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Effect of platelet activating factor on reticulo-endothelial system function
Bums (1991) 17, (3, 193-197
prinfd in GreufBrifuin
193
actiw@n~ factor on reticub m functbn M. Trop. E. J. Schi8ii.n and E. A. Carter Departments of Pediatrics, Combined Program in Pediatric Gastroenterology and Nutrition, Massachusetts General Hospital and Shriners Burns Institute, Boston, Massachusetts, USA
Tke &cf ofp&&f acfimfing factor (pAF) injecfiom on the upfake of ** Tc-SC ~9”Tc-SC pp”Tc-sdphtu w&d) was a&mind in vim umsfrainedrats PAF (2 M) injecfdinfm* infounanmfhefized, wasasociafedwithfkcddqmnf~ofinfhesmallinfesfine~ alferafion qf99mTc-SCupf& in vivo. ppmTc-SCupfde infothebug was itumasedwhilesplcEn~uxcldacrparad.Rzfmfmmfoffh8atlti witha PAF a&p& sKlde441, prwtxfd fhe it&did k+ot~~d alferafhs of DPmTc-SC fhePAF-MeIf rats,
Introduction The reticuloendothehal (RFS) system is responsible for clearing micro-orgarttsms from the blood and can be evaluated using 99mTc-solphur c&id (99”Tc-SC) injected intravenously. Thus, it has been demonstrated that alterations in the RF&S system, as measured by alterations in 99mTc-SCuptake, are assodated with the development of septicaemia in cirrhotic patients (Rimola et al., 1984). In a previous study we demonstrated that burn trauma to rats was associated with a marked alteration in RES function as measured by uptake of 99”rc-SC. In particular, 99mTc-SC uptake was increased in the lung and decreased in the spleen, while uptake by the liver was una&cted following either a small (20 per cent BSA) or large (40 per cent BSA), full skin thickness scald burn injury (Trap et al, 1989). In the course of studies to determine the mechanism(s) for this alteration, we have examined a number of possibilities, including blood-borne factors. Lethal burn trauma is associated with the devehqmumt of intestinal necrosis and alterations of immw flmction includmg RES function in vivo (Trap et al., 1989). $ince PAP inj43cSonis astitedtithe t of intestinai necrosis (Sun as with a&&rations of immunoet al., 19&W),the possibility that PAP could also a&r Ri% activity in-vivo Was examined in this report. 0 1991 But&worth-Heinemann Ltd 0305-4179J91/030193-05
Methods and materials Female CD rats (body wt 175-200 &’Chades River Laboratories, Wilmington, MA, USA) were used throughout the study. The animals were fasted for 24 h prior to experimentation. Catheters were placed in the tail vein under ether anaesthesia, as described previously (Trap et al., 1989). subsequentiy, the animals allowed to recover. PAP preparedfreshdailyand . catheter into the e rat. fkidy, the PAF lyophilized mate&l was resuspended in 100 per cent ethanolandthendkidedbetweenpI&ictubeswherethe ethanol was removed with a nitrogen gas stream. Subsequently, a fixed volume of saline co&ining 250 mg bovine serum albuminkil was added to each tube, mixed and injected into each unanae&etized rat. 99mTc-SC uptake was d&rmined, as described previously (Trap et al., 1989). Briefly, the radio@elied material, prepared fresh by the Massachusetts General Hospital Radiopharmacy, was injected into the tail catheter of the unanaesthetized rats 5 min prior to death. The animals were killed 2-3 h after injection of PAF by cervical dkslocation, and the liver, lung, spleen and kidneys were removed, weighed and then counted in a gamma counter. All experiments were completed within IO h of 9p”Tc_SC preparation. Lung lavage cells were utilized in the oxidative burst assay and bead uptake as described previously (Trinlde et al., 1987), followed by flow cytometer analysis. Lung lavage was carried out on anaesthetized rats. The cells were obtained from a 201d washing with Hank’s baked salt solution without Ca
of 1 X lob per mil&tEreof HEIS, without calcium or magnes~urn. Abquots were theEI ixwmb&d witfi &.&lorofluomscein diacetate (DCP-DA), f&al conomtmtjon 50 t.krrtol,or fluorescent beads (Polys&nces). The mixtures
194
Bums (1991) Vol. 17/No. 3
Figure 1. Histological appearance of stomach after PAF injection.
