- Email: [email protected]
Tolerance and sensitivity: Ethanol and Kupffer cells
494
EDITORIALS
GASTROENTEROLOGY Vol. 115, No. 2
Tolerance and Sensitivity: Ethanol and Kupffer Cells See article on page 443.
he liver is a major target organ for the action of ethanol (EtOH), and its effects involve virtually all types of cells within this organ. Kupffer cells play a major role in this regard because their functions are directly affected by EtOH and, through intercellular communications, they contribute to the orchestration of the overall hepatic effects of EtOH. Numerous experimental data indicate that EtOH may both stimulate and desensitize Kupffer cells, especially when it is given acutely or in a binge-type mode. The article by Enomoto et al.1 in this issue of GASTROENTEROLOGY deals with some effects of alcohol that reflect both tolerance and sensitization of rat Kupffer cells to subsequent stimulus. One of their findings is that 2 hours after EtOH administration, the lipopolysaccharide (LPS)-induced increase in tumor necrosis factor (TNF)-a release by Kupffer cells was diminished by 50%.1 Sterilization of the gut with antibiotics abolished this change. The authors concluded that EtOHmediated influx of endogenous endotoxin into the circulation from the gut was responsible for the reduced sensitivity of Kupffer cells to the stimulating action of exogenous LPS in vitro. Their conclusion suggests that this desensitizing/tolerizing effect of EtOH is an indirect one due to LPS mediation. However, there are also conditions whereby EtOH may directly down-regulate a function of the Kupffer cells in response to LPS. Thus, we have previously shown that acute EtOH intoxication diminished LPS-induced TNF production in vivo and that plasma EtOH concentrations inversely correlated with peak LPS-induced serum TNF activities.2 The inhibitory effects of EtOH and/or LPS on Kupffer cell function have been studied under a variety of conditions using different time frames for the observations. To enhance our understanding of these effects, we propose the following working hypothesis: the inhibitory actions of acute EtOH or LPS on Kupffer cells may be observed as an almost immediate hyporeactive state, as down-regulation of a particular function that may take many minutes to develop, or as the condition of tolerance that may take a number of hours or days to manifest. It is not known whether the mechanisms responsible for the development of these states are entirely different or not, and thus whether these three conditions are indeed distinct or they represent a continuum is also uncertain. In the following paragraphs, we will mention a number
T
of earlier studies that could serve as examples of hyporeactivity, down-regulation, or tolerance. Several studies have indicated that stimulation of Kupffer cells in vivo elicits superoxide anion production. This has been shown in the subsequently perfused isolated liver and in the isolated Kupffer cells after in vivo LPS administration,3 TNF-a infusion,4 or phagocytosis of latex particles.5 These effects exhibit a well-defined time course, and peak, in the case of LPS, at 3 hours after administration. Maintaining a constant blood ethanol concentration at approximately 175 mg/dL also acts as a stimulant for Kupffer cells to release superoxide anions. This effect is also highly time dependent, with a peak at approximately 3 hours. The effect is almost completely over by 5 or 7 hours of ethanol infusion.6 The alcohol moiety does not need to be metabolized to elicit this effect, and generation of prostaglandins plays a role in mediating the effect.6 When LPS was administered at the beginning of the 3-hour infusion of ethanol, this resulted in decreased superoxide release by the liver compared with either EtOH administration or LPS alone.6,7 Thus, in contrast to the stimulatory actions of LPS or ethanol, the presence of both agents resulted in hyporeactivity. LPS injection (but not EtOH administration alone) caused a marked migration of polymorphonuclear leukocytes (PMNs) to the liver. The simultaneous EtOH administration did not alter this effect.7 Other studies showed that EtOH