Hormonal factors and liver growth

A novel herbal formulation "LiverCare" differentially regulates primary rat hepatocyte and hepatocarcinoma cell proliferation in vitro

Hepatocyte growth factor (HGF) plays an important role in hepatocyte proliferation. HGF expression is regulated by various signaling molecules and nuclear receptors. In the present study, LiverCare(®) (LC), a novel polyherbal formulation (The Himalaya Drug Company, Bangalore, India), was evaluated for its efficacy, using co-cultures of primary rat hepatocytes-non-parenchymal cells (NPCs) and human hepatocellular carcinoma cells (HepG2). The rate of primary hepatocyte co-culture proliferation was significantly and dose-dependently increased by LC as determined by [(3)H]thymidine incorporation into newly synthesized DNA and cell proliferation assay. LC also increased HGF expression in primary hepatocyte co-culture. Albumin and urea content remained constant during proliferation of hepatocyte co-cultures in the presence of LC with decreased activity of alanine aminotransferase. It is interesting that LC inhibited incorporation of [(3)H]thymidine into DNA in HepG2 cells. LC enhanced peroxisome proliferator-activated receptor-α expression during hepatocyte proliferation, whereas tumor necrosis factor-α expression remained unaffected. In conclusion, our study clearly showed that LC differentially regulates primary rat hepatocytes and human hepatocarcinoma cell proliferation. LC may be a promising candidate for treating degenerative liver diseases by enhancing liver regeneration.

Liver regeneration after partial hepatectomy: critical analysis of mechanistic dilemmas

Liver regeneration after partial hepatectomy is one of the most studied models of cell, organ, and tissue regeneration. The complexity of the signaling pathways initiating and terminating this process have provided paradigms for regenerative medicine. Many aspects of the signaling mechanisms involved in hepatic regeneration are under active investigation. The purpose of this review is to focus on the areas still not well understood. The review also aims to provide insights into the ways by which current concepts of liver regeneration can provide understanding regarding malfunction of the regenerative process in liver diseases, such as acute liver failure.

Cell cycle effects resulting from inhibition of hepatocyte growth factor and its receptor c-Met in regenerating rat livers by RNA interference

Hepatocyte growth factor (HGF) and its receptor c-Met are involved in liver regeneration. The role of HGF and c-Met in liver regeneration in rat following two-thirds partial hepatectomy (PHx) was investigated using RNA interference to silence HGF and c-Met in separate experiments. A mixture of 2 c-Met-specific short hairpin RNA (ShRNA) sequences, ShM1 and ShM2, and 3 HGF-specific ShRNA, ShH1, ShH3, and ShH4, were complexed with linear polyethylenimine. Rats were injected with the ShRNA/PEI complex 24 hours before and at the time of PHx. A mismatch and a scrambled ShRNA served as negative controls. ShRNA treatment resulted in suppression of c-Met and HGF mRNA and protein compared with that in controls. The regenerative response was assessed by PCNA, mitotic index, and BrdU labeling. Treatment with the ShHGF mixture resulted in moderate suppression of hepatocyte proliferation. Immunohistochemical analysis revealed severe suppression of incorporation of BrdU and complete absence of mitosis in rats treated with ShMet 24 hours after PHx compared with that in controls. Gene array analyses indicated abnormal expression patterns in many cell-cycle- and apoptosis-related genes. The active form of caspase 3 was seen to increase in ShMet-treated rats. The TUNEL assay indicated a slight increase in apoptosis in ShMet-treated rats compared with that in controls.

CONCLUSION

The data indicated that in vivo silencing of c-Met and HGF mRNA by RNA interference in normal rats results in suppression of mRNA and protein, which had a measurable effect on proliferation kinetics associated with liver regeneration.

Growth potential of adult hepatocytes in mammals: Highly replicative small hepatocytes with liver progenitor‐like traits

The liver is one of the few organs that is capable of completely regenerating itself without using a stem cell population. When damaged, growth factors and cytokines are released, stimulating terminally differentiated adult hepatocytes and making them re-enter the cell cycle. We have been developing a series of studies on the growth potential of rat and human hepatocytes to identify a population of hepatocytes that is responsible for the regeneration of the injured liver. For this purpose, we established an appropriate culture method for hepatocytes by which growth and differentiation capacities are practically examined under various experimental conditions. This in vitro assay system allows us to identify small hepatocytes that are prominently replicative compared to large hepatocytes. Non-parenchymal cells play critical roles in the proliferation of small hepatocytes. These hepatocytes are present in both rat and human liver and are located in portal regions there. Phenotypic features were examined at morphological and gene/protein levels in detail, which showed the phenotypic plasticity in vitro. Mammalian liver includes a population of small hepatocytes in normal adults with a minute occupancy rate. We speculate that small hepatocytes play a role in regenerating the injured liver and in compensating for apoptotic hepatocytes in the physiological turnover of hepatocytes.

Extracellular ATP activates c-jun N-terminal kinase signaling and cell cycle progression in hepatocytes

Partial hepatectomy leads to an orchestrated regenerative response, activating a cascade of cell signaling events necessary for cell cycle progression and proliferation of hepatocytes. However, the identity of the humoral factors that trigger the activation of these pathways in the concerted regenerative response in hepatocytes remains elusive. In recent years, extracellular ATP has emerged as a rapidly acting signaling molecule that influences a variety of liver functions, but its role in hepatocyte growth and regeneration is unknown. In this study, we sought to determine if purinergic signaling can lead to the activation of c-jun N-terminal kinase (JNK), a known central player in hepatocyte proliferation and liver regeneration. Hepatocyte treatment with ATPgammaS, a nonhydrolyzable ATP analog, recapitulated early signaling events associated with liver regeneration-that is, rapid and transient activation of JNK signaling, induction of immediate early genes c-fos and c-jun, and activator protein-1 (AP-1) DNA-binding activity. The rank order of agonist preference, UTP>ATP>ATPgammaS, suggests that the effects of extracellular ATP is mediated through the activation of P2Y2 receptors in hepatocytes. ATPgammaS treatment alone and in combination with epidermal growth factor (EGF) substantially increased cyclin D1 and proliferating cell nuclear antigen (PCNA) protein expression and hepatocyte proliferation in vitro. Extracellular ATP as low as 10 nM was sufficient to potentiate EGF-induced cyclin D1 expression. Infusion of ATP by way of the portal vein directly activated hepatic JNK signaling, while infusion of a P2 purinergic receptor antagonist prior to partial hepatectomy inhibited JNK activation. In conclusion, extracellular ATP is a hepatic mitogen that can activate JNK signaling and hepatocyte proliferation in vitro and initiate JNK signaling in regenerating liver in vivo. These findings have implications for enhancing our understanding of novel factors involved in the initiation of regeneration, liver growth, and development.

