Hepatic denervation alters hemodynamic response to hemorrhage in conscious rats

Different uptake of 123I-MIBG in the two main liver lobes: A persistant unsolved mistery

PURPOSE

After radiopharmaceutical injection, a heightened ¹²³I-MIBG concentration is frequently observed in the left hepatic lobe compared to the right one, but the reason of this finding remains unknown. Our aim was to retrospectively analyze the different ¹²³I-MIBG uptake pattern between the two hepatic lobes and correlate our results with some epidemiological/clinical features.

MATERIAL AND METHODS

Ninety-four ¹²³I-MIBG scintigraphies from 71 patients were selected. Regions of interest were drawn in the right and left lobes using transverse tomographic sections and left to right activity ratios (L/R ratio) were calculated at 6 and 24h after radiotracer administration.

RESULTS

Twenty-seven examinations were positive for hypermetabolic lesions while the remaining 67 were negative. In all cases mean early and delayed L/R ratios were greater than 1.00; average early L/R ratio was 1.37 and delayed L/R ratio 1.52. The delayed L/R ratio was significantly higher than the early one. There was no difference in the L/R ratios with regard to age, gender, primary disease and result of scintigraphy.

CONCLUSIONS

¹²³I-MIBG uptake was higher in left hepatic lobe compared to right and this ratio did not correlate with any epidemiological or clinical feature. The reason of this metabolic is not yet explained and some biomolecular hypotheses could be tested in 3D dynamic in vitro models.

Crystalloid flush with backward unclamping may decrease post-reperfusion cardiac arrest and improve short-term graft function when compared to portal blood flush with forward unclamping during liver transplantation

During liver transplant (LT), the release of vasoactive substances into the systemic circulation is associated with severe hemodynamic instability that is injurious to the recipient and/or the post-ischemic graft. Crystalloid flush with backward unclamping (CB) and portal blood flush with forward unclamping (PF) are two reperfusion methods to reduce reperfusion-related cardiovascular perturbations in our center. The primary aim of this study was to compare these two methods. After institutional review board (IRB) approval, cadaveric whole LT cases performed between 2003 and 2008 were reviewed. Patients were divided into two groups based on reperfusion methods: CB or PF. After background matching with propensity score, the effect of each method on post-operative graft function was assessed in detail. In our cohort of 478 patients, CB was used in 313 grafts and PF in 165. Thirty-day graft survival was lower, and risk of retransplantation was higher in PF. Multivariable model showed that CB is an independent factor to reduce primary non-function, cardiac arrest and improve 30-d graft survival. Also, the incidence of ischemic-type biliary lesions was significantly higher in the PF group. Reperfusion methods affect intraoperative hemodynamics and post-transplant outcome. CB allows for control over temperature and composition of the perfusate, perfusion pressure, and the rate of infusion.

Transplanted liver: consequences of denervation for liver functions

Following liver transplantation, all hepatic nerves are transected; thus, liver allografts are completely isolated from neural control of their hosts. Despite this absolute denervation, liver allograft function does not appear to be significantly impaired after successful transplantation. In experimental animal models, hepatic denervation has no major effects on bile acid production and biotransformation, while it increases blood pressure and salt retention; decreases the number of hepatic progenitor cells, cholangiocyte proliferation, and liver regeneration; and influences the hepatic microcirculation, diet behavior, and glycemic control. In humans, hepatic denervation after liver transplantation has no major deleterious effects on bile secretion, liver regeneration, and hepatic blood flow. Insulin resistance and postprandial hyperglycemia, changes in ingestion behavior, and reduced stimulation of hepatic progenitor cells in the canals of Hering are the major side effects of absent liver innervation. Despite these abnormalities, patients can lead a new life with improved quality of life.

The effect of pregnancy on the response to blood loss in a rat model

STUDY OBJECTIVES

A commonly held belief is that the blunted hemodynamic response to hemorrhage observed in pregnant women is secondary to expanded blood volume. In addition to increased blood volume, pregnancy is also a vasodilated state. Vasodilatation may have deleterious effects on the response to hemorrhage by inhibiting central blood shunting after blood loss. How these conflicting variables of increased blood volume and vasodilatation integrate into a whole body model of maternal hemorrhagic shock has yet to be studied in a controlled experiment. We tested the null hypothesis that there would be no difference in the hemodynamic and metabolic responses to hemorrhage between pregnant (PRG) and non-pregnant (NPRG) rats.

