- Email: [email protected]
Effects on platelet aggregation and fibrinolytic activity during upright posture and exercise in healthy men
MISCELLANEOUS
Effects on Platelet Aggregation and Fibrinolytic Activity During Upright Posture and Exercise in Healthy Men Kaj Winther, MD, PhD, William Hillegass, MD, Geoffrey H. Tofler, MB, Alfred0 Jimenez, MD, Damian A. Brezinski, MD, Andrew I. Schafer, MD, Joseph Loscalzo, MD, PhD, Gordon H. Williams, MD, and James E. Muller, MD
The circadian variation of acute myocardial infarction suggests that daily activities such as assuming the upright posture and performing different daily activities may trigger the onset of coronary thrombosfs. Such triggering may result from unfavorable alterations in the balance between the prothrombotic and antfthrombotic properties of the blood. The present study compares the effects of 2 common daily activities, assuming the upright posture and exercise, on platelet aggregation and fibrindytfc activity. In healthy male subjects, assuming the upright posture in the morning dgnificantly increased platelet aggregation and produced only a moderate increase in ffbrinolytic activity within 10 minutes. These changes were sttll present after 90 minutes in the upright posture. Supine posture for 45 minutes resulted in levels of ffbrinolytZc actfvfty and platelet aggregation comparable to that observed before initially assuming the upright posture in the morning. Return to the supine posture for 45 minutes resulted in levels of fibrlnofytfc actfvity and platelet aggregation comparable to that observed before the initial assumption of upright posture. The changes recurred when upright posture was taken later in the day. Exercise dkl not increase platelet aggregation to levels beyond that produced by the upright posture, but was assocfated with a marked increase in ffbrinolyttc activity. Thus, exercise and upright posture produce distinctive alterations in the thrombogenfc potential of the blood that may influence the timing of clinfcal vascular events. (Am J Cardiol 1992;70:1051-1055)
he frequenciesof onset of myocardial infarction and sudden cardiac death have a prominent circadian variation, with an increase in the period from 6 A.M. to noon.1,2During this time period, subjects assumethe upright posture and perform physical exertion - 2 activities that activate the sympathetic nervous system and may cause systemic changesin blood clotting that predisposeto coronary artery thrombosis.3,4 Assumption of the upright posture in the morning is associated with increased platelet aggregability.4 However, the ability of the upright posture to increaselibrinolytic activity, a change that would tend to reduce the thrombotic potential of the blood, has not been previously described.Although it is agreed that exercise increaseslibrinolysis,5~6the effects of exerciseon platelet aggregation are controversial.7-11 The goalsof this study, therefore, were to answerthe following questionsconcerning the effectsof the upright posture and exerciseon platelet aggregability and librinolysis: (1) What is the time course of the effect of the upright posture in the morning on platelet aggregability? (2) Does assuming the upright posture at a later time of day causea similar increase?(3) Is the adverse effect, if it occurs, of assuming the upright posture on platelet aggregability counterbalancedby an increasein fibrinolytic activity? (4) Does exercise produce an increasein platelet aggregability beyond that produced by the upright posture? (5) What are the relative profiles of the effects of the upright posture and exercise on these determinants of thrombosis?
T
METHOD9
This report describes2 studiesof 12 male volunteers, each drawn from a total pool of 22 subjects,aged 20 to 32 years (mean 24), who were all nonsmokers,and taking no aspirin or other medication in the previous 2 weeks.All had given informed consent. On the day before the study, all subjectswere admitted to the Clinical Research Center of the Brigham and Women’s HospiFrom the Harvard Medical School, Boston,Massachusetts.This study tal. Lights were turned out at midnight, and subjects was supported in part by Grants HL 36045 and HL 40411 from the were awakened at 7:30 A.M. the following morning for National Institutes of Health, Bethesda,Maryland; and grants from the initiation of the study. After arrival at the hospital, the Danish Medical ResearchCouncil, the Danish Heart Foundation,and subjects received a controlled fmed diet. The subjects Sandoz Pharmaceuticals,and was conductedat the Clinical Research Center of the Brigham and Women’s Hospital, Harvard Medical did not drink any coffee,tea or hot chocolate after they School, Boston, Massachusetts,supported by Grant 5MOI-RR02635 were awakened on the study morning. Coffee was not from the National Institutes of Health. The data were analyzed in a provided during the study; however, tea and chocolate CLINFO facility supported by the same grant. Manuscript received were available in the evening before the study. The efJanuary 15, 1992; revised manuscript received and acceptedJune 15, fects of these agents would have have worn off before 1992. Addressfor reprints: Kaj Winther, MD, PhD, Department of Clini- the morning studies, during which 250 ml of juice and drinking water were available. cal Chemistry, Glostrup Hospital, DK-2600 Glostrup, Denmark. POSTURE CHANGE, EXERCISE, PLATELETS AND FIBRINOLYSIS
1051
Phase I was designed to determine (1) the time course of the effect of the upright posture in the moming on plasma catecholamine levels and platelet aggregability; and (2) whether the upright posture at a later time of day causes similar changes. After waking at 7:30 A.M., the 12 subjects remained supine for 30 minutes. Then, they assumedthe upright posture, remained upright until 9:30 A.M., lay supine until 11:30 A.M., and returned to the upright posture for 90 minutes at the end of the protocol (Figure 1). Blood sampleswere obtained at 8 A.M. while the subjects were still supine in bed, and after 6,45 and 90 minutes in the upright position. Blood sampleswere then obtained after 2 hours in the supine position, and finally 90 minutes after patients had returned to reassumethe upright posture. PhaseII was designedto determine (1) whether the adverseeffect of the upright posture on platelet aggregability is associatedwith an increasein fibrinolytic activity; (2) if exercise produces an increase in platelet aggregability beyond that produced by the upright posture; and (3) the relative profiles of the effects of the 2 activities - upright posture or exercise- on platelet aggregability and librinolytic activity.
