Pressure-flow relationships and effects of noradrenaline and isoprenaline on the hepatic arterial and portal venous vascular beds of the dog

Stomach, liver, kidney and skeletal muscle autoregulation evaluated by near-infrared spectroscopy in a swine model

PURPOSE

Different organs have different autoregulatory capacities for blood pressure changes and/or circulatory volume changes. This study assessed the autoregulation of the stomach, liver, kidney and skeletal muscle, under baseline, hypovolemic, and post-fluid-resuscitation conditions using near-infrared spectroscopy (NIRS).

METHODS

Ten pigs (bodyweight 24.5 ± 0.5 kg) were anesthetized with 2.5% isoflurane and administered 0.5, 1, 2 and 5 µg kg^- 1 min^- 1 of phenylephrine at 10-min intervals, followed by similar stepwise infusion of sodium nitroprusside (SNP) to induce a wide range of mean arterial pressures (MAPs). A 600-ml bleed was induced to create the hypovolemic condition, and only phenylephrine was re-administered. Hydroxyethyl starch (600 ml) was infused to create the post-fluid-resuscitation condition, and phenylephrine and SNP were re-administered. Average relationships between mean arterial pressure (MAP) and each tissue oxygenation index (TOI) were assessed, and the individual relationships were evaluated based on the correlation coefficients between MAP and TOI during each vasoactive drug infusion.

RESULTS

Based on the evaluation using each TOI as a substitute of blood flow, the kidney autoregulation was robust, similar to muscle, but had a prominent lower limit. The stomach had weaker autoregulation than the kidney and muscle. The liver had no autoregulation. The kidney TOI showed 2-fold greater changes in response to volume condition changes than the stomach and liver TOIs.

CONCLUSION

In our NIRS-based assessment of autoregulatory capacity, the liver oxygenation is highly blood pressure dependent, and the kidney is highly susceptible and the skeletal muscle is highly tolerable to low blood pressure and volume loss.

Effect of norepinephrine infusion on hepatic blood flow and its interaction with somatostatin: an observational cohort study

Background

Norepinephrine (NE) is a α₁-adrenergic mediated vasopressor and a key player in the treatment of perioperative hypotension. Apart from modulating systemic hemodynamics, NE may also affect regional blood flow, such as the hepatic circulation, which contains a wide variety of adrenergic receptors. It may alter regional vascular tonus and hepatic blood flow (HBF) by reducing portal vein flow (PVF) or hepatic arterial flow (HAF). The aim of this study was to assess the effects of NE on HBF.

Methods

Patients scheduled for pancreaticoduodenectomy were included. All patients received standardized anesthetic care using propofol and remifentanil and were hemodynamically stabilized using a goal-directed hemodynamic strategy guided by Pulsioflex™. On surgical indication, somatostatin (SOMATO) was given to reduce pancreatic secretion. HBF measurements were performed using transit-time ultrasound (Medistim™). Baseline hemodynamic and HBF measurements were made after pancreatectomy, at T1. Afterwards, NE infusion was initiated to increase mean arterial pressure (MAP) by 10 – 20% of baseline MAP (T2) and by 20 – 30% of baseline MAP (T3). HBF and hemodynamic measurements were performed simultaneously at these three time-points.

Results

A total of 28 patients were analyzed. Administration of NE significantly increased MAP but had no effect on cardiac index. NE infusion reduced total HBF in all patients (p < 0.01) by a reduction HAF (p < 0.01), while the effect on PVF remained unclear. Post-hoc analysis showed that SOMATO-treated patients had a significant lower PVF at baseline (p < 0.05), which did not change during NE infusion. In these patients, reduction of total HBF was primarily related to a reduction of HAF (p < 0.01). In untreated patients, NE infusion reduced total HBF both by a reduction HAF (p < 0.01) and PVF (p < 0.05).

Conclusion

Administration of NE reduced total HBF, by decreasing HAF, while the effect on PVF remained unclear. SOMATO-treated patients had a lower PVF at baseline, which remained unaffected during NE infusion. In these patients the decrease in total HBF with NE was entirely related to the decrease in HAF. In SOMATO-untreated patients PVF also significantly decreased with NE.

Trial registration

Study protocol EC: 2019/0395.

EudraCT n°: 2018–004,139-66 (25 – 03 – 2019).

Clin.trail.gov: NCT03965117 (28 – 05 – 2019).

The effects of terlipressin and direct portacaval shunting on liver hemodynamics following 80% hepatectomy in the pig

Liver failure is the major cause of death following liver resection. Post-resection portal venous pressure (PVP) predicts liver failure, is implicated in its pathogenesis, and when PVP is reduced, rates of liver dysfunction decrease. The aim of the present study was to characterize the hemodynamic, biochemical, and histological changes induced by 80% hepatectomy in non-cirrhotic pigs and determine if terlipressin or direct portacaval shunting can modulate these effects. Pigs were randomized (n=8/group) to undergo 80% hepatectomy alone (control); terlipressin (2 mg bolus + 0.5-1 mg/h) + 80% hepatectomy; or portacaval shunt (PCS) + 80% hepatectomy, and were maintained under terminal anesthesia for 8 h. The primary outcome was changed in PVP. Secondary outcomes included portal venous flow (PVF), hepatic arterial flow (HAF), and biochemical and histological markers of liver injury. Hepatectomy increased PVP (9.3 ± 0.4 mmHg pre-hepatectomy compared with 13.0 ± 0.8 mmHg post-hepatectomy, P<0.0001) and PVF/g liver (1.2 ± 0.2 compared with 6.0 ± 0.6 ml/min/g, P<0.0001) and decreased HAF (70.8 ± 5.0 compared with 41.8 ± 5.7 ml/min, P=0.002). Terlipressin and PCS reduced PVP (terlipressin = 10.4 ± 0.8 mmHg, P=0.046 and PCS = 8.3 ± 1.2 mmHg, P=0.025) and PVF (control = 869.0 ± 36.1 ml/min compared with terlipressin = 565.6 ± 25.7 ml/min, P<0.0001 and PCS = 488.4 ± 106.4 ml/min, P=0.002) compared with control. Treatment with terlipressin increased HAF (73.2 ± 11.3 ml/min) compared with control (40.3 ± 6.3 ml/min, P=0.026). The results of the present study suggest that terlipressin and PCS may have a role in the prevention and treatment of post-resection liver failure.