Induction of DNA synthesis in primary cultures of rat hepatocytes by serotonin: possible involvement of serotonin S2 receptor

The involvement of serotonin and its receptor subtype in the induction of hepatocyte DNA synthesis was investigated in primary cultures of adult rat hepatocytes. Serotonin caused a dose-dependent increase in DNA synthesis in primary cultures of rat hepatocytes in the presence of epidermal growth factor (EGF) and insulin, as measured by [3H]thymidine incorporation. The serotonin S2 receptor antagonists, ketanserin (10(-6) mol/L) and spiperone (10(-6) mol/L), blocked stimulation of DNA synthesis by serotonin. Displacement studies on [3H]5-hydroxytryptamine (5-HT) binding to crude membranes from control and regenerating liver tissue, using cold ketanserin and spiperone, showed an increased involvement of S2 receptors of serotonin in the regenerating liver during the DNA-synthetic phase. Serotonin enhanced the phosphorylation of a 40-kd substrate protein of protein kinase C (PKC) in the regenerating liver during the DNA synthetic phase of the hepatocyte cell cycle. This was blocked by ketanserin, indicating that serotonin S2 receptor activates PKC, an important second messenger in cell growth and division, during rat liver regeneration. Our results show that serotonin can act as a potent hepatocyte comitogen and induce DNA synthesis in primary cultures of rat hepatocytes, which is suggested to be mediated through the serotonin S2 receptors of hepatocytes.

Amelioration of disordered hepatic protein synthesis by the deleted form of hepatocyte growth factor in models of liver failure in rats

Because the liver plays an important role in protein synthesis and cholesterol metabolism and reductions in these functions are observed in almost all hepatic disorders, the effects of the deleted form of hepatocyte growth factor (dHGF) on disordered hepatic protein synthesis were studied in various liver-injured rat models using Wistar male rats. In the 70% hepatectomized rats, plasma clotting time was prolonged and the serum level of total protein and the liver protein content were decreased. The treatment of the animals with dHGF (100-500 micrograms kg-1, i.v., twice daily) ameliorated these parameters at 48 or 72 h. The administration of carbon tetrachloride or D-galactosamine to hepatectomized rats induced a marked prolongation of plasma clotting time and hypoproteinaemia. In the animals treated with dHGF (500 micrograms kg-1, i.v., twice daily) these parameters were rapidly reversed compared with those of control groups. In a hepatocellular necrosis model induced by dimethylnitrosamine, the plasma clotting time was extremely prolonged, and liver protein content, serum total protein, albumin, HDL-cholesterol (as an index of lipoprotein) and plasma lecithin-cholesterol acyltransferase activity severely reduced. In this severely injured model, dHGF (5-500 micrograms kg-1, i.v., twice daily for 28 days) dose-dependently prevented the loss of liver protein content and improved the disordered plasma coagulability and serum protein levels. These results suggest that dHGF is useful for ameliorating the disorders in hepatic functions such as protein synthesis.

Glutamic acid potentiates hepatocyte response to mitogens in primary culture

Adult rat hepatocytes in primary culture responded to epidermal growth factor (EGF) by increased DNA synthesis. When hepatocytes were cultured in Leibovitz L-15 medium, their response to EGF was low compared with that in Williams' medium E or Koga's medium L. Furthermore, female rat hepatocytes showed almost no response to the mitogenic action of EGF compared with male rat hepatocytes in L-15 medium. Addition of glutamic acid (1-20 mM) to EGF-containing L-15 medium not only enhanced DNA synthesis > tenfold in both male and female hepatocytes, but eliminated the sex differences in DNA synthesis. Aspartic acid, glutamine, or ornithine at 20 mM did not replace the glutamic acid effect on DNA synthesis. Proline also enhanced EGF-induced DNA synthesis, although it was less effective than glutamic acid. Therefore, this effect may be specific to a high concentration of glutamic acid. Glutamic acid by itself did not stimulate DNA synthesis at any concentrations tested. In the presence of glutamic acid, EGF showed a dose-dependent (0.5-20 ng/ml) stimulation of DNA synthesis with a maximal effect at 10 ng/ml. Almost the same effect was obtained with transforming growth factor alpha (0.5-20 ng/ml). Glutamic acid also induced an expansion of the mitogenic action of angiotensin II. Since glutamic acid did not affect [125I]EGF binding to hepatocytes or its processing, the effect may occur internal to the receptor. These results suggest that glutamic acid modulates the sensitivity of the hepatocyte response to mitogens.

Effects of human epidermal growth factor on the development of bile canaliculi in neonatal rat hepatocytes in primary culture

We have examined the effects of human epidermal growth factor (hEGF), a growth-promoting factor for hepatocytes, on the cytoskeletal structure and intercellular contacts in neonatal hepatocytes in primary culture. The ultrastructural characteristics of cellular contacts and bile canaliculi (BC) were examined using a newly developed technique of scanning electron microscopy for cultured hepatocytes. The neonatal hepatocytes incubated with hEGF plus insulin for 3 h showed more variety in shape than controls, and their cellular contacts were very loose with many long fibers. At this time, there were no changes in the distribution of microtubules or microfilaments. After treatment with hEGF plus insulin for 21 h, the distribution of microfilaments was altered. Actin filaments no longer surrounded BC, but were observed near the cell periphery; in addition, DNA synthesis was increased to 3.9 times the rate in controls. Treatment with dexamethasone for 3 h caused tight straight cellular contacts, and after 21 h actin filaments appeared around slightly dilated BC, but there was no increase in DNA synthesis. Transmission electron microscopy showed that the transport and secretion of horseradish peroxidase in BC was inhibited after 3-h incubation with hEGF. These results suggested that hEGF first affected the cellular contacts of hepatocytes necessary for the development of cellular polarity, and then affected the distribution of actin filaments, the development of functioning BC being suppressed.

Down regulation of epidermal growth factor receptors in liver proliferation induced by a mixture of triiodothyronine, amino acids, glucagon, and heparin (TAGH)

This study investigated the mechanisms by which TAGH solution (a mixture of triiodothyronine, amino acids, glucagon, and heparin) induces DNA synthesis in hepatocytes in the liver of intact rats, with particular reference to events at the epidermal growth factor (EGF) receptor. Both partial hepatectomy and infusion of TAGH stimulated DNA synthesis at 24 hours and both procedures resulted in a reduction of EGF receptors assessed in plasma membranes isolated from rat liver at this time. In cell cultures, while EGF strongly stimulated DNA synthesis and started EGF receptor down regulation, TAGH had only a minor effect (1.5 x basal) on DNA synthesis and did not interact with or down regulate the EGF receptor. Membrane phosphorylation studies, however, showed that TAGH induced phosphorylation of tyrosine residues in the EGF receptor. The in vivo action of TAGH seems to entail recruitment of similar changes in the EGF receptor to those that occur after partial hepatectomy.

