Expression of hepatocyte growth factor mRNA in regenerating rat liver after partial hepatectomy.

Hepatocyte Growth Factor (HGF) is a potent complete mitogen for primary cultures of hepatocytes in vitro. There is strong evidence that this novel growth factor may mediate hepatocyte regeneration after liver damage. We have shown previously that the amount of immunoreactive HGF markedly increases in the serum of rats soon after partial hepatectomy or CCl4 administration. In the present paper, we demonstrate that the level of HGF mRNA in rat liver also dramatically increases from 3 to 6 hours post hepatectomy, peaks at 12 hr and gradually returns to undetectable levels by 72 to 96 hours post hepatectomy. In separate experiments, DNA synthesis (in vivo) was determined in rat liver remnants after partial hepatectomy. DNA synthesis peaked 24 hr after hepatectomy, 12 hr after the peak of HGF mRNA expression. These results suggest that HGF may be one of the major early signals that triggers hepatocyte proliferation during liver regeneration.     

Possible endocrine control by hepatocyte growth factor of liver regeneration after partial hepatectomy.

Hepatocyte Growth Factor (HGF), which is a most potent growth factor for primary cultured hepatocytes, may act as a trigger for liver regeneration. After 70% of the rat liver was removed, HGF activity in the remnant liver began to increase within 24 h. In parallel with the activity, the HGF mRNA level in the remnant liver increased at 12 h after the operation and reached a maximum at 24 h. Increases in HGF activity and in the mRNA level were much lower and later than those in the liver of rats with hepatitis induced with CCl4. However, the first increase in HGF activity in the plasma of hepatectomized rats was noted 3 h after the resection, that is much earlier than the initial DNA synthesis in the remnant liver. Thus, while HGF production was induced in the remnant liver during regeneration after partial hepatectomy, the initial trigger may not be the liver-derived HGF, rather, it may be HGF derived from extrahepatic organs, via blood circulation.     

Folate metabolism in the rat liver during regeneration after partial hepatectomy

1. Folate metabolism was studied during the early phases of liver regeneration after partial hepatectomy in rats accustomed to eating during the first 8h of a daily 12h dark period. 2. The content of 5-CH(3)-H(4)folate was drastically decreased during the first hours of regeneration. 3. The total HCO-H(4)folate coenzymes showed a constant decrease during the first 3 days of regeneration, and a continuous interconversion between 5-HCO-H(4)folate and 10-HCO-H(4)folate. 4. 10-HCO-H(4)folate synthetase, serine hydroxymethyl-transferase and 5,10-CH(2)-H(4)folate dehydrogenase activities were relatively low during the first hours after the operation, and increased only several hours later. 5. The increase in enzyme activities showed a stepwise pattern, apparently due to an interaction between the regeneration process and the controlled feeding schedules.     

Dynamics of Hlo content in rat liver after partial hepatectomy

• 1.1. The changes in the lysine-rich histone subfraction hl₀ have been quantitatively studied in rat liver during the regeneration period after partial hepatectomy.
• 2.2. A gradual decrease in this protein was found early after operation with a minimal value around the time of maximal mitotic activity.
• 3.3. The reduction in the hl₀ content paralleled well the increasing number 0f cells in the cell cycle.

     

Expression and role of vascular endothelial growth factor in liver regeneration after partial hepatectomy in rats.

Vascular endothelial growth factor (VEGF) plays a major role in angiogenesis, which is essential for both healing of injured tissue and proliferation of carcinoma cells. In this study we elucidated the expression and role of VEGF in rat liver regeneration after partial hepatectomy. VEGF expression was mainly detected in periportal hepatocytes and reached a maximal level 48-72 hr after partial hepatectomy by both immunohistochemistry and in situ hybridization. Similarly, immunohistochemistry for Ki-67 showed that the proliferative activity of sinusoidal endothelial cells was highest in the periportal area and reached a maximal level 72 hr after partial hepatectomy. Moreover, neutralization of VEGF significantly inhibited proliferative activity of hepatocytes (p<0. 0001), as well as sinusoidal endothelial cells (p<0.001), at 48 and 96 hr after partial hepatectomy. Conversely, injection of VEGF significantly promoted proliferative activity of hepatocytes (p<0. 0001) as well as sinusoidal endothelial cells (p<0.0005) at 48 hr after partial hepatectomy. These results suggest that VEGF promotes proliferation of hepatocytes through reconstruction of liver sinusoids by proliferation of sinusoidal endothelial cells. Furthermore, these data point to a new therapeutic strategy, the use of VEGF and other hepatocyte growth factors in fulminant or severe acute hepatitis.     

