Effects of Increased Pressure upon Sarcoma 180'

ALVINM. ARKIN,M.D., ANDKANEMATSUSUGIURA,Sc.D.

(From the Sloan-Kettering Institute for Cancer Research, Memorial Hospital, New York, N.Y.)

The clinical behavior of neoplasms frequentlysuggests a relationship between pressure and tumor growth. For example, the increase in the rateof tumor growth, after the constriction of a capsule or another structure has been removed bybiopsy or spontaneous perforation, is familiar toevery surgeon. A scirrhous carcinoma of thebreast, enmeshed and compressed by dense fibroustissue, is notoriously slow-growing; yet, these samecells, or their daughter cells, will grow rapidly oncethey escape to the relatively loose tissue of the regional lymph nodes. Keloids, too, may not appearin regions subject to pressure, such as is exertedby a hat or collar. Numerous other examples willsuggest themselves—all susceptible of an interpretation indicating that local pressure or constriction will hinder tumor growth.

The reverse of this relationship—that decreasedlocal pressure tends to initiate neoplastic growth—has been suggested, and the overgrowth in amputation neuromas has been considered a local manifestation of such a "release phenomenon"(2).

There has been little experimental investigationof this problem. Basset (3) has shown that, in vitro, mouse Sarcoma 37, suspended in physiologicalsaline, can survive a pressure of 1,000 atmospheresfor 5 hour. Other investigators have been concerned with the effects of high or low oxygen concentrations upon tumor growth and have used increased pressures only incidentally, as a means ofincreasing oxygen tension. Pressure, itself, wasconsidered to be without effect. Thus, de Almeida(1) exposed lloffo spindle-cell rat sarcoma in vivoto six atmospheres of oxygen for 5 hour. After 10days the tumor was heinorrhagic, and tumor cellswere destroyed. Campbell (4) could not confirmthese results, using Walker rat carcino-sarcoma256, Bashford mouse carcinoma 63, Twort mousecarcinoma, or spontaneous mammary carcinoma ofmice. His rats would tolerate only five atmospheresfor 1 hour; the mice only four atmospheres for 1hour. Campbell and Cramer (5) found that at totalpressures of one atmosphere, 60 per cent of an at-

* This work was supported by a grant made to the Sloan-Kettering Institute for Cancer Research by the AmericanCancer Society.

Received for publication, December 12, 1949.

inosphere partial pressure of oxygen for 2 weeks,caused no inhibition of tumor growth. On the contrary, they, and Warburg et al. (11), found thatoxygen starvation liad some temporary effect ininhibiting tumor growth, and sometimes producedtumor necrosis. Campbell (4) concluded that variations in the partial pressure of oxygen were of novalue, by themselves, in tumor therapy. Similarconclusions were reached by Pollack et al. (8), whoused air at 15- and 30-pound-pressure and subcutaneous injections of oxygen.

Marsh (7) used compressed air at a gauge pressure of 30 pounds. This yielded the same partialpressure of oxygen as Campbell and Cramer used,although the total atmospheric pressure wastripled. He found that the incidence of spontaneous tumors in a tumor-prone strain of albinomice was slightly reduced, and the longevity andtumor age were increased.

This paper presents some results of compressionof Sarcoma 180. Two main types of compressionwere studied. Local compression of the tumor wasproduced by implanting it into the tail of micewhere its growth would lead to compression by thedense skin overlying this region. In another seriesof mice, the entire tumor-bearing mouse was compressed by increased atmospheric pressure in acompression chamber.

EXPERIMENTALCompression by tail implantations.—Sarcoma

180 was implanted into the ventral or dorsal surface of the tail in 58 albino mice of the RocklandFarms strain, using small pieces of tumor, eachweighing about 2 mg. A small trocar was used forimplantation. Each tumor was transplanted intoapproximately ten mice. Six experiments weredone, summarized in Table 1. No difference wasnoted between ventral and dorsal implantations.

