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B H Pannen

Publications and source records attributed to B H Pannen.

13 recordsLinked to original sources
PubMed1998

Role of endothelins and nitric oxide in hepatic reperfusion injury in the rat.

We determined the functional role of nitric oxide (NO) and endothelins (ET), two potent vasoactive mediator systems in the liver, for the pathogenesis of sinusoidal perfusion failure and lethal hepatocyte injury after low-flow ischemia/reperfusion in the isolated perfused rat liver. NO synthase blockade with Nomega-nitro-L-arginine methyl ester (L-NAME) (10[-3] mol/L) before reperfusion prevented increased N02-/NO3- the final products of NO oxidation, which could be observed in the vehicle group. Epifluorescence microscopy revealed that the decrease in functional sinusoid density during reperfusion was much more profound compared with vehicle. This was associated with a lower surface PO2, a substantially higher number of nonviable hepatocytes, as assessed by in situ propidium iodide staining, and enhanced enzyme release into the perfusate compared with vehicle. In contrast, reperfusion in the presence of the endothelinA+B receptor antagonist bosentan (2 x 10(-4) mol/L) restored functional sinusoid density and surface PO2 to baseline values, resulted in a small reduction in the number of propidium iodide-positive hepatocytes, and caused similar increases in enzyme release as compared with vehicle. This indicates that hepatic generation of NO attenuates sinusoidal perfusion failure and improves liver tissue oxygenation, thus limiting hepatocyte injury during early reperfusion after hepatic low-flow ischemia. In contrast, endothelins counteract the microcirculatory effects of NO, i.e., mediate the no-reflow in hepatic sinusoids; however, the restoration of functional sinusoid density with bosentan resulted only in a small reduction in tissue damage, suggesting that additional components, which are independent of microcirculatory failure, contribute to hepatic reperfusion injury under these conditions.

Animals↗
PubMed1998

Expression pattern of heme oxygenase isoenzymes 1 and 2 in normal and stress-exposed rat liver.

Heme oxygenase (HO) catalyzes the oxidative cleavage of the alpha-mesocarbon of Fe-protoporphyrin-IX yielding equimolar amounts of biliverdin-IXa, iron, and carbon monoxide. The HO-system consists of two isoenzymes, namely HO-2 and the inducible isoform HO-1, also referred to as heat shock protein (hsp) 32. Although both parenchymal and non-parenchymal liver cells participate in heme metabolism, the expression pattern of the isoenzymes in normal and stress exposed liver is unknown. To study this, rats underwent either endotoxin (lipopolysaccharide [LPS]) challenge, hemorrhagic hypotension, glutathione (GSH) depletion, or cobalt chloride injection, all known to provoke oxidative stress. HO-2 messenger RNA (mRNA) and protein were constitutively expressed in hepatocytes, Kupffer/endothelial-, and stellate (Ito-) cell enriched fractions. Although both non-parenchymal cell fractions expressed HO-1 transcripts, HO-1 immunoreactive protein was restricted to Kupffer cells in the normal liver. In contrast to HO-2, a significant increase in HO-1 on the whole organ level was noted by hemorrhagic hypotension, GSH depletion, and cobalt chloride injection. However, the distinct stress models led to a strikingly different cell-type specific and sublobular expression pattern of HO-1 gene expression. HO-1 was inducible in sinusoidal lining cells (hemorrhagic hypotension, LPS challenge), in periportal (cobalt chloride), or pericentral (GSH depletion, hemorrhagic hypotension) hepatocytes. The blockade of protein translation before hemorrhage by cycloheximide reduced upregulation of HO-1/hsp32 mRNA significantly (65.4% reduction, P < .05), whereas the inducibility of hsp70 transcript was maintained. In addition to transcriptional regulation, HO-1 seems to be subject to posttranscriptional control in particular in non-parenchymal cells.

Animals↗
PubMed1998

Differential regulation of hepatic arterial and portal venous vascular resistance by nitric oxide and carbon monoxide in rats.

