Plasma beta-endorphin levels in silent myocardial ischemia induced by exercise

PlasmaBeta-Endorphinlevels in Silent MyocardiallschemiaInducedby Exercise GARY V. HELLER, MD, PhD, CAROL EWING GARBER, MA, MARK J. CONNOLLY, MS, CATHERINE F. AUN-ROWLANDS, MT, STEVEN F. SICONOLFI, PhD, DONALD S. GANN, MD, and RICHARD A. CARLETON, MD

Aithough silent myocardiai ischemia is a well recognized phenomenon, the reasons for the lack of symptoms in patients with coronary artery disease (CAD) is unclear. Because the endogenous opioid fl-endorphin has been related to pain modulation, plasma fl-endorphin levels were studied before, during and after exercise-induced ischemia in syrnptomatk and asymptomatk men. Because &endorphin responses have been closely linked to adrenocorticotropk hormone (ACTH) and cortkoi responses, these hormones aiso were measured. Nine symptomatic and 12 asymptomatic patients with a high probabiitty (at least 95%) of CAD and 8 apparently healthy men completed a Bruce protocol

treadmill test. Blood samples were drawn before, during and 10 minutes after exercise. During exercise the measured hormones showed no significant increases from basal levels. However, plasma @-endorphin, ACTH and cortkoi levels were significantly elevated (p 10.01) 10 minutes after exercise in ail 3 groups. There was no significant difference in plasma fl-endorphin levels during or after exercise between the symptomatic and asymptomatk patients with CAD. Thus, differences in circulating ieveis of /?-endorphin, ACTH and corttsoi are not associated with the presence or absence of pain during exercise-induced myocardiai tschemia. (Am J Cardioi 1987;59:735-739)

S

ilent myocardial &hernia is recognized as an important clinical entity occurring in patients with significant coronary artery disease (CAD). The reasons for absence of chest pain during ischemic events are unclear: some investigators suggest that a combination of hormonal, neural and psychological factors contribute.’ Results from recent studies suggest that the perception of pain may be altered in patients with silent ischemia.z-4 The perception or modulation of pain such as observed in long distance runners and women who are in labor may be related to levels of endoge-

nously secreted opioid-like peptides, P-endorphins.s-7 These data suggest a link between presence or absence of symptoms during myocardial ischemia and plasma ,!I-endorphin levels. We evaluated the relation between 3 stress hormones &endorphin, ACTH and cortisol) and development of angina pectoris during exercise-induced myocardial ischemia in patients with documented CAD.

Methods Twenty-two patients with CAD volunteered for the study. Each patient had a previous positive exercise test response (horizontal ST-segment depression of 2 mm or greater) and either previous myocardial infarction, positive exercise thallium-201 scintigraphic findings, known coronary artery stenosis of at least 70% diameter reduction assessed by cineangiography or a posttest likelihood of disease greater than 98% (Diamond and Forrestefl), Ten patients had typical exercise-induced angina accompanied by significant STsegment depressions during a previous test. Twelve patients had positive electrocardiographic responses without angina1 symptoms during a previous test. Of patients who were asymptomatic during testing, none had pretest symptoms. Eight of those patients had pre-

From the Division of Cardiology, Department of Medicine, Memorial Hospital, Pawtucket, and the Department of Surgery, Rhode Island Hospital, Brown University Program in Medicine, Providence, Rhode Island. This study was supported in part by a Biomedical Research Support Grant, S07RR05862-02 from the Department of Health and Human Services, Bethesda, Maryland. Dr. Siconolfi’s present affiliation: Springfield College, Springfield, Massachusetts. Manuscript receive September 16, 1986; revised manuscript received November 17,1986, accepted November 20,1986. Address for reprints: Gary V. Heller, MD, PhD, Division of Cardiology, The Memorial Hospital, Pawtucket, Rhode Island 02860. 735