Hepatic pyruvate metabolism during liver regeneration after partial hepatectomy in the rat

Hepatic pyruvate kinase (PK) and pyruvate dehydrogenase (PDHa) specific activities were decreased after partial hepatectomy or sham operation. The decreases were more marked and sustained after partial hepatectomy. These activity changes ensure that hepatic carbon flux after partial hepatectomy is predominantly in the direction of gluconeogenesis. The decrease in PK specific activity observed after partial hepatectomy was associated with a decreased PK activation ratio (activity measured at 0.15 mM PEP: activity measured at 5.0 mM PEP), and hepatic concentrations of PEP were increased. The low hepatic PDHa activity observed at the first day after partial hepatectomy occurred concomitantly with an increased fatty acid concentration. PDHa activity increased after inhibition of lipolysis. The results indicate that carbohydrate utilization is unimportant for hepatic energy supply during liver regeneration. There was no evidence that the control of PK or PDH in the regenerative liver after partial hepatectomy differed from that observed in the liver of the unoperated rat.     

Hyperbaric oxygen preconditioning promotes angiogenesis in rat liver after partial hepatectomy

Hyperbaric oxygen preconditioning (HBO-PC) increases the level of HIF-1alpha (hypoxia inducible factor-1alpha) and its target gene VEGF (vascular endothelial growth factor) which is involved in angiogenesis. Liver regeneration is an angiogenesis-dependent process. We hypothesized that HIF-1alpha and VEGF mediated the angiogenesis effect of HBO-PC on regenerating rat liver. Male Sprague Dawley rats received HBO-PC followed by 70% partial hepatectomy. Proliferation of hepatocytes and endothelial cells was evaluated by BrdU (bromodeoxyuridine) staining. Microvascular density was assessed by immunohistochemistry. mRNA expression of HIF-1alpha was assessed by quantitative RT-PCR and protein levels of HIF-1alpha and VEGF were assessed by western blot. HIF-1alpha DNA-binding activity was determined with an ELISA-based kit. HBO-PC increased the proliferation index of endothelial cells and microvascular density at 48 h after partial hepatectomy. The protein level and DNA-binding activity of HIF-1alpha and the protein level of VEGF were increased by HBO-PC before and after partial hepatectomy. Partial hepatectomy alone also increased proliferation index and the expressions of HIF-1alpha and VEGF. Our results indicated that the angiogenesis effect of HBO-PC on liver after partial hepatectomy could be achieved by increased HIF-1alpha activity and VEGF expression. However, the angiogenic effect of HBO-PC is moderate and HBO-PC failed to produce additional effect on the enhancement of HIF-1alpha and VEGF induced by partial hepatectomy alone.     

Turnover of ribosomal proteins in regenerating rat liver after partial hepatectomy

The rates of synthesis and degradation of ribosomal proteins, prelabelled with [14C]bicarbonate, were determined as an index of the rate of ribosome turnover in regenerating rat liver. The half-life of ribosomes is about 178 and 75 hr in regenerating and normal liver, respectively. The comparison of turnover rates of ribosomal proteins with the corrected values of rRNA, based on re-utilization of nucleotides, suggests that ribosomes are metabolized as a unit in vivo. There is at least 70% overestimation for ribosome half-life when orotate-labelled RNA is used for turnover determinations. The absolute rate of synthesis is estimated as 3925 and 1081 ribosomes/min per cell in 24 hr regenerating and normal rat liver, respectively.     

Formation and accumulating of hypotaurine in rat liver regenerating after partial hepatectomy

Hypotaurine is considered to be an intermediate in the major pathway for the biosynthesis of taurine in mammals yet is rarely detected in mammalian tissue. The activity of cysteinesulfinic acid decarboxylase, the enzyme presumably responsible for the biosynthesis of hypotaurine, is frequently present in great amounts in tissue, whereas the mechanism for the conversion of hypotaurine to taurine is poorly understood, there being some doubt at present if an enzyme exists for such a purpose. This paper reports the accumulation of hypotaurine in the liver of rats regenerating after partial hepatectomy. Further, the formation and accumulation of [³⁵S]hypotaurine from [³⁵S]methionine under the same conditions was observed. No hypotaurine was detected in liver of sham-operated control animals, even after the intraperitoneal injection of authentic hypotaurine. These observations suggest that rat liver normally possesses a mechanism for the rapid conversion of hypotaurine to taurine and that this mechanism is impeded in liver regenerating after partial hepatectomy.     

Role of endogenous TNF-alpha and sphingosine in induced DNA synthesis in regenerating rat liver after partial hepatectomy.

Cytokine-stimulated metabolism of sphingomyelin results in the accumulation of ceramide and sphingosine which play a part in the regulation of cell proliferation, differentiation, and reception, as well as in oncogenesis. Formation of TNF-alpha (a member of the cytokine family), accumulation of sphingosine, and DNA synthesis (measured by immunoblotting, HPLC, and [3H]thymidine incorporation, respectively) were studied in rat liver after partial hepatectomy. The content of TNF-alpha was found to increase during 12 h following hepatectomy. The maximum of sphingomyelinase activity and accumulation of sphingosine precede the maximum of DNA synthesis. Sphingosine is known to inhibit protein kinase C. On the other hand, it stimulates the metabolism of phosphatidylinositol, thus causing accumulation of diacylglycerol and inositol-1,4,5-triphosphate, which in turn activate protein kinase C. Hence, the release of TNF-alpha in regenerating liver may modulate DNA synthesis through the accumulation of sphingosine which is involved in regulation of protein kinase C activity and of phosphatidylinositol turnover.