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Send reprint requests to: G. J. Grega, Ph.D.,1)epartment of Physiology, Michigan State Univen-�it:�-. East Lansing. Mich.
452
THE JOURNAL OF PHARMACOLOGY AND EXPF,RIMENTAL THERAPEtTICS
Copyright � 1975 by Tue Williams & \Viikins Co.
Vol. 193. No. 2Pr,,,ted in U.S.A.
PRESSURE-DEPENDENT FACTORS IN EDEMA
FORMATION IN CANINE FORELIMBS1
ROBERT L. KLINE.2 DANIEL P. SAK, FRANCIS ,J.
HADI)Y AND GEORGE J. GREGA
Depaitntent of Physiology, Michigan State University,
East Lansing, Michigan
Atcepteti for publication December 26, 1974
ABSTRACT
KLINE, ROBERT L.. 1)ANIEI� P. SAK, FRANCIS J. HADDY AND GEORGE 1. GREGA:
Pressure-depentient factors in edema formation in canine forelimbs. J. Pharmacol.
Exp. Tiler. 193: 452-459, 1975.
‘\c(’tvlcholine (10 jtg/unin) infused intra-arterially for 30 minutes into naturally perfused
fortiimbs increased forelimb weight 23 g, largely due to edema formation. The weight
g tin w�:is associated �vith marketllv elevated skin and skeletal muscle blood flows and
small vein pne�sures, suggesting tilat tile edema was attributable, in part., to a rise in
microvascuular pressures. Mechanically increasing venous pressure and blood flow to
similar levels for 30 minutes in l)ulmp-perfused forelimbs produced a weight gain of
27 g. Tile rate of weight gain for the acetvlcholine and mechanical alterations was nearly
itielltical. Acetvlcllolille and mechanical alterations both increaseti forelimb lymph flow
rate i)ut failed to increase lymph total protein concentration significantly. These studies
illdi(ate that ill the (log forelimb elevated microvascular pressures result in edema forma-
t’oui iW increasing the transcapiliary ilydrostatic l)re�ure gradient without producing an
inli)ortant� (iecrease in tile transcapillary colloid osmotic l)nessure gradient. Increased
l)nessture is not associateti with a large increase in microvascuiar permeability to plasma
proteins as is seen with the administration of high doses of histamine and bradykinin.
lle�tuitlv � have described pressure-depend-
eitt aul(i l)r(’��urt-ii1depeuldent mechanisms in-
vol�eii iii e(iennt formation in canine foreiimbs
l)U lO(allv atlininitered histamine (Grega et at.,
1972; Iladtiv et a!., 1972) and bradykinin
(Kline et (ii., 1973) . Pressure-independent fac-
tors. j.(� ., a direct effect on mierovascular per-
Received for publication October 15, 1974.1 This study was supported by a grant from the
National Heart and Lung Institute.2 Current address : Department of Physiology,
Health Sciences Centre, University of WesternOntario. London, Ontario, Canada N6A 3K7.
me�li)ility to l)laslna proteins, were found to be
important for edema formation during infusions
of iligh doses of these two vasoactive agents.
Forelimb weight. as well as lymph flow and
protein concentration increased dramatically(luring infusion of these agents, even under
constant flow conditions where microvascular
pressures were probably not elevated.It is difficult to assess the role of pressure-
dependent mechanisms in edema formation
when using agents which directly alter micro-
vascular permeability an(! thus influence trans-
vascular fluid ullovement. Forelimb microvascular
l)ressllres were undoubtedly also increased by1)0th agents (Gregs et a!., 1972; Kline et a!.,
1973 ) . Elevated microvascular pressures alone
1975 PRESSURE-DEPENDENT FACTORS IN EDEMA 453
will result in fluid filtration according to the
Starling-Landis hypothesis. What is not entirely
clear is whether or not, and if so, to what
extent elevated microvascular pressures affect
permeability to plasma proteins (Garlick and
Renkin. 1970 : Grotte, 1956 ; Haddy et ci.,
1972) . A decreased transmural coiloid osmotic
pressure gradient could also contribute to the
extent of fluid loss caused by increased micro-
vascular pressures.