METHODS

Twenty-four adult female Sprague-Dawley rats (12 PRG and 12 NPRG) were anesthetized with Althesin via the intraperitoneal route. Femoral arteries were cannulated by cut-down. Twelve (six PRG and six NPRG) rats underwent controlled catheter hemorrhage of 25% of their total blood volume. Twelve rats (six PRG and six NPRG) served as non-hemorrhage controls. Mean arterial pressure (MAP) and base excess (BE) were measured pre-hemorrhage and then every 15 min post-hemorrhage for the next 90 min. Data were reported as mean+/-standard error of the mean (S.E.M.) over the 90-min post-hemorrhage observation period. Group comparisons were analyzed by ANOVA with repeated values post-hoc by Bonferroni. Statistical significance was defined by an alpha=0.05.

RESULTS

PRG and NPRG rats were evenly matched for MAP (P=0.788) and BE (P=0.146) pre-hemorrhage. Post-hemorrhage there were no mortalities in either group. Post-hemorrhage both the PRG and NPRG groups experienced significant (P=0.011) drops in systolic and diastolic blood pressures as compared to their non-hemorrhage controls. Post-hemorrhage there was no significant (P=0.43) difference in MAP between the PRG (89+/-2 mmHg) and NPRG (80+/-2 mmHg) rats. BE also dropped significantly within both PRG (P=0.004) and NPRG (P=0.001) groups post-hemorrhage. No significant (P=0.672) difference was noted in BE between PRG and NPRG groups post-hemorrhage -6.1+/-0.3 mEq/l and -6.9+/-0.4 mEq/l, respectively.

CONCLUSION

After a controlled hemorrhage of 25% of total blood volume we found no significant differences in MAP and BE between pregnant and non-pregnant rats. Pregnancy does not affect the response to hemorrhage.

Effect of dopamine infusion on hemodynamics after hepatic denervation

BACKGROUND

. The effects of dopamine (DA) on systemic hemodynamics are better understood than its effects on hepatic hemodynamics, especially after liver denervation occurring during liver transplantation. Therefore, a porcine model was used to study DA's effects on hemodynamics after hepatic denervation.

MATERIALS AND METHODS

Fifteen pigs underwent laparotomy for catheter and flow probe placement. The experimental group (n = 7) also underwent hepatic denervation. After 1 week, all pigs underwent DA infusion at increasing doses (3-30 mcg/kg/min) while measuring hepatic parameters [portal vein flow (PVF), hepatic artery flow (HAF), total hepatic blood flow (THBF = HAF + PVF), portal and hepatic vein pressures] and systemic parameters [heart rate (HR), mean arterial pressure (MAP)].

RESULTS

There was a significant increase in HAF from baseline to the 30 mcg/kg/min DA infusion rate (within-subjects P < 0.01), but the differences between the two groups were not significant. PVF and THBF showed large effects (increases) with denervation, but the increase in flow with DA infusion was not present after denervation. Perihepatic pressures were unchanged by denervation or DA. Heart rate differed significantly between the control and denervated animals at baseline, 3, 6, 12 (all P < 0.05), and 30 mcg/kg/min DA (P = 0.10). Control vs denervation MAP at baseline was 100 +/- 4 vs 98 +/- 4 Torr and at 30 mcg/kg/min it was 110 +/- 3 vs 101 +/- 5 mm Hg.

CONCLUSIONS

Hepatic flows tended to be higher after denervation. HAF showed similar increases with DA in both control and denervation groups. Increases in PVF and THBF with DA infusion were not present after denervation. HR was significantly decreased and MAP tended to be lower after denervation. The HR and MAP response to DA was similar in both groups. Therefore, both denervation and DA infusion have an effect on systemic and hepatic hemodynamics.

Hepatic denervation induces supersensitivity to terbutaline of the hepatic arterial system in conscious dogs

The effects of hepatic denervation on liver blood flow and the influence of the denervation on the hemodynamic response to exogenously administered agents remain equivocal. This study examined the effects of the beta 2-adrenoceptor agonist, terbutaline, on liver blood flow and how these effects were influenced by surgical hepatic denervation in a conscious canine model. Two weeks after denervation, hepatic arterial flow, portal venous flow, and aortic blood flow were measured during intravenous infusion of terbutaline at 0.1, 0.2, 0.4, and 0.8 microgram/kg/min, and responses were compared between the hepatic denervated and sham-operated dogs. Implantable transit-time ultrasonic flowmeter and probes were used. Hepatic arterial flow increased dose-dependently in response to terbutaline in denervated dogs, while it remained unchanged in control dogs except at the highest dose of terbutaline. The increase in hepatic arterial flow of denervated dogs was significantly greater than that of controls at all doses of terbutaline. Aortic blood flow-indexed hepatic arterial flow in response to terbutaline also differed substantially between the two groups. Terbutaline produced a marked dose-dependent increase of portal venous flow similarly in both groups. These results suggest that the beta 2-adrenoceptor agonist terbutaline should be effective for increasing liver blood flow and could lessen postoperative liver ischemia. We speculate that hepatic denervation induces supersensitivity of the hepatic arterial system to intravenous terbutaline.

