Functional and structural characterization of isolated perfused stingray liver including effects of ischaemia/reperfusion

The morphological and functional characteristics of stingray liver were studied, including the effect of ischaemia/reperfusion. With an isolated perfused model, it was shown that the stingray liver was more resistant than the rat liver to ischaemia/reperfusion injury; this was consistent with the differing partial oxygen tensions usually present in the two species. This study confirmed that whereas stingray hepatocytes form tubules with central bile canaliculi as in other fish, the stingray liver has portal triads and a lobular architecture as in mammals. Apoptosis of hepatocytes, demonstrated in the normal liver, was only marginally enhanced by ischaemia/reperfusion. Resulting apoptotic bodies were phagocytized by macrophage-like cells in hepatocyte tubules. In contrast to rat liver, the stingray liver showed no necrosis after ischaemia-reperfusion. (C) 1998 W.B. Saunders Company Limited.

Hepatic structure-pharmacokinetic relationships: The hepatic disposition and metabolite kinetics of a homologous series of O-acyl derivatives of salicylic acid

1 The hepatic disposition and metabolite kinetics of a homologous series of O-acyl (acetyl, propionyl, butanoyl, pentanoyl, hexanoyl and octanoyl) esters of salicylic acid (C2SA, C3SA, C4SA, C5SA, C6SA and C8SA, respectively) was determined using a single-pass, in-sills rat liver preparation. 2 The hepatic venous outflow profiles for the parent esters and the generated metabolite, salicylic acid (SA) were analysed by HPLC. Non-parametric moments analysis was used to determine the area under the curve (AUC'), mean transit time (MTT) and normalized variance (CV2) for the parent esters and generated SA. 3 Pregenerated SA ([C-14]-salicylic acid) was injected into each liver with the parent ester to determine its distribution characteristics. 4 The overall recovery of ester plus metabolite was 89% of the ester dose injected and independent of the ester carbon number, suggesting that ester extraction was due to hepatic metabolism to salicylic acid. 5 The metabolite AUC' value increased directly with the lipophilicity of the parent ester (from 0.12 for C2SA to 0.95 for C8SA). By contrast, the parent AUC' decreased with the lipophilicity (from 0.85 for C2SA to zero for C8SA). The metabolite MTT value also showed a trend to increase with the lipophilicity of the parent ester (from 15.72 s for C3SA to 61.97 s for C8SA). However, the parent MTT value shows no significant change across the series. 6 The two-compartment dispersion model was used to derive the kinetic parameters for parent ester, pregenerated SA and generated SA. Consequently, these parameters were used to estimate the values of AUG', MITT and CV2 for the parent ester and metabolite. The moments values obtained using the two-compartment dispersion model show similar trends to the corresponding moments values obtained from the outflow profiles using a non-parametric approach. 7 The more lipophilic aspirin analogues are more confined to the portal circulation after oral administration than aspirin due to their more extensive hepatic elimination avoiding systemic prostacyclin inhibition. Given that aspirin's selectivity as an anti-thrombotic agent has been postulated to be due to selective anti-platelet effects in the portal circulation, the more lipophilic and highly extracted analogues are potentially more selective anti-thrombotic agents than aspirin.

Hepatic disposition and metabolite kinetics of a homologous series of diflunisal esters