This paper is an attempt to look more
closely at transvaseular fluid fluxes resulting
purely from pressure-dependent factors, under
simiiar hemodynamic conditions seen during
infusion of histamine and bradykinin. Hemo-
dynamic alterations in the forelimb were pro-
duced by mechanically elevating blood flow and
vein pressures or by local infusions of acetyl-
choline. Transvascular fluid fluxes were esti-
mated by continually monitoring forelimb
weight. Changes in microvascuiar permeability
to plasma proteins were evaluated by measuring
iympil flow anti protein concentration.
Methods
Mongrel dogs of either sex, having an average
weight of 20 kg (range 17-24 kg) were used in
this study. All animals were anesthetized with
sodium pentobarbital (30 mg/kg) and ventilatedwith room air using a Harvard respiratory pump.
Hemodynamic measurements. The collateral-
free, innervated forelimb preparation was used to
investigate the hemodynamic aspects of prolongedinfusions of acetylcholine. A detailed description ofthe preparation has been published previously
(Grega at al., 1972). Briefly, the forelimb skin andmuscle above the elbow was sectioned by electro-
cautery, and the humerus was cut, leaving a neur-ally intact, vascularly isolated forelimb. Blood en-
tered the limb only through the brachial artery and
exited only through the brachial and cephalic veins.After heparin treatment (10 mg/kg), forelimb
pressures were measured from small arteries andsmall and large veins in both skin and skeletal
muscle. Small artery catheters were inserted in a
downstream direction, whereas small vein catheterswere inserted in an upstream direction. Pressures
were measured with low-volume displacement
Statharn transducers and recorded on a Sanborndirect-writing oscillograph.
The brachial and cephalic veins were cannulated
with a short section of large-bore polyethylene
tubing, and the outflow was directed into a reser-voir, which continuously returned blood to the
animal via the jugular vein. Blood flow through
skin and skeletal muscle was estimated by timed
collections of the cephalic and brachial venous out-flows, respectively. Forelimb weight was continually
monitored by placing the limb on a calibrated
I-beam balance. The addition of a 2-g weight
usually caused a pen deflection of 10 to 20 mm of
paper. Mean arterial pressure was measured from a
catheter in the lower abdominal aorta. Acetyicho-
line chloride was infused for 30 minutes into the
brachial artery, via a side branch, at an infusion
rate of 10 i�g of base per mm. The volume of theinfusate was 02 mi/mm. Pressures and flows were
determined twice during the control period, 2, 5,
10, 15 and 30 minutes after the infusion was mi-tiated and again 15 minutes after the infusion was
terminated. Total and segmental (large artery,
small vessel, large vein) vascular resistances in skin
and skeletal muscle were calculated as describedpreviously (Grega et a!., 1972).
In a second series of animals, the hemodynamic
aspects of prolonged increases in blood flow andvein pressures were investigated by mechanically
increasing these parameters in pump-perfused fore-
limbs. Arterial blood obtained from a femoral
artery was pumped into the brachiai artery with a
Sigmamotor pump. Initially the flow was adjustedso that the brachial artery perfusion pressure wassimilar to systemic pressure. After a control period,
blood flow and vein pressures were elevated simul-
taneously to simulate the conditions seen duringinfusion of acetyicholine, bradykinin (Kline et al.,
1973) or histamine (Grega et al., 1972) . Blood flowwas increased by speeding up the pump, while vein
pressures were adjusted to the desired level by
tightening screw clamps fastened to the venousoutflow catheters. Pressures, flows and limb weightwere monitored as above for 30 minutes underthese conditions, and 15 minutes after the neduc-
tion of flow and vein pressures to the control
levels.
Lymph studies. Samples of forelimb lymph were
obtained using a technique described previously
(Haddy et al., 1972) . Briefly, in essentially intact
foreimbs, the lymph vessels in the area of the
cephalic vein above the elbow were isolated andtwo or three of these were tied centrally. Another
lymph vessel was cannulated distally with a 10-cm
length of PE-lO tubing which had been beveled atthe cannulating end. Lymph was collected for 10-minute periods using miniature 0.5-mi graduated
cylinders. Forelimb small skin vein pres’nire and
aortic pressure were measured as in the hemody-
namic studies at the end of each 19-minute period.