-
6o B 2 50B 8 40 b 3 30. 8 20% $ to0SVPlM am8
“p,lpht
Supne
9
to
TIME I~<005
1052
VERSUS
tt
urmqtlt
I2
I 1
2Pm
OF DAY
PREVIOUS
TIMEPOINT
THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 70
After they were awakened at 7:30 A.M., 12 subjects (2 of whom participated in phaseI) remained in bed for 30 minutes. Then, they assumedthe upright posture (as in phaseI), remained upright for 90 minutes, lay supine for another 45 minutes, returned to the upright posture for 90 minutes, and then performed a standardized bicycle test (Figure 2). Blood sampleswere obtained at 8 A.M. while the subjectswere still supine in bed, at 10 and 90 minutes after taking the upright posture, and 10 and 45 minutes after they returned to the supine position. At 11:45 A.M., after being in the upright posture for 90 minutes, they were placed on a cycle ergometer with a mechanically controlled brake to regulate the work load. Blood was drawn at 11:55 A.M., immediately before exercise,and again at 12:05 P.M. immediately after exercise.The initial work load of 50 W was increased by 50 W every 3 minutes of exercise.Subjectsexercised until approximately 90% of maximal working capacity was achieved (mean exercise duration 10.4 minutes). Blood pressure was measured at 8:02 A.M. (2 minutes after assumingthe upright posture), at 11:55A.M. while sitting on the bicycle, and immediately after exercise using a mercury sphygmomanometer;heart rate was determined at the same time points. Blaod sampling: Blood sampleswere drawn without stasis from an antecubital vein with the use of a 21 gaugebutterfly needle,and processedimmediately. Sep arate venipunctures were performed at each time point. Twenty-sevenmilliliters of blood was drawn into a plastic syringe containing 3 ml 3.8% sodium citrate for platelet aggregationand euglobulin clot lysis time. Samples of 5 ml were collected in alternate syringes for analysis of catecholamines,plasma renin activity, hematocrit value and platelet count; and another 5 ml samplewas drawn for tissue-typeplasminogenactivator antigen and plasminogen activator inhibitor activity. Platelet aggregation, plasma catecholamines,renin activity, hematocrit and platelet count were determined as previously described.3*4Euglobulin clot lysis time was estimatedaccording to normal laboratory routine.‘* Tissue-type plasminogen activator antigen (ELISA) and plasminogen activator inhibitor activity (chromogenic method) were determined using reagents from the STAG0 Diagnostic System. Statistkal analysis: Comparison between the mean values at different time points was performed with the Wilcoxon signed rank test for paired data. Variations from mean values are expressedas f standard error of the mean. Two-tailed p values 10.05 were regarded as statistically significant. RESULTS Phase I: time course of platelet aggregability CmlldCabChOhlllifle
dUllgeS:
PLATELET AGGREGABILITY:
Adenosine diphosphate-induced platelet aggregability significantly increased after 45 minutes in the upright position as indicated by a decreasein mean adenosine diphosphatethreshold concentrationsfrom 4.1 f 0.4 to 2.7 f 0.2 PM (p
TABLE I Platelet Aggregation, t-PA Antigen, Inhibitor Against t-PA (plasminogen activator inhibitor), Platelet Count, Hematocrit, and Plasma Epinephrine, Norepinephrine and Renin are Given at Different Time Points for Subjects During Phase II Supine
Platelet aggregation (ADP thresholds bM) t-PA antigen (rig/ml) PAI activity (IU/ml) Platelet count (103/mm3) Hematocrit (%I Plasma epinephrine (pgiml) Plasma noreplnephrine (pg/ml) Plasma renin activity (nlimllhour)
(8 A.M.)
Upright (8.10 A.M.)
(9.30
Upright
Supine
5.4 + 0.6
4.0 + 0.5
4.4 + 0.4
4.0 + 0.4
4.7 ‘- 1.2 1.06 + 0.4 261 + 16
7.7 t 1.7* 0.97 T 0.3 295 2 90*
5.9 2 1.7 0.94 + 0.3 285 k 16
42.8 t 0.61 32.2 -t 4.8
44.0 2 0.61* 54.0 + 5.6*
164 i: 23 1.14 2 0.2
A.M.)
(9.40
Supine (10.15 A.M.)
A.M.)
Upright
(11.55
A.M.)
Exercise (12.05 P.M.)
5.2 2 0.2t
4.3 + 0.4*
3.8 + 0.4
4.9 Yk 1.2* 1.09 k 0.4 273 -t 17*
4.7 2 1.3 0.80 -c 0.4 275 k 18
4.9 + 1.1 0.63 t 0.3 293 + 21*
17.7 + 4.0t 0.77 k 0.2 345 2 20t
44.3 -t 0.71 50.5 k 8.3
43.3 zk 0.61* 33.0 + 7.1*
42.9 k 0.51 28.5 1 1.9
43.8 k 0.6* 42.5 ‘- 5.1*
47.1 ? 0.7* 213 + 34t
310 + 40*
335 + 47
207 ? 31*
202 + 26
295 -c 32*
1670 k 314t
1.45 k 0.2*
2.88 k 0.6*
2.28 + 0.4
1.40 + 0.4*
2.73 + 0.7*
3.38 k 0.5
*p CO.05 versus prewus time point: tp CO.05 versus 9:30 A.M. Valuesare mean i SEM, n = 12. ADP = adenoslne dlphosphate: PAI = plasmlnogen activator InhibItor:
t-PA = tissue-type
plasminogen
activator.
