Are Pulmonary Capillaries Susceptible to Mechanical ... - Journal

Are Pulmonary Capillaries
Susceptible to Mechanical
Stress?*
Oc/i/u’ A. ltIat/uiu’u-Co.sts’//o, P/iD.; uuud Johuu B. %Vc.s’t, \I.D., P/u.D.
T tie extreme thinness of the puuluimonarv blood-gas
barrier has lomig beesm recognized. Its fact. large
portiouis of the batrrier are so thin that they’ asre aut the limit
of time power of resohsutiomi of the light microscope. It is
omihy’ with the advent of electromi umiicroscopv that tise
cellular strumctcmre of the blood-gaus barrier wats ehumcidasted.
Forty years asgo. Fraunk Low’ publishiedl time first electrous
msmicreigraphms of the luumsg parenchsvuiia in laboratory asmi-
mats asmid lmuumauis, and cleuiionstrated time presemice of as
comitiustuotus epithseliall limming cif the alveolar \vall. Since
theum, the reusuarkable thiinness of the pulnieinarv blood-
gas harrier lists usmaimily’ beemi viewed in terms of the
clmaracteristics tlmat make it so effective for diffusioum.
Respiratory gases are transferred! by isassive diffusiomi and
therefore aut as given partial pressure cliffereuice across the
harrier, increasedi passage cif gasses occurs with greater
sumrfauce atreal aumd reduced tissue tlsickmiess, according to
the Fick law of diffusion.
In time Iiuuimatus Iuung, the alveolamr surfatc’e area is very
large (sup to 150 mmm2), approximately half of which is oui tIme
thu side of the blood-gass barrier with a thickness of omihy
0.2 to 0.4 tmii.1 As noted elsewhere,’-4 however, there is
evidence of diffusion-limitation of 0, uptake imi elite
athletes chmring ussaximaul exercise,5-5 suggesting that the
blood-gas barrier c’oumld umot be amsv thicker without feur-
titer himmiitautiouis of 0, uptake duuring heavy exercise. At
the sausme tiusme, the pulmonary blood-gas harrier must be
vemv strong tdi maintaimi its structuraul imitegrity in spite of
its extreme thinness, and to withstand the high wall
stresses ciurimig iustense activity. The stremigth of the
blood-gas barrier.4 and the pathiophmvsiologic conditiomis
where it fails hecausse of stress fasilumre of putmimonaury
capillaries,’- have umot been previd)ushy recognized.
STuSENGTIt OF Bu.ooD-CAs BsRusuEB ANu) FoRcEs ACTING
ON’!’ lIE Auxeou,.Aus WALL
There is evidence that the nieclmanical strength of the
pulmoumarv blood-gas harrier comes from the extracellu-
tar ussatrix.4 On time thin side of the blood-gas barrier, the
extracehiumlaur unatrix is uruainlv redsuced to the fused base-
nseust ummembramies of the epitisehial amid endothiehiatl layers.
The electron demise ceumter portiomi of the bassement mem-
hramie, or launina densa, coustains collaugemi IV whichi con-
fers tensile strengths to the’ usuattrix.49
The three unauimm forces actimig oum the pulmonary blood
gas barrier (Fig 1) have been identified.’ First, the hoop
*Froumm the De’partosc’mst (if Medicine, Sclmool of Mediciuse, Ummi-
versitv of Cauhiforusiau, Sauus Diego, Las Jolla, Calif.
This stuudy wats suupported by NIlI prograuus project HL 17331
amumd HO1 1IL46190.
Repriu,t requests: Dr Z%Iat/uieuu-Cu.ste//o, Deparinueuut of ?Iedic/tue.