After two control periods, acetyicholine chloride-was infused intra-artenially via a side branch of
the brachial artery for 30 minutes at a rate of 1(�
Infusion Period
�) Miii 10 Mm 15 lilin :5) ?iliri
(out rol , �
� -:;�u��� ,� I
.� �veig1it (g) t) . 0 �
0 �lin 2 �\Iii�
0 . () 7 . 4a
PA (111111 fIg) 1 it) 110 104
P5MA (mm Hg) M4 84 � 49’
‘�SSA (null Hg) � S2 � S2 � 52’
Pt4%IV (mm Hg) � 12.6 � 12.3 � 2$.9’P55v (mm Hg) 15 . I � 14 . 6 � 24 . 4a
P.�iv (mm Hg 7.5 � 7.3 � i6.5�
Pt.sv (nInA Hg) 4.M 5.1 10.3”
F1, (Ini/nAin/10() g) 9. 7 � 9.�.) 25.5”
F( (mi/nlin/iOOg) 12.6 � i3.() 25.0”
Postinfusion15 Mm
10.5’
10555”54”26 . 4”27 . 1”16 . 6’12 . 9”
28. 7’29.6”
14. 1”109
63”
62a27.2”26.6”16.0”13.1”27.7”
28.7”
17.5”101)
66’6i”24.0”25 . (1”
15.5”
12 . 5”
26.2”25.0”
23.2”105
71”
65’20. 1”
22.6”12.6”11.1”
21 . 9”
24 . 0”
16.7”101)
Si
549.1)
13.3
6.6
5.15.0
11.5
454 KLINE ET AL. Vol. 193
S i� < .05 compared to zero time.
�Lg of base per mm. Tile volume of the infusate
%%.#{149}�$ 02 mi/mm. Lymph was collected and pressures
were measured during a final 10-niinute. postinfu-
sit)n period. In PLIII1P perfusion stu(lies, lymph was(t)ilects(I and l)1�sst1��5 were mtasured before. dun-
ing an(I after tue mechanical elevation of blood flowand vein l)re�1r( to levels similar to those produced
in the hemodvnamic study. Vein pressure was dc-
vattti i)\ partially occluding venous outflow by
tightening a wire around the forelimb above the
elbow (excluding tile brachial artery).
Total protein concentration in 1mph was meas-
tired i)v a spectrophotometnic (Beckman DBspectrophotometer) method of Waddeli (1956) . All
data from the ilemodynamic anti lymph studies
%%�(��( analyzed using tile Student’s I test modified
for i)aired replicates. Comparisons between groups
�vtre i)erfonined using tile t test for nonpained data.
Results
I-Ie?nod!,n(1m 1C lIe(lSU1e in e iuts
Forelimb weight (tables 1 antI 2 ; fig. 1).
.\(tvicholine ( lOp.g/min for 30 minutes) in-
fa�d mt na-arterially into naturally perfuseci
forelimbs significant iv increased forelimb weigilt.
Aft(r all initial raputi weigilt gain (0-2 minutes)
forelimb weight contiulued to increase at a
ule:Inlv steaciv rate througilout the infusion
penio(l. Immediately after the infusion was
stopped. forelimb weight decreased rapidly by
all amount similar to that gained (luring the
first 2 minutes.
In pump-perfused forelimbs, the forelimb
weight response to prolonged increases in venous
pressure and blood flow was similar to thatseen in the acetyleholine experiments at ilatural
flow, i e., an initial rapid weight gain followed
by a steady rate of weight gain. Returning vein
pressures anti flow to the control levels resulted
in a rapid loss of weight similar in magnitude to
that gained from minutes 0 to 2. There was
110 significant difference between the rate of
weight gain nor tile total weight gaineti over
30 minutes for tile acetvlcholine and increased
pressure flow groups.
