OBJECTIVE:Preclinical and human studies suggest that ictal and interictal modulation of the sympathetic and parasympathetic systems contributes to cardiovascular changes that may induce sudden unexpected death in epilepsy. We therefore investigated the effects of convulsive seizures on cardiovascular and autonomic function in nonanesthetized sheep. METHODS:Adult female sheep were instrumented to record arterial pressure, heart rate, electroencephalogram, electrocardiogram, and either cardiac output or cardiac and renal sympathetic nerve activity (SNA). Arterial blood samples were collected to assess blood biochemistry. Seizures were induced in nonanesthetized sheep by intravenous infusion of the proconvulsant pentylenetetrazol (PTZ; 5.0 mg/kg/min for 4 min). RESULTS:PTZ induced consistent generalized tonic-clonic seizures associated with abnormal activity on electroencephalogram. Convulsive seizures increased mean arterial pressure (79.1 ± 4.5 mmHg to 128.5 ± 5.6 mmHg, p < .0001) and cardiac output (4.1 ± .2 to 7.9 ± .5 L/min, p < .0001) at 10 min postseizure; these remained significantly above baseline for 60 min (both n = 12). Heart rate variability decreased (4826.1 ± 766.6 to 210.9 ± 97.7 ms, n = 6, p = .0155) at 10 min and corrected QT interval increased (399 ± 9.1 to 449.7 ± 11 ms, p = .003) at 30 min postictally. Seizures increased cardiac SNA (682 ± 86 to 7558 ± 3955 spikes/min, n = 4, p = .007), whereas renal SNA decreased (4296 ± 784 to 1139 ± 284 spikes/min (p = .047). Seizures decreased blood potassium (3.9 ± .1 to 3.4 ± .1 mmol·L-1, p = .0268) and increased lactate (.68 ± .05 to 12.2 ± 1.39 mmol·L-1; p < .0001). SIGNIFICANCE:Seizures induced by PTZ in nonanesthetized sheep caused autonomic and cardiovascular disturbances, including postictal tachycardia and arrhythmias, which may contribute to an increased risk of sudden unexpected death in epilepsy.

Heart failure (HF) remains a clinical challenge with cardiac dysfunction typically progressing even with treatment, and heart transplants only available to small numbers. We previously identified phosphoinositide 3-kinase (PI3K, p110α) as a master regulator of exercise-induced cardioprotection, and showed that gene therapy, incorporating a constitutively active form of PI3K (caPI3K) improved function of the failing mouse heart. However, this approach was not cardiac-specific and the gene therapy was challenging to manufacture. The aim of this study was to develop new PI3K-based gene therapies with more optimal properties for clinical translation. We generated and assessed adeno-associated viruses (AAV6) encoding various PI3K constructs, with different enhancers, promoters and transgene components in healthy adult male mice. The most promising AAV construct based on AAV expression, cardiac-specificity, and ease of manufacture contained a cardiac troponin T (cTnT) promoter together with a small region of the regulatory subunit of PI3K (iSH2), and an intron from the β-globin gene which enhances transcription (IVS2). This AAV (1 × 1012, 2 × 1012 vg) was administered to mice with myocardial ischemia/reperfusion injury (I/R: 1 h ischemia with reperfusion; AAV delivered 24 h post-I/R). Direct cardiac injections of PI3K-based AAVs were also performed in healthy adult female sheep. I/R mouse hearts treated with the AAV6-cTnT-IVS2-iSH2 displayed increased phosphorylation of Akt, but no improvement in cardiac function or structure was observed. AAV6-cTnT-IVS2-iSH2 successfully transduced healthy sheep hearts which increased endogenous PI3K catalytic activity. Further testing/optimization of the AAV (time of delivery and/or duration) will be required to assess the therapeutic potential of this approach.