Comparative analysis of mitogenic and morphogenic effects of HGF and EGF on rat and human hepatocytes maintained in collagen gels

Hepatocytes maintained in collagen gels remain differentiated for prolonged periods of time compared to cells maintained on conventional cultures. Previous studies with other culture systems in which chemical supplements or substratum modifications enhanced hepatocyte differentiation showed that in all of these systems hepatocytes do not respond to mitogens. In this study it is shown that hepatocytes maintained between two layers of collagen gels respond to mitogens HGF (also known as scatter factor (HGF/SF)) and epidermal growth factor (EGF). Cell density did not affect the responsiveness to mitogens as in conventional cultures. In addition both mitogens (HGF more pronounced) induce characteristic morphogenic changes in which hepatocytes form processes and join in formation of cords. Hepatocytes respond to mitogens for up to 6 days in culture at which point they become refractory to further mitogenic stimulation. This occurs despite electron microscopic evidence that these cells are fully viable when they become refractory to mitogenesis. The refractory state is not modified by substitution of one growth factor for the other or by addition of growth factors at different times. Hepatocytes in the refractory state become again responsive to mitogens when the collagen gels are dispersed by collagenase and the cells are replated on conventional substrates.

Inhibition by verapamil of hepatocarcinogenesis induced by N-nitrosomorpholine in Sprague-Dawley rats

The effect of verapamil on hepatocarcinogenesis induced by N-nitrosomorpholine (NNM) was investigated in male Sprague-Dawley rats. Rats were given drinking water containing NNM for 8 weeks and received i.p. injections of verapamil or vehicle every other day for 16 weeks from the start of the experiment. Pre-neoplastic and neoplastic lesions staining positive for gamma-glutamyl transpeptidase (GGT) or the placental type of glutathione-S-transferase (GST-P) were examined histochemically at week 16. Prolonged administration of verapamil resulted in a significant decrease in the number of GGT-positive and GST-P-positive lesions. The incidence and volume as a percentage of parenchyma of hepatocellular carcinomas were also significantly less in rats treated with verapamil than in controls. Administration of verapamil significantly decreased the labelling indices of pre-neoplastic lesions and adjacent liver. These findings indicate that verapamil inhibits hepatocarcinogenesis and that this may be related to its inhibitory effect on cell proliferation in neoplastic lesions and surrounding hepatocytes.

Enhancement by isoproterenol of hepatocarcinogenesis induced by N-nitrosomorpholine in Sprague-Dawley rats

The effect of isoproterenol on hepatocarcinogenesis induced by N-nitrosomorpholine (NNM) was investigated in male Sprague-Dawley rats. Rats were given drinking water containing NNM for 8 weeks and s.c. injections of isoproterenol or vehicle every other day for 13 weeks. Pre-neoplastic and neoplastic lesions staining positive for gamma-glutamyl transpeptidase (GGT) or the placental type of glutathione-S-transferase (GST-P) were examined histochemically at week 13. Prolonged administration of isoproterenol resulted in a significant increase in the number of GGT-positive, but not GST-P-positive, lesions. The incidence, number and size of hepatocellular carcinomas were also significantly greater in rats treated with isoproterenol than in controls. Administration of isoproterenol significantly increased the intracellular cAMP and the labeling indices of pre-neoplastic lesions and adjacent liver. These findings indicate that isoproterenol enhances hepatocarcinogenesis and that this may be related to its enhancing effect, mediated by cAMP, on cell proliferation in neoplastic lesions and surrounding hepatocytes.

Mitogenic effects of hepatic stimulator substance on cultured nonparenchymal liver epithelial cells

We determined whether hepatic stimulator substance shares its mitogenic specificity for hepatocytes with nonparenchymal epithelial cells in the hepatocyte lineage. Cell lines designated HTC (derived from a rat hepatoma known to respond to hepatic stimulator substance) and FNRL, K-16 and K-22 (derived from rat liver nonparenchymal epithelial cells) were used. After exposure to hepatic stimulator substance, [3H]-thymidine incorporation into DNA was significantly increased (p less than 0.001) in HTC, FNRL and K-16 cells, but not in K-22 cells. Fluorescence-activated cell sorting demonstrated that the mitogenic response to hepatic stimulator substance was associated with a greater proportion of cells entering the S phase. Epidermal growth factor, alone or in combination with hepatic stimulator substance, had no significant mitogenic effect on FNRL cells, but exposure of these cells to transforming growth factor-beta 1 inhibited [3H]-thymidine incorporation into DNA and reduced the proportion of cells in the S and G2/M phases. Simultaneous exposure of FNRL cells to hepatic stimulator substance and transforming growth factor-beta 1 abrogated the inhibitory effect of transforming growth factor-beta 1. Comparison of butyrate-synchronized HTC cells with hepatic stimulator substance-treated HTC cells showed that S-phase progression in these conditions was different, with no intervening cell cycle arrest after treatment with hepatic stimulator substance. Mitogenic stimulation of FNRL and K-16 cells with the liver-specific growth factor hepatic stimulator substance suggests that these cells are of hepatocyte lineage. These results strengthen the evidence for a possible link between hepatocytes and nonparenchymal liver epithelial cells during liver biogenesis and differentiation.

Insulin and glucagon levels in fulminant hepatic failure in man

The behavior of insulin and glucagon and related metabolic substrates was assayed in plasma of patients with fulminant hepatic failure. All 12 subjects were provided the same nutritional support. High levels of insulin and glucagon were present at all times and no difference was observed between surviving patients (four) and those who died (8). Elevated values for branched-chain and aromatic amino acids as well as alanine were present. Statistically significant lower levels of aromatic amino acids and consequently a greater branched chain-aromatic amino acid ratio was found in surviving vs nonsurviving patients. A significantly greater level of alpha-fetoprotein was found in patients who survived as compared to those who died.

