Hepatic venoconstriction is involved in anaphylactic hypotension in rats

Cardiac return assist blanket (CRAB) safely increases central venous pressure

OBJECTIVE

The cardiac return assist blanket (CRAB) has been designed to increase central venous pressure (CVP) to manage severe hypotension associated with anaphylaxis. This interventional study aimed to identify the relationship between CRAB pressure and CVP. CRAB pressure was also compared with the change in CVP associated with a straight leg raise (SLR), the Trendelenburg position, and 1 L of compound sodium lactate.

METHODS

Sixteen healthy, fasted volunteers were exposed to CRAB pressure at 10, 20, 30, and 40 cmH2O, the SLR, and 15 degrees of the Trendelenburg position. The volunteers were then fed and hydrated with 1 L of CSL over 30 minutes and the protocol was repeated.

RESULTS

The initial 10 cmH2O of CRAB pressure increased CVP by 3.7 mmHg (95% confidence interval 2.7, 4.7). Each subsequent 10-cmH2O rise in CRAB pressure increased CVP by 0.9 mmHg (95% confidence interval 0.55, 1.25). The SLR, Trendelenburg position, and 1 L of CSL increased CVP by 0.97 , 0.75 , and 0.69 mmHg, respectively.

CONCLUSIONS

The CRAB controllably increases CVP, and 40 cmH2O of CRAB pressure increases CVP by 6.41 mmHg. The effect of the CRAB is greater than that with the SLR, Trendelenburg position, or 1 L of CSL.This trial was registered with the ANZCTR (ACTRN12621000840886: https://www.anzctr.org.au).

Intravenous dexmedetomidine, morphine, or a combination can result in gallbladder wall thickening; with no significant association with plasma histamine concentrations

The gallbladder is routinely evaluated during ultrasonographic examinations in dogs. However, published studies describing the effects of sedative agents on gallbladder wall thickness are currently lacking. The aims of this prospective, blinded, randomized crossover pilot study were to test hypotheses that IV morphine would result in gallbladder wall thickening, that morphine administration would increase plasma histamine concentrations, and that combining IV morphine with dexmedetomidine would potentiate gallbladder wall thickening. Six healthy Beagle dogs were sedated with intravenous (IV) morphine 0.4 mg/kg (group M), dexmedetomidine 7 μg/kg (group D), or a combination of the two (group MD). Physiologic parameters were measured at baseline and at regular intervals until the last ultrasonographic scan. Ultrasonographic scans were performed at baseline, 90 s, and at 5, 15, 30, 45, 60, 90, and 120 min. Plasma histamine samples were taken at baseline, 90 s, and 5 and 60 min. Cochran's Q-test was used to compare gallbladder wall thickening between groups, while the association between histamine plasma concentration and gallbladder wall thickness was compared with a mixed-effects model. Baseline gallbladder wall thickness was not significantly different between groups. Six of 18 treatments/dogs (33%) developed gallbladder thickening, with no difference between groups. There was no significant difference in baseline plasma histamine concentrations between groups, and no association between plasma histamine concentration and gallbladder wall thickness. Gallbladder wall thickening was observed in at least one dog in each group, therefore caution is recommended for gallbladder wall thickness ultrasonographic interpretation in dogs when these drugs have been administered.

Angiopoietin-2 is released during anaphylactic hypotension in anesthetized and unanesthetized rats

Angiopoietin (Angpt)-2, a permeability-increasing growth factor, is involved in vascular leakage of sepsis and acute lung injury, and could be released from endothelium in response to anaphylaxis-related secretagogues such as histamine and leukotrienes, or cytokines. However, roles of Angpt-2 in the hyperpermeability during systemic anaphylaxis are not known. Thus, we determined plasma levels of Angpt-2 and cytokines and vascular permeability during anaphylactic hypotension in unanesthetized rats. Anaphylaxis was induced by an intravenous injection of ovalbumin antigen. Mean arterial blood pressure (MBP) was measured, and hematocrit (Hct) and plasma levels of Angpt-2 and cytokines were assessed for 24 h after antigen injection. Separately, vascular permeability was measured in various organs using the Evans blue dye method, and Angpt-2 mRNA expression in liver was measured. After antigen injection, MBP decreased to the nadir at 6 min, and returned to baseline at 45 min, and Hct peaked at 20 min and thereafter progressively declined, suggesting that vascular leak and hypotension occurred within 20 min. Plasma Angpt-2 levels began to increase significantly at 1 h after antigen, reaching the peak 2.7-fold baseline at 6 h with a return to baseline at 24 h. Detected cytokines of IL-1α, IL-1β, IL-6, IL-10, and TNF-α peaked 1 or 2 h after antigen. Angpt-2 mRNA increased at 2 h and showed an increasing tendency at 6 h. Vascular permeability in bronchus, trachea, intestines, mesentery and skeletal muscle was increased at 10 min but not at 6 h after antigen. In addition, we confirmed using anesthetized rat anaphylaxis models that plasma Angpt-2 levels increased at 1 h after antigen. In conclusion, plasma Angpt-2 is elevated presumably due to increased cytokines and enhanced gene transcription during anaphylaxis in anesthetized and unanesthetized rats.

Tonic contraction develops in the colon during anaphylactic hypotension in anesthetized rats

Diarrhea is a gastrointestinal symptom associated with systemic anaphylaxis and could be induced by increased colonic motility. We determined colonic motility and expulsion by measuring the intracolonic pressure (ICP) and expelled fluid weight in anesthetized rats during anaphylactic hypotension. Substantial systemic hypotension occurred in every sensitized rat after antigen injection. One min after antigen injection, ICP began to increase and remained elevated for 5 min, which was revealed to represent tonic contraction by the video-recording procedure, and was accompanied by increased colonic fluid expulsion. Parasympathectomy composed of subdiaphragmatic vagotomy combined with pelvic nerve transection reduced the duration of the tonic contraction, but not expelled colonic fluid. Furthermore, denervation of afferent parasympathetic nerves produced essentially the same effect as parasympathectomy. Sympathectomy did not significantly change any parameters. In conclusion, the colonic motility during anaphylactic hypotension is characterized by 5-min lasting tonic contraction which is associated with increased colonic fluid expulsion and is involved by parasympathetic nerves, especially their afferents, but not sympathetic nerves, in anesthetized rats.