pretreatment blunted LPS-induced superoxide release by Kupffer cells7 and, at the same time, diminished the LPS-induced increase in glucose uptake by these cells.8 These two effects could be causally related via the hexosemonophosphate shunt activity that plays an important role in superoxide generation in Kupffer cells.9 Because the ethanol effect in these experiments was observed after 4 hours of ethanol infusion, down-regulation of some Kupffer cell function may have occurred. LPS has also been shown to induce enhanced hepatic sequestration of inflammatory neutrophils and priming of these cells for superoxide release to subsequent stimuli (e.g., phorbol myristate acetate or zymosan). Serum transaminase activity was also elevated.7 Intravenous infusion of ethanol for 7 hours did not induce hepatic sequestration of PMNs and did not suppress LPS-mediated sequestration of inflammatory PMNs to the liver. However, priming by LPS of these cells to subsequent stimuli was suppressed by EtOH.7 Also, concurrent EtOH administration (for 12 hours) virtually abolished the inducible nitric oxide synthase messenger
August 1998
RNA induction observed 12 hours after LPS administration in Kupffer cells.10 Thus, EtOH may selectively down-regulate some of the many functions of these cells. Endotoxin tolerance is known to protect against LPS lethality and to blunt various effects of LPS on the liver. In a previous study, we showed that hepatic superoxide release after LPS administration is decreased in endotoxintolerant animals. Tolerance was induced in these experiments by a sensitizing dose of LPS given 48 hours before the challenging dose. This phenomenon was time dependent and was not present 12 or 24 hours after the sensitizing dose.11 Serum TNF and hepatic liver enzymes released into the blood after LPS administration were also markedly diminished in the tolerant animals, indicating protection against liver damage.11 It has been known from a number of previous studies that tolerance to LPS is not specific to the action of LPS and that cross-tolerance exists with a number of agents.12 Therefore, in a previous study we addressed two questions: (1) does prior exposure to LPS induce crosstolerance for the hepatic effects of a subsequent shortterm alcohol intoxication, and (2) does short-term alcohol intoxication render the liver resistant to the effects of acute endotoxemia. The results of these studies showed that the stimulatory effect of ethanol on superoxide release by the liver is virtually eliminated in animals made LPS tolerant 48 hours before EtOH administration. Conversely, a 5-hour EtOH infusion blunts a stimulatory effect of LPS on the liver with regard to superoxide anion release. Such EtOH pretreatment also markedly diminished serum TNF-a concentration and serum alanine transaminase activity (an indication of incipient liver injury) after LPS administration. EtOH pretreatment also attenuated the lethal effect of a high dose of LPS administration in these animals.13 It should be noted that all the manifestations of these cross-tolerance phenomena are highly time dependent and occur only in a specified time window. As mentioned earlier, the mechanisms for ethanolinduced hyporeactivity, down-regulation, and tolerance are not well understood. It is likely that multiple mechanisms are responsible for them. The following are some possible mechanisms that have been implicated in the past: (1) LPS release from the gut (as postulated by Enomoto et al.); (2) alterations in signal transduction mechanisms (e.g., protein kinase C,14 transcription factor NF-kB, and others15–17; (3) direct effect on membrane structure18; (4) changes in hexosemonophosphate shunt activity and subsequent reduced nicotinamide adenine dinucleotide phosphate generation9; (5) prostaglandin production via cyclooxygenases19; (6) NO production (NO synthase induction) and subsequent scavenging of
EDITORIALS
495
