Occupational and Environmental Medicine 1996;53:118-124

Serum endothelin concentrations in workersexposed to vibration

K T Palmer, H Mason

AbstractObjectives-Endothelin 1 (ET1) is one of anewly discovered family of potent natu-rally occurring vasoconstrictors producedby the endothelium. A few publicationsindicated that the peptide may have a rolein idiopathic Raynaud's phenomenon andRaynaud's phenomenon secondary toconnective tissue disease. The aim of thisstudy was to compare serum endothelinconcentrations in people with vibrationinduced white finger (VWF) with those ofcontrols exposed to vibration, and unex-posed (pure) controls.Subjects and methods-Male volunteersfrom a stonemasonry, two quarries, andan insurance company were classified byquestionnaire and clinical examinationinto men with VWF (cases, n = 31),exposed controls (n = 22), or pure con-trols (n = 36). All subjects were asked toprovide two venous blood specimens: abaseline sample after a period of warmequilibration (30 minutes seated in awarm room and 20 minutes with bothhands immersed in a water bath at 371C);and again after cold challenge (bothhands immersed in a water bath at 60Cfor six minutes). Serum concentrations ofthe 21 amino acid peptide endothelinET,21 were measured by radioimmunoas-say.Results-Baseline concentrations ofET,,were found to be lower in cases (mean =12*2 pmoMl) than in the two controlgroups (mean = 14*7 pmol/l in exposedcontrols; mean = 14*3 pmolll in purecontrols). Among cases there was a broadinverse relation between severity, as mea-sured by the Griffin blanching score, andbaseline ET,2, (Spearman rank correla-tion coefficient - 0 58, P < 0.001). Coldchallenge provoked an overall rise inET,,, in all groups, but larger and signifi-cant mean absolute and percentage riseswere found in cases (4.1 pmol/l and 54%)than in the control groups (2.6 pmol/l and21% in exposed controls; 1*5 pmolI and20% in pure controls). Similar but moreobvious differences occurred when con-trols were compared with those cases whogave a more severe history of disease(Griffin blanching score > 24) and thosecases found to blanch after cold challenge.In these case subsets baseline ET,,, wasnearly 50% lower than for controls and afour and a halfto fivefold greater percent-

age rise in ET,21 occurred upon cold chal-lenge. Differences were significant. Closematching for age and smoking did notalter the principal findings. No significantdifferences, whether in baseline or coldresponse, were found between unexposedand exposed controls.Conclusions-Baseline findings seem tocontradict various published series andattempts are made to reconcile the differ-ences. It is suggested that a lower baselineET,2, in cases may result from a diseasecompensation mechanism or damageeffect. The large relative rise in serumET-21 when cases are cold challenged maycontribute directly or indirectly tovasospasm, but a simple mechanism isunlikely and interpretation is limited bythe absence of measurements of forearmblood flow.

(Occup Environ Med 1996;53:118-124)

Keywords: vibration; endothelin; vibration inducedwhite finger

Vibration induced white finger (occupationallyinduced Raynaud's phenomenon secondary tohand arm vibration) is characterised by spas-modic blanching of the digits, especially inresponse to cold.' The mechanisms that pro-duce blanching are imperfectly understooddespite much research: however, bothvasospasm and fixed obstruction of the lumenof the digital vessels may operate, to a greater orlesser extent.2

In 1973 Nerem suggested that sheer stressinduced by vibration could provoke damage tothe endothelial wall and accompanying bloodabnormalities.3 Other workers have describedabnormal blood rheology in hand arm vibra-tion syndrome including abnormalities ofplatelet function,4 blood viscosity,5 and plasmafibrinogen,6 but the role of the endotheliumhas been little explored.By contrast, in research physiology, the

vasoregulatory activity of the endothelium hasbeen closely studied, and in the past decademany endothelium derived vasodilator (relax-ing) factors (EDRFs) and endotheliumderived constrictor factors (EDCFs) havebeen discovered and investigated duringhealth and disease.78 Among these, the novel21 amino acid peptide endothelin ET, 21 hasprovoked most excitement because of two veryspecial properties: extraordinary vasoconstric-tor potency (log orders of magnitude greater

