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Autoradiographic study of the regional distribution of gastric blood flow in portal hypertensive rats
GASTROENTEROLOGY 1989;97:1109-14
Autoradiographic Study of the Regional Distribution of Gastric Blood Flow in Portal Hypertensive Rats JAMES G. GERAGHTY, WILSON J. ANGERSON, and DAVID C. CARTER University Department of Surgery, Royal Infirmary, Glasgow, United Kingdom; and University Department of Surgery, Royal Infirmary, Edinburgh, United Kingdom
This study measures regional gastric blood flow in portal hypertensive rats at three separate periods after portal vein ligation using quantitative autoradiography with 14C-labeled iodoantipyrine. The level of corpus mucosal blood flow was significantly reduced in S-day portal vein-ligated animals compared with sham-operated control animals (30.4rt 2.3 vs. 47.1 + 5.6 ml/l00 g * min). There was no significant difference in corpus mucosal blood flow between portal vein-ligated and sham-operated animals at 7- and 26-day periods, although the level of perfusion was higher in the 28-day portal veinligated group. There was no significant difference in antral mucosal or muscle blood flow between portal hypertensive and control animals at any of the study periods. We conclude that the acute period after portal vein ligation is associated with a reduced corpus mucosal microcirculation but that this effect is not sustained in portal hypertensive animals studied at later intervals after portal vein ligation.
portal vein ligation is associated with a changing sequence of hemodynamic events (8) but the extent to which these changes affect the level of gastric mucosal perfusion has not been clearly defined. Therefore, the first aim of this study was to measure gastric mucosal blood flow in portal hypertensive compared with control animals at three different intervals after portal vein ligation. Given that redistribution of flow within the stomach wall may contribute to conflicting reports surrounding the level of gastric mucosal perfusion in portal hypertension, this study compares flow in [a) gastric mucosal and muscle layers, (b] corpus and antral mucosal regions, (c) the peaks and valleys of gastric mucosal folds, and (d) the superficial and deep layers of the gastric mucosa in portal vein-ligated and control animals.
It
experiments. Animals were fed a standard rat diet and were housed in an environment with a 12-h light/dark cycle. Each animal was fasted over a 24-h period before each experiment in wire-bottomed stainless steel cages.
is now well established that portal hypertension is associated with hyperdynamic systemic and splanchnic circulatory states in which splanchnic arterial flow is significantly increased (l-3). However, the effect of this hyperkinetic circulatory state on the level of gastric mucosal perfusion in portal hypertension is controversial. Manabe et al. (4) have shown that 1 day after portal vein ligation rabbits have a reduction in corpus mucosal blood flow, whereas Pique et al. (5) have more recently shown that 2 days after staged occlusion of the portal vein rats have gastric mucosal hyperperfusion. Furthermore, total gastric blood flow has been reported as increased (1,6)or unchanged (7) in rat models of chronic prehepatic portal hypertension. It has been shown that the evolution of portal hypertension after
Materials
and Methods
Animals Male Sprague-Dawley rats (Bantin and Kingman Ltd., Hull, U.K.), weighing 300-400 g were used in all
Portal Vein Ligation Prehepatic portal hypertension was produced using a standardized portal vein ligation technique 19). Under ether anesthesia an upper midline abdominal incision was made, and the portal vein was mobilized just distal to its division into right and left hepatic branches. A
Abbreviations used in this paper: PVL, portal vein ligation; SO, sham operation. 0 1989 by the American Gastroenterological Association 0016-5085/09/$3.50
GASTRIC MUCOSAL BLOOD FLOW IN PORTAL HYPERTENSION 1109
November 1989
al-gauge needle was placed alongside the mobilized segment of portal vein, and a 3-0 silk tie was placed around both vein and needle. Removal of the needle resulted in a calibrated resistance to portal venous flow. The abdomen then was closed in two layers. In sham-operated control animals the portal vein was mobilized but not stenosed.
moved and placed in a y-scintillation counter (Autogamma 500) for measurement of radioactivity. The kidneys also were removed and radioactivity was measured to ensure that leaching and lung shunting were not present. The degree of portasystemic shunting (PS) was calculated as follows: PS =
Study Design Experiments were divided into two separate groups. The first series of experiments was performed to measure portal venous pressure and the degree of portasystemic shunting after either portal vein ligation (PVL) or sham operation (SO) at 3- (PVL, n = 7; SO, n = 3), 7- (PVL, n = 9; SO, n = 4), and 28- (PVL, n = 8; SO, n = 4) day intervals. In the second group of experiments gastric mucosal blood flow was measured at 3 days (PVL, n = 9; SO, n = 7), 7 days (PVL, n = 6; SO, n = 6), and 28 days (PVL, n = 11; SO, n = 7).
Measurement
of Portal
Venous
Pressure
Each animal was fasted for 24 h and anesthesia was induced using 4% halothane in a 2:l nitrous oxide/oxygen mixture. A tracheostomy was performed and artificial ventilation maintained (Harvard rat ventilator) using 0.5% halothane in the same nitrous oxide/oxygen mixture. A femoral arterial cannula (polyethylene tubing) was inserted and connected to a strain gauge transducer (Statham) to record mean arterial pressure (Gould series recorder). Arterial blood samples were taken for blood gas analysis (ABL2, Radiometer), and the ventilation rate was adjusted if necessary to maintain the PCO, in the range of 35-42 mmHg. Arterial PO, was >90 mmHg and pH was >7.3 in all experiments. A laparotomy was performed and the ileocolic branch of the portal vein was cannulated (polyethylene tubing, outside diameter = 0.96 mm). The cannula was connected to a second strain gauge transducer placed at the level of the right atrium to measure portal pressure. The transducer was calibrated before and after measurement of portal pressure to ensure that drift had not occurred, and formal readings were taken only when a respiratory pattern was present on the portal venous tracing.
Measurement
of Portasystemic
Shunting
After mean arterial and portal venous pressures were recorded the magnitude of portasystemic shunting was measured as described by Chojkier and Groszmann (10). Briefly, a 0.2-ml suspension containing -100,000 y-labeled microspheres (New England Nuclear, Boston, Mass.) was vortexed for 30 s and injected into the portal venous system via the ileocolic cannula. The same volume of saline was used to flush the cannula. The microspheres, which measure 15 * 1 pm in diameter (mean 5 SD), were suspended in 10% Dextran with 0.01% of surfactant Tween 80 to prevent clumping. At death, 5 min after injection of microspheres, the liver and lungs were re-
cPmungs wmh
x 100.