I
2.2 to 4.7 f 1.5 PM (p <0.06). Return to the supine posture for 2 hours was sufficient to permit return of platelet aggregability to the level observedafter the 8hour overnight supine period (Figure 1). Finally, reassumption of the upright posture produced an increasein aggregability indistinguishable from that observedafter initially assuming the upright posture. PLASMACATECHOLAMINELEVELS: Therewasa marked surge in the levels of plasma catecholamines after assuming the upright posture. Within 10 minutes, plasma epinephrine and norepinephrine more than doubled (Figure 1, p <0.02). Return to the supine posture for 2 hours resulted in a reduction in values to levels comparable to those observed at 8 A.M., whereas subsequent return to the upright posture resulted in a similar-pattern to that observed earlier in the day (Figure 1, p
tha
dkCt
Of
aXemiNi
plasminogenactivator inhibitor activity (Table I). These changeswere less pronounced 90 minutes after assuming the upright posture. Return to the supine posture for 45 minutes resulted in tissue-typeplasminogenactivator levels similar to those observed before the initial assumption of upright posture in the morning (Table I). Returning to the upright posture resulted in euglobulin clot lysis time changessimilar to those noted at the initial upright posture. Exercise causeda marked shortening of the euglobulin clot lysis time and an increase in tissue-type plasminogen activator antigen from 4.9 f 1.1 to 17.7 f 4.0 rig/ml (p
PLATELET AGGREGABILITY:
Platelet aggregability increased 10 and 90 minutes after initial assumptionof the upright posture as indicated by a decreasein the mean threshold values of adenosine diphosphate and epinephrine (Table I, Figure 2). Return to supine posture for 10 minutes did not alter platelet aggregation; however,aggregation returned to initial 8 A.M. levels after 45 minutes in the supine position (Table I, Figure 2). When subjects reassumedthe upright posture, the changesin platelet aggregation were cornparable to those observedafter initial assumptionof the upright posture. Exercise, however,did not causea further increase in platelet aggregation as indicated by similar threshold concentrations of 4.3 f 0.4 and 3.8 f 0.4 PM for adenosinediphosphate and 1.0 f 0.2 and 1.1 f 0.4 PM for epinephrine (Table I, Figure 2). FIBRINOLYTIC ACTIVITY: Fibrinolytic activity increased 10 minutes after initially assuming the upright posture as indicated by a shortening of the euglobulin clot lysis time from 130 f 20 to 95 f 17 minutes (p <0.02) (Figure 2) and an increase in tissue-type plasminogen activator antigen from 4.7 f 1.2 to 7.7 f 1.7 rig/ml (p
F B 2 5 $ 6-
L I 8om * P’O.05
I
9
VERSUS
I
I
10
L
PREVIOUS
I I 11
, 12
TIMEPOINT
FlGURE2.Shdhmomdungarinpbtakt~lity
(M , w wS
Blmheldv~)end~sls(~det ~posbedumgesmdexer-
d -ds,mmze
hreasesadythefomer(v~ra-fM,n=l?).
POSTURE CHANGE, EXERCISE, PLATELETS AND FIBRINOLYSIS
1053
PLASMA CATECHOLAMINE AND RENIN CHANGES: Assuming the upright posture resulted in an increase in plasma catecholaminescomparable to that observedin phaseI, whereasexerciseincreasedthe plasmacatecholamine level more than fivefold (Table I). An increasein plasma renin activity was observedafter 10 and 90 minutes in the upright posture (p
suming the upright posture, and exercise. It demonstrates that (1) assuming the upright posture in the morning produces a rapid surge in plasma catecholamine and renin activity levels that is accompaniedby increased platelet aggregability; (2) the changes produced by the upright posture ceasewithin 45 minutes after return to the supine position; (3) taking the upright posture later in the day produceschangessimilar to those produced in the morning; (4) the upright posture producesa moderate increasein librinolytic activity that tends to be less pronounced after 90 minutes in the upright position; (5) exercise does not increase platelet aggregability to a level higher than that caused by the upright posture but is associatedwith a signilicant increasein catecholamines,fibrinolytic activity and hematocrit value. Thus, the upright posture and exercise produce different profiles of changesin thesedeterminants of thrombosis. The demonstration in the present study that upright posture causesan increasein platelet aggregability (Figures 1 and 2, Table I) confirms previous reports of this phenomenon in normal subjects and in patients with coronary artery disease.4J3The present study adds new findings: This increasecan be reversedby return to the supine position, and it can be reproduced by assuming upright posture at a later time of day. The degree to which the increase in fibrinolytic activity associatedwith the upright posture modifies the overall thrombotic tendency of the blood is unknown, since it is not possible simply to add or subtract the results of the 2 processes.However, changesin platelet aggregation and fibrinolytic activity are homeostatic or DISCUSSION This study clarifies several aspectsof the changesin autoregulatory, serving to maintain blood fluidity (Figdeterminants of thrombus formation produced by as- ures 2 and 3 [a and b]). It is uncertain whether patients UPRIGHT POSTURE Platelef Aggregobifiy
ECLT
EPI
a
1054
y pco.01
ADP
1
EXERCISE
Acfhi/y
t-PA Ag
vs supme
THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 70
b
*p
OCTOBER 15, 1992
“5
PRE-EXERCISE
t-PA Aa
with vascular disease, as opposed to normal subjects, demonstrate a similar antithrombotic tibrinolytic increase after assuming upright posture, since basal Iibrinolytic activity has been reported to be decreased in patients with coronary artery disease.i4J5 The failure of platelet aggregability to increase with strenuous exercise despite a five- to sixfold increase in plasma catecholamine levels is at variance with the previously reported association between platelet aggregability and even smaller plasma catecholamine increases3J3 It is possible that (1) the functional state of platelet adrenoceptors is down-regulated by high levels of catecholamine during exercise,7,16a change that may not be triggered by the relatively small catecholamine increase observed after the upright posture; (2) prostacyclin, a prostanoid which inhibits platelet aggregation, increases in plasma during exercise,17 whereas the increase in prostacyclin during assumption of the upright posture may be more limited, and (3) the surge of tissue-type plasminogen activator observed during exercise may disaggregate platelets, as reported in viv~.~~Although exercise does not produce an increase in platelet aggregability beyond that produced by the upright posture, it causes a significant increase in hematocrit that would increase whole blood viscosity. This tendency, which may increase the thrombotic potential, is countered by a marked increase in fibrinolytic activity (Figures 2 and 3 [a and b]). The sum effect of these opposing changes on thrombotic potential, and how this balance is modified during different daily activities in patients with coronary artery disease, is uncertain. These observations are of importance in light of a newly proposed hypothesis of the mechanism of triggering of coronary thrombosis. l9 It has been proposed that the process leading to coronary thrombosis begins when an external activity such as assuming the upright posture or exercise ruptures a vulnerable atherosclerotic plaque. Once the rupture occurs, the coagulability of the blood may determine whether a harmless mural thrombosis or life-threatening occlusive thrombus forms. The present study demonstrates that a stress such as near-maximal exercise, which could conceivably cause rupture of a vulnerable plaque owing to transient arterial hypertension, may also have a transient beneficial effect on blood coagulation, thereby delaying the onset of occlusive thrombosis. This possible scenario in-
dicates the need for further characterization of the changes in the determinants of blood coagulation produced by activities that may trigger coronary artery thrombosis.