Nitric oxide (NO), a gaseous mediator that accounts for the biological activity of endothelium-derived relaxing factor, has been shown to play an important role in the reduction of basal vascular tone in multiple vascular beds, including the hepatic circulation. On the other hand, recent studies have provided first evidence that endogenously generated carbon monoxide (CO) may exert vasodilatory effects in the hepatic portal vein and within sinusoids. Thus, we defined the differential role of NO and CO in the regulation of vascular resistance in the two inflows to the liver in the normal rat in vivo. Male Sprague-Dawley rats were anesthetized with pentobarbital sodium and surgically instrumented in order to study the change in hepatic arterial (Rha) and portal venous vascular resistance (Rpv) in response to intravenous bolus administration of either the NO-synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) (1 mg/kg; n = 7 animals) or of tin protoporphyrin-IX (SnPP-IX) (50 micromol/kg), a specific inhibitor of the CO-generating enzyme heme oxygenase (n = 8 animals). While L-NAME caused a substantial increase in Rha, Rpv increased only slightly under these conditions. In sharp contrast, SnPP-IX did not affect Rha, but caused a profound increase in Rpv. In conclusion, Rha and Rpv are differentially regulated by NO and CO in the normal rat liver in vivo, i.e., NO serves as a potent vasodilator in the hepatic arterial circulation, but exerts only a minor vasodilatory effect in the portal venous vascular bed. In contrast, while there is no intrinsic CO-mediated vasodilation in the hepatic artery, CO acts to maintain portal venous vascular tone in a relaxed state.

Animals↗
PubMed1997

Remodeling of hepatic microvascular responsiveness after ischemia/reperfusion.

Although there is substantial evidence suggesting that the integrity of the microcirculation is an important determinant of tissue viability during reperfusion after ischemia in the liver, as well as other tissues, the mechanisms responsible for microvascular failure are not fully understood. It is now recognized that the microvascular response to reperfusion, similar to the whole organism response to shock, can consist of either a rapid exacerbation of injury after a severe ischemic episode or, alternatively, a more slowly developing alteration in responsiveness that occurs after a less severe insult. In the more slowly developing response, the alterations in vascular status are the result of up-regulation of stress-induced vascular mediators such as endothelin, nitric oxide synthase (NOS), and heme oxygenase, as well as changes in the reactivity of the effector cells to the mediators. The mechanisms for change in reactivity of vascular cells range from changes in receptor expression to overt phenotypic transformation, as can occur in the hepatic stellate cells in response to repeated injury. When maintained in balance, these counteracting constrictor and dilator influences can be protective; however, local imbalance can result in focal ischemia, thus propagating the injury. Thus, the remodeling of the hepatic microvascular responsiveness during reperfusion after ischemia may serve as a useful paradigm for consideration of the overall response of the organism to shock.

Animals↗
PubMed1997

Regulation of hepatic blood flow during resuscitation from hemorrhagic shock: role of NO and endothelins.

We determined the role of nitric oxide (NO) and endothelins (ETs) in the regulation of hepatic blood flow during resuscitation from hemorrhagic shock (HS) in anesthetized rats. Volume resuscitation restored systemic hemodynamics and increased hepatic arterial and portal venous flow above baseline in the vehicle group. Presence of N omega-nitro-L-arginine methyl ester (L-NAME, 1 mg/kg) during resuscitation increased systemic vascular resistance (SVR) above baseline, prevented the restoration of hepatic arterial flow, and abolished portal hyperemia. Although the ETA+B-receptor antagonist bosentan (10 mg/kg) did not alter the systemic hemodynamic response, it abolished the hepatic arterial and portal hyperemia. The ETA-receptor antagonist BQ-610 (150 micrograms/kg) reduced SVR below baseline, allowed hepatic arterial hyperemia to occur, and further enhanced the portal venous hyperemia. This indicates that 1) NO reduces SVR and acts to preserve hepatic blood flow during resuscitation from HS; 2) ETA-receptor-mediated vasoconstriction counteracts the systemic and portal hemodynamic effects of NO; and 3) simultaneous ETB-receptor stimulation enhances blood flow to the liver and may serve to modulate the ETA-receptor-mediated vasoconstrictive effects of ETs.