In all tail tumors growth was extremely slow,and the tumors never became as large as the controls implanted in the usual subcutaneous axillaryregion (Fig. 1). In five mice the tumors didnot take. Of the remainder, 35 became hemor-rhagic, the discoloration being clearly visiblethrough the skin of the tail. In 38 mice, the tailtumors regressed completely. (This constitutes 72

272

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ARKINANDSUGIURA--Increased Pressure on Sarcoma 180 273

per cent regressions, as compared with a regressionrate of 6 per cent in over 1,000 Sarcoma 180 tumorsimplanted in the usual site and observed in thelast 18 months.) Twenty-one of the 58 mice died ofthe original tumors, from métastases or extensionsof the implanted tumors, from a spontaneous andapparently unrelated tumor in one case, and fromall other causes. In some cases death occurred frommétastases, even though the original tumors hadregressed. All the survivors remained free of Sarcoma 180. In two cases the tail was sloughed offdistal to the implantation site. The remaining miceshowed no evidence of impairment of circulationby growth of the tumor.

Figure 1 illustrates the growth of the tumors inthe tail (Table 1, Exp. 3). Figure 2 is a photographof a tumor 16 days after tail implantation. Thetumor was markedly hemorrhagic and regressedcompletely after 41 days (Fig. 3).

Compression by increased atmospheric pressure.—

In another type of experiment the entire tumorousmouse was compressed by increased atmosphericpressure in a pressure chamber. Three such chambers were used in these experiments. A low pressurechamber was made of brass pipe 4 in. in diameter.One end was closed by a screw cap, fitted with a

flanged and beveled lucite window, bedded insealing compound. An insulated wire leading to aninternal electric light was introduced through thecap. The other end of the pipe was closed by ablank cast-iron flange held on by bolts and sealedby a rubber gasket. The mice were inserted at the

TABLE 1TAILIMPLANTATIONS—SARCOMAiso

Exp.No.1•i3466TotalsNumber

oftumorsim

planted(numberof

mice)911)109101(1,->sNumberoftakes9798101053/58

(91 percent)Numberbecominghemor-rhagic855S5935/53

((i«percent)Numberof

tumorregres

sions76¡165538/53

(72 percent)Deathfrom

allcauses3¿12S521/58

(36 percent)

flange end. This chamber was used for pressures upto 110 pounds per square inch. .All pressures givenin this paper are gauge pressures; total pressuresare 1.5 pounds higher.

Figures 4 and 5 show an improved chamber usedfor higher pressures. This was made of a seamless

Growth of Sarcoma 180 inMiceIn12345678910Axillary

RegionT•tt••t•t£•14

2ldays•

>*t

0<90•Ó0

t9&

ÉÉ^•r^ííf\•tIn

Tail7

14 2l 28 35 42 49 96 6370i

i 1 0 0 0 0 e •¿�8—¿�2«

•¿� § •¿� •¿� •¿� o —¿� —¿�—¿�3

. t t •¿� t .___—¿�4

•¿� •¿� t f * •¿� —¿� —¿� —¿�—¿�5

. •¿� f «,—____6

•¿� f 0 ©t7«

•¿� f.—_____8

—¿� •¿� 0_______9

—¿� •¿� •¿� « —¿� —¿� —¿� —¿� —¿�—¿�10

—¿� —¿� —¿� —¿� —¿� —¿�____TA

FlG. 1.—Area diagrams showing the effects of tail-pressure on the growth of Sarcoma ISO

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274 Cancer Research

high-pressure steel pipe, 6 in. in diameter and 14in. long. The caps and flanges were triple welded.This chamber was used for pressures up to 360pounds per square inch. (A similar, smaller chamber, without a light or window, was used for highpressure work, before the one illustrated in Figs.4 and 5 was available.) The flange of the high pressure chamber in Figure 4 was made of lj-in. steel,and its weight made it necessary to mount it on

The pressure was controlled and maintained bythe commercial reducing valve apparatus illustrated in Figure 5. Other features are illustrated inthe photograph.

Effect of pressure on transplantability of Sarcoma 180.—In six experiments Sarcoma 180 was

compressed just before transplantation to determine the effect of compression on transplantabil-ity. All mice used were of the Ilockland Farms al-

FIG. 2.—Sarcoma 180—16days after implantation in thetail. The tumor shows marked hemorrhage.

hinges. A Incite window was fitted. The insulatedwire leading to the electric light was led in betweentwo layers of a rubber gasket. The chamber endof the outlet tube was screened with wire, afterseveral occasions when an inquisitive mouse wasimpacted into it. The inlet tube required no screening and was a simple length of small-diameter copper tubing similar to that used in compressed-gasmanifold tubing, welded in. The outlet tube led toa Y fitting with a gauge on one arm and an adjustable needle-valve for the exhaust on the other.

