recorded during t 8' Dazoxiben or verapamil. In the two exercise tests performed before treatment a sig(X = 369 2 38.5 pg/l) was renificant increase in serum TxB corded (p< 0.01). During treat & ent with Dagoxiben post-exercise values of serum TxB remained suppressed (X = 81.5 2 16.5 pg/l) (fig. 2),whereas duging verapamil therapy no depressing effect on post-exercise serum TxB2 values (2 = 346 Z! 41 pg/l) was recorded.
FIG. 1 Effect on maximal exercise duration of verapamil (left) and Dazoxiben (middle section). Comparison of baseline values of the individual patients before treatment with verapamil and Dazoxi< 0.01. ben (right section). Mean f: S.E.M. +-+
Vo1.37, No.2
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TABLE 1. Effects of Dazoxiben and Verapamil on Exercise Tolerance, Resting and Exercise Heart Rate, Blood Pressure, and Exercise Duration until Pain. Mean 2 standard deviation. n.s. = not significant. Baseline values before verapamil
Verapamil therapy 360 mg/day
Baseline Dazoxiben thevalues rapy 300 before Dazoxibenmg/day
Resting results Heart rate (HR)beats/min. 84214 n.s. 78213 Systolic BP 138216 ~0.05 128215 mm Hg Diastolic BP mm Hg 882 7 pco.01 78+12
85+10 n.s. 89+14 149220 n.s.145222 90210 n.s. 88212
Exercise results Exercise duration until pain sec. Total exercise duration sec. Peak HR beats/min. Peak syst. BP mm Hg Peak diast. BP mm Hg
490?130n.s.503?142 146215 n.s.151?19 177219 n.s.173+22 88211 n.s. 86211
3,00+75p
144216 n.s. 139217 174225 p
87+, 9pCO.01 75+11
FIG. 2 Effect on TxB levels in serum of submaximal exercise test in patients with'stable angina pectoris without treatment (left), during Dazoxiben (middle) and verapamil therapy (right). TxB concentrations in pg/l. Mean f S.E.M. are indicated by dottea lines and brackets in the figure.
264
DAZOXIBEN EFFECT IN EFFORT ANGINA
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DISCUSSION Prostacyclin mainly produced by endothelial cells and thromboxane A2 produced by platelets are naturally occurring potent antagonizing prostaglandin derivatives endogenously produced from arachidonic acid located in the cell membranes. The vasodilatory and platelet inhibitory effect of prostacyclin in conjunction with the vasoconstrictive and platelet activating effect of TxB has led to the suggestion that the balance between these tw i; potent but shortlived prostaglandins plays a major role in the regulation of vascular tone, as well as in pathological conditions involving vasoconstriction, local ischemia, and platelet aggregation formation and platelet deposition. It has been shown in man that increased TxA production in the myocardial circulation is related to atgacks of unstable angina pectoris (3). A fivefold increase in the difference between thromboxane levels in aorta and the coronary sinus has been recorded in spontaneously occurring angina. A logical approach seems thus to be a specific inhibition of the thromboxane synthesizing capacity, i.e. an inhibition of thromboxane synthetase in platelets. According to present knowledge this should lead to a reduction in platelet plasma thromboxane levels and an inhibition of increased thromboxane production in pathological conditions involving platelet activation. It has further been suggested by Needleman et al. (7) that inhibition of platelet thromboxane synthetase would lead to an accumulation of endoperoxides in platelets which can be diverted to endothelial cells and function as a substrate for the prostacyclin synthetase thus leading to an increased prostacyclin production. In order to test the hypothesis of the importance of the prostaglandins in angina pectoris we have treated patients with stable angina with a specific thromboxane synthetase inhibitor, Dazoxiben, comparing the clinical and biochemical reaction to a standardized physical stress test with the responses in the same patient on non-angina therapy and on therapy with a known antianginal drug, the calciumantagonist verapamil. During exercise a significant increase in serum TxB but not in plasma TxB2 was demonstrated in the non-treatmen $ and verapamil treatment periods. The increase in serum TxB abolished by Dazoxiben treatment, but the plasma TxB 2 4aZs were normal and unaffected by this treatment. This 1 st observation was also made by Reuben et al. (9). The plasma TxB2 in the levels reflect the actual circulating levels of TxB patient's plasma at the time when the samples were 2 rawn. The serum TxB values represent the maximal TxB2 production capacity of t4 e patient's platelets, when gxposed to thrombin during clotting in the test tube at 37 C for 60 minutes. The effects on platelets of the standardized physiological stress of the ergometer-cycle test is an increase in their maximal This TxB2 synthesizing capacity when exposed to thrombin. increase in TxB2 synthesizing capacity may be secondary to an increase in platelet reactivity induced by the increased me-
Vo1.37,No.2
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chanical forces on circulating cells in peripheral blood during periods of elevated cardiac output and blood pressure. The plasma levels of TxB2 was not elevated by the standard physical or other biochemical stress test indicating that no thrombin 9%~ production inducers were present in the patient's circulat$on at the time of experiment to challenge the increased TxB synthesizing capacity of platelets. The results of the pregent study indicate that the standardized physical stress test in stable angina pectoris does not produce a state Of platelet activation involving significant TxB2 generation. This is in contrast to findings in unstable angina (3). synthetase inhibition is thus an inappropriSpecific TxB ate approach to $he pathophysiological mechanism and hence without clinical effect as demonstrated in this study. The synthesis induced by thrombin. in the serum inhibition of TxB samples reflects & erely the biochemical activity of the drug, while the lack of consistent effects on platelet aggregation formed from the reflects the opposing effect of accumulated endoperoxides during TX During specific thromboxane clinical or electrocardiographical parameter indicated improved physical performance of the patient. In contrast, verapamil caused a highly significant prolongation of exercise time. This indicates that the participating patients responded adequately to antianginal therapy and that the physical strain during the exercise tests was sufficient to induce myocardial ischemia (10). We conclude, that specific TxA2 synthetase inhibition with Dazoxiben in patients with stable angina pectoris is capable of reducing the serum levels of TXB significantly, but has no effect on plasma TxB plasma 6-kets-PGF and on clinical and 1 parameters in exe 1e* cise tests. electrocardiographic 2'
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IN EFFORT ANGINA
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REUBEN, S.R., KUAN, P., CAIRNS, J. and GYDE, O.H. Effects of Dazoxiben on exercise performance in chronic stable angina. Br J Clin Pharmac 15, suppl.: Dazoxiben - clinical prospects for a thromboxane synthetase inhibitor, 83 S 86
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PINE, M.B., CITRON, P.D., BAILLY, D-J., BUTMAN, S., PLASENCIA, G.O., LANDA, D.W. and WONG, R.K. Verapamil versus placebo in relieving stable angina pectoris. Circulation 65, 17-22, 1982.
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BERTELk, V. FALANGA, A., TOMASIAK, M., CHIABRANDO, C., CERLETTI, C. and DE GAETANO, G. Pharmacological inhibition of thromboxane synthetase and platelet aggregation: Modulatory role of cyclooxygenase products. Blood 63, 1460-1466, 1984.