Forelimb pressures (tables 1 and 2) . Small
artery lresstlres in bOtil skin and skeletal
muscle were significantly decreased by acetyl-
choline. As iii a �)reviolls study with bradykinin
(Kline et ci!., 1973), these pressures gradually
returned towarci control during the infusion
period. Systemic arterial lresstine was unchangedtilroughout the infu�ion period. Small and large\.ein ijressures in botil skin and skeletal muscle
were significantly increaseti by acetylcholine.
The vein pressures remained greatly increased
throughout tile infusion period and returned to
TABLE 1
I?fJecl of aee!ylcholint ( JO /.uJ/?flifl) infused intra-arterially into collateral-free, innervated, naturally perfuse4
foreli;nbs
Pt = 7: ii�ean control forelimb weight = 506 ± 25 g. Abbreviations used are: PA, mean aortic pressure;
‘�SMA, nluscie small artery pressure; PSSA, skiui small artery pressure; PSMV, muscle small vein pressure;� skiti small vein i)Iesslule; PLMV, muscle large vein pressure; PLSV, skin large vein pressure; FB, bnachiai
venous OUtfloW (muscle) ; F�, cephalic venous outflow (skin).
TABLE 2
Effect of prolonged increase in pressure and flow in pump-perfused, collateral-free, in ncrvated forelinib.s”
U = 7 ; mean (‘OlitEol forelimb weight = 520 ± 25 g. Abbreviations used are: PHA, hracilial artery perfusioti
jresstiie : all other ai)breviations 8$ listed in table 1.
I Pressure, I Flow
(I Mmii 2 Mm � Mm
( oi,trol- 3
O.()
101
Si)
SI)
10.6
1 1 .1)6.36.1)
I I . (1
I 7.6
-� weight (g)
PHA (nun Hg)PSMA (mm Hg)
‘�5SA (mm Hg)P5MI (fIlm Hg)P551. (mm Hg)PI.MV (mm Hg)P.5v (mm Hg)FR (mi/min/10() g)F� (11ul/uliin/iO() g)
0.0
I 0251
8010.211.6
6.3
6.611.6is. i
7 . 6�
l5S�134b
135b
25.lb25 . 5”
18.3”19.2”22.8”23.1”
10 Mm
I 3.9”157”128”
123’24.9”24.9”
17.8”
18.6”22.2”23.8”
10.2”
159”125”125”
24.1)”25.3”
17.8”
18.9”
22.4”24.1”
u; Mm
I 7 .
160”
I 27”126”
25. 4”24.5”17.9”
15.9622.5”23 . 7b
I’ostcontrol
30 i\lin � 4?; �%Iiz,
27.0” � 20.2”177b � 131”
142” � 103”141” 94
24.96 � 9.524.0” 10.317.96 � 5.518.2” � 5.6
22.2’ � 11.0
23.5” � 15.1
“ \ein iiesstures and 1)100(1 floiv were increased simultaneously by partially constnictitig venous outflowand increa.sitig 1)11�i) speed.
b p < .05 compared to zero time.
5-10 10-15
TIME PERIOD IN MINUTES
1975 PRESSURE-DEPENDENT FACTORS IN EDEMA 455
tile control level following termination of the
infusion.
Mecilanicaliv increasing venous pressures and
flow in l)IIml)-perfuse(i forelimbs produced
rai)i(i :111(1 significant increases in brachial artery
l)erfusioll l)resstlre aiid small artery pressures in
C
E0’
tn
FI;. 1. Rate of forelimb weight gain during edemaformation induced by mechanically increasing pres-sure and flow (1 P, I F), acetylcholine (Ach), his-tamine (Hist) , on bradykinin (Brady). Drugs wereadmirnstered intra-arteniailv at natural flow in thefollowing doses: Ach, 10 �&g/min ; Hist, 60 �zg/min;Brady, 10 �tg/min. Hist data calculated from Gregaet a!. (1972) ; Brady data calculated from Klineet a!. (1973). Numbers in parentheses are the num-her of animals pen group. � P < .05 when comparedto either �‘ P, I F or Ach.
both skin and skeletal muscle. The increased
pressures persisted throughout the experimental
period, and brachial artery perfusion pressure
and small artery pressure in muscle remained
elevated for 15 minutes after return of flow and
vein pressures to control values. Small and
large vein pressures remained elevated for tile
30-minute period of mechanically increased
blood flow and venous outflow resistance, tile
former pressure approximately at tile level seei�
during acetylcholine infusion.