FIG. 3.—Samemouse 41 days later. There is complete absorption of the tumor and absence of ulcer. The animnl is ofnorinal appearance.

bino strain. In each case, two mice were selected inwhich the tumors were growing well in the usualaxillary site 7 days after implantation. Both micewere killed simultaneously. One was subjected tocompression for a varying period of time, and thena small piece (weighing about 6 mg.) of each tumorwas implanted, by the usual trocar technic, intoten mice. Where hemorrhage was noted in thepost-compression tumors, a nonhemorrhagic areawas used for transplantation. The control mousewas left outside, on the top of the chamber. When

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ARKINANDSUGIURA—IncreasedPressure on Sarcoma 180 375

the high compression chamber was used, the control mouse was left in the low pressure chamberwith the flange open. Both mice were killed at thesame time, and both tumors were transplanted atthe same time. One or more out of each ten micetransplanted with compressed tumor failed toshow tumor growth; all the controls grew (Table2). Both the compressed tumors and the controlswere somewhat smaller than normal, as measuredat 1 week, particularly if the mouse had been deadfor 6 hours, or more, before transplantation.1

Effect of increased atmospheric pressure ongrowth of Sarcoma 180.—The effect of increased atmospheric pressure on the growth of Sarcoma 180,implanted into the usual axillary site, is summarized in Table 3. Pressures of 30 pounds per squareinch were obtained from the building's pi(>cd com

pressed air supply. All other pressures were obtained by using air, or other gases, as supplied inthe usual 220-cubic-foot compressed gas tanks. Allgas mixtures used in this experiment were suppliedready-mixed in the tanks by the manufacturer.The rale of flow was adjusted to exceed 4 cc. of air/gram of mouse/minute, or the equivalent in oxygen.

The mice in Experiment 2 were left in the chamber uninterruptedly for 7 days, with food and water supplied ad libitum. In all other experiments,except the controls, the mice were slowly decompressed every 2 days. The time of decompressionfrom 30 pounds was 1 hour. Two hours were usedto decompress the mice from gauge pressures of1-tO or 185 pounds; 2| hours from 318 pounds. Asdecompression proceeded below .50or 70 pounds Ihe

turn were placed in the chamber, and the micewere immediately recompressed, the process taking 5 or 10 minutes. As the pressure increased, themice would scratch at their ears but seemed other-

FIGS.4 and 5.—Photographs of compression chamber

Tumortake«

Tumi ir

TABLE 2THE EKKECTOKINCREASEDATMOSPHERICPRESSUREONTRAXSPLANTABILITYOFSARCOMA180

Tumort;,kc«

Tumortransplants

(Controls)

10/1010/1010/1010/1010/1010/10

100 per cent

Exp.no.123456UauKe(pressure-pounds)80105110195-110210285Time(hours)544*l6}«iDecompression(minutes)50654")301511)GasAirAirAirAirAirii.'i

per centair66per cent nitrogenTotals:trans

plants8/105/109/10S

10<••III9/1075

per cent

gas used was changed to compressed air. The chamber was then cleaned, a supply of Purina laboratory chow (2 gm./mouse/day) and water ad libi-

1The duration of viability of the tumor in the dead host waspreviously established for mouse sarcoma 180 (10). The trans-plantability of mouse sarcoma 180 was not changed when thetumor remained in the host for 9 hours at 22°('. after the hosthad been killed by a blow or by ether anesthesia.

wise unaffected. At high pressures (beginning at300 pounds, most marked at 360 pounds), the micewould exhibit ataxia and a staggering gait andwould rub at their noses.

The 2 gin. of food/mouse/day were completelyeaten. In earlier experiments it was found that,when more food was given, it was not always fin-

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276 Cancer Research

¡shed.Loss of weight was a constant finding in allthe mice in Table 3, averaging 20-25 per cent.