The hepatic disposition and metabolite kinetics of a homologous series of diflunisal O-acyl esters (acetyl, butanoyl, pentanoyl, anti hexanoyl) were determined using a single-pass perfused in situ rat liver preparation. The experiments were conducted using 2% BSA Krebs-Henseleit buffer (pH 7.4), and perfusions were performed at 30 mL/min in each liver. O-Acyl esters of diflunisal and pregenerated diflunisal were injected separately into the portal vein. The venous outflow samples containing the esters and metabolite diflunisal were analyzed by high performance liquid chromatography (HPLC). The normalized outflow concentration-time profiles for each parent ester and the formed metabolite, diflunisal, were analyzed using statistical moments analysis and the two-compartment dispersion model. Data (presented as mean +/- standard error for triplicate experiments) was compared using ANOVA repeated measures, significance level P < 0.05. The hepatic availability (AUC'), the fraction of the injected dose recovered in the outflowing perfusate, for O-acetyldiflunisal (C2D = 0.21 +/- 0.03) was significantly lower than the other esters (0.34-0.38). However, R-N/f(u), the removal efficiency number R-N divided by the unbound fraction in perfusate f(u), which represents the removal efficiency of unbound ester by the liver, was significantly higher for the most lipophilic ester (O-hexanoyldiflunisal, C6D = 16.50 +/- 0.22) compared to the other members of the series (9.57 to 11.17). The most lipophilic ester, C6D, had the largest permeability surface area (PS) product (94.52 +/- 38.20 mt min-l g-l liver) and tissue distribution value VT (35.62 +/- 11.33 mL g(-1) liver) in this series. The MTT of these O-acyl esters of diflunisal were not significantly different from one another. However, the metabolite diflunisal MTTs tended to increase with the increase in the parent ester lipophilicity (11.41 +/- 2.19 s for C2D to 38.63 +/- 9.81 s for C6D). The two-compartment dispersion model equations adequately described the outflow profiles for the parent esters and the metabolite diflunisal formed from the O-acyl esters of diflunisal in the liver.

Magnetic resonance imaging and diseases of the liver and biliary tract. Part 2. Magnetic resonance cholangiography and angiography and conclusions

Magnetic resonance cholangiography (MRC) relies on the strong T-2 signal from stationary liquids, in this case bile, to generate images. No contrast agents are required, and the failure rate and risk of serious complications is lower than with endoscopic retrograde cholangiopancreatography (ERCP). Data from MRC can be summated to produce an image much like the cholangiogram obtained by using ERCP. In addition, MRC and conventional MRI can provide information about the biliary and other anatomy above and below a biliary obstruction. This provides information for therapeutic intervention that is probably most useful for hilar and intrahepatic biliary obstruction. Magnetic resonance cholangiography appears to be similar to ERCP with respect to sensitivity and specificity in detecting lesions causing biliary obstruction, and in the diagnosis of choledocholithiasis. It is also suited to the assessment of biliary anatomy (including the assessment of surgical bile-duct injuries) and intrahepatic biliary pathology. However, ERCP can be therapeutic as well as diagnostic, and MRC should be limited to situations where intervention is unlikely, where intrahepatic or hilar pathology is suspected, to delineate the biliary anatomy prior to other interventions, or after failed or inadequate ERCP. Magnetic resonance angiography (MRA) relies on the properties of flowing liquids to generate images. It is particularly suited to assessment of the hepatic vasculature and appears as good as conventional angiography. It has been shown to be useful in delineating vascular anatomy prior to liver transplantation or insertion of a transjugular intrahepatic portasystemic shunt. Magnetic resonance angiography may also be useful in predicting subsequent variceal haemorrhage in patients with oesophageal varices. (C) 2000 Blackwell Science Asia Pty Ltd.

Systematic review: Terlipressin in acute oesophageal variceal haemorrhage

Background: Controversy exists surrounding pharmacological therapy in acute variceal bleeding. Methods: To determine the efficacy and safety of terlipressin. Methods: Randomized trials were identified and duplicate, independent, review identified 20 randomized trials involving 1609 patients that compared terlipressin with placebo, balloon tamponade, endoscopic treatment, octreotide, somatostatin or vasopressin for treatment of acute oesophageal variceal haemorrhage. Results: Meta-analysis showed that compared to placebo, terlipressin reduced mortality (relative risk 0.66, 95% CI 0.49-0.88), failure of haemostasis (relative risk 0.63, 95% CI 0.45-0.89) and the number of emergency procedures per patient required for uncontrolled bleeding or rebleeding (relative risk 0.72, 95% CI 0.55-0.93). When used as an adjuvant to endoscopic sclerotherapy, terlipressin reduced failure of haemostasis (relative risk 0.75, 95% CI 0.58-0.96), and had an effect on reducing mortality that approached statistical significance (relative risk 0.74, 95% CI 0.53-1.04). No significant difference was demonstrated between terlipressin and endoscopic sclerotherapy, balloon tamponade, somatostatin or vasopressin. Haemostasis was achieved more frequently with octreotide compared to terlipressin (relative risk 1.62, 95% CI 1.05-2.50), but this result was based on unblinded studies. Adverse events were similar between terlipressin and the other comparison groups except for vasopressin, which caused more withdrawals due to adverse events. Conclusions: Terlipressin is a safe and effective treatment for acute oesophageal variceal bleeding, with or without adjuvant endoscopic sclerotherapy. Terlipressin appears to reduce mortality in acute oesophageal variceal bleeding compared to placebo, and is the only pharmacological agent shown to do so. Future studies will be required to detect potential mortality differences between terlipressin and other therapeutic approaches.