INTRODUCTION:Intra-operative hypotension is common during cardiopulmonary bypass and may contribute to tissue hypoxia. Tissue hypoxia has been linked to the development of postoperative kidney and brain injury. Vasopressors are used to treat hypotension during and after cardiopulmonary bypass. However, the effects of these drugs on renal and cerebral tissue oxygenation and perfusion are unknown. We tested the effects of four vasopressors on renal and cerebral tissue perfusion and oxygenation in a clinically-relevant ovine model of cardiopulmonary bypass. METHODS:We studied 16 sheep before and after induction of anaesthesia and during 2.5 h of cardiopulmonary bypass. After commencing cardiopulmonary bypass at a target non-pulsatile flow of 2.4 l.min-1.m-2, we observed a baseline period with a target mean arterial pressure of 50-60 mmHg, after which we targeted a mean arterial pressure of 75-85 mmHg using a continuous infusion of metaraminol (n = 8); noradrenaline (n = 8); phenylephrine (n = 8); or vasopressin (n = 7). Sheep were allocated randomly to receive two of the four vasopressors. RESULTS:Compared with the pre-induction state, cardiopulmonary bypass significantly decreased renal medullary tissue perfusion (median (IQR [range]) decrease 55 (4-82 [1-99])%; p = 0.01) and medullary oxygen tension (mean (SD) difference 3.1 (2.5) kPa; p < 0.001). Cardiopulmonary bypass did not significantly alter cerebral tissue perfusion or oxygenation compared with the pre-induction state. Infusing noradrenaline significantly decreased medullary oxygen tension (mean (SD) difference 2.7 (1.6) kPa; p = 0.003). This decrease in medullary oxygen tension was significant compared with vasopressin (mean difference -3.4 kPa, 95%CI -5.7 to -1.0; p = 0.008). No vasopressor infusion significantly altered renal medullary perfusion, cerebral tissue perfusion or oxygenation. DISCUSSION:Intra-operative noradrenaline during ovine cardiopulmonary bypass worsens renal medullary tissue oxygenation relative to vasopressin. These findings suggest that the choice of vasopressors may affect renal oxygenation.

Chronic kidney disease (CKD) affects 50% of patients with heart failure. The pathophysiology of CKD in heart failure is proposed to be driven by macrocirculatory hemodynamic changes, including reduced cardiac output and elevated central venous pressure. However, our understanding of renal microcirculation in heart failure and CKD remains limited. This is largely due to the lack of noninvasive techniques to assess renal microcirculation in patients. Moreover, there is a lack of clinically relevant animal models of heart failure and CKD to advance our understanding of the timing and magnitude of renal microcirculatory dysfunction. Patients with heart failure and CKD commonly require cardiac surgery with cardiopulmonary bypass (CPB) to improve their prognosis. However, acute kidney injury (AKI) is a frequent unresolved clinical complication in these patients. There is emerging evidence that renal microcirculatory dysfunction, characterized by renal medullary hypoperfusion and hypoxia, plays a critical role in the pathogenesis of cardiac surgery-associated AKI. In this review, we consolidate the preclinical and clinical evidence of renal macro- and microcirculatory perturbations in heart failure and cardiac surgery requiring CPB. We also examine emerging biomarkers and therapies that may improve health outcomes for this vulnerable patient population by targeting the renal microcirculation.