x
192
Figure 2. Histological appearance of small intestine after PAF injection.
were incubated for I5 or 30 min at 37°C for the DCF-DA or fluorescent beads, respectively. The reactions were stopped by centrifugation of the tubes at l0oOg for 5 min. The supematants were removed and the pellets resuspended in 0.5 ml of I per cent paraformaldehyde in half-strength HBSS. Flow cytometric analysis, using narrow forward angle light scatter as an indication of relative cell size, and the log of green fluorescence as an indication of either the production of hydrogen peroxide or uptake of fluorescence beads, was carried out on an Epics 452 flow rytometer. Rat intestines were removed at the time of necropsy, placed in formalin and processed for routine microscopic examination of haematoxylin-eosin-stained samples.
x
192.
Students’ f test was used to compare fluoresence associated with H,O, generation.
Results PAF injection produced marked alterations of the stomach and intestines (Figures1,~). There is a definite development of haemorrhagic lesions in the stomach (FigureI) and the fundic mucosa showed haemorrhagic ulcerations that involved the luminal area of the mucosa. The small intestine showed a patchy pattern of lesions (Figure2). There is necrosis of the tips of the villi intercalated with normal musoca, as well as obvious lesions in the caecum .of the
Trop et al.: H&t of platelet activating factor
195
Figure 3. Histological appearance of caecum after PAF injection.
T
-
conlrol
:
= PAP
x
212
the lung and spleen was essentially the same as that of the controls. Finally, the ability of the lung lavage macrophages of PAF-treated rats to produce hydrogen peroxide, a requirement to kill bacteria, was measured. There was no di&rence in the size of the cells obtained from either group. Under these conditions there was a marked reduction in the percentage of cells showing an increase in fluorescence associated with the hydrogen peroxide generation (36 f 3 vs 63 f 5, PAF vs control, PC 0.01). There was no difference in the uptake of the fluorescent beads.
Discussion
Figure4 Effect of PAF injection on the uptake of 99mTc-SC in viva by spleen and lung. There were six to eight animals in each group. The asterisk indicates statistically significant differences, PC 0.01 (using Student’s f test).
PAF-treated rats (Figure 3). The histological lesions involved both the mucosa and submucosa, as seen in Figure3. The mucosa showed extensive areas of ulceration with inflammatory infiltration of the lamina propria and mucous depletion. The submucosa showed oedema and inflammatory infiltration. These changes were associated with an alteration in uptake of the 99mTc-SC.As iilustrated in Figure4, there is a definite increase in 99”‘Tc-SC uptake by the lungs of the PAF-treated animals compared to the controls, while the spleen uptake was dramatically reduced. Liver and kidney uptake of the colloid was unaffected. Pretreatment of animals with the PAP antagonist (SR-416441) (Handkzy et al., 1986) 15min prior to the PAP injection prevented the changes at the macroscopic or microscopic levels of the stomach, small intestines, or caecum (data not shown). Such pretreatment completely blocked the change in @““T&C uptake associated with PAF injection observed previously (Figure4). Thus the uptake by
The major reason for death in burn patients is septicaemia (Rocco et al., 1989). One possible source of contamination and subsequent development of septicaemia in the burned patient could be the bacterial flora found in the intestines (Burke et al., 1977). An increase in permeability of the small intestine following acute burn trauma has been demonstrated (Carter et al., 1987). There is also evidence for enhanced translocation of bacteria to the mesenteric lymph nodes, in burned rats (Deitch et al., 1988). Fiiy, the muco+l mass of the small intestine of the burned rat or burney guinea-pig is reduced following trauma (Mochizuki et aL, 1984; Carter et al., 1986). Bacterial translocation to the mesenteric lymph nodes is a common finding in the rodent (Wells et al., 1988). This translocation may exist under normal circumstances because of the ~lationship of the bacterial flora to the priming of the imm ological system. However, in burn trauma, where perme bility of the intestines increases, the passage of viable bad a through the mucosal barrier is enhanced (Deitch et al., 19 8). Th5 RES is the primary system for t&ring microorganisms from the blood. Thus, an animal model was developed to examine theei?ectofbumtraumauponREs function. We injected non-anaesthetized rats with 9Q”Tc-SC intravenously and found that burn trauma was associated in uptake. The lung appear& to accumulate the radiolabelled material after burn injury than th?