Anaphylaxis stimulates afferent vagal nerve activity and efferent sympathetic nerve activity in the stomach of anesthetized rats

Systemic anaphylaxis is a life-threatening and allergic reaction that affects various organs. We previously reported that, in the stomach, gastric vasoconstriction occurring at the late phase (15-55 min after injection of ovalbumin antigen) was observed in anesthetized rats sensitized with ovalbumin. In addition, anaphylaxis enhances gastric motility and delays emptying. However, the role of extrinsic autonomic nervous system on antigen-induced gastric alterations was not known. Thus, using the same rat anaphylaxis model, we aimed to determine the changes in the efferent and afferent autonomic nerve activities in the stomach during anaphylactic hypotension. The findings showed that injection of ovalbumin antigen caused substantial systemic hypotension in all sensitized rats. The efferent gastric sympathetic nerve activity (ef-GSNA), but not the efferent vagal nerve activity, increased only at the early phase (1-10 min after injection of ovalbumin antigen) and showed baroreceptor reflex, as evidenced by a stimulatory response to sodium nitroprusside-induced hypotension. In general, excitation of ef-GSNA could induce pylorus sphincter contraction and gastric vasoconstriction. In the present study, we found that sympathectomy attenuated the anaphylaxis-induced decrease in gastric flux but not the increase in gastric vascular resistance. Thus, the increase in ef-GSNA may cause anaphylactic pylorus sphincter contraction but not anaphylactic gastric vasoconstriction. On the other hand, the afferent gastric vagal nerve activity, but not the afferent sympathetic nerve activity, increased during the early phase of anaphylactic hypotension. However, vagotomy produced no effects on the anaphylactic gastric dysfunction. In conclusion, the gastric sympathetic nerves partly modulate stomach function during systemic anaphylaxis.

IgE induces hypotension in asthma mice by down-regulating vascular NCX1 expression through activating MiR-212-5p

Immunoglobulin E (IgE) has been suggested as a risk factor for allergy-induced low blood pressure, which has not been well explained in molecular details. Our current study shows a novel mechanism involving IgE, FcɛR1, miRNA-212-5p (miR-212-5p), and sodium/calcium exchanger protein 1(NCX1) for asthma to induce hypotension. In arterial smooth muscle cells, IgE up-regulated miR212-5p via its receptor FcɛR1, which resulted in down-regulation of NCX1 that is a regulating factor for blood pressure. In mice, asthma induced hypotension by interfering vasoconstrictive function; knockout of FcɛR1 kept the asthmatic mice from developing hypotension; knock-down of miR-212-5p in asthmatic mice resulted in a significant restoration of blood pressure. In human, asthma and IgE were positively correlated with hypotension in cohort study on NIH epidemiological data. This study suggests a novel therapeutic target (miR-212-5p) for treatment of asthma-induced hypotension.

The Role of Lumbar Sympathetic Nerves in Regulation of Blood Flow to Skeletal Muscle during Anaphylactic Hypotension in Anesthetized Rats

During hypovolemic shock, skeletal muscle blood flow could be redistributed to vital organs via vasoconstriction in part evoked by activation of the innervating sympathetic nerve activity. However, it is not well known whether this mechanism operates during anaphylactic shock. We determined the femoral artery blood flow (FBF) and lumbar sympathetic nerve activity (LSNA) mainly regulating the hindquater muscle blood flow during anaphylactic hypotension in anesthetized rats. Anesthetized Sprague-Dawley rats were randomly allocated to the following groups (n = 7/group): (1) non-sensitized, (2) anaphylaxis, (3) anaphylaxis-lumbar sympathectomy (LS) and (4) anaphylaxis-sinoaortic denervation (SAD) groups. Anaphylaxis was induced by an intravenous injection of the ovalbumin antigen to the sensitized rats. The systemic arterial pressure (SAP), heart rate (HR), central venous pressure (CVP), FBF and LSNA were continuously measured. In the anaphylaxis group, LSNA and HR increased, while SAP and FBF decreased after antigen injection. In the anaphylaxis-SAD group, LSNA did not significantly change during the early phase, but the responses of SAP and FBF were similar to those in the anaphylaxis group. In the anaphylaxis-LS group, both FBF and SAP decreased similarly to the anaphylaxis group during anaphylactic hypotension. These results indicated that LSNA increased via baroreceptor reflex, but this sympathoexcitation or LS did not affect antigen-induced decreases in FBF or SAP. Lumbar sympathetic nerves are not involved in regulation of the blood flow to the hindlimb or systemic blood pressure during anaphylactic hypotension in anesthetized rats.

Effects of anesthetics on the renal sympathetic response to anaphylactic hypotension in rats

The autonomic nervous system plays an important role in rat anaphylactic hypotension. It is well known that sympathetic nerve activity and cardiovascular function are affected by anesthetics. However, the effects of different types of anesthesia on the efferent renal sympathetic nerve activity (RSNA) during anaphylactic hypotension remain unknown. Therefore, we determined the renal sympathetic responses to anaphylactic hypotension in anesthetized and conscious rats and the roles of baroreceptors in these responses. Sprague-Dawley rats were randomly allocated to anesthetic groups that were given pentobarbital, urethane, or ketamine-xylazine and to a conscious group. The rats were sensitized using subcutaneously injected ovalbumin. The systemic arterial pressure (SAP), RSNA and heart rate (HR) were measured. The effects of sinoaortic baroreceptor denervation on RSNA during anaphylaxis were determined in pentobarbital-anesthetized and conscious rats. In all of the sensitized rats, the RSNA increased and SAP decreased after antigen injection. At the early phase within 35 min of the antigen injection, the antigen-induced sympathoexcitation in the conscious rats was significantly greater than that in the anesthetized rats. Anaphylactic hypotension was attenuated in the conscious rats compared to the anesthetized rats. The anesthetic-induced suppression of SAP and RSNA was greater in the order ketamine-xylazine >urethane = pentobarbital. Indeed, in the rats treated with ketamine-xylazine, RSNA did not increase until 40 min, and SAP remained at low levels after the antigen injection. The baroreceptor reflex, as evaluated by increases in RSNA and HR in response to the decrease in SAP induced by sodium nitroprusside (SNP), was suppressed in the anesthetized rats compared with the conscious rats. Consistent with this finding, baroreceptor denervation attenuated the excitatory responses of RSNA to anaphylaxis in the conscious rats but not in the pentobarbital-anesthetized rats. RSNA was increased markedly in conscious rats during anaphylactic hypotension. Anesthetics attenuated this antigen-induced renal sympathoexcitation through the suppression of baroreceptor function.

