Bile secretion and liver regeneration in partially hepatectomized rats

The effect of silymarin on hepatic regeneration after partial hepatectomy: is silymarin effective in hepatic regeneration?

AIM

Silymarin from Silybum marianum was found to reduce liver injury. The aim of the present study was to investigate the effects of silymarin on hepatic regeneration in partially hepatectomized rats.

METHODS

Thirty Wistar-Albino rats were divided into 3 groups of 10 animals as sham, control and experimental groups. In the sham group (n=10) abdominal incision was closed after laparotomy. In the control group (n=10), the rats underwent 70% hepatectomy after laparotomy. In the experimental group (n=10) after partial 70% hepatectomy, silymarin (200 mg/kg/d) were given to rats for 10 days. Rats in three groups were sacrificed on 10 days. Aspartate (AST) and alanine transaminase (ALT), gamma glutamyl transferase (GGT), ALP, LDH and total bilirubin levels were measured using intracardiac blood samples. Tissue malondialdehyde (MDA) and tissue glutathion (GSH) and Superoxide dismutase (SOD) levels were measured. To reveal the increase in the mass of the remnant liver tissue in the control and experimental groups relative weight of the liver was calculated. Histopathological analysis of the liver was performed using a semi-quantitative scoring system.

RESULTS

A statistically significant difference among three groups was not shown for AST and ALT levels. A statistically significant difference was found between the groups as for total bilirubin and gamma glutamyl transferase levels. Increases in relative liver weights were seen with time in Groups 2 and 3. A statistically significant difference was not found for tissue malondialdehyde, Glutathion and Superoxide dismutase levels between hepatectomy and hepatectomy + silymarin groups. On liver tissue sections of the rats in the hepatectomy + silymarin group, increased regeneration and lipid peroxidation were observed accompanied by decreased antioxidant response.

CONCLUSION

It has been observed that silymarin with many established functions such as antiproliferative, anti-inflammatory and energy antioxidant effects, does not contributed to proliferative regeneration of the liver-which has very important metabolic functions -after partial hepatectomy; instead it will decrease serum levels of transaminases.

Leptin increases mitotic index and regeneration ratio in hepatectomized rats

Background

The aim of this study was to evaluate the potential effect of intraperitoneal administration of leptin on the hepatic regeneration and the mitotic index.

Material/Methods

56 Sprague-Dawley rats were divided into 7 groups each containing 8 rats. Group 1 was evaluated as the sham group and no surgical procedure was performed on animals. The rats in groups 2, 3, and 4 (named C24, C48, C72, respectively) were given intraperitoneal injection of 2 ml/kg normal saline 60 minutes before the surgical procedure consisting of laparotomy and 70% hepatectomy. These groups were used as controls at 24, 48, and 72 hours. The rats in groups 5, 6, and 7 (named L24, L48, and L72, respectively) were given intraperitoneal injection of 20 μg/kg doses of recombinant mouse leptin 60 minutes before the same surgical procedure. These groups were evaluated as the experiment groups at 24, 48, and 72 hours. Blood samples were collected for aspartate aminotransferase (AST) and alanine aminotransferase (ALT) and the remaining tissue samples were obtained for liver histopathology, regeneration rate, and mitotic index (MI). The weights of the remaining livers were also noted.

Results

The values of AST and ALT were higher in the groups that were administered leptin and they had significantly higher mitotic index than the other groups. Leptin also significantly increased the regeneration ratio as compared to the control group. The weights of the remaining livers were also higher in the leptin groups.

Conclusions

Intraperitoneal administration of leptin was observed to increase liver regeneration and mitotic rate in 70% hepatectomized rats.

No harmful effect of mycophenolate mofetil on liver regeneration: an experimental study

AIM

The aim of this experimental study was to examine the effects of mycophenolate mofetil (MMF) on liver regeneration in a partial hepatectomy model.

METHODS

Rats were divided into 3 groups immediately following partial liver resection: saline, controls intraperitoneally (MMF; Group 1); MMF (15 mg/kg/d; Group II), and MMF (30 mg/kg/d; Group III). On days 3 and 7 following liver resection we humanely killed half of the rats in each group to measure alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels and to evaluate Ki-67 using immunohistochemistry. We calculated liver regeneration rates.

RESULTS

The difference between ALT levels on days 3 and 7 was not significantly different among the groups (P = .157; P = .292; P > .05, respectively). The AST levels were significantly different at 3 days (P = .018) but not 7 days (P = .385). The Ki-67 level were different among groups at day 3 (P = .002) but not at day 7 (P = .290). Liver regeneration rates were not different among the groups either at 3 or at 7 days (P = .264 and P = .925, respectively).