Animals↗
PubMed1996

Evidence for a functional link between stress response and vascular control in hepatic portal circulation.

Heme oxygenase (HO)-derived carbon monoxide (CO) may contribute to vascular control through elevation of guanosine 3',5'-cyclic monophosphate. In the present study, we investigated the functional significance of expression of the isoenzyme HO-1 (heat-shock protein 32) in liver after hemorrhage/resuscitation (H/R) in rats anesthetized with pentobarbital sodium. An increase of mRNA levels for HO-1 was observed at 3 h after resuscitation, followed by induction of the protein at 6 h in pericentral hepatocytes and sinusoidal lining cells. Concomitantly, lower portal resistance was observed in H/R (0.33 +/- 0.060 mmHg.ml-1.min) compared with control rats (0.47 +/- 0.035 mmHg.ml-1.min). Blockade of the HO-CO pathway by tin protoporphyrin-IX (SnPP-IX) led to a transient increase in portal pressure with no effect on portal low in controls, whereas an increase in pressure and a decrease in flow contributed to the sustained increase in portal resistance after H/R. These results indicate that HO contributes to maintenance of hepatic perfusion in vivo under stressful conditions, suggesting a functional link between stress response and vascular control in portal circulation.

Animals↗
PubMed1996

Endotoxin pretreatment enhances portal venous contractile response to endothelin-1.

To test whether endotoxin pretreatment modulates the portal hemodynamic response to endothelin (ET)-1 and phenylephrine (PE), two potent vasoconstrictors in the portal circulation of the normal liver, rats received intraperitoneal injections of Escherichia coli lipopolysaccharide (LPS; 1 mg/kg body wt) or saline. Livers were isolated after 6 or 24 h and perfused with Krebs buffer containing 5% autologous erythrocytes. Analyses of portal pressure-flow (P-Q) relationships and epifluorescence video microscopy were performed before and after ET-1 (10(-9) M) or PE (10(-5) M) administration. LPS pretreatment increased total portal resistances (Rt), zero-flow pressures (PQ = 0), and linear regression slopes of P-Q relationships, and decreased the sinusoidal diameters (Ds) and sinusoidal volumetric flow (Qv). The response to ET-1 was enhanced 6 and 24 h after LPS administration, leading to greater increases in Rt, PQ = 0, and slope and more pronounced decreases in Dx, red blood cell velocity (VRBC), and Qv. In contrast, PE effects were similar (PQ = 0, slope, Ds) or even attenuated (Rt, VRBC, Qv) in livers from LPS-treated compared with control animals. Thus endotoxin pretreatment increased the portal contractile response to ET-1 but not to PE. This enhanced ET-1 response appeared to occur at sinusoidal and presinusoidal levels and may contribute to endotoxin-induced hepatic microcirculatory failure.

Animals↗
PubMed1996

A time-dependent balance between endothelins and nitric oxide regulating portal resistance after endotoxin.

To test whether endothelins are involved in the regulation of portal resistance after endotoxin pretreatment and whether their effects are modulated by nitric oxide (NO), rats received intraperitoneal injections of Escherichia coli lipopolysaccharide (LPS, 1 mg/kg body wt) or saline. Six and twenty-four hours later, livers were isolated and perfused. Analyses of portal pressure-flow (P-Q) relationships and epifluorescence microscopy were performed before and after administration of 1) the NO synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 10(-3) M), followed by L-arginine (2 x 10(-3) M), or 2) the endothelin ETA/ETB-receptor antagonist bosentan (2 x 10(-4) M), followed by L-NAME (10(-3) M). LPS pretreatment increased all measures of resistance, which included total portal resistance, zero flow, incremental resistance (slopes of P-Q relationship), and sinusoid resistance. L-NAME had no effect in sham controls but increased all measures of resistance at 6 h after LPS and increased total and incremental resistance 24 h after LPS. L-Arginine reversed these changes. Bosentan reduced total and sinusoid resistance slightly in control livers and caused substantial reductions in all measures of resistance at 6 and 24 h after LPS; these were partially reversed after L-NAME at 6 but not at 24 h. Our data support the hypothesis that a critical balance between endothelin-mediated vasoconstrictor influences and NO-mediated vasodilator influences controls portal resistance after endotoxin pretreatment.