Mouse anaphylactic shock is caused by reduced cardiac output, but not by systemic vasodilatation or pulmonary vasoconstriction, via PAF and histamine

AIMS

Systemic anaphylaxis is life-threatening, and its pathophysiology is not fully clarified. Mice are frequently used for experimental study on anaphylaxis. However, the hemodynamic features and mechanisms of mouse anaphylactic hypotension remain unknown. Therefore, we determined mechanisms of systemic and pulmonary vascular response to anaphylactic hypotension in anesthetized BALB/c mice by using receptor antagonists of chemical mediators.

MAIN METHODS

Anaphylaxis was actively induced by an intravenous injection of the ovalbumin antigen into open-chest artificially ventilated sensitized mice. Mean arterial pressure (MAP), pulmonary arterial pressure (PAP), left atrial pressure, central venous pressure, and aortic blood flow (ABF) were continuously measured.

KEY FINDINGS

In sensitized control mice, MAP and ABF showed initial, transient increases, followed by progressive decreases after the antigen injection. Total peripheral resistance (TPR) did not decrease, while PAP initially and transiently increased to 18.5±0.5mmHg and pulmonary vascular resistance (PVR) also significantly increased. The antigen-induced decreases in MAP and ABF were attenuated by pretreatment with either a platelet-activating factor (PAF) receptor antagonist, CV6209, or a histamine H1 receptor antagonist, diphenhydramine, and were abolished by their combination. Diphenhydramine augmented the initial increases in PAP and PVR, but did not affect the decrease of the corresponding MAP fall. The antagonists of either leukotriene C4 or serotonin, alone or in combination with CV6209, exerted no significant effects.

SIGNIFICANCE

Mouse anaphylactic hypotension is caused by a decrease in cardiac output but not vasodilatation, via actions of PAF and histamine. The slight increase in PAP is not involved in mouse anaphylactic hypotension.

MRI reveals edema in larynx (but not in brain) during anaphylactic hypotension in anesthetized rats

Purpose

Anaphylactic shock is sometimes accompanied by local interstitial edema due to increased vascular permeability. We performed magnetic resonance imaging (MRI) to compare edema in the larynx and brain of anesthetized rats during anaphylactic hypotension versus vasodilator-induced hypotension.

Methods

Male Sprague Dawley rats were subjected to hypotension induced by the ovalbumin antigen (n=7) or a vasodilator sodium nitroprusside (SNP; n=7). Apparent diffusion coefficient (ADC) and T2-relaxation time (T2RT) were quantified on MRI performed repeatedly for up to 68 min after the injection of either agent. The presence of laryngeal edema was also examined by histological examination. Separately, the occurrence of brain edema was assessed by measuring brain water content using the wet/dry method in rats with anaphylaxis (n=5) or SNP (n=5) and the non-hypotensive control rats (n=5). Mast cells in hypothalamus were morphologically examined.

Results

Mean arterial blood pressure similarly decreased to 35 mmHg after an injection of the antigen or SNP. Hyperintensity on T2-weighted images (as reflected by elevated T2RT) was found in the larynx as early as 13 min after an injection of the antigen, but not SNP. A postmortem histological examination revealed epiglottic edema in the rats with anaphylaxis, but not SNP. In contrast, no significant changes in T2RT or ADC were detectable in the brains of any rats studied. In separate experiments, the quantified brain water content did not increase in either anaphylaxis or SNP rats, as compared with the non-hypotensive control rats. The numbers of mast cells with metachromatic granules in the hypothalamus were not different between rats with anaphylaxis and SNP, suggesting the absence of anaphylactic reaction in hypothalamus.

Conclusion

Edema was detected using the MRI technique in the larynx during rat anaphylaxis, but not in the brain.

Alpha-adrenoceptor antagonists and chemical sympathectomy exacerbate anaphylaxis-induced hypotension, but not portal hypertension, in anesthetized rats

Anaphylactic shock is sometimes life-threatening, and it is accompanied by hepatic venoconstriction in animals, which, in part, accounts for anaphylactic hypotension. Roles of norepinephrine and α-adrenoceptor in anaphylaxis-induced hypotension and portal hypertension were investigated in anesthetized ovalbumin-sensitized Sprague-Dawley rats. The sensitized rats were randomly allocated to the following pretreatment groups (n = 6/group): 1) control (nonpretreatment), 2) α1-adrenoceptor antagonist prazosin, 3) nonselective α-adrenoceptor antagonist phentolamine, 4) 6-hydroxydopamine-induced chemical sympathectomy, and 5) surgical hepatic sympathectomy. Anaphylactic shock was induced by an intravenous injection of the antigen. The systemic arterial pressure (SAP), central venous pressure (CVP), portal venous pressure (PVP), and portal venous blood flow (PBF) were measured, and splanchnic [Rspl: (SAP-PVP)/PBF] and portal venous [Rpv: (PVP-CVP)/PBF] resistances were determined. Separately, we measured efferent hepatic sympathetic nerve activity during anaphylaxis. In the control group, SAP markedly decreased, followed by a gradual recovery toward baseline. PVP and Rpv increased 3.2- and 23.3-fold, respectively, after antigen. Rspl decreased immediately, but only transiently, after antigen, and then increased 1.5-fold later than 10 min. The α-adrenoceptor antagonist pretreatment or chemical sympathectomy inhibited the late increase in Rspl and the SAP recovery. Pretreatment with α-adrenoceptor antagonists, or either chemical or surgical hepatic sympathectomy, did not affect the antigen-induced increase in Rpv. Hepatic sympathetic nerve activity did not significantly change after antigen. In conclusion, α-adrenoceptor antagonists and chemical sympathectomy exacerbate anaphylaxis-induced hypotension, but not portal hypertension, in anesthetized rats. Hepatic sympathetic nerves are not involved in anaphylactic portal hypertension.

Portal venular constriction during anaphylactic shock in anesthetized rats

Hepatic venoconstriction occurs in rat anaphylactic hypotension. However, the exact venoconstrictive site remains unknown, and we therefore attempted to determine its location by using hepatic venography and histology. Anaphylaxis was induced in anesthetized Sprague-Dawley rats by i.v. administration of ovalbumin antigen. Venography of the portal vein (n = 8) was obtained at baseline and maximal hepatic venoconstriction. We separately examined photomicrographs of the liver sections. Along with systemic hypotension, portal venous pressure increased to a peak of 28 ± 3 cm- H2O at 2 min after antigen injection. Post-antigen portal venography revealed that 40% of portal venuls (76 vessels/total 188 vessels) with diameters from 160 to 300 μm were not visualized, suggesting that stenosis or obliteration occurred distally. The corresponding upstream portal vessels exhibited markedly bulging. Stenosis was also observed in some portal branches with diameters from 180 to 420 μm (9%; 17 vessels/total 188 vessels). Light microscopically, most portal venules with an estimated baseline diameter less than 110 μm showed stenosis, but statistically significant stenosis was found in those with baseline diameters of 20-70 μm. In conclusion, anaphylactic hepatic venoconstriction occurs over a wide range of portal veins with diameters less than 420 μm, and occurs markedly in portal venules with diameters less than 70 μm in anesthetized rats.

