Effects of in vivo lipopolysaccharide infusion on vasoconstrictor function of rat isolated mesentery, kidney, and aorta

Time and sex dependency of hemodynamic, renal, and survivability effects of endotoxemia in rats

Widely different exposure times to endotoxic insults have been employed in reported studies. The current experimental study systematically evaluated the time-course and sex influences of endotoxic insult on survivability and cardiovascular and renal functions. Rats received i.p. lipopolysaccharide (LPS, 5 mg/kg) once or twice (over 2 successive days). Systolic blood pressure (SBP), biomarkers of renal function and inflammation, and vasodilator responsiveness of isolated perfused kidneys to acetylcholine (ACh) or N-ethylcarboxamidoadenosine (NECA) were evaluated 6 hr after first LPS injection or 1, 2, or 6 days later. A single 6-hr LPS challenge caused (i) sex-unrelated elevations in serum urea and creatinine and reductions in NECA, but not ACh, vasodilations, (ii) more increases in renal NF-κB/iNOS expressions in male than in female rats, and (iii) hypotension and tachycardia only in male rats. These parameters, except for hemodynamic changes, were restored to near-control levels 1 day after single LPS dosing. The 2-days dosing with LPS had no effects on renal function biomarkers, but caused hypotension, tachycardia, and increases in renal NF-κB/iNOS expression and NECA and ACh vasodilations in both rat sexes. None of these parameters were different from control values when measured 6 days after the endotoxic insult. Alternatively, the rat mortality was observed during first 2 days of the study and was notably higher in male than in female rats. Our data suggest that the frequency and time elapsed after LPS exposure as well as rat sex are important determinants of the magnitude and direction of detrimental effects of endotoxemia.

Cecal inoculum peritonitis: An alternative model for sepsis vascular dysfunction study

AIMS

Sepsis is a life threatening condition that is characterized by the loss of vascular reactivity. The factor(s) responsible for the diminished vascular function seen in sepsis are not well understood. The purpose of this study was to characterize the vascular dysfunction from the rat cecal inoculum (CI) sepsis model using cecal ligation and puncture (CLP), and lipopolysaccharide (LPS) sepsis as reference models.

MATERIALS AND METHODS

Experiments were performed on isolated aorta from CI, CLP and LPS treated rats using a combination of pharmacological approaches.

KEY FINDINGS

Phenylephrine (PE)-induced aortic contraction was significantly decreased in each model (p<0.05) and not normalized by L-NAME or indomethacin. The vascular response elicited in the CI model for acetylcholine (Ach) was more similar to that seen in the CLP than the LPS model. The removal of the endothelial layer increased sensitivity to L-NAME (p<0.05) in aortae from CI group. Inhibition of the large conductance Ca(2+)/voltage sensitive K(+) (BKCa) channel did not normalize PE hyporesponsiveness but did abolish sepsis-induced contractile oscillation. Inhibition of the voltage dependent Kv1.5 channel was not able to reverse the vascular hyporesponsiveness, however, inhibition of the ATP dependent (KATP) channel inhibition partially restored the contractile response (p<0.05). Elevation of VCAM expression and aortic structural alternation were observed in each model.

SIGNIFICANCE

These results suggest that the CI model may be an additional tool that could be used to investigate the mechanisms of vascular hyporesponsiveness in sepsis.

Redox signaling and splicing dependent change in myosin phosphatase underlie early versus late changes in NO vasodilator reserve in a mouse LPS model of sepsis

Microcirculatory dysfunction may cause tissue malperfusion and progression to organ failure in the later stages of sepsis, but the role of smooth muscle contractile dysfunction is uncertain. Mice were given intraperitoneal LPS, and mesenteric arteries were harvested at 6-h intervals for analyses of gene expression and contractile function by wire myography. Contractile (myosin and actin) and regulatory [myosin light chain kinase and phosphatase subunits (Mypt1, CPI-17)] mRNAs and proteins were decreased in mesenteric arteries at 24 h concordant with reduced force generation to depolarization, Ca(2+), and phenylephrine. Vasodilator sensitivity to DEA/nitric oxide (NO) and cGMP under Ca(2+) clamp were increased at 24 h after LPS concordant with a switch to Mypt1 exon 24- splice variant coding for a leucine zipper (LZ) motif required for PKG-1α activation of myosin phosphatase. This was reproduced by smooth muscle-specific deletion of Mypt1 exon 24, causing a shift to the Mypt1 LZ+ isoform. These mice had significantly lower resting blood pressure than control mice but similar hypotensive responses to LPS. The vasodilator sensitivity of wild-type mice to DEA/NO, but not cGMP, was increased at 6 h after LPS. This was abrogated in mice with a redox dead version of PKG-1α (Cys42Ser). Enhanced vasorelaxation in early endotoxemia is mediated by redox signaling through PKG-1α but in later endotoxemia by myosin phosphatase isoform shifts enhancing sensitivity to NO/cGMP as well as smooth muscle atrophy. Muscle atrophy and modulation may be a novel target to suppress microcirculatory dysfunction; however, inactivation of inducible NO synthase, treatment with the IL-1 antagonist IL-1ra, or early activation of α-adrenergic signaling did not suppressed this response.