MRC EnvironmentalEpidemiology Unit,Southampton GeneralHospital,SouthamptonK T PalmerBiomedical SciencesGroup, Health andSafety Laboratory,Broad Lane, SheffieldH MasonCorrespondence to:Dr K T Palmer,MRC EnvironmentalEpidemiology Unit,Southampton GeneralHospital, SouthamptonS016 6YD.Accepted 26 September1995

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Serum endothelin concentrations in workers exposed to vibration

than for other EDCFs); and an unusually pro-longed time course of activity.9

Raised concentrations of endothelin havebeen found after cold challenged and in arange of vascular diseases.' 1-4 Workinghypotheses suggest that endothelin causes, orcontributes to, pathological vasospasm, and isitself often produced as a result of endothelialdamage.

Despite its plausible credentials, there havebeen relatively few peer reviewed reports con-cerning the mechanistic role of endothelinin Raynaud's phenomenon. Zamora et al,5studying women with primary Raynaud's phe-nomenon, reported a threefold increase inbaseline (warm equilibration) concentrationsand an exaggerated cold response in sevencases compared with matched controls. A sec-ond group of workers reported similar but lessclear cut findings in a population with sec-ondary Raynaud's phenomenon of mixed,non-occupational origin.'6 More recently his-tochemical investigations have highlighted ageneral depletion of vasoactive peptides in thecutaneous nerve fibres supplying the fingers ofpatients with VWF.17 The only occupationalstudy of serum endothelins compared riveterswith matched controls: workers exposed tovibration, some of whom had VWF, werefound to have a slightly lower baseline ET,.'8Cold responsiveness was not examined.

Interpretation of these limited publicationsis hampered by differing methods in-forexample, temperature control, sampling andimmunoassay, population mixes, case defini-tion, and allowance for potential con-founders-still leaving open some questions ofimportance to the occupational physician.

STUDY OBJECTIVESThe aim of the present study was to examinethe relation between serum ET, and long termhand arm vibration. In particular, answerswere sought to the following questions.

(1) Are there differences in the baseline(warm equilibration) concentrations of ET,when cases of VWF are compared with con-trols? If so, do the differences correlate withseverity of disease?

(2) Are there differences in the baselineconcentration of ET, in people exposed tovibration compared with unexposed people? Ifso, do the differences correlate with degree ofexposure to vibration?

(3) Do serum endothelins rise in responseto cold challenge? If so, are there differences inresponse between VWF cases and controls,and can these differences be related to severityof disease or manifestations of blanching? Arethere differences in response between exposedand non-exposed groups and if so, can the dif-ferences be related to degree of exposure tovibration?The study design and protocol were in

agreement with the principles of the Helsinkideclaration on biomedical research 1964 and1989 and were reviewed by the Health andSafety Executive's Research Advisory Team.Participants gave their written informed con-sent to all procedures.

MethodsSTUDY POPULATIONSIn 1990 the Health and Safety Executivereceived a series of case reports ofVWF underthe Reporting of Injuries, Diseases, andDangerous Occurrences Regulations (RID-DOR) 1985. The cases arose from two work-ing populations on the Isle of Portland inDorset: stonemasons and quarrymen.Exposure to vibration in these trades has tradi-tionally been high.

In the stonemasons, banker and line masonshand worked limestone blocks with chippinghammers and other tools with hazardousvibration characteristics. Other job descrip-tions entailed occasional use of air poweredtools-for example, plane machine operator-or previous experience as a mason-for exam-ple, sawyer foreman-and job mobility wassuch that few men had escaped significantoccupational exposure to vibration.