Regulation of hepatic energy metabolism by epidermal growth factor

Employing the non-recirculating perfused rat liver preparation, we have investigated the regulation of hepatic gluconeogenesis, and metabolic fluxes through the tricarboxylic acid cycle and 2-oxoglutarate dehydrogenase reaction by epidermal growth factor (EGF) which mimics the actions of both insulin and Ca(2+)-mobilizing hormones (e.g. vasopressin). As monitored by the rate of 14CO2 production from [2-14C]pyruvate (0.5 mM), EGF (10 nM) transiently stimulated the activity of the tricarboxylic acid cycle. EGF also transiently stimulated hepatic gluconeogenesis from pyruvate. The transient stimulation of tricarboxylic acid cycle activity and gluconeogenesis were accompanied by an increase in perfusate Ca2+ content indicating that EGF also altered hepatic Ca2+ fluxes. EGF-elicited stimulation of gluconeogenesis was, at least in part, the result of a transient (50%) inhibition of pyruvate kinase activity. Likewise, EGF-mediated stimulation of tricarboxylic acid cycle activity can, in part, be attributed to EGF-elicited stimulation of metabolic flux through the mitochondrial, Ca(2+)-sensitive, 2-oxoglutarate dehydrogenase reaction. The regulation of hepatic metabolism by EGF appears to be the manifestation of alteration in cellular Ca2+ content since in experiments performed under conditions known to abolish the ability of EGF to alter cytosolic free-Ca2+ concentrations, i.e. in livers of pertussis-toxin-treated rats, EGF did not alter either perfusate Ca2+ content or any of the metabolic parameters monitored. Additionally, experiments involving pulsatile infusion of either EGF or phenylephrine into livers demonstrated that, unlike the alpha 1-adrenergic receptor, homologous desensitization of the EGF receptor occurs. Such a homologous desensitization of the EGF receptor can explain the transient nature of EGF-elicited stimulation of various metabolic processes. Since protein kinase C activation by EGF can lead to receptor desensitization, experiments were performed with phorbol esters which either activate or do not alter protein kinase C activity. While the inactive phorbol ester 4 alpha-phorbol 12,13-didecanoate did not modulate the hepatic actions of EGF, activation of protein kinase C by 4 beta-phorbol 12-myristate 13-acetate (70 nM) abolished the ability of EGF to stimulate gluconeogenesis, tricarboxylic acid cycle activity and metabolic flux through the 2-oxoglutarate dehydrogenase complex.

Altered levels of phosphoinositide metabolites and activation of guanine-nucleotide dependent phospholipase C in rat hepatic tumors

The metabolism of phosphatidylinositol was studied in normal quiescent hepatocytes, hepatocellular carcinomas induced by single dose of diethylnitrosamine, followed by 2-acetylaminofluorene and partial hepatectomy (Solt-Farber model), and in an established hepatoma cell line, JB1. The JB1 hepatoma cell line and hepatocellular carcinomas demonstrated a 4- to 5-fold higher rate of turnover of [3H]-inositol and [3H]-glycerol than the control hepatocytes. Significantly, elevated levels of second messengers inositol 1,4,5-trisphosphate and sn-1,2-diacylglycerol were noted in hepatic tumor cells within 4 hr of labeling with precursor molecules, whereas no detectable level of 3H-labeled inositol trisphosphate was noted in quiescent hepatocytes, even after incubation with 10 mM LiCl for 30 min. Approximately 2.5-fold higher specific activities of a guanine nucleotide and Ca+2 dependent phosphatidylinositol 4,5-bisphosphate specific phospholipase C were detected in the hepatocellular carcinoma cells. The cellular location of the phospholipase C activity was also different, being membrane bound in hepatocytes and equally distributed between cytosolic and membrane factions in the hepatomas. These data are consistent with the hypothesis that the enhanced production of diacylglycerol and inositol 1,4,5-trisphosphate in hepatocellular carcinomas may be due to the activation of a guanine nucleotide dependent phosphatidylinositol 4,5-bisphosphate specific phospholipase C. These data are the first to compare phosphoinositide turnover in normal liver and hepatic tumor cells and suggest that the sustained levels of second messengers is closely associated with the transformation and enhanced growth rate in hepatic tumor cells.

Lack of effects of viral sialoadenitis and depletion of epidermal growth factor on initiation of hepatic carcinogenesis in the rat

Sialodacryoadenitis (SDA) is a commonly-encountered coronaviral infection in laboratory rats that causes acute destruction of submandibular salivary glands. SDA results in depletion of salivary epidermal growth factor (EGF) and may thereby affect EGF-dependent cell growth processes. The purpose of this study was to determine the effects of SDA virus (SDAV) infection on the growth factor-dependent stages of experimental liver carcinogenesis. Rats were injected ip with the carcinogen diethylnitrosamine (DENA) at 1, 2, or 3 weeks following inoculation with SDAV. Uninfected control rats were treated only with DENA. The salivary glands of SDAV-inoculated and control rats were stained using the immunoperoxidase method for the detection of EGF. Residual submandibular salivary gland lesions and focal depletion of EGF were still evident in affected submandibular glands for up to 42 days after SDAV infection. Serum EGF concentrations measured at 9, 28, and 42 days following SDAV inoculation were reduced, but were not significantly different in comparison with non-inoculated, DENA-treated control rats. Initiated hepatocytes were detected 21 days after DENA treatment in formalin-fixed sections by an immunoperoxidase stain for the P isoenzyme of the enzyme glutathione S-transferase (GST-P). There was no significant difference in the number of foci of GST-P positive cells in a comparison of initiated cells in SDAV-inoculated and non-inoculated rats. Based on this model, concurrent infection with SDAV does not appear to have any significant effects on the initial stages of chemical hepatocarcinogenesis in the rat.

Transforming growth factor alpha in developing rats

Transforming growth factor-alpha (TGF-alpha) concentrations were measured in lung, brain, liver, and kidney of rats at three different ages (20 days gestation and 9 and 50 days postnatal). TGF-alpha concentrations were maximal in the lung and brain by 20 days of gestation and showed minimal changes during nursing (day 9) and young adulthood (day 50). The liver, which also showed maximal TGF-alpha concentration by 20 days of gestation, demonstrated a progressive reduction with age to nadir values in the young adult. In contrast to the pattern in other tissues, kidney had the lowest concentration of TGF-alpha in late gestation and showed an increase by 50 days of age. As TGF-alpha acts via the epidermal growth factor (EGF) receptor, its function in development may be analogous to that of EGF. Thus TGF-alpha may have a role in lung maturation and postinjury repair, liver repair and regeneration, and neuronal cell growth.

Effect of epidermal growth factor on the expression of protooncogenes c-myc and c-Ha-ras in short-term primary hepatocyte culture

We have characterized the effect of the hepatomitogen epidermal growth factor (EGF) on the expression of the cellular protooncogenes c-Ha-ras and c-myc in short-term (48 hours) primary hepatocyte culture. mRNA concentrations of both protooncogenes increased dramatically in nonproliferating cultures and in the absence of EGF, suggesting that the isolation procedure or the culture conditions may trigger expression of these genes or potentially increase the lifetime of transcripts in vitro, regardless of the presence of a mitogen. In cells treated with EGF, a distinct peak in c-Ha-ras expression was seen 24 hours after EGF treatment. This coincided with the onset of DNA synthesis. No such peak was seen in cultures not treated with EGF. The c-myc mRNA concentrations were increased relatively equally in all cultures with or without the addition of EGF. These data show a differential response of these two cell-cycle-associated genes to the culture conditions and EGF stimulation. It also demonstrated that enhanced gene expression for Ha-ras and myc in hepatocytes can occur in the absence of cell proliferation.