Calcium desensitisation in late polymicrobial sepsis is associated with loss of vasopressor sensitivity in a murine model

Background

Sepsis is characterised by diminished vasopressor responsiveness. Vasoconstriction depends upon a balance: Ca²⁺-dependent myosin light-chain kinase promotes and Ca²⁺-independent myosin light-chain phosphatase (MLCP) opposes vascular smooth muscle contraction. The enzyme Rho kinase (ROK) inhibits MLCP, favouring vasoconstriction. We tested the hypothesis that ROK-dependent MLCP inhibition was attenuated in late sepsis and associated with reduced contractile responses to certain vasopressor agents.

Methods

This is a prospective, controlled animal study. Sixteen-week-old C57/BL6 mice received laparotomy or laparotomy with caecal ligation and puncture (CLP). Antibiotics, fluids and analgesia were provided before sacrifice on day 5. Vasoconstriction of the femoral arteries to a range of stimuli was assessed using myography: (i) depolarisation with 87 mM K⁺ assessed voltage-gated Ca²⁺ channels (L-type, Ca_v1.2 Ca²⁺ channels (LTCC)), (ii) thromboxane A₂ receptor activation assessed the activation state of the LTCC and ROK/MLCP axis, (iii) direct PKC activation (phorbol-dibutyrate (PDBu), 5 μM) assessed the PKC/CPI-17 axis independent of Ca²⁺ entry and (iv) α₁-adrenoceptor stimulation with phenylephrine (10⁻⁸ to 10⁻⁴ M) and noradrenaline (10⁻⁸ to 10⁻⁴ M) assessed the sum of these pathways plus the role of the sarcoplasmic reticulum (SR). ROK-dependent MLCP activity was indexed by Western blot analysis of P[Thr855]MYPT. Parametric and non-parametric data were analysed using unpaired Student's t-tests and Mann-Whitney tests, respectively.

Results

ROK-dependent inhibition of MLCP activity was attenuated in both unstimulated (n = 6 to 7) and stimulated (n = 8 to 12) vessels from mice that had undergone CLP (p < 0.05). Vessels from CLP mice demonstrated reduced vasoconstriction to K⁺, thromboxane A₂ receptor activation and PKC activation (n = 8 to 13; p < 0.05). α₁-adrenergic responses were unchanged (n = 7 to 12).

Conclusions

In a murine model of sepsis, ROK-dependent inhibition of MLCP activity in vessels from septic mice was reduced. Responses to K⁺ depolarisation, thromboxane A₂ receptor activation and PKC activation were diminished in vitro whilst α₁-adrenergic responses remained intact. Inhibiting MLCP may present a novel therapeutic target to manage sepsis-induced vascular dysfunction.

Curcumin protects against lipopolysaccharide-induced vasoconstriction dysfunction via inhibition of thrombospondin-1 and transforming growth factor-β1

Sepsis is a complex syndrome characterized by the development of progressive dysfunction in multiple organs. The aim of the present study was to investigate the protective effect of curcumin against lipopolysaccharide (LPS)-induced vasoconstrictive dysfunction, and to investigate the possible underlying mechanism. Male Sprague-Dawley rats were randomly divided into the following groups: Control, sepsis and curcumin. A sepsis model was established by an intraperitoneal (i.p.) injection of 5 mg/kg LPS. Thoracic aortic rings obtained from the rats were mounted in an organ bath and the vasoconstriction of the rings was recorded. In addition, the serum E-selectin levels were determined by an enzyme-linked immunosorbent assay. The expression levels of thrombospondin (TSP)-1 and transforming growth factor (TGF)-β1 in the aortic tissue were detected by immunohistochemistry. Vasoconstriction of the aortic rings was found to significantly decrease in the sepsis rats when compared with the control group. However, curcumin (10 or 20 mg/kg, i.p.) prevented the vasoconstrictive dysfunction induced by LPS. The serum level of E-selectin and the expression levels of TSP-1 and TGF-β1 significantly increased in the sepsis rats when compared with the control group rats; however, the levels decreased significantly following treatment with curcumin (10 or 20 mg/kg). Furthermore, hematoxylin and eosin staining revealed that curcumin alleviated the LPS-induced damage in the aortic tunica intima and tunica media. Therefore, the results indicated that curcumin alleviates LPS-induced vasoconstrictive dysfunction in the thoracic aorta of rats. In addition, the inhibition of TSP-1 and TGF-β1 expression may be involved in the mechanism underlying this protective effect.