[Results of the modified Appleby procedure]

AIM

To evaluate safety and efficacy of distal pancreatectomy with en bloc celiac artery resection (DP-CAR) for pancreatic malignancy.

MATERIAL AND METHODS

Medical reports of 17 patients who underwent DP-CAR procedure (15 of them with pancreatic malignancy) were retrospectively analyzed. Also we studied 27 publications describing more than 2 cases of DP-CAR.

RESULTS

R0- and R1-resection was performed in 14 (82%) and 3 (18%) patients respectively. Postoperative complications ware observed in 11 (65%) cases. Nine of them were successfully treated. Full pain control was achieved in all patients. There were no any ischemic complications. 16 patients received chemotherapy. 2 (11%) patients died in early postoperative period due to aortic dissection in 10 days and fungal sepsis in 44 days after surgery. Median survival was 20 months. Literature review included 27 articles describing 311 operations. Herewith postoperative complications developed in 43% of cases and 90-day postoperative mortality was 4%. Median survival ranged from 9.3 to 26 months.

CONCLUSION

DP-CAR is effective and safe procedure in certain patients with locally advanced pancreatic cancer.

The role of hepatic arterial flow on portal venous and hepatic venous wedged pressure in the isolated perfused CCl4-cirrhotic liver

In cirrhosis, hepatic venous pressure gradient is used to measure portal venous and sinusoidal pressures, as well as drug-induced decreases of elevated pressures. The aim of this study was to investigate the influence of hepatic arterial flow (HAF) changes on portal venous perfusion (PVPP) and wedged hepatic venous pressure (WHVP). Normal and CCl4-cirrhotic rats were subjected to a bivascular liver perfusion with continuous measurements of PVPP, WHVP, and hepatic arterial perfusion pressure. Flow-pressure curves were performed with the use of different flows either through the portal vein (PVF: 20-32 ml/min) or HAF (5-15 ml/min). Increases in HAF lead to significant absolute and relative increases in PVPP (P = 0.002) and WHVP (P < 0.001). Absolute changes in HAF correlated to absolute changes in PVPP (cirrhosis: r = 0.64, P < 0.001; control: r = 0.67, P < 0.001) and WHVP (cirrhosis: r = 0.71, P < 0.001; control: r = 0.82, P < 0.001). Changes in PVPP correlated to changes in WHVP due to changes in PVF only in cirrhosis (r = 0.75, P < 0.001), whereas changes in HAF correlated in both cirrhosis (r = 0.92, P < 0.001) and control (r = 0.77, P < 0.001). In conclusion, increases and decreases in HAF lead to respective changes in PVPP and WHVP. This suggests a direct influence of HAF on PVPP and WHVP most likely due to changes in sinusoidal perfusion.

A model of hydraulic interactions in liver parenchyma as forces behind the intrahepatic bile flow

The small diameters of bile canaliculi and interlobular bile ducts make it hard to attribute the bile flow solely to the process of secretion. In the model liver within its capsule is considered a limited space in which volume expansions of one part are possible only through the shrinking of other parts. The liver capsule allows only very slow volume changes. The rate of blood flow through the sinusoides is governed by the Poisseuill-Hagen law. The model is based on a concept of circulatory liver units. A unit would contain a group of acini sharing the same conditions of arterial flow. We can imagine them as an acinar group behind the last pressure reducer on one arterial branch. Acini from neighboring units compose liver lobules and drain through the same central venule. One lobule can contain acini from several neighboring circulatory units. The perfusion cycle in one unit begins with a transient tide in the arterial flow, governed by local mediators. Corresponding acini expand, grabbing the space by compressing their neighbors in the same lobules. Vascular resistance is reduced in dilated and increased in compressed acini. Portal blood flows through the dilated acini, bypassing the compressed neighbors. The cycle ends when the portal tide slowly diminishes and acinar volume is back on the interphase value until the new perfusion cycle is started in another circulatory unit. Each cycle probably takes minutes to complete. Increased pressures both in dilated and in compressed acini force the bile to move from acinar canalicules. Both up and down changes in acinar volume might force the acinar biliary flow. In cases of arterial vasoconstriction, increased activity of vasoactive substances would keep most of the circulatory units in the interphase and increased liver resistance can be expected. Liver fibrosis makes all acini to be of fixed volume and result in increased resistance. Because of that, low pressure portal flow would be more compromised, as reported. In livers without arterial blood flow, although some slow changes in the portal flows can be expected, acinar volume changes should be reduced. In acute liver injury, enlarged hepatocytes would diminish sinusoidal diameter and increase acinar resistance. In liver tumors, areas of neovascularization with reduced resistance would divert the arterial flow from the normal tissue, while in the compressed perifocal areas, increased vascular resistance should diminish mainly the portal flow.

Organ blood flow after partial hepatectomy in rats: modification by endotoxin-neutralizing bactericidal/permeability-increasing protein (rBPI23)

BACKGROUND/AIM

Both maintenance of adequate perfusion and regeneration of the remnant liver are important in the recovery of liver function after partial hepatectomy. In previous experiments, we have shown that profound hypotension and liver injury can be attenuated by neutralizing endotoxins. The relative contribution of endotoxemia to changes in liver blood flow and blood flow to other major organs after partial hepatectomy is not known. The aim of this study was to examine the effect of endotoxin neutralization on individual organ blood flows including hepatic artery and splanchnic blood flow after experimental partial hepatectomy and its relation to liver cell proliferation.

METHODS

Male Wistar rats underwent either two-thirds partial hepatectomy or sham operation. Treatment consisted of continuous infusion of recombinant N-terminal bactericidal/permeability-increasing protein (rBPI23) or control protein. At 4 h after surgery, organ blood flows were measured using the radiolabeled microsphere technique, and at 24 h, proliferation index in liver tissue was calculated.