Quarrymen extracted the large limestoneblocks used in the masonry and in dimensionalconstruction work. The dimensional quarry-man's skill lay in identifying fault lines in stone.A line of holes was then made in the stone witha consolidated pneumatic rock drill and wedgeswere driven into the holes with a consolidatedpneumatic road breaker. Eventually the stonesplit. This traditional method has been used formore than one hundred years. In the extractionof dimensional stone much effort is expendedin preserving the integrity and shape of theextracted block and the relative precision of theoperation has until recently delayed attempts atmechanisation. Frequency weighted vibrationexposures in excess of 20 ms-2 root meansquared (rms) have been common overthe years, although conditions have sinceimproved. Persistence of traditional methodsand the unusually low job mobility of Portlandworkers provided a cohort of subjects with welldocumented high lifetime occupational expo-sures to vibration.

All male employees from a stonemasonryand two quarries were invited to participate.Out of 69 workers 55 (80%) agreed, but twowere ineligible according to defined study crite-ria-namely clinical diseases which were knownto cause secondary Raynaud's phenomenon orotherwise independently affect serum ET,-and this led to an overall response rate of 77%.Also, owing to the sparse number of people(five) without occupational exposure to vibra-tion, the non-exposed (pure) control group wassupplemented by an age stratified random sam-ple of male employees from a Hampshire insur-ance company. All respondents completed aquestionnaire, and all those fulfilling inclusioncriteria participated. They provided a further31 controls with one exclusion (a response rateof 21%).

STUDY METHODSAll participants were seen on two occasions inthe summer. On the first, a diagnostic ques-tionnaire was given by a trained nurse or doctorand was accompanied by a clinical examina-tion of the hands and upper limb pulses; and asingle blood pressure reading from the right

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arm was taken when sedentary and rested. Onthe basis of this assessment participants werelater classified as cases, exposed controls, purecontrols, or were excluded according to prede-termined criteria applied by a single observer.Severity of disease and degree of exposure tovibration were also assessed.

Second sessions took place before work onMonday mornings, allowing a weekend breakfrom use of vibratory tools. Participants wereasked to abstain from smoking on the day ofthe study and to limit alcohol consumption totwo units on the preceding evening.

At their second attendance participants satfor 30 minutes in a warm room (18 to 230C)and were then randomly allocated to one ofthree identical research stations, comprising aresearcher with thermostatically regulatedwarm and cold water baths. Subjects firstimmersed their hands in a warm water bath setat 370C (+ 50 C) for 20 minutes. At the end ofthe warm equilibration period participants hadtheir oral temperature measured: all values fellwithin the normal physiological range for corebody temperature. A 10 ml venous blood sam-ple was taken from the antecubital vein, thearm conventionally selected was, in cases withasymmetric disease, the side worse affected; incases with disease of equal severity in bothhands, and in non-cases, from the side of thedominant hand. This warm equilibration(baseline) blood sample was drawn into anEDTA tube, mixed and immediately cen-trifuged at 4VC then separated, and the plasmastored below - 1 5'C for later analysis.

Participants then placed both hands into acold water bath at 60C (+ 10 C) for six min-utes. The duration of the challenge wasdecided on the basis of a small pilot study inforestry workers. A second blood specimenwas taken from the same arm immediatelyafter the cold challenge and processed in thesame way as the baseline specimen. Subjects'hands were quickly dried and evidence ofblanching sought. Clinical observations wererecorded and where possible photographed.