Vascular perfusion limits mesenteric lymph flow during anaphylactic hypotension in rats

To determine fluid extravasation in the splanchnic vascular bed during anaphylactic hypotension, the mesenteric lymph flow (Qlym) was measured in anesthetized rats sensitized with ovalbumin, along with the systemic arterial pressure (Psa) and portal venous pressure (Ppv). When the antigen was injected into the sensitized rats ( n = 10), Psa decreased from 125 ± 4 to 37 ± 2 mmHg at 10 min with a gradual recovery, whereas Ppv increased by 16 mmHg at 2 min and returned to the baseline at 10 min. Qlym increased 3.3-fold from the baseline of 0.023 ± 0.002 g/min to the peak levels of 0.075 ± 0.009 g/min at 2 min and returned to the baseline within 12 min. The lymph protein concentrations increased after antigen, a finding indicating increased vascular permeability. To determine the role of the Ppv increase in the antigen-induced increase in Qlym, Ppv of the nonsensitized rats ( n = 10) was mechanically elevated in a manner similar to that of the sensitized rats by compressing the portal vein near the hepatic hilus. Unexpectedly, Ppv elevation alone produced a similar increase in Qlym, with the peak comparable to that of the sensitized rats. This finding aroused a question why the antigen-induced increase in Qlym was limited despite the presence of increased vascular permeability. Thus the changes in splanchnic vascular surface area were assessed by measuring the mesenteric arterial flow. The mesenteric arterial flow was decreased much more in the sensitized rats (75%; n = 5) than the nonsensitized Ppv elevated rats (50%; n = 5). In conclusion, mesenteric lymph flow increases transiently after antigen presumably due to increased capillary pressure of the splanchnic vascular bed via downstream Ppv elevation and perfusion and increased vascular permeability in anesthetized rats. However, this increased extravasation is subsequently limited by decreases in vascular surface area and filtration pressure.

Portacaval shunting attenuates portal hypertension and systemic hypotension in rat anaphylactic shock

Anaphylactic shock in rats is characterized by antigen-induced hepatic venoconstriction and the resultant portal hypertension. We determined the role of portal hypertension in anaphylactic hypotension by using the side-to-side portacaval shunt- and sham-operated rats sensitized with ovalbumin (1 mg). We measured the mean arterial blood pressure (MAP), portal venous pressure (PVP), and central venous pressure (CVP) under pentobarbital anesthesia and spontaneous breathing. Anaphylactic hypotension was induced by an intravenous injection of ovalbumin (0.6 mg). In sham rats, the antigen caused not only an increase in PVP from 11.3 cmH(2)O to the peak of 27.9 cmH(2)O but also a decrease in MAP from 103 mmHg to the lowest value of 41 mmHg. CVP also decreased significantly after the antigen. In the portacaval shunt rats, in response to the antigen, PVP increased slightly, but significantly, to the peak of 17.5 cmH(2)O, CVP did not decrease, and MAP decreased to a lesser degree with the lowest value being 60 mmHg. These results suggest that the portacaval shunt attenuated anaphylactic portal hypertension and venous return decrease, partially preventing anaphylactic hypotension. In conclusion, portal hypertension is involved in rat anaphylactic hypotension presumably via splanchnic congestion resulting in decreased venous return and thus systemic arterial hypotension.

Ethanol predominantly constricts pre-sinusoids of isolated perfused livers of rat, guinea pig and mouse

AIMS

Ethanol constricts hepatic vessels of isolated perfused livers of rats, but not dogs. However, it is not known whether ethanol constricts or dilates the hepatic vessels in other species such as guinea pigs and mice. In addition, the sites of hepatic venoconstriction induced by ethanol were not known in rat livers. We therefore studied the effects of ethanol on the segmental hepatic vascular resistance and liver weight of mice, rats and guinea pigs.

METHODS

The isolated livers were portally perfused with diluted blood at constant flow. The sinusoidal pressure was measured by the double occlusion method and was used to determine the pre- and post-sinusoidal resistance. The change of liver weight was also measured. Ethanol was administered cumulatively into the perfusate to gain clinically relevant concentrations of 1-300 mM.

RESULTS

Ethanol dose dependently caused predominant pre-sinusoidal constriction in livers of all three species. When compared with the livers of the guinea pigs and rats, the mouse livers were the weakest in response. Dose-dependent decreases in liver weight and bile flow accompanied predominant pre-sinusoidal constriction in guinea pigs and rats.

CONCLUSION

Ethanol predominantly constricts pre-sinusoids in rat, guinea pig and mouse livers, although the mouse liver response was much weaker. Ethanol-induced pre-sinusoidal constriction is accompanied by reduction of liver blood volume in guinea pigs and rats.

Mast cells are not involved in the ischemia-reperfusion injury in perfused rat liver

BACKGROUND

It is reported that mast cells are involved in ischemia-reperfusion (I/R) injury of several organs such as intestine, heart, and brain in rats. However, the roles of mast cells are not known in rat hepatic I/R injury. We determined using genetically mast cell deficient (Ws/Ws) rats whether mast cells participate in the genesis of hepatic I/R injury.

METHODS

Isolated livers from male Ws/Ws rats (n = 6), their wild type +/+ rats (n = 6), and Sprague Dawely (SD) rats (n = 12) were perfused portally with diluted blood (Hct 8%) at a constant blood flow. Ischemia was induced at room temperature by occlusion of the inflow line of the portal vein for 1 h, followed by 1-h reperfusion in a recirculating manner. The pre- and post-sinusoidal resistances were determined by measuring the portal venous pressure (Ppv), hepatic venous pressure, blood flow and the sinusoidal pressure, which was assessed by the double occlusion pressure (Pdo). Liver injury was assessed by blood alanine aminotransferase (ALT) levels, bile flow rate and histology of the livers.

