Influence of nicardipine on post-hypoxic injury in the isolated perfused rat liver.

We investigated microcirculatory changes and hepatocellular injury due to hypoxia/reoxygenation and the effects of nicardipine, a calcium channel blocker, using the isolated perfused rat liver technique. Liver perfusion was carried out in three consecutive phases: 30-min pre-hypoxia perfusion, 120-min hypoxia perfusion and 30-min reoxygenation perfusion in two groups, a control (n = 5) group and a nicardipine group (n = 5). In the nicardipine group, nicardipine (2 x 10(-6) M) was added to the perfusate prior to the hypoxia perfusion. Intrahepatic volumes, sinusoidal volume and extravascular volume accessible to albumin, were assessed by the multiple indicator dilution technique. Though 120-min hypoxia per se caused only a slight increase in the lactate dehydrogenase (LDH) release and no significant alterations in perfusion pressure and intrahepatic volumes, reoxygenation elicited hepatocellular injury assessed by the LDH level in the perfusate along with a substantial increase in perfusion pressure and an increase in extravascular volume. Nicardipine pretreatment attenuated the increase in LDH level, perfusion pressure and intrahepatic volumes after reoxygenation, but there were no difference in liver microcirculation during 120-min hypoxia. The data of the current study emphasized the crucial role of Ca2+ influx in hypoxic/reoxygenation hepatocellular injury and suggested that a direct vasodilating effect of nicardipine on the intrahepatic vasculature during hypoxia is unlikely as the mechanism for its cytoprotective effects.     

Nicotine increases hepatic oxygen uptake in the isolated perfused rat liver by inhibiting glycolysis

Nicotine influences energy metabolism, yet mechanisms remain unclear. Since the liver is one of the largest organs and performs many metabolic functions, the goal of this study was to determine whether nicotine would affect respiration and other metabolic functions in the isolated perfused liver. Infusion of 85 microM nicotine caused a rapid 10% increase in oxygen uptake over basal values of 105 +/- 5 micromol/g/h in perfused livers from fed rats, and an increase of 27% was observed with 850 microM nicotine. Concomitantly, rates of glycolysis of 105 +/- 8 micromol/g/h were decreased to 52 +/- 9 micromol/g/h with nicotine, whereas ketone body production was unaffected. Nicotine had no effect on oxygen uptake in glycogen-depleted livers from 24-h fasted rats. Furthermore, addition of glucose to perfused livers from fasted rats partially restored the stimulatory effect of nicotine. Infusion of atractyloside, potassium cyanide, or glucagon blocked the nicotine-induced increase in respiration. Intracellular calcium was increased in isolated hepatocytes by nicotine, a phenomenon prevented by incubation of cells with d-tubocurarine, a nicotinic acetylcholine receptor antagonist. Respiration was also increased approximately 30% in hepatocytes isolated from fed rats by nicotine, whereas hepatocytes isolated from fasted rats showed little response. In the presence of N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89), an inhibitor of cyclic AMP-dependent protein kinase A, nicotine failed to stimulate respiration. These data support the hypothesis that inhibition of glycolysis by nicotine increases oxygen uptake due to an ADP-dependent increase in mitochondrial respiration.     

Nonlinear pharmacokinetics of tissue-type plasminogen activator in three animal species and isolated perfused rat liver