Effects of lipopolysaccharide on the neuronal control of mesenteric vascular tone in rats: mechanisms involved

The aim of the present study was to investigate the effects of lipopolysaccharide (LPS) on the contractile response induced by electrical field stimulation (EFS) in rat mesenteric segments, as well as the mechanisms involved. Effects of LPS incubation for 2 or 5 h were studied in mesenteric segments from male Wistar rats. Vasomotor responses to EFS, nitric oxide (NO) donor DEA-NO, and noradrenaline (NA) were studied. Phosphorylated neuronal NO synthase protein expression was analyzed, and NO, superoxide anion (O2·), and peroxynitrite releases were also determined. Lipopolysaccharide increased EFS-induced vasoconstriction at 2 h. This increase was lower after 5-h preincubation. N-nitro-L-arginine methyl ester increased vasoconstrictor response only in control segments. Vasodilator response to DEA-NO was increased by LPS after 5-h preincubation and was decreased by O2· scavenger tempol. Basal NO release was increased by LPS. Electrical field stimulation-induced NO release was reduced by LPS compared with control conditions. Lipopolysaccharide exposure increased both O2· and peroxynitrite release. Vasoconstriction to exogenous NA was markedly increased by LPS compared with control conditions after 2-h incubation and remained unchanged after 5-h incubation. Short-term exposure of rat mesenteric arteries to LPS produced a time-dependent enhanced contractile response to EFS. The early phase (2 h) was associated to a reduction in NO from neuronal NO synthase and an enhanced response to NA. After 5 h of LPS exposure, this enhancement was reduced, because of restoration of the adrenergic component and maintenance of the nitrergic reduction.

Chinese medicine Tongxinluo modulates vascular endothelial function by inducing eNOS expression via the PI-3K/Akt/HIF-dependent signaling pathway

AIM OF THE STUDY

To investigate the molecular mechanisms whereby the Chinese medicinal compound Tongxinluo improves vascular endothelial function through studying the induction of endothelial nitric oxide synthase (eNOS) and its upstream signaling pathway.

MATERIALS AND METHODS

Hyperhomocysteinemia was induced in Wistar rats by a methionine-rich diet followed by Tongxinluo treatment. The aorta ring was isolated for measuring vascular dilation of aorta and eNOS expression. Human umbilical vein endothelial cells (HUVECs) were transfected with AP-1, NF-κB, HRE or eNOS reporter plasmid followed by Tongxinluo exposure. Expression of the reporter genes was measured by luciferase assay. The level of eNOS was studied by western blot and the nitric oxide content was measured using the nitrate reductase method. HUVECs were also transiently transfected with the dominant negative mutant of HIF-1, PI-3K or Akt to explore the role of HIF and PI-3K/Akt pathway in eNOS induction by Tongxinluo.

RESULTS

Tongxinluo could significantly up-regulate the expression of eNOS in the aortic tissue and improve the endothelium-dependent vasodilation of the aorta ring. Additionally, Tongxinluo at various doses could significantly enhance the expression of HRE and eNOS reporter gene as well as up-regulate the protein level of eNOS. Meanwhile, Tongxinluo caused a dose-dependent increase in the NO content in the supernatant of HUVECs. Suppression of HIF-1 activation by DN-HIF or inhibition of PI-3K/Akt pathway by ΔP85 or DN-Akt both attenuated HRE reporter gene activation and eNOS induction by Tongxinluo.

CONCLUSION

Tongxinluo, a compound Chinese traditional medicine, up-regulates the expression of eNOS via the PI-3K/Akt/HIF-dependent signaling pathway, thus improving the endothelium-dependent vasodilation.