superoxide20; (7) imbalance between inflammatory and anti-inflammatory cytokines21,22; (8) alterations in glucocorticoid homeostasis23; and (9) altered G-protein function.24 Finally, the question of relevance and significance of the observed down-regulation/hyporeactivity/tolerance should also be raised. This is very difficult to address because of the highly time-dependent nature of these observations. However, it is likely that either EtOH or LPS acts primarily as a stimulant of Kupffer cells. When their action changes into inhibition, this may serve as a protective mechanism in an effort to limit an inflammatory or other noxious insult and thus preserve the normal functioning of this arm of the host defense system. JOHN J. SPITZER ABRAHAM P. BAUTISTA Department of Physiology LSU Medical Center New Orleans, Louisiana
References 1. Enomoto N, Ikejima K, Bradford B, Rivera C, Kono H, Brenner DA, Thurman RG. Alcohol causes both tolerance and sensitization of rat Kupffer cells via mechanisms dependent on endotoxin. Gastroenterology 1998;115:443–451. 2. D’Souza NB, Bagby GJ, Nelson S, Lang CH, Spitzer JJ. Acute alcohol infusion suppresses endotoxin-induced serum tumor necrosis factor. Alcohol Clin Exp Res 1989;13:295–298. 3. Bautista AP, Me´sza´ros K, Bojta J, Spitzer JJ. Superoxide anion generation in the liver during the early stage of endotoxemia in rats. J Leukoc Biol 1990;48:123–128. 4. Bautista AP, Schuler A, Spolarics Z, Spitzer JJ. Tumor necrosis factor a stimulates superoxide anion generation by perfused rat liver and Kupffer cells. Am J Physiol 1991;261:G891–G895. 5. Bautista AP, Schuler A, Spolarics Z, Spitzer JJ. In vivo latex phagocytosis primes the Kupffer cells and hepatic neutrophils to generate superoxide anion. J Leukoc Biol 1992;51:39–45. 6. Bautista AP, Spitzer JJ. Acute ethanol intoxication stimulates superoxide anion production by in situ perfused rat liver. Hepatology 1992;15:892–898. 7. Bautista AP, D’Souza NB, Lang CH, Bagwell J, Spitzer JJ. Alcoholinduced down-regulation of superoxide anion release by hepatic phagocytes in endotoxemic rats. Am J Physiol 1991;260:R969– R976. 8. D’Souza NB, Bautista AP, Bagby GJ, Lang CH, Spitzer JJ. Acute ethanol intoxication suppresses E. coli lipopolysaccharide enhance glucose utilization by hepatic nonparenchymal cells. Alcohol Clin Exp Res 1991;15:249–254. 9. Spolarics Z. Endotoxemia, pentose cycle, and the oxidant/ antioxidant balance in the hepatic sinusoid. J Leukoc Biol 1998; 63:534–541. 10. Spolarics Z, Spitzer JJ, Wang JF, Xie J, Kolls J, Greenberg S. Alcohol administration attenuates LPS-induced expression of inducible nitric oxide synthase in Kupffer and hepatic endothelial cells. Biomed Biophys Res Commun 1993;197:606–611. 11. Bautista AP, Spitzer JJ. Acute endotoxin tolerance down-regulates superoxide anion release by the perfused liver and isolated hepatic nonparenchymal cells. Hepatology 1995;21:855–862. 12. Cavaillon J-M. The nonspecific nature of endotoxin tolerance. Trends Microbiol 1995;3:320–324. 13. Bautista AP, Spitzer JJ. Cross-tolerance between acute alcohol
496
14.
15.
16.
17. 18.
19.
20.
EDITORIALS
intoxication and endotoxemia. Alcohol Clin Exp Res 1996;20: 1395–1400. West MA, LeMieur T, Clair L, Bellingham J, Rodriguez JL. Protein kinase C regulates macrophage tumor necrosis factor secretion: direct protein kinase C activation restores tumor necrosis factor production in endotoxin tolerance. Surgery 1997;122:204–211. Blackwell TS, Blackwell TR, Christman JW. Induction of endotoxin tolerance depletes nuclear factor-kB and suppresses its activation in rat alveolar macrophages. J Leukoc Biol 1997;62:885–891. Kohler NG, Joly A. The involvement of an LPS inducible I kappa B kinase in endotoxin tolerance. Biochem Biophys Res Commun 1997;232:602–607. Ziegler-Heitbrock HW. Molecular mechanism in tolerance to lipopolysaccharide (review). J Inflamm 1995;45:13–26. Taraschi TF, Ellingson JS, Wu A, Zimmerman R. Phosphatidylimositol from ethanol-fed rats confers membrane tolerance to ethanol. Proc Natl Acad Sci USA 1986;83:9398–9402. Zingarelli B, Chen H, Caputi AP, Halushka PV, Cook JA. Reorientation of macrophage mediator production in endotoxin tolerance. Prog Clin Biol Res 1995;392:529–537. Fahmi H, Charon D, Mondange M, Chaby R. Endotoxin-induced desensitization of mouse macrophages is mediated in part by nitric oxide production. Infect Immun 1995;63:1863–1869.