CONCLUSION

MMF stimulates mitosis but its effect on regeneration is not clear. MMF appeared to show no adverse effects on liver regeneration.

Bile acid transporters and regulatory nuclear receptors in the liver and beyond

Bile acid (BA) transporters are critical for maintenance of the enterohepatic BA circulation where BAs exert their multiple physiological functions including stimulation of bile flow, intestinal absorption of lipophilic nutrients, solubilization and excretion of cholesterol, as well as antimicrobial and metabolic effects. Tight regulation of BA transporters via nuclear receptors is necessary to maintain proper BA homeostasis. Hereditary and acquired defects of BA transporters are involved in the pathogenesis of several hepatobiliary disorders including cholestasis, gallstones, fatty liver disease and liver cancer, but also play a role in intestinal and metabolic disorders beyond the liver. Thus, pharmacological modification of BA transporters and their regulatory nuclear receptors opens novel treatment strategies for a wide range of disorders.

Expansion of hepatic progenitor cell in fatty liver graft after living donor liver transplantation

Although it is known that steatotic livers have a reduced ability to regenerate, most individuals with steatosis show generally benign prognosis. We hypothesized that a proliferative blockade in steatotic hepatocytes results in the compensatory expansion of hepatic progenitor cells (HPC) during fatty liver regeneration. Fifty-four cases of living donor liver transplantation (LDLT) with a liver biopsy performed at the postoperative 10th day were examined. HPC were counted by immunofluorescence histochemical dual-staining technique using cytokeratin 7 and Ki-67, and the replicative arrest of hepatocytes was assessed by p21 immunohistochemistry. The degree of ductular proliferation during regeneration 10 days after LDLT correlated both with the degree of steatosis and the number of HPC (P < 0.001). There was no difference in the average number of HPC and the replicative arrest index between donors with or without steatosis before LDLT (P = 0.111 and P = 0.062). However, degree of steatosis correlated with both the expansion of HPC and the replicative arrest index during liver regeneration 10 days after LDLT (P < 0.001 and P < 0.001, respectively). Moreover, increased replicative arrest was strongly associated with HPC expansion (P < 0.001). In conclusion, the compensatory expansion of HPC as a result of impaired hepatocyte replication occurred during steatotic liver regeneration after LDLT.

Herb-drug interaction of silymarin or silibinin on the pharmacokinetics of trazodone in rats

Silymarin, one of the most popular herbal medicines, has been widely used for its hepatoprotective effects. This study investigates the effects of repeated dose of silymarin and its major ingredient, silibinin, on the pharmacokinetics of the antidepressant trazodone. Treatment groups included vehicle control group, concomitant silymarin at 1.0g/kg dose, and four 7-day repeated dose induction groups of 0.5 and 1.0g/kg silymarin and 0.175 and 0.35g/kg silibinin. Microdialysis coupled with high performance liquid chromatography (HPLC) was used to simultaneously monitor blood and bile concentrations of trazodone in the rats. Results indicate that pretreatment with an extremely high dose of 1.0g/kg silymarin significantly decreases trazodone's area under concentration curve (AUC), distribution half-life (t(1/2,alpha)), elimination half-life (t(1/2,beta)), and mean residence time (MRT). In conclusion, the present study finds no marked effects of silymarin and silibinin on the pharmacokinetics of trazodone under normal daily doses and the relative safety of taking the herb with trazodone.

Role of bile in intestinal motility after massive liver resection in conscious rats

AIM

To investigate the effect of 90% partial hepatectomy (90% PHx) and the involvement of bile on ileal motility in conscious rats.

METHODS

Two strain gauge force transducers were chronically implanted in the ileum of each of 20 rats. The rats were divided into four groups, three of which underwent 90% PHx. The experiments were performed with the rats in a conscious, fasted state. After ileal motility was recorded, bile or saline was perfused into the duodenum of each rat in two of the 90% PHx groups. The effects of the perfusion on ileal motility were observed and recorded using the motility index (MI), defined as the area under the contraction cues after surgery and expressed as the ratio to the MI in the preoperational motility. The time of the first passage of stool after surgery was recorded.