196
control, while the spleen took up less than the control (Trap et al., 1989). Having developed the animal model, attemps were made to elucidate the mechanism(s) responsible for this alteration. There are at least three possible explanations for the change. The first and second relate to a direct effect of the burn trauma upon the RES organs involved. Therefore, burn trauma may produce a marked hypotension that alters the basic functions of the organs. However, in a study in which mean arterial pressure (MAP) in animals prior and subsequent to acute burn trauma was measured, there was no alteration in MAP following acute burn trauma (Trop et al., 1990, unpublished observations). Because it was necessary to burn injure the animals under anaesthesia, and the ether itself produced a drop in MAP, no further changes following the bum injury were observed. Secondly, thermal injury affecting the dorsal surface of the skin may somehow elevate the core temperature of the animal, and this elevation may physically damage the organs involved in RES function. Again when an extensive investigation measuring the core temperature (rectal and oesophageal) of animals subjected to burn trauma was carried out we were unable to demonstrate any elevation in body temperature to greater than approximately 40°C (M. Trop et al., 1990, unpublished observations). Hence, it is assumed that neither a change in blood pressure nor an increase in core temperature are responsible for the alterations that have been observed in phagocytic activity in vivo following burn trauma. The third possible mechanism is that factors released from the wound enter the systemic blood and then alter RES function in vivo. It was possible to demonstrate that when animals were subjected to acute burn injury and their wound eschar was removed within minutes, the change in phagocytic activity observed in vivo after burn trauma was still different from that seen in the ‘sham’control (Trop et al., 1990). For these reasons, it is assumed that there are factors released from the wound that travel through the systemic circulation, going first to the lung and subsequently to the intestine and liver. Possibly, given the work of Sun and Hsueh (1988), a hypothesis could be developed whereby lipopolysaccaride (LPS) could trigger the production of tumour necrosis factor (TNF), and the TNF could trigger the release of PAF at the intestinal level. This hypothesis is supported by the recent demonstration that TNF is present in the blood of our burned animals (E. A. Carter, 1990, unpublished observations), and because PAF has been demonstrated to have clear effects on the intestine, as a result of the development of necrosis (Gonzalez-Crussi and Hsueh, 1983). Therefore, a cycle could be proposed whereby an injury to the surface of the rat could release factors that might initially go to the lung and then to the intestine, resulting in the change in permeability and the passage of endotoxin and/or bacteria into the portal blood system. Subsequently, the material might overwhelm the filtering capacity of the liver, eventually resulting in systemic contamination. In the present study, the effect of PAF injected intravenously into unanaesthetized rats on RES function was examined as measured by 99mTc-SCuptake in vivo. The PAF was injected into the unanaesthetized animals, first to prevent the effects of the anaesthesia from confounding the results (anaesthetics have been shown to alter the subsequent rate of excretion of LPS (Kleine et al., 198511,and secondly because burn victims usually receive their injury in a conscious state. The present results confirm previous data,
Bums (1991) Vol. 17/No. 3
demonstrating that PAF has a marked necrotic effect on the small intestine (Gonzalez-Crussi and Hsueh, 1983). PAF injection also had a marked effect on RES function, as measured by 99mTc-SCuptake. The increased uptake by the lung and decreased uptake by the spleen is similar to that observed in burn-injured animals (Trop et al., 1989). It has been shown that this effect is clearly related to the presence of PAF, since when the animals were pretreated with a PAF antagonist, both the organ lesions and the changes in phagocytic activity in viva were prevented. The present results, plus the TNF elevation in the blood observed in our burned rats, support the hypothesis that the alterations observed in RES function in the burn-injured rat model are related, at least in part, to soluble factors such as PAF.
Acknowledgement This study was supported in part by NIH grant DK 34854 and The Shriners Hospital for Crippled Children.