ASSAYSeveral protocols exist for the measurement ofET, and ET like immunoreactivity.'5 19-21Samples in this study were analysed with aprotocol and assay system to specificallymeasure ET, 21 (RPA 555, AmershamInternational, UK). This assay system is

Table I Demographic and exposure differences between case and control study groups

Cases Exposured controls Pure controls(n = 31) (n = 22) (n = 36)

Age (y):Mean (SD) 44-7 (13 3)* 33.8 (14 7) 43 1 (10 7)Range 16-63 18-62 25-53

Blood pressure: (mean (SD) (mmHg)):Systolic 129 (17 9)* 116 (15-7) 123 (17-0)_GDiastolic 81 (12-0) 75 (14-1) 81 (11 4)

Tool use (h):Median 24 500t 1650tRange 2630-100 800 150-65 200

Smoking (%):Current smoker 14 (45) 6 (27) 12 (33)Exsmoker 13 (42) 6 (27) 11 (31)Non-smoker 4 (13) 10 (46) 13 (36)

*P < 0 05 cases v exposed controls; t P < 0-001, Mann Whitney test.

designed to measure specific ET, 21 with lim-ited cross reactivity (04%) to big endothelin(ET, 38 ), the precursor of the potent, circulat-ing vasoconstrictor of interest.The assay is based on the extraction of

ET, 21 from acidified plasma with Amprep 500mg C2 columns. After elution by acetonitrileand drying down under nitrogen, the reconsti-tuted sample is analysed by 125I radioim-munoassay with a primary rabbit antibody anddonkey anti-rabbit precipitating antibody. Allsamples were randomised and processed blindin the laboratory. The precision of the assay,calculated from quality control materialassayed with the study samples, was 6-7% at amean concentration of 10-8 pmol/l.

STATISTICAL METHODSThe Student-Newman-Keuls test was used inthe multiple comparison of means, cases vcontrol groups; and the Mann-Whitney test innon-parametric comparison of cases v controlsets. The comparison of means in matchedcase v control sets and the null hypothesis"cold causes no absolute change in endothe-lin" were tested with the paired t test.

ResultsCASES AND CONTROLSOn the basis of the questionnaire 31 cases ofVWF were identified, together with 22exposed controls and 36 pure controls. All butone of these cases had a past or present jobdescription of mason or quarryman. Amongthose with a history of VWF 14 out of 31(45%) blanched after cold challenge. Theseverity of cases was scored with the blanchingscore proposed by Griffin22 summed from theindividual scores for each hand. Scores rangedfrom 1 to 60, the modal and median scoreswere both 24.To examine the possible association

between case severity and ET, in the analysisof data two case subsets were defined: (a)those men with the worst case histories-arbi-trarily taken as a Griffin blanching score of 24or more (worst cases, n = 14); and (b) thosewho blanched under cold challenge (blanch-ers, n = 14).

DEMOGRAPHIC FACTORSTable 1 shows the major demographic factorsfor the study groups-age, blood pressure,smoking, and exposure-with estimated hoursof tool use as a rough but convenient proxy.Differences were as anticipated: cases wereolder than exposed controls and had usedvibrating tools for longer; older subjects hadhigher mean blood pressures; and were morelikely to be smokers or exsmokers QX2 test:cases v exposed controls, P < 0 05). Differ-ences were accentuated in the subset of severecases who were older again (mean (SD) agefor the worst cases 52 (1 1-6); and for blanch-ers 47-6 (12-9)), and had greater mean andmedian tool use (median up to 39 300 hoursin the worst case group).The demographic comparison between

cases and pure controls was closer for age and

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Table 2 Baseline (warm equilibration) serum ET, levels in the study groups

CasesBaseline Exposed PureET, 21 All Worst Blanchers controls controls(pmolll) (n =31) (n = 14) (n =14) (n = 22) (n = 36)

Mean 12-17* 10-01** 10-73** 14-72 14-26Median 12 99t 9-67t 9-67t 15-16 14-36SD 4-3 3-57 3 93 2-33 4-5SEM 0 77 0-94 1-05 0 5 0 75Range 5-99-20-77 5-99-15-72 5-99-16-62 12-84-17-41 5-74-24-85

*P < 0-05; **P < 0-01; t P < 0-02 case v both control groups.

blood pressure, although the blue collargroup still contained a smaller proportion ofnon-smokers than the white collar insuranceworkers.