RESULTS

A typical migrating motor complex (MMC) pattern was observed in normal fasted rats. Increased MMC cycle lengths and a decreased MI at 1 day and 3 days after 90% PHx were observed. The MMC after 90% PHx was characterized by an increased duration of Phase 2-like activity. The MMC cycle length, the MI, and the time of the first passage of stool after 90% PHx were improved by perfusion of bile into the duodenum through the biliary cannula but were not influenced by perfusion of saline into the duodenum through the biliary cannula.

CONCLUSION

The MMC cycle length and the MI were inhibited after 90% PHx, with the involvement of decreased bile flow into the gastrointestinal tract by liver resection.

Role of ischaemic preconditioning in liver regeneration following major liver resection and transplantation

Liver ischaemic preconditioning (IPC) is known to protect the liver from the detrimental effects of ischaemic-reperfusion injury (IRI), which contributes significantly to the morbidity and mortality following major liver surgery. Recent studies have focused on the role of IPC in liver regeneration, the precise mechanism of which are not completely understood. This review discusses the current understanding of the mechanism of liver regeneration and the role of IPC in this setting. Relevant articles were reviewed from the published literature using the Medline database. The search was performed using the keywords “liver”, “ischaemic reperfusion”, “ischaemic preconditioning”, “regeneration”, “hepatectomy” and “transplantation”. The underlying mechanism of liver regeneration is a complex process involving the interaction of cytokines, growth factors and the metabolic demand of the liver. IPC, through various mediators, promotes liver regeneration by up-regulating growth-promoting factors and suppresses growth-inhibiting factors as well as damaging stresses. The increased understanding of the cellular mechanisms involved in IPC will enable the development of alternative treatment modalities aimed at promoting liver regeneration following major liver resection and transplantation.

Hepatic steatosis is associated with intrahepatic cholestasis and transient hyperbilirubinemia during regeneration after living donor liver transplantation

A clear understanding of the mechanisms in steatotic livers that trigger cholestasis or hyperbilirubinemia after living donor liver transplantation (LDLT) remains elusive. We hypothesized that microarchitectural disturbance might occur within regenerating steatotic livers without impairment of hepatic proliferative activity. Liver biopsy specimens from 67 LDLT recipients taken at the 10th postoperative day were scored for the numbers of portal tracts per area (nPT/A) of liver tissue and for intrahepatic cholestasis, and immunostained by proliferating cell nuclear antigen (PCNA) and Ki-67. The preoperative degree of macrovesicular steatosis (MaS) was independently associated with cholestasis after LDLT (P < 0.001). Serum total bilirubin results on the 1st, 3rd, and 7th days post-LDLT in MaS+ (5-30% of MaS; n = 37) patients were significantly higher than those in MaS- (<5% of MaS; n = 30) patients (P = 0.030, 0.042, and 0.019, respectively). Mean numbers of positively stained hepatocytes were 53.1 +/- 12.0 in patients with MaS and 48.0 +/- 17.1 in those without MaS by PCNA (P = 0.390), and 24.4 +/- 10.5 and 24.0 +/- 14.0 by Ki-67 (P = 0.940). However, a significant negative correlation was found between the degree of MaS and nPT/A (P = 0.013), and nPT/A was correlated with the grade of histological cholestasis (r = 0.350, P = 0.039). Intrahepatic cholestasis and hyperbilirubinemia after LDLT could be caused by scanty morphologic change of portal tract during steatotic liver regeneration.

Biliary lipid output in the early stage of acute liver failure induced by 90% hepatectomy in the rat

BACKGROUND

Differences in biliary lipid output were compared in rats after 70% or 90% hepatectomy (Hx) to evaluate a possible index of the early stage of acute liver failure.

METHODS

Male Sprague-Dawley (SD) rats weighing 300 to 350 g were randomly divided into two groups for 70% Hx or 90% Hx, and animals were sacrificed at 0, 6, 24, and 48 h after Hx. Before sacrifice, a polyethylene tube was cannulated into the bile duct and bile was collected for 1 h. Outputs of total bile acids, phospholipid, and total cholesterol in serum and bile were determined. Biliary total cholesterol, bile acid concentrations, and bile acid component levels were determined using gas liquid chromatography. Hepatic microsomal cholesterol 7alpha-hydroxylase and sterol 12alpha-hydroxylase activities were also determined using high performance liquid chromatography.

RESULTS

The 3-day survival rate after 90% Hx was 50%. In the 90% Hx group, the serum total bile acid concentration at each point was significantly higher than it was in the 70% Hx group. The bile flow rate and biliary outputs of cholesterol, phospholipid, and bile acids were significantly lower at 6 h after 90% Hx than after 70% Hx. Among bile acid species, cholic and chenodeoxycholic acid outputs into bile were significantly less at 6 h after 90% Hx. The activities of cholesterol 7alpha-hydroxylase and sterol 12alpha-hydroxylase were decreased after 90% Hx.