Uuuit:ei’.s’itj of Ca/iforuuia. Sa,u Diego .9209.3-0623
SESSION 9
or circumferential tensiomi in the catpillar watt1 is caused
by time capillary transmural pressumre actimig omi time ceurveci
surface. It can be calculated via time Laplace relationship
which states that the circumferential tension is tIn’ prod-
uct of transmural pressure and ratdius of curvature. The
secomid force is time surface tensiomi of time aulveolasr hiniuig
layer, and third is time longitudinal tensioui in time alveolar
wall associated with luuig inflation. Seurfauce tension (force
2) is thought to be protective, based oui the fact that
capillaries bulge into the alveoli at high capillarY transmural
presssure.3-’#{176} On the contrary. the iongitumdinal tension of
the tissue elememits in the alveolar watt (force :3) predis-
pose time capillary wall to stress failumre. \Ve summmarize
below experiments from osur laboratory showing that the
mncidemice of stress failure of puslmonarv capillaries imi-
creases at hugh lung volume.’’
\Vhietlier or not the capillary wall fails cinder the hoop
tension (force 1) does miot depend on the wall teuision per
Se, hut rather oui wall stress which is tin’ ratio of wall
tension to thickness. In the following section, we summa-
rize our studies in rabbit lung, showing that stress failusre
of pulmonam’v capillaries consistently occurs at a capillary
transmural pressure of 52.5 cm H,0, ie, abotmt 40 mm
Hg.’-’2 At this transmural pressumre of 52.5 cm H,O, time
wall stress at a nonsinal capillary radius of curvature of 5
h.tm anci a wall thickness of 0.3 (.tni is 9 x 10’ N/mn2 (or
9 x 10 dynes/cmn2), which is an extremely high stress. It is
comparable to that in time wall of the humasn aorta,’ which
is subjected to a much higher transmural pressumre (100
ENDOTHELIUM
INTERSTITIUM
EPITHELIUM
Fucu se 1. Putunonauy capillary iii an alveolar watll, simowiusg the three
maims forces actiusg on tise blood gas barrier. (1) Circuusiferential or
isoop tension is given by capillary tramssumiural pressure x rascihus of
cuurs’ature; (2) surface teosioum of the aslveolasr liniusg layer is ttmooghst
to be protective; and (3) longitudinal teussion in the aulveolar wall
associated with tumng inflatiomi increauses hoop tension aimcl therefore
the likelihood of stress fauilure. (With permission.3)
1 O2S 36th Annual Aspen Lung Conference
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mm Hg) and has a mucim greater radiums of curvature
(1.3 cm) but also has a much thicker wall (2 mm) and
harge amounts of collagen and elastin. In other words, the
high stress imposedl on the pulmonary capihiary, in spite
of its small radius of curvature, is due to the extreme wall
thinness, one of the design requirements for aui adequate
transfer of gas by passive diffusion.
STRESS FAILURE OF PULMONARY CAPILLARIES IN RABBIT
We examined the ultrastructure of the blood-gas bar-
rier in rabbit lumngs exposed to increased capihiary
transmuurai pressumre.1-’2#{176} Briefly, the following experi-
mental preparation was used to expose the isung to a
known capillary tramisunural pressure and themu fix it for
electron microscopy at the same pressure. Anesthetized
animals were exsanguinated, the chest was openeci, the
pulmonary artery and left atrium cannulated to control
inflow and outflow perfusion pressumres, and a cannula
was placed in time trachea to control alveolar pressure.
The hung was first perfused with the animal’s own blood
for 1 mm, followed by saline soiutionldextran (3 miii) atnd
then buffered glumtaraldehyde fixative (10 miii) at the
sanue pressure. Puilmonary artery pressures of 20, 40, 60,
and 80 cm H,0 were used, with pulmnonary venous
pressures 5 cni 11,0 below arterial pressumre and an
alveolar pressure of 5 cm 11,0. Therefore, capiliarv
transmuratl pressures, Ic, the pressure differences be-
tweems the inside anel outside of time capillary, were 12.5,
32.5, 52.5, and 72.5 ± 2.5 cm H,0. Three animals were
atnalyzed at each pressure, except for 32.5 cm H,O
transmumral pressure (Ptm) where six animals were stud-
ied.