References Burke J. F., Quinby W. C., Bondoc C. C. et al. (1977) The contribution of a bacterially isolated environment to the prevention of infection in seriously burned patients. Ann. Snrg.
186,377. Carter E. A., Harmatz P. R., Udall J. N. et al. (1987) Barrier defense function of the small intestine: effect of ethanol and acute burn trauma. Ado. Erp. Med. Biol. 216,829. Carter E. A., Udall J. K., Kirkham S. E. et al. (1986) Thermal injury and gastrointestinal function: I Small intestinal nutrient absorption and DNA synthesis. J Burn Care Reha&d. 7,469. Carter E. A., Tompkins R. G., Schiffrin E. et al. (1990) Cutaneous thermal injury alters macromolecular permeability of rat small intestine. Surgery 107,335. Deitch E. A., Bridges W., Baker J. et al. (1988) Hemorrhagic shock-induced bacterial translocation is reduced by xanthine oxidase inhibition or inactivation. Surgey 104,191. D&oust A., Salem P., Vivier, E. et al. (1988) Immunoregulatory functions of PAF-acether (Platelet-Activating Factor). Prog. Clin. Biol. Res. 282, 87.
Gonzalez-Crussi F. and Hsueh W. (1983) Experimental model of ischemic bowel necrosis: the role of platelet-activating factor and endotoxin. Am. J. Pathol. 112, 127. Handley D. A., Tome&J. C. and Saunders R. N. (1986) Inhibition of PAF-induced systemic responses in the rat, guinea pig, dog and primate by the receptor antagonist SRI 63-441.Thromb. Haemost. 56, 40. Kleine B., Frendenberg M. A. and Galanos C. (1985)Excretion of radioactivity in faeces and urine of rats injected with 3H,“Clipopolysaccaride. Br. 1. k-p. P&d 66,303. Mochizuki H., Trocki O., Dominioni L. et al. (1984) Mechanism of prevention of postburn hypermetabolism and catabolism by early enteral feeding. Arm. Surg. 200,297. Rimola A., Soto R., Bory F. et al. (1984) Reticuloendothelial system phagocytic activity in cirrhosis and its relation to bacterial infections and prognosis. He+ology 4,53. Rocco J., Goldfarb I. W. and Slater H. (1989) Septic death in bum patients: a lack of progress. Proc.Am. Bum Assoc. 21,107. Sun X. and Hsueh W. (1988) Bowel necrosis induced by tumor necrosis factorin rats is mediated by platelet-activating factor. 1, Ch. Inoest. 81, 1328.
Trop et al.: Effect of platelet activating factor
197
TrinkJe L. S., WeJJhausen S. R. and McLeish K. R. (1987) A simultaneous flow cytometric measurement of neutrophil phagocytosis and oxidative burst in whole blood. Diugr~.Clin. lmmutwl. 5,62. Trop M., S&i&in E. J., Jung W. K. et al. (1989) Effect of acute bum trauma on reticuloendothelial phagocytic activity in rats. J. Burn care Rehabil. 10,388. Trop M., ScMfrin E. J. and Carter E. A. (1990) Role of the skin in the burn-imduced reduction of reticuloendothelial phagocytic activity in rats. Bum 16,57.
Wells C. L., Maddaus M. A. and Sirnmons R L. (1988) Proposed mechanisms for the translocation of intestinal bacterias. Rev. Infect. Dis. 10,958. Paper accepted 17 January 1991.
Correspondmce shouM be a&d to: Dr Edward A. Carter, Combined Program in Pediatic Gastroenterology and Nutrition, Massachusetts General Hospital, Boston, MA 02114, USA
1st European Conference on Advances in Wound Management The 1st European Conference on Advances in Wound Management will take place on 4-6 September 1991 at the University of Cardiff, Wales - a multidisciplinary conference aimed at all healthcare professionals concerned with Wound Management. Call for Papers Papers are invited for concurrent sessions - any subject is welcome but priority will be given to the following provisional topics: 0 0 0 0 0 0 0 0 0 0
Experimental Wound Healing Prevalence Surveys of Wounds Research Methodology Nutritional Aspects Infection Specific Dressings for Specific Wounds Management of Complex Wounds Leg Ulcers Pressure Sores Acute Trauma
Deadline for papers is May 3 1 1991. Delegate Registrations Registrations are now being taken for the conference and an agenda is available on request. For further details and a registration form call the Conference O&e on 071 836 6633 or write to the First European Conference on Advances in Wound Management, MacmilJan Conferences, 4 Little Essex Street, London WC2R 3LF.