REFERENCES 1. Muller JE, Stone PH. Turi ZG, Rutherford JD, Czeisler CA, Parker C, Poole
WK. Passamani E, Roberts R, Robertson T, Sobel BE, WilIerson JT, Braunwald E, and the MILIS Study Group. Circadian variation in the frequency of onset of acute myocardial infarction. N Engl J Med 1985;313:1315-1322. 2. Muller JE, Ludmer PL, Willich SN, Toner GH, Aylmer G, Klangos I, Stone PH. Circadian variation in the freouencv . _ of sudden cardiac death. Circulation 1987;75:131-138. 3. Toner GH, Brexinski DA, Schafer AI, Cxcisler CA, Rutherford JD, Willich SN, Gleason RE, Williams GH, Muller JE. Concurrent morning increase in platelet aggregability and the risk of myocardial infarction and sudden cardiac death. N Et&?/J Med 1987:316:1514-1518. 4. Brezinski DA, Toner GH,‘Muller JE, Pohjola-Sintonen S, Willich SN, Schafer AI, Caeisler CA, Williams GH. Morning increase in platelet aggregability: association with assumption of the upright posture. Circulation 1988;78:35-40. 5. Rosing DR, Brakman P, Redwood DR, Goldstein RE, Beiir GD, Astrup T, Eostein SE. Blood tibrinolvtic activitv in man: diurnal variation and the resoonse a ~~~~ to varying intensities of exercise. Ci;c Res 1970;27:171-184. 6. speiser W, Ianger W, P&rick A, Selmavr E, Ibe B, Nowacki PE, MullerBerghaus G. Incre&d blood tibrinolytic activity after physical exercise: comparative study in individuals with different sporting activities and in patients after myocardial infarction taking part in a rehabilitation sports program. Thromb Res 1988;51:543-555. 7. Winther K, Trap-Jensen J. The effect of exercise on platelet beta-adrenoceptor function and platelet aggregation in healthy human volunteers. C/in Phys 1988;8:147-153. 6. FitxGerald DJ, Ray L, Catella F, FitzGerald GA. Platelet activation in unstable coronary disease. N Engl J Med 1986;315:983-989. 9. Warlow CP. Oeston D. Effect of exercise on olatelet count. adhesion and aggregation. Aha kaemaiol 1974;52:47-52. ’ 10. Mant MJ, Kappagcda CT, Quinlan J. Lack of effect of exercise on platelet activation and platelet reactivity. J Appf Physior 1984;57:1333-1337. 11. Knudsen JB, Brodhagen U, Gormsen J, Jordal R, Norregaard-Hansen K, Paulev PE. Platelet function and librinolytic activity following distance running. Stand J Haematol 1982;29:425-430. 12. Hedner U, Nilsson IM. The role of tibrinolysis. Clin Haemafol 1981;lO: 327-342. 13. Willich SN, Pohjola-Sintonen S, Bhatia S, Shook TL, Toner GH, Muller JE, Curtis DG, Williams GH, Stone PH. Suppression of silent ischemia by metoprolol without altering the morning increase of platelet aggregability in patients with stable coronary artery disease. Circulation 1989;79:557-565. 14. Walker ID, Davidson JF, Hutton I, Lawrie TDV. Disordered “fibrinolytic potential” in coronary heart disease. Thromb Res 1977;10:509-520. 15. Hamsten A, Wiman B, de Faire U, Blomback M. Increased plasma levels of a rapid inhibitor of tissue plasminogen activator in young survivors of myocardial infarction. N Eng/ J Med 1985;313:1557-1563, 16. Hollister AS, Onrot J, Lance S, Nadeau JH, Robertson D. Plasma catecholamine modulation of alphaa adrenoceptor agonist affinity and sensitivity in normotensive and hypertensive human platelets. J C/in hesr 1986,77:1416-1421. 17. Mehta J, Mehta P, Horalek C. The significance of platelet-vessel wall prostaglandin equilibrium during exercise-induced stress. Am Heart J 1983;105: 895-904. 16. Los&m J, Vaughan DE. Tissue plasminogen activator promotes platelet disaggregation in plasma. J Chin Invest 1987;79:1749-1755. 19. Muller JE, Tofler GH, Stone PH. Circadian variation and triggers of onset of acute cardiovascular disease. Circulation 1989;79:733-743.