Tissue-type plasminogen activator (t-PA) is cleared rapidly from the circulation via hepatic catabolism, but the capacity of this process is unknown. In this study, increasing doses of human t-PA were administered to rats, rabbits and marmoset monkeys, and in an isolated perfused rat liver system. t-PA concentrations in plasma and perfusate were analyzed pharmacokinetically using procedures in which nonlinear multicompartment models with Michaelis-Menten elimination were fitted to data sets from all doses simultaneously for each species. Elimination of t-PA was saturable, with Km = 12-15 micrograms/ml and Vmax = 200-350 micrograms/ml/hr in vivo. In isolated rat liver, t-PA elimination capacity was considerably reduced, with Km = 1.5 micrograms/ml and Vmax = 3.7 micrograms/ml/hr. At nonsaturating doses, plasma clearance in vivo was 18-23 ml/min/kg and the dominant half-life was 1.1-2.4 min, compared with 8 ml/min/kg and 4.4 min, respectively, in humans; rat liver perfusate clearance was 0.29 ml/min/g. It is concluded that disposition kinetics of t-PA are very similar across species, extrahepatic clearance may be significant in vivo and clearance capacity becomes limited only at plasma concentrations far in excess of clinical therapeutic values. Nonlinearity is, however, of practical significance in liver perfusion and in animal pharmacology studies utilizing high t-PA doses.     

Effect of ischemic preconditioning on reactive oxygen species-mediated ischemia--reperfusion injury in the isolated perfused rat lung

OBJECTIVE: To investigate the protective effect of ischemic preconditioning (IP) in the early phase of reperfusion injury. DESIGN AND METHODS: Control rat lungs were subjected to 3 h of perfusion, whereas the lungs of the ischemia-then-reperfusion (I/R) group were subjected to 2 h of cold ischemia following 30 min of perfusion. IP was performed by two cycles of 5-min ischemia followed by 5 min of reperfusion prior to 2-h cold ischemia. Lipid peroxidation and antioxidant status were determined in tissue samples. RESULTS: Lipid peroxidation and reduced/oxidized glutathione (GSH/GSSG) ratio were increased; antioxidant enzyme activities were decreased in the I/R group whereas lipid peroxidation and GSH/GSSG ratio were decreased; antioxidant enzyme activities were increased in the IP group. CONCLUSION: IP appeared to have a protective effect against reactive oxygen species-mediated I/R injury in isolated rat lung.     

Release of colony-stimulating activity from the isolated perfused rat liver.

1. Colony-stimulating activity appeared in the perfusate of the isolated rat liver during perfusions with either whole rat blood, rat plasma or an artificial perfusate of Eagle's medium and albumin. 2. Dialysable inhibitors of colony formation were also released during perfusions. 3. Colony-stimulating activity in artificial perfusate could be enhanced by the addition of rat plasma in vitro. Concentrations of cycloheximide that inhibited albumin synthesis by the liver did not inhibit the release of colony-stimulating activity.     

Verapamil and flunarizine protect the isolated perfused rat liver against warm ischemia and reperfusion injury

Using the model of the isolated perfused rat liver, we investigated the influence of the two pharmacologically different calcium channel blockers, verapamil and flunarizine, on changes of ion homeostasis, liver weights, pH deviations and enzyme activities during warm ischemia (37°C) and reperfusion. The LDH and GLDH activities were determined and the calcium, potassium, and sodium concentrations were measured in the effluent. Warm ischemia (180 min) caused an increased enzyme release, a high influx of calcium and sodium into the liver and a massive potassium efflux current. Normoxic reperfusion led to a further increase in hepatic enzyme release and although the loss of potassium ceased, the calcium influx into the liver continued. By the end of reperfusion the liver weight had increased significantly (P<0.01) in the control group. The two calcium entry blockers were added to the perfusate in various concentrations. Both substances protected the liver against warm ischemia and normoxic reperfusion damage, but they did not inhibit calcium inflow. However, the potassium efflux was significantly reduced by all concentration tasted (P<0.001). After reperfusion the liver weights were significantly lower in the treated groups (P<0.001) than in control animals. Thus, the calcium entry blockers verapamil and flunarizine protect liver cells against damage caused by warm ischemia and reperfusion. Furthermore, they prevent the disruption of intracellular potassium homeostasis, which seems to be related to improved volume regulation of liver cells.     