Forelimb blood flow (tables 1 anci 2).
Acetyiciloline significantly increased blood flow
through both skin and skeletal muscle. The flow
remained elevated throughout the infusion
period, and returned to control levels during
the 15 minutes after tile infusion was termi-
nated.
In pump-perfused forelimbs, elevation of
blood flow resulted in increased flow through
both skeletal muscle and skin at levels slightly
below tilose seen during acetylchoiine infusion.
The increment in flow from control was greater
in skeletal muscle.
Forelimb vascular resistances (tables 3
and 4) . Acetylcholine significantly ciecreaseci
skin and skeletal muscle large artery, small
vessel and total resistances, and skin large vein
TABLE 3
Effect of acetijicholine (10 �iq/nlin)iflfi4N(’(l intra-arterially into collateral-free, innervated, naturally perfusedforel��,b.s
a = 7. Al)I)1eViati(,Iis useti are: H, resistance (mm Hg/nil/mill/lOt) g limb) ; RAS, skin large artery resist-
ali(P; I?5v)s, skin small vessel resistance; R�5, skill large vein resistance; RT5, total skiti resistance; RA�f,
miistie large artery resistance; R(g_v) M, muscle small vessel resistance; RVM, muscle large vein resistance
RTM, total nlllscle reSisI�liice RAT, total forelimb large artery resistance; R(s.v)T, total forelimb smallvessel resistance; HVT, total forelimb large vein resistatice; R�, total forelimb resistance.
(‘uiitrol(�mtrol
- :�
2.6
5.3
I.’
12.0
:� .05.7I). 5
12.21.3
:� .8
0.3
5.6
HAS
lt(S_V)S
H1-5HTS
RAM
11(5_I) M
M
M
RAT �
R(S-V)T
RVT
RT
Infusion Period
I) Miii � 2 Mm 5 Miii 10 Mi,� 15 i�1in 30 Mm
2.6 2.1 2.0 1.9 1.9 1.6”5.0 1.1” 0.9” 1.4#{176} 1.4” 2.3#{176}1.0 0.7” 0.6#{176} 0.5#{176} 0.5#{176} 0.5#{176}
11.6 3.9#{176} 3.5#{176} 3.8#{176} 3.9” 4.5#{176}:L() 2.3#{176} 1.6#{176} 1.6#{176} 1.6#{176} 1.6#{176}
8.5 0.8#{176} 1.1#{176} 1.3#{176} 1.6#{176} 2.4#{176}0.5 0.5 0.3 0.4 0.3 0.3
12.0 3.6#{176} 3.1#{176} 3.3� 3.6#{176} 4.3#{176}1.3 1.1 0.9#{176} 0.8#{176} 0.8#{176} 0.8#{176}3.7 0.4#{176} 0.5#{176} 0.6#{176} 0.7#{176} 1.1”
0.3 0.3 0.2 0.2 0.2 0.25.4 1.8#{176} 1.6#{176} 1.7#{176} 1.8#{176} 2.2#{176}
Postinftision45 Mi,i
2.4S .0
0.5
11.12.7
11.6#{176}0.4
14.8#{176}1.24.6#{176}0.36.2”
a 1� < .05 when comI)ared to zero time.
TABLE 4
Ez’Ject of prolonged increase in pressure and flow in pump-perfused, collateral-free, innervated forelimb.l”
H = 7. Abhreviat H)IiS 11.5 listed iii table 3.
I Pressure. I Flow
2 Miii .5 Miii 10 Miii 15 Miii
HAS
H(5-V)S
‘ITS
RAM
11(5-1’) II
‘Iv si
HTM
HAT
H 51)T
HIT
‘IT
Control- :� �Iiii
4.50.3
6 . 1
1 .1)
750.5
9.9
0.7
2.7
0.23.7
:10 Mm
Postcontrol
4iS I�1un(I Mm
1.3
4.40.3
6.0
I .11
7.50.5
9.9
0.7
2.7
U. 2
:3.7
1.45 . 5’,
0.37 . 5’,
1.45.0”
0.4
6.960.7
2.5
0.2
3.4
1.55 . 2”0.37.961.44 . 8’
0.36.6”0.7
2.3”
0.13 . 3”
1.55.1”0.37.0”1.44 . 8b
0.36. 6b
0.7
2.3”0.13 . 3b
1.65�3b
0.37.1”
1.64.7’0.4
6. 6”0.52 . 3’0. 13.3”
1.76.3”
8.3”
1.65 .