Vasogenic shock physiology

Shock means inadequate tissue perfusion by oxygen-carrying blood. In vasogenic shock, this circulatory failure results from vasodilation and/or vasoplegia. There is vascular hyporeactivity with reduced vascular smooth muscle contraction in response to α1 adrenergic agonists. Considering vasogenic shock, one can understand its utmost importance, not only because of its association with sepsis but also because it can be the common final pathway for long-lasting, severe shock of any cause, even postresuscitation states. The effective management of any patient in shock requires the understanding of its underlying physiology and pathophysiology. Recent studies have provided new insights into vascular physiology by revealing the interaction of rather complicated and multifactorial mechanisms, which have not been fully elucidated yet. Some of these mechanisms, such as the induction of nitric oxide synthases, the activation of adenosine triphosphate-sensitive potassium channels, and vasopressin deficiency, have gained general acceptance and are considered to play an important role in the pathogenesis of vasodilatory shock. The purpose of this review is to provide an update on the pathogenesis of vasogenic shock.

Lack of effect of norfloxacin on hyperdynamic circulation in bile duct-ligated rats despite reduction of endothelial nitric oxide synthase function: result of unchanged vascular Rho-kinase?

BACKGROUND/AIMS

In cirrhosis, portal hypertension is maintained by splanchnic vasodilation owing to overproduction of the vasodilator nitric oxide (NO) and defective contractile signalling by Rho-kinase. NO overproduction is partially caused by bacterial translocation from the gut to mesenteric lymph nodes. However, the effects of intestinal bacterial decontamination on hyperdynamic circulation or vascular contractility are unknown. We investigated the haemodynamic and vascular effects of norfloxacin in rats with secondary biliary cirrhosis.

METHODS

Cirrhosis was induced by bile duct ligation (BDL). One group was treated with norfloxacin (20 mg/kg/day, 5 days, orally). Bacterial growth in the lymph nodes was determined on blood agar plates. Invasive haemodynamic measurements were combined with coloured microspheres. Aortic contractility was assessed myographically. Protein expression/phosphorylation was examined by Western blot analysis.

RESULTS

Norfloxacin treatment of BDL rats abolished bacterial translocation to mesenteric lymph nodes. BDL rats had hyperdynamic circulation, including portal hypertension and splanchnic vasodilation. None of these parameters was changed by norfloxacin, although norfloxacin reduced endothelial NO synthase expression and phosphorylation. The latter was associated with a diminished activity of protein kinase G (PKG), which mediates NO-induced vasodilation. However, norfloxacin had no effect on aortic contractility to methoxamine or Ca2+, or the aortic expression of RhoA, Rho-kinase and beta-arrestin 2, or the phosphorylation of the Rho-kinase substrate moesin.

CONCLUSIONS

Short-term treatment of BDL rats with norfloxacin does not change hyperdynamic circulation or vascular contractility, despite reduction of PKG activity.

Voltage-independent calcium channels mediate lipopolysaccharide-induced hyporeactivity to endothelin-1 in the rat aorta

The roles of intracellular calcium concentration ([Ca(2+)](i)) and Ca(2+) sensitization in lipopolysaccharide (LPS)-induced vascular smooth muscle (VSM) hyporesponsiveness are incompletely understood. To investigate these roles, contraction responses to endothelin-1 (ET-1) and 80 mM KCl; relaxation responses to nifedipine; the expression levels of mRNAs of ET-1 and its receptors (ET(A) or ET(B)); the expression levels of protein kinase C (PKC) and phosphorylation of Rho kinase (ROKalpha), CPI-17, and myosin phosphatase target subunit-1 (MYPT1); and changes in aortic VSM cell [Ca(2+)](i) were measured in LPS-treated aortic rings from male Wistar rats (250-300 g). LPS (10 mug/ml, 20 h) decreased contraction induced by ET-1 (0.3-100 nM) or 80 mM KCl. LPS-induced hypocontractility was not observed in the absence of external Ca(2+), but LPS-treated aorta remained hypocontractile on subsequent stepwise restoration of extracellular Ca(2+) (0.01-10 mM). Vascular relaxation to nifedipine; mRNA expression levels of ET-1, ET(A), or ET(B); protein expression levels of PKC; and phosphorylation levels of ROKalpha, CPI-17, and MYPT1 were not affected by LPS. In isolated aortic VSM cells, ET-1 caused a transient initial increase in [Ca(2+)](i), followed by a maintained tonic increase in [Ca(2+)](i), which was decreased by LPS pretreatment and was dependent on external Ca(2+). Subsequent restoration of extracellular Ca(2+) increased [Ca(2+)](i), but this increase was lower in the LPS-treated group. This difference in response to extracellular Ca(2+) addition was not affected by diltiazem, but was abolished by SKF-96365. Therefore, LPS induces hyporeactivity to ET-1 in rat aorta that depends on external Ca(2+) influx through non-voltage-operated Ca(2+) channels, but not on ET-1 receptor expression or Ca(2+) sensitization.