GASTROENTEROLOGY Vol. 115, No. 2
21. Knolle PA, Loser E, Protzer U, Duchmann R, Schmitt E, zum Buschenfelde KH, Rose-John S, Gerken G. Regulation of endotoxininduced IL-6 production in liver sinusoidal endothelial cells and Kupffer cells IL-10. Clin Exp Immunol 1997;107:555–561. 22. Van der Poll T, Coyle SM, Moldawer LL, Lowry SF. Changes in endotoxin-induced cytokine production by whole blood after in vivo exposure of normal humans to endotoxin. J Infect Dis 1996;174: 1356–1360. 23. Amano T, Lee SW, Allison AC. Inhibition of glucocorticoids of the formation of interleukin 1b and interleukin 6: mediation by decreased mRNA stability. Mol Pharmacol 1993;43:176–182. 24. Makhlouf MS, Ashton H, Hildebrandt J, Mehta N, Gettys TW, Halushka PV, Cook JA. Alterations in macrophage G proteins are associated with endotoxin tolerance. Biochim Biophys Acta 1996; 1312:163–168.
Address requests for reprints to: John J. Spitzer, M.D., Department of Physiology, LSU Medical Center, 1901 Perdido Street, New Orleans, Louisiana 70112. Fax: (504) 568-6158. r 1998 by the American Gastroenterological Association 0016-5085/98/$3.00
EDITORIALS
GASTROENTEROLOGY Vol. 115, No. 2
Tolerance and Sensitivity: Ethanol and Kupffer Cells See article on page 443.
he liver is a major target organ for the action of ethanol (EtOH), and its effects involve virtually all types of cells within this organ. Kupffer cells play a major role in this regard because their functions are directly affected by EtOH and, through intercellular communications, they contribute to the orchestration of the overall hepatic effects of EtOH. Numerous experimental data indicate that EtOH may both stimulate and desensitize Kupffer cells, especially when it is given acutely or in a binge-type mode. The article by Enomoto et al.1 in this issue of GASTROENTEROLOGY deals with some effects of alcohol that reflect both tolerance and sensitization of rat Kupffer cells to subsequent stimulus. One of their findings is that 2 hours after EtOH administration, the lipopolysaccharide (LPS)-induced increase in tumor necrosis factor (TNF)-a release by Kupffer cells was diminished by 50%.1 Sterilization of the gut with antibiotics abolished this change. The authors concluded that EtOHmediated influx of endogenous endotoxin into the circulation from the gut was responsible for the reduced sensitivity of Kupffer cells to the stimulating action of exogenous LPS in vitro. Their conclusion suggests that this desensitizing/tolerizing effect of EtOH is an indirect one due to LPS mediation. However, there are also conditions whereby EtOH may directly down-regulate a function of the Kupffer cells in response to LPS. Thus, we have previously shown that acute EtOH intoxication diminished LPS-induced TNF production in vivo and that plasma EtOH concentrations inversely correlated with peak LPS-induced serum TNF activities.2 The inhibitory effects of EtOH and/or LPS on Kupffer cell function have been studied under a variety of conditions using different time frames for the observations. To enhance our understanding of these effects, we propose the following working hypothesis: the inhibitory actions of acute EtOH or LPS on Kupffer cells may be observed as an almost immediate hyporeactive state, as down-regulation of a particular function that may take many minutes to develop, or as the condition of tolerance that may take a number of hours or days to manifest. It is not known whether the mechanisms responsible for the development of these states are entirely different or not, and thus whether these three conditions are indeed distinct or they represent a continuum is also uncertain. In the following paragraphs, we will mention a number
T