BASELINE ET, CONCENTRATIONS IN STUDYGROUPS

The mean baseline in cases was lower than ineither control group (table 2). The same wastrue when medians were compared.Differences were significant at the 5% level.The mean and median baseline ET1 2, in thesubsets of worse cases and blanchers were

even lower. Again differences were significant.The Spearman rank correlation coefficientbetween Griffin blanching score and baselineET, 21 in cases was calculated and found to be- 0-58 (P < 00 1), further suggesting a broadinverse relation between baseline ET, 21 andcase severity. No correlation between baselineET, 2, and hours of use of vibrating tools wasfound among the cases.The difference in baseline between exposed

controls and pure controls did not reach sig-nificance. Nor was any significant correlationfound between baseline serum ET, 21 andhours of use of vibrating tools in exposed con-trols.

RESPONSE TO COLD

Four men (one case, one exposed control, andthree pure controls) failed to provide an ade-quate blood specimen after cold challenge.Table 3 summarises the cold response in theremaining subjects. An absolute rise in meanET, was found in response to cold in allgroups. Larger absolute and percentage riseswere found in cases than in controls, and thelargest rises were found in the two subsets,worst cases and blanchers. The null hypothe-sis, that cold has no effect other than bychance on serum ET,, was tested. In cases andcase subsets the null hypothesis was suffi-ciently unlikely that cold challenge seems to beassociated with a rise in serum ET, 2,; how-

ever, the null hypothesis could not be rejectedin controls. Similar percentage increases wereseen in the control groups (about 20%), butthe mean rise in cases was two and a half timesgreater, that of the worst cases four timesgreater, and in those who blanched the average

rise was nearly 100%-almost five timesgreater than the response in controls. The dif-ference between subsets and control groupswas significant at the 1% level.The SDs for percentage change were large

in all groups, reflecting a wide variation inresponse. However, the SD for cases wasnearly twice as great as that for controls. Thisdifference was also significant (comparison oftwo variances, cases v either control group:P < 0-01). Although relative change differedsignificantly between the groups, it should benoted that no significant differences werefound when the values after cold challengewere compared. This arises because the valuesfrom cases started from a lower baseline butrose further.

MATCHING

The data point to clear differences betweencases and non-cases, whether exposed tovibration or not. However, in view of thedemographic differences between case andcontrol groups an exercise in matching wasundertaken to consider whether these differ-ences were due to disease correlates, ratherthan disease status itself. Cases were matchedagainst controls on a one to one pairing-thebasis being the same smoking status and near-est age. To provide sufficient controls for a

satisfactory match, all non-cases were consid-ered as a single control group, with exposedand pure control subjects available equally formatching. The exercise was repeated threetimes, to provide matched control groups forthe three case groups previously considered(all, worst, and blanchers). Fifty pairs were

thus matched, with a complete match forsmoking in all pairs and an age match of plus or

Table 3 Absolute and proportionate changes in serum ET,1 2 after cold challengeCases

All Worst Blanchers Exposed controls Pure controls(n = 30) (n = 14) (n =14) (n = 21) (n = 33)

After cold challenge ET, 2:Mean (SEM) 15-86(1-08) 16-73(1-36) 15-98(1-59) 17-41(1-50) 15-52(1-11)

Absolute change:Mean (SEM) 4-05(1-36)** 6-71(1-66)** 5.83(2.35)* 2-64(1.54)Ns 1 51(1.26)NS

Percentage change:Mean (SEM) 54-3(17-5)** 86-8(23.6)**t 99-3(32-3)**t 20.8(10.4)Ns 20-4(10-0)NS

* P < 0 05; ** P < 0-01, paired t test (null hypothesis (after cold challenge = baseline)); tP < 0-01 cases v both control groups:multiple mean comparison test.