prinfd in GreufBrifuin
193
actiw@n~ factor on reticub m functbn M. Trop. E. J. Schi8ii.n and E. A. Carter Departments of Pediatrics, Combined Program in Pediatric Gastroenterology and Nutrition, Massachusetts General Hospital and Shriners Burns Institute, Boston, Massachusetts, USA
Tke &cf ofp&&f acfimfing factor (pAF) injecfiom on the upfake of ** Tc-SC ~9”Tc-SC pp”Tc-sdphtu w&d) was a&mind in vim umsfrainedrats PAF (2 M) injecfdinfm* infounanmfhefized, wasasociafedwithfkcddqmnf~ofinfhesmallinfesfine~ alferafion qf99mTc-SCupf& in vivo. ppmTc-SCupfde infothebug was itumasedwhilesplcEn~uxcldacrparad.Rzfmfmmfoffh8atlti witha PAF a&p& sKlde441, prwtxfd fhe it&did k+ot~~d alferafhs of DPmTc-SC fhePAF-MeIf rats,
Introduction The reticuloendothehal (RFS) system is responsible for clearing micro-orgarttsms from the blood and can be evaluated using 99mTc-solphur c&id (99”Tc-SC) injected intravenously. Thus, it has been demonstrated that alterations in the RF&S system, as measured by alterations in 99mTc-SCuptake, are assodated with the development of septicaemia in cirrhotic patients (Rimola et al., 1984). In a previous study we demonstrated that burn trauma to rats was associated with a marked alteration in RES function as measured by uptake of 99”rc-SC. In particular, 99mTc-SC uptake was increased in the lung and decreased in the spleen, while uptake by the liver was una&cted following either a small (20 per cent BSA) or large (40 per cent BSA), full skin thickness scald burn injury (Trap et al, 1989). In the course of studies to determine the mechanism(s) for this alteration, we have examined a number of possibilities, including blood-borne factors. Lethal burn trauma is associated with the devehqmumt of intestinal necrosis and alterations of immw flmction includmg RES function in vivo (Trap et al., 1989). $ince PAP inj43cSonis astitedtithe t of intestinai necrosis (Sun as with a&&rations of immunoet al., 19&W),the possibility that PAP could also a&r Ri% activity in-vivo Was examined in this report. 0 1991 But&worth-Heinemann Ltd 0305-4179J91/030193-05
Methods and materials Female CD rats (body wt 175-200 &’Chades River Laboratories, Wilmington, MA, USA) were used throughout the study. The animals were fasted for 24 h prior to experimentation. Catheters were placed in the tail vein under ether anaesthesia, as described previously (Trap et al., 1989). subsequentiy, the animals allowed to recover. PAP preparedfreshdailyand . catheter into the e rat. fkidy, the PAF lyophilized mate&l was resuspended in 100 per cent ethanolandthendkidedbetweenpI&ictubeswherethe ethanol was removed with a nitrogen gas stream. Subsequently, a fixed volume of saline co&ining 250 mg bovine serum albuminkil was added to each tube, mixed and injected into each unanae&etized rat. 99mTc-SC uptake was d&rmined, as described previously (Trap et al., 1989). Briefly, the radio@elied material, prepared fresh by the Massachusetts General Hospital Radiopharmacy, was injected into the tail catheter of the unanaesthetized rats 5 min prior to death. The animals were killed 2-3 h after injection of PAF by cervical dkslocation, and the liver, lung, spleen and kidneys were removed, weighed and then counted in a gamma counter. All experiments were completed within IO h of 9p”Tc_SC preparation. Lung lavage cells were utilized in the oxidative burst assay and bead uptake as described previously (Trinlde et al., 1987), followed by flow cytometer analysis. Lung lavage was carried out on anaesthetized rats. The cells were obtained from a 201d washing with Hank’s baked salt solution without Ca
of 1 X lob per mil&tEreof HEIS, without calcium or magnes~urn. Abquots were theEI ixwmb&d witfi &.&lorofluomscein diacetate (DCP-DA), f&al conomtmtjon 50 t.krrtol,or fluorescent beads (Polys&nces). The mixtures
194
Bums (1991) Vol. 17/No. 3
Figure 1. Histological appearance of stomach after PAF injection.
