Platelet- and macrophage-derived endogenous cannabinoids are involved in endotoxin-induced hypotension

Macrophages are the primary cellular targets of bacterial lipopolysaccharide (LPS), but the role of macrophage-derived cytokines in LPS-induced septic shock is uncertain. Recent evidence indicates that activation of peripheral CB1 cannabinoid receptors contributes to hemorrhagic hypotension and that macrophage-derived anandamide as well as unidentified platelet-derived substances may be contributing factors. Here we demonstrate that rat platelets contain the endogenous cannabinoid 2-arachidonyl glyceride (2-AG), as identified by reverse phase high-performance liquid chromatography, gas chromatography, and mass spectrometry, and that in vitro exposure of platelets to LPS (200 microg/ml) markedly increases 2-AG levels. LPS-stimulated, but not control, macrophages contain anandamide, which is undetectable in either control or LPS-stimulated platelets. Prolonged hypotension and tachycardia are elicited in urethane-anesthetized rats treated 1) with LPS (15 mg/kg i.v.); 2) with macrophages plus platelets isolated from 3 ml of blood from an LPS-treated donor rat; or 3) with rat macrophages or 4) platelets preincubated in vitro with LPS (200 microg/ml). In all four cases, the hypotension but not the tachycardia is prevented by pretreatment of the recipient rat with the CB1 receptor antagonist SR141716A (3 mg/kg i.v.), which also inhibits the hypotensive response to anandamide or 2-AG. The hypotension elicited by LPS-treated macrophages or platelets remains unchanged in the absence of sympathetic tone or after blockade of nitric oxide synthase. These findings indicate that platelets and macrophages generate different endogenous cannabinoids, and that both 2-AG and anandamide may be paracrine mediators of endotoxin-induced hypotension via activation of vascular CB1 receptors.     

Cause of hypotension during spinal anesthesia--the relation between the level of anesthesia and the hypotension

A retrospective study was conducted on the cause of hypotension during spinal anesthesia and also on the relation between the level of anesthesia and the hypotension. Two hundred twenty three patients who had received spinal anesthesia for gynecological surgery were divided into two groups. Group I consisted of 87 patients with a significant decrease in blood pressure, while group II consisted of 136 patients with no significant decrease in blood pressure. First, the age, dosage of spinal anesthesia, amount of preoperative transfusion, and level of spinal anesthesia were reviewed and compared between the group I and II. Next, all the patients were classified by the level of spinal anesthesia, and the degree of decrease in blood pressure and the frequency of a significant decrease in blood pressure were examined by each level of spinal anesthesia. Only the level of spinal anesthesia was found to differ significantly between the group I and II. The degree of hypotension was greater at higher levels of spinal anesthesia. More than 50% of the patients with T5 or higher levels of anesthesia had a significant decrease in blood pressure. We conclude that the cause of the significant decrease in blood pressure during high spinal anesthesia is in most part due to the blockade of the cardiac sympathetic nerve.     

Pulmonary shunting during anesthesia with deliberate hypotension

Pulmonary shunting (Qs/Qt with FIO2 = 1) was measured in 18 anesthetized patients during deliberate hypotension. Hypotension was induced in 12 patients with sodium nitroprusside and light halothane anesthesia and in six others with deep halothane anesthesia and mechanical hyperventilation. Similar results were observed in the two groups. During the hypotensive period mean arterial pressure (MAP) was reduced to 49 +/- 2 torr, a 37 per cent decrease from the control level after the onset of operation and a 40 per cent decrease compared with the recovery level during closure of the wound. Qs/Qt, however, remained unchanged throughout the study: 5.2 +/- 0.9 per cent initially, 5.4 +/- 0.8 per cent during hypotension, and 4.7 +/- 0.5 per cent during recovery. It is concluded that pulmonary shunting need not develop during deliberate hypotension induced with either technique.     

Prevention and treatment of hypotension during spinal anesthesia

Spinal and epidural anaesthesias alter self-regulation of arterial pressure as they lead to a sympathetic blockade. The extent and the speed of appearance of this blockade conditions the magnitude of the decrease of arterial pressure. So, epidural or spinal anaesthesias may only be performed on hemodynamically stable patients for a non hemorrhagic surgery. The routine fluid preloading is illogical and poorly efficient. Correcting a deep arterial hypotension demands first of all the use of vasoconstricting agents the choice of which depends on the site of the anaesthesia and on the cardiovascular condition of the patient. The occurrence of bradycardia more often indicates a hypovolaemic state.     