RESULTS

In the +/+ group, liver injury occurred after reperfusion; blood ALT levels increased from 19 ± 4 (SD) to 71 ± 18 and 135 ± 30 (IU/L) at 30 and 60 min, respectively, and bile flow decreased to 51% ± 6% of the baseline at 60 min after reperfusion. Histologic examination revealed marked hepatic degeneration. Similar changes were observed in the Ws/Ws rats and the SD rats (n = 6), and there were no significant differences in the variables among the Ws/Ws, +/+, and SD groups. In any ischemia groups, immediately after reperfusion, Ppv substantially, but Pdo only slightly, increased, followed by a return towards the baseline, indicating a predominant increase in pre-sinusoidal resistance over post-sinusoidal resistance. Liver weight significantly increased at 60 min after reperfusion. In the control SD rats without I/R (n = 6), no significant changes were observed in the variables.

CONCLUSIONS

I/R injury occurs in the absence of hepatic mast cells in the isolated perfused rat liver model of I/R injury.

Effects of β-adrenoceptor antagonists on anaphylactic hypotension in conscious rats

Anaphylactic shock is sometimes fatal or resistant to therapy in patients treated with propranolol, a nonselective β-adrenoceptor antagonist, against cardiovascular diseases. However, it remains unknown which subtype of β-adrenoceptors, β(1)- or β(2)-adrenoceptor, is primarily responsible for the detrimental effects of propranolol on anaphylactic hypotension. Effects of β(1)- and β(2)-adrenoceptor antagonists were therefore determined on the survival rate and systemic hypotension in conscious Sprague-Dawley rats that suffered from anaphylactic shock. Mean arterial pressure and portal venous pressure were simultaneously measured. The control rats showed a decrease in mean arterial pressure and an increase in portal venous pressure, but did not die within 48h after an injection of ovalbumin antigen. The survival rate of the rats pretreated with propranolol (1mg/kg; n=7), the selective β(2)-adrenoceptor antagonist ICI 118,551 (0.5mg/kg; n=7), or adrenalectomy (n=7) was significantly smaller than that with the selective β(1)-adrenoceptor antagonist atenolol (2mg/kg; n=7). However, the changes in mean arterial pressure and portal venous pressure were similar for 10min after antigen among any groups, although propranolol and atenolol attenuated the antigen-induced increase in heart rate. Furthermore, bolus injections of epinephrine (3μg/kg) at 3 and 5min after antigen prevented the death of the atenolol-pretreated rats, but only marginally prolonged the survival rates for the ICI 118,551- or propranolol-pretreated and adrenalectomized rats. In conclusion, in rat anaphylactic shock, inhibition of β(2)-adrenoceptor causes more detrimental effects than that of the β(1)-adrenoceptor. These β-adrenoceptor antagonists may exert detrimental effects on rat systemic anaphylaxis via inhibiting beneficial actions of catecholamines endogenously released from the adrenal gland.

Hepatic microvascular pressure during anaphylactic shock in anesthetized rats

OBJECTIVE

Hepatic venoconstriction plays a significant role in anaphylactic hypotension in anesthetized rats. The purpose of this study is to determine whether the primary site of anaphylactic venoconstriction in the liver venous circulation occurs prior to or distal to the sinusoidal capillaries. We also determined whether the hepatic blood volume is increased during anaphylactic hypotension.

METHODS

We measured, using a servo-null micropipette pressure-measuring system, the hepatic venular transmural pressure (P micro hv) at the liver surface of anesthetized rats sensitized with the antigen of ovalbumin (1 mg). We also measured the liver lobe thickness, using the ultrasonic crystal dimension measuring system. Anaphylactic hypotension was induced by an intravenous injection of 0.6 mg ovalbumin.

RESULTS

When the antigen was injected, the systemic arterial pressure decreased profoundly from 118+/-9 to 45+/-4 mm Hg, which was accompanied by an increase in Ppv and P micro hv: P micro hv only transiently increased from 3.1+/-0.9 to 8.8+/-1.5 cm H(2)O at 1 min and then rapidly returned to the baseline within 2 min, when Ppv continued to increase and reached the peak of 36+/-7 cm H(2)O at 3.5 min after antigen. This greater increase in Ppv-to-P micro hv gradient than that in P micro hv-to-Pcv gradient after antigen indicated that the constriction of the portal veins and the sinusoids much predominates over that of the hepatic veins. Along with this hepatic pre- and sinusoidal constriction, the liver lobe thickness significantly decreased by 4% after antigen.

CONCLUSION

Pre-sinusoidal constriction during anaphylactic shock in anaesthetized rats increased the portal venous pressure while the hepatic venular pressure only increased slightly and transiently. This predominant pre-sinusoidal constriction is accompanied by a decrease in liver volume.

Venous resistance increases during rat anaphylactic shock

Anaphylactic shock is a sudden, life-threatening allergic reaction associated with severe hypotension. The increased venous resistance accounts for the anaphylactic hypotension in anesthetized dogs. However, the change in peripheral vascular resistances during anaphylactic hypotension in other animals such as rats is not known. We measured the mean circulatory filling pressure using the mechanical occlusion method of inflation of the right atrial balloon along with systemic arterial pressure (Psa), central venous pressure, and portal venous pressure. Cardiac output was also measured with the thermodilution method. From these hemodynamic variables, we calculated the total peripheral and venous (Rv) resistances during anaphylactic hypotension in anesthetized rats. These hemodynamic variables were compared with those in the hemorrhagic shock. After an intravenous injection of 0.6 mg antigen ovalbumin in sensitized rats, Psa decreased from 119 +/- 4 to 43 +/- 2 mmHg, cardiac output decreased from 84.5 +/- 5.7 to 37.8 +/- 2.1 mL min, central venous pressure decreased from 0.9 +/- 0.1 to 0.1 +/- 0.1 mmHg, and mean circulatory filling pressure also decreased from 6.0 +/- 0.2 to 5.2 +/- 0.3 mmHg. Thus, the Rv increased from 0.06 +/- 0.05 to 0.15 +/- 0.02 mmHg mL(-1) min(-1), but total peripheral resistance did not significantly change. Portal venous pressure also increased from 5.6 +/- 0.5 to 21.5 +/- 0.9 mmHg. Hematocrit markedly increased from the baseline values of 43% +/- 1% to 55% +/- 1% at 15 min after antigen. During hemorrhagic shock, Psa decreased in the manner similar to anaphylactic shock; however, Rv did not significantly change, and portal venous pressure decreased. In conclusion, in rat anaphylactic shock, a substantial increase in Rv presumably due to hepatic venoconstriction may decrease venous return, resulting in systemic hypotension.