Periportal localization of lorazepam glucuronidation in the isolated perfused rat liver

The relative effects of pretreatment with allyl alcohol and carbon tetrachloride on oxidative and glucuronide metabolism of lorazepam have been compared in the isolated perfused rat liver. Livers from rats pretreated for 24 hr with allyl alcohol (1.8 ml/kg, 1:50 solution, to induce pericentral hepatic necrosis), carbon tetrachloride (0.8 mg/kg in corn oil, to induce perivenular hepatic necrosis), or vehicle were perfused with 20% rat blood, 80% Krebs bicarbonate buffer at 20 ml/min. After 300 micrograms of lorazepam had been added to the reservoir, perfusate concentrations of lorazepam were measured in the perfusate at timed intervals. After 180 min, lorazepam and lorazepam glucuronide were measured in perfusate, bile, and liver homogenate. Allyl alcohol and carbon tetrachloride lowered lorazepam clearance by 47% and 77%, respectively. Recovery of lorazepam glucuronide after 180 min was lowered by 35% by treatment with allyl alcohol and increased 73% by treatment with carbon tetrachloride. Glucuronide recovery permitted estimation of fractional glucuronide vs. nonglucuronide clearance. In control rats, glucuronide clearance accounted for 25% of total clearance. Allyl alcohol caused a 64% reduction in glucuronide clearance but only a 39% reduction in nonglucuronide clearance. In contrast, carbon tetrachloride caused a 60% reduction in glucuronide clearance but an 83% reduction in nonglucuronide clearance. The differences in ratios of the changes in glucuronide and nonglucuronide clearance provide further circumstantial evidence that is consistent with the hypothesis of predominant periportal localization of glucuronidation and pericentral localization of oxidative metabolism of lorazepam.     

Cytosolic and nuclear estrogen receptors in the isolated perfused rat liver

The isolated perfused rat liver was investigated as a potential model to analyze binding of 17 beta-[3H]estradiol (E2) to cytosolic and nuclear estrogen receptors. Viability of the isolated perfused liver was monitored by measuring leakage of cytosolic enzymes into the perfusate. These studies indicated that the liver remained viable for at least a 90-min perfusion period although significant decreases in cytosolic estrogen receptor concentrations occurred during this perfusion period. Estrogen receptor loss was minimized by supplementing the red blood cell-free perfusion medium with 5 micrograms of insulin per ml. Uptake of [3H]E2 by hepatic cytosolic estrogen receptors of the isolated perfused liver was rapid as measured by partial purification of radiolabeled ligand receptor complexes after varying times of perfusion. Peak liver concentrations of receptor-bound E2 were achieved 15 min after the onset of perfusion when using livers from either male or female rats. After 15 min, radiolabeled cytosolic ligand receptor complexes decreased rapidly, reaching lowest concentrations at 60 min. Radiolabeled salt-extractable nuclear-binding sites increased up to 30 min and then decreased slightly between 30 and 90 min. Both 4S and 5S forms of nuclear binding sites were detected in the isolated perfused livers as evaluated by sedimentation analysis on 5 to 20% sucrose density gradients. Concentrations of radiolabeled cytosolic and nuclear receptors were greater in females than males at all perfusion periods examined when the initial concentration of [3H]E2 was 4 nm. Sex differences in receptor uptake were not as great when higher concentrations of [3H]E2 were added to the perfusion medium. These studies suggest that the isolated perfused liver is a suitable model to investigate short-term uptake of estrogens by cytosolic and nuclear receptors.     