0 . :�7.5”
0.8
2.7
0. 13.8
2. 1”5.7”
I) .35.0”
2 . 5”
10.6”(1.4
13.6”1.1”:3.7”
0.2
5.0”
(1 \rej,i Jre.”.stire aiitl 1)100(1 floss- were iiicrea.seti simultaneously by 1)artialiy constricting venous outflow
anti increasing I)t1lllP speed.
“ l� < .05 wheui (on�1)ateti It) ZdIi) tin�e
456 KLINE ET AL. Vol. 193
TABLE 5
Effect oflocally administered acetylcholine (10 �g/nhin)
at natural flow
Abbreviations used are: PA, mean aortic pressure;P851., small skin veiii pressure; FL, lymph flow;
TP,. lymph total 1)rotein ; ACh, acetyicholine.
a = 6.
a Vein pressure and arterial pressure measured at
the end of each 10-minute period.
b p < .05 compared to controls.
1975 PRESSURE-DEPENDENT FACTORS IN EDEMA 457
resistailce. Total and small vessel resistances
were lowest during tile 2- to 5-mm period,
gra(iuailv increased from 5- to 30 minutes, but
still remained well below the control level at the
en(i of the infusion. Fifteen minutes after stop-
J)ing the infusion, muscle small vessel resistance
was significantly increased, leading to increased
total muscle and limb resistances.
Mechanically raisillg venous pressure and
blood flow resulted in differential resistance
responses in skin and skeletal muscle. Skin
small vessel and total resistances were signifi-
cantiy increased during anti after the 30 minutes
of elevated pressure and flow. Small vessel re-
sistance ill muscle was significantiy decreased
during the 30 minutes, leading to a drop in
total muscle resistance. After the return to
control contiitions. muscle small vessel and total
resistance were significantly increased. Large
vessel resistances were only minimally affected
(luring tile 30-minute experimental period. The
differential responses in skin and muscle resulted
in a sligllt decrease in combined forelimb small
vessel resistance aild total resistance during the
30-minute period.
Lymph Studies (tables 5 and 6)
Lymph flow rate, but not total protein con-
cent rat 1011 , was progressively and significantly
increased by the intra-arterial infusion of ace-
I).%� IL TPL
nil?’ flu �ii;n Jig ml! 10 mm c,/Ioo nit
Control 119 14 0.03 2.4
Control 122 14 0.03 2.5ACh, 10 fllili 124 98b
0�#{216}7b 2.7ACh, 20 mm 126 95b 0. 16” 2.8ACh, 30 miii 124 27” 0.296 2.5Po.st-ACh 123 14 0. 12” 2.3
TABLE 6
Effect of prolonged increase in pre.ssure and flow pt
pump-perfused forelirnbs
Abbreviations used are: PRA, bnachiai areteny
perfusion pressure; other abbreviations as in tai)le 5.
n = 8.
PBA#{176} PSSV#{176} F�. TI’L
u/ IlK)“7,’ “U mm Jig nit/JO t�iin
Control 10’2 13 0.02 2.3Control 1(14 13 0.02 2�3
I F, I P, 10 miii 162#{176} 28” 0. 096 2.5
I F, I P, 20 mm l57b 25” 0. 10” 2.7
I F, I P, 30 mm iss” 2S� 0. 14” � 2.7
PostS IF, IP 114 14 0.196 � 2.4
a Vein pressure and arterial pressure at the cud of
each 1(1-minute period.
6 � < � compared to controls.
tylcholine. Tile lymph flow rate remained dc-
skin and skeletal muscle infusion was termi-
nated. Skin small vein pressure was increased
and systemic arterial pressure was unaffected
as in the hemodvnamic studies.