Acidic fibroblast growth factor (HBGF-1) stimulates DNA synthesis in primary rat hepatocyte cultures

Acidic fibroblast growth factor (aFGF) stimulated DNA synthesis in primary rat hepatocyte cultures in a dose-dependent manner with maximal effect at 10-50 ng ml-1. This activity was dependent on the presence of heparin at a concentration of 10-50 micrograms.ml-1. Insulin interacted synergistically with aFGF, as it did with epidermal growth factor (EGF). The response to aFGF was only 50% that found with EGF. The disparity was not due to different kinetics of DNA synthesis, since the peak response for both growth factors occurred at 36-72 hr after plating of the hepatocytes. The potential relevance of this novel hepatocyte mitogen to normal and pathological liver growth is discussed.

Altered responses of regenerating hepatocytes to norepinephrine and transforming growth factor type beta

Norepinephrine (NE), acting through the alpha 1-adrenergic receptor, modules the response of rat hepatocytes in primary culture to transforming growth factor type beta 1 (TGF beta) by increasing the amount of TGF beta required for a given degree of inhibition of epidermal growth factor (EGF)-induced DNA synthesis (Houck et al., J. Cell. Physiol. 135:551-555, 1988). This effect was also found in hepatocytes isolated from regenerating livers but was greatly magnified in cells isolated between 12 and 18 hr after two-thirds partial hepatectomy (PHX). During this period of enhanced sensitivity, NE was equally potent in terms of dose but more efficacious in the regenerating hepatocytes. As it did in control hepatocytes (Cruise et al., Science 227:749-751, 1985), the alpha 1-adrenergic receptor mediated the activity of NE in regenerating hepatocytes. Vasopressin (VP) and angiotensin-II (AG) also antagonized the effect of TGF beta and showed increased activity in regenerating hepatocytes but at only 50% or less of the maximal effect reached by NE. Regenerating hepatocytes isolated 24-72 hr after PHX exhibited decreased sensitivity to inhibition by TGF beta, with a nadir in 48-hr-regenerating cells. These findings suggest that NE may be involved in triggering the early phase of DNA synthesis during liver regeneration, with the subsequent acquisition of innate resistance to TGF beta responsible for continued proliferation at a time when TGF beta mRNA is known to be increasing in the liver (Braun et al., Proc. Natl. Acad. Sci. USA 85:1539-1543, 1988). EGF induced increased DNA and protein synthesis in cultures of control hepatocytes; TGF beta inhibited the EGF-induced DNA synthesis but had no effect on protein synthesis. This may be relevant to the latter stages of liver regeneration, when high levels of TGF beta mRNA are detected in liver and cellular hypertrophy predominates over hyperplasia.

Epidermal growth factor stimulates rat cardiac adenylate cyclase through a GTP-binding regulatory protein

In isolated perfused rat hearts, epidermal growth factor (EGF; 15 nM) increased cellular cyclic AMP (cAMP) content by 9.5-fold. In rat cardiac membranes, EGF also stimulated adenylate cyclase activity in a dose-dependent manner, with maximal stimulation (35% above control) being observed at 10 nM-EGF. Half-maximal stimulation of adenylate cyclase was observed at 40 pM-EGF. Although the beta-adrenergic-receptor antagonist propranolol markedly attenuated the isoprenaline-mediated increase in cAMP content of perfused hearts and stimulation of adenylate cyclase activity, it did not alter the ability of EGF to elevate tissue cAMP content and stimulate adenylate cyclase. The involvement of a guanine-nucleotide-binding protein (G-protein) in the activation of adenylate cyclase by EGF was indicated by the following evidence. First, the EGF-mediated stimulation of adenylate cyclase required the presence of the non-hydrolysable GTP analogue, guanyl-5'-yl-imidodiphosphate (p[NH]ppG). Maximal stimulation was observed in the presence of 10 microM-p[NH]ppG. Secondly, in the presence of 10 microM-p[NH]ppG, the stable GDP analogue guanosine 5'-[beta-thio]diphosphate at a concentration of 10 microM blocked the stimulation of the adenylate cyclase by 1 nM- and 10 nM-EGF. Third, NaF + AlCl3-stimulated adenylate cyclase activity was not altered by EGF. The ability of EGF to stimulate adenylate cyclase was not affected by pertussis-toxin treatment of cardiac membranes. However, in cholera-toxin-treated cardiac membranes, when the adenylate cyclase activity was stimulated by 2-fold, EGF was ineffective. Finally, PMA by itself did not alter the activity of cardiac adenylate cyclase, but abolished the EGF-mediated stimulation of this enzyme activity. The experimental evidence in the present paper demonstrates, for the first time, that EGF stimulates adenylate cyclase in rat cardiac membranes through a stimulatory GTP-binding regulatory protein, and this effect is manifested in elevated cellular cAMP levels in perfused hearts exposed to EGF.

Inhibition by cysteamine of hepatocarcinogenesis induced by N-nitrosomorpholine in Sprague-Dawley rats

The effect of cysteamine (2-aminoethanethiol hydrochloride) on hepatocarcinogenesis induced by N-nitrosomorpholine (NNM) was investigated in male Sprague-Dawley rats. Rats received alternate-day s.c. injections of cysteamine, and beginning in experimental week 3 were given drinking water containing NNM for 8 weeks. Pre-neoplastic and neoplastic lesions staining positive for gamma-glutamyl transpeptidase (GGT) or glucose-6-phosphate dehydrogenase (G6PD) were examined by histochemical techniques. In week 18, quantitative histological analysis showed that prolonged administration of cysteamine resulted in a significant reduction in the number of GGT-positive and G6PD-positive hepatic lesions. Histologically, hepatocellular carcinomas were significantly fewer and smaller in GGT-positive and G6PD-positive lesions in rats treated with cysteamine than in untreated rats. Administration of cysteamine also caused a significant decrease in the liver norepinephrine concentration and in the labelling indices of pre-neoplastic lesions and the surrounding liver. Our findings indicate that cysteamine inhibits hepatocarcinogenesis; this may be related to its reducing effect on norepinephrine concentration in the liver and its subsequent inhibition of cell proliferation in neoplastic lesions and surrounding hepatocytes.