of earlier studies that could serve as examples of hyporeactivity, down-regulation, or tolerance. Several studies have indicated that stimulation of Kupffer cells in vivo elicits superoxide anion production. This has been shown in the subsequently perfused isolated liver and in the isolated Kupffer cells after in vivo LPS administration,3 TNF-a infusion,4 or phagocytosis of latex particles.5 These effects exhibit a well-defined time course, and peak, in the case of LPS, at 3 hours after administration. Maintaining a constant blood ethanol concentration at approximately 175 mg/dL also acts as a stimulant for Kupffer cells to release superoxide anions. This effect is also highly time dependent, with a peak at approximately 3 hours. The effect is almost completely over by 5 or 7 hours of ethanol infusion.6 The alcohol moiety does not need to be metabolized to elicit this effect, and generation of prostaglandins plays a role in mediating the effect.6 When LPS was administered at the beginning of the 3-hour infusion of ethanol, this resulted in decreased superoxide release by the liver compared with either EtOH administration or LPS alone.6,7 Thus, in contrast to the stimulatory actions of LPS or ethanol, the presence of both agents resulted in hyporeactivity. LPS injection (but not EtOH administration alone) caused a marked migration of polymorphonuclear leukocytes (PMNs) to the liver. The simultaneous EtOH administration did not alter this effect.7 Other studies showed that EtOH pretreatment blunted LPS-induced superoxide release by Kupffer cells7 and, at the same time, diminished the LPS-induced increase in glucose uptake by these cells.8 These two effects could be causally related via the hexosemonophosphate shunt activity that plays an important role in superoxide generation in Kupffer cells.9 Because the ethanol effect in these experiments was observed after 4 hours of ethanol infusion, down-regulation of some Kupffer cell function may have occurred. LPS has also been shown to induce enhanced hepatic sequestration of inflammatory neutrophils and priming of these cells for superoxide release to subsequent stimuli (e.g., phorbol myristate acetate or zymosan). Serum transaminase activity was also elevated.7 Intravenous infusion of ethanol for 7 hours did not induce hepatic sequestration of PMNs and did not suppress LPS-mediated sequestration of inflammatory PMNs to the liver. However, priming by LPS of these cells to subsequent stimuli was suppressed by EtOH.7 Also, concurrent EtOH administration (for 12 hours) virtually abolished the inducible nitric oxide synthase messenger
August 1998
RNA induction observed 12 hours after LPS administration in Kupffer cells.10 Thus, EtOH may selectively down-regulate some of the many functions of these cells. Endotoxin tolerance is known to protect against LPS lethality and to blunt various effects of LPS on the liver. In a previous study, we showed that hepatic superoxide release after LPS administration is decreased in endotoxintolerant animals. Tolerance was induced in these experiments by a sensitizing dose of LPS given 48 hours before the challenging dose. This phenomenon was time dependent and was not present 12 or 24 hours after the sensitizing dose.11 Serum TNF and hepatic liver enzymes released into the blood after LPS administration were also markedly diminished in the tolerant animals, indicating protection against liver damage.11 It has been known from a number of previous studies that tolerance to LPS is not specific to the action of LPS and that cross-tolerance exists with a number of agents.12 Therefore, in a previous study we addressed two questions: (1) does prior exposure to LPS induce crosstolerance for the hepatic effects of a subsequent shortterm alcohol intoxication, and (2) does short-term alcohol intoxication render the liver resistant to the effects of acute endotoxemia. The results of these studies showed that the stimulatory effect of ethanol on superoxide release by the liver is virtually eliminated in animals made LPS tolerant 48 hours before EtOH administration. Conversely, a 5-hour EtOH infusion blunts a stimulatory effect of LPS on the liver with regard to superoxide anion release. Such EtOH pretreatment also markedly diminished serum TNF-a concentration and serum alanine transaminase activity (an indication of incipient liver injury) after LPS administration. EtOH pretreatment also attenuated the lethal effect