+ lungs
Gastric Mucosal Blood Flow Gastric mucosal blood flow was measured using iodo[‘4C]antipyrine autoradiography as described (11). In brief, each animal was anesthetized and ventilated with the same nitrous oxideioxygenlhalothane mixture and the femoral artery and the veins on both sides were cannulated. Arterial blood samples were taken for blood gas analysis, and mean arterial pressure was measured via one of the femoral artery catheters. Core temperature was kept at 37” 2 0.5”C by means of a heat lamp. iodoantipyrine disFifty microcuries of ‘%-labeled solved in 1.5 ml of saline was infused over 30 s into the right femoral vein, while timed arterial blood samples were taken during the infusion to define the arterial No concentration curve of 14C-labeled iodoantipyrine. change in blood pressure occurred during this procedure. After 30 s the animal was killed with an intravenous bolus of saturated KCl, and the stomach was removed and frozen in isopentane at -45°C to prevent redistribution of 14Clabeled iodoantipyrine. The blood samples, which were collected on preweighed filter disks, were reweighed and then bleached with hydrogen peroxide before radioactivity was counted in a Packard Tri-Carb 2660 liquid scintillation counter with automatic quench correction. Quenched 14C standards were used to calibrate the scintillation counter. The glandular stomach was divided into proximal corpus, distal corpus, and antral regions from which transverse sections, 20 pm thick, spaced -400 pm apart, were cut using a cryostat (Bright OTFIAF) at -20°C. Six to nine sections were taken from each region, mounted on microscopic slides that were dried on a hot plate, and then placed in x-ray cassettes together with a calibrated set of autoradiographic standards. Autoradiograms were exposed on Kodak GRS x-ray film at room temperature for 14 days and developed in a Kodak X-OMAT automatic developing machine. Each section then was stained to allow comparison with the corresponding autoradiogram. The optical density of autoradiograms was measured using a Quantimet 720 image analyzer (Cambridge Instruments) and then converted to tissue 14C concentrations using a calibration curve derived from measurements taken from autoradiographic standards on the same film. A gradient in radioactivity perpendicular to the plane of the mucosal layer was seen in corpus mucosa and the mean concentration of tracer across the full thickness of the layer was used for calculation of corpus mucosal blood flow. We have suggested (11) that this gradient is due to rapid efflux of tracer from blood in the basal part of the gastric mucosa where it first enters capillaries, but it has
1110
GERAGHTY ET AL.
GASTROENTEROLOGY Vol.
been proposed (12) that it may be related to differences in capillary density between basal and luminal mucosa. In either case a redistribution of blood flow between basal and luminal regions of mucosa could be expected to alter
the gradient and therefore we performed additional measurements of tracer concentration in the most basal and most luminal 200-pm regions of corpus mucosa. Measurements were taken separately on the crests and valleys of gastric mucosal folds, on antral mucosa, and on the muscle layer of the gastric wall. Gastric mucosal blood flow values were calculated using the following equation (13):
Ct(T)
=I
T
mF
Ca(t) exp [ - mF(T - t)lh] dt,
0
where Ct(T) is the concentration of tracer in tissue at the time of death (T), Ca(t] is the concentration of tracer in arterial blood at time t, h is the partition coefficient for iodoantipyrine between tissue and blood, F is flow per unit mass of tissue, and m expresses the degree to which the tracer attains diffusion equilibrium between tissue and blood during a capillary transit. This was assumed to have a value of 1. The partition coefficient for iodoantipyrine was 0.91as described (11). Results are presented as mean C SEM. Statistical analysis was performed using the Mann-Whitney test.
Results Portal Hypertensive
Model
There was no significant difference in mean arterial pressure between portal vein-ligated and sham-operated groups at any of the three study intervals (Table 1). Mean portal venous pressure gradually declined from 21.3 + 0.9 mmHg (n = 7), at 3 days, to 11.3 ? 0.6 mmHg (n = 8) 28 days after portal vein ligation, and mean portal pressure in sham-operated control groups did not exceed 7.9 mmHg (Table 1). As portal pressure fell the degree of portasystemic shunting rose from 37.4% 2 6.5% at the 3-day check, to a peak of 60.4% ? 8.8% 7 days after portal vein ligation (Table 1). The magnitude of
Table
1. Mean Arterial Hypertension
Pressures,
Portal
Venous 3
PVL (n = 7) Mean arterial pressure
(mmHg)
Portal venous pressure
(mmHg)
Portasystemic
(%)
shunting
103.6
in sham-operated
Corpus mucosal blood jlow. Corpus mucosal blood flow was significantly reduced [Table 2, Figure 1)in S-day portal vein-ligated animals (p < 0.01,n = 9) compared with controls (n = 7). There was no significant difference in corpus mucosal blood flow between portally hypertensive and control animals at 7 days. After 28 days, portal vein-ligated animals had an increase in corpus mucosal blood flow but the difference was not statistically significant compared with controls. The level of perfusion in control animals ranged from relatively low values at 3 days to a marked increase at 7 days and a value intermediate between both intervals at 28 days. Antral mucosal blood flow. In contrast to corpus mucosal blood flow there was no significant reduction in antral mucosal blood flow in the acute period after portal vein ligation (Table 2). In similar fashion to gastric corpus there was a large increase in antral mucosal blood flow 7 days after both portal vein ligation and sham operation, but this effect had disappeared by 28 days. Muscle blood jlow. There was no significant difference in muscle blood flow between portal veinligated and sham-operated animals at each of the study periods [Table 2), although flow tended to be lower in the 3-day portally hypertensive group and higher in 7- and 28-day portal vein-ligated animals compared with controls. Corpus mucosal folds. The pattern of flow in the crests and valleys of mucosal folds mirrored the changes seen in corpus mucosal blood flow in portal vein-ligated and sham-operated animals at all three study periods (Table 3). The ratio of flow in crests compared with valleys was significantly different from 1 in portal hypertensive and control animals at 7- and 28-day study periods. This significant differ-
and Portasystemic
Shunting
in Prehepatic
Portal
7 day (nSZ3)
23.3 6.3 to.4 0.1
control
Gastric Blood Flow in Portal Hypertension
day
96.7
k4.0 21.3' to.9 37.4 26.5
PVL, portal vein ligation; SO, sham operation.
Pressure,
shunting was negligible animals (Table 1).
97, No. 5
28 day PVL
PVL (n = 9) 104.0 k3.7 14.8" 50.9 60.4 k-8.8
(n = 8) 102.5 -r-4.3 6.7 20.7 0.7
Values are mean + SEM. a p < 0.001. b p < 0.01.