Methylprednisolone inhibits low-flow hypoxia-induced mitochondrial dysfunction in isolated perfused rat liver

OBJECTIVE: To investigate the mechanism by which methylprednisolone protects the liver from hypoxia-induced injury. DESIGN: Prospective control study using the isolated rat liver. SETTING: Animal research facility. SUBJECTS: Male, fasted, pathogen-free Sprague-Dawley rats. INTERVENTIONS: Low-flow hypoxia was produced by reducing afferent perfusate pressure from 10 to 2.5 cm H(2)O; isolated livers were portally perfused for 2 hrs. MEASUREMENTS AND MAIN RESULTS: We measured mitochondrial membrane potential and hydrogen peroxide production by imaging rhodamine 123 and 2'-7'-dichlorofluorescein fluorescence, respectively. Leakage of mitochondrial enzymes was also monitored by assaying mitochondrial aspartate aminotransferase activity in the outflow perfusate, and the radical-scavenging effect of methylprednisolone was assessed by measuring luminol-dependent hydrogen peroxide chemiluminescence. Apoptosis in liver cells was determined by using terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick-end labeling. Rhodamine 123 fluorescence was significantly diminished in the hypoxic liver, especially in the region of the terminal hepatic venules, which is indicative of membrane depolarization in the mitochondria in those areas. Hypoxia-induced mitochondrial dysfunction was indicated by leakage of aspartate aminotransferase into the outflow perfusate, and increased 2'-7'-dichlorofluorescein fluorescence indicated increased hydrogen peroxide levels, particularly in the midzone. Pretreatment with 30, 10, or 3 mg/kg of methylprednisolone inhibited the hypoxia-induced mitochondrial membrane depolarization and enzyme leakage, although hydrogen peroxide levels and apoptosis in sinusoidal endothelial cells were unaffected. CONCLUSIONS: Methylprednisolone does not protect the liver from hypoxia-induced injury by suppressing hydrogen peroxide production. Instead, the beneficial effect of methylprednisolone seems to be related to its ability to protect against mitochondrial membrane depolarization under hypoxic conditions.     

Experimental glomerulonephritis in the isolated perfused rat kidney.

The development of immune deposits on the subepithelial surface of the glomerular capillary wall was studied in isolated rat kidneys perfused at controlled perfusion pressure, pH, temperature, and flow rates with recirculating oxygenated perfusate containing bovine serum albumin (BSA) in buffer and sheep antibody to rat proximal tubular epithelial cell brush border antigen (Fx1A). Control kidney were perfused with equal concentrations of non-antibody immunoglobulin (Ig)G. Renal function was monitored by measuring inulin clearance, sodium reabsorption, and urine flow as well as BSA excretion and fractional clearance. Perfused kidneys were studied by light, immunofluorescence, and electron microscopy. All kidneys perfused with anti-Fx1A developed diffuse, finely granular deposits of IgG along the glomerular capillary wall by immunofluorescence. Electron microscopy revealed these deposits to be localized exclusively in the subepithelial space and slit pores. Similar deposits were produced in a nonrecirculating perfusion system, thereby excluding the formation of immune complexes in the perfusate caused by renal release of tubular antigen. Control kidneys perfused with nonantibody IgG did not develop glomerular immune deposits. Renal function and BSA excretion were the same in experimental and control kidneys. Glomerular deposits in antibody perfused kidneys were indistinguishable from deposits in rats injected with anti-Fx1A or immunized with Fx1A to produce autologous immune complex nephropathy. These studies demonstrate that subepithelial immune deposits can be produced in the isolated rat kidney by perfusion with specific antibody to Fx1A in the absence of circulating immune complexes. In this model deposits result from in situ complex formation rather than circulating immune complex deposition.     

Effects of rifampin and isoniazid on the isolated perfused rat liver

The effect of the antitubercular drugs rifampin and isoniazid on the function of the isolated, perfused rat liver was evaluated by monitoring the rate of bile flow and sulfobromophthalein (BSP) clearance. The effect of rifampin on bile flow was biphasic: rifampin concentration of 100 micrograms/ml increased the flow to 134% of baseline, while 1,000 micrograms/ml decreased the flow to 58% of baseline (p less than 0.01 for both). Rifampin also caused a dose-dependent inhibition of BSP removal from the perfusate and excretion in the bile. Isoniazid had no adverse effect on bile flow and BSP clearance, and the combination of isoniazid and rifampin had the same effects on the perfused liver as rifampin alone.     