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Table 4 Comparison ofstudyfindings after matchingfor age and smoking status

Matched Worst Matched MatchedAU cases v controls cases v controls Blanchers v controls(n = 24) (n = 24) (n = 12) (n = 12) (n = 14) (n = 14)

Age (y):Mean (SD) 43 1 (14-8) 43-6 (12 7) 50 7(11 9) 50 2 (11 3) 47-6 (12 9) 47-1(12 3)Range 22-63 21-63 21-63 21-63 24-63 23-63

Systolic BP (mm Hg):Mean (SD) 128 (19 1) 122-3 (184) 135-1 (17) 124 (13) 130-8 (18-1) 122-1(12-1)

Diastolic BP (mm Hg):Mean (SD) 81 6 (12-4) 82 (12-4) 81-6 (10-0) 82-2 (6-9) 80-6 (10-8) 83-4(6-4)

Base line ET, (pmol/l):Mean (SD) 11 89 (4 45) 14-91 (4 3) 10-07 (3-54) 14-34 (5 53) 10-25 (4 17) 14 03 (4 95)

* * *

Absolute change after coldchallenge in ETl (pmol/l):Mean (SD) 4-51 (8 02) 2-34 (8 14) 7 09 (6-78) 5 39 (9 32) 5-83 (8 8) 1 53 (6 37)

t NS t NS t NSProportionate change after cold

challenge in ET, (%):Mean (SD) 59 5 (100 6) 26-3 (67) 92 5 (95 9) 47-6 (71-2) 99 3 (120-7) 22-4 (56 2)

t NS t t t NS

* P < 0-05, Paired t test: null hypothesis (case = matched control); t P < 0-01, t P < 0 05, paired t test: null hypothesis (after coldchallenge = baseline).

minus one year in 43 of the 50 pairs.Table 4 summarises the outcome of the

matching exercise. Despite a close match forage and smoking, the findings were manifestlysimilar: a lower baseline ET, 21 in cases thancontrols, broadly associated with diseaseseverity; greater absolute and percentage risesin cases than controls after cold challenge,with the largest rises in those worst affected;and the results of significance tests were similar.Hence, matching for age and smoking did notalter the principal findings.

DiscussionThe current investigation has several potentiallimitations. Participants were volunteers, so itis necessary to ask whether such populationsof convenience differ materially from ran-domly selected ones. In populations exposedto vibration there is no reason to suppose so:the overall response rate was good and thestudy populations, setting, and clinical find-ings were typical of those expected in VWFresearch based in industry. Among pure con-trols the situation is less certain; the responserate was lower and it is known, for example,that several volunteers were regular blooddonors. Pure controls had to be recruited froma different working population and there wereclear cut social class differences betweengroups. We know of no scientific literatureabout the effects of social class and geographyon serum ET, 2,, but the possibility exists thatunknown confounders contribute to the differ-ences found between cases and pure controls.

However, the study examined two controlgroups. Controls exposed to vibration werewell matched with cases from the socioeco-nomic and geographical standpoint and thedifferences here were just as clear cut as forpure controls; furthermore, the two controlgroups, although drawn from different set-tings, provide remarkably similar results;finally the protocol excluded controls with dis-eases of known relevance and the most readilyidentifiable confounders (age, smoking, bloodpressure) have been considered in thematched pairs analysis. So there are groundsfor considering these demographic differences

to be unimportant compared with the differ-ences between health and disease.

Case definition gives further scope for classi-fication errors and biases. The study used aquestionnaire, predetermined diagnostic crite-ria, and classification by a single observer.This approach has the advantage of minimis-ing within observer variation and ensuring aconsistent classification scheme even thoughthat might still cause misclassification.The case definition was modelled on that of

Gemne et al-namely "attacks of well demar-cated, local blanching and accompanyingnumbness of the affected parts of the fingerskin triggered by exposure to environmentalcold... with a distribution that agrees wellwith the strongest vibration exposure".23Special emphasis was given to demarcation ofcolour change and a minimum duration ofresponse. The definition insisted on tool usebefore the start of symptoms. This excludedobvious cases of primary Raynaud's disease. Itmay not have excluded every case ofRaynaud's disease in a male tool user (5% to10% of men admit to occasional blanching ofthe fingers or thumbs), but the high preva-lence of disease in the Portland populationsmakes it likely that relatively few men said tohave secondary disease actually had primary.