PAF, rather than histamine, participates in mouse anaphylactic hypotension

We determined the roles of platelet-activating factor (PAF) and histamine in anaphylactic hypotension in ovalbumin-sensitized anesthetized BALB/c mice. The effects of PAF and histamine on hemodynamic variables were studied by measuring the systemic arterial (Psa), portal venous (Ppv) and central venous (Pcv) pressures. Intravenous PAF evoked a biphasic Psa response, an initial rapid and transient drop followed by marked hypotension, accompanied by a decrease in Pcv. Histamine caused only mild systemic hypotension. Both agents similarly increased Ppv by approximately 4 cm H(2)O at high doses. After an injection of antigen, Psa initially increased slightly and then decreased from the baseline of 94 +/- 1 mm Hg to 46 +/- 1 mm Hg at 10 min after antigen administration, with Pcv decreasing by 2.5 cm H(2)O. Ppv increased by 3.5 cm H(2)O at 5 min after antigen injection. Pretreatment with either CV-6209 (PAF receptor antagonist, 1 mg/kg) or diphenhydramine (histamine H(1) receptor antagonist, 20 mg/kg) significantly attenuated an antigen-induced decrease in Psa. The inhibitory action of CV-6209 was greater than that of diphenhydramine, and the combination of these 2 antagonists almost completely inhibited the anaphylactic hypotension. In contrast, the antigen-induced increase in Ppv was attenuated by CV-6209 alone but augmented by diphenhydramine. It is concluded that anaphylactic hypotension is mainly mediated by PAF and, to a lesser extent, by histamine in anesthetized BALB/c mice.

Increased sinusoidal resistance is responsible for the basal state and endothelin-induced venoconstriction in perfused cirrhotic rat liver

The localization of increased intrahepatic vascular resistance and the segmental vascular responsiveness to endothelin-1 are not well known in liver cirrhosis. We determined the segmental vascular resistances and their response to endothelin-1 of isolated portally perfused bile duct ligation (BDL)-induced cirrhotic rat livers. The portal occlusion pressure (Ppo) and the hepatic venous occlusion pressure (Phvo) were obtained by analyzing the profiles of the portal (Ppv) and hepatic venous (Phv) pressures during the double occlusion maneuver of simultaneous occlusions of the inflow and outflow perfusion lines. From the pressure gradients among Ppv, Ppo, Phvo, and Phv, the portal-hepatic venous resistance was assigned to three segments of the portal [Rpv = (Ppv - Ppo)/blood flow (Q)], sinusoidal [Rsinus = (Ppo - Phvo)/Q] and hepatic venous [Rhv = (Phvo - Phv)/Q] resistances. Rsinus, but not Rpv or Rhv, was significantly greater in BDL livers than in sham livers. Endothelin-1 (0.1-1 nM) increased Rpv and Rsinus to a similar magnitude, but not Rhv, in both sham and BDL. At 3 nM, the responsiveness of Rpv was smaller in BDL than in sham, but that of Rsinus were similar between in BDL and sham. In conclusion, increased sinusoidal resistance accounts for increased intrahepatic resistance of BDL-induced liver cirrhosis. Endothelin-1 contracts portal veins and sinusoids, but not hepatic veins, in both sham and cirrhotic livers. Sinusoidal contractility to endothelin-1 is not impaired in cirrhotic livers.

The roles of mast cells and Kupffer cells in rat systemic anaphylaxis

Mast cells and other cells such as macrophages have been shown to mediate systemic anaphylaxis. We determined the roles of mast cells and Kupffer cells in hepatic and systemic anaphylaxis of rats. Roles of mast cells were examined by using the mast cell-deficient white spotting (Ws/Ws) rat; the Ws/Ws and wild type (+/+) rats were sensitized with ovalbumin (1 mg). Roles of Kupffer cells were examined by depleting Kupffer cells using gadolinium chloride or liposome-encapsulated dichloromethylene diphosphonate in the Ws/Ws and Sprague-Dawley rats. An intravenous injection of 0.6 mg ovalbumin caused substantial anaphylactic hypotension in both the Ws/Ws and +/+ rats; however, the occurrence was delayed in the Ws/Ws rats. After antigen, portal venous pressure increased by 13.1 cmH2O in the +/+ rats, while it increased only by 5.7 cmH2O in the Ws/Ws rats. In response to antigen, the isolated perfused liver of the Ws/Ws rats also showed weak venoconstriction, the magnitude of which was one tenth as large as that of the +/+ rats, indicating that hepatic anaphylaxis was primarily due to mast cells. In contrast, Kupffer cell depletion did not attenuate anaphylactic hepatic venoconstriction in isolated perfused livers. In conclusion, mast cells are involved mainly in anaphylactic hepatic presinusoidal portal venoconstriction but only in the early stage of anaphylactic systemic hypotension in rats. Macrophages, including Kupffer cells, do not participate in rat hepatic anaphylactic venoconstriction.

Involvement of splanchnic vascular bed in anaphylactic hypotension in anesthetized BALB/c mice

Using in vivo and isolated perfused liver preparations of BALB/c mice, we determined the roles of the liver and splanchnic vascular bed in anaphylactic hypotension. Intravenous injection of ovalbumin antigen into intact-sensitized mice decreased systemic arterial pressure (Psa) from 92 ± 2 to 39 ± 3 (SE) mmHg but only slightly increased portal venous pressure (Ppv) from 6.4 ± 0.1 cmH2O to the peak of 9.9 ± 0.5 cmH2O at 3.5 min after antigen. Elimination of the splanchnic vascular beds by ligation of the celiac and mesenteric arteries, combined with total hepatectomy, attenuated anaphylactic hypotension. Ligation of these arteries alone, but not partial hepatectomy (70%), similarly attenuated anaphylactic hypotension. In contrast, isolated sensitized mouse liver perfused portally at constant flow did not show anaphylactic venoconstriction but, rather, substantial constriction in response to the anaphylaxis-associated platelet-activating factor, indicating that venoconstriction in mice in vivo may be induced by mediators released from extrahepatic tissues. These results suggest that splanchnic vascular beds are involved in BALB/c mouse anaphylactic hypotension. They presumably act as sources of chemical mediators to cause the anaphylaxis-induced portal hypertension, which induced splanchnic congestion, resulting in a decrease in circulating blood volume and, thus, systemic arterial hypotension. Mouse hepatic anaphylactic venoconstriction may be induced by factors outside the liver, but not by anaphylactic reaction within the liver.