Influence of Cl- on organic anion transport in short-term cultured rat hepatocytes and isolated perfused rat liver.

Transport of 35S-labeled sulfobromophthalein [35S]BSP was studied in short-term cultured rat hepatocytes incubated in bovine serum albumin. At 37 degrees C, initial uptake of [35S]BSP was 5-10-fold that at 4 degrees C, linear for at least 15 min, saturable, inhibited by bilirubin, and reduced by greater than 70% after ATP depletion or isosmotic substitution of sucrose for NaCl in medium. Replacement of Na+ by K+ or Li+ did not alter uptake, whereas replacement of Cl- by HCO-3 or gluconate- reduced uptake by approximately 40%. Substitution of Cl- by the more permeant NO-3 enhanced initial BSP uptake by 30%. Efflux of [35S]BSP from cells to media was inhibited by 40% after ATP depletion or sucrose substitution. To confirm these results in a more physiologic system, transport of [3H]bilirubin was studied in isolated livers perfused with control medium or medium in which Cl- was replaced by gluconate-. Perfusion data analyzed by the model of Goresky, revealed 40-50% reductions in influx and efflux with gluconate- substitution. These results are consistent with existence of a Cl-/organic anion-exchange mechanism similar to that described by others in renal tubules.     

Apocynin attenuates lipopolysaccharide-induced lung injury in an isolated and perfused rat lung model

Apocynin (Apo) suppresses the generation of reactive oxygen species that are implicated in lipopolysaccharide (LPS)-induced lung injury (LPSLI). We thus hypothesized that Apo may attenuate LPSLI. In addition, we explored the cellular and molecular mechanisms of Apo treatment in LPSLI. Lipopolysaccharide-induced lung injury was induced by intratracheal instillation of 10 mg/kg LPS in isolated and perfused rat lung model. Apocynin was administered in the perfusate at 15 min before LPS was administered. Hemodynamics, lung injury indices, inflammatory responses, and activation of apoptotic pathways were assessed. There was an increase in lung vascular permeability associated with lung weight gain after LPS exposure. The levels of interleukin 1β (IL-1β), tumor necrosis factor α (TNF-α), macrophage inflammatory protein 2, H2O2, and albumin increased in the bronchoalveolar lavage fluid. Adhesion molecule of neutrophil (CD31) was upregulated. The expression of TNF-α, IL-1β, glutathione, myeloperoxidase, JNK, P38, caspase 3, p-AKT, and plasminogen activator inhibitor 1 in lung tissue was greater in the LPS groups when compared with the control group. Upregulation and activation of nuclear factor κB occurred along with increased histopathologic lung injury score in LPSLI. The Apo attenuated these inflammatory responses including the levels of CD31, H2O2, TNF-α, IL-1β, myeloperoxidase, P38, and nuclear factor κB along with downregulation of apoptosis as reflected by caspase 3 and p-AKT. In addition, Apo attenuated the increase in lung weight, bronchoalveolar lavage fluid albumin content, and the histopathologic lung injury score. In conclusion, LPSLI is associated with increased inflammatory responses, apoptosis, and coagulation. The administration of Apo attenuates LPSLI through downregulation of the inflammatory responses and apoptosis.     

Apocynin attenuates ventilator-induced lung injury in an isolated and perfused rat lung model

Rationale  

Apocynin suppresses the generation of reactive oxygen species (ROS) that are implicated in ventilator-induced lung injury (VILI). We thus hypothesized that apocynin attenuates VILI.     

Coordinate pulsatile insulin secretion by chronic intraportally transplanted islets in the isolated perfused rat liver.