CONCLUSIONS

Our results suggest that determinations of the bile flow rate and biliary lipid outputs are supposed to be useful for early detection of hepatic failure after extensive hepatectomy.

The Effect of Amrinone on Liver Regeneration in Experimental Hepatic Resection Model1

BACKGROUND

The phosphodiesterase inhibitors (PDEIs) have been proposed to improve hepatic reperfusion injury and hepatosplanchnic circulation, but the effects of these agents on liver regeneration have not been investigated thoroughly. The aim of this study was to investigate the effect of amrinone, a PDEI, on liver regeneration in rats.

MATERIALS AND METHODS

Sixty rats were divided into two groups, control and amrinone. Each group was then divided into three groups (n=10). An infusion of amrinone to the study group and of 0.9% NaCl to the control group was performed. Seventy percent liver resection was performed to the rats during the first hour of infusion. The infusion was maintained for 17 h after resection. A total of 18 h infusion was performed. Rats were allowed to survive for 24, 48, and 72 h, and then they were sacrificed. Biochemical, morphological, hematological, and histopathologic measurements and assessments were performed.

RESULTS

There were statistically significant differences between the amrinone and control groups in alkaline phosphatase and relative liver weights at 24, 48, and 72 h (P<0.05). There also were statistically significant differences between the groups in AST, bilirubin, and albumine levels at 24 h, ALT and prothrombine time levels at 48 h, and aspartate aminotransferase and alanine aminotransferase levels at 72 h (P<0.05). Hepatic ATP levels, mitotic index, and proliferating cell nuclear antigen labeling index were significantly higher in amrinone group compared with control group at all three time intervals (P<0.05).

CONCLUSIONS

Amrinone improves both morphological and functional liver regeneration after liver resection.

Sustained spatial disturbance of bile canalicular networks during regeneration of the steatotic rat liver

BACKGROUND

Although it is generally considered that livers with moderate steatosis can be safely used in the setting of living-donor liver transplantation, the effect of the regenerative process of such a graft on postoperative liver function is incompletely understood. We assessed the morphologic and functional alterations during the regeneration of fatty liver, with special reference to the biliary system.

METHODS

Wistar rats with normal or fatty livers induced by a choline-deficient diet were subjected to 70% partial hepatectomy (PH). The regenerated liver weight and serum parameters were compared. Furthermore, to assess the spatial alterations of bile canalicular networks, the distribution of AGp110, a fibronectin receptor that localizes on the apical (bile canalicular) membrane of the hepatocytes, was analyzed immunohistochemically.

RESULTS

The serum albumin levels of the fatty-liver rats decreased significantly after 24 hours, and this continued until day 7. The increase in the total bile acid levels of the fatty-liver group was higher and more prolonged compared with that of the normal-liver group. At 24 hours after PH, discontinuity of the AGp110-positive canalicular network was evident in both groups. At 7 days after PH, the typical AGp110-positive canalicular network was almost restored in the normal-liver group. In contrast, the fatty-liver group showed sustained discontinuity of canalicular networks at the same time point.

CONCLUSIONS

The livers with moderate steatosis are associated with prolonged cholestasis after 70% PH, and this was caused, in part, by sustained spatial disturbance of bile canalicular networks during the regenerative process.

Biliary bile acid concentration is a simple and reliable indicator for liver function after hepatobiliary resection for biliary cancer

BACKGROUND

The functional recovery of the remnant liver after an extended hepatectomy is critical for the outcome of the patient. The aim of this prospective study was to examine whether biliary bile acids could be an indicator for postoperative liver function.

METHODS

Externally drained bile samples were obtained from 51 patients with biliary or periampullary carcinomas before and after surgery. Patients were categorized into 3 groups: group A, 29 hepatectomized patients without liver failure; group B, 7 hepatectomized patients with liver failure (maximum serum bilirubin level, >10 mg/dL); and group C, 15 patients who underwent biliopancreatic resection without hepatectomy, with a good postoperative course. Bile samples were withdrawn 1 day before surgery and on postoperative days 1, 2, 3, 4, 6, and 7. Total bile acids were measured with a 3 alpha-hydroxysteroid dehydrogenase method.