POSTURE
CHANGE,
EXERCISE,
PLATELETS
AND FIBRINOLYSIS
1055
Effects on Platelet Aggregation and Fibrinolytic Activity During Upright Posture and Exercise in Healthy Men Kaj Winther, MD, PhD, William Hillegass, MD, Geoffrey H. Tofler, MB, Alfred0 Jimenez, MD, Damian A. Brezinski, MD, Andrew I. Schafer, MD, Joseph Loscalzo, MD, PhD, Gordon H. Williams, MD, and James E. Muller, MD
The circadian variation of acute myocardial infarction suggests that daily activities such as assuming the upright posture and performing different daily activities may trigger the onset of coronary thrombosfs. Such triggering may result from unfavorable alterations in the balance between the prothrombotic and antfthrombotic properties of the blood. The present study compares the effects of 2 common daily activities, assuming the upright posture and exercise, on platelet aggregation and fibrindytfc activity. In healthy male subjects, assuming the upright posture in the morning dgnificantly increased platelet aggregation and produced only a moderate increase in ffbrinolytic activity within 10 minutes. These changes were sttll present after 90 minutes in the upright posture. Supine posture for 45 minutes resulted in levels of ffbrinolytZc actfvfty and platelet aggregation comparable to that observed before initially assuming the upright posture in the morning. Return to the supine posture for 45 minutes resulted in levels of fibrlnofytfc actfvity and platelet aggregation comparable to that observed before the initial assumption of upright posture. The changes recurred when upright posture was taken later in the day. Exercise dkl not increase platelet aggregation to levels beyond that produced by the upright posture, but was assocfated with a marked increase in ffbrinolyttc activity. Thus, exercise and upright posture produce distinctive alterations in the thrombogenfc potential of the blood that may influence the timing of clinfcal vascular events. (Am J Cardiol 1992;70:1051-1055)
he frequenciesof onset of myocardial infarction and sudden cardiac death have a prominent circadian variation, with an increase in the period from 6 A.M. to noon.1,2During this time period, subjects assumethe upright posture and perform physical exertion - 2 activities that activate the sympathetic nervous system and may cause systemic changesin blood clotting that predisposeto coronary artery thrombosis.3,4 Assumption of the upright posture in the morning is associated with increased platelet aggregability.4 However, the ability of the upright posture to increaselibrinolytic activity, a change that would tend to reduce the thrombotic potential of the blood, has not been previously described.Although it is agreed that exercise increaseslibrinolysis,5~6the effects of exerciseon platelet aggregation are controversial.7-11 The goalsof this study, therefore, were to answerthe following questionsconcerning the effectsof the upright posture and exerciseon platelet aggregability and librinolysis: (1) What is the time course of the effect of the upright posture in the morning on platelet aggregability? (2) Does assuming the upright posture at a later time of day causea similar increase?(3) Is the adverse effect, if it occurs, of assuming the upright posture on platelet aggregability counterbalancedby an increasein fibrinolytic activity? (4) Does exercise produce an increasein platelet aggregability beyond that produced by the upright posture? (5) What are the relative profiles of the effects of the upright posture and exercise on these determinants of thrombosis?
T
METHOD9
This report describes2 studiesof 12 male volunteers, each drawn from a total pool of 22 subjects,aged 20 to 32 years (mean 24), who were all nonsmokers,and taking no aspirin or other medication in the previous 2 weeks.All had given informed consent. On the day before the study, all subjectswere admitted to the Clinical Research Center of the Brigham and Women’s HospiFrom the Harvard Medical School, Boston,Massachusetts.This study tal. Lights were turned out at midnight, and subjects was supported in part by Grants HL 36045 and HL 40411 from the were awakened at 7:30 A.M. the following morning for National Institutes of Health, Bethesda,Maryland; and grants from the initiation of the study. After arrival at the hospital, the Danish Medical ResearchCouncil, the Danish Heart Foundation,and subjects received a controlled fmed diet. The subjects Sandoz Pharmaceuticals,and was conductedat the Clinical Research Center of the Brigham and Women’s Hospital, Harvard Medical did not drink any coffee,tea or hot chocolate after they School, Boston, Massachusetts,supported by Grant 5MOI-RR02635 were awakened on the study morning. Coffee was not from the National Institutes of Health. The data were analyzed in a provided during the study; however, tea and chocolate CLINFO facility supported by the same grant. Manuscript received were available in the evening before the study. The efJanuary 15, 1992; revised manuscript received and acceptedJune 15, fects of these agents would have have worn off before 1992. Addressfor reprints: Kaj Winther, MD, PhD, Department of Clini- the morning studies, during which 250 ml of juice and drinking water were available. cal Chemistry, Glostrup Hospital, DK-2600 Glostrup, Denmark. POSTURE CHANGE, EXERCISE, PLATELETS AND FIBRINOLYSIS
1051
Phase I was designed to determine (1) the time course of the effect of the upright posture in the moming on plasma catecholamine levels and platelet aggregability; and (2) whether the upright posture at a later time of day causes similar changes. After waking at 7:30 A.M., the 12 subjects remained supine for 30 minutes. Then, they assumedthe upright posture, remained upright until 9:30 A.M., lay supine until 11:30 A.M., and returned to the upright posture for 90 minutes at the end of the protocol (Figure 1). Blood sampleswere obtained at 8 A.M. while the subjects were still supine in bed, and after 6,45 and 90 minutes in the upright position. Blood sampleswere then obtained after 2 hours in the supine position, and finally 90 minutes after patients had returned to reassumethe upright posture. PhaseII was designedto determine (1) whether the adverseeffect of the upright posture on platelet aggregability is associatedwith an increasein fibrinolytic activity; (2) if exercise produces an increase in platelet aggregability beyond that produced by the upright posture; and (3) the relative profiles of the effects of the 2 activities - upright posture or exercise- on platelet aggregability and librinolytic activity.