736

BETA-ENDORPHINS

IN SILENT

ISCHEMIA

vious infarction and were referred for risk stratification and 4 were evaluated for other reasons.A third group consistedof 10 normal, healthy, asymptomatic personswho volunteeredand had a likelihood of significant CAD of less than 10%. The routine exercisehabits of all 32 subjectswere evaluatedusing a modified Paffenbargerphysical activity index9andwere found to be similar and relatively sendentary.Each patient was instructed to abstain from alcohol, caffeine and P-blocker use for 24 hours before exercisetesting.All other antianginal medication use was continued. Each patient was restricted from oral intake other than water for at least 4 hours before testing. All testing was performed at approximately the same hour of the day for all subjects to minimize diurnal variations of the hormones being studied. Upon arrival at the Human PerformanceLaboratory, the purpose,details and protocolsbeing usedwere discussedwith the subject, who then gave informed consent[approvedby the Human Studies Committee, The Memorial Hospital). An intravenous catheterinsertedinto antecubitalfossawas kept patentwith heparinized saline solution. To minimize fluctuations of hormone levels due to psychologicalstress,the subject was allowed to relax for 1 hour. All subjectsexercisedon a treadmill using a standard Bruce protocol.Twelve-lead electrocardiograms were recorded at least every minute during exercise and for 10minutes after exercise[or until the electrocardiogram returned to normal]. The exercise endpoint for the control patientswas attainment of at least 90% of maximal predicted heart rate. Patients with CAD exerciseduntil progressiveangina pectoriswith ST-segmentdepressiondevelopedor when 90% of the maximal predicted heart rate was achieved. In the asymptomaticpatients,exercisewas continued until a predictive heart rate was achieved or severeST-seg ment depression(4 mm) was seen. Blood samples were drawn in duplicate immediately before testing and then singly every 3 minutes during the exerciseperiod. Postexercisesampleswere drawn 10minutes after exercisein all subjectsand 20 and 30 minutes after exercisein 19.The lo-ml blood sampleswere drawn into polyethelenesyringes,divided and placed immediately into 2 iced test tubes containing either 25 ml of Traysole (Aprotinin) for p-endorphin assaysor 10 ml of heparin for ACTH and cortisol. The test tubes were centrifuged at 2OCand 3,000rpm for 15 minutes. Plasmawas storedat -8OOC until the assayswere performed. Hormone assayswere performed at Rhode Island Hospital, Providence. Plasma ACTH was extracted and measuredby radioimmunoassayas describedby Reeset al.1°The antiserum was raised in rabbits by immunization with ACTH conjugatedto bovine serum albumin in complete Freund’s adjuvant. This antiserum showed 100% cross-reactivitywith ACTH (1-24 and l-39). There was 0.06% cross-reactivity with ACTH (11-24) and 0.02% cross-reactivitywith ACTH (l-10,4-lO, ll-19 and 17-24) /3-endorphinand a-melanocyte stimulating hormone. Plasma values of ACTH

measuredusingthis antiserumwere not different from those obtained in this laboratory using an antiserum obtained from Dr. Mary Dallman, University of California, San Francisco.ll This assayhad a working detectability range of 2 to 250PM/liter. The intra- and interassaycoefficients of variation on the measurement of a 10PM/liter plasmapool were 12% and 20%. Plasma P-endorphin was extracted and measured by radioimmunoassay(Immuno Nuclear Corp.). The /I-endorphin antiserum used showed less than 5% cross-reactivitywith @-lipotropinand no cross-reactivity with a-melanocyte stimulating hormone, met-enkephlin, leu-enkephalin or ACTH (l-39 and 1-24). The assayhad a working rangeof detectability of 2 to 100PM/liter. The intra- and interassaycoefficient of variation on the measurementof a 15-PM/liter plasma pool were 8% and l5%, respectively. Plasma cortisol was measuredby radioimmunoassay asmodified from the method describedby Castercane and Allen-Rowlands12for measurementof corticosterone.The antiserum was obtained from Dr. J.C. Rose.13The working range of detectability was from 0.2 to 100&dl. The intra- and interassaycoefficient of variationson measurementof a 8 lug/d1plasmapool were 5% and 1070,respectively. Statistical analyseswere performed using a multivariate repeated-measuresanalysisof variancedesign using BMDP program 4V.l4 A log transformation was performed before analysis becausethe data were not normally distributed. Post hoc analysis of significant main effects were performed using a Tukey honestly significant difference test.15

Results Thirty-two men completed the study. Data from 1 subject were eliminated becauseall hormone levels were at least 3 standarddeviations beyondthat of the sample mean and probably representedsampling error. Data from 2 asymptomatic control patients who had positive electrocardiographicresponsesto the exercise test were also eliminated. Demographic and clinical data from the other 29 subjectsare shown in Table I. There were no significant differences between the 2 groups with CAD with respect to age, number of previous myocardial infarctions or degree of ST-segmentdepressionduring exercise.Duration of exercise,maximally achieved heart rate and exercise intensity expressedasa percentageof predicted maximal heart rate were significantly greaterin the control groupthan in either groupof patientswith CAD. There were no differences between the 2 CAD groupswith respect to these same exercise variables, except the duration of exercisewas greaterin the asymptomatic group. Resultsof the the /3-endorphin,ACTH and cortisol levels measuredbefore, during and after exerciseare shown on TablesII, III and IV, respectively.The direct data from all 3 hormoneswere not used for statistical analysis becausethey were not normally distributed. These data were logarithmically transformed and are representedin Figures1,2 and 3.There was no significant increasein any of the hormone levels during ex-

April I,1987

TABLE I Population

Demographic

and

Age (yr) Previous MI Focal thallium abnormality with ex. Exercise duration (min) Peak ex. heart rate (beatslmin) Exercise intensity (% MHR)$ ST-segment depression at peak (mm) Angina pectoris

Exercise

Data

of the Study

TABLE Exercise

Symptomatic lschemia (n = 9)

Asymptomatic lschemia (rl = 12)

Control (n = 8)

52 f 5 5 4

57 f 5 8 3

46 f 6 0 0

11 f

1’

12 f

27

152 f

17

179 f

lot

91 i

10

110 f

5t

3.2 f

1.0

6f2 143 *

13

a4 f 9 3.1 f

0.6

0

0

9

Values are mean f standard deviation. ‘p