An optimized model for rat liver perfusion studies

Conditions which influence the viability, integrity, and extraction efficiency of the isolated perfused rat liver were examined to establish optimal conditions for subsequent work in reperfusion injury studies including the choice of buffer, use of oncotic agents, hematocrit, perfusion flow rate, and pressure. Rat livers were perfused with MOPS-buffered Ringer solution with or without erythrocytes. Perfusates were collected and analyzed for blood gases, electrolytes, enzymes, radioactivity in MID studies, and lignocaine in extraction studies. Liver tissue was sampled for histological examinations, and wet:dry weight of the liver was also determined. MOPS-buffered Ringer solution was found to be superior to Krebs bicarbonate buffer, in terms of pH control and buffering capacity, especially during any prolonged period of liver perfusion. A pH of 7.2 is chosen for perfusion since this is the physiological pH of the portal blood. The presence of albumin was important as an oncotic agent, particularly when erythrocytes were used in the perfusate. Perfusion pressure, resistance, and vascular volume are how-dependent and the inclusion of erythrocytes in the perfusate substantially altered the flow characteristics for perfusion pressure and resistance but not vascular volume. Lignocaine extraction was relatively flow-independent. Perfusion injury as defined by enzyme release and tissue fine structure was closely related to the supply of O-2. The optimal conditions for liver perfusion depend upon an adequate supply of oxygen. This can be achieved by using either erythrocyte-free perfusate at a how rate greater than 6 ml/min/g liver or a 20% erythrocyte-containing perfusate at 2 ml/min/g. (C) 1996 Academic Press, Inc.

Effects of pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) on hormone secretion from sheep pituitary cells in vitro

Although vasoactive intestinal polypeptide (VIP) is thought to be a prolactin releasing factor, in vivo studies on sheep suggest that it is inactive in this species. Recent studies, based primarily on the rat, suggest that the related pituitary adenylate cyclase-activating polypeptide (PACAP) is also a hypophysiotrophic factor but again in sheep, this peptide has no in vivo effects on hormone secretion despite being a potent activator of adenylate cyclase in vitro. This lack of response to either peptide in vivo in sheep could be due to the low concentration of peptide that reaches the pituitary gland following peripheral injection. In the present study we therefore adopted an alternative approach of evaluating in vitro effects of these peptides on GH, FSH, LH or prolactin secretion from dispersed sheep pituitary cells. In a time-course study, PACAP (1 mu mol/l) increased GH concentrations in the culture medium between 1 and 4 h and again at 12 h but had no effect in the 6 and 24 h incubations. Prolactin, LH and FSH were not affected by PACAP. The response to various concentrations of PACAP (1 nmol/l-1 mu mol/l) were then evaluated using a 3 h incubation. Again prolactin and LH were not affected by PACAP and there was a small increase in GH concentrations but only at high concentrations of PACAP (0.1 and 1 mu mol/l; P<0.05), PACAP also stimulated FSH secretion in cells from some animals although this effect was small, The GH response to PACAP was inhibited by PACAP(6-38), a putative PACAP antagonist; but not by (N-Ac-Tyr(1), D-Arg(2))-GHRH(1-29)-NH2, a GH-releasing hormone (GHRH) antagonist. The cAMP antagonist Rp-cAMPS was unable to block the GH response to PACAP suggesting that cAMP does not mediate the secretory response to this peptide. At incubation times from 1-24 h, VIP (1 mu mol/l) had no effects on prolactin, LH or GH secretion and, in a further experiment based on a 3 h incubation, concentrations of VIP from 1 nmol/l-1 mu mol/l were again without effect on prolactin concentrations. Interactions between PACAP and gonadotrophin releasing hormone (GnRH), GHRH and dopamine were also investigated. PACAP (1 nmol/l-1 mu mol/l) did not affect the gonadotrophin or prolactin responses to GnRH or dopamine respectively. However, at a high concentration (1 mu mol/l), PACAP inhibited the GH response to GHRH. In summary, these results show that PACAP causes a modest increase in FSH and GH secretion from sheep pituitary cells but only at concentrations of PACAP that are unlikely to be in the physiological range. The present study confirms that VIP is not a prolactin releasing factor in sheep.