-
6o B 2 50B 8 40 b 3 30. 8 20% $ to0SVPlM am8
“p,lpht
Supne
9
to
TIME I~<005
1052
VERSUS
tt
urmqtlt
I2
I 1
2Pm
OF DAY
PREVIOUS
TIMEPOINT
THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 70
After they were awakened at 7:30 A.M., 12 subjects (2 of whom participated in phaseI) remained in bed for 30 minutes. Then, they assumedthe upright posture (as in phaseI), remained upright for 90 minutes, lay supine for another 45 minutes, returned to the upright posture for 90 minutes, and then performed a standardized bicycle test (Figure 2). Blood sampleswere obtained at 8 A.M. while the subjectswere still supine in bed, at 10 and 90 minutes after taking the upright posture, and 10 and 45 minutes after they returned to the supine position. At 11:45 A.M., after being in the upright posture for 90 minutes, they were placed on a cycle ergometer with a mechanically controlled brake to regulate the work load. Blood was drawn at 11:55 A.M., immediately before exercise,and again at 12:05 P.M. immediately after exercise.The initial work load of 50 W was increased by 50 W every 3 minutes of exercise.Subjectsexercised until approximately 90% of maximal working capacity was achieved (mean exercise duration 10.4 minutes). Blood pressure was measured at 8:02 A.M. (2 minutes after assumingthe upright posture), at 11:55A.M. while sitting on the bicycle, and immediately after exercise using a mercury sphygmomanometer;heart rate was determined at the same time points. Blaod sampling: Blood sampleswere drawn without stasis from an antecubital vein with the use of a 21 gaugebutterfly needle,and processedimmediately. Sep arate venipunctures were performed at each time point. Twenty-sevenmilliliters of blood was drawn into a plastic syringe containing 3 ml 3.8% sodium citrate for platelet aggregationand euglobulin clot lysis time. Samples of 5 ml were collected in alternate syringes for analysis of catecholamines,plasma renin activity, hematocrit value and platelet count; and another 5 ml samplewas drawn for tissue-typeplasminogenactivator antigen and plasminogen activator inhibitor activity. Platelet aggregation, plasma catecholamines,renin activity, hematocrit and platelet count were determined as previously described.3*4Euglobulin clot lysis time was estimatedaccording to normal laboratory routine.‘* Tissue-type plasminogen activator antigen (ELISA) and plasminogen activator inhibitor activity (chromogenic method) were determined using reagents from the STAG0 Diagnostic System. Statistkal analysis: Comparison between the mean values at different time points was performed with the Wilcoxon signed rank test for paired data. Variations from mean values are expressedas f standard error of the mean. Two-tailed p values 10.05 were regarded as statistically significant. RESULTS Phase I: time course of platelet aggregability CmlldCabChOhlllifle
dUllgeS:
PLATELET AGGREGABILITY:
Adenosine diphosphate-induced platelet aggregability significantly increased after 45 minutes in the upright position as indicated by a decreasein mean adenosine diphosphatethreshold concentrationsfrom 4.1 f 0.4 to 2.7 f 0.2 PM (p
TABLE I Platelet Aggregation, t-PA Antigen, Inhibitor Against t-PA (plasminogen activator inhibitor), Platelet Count, Hematocrit, and Plasma Epinephrine, Norepinephrine and Renin are Given at Different Time Points for Subjects During Phase II Supine
Platelet aggregation (ADP thresholds bM) t-PA antigen (rig/ml) PAI activity (IU/ml) Platelet count (103/mm3) Hematocrit (%I Plasma epinephrine (pgiml) Plasma noreplnephrine (pg/ml) Plasma renin activity (nlimllhour)
(8 A.M.)
Upright (8.10 A.M.)
(9.30
Upright
Supine
5.4 + 0.6
4.0 + 0.5
4.4 + 0.4
4.0 + 0.4
4.7 ‘- 1.2 1.06 + 0.4 261 + 16
7.7 t 1.7* 0.97 T 0.3 295 2 90*
5.9 2 1.7 0.94 + 0.3 285 k 16
42.8 t 0.61 32.2 -t 4.8
44.0 2 0.61* 54.0 + 5.6*
164 i: 23 1.14 2 0.2
A.M.)
(9.40
Supine (10.15 A.M.)
A.M.)
Upright
(11.55
A.M.)
Exercise (12.05 P.M.)
5.2 2 0.2t
4.3 + 0.4*
3.8 + 0.4
4.9 Yk 1.2* 1.09 k 0.4 273 -t 17*
4.7 2 1.3 0.80 -c 0.4 275 k 18
4.9 + 1.1 0.63 t 0.3 293 + 21*
17.7 + 4.0t 0.77 k 0.2 345 2 20t
44.3 -t 0.71 50.5 k 8.3
43.3 zk 0.61* 33.0 + 7.1*
42.9 k 0.51 28.5 1 1.9
43.8 k 0.6* 42.5 ‘- 5.1*
47.1 ? 0.7* 213 + 34t
310 + 40*
335 + 47
207 ? 31*
202 + 26
295 -c 32*
1670 k 314t
1.45 k 0.2*
2.88 k 0.6*
2.28 + 0.4
1.40 + 0.4*
2.73 + 0.7*
3.38 k 0.5
*p CO.05 versus prewus time point: tp CO.05 versus 9:30 A.M. Valuesare mean i SEM, n = 12. ADP = adenoslne dlphosphate: PAI = plasmlnogen activator InhibItor:
t-PA = tissue-type
plasminogen
activator.