RESULTS

After partial hepatectomy, blood flows to virtually all organs were significantly lower as compared to values obtained in sham-operated rats. rBPI23 greatly improved hepatic artery flow (p<0.001) but not portal venous flow. These effects of rBPI23 on liver flow preceded an equally enhanced liver cell proliferation (p<0.01). Endotoxin neutralization led to significantly higher flows to some but not all splanchnic organs. Lung perfusion was significantly improved by rBPI23.

CONCLUSIONS

Neutralization of endogenous endotoxins improves liver blood flow after partial hepatectomy and also periportal and pericentral liver cell proliferation. This proliferation effect may result from an increased hepatic artery flow. Lung, colon, spleen and pancreas flow but not kidney flow was greatly enhanced by rBPI23.

Preserved arterial flow secures hepatic oxygenation during haemorrhage in the pig

1. This study examined the extent of liver perfusion and its oxygenation during progressive haemorrhage. We examined hepatic arterial flow and hepatic oxygenation following the reduced portal flow during haemorrhage in 18 pigs. The hepatic surface oxygenation was assessed by near-infrared spectroscopy and the hepatic metabolism of oxygen, lactate and catecholamines determined the adequacy of the hepatic flow. 2. Stepwise haemorrhage until circulatory collapse resulted in proportional reductions in cardiac output and in arterial, central venous and pulmonary wedge pressures. While heart rate increased, pulmonary arterial pressure remained stable. In addition, renal blood flow decreased, renal vascular resistance increased and there was elevated noradrenaline spill-over. Further, renal surface oxygenation was lowered from the onset of haemorrhage. 3. Similarly, the portal blood flow was reduced in response to haemorrhage, and, as for the renal flow, the reduced splanchnic blood flow was associated with an elevated noradrenaline spill-over. In contrast, hepatic arterial blood flow was only slightly reduced by haemorrhage, and surface oxygenation did not change. The hepatic oxygen uptake was maintained until the blood loss represented more than 30 % of the estimated blood volume. At 30 % reduced blood volume, hepatic catecholamine uptake was reduced, and the lactate uptake approached zero. 4. Subsequent reduction of cardiac output and portal blood flow elicited a selective dilatation of the hepatic arterial vascular bed. Due to this dilatation liver blood flow and hepatic cell oxygenation and metabolism were preserved prior to circulatory collapse.

Localisation of hepatic vascular resistance sites in the isolated dual-perfused rat liver

The locations of the vascular resistance sites which regulate vascular tone in the hepatic arterial and portal venous vasculatures of the rat liver were identified using a new, in vitro, dual-perfused liver preparation. Twelve livers of male Wistar rats were perfused via the hepatic artery and portal vein at fixed flow and at physiological pressure. Dose-related vasoconstriction to injections or infusions of noradrenaline was measured as transient or sustained increases in perfusion pressure, respectively, in the hepatic arterial and portal venous vasculatures. Direct injections/infusions of noradrenaline refer to those administered into the vasculature from which pressure was recorded, e.g., the effects of hepatic arterial (direct) injections/infusions of noradrenaline upon hepatic arterial perfusion pressure. Indirect injections/infusions of noradrenaline were those administered to the adjacent afferent vasculature, e.g., the effects of portal venous (indirect) injections of noradrenaline upon hepatic arterial perfusion pressure. The converse applies for recordings of portal venous perfusion pressure. The -log(M) ED50 values to direct (hepatic arterial) and indirect (portal venous) injections in the hepatic artery were 4.25+/-0.20 and 3.40+/-0.10, respectively, and were significantly different (P < 0.01, Student's unpaired t-test); the -log(M) ED50 values to direct (portal venous) and indirect (hepatic arterial) injections in the portal vein were 3.91+/-0.08 and 3.85+/-0.11, respectively, and were not significantly different (P > 0.05, Student's unpaired t-test). Similarly, the -log(M) ED50 values to direct (hepatic arterial) and indirect (portal venous) infusions in the hepatic artery were 5.28+/-0.11 and 3.75+/-0.12, respectively, and were significantly different (P < 0.01, Student's unpaired t-test); the -log(M) ED50 values to direct (portal venous) and indirect (hepatic arterial) infusions in the portal vein were 5.31+/-0.19 and 5.70+/-0.16, respectively, and were not significantly different (P > 0.05, Student's unpaired t-test). These results demonstrated that there is little transfer of noradrenaline from the portal venous to the hepatic arterial resistance sites, but significant transfer from the hepatic artery to the portal venous suggesting that; (a) the portal venous resistance sites are located at the sinusoidal or post-sinusoidal level; and (b) the hepatic arterial resistance sites are located at the pre-sinusoidal level.

Differential effects of dobutamine, dopamine, and noradrenaline on splanchnic haemodynamics and oxygenation in the pig

Supranormal oxygen (O2) transport may benefit critically ill patients. Catecholamines are clinically employed for this purpose. However, their effects on splanchnic haemodynamics and oxygenation are now well defined. The effects of dobutamine (DOBU), dopamine (DOPA), and noradrenaline (NA) on splanchnic blood flows electromagnetic flow probes), O2 deliveries and uptakes (catheterisation of portal and hepatic veins) were studied in nine anaesthetised (ketamine/flunitrazepam), ventilated, paralysed, and laparotomised pigs. All three catecholamines (DOPA at 15 micrograms.kg-1.min-1, DOBU at 13 micrograms.kg-1.min-1, NA at 0.4 micrograms.kg-1.min-1) significantly (P < 0.05) increased cardiac output and systemic O2 delivery. Only DOPA increased small intestinal and total hepatic blood flows, and O2 deliveries, and decreased O2 extractions. The same parameters did not change during DOBU. During NA, total hepatic blood flow and O2 delivery decreased, and hepatic O2 extraction increased. During all three catecholamines, small intestinal and total hepatic O2 uptakes did not change significantly. Whereas hepatic arterial blood flow decreased during both DOPA and NE, portal venous flow increased during DOPA. These data suggest that in the experimental model used splanchnic O2 supply and O2 reserve capacity appear improved by DOPA, unaffected by DOBU, and impaired by NA.