Reliance on clinical history poses the addi-tional problem that participants could makeup or exaggerate symptoms for personal gain.However, it is worth emphasising that theeffect of misleading case histories, misclassifi-cations, and inaccurate grading of diseasewould be to make genuine differences betweengroups harder to detect. The differencesdescribed in this study seem to be sufficientlylarge and robust to stand out despite theseproblems. Furthermore, the broad relationbetween case severity and the findings addsweight to the data. Finally, the blancher subsetwas the group in which the diagnosis was mostclear cut, a group that actually manifested thephenomenon of interest around the time thatblood was drawn: findings broadly accordedwith those with the worst case histories. Thesecombined findings indicate that the problemsof case definition have not influenced out-come.

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The baseline findings contradict those exist-ing studies for Raynaud's disease and sec-ondary Raynaud's phenomenon due to causesother than vibration, in which a raised baselineET, 2, has been described'5 16 However, theyaccord with the only other study of ET, inworkers exposed to vibration, which examinedvariation within a shift in finger systolic bloodpressure in riveters and age matched controls,and as a subsidiary enquiry, measured ET, ina subset of non-smoking volunteers.'8Unfortunately the proportion of workers withVWF and the degree of success in controlmatching in the subgroup was not clearlyspecified, and the protocol did not include anassay after cold challenge, making direct com-parison of results impractical. However, alower mean baseline was described, as in thisreport.The disparity is most likely to be accounted

for by differences in methodology, especiallythe radioimmunoassay. The ET, 2, is secretedas a precursor (ET, 38 ) and then cleaved.Older assay techniques have measured ET likeimmunoreactivity, which may be a compositeof immunologically related but physiologicallydiscrete secretion moieties. The Amershamassay, which was also used in the study of riv-eters,'8 has a very low cross reactivity for othercleavage fragments, and is effectively ET, 2,specific. The findings of different researchgroups can be reconciled if cases have raisedserum concentrations of the precursor ET, 38but lower serum ET, 21 at baseline, a hypothe-sis untested so far to our knowledge.An inverse association between baseline

ET, 2, and disease severity is an unexpectedfinding, given endothelin's known constrictorpotential. However, ET, 2, is a complex agentwith complex pharmacodynamics: dependingon production pattern and the intrinsic tone ofvascular beds it may act as a vasodilator24; it isknown that ET, 21 is present in peripheralvenous blood in concentrations several logorders of magnitude lower than those con-stricting isolated vascular rings; that ET1 21potentiates noradrenalin and serotonin, andperhaps other agents too25; and that thereexists a complex balance between EDRFs andEDCFs, the details of which are only partiallyunderstood. At warm equilibration tempera-tures vasospasm is absent in all but the mostsevere cases, so there is no intrinsic reason forassuming a simple relation such as a raisedET, 21 under these conditions. Finally, the cir-cumstances that regulate the cleavage of ET, 38to ET, 21 are not fully known.A lower baseline concentration could arise

as part of a disease compensation mecha-nism-for example, local production of ET, 21could be down regulated in response to theeffects of fixed lumen obstruction of the digitalartery; or to compensate for pre-existing dis-tortions of vascular tone or the balance ofEDRF and EDCF effects. It might also ariseas part of a more widespread damage effectconsequent on endothelial sheer stress.Arteriographic studies of occlusive change inthe digital arteries of some patients26 27 and thereported depletion of vasoactive peptides in

the cutaneous nerve supply of others,'7 providesupporting evidence for a damage effect.The cold response of cases and controls is

of considerable interest. An active mechanisticagent might be expected to show the patterndescribed-that is, a rise in response to coldgreater in cases than controls and more note-worthy again in the worst cases and especiallyin those men with vasospasm. However, thesefindings need to be interpreted cautiously, asagain the situation may be more complex thanat first appears. Zamora et al showed a similarresponse in primary Raynaud's phenomenonbut not until an 80% decrement in pulsatilityhad already occurred (they postulated thatET1 21 was a player but not a prime mover inthe vasospasm found). I5