Further characterisation of 'hepatotropin', a high molecular weight hepatotrophic factor in rat serum

We report further characterisation of the hepatocyte growth factor 'hepatotropin' which is found in rat serum 24 h after partial hepatectomy. Hepatotropin enhances DNA synthesis in primary cultures of adult rat hepatocytes, and is of high molecular weight. Serum fractions were separated by gel filtration, heparin-sepharose affinity chromatography and ion-exchange chromatography. Sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE) identified a band of apparent subunit relative molecular weight (Mr) 100,000 associated with biological activity, although purification to homogeneity has not been achieved. The activity is heat-labile, trypsin-sensitive, and stable to lyophilisation, but loses activity after dilution and reconcentration. In combination with known peptide hepatocyte growth modulators, hepatotropin acted synergistically with insulin and epidermal growth factor (EGF) but its action was not enhanced by glucagon. Studies on isolated rat hepatocyte membranes showed no evidence of enhanced phosphorylation of the EGF receptor by hepatotropin. The relationship of hepatotropin to previously described serum and platelet-derived growth factors is discussed.

Tumor necrosis factor stimulates DNA synthesis in the liver of intact rats

TNF is cytotoxic to tumor cell lines but enhances growth of some nontransformed cells. Because animals administered TNF have an increase in liver size, we studied the [3H]thymidine incorporation into DNA in the liver of intact rats. A significant increase in [3H]thymidine incorporation is seen 20 hours following TNF administration and peaks at 24 hours. The lowest dose of TNF that increases DNA synthesis is 10 micrograms/200 g rat with a maximal increase occurring with 25 micrograms/200 g, considerably less than the dose required for maximally increasing plasma triglycerides. The increase in [3H]thymidine incorporation was shown to be due to an increase in DNA polymerase alpha activity (associated with the replication of DNA) rather than DNA polymerases beta (associated with DNA repair) plus gamma activity. These results indicate that TNF administration stimulates DNA replication in the liver of intact animals.

Liver epithelial cell migration induced by epidermal growth factor or transforming growth factor alpha is associated with changes in the gene expression of secreted proteins

Rat liver epithelial cells are induced to migrate by epidermal growth factor (EGF) or transforming growth factor alpha (TGF-alpha) in serum-free medium supplemented with insulin. Immunohistological staining of the migration tracks containing laminin and fibronectin has allowed a quantitative analysis of the process. The growth factor-induced migration is relatively slow, but very efficient. Between 24 and 48 h after exposure to EGF (or TGF-alpha), 50 to 70% of the cells have migrated away from their site of initial attachment and spreading. This delayed effect of the interaction of the receptor with its ligands is associated with changes in gene expression, but is not associated with a stimulation of cell proliferation. In serum-free medium supplemented with insulin, the cells secrete six major proteins, as revealed by SDS-polyacrylamide gel electrophoresis. The media of cultures supplemented with insulin plus EGF (or TGF-alpha) contain in addition two new proteins and an increased amount of fibronectin. One secreted protein is synthesized in significantly reduced amounts. The most conspicuously EGF-induced protein (EIP-1; Mr 47,000) is detected within 2 h, depends on the continued presence of the growth factor, and has not been detected as bound to the substratum. The stringent regulation of EIP-1 suggests that this gene product might participate in the modulation of the changes induced by the growth factor. The system is being used for the further analysis of the regulation of gene expression by EGF and of the migration of normal and neoplastically transformed epithelial cells.

Ethanol inhibits some of the early effects of epidermal growth factor in vivo

Charles River male Wistar rats (200-300 g) were meal fed for 9-10 days, injected with either saline, epidermal growth factor (EGF), ethanol, or ethanol combined with EGF and their livers were freeze clamped 5 min after intraperitoneal injection of EGF. Metabolites were measured and the redox state and phosphorylation potential were calculated. Epidermal growth factor alone elevated hepatic content of glucose 1-P, glucose 6-P, fructose 6-P, and 3-phosphoglycerate 1.2-1.3-fold when compared to saline treatment. Ethanol alone decreased hepatic content of 3-phosphoglycerate and phosphoenolpyruvate 3.2-3.7-fold below saline-treated levels. Ethanol, in combination with EGF, decreased hepatic values for 3-phosphoglycerate and phosphoenolpyruvate 2.0-2.3-fold from saline treatment but elevated the content of phosphoenolpyruvate 1.6-fold over ethanol treatment alone. Epidermal growth factor inhibited pyruvate kinase activity 1.3-fold when compared to saline controls but ethanol in the presence of EGF facilitated the recovery of activity of this enzyme.

Liver-specific growth factors

Experimental evidence of the existence of liver-specific growth factors has been collected for more than two decades. Blood-borne growth-promoting activity of hepatocytes may be separated into plasma and platelet-derived factors. Several groups have observed the stimulation of hepatocyte growth in vitro by some platelet-associated activity, which was recently isolated from rat platelets as a 27-kDa protein called platelet growth factor (PGF). There is evidence of at least two different growth factors for hepatocytes derived from platelet-poor rat plasma, 'hepatopoietin' A and B. The partial purification of several other factors has been reported. One of these factors was prepared from the plasma of patients with fulminant hepatic failure. In addition to these 'humoral' factors, cytosolic growth-promoting activity has been partially purified by several groups. While the humoral factors described so far are only active on normal hepatocytes, the cytosolic 'hepatic stimulator substance' (HSS) also promotes the proliferation of differentiated hepatoma cells. In addition, it appears to depend on the permissive action of epidermal growth factor (EGF). None of the liver-specific growth factors except PGF has been purified to homogeneity. Thus, their significance for the control of the proliferation of normal and transformed hepatocytes is still an unsettled issue.

Alpha 1-adrenergic effects and liver regeneration

The effects of several treatments involving alpha-adrenergic mechanisms upon the early stages of rat liver regeneration were examined. Catecholamine concentrations in rat plasma were measured at various times after hepatectomy and were found to be elevated relative to those in plasma from sham-operated rats. Surgical hepatic denervation or injection of an alpha 1-adrenergic receptor antagonist (prazosin) reduced incorporation of [3H]thymidine into liver DNA during the first 24 hr after partial hepatectomy. Chronic guanethidine injections (3 to 6 weeks) reduced liver catecholamine levels, but did not affect its ability to regenerate. The inhibition of regenerative DNA synthesis by prazosin was preceded by an alteration in the binding of epidermal growth factor to regenerating liver, which was apparently the result of an increased number of epidermal growth factor receptors. Thus, alpha 1-adrenergic blockade, which affects both epidermal growth factor receptor binding and subsequent DNA synthesis in hepatocyte primary cultures, can also modulate these processes during liver regeneration in vivo.