The transhepatic response to noradrenaline in the rabbit liver: the influence of arterioportal pressure gradient

The dose-related responses of the hepatic arterial and portal venous vascular beds to bolus administration of noradrenaline (10(-10)-10(-4) mol), injected into the hepatic artery and portal vein, were studied in the isolated dual-perfused rabbit liver at both basal and raised tone. The transhepatic ratio, defined as the ratio between the intra-arterial molar ED50 dose and the intraportal dose required to give the same arterial response, was calculated for arterial and venous responses to noradrenaline. At basal tone, the transhepatic ratio for hepatic arterial vasoconstrictive responses was 500. Portal venous vasoconstrictive responses were similar in potency independent of injection site but differed significantly in analysis of dose-response slope and maximal response. At raised tone, the arterio-portal pressure gradient increased by 68.5 mmHg and there was a 10-fold increase in the transhepatic ratio for hepatic arterial responses, while the portal venous responses remained unchanged. These results demonstrate that arterio-portal pressure gradient has a powerful effect on transhepatic action of noradrenaline, and suggest a pre-sinusoidal site for the generation of both hepatic arterial and portal venous vascular resistance.

Biochemical and morphological changes in the liver after hepatic artery ligation in the presence or absence of extrahepatic cholestasis

The present study was carried out to investigate the biochemical and morphological changes in the liver after ligation of the hepatic artery (HA) in the presence and in the absence of extrahepatic cholestasis (EHC). The study was conducted on 100 rats divided into four groups of 25 animals each: group 1, sham operation; group 2, hepatic artery ligation (HAL); group 3, bile duct ligation (BDL); and group 4, HAL plus BDL. All animals were sacrificed 7 days after surgery when total bilirubin and fractions, alkaline phosphatase (AP), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were measured in serum and on the inner hepatocyte mitochondrial membrane (IHMM); the incidence of necrosis and the volume fractions of vessels, bile ducts and hepatocytes in the liver were also determined. HAL reduces the relative volumes of bile ducts, with no changes in levels of bilirubin and fractions, AP, ALT, AST and IHMM, but HAL associated with EHC reduces duct proliferation and the liver becomes more vulnerable to necrosis. In conclusion, the normal liver depends on HA flow and this dependence is more evident in the presence of EHC.

Diminished hyperaemic response of the hepatic artery to portal venous occlusion (the buffer response) in Asian hybrid minipigs: a comparison of the response to that observed in dogs

The hyperaemic response of the hepatic artery to portal vein occlusion (the buffer response) and the action of exogenous adenosine upon hepatic artery blood flow was studied in Asian hybrid minipigs as a potential alternative experimental model to that previously developed in dogs. Adenosine produced a dose-dependent hepatic artery vasodilatation, but of lesser extent than that observed in dogs. A greatly diminished buffer response was observed in the pigs compared to that seen in dogs, and could not be replicated consistently. The adenosine uptake inhibitor dipyridamole did not potentiate responses to adenosine or the buffer response. It is concluded that the minipig is an unsuitable alternative model for the study of the hepatic artery buffer response.

The actions of two sensory neuropeptides, substance P and calcitonin gene-related peptide, on the canine hepatic arterial and portal vascular beds

1. The two peptides, calcitonin gene-related peptide (CGRP) and substance P (SP) were administered individually as bolus injections into the separately perfused hepatic arterial and portal vascular beds of the anaesthetized dog to assess their actions and relative molar potencies at these sites. 2. CGRP caused an immediate dose-related increase in hepatic arterial flow when injected close-arterially, reflecting a fall in resistance. This vasodilator effect was slightly increased by the prior administration of the selective beta 2-adrenoceptor antagonist, ICI 118,551. 3. On a molar basis, CGRP was more potent as an hepatic arterial vasodilator than the non-selective beta-adrenoceptor agonist, isoprenaline (Iso). 4. Intra-portal injection of CGRP also evoked hepatic arterial vasodilatation unaccompanied by other cardiovascular changes. 5. CGRP in doses up to 10 nmol had no effect on portal vascular resistance when administered intra-portally. 6. SP evoked a rapid, dose-related increase in hepatic arterial flow when injected intra-arterially. The molar ED50 for this hepatic vasodilatation was 40.2 fmol, significantly less than the ED50 for either CGRP or Iso. SP was the most potent hepatic arterial vasodilator yet examined. The vasodilator effect of SP was slightly potentiated by prior beta 2-adrenoceptor blockade. 7. SP caused hepatic arterial vasodilatation when administered by intra-portal injection; its absolute and relative potency was much reduced. 8. SP when injected intra-portally caused a graded increase in hepatic portal inflow resistance. The molar potency for this portal vasoconstriction was significantly greater than that for noradrenaline (NA); however, the maximum increase in portal resistance was significantly less to SP than to NA.9. In view of the location of the peptides CGRP and SP within the afferent innervation of the liver, it is proposed that they play an important function in controlling the hepatic microvasculature in response to sensory stimuli, particularly those arising from changes in portal blood composition secondary to change in metabolic activity within the gastrointestinal tract (GIT).10. Since the peptides are released from the GIT into the hepatic portal inflow, they may modify hepatic arterial blood flow, the extent of which is related to events within the GIT.

Effect of total hepatectomy on coagulation and glucose homeostasis in the pig

It has been suggested recently that patients with fulminant liver failure should be prepared for transplantation by early hepatectomy, yet the acute effects of removal of the liver upon the coagulation profile and certain hormones are not known. This study was conducted on totally hepatectomized pigs that survived up to 27 hr. Measurements were made of serum insulin, plasma glucagon (IRG and GLI), glucose, catecholamines, and the coagulation profile. The increase in serum insulin was directly related to levels of plasma glucose--there was a 100-fold increase in animals with plasma glucose levels greater than 400 mg/100 ml and none when blood glucose was less than 100 mg/100 ml. Plasma glucagon showed a sharp transient increase within 1 hr of hepatectomy and a slow rise thereafter with levels apparently unrelated to serum insulin or plasma glucose. There was a transient increase in plasma adrenaline but a sharp continuous increase in plasma norepinephrine. No changes of note occurred in the coagulation profile--even levels of fibrinogen only declined by 20% in 27 hr. The study has shown that early total hepatectomy is safe as far as changes in coagulation are concerned but changes in serum insulin and especially plasma norepinephrine may be of more significance.