Even if food was supplied ad libitum, weight lossunder pressure occurred in all experiments, described in this paper, which lasted more than 1-2

hours.

pheric pressures of 140 pounds/sq. inch and overinhibit the growth of Sarcoma 180. The growth ofthese tumors is shown graphically in Figure 6. Alltumors resumed growth at the normal rate whenreturned to normal pressure, with the possible exception of those exposed to 318 pounds (Fig. 6).

TABLE 3

EFFECT OF IXCREASKDATMOSPHERICPRESSUREON GROWTHOFSARCOMA180

Exp.nu.

23

SA

4

5

Number oftumors

fi

6

same 5 asin Xo. 3

Gauge(pounds)

0

so140

so

185

Õ60-18

Gai

66 per cent oxygen83 per cent nitrogenAir83 per cent air(>6per cent nitrogenAir

Ì5per cent air75 per cent nitrogen15 per cent air85 per cent nitrogen

All the experiments summarized in Table 3were done under the same partial pressure of oxygen but differ in total pressure. The first experiment confirms the findings of Campbell and Cramer that increase in the partial pressure of oxygen,by itself, has little effect on tumor growth.

Effect of Increased Pressure

on Growth of Sarcoma 160 in Mice

controls

1•¿�•¿�••¿�•¿�<•¿�

0 Ibs.14

•¿�ft o

f

140 Ibs.14

f

185 Ibi.14

•¿�è•¿�t318 IDS.

7 14 days

FIG. 6.—Adefinite retardation of growth of mouse Sarcoma180 in mice subjected to atmospheric pressures of 140 poundsand over is shown. Shaded areas indicate hemorrhage or scabformation. 0 pounds: 66 per cent oxygen plus 33 per centnitrogen; 140 pounds: 33 per cent air plus 66 per cent nitrogen;185 pounds: 25 per cent air plus 75 per cent nitrogen; 318pounds: 15 per cent air plus 85 percent nitrogen.

No inhibition of growth was found after 1 weekat 30 pounds gauge pressure of compressed air. Inthis experiment compression was started the dayafter transplantation of the tumor. In all other experiments in Table 3 the compression was begunthe day of transplantation.

Experiments 3, 4, and 5 indicated that atmos-

Partialpressureofoxygen

(Ib.)10

91091010Time

underpressure

(days)7

77777

Food(gm/mouse/day)

ad libitumi

Effect at end of1 week

Xo inhibitionXo inhibitionModerate inhibition

Resumed growth atnormal rate

Slight inhibition

Market! inhibition

After 1 week at 140 pounds per square inch, themice in Experiment 3 were placed in compressedair at 30 pounds /sq. inch for 1 week, as indicatedin Experiment 3A, and these mice, too, resumedapparently normal growth under 30 pounds pressure.

The mice in Experiment 5 were compressed to300 pounds for the first 24 hours, then to 318pounds for the remaining 0 days. At these pressures, 1 week of exposure proved quite toxic.One of the mice died after 5 days, and two moredied at the end of the treatment. No hemorrhagewas visible in any of the tumors in Table 3 at thecompletion of treatment, with the single exceptionindicated under 318 pounds in Figure 0, whichshowed partial hemorrhage. None of these tumorsregressed.

Effect of increased atmospheric pressure on hemorrhage in Sarcoma 180.—In the earlier portion ofthis part of the work, dilution of air with nitrogenwas obtained by connecting one tank of compressed air with one or more of nitrogen, by meansof manifold tubing, with the resulting mixture fedto the compression chamber. This procedure wasdiscontinued, subsequently, the tanks being ready-mixed by the manufacturer. Experiments 1 and 2in Table 4 summarize all the experiments donewith manifold mixed gases at pressures and durations within the indicated limits. Experiment 1represents the aggregate of ten separate experiments. All others in this table represent experiments done with gases ready-mixed in the tank bythe manufacturer. In all experiments in Table 4,except the anoxic ones, the rate of flow of the gas

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ARKIN AND SUGIURA—Increased Présure on Harcoma 180 'ill

was adjusted to exceed 4 cc. of air/gram of mouse/minute, or its equivalent in oxygen. This optimumflow was not always maintained (particularly inExp. 1) due to gradual clogging of the outlet valve.All mice were implanted with a single tumor in theright axillary region.