Background: Acute kidney injury (AKI) is a major unresolved complication of cardiac surgery, particularly in patients with pre-existing heart failure (HF). Mechanistic insight has been limited by the lack of large animal models replicating this complex clinical scenario. We developed a novel ovine model of HF with continuous, region-specific assessment of renal perfusion and oxygenation before, during, and after cardiopulmonary bypass (CPB). Methods: Merino ewes (30-45 kg) were instrumented to continuously measure cardiac output (CO), mean arterial pressure (MAP), renal blood flow (RBF), renal oxygen delivery (RDO 2 ), and renal cortical and medullary perfusion and oxygenation (PO 2 ) across the pre- (conscious), intra- (anesthetized) and post-CPB (conscious) phases. HF was induced via coronary artery ligation and defined by ≥30% increase in heart rate and ≥30% reduction in left ventricular ejection fraction. HF (n=9) and healthy control (n=8) animals underwent 2 h of CPB with aortic cross-clamp (pump flow 2.4 L/min/m 2 , target MAP 70 mmHg), followed by 48 h recovery. Results: Compared to the pre-CPB (conscious) state, CPB reduced RBF and RDO 2 similarly in both groups (RBF: −56% HF, −55% control; RDO 2 : −64% HF, −68% control; all p<0.01). Renal medullary perfusion and PO 2 also declined in both groups during CPB (perfusion: HF −71%, p=0.02; control −56%, p=0.08; PO 2 : HF −42%, p=0.03; control −46%, p=0.5), with no significant intergroup differences. However, by 48 h post-CPB, medullary PO 2 had recovered in controls but remained markedly suppressed in HF animals (8.0 ± 3.7 vs 30.6 ± 5.5 mmHg, p=0.02), despite similar MAP, CO, RBF, cortical perfusion, and cortical PO 2 . Postoperative AKI was more frequent in HF animals (55% vs 12.5%, OR 8.75). Across all animals, those with AKI had lower post-CPB medullary PO 2 than those without AKI (18.7 ± 3.5 vs 31.3 ± 3.5 mmHg, p=0.04). Conventional markers (urine output, creatinine clearance) did not differ significantly between groups at any stage, underscoring their limited sensitivity to early, region-specific injury. Conclusion: This is the first large-animal model to replicate the perioperative course of cardiac surgery with CPB in the setting of heart failure, enabling continuous, region-specific monitoring of renal oxygenation. Persistent medullary hypoxia emerged as a key driver of postoperative AKI, highlighting a novel and potentially targetable mechanism in high-risk patients with HF.

Healthcare-associated infections (HAIs) pose significant risks, leading to increased morbidity, mortality, and costs, exacerbated by multi-drug-resistant microorganisms. This study aimed to evaluate pharmacological prophylaxis targeting sympathetic reflex control of immunity to mitigate systemic infections, offering a novel approach to combating HAIs. The study included animal experiments and a retrospective analysis of orthopedic surgery patients in Romagna, Italy. Young female pigs were intravenously inoculated with Escherichia coli (E. coli) and divided into two groups: propranolol-treated (non-selective β-blocker; 3 mg/kg; 3x/day orally) and vehicle-treated, starting two days before infection. Parameters such as bacteraemia, serum cytokines, biochemical profile, blood count, lactate, glycemia, and flow cytometry were assessed. Additionally, a retrospective analysis of 92,649 orthopedic surgery hospitalizations (2017-2022) examined the association of non-selective and selective β1-blockers with HAI development using conditional logistic regression. Propranolol-treated pigs exhibited a disinhibited immune response to systemic infection, clearing circulating bacteria much earlier than vehicle-treated animals. The retrospective analysis showed that patients on non-selective beta-blockers had a 71.7% reduced risk of developing HAIs, while those on selective β1-blockers had an 18% higher risk. These findings suggest that targeting sympathetic reflex control of immunity via pharmacological prophylaxis may reduce HAIs in surgical patients.

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) reduce chronic kidney disease progression in people with type 2 diabetes mellitus. Sepsis is the leading cause of acute kidney injury (AKI). This study investigated whether GLP-1 is renoprotective in an ovine model of gram-negative septic AKI. Sixteen healthy merino ewes were surgically instrumented to measure mean arterial pressure, cardiac output, renal blood flow, renal cortical and medullary perfusion and oxygenation, and renal function. After a 5-day recovery period, sepsis was induced via continuous intravenous infusion of live Escherichia coli for 30 h. After 24 h, the sheep were randomized to receive an intravenous infusion of 3.6 pmol/kg/min GLP-1 (n = 8) or a fluid-matched vehicle (n = 8) for 6 h. After 24 h of sepsis, 7/8 sheep in each group developed AKI. GLP-1 treatment increased renal blood flow compared to placebo + 13 vs. − 3.4 ml/min difference (95% CI) = 16 (− 7–40) P = 0.0054), and maintained renal cortical oxygenation + 2.5 mmHg vs. = − 7.2 mmHg, difference (95% CI) = 9.7 (5.2–14.4) P < 0.001. GLP-1 maintained renal medullary perfusion + 1.7 vs. vehicle − 213 perfusion units, difference (95% CI) = 214 (− 21–450) P = 0.07. However, GLP-1 did not significantly improve the primary endpoint of renal medullary oxygenation − 1.6 vs. − 11.5, difference (95% CI) = 9.9 (− 6.8–26.7) P = 0.21. In an ovine model of gram-negative sepsis-associated AKI, GLP-1 infusion supported global renal perfusion, renal oxygen delivery, and cortical oxygenation but failed to improve renal medullary oxygenation and kidney function.