x
192
Figure 2. Histological appearance of small intestine after PAF injection.
were incubated for I5 or 30 min at 37°C for the DCF-DA or fluorescent beads, respectively. The reactions were stopped by centrifugation of the tubes at l0oOg for 5 min. The supematants were removed and the pellets resuspended in 0.5 ml of I per cent paraformaldehyde in half-strength HBSS. Flow cytometric analysis, using narrow forward angle light scatter as an indication of relative cell size, and the log of green fluorescence as an indication of either the production of hydrogen peroxide or uptake of fluorescence beads, was carried out on an Epics 452 flow rytometer. Rat intestines were removed at the time of necropsy, placed in formalin and processed for routine microscopic examination of haematoxylin-eosin-stained samples.
x
192.
Students’ f test was used to compare fluoresence associated with H,O, generation.
Results PAF injection produced marked alterations of the stomach and intestines (Figures1,~). There is a definite development of haemorrhagic lesions in the stomach (FigureI) and the fundic mucosa showed haemorrhagic ulcerations that involved the luminal area of the mucosa. The small intestine showed a patchy pattern of lesions (Figure2). There is necrosis of the tips of the villi intercalated with normal musoca, as well as obvious lesions in the caecum .of the
Trop et al.: H&t of platelet activating factor
195
Figure 3. Histological appearance of caecum after PAF injection.
T
-
conlrol
:
= PAP
x
212
the lung and spleen was essentially the same as that of the controls. Finally, the ability of the lung lavage macrophages of PAF-treated rats to produce hydrogen peroxide, a requirement to kill bacteria, was measured. There was no di&rence in the size of the cells obtained from either group. Under these conditions there was a marked reduction in the percentage of cells showing an increase in fluorescence associated with the hydrogen peroxide generation (36 f 3 vs 63 f 5, PAF vs control, PC 0.01). There was no difference in the uptake of the fluorescent beads.
Discussion
Figure4 Effect of PAF injection on the uptake of 99mTc-SC in viva by spleen and lung. There were six to eight animals in each group. The asterisk indicates statistically significant differences, PC 0.01 (using Student’s f test).
PAF-treated rats (Figure 3). The histological lesions involved both the mucosa and submucosa, as seen in Figure3. The mucosa showed extensive areas of ulceration with inflammatory infiltration of the lamina propria and mucous depletion. The submucosa showed oedema and inflammatory infiltration. These changes were associated with an alteration in uptake of the 99mTc-SC.As iilustrated in Figure4, there is a definite increase in 99”‘Tc-SC uptake by the lungs of the PAF-treated animals compared to the controls, while the spleen uptake was dramatically reduced. Liver and kidney uptake of the colloid was unaffected. Pretreatment of animals with the PAP antagonist (SR-416441) (Handkzy et al., 1986) 15min prior to the PAP injection prevented the changes at the macroscopic or microscopic levels of the stomach, small intestines, or caecum (data not shown). Such pretreatment completely blocked the change in @““T&C uptake associated with PAF injection observed previously (Figure4). Thus the uptake by
The major reason for death in burn patients is septicaemia (Rocco et al., 1989). One possible source of contamination and subsequent development of septicaemia in the burned patient could be the bacterial flora found in the intestines (Burke et al., 1977). An increase in permeability of the small intestine following acute burn trauma has been demonstrated (Carter et al., 1987). There is also evidence for enhanced translocation of bacteria to the mesenteric lymph nodes, in burned rats (Deitch et al., 1988). Fiiy, the muco+l mass of the small intestine of the burned rat or burney guinea-pig is reduced following trauma (Mochizuki et aL, 1984; Carter et al., 1986). Bacterial translocation to the mesenteric lymph nodes is a common finding in the rodent (Wells et al., 1988). This translocation may exist under normal circumstances because of the ~lationship of the bacterial flora to the priming of the imm ological system. However, in burn trauma, where perme bility of the intestines increases, the passage of viable bad a through the mucosal barrier is enhanced (Deitch et al., 19 8). Th5 RES is the primary system for t&ring microorganisms from the blood. Thus, an animal model was developed to examine theei?ectofbumtraumauponREs function. We injected non-anaesthetized rats with 9Q”Tc-SC intravenously and found that burn trauma was associated in uptake. The lung appear& to accumulate the radiolabelled material after burn injury than th?