The great majority of the mice in Experiment 1died of oxygen poisoning. When the windowlesschamber, which was being used at that time, wasopened, they were found dead, with distended abdomens, rigidly outstretched hind legs, and coagulated froth exuded from the nostrils. The lungs

showed marked congestion, and, as indicated inthe table, most' tumors showed marked hemor

rhage. Marked hemorrhage (HHH) was considereda hemorrhage which converted all or most of thetumor into a grossly hemorrhagic mass (Fig. 7).It was usually visible through the skin, if the tumor were of sufficient size, and frequently theblood seemed under tension and would spurt outas the tumor was divided by the knife. Mildhemorrhage (HH) was considered a hemorrhagewhich involved less than 5 the tumor. The symbol(H) in Table 4 represents a hemorrhage around the

TABLE 4

HKMORRHAGKIN SARCOMA180

Exp.no.1234S678¡iId11UISUl.iHi17181!)¿IINumberoftumors6085S5656SS61055555S55Age

oftu

mors(days)2-89t44,">785S7755747777Ga ufíepressure(Ib.)285-3608006SKI310:i(ì<>315318606060315345320315181830-4540315GHSmixture(ratio

ofair/nitrogen)33/0620/80heliumair80/20oxygen15/8515/8515/8515/8515/85oxygenoxygenoxygen50/5050/5050/5050/50oxygenoxygenoxygenoxygen15/85&Partialpressureoxygendb.)15-2312«1101010.8101075767533363333333345-6055below

10Time

atpressure(hours)11-181615Îèè256.5ilî112|lisi3Ì3èSi53JSìTime

ofdecompres

sion(minutes)90-1107002140121513200045105100100013Hemorrhage*HHHHHH0HHH00000HHHHHHHHHHHH00HHHHHHHHH

21 77 40

22 47 300

23 57 200

24 5 7 O

•¿�i.-, 6

nitrogen" below 1.7 ,'i

0

50 50a nil

15 85Ion

10

10

10

0

HHH

HH

HH

0

0

* II: hemorrhage around tumor.HH: mild hemorrhage.HHH: marked hemorrhage.

RemarksAggregate of ten experiments. H-HHII

in all. Mostly HHH; most dead atend of experiment.

All dead at end. | HHH.

! dead at end. No hemorrhage in any.Killed by decompression. All had hem

orrhage around tumor.Killed with ether. Four had hemorrhage

around tumor.Killed by decompression. Four had

hemorrhage around tumor.Two killed by decompression; three

killed with ether. No hemorrhage.Three killed by decompression; three

killed with ether. No hemorrhage.Died under pressure. No hemorrhage.Died under pressure. No hemorrhage.Died under pressure. No hemorrhage.Died under pressure. All marked hem

orrhage.Two died under pressure; two mice

HHH, 3 mice H.Two died under pressure; two mice

HHH, one H.One died under pressure. Four killed by

decompression, two mice HHH,one H.

Killed with ether. No hemorrhage.Killed with ether. No hemorrhage.Four died under pressure; one died

shortly. All HHH.All died under pressure. All HHH.Anoxic death under pressure. All HHH.

Two anoxic death under pressure after3 hours. HHH.

Five died after 1 hour and left in chamber 2 hours more—nohemorrhage.

Anoxic death under pressure. Mildhemorrhage.

Anoxic death under pressure. Mildhemorrhage.

Four anoxic death without pressure. Nohemorrhage.

Anoxic death without pressure. Nohemorrhage.

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278 Cancer Research

tumor, in the tumor bed, and not in the tumor itself. Apparently, the hemorrhage produced inthese experiments always began at the peripheryof the tumor. Central hemorrhage, if noted, wasconsidered spontaneous in all cases. In some experiments, some of the mice showed markedhemorrhage, and some showed little, or merely ahemorrhage in the tumor bed. These differences

fusely mixed. At the edge of the Sarcoma 180, nearthe subcutaneous tissue, there were small areas oftumor necrosis but most of each tumor was viableand actively growing.

Nearly all the mice summarized in Experiment 1were killed by their exposure, apparently fromoxygen poisoning. Exposure to the same conditions, including the same partial pressure of oxy-

FIG. 7.—Photograph of the marked hemorrhage in Sarcoma180 in a treated mouse (300 pounds pressure, 50 per centair and 50 per cent nitrogen, 5f hours exposure) is contrasted

were sometimes thought due to differences in timeof death (as in Exp. 21) but more often werethought to be due to individual variations (compare Exps. 12 and 15).