The clinical research enterprise in critical care: what's right, what's wrong, and what's ahead?

Intensivists have been remarkably successful in using randomized controlled trials to assess aspects of current practice. Unfortunately, this success has not been mirrored in trials of new pharmacotherapy, despite convincing pathophysiological rationales and encouraging preliminary studies. Misunderstandings of biological processes and flawed early clinical studies have led to the almost universal failure of fundamentally new treatments subjected to large phase III trials, despite their sound methodology. Compounding these problems is the tendency for new approaches to be either implemented widely on the basis of relatively poor studies or ignored despite strong supporting evidence. Having mastered the principles of evidence-based medicine in assessing existing therapy, intensivists have established a strong foundation. Critical care medicine must now embrace the challenge of translating a more solid understanding of basic disease mechanisms into widely implemented treatments.

Vascular biology in sepsis: pathophysiological and therapeutic significance of vascular dysfunction

Sepsis is the leading cause of mortality in critically ill patients. In this pathological syndrome, septic shock and sequential multiple organ failure correlate with poor outcome. The pathophysiology of sepsis with acute organ dysfunction involves a highly complex, integrated response that includes activation of number of cell types, inflammatory mediators, and the hemostatic system. Central to this process may be alterations in vascular functions. This review article provides a growing body of evidence for the potential impact of vascular dysfunction on sepsis pathophysiology with a major emphasis on the endothelium. Furthermore, the role of apoptotic signaling molecules in the mechanisms underlying endothelial cell injury and death during sepsis and its potential value as a target for sepsis therapy will be discussed, which may help in the assessment of ongoing therapeutic strategies.

N-Allylsecoboldine as a novel agent prevents acute renal failure during endotoxemia

Blockades of cytokine and oxygen radicals release are considered to be beneficial in reducing multiple organ injury and increasing the survival rate in sepsis/septic shock. Thus, we examined the protective efficacy of N-allylsecoboldine, a secoaporphine derivative with antioxidant and alpha1-adrenoceptor blocking activities, in rats treated with endotoxin (E. coli lipopolysaccharide, LPS). Pretreatment of LPS-treated rats with N-allylsecoboldine significantly attenuated the late-phase hypotension, hypoglycemia and incremental plasma tumor necrosis factor (TNF)-alpha. Overproduction of plasma nitrate in endotoxemia was not changed but the continuous decrease of urinary nitrate appeared to be partially ameliorated by N-allylsecoboldine. However, N-allylsecoboldine inhibited the inducible nitric oxide synthase (iNOS) protein expression in the renal cortex of endotoxemic rats. N-allylsecoboldine also improved the endotoxemia-induced organ injury as demonstrated from the conspicuous recovery of marker enzymes in the LPS-treated rats. Endotoxemia was associated with renal dysfunctions as indicated by decreases in renal blood flow, urinary potassium excretion, and renal nitrate clearance. However, pretreatment with N-allylsecoboldine showed significant alleviation of these renal dysfunctions. In addition, a lower dose of N-allylsecoboldine ameliorated the mortality of LPS-treated mice. This study demonstrates N-allylsecoboldine's ability to avail against acute renal failure and increase survival rate during endotoxemia. These beneficial effects may be attributed to the inhibition of iNOS expression, TNF-alpha production, and free radical scavenging activities. However, the role of alpha1-adrenoceptor antagonism for N-allylsecoboldine in sepsis remains unclear.