of a high dose of LPS administration in these animals.13 It should be noted that all the manifestations of these cross-tolerance phenomena are highly time dependent and occur only in a specified time window. As mentioned earlier, the mechanisms for ethanolinduced hyporeactivity, down-regulation, and tolerance are not well understood. It is likely that multiple mechanisms are responsible for them. The following are some possible mechanisms that have been implicated in the past: (1) LPS release from the gut (as postulated by Enomoto et al.); (2) alterations in signal transduction mechanisms (e.g., protein kinase C,14 transcription factor NF-kB, and others15–17; (3) direct effect on membrane structure18; (4) changes in hexosemonophosphate shunt activity and subsequent reduced nicotinamide adenine dinucleotide phosphate generation9; (5) prostaglandin production via cyclooxygenases19; (6) NO production (NO synthase induction) and subsequent scavenging of
EDITORIALS
495
superoxide20; (7) imbalance between inflammatory and anti-inflammatory cytokines21,22; (8) alterations in glucocorticoid homeostasis23; and (9) altered G-protein function.24 Finally, the question of relevance and significance of the observed down-regulation/hyporeactivity/tolerance should also be raised. This is very difficult to address because of the highly time-dependent nature of these observations. However, it is likely that either EtOH or LPS acts primarily as a stimulant of Kupffer cells. When their action changes into inhibition, this may serve as a protective mechanism in an effort to limit an inflammatory or other noxious insult and thus preserve the normal functioning of this arm of the host defense system. JOHN J. SPITZER ABRAHAM P. BAUTISTA Department of Physiology LSU Medical Center New Orleans, Louisiana
References 1. Enomoto N, Ikejima K, Bradford B, Rivera C, Kono H, Brenner DA, Thurman RG. Alcohol causes both tolerance and sensitization of rat Kupffer cells via mechanisms dependent on endotoxin. Gastroenterology 1998;115:443–451. 2. D’Souza NB, Bagby GJ, Nelson S, Lang CH, Spitzer JJ. Acute alcohol infusion suppresses endotoxin-induced serum tumor necrosis factor. Alcohol Clin Exp Res 1989;13:295–298. 3. Bautista AP, Me´sza´ros K, Bojta J, Spitzer JJ. Superoxide anion generation in the liver during the early stage of endotoxemia in rats. J Leukoc Biol 1990;48:123–128. 4. Bautista AP, Schuler A, Spolarics Z, Spitzer JJ. Tumor necrosis factor a stimulates superoxide anion generation by perfused rat liver and Kupffer cells. Am J Physiol 1991;261:G891–G895. 5. Bautista AP, Schuler A, Spolarics Z, Spitzer JJ. In vivo latex phagocytosis primes the Kupffer cells and hepatic neutrophils to generate superoxide anion. J Leukoc Biol 1992;51:39–45. 6. Bautista AP, Spitzer JJ. Acute ethanol intoxication stimulates superoxide anion production by in situ perfused rat liver. Hepatology 1992;15:892–898. 7. Bautista AP, D’Souza NB, Lang CH, Bagwell J, Spitzer JJ. Alcoholinduced down-regulation of superoxide anion release by hepatic phagocytes in endotoxemic rats. Am J Physiol 1991;260:R969– R976. 8. D’Souza NB, Bautista AP, Bagby GJ, Lang CH, Spitzer JJ. Acute ethanol intoxication suppresses E. coli lipopolysaccharide enhance glucose utilization by hepatic nonparenchymal cells. Alcohol Clin Exp Res 1991;15:249–254. 9. Spolarics Z. Endotoxemia, pentose cycle, and the oxidant/ antioxidant balance in the hepatic sinusoid. J Leukoc Biol 1998; 63:534–541. 10. Spolarics Z, Spitzer JJ, Wang JF, Xie J, Kolls J, Greenberg S. Alcohol administration attenuates LPS-induced expression of inducible nitric oxide synthase in Kupffer and hepatic endothelial cells. Biomed Biophys Res Commun 1993;197:606–611. 11. Bautista AP, Spitzer JJ. Acute endotoxin tolerance down-regulates superoxide anion release by the perfused liver and isolated hepatic nonparenchymal cells. Hepatology 1995;21:855–862. 12. Cavaillon J-M. The nonspecific nature of endotoxin tolerance. Trends Microbiol 1995;3:320–324. 13. Bautista AP, Spitzer JJ. Cross-tolerance between acute alcohol
496
14.