RESULTS

Before surgery, the concentration of bile acids was higher in groups A and C than in group B, and correlated significantly with the indocyamine green disappearance rate (KICG) values (R(2) = 0.557; P <.0001). After surgery, bile acid concentrations decreased in all 3 groups until postoperative day 2, which was followed by a gradual increase. The concentration recovered to the preoperative level in groups A and C but remained low in group B. Biliary bile acid concentrations on day 2 correlated significantly with remnant liver KICG values (R(2) = 0.257; P =.0019). Among several parameters studied, including KICG, remnant liver KICG, biliary bile acids, and biliary bilirubin, biliary bile acid concentration had the most predictive power for occurrence of postoperative liver failure.

CONCLUSION

Biliary bile acid concentration could be a simple, real-time, reliable indicator of preoperative and postoperative liver function.

Effects of endotoxin tolerance on liver function after hepatic ischemia/reperfusion injury in the rat

OBJECTIVE

It is known that endotoxin tolerance prevents lethality after ischemia/reperfusion injuries (e.g., myocardial infarction) in laboratory animals. We used a rat model of partial hepatic ischemia/reperfusion to investigate whether endotoxin tolerance prevents associated lethality and disorders of liver function.

DESIGN

Prospective animal study.

SETTING

University research facility.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Hepatic ischemia was initiated by atraumatic clipping across the portal venous and hepatic arterial blood supply to the left lateral lobe for 90 mins. The common bile duct was canalized, and in a second set of experiments the bile duct of the left lateral lobe was canalized selectively. Bile flow, bile acids, and transaminases were determined during ischemia and 300 mins of reperfusion in endotoxin-tolerant and -nontolerant rats.

MEASUREMENTS AND MAIN RESULTS

Endotoxin-nontolerant animals showed a 50% lethality after hepatic ischemia/reperfusion injuries. All endotoxin-tolerant rats survived and did not react with any change in bile flow, showing a constant flow. The amount of bile acids in the common bile duct was reduced during ischemia and regained the concentrations of sham-operated animals 60 mins after reperfusion. From 180 mins after reperfusion, the difference between endotoxin-tolerant and -nontolerant animals was statistically significant. When bile acid concentration was determined in the ischemic left lateral lobe, ischemia/reperfusion was found to significantly decrease in endotoxin-nontolerant rats 60 mins after reperfusion. In contrast, endotoxin-tolerant rats produced normal amounts of bile acids 60 mins after reperfusion. At 120 mins after reperfusion, the amount of bile acids in the formerly ischemic left lateral lobe was more than normal.

CONCLUSIONS

In this model of partial hepatic ischemia/reperfusion, endotoxin tolerance prevents ischemia/reperfusion injury-associated lethality and local disorders of liver function. This phenomenon induced by endotoxin tolerance may be useful in liver surgery to prevent ischemia/reperfusion injury.

Nifedipine modulation of biliary GSH and GSSG/ conjugate efflux in normal and regenerating rat liver

Canalicular glutathione secretion provides the major driving force for bile acid-independent bile flow (BAIF), although the pathways involved are not established. The hypothesis that GSH efflux proceeds by a route functionally distinct from the high-affinity, low-capacity, mrp2-mediated pathway was tested by using perfused rat liver and three choleretic compounds that modify biliary secretion of GSH (the dihydropyridine nifedipine and organic anion probenecid) or GSSG [sodium nitroprusside (SNP)]. Whereas nifedipine (30 microM) stimulated GSH secretion and blocked SNP-stimulated GSSG efflux and choleresis, SNP (1 mM) was ineffective against nifedipine-stimulated GSH efflux or BAIF, suggesting that most GSSG exits through a GSH-inhibitable path independent of high-affinity GSSG/glutathione conjugate transport. Three observations support this proposal. SNP, but not nifedipine, significantly inhibited bromosulfophthalein (BSP, 1 microM) excretion. Probenecid (1 mM) blocked resting or nifedipine-stimulated GSH secretion but only weakly inhibited BSP excretion. Glutathione, but not BSP, efflux capacity was reduced following partial hepatectomy. We suggest GSH efflux is mediated by a high-capacity organic anion pathway capable of GSSG transport when its high-affinity route is saturated.

Differential expression of basolateral and canalicular organic anion transporters during regeneration of rat liver

BACKGROUND & AIMS

Liver regeneration in response to various forms of injury or surgical resection is a complex process resulting in restoration of the original liver mass and maintenance of liver-specific functions such as bile formation. However, liver regeneration is frequently associated with cholestasis, whose molecular pathogenesis remains unknown.