In tue lungs exposed to a Ptm of 52.5 cm H,O amnd
A
ahcive, ciisrumptions of time blood-gas harrier were coimsis-
teumtly found. They’ inclumded chisruptiomi of the eneiothmehial
layer or the alveolaur lay’er, or sousmetimnes at11 layers eif tIme
wall.3-’2’-’ A frequemit finding wats that the capihiaurx’ emido-
theliah or alveoIasr epithehial layers were disrupted, butt
time basement meusibrause WtS cd)mmtin(uous (Fig 2). Also,
platelets dir red blood cells were (iftcmm seen at time site of
clisreuption. imm close vicinity of tIle exposed basement
memnbrane (Fig 2B). Qumamitification of the extent of
damage of time blood-gass barrier’2 showed that the nuumn-
her of breaks per mnihiimneter of epithehiath atndi emmelothiehial
boundary length increaused niarkeeilv with increaseei Ptm.
No breatk \vats foumnd at a, Ptmsu of 12.5 cums H,O audi a few
breaks were seems at 32.5 cm H,O Ptmn, usiostly in omie
ammiunal. From a Ptmn of 52.5 to 72.5 cmii H,O. the mmtummmber
of breaks per unullimeter rose frons 8.5 ± 3.2(SE) to
27.8 ± 8.6 for endlothmehi,um auscl from 10.4 ± 4.3 to
13.6 ± 1.4 for epithiehiuni. On average, time length of the
breaks as seen by transussissid)Ii electroum Iimicroscopv of
sectiomis, was about 1 to 2 Inn for eneiothehiuum and 2 to :3
lImms for epitheliumsi. break lemigtis being significantly greater
ims epithietiumm comparedi to enciotimehiummn omilv at the
Isigimest pressuure (72.5 emit 11,0 Ptmsm). There was umo
sigisificauut difference in break iengthm with imicreasing
pressure eithmer fcir emidothehiumis or epithsehiummi, suggest-
ing that once chisruptiomis imaudi occurred, time stresses were
greatl’ relieved. The i)atsemmsent miiemnhratmme was contimmu-
mis in approximately htlf of the ermdotlmeliai aund epithelial
breaks, at leaust ims time plane of the sectioms. underlining
the greater strength of time extraceilumlar mnatrix compared
to the cellular linings. TIn’ thickumess of tIme blood-gas
barrier iuucreasecl markedly’ above 32.5 cmii 1-1,0 Ptns. This
was entirely dume to the svidemsing of time imiterstitimmumu as a
restult of eclensa, while time thuickmmess of both time emidothe-
Fuccusu; 2. Traussumiissioms elec’troum micrographis shsowiumg disruption of thue blood-gas baurrier iuu rabbit
bug exposed to a capillary’ transumiural pressiure of 52.5 cmii 11,0. A /uft), capihlarv eumdothsehiuuuis is
disrupted (amrrow), bumt alveolar epitheliuuumm ammd two basenmeuut uisenmiiraumes are coumtinuuouus iii tlme plaume
of time sectiomi. B (rig/it), atlveolar epithehiuun (open aurrows) asmmd catpillars- emmciothehia,l layer (solid
arrows) aure disrupted; note a platelet protruding into tise eumelothsetiatl openiumg and closely applied to
tIme exposed basement ussensbramse. Transpumhmmmonasrv pressuure was 5 cull 11,0. (Witlm peruuuissioum. I)
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CHEST / 105 / 3 / MARCH. 1994 / Supplement 103S

hiumn amid epithmehiumn was uiot changed. ‘
Fuirther iumsighut iisto the pattern of disruption of the
blciod-gas harrier svats obtairsed by examimuation of adja-
edit saumuptes by scanusing electron microscopy (SE M ). ‘
Evielemuce of disrumptiomu of the alveolar surface was consis-
temstly foummici att Ptusm (if 52.5 cmss H,O aund above. The
mmsajoritv of tIme breaks were elongated slits, oriemuted
perpemudicuulatr to time capillary axis (Fig 3A). Most breaks
were complete disruptions of all layers of time lulood-gas
barrier. Figumre 3B shmows a red blood cell protrudimsg into
time alveolus. \Vhsile several breaks were in close vicinity to