Cardiopulmonary bypass (CPB) may decrease the renal functional reserve (RFR). However, the temporal changes in RFR after during the recovery period after CPB remains unknown. We assessed RFR before and then weekly after CPB over four weeks following CPB in non-anaesthetised sheep. In 10 Merino ewes, amino acids were infused before CPB and weekly for four weeks to assess RFR. At each assessment, we measured renal blood flow (RBF), renal oxygen delivery (RDO2), creatinine clearance and medullary and cortical oxygenation. Histological assessment was performed at 4 weeks. Before CPB, amino acid infusion increased RBF from (mean ± SD) 6.60 ± 1.64 to 8.56 ± 1.80 mL/kg/min, and RDO2 from 0.80 ± 0.28 to 1.12 ± 0.37 mL O2/kg/min. These renal macro-circulatory responses remained consistent across all weekly assessments after CPB. Amino acid infusion also increased creatinine clearance (from 62.5 ± 15.0 to 110 ± 30.6 mL/h pre-CPB) throughout the study period. RFR remained unchanged over time (P = 0.53). However, compared with pre-CPB values, medullary (33.9 ± 9.0 pre-CPB to 15.1 ± 13.2 mmHg at 4 weeks, P = 0.0068) and cortical tissue PO2 (46.0 ± 14.2 to 17.2 ± 6.5 mmHg, P = 0.0029) decreased over time. Furthermore, the response of the medullary (but not cortical) PO₂ to amino acid infusion changed over time (P = 0.0064). While medullary PO₂ did not change in response to amino acid infusion pre-CPB and at one week after CPB, it appeared to fall from two weeks thereafter (P = 0.039 and 0.091 at weeks 2 and 3, respectively). Despite preserved RFR, sheep exposed to CPB showed greater peritubular inflammation, interstitial fibrosis and tubular casts compared with healthy controls (P = 0.007, 0.021, 0.007, respectively). In this large mammalian model of CPB, weekly amino acid administration consistently recruited RFR over four weeks, despite the presence of histological injury. However, it was associated with the development of renal medullary hypoxia after two weeks. These findings highlight the complexity of the pathophysiological response of the kidney to CPB.

INTRODUCTION:Hemoadsorption has emerged as a potential intervention for the removal of ticagrelor. We aimed to evaluate the efficacy of the HA380 hemoadsorption cartridge for this purpose. METHODS:Six healthy adult sheep received 270 mg of ticagrelor via an orogastric tube, followed by hemoadsorption using a HA380 cartridge for a duration of 4 h. The sorbent-based removal ratio, clearance, and mass removal rate were assessed at multiple time points. RESULTS:The HA380 cartridge achieved an initial sorbent-based removal ratio of 48.9% (SD 11.8) at 10 min, which declined rapidly to 2.66% (SD 18.5) at 120 min and 0.48% (SD 17.0) at 240 min. Clearance followed a similar trend, starting at 46.1 mL/min (SD 11.4) and decreasing to 0.08 mL/min (SD 16.8) at 240 min. The mass removal rate also dropped significantly over time, from 3.74 ng/min (SD 2.54) at 10 min to near zero at 120 and 240 min. CONCLUSION:HA with the HA380 cartridge can achieve an early 50% adsorption level for ticagrelor. If frequently changed, the HA380 cartridge may serve as a potential option for ticagrelor removal, when clinically indicated.