Cell cycle parameters of adult rat hepatocytes in a defined medium. A note on the timing of nucleolar DNA replication

Hepatocytes, isolated from adult (250-350 g) rats, attached and survived well in primary culture on highly diluted (less than 1 microgram/cm2) collagen gel in a synthetic medium without serum or hormones. About 20% of the cells "spontaneously" entered S phase during the first 4 days of culturing, and mitoses were easily demonstrated at the near physiological concentration (1.25 mM) of Ca++ prevailing in the medium. Cultures given 9 nM epidermal growth factor (EGF) and 20 nM insulin 20 h after inoculation showed vigorous DNA synthesis and mitotic activity. Autoradiography of such cells exposed to [3H]thymidine allowed the determination of the following cell cycle parameters: Lag period from EGF/insulin stimulation till onset of increased DNA synthesis, 17 h; rate of entry into S phase (kG1/S), 0.028/h; duration of S phase, 8.4 h; duration of G2 phase, 2.7 h. The peak DNA synthesis (pulse labelling index, 24%) and peak mitotic activity (mitotic index, 1.7%) occurred 35 and 43 h, respectively, after the stimulation with EGF/insulin. These values are comparable to those reported during the in vivo compensatory hyperplasia following partial hepatectomy of adult rats. A marked variation of the intranuclear [3H]thymidine pulse labelling pattern was noted: During the first 1.5 h of the S phase, the labelling was extranucleolar and during the last 1.5 h chiefly nucleolar. The cells survived well in the absence of glucocorticoid, whose effect on cell cycle parameters therefore could be studied. Dexamethasone (25-250 nM) did not appreciably affect the durations of S phase and G2 phase or the pattern of preferential extranucleolar and nucleolar DNA synthesis within the S phase.

Epidermal growth factor stimulates serine and tyrosine phosphorylation in a 59-kD protein in purified plasma membranes from rat liver

Preincubation of purified plasma membranes from rat liver with EGF stimulates the level of phosphorylation on serine and tyrosine residues in a 59-kD protein. Such an increased phosphoserine and phosphotyrosine content of the 59-kD protein occurs at the expense of the phosphorylation on threonine residues. The effect is observed under conditions where the plasma membranes have been extracted at pH 10. It is not observed when the membranes are simply washed at pH 7.5 before further purification. A number of experiments, including TBR-IgG phosphorylation in immunoprecipitates and partial hydrolysis with varying concentrations of the V8 protease, suggest that the 59-kD protein modified upon EGF treatment could be a representative of the c-src gene product from hepatocytes.

Norepinephrine decreases EGF binding in primary rat hepatocyte cultures

Norepinephrine (NE) produced a dose-dependent inhibition of 125I-epidermal growth factor (EGF) binding to adult rat hepatocytes in primary culture. This effect was maximal after 1 hr of incubation with NE and could be blocked by the presence of an alpha 1-specific adrenergic receptor antagonist. The inhibition of binding correlates with the ability of NE to enhance hepatocyte DNA synthesis in the presence of EGF and appears to be mediated by a reduction in EGF receptor number, without a significant change in receptor affinity.

The effects of epidermal growth factor and the state of confluence on enzymatic activities of cultured rat liver epithelial cells

In cultured normal rat liver epithelial cells, the specific activity and/or isozyme expression of NADH-diaphorase (NADH-D), pyruvate kinase (PK), glucose-6 phosphate dehydrogenase (G6PD), gamma-glutamyl transpeptidase (GGT), and alkaline phosphatase (AP) were markedly dependent on the growth state of the cultures. Proliferating, preconfluent cells had higher specific activities of PK, NADH-D, and G6PD but lower activities of GGT and AP than did the more stationary confluent cells. Addition of epidermal growth factor [EGF] to the media of proliferating cells enhanced the specific activities of PK, NADH-D, G6PD, GGT, and lactate dehydrogenase (LDH) of these cells, but the specific activity of AP was markedly depressed. The increase in activity of PK and GGT by EGF appeared to involve new protein synthesis, whereas the effect of EGF on AP appeared to involve the EGF-directed suppression of the synthesis of a form of AP that is produced exclusively by cells in confluent cultures. Furthermore, the preconfluent cells were more responsive to the action of EGF on AP than were confluent cells, i.e., the EGF-mediated decrease in AP activity was seen at lower concentration in preconfluent than in confluent cells. Paradoxically, confluent cells exhibited a two-to threefold higher capacity to bind [125 I]EGF because of an increase in surface receptor number. The results of this study indicate that enzymatic or other biochemical studies performed on cultured cells must take into account the growth-state of the cultures. EGF can modulate enzyme activity in growing and nongrowing cells; one effect of EGF is to maintain higher activity of glycolytic enzymes, suggesting that EGF or EGF-like factors may contribute to the high rate of glycolysis in certain neoplasms.

Choline deficiency and chemical carcinogenesis

We have reviewed the current status of our knowledge concerning the biologic effects of dietary choline (lipotrope) deficiency in modifying chemical carcinogenesis in experimental animals and discussed its possible mechanisms. Choline deficiency produces various pathologic lesions, involving virtually every organ of the body, as a result of a decrease in phospholipid and acetylcholine synthesis and in the supply of labile methyl groups. The liver is the only organ in which a relationship has been consistently demonstrated between choline deficiency and chemically induced tumors. The deficient diet enhances the initiating potency of several carcinogens and acts as a strong cocarcinogen. Diet also exerts a strong promoting effect, though the possibility that it is a complete carcinogen cannot be ruled out. Phase I enzymes of the carcinogen metabolizing system are uniformly depressed by choline deficiency, but very little information is available regarding the effects of diet on Phase II enzymes that detoxify carcinogen metabolites. Possible modifications of carcinogen-induced DNA damage and their repair processes have not been adequately scrutinized. Solid evidence suggests that feeding a choline-deficient diet leads to enhanced liver cell proliferation, an inadequate supply of methyl groups for transmethylation reactions, and membrane lipid peroxidation. Induced cell proliferation and hypomethylation of DNA may alter the state of gene expression, including that of specific cellular oncogenes. Lipid peroxidation may alter the structure and function of membrane receptors related to liver cell growth or may directly damage cellular DNA. Thus these alterations, individually or in combination, could play a critical role in the diet-induced modification of chemical carcinogenesis.