Schistosomiasis in the People's Republic of China: Prospects and challenges for the 21st century

Schistosomiasis japonica is a serious communicable disease and a major disease risk for more than 30 million people living in the tropical and subtropical zones of China. Infection remains a major public health concern despite 45 years of intensive control efforts. It is estimated that 865, 000 people and 100,250 bovines are today infected in the provinces where the disease is endemic, and its transmission continues. Unlike tire other schistosome species known to infect humans, the oriental schistosome, Schistosoma japonicum, is a true zoonotic organism, with a range of mammalian reservoirs, making control efforts extremely difficult. Clinical features of schistosomiasis range from fever; headache, and lethargy to severe fibro-obstructive pathology leading to portal hypertension, ascites, and hepatosplenomegaly, which can cause premature death. Infected children ale stunted and have cognitive defects impairing memory and learning ability. Current control programs are heavily based on community chemotherapy with a single dose of the drug praziquantel, but vaccines (for use in bovines and humans) in combination with other control strategies ale needed to make elimination of the disease possible. In this article, we provide an overview of the biology, epidemiology clinical features, and prospects for cona ol of oriental schistosomiasis in the People's Republic of China.

Neonatal hepatic drug elimination

After the transition from in utero to newborn life, the neonate becomes solely reliant upon its own drug clearance processes to metabolise xenobiotics. Whilst most studies of neonatal hepatic drug elimination have focussed upon in vitro expression and activities of drug-metabolising enzymes, the rapid physiological changes in the early neonatal period of life also need to be considered. There are dramatic changes in neonatal liver blood how and hepatic oxygenation due to the loss of the umbilical blood supply, the increasing portal vein blood flow, and the gradual closure of the ductus venosus shunt during the first week of life. These changes which may well affect the capacity of neonatal hepatic drug metabolism. The hepatic expression of cytochromes P450 1A2, 2C, 2D6, 2E1 and 3A4 develop at different rates in the postnatal period, whilst 3A7 expression diminishes. Hepatic glucuronidation in the human neonate is relatively immature at birth, which contrasts with the considerably more mature neonatal hepatic sulfation activity. Limited in vivo studies show that the human neonate can significantly metabolise xenobiotics but clearance is considerably less compared with the older infant and adult. The neonatal population included in pharmacological studies is highly heterogeneous with respect to age, body weight, ductus venosus closure and disease processes, making it difficult to interpret data arising from human neonatal studies. Studies in the perfused foetal and neonatal sheep liver have demonstrated how the oxidative and conjugative hepatic elimination of drugs by the intact organ is significantly increased during the first week of life, highlighting that future studies will need to consider the profound physiological changes that may influence neonatal hepatic drug elimination shortly after birth.