immterceltular jummctiomss (Fig 3A aundi B), almost no break
was seen at the jumnction itself, suggesting greater me-
c’hmaummic’al stremmgth att time junction. TIme dhiuiuensions of the
elomsgattedl slits of time blood-gas barrier were about 71.1111 in
lengths for at width of aubout 1.5 ltmms. They varied little withs
pressutre, confirmnimmg oumr previous observation by transumsissi(in
electromm nsicroscopy (TEM) and suggestimug the
relief’ of stresses ommce disrumption has occtmrred. Further
strikimmg similarities with our previoums TEM sttmdies’-’2
were due extemst of disruuptioms of the blood-gas basrrier as
a fuunctioms of Ptun. tIme SEM appearance of the breaks, and
tIme close mmsorphmommmetric estimsuates of their frauctional
demmsity comsipared with TEM. ‘‘ This inciicated thsaut simnular
ruuptsures were examimimseci by the two techniques, even
atl’ter greatly’ cliffereimt tissue processing and preparation
proceduires.
Time effect of fixattiomm on the imicidence of breauks its the
blooci-gats hatrrier was imivestigated by raisiusg Ptm to 52.5
cmii 1-1,0 for blood perfuusion (1 mum) and then reducing
time capillary pressure for either perfusion with saline
solumtiomm ammsdl glutarasldeisyde fixative at lower pressure,’4
or imistillatioms of fixautive via the airways. Perfeusion with
sathimme sohuutiomm amid tlsems fixastive at reduced Ptmsm (12.5 cmii
H,O) resuitteel in at lesser number of both endothelial and
epithielial breaks comnpasred with the perfuusions with
sahimme sohumtion mimic! fixative at high pressure. Interestiuigly,
time breauks uso longer seen’4 were those that were immitially
smmuatll amici were associatted with a comitimmuuous basement
mmseumsbraumme imm tile previous study. 2 Ve attrihumted this to
tIme rapid reversibility of somuse breaks atfter the pressure
was lowered,’4 comusistemst withs fusnctiousal stuidies which
docuummsemmted the rapid reversibility’ of the imucreased cap-
ihiatry’ permeability’ observed imm the iumng aufter short peru-
ods of Imigim vascuuiar presssmre.t After fixation h’ airway
iimstillamtioum i imsmuuediattely’ after 1 mjms blood perfusion at
Imighm pressumre. ‘‘ the msuumber of emuclotheliat breaks \vats
simsuilatr to tisat seemu us time previotus study with perfusion-
fixuttioum att high pressure. ‘ This indicated thiast stress
fauulumre of puulmmsonaury capillaries occurred within the first
mumimmute of perfumsioms with blood. Also, it ruled oumt a
sigmuificatmst effect of the ghuutauralclehyde perfusiomm at high
pressumre in causimmg caupillar\’ stress failure in the previous
stimcly, 2 simuce ass great a msumsuber of endothelial l)reaks was
found aufter fixatiomi by auins’ays imsstiliation, Ic, withuosut
vascular perfusion fixation at Isigh pressure. Amuother
imuterestimug f’indimsg was that tIle mncidemice of disruptions
of time e1)itlmehtuumm was lower in the lungs with instillation
iuumusmeciiately aufter I musin blood perfsusion tisami its those
perfuused sviths sahimse soltmtioum (3 mum) amsd thems glumtaraide-
hyde fixative at high pressure. This suggested that addi-
Fucu: use 3. Sc’auuiui umg elec’troum iumic’rograuphs showiumg disruuptioums of’
the blouicl_gas l)arrier jul rabbit luuumgs exposed to a Ptumm of 72.5
(A) amid 52.5 (B) c’mnH,O. A (top), elomigatted slit of’ tIme btooel_gas
barrier (unbid arrow) very close (about (1.4 fun) to aum intercellular
juuumc’tion (white aurrow). B (bottom), disruptioum of tIme blood gas
baurrier c’rossimmg aim iumtercellumlar juuuuctium,u (white arrow) atnd
shmowiuig a reel bldmodl cell (asterisk) protruuding ilutem tIme alveolus.