Effects of l-NAME on thromboxane A2-induced venoconstriction in isolated perfused livers from rat, guinea pig and mouse

Effects of L-NAME on U-46619 (a thromboxane A(2), analogue) -induced hepatic segmental venoconstriction were examined in mouse, rat and guinea pig isolated perfused livers. All livers were perfused portally and recirculatingly at a constant flow with diluted blood. U-46619 was administrated into the reservoir in a cumulative manner to gain the concentrations of 0.001-3 microM at 10 min after L-NAME or D-NAME (100 microM). The portal venous pressure, hepatic venous pressure and perfusate flow were monitored. In addition, the sinusoidal pressure was measured by the double occlusion pressure, and was used to determine the pre- (Rpre) and post-sinusoidal (Rpost) resistances. U-46619 concentration-dependently caused predominant presinusoidal constriction in all three species. The rat livers were the strongest while the mouse livers were the weakest in responsiveness and sensitivity to U-46619. L-NAME mainly augmented the U-46619-induced increases in Rpre, but not in Rpost, in rat and guinea pig. This augmentation was stronger in rat. However, L-NAME did not augment the response to U-46619 in mouse. In conclusion, in rat and guinea pig, NO may be released selectively from the presinusoids in response to U-46619, and then attenuate the U-46619-induced presinusoidal constriction. In mouse, U-46619-induced venoconstriction is weak and not modulated by NO.

Leukotrienes and cyclooxygenase products mediate anaphylactic venoconstriction in ovalbumin sensitized rat livers

Hepatic anaphylactic venoconstriction is partly involved in anaphylactic hypotension. We determined the chemical mediators responsible for anaphylaxis-induced segmental venoconstriction in perfused livers isolated from ovalbumin-sensitized rats. Livers were perfused portally and recirculatingly at constant flow with diluted blood. The portal venous pressure (Ppv), hepatic venous pressure (Phv), liver weight and hepatic oxygen consumption were continuously measured. The sinusoidal pressure was measured by the double occlusion pressure (Pdo), and was used to determine the pre-sinusoidal (Rpre) and post-sinusoidal (Rpost) resistances. After antigen injection, both Ppv and Pdo increased, resulting in 5.6- and 1.6-fold increases in Rpre and Rpost, respectively. Liver weight showed a biphasic change of an initial decrease followed by an increase. Hepatic oxygen consumption significantly decreased after antigen. Anaphylaxis-induced increase in Rpre was most extensively inhibited by 38.6% by pretreatment with ONO-1078 (100 microM, a cysteinyl leukotriene receptor-1 antagonist), among all antagonists or inhibitors administrated individually including TCV-309 (20 microM), AA-2414 (10 microM), ketanserin (10 microM) and indomethacin (10 microM). Combined pretreatment with indomethacin and ONO-1078 exerted additive inhibitory effects and attenuated Rpre by 65.8%. However, TCV-309, a platelet activating factor (PAF) receptor antagonist, did not affect the anaphylactic response. In contrast, anaphylaxis-induced increase in Rpost was attenuated only by ONO-1078 combined pretreatment. The antigen-induced changes in liver weight and hepatic oxygen consumption were attenuated significantly when hepatic venoconstriction was attenuated. It is concluded that cysteinyl leukotrienes and cyclooxygenase products, but not PAF, are mainly involved in anaphylaxis-induced pre-sinusoidal constriction in isolated perfused rat livers.

N(G)-nitro-L-arginine methyl ester, but not methylene blue, attenuates anaphylactic hypotension in anesthetized mice

To clarify the role of NO in mouse anaphylactic hypotension, effects of a nitric oxide (NO) synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), on antigen-induced hypotension and portal hypertension were determined in anesthetized BALB/c mice. Systemic arterial pressure (Psa), central venous pressure (Pcv), and portal venous pressure (Ppv) were directly and simultaneously measured. Mice were first sensitized with ovalbumin, and then the injection of antigen was used to decrease Psa and increase Ppv. Pretreatment with L-NAME (1 mg/kg) attenuated this antigen-induced systemic hypotension, but not the increase in Ppv. The effect of inhibitors of soluble guanylate cyclase on anaphylactic hypotension were studied with either methylene blue (3.0 mg/kg) or 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (10 mg/kg). Neither modulated any antigen-induced changes. Furthermore, methylene blue did not improve systemic hypotension induced by Compound 48/80 (4.5 mg/kg), a mast cell degranulator, which can produce non-immunological anaphylactoid reactions. These data show in anesthetized BALB/c mice that L-NAME attenuated anaphylactic hypotension without affecting portal hypertension. This beneficial effect of L-NAME appears not to depend on the soluble guanylate cyclase pathway.

L-NAME augments PAF-induced venoconstriction in isolated perfused livers of rat and guinea pig, but not mouse

Platelet-activating factor (PAF), one of vasoconstrictive lipid mediators, is involved in systemic anaphylaxis. On the other hand, nitric oxide (NO) is known to attenuate anaphylactic venoconstriction of the pre-sinusoids in isolated guinea pig and rat livers. However, it is not known whether NO attenuates PAF-induced hepatic venoconstriction. We therefore determined the effects of L-NAME, a NO synthase inhibitor, on PAF-induced venoconstriction in blood- and constant flow-perfused isolated livers of mice, rats and guinea pigs. The sinusoidal pressure was measured by the double occlusion pressure (Pdo), and was used to determine the pre- (Rpre) and post-sinusoidal (Rpost) resistances. PAF (0.01-1 microM) concentration-dependently caused predominant pre-sinusoidal constriction in all livers of three species studied. The guinea pig livers were the most sensitive to PAF, while the mouse livers were the weakest in responsiveness. L-NAME pretreatment selectively increased the basal Rpre in all of three species. L-NAME also significantly augmented the PAF-induced increases in Rpre, but not in Rpost, in rat and guinea pig livers. This augmentation was stronger in rat livers than in guinea pig livers at the high concentration of 0.1 microM PAF. However, L-NAME did not augment PAF-induced venoconstriction in mouse livers. In conclusion, in rat and guinea pig livers, NO may be released selectively from the pre-sinusoids in response to PAF, and then attenuate the PAF-induced pre-sinusoidal constriction. In mouse liver, PAF-induced venoconstriction is weak and not modulated by NO.