I
2.2 to 4.7 f 1.5 PM (p <0.06). Return to the supine posture for 2 hours was sufficient to permit return of platelet aggregability to the level observedafter the 8hour overnight supine period (Figure 1). Finally, reassumption of the upright posture produced an increasein aggregability indistinguishable from that observedafter initially assuming the upright posture. PLASMACATECHOLAMINELEVELS: Therewasa marked surge in the levels of plasma catecholamines after assuming the upright posture. Within 10 minutes, plasma epinephrine and norepinephrine more than doubled (Figure 1, p <0.02). Return to the supine posture for 2 hours resulted in a reduction in values to levels comparable to those observed at 8 A.M., whereas subsequent return to the upright posture resulted in a similar-pattern to that observed earlier in the day (Figure 1, p
tha
dkCt
Of
aXemiNi
plasminogenactivator inhibitor activity (Table I). These changeswere less pronounced 90 minutes after assuming the upright posture. Return to the supine posture for 45 minutes resulted in tissue-typeplasminogenactivator levels similar to those observed before the initial assumption of upright posture in the morning (Table I). Returning to the upright posture resulted in euglobulin clot lysis time changessimilar to those noted at the initial upright posture. Exercise causeda marked shortening of the euglobulin clot lysis time and an increase in tissue-type plasminogen activator antigen from 4.9 f 1.1 to 17.7 f 4.0 rig/ml (p
PLATELET AGGREGABILITY:
Platelet aggregability increased 10 and 90 minutes after initial assumptionof the upright posture as indicated by a decreasein the mean threshold values of adenosine diphosphate and epinephrine (Table I, Figure 2). Return to supine posture for 10 minutes did not alter platelet aggregation; however,aggregation returned to initial 8 A.M. levels after 45 minutes in the supine position (Table I, Figure 2). When subjects reassumedthe upright posture, the changesin platelet aggregation were cornparable to those observedafter initial assumptionof the upright posture. Exercise, however,did not causea further increase in platelet aggregation as indicated by similar threshold concentrations of 4.3 f 0.4 and 3.8 f 0.4 PM for adenosinediphosphate and 1.0 f 0.2 and 1.1 f 0.4 PM for epinephrine (Table I, Figure 2). FIBRINOLYTIC ACTIVITY: Fibrinolytic activity increased 10 minutes after initially assuming the upright posture as indicated by a shortening of the euglobulin clot lysis time from 130 f 20 to 95 f 17 minutes (p <0.02) (Figure 2) and an increase in tissue-type plasminogen activator antigen from 4.7 f 1.2 to 7.7 f 1.7 rig/ml (p
F B 2 5 $ 6-
L I 8om * P’O.05
I
9
VERSUS
I
I
10
L
PREVIOUS
I I 11
, 12
TIMEPOINT
FlGURE2.Shdhmomdungarinpbtakt~lity
(M , w wS
Blmheldv~)end~sls(~det ~posbedumgesmdexer-
d -ds,mmze
hreasesadythefomer(v~ra-fM,n=l?).
POSTURE CHANGE, EXERCISE, PLATELETS AND FIBRINOLYSIS
1053
PLASMA CATECHOLAMINE AND RENIN CHANGES: Assuming the upright posture resulted in an increase in plasma catecholaminescomparable to that observedin phaseI, whereasexerciseincreasedthe plasmacatecholamine level more than fivefold (Table I). An increasein plasma renin activity was observedafter 10 and 90 minutes in the upright posture (p
suming the upright posture, and exercise. It demonstrates that (1) assuming the upright posture in the morning produces a rapid surge in plasma catecholamine and renin activity levels that is accompaniedby increased platelet aggregability; (2) the changes produced by the upright posture ceasewithin 45 minutes after return to the supine position; (3) taking the upright posture later in the day produceschangessimilar to those produced in the morning; (4) the upright posture producesa moderate increasein librinolytic activity that tends to be less pronounced after 90 minutes in the upright position; (5) exercise does not increase platelet aggregability to a level higher than that caused by the upright posture but is associatedwith a signilicant increasein catecholamines,fibrinolytic activity and hematocrit value. Thus, the upright posture and exercise produce different profiles of changesin thesedeterminants of thrombosis. The demonstration in the present study that upright posture causesan increasein platelet aggregability (Figures 1 and 2, Table I) confirms previous reports of this phenomenon in normal subjects and in patients with coronary artery disease.4J3The present study adds new findings: This increasecan be reversedby return to the supine position, and it can be reproduced by assuming upright posture at a later time of day. The degree to which the increase in fibrinolytic activity associatedwith the upright posture modifies the overall thrombotic tendency of the blood is unknown, since it is not possible simply to add or subtract the results of the 2 processes.However, changesin platelet aggregation and fibrinolytic activity are homeostatic or DISCUSSION This study clarifies several aspectsof the changesin autoregulatory, serving to maintain blood fluidity (Figdeterminants of thrombus formation produced by as- ures 2 and 3 [a and b]). It is uncertain whether patients UPRIGHT POSTURE Platelef Aggregobifiy
ECLT
EPI
a
1054
y pco.01
ADP
1
EXERCISE
Acfhi/y
t-PA Ag
vs supme
THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 70
b
*p
OCTOBER 15, 1992
“5
PRE-EXERCISE
t-PA Aa
with vascular disease, as opposed to normal subjects, demonstrate a similar antithrombotic tibrinolytic increase after assuming upright posture, since basal Iibrinolytic activity has been reported to be decreased in patients with coronary artery disease.i4J5 The failure of platelet aggregability to increase with strenuous exercise despite a five- to sixfold increase in plasma catecholamine levels is at variance with the previously reported association between platelet aggregability and even smaller plasma catecholamine increases3J3 It is possible that (1) the functional state of platelet adrenoceptors is down-regulated by high levels of catecholamine during exercise,7,16a change that may not be triggered by the relatively small catecholamine increase observed after the upright posture; (2) prostacyclin, a prostanoid which inhibits platelet aggregation, increases in plasma during exercise,17 whereas the increase in prostacyclin during assumption of the upright posture may be more limited, and (3) the surge of tissue-type plasminogen activator observed during exercise may disaggregate platelets, as reported in viv~.~~Although exercise does not produce an increase in platelet aggregability beyond that produced by the upright posture, it causes a significant increase in hematocrit that would increase whole blood viscosity. This tendency, which may increase the thrombotic potential, is countered by a marked increase in fibrinolytic activity (Figures 2 and 3 [a and b]). The sum effect of these opposing changes on thrombotic potential, and how this balance is modified during different daily activities in patients with coronary artery disease, is uncertain. These observations are of importance in light of a newly proposed hypothesis of the mechanism of triggering of coronary thrombosis. l9 It has been proposed that the process leading to coronary thrombosis begins when an external activity such as assuming the upright posture or exercise ruptures a vulnerable atherosclerotic plaque. Once the rupture occurs, the coagulability of the blood may determine whether a harmless mural thrombosis or life-threatening occlusive thrombus forms. The present study demonstrates that a stress such as near-maximal exercise, which could conceivably cause rupture of a vulnerable plaque owing to transient arterial hypertension, may also have a transient beneficial effect on blood coagulation, thereby delaying the onset of occlusive thrombosis. This possible scenario in-
dicates the need for further characterization of the changes in the determinants of blood coagulation produced by activities that may trigger coronary artery thrombosis.