103.5 rt1.2 11.3b k-O.6 50.7 29.4
107.2 k4.4 7.9 20.3 0.1
November
GASTRIC MUCOSAL BLOOD FLOW IN PORTAL HYPERTENSION
1989
1111
A Figure
1. Autoradiographs of transverse sections of stomach from a 3-day portal vein-ligated animal (A) and a 3-day sham-operated animal (B) illustrating the reduction in corpus mucosal blood flow in the 3-day portal vein-ligated group. This reduction was present in both the crests and valleys of gastric mucosal folds. Flow in antral mucosa (bottom of section] was not reduced.
ence was not present, however, in S-day portal vein-ligated and control animals. 14C-labeled iodoantipyrine concentrations in basal and iuminal corpus mucosa. There was no significant difference in the ratio of ‘*C-labeled iodoantipyrine concentration in luminal and basal regions of corpus mucosa between portally hypertensive and control animals at any of the study periods (Table 4, Figure 2).
Discussion There is much clinical and experimental evidence to suggest that the gastric microcirculation is altered in portal hypertension. Gastric mucosal vascular ectasia (14) and submucosal arteriovenous shunts (15) have been described in patients with portal hypertension, whereas animals with prehepatic portal hypertension have an increase in the
Table 2. Regional Gastric Blood Flow in Portal Hypertension 3 day
7
PVL (II = 9) Corpus mucosa (mJ1100 g min) Antral mucosa (ml/100 g min) Muscle (ml1100 g min]
30.4 22.3 108.8 516.3 27.7 54.4
PVL, portal vein ligation; SO, sham operation.
PVL (n = 6) 47.1U ~5.6 115.3 211.7 39.3 211.8
112.7 c10.0 202.7 213.1 57.3 k6.7
Values are mean ‘- SEM. a p < 0.01
day
28 day
(n’f6)
PVL (n = 11)
109.8
95.5
26.9 196.5 539.9 39.5 k4.5
"14.4 125.0 lr14.1 45.3 23.8
77.7 k11.0 110.0 212.5 41.4 24.6
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GERAGHTY ET AL.
GASTROENTEROLOGY Vol. 97, No. 5
Table 3. Blood Flow in Gastric Mucosal Folds 3 day
PVL (n = 9) Corpus crests Corpus valleys Ratio
30.5 21.9 30.4 k2.2 1.04 50.05
PVL, portal vein ligation; SO, sham operation. significantly different from 1.00 using bnpaired
28 day
7 day (ns!7) 44.7 e4.7 49.4 26.8 0.94 20.07
PVL (n = 6) 130.9 212.1 103.5 k10.6 1.28' kO.07
(nS=Os)
PVL (n = 11)
(n’=O7)
118.2 27.9 101.3 29.1 l.lga to.08
101.6 f15.3 89.7 k13.5 1.15O TO.03
85.6 f12.9 73.1 k10.0 1.16a eo.03
Ratios are of crests to valleys in each comparison. t-test.
cytoplasmic area of gastric mucosal endothelial cells (16). Despite this body of histologic evidence suggesting the presence of a gastric mucosal vasculopathy in portal hypertension there is little information on the effects of a raised portal pressure on gastric mucosal blood flow. This study shows that corpus mucosal blood flow was significantly and selectively reduced in animals 3 days after portal vein ligation, but this reduction was not sustained in animals at later time intervals. Sikuler et al. (8) have demonstrated a changing sequence of hemodynamic events occurring with time after portal vein ligation ranging from a reduction in splanchnic blood flow within the first few days to a new steady state characterized by raised splanchnic inflow 7 days after portal vein ligation. However, the extent to which these changes are reflected in the perfusion of the gastric mucosa has not been clearly defined in a sequential study. This study and that of Manabe et al. (4) show that gastric mucosal blood flow is reduced within the first 3 days of portal vein ligation, and these findings are in keeping with the theory that the increased resistance to portal blood flow produced by portal vein ligation has the dominant effect on the level of gastric mucosal perfusion during this acute period. In contrast to animals with acute prehepatic portal hypertension, total gastric blood flow as measured with radiolabeled microspheres has been reported to be unchanged (7) or increased (1,6) in animals with
Values are mean of- SEM. ’ Ratio
chronic prehepatic portal hypertension. Only two previous studies have measured gastric mucosal blood flow in this experimental condition, to our knowledge, both of which, reported it to be increased (5,6). In the present study, gastric mucosal blood flow was essentially equal in portal hypertensive and control animals 7 days postoperatively, whereas at 28 days there was a 23% increase in the
Table 4. Ratio of ‘%-Labeled
Iodoantipyrine Concentration in Luminal and Basal 200-pm Regions of Corpus Mucosa Portal vein ligated
3 days 7 days 28 days
0.377k 0.027 0.326k 0.037 0.307Ii0.022
Sham operated 0.364k 0.068 0.353k 0.013 0.338k 0.042
Ratios are of luminal to basal regions in each comparison. There was no significant difference in the ratio of tracer concentration in luminal and basal corpus mucosa between portal vein-ligated and control groups at any study interval.
Figure 2. Autoradiograph taken from transverse section of stomach in a 28-day portal vein-ligated animal. There was no significant difference in the ratio of luminal to basal tracer concentration in corpus mucosa between portal hypertensive and control animals at any of the study periods.