15.
16.
17. 18.
19.
20.
EDITORIALS
intoxication and endotoxemia. Alcohol Clin Exp Res 1996;20: 1395–1400. West MA, LeMieur T, Clair L, Bellingham J, Rodriguez JL. Protein kinase C regulates macrophage tumor necrosis factor secretion: direct protein kinase C activation restores tumor necrosis factor production in endotoxin tolerance. Surgery 1997;122:204–211. Blackwell TS, Blackwell TR, Christman JW. Induction of endotoxin tolerance depletes nuclear factor-kB and suppresses its activation in rat alveolar macrophages. J Leukoc Biol 1997;62:885–891. Kohler NG, Joly A. The involvement of an LPS inducible I kappa B kinase in endotoxin tolerance. Biochem Biophys Res Commun 1997;232:602–607. Ziegler-Heitbrock HW. Molecular mechanism in tolerance to lipopolysaccharide (review). J Inflamm 1995;45:13–26. Taraschi TF, Ellingson JS, Wu A, Zimmerman R. Phosphatidylimositol from ethanol-fed rats confers membrane tolerance to ethanol. Proc Natl Acad Sci USA 1986;83:9398–9402. Zingarelli B, Chen H, Caputi AP, Halushka PV, Cook JA. Reorientation of macrophage mediator production in endotoxin tolerance. Prog Clin Biol Res 1995;392:529–537. Fahmi H, Charon D, Mondange M, Chaby R. Endotoxin-induced desensitization of mouse macrophages is mediated in part by nitric oxide production. Infect Immun 1995;63:1863–1869.
GASTROENTEROLOGY Vol. 115, No. 2
21. Knolle PA, Loser E, Protzer U, Duchmann R, Schmitt E, zum Buschenfelde KH, Rose-John S, Gerken G. Regulation of endotoxininduced IL-6 production in liver sinusoidal endothelial cells and Kupffer cells IL-10. Clin Exp Immunol 1997;107:555–561. 22. Van der Poll T, Coyle SM, Moldawer LL, Lowry SF. Changes in endotoxin-induced cytokine production by whole blood after in vivo exposure of normal humans to endotoxin. J Infect Dis 1996;174: 1356–1360. 23. Amano T, Lee SW, Allison AC. Inhibition of glucocorticoids of the formation of interleukin 1b and interleukin 6: mediation by decreased mRNA stability. Mol Pharmacol 1993;43:176–182. 24. Makhlouf MS, Ashton H, Hildebrandt J, Mehta N, Gettys TW, Halushka PV, Cook JA. Alterations in macrophage G proteins are associated with endotoxin tolerance. Biochim Biophys Acta 1996; 1312:163–168.
Address requests for reprints to: John J. Spitzer, M.D., Department of Physiology, LSU Medical Center, 1901 Perdido Street, New Orleans, Louisiana 70112. Fax: (504) 568-6158. r 1998 by the American Gastroenterological Association 0016-5085/98/$3.00