Simiiar results were obtained when venous
pressure and blood flow were mechanically dc-
vated to levels resembling those seen ill tile
hemodynamic study. There was a significant in-
crease in lymph flow rate, with no significant
change in lrotein concentration. Skin small vein
pressure and brachial artery perfusion presstire
were increased as discussed previously.
Discussion
Acetylcholine ( 10 �tg/rnin) infused into the
brachial artery for 30 minutes in foreiinlbs
perfused at natural flow increased forelimbweight 23 g. The majority of the weight gain
occurred from minutes 5 to 30 and can be altri-
buted to an increased extravascular fluid volume,
since all segmental vascular resistances were
constant or rising from minutes 2 to 5 onward.
A constant or increasing vascular resistance
suggests that mean vessel caliber was either
constant or decreasing, hence vascular volume
changes cannot account for tile large increase
ill forelimb weigilt. In addition, Diana and
Shaciur (1973) have shown in a similar prepara-
tion tllat the slow, steady component of weight
458 KLINE ET AL. Vol. 193
gaul is a result of tn:lllseapiliarv fluiti nlovement
all�i hot tiit’ re�ult t)f a slow conlponent of
vascular pooling. Time weight gain was associated
Wltil :111 increase ill blood flow and small vein
pressure in i)Otil skiii an(i skeletal muscle. Tile
marked rise in sillail 1-cia pressures, which repre-
sent a minimum for cal)iliary hydrostatic pres-
su r(’ , suggests t ii:i t t he i Ilcrea�t’(i ext ravascuia r
fluid volume resulting from infusion of high
doses of aeetVlcilOline � attrihutetl to fluid
filtration due to a rise in microvascular l)ressures.
\Ieciia nicailv i licreasilig blood flow a 11(1 venous
pressure for 30 nlinutes in l)ulllp-perfused fore-
iifl1l)S resulted ill a forelimb weight gain of 27 g.
By similar resistance analyses, it �un be sho�vn
tilat tile nlajonitv of this weight gain was due
to transcapillary fluid moveillent, not to changes
in vascular volume. The rate of forelimb weight
gain in these Pn(’l):(rations �va nearly identical
to tilat seen in tile acetvlcholine series and was
aeconll)anied I)y Silllii:Lr increases in small vein
l)resstlrt’s. Again . the increa�ed extravascularfluid Voillllle can he eXl)l�tiIle(i bY fluid filtration
resultillg from increased nlicrovascular pressures.
Available evideitce (ioes not support a direct
increase in capillary i)ermeahiiity by acetyl-
(‘hOhille, SiIlCd tile permeability-surface area
I)rotiuct for 1)laslfla proteins or Dextn:in-1 10 waslint increased during intra-arteriai administra-
tiOll of acetylchohine, 5 pg/mill (Joyner et at.,
1974). In addition. acetylcilohille applied locally
to tile mesenteric vascuiatune after an intra-
\‘(‘llOils injection of colloidal carbon did not re-
stilt in a blackening of tile microvessels (North-
OVer and Northover, 1970) . Thus, the above
ht’modvnaimc tiata suggest that high doses of
:ieetvlchohine alld mechanically increased micro-
vascuiar pressures share a similar pressure-
dependent mechanism of etlenia formation, i.e.,iLli increased transcapillary hydrostatic pressure
gradient. However a decreased transcapillary col-
bid osmotic pressure gradient would also con-
tribute to the fluid movement out of the
vascuiature if increased micnovascuiar pressures
produced �ll increase in microvascular perme-ability to plasma proteins such that the con-
centration of protein in the interstitial fluid
rose.
To examine further tile possibility of a de-
creased transcapillary cohloid osmotic pressure
gradient during tile prolonged increases in
microvascular pressures seen in tile-c experi-
ments, lympil flow rate and total protein con-
centration were measured in the clog forelimb.
It. was assumed that lymph protein concentra-
tion as measured in these experiments reflects
the protein concentration in the interstitial
fluid (Haddy et ci., 1972) . Both acetylchohine
infusion and prolonged mechanical increases in
Vein pressure and flow markedly increased
lymph flow rate but had no significant effect
on lymph total protein concentration.