An isolated dual-perfused rabbit liver preparation for the study of hepatic blood flow regulation

An original, isolated dual-perfused rabbit liver preparation was developed for investigations into mechanisms that control the hepatic vascular tone. The hepatic artery (HA) and portal vein (PV) were perfused at constant flows of 0.16 +/- 0.01 and 0.64 +/- 0.05 mL/g/min (n = 5), respectively. Responses of the hepatic arterial and portal venous vascular beds to noradrenaline (NA) were measured as changes in perfusion pressure. Noradrenaline injected directly into the hepatic artery and portal vein produced dose-dependent increases in pressure in the respective vascular beds, the maximum response in the hepatic arterial bed being two to three times greater than that in the portal venous bed. A restricted transmission of vasoconstrictor stimulus between the intrahepatic portal venous and hepatic arterial vasculature was demonstrated. The results demonstrate the suitability of the dual-perfused rabbit liver model for detailed studies of the control of hepatic vascular tone.

Control of glycogenolysis and blood flow by arterial and portal adrenaline in perfused liver

In isolated liver from fed rats, simultaneously single-pass-perfused via both the hepatic artery (80 mmHg, 30-35% flow) and the portal vein (10 mmHg, 70-65% flow), adrenaline was infused either singly or jointly via the hepatic artery or the portal vein in the absence or presence of the alpha 1-blocker prazosin and the beta 2-blocker butoxamine. It was found that: (1) arterial adrenaline caused increases in glucose and lactate output which were slower in onset, smaller in peak height but longer in duration than did portal adrenaline; (2) arterial adrenaline elicited a much more pronounced decrease in flow and increase in pressure in the ipsilateral vessel than did portal adrenaline, and arterial, but not portal, adrenaline elicited qualitatively similar alterations also in the contralateral vessel; (3) arterial adrenaline caused metabolic changes mainly via alpha 1-receptors, with beta 2-receptors playing a permissive role via haemodynamic alterations, whereas portal adrenaline acted only via alpha 1-receptors; (4) arterial adrenaline decreased arterial flow via alpha 1-receptors counteracted via beta 2-receptors and operated on portal flow as portal adrenaline only via alpha 1-receptors; and (5) arterial adrenaline was extracted to a far greater extent than portal adrenaline. The results indicate that the hepatic artery and the portal vein can function as independent sites of hormonal signal input, which interact by complex, still undefined, mechanisms.

Control of glycogenolysis and blood flow by arterial and portal norepinephrine in perfused liver

In isolated rat liver single pass perfused via both the hepatic artery (80 mmHg, 30% flow) and the portal vein (10 mmHg, 70% flow), norepinephrine (NE) was infused either singly or jointly via the hepatic artery or the portal vein in the absence or presence of the alpha 1-blocker prazosin or the beta 2-blocker butoxamine. Arterial NE caused an increase in glucose output and a shift from lactate uptake to release that was slower in onset and smaller in peak height but longer in duration than the alterations affected by portal NE. The sum of the metabolic changes by arterial and portal NE was not equal to the changes by jointly applied arterial plus portal NE. The metabolic alterations by arterial NE were mediated via alpha 1-receptors, with beta 2-receptors probably having a permissive function, but those by portal NE were transmitted only via alpha 1-receptors. Arterial NE caused a strong decrease in arterial flow and contralaterally also a smaller reduction of portal flow. Portal NE decreased portal flow but did not significantly influence arterial flow. The sum of the alterations in flow by arterial and portal NE was not equal to the changes by jointly applied NE. The hemodynamic alterations in the artery by arterial NE were the results of actions via alpha 1-receptors and counteractions via beta 2-receptors, whereas the changes in the portal vein by arterial NE and portal NE were mediated via alpha 1-receptors. About 65% of arterial and only 30% of portal NE was extracted during a single path. The results indicate that the hepatic artery and the portal vein can function as independent sites of hormonal signal input, which interact by complex but still undefined mechanisms in the regulation of metabolism and hemodynamics.

The actions of human atrial natriuretic factor on hepatic arterial and portal vascular beds of the anaesthetized dog

1. The vascular actions of atrial natriuretic factor (ANF) have been assessed with other vasoactive agents on the hepatic arterial and portal vascular beds of the anaesthetized dog. 2. Intra-arterial bolus injections of ANF (0.1-50 nmol) caused graded increases in hepatic arterial blood flow representing a vasodilatation of relatively short duration. Vasoconstriction was never observed. 3. The maximum increase in hepatic arterial blood was the same for ANF and isoprenaline (Iso) i.e. approximately 60-70% increase over control flow. 4. On a molar basis, ANF was less potent than Iso although over the higher dose range (10(-9)-10(-7) mol) its vasodilator activity exceeded that of the endogenous vasodilator adrenaline. 5. Intraportal bolus injections (1.0-50 nmol) of ANF did not alter portal inflow resistance since no changes in portal inflow pressure occurred when the portal circuit was perfused at constant inflow volume. 6. This differential action of ANF on the hepatic arterial and portal vascular beds may provide a change in total liver blood flow in favour of the arterial component. 7. ANF, by altering hepatic haemodynamics to favour formation of trans-sinusoidal fluid exchange, may provide a temporary expansion of the extravascular fluid reservoir to buffer any increased venous pressure. However, chronically elevated plasma levels of ANF would encourage the formation of ascitic fluid.