Note abumusdamumce of proteiumaceoums ummaterial (A atumd B) ammd red
blood cell (A) ous tIme alveolaur surface. Traimspulmmtoiuaury pressure
waus 5 cmmm11,0. (With permmmiSSiOum. 3)
tional time mssatv be mmecessarv f(ir epithmelial rupture to
occur sifter stress fatihumre of puhimmommary capillaries. dc-
pending on tIme accimmssuhatieimm of fluid! ims time iuiterstitiuumm.
EFFECT OF Hmcu Luxc \‘oi,UmuE
At the saiuse capihlaury Ptnu of 32.5 or 52.5 cuss H,O, time
immcidemsce of capillary stress failure was greatly increased
whiemm rabbit luuumgs were perfused att highm lummg voltumsse, ie,
wlsile immflatecl to a traumspulussonary pressure (if 20 cumu
11,0, comssparee! to the low lummg volummue (5 cmms 11,0
traumssptmimomsary pressumre) uused imm ciur previous
(Fig 4). Interestingly, time ilicreasse ims time f’reqiiemscy of
both emidothueliatl atnd epithielial brc’atks was a,hxicmt the same
for approximsuately thse sammue rise ui transpuulmmsomsary pres-
sure (15 cmii H,O, from 5 to 20 cmmm 11,0: Fig 4. left patmmei)
dir Ptmss (20 ciii H,O, fromms 32.5 to 52.5 ecu 1-1,0; opemm
columuimus, Fig 4). It suggests mimi equuivahemit effect of tlse
104S 36th Annual Aspen Lung Conference
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20
increase in traumspuhmomiary pressumre or Ptnu in tiuese
comuditiomss. Measumremsient of blood-gas barrier tluickmuess
reveaheci a thsickening of due interstitium at high iuuusg
volimmsue, consistent with the presence of eciemsia.
Disruptions of the eiuciothehitmmuu with red blood cells
protruding into tlse opening were foumudl both on the tisimu
mine! thsick sides of time blood-gas harrier. As imu ouur
previous sttmdv at low lumumg the batsemuuemmt mmuemiu-
brane was continuouus in abouut half of the endothiehiat and
epithselial breaks. Exasmmsinautiouu by scamsmuimug electron miii-
crosc’op reveauled thiast at highs lummmg ‘ohumne’, the hireatks
temucled to be of simsmilatr lemmgtls humt muasrro\s’er thmamu sit low
hsmusg s’ohuunme, for a sinsilaur Ptnu. Fewer hreauks we’re’
oriented! perpendictular to time capillary axis while breaks
vithm mmuultipie segmsuents of differemut oriemutaitiomu, muot seems
at low lung voluuusie, were foummud. They were possibl’ clue
to tlse increatseci svssll stress in au directions with thue
tmmsiformiu stretchsiuig of time alveolar waull ait high luusg
voluumue. Commuparison cif msseasuuremsmesmts 1)51 SE M amid TE M
indicated that simsuilar ruptlmres were anasIy’zed by the two
techniques.’’