November
1989
GASTRIC MUCOSAL BLOOD FLOW IN PORTAL HYPERTENSION
level of perfusion in the portally hypertensive group, although this difference did not reach statistical significance. The evidence is therefore unanimous that gastric mucosal blood flow is at least preserved in chronic prehepatic models of portal hypertension, but is in conflict over whether it is increased. These studies in both acute and chronic prehepatic portal hypertension support the concept suggested by Sikuler et al. (8) that portal vein ligation produces a temporal change in splanchnic hemodynamics, and it is possible that this change is due to the release of splanchnic vasodilators such as glucagon into the systemic circulation via portasystemic collateral vessels (17), which we have shown to attain a maximum 7 days after portal vein ligation (18). Although total gastric blood flow may be increased in experimental portal hypertension (1,2) there is evidence to suggest that a redistribution of blood flow may occur within the gastric wall. The existence of arteriovenous shunting has been demonstrated using silicone cast techniques in the gastric submucosa of patients with portal hypertension (15), whereas Manabe and colleagues (4) have shown, using radioactive microspheres, that a 19.5% magnitude arteriovenous shunting was present in the gastric submucosa of rabbits 24 h after portal vein ligation. In similar fashion, that study also showed submucosal shunting in animals with experimental cirrhosis and these results suggest that gastric mucosal hypoperfusion could occur despite an increase in total gastric blood flow. Our study shows, irrespective of the existence of gastric submucosal arteriovenous shunting, that gastric mucosal blood flow is at least preserved in animals with chronic portal hypertension, and these results are consistent with the findings of Benoit et al. (6) in animals studied 10 days after portal vein ligation. It has been suggested (19) that redistribution of blood flow may occur within the gastric mucosa itself, giving rise to differences in flow between the superficial and deep portions of the gastric mucosa in portal hypertension. As discussed, the distribution of iodoantipyrine in corpus mucosa is not uniform across the width of the mucosal layer for reasons that may be unrelated to variations in blood flow. Hence, this technique is not ideally suited to studying differences in flow between superficial and deep mucosa. However, any such variations that occur in association with portal hypertension would be expected to alter the distribution of blood flow tracer, whereas we found the concentration gradient across the width of the mucosa to be similar in portal vein-ligated and sham-operated animals at all three study intervals. This study also examines the effect of portal hypertension on the regional distribution of gastric
1113
blood flow with specific reference to flow in (a) crests and valleys of gastric mucosal folds, (b) corpus and antral mucosa, and (c) basal and luminal aspects of corpus mucosa. Mersereau and Hinchey (20) reported that transmucosal potential difference was reduced on the crests of gastric folds, which they suggested could be associated with a local perfusion defect, but our experiments show no evidence of hypoperfusion in mucosal crests in either portal hypertensive or control animals. Although flow tended to be higher in the crests of mucosal folds, there was no significant difference in flow either in mucosal crests or valleys between portally hypertensive and control groups. The level of perfusion to antral mucosa was higher compared with corpus mucosa in both portal vein-ligated and sham-operated animals at all study intervals. There was no significant reduction in antral mucosal or muscle blood flow in the s-day portal vein-ligated group compared with controls. Therefore, mucosal hypoperfusion at this period in portal hypertensive animals was exclusive to corpus mucosa. One interesting finding in this study was the change in the level of mucosal perfusion with time after laparotomy. This finding contrasts with that of Sikuler et al. (8), who demonstrated little change in splanchnic blood flow in sham-operated animals during this period. The results of the present study, however, were limited to the measurement of gastric blood flow, which represents a small fraction of total splanchnic blood flow. We have found (unpublished observations) that taurocholate-induced gastric mucosal injury is increased in animals 3 days after sham operation compared with nonoperated controls in association with a reduction in gastric mucosal blood flow. Animals studied 7 days after sham operation have a reduction in mucosal susceptibility to injury when compared with nonoperated controls. We are unaware of any studies examining the more long-term effects of laparotomy on either gastric mucosal blood flow or susceptibility to injury. This study shows that the acute rise in portal venous pressure shortly after portal vein ligation is associated with a stagnant gastric corpus mucosal microcirculation, and this result is consistent with reports that gastric mucosal susceptibility to injury is increased in acute prehepatic portal hypertension (1921). In contrast, animals with chronic portal hypertension had no reduction in gastric mucosal blood flow. It remains to be seen what effect raised portal pressure has on gastric mucosal susceptibility to injury at later intervals after portal vein ligation. References 1. Vorobioff J, Bredfeldt JE, Groszmann RJ. Hyperdynamic culation in portal hypertensive
cirrat model: a primary factor for
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2.
3.
4.
5.
6.
7. 8.
9. 10.
11.
12.
GERAGHTY ET AL.
maintenance of chronic portal hypertension. Am J Physiol 1983;244:G52-7. Vorobioff J, Bredfeldt JE, Groszmann RJ. Increased blood flow through the portal system in cirrhotic rats. Gastroenterology 1984;87:1120-6. Benoit JN, Womack WA, Hernandez L, Granger DN. Forward and backward flow mechanisms in portal hypertension. Gastroenterology 1985;89:1092-6. Manabe T, Suzuki T, Monjo I. Changes of gastric blood flow in experimentally induced cirrhosis of the liver. Surg Gynecol Obstet 1978;147:753-7. Pique JM, Lenng FW, Kitahora T, Sarfeh IJ, Tarnowski A, Guth PH. Gastric mucosal blood flow and acid secretion in portal hypertensive rats. Gastroenterology 1988;95:727-33. Benoit JN, Womack WA, Kurthins RJ, Wilborn WH, Granger DN. Chronic portal hypertension: effects on gastrointestinal blood flow distribution. Am J Physiol 1986;250:G535-9. Blanchet L, Lebrec D. Changes in splanchnic blood flow in portal hypertensive rats. Eur J Clin Invest 1982;12:1002-7. Sikuler E, Kravetz D, Groszmann RJ. Evolution of portal hypertension and mechanisms involved in its maintenance in a rat model. Am J Physiol 1985;248:G618-25. Halvorsen JF, Myking AO. Prehepatic portal hypertension in the rat. Eur Surg Res 1979;11:89-98. Chojkier M, Groszmann RJ. Measurement of portal systemic shunting in the rat using gamma-labelled microspheres. Am J Physiol 1981;240:G371-5. Angerson WJ, Geraghty JG, Carter DC. An autoradiographic study of regional distribution of gastric mucosal blood flow. Am J Physiol 1988;254:G566-74. Hudson D, Scremin OU, Guth PH. Measurement of regional gastroduodenal blood flow with iodo [“Cl antipyrine autoradiography. Am J Physiol 1985;248:C539-44.
GASTROENTEROLOGY Vol. 97, No. 5
13. Kety SS. The theory and applications 14.
15. 16.
17.
18.
19.
20. 21.
of the exchange of inert gas at the lungs and tissues. Pharmacol Rev 1951;3:1--41. Quintero E, Pique JM, Bombi JA, et al. Gastric mucosal vascular ectasias causing bleeding in cirrhosis. Gastoenterology 1987;93:1054-61. Hashizume M, Tanaka K, Inokudi K. Morphology of gastric microcirculation in cirrhosis. Hepatology 1983;3:1008-12. Tarnowski A, Sarfeh IJ, Strachura J, Hajduczek A, Bui I-IX. Portal hypertensive gastropathy or vasculopathy (abstr)? Gastroenterology 1987;92:1786. Benoit JN, Zimmerman B, Premen AJ, Go VLW, Granger DN. Role of glucagon in splanchnic hyperaemia of chronic portal hypertension. Am J Physiol 1986;251:G674-7. Geraghty JG, Angerson WJ, Carter DC. Portal venous pressure and portasystemic shunting in experimental portal hypertension Am J Physiol 1989;257:G52-7. Sarfeh IJ, Tarnowski A. Gastric mucosal vasculopathy in portal hypertension (editorial). Gastroenterology 1987;93: 1129-31. Mersereau WA, Hinchey EJ. Role of gastric mucosal folds in formation of focal ulcers in the rat. Surgery 1982;91:150-5. Sarfeh IJ, Tarnowski A, Malki A, Mason GR, Mach T, Ivey KJ. Portal hypertension and gastric mucosal injury in rats. Gastroenterology 1983;84:987-93.
Received December 19, 1988. Accepted May 8, 1989. Address requests for reprints to: James G. Geraghty, University Department of Surgery, Royal Infirmary, Glasgow G3l 2ER, Scotland, United Kingdom. This work was supported by grants from the Scottish Hospitals Endowment Research Trust and from the Fraser Foundation. The authors thank Sheelah Smith and Graeme Fyffe for technical assistance, and Margaret Tosh for typing the manuscript. They also thank Professor A. Murray Harper and staff for access to the Quantimet image analyzer.