In the present studies we sought to address the following questions: do chronically transplanted intrahepatic islets (IHI-Tx) secrete insulin in a coordinate pulsatile manner, and, if so, is reestablishment of this coordinate pulsatility a function of time after transplantation? We studied isolated perfused livers at 10 mM glucose from 27 rats rendered diabetic with streptozotocin and then transplanted with approximately 2 x 10(3) islets, 2 (n = 5), 7 (n = 5), 30 (n = 5), and 200 (n = 12) d after transplantation. 12 out of 12 of the 200-d IHI-Tx secreted insulin in coordinate pulses (frequency 3.9 +/- 0.3 pulses/h, amplitude 15.2 +/- 2.4 nmol/min). In contrast, one out of five 2-d, zero out of five 7-d, and one out of five 30-d IHI-Tx showed pulsatile insulin secretion. Insulin secretion was markedly greater (76 +/- 13 vs 13 +/- 3 nmol/min, P < 0.0001) in the 200-d versus early IHI-Tx. Pentobarbital 25 micrograms/ml had no effect on total (13.9 +/- 3.9 vs 15.9 +/- 3.9 nmol/min), nonpulsatile (12.9 +/- 3.5 vs 14.1 +/- 3.3 nmol/min), or pulsatile (pulse amplitude 17.6 +/- 4.5 vs 20.0 +/- 4.2 nmol/min, pulse frequency 4.1 +/- 0.3 vs 4.0 +/- 0.7 pulses/h) insulin secretion. Using synaptophysin, islet innervation was documented in 12 out of 12 200-d IHI-Tx but in none of the early IHI-Tx. We conclude that established (approximately 200 d) IHI-Tx secrete insulin in a coordinate pulsatile manner and that establishment of coordinate pulsatile insulin secretion by IHI-Tx is accompanied by increased total insulin secretion and is associated with islet reinnervation.     

Hepatic bilirubin uptake in the isolated perfused rat liver is not facilitated by albumin binding.

Bilirubin uptake by the liver is a rapid process of high specificity that has kinetic characteristics which suggest carrier-mediation. In the circulation, bilirubin is readily bound to albumin, from which it is extracted by the liver. Although several studies suggested that it is the small, unbound fraction of bilirubin which interacts with hepatocytes and is removed from the circulation, recent experiments have been interpreted as suggesting that binding to albumin facilitates ligand uptake. A liver cell surface receptor for albumin has been postulated. The present study was designed to examine directly whether albumin facilitates the hepatic uptake of bilirubin and whether uptake of bilirubin depends on binding to albumin. Rat liver was perfused with a protein-free fluorocarbon medium, and single-pass uptake of 1, 10, or 200 nmol of [3H]bilirubin was determined after injection as an equimolar complex with 125I-albumin, with 125I-ligandin, or free with only a [14C]sucrose reference. Uptake of 10 nmol of [3H]bilirubin was 67.5 +/- 3.7% of the dose when injected with 125I-albumin, 67.4 +/- 6.5% when injected with 125I-ligandin, and 74.9 +/- 2.4% when injected with [14C]sucrose (P greater than 0.1). At 200 nmol, uptake fell to 46.4 +/- 3.1% (125I-albumin) and 63.3 +/- 3.4% [( 14C]sucrose) of injected [3H]bilirubin (P less than 0.01), which suggests saturation of the uptake mechanism. When influx was quantitated by the model of Goresky, similar results were obtained. When [3H]bilirubin was injected simultaneously with equimolar 125I-albumin and a [14C]sucrose reference, there was no delay in 125I-albumin transit as compared with that of [14C]sucrose. This suggested that the off-rate of albumin from a putative hepatocyte receptor would have to be very rapid, which is unusual for high affinity receptor-ligand interaction. There was no evidence for facilitation of bilirubin uptake by binding to albumin or for interaction of albumin with a liver cell surface receptor. These results suggest that the hepatic bilirubin uptake mechanism is one of high affinity which can extract bilirubin from circulating carriers such as albumin, ligandin, or fluorocarbon.