Role of adenosine in noradrenergic neurotransmission during hemorrhagic hypotension

Glucagon-like peptide-1-(7-36) amide (GLP-1) and glucose-dependent insulinotropic peptide (GIP) are known incretin hormones, released from enteroendocrine cells in response to food, that enhance insulin secretion, but only in the presence of elevated blood glucose. We used a rat insulinoma cell line, RIN 1046-38, to study the mechanisms underlying the interaction of incretins and glucose. We measured insulin secretion using RIA and the reverse hemolytic plaque assay. GLP-1 stimulates insulin secretion, with a half-maximal concentration of 34 pM. GLP-1 is approximately 2 orders of magnitude more potent than GIP. GLP-1 and GIP have additive effects at submaximal concentrations, but probably not at maximal concentrations, suggesting a common signal transduction pathway. The glucose requirement for GLP-1 action can be replaced by cell membrane depolarization (20 mM KCl in the extracellular medium), suggesting that a rise of intracellular Ca2+ may be an early step required for GLP-1 action. GLP-1 stimulates insulin secretion by significantly increasing the maximum rate of insulin secretion from 10.3 +/- 2.25 to 25.2 +/- 2.94 ng insulin/mg protein.h. GLP-1 acts by recruiting 1.5-fold more cells to secrete insulin as well as enhancing insulin secretion by individual cells. Combinations of stimuli, such as glucose, cell membrane depolarization, and GLP-1, can recruit 90% of RIN 1046-38 cells to secrete insulin.     

Assessment of 3 audible monitors during hypotension in anesthetized dogs

Severe hypotension was produced in 8 dogs during halothane anesthesia. Three monitors detecting respiratory rate, Doppler signal and pulse rate were compared to direct blood pressure measurements. Deep anesthesia was most consistently detected using the respiratory monitor. The signal fade of the Doppler device was best at detecting hypotension from blood loss. Changes in heart rate were not useful.     

Complement activation as a cause of transient hypotension during plasmapheresis

Hypotension is one of the most common adverse effect of plasmapheresis (PP) and often is attributed to hypovolemia due to extracorporeal circulation and the vasovagal reflex. Complements are activated during PP, and the activated complements are strong anaphylatoxins and potent vasodilators. Therefore, we studied the relationship between the transient hypotension and the plasma levels of activated complements during and after PP in 8 sessions of 7 patients using the Plasmafro OP-08 as a plasma separator. Five of the patients underwent immunoadsorption PP using the IM-TR 350 or IM-PH 350 as the adsorption column. The other underwent double filtration PP using the Evaflux 4A as a second filter. In 4 of 8 sessions, patients experienced transient hypotension with significantly elevated plasma levels of activated complements C3a and C5a. In contrast, patients without hypotension showed no increases in C3a and C5a values during PP. In this report, we emphasize the critical role of activated complements for hypotension during PP.     

Oral arginine supplementation does not affect lymphocyte proliferation during endotoxin-induced inflammation in rats

Earlier studies from this laboratory were unable to confirm reported immunostimulatory effects of supplemental dietary arginine on healthy, unstressed young or aged rats. The present study was undertaken to determine effects of oral arginine supplementation on in vitro measures of immune function using a stressed rat model. The stressor used was intraperitoneal injection of bacterial lipopolysaccharide (1 mg/kg body wt). Four-month-old male Sprague-Dawley rats were placed in either a control or an arginine-supplemented (7.5 g/L arginine-HCl in drinking water) group for 7 d, after which control and supplemented rats received injections of endotoxin or phosphate-buffered saline. Rats were killed 3 d following injections. Endotoxin treatment resulted in lower food intake, less thymic cellularity and greater splenic weight. Endotoxin injections also enhanced proliferative response of rat splenocytes to pokeweed mitogen (1 mg/L) and lipopolysaccharide (25 and 100 mg/L) and enhanced response of thymocytes to concanavalin A (10 mg/L), phytohemagglutinin (25 and 100 mg/L) and pokeweed mitogen (1 mg/L). Supplemental arginine did not reduce thymic weight loss or influence mononuclear cell proliferation or interleukin-2 production in the presence or absence of endotoxin stress. These data indicate no benefit of arginine supplementation during endotoxin stress in rats.     

Near infrared spectroscopy detects cerebral ischemia during hypotension in piglets

OBJECTIVE: To determine if platelet angiotensin II binding density during the second or third trimester of pregnancy can be used as a marker for early detection of women who will develop preeclampsia. METHODS: We collected blood samples from 412 nulliparous pregnant women during their second or third trimesters. They were classified in four groups after delivery: normotensive (n=297), transient hypertensive (n=54), preeclamptic (n=39), and chronic hypertensive (n=22). We also studied 35 nonpregnant women and 122 women in the peripartum period. The binding capacity of platelet angiotensin II receptors was analyzed in each patient. RESULTS: In normotensive pregnancies, there was a significant decrease in mean (+/-standard error of the mean [SEM]) platelet binding in the second trimester (1.6+/-0.2 fmol/10(9) cells) compared with nonpregnant women (3.3+/-0.7 fmol/10[9] cells). No statistical differences were observed in the mean (+/-SEM) number of platelet angiotensin II binding sites between the groups studied in the third trimester (normal: 1.7+/-0.1 fmol/10(9) cells; transient hypertensive: 2.3+/-0.4 fmol/10(9) cells; preeclamptic: 1.6+/-0.4 fmol/10(9) cells, and chronic hypertensive: 1.6+/-0.6 fmol/10(9) cells), nor were any significant differences found in second-trimester values. At cutoff levels providing identical sensitivities, angiotensin II binding showed significantly lower positive predictive values than mean arterial pressure (P < .05). With this study's sample size, we could have demonstrated an improvement in positive predictive values of 20% with a statistical power (1-beta) of 90%. CONCLUSION: The measurement of platelet angiotensin II receptor density cannot be recommended for the early detection of preeclampsia.     

