Prevention of endotoxin-induced increase of cerebral oxygen consumption in dogs by propranolol pretreatment

Transcerebral net exchange of vasoactive peptides and catecholamines during lipopolysaccharide-induced systemic inflammation in healthy humans

The systemic inflammatory response triggered by lipopolysaccharide (LPS) is associated with cerebral vasoconstriction, but the underlying mechanisms are unknown. We therefore examined whether a 4-hour intravenous LPS infusion (0.3 ng·kg^-1) induces any changes in the transcerebral net exchange of the vasoactive peptides endothelin-1 (ET-1) and calcitonin-gene related peptide (CGRP) and catecholamines in human volunteers. Cerebral blood flow was measured by the Kety-Schmidt technique, and paired arterial-to-jugular venous blood samples were obtained for estimating the transcerebral exchange of ET-1, CGRP, and catecholamines by the Fick principle in 12 volunteers before and after LPS infusion. The cerebrovascular release of ET-1 was enhanced, whereas the transcerebral net exchange of CGRP and catecholamines was unaffected. Our findings thus point towards locally produced ET-1 within the cerebrovasculature as a contributor to cerebral vasoconstriction after LPS infusion.

Cerebrovascular involvement in liposome-induced cardiopulmonary distress in pigs

Intravenous administration of liposomes, including Doxil, can cause severe life-threatening hemodynamic changes in pigs. The reaction is due to complement activation, and it is characterized by massive pulmonary hypertension, systemic hypotension, and severe cardiac abnormalities including falling cardiac output, tachy-or bradycardia with arrhythmia. There were no data suggesting the involvement of cerebrovascular changes in this reaction; however, clinical observations allowed this hypothesis. Here we measured the accompanying changes during liposome infusion by monitoring pulsatile electrical impedance (rheoencephalogram- REG) on the skull (n=24 pigs, 57 trials, 19 types of liposomes). A transient but significant decrease of REG pulse amplitudes followed the injection of liposomes (78.43% in the total sample, and 91.66% in the Doxil subgroup; P=0.003, n=12), indicating the involvement of cerebrovascular reaction during liposome infusion.

The neuropathology of septic shock

The neuropathological correlates of encephalopathy and autonomic dysfunction in septic shock are unclear. We performed post mortem analysis of 5 brain areas susceptible to ischemia and 5 autonomic nuclei (AN) in 23 patients who had died in our intensive care unit (ICU) from septic shock and 8 dying from non-septic shock as well as 5 controls who had died suddenly from extracranial injury. Proinflammatory cytokine (IL1-beta and TNF-alpha) and inducible nitric oxide synthase (iNOS) expression was assessed by immunocytochemistry. Abnormalities in septic shock were: hemorrhages (26%), hypercoagulability syndrome (9%), micro-abscesses (9%), multifocal necrotizing leukoencephalopathy (9%) and ischemia (100%). The incidence of cerebral hemorrhage or hypercoagulability syndrome was not related to clotting disturbances. The intensity of ischemia within susceptible areas was the same in both ICU groups, but more pronounced in the autonomic centers of septic patients (P < 0.0001). Neuronal apoptosis assessed using anti-caspase 3 immunocytochemistry and in situ end labeling was more pronounced in the autonomic nuclei of septic patients. (P < 0.0001). TNF-alpha expression did not differ between groups but vascular iNOS expression assessed by immunocytochemistry was higher in sepsis (P<0.0001) and correlated with autonomic center neuronal apoptosis (P < 0.02). We conclude that septic shock is associated with diffuse cerebral damage and specific autonomic neuronal apoptosis which may be due to circulating factors particularly iNOS.

An alteration in the gamma-aminobutyric acid receptor system in experimentally induced septic shock in rats

OBJECTIVE

To investigate the role of the brain gamma-aminobutyric acid receptor system in septic shock.

DESIGN

Prospective, controlled study.

SETTING

Animal laboratory.

SUBJECTS

Twenty-one male Wistar rats (7 wks old) were randomized to three groups: group 1 (n = 7, control); group 2 (n = 7, sham-operated); group 3 (n = 7, cecal ligation and puncture group).

INTERVENTIONS

Under light ether anesthesia, the rats were treated as described above. Twenty-four hours after treatment, the rats were killed by decapitation. Plasma amino acid concentrations were measured using the collected blood. The brain was excised as rapidly as possible, and separated into forebrain, cerebellum, and brain stem. The brain gamma-aminobutyric acid concentration was measured at each of the three regions. Using 3H-musimol, which is a gamma-aminobutyric acid receptor agonist, as a radioligand, the gamma-aminobutyric receptor densities were measured in these three regions by a radio-receptor assay.

MEASUREMENTS AND MAIN RESULTS

The concentrations of the branch-chain amino acids (leucine, isoleucine, valine) were lower in the cecal ligation and puncture group than in the control and sham operated groups. The concentrations of the sulfur-containing amino acids (cysteine and taurine) were increased in the cecal ligation and puncture group compared with the other two groups, but the methionine concentration was increased in the sham-operated and the cecal ligation and puncture groups compared with the control group (p < .05). The plasma gamma-aminobutyric acid concentration was not detectable in any of the three groups. The ammonia concentration was greater in the cecal ligation and puncture group than in the other two groups. There was no significant difference in the brain gamma-aminobutyric acid concentration among the three groups. The maximum number of binding sites in the forebrain of the cecal ligation and puncture group was higher than in the other two groups at both high- and low-affinity sites (control group: high-affinity sites 0.34 +/- 0.03, low-affinity sites 2.93 +/- 0.28; sham-operated group: high-affinity sites 0.35 +/- 0.03, low-affinity sites 2.73 +/- 0.18; cecal ligation and puncture group: high-affinity sites 0.59 +/- 0.13, low-affinity sites 3.53 +/- 0.21; mean +/- SEM pmol/mg protein) (p < .05). There were no significant differences observed in other regions of the brain (cerebellum and brain stem) in the three groups. The dissociation constants for 3H-musimol were almost unchanged in the three groups.