Autoradiographic Study of the Regional Distribution of Gastric Blood Flow in Portal Hypertensive Rats JAMES G. GERAGHTY, WILSON J. ANGERSON, and DAVID C. CARTER University Department of Surgery, Royal Infirmary, Glasgow, United Kingdom; and University Department of Surgery, Royal Infirmary, Edinburgh, United Kingdom
This study measures regional gastric blood flow in portal hypertensive rats at three separate periods after portal vein ligation using quantitative autoradiography with 14C-labeled iodoantipyrine. The level of corpus mucosal blood flow was significantly reduced in S-day portal vein-ligated animals compared with sham-operated control animals (30.4rt 2.3 vs. 47.1 + 5.6 ml/l00 g * min). There was no significant difference in corpus mucosal blood flow between portal vein-ligated and sham-operated animals at 7- and 26-day periods, although the level of perfusion was higher in the 28-day portal veinligated group. There was no significant difference in antral mucosal or muscle blood flow between portal hypertensive and control animals at any of the study periods. We conclude that the acute period after portal vein ligation is associated with a reduced corpus mucosal microcirculation but that this effect is not sustained in portal hypertensive animals studied at later intervals after portal vein ligation.
portal vein ligation is associated with a changing sequence of hemodynamic events (8) but the extent to which these changes affect the level of gastric mucosal perfusion has not been clearly defined. Therefore, the first aim of this study was to measure gastric mucosal blood flow in portal hypertensive compared with control animals at three different intervals after portal vein ligation. Given that redistribution of flow within the stomach wall may contribute to conflicting reports surrounding the level of gastric mucosal perfusion in portal hypertension, this study compares flow in [a) gastric mucosal and muscle layers, (b] corpus and antral mucosal regions, (c) the peaks and valleys of gastric mucosal folds, and (d) the superficial and deep layers of the gastric mucosa in portal vein-ligated and control animals.
It
experiments. Animals were fed a standard rat diet and were housed in an environment with a 12-h light/dark cycle. Each animal was fasted over a 24-h period before each experiment in wire-bottomed stainless steel cages.
is now well established that portal hypertension is associated with hyperdynamic systemic and splanchnic circulatory states in which splanchnic arterial flow is significantly increased (l-3). However, the effect of this hyperkinetic circulatory state on the level of gastric mucosal perfusion in portal hypertension is controversial. Manabe et al. (4) have shown that 1 day after portal vein ligation rabbits have a reduction in corpus mucosal blood flow, whereas Pique et al. (5) have more recently shown that 2 days after staged occlusion of the portal vein rats have gastric mucosal hyperperfusion. Furthermore, total gastric blood flow has been reported as increased (1,6)or unchanged (7) in rat models of chronic prehepatic portal hypertension. It has been shown that the evolution of portal hypertension after
Materials
and Methods
Animals Male Sprague-Dawley rats (Bantin and Kingman Ltd., Hull, U.K.), weighing 300-400 g were used in all
Portal Vein Ligation Prehepatic portal hypertension was produced using a standardized portal vein ligation technique 19). Under ether anesthesia an upper midline abdominal incision was made, and the portal vein was mobilized just distal to its division into right and left hepatic branches. A
Abbreviations used in this paper: PVL, portal vein ligation; SO, sham operation. 0 1989 by the American Gastroenterological Association 0016-5085/09/$3.50
GASTRIC MUCOSAL BLOOD FLOW IN PORTAL HYPERTENSION 1109
November 1989
al-gauge needle was placed alongside the mobilized segment of portal vein, and a 3-0 silk tie was placed around both vein and needle. Removal of the needle resulted in a calibrated resistance to portal venous flow. The abdomen then was closed in two layers. In sham-operated control animals the portal vein was mobilized but not stenosed.
moved and placed in a y-scintillation counter (Autogamma 500) for measurement of radioactivity. The kidneys also were removed and radioactivity was measured to ensure that leaching and lung shunting were not present. The degree of portasystemic shunting (PS) was calculated as follows: PS =
Study Design Experiments were divided into two separate groups. The first series of experiments was performed to measure portal venous pressure and the degree of portasystemic shunting after either portal vein ligation (PVL) or sham operation (SO) at 3- (PVL, n = 7; SO, n = 3), 7- (PVL, n = 9; SO, n = 4), and 28- (PVL, n = 8; SO, n = 4) day intervals. In the second group of experiments gastric mucosal blood flow was measured at 3 days (PVL, n = 9; SO, n = 7), 7 days (PVL, n = 6; SO, n = 6), and 28 days (PVL, n = 11; SO, n = 7).
Measurement
of Portal
Venous
Pressure
Each animal was fasted for 24 h and anesthesia was induced using 4% halothane in a 2:l nitrous oxide/oxygen mixture. A tracheostomy was performed and artificial ventilation maintained (Harvard rat ventilator) using 0.5% halothane in the same nitrous oxide/oxygen mixture. A femoral arterial cannula (polyethylene tubing) was inserted and connected to a strain gauge transducer (Statham) to record mean arterial pressure (Gould series recorder). Arterial blood samples were taken for blood gas analysis (ABL2, Radiometer), and the ventilation rate was adjusted if necessary to maintain the PCO, in the range of 35-42 mmHg. Arterial PO, was >90 mmHg and pH was >7.3 in all experiments. A laparotomy was performed and the ileocolic branch of the portal vein was cannulated (polyethylene tubing, outside diameter = 0.96 mm). The cannula was connected to a second strain gauge transducer placed at the level of the right atrium to measure portal pressure. The transducer was calibrated before and after measurement of portal pressure to ensure that drift had not occurred, and formal readings were taken only when a respiratory pattern was present on the portal venous tracing.
Measurement
of Portasystemic
Shunting
After mean arterial and portal venous pressures were recorded the magnitude of portasystemic shunting was measured as described by Chojkier and Groszmann (10). Briefly, a 0.2-ml suspension containing -100,000 y-labeled microspheres (New England Nuclear, Boston, Mass.) was vortexed for 30 s and injected into the portal venous system via the ileocolic cannula. The same volume of saline was used to flush the cannula. The microspheres, which measure 15 * 1 pm in diameter (mean 5 SD), were suspended in 10% Dextran with 0.01% of surfactant Tween 80 to prevent clumping. At death, 5 min after injection of microspheres, the liver and lungs were re-
cPmungs wmh
x 100.