METHODS

To study the molecular mechanisms leading to cholestasis, expression of all major hepatic organic anion transporters contributing to bile formation was determined for up to 2 weeks in rats after 70% partial hepatectomy.

RESULTS

Inversely related to serum bile acid levels, basolateral transporters including the sodium-taurocholate cotransporter (Ntcp) and the organic anion transporting polypeptides Oatp1 and Oatp2 were markedly down-regulated at both protein and steady-state mRNA levels by 50%-60% of controls (P < 0.05) during early replicative stages of regeneration (12 hours to 2 days) with a slightly delayed time course for Oatp2. Expression of all basolateral transporters returned to control values between 4 and 4 days after partial hepatectomy. In contrast, protein and mRNA expression of both the canalicular ATP-dependent bile salt export pump (Bsep) and the multiorganic anion transporter Mrp2 remained unchanged or were slightly increased during liver regeneration, but also returned to control values 7-14 days after partial hepatectomy.

CONCLUSIONS

The data suggest a differential regulation of basolateral and canalicular organic anion transporters in the regenerating liver. Unaltered expression of Bsep and Mrp2 provides a potential molecular mechanism for regenerating liver cells to maintain or even increase bile secretion expressed per weight of remaining liver. However, down-regulation of basolateral organic anion transporters might protect replicating liver cells by diminishing uptake of potentially hepatotoxic bile salts, because the remaining liver initially cannot cope with the original bile acid pool size.

Changes in glutathione homeostasis during liver regeneration in the rat

We have shown previously that plating primary cultures of rat hepatocytes under low density, which stimulates hepatocytes to shift from the G0 to the G1 phase of the cell cycle, resulted in increased levels of glutathione (GSH) and cysteine, and increased activity of gamma-glutamylcysteine synthetase (GCS), the rate-limiting enzyme in GSH synthesis (Lu et al., Am. J. Physiol. 1992;263:C1181-C1189). In the current work we examined changes in GSH homeostasis after two-thirds partial hepatectomy (PH). Male Sprague-Dawley rats underwent two-thirds PH or sham operation. GSH, oxidized glutathione (GSSG), cysteine, GSH efflux, DNA synthesis, changes in GCS subunit messenger RNA (mRNA), and protein levels were measured 12 and 24 hours after PH. Both liver GSH and cysteine levels were doubled at 12 hours and remained elevated at 24 hours after PH. GSSG levels also increased, but the ratio of GSH to GSSG levels remained unchanged. The increase in GSH and cysteine levels preceded the increase in DNA synthesis. Sinusoidal GSH efflux was unchanged after two-thirds PH, but biliary GSH efflux decreased. However, total GSH efflux was minimally altered after two-thirds PH. The increase in GSH can be largely accounted for by the increase in both cysteine availability and the activity of GCS. The steady-state mRNA and protein levels of the GCS heavy subunit were increased at 12 hours after PH. The mRNA level of the GCS light subunit was unchanged. In summary, early in the course of liver regeneration the steady-state hepatic GSH levels double because of an increase in the biosynthesis of GSH.

Liver regeneration

Liver regeneration after the loss of hepatic tissue is a fundamental parameter of liver response to injury. Recognized as a phenomenon from mythological times, it is now defined as an orchestrated response induced by specific external stimuli and involving sequential changes in gene expression, growth factor production, and morphologic structure. Many growth factors and cytokines, most notably hepatocyte growth factor, epidermal growth factor, transforming growth factor-alpha, interleukin-6, tumor necrosis factor-alpha, insulin, and norepinephrine, appear to play important roles in this process. This review attempts to integrate the findings of the last three decades and looks toward clues as to the nature of the causes that trigger this fascinating organ and cellular response.

Hepatic bile acid synthesis and DNA synthetic rate after partial hepatectomy

The relationship between hepatic DNA synthetic rate and activity of cholesterol 7 alpha-hydroxylase, the rate limiting enzyme for bile acid synthesis, was examined in regenerating liver after partial hepatectomy or sham operation in rats. Hepatic cholesterol 7 alpha-hydroxylase activity was significantly (P < 0.001) suppressed on days 1 and 2, returned to the control level on day 3, and was significantly raised on day 7 after hepatectomy. The rate of DNA synthesis was significantly (P < 0.001) activated during the first 3 days after hepatectomy and returned to the control level on day 7. Enzyme activities regulating hepatic bile acid synthesis and DNA synthesis change inversely during liver regeneration after hepatectomy.