CONCLUSIONS

An increase in the gamma-aminobutyric acid-A receptor density was observed in the forebrain of the cecal ligation and puncture model rats. This alteration may be closely related to the pathogenesis of brain dysfunction during septic shock.

Effects of arterial hypoxia and beta-adrenoceptor blockade on cerebral blood flow and oxygen uptake following E. coli endotoxin in dogs

Earlier studies in normoxia have shown that an endotoxin injection in dogs leads to an increase in cerebral metabolic rate of oxygen (CMRo2), a decrease in cerebral blood flow (CBF) and increased concentrations of monoamines in blood and cerebrospinal fluid (CSF). In animals pretreated with propranolol (PPL) the CMRo2 increase was abolished and thus beta-adrenoceptor mediated. Arterial hypoxia normally increases CBF without any influence on CMRo2. The aim of this study was to investigate the effects of moderate arterial hypoxia on CBF, CMRo2 and catecholamine concentrations in blood and CSF after endotoxin with and without pretreatment with PPL. Three groups of dogs were studied. Group 1: Six animals were subjected to arterial hypoxia without any other intervention. Group 2: Six animals were given an endotoxin injection (E. coli lipopolysaccharide O 111: B 4), before the induction of hypoxia. Group 3: Eight animals were pretreated with PPL per os, 12.5 mg.kg-1 twice a day for one week before the experiments, and the effects of arterial hypoxia were studied both before and after an intravenous injection of endotoxin. Two levels of hypoxia were studied; oxygen saturation in arterial blood aiming at 75 and 50%. Endotoxin was given intravenously in a dose of 1 mg.kg-1 bodyweight over a 5 minute period. After an endotoxin injection, the response to arterial hypoxia was an increase in CMRo2, in contrast to the unchanged CMRo2 without endotoxin. After pretreatment with PPL the increase in CMRo2 after endotoxin was prevented. The CBF reaction to hypoxia was uniformly an increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of propranolol pretreatment on cerebral blood flow, oxygen uptake and catecholamines during metabolic acidosis following E. coli endotoxin in dogs

After an intravenous injection of E. coli endotoxin in dogs a decrease in cerebral blood flow (CBF) and an increase in cerebral metabolic rate of oxygen (CMRo2) have been shown to occur. In metabolic acidosis following endotoxin CMRo2 increased with decreasing pH. A possible explanation for the increased CMRo2 after endotoxin and metabolic acidosis seems to be a damage of the blood-brain barrier (BBB) by endotoxin. This gives possibilities for a leakage of hydrogen ions and circulating monoamines from the blood to the brain, thus affecting the cerebral blood flow and metabolism. The effects of an E. coli endotoxin injection on CBF and CMRo2 during metabolic acidosis and beta-adrenoceptor blockade were studied in eight anaesthetized dogs. All the dogs were pretreated with propranolol (PPL), per os 12.5 mg.kg-1 twice a day for one week. Metabolic acidosis (pH 7.01-7.30) was achieved by an intravenous infusion of hydrochloric acid. Endotoxin E. coli lipopolysaccharide O 111:B 4 was given as an intravenous injection of 1 mg.kg-1 bodyweight over a 5 min period. Another five animals, published earlier, with the same experimental protocol but without PPL, constituted a control group. After endotoxin no increase in CMRo2 or CBF was observed with increasing acidosis in the PPL-group. In the control group, after endotoxin, both CBF and CMRo2 increased with decreasing pH. This resulted in a significant difference in both CBF and CMRo2 between the groups in the pH range 7.01-7.15. The present results indicate that the increase in CMRo2 and CBF with metabolic acidodis in endotoxinaemia is mediated via beta-adrenoceptors.

Effects of metabolic pH-alterations on cerebral blood flow and oxygen uptake following E. coli endotoxin in dogs

The aim of the present study was to investigate if metabolic pH-alterations have an influence on cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) after an injection of E. coli endotoxin. Following endotoxin in dogs with normal pH a decreased CBF and an increased CMRO2 have earlier been found. Thirteen anaesthetized dogs were subjected to metabolic pH-variations in blood by infusion of hydrochloric acid or sodium bicarbonate. Ten dogs received E. coli endotoxin in a dose of 1 mg.kg-1 bodyweight. CBF, CMRO2 and noradrenaline and adrenaline concentrations in blood and cerebrospinal fluid were measured repeatedly during normoxia and normocarbia. Measurements before endotoxin served as controls, together with three additional animals, where endotoxin was never given. In control measurements pH showed no influence on the variables studied. After endotoxin CBF, CMRO2 and noradrenaline in cerebrospinal fluid increased with decreasing arterial blood pH. The influence exerted by metabolic pH alterations in blood after endotoxin may be explained by hydrogen ions and monoamines passing over a blood-brain barrier (BBB), damaged by endotoxin, into the brain tissue causing vasodilation and neuronal activation.

Distribution of radioactive microspheres injected into the vertebral artery of the dog

The aim of the present study was to evaluate the use of the vertebral artery for cerebral blood flow studies. In eight dogs a small catheter was introduced into an unligated a. vertebralis sin. Radioactive microspheres (141Cerium) were injected and detected with a gamma camera. The microspheres were distributed to all parts of the brain. The concentrations were highest in the cerebellum, pons and medulla oblongata, while the total activity was greatest in the cerebrum because of its higher weight. The activity in the extracerebral tissues in the head was found to be less than 5% of the brain activity.