Histological examinations of a number of tumors in animals subjected to high pressures (Figs.8 and 9) showed an abnormal vascularity, withdilated capillaries filled with blood. There wereareas where the capillary walls had broken downand blood had entered the tumor tissue. Erythro-cytes and sarcoma cells were here freely and dif-

with the absence of hemorrhage in the tumor of a controlmouse (right side). Arrows point to the tumors.

gen, but with lower total pressures, caused neitherdeath nor tumor hemorrhage (Exp. 3). When helium was substituted for nitrogen as a diluent, nodifference was noted (Exp. 2). Apparently an increase in total pressure increases the toxicity ofoxygen or is itself toxic.

Experiments 4-25 were carried out under observation in the windowed chamber illustrated inFigure 3. In Experiments 4-8 the tumorous micewere exposed to pressures of 300-360 pounds/sq.inch for 5-65 hours. These conditions were not

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ARKIN ANDSUGIURA—Increased Pressure on Sarcoma 180 279

lethal for the mice, some of which were killed byrapid decompression and some slowly decompressed and killed with ether. The time of decompression seemed to make no difference in the degree of hemorrhage, which appeared in about halfof the experiments, and was restricted to thetumor-bed.

Experiments 9-11 summarize experimental con-ditions similar to those used by de Almeida (1)and Campbell (4). After some time, at 60 poundsgauge-pressure of oxygen, these mice would be-

In Experiments 18 and 19 the animals werekilled by oxygen poisoning in an atmosphere ofpure oxygen. The pressure here was considerablylower than that used in Experiments 9-11; hence,

the mice died more slowly. Marked tumor hemorrhage appeared in these mice.

The remaining experiments in Table 4 indicatethat the production of tumor hemorrhage does notrequire oxygen poisoning but may accompany exposure to pressure under anoxic conditions. Thereis, again, some individual variation in response,

Si, r^C':; >;;;•^^^ ;-i.;...-.•. -:.^. V; V :•.;•:,-'••-•.•'-.'•r...,'*'.«'.'f.';-:-. : 'V'"." V

a¿í.•vs's.'jtV:< ' ' -':' '•':'. •¿�'.'' •¿�V.\ ' '-M¿'<'*y-'; "•'•'•'.

FIG. 8.—Histológica!appi-armi«1of treated Sarcoma 18(1illustrated in Fig. 7. Sarcoma 18(1shows an abnormal vascular-ization with dilated capillaries filled with blood. There are

areas where the capillary wall has broken down ami bloodhas entered the tumor. Hernatoxylin and eosin stain. X150.

come extremely hyperactive, even frenzied, andwould die in convulsions before 2 hours hadelapsed. None of the tumors showed hemorrhage.These results are not comparable, since differenttumors were used, but seem to resemble Campbell's, in the absence of tumor hemorrhage.

Experiments 12-15 again demonstrate the oc

currence of marked tumor hemorrhage when deathby oxygen poisoning takes place under high pressures. The mice in Experiments 10 and 13 were implanted with fragments of the same parent tumor,and this is also true in Experiments 14 and 16. Examination of these experiments indicates thattumor hemorrhage is related to the total pressurerather than the partial pressure of oxygen.

due to factors which are not well understood, in tin-degree of hemorrhage produced under these conditions. (These individual differences also appearedin the tail implantations outlined in Table 1. Theymay be related to factors of immunity and resistance.)

The mice in Experiment 20 were brought to theindicated pressure using nitrogen with a 15 percent admixt ure of air. After 2 hours the oxygen content of the chamber gas was reduced by gradual replacement with pure nitrogen, and this was continued until the animals died some .'5hours later. In

the other anoxic experiments, the proportions ofpure nitrogen, and of nitrogen with 15 per cent admixture of air, were adjusted to the point where

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Fia. 9.—Higher-powerview of Fig. 8 to show hemorrhage FIG. 10.—Higher-powerview of Fig. 8 to show necrosis ininto the tumor. X240. the tumor. X240.