Time mncreaused vumimierabihitv of the pumiumsomman’ caupiltaur-
ies to stress failure at high degree of immflation provides at
physiologic msuechsanismss for studies sisowiusg increased psulmssomsarx’
mnicrovascuiar pernueabmiit withu o’erimsf1atiomm, ‘‘ It
hams imusportant immiplicsutions in tlse criticsul care setting
where greaut casre slsouuld lie tsikeuu to 1)rcveuit datussasge to
the lung clue to overdistemusioms citmrimug usseclsanicaul vemsti-
lation. As poimuted out elsewhere,7 this is often at catchm-22
situmsstion becaumse high imuflaution pressumres mimic! lsighs levels
of positive emud-expiratorv pressumre are msecessarx’ to umiaius-
tasium arterial Po, at sin ascceptambie level. However, the
imscreaseci stress oms tise blood-gats harrier hiecasuse of tIme
highs inflaution msmsukes it s’umhmmerable to ruuptture at a lower
capihlasrs’ Ptmus, at process fumrther accelerated if pastimologic
chamuges hatve occurred. ie, tIme l)lo(ud-gaus baurrier or edt-
lagen IV are weakemsed.
I
z
4o
50
E
E
F:
LUNG VOLUME
low
high
Endo- Epi-
thehium thelium
Endothelium
iii 111
Epi-
thelium
1L1
tm 32.5 cm H20 tm 52.5 cm 1120
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P\TIu(iI’IussI(iu.o;uc (Nsu:#{231}mdFx(:!-;s ou. Sru,ess Fsuiu iii’; u’
Fu;uuu’: 4. I Iistograumiu of auveu’auge mmuuumlhi,’r of’ hu’eaks
per uiuitlimumeter houiumdatrv leumgthm oh (‘uudotlme’liuuuuu atmm(I
epithmeti m ummstt 20 ( Im1gb hummug soh mummmc) some1 .5 c umm11,0
trauuuspuulmmmuimmaurs- pressure (loss’ luuusg \-ol uuumme),Ate,’i.sk,
sigumi I ic’asuutlv greater (p

tions where the extracehlular matrix weakened, for ex-
ample in Goodpasture’s syndrome where autoantibodies
attack type IV collagen,25 causing bleeding in the lung and
also glomeruli.
We recently obtained evidence that exercise-induced
pulmonary hemorrhage (EIPH) in thoroughbred race-
horses is caused by stress failure of pulmonary capillar-
ies.26 This study was done in collaboration with Drs. Eric
Birks, James Jones, John Pascoe, and Walter Tyler of the
School of Veterinary Medicine, University of California,
Davis. The lungs of three thoroughbred horses with
known EIPH were removed and fixed for electron mi-
croscopy after the horse had galloped at high speed (13 to
16 m/s) on a treadmill. Evidence of intrapulmonary
bleeding was confirmed by bronchoscopy in one animal,
Tissue fixation was either by airways instillation (one
animal) or vascular perfusion of glutaraldehyde solution
at 30 ± 5 cm H,O Ptm (two animals). Ultrastructural
evidence of stress failure of pulmonary capillaries was the
presence of a large number of red blood cells in the
interstitium, disruption of the capillary endothehiai or
alveolar epithehial layers, protemneous material amid red
blood cells in the alveolar spaces, interstitial edema, and
fluid-filled protrusions of the endothelium into the capil-
lary lumen.26 These are the same appearances we have
found in rabbit lungs exposed to high capillary transmurai
pressure .
Pulmonary vascular pressures are extremely high in
thoroughbred horses during galloping. Jones and cowork-
ers27 measured pulmonary arterial and heft atrium pres-
sures of up to 120 mm Hg and 70 mm Hg, respectively,
in thoroughbreds galloping at speeds up to 10 rn/s,27
indicating that capillary pressures must also be very high.