Joyner et a!. (1974) , using a dog hindlimb
preparation, also observed increased lymph flow
without increased protein concentration during
ultra-arterial infusion of acetylcholine (5 jig!
mm) . Similar findings have been reported for
certain other vasodilators such as methacholine,
l)apavcrine and isoproterenol (Joyner et a!.,1974) and for serotonin (Joyner et ci., 1974;
Merrill et at., 1974) which also probably in-
creases microvascular pressures. Haddy et al.
( 1972) reported an increased forelimb lymph
flow with a significant increase in lymph pro-
tein concentration during intrabrachial infusion
of acetyicholine (5 j.tg/min) and during me-
chanicaiiy induced increases in flow and venous
pressure, but the increase in lymph protein
concentration was very small.
These data suggest that increased micro-
vascular pressures have little if any effect on
interstitial fluid protein concentration, as deter-
mined by an analysis of lymph protein. Since
protein transport increases roughly in propor-
tion to lymph flow, a decreased transcapillary
colloid osmotic pressure gradient does not con-
tribute importantly to the fluid effiux. In addi-
tion, increased pressure is not associated with
a large increase in microvascular permeability
to piasma� proteins as is seen with histamine
and bradykinin.
Combining data from this study with those
presented previously for histamine (Grega et a!.,1972) and bradykinin (Kline et al., 1973)
permits a relative comparison of pressure-
dependent and pressure-independent factors in-
volved in edema formation by these vasoactive
agents. Figure 1 shows that, after initial vas-
cular volume changes (0-2 minutes) , there was
a marked difference in the rate of weight gain
caused by high doses of histamine and brady-
kinin compared to acetyichohine and mechanical
alterations, despite similar hemodynamic con-
ditions. In fact, vein pressures and flow were
1975 PRESSURE-DEPENDENT FACTORS IN EDEMA 459
fl1:lilltaill(’(i at a Iligher level throughout tile
experimental period for the acetylcholine and
mecilanicai cilanges reporteci in this study. It is
:tl)l)arellt tilat, Witil these doses of histamine
a 11(1 i)r:l(ivkillin , t he pressure-dependent mech-
allisfll colltributed less to their edemogenic
actioll tilan tile pressure-independent mech-
01115111, at least during tile first 10 minutes of
the infusion when nlost fluid filtration occurred.
It may be argued that acetVicilOiille, unlike
histanline. (loes ilot increase tile surface area
for exchange (Gabel (‘t at., 1964) , but probably
olllV ciecre:ises tile pre-/postcapillary resistance
ratio re�ulting ill increased ifow and pressure
ill existing microvascular channels. Thus, the
rate of weigilt gain is greater for histamine due
to a l)ossibie redistribution of blood flow and a
i:lrger �urfaee area (Baker and Menninger,
1974 ; Diana et a!., 1972) . However, increased
surface area alolle ill tile presence of elevated
microvascular l)ressures couici not explain the
large illcrease ill lymph protein concentration
SCCII �vitii ilistamine (Hadciv et at., 1972) and
hradvkinin (Kline et al., 1973). Reactive hy-
l)eremia after a I)eriod of prolonged ischemiaincreases blood flow all(i, very likely, micro-
vascular pressures and �voi.ild be expected to
increase surface area for exchange (Friedman,
1971) , bitt a significant� increase in lymph pro-
teill concelltration does not occur (Miller et at.,
1975L
Acknowledgments. The autilors wish to
tilank E. Gersabeck anti ,J. Johnston for their
assistance Ivitil tile experimellts anti M. Allen
for her hitIp ill �)re�)aring tile manuscript.
References
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DIANA, .J. M., LONG, S. C. AND �AO, H. : Effect ofiiist:tiliilll’ on equival(’Ilt jore radius in capillaries
on isolated dog hindhmb. Microvasc. Res. 4:413-437, 1972.
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FRIEDMAN, J. J. : ��Rb extraction as an indicator ofca�)illary flow. Circ. Res. 28 and 29: 1-15-1-20,1971.
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