+ lungs
Gastric Mucosal Blood Flow Gastric mucosal blood flow was measured using iodo[‘4C]antipyrine autoradiography as described (11). In brief, each animal was anesthetized and ventilated with the same nitrous oxideioxygenlhalothane mixture and the femoral artery and the veins on both sides were cannulated. Arterial blood samples were taken for blood gas analysis, and mean arterial pressure was measured via one of the femoral artery catheters. Core temperature was kept at 37” 2 0.5”C by means of a heat lamp. iodoantipyrine disFifty microcuries of ‘%-labeled solved in 1.5 ml of saline was infused over 30 s into the right femoral vein, while timed arterial blood samples were taken during the infusion to define the arterial No concentration curve of 14C-labeled iodoantipyrine. change in blood pressure occurred during this procedure. After 30 s the animal was killed with an intravenous bolus of saturated KCl, and the stomach was removed and frozen in isopentane at -45°C to prevent redistribution of 14Clabeled iodoantipyrine. The blood samples, which were collected on preweighed filter disks, were reweighed and then bleached with hydrogen peroxide before radioactivity was counted in a Packard Tri-Carb 2660 liquid scintillation counter with automatic quench correction. Quenched 14C standards were used to calibrate the scintillation counter. The glandular stomach was divided into proximal corpus, distal corpus, and antral regions from which transverse sections, 20 pm thick, spaced -400 pm apart, were cut using a cryostat (Bright OTFIAF) at -20°C. Six to nine sections were taken from each region, mounted on microscopic slides that were dried on a hot plate, and then placed in x-ray cassettes together with a calibrated set of autoradiographic standards. Autoradiograms were exposed on Kodak GRS x-ray film at room temperature for 14 days and developed in a Kodak X-OMAT automatic developing machine. Each section then was stained to allow comparison with the corresponding autoradiogram. The optical density of autoradiograms was measured using a Quantimet 720 image analyzer (Cambridge Instruments) and then converted to tissue 14C concentrations using a calibration curve derived from measurements taken from autoradiographic standards on the same film. A gradient in radioactivity perpendicular to the plane of the mucosal layer was seen in corpus mucosa and the mean concentration of tracer across the full thickness of the layer was used for calculation of corpus mucosal blood flow. We have suggested (11) that this gradient is due to rapid efflux of tracer from blood in the basal part of the gastric mucosa where it first enters capillaries, but it has
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GASTROENTEROLOGY Vol.
been proposed (12) that it may be related to differences in capillary density between basal and luminal mucosa. In either case a redistribution of blood flow between basal and luminal regions of mucosa could be expected to alter
the gradient and therefore we performed additional measurements of tracer concentration in the most basal and most luminal 200-pm regions of corpus mucosa. Measurements were taken separately on the crests and valleys of gastric mucosal folds, on antral mucosa, and on the muscle layer of the gastric wall. Gastric mucosal blood flow values were calculated using the following equation (13):
Ct(T)
=I
T
mF
Ca(t) exp [ - mF(T - t)lh] dt,
0
where Ct(T) is the concentration of tracer in tissue at the time of death (T), Ca(t] is the concentration of tracer in arterial blood at time t, h is the partition coefficient for iodoantipyrine between tissue and blood, F is flow per unit mass of tissue, and m expresses the degree to which the tracer attains diffusion equilibrium between tissue and blood during a capillary transit. This was assumed to have a value of 1. The partition coefficient for iodoantipyrine was 0.91as described (11). Results are presented as mean C SEM. Statistical analysis was performed using the Mann-Whitney test.
Results Portal Hypertensive
Model
There was no significant difference in mean arterial pressure between portal vein-ligated and sham-operated groups at any of the three study intervals (Table 1). Mean portal venous pressure gradually declined from 21.3 + 0.9 mmHg (n = 7), at 3 days, to 11.3 ? 0.6 mmHg (n = 8) 28 days after portal vein ligation, and mean portal pressure in sham-operated control groups did not exceed 7.9 mmHg (Table 1). As portal pressure fell the degree of portasystemic shunting rose from 37.4% 2 6.5% at the 3-day check, to a peak of 60.4% ? 8.8% 7 days after portal vein ligation (Table 1). The magnitude of
Table
1. Mean Arterial Hypertension
Pressures,
Portal
Venous 3
PVL (n = 7) Mean arterial pressure
(mmHg)
Portal venous pressure
(mmHg)
Portasystemic
(%)
shunting
103.6
in sham-operated
Corpus mucosal blood jlow. Corpus mucosal blood flow was significantly reduced [Table 2, Figure 1)in S-day portal vein-ligated animals (p < 0.01,n = 9) compared with controls (n = 7). There was no significant difference in corpus mucosal blood flow between portally hypertensive and control animals at 7 days. After 28 days, portal vein-ligated animals had an increase in corpus mucosal blood flow but the difference was not statistically significant compared with controls. The level of perfusion in control animals ranged from relatively low values at 3 days to a marked increase at 7 days and a value intermediate between both intervals at 28 days. Antral mucosal blood flow. In contrast to corpus mucosal blood flow there was no significant reduction in antral mucosal blood flow in the acute period after portal vein ligation (Table 2). In similar fashion to gastric corpus there was a large increase in antral mucosal blood flow 7 days after both portal vein ligation and sham operation, but this effect had disappeared by 28 days. Muscle blood jlow. There was no significant difference in muscle blood flow between portal veinligated and sham-operated animals at each of the study periods [Table 2), although flow tended to be lower in the 3-day portally hypertensive group and higher in 7- and 28-day portal vein-ligated animals compared with controls. Corpus mucosal folds. The pattern of flow in the crests and valleys of mucosal folds mirrored the changes seen in corpus mucosal blood flow in portal vein-ligated and sham-operated animals at all three study periods (Table 3). The ratio of flow in crests compared with valleys was significantly different from 1 in portal hypertensive and control animals at 7- and 28-day study periods. This significant differ-
and Portasystemic
Shunting
in Prehepatic
Portal
7 day (nSZ3)
23.3 6.3 to.4 0.1
control
Gastric Blood Flow in Portal Hypertension
day
96.7
k4.0 21.3' to.9 37.4 26.5
PVL, portal vein ligation; SO, sham operation.
Pressure,
shunting was negligible animals (Table 1).
97, No. 5
28 day PVL
PVL (n = 9) 104.0 k3.7 14.8" 50.9 60.4 k-8.8
(n = 8) 102.5 -r-4.3 6.7 20.7 0.7
Values are mean + SEM. a p < 0.001. b p < 0.01.
103.5 rt1.2 11.3b k-O.6 50.7 29.4
107.2 k4.4 7.9 20.3 0.1
November
GASTRIC MUCOSAL BLOOD FLOW IN PORTAL HYPERTENSION
1989
1111
A Figure
1. Autoradiographs of transverse sections of stomach from a 3-day portal vein-ligated animal (A) and a 3-day sham-operated animal (B) illustrating the reduction in corpus mucosal blood flow in the 3-day portal vein-ligated group. This reduction was present in both the crests and valleys of gastric mucosal folds. Flow in antral mucosa (bottom of section] was not reduced.
ence was not present, however, in S-day portal vein-ligated and control animals. 14C-labeled iodoantipyrine concentrations in basal and iuminal corpus mucosa. There was no significant difference in the ratio of ‘*C-labeled iodoantipyrine concentration in luminal and basal regions of corpus mucosa between portally hypertensive and control animals at any of the study periods (Table 4, Figure 2).