Hemodynamic changes in blood flow through the denervated liver in pigs

We investigated the effects of liver denervation on hemodynamic circulation in seven anesthetized pigs. Simultaneous measurements of the hepatic artery and portal vein were performed with an ultrasound Doppler flow meter before and after liver denervation. Neither resting systemic nor hepatic hemodynamics changed following liver denervation. However, temporary occlusion of the portal vein resulted in a significant increase in hepatic artery flow in the innervated liver (from 123 +/- 15 ml/min to 177 +/- 17 ml/min, p < .01), whereas, in the denervated liver, a significant decrease was observed (from 128 +/- 11 ml/min to 106 +/- 19 ml/min, p < .05). Thus, the reciprocity between the hepatic artery and portal vein in the hepatic artery flow during portal vein occlusion might intensify symptoms of portal vein thrombosis in liver transplantation. In the denervated liver, a significant decrease also occurred in systolic blood pressure and central venous pressure from 1 to 3 min after portal vein occlusion. Since the liver plays a crucial role in the maintenance of cardiovascular homeostasis during blood loss, it is likely that denervation at the porta hepatis induced a lack of vasoconstriction in the portal territory. Liver denervation might further exacerbate this response to hypotension. The current study confirms that the hepatic nerves play an important role in hepatic arterial and portal venous interactions aimed at maintaining a constant blood flow through the liver. We also suggest that the hepatic nerves are important for cardiovascular homeostasis.

Effect of orthotopic transplantation and chemical denervation of the liver on hepatic hemodynamics in the rat

The involvement of the sympathetic nervous system in the control of basal hepatic hemodynamics was investigated. Hepatic denervation was achieved by orthotopic transplantation or chemical denervation of the organ. In male Lewis rats, transplantation with rearterialization of the graft was performed. Chemical denervation was achieved by intraportal injection of 6-hydroxydopamine (75 mg/kg). Normal liver physiology was confirmed by histology and liver function tests. Four weeks post-transplantation and 7 days post-denervation, histological examination revealed no differences between transplanted, denervated and untreated or sham-operated control animals. Liver function measured by standard tests (e.g., plasma SGOT, bilirubin) was normal in all groups. The rate constants for aminopyrine breakdown in transplanted (0.015 +/- 0.005 min-1), denervated (0.015 +/- 0.0012 min-1) and control rats (0.015 +/- 0.001 min-1) were not significantly different. No significant difference in the rate of galactose breakdown was found. Total liver blood flow (measured by the 133Xe clearance technique in the anesthetized animal) was unaffected by transplantation (rate constant, 0.245 +/- 0.062 min-1; control 0.279 +/- 0.011 min-1). The interlobular distribution of portal blood flow was tested by intraportal injection of 51Cr-labelled microspheres. A linear relationship between flow to lobe and lobe size was confirmed in control (r = 0.95), denervated, (r = 0.99) and transplanted rats (r = 0.97) and the 'relative' flow to each lobe was not significantly different in the 3 groups. No significant differences in the 'core' to 'periphery' distribution of portal blood flow were found in the 3 groups. A small but significant portal systemic shunt was found in transplanted but not denervated or control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective sympathectomy of the liver: a comparison of orthotopic liver transplantation and intraportal 6-hydroxydopamine injection

1. Tissue noradrenaline (NA) levels correlate well with the extent of sympathetic innervation of that tissue. 2. In this study the distribution of NA throughout the different lobes of the rat liver was studied. The extent of sympathectomy by means of either orthotopic liver transplantation (OLT) (n = 7) or chemical denervation by intraportal administration of 6-hydroxydopamine (6-OH-DA) (n = 8) was examined. 3. In the normally innervated rat liver, NA was homogeneously distributed throughout the organ. Tissue NA was decreased both by OLT (> 99%) and 6-OH-DA (93%) (both P < 0.001 versus control). 4. Samples of the renal cortex and left ventricle were taken as reference tissues. OLT did not result in any change in reference tissue NA, however, 6-OH-DA decreased renal cortex NA by 93% and ventricular NA by 76%, respectively (both P < 0.01 versus OLT). 5. We conclude that OLT causes selective and complete hepatic sympathectomy but that 6-OH-DA causes incomplete denervation of the liver and significant denervation of other organs.