Relationship between splenic and superior mesenteric venous circulation

We took advantage of routine hemodynamic examinations to determine the relationship between splenic and intestinal circulation by infusing prostaglandin E1 into the superior mesenteric artery and observing the portal hemodynamic changes in patients with chronic liver disease. Relative blood flow rate in various vessels of the portal system were measured percutaneously using an ultrasonic duplex system, while portal venous pressure was measured directly using a transducer. The superior mesenteric venous blood flow increased significantly as did the portal venous blood flow and pressure, though the degree of change of portal venous blood flow was less than was expected from the change of portal venous blood flow in the superior mesenteric venous blood flow. Splenic venous blood flow decreased significantly. This decrease is perhaps due to a mechanism that acts to compensate for the increase induced in the superior mesenteric venous blood flow to maintain portal flow at approximately the same level. The measured changes suggest a relationship between splenic and intestinal blood flows that is regulated according to the hepatic circulatory condition. The regulatory mechanism should be considered when designing the treatment of portal hypertension.

Ex vivo perfusion for accurate assessment of liver graft viability in dogs

A new type of ex vivo liver perfusion model (EVPM) was developed. The system includes a physiological porto-portal connection, using a centrifugal pump and an aorto-aortal connection, through a heparin-coated tube. Ten pairs of mongrel dogs, weighing 13-20 kg, were used. Grafts of the liver procured from donors were perfused on the EVPM for 3 h. These grafts were divided into two groups: group A (n = 5), nonpreserved graft; group B (n = 5), 8-h graft preserved with lactated Ringer's solution (4 degrees C). The orthotopic liver transplantation (OLTx) series with the nonpreserved graft was reviewed, and dogs surviving for over 7 days following OLTx, group C (n = 5), were selected for liver grafts in the actual OLTx. In comparison with groups A and C, no difference was noted among enzyme levels (sGOT, sGPT, LDH) or in the recovery rate of ATP content in the graft liver tissue after revascularization. There were significant differences between group A and group B after revascularization. This simple and physiological EVPM accurately reflects graft function and hemodynamics in the actual OLTx. Graft viability, as a substitute for OLTx, in large animals can be reliably assessed. This EVPM is expected to contribute to research on events related to liver transplantation.

Hepatic circulation: potential for therapeutic intervention

In recent years, knowledge of the physiology and pharmacology of hepatic circulation has grown rapidly. Liver microcirculation has a unique design that allows very efficient exchange processes between plasma and liver cells, even when severe constraints are imposed upon the system, i.e. in stressful situations. Furthermore, it has been recognized recently that sinusoids and their associated cells can no longer be considered only as passive structures ensuring the dispersion of molecules in the liver, but represent a very sophisticated network that protects and regulates parenchymal cells through a variety of mediators. Finally, vascular abnormalities are a prominent feature of a number of liver pathological processes, including cirrhosis and liver cell necrosis whether induced by alcohol, ischemia, endotoxins, virus or chemicals. Although it is not clear whether vascular lesions can be the primary events that lead to hepatocyte injury, the main interest of these findings is that liver microcirculation could represent a potential target for drug action in these conditions.

Arterial occlusion reduces tumour cell lodgement in the rat liver

The lodgement of tumour cells (TCs) is a key event in the development of metastases in distant organs. Experimental and clinical studies have shown that ligation of the hepatic artery may reduce the mass of established metastases. In the present study the effect of hepatic artery or portal vein occlusion on the early phase of metastasis development, i.e. TC lodgement, was investigated. Occlusion of the hepatic artery immediately before intraportal TC infusion reduced TC lodgement, while a temporary occlusion of the portal vein directly after the TC infusion led to increased TC lodgement. It is speculated that the decrease in TC lodgement after arterial occlusion is due to local increase in blood flow, which might enhance the passage of the TCs through the liver, and to a decrease in pH causing an increased rate of TC destruction. The increased TC lodgement after portal vein occlusion, on the other hand, should mainly be due to flow reduction, promoting TC trapping in the liver microvasculature.

The actions of neuropeptide Y and peptide YY on the hepatic arterial and portal vascular beds of the anaesthetized dog

1. The vascular actions of the two peptides, neuropeptide Y (NPY) and peptide YY (PYY) were compared with the transmitter noradrenaline (NA) on the arterial and portal vascular beds of the in situ liver of the anaesthetized dog. 2. The sole vascular response of the hepatic arterial vasculature to intra-arterial administration of either NPY or PYY was vasoconstriction; the duration of these responses was longer than that to NA. 3. The maximum hepatic arterial vasoconstrictor responses to PYY and to NPY were significantly different and they were both significantly less than the maximum to NA (P less than 0.001). 4. In contrast to its activity on the splenic arterial vasculature PYY was not more potent, on a molar basis, than NPY as an hepatic arterial vasoconstrictor agent. However, both peptides were significantly more potent than NA (P less than 0.005). 5. Neither peptide, when injected intraportally, caused any change in intrahepatic portal inflow resistance. 6. Both peptides when administered intraportally in doses which were free of systemic effects caused hepatic arterial vasoconstriction.

Reduction of intrahepatic vascular space in the pathogenesis of portal hypertension. In vitro and in vivo studies in the rat

To elucidate a possible role for reduction of intrahepatic vascular space in the pathogenesis of portal hypertension, we studied a partially hepatectomized rat model in vitro and in vivo. The in vitro study used livers from normal, 1/3-hepatectomized, and 2/3-hepatectomized rats, and rats with cirrhosis caused by chronic bile duct ligation, for isolated, perfused flow-pressure plotting. Resistance to perfusion increased such that significant differences were found between all groups except the last two, which showed similar resistances. The in vivo study measured splanchnic blood flow by radioactive microspheres and portal pressure in anesthetized sham-operated and 1/3- and 2/3-hepatectomized rats. Although absolute portal tributary blood flows did not change, portal flow per gram of remnant liver showed significant increases: 1.57 +/- 0.32 ml/min X g liver, 2.52 +/- 0.60 ml/min X g liver, p less than 0.01; 3.48 +/- 1.04 ml/min X g liver, p less than 0.01, respectively. Although intrahepatic resistance increased significantly only in the 2/3-hepatectomized group, portal pressures increased significantly in both groups of hepatectomized rats: normal, 7.5 +/- 1.1 mmHg; 1/3-hepatectomized, 9.4 +/- 1.1 mmHg; and 2/3-hepatectomized, 11.1 +/- 1.2 mmHg. Thus, decreased intrahepatic vascular space caused by resection and hepatocellular hypertrophy leads to portal hypertension, thereby suggesting that this reduction in space may be the pathogenic factor common to a number of different theories of portal hypertension.