Animals↗
PubMed1995

Hepatic heat shock and acute-phase gene expression are induced simultaneously after celiotomy in the anesthetized pig.

BACKGROUND: The liver plays a central role in the whole organism's response to injury. Expression of hepatic acute-phase and heat-shock genes likely contributes to the restoration of homeostasis after stressful events. However, after prolonged ischemia, hepatic transcription of heat-shock genes can exclude the simultaneous transcription of acute-phase genes. The issue of whether hepatic 72-kd heat-shock protein (hsp72) gene expression is induced under perioperative conditions that do not result in prolonged liver ischemia and whether this might further affect the expression of the acute-phase reactant inter-alpha-trypsin inhibitor (alpha-Ti) was examined. METHODS: Pigs were anesthetized with sodium pentobarbital and ketamine hydrochloride, tracheally intubated, and their lungs ventilated. After celiotomy, a hepatic biopsy sample was obtained. Arterial blood pressure, cardiac output, and total hepatic blood flow were measured. Subsequent biopsies were obtained at 1, 2, 3, 4, and 6 h after the initial biopsy. Arterial norepinephrine concentrations were measured using high-pressure liquid chromatography. Nuclear runoff (run on) analysis and Northern blotting were applied to estimate changes in hsp72 and alpha-Ti gene transcription rates and RNA levels. Western blotting was used to estimate changes in hsp72 levels. RESULTS: Hemodynamic parameters did not change significantly over time. Arterial norepinephrine concentrations were increased at all time points. Hepatic hsp72 RNA levels increased up to sixfold while nuclear runoff assays did not detect significant changes in hsp72 gene transcription rates. The increases in hsp72 RNA levels correlated with accumulation of hsp72 (up to sevenfold). Increases in alpha-Ti transcription rates up to 42-fold were associated with respective increases in alpha-Ti RNA levels (up to 17-fold). CONCLUSIONS: These data demonstrate that hepatic expression of hsp72 is not confined to conditions that lead to prolonged liver ischemia but is also part of the response of the liver to surgery under general anesthesia. Furthermore, these conditions are permissive for the simultaneous RNA expression of the acute-phase reactant alpha-Ti.

Abdomen↗
PubMed1995

Chronic ethanol consumption exacerbates liver injury following hemorrhagic shock: role of sinusoidal perfusion failure.

Although the deleterious effect of chronic ethanol consumption on subsequent stressful events has long been recognized, the pathophysiological mechanisms are incompletely understood. This study tested whether chronic ethanol consumption in doses that increase sinusoidal contractility increases susceptibility to hepatic microvascular failure and liver injury after hemorrhagic shock. Liver microcirculation was assessed by in vivo microscopy during hemorrhage and up to 24 h after onset of resuscitation and was compared with liver histology and serum enzyme levels. Mean sinusoidal blood flow was neither impaired by chronic ethanol feeding at baseline nor during hemorrhage and early resuscitation. However, failure of individual sinusoids to conduct flow was observed more frequently after fluid resuscitation in ethanol-fed animals (e.g. at 1 h after onset of volume therapy: 26% of sinusoids) than in controls (11%), reflecting substantial flow heterogeneity. Failing sinusoids had substantially smaller diameters than sinusoids conducting flow with a more profound and sustained response in ethanol-fed rats. At 24 h marked pericentral necrosis and increase in serum alanine aminotransferase levels were observed in six of nine surviving ethanol-fed animals but only in 1 of 10 pair fed controls and correlated with microvascular failure. These data suggest that early as well as late microvascular failure in this model of hemorrhagic shock and resuscitation is primarily mediated at the level of individual sinusoids. Chronic ethanol feeding exacerbates microvascular and hepatocellular injury after shock/resuscitation, probably involving increased sinusoidal contractile responsiveness.