BACKGROUND:The sustained renal effects of exposure to cardiopulmonary bypass are unknown. This study aimed to test whether cardiopulmonary bypass (CPB) is associated with sustained renal tissue hypoxia and whether such hypoxia is associated with histologic injury. METHODS:The study included 12 adult female sheep undergoing CPB with a 2-h aortic cross-clamp. Systemic and renal hemodynamics and oxygen delivery, kidney function, and renal tissue oxygenation were measured before and during CPB, in the 48 h after CPB, and weekly for 4 weeks. The sheep were euthanized at 4 weeks and obtained renal tissue to perform histopathologic assessments for comparison with an independent cohort of five healthy animals that were euthanized without undergoing surgical or experimental interventions. These histologic assessments were performed by an independent, treatment-blinded pathologist. RESULTS:Compared with baseline, renal blood flow and renal medullary tissue oxygenation decreased significantly during CPB. In the first 48 h after CPB, there was a continuing significant decrease in medullary tissue oxygenation (from 39.2 ± 13.8 mmHg at baseline to 21.7 ± 16.2 mmHg at 48 h; Ptime = 0.006) with stage 1 acute kidney injury in 42% of the animals. Moreover, in the following 4 weeks, medullary (16.1 ± 12.9 mmHg at 4 weeks; Ptime = 0.005) and cortical (17.2 ± 6.5 mmHg at 4 weeks; Ptime = 0.005) tissue oxygenation remained significantly lower than baseline. Finally, compared with healthy sheep, at 4 weeks after CPB, sheep kidneys had significantly more peritubular inflammation (8 of 8 vs . 1 of 5; P = 0.007), interstitial fibrosis (6 of 8 vs . 0 of 5; P = 0.021), and tubular casts (8 of 8 vs . 1 of 5; P = 0.007). CONCLUSIONS:Exposure to CPB triggers sustained medullary and cortical tissue hypoxia and is associated with histopathologic renal injury. These findings suggest that the renal effect of exposure to CPB may be more profound and longer lasting than currently appreciated.

Renal arterial infusion of tempol (RAT) at the onset of Gram-negative sepsis can prevent sepsis-induced medullary tissue hypoxia and acute kidney injury (AKI). However, it is not known whether treatment with tempol at a clinically relevant time point of sepsis is similarly effective. Thus, we examined whether tempol can reverse renal medullary tissue hypoxia after ovine Gram-negative septic AKI. Following right unilateral nephrectomy, the left kidney was instrumented with a renal arterial catheter and oxygen-sensing fibre-optic probes into the renal medulla. After 23 h of Escherichia coli infusion, conscious sheep were fluid resuscitated with Hartmann's solution (30 mL/kg over 0.5 h) and randomized to intravenous tempol (IVT; n = 7) at 30 mg/kg/h, RAT (3 mg/kg/h; n = 6) or vehicle (n = 5) from 24 to 31 h of sepsis. At 31 h, E. coli infusion ceased, and sheep received ceftriaxone (1 g) and were allowed a 48 h recovery period. At 23 h of E. coli infusion, septic sheep developed a 2.2 ± 0.8-fold increase in plasma creatinine and a 57% ± 6% decrease in urine output, and the renal medulla was ischaemic and hypoxic. Neither RAT nor IVT attenuated the sepsis-induced renal medullary tissue hypoxia during the 7 h intervention period. Renal medullary tissue partial pressure of O2 returned to the pre-morbid levels in all groups by 16 h after treatment cessation, and sepsis was resolved with antibiotics. In conclusion, in sheep with established septic AKI, treatment with RAT or IVT did not improve renal medullary oxygenation or kidney function, in contrast to the effectiveness we have shown in early sepsis. These findings emphasize the dramatically different response to a treatment in early compared with late stages of sepsis.