These very high vascular pressures are associated with
the extremely high cardiac outputs (>750 mI/mimi/kg)
achieved in these animals, which require very high left
atrial pressure for adequate ventricular filling.26 At the
same time, the extremely high VO,max achieved during
maximal exercise (180 mI/mm/kg) requires that the blood-
gas barrier be extremely thin. However, exercise-induced
hypoxemia in thoroughbreds during heavy exercise was
shown to be the result of diffusion limitation,25 indicating
that the barrier could not be any thicker without further
limitation to VO2m’ax. In other words, selection for in-
creased aerobic performance imposes contradictory re-
quirements on the heart-lung system. In thoroughbreds,
those requirements have reached the point of failure of
the blood-gas barrier. The selective breeding of thor-
oughbreds for a large number of generations has pro-
vided animals with enormous 0, uptake rates, which
necessitate not only a very thin pulmonary blood-gas
barrier but also extremely high cardiac outputs, which in
turn require pulmonary pressures to be so high that they
exceed the mechanical strength of the thin blood-gas
barrier, causing failure of pulmonary capillaries and
alveolar hemorrhage.26
Interestingly, while a large number of red blood cells
were found in the alveoli and interstitium in areas show-
ing clear abnormalities macroscopically, actual endothe-
hal and epithehial breaks were difficult to find. This was
probably due to the reversibility of ruptures once the
vascular pressure was reduced, fronu the end of the gallop
to tissue fixation 60 to 70 mi’tin later. In addition, platelets
and cytoplasmic extension of leukocytes were seen in
close vicinity to the exposed basement membrane at the
site of disruption of the capillary wall, suggesting platelet
and white blood cell activation and the initiation of an
inflammatory process.26 As mentioned earlier, inflamma-
tory markers were found in lavage fluid of rabbit lungs
perfused at high pressure,24 as well as in bronchoalveolar
fluid of patients with HAPE,23 suggesting that stress
failure of pulmonary capillaries is the mechanism of
HAPE.
In summary, pulmonary capillaries are subjected to
high mechanical stress in spite of their small radius of
curvature, because of the extreme thinness of the alveolar
wail, which in turn is required for the adequate transfer
of gases by passive diffusion. The contradictory design
requirements imposed on the blood-gas barrier, which
must be thin enough not to limit diffusion but at the same
time very strong to withstand high stresses across such a
thin barrier, have only recently been recognized. Stress
failure of pulmonary capillaries plays a role in several
pathophysiologic conditions causing high-permeability
edema and pulmonary hemorrhage. A dramatic example
is exercise-induced pulmonary hemorrhage in thorough-
bred horses where selective breeding for extreme aerobic
performance over a large number of generations has
allowed the cardiovascular system to develop beyond the
mechanical strength of the pulmonary blood-gas barrier.
ACKNOWLEDGMENTS: This work was done in collaboratioms
witim Michael Costello, Ann Elliott, Zhenxing Fu, Sanli Kurdak,
Yasuo Namnba, Koicimi Tsukinuoto, and Reoato Prediletto.
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1 OBS 36th Annual Aspen Lung Conference
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Centripetal Tension and
Endothelial Retraction*
A/aim B. Moy, M.D.; Rebecca Site/don, BA.; Kntituj Liimd-’deuj. BA.;
Sandra Sima.sbm,, BA.; amid D. ,\ufcitael S/tathy. M. I).
I nflatusumsiatorv misolecumles suicim as histaumsuiuue incresuse
eumclothsehial permmseabihity by imsitiatimig retrstctioum of
ssdjsscemut eumdotluehial cells. We recemstly reported that ims
hmsummuamu umnubilic’al vein emidothueliash (I! UVE) cells huista-
mssimie imucresuseci phuosphorylatioms of thse light chmaimm tif
mssyosimu (MLC) by 0.18 ± 0.02 moles phsosphmsitc’ p’ mndile
MLC (ussolP/nmolMLC). This is consistemmt with time his’-
pothesis timsit Imistamimme initiates retrsicti(imi by increasimsg
ceistripetath temmsiomu within euidothmehial cells. However,
chselatiomi of extracehlular calcitumsi whelm interrumpts cell-
cell amid ceil-sul)strate hiiumding also increases endotimehial
permnestl)ility simmcl causes emmdothselistl cell retrstetioms hiothu
itt situ immperfumsed lummgs mudl iii vitro with cultmureei cells.