196
control, while the spleen took up less than the control (Trap et al., 1989). Having developed the animal model, attemps were made to elucidate the mechanism(s) responsible for this alteration. There are at least three possible explanations for the change. The first and second relate to a direct effect of the burn trauma upon the RES organs involved. Therefore, burn trauma may produce a marked hypotension that alters the basic functions of the organs. However, in a study in which mean arterial pressure (MAP) in animals prior and subsequent to acute burn trauma was measured, there was no alteration in MAP following acute burn trauma (Trop et al., 1990, unpublished observations). Because it was necessary to burn injure the animals under anaesthesia, and the ether itself produced a drop in MAP, no further changes following the bum injury were observed. Secondly, thermal injury affecting the dorsal surface of the skin may somehow elevate the core temperature of the animal, and this elevation may physically damage the organs involved in RES function. Again when an extensive investigation measuring the core temperature (rectal and oesophageal) of animals subjected to burn trauma was carried out we were unable to demonstrate any elevation in body temperature to greater than approximately 40°C (M. Trop et al., 1990, unpublished observations). Hence, it is assumed that neither a change in blood pressure nor an increase in core temperature are responsible for the alterations that have been observed in phagocytic activity in vivo following burn trauma. The third possible mechanism is that factors released from the wound enter the systemic blood and then alter RES function in vivo. It was possible to demonstrate that when animals were subjected to acute burn injury and their wound eschar was removed within minutes, the change in phagocytic activity observed in vivo after burn trauma was still different from that seen in the ‘sham’control (Trop et al., 1990). For these reasons, it is assumed that there are factors released from the wound that travel through the systemic circulation, going first to the lung and subsequently to the intestine and liver. Possibly, given the work of Sun and Hsueh (1988), a hypothesis could be developed whereby lipopolysaccaride (LPS) could trigger the production of tumour necrosis factor (TNF), and the TNF could trigger the release of PAF at the intestinal level. This hypothesis is supported by the recent demonstration that TNF is present in the blood of our burned animals (E. A. Carter, 1990, unpublished observations), and because PAF has been demonstrated to have clear effects on the intestine, as a result of the development of necrosis (Gonzalez-Crussi and Hsueh, 1983). Therefore, a cycle could be proposed whereby an injury to the surface of the rat could release factors that might initially go to the lung and then to the intestine, resulting in the change in permeability and the passage of endotoxin and/or bacteria into the portal blood system. Subsequently, the material might overwhelm the filtering capacity of the liver, eventually resulting in systemic contamination. In the present study, the effect of PAF injected intravenously into unanaesthetized rats on RES function was examined as measured by 99mTc-SCuptake in vivo. The PAF was injected into the unanaesthetized animals, first to prevent the effects of the anaesthesia from confounding the results (anaesthetics have been shown to alter the subsequent rate of excretion of LPS (Kleine et al., 198511,and secondly because burn victims usually receive their injury in a conscious state. The present results confirm previous data,
Bums (1991) Vol. 17/No. 3
demonstrating that PAF has a marked necrotic effect on the small intestine (Gonzalez-Crussi and Hsueh, 1983). PAF injection also had a marked effect on RES function, as measured by 99mTc-SCuptake. The increased uptake by the lung and decreased uptake by the spleen is similar to that observed in burn-injured animals (Trop et al., 1989). It has been shown that this effect is clearly related to the presence of PAF, since when the animals were pretreated with a PAF antagonist, both the organ lesions and the changes in phagocytic activity in viva were prevented. The present results, plus the TNF elevation in the blood observed in our burned rats, support the hypothesis that the alterations observed in RES function in the burn-injured rat model are related, at least in part, to soluble factors such as PAF.