Abstract Background People with type 2 diabetes mellitus treated with sodium-glucose transporter-2 inhibitors (SGLT2i) have lower rates of acute kidney injury (AKI). Sepsis is responsible for the majority of AKI in critically ill patients. This study investigated whether SGLT2i is renoprotective in an ovine model of Gram-negative septic AKI. Methods Sixteen healthy merino ewes were surgically instrumented to enable measurement of mean arterial pressure, cardiac output, renal blood flow, renal cortical and medullary perfusion, and oxygenation. After a 5-day recovery period, sepsis was induced via slow and continuous intravenous infusion of live Escherichia coli. Twenty-three hours later, sheep were randomized to receive an intravenous bolus of 0.2 mg/kg empagliflozin (n = 8) or a fluid-matched vehicle (n = 8). Results Empagliflozin treatment did not significantly reduce renal medullary hypoperfusion or hypoxia, improve kidney function, or induce histological changes. Renal cortical oxygenation during the intervention period was 47.6 ± 5.9 mmHg in the empagliflozin group compared with 40.6 ± 8.2 mmHg in the placebo group (P = 0.16). Renal medullary oxygenation was 28.0 ± 18.5 mmHg in the empagliflozin compared with 25.7 ± 16.3 mmHg (P = 0.82). Empagliflozin treatment did not result in significant between-group differences in renal blood flow, kidney function, or renal histopathological changes. Conclusion In a large mammalian model of septic AKI, a single dose of empagliflozin did not improve renal microcirculatory perfusion, oxygenation, kidney function, or histopathology.

Acute kidney and brain injury are frequent major unresolved clinical complications following cardiac surgery requiring cardiopulmonary bypass (CPB). We have developed a sheep model of CPB in which renal and cerebral tissue microcirculatory perfusion and oxygenation can be continuously monitored before, during and 48-hours after the cardiac surgical procedure. We hypothesised that renal medullary and cerebral tissue hypoxia would be associated with the development of CPB-induced kidney and brain injury.

Healthcare-associated infections (HAIs) pose significant risks, leading to increased morbidity, mortality, and costs, exacerbated by multi-drug-resistant microorganisms. This study aimed to evaluate pharmacological prophylaxis targeting sympathetic reflex control of immunity to mitigate systemic infections, offering a novel approach to combating HAIs. The study included animal experiments and a retrospective analysis of orthopedic surgery patients in Romagna, Italy. Young female pigs were intravenously inoculated with Escherichia coli (E. coli) and divided into two groups: propranolol-treated (non-selective β-blocker; 3mg/kg; 3x/day orally) and vehicle-treated, starting two days before infection. Parameters such as bacteraemia, serum cytokines, biochemical profile, blood count, lactate, glycemia, and flow cytometry were assessed. Additionally, a retrospective analysis of 92,649 orthopedic surgery hospitalizations (2017–2022) examined the effects of non-selective and selective β1-blockers on HAIs development using conditional logistic regression. Propranolol-treated pigs exhibited a disinhibited immune response to systemic infection, clearing circulating bacteria much earlier than vehicle-treated animals. The retrospective analysis showed that patients on non-selective beta-blockers had a 71.7% reduced risk of developing HAIs, while those on selective β1-blockers had an 18% higher risk. These findings suggest that targeting sympathetic reflex control of immunity via pharmacological prophylaxis may reduce HAIs in surgical patients.

Attention deficits are frequently reported within the clinical autism population. Despite not being a core diagnostic feature, some aetiological theories place atypical attention at the centre of autism development. Drugs used to treat attention dysfunction are therefore increasingly prescribed to autistic patients, though currently off-label with uncertain efficacy. We utilised a rodent-translated touchscreen test of sustained attention in mice carrying an autism-associated R451C mutation in the neuroligin-3 gene (Nlgn3(R451C)). In doing so, we replicated their cautious but accurate response profile and probed it using two widely prescribed attention-modulating drugs: methylphenidate (MPH) and atomoxetine (ATO). In wild-type mice, acute administration of MPH (3 mg/kg) promoted impulsive responding at the expense of accuracy, while ATO (3 mg/kg) broadly reduced impulsive responding. These drug effects were absent in Nlgn3(R451C) mice, other than a small reduction in blank touches to the screen following ATO administration. The absence of drug effects in Nlgn3(R451C) mice likely arises from their altered behavioural baseline and underlying neurobiology, highlighting caveats to the use of classic attention-modulating drugs across disorders and autism subsets. It further suggests that altered dopaminergic and/or norepinephrinergic systems may drive behavioural differences in the Nlgn3(R451C) mouse model of autism, supporting further targeted investigation.image