Interrelationship between splenic and superior mesenteric venous circulation manifested by transient splenic arterial occlusion using a balloon catheter

We examined the hemodynamic changes induced by transient splenic arterial occlusion using a balloon catheter to investigate the hemodynamic effect of transcatheter splenic arterial embolization--a procedure that has been used since its introduction in 1973 as therapy for hypersplenism and more recently for portal hypertension. The blood flow volume was measured in 20 patients with liver disease using an ultrasonic duplex system (Toshiba SAL50A/SDL-01A). The portal venous pressure was also measured via a 3F catheter using a transducer. The catheter was placed in position by substituting it for a 25-gauge needle that had been inserted into the portal vein under ultrasonic guidance percutaneously and transhepatically. Splenic arterial occlusion caused a drop in splenic venous blood flow from 708 +/- 487 to 241 +/- 155 ml per min, in portal venous blood flow from 993 +/- 439 to 807 +/- 419 ml per min and in portal venous pressure from 17.4 +/- 7.2 to 14.4 +/- 6.1 mm Hg. The latter two reductions were less than expected from the decrease in the splenic venous blood flow volume. This phenomenon was caused by an increase in the mesenteric venous blood flow from 475 +/- 126 to 630 +/- 270 mm per min. This increase may be due to a compensatory mechanism under the control of a regulatory loop in the liver or portal vein, and there seems to be a relationship between splenic and intestinal circulation in portal hypertension that maintains hepatic circulation.

Acute hepatic failure after open-heart surgery in children

Acute hepatic failure (AHF) combined with acute renal failure (ARF) is a well-known complication of open-heart surgery in adults. The occurrence of this complication in two children after open-heart surgery for correction of congenital heart disease is reported. Hypotension occurred during the operation and was treated by catecholamine vasopressors. AHF set in during the postoperative course; it was manifested by impaired consciousness, hypoglycemia, hyperbilirubinemia, hyperammonemia, elevated liver enzymes and prolongation of the prothrombin time with failure of hemostasis. ARF also developed in both children. One of the patients survived the acute episode of hepatic failure. The importance of early diagnosis, routine close monitoring, and appropriate selection of vasopressors is emphasized.

Capacitance of the rabbit portal vein and inferior vena cava

1. We used vessel strips and whole vessels in vitro to determine the length-tension and pressure-volume relationships of two veins with similar diameter and wall thickness, the portal vein and inferior vena cava of rabbits. 2. Length-tension studies indicate that longitudinal and circular strips of the portal vein have significantly smaller elastic moduli than similar strips of the inferior vena cava (P less than 0.05). 3. Pressure-volume relationships of intact vessels indicate that pressures greater than 5 mmHg do not produce significant increases in volume of the inferior vena cava, whereas volume of the portal vein increases significantly over a range of pressures from 2 to 15 mmHg. 4. Activation of smooth muscle with noradrenaline reduces the volume of the vena cava at distending pressures less than or equal to 5 mmHg. In contrast, noradrenaline reduces the volume of the portal vein at pressures up to 10 mmHg. During inactivation in calcium-free solution and activation with noradrenaline, the portal vein is more compliant than the inferior vena cava (P less than 0.05). 5. Morphometric studies demonstrate more collagen in the inferior vena cava than in the portal vein. Differences in capacitance of the vessels may be related, in part, to greater collagen content in the inferior vena cava.

A portal-arterial glucose concentration gradient as a signal for an insulin-dependent net glucose uptake in perfused rat liver

Since in the usual perfusion of isolated rat liver via the portal vein an insulin-dependent increase of hepatic glucose uptake could not be demonstrated, the possibility was considered that hepatic glucose uptake might not be a function of the absolute concentration of this substrate but of its concentration gradient between the portal vein and the hepatic artery. Therefore a new method was established for the simultaneous perfusion of isolated rat liver via both the hepatic artery (20-35% flow) and the portal vein (80-65% flow). When glucose was offered in a concentration gradient, 9.5 mM in the portal vein and 6 mM in the hepatic artery, insulin given via both vessels caused a shift from net glucose release to uptake. This insulin-dependent shift was not observed when glucose was offered without a gradient or with an inverse gradient, 6 mM in the portal vein and 9.5 mM in the hepatic artery. Using a portal-arterial glucose gradient as a signal the liver might be able to differentiate between endogenous and exogenous glucose.

Measurement of portal vascular resistance in patients with portal hypertension

Portal vascular resistance was measured percutaneously in 60 patients with chronic liver disease and in 5 control subjects. The portal vascular resistance (PVR) was calculated, using the following equation, from the portal blood flow (QPV), portal venous pressure (PPV), and hepatic venous pressure (PHV): PVR = (PPV - PHV)/QPV. The portal blood flow was measured using an ultrasonic Doppler duplex system, and the portal venous and hepatic venous pressures were measured using percutaneous transhepatic catheterization and venous catheterization, respectively. The wedged hepatic venous pressure was measured by occluding the hepatic venous branch using a balloon catheter. The portal vascular resistance was 0.25 +/- 0.13 mmHg X ml-1 X min X kg body weight (mean +/- SD, n = 5) in the control group, 0.64 +/- 0.29 mmHg X ml-1 X min X kg body wt (n = 13) in the chronic active hepatitis group, 1.34 +/- 0.79 mmHg X ml-1 X min X kg body wt (n = 30) in the cirrhosis group, and 0.85 +/- 0.69 mmHg X ml-1 X min X kg body wt (n = 13) in the idiopathic portal hypertension group.