TIse effects of cstlc’iuummu elmc’lattioms sire’ coumsistemit ss’ithm tlue
hiy’potiuesis tlmaut retesuse of forces tetlmerimug emidothuelial
cells imi plaice atllows expressiuiui of’ at e(immstitultive centrip-
etal teumsioms. Ims our receumt report, we fouund commstitumtive
)lmospImorylsitiomm of M LC at 0.20 ± 0.02 msmolP/ummolMLC,
coumsistemit with si c’onstituutive’ atctommsy’osimi-mmsediatu’d teum-
siomm. \Vc’ asked if reclumctioum of Ni LC phmosphorvhaitioum
woumld prevemmt tile respomise to hmiststmmmimue or calciuumui
chmel5ution. aimscl conversely, if iuscrestsedi comistitustive, Ni LC
plmosphorylsitiomm wosmld cause cell retrsictioms.
1mmcommtrot amid huistsimimse-stuimiumlateel H UVE cells amid imm
comutreil porcimie puhmmiomuary arterv eutdothmelissh (PPAE)
cells tryptic peptide misaps indicated that M LC was phmos-
phmom’y’lamtecl by the csulcisumss calmimoduhimi -dlepemudemut myosimi
light clmsuin kinase. Pretreatm#{236}ment cif H UVE cells withs
cAMP pres’emmtsc! the huistamnimme-stimsiuulatech immcrease imm
MLC phsosphmorylation (-0.08 ± 0.02 mmuolP/mssoIMLC) ammcl
a huistsumuimme imuitiated imscreasse iii H UVE cell misonolaver
periuueal)ility (-12 ± 1 percemmt). Pretreatumiemut of IIUVE
cells withm tue cathciumui-csulmnodulims inhmihiitor, Ni L-9, also
prevented time huistsimisimse stimsmulated imicreutse its Ni LC
pluosphmorylation (-0.29 ± 0.04 muuolP/mmsolM LC) mmmc! tIme
iumcrease imu HUVE cell msuonolayer permeability (14 ± 4
percemmt of time coumtrol response). Simssihstrlv, pretreatmsmemmt
of PPAE cells with cAMP reduced bstssih MLC phsplm-
rylatiomm (-0.16 ± 0.O3molP/molM LC) amid reduced tIle
increase in mmsoncilayer permssesuhility fohlowimsg calciumms
chelatioum (21 ± 14 percemut of tIle c’ommtrol response). Pre-
treatmuuemst of PPAE cells witls ML-9 also reduced bausath
M LC phmosphmorvlation (-0.13 ± 0.02 mmsolP/miucil M LC) atnel
reduced the imseresise iii msmousolaver permuueahuhitv fohlosv-
imug calciumsu chielsttiomm (47 ± 5 percent of control re-
5l)onse).
TIse hstsai level of M LC phmosplmoryhsutiomm likely rehire-
sents comustituitive kiumatse stud pImsplmsutsise activity. Okadstic’
stcid iumcreaseei Ni LC )imosphmorylsstiomm ium i’PAE cells (1
j.tM, 0.06 ± 0.O4mmsolP/mmuo1MLC siumel 10 1.tM, 0.17 ± 0.05
uiuotP/umsolMLC ) iii su dose-depemsdemut muistumumer, simucl 10
f.LM (289 ± 32 1)ercemst) but hot I i.sM (4 ± 5 perce’mmt)
okssciatic atcid imscrestseci PPAE cell umueimmolsive’r permumesthil-
6Frouus thue Ummivc’rsity- of Iowa College of Mediciuue, Iowa City’.
CHEST / 105 / 3 / MARCH, 1994 / Supplement 107S