Discussion There is much clinical and experimental evidence to suggest that the gastric microcirculation is altered in portal hypertension. Gastric mucosal vascular ectasia (14) and submucosal arteriovenous shunts (15) have been described in patients with portal hypertension, whereas animals with prehepatic portal hypertension have an increase in the
Table 2. Regional Gastric Blood Flow in Portal Hypertension 3 day
7
PVL (II = 9) Corpus mucosa (mJ1100 g min) Antral mucosa (ml/100 g min) Muscle (ml1100 g min]
30.4 22.3 108.8 516.3 27.7 54.4
PVL, portal vein ligation; SO, sham operation.
PVL (n = 6) 47.1U ~5.6 115.3 211.7 39.3 211.8
112.7 c10.0 202.7 213.1 57.3 k6.7
Values are mean ‘- SEM. a p < 0.01
day
28 day
(n’f6)
PVL (n = 11)
109.8
95.5
26.9 196.5 539.9 39.5 k4.5
"14.4 125.0 lr14.1 45.3 23.8
77.7 k11.0 110.0 212.5 41.4 24.6
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GASTROENTEROLOGY Vol. 97, No. 5
Table 3. Blood Flow in Gastric Mucosal Folds 3 day
PVL (n = 9) Corpus crests Corpus valleys Ratio
30.5 21.9 30.4 k2.2 1.04 50.05
PVL, portal vein ligation; SO, sham operation. significantly different from 1.00 using bnpaired
28 day
7 day (ns!7) 44.7 e4.7 49.4 26.8 0.94 20.07
PVL (n = 6) 130.9 212.1 103.5 k10.6 1.28' kO.07
(nS=Os)
PVL (n = 11)
(n’=O7)
118.2 27.9 101.3 29.1 l.lga to.08
101.6 f15.3 89.7 k13.5 1.15O TO.03
85.6 f12.9 73.1 k10.0 1.16a eo.03
Ratios are of crests to valleys in each comparison. t-test.
cytoplasmic area of gastric mucosal endothelial cells (16). Despite this body of histologic evidence suggesting the presence of a gastric mucosal vasculopathy in portal hypertension there is little information on the effects of a raised portal pressure on gastric mucosal blood flow. This study shows that corpus mucosal blood flow was significantly and selectively reduced in animals 3 days after portal vein ligation, but this reduction was not sustained in animals at later time intervals. Sikuler et al. (8) have demonstrated a changing sequence of hemodynamic events occurring with time after portal vein ligation ranging from a reduction in splanchnic blood flow within the first few days to a new steady state characterized by raised splanchnic inflow 7 days after portal vein ligation. However, the extent to which these changes are reflected in the perfusion of the gastric mucosa has not been clearly defined in a sequential study. This study and that of Manabe et al. (4) show that gastric mucosal blood flow is reduced within the first 3 days of portal vein ligation, and these findings are in keeping with the theory that the increased resistance to portal blood flow produced by portal vein ligation has the dominant effect on the level of gastric mucosal perfusion during this acute period. In contrast to animals with acute prehepatic portal hypertension, total gastric blood flow as measured with radiolabeled microspheres has been reported to be unchanged (7) or increased (1,6) in animals with
Values are mean of- SEM. ’ Ratio
chronic prehepatic portal hypertension. Only two previous studies have measured gastric mucosal blood flow in this experimental condition, to our knowledge, both of which, reported it to be increased (5,6). In the present study, gastric mucosal blood flow was essentially equal in portal hypertensive and control animals 7 days postoperatively, whereas at 28 days there was a 23% increase in the
Table 4. Ratio of ‘%-Labeled
Iodoantipyrine Concentration in Luminal and Basal 200-pm Regions of Corpus Mucosa Portal vein ligated
3 days 7 days 28 days
0.377k 0.027 0.326k 0.037 0.307Ii0.022
Sham operated 0.364k 0.068 0.353k 0.013 0.338k 0.042
Ratios are of luminal to basal regions in each comparison. There was no significant difference in the ratio of tracer concentration in luminal and basal corpus mucosa between portal vein-ligated and control groups at any study interval.
Figure 2. Autoradiograph taken from transverse section of stomach in a 28-day portal vein-ligated animal. There was no significant difference in the ratio of luminal to basal tracer concentration in corpus mucosa between portal hypertensive and control animals at any of the study periods.
November
1989
GASTRIC MUCOSAL BLOOD FLOW IN PORTAL HYPERTENSION
level of perfusion in the portally hypertensive group, although this difference did not reach statistical significance. The evidence is therefore unanimous that gastric mucosal blood flow is at least preserved in chronic prehepatic models of portal hypertension, but is in conflict over whether it is increased. These studies in both acute and chronic prehepatic portal hypertension support the concept suggested by Sikuler et al. (8) that portal vein ligation produces a temporal change in splanchnic hemodynamics, and it is possible that this change is due to the release of splanchnic vasodilators such as glucagon into the systemic circulation via portasystemic collateral vessels (17), which we have shown to attain a maximum 7 days after portal vein ligation (18). Although total gastric blood flow may be increased in experimental portal hypertension (1,2) there is evidence to suggest that a redistribution of blood flow may occur within the gastric wall. The existence of arteriovenous shunting has been demonstrated using silicone cast techniques in the gastric submucosa of patients with portal hypertension (15), whereas Manabe and colleagues (4) have shown, using radioactive microspheres, that a 19.5% magnitude arteriovenous shunting was present in the gastric submucosa of rabbits 24 h after portal vein ligation. In similar fashion, that study also showed submucosal shunting in animals with experimental cirrhosis and these results suggest that gastric mucosal hypoperfusion could occur despite an increase in total gastric blood flow. Our study shows, irrespective of the existence of gastric submucosal arteriovenous shunting, that gastric mucosal blood flow is at least preserved in animals with chronic portal hypertension, and these results are consistent with the findings of Benoit et al. (6) in animals studied 10 days after portal vein ligation. It has been suggested (19) that redistribution of blood flow may occur within the gastric mucosa itself, giving rise to differences in flow between the superficial and deep portions of the gastric mucosa in portal hypertension. As discussed, the distribution of iodoantipyrine in corpus mucosa is not uniform across the width of the mucosal layer for reasons that may be unrelated to variations in blood flow. Hence, this technique is not ideally suited to studying differences in flow between superficial and deep mucosa. However, any such variations that occur in association with portal hypertension would be expected to alter the distribution of blood flow tracer, whereas we found the concentration gradient across the width of the mucosa to be similar in portal vein-ligated and sham-operated animals at all three study intervals. This study also examines the effect of portal hypertension on the regional distribution of gastric