It has been proposed that diuretics can improve renal tissue oxygenation through inhibition of tubular sodium reabsorption and reduced metabolic demand. However, the impact of clinically used diuretic drugs on the renal cortical and medullary microcirculation is unclear. Therefore, we examined the effects of three commonly used diuretics, at clinically relevant doses, on renal cortical and medullary perfusion and oxygenation in non-anaesthetised healthy sheep. Merino ewes received acetazolamide (250 mg; n = 9), furosemide (20 mg; n = 10) or amiloride (10 mg; n = 7) intravenously. Systemic and renal haemodynamics, renal cortical and medullary tissue perfusion and P O 2 ${P_{{{\mathrm{O}}_{\mathrm{2}}}}}$ , and renal function were then monitored for up to 8 h post-treatment. The peak diuretic response occurred 2 h (99.4 ± 14.8 mL/h) after acetazolamide, at which stage cortical and medullary tissue perfusion and P O 2 ${P_{{{\mathrm{O}}_{\mathrm{2}}}}}$ were not significantly different from their baseline levels. The peak diuretic response to furosemide occurred at 1 h (196.5 ± 12.3 mL/h) post-treatment but there were no significant changes in cortical and medullary tissue oxygenation during this period. However, cortical tissue P O 2 ${P_{{{\mathrm{O}}_{\mathrm{2}}}}}$ fell from 40.1 ± 3.8 mmHg at baseline to 17.2 ± 4.4 mmHg at 3 h and to 20.5 ± 5.3 mmHg at 6 h after furosemide administration. Amiloride did not produce a diuretic response and was not associated with significant changes in cortical or medullary tissue oxygenation. In conclusion, clinically relevant doses of diuretic agents did not improve regional renal tissue oxygenation in healthy animals during the 8 h experimentation period. On the contrary, rebound renal cortical hypoxia may develop after dissipation of furosemide-induced diuresis.

Background The mechanisms by which megadose sodium ascorbate improves clinical status in experimental sepsis is unclear. We determined its effects on cerebral perfusion, oxygenation, and temperature, and plasma levels of inflammatory biomarkers, nitrates, nitrites, and ascorbate in ovine Gram-negative sepsis. Methods Sepsis was induced by i.v. infusion of live Escherichia coli for 31 h in unanaesthetised Merino ewes instrumented with a combination sensor in the frontal cerebral cortex to measure tissue perfusion, oxygenation, and temperature. Fluid resuscitation at 23 h was followed by i.v. megadose sodium ascorbate (0.5 g kg−1 over 30 min+0.5 g kg−1 h−1 for 6.5 h) or vehicle (n=6 per group). Norepinephrine was titrated to restore mean arterial pressure (MAP) to 70–80 mm Hg. Results At 23 h of sepsis, MAP (mean [sem]: 85 [2] to 64 [2] mm Hg) and plasma ascorbate (27 [2] to 15 [1] μM) decreased (both P<0.001). Cerebral ischaemia (901 [58] to 396 [40] units), hypoxia (34 [1] to 19 [3] mm Hg), and hyperthermia (39.5 [0.1]°C to 40.8 [0.1]°C) (all P<0.001) developed, accompanied by malaise and lethargy. Sodium ascorbate restored cerebral perfusion (703 [121] units], oxygenation (30 [2] mm Hg), temperature (39.2 [0.1]°C) (all PTreatment<0.05), and the behavioural state to normal. Sodium ascorbate slightly reduced the sepsis-induced increase in interleukin-6, returned VEGF-A to normal (both PGroupxTime<0.01), and increased plasma ascorbate (20 000 [300] μM; PGroup<0.001). The effects of sodium ascorbate were not reproduced by equimolar sodium bicarbonate. Conclusions Megadose sodium ascorbate rapidly reversed sepsis-induced cerebral ischaemia, hypoxia, hyperthermia, and sickness behaviour. These effects were not reproduced by an equimolar sodium load.