NG-NITRO-l-ARGININE METHYL ESTER POTENTIATES ANAPHYLACTIC VENOCONSTRICTION IN RAT PERFUSED LIVERS

1. The effects of the nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) on anaphylaxis-induced venoconstriction were examined in rat isolated livers perfused with blood-free solutions in order to clarify the role of NO in anaphylactic venoconstriction. 2. Rats were sensitized with ovalbumin (1 mg) and, 2 weeks later, livers were excised and perfused portally in a recirculating manner at a constant flow with Krebs'-Henseleit solution. The antigen (ovalbumin; 0.1 mg) was injected into the reservoir 10 min after pretreatment with L-NAME (100 micromol/L) or D-NAME (100 micromol/L) and changes in portal vein pressure (Ppv), hepatic vein pressure (Phv) and perfusate flow were monitored. In addition, concentrations of the stable metabolites of NO ( and ) were determined in the perfusate using an HPLC-Griess system. 3. The antigen caused hepatic venoconstriction, as evidenced by an increase in Ppv from a mean (SEM) baseline value of 7.7 +/- 0.1 cmH2O to a peak of 21.4 +/- 1.1 cmH2O at 3 min in D-NAME-pretreated livers. Pretreatment with L-NAME augmented anaphylactic venoconstriction, as reflected by a higher Ppv (27.4 +/- 0.8 cmH2O) after antigen than observed following D-NAME pretreatment. The addition of L-arginine, a precursor for the synthesis of NO, reversed the augmentation of anaphylactic venoconstricion by L-NAME. This suggests that hepatic anaphylaxis increased the production of NO, which consequently attenuated anaphylactic venoconstriction. However, perfusate NOx levels did not increase significantly after antigen in livers pretreated with either L-NAME or D-NAME. 4. In conclusion, L-NAME potentiates rat anaphylactic hepatic venoconstriction, suggesting that NO contributes to the attenuation of the venoconstriction. However, this functional evidence was not accompanied by corresponding changes in perfusate NOx concentrations.

OXYGEN CONSUMPTION, ASSESSED WITH THE OXYGEN ABSORPTION SPECTROPHOTOMETER, DECREASES INDEPENDENTLY OF VENOCONSTRICTION DURING HEPATIC ANAPHYLAXIS IN PERFUSED RAT LIVER

Anaphylactic shock is accompanied by a decrease in oxygen consumption. However, it is not well known whether oxygen consumption decreases during local anaphylactic reaction in liver. We determined the effects of anaphylaxis and norepinephrine on oxygen consumption in isolated rat livers perfused portally and recirculatingly at constant flow with blood (hematocrit, 12%). Oxygen consumption was continuously measured by monitoring the portal-hepatic venous oxygen saturation differences using the absorption spectrophotometer, the probes of which were built in perfusion lines. Hepatic anaphylaxis was induced by an injection of ovalbumin (0.01 or 0.1 mg) into the perfusate of the isolated liver of the rat sensitized with subcutaneous ovalbumin (1 mg). Hepatic venoconstriction and liver weight loss were similarly observed in response to norepinephrine (0.01-10 micromol L(-1)) and anaphylaxis. However, hepatic anaphylaxis reduced oxygen consumption, whereas norepinephrine increased it. There was a possibility that anaphylactic venoconstriction could reduce the perfused surface area, resulting in decreased oxygen consumption. However, pretreatment with a vasodilator of sodium nitroprusside substantially attenuated venoconstriction but not the decrease in oxygen consumption during anaphylaxis. Thus, we conclude that local hepatic anaphylaxis decreases oxygen consumption independently of venoconstriction in isolated blood-perfused rat livers.

Effects of platelet-activating factor, thromboxane A2 and leukotriene D4 on isolated perfused rat liver

Vasoconstrictive lipid mediators, thromboxane A(2) (TxA(2)), platelet-activating factor (PAF) and leukotriene D(4) (LTD(4)) have been implicated as mediators of liver diseases. There are species differences in the primary site of hepatic vasoconstriction in response to these mediators. We determined the effects of a TxA(2) analogue (U-46619), PAF and LTD(4) on the vascular resistance distribution, weight and oxygen consumption of isolated rat livers portally perfused with blood. The sinusoidal pressure was measured by the double occlusion pressure (P(do)), and was used to determine the pre- (R(pre)) and post-sinusoidal (R(post)) resistances. All these three mediators increased the hepatic total vascular resistance (R(t)). The responsiveness to PAF was 100 times greater than that to U-46619 or LTD(4). Both of PAF and U-46619 predominantly increased R(pre) over R(post). At the comparable increased R(t) levels, U-46619 more preferentially increased R(pre) than PAF. In contrast, LTD(4) increased both the R(pre) and R(post) to similar extent. U-46619 caused liver weight loss, while high concentrations of either LTD(4) or PAF produced liver weight gain, which was caused by substantial post-sinusoidal constriction and increased P(do). PAF and U-46619 decreased hepatic oxygen consumption while LTD(4) induced biphasic change of an initial transient decrease followed by an increase. In conclusion, PAF is the most potent vasoconstrictor of rat hepatic vessels among these three mediators. Both TxA(2) and PAF constrict the pre-sinusoidal veins predominantly. TxA(2) more preferentially constricts the pre-sinusoids than PAF, resulting in liver weight loss. However LTD(4) constricts both the pre- and post-sinusoidal veins similarly. High concentrations of LTD(4) and PAF cause liver weight gain by substantial post-sinusoidal constriction. PAF and TxA(2) decrease hepatic oxygen consumption, whereas LTD(4) causes a biphasic change of it.

Effects of Hct on L-NAME-induced Potentiation of Anaphylactic Presinusoidal Constriction in Perfused Rat Livers

Effects of hematocrit (Hct) on N-nitro-L-arginine methyl ester (L-NAME)-induced modulation of anaphylactic venoconstriction were determined in isolated perfused rat livers. The rats were sensitized with ovalbumin (1 mg), and the livers were excised 2 weeks later and perfused portally and recirculatingly under constant flow at Hct of 0%, 5%, 16%, and 22%. The hepatic sinusoidal pressure was estimated via the double occlusion pressure (Pdo), and the presinusoidal resistance (Rpre) and the postsinusoidal resistance (Rhv) were calculated. The antigen of ovalbumin 0.1 mg was injected into the reservoir at 10 minutes after pretreatment with L-NAME (100 microM) or D-NAME (100 microM). Perfusate viscosity, a determinant of vascular resistance and shear stress, was increased in parallel with Hct. In the D-NAME groups, antigen caused predominant presinusoidal constriction. The magnitude of venoconstriction was significantly smaller at Hct 0% than at Hct 5% to 22%, whereas no significant differences were found among Hct 5% to 22%. L-NAME potentiated the antigen-induced increase in Rpre, but not in Rpost at Hct 5% to 22% as compared with D-NAME. But the augmentative effects of L-NAME were similar in magnitude among Hct 5% to 22%. These findings suggest that hepatic anaphylaxis increases production of nitric oxide, which consequently attenuates anaphylactic presinusoidal constriction in rat livers, and that these effects are independent of perfusate Hct or viscosity in blood-perfused rat livers.