Norepinephrine and epidermal growth factor: dynamics of their interaction in the stimulation of hepatocyte DNA synthesis

Primary cultures of adult rat hepatocytes are stimulated to enter DNA synthesis by norepinephrine (NE). This stimulation is maximal if the hepatocytes are incubated with NE for more than 12 hr, beginning no later than 2-4 hr after the cells are first plated. After 24 hr in culture, hepatocytes are unresponsive to NE stimulation. A strong synerergistic interaction between NE and epidermal growth factor (EGF) may be observed in cultures incubated with both EGF and NE, or pretreated with NE, then exposed to EGF. This interaction may be related to the finding that NE, in similarity with other factors that enhance EGF stimulation, reduces binding at the EGF receptor during the first 24 hr in culture.

Differential effects of lysosomotropic amines and polyamines on processing and biological activity of EGF

The effects of lysosomotropic amines and polyamines on rat fibroblasts were studied after the administration of epidermal growth factor (EGF) in order to determine whether the intracellular processing of EGF was important for transmission of its biological signal. Following the addition of EGF, cell cultures exhibited a dose-dependent increase in ornithine decarboxylase (ODC) activity. This increase in ODC activity was drastically reduced by both methylamine, a representative lysosomotropic amine, and putrescine, a polyamine precursor. However, inasmuch as methylamine inhibited EGF-induced DNA synthesis by greater than 50%, putrescine had no inhibitory effect. Lysosomotropic amines, but not polyamines, prevented EGF processing as evidenced by their ability to block the release of intracellular 125EGF and by their ability to inhibit the formation of the final intracellular processed product of EGF, as determined by isoelectric focusing. These data suggest that the processing of EGF is consistent with the induction of DNA synthesis and ODC activity. The cellular mechanisms involved in inhibition of ODC induction by polyamines appear to be distinct from those involved in lysosomotropic amines.

Regulation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase and cholesterol synthesis and esterification during the first cell cycle of liver regeneration

The regenerating rat liver provides a unique in vivo synchronized system for study of the interrelationships between mevalonate and sterol metabolism during the cell cycle. The regulation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, cholesterol synthesis and acyl coenzyme A: cholesterol acyltransferase during the first cell cycle was investigated. At 8 h postoperative and prior to onset of DNA synthesis or S phase, cholesterol synthesis was depressed in the regenerating liver relative to that in sham-operated controls. This suppression was observed whether assayed in vitro with liver homogenates utilizing radiolabeled acetate, mevalonate or water or in vivo with tritium water. In contrast, at this time point, 3-hydroxy-3-methylglutaryl-CoA reductase activity was increased in microsomes prepared both in the presence and absence of NaF. By 24 h, well into S phase and approaching mitosis, reductase activity and cholesterol synthesis both approached levels observed in the sham-operated control animals. There were no detectable changes in acyl-CoA: cholesterol acyltransferase activity at any time point. Thus, at the 8 h time point, the regulation of the three processes appeared uncoupled. The increased levels of in vitro expressed 3-hydroxy-3-methylglutaryl-CoA reductase activity compared with the decrease in the rate of both cholesterol and squalene biosynthesis suggested diversion of mevalonate into products other than squalene or sterols. We propose that this may reflect the needs of the cell for a nonsterol metabolite of mevalonate necessary for entry of cells into S phase.

Insulin inhibits the glucocorticoid-mediated increase in hepatocyte EGF binding

Hydrocortisone and dexamethasone produced a time-dependent increase [125I]epidermal growth factor [( 125I]EGF) binding in primary cultures of isolated rat hepatocytes. Maximally effective doses of glucocorticoids resulted in a 70-100% increase in binding. The effect was similar when hepatocytes were maintained on collagen-coated plates or directly on culture dishes. The glucocorticoid-mediated increase in [125I]EGF binding could be detected after 4 h exposure to glucocorticoid and was substantial by 8 h. The major effect of glucocorticoid appeared to be to increase the number of EGF receptors. While insulin (100 nM) had no effect on basal [125I]EGF binding, it significantly inhibited the increase produced by the glucocorticoid. Since the inhibitory effect of insulin was only observed when insulin was added with the inducing glucocorticoid, insulin appears to inhibit an early hydrocortisone-mediated event.

Factors effective in reducing rat mortality due to acute liver failure as induced by D-galactosamine poisoning

Mortality from D-galactosamine hydrochloride (D-GalN)-induced acute liver failure (ALF) in rats can be reduced by (1) transplanting intact hepatocytes; (2) injecting cytosol from fractionated hepatocytes dispersed from a liver subjected to 70% hepatectomy 24 hr earlier (CYT-H); (3) injecting a cell-free supernate derived from cultured hepatocytes (SUP); or (4) injecting neuraminidase-treated plasma where the plasma is drawn 24 hr after donor rats are subjected to 70% hepatectomy (PHP-neu). These treatments are effective when administered 20-24 hr after D-GalN poisoning, but experiments to determine the alterations in mortality rates as a function of time of treatment in relation to poisoning have not been performed. Two experiments are reported here. In the first the survival of lethally poisoned rats was compared after intravenously injecting either SUP prepared from cultured hepatocytes of syngeneic adult or fetal rat sources, or CYT-H from syngeneic adult rats 20 hr after poisoning. Untreated rats, rats treated with culture media alone, or rats treated with CYT from a nonregenerating source had an 88-100% mortality, with all deaths occurring within 72 hr following poisoning. Improved survival followed all other treatments: 55% of the rats receiving adult SUP, 70% of the rats receiving fetal SUP, and 80% of the rats receiving CYT-H survived. In the second experiment the survival of poisoned rats was compared after injecting them with PHP-neu, PHP not treated with neuraminidase (PHP without neu), and neuraminidase-treated plasma from sham-operated rats (SP-neu) or normal, nonoperated rats (NP-neu) 20 hr after poisoning.(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphorylation of the hepatic EGF receptor with cAMP-dependent protein kinase

The 170 000 dalton hepatic epidermal growth factor (EGF) receptor is phosphorylated on serine and tyrosine residues. The evidence indicates that distinct protein kinases are involved. Since EGF and agents that elevate cAMP are believed to participate in the regulation of liver regeneration, we tested whether or not the catalytic subunit of cAMP-dependent protein kinase (catalytic subunit), a known serine kinase, would utilize the EGF receptor as a substrate. The catalytic subunit increased phosphorylation of the EGF receptor in purified rat liver plasma membranes. The serine specificity of the catalytic subunit was established by phosphoamino acid analysis of electrophoretically purified EGF receptor. The result was confirmed by catalytic subunit phosphorylation of affinity purified preparations of the EGF receptor. The rates of dephosphorylation of the membrane-associated EGF receptor phosphorylated on different residues were compared. Dephosphorylation of serine residues (after catalytic subunit phosphorylation) was considerably slower (t1/2 greater than 120 sec) than the removal of phosphotyrosine after stimulation with EGF (t1/2 less than 30 sec).