Acknowledgement This study was supported in part by NIH grant DK 34854 and The Shriners Hospital for Crippled Children.
References Burke J. F., Quinby W. C., Bondoc C. C. et al. (1977) The contribution of a bacterially isolated environment to the prevention of infection in seriously burned patients. Ann. Snrg.
186,377. Carter E. A., Harmatz P. R., Udall J. N. et al. (1987) Barrier defense function of the small intestine: effect of ethanol and acute burn trauma. Ado. Erp. Med. Biol. 216,829. Carter E. A., Udall J. K., Kirkham S. E. et al. (1986) Thermal injury and gastrointestinal function: I Small intestinal nutrient absorption and DNA synthesis. J Burn Care Reha&d. 7,469. Carter E. A., Tompkins R. G., Schiffrin E. et al. (1990) Cutaneous thermal injury alters macromolecular permeability of rat small intestine. Surgery 107,335. Deitch E. A., Bridges W., Baker J. et al. (1988) Hemorrhagic shock-induced bacterial translocation is reduced by xanthine oxidase inhibition or inactivation. Surgey 104,191. D&oust A., Salem P., Vivier, E. et al. (1988) Immunoregulatory functions of PAF-acether (Platelet-Activating Factor). Prog. Clin. Biol. Res. 282, 87.
Gonzalez-Crussi F. and Hsueh W. (1983) Experimental model of ischemic bowel necrosis: the role of platelet-activating factor and endotoxin. Am. J. Pathol. 112, 127. Handley D. A., Tome&J. C. and Saunders R. N. (1986) Inhibition of PAF-induced systemic responses in the rat, guinea pig, dog and primate by the receptor antagonist SRI 63-441.Thromb. Haemost. 56, 40. Kleine B., Frendenberg M. A. and Galanos C. (1985)Excretion of radioactivity in faeces and urine of rats injected with 3H,“Clipopolysaccaride. Br. 1. k-p. P&d 66,303. Mochizuki H., Trocki O., Dominioni L. et al. (1984) Mechanism of prevention of postburn hypermetabolism and catabolism by early enteral feeding. Arm. Surg. 200,297. Rimola A., Soto R., Bory F. et al. (1984) Reticuloendothelial system phagocytic activity in cirrhosis and its relation to bacterial infections and prognosis. He+ology 4,53. Rocco J., Goldfarb I. W. and Slater H. (1989) Septic death in bum patients: a lack of progress. Proc.Am. Bum Assoc. 21,107. Sun X. and Hsueh W. (1988) Bowel necrosis induced by tumor necrosis factorin rats is mediated by platelet-activating factor. 1, Ch. Inoest. 81, 1328.
Trop et al.: Effect of platelet activating factor
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Correspondmce shouM be a&d to: Dr Edward A. Carter, Combined Program in Pediatic Gastroenterology and Nutrition, Massachusetts General Hospital, Boston, MA 02114, USA
1st European Conference on Advances in Wound Management The 1st European Conference on Advances in Wound Management will take place on 4-6 September 1991 at the University of Cardiff, Wales - a multidisciplinary conference aimed at all healthcare professionals concerned with Wound Management. Call for Papers Papers are invited for concurrent sessions - any subject is welcome but priority will be given to the following provisional topics: 0 0 0 0 0 0 0 0 0 0
Experimental Wound Healing Prevalence Surveys of Wounds Research Methodology Nutritional Aspects Infection Specific Dressings for Specific Wounds Management of Complex Wounds Leg Ulcers Pressure Sores Acute Trauma
Deadline for papers is May 3 1 1991. Delegate Registrations Registrations are now being taken for the conference and an agenda is available on request. For further details and a registration form call the Conference O&e on 071 836 6633 or write to the First European Conference on Advances in Wound Management, MacmilJan Conferences, 4 Little Essex Street, London WC2R 3LF.