Workers have questioned whether the risefound by Zamora et al could be explained byhaemoconcentration or altered forearm bloodflow.20 In the present study concentrations ofserum albumin and von Willebrand's factorwere also measured at baseline and after coldchallenge. The mean (SEM) percentagechange in serum albumin was similar in cases(-1-9% (1-8%)) and controls (-2-1%(2.0%) in exposed controls; 2-8% (1-6%) inpure controls), so haemoconcentration doesnot explain the large relative rise in ET1 21among patients. However, it is more difficultto discount the effects of forearm blood flow.Measurements of ET1 21 in venous and arterialblood have shown that the forearm is a site ofET production,28 so the notable fall in bloodflow that accompanies vasospasm could createthe impression of raised local production arti-factually. In our data set the mean (SEM) per-centage changes in the VWF, which isproduced by the endothelium, were not signif-icantly different between cases and controls(+0 4% (8 7%) for cases, -4-7% (5 7%) forpure controls, and -4 1% (9 5%) for exposedcontrols), lending tentative support to the viewthat forearm blood flow does not account forthe changes found. However, this questionneeds to be considered by further workencompassing specific measurements of fore-arm blood flow or measurements in ET1 21 inboth venous and arterial blood. Forearmblood flow is an important unknown quantityin interpreting the present data.The clinical pattern found in the blanching

group in this study was decidedly heteroge-neous: in some cases blanching was immediateand brief; in others it developed a few minutesafter cold challenge; and one quarryman hadalmost permanent blanching reversed brieflyby cold challenge!

This may be reflected in the wide variationin measured ET1 21 in individual cases, withrises of more than 300% in some, falls in oth-ers, and stable values in some men found toblanch. The ET1 21 alone is not a completeexplanation of blanching.

It is worth noting in the context of this clin-ical diversity of response that the SD for per-centage change in ET, 2, is almost twice asgreat in cases as controls. The probability thata difference as large as this arises by chancealone is less than 0 01 and may reflect the rela-

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tively greater instability of ET, 21 concentra-tions (or forearm blood flow) after cold chal-lenge in cases.

Given the significant associations found inthis study it is tempting to hypothesise thatET, 21 has a role in the vascular manifestationsof VWF: that baseline ETI 21 concentrationsadjust in circumstances of warm equilibrationto compensate for the disease process and thatan unstable, but generally exaggerated produc-tion of ETI 21 is implicated directly or indi-rectly in cold vasospasm. However, thepossibility that the associations described mea-sure effect rather than cause, cannot fully bediscounted and needs further work.

Several avenues could be fruitful.Measurement of ET1 21 binding to its receptorscould be used to identify the effective localconcentrations at sites of vasospasm, ratherthan in the venous overspill as at present.Further histochemical work and the use ofrecently developed ET receptor blockers may

enable a more specific exploration to takeplace. The ultimate test of the significance ofET1 21 in VWF may be judged from the thera-peutic impact of ET blockage on this indus-trial complaint and its natural diseasecounterparts.

We acknowledge the assistance ofmembers of the EmploymentMedical Advisory Service team from the Area South office andof colleagues from the Health and Safety Laboratory, whoundertook the novel assays that form the cornerstone of thisreport. Helpful advice was also received from the HSE'sResearch Advisory Team and Drs Crane, Coggon, McCaig,and Noble: we thank them.

1 Loriga G. Il Lavorco co i martelli pneumatici? Boll InspettLavoro 191 1;2:35-60.

2 Griffin MJ. The effects of vibration on health. Southampton:University of Southampton Institute of Sound andVibration Research, 1982. (Memorandum 632.)

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