REFERENCES 1. Muller JE, Stone PH. Turi ZG, Rutherford JD, Czeisler CA, Parker C, Poole
WK. Passamani E, Roberts R, Robertson T, Sobel BE, WilIerson JT, Braunwald E, and the MILIS Study Group. Circadian variation in the frequency of onset of acute myocardial infarction. N Engl J Med 1985;313:1315-1322. 2. Muller JE, Ludmer PL, Willich SN, Toner GH, Aylmer G, Klangos I, Stone PH. Circadian variation in the freouencv . _ of sudden cardiac death. Circulation 1987;75:131-138. 3. Toner GH, Brexinski DA, Schafer AI, Cxcisler CA, Rutherford JD, Willich SN, Gleason RE, Williams GH, Muller JE. Concurrent morning increase in platelet aggregability and the risk of myocardial infarction and sudden cardiac death. N Et&?/J Med 1987:316:1514-1518. 4. Brezinski DA, Toner GH,‘Muller JE, Pohjola-Sintonen S, Willich SN, Schafer AI, Caeisler CA, Williams GH. Morning increase in platelet aggregability: association with assumption of the upright posture. Circulation 1988;78:35-40. 5. Rosing DR, Brakman P, Redwood DR, Goldstein RE, Beiir GD, Astrup T, Eostein SE. Blood tibrinolvtic activitv in man: diurnal variation and the resoonse a ~~~~ to varying intensities of exercise. Ci;c Res 1970;27:171-184. 6. speiser W, Ianger W, P&rick A, Selmavr E, Ibe B, Nowacki PE, MullerBerghaus G. Incre&d blood tibrinolytic activity after physical exercise: comparative study in individuals with different sporting activities and in patients after myocardial infarction taking part in a rehabilitation sports program. Thromb Res 1988;51:543-555. 7. Winther K, Trap-Jensen J. The effect of exercise on platelet beta-adrenoceptor function and platelet aggregation in healthy human volunteers. C/in Phys 1988;8:147-153. 6. FitxGerald DJ, Ray L, Catella F, FitzGerald GA. Platelet activation in unstable coronary disease. N Engl J Med 1986;315:983-989. 9. Warlow CP. Oeston D. Effect of exercise on olatelet count. adhesion and aggregation. Aha kaemaiol 1974;52:47-52. ’ 10. Mant MJ, Kappagcda CT, Quinlan J. Lack of effect of exercise on platelet activation and platelet reactivity. J Appf Physior 1984;57:1333-1337. 11. Knudsen JB, Brodhagen U, Gormsen J, Jordal R, Norregaard-Hansen K, Paulev PE. Platelet function and librinolytic activity following distance running. Stand J Haematol 1982;29:425-430. 12. Hedner U, Nilsson IM. The role of tibrinolysis. Clin Haemafol 1981;lO: 327-342. 13. Willich SN, Pohjola-Sintonen S, Bhatia S, Shook TL, Toner GH, Muller JE, Curtis DG, Williams GH, Stone PH. Suppression of silent ischemia by metoprolol without altering the morning increase of platelet aggregability in patients with stable coronary artery disease. Circulation 1989;79:557-565. 14. Walker ID, Davidson JF, Hutton I, Lawrie TDV. Disordered “fibrinolytic potential” in coronary heart disease. Thromb Res 1977;10:509-520. 15. Hamsten A, Wiman B, de Faire U, Blomback M. Increased plasma levels of a rapid inhibitor of tissue plasminogen activator in young survivors of myocardial infarction. N Eng/ J Med 1985;313:1557-1563, 16. Hollister AS, Onrot J, Lance S, Nadeau JH, Robertson D. Plasma catecholamine modulation of alphaa adrenoceptor agonist affinity and sensitivity in normotensive and hypertensive human platelets. J C/in hesr 1986,77:1416-1421. 17. Mehta J, Mehta P, Horalek C. The significance of platelet-vessel wall prostaglandin equilibrium during exercise-induced stress. Am Heart J 1983;105: 895-904. 16. Los&m J, Vaughan DE. Tissue plasminogen activator promotes platelet disaggregation in plasma. J Chin Invest 1987;79:1749-1755. 19. Muller JE, Tofler GH, Stone PH. Circadian variation and triggers of onset of acute cardiovascular disease. Circulation 1989;79:733-743.
POSTURE
CHANGE,
EXERCISE,
PLATELETS
AND FIBRINOLYSIS
1055