Angiopoietin-1 increases arteriolar vasoconstriction to phenylephrine during sepsis

Sepsis leads to a reduction in vascular tone and a loss of vasoconstriction in response to catecholamines. We propose that angiopoietin-1 (Ang-1), which is known to modulate vascular inflammation and nitric oxide (NO), could improve responsiveness to vasopressor agents during sepsis. Mesenteric arterioles (300-400 microm) from rats (n=19) were mounted in a pressurized myograph and incubated with lipopolysaccharide (LPS, 50 microg/mL) for up to 4 h to model sepsis. Vasoconstriction (mean+/-SD) to phenylephrine (10(-8)-10(-3) M) was reduced in the presence of LPS (4 h, pD2: 5.8+/-0.2 (controls, n=6), 1.4+/-2.2 (LPS, n=6); maximal constriction: 48.2+/-4.8% (controls), 2.6+/-5.8% (LPS), P<0.05). However, in the presence of Ang-1 (250 ng/mL) phenylephrine caused greater vasoconstriction compared to LPS alone (4 h, pD2: 4.5+/-2.1; maximal constriction: 12.6+/-4.0% (n=7), P<0.05). In conclusion, Ang-1 increases vasoconstriction to phenylephrine in the presence of LPS. During sepsis therefore, Ang-1 increases vascular reactivity and has the potential to increase blood pressure and decrease vasopressor requirements in vivo.

Maintenance of renal vascular reactivity contributes to acute renal failure during endotoxemic shock

Septic shock is characterized by hypotension and decreased systemic vascular resistance and impaired vascular reactivity. Renal vasoconstriction markedly contrasts with sepsis-induced generalized systemic vasodilation, which is strongly dependent on nitric oxide. Whether maintained renal vascular reactivity to vasoconstrictors contributes to the decrease in renal blood flow (RBF) and GFR observed during LPS-induced sepsis was tested by assessment of the acute effects of pressor agents on mean arterial pressure (MAP) and renal hemodynamics in endotoxemic and control mice. LPS-injected mice displayed lower MAP, RBF, and GFR than controls (P < 0.001). Despite a lower MAP, basal renal vascular resistance (RVR) was higher during endotoxemia (P < 0.02). Angiotensin II infusion produced a weaker MAP response in septic mice (24 versus 37%; P < 0.005), suggesting impaired vasoconstriction and hyporeactivity. A similar MAP increase was observed between groups during norepinephrine (NE) infusion. The MAP increase to nitric oxide synthase inhibition by N(G)-nitro-L-arginine methyl ester (L-NAME) was much greater in LPS-treated mice (41 versus 15%, P = 0.01), indicating a strong influence of nitric oxide in sepsis. In contrast, the RBF and RVR responses to angiotensin II, NE, or L-NAME were similar in both groups. Moreover, vasopressin produced greater changes in MAP, RBF, and RVR in septic mice than in controls. Among the vasoconstrictor challenges, only NE ameliorated the decrease in GFR 14 h after LPS injection. The in vivo results demonstrate that the renal microvasculature displays a normal or enhanced reactivity to constrictor agents as compared with nonrenal circulatory beds. Such responsiveness may contribute to reduced RBF and GFR during endotoxemia.

Regional and temporal changes in cardiovascular responses to norepinephrine and vasopressin during continuous infusion of lipopolysaccharide in conscious rats

BACKGROUND

Reduced pressor responsiveness to norepinephrine (NE) in sepsis is well documented but the associated regional haemodynamic changes are less well characterized, and there are varying reports of changes in haemodynamic responses to arginine vasopressin (AVP). We compared changes in regional haemodynamic responsiveness to AVP and NE during a 24 h continuous infusion of lipopolysaccharide (LPS) in conscious rats.

METHODS

Conscious, male Sprague-Dawley rats were infused with saline (0.4 ml h(-1)) or LPS (150 micro g kg(-1) h(-1)). Renal, mesenteric, and hindquarter haemodynamic responses to 3 min infusions of AVP (0.25, 0.625, and 1.25 ng kg(-1) min(-1)) or NE (75, 250, and 750 ng kg(-1) min(-1)) were assessed 2, 6, and 24 h after the onset of LPS or saline.

RESULTS

Two and six hours after the onset of LPS, all haemodynamic effects of NE were markedly reduced, but by 24 h, there was some recovery in the vasoconstrictor actions of NE although the pressor and bradycardic effects were still depressed. Two hours after the onset of LPS, the cardiovascular effects of AVP were depressed but there was some recovery in vascular responsiveness at 6 h. By 24 h, only the mesenteric vasoconstrictor effect of AVP was consistently reduced.

CONCLUSIONS

During low dose LPS infusion, there are differential changes in haemodynamic responsiveness to AVP and NE, which show different temporal and regional profiles of recovery with time. Furthermore, reduced pressor responsiveness to NE is not necessarily accompanied by a reduced capacity of vessels for vasoconstriction.