Role of myofibroblasts in tumour encapsulation of hepatocellular carcinoma in haemochromatosis

Background/Aims: Hepatocellular carcinoma is a carcinoma malignancy and a major complication of untreated haemochromatosis. Encapsulation of liver tumours has been associated with a better prognosis and longer disease-free periods following resection, This study investigated the source of the tumour capsule in patients with haemochromatosis and coexisting hepatocellular carcinoma and examined potential factors influencing development. Methods: Five haemochromatosis patients with encapsulated hepatocellular carcinoma were studied. Myofibroblasts were identified using combined immunohistochemistry and in situ hybridisation for a-smooth muscle actin and procollagen alpha (1)(I) mRNA, respectively. Immunohistochemistry was also performed for transforming growth factor (TGF)-beta (1), platelet-derived growth factor (PDGF)-beta receptor and malondialdehyde. Results. Procollagen alpha (1)(I) mRNA co-localised to alpha -smooth muscle actin positive myofibroblasts. The number of myofibroblasts was maximal within the capsule and decreased away from the tumour. TGF-beta (1) protein was expressed in iron-loaded cells in non-tumour liver at the interface of tumour capsule. PDGF-beta receptor expression was observed in mesenchymal cells in the tumour capsule and in portal tracts. Malondialdehyde adducts were observed in the tumour, non-tumour tissue and in the capsule. Conclusions: This study provides evidence that myofibroblasts are the cell type responsible for collagen production within the tumour capsule surrounding hepatocellular carcinoma in haemochromatosis, The production of TGF-beta (1) by iron-loaded hepatic cells at the tumour capsule interface may perpetuate the myofibroblastic phenotype, resulting in, the formation of the tumour capsule.

The spironolactone renaissance

Until recently, spironolactone was considered only as an antagonist at the aldosterone receptors of the epithelial cells of the kidney and was used clinically in the treatment of hyperaldosteronism and, occasionally, as a K+-sparing diuretic. The spironolactone renaissance started with the experimental finding that spironolactone reversed aldosterone-induced cardiac fibrosis by a cardiac action. Experimentally, spironolactone also has direct effects on blood vessels. Spironolactone reduces vascular fibrosis and injury, inhibits angiogenesis, reduces vascular tone and reduces portal hypertension. The rationale for the Randomized Aldactone Evaluation Study (RALES) of spironolactone in heart failure was that ‘aldosterone escape’ occurred through non-angiotensin II mechanisms. The RALES clinical trial was stopped early when it was shown that there was a 30% reduction in risk of death among the spironolactone patients. In RALES, spironolactone also reduced hospitalisation for worsening heart failure and improved the symptoms of heart failure. Other recent clinical trials have shown that spironolactone reduces cardiac and vascular collagen turnover, improves heart variability, reduces ventricular arrhythmias, improves endothelial dysfunction and dilates blood vessels in human heart failure and these effects probably all contribute to the increased survival in heart failure. Spironolactone may also be useful in the treatment of left ventricular hypertrophy, portal hypertension and cirrhosis. There have also been some recent small clinical trials of spironolactone as an anti-androgen showing potential in acne, hirsutism and precocious puberty.

Effects of dofetilide on cardiovascular tissues from normo- and hypertensive rats

The aim was to test whether dofetilide has some potential for use in the treatment of heart failure. Dofetilide at less than or equal to 3 x 10(-5) m had no effect on the quiescent Wistar Kyoto (WKY) rat aorta, mesenteric and intralobar arteries, or the spontaneous contractions of the WKY rat portal vein. Dofetilide at 10(-6) to 3 x 10(-5) m relaxed the KCl-contracted aorta. Dofetilide at 10(-9)-10(-7) m augmented the force of contraction of left ventricle strips from 12- and 18-month-old WKY rats at 2 Hz. Spontaneously hypertensive rats (SHRs) at 12 and 17-21 months of age are models of cardiac hypertrophy and failure, respectively. The augmentation of force at 2 Hz with dofetilide was similar on 12- and 18-month-old WKY rats and 12-month-old SHRs but reduced on the 18-month-old SHR left ventricle. At a higher more physiological frequency, 4 Hz, the threshold concentration of dofetilide required to augment the force responses of 21-month-old SHR left ventricles was markedly increased and the maximum augmenting effect was decreased. Dofetilide at 10(-7)-10(-5) m reduced the rate of the 17-month-old WKY rat right atrium, and had a similar effect on age-matched SHR right atrium. In summary, dofetilide is a positive inotrope and negative chronotrope in the rat. However, as the positive inotropic effect is not observed with clinically relevant concentrations at a physiological rate in heart failure, dofetilide is unlikely to be useful as a positive inotrope in the treatment of heart failure.