1113
blood flow with specific reference to flow in (a) crests and valleys of gastric mucosal folds, (b) corpus and antral mucosa, and (c) basal and luminal aspects of corpus mucosa. Mersereau and Hinchey (20) reported that transmucosal potential difference was reduced on the crests of gastric folds, which they suggested could be associated with a local perfusion defect, but our experiments show no evidence of hypoperfusion in mucosal crests in either portal hypertensive or control animals. Although flow tended to be higher in the crests of mucosal folds, there was no significant difference in flow either in mucosal crests or valleys between portally hypertensive and control groups. The level of perfusion to antral mucosa was higher compared with corpus mucosa in both portal vein-ligated and sham-operated animals at all study intervals. There was no significant reduction in antral mucosal or muscle blood flow in the s-day portal vein-ligated group compared with controls. Therefore, mucosal hypoperfusion at this period in portal hypertensive animals was exclusive to corpus mucosa. One interesting finding in this study was the change in the level of mucosal perfusion with time after laparotomy. This finding contrasts with that of Sikuler et al. (8), who demonstrated little change in splanchnic blood flow in sham-operated animals during this period. The results of the present study, however, were limited to the measurement of gastric blood flow, which represents a small fraction of total splanchnic blood flow. We have found (unpublished observations) that taurocholate-induced gastric mucosal injury is increased in animals 3 days after sham operation compared with nonoperated controls in association with a reduction in gastric mucosal blood flow. Animals studied 7 days after sham operation have a reduction in mucosal susceptibility to injury when compared with nonoperated controls. We are unaware of any studies examining the more long-term effects of laparotomy on either gastric mucosal blood flow or susceptibility to injury. This study shows that the acute rise in portal venous pressure shortly after portal vein ligation is associated with a stagnant gastric corpus mucosal microcirculation, and this result is consistent with reports that gastric mucosal susceptibility to injury is increased in acute prehepatic portal hypertension (1921). In contrast, animals with chronic portal hypertension had no reduction in gastric mucosal blood flow. It remains to be seen what effect raised portal pressure has on gastric mucosal susceptibility to injury at later intervals after portal vein ligation. References 1. Vorobioff J, Bredfeldt JE, Groszmann RJ. Hyperdynamic culation in portal hypertensive
cirrat model: a primary factor for
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2.
3.
4.
5.
6.
7. 8.
9. 10.
11.
12.
GERAGHTY ET AL.
maintenance of chronic portal hypertension. Am J Physiol 1983;244:G52-7. Vorobioff J, Bredfeldt JE, Groszmann RJ. Increased blood flow through the portal system in cirrhotic rats. Gastroenterology 1984;87:1120-6. Benoit JN, Womack WA, Hernandez L, Granger DN. Forward and backward flow mechanisms in portal hypertension. Gastroenterology 1985;89:1092-6. Manabe T, Suzuki T, Monjo I. Changes of gastric blood flow in experimentally induced cirrhosis of the liver. Surg Gynecol Obstet 1978;147:753-7. Pique JM, Lenng FW, Kitahora T, Sarfeh IJ, Tarnowski A, Guth PH. Gastric mucosal blood flow and acid secretion in portal hypertensive rats. Gastroenterology 1988;95:727-33. Benoit JN, Womack WA, Kurthins RJ, Wilborn WH, Granger DN. Chronic portal hypertension: effects on gastrointestinal blood flow distribution. Am J Physiol 1986;250:G535-9. Blanchet L, Lebrec D. Changes in splanchnic blood flow in portal hypertensive rats. Eur J Clin Invest 1982;12:1002-7. Sikuler E, Kravetz D, Groszmann RJ. Evolution of portal hypertension and mechanisms involved in its maintenance in a rat model. Am J Physiol 1985;248:G618-25. Halvorsen JF, Myking AO. Prehepatic portal hypertension in the rat. Eur Surg Res 1979;11:89-98. Chojkier M, Groszmann RJ. Measurement of portal systemic shunting in the rat using gamma-labelled microspheres. Am J Physiol 1981;240:G371-5. Angerson WJ, Geraghty JG, Carter DC. An autoradiographic study of regional distribution of gastric mucosal blood flow. Am J Physiol 1988;254:G566-74. Hudson D, Scremin OU, Guth PH. Measurement of regional gastroduodenal blood flow with iodo [“Cl antipyrine autoradiography. Am J Physiol 1985;248:C539-44.
GASTROENTEROLOGY Vol. 97, No. 5
13. Kety SS. The theory and applications 14.
15. 16.
17.
18.
19.
20. 21.
of the exchange of inert gas at the lungs and tissues. Pharmacol Rev 1951;3:1--41. Quintero E, Pique JM, Bombi JA, et al. Gastric mucosal vascular ectasias causing bleeding in cirrhosis. Gastoenterology 1987;93:1054-61. Hashizume M, Tanaka K, Inokudi K. Morphology of gastric microcirculation in cirrhosis. Hepatology 1983;3:1008-12. Tarnowski A, Sarfeh IJ, Strachura J, Hajduczek A, Bui I-IX. Portal hypertensive gastropathy or vasculopathy (abstr)? Gastroenterology 1987;92:1786. Benoit JN, Zimmerman B, Premen AJ, Go VLW, Granger DN. Role of glucagon in splanchnic hyperaemia of chronic portal hypertension. Am J Physiol 1986;251:G674-7. Geraghty JG, Angerson WJ, Carter DC. Portal venous pressure and portasystemic shunting in experimental portal hypertension Am J Physiol 1989;257:G52-7. Sarfeh IJ, Tarnowski A. Gastric mucosal vasculopathy in portal hypertension (editorial). Gastroenterology 1987;93: 1129-31. Mersereau WA, Hinchey EJ. Role of gastric mucosal folds in formation of focal ulcers in the rat. Surgery 1982;91:150-5. Sarfeh IJ, Tarnowski A, Malki A, Mason GR, Mach T, Ivey KJ. Portal hypertension and gastric mucosal injury in rats. Gastroenterology 1983;84:987-93.
Received December 19, 1988. Accepted May 8, 1989. Address requests for reprints to: James G. Geraghty, University Department of Surgery, Royal Infirmary, Glasgow G3l 2ER, Scotland, United Kingdom. This work was supported by grants from the Scottish Hospitals Endowment Research Trust and from the Fraser Foundation. The authors thank Sheelah Smith and Graeme Fyffe for technical assistance, and Margaret Tosh for typing the manuscript. They also thank Professor A. Murray Harper and staff for access to the Quantimet image analyzer.