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ARKIN ANDSUGIURA—Increased Pressure on Sarcoma 180 281

respiratory distress was evidence by slow, deep,gasping respirations, dizziness, and incoordination. The mice were maintained in this state byvarying the proportions of the gases, and wereasphyxiated, at the end of the interval indicated inthe table, by introducing pure nitrogen. The mixtures were alternated by using a tank of each gas,both connected to the reducing valve by manifoldtubing, and the valves of the tanks were opened alternately to furnish the desired gas. Control experiments at atmospheric pressure were done withan equal mixture of nitrogen and air. The controlmice were asphyxiated by the 15 per cent air-nitrogen mixture (lethal at this pressure), at theend of the indicated time.

In these anoxic experiments the rate of air-flowfell below the level of 4 cc/gram of mouse/minutesof air, or the equivalent in oxygen. Hence, the expired COj was not washed out of the chamber tothe same extent as in the previous experiments. Itis not known whether the increased CO? concentration played any part in the production ofhemorrhage. However, in Experiment 23 hemorrhage appeared, despite the inclusion of "Bara-lime" in the chamber to absorb carbon dioxide.

In brief, the experiments detailed in Table 4seem to indicate that tumor hemorrhage occurswhen the experimental animal is killed, or almostkilled, under the indicated conditions of pressure,either by oxygen poisoning or by anoxia, over a period of time exceeding approximately 3 hours. Ifone assumes that hemorrhage is an indication ofsome damage to the tumor (note the frequency ofregression associated with hemorrhage both clinically and in Table 4), then conditions of increasedpressure make the tumor more susceptible to damage by the two agents tested. However, with bothanoxia and oxygen poisoning, the margin of safetyunder the conditions outlined was narrow, so thattumor hemorrhage was best obtained only whenthe organism itself was brought to the point ofdeath (and, in some cases, not even then).

In all the experiments, the effect of pressureseems to have been concentrated on the tumor orthe region immediately around the tumor. Theother tissues and organs remained grossly and his-tologically unaffected by pressure of 300 pounds,except for loss of body weight, which was a constant finding. Congestion and hemorrhage of thelungs was noted whenever the oxygen concentration was high and was not related to the total pressure.

A small number of spontaneous mammary tumors in mice were exposed to pressures of 105pounds/sq. inch, ,50 per cent air and .50 per centnitrogen, for 18 hours in vivo. Hemorrhage ap

peared during compression and was visible throughthe skin, upon removal from the chamber. All survived compression.

DISCUSSION

The experiments described in this paper confirm the clinical observation that pressure inhibitstumor growth. It is emphasized that this inhibitionis due to the pressure itself and not to any variations in the concentrations of component gases.The following theory of pressure's mode of action

is proposed as a working hypothesis, with the stipulation that many other factors, not discussedhere, play major roles in growth and metabolism.

iiThe effects of pressure on chemical reactions aredescribed by Le Châtelier'sLaw, which states that

the equilibrium of a system, when disturbed by astress, is displaced in such a way as to tend to relieve the stress. Thus, pressure would affect anyreaction in the growth process which is accompanied by volumetric change, inhibiting those whichlead to an increase in volume. (The hydrolysis ofcertain proteins, for example, [6, 9] is accompaniedby a decrease in volume.)

It is suggested that intracellular or intranuclearpressures (hence, the surface tension in their walls)may, through this mechanism, play a part in physiological as well as pathological metabolic processesof the cell contents.

SUMMARY

Sarcoma 180 was subjected to increased localcompression, by implantation into the tail of miceof the Uockland Farms albino strain, with resulting retardation of tumor growth, increase in thefrequency of tumor hemorrhage, and increase inthe regression rate.

Compression decreased the transplantability ofthis tumor, under the conditions outlined.

Compression of the tumor-bearing mice, in vivo,resulted in retardation of tumor growth and increased susceptibility to tumor hemorrhage.

These effects seem to have been due to compression itself and not to any variation in the concentration of oxygen.

ACKNOWLEDGMENTS

It is a pleasure to acknowledge our indebtedness to Doctor C. P. Rhoads for his interest andencouragement.

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282 Cancer Research

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1950;10:272-282. Cancer Res   Alvin M. Arkin and Kanematsu Sugiura  Effects of Increased Pressure upon Sarcoma 180

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