Liver denervation, 5-HT3 receptor antagonist, and intake of imbalanced amino acid diet

The serotonin3 receptor antagonist ICS 205-930 (ICS) may act peripherally to attenuate the anorectic response of rats given an imbalanced amino acid (IMB) diet. Rats were divided into four groups: SHAM+saline (sal); SHAM+ICS; total liver denervation (TLD) + sal; and TLD+ICS. Rats were then given a purified basal diet for 16 days. Next, the groups were injected with sal or 9 mg/kg BW of ICS at 0800 h and at 0900 h (lights out) an isoleucine IMB diet was presented. By 12 h postinjection, the food intake (FI) of TLD and SHAM rats receiving ICS was similarly higher (p < 0.02) than sal-injected counterparts whose FI was also similar; BW followed FI. By day 3, the SHAM groups had similar low FI, whereas the FI of the TLD groups was increasing. The above study was repeated with similar results. Liver innervation is not required for ICS attenuation of IMB diet-induced hypophagia. Also, while sal-injected TLD rats show a normal attenuation of consumption of the IMB diet on the first day of exposure, they subsequently consume more of the IMB diet than SHAM rats. The reason for this difference in TLD rats is not clear but may be related to metabolism of the IMB diet or possibly learning.

Immunohistochemical studies on the innervation of human transplanted liver

The changing pattern of innervation in the human transplanted liver was studied from the day of transplantation to 5 years later. Seven liver biopsies from non-transplant controls, 37 liver biopsies from 22 transplant patients, and one of these biopsied livers removed at retransplantation, were available for the study. Sections were immunostained for protein gene product 9.5 (PGP 9.5), neurone-specific enolase (NSE), S-100 protein, and vasoactive intestinal polypeptide. NSE and PGP 9.5 demonstrated nerves most successfully in our tissues. Staining for most small nerves was reduced by day 5 post-transplantation. Scanty fine nerves could be detected from day 13 to day 241 in occasional biopsies. Consistently identifiable immunostaining of PGP 9.5 and NSE nerve fibres was again apparent in portal areas after this time in all but one case. The findings indicate that in transplanted liver limited reinnervation can eventually take place. This could be due to either proliferation of intrinsic nerves, or regrowth of extrinsic nerves, or both.

The effect of liver denervation on hepatic hemodynamics during hypovolemic shock in swine

This study tested the hypothesis that the denervated liver is more susceptible to hypovolemic shock than the normal liver. Fourteen swine, seven nondenervated and seven after liver denervation, were studied during hypovolemic shock to 50% of baseline blood pressure. Hepatic artery and portal vein flows were measured using transonic flow probes, and cardiac output and central venous pressure were measured using Swan-Ganz catheters. Hepatic artery flow fell equivalently in the two groups, from 132 +/- 71 to 94 +/- 17 ml/min in the nondenervated group compared with 149 +/- 56 to 91 +/- 55 ml/min in the denervated group. In contrast, portal flow in the denervated group (276 +/- 71 to 119 +/- 53 ml/min) fell significantly (p less than 0.001) more than in the nondenervated group (289 +/- 135 to 194 +/- 70 ml/min). The 58% reduction from baseline in portal flow in the denervated group compared with the 30% reduction in the nondenervated group suggests that the normal compensatory mechanism to maintain portal flow during hypovolemic shock is neurally mediated. It can be hypothesized that sensory afferent fibers might initiate a feedback to splanchnic vasodilatation in response to reduced portal flow. This study supports the hypothesis that the denervated liver is more susceptible to hypovolemic shock.

Differential influence of laboratory anaesthetic regimens upon renal and hepatosplanchnic haemodynamics in the rat

Renal blood flow in rats anaesthetized with the combination alphaxolone/alphadolone (3.90 mL min-1 (g tissue)-1) was significantly (P less than 0.05) greater than in rats anaesthetized with ketamine midazolam (3.24 mL min-1 (g tissue)-1, pentobarbitone (3.19 mL min-1 (g tissue)-1), fentanyl/fluanisone midazolam (2.84 mL min-1 (g tissue)-1) or urethane (1.99 mL min-1 (g tissue)-1). Renal blood flow in the urethane anaesthetized rats was significantly (P less than 0.05) lower than in animals anaesthetized with the other anaesthetic regimens, and is consistent with literature reports of a depressive effect of urethane anaesthesia upon xenobiotic renal clearance in the rat. Hepatosplanchnic blood flow was highest in the alphaxolone/alphadolone anaesthetized animals (71.7 mL min-1 kg-1), with the urethane anaesthetized animals demonstrating a significantly (P less than 0.05) lower (33.4 mL min-1 kg-1) blood flow. The fentanyl fluanisone/midazolam (65.4 mL min-1 kg-1), pentobarbitone (61.1 mL min-1 kg-1), and ketamine/midazolam (51.4 mL min-1 kg-1) regimens resulted in hepatosplanchnic blood flows of intermediate magnitude. The observed marked differential effects of the anaesthetic regimens upon renal and hepatosplanchnic blood flows may dramatically influence drug disposition in the experimental animal, and be of significance to laboratory pharmacokinetic studies in which anaesthesia is used.