The comparative effect of administration of substances via the hepatic artery or portal vein on hepatic arterial resistance, liver blood volume and hepatic extraction in cats

Compounds reaching the liver do so via either the hepatic artery or the portal vein. This paper reports on the effectiveness of administration of compounds into these alternate routes for their effects on the hepatic parenchymal cells, the hepatic arterial resistance vessels (blood flow) and hepatic capacitance (blood volume responses). All tests were done on cats under pentobarbital anesthesia. Perfusion of the parenchymal cell mass was assessed by comparing the hepatic elimination of indocyanine green (ICG) administered via the two vascular routes. The ICG uptake was assessed by measuring relative areas under the hepatic venous outflow curve obtained following bolus injections of ICG into the artery and portal vein. In a separate series, using different methods, the hepatic venous levels reached early (2 min) and later (5 min) during a constant infusion were compared during administration via the two routes and found to be equal. Parenchymal cell functions (ICG extraction, bile salt stimulation of bile flow) indicate that blood from the artery and portal vein supplies the hepatic parenchymal cells equally well. This suggests a well-mixed blood supply prior to exposure of either blood stream to parenchymal cells. Substances being processed by the liver are thus equally well handled if reaching the liver via either the arterial or portal blood stream. This has significance in validating the use of some isolated liver perfusion methods that perfuse only via the portal vein. Access of vasoactive compounds in the two blood streams to hepatic arterial resistance vessels was assessed using electromagnetic flow probes.(ABSTRACT TRUNCATED AT 250 WORDS)

The hepatic haemodynamic response to acute portal venous blood flow reductions in the dog

The hepatic haemodynamic response to acute reductions in portal venous blood flow was investigated in 14 anaesthetized normal dogs. A side-to-side mesocaval anastomosis was constructed to enable varying degrees of portal flow to be diverted into the inferior vena cava by suitable manipulations of the shunt diameter. Measurements of portal venous and hepatic arterial blood flow were made with electromagnetic flowmeters. A linear relationship was observed between the degree of reduction in portal flow and the magnitude of the resulting hepatic arterial hyperaemic response. Hepatic arterial vascular resistance showed a decrease which became more pronounced the greater the degree of reduction in portal flow. For every 1.0 ml X min-1 100 g-1 decrease in portal flow, the hepatic arterial flow increased by a mean of 0.24 ml X min-1 X 100 g-1, a value representing the average compensatory capacity of the arterial response. Arterial flow improvement therefore provided some degree of protection against severe falls in total liver blood flow. However, it provided even more effective protection against any fall in total hepatic oxygen consumption, which showed only a very gradual decrease with reduced hepatic portal blood flow.

Erythrocyte uptake by the dog's spleen during splenic venous pressure elevation

The spleens of chloralose-urethane anaesthetized dogs were isolated, placed in a plethysmograph and perfused at constant arterial pressure from a cannulated femoral artery. Splenic venous pressure (PV) was elevated by between 2.5 and 20 cm H2O: it caused pressure-dependent increases in spleen volume of up to 98 +/- 12 ml/100 g spleen weight. The increase in spleen volume could be separated into an initial phase associated with passive distension of capacitance vessels (Phase-1) followed by a more continuous increase in spleen volume (Phase-2). We used techniques designed to distinguish these components of the volume response to PV elevation, and found Phase-2 rates of increase in spleen volume of 5--10 ml min-1 mm Hg-1 100 g-1 expressed in terms of PV elevation and terminal, drained and trimmed spleen weight. Splenic venous haematocrit determination showed selective sequestration of RBCs during the Phase-2 volume response to PV elevation which was related to the extent of the PV elevation. Both the Phase-2 volume response and the haematocrit changes were reduced by splenic nerve stimulation or i.a. infusions of adrenaline but were unaffected by i.a. infusions of bradykinin.

The effects of intraportal infusions of glucagon on the hepatic arterial and portal venous vascular beds of the dog: inhibition of hepatic arterial vasoconstrictor reponses to noradrenaline

The sympathetically-innervated hepatic arterial and portal venous vascular beds of the dog were perfused simultaneously in situ. Glucagon was infused into the hepatic portal vein (1--10 microgram/min); it caused increases in hepatic portal vascular resistance and tended to reduce the hepatic arterial vascular resistance. Extrahepatic effects of intraportal infusions of glucagon included increases in superior mesenteric blood flow and heart rate and falls in systemic arterial pressure. A test dose of noradrenaline (10 microgram) injected into either the hepatic artery or the portal vein caused both hepatic arterial and portal venous vasoconstriction. The hepatic arterial constrictor responses to noradrenaline were antagonized by intraportal infusions of glucagon. In contrast, intraportal glucagon did not antagonize the portal constrictor responses to intraarterial or intraportal noradrenaline. Elevated portal blood glucagon concentrations may "protect" the hepatic arterial blood flow from vasoconstriction due to elevated systemic levels of vasoactive substances including catecholamines.

Responses of the simultaneously-perfused hepatic arterial and portal venous vascular beds of the dog to histamine and 5-hydroxytryptamine

1 The sympathetically-innervated hepatic arterial and portal venous vascular beds of the dog were perfused simultaneously in situ. 2 Histamine and 5-hydroxytryptamine (5-HT) were injected intra-arterially and intraportally in graded, increasing doses. 3 Intra-arterial histamine evoked decreases in hepatic arterial vascular resistance (HAVR) and increases in hepatic portal vascular resistance (HPVR). 4 Intraportal injections of histamine caused increases in HPVR and decreases in HAVR. 5 The time courses of the arterial responses to intraportal histamine and of the portal responses to intra-arterial histamine, compared with any systemic effects, showed that these effects on the liver vasculature could not be the result of recirculation of histamine. 6 Intra-arterial 5-HT evoked biphasic changes in HAVR and small falls in HPVR. Intraportal 5-HT caused falls in HPVR at low doses and rises at high doses, together, typically, with biphasic effects on HAVR. 7 It is unlikely that the arterial effects of intraportal 5-HT and the portal effects of intra-arterial 5-HT were due to recirculation of the vasoactive material. 8 Pathophysiologically, both histamine and 5-HT are released from the gastrointestinal tract into the portal vein. These experiments show that such release may affect the hepatic arterial vascular resistance (and therefore blood flow) even though vasoactive levels of the autacoids are not attained in the systemic circulation.