Alanine Transaminase↗
PubMed1995

The acute-phase response.

Inflammation and tissue injury elicit profound changes in the concentrations of several plasma proteins. These proteins are predominantly synthesized in the liver and named acute-phase proteins. The regulatory mechanisms that control this response are highly complex and include the release of various mediators affecting specific subsets of acute-phase genes. Individual mediators can either synergistically enhance or inhibit the effects of other mediators. Binding of mediators to their respective receptors on hepatocytes and transduction of this signal induce changes in acute-phase protein gene expression that are primarily regulated on a transcriptional level. However, under certain conditions post-transcriptional mechanisms may also be involved in this process. Although some acute-phase proteins have been shown to minimize tissue damage, as well as to participate in hemostasis, tissue repair, and regeneration in response to injury, the actual in vivo functions of several acute-phase reactants remain speculative. Measurements of acute-phase protein plasma concentrations can be of diagnostic or prognostic value under certain clinical conditions. Further characterization of the regulatory mechanisms that govern the acute-phase response in vivo could lead to the development of new therapeutic strategies aimed at improving the organism's integrated response to injury.

Acute-Phase Proteins↗
PubMed1995

Chronic ethanol consumption increases hepatic sinusoidal contractile response to endothelin-1 in the rat.

Recent evidence suggests that hepatic stellate cells function as liver-specific pericytes that are highly contractile in response to endothelin-1 (ET-1). Liver injury has been shown to lead to "activation" of stellate cells producing a phenotypic change to a more myofibroblastic cell type including loss of vitamin A and increased contractility. The present study was undertaken to test the effects of short-term chronic ethanol consumption (36% of total calories for 5 weeks according to the Lieber-DeCarli protocol) on hepatic vitamin A storage, expression of smooth muscle alpha-actin, and sinusoidal contractility in Sprague-Dawley rats. Using in vivo epifluorescence video microscopy, we quantified the number of sites of vitamin A fluorescence (purportedly stellate cells) and assessed sinusoidal microhemodynamics at baseline and during a 20-minute infusion period of ET-1 (1 pmol * 100 g body weight [bw]*1*min-1). Retinol and retinyl palmitate were measured after the experiment by means of high-pressure liquid chromatography (HPLC). A highly significant decrease in liver retinyl palmitate level (control: 622.5 +/- 50.9; ethanol: 273.0 +/- 38.0 microgram/g liver; P< .001) was found that correlated with a decrease in sites of vitamin A fluorescence (control: 531.4 +/- 76.1; ethanol: 141.1 +/- 30.2* mm-2; r = .82, P <.001). Concomitantly scattered expression of smooth muscle alpha-actin in sinusoids was observed. Although sinusoidal hemodynamics were not affected at baseline, a significant increase in sinusoidal contractility on endothelin-1 infusion (e.g., sinusoidal resistance [% of baseline value]: control: 10 minutes: 288.7 +/- 71.7, 20 minutes: 200.5 +/- 46.9; ethanol: 10 minutes: 1,916.0 +/- 701.7, 20 minutes: 656.8 +/- 103.3; P < .05 and .01, respectively) was observed. These data indicate that chronic ethanol consumption in this moderate model initiates stellate cell activation. Increased sinusoidal responsiveness to the vasoconstrictor ET-1 in vivo may contribute to the increased susceptibility of ethanol-fed rats to secondary stresses that increase ET-1 expression, such as endotoxemia.

Actins↗