Induced hypotension during anesthesia with special reference to orthognathic surgery

Since Gardner first used arteriotomy during anesthesia to improve visibility in the surgical field, various techniques and pharmacological agents have been tried for the same purpose. With reports documenting the spread of acquired immune deficiency syndrome through blood transfusions, prevention of homologous blood transfusions during surgery has also become a major concern. Induced hypotension has been used to reduce blood loss and thereby address both issues. In orthognathic surgery, induced hypotension during anesthesia has been used for similar reasons. It is recommended that hypotensive anesthesia be adjusted in relation to the patient's preoperative blood pressure rather than to a specific target pressure and be limited to that level necessary to reduce bleeding in the surgical field and in duration to that part of the surgical procedure deemed to benefit by it. A mean arterial blood pressure (MAP) 30% below a patient's usual MAP, with a minimum MAP of 50 mm Hg in ASA Class I patients and a MAP not less than 80 mm Hg in the elderly, is suggested to be clinically acceptable. Various pharmacological agents have been used for induced hypotension during orthognathic surgery. In addition, there are many drugs that have been used in other types of surgery that could be used in orthognathic surgery to induce hypotension. Recent reports using control groups do not show significant differences in morbidity and mortality attributable to induced hypotension during anesthesia. Appropriate patient evaluation and selection, proper positioning and monitoring, and adequate fluid therapy are stressed as important considerations in patients undergoing induced hypotension during orthognathic surgery.     

Release of renal kallikrein to the perfusate by isolated rat kidney

The addition of furosemide to the fluid used to perfuse isolated rat kidney increases the kallikrein activity found in the perfusion fluid. The experiments favour the concept that furosemide activates a kallikrein precursor or/and the synthesis and release of kallikrein in the kidneys.     

Role of nitric oxide in regulation of brain stem circulation during hypotension

We tested the hypothesis that nitric oxide (NO) plays a role in CBF autoregulation in the brain stem during hypotension. In anesthetized rats, local CBF to the brain stem was determined with laser-Doppler flowmetry, and diameters of the basilar artery and its branches were measured through an open cranial window during stepwise hemorrhagic hypotension. During topical application of 10(-5) mol/L and 10(-4) mol/L N(omega)-nitro-L-arginine (L-NNA), a nonselective inhibitor of nitric oxide synthase (NOS), CBF started to decrease at higher steps of mean arterial blood pressure in proportion to the concentration of L-NNA in stepwise hypotension (45 to 60 mm Hg in the 10(-5) mol/L and 60 to 75 mm Hg in the 10(-4) mol/L L-NNA group versus 30 to 45 mm Hg in the control group). Dilator response of the basilar artery to severe hypotension was significantly attenuated by topical application of L-NNA (maximum dilatation at 30 mm Hg: 16 +/- 8% in the 10(-5) mol/L and 12 +/- 5% in the 10(-4) mol/L L-NNA group versus 34 +/- 4% in the control group), but that of the branches was similar between the control and L-NNA groups. Topical application of 10(-5) mol/L 7-nitro indazole, a selective inhibitor of neuronal NOS, did not affect changes in CBF or vessel diameter through the entire pressure range. Thus, endothelial but not neuronal NO seems to take part in the regulation of CBF to the the brain stem during hypotension around the lower limits of CBF autoregulation. The role of NO in mediating dilatation in response to hypotension appears to be greater in large arteries than in small ones.     

Nicardipine versus nitroprusside for controlled hypotension during spinal surgery in adolescents

Nicardipine or nitroprusside was used to induce controlled hypotension in healthy adolescents with idiopathic scoliosis undergoing spinal fusion. Twenty patients were randomly assigned to the nitroprusside (N) or nicardipine (C) group. All patients received a standardized anesthetic. A target mean arterial blood pressure (MAP) of 60 mm Hg was achieved by varying the vasoactive infusions only. Moderate hemodilution (PCV = 25) and intraoperative blood salvage were used in all cases. Hemodynamic variables, blood loss, occurrence of reflex tachycardia, and reversibility of the hypotensive state were compared between the two groups. Significant differences were observed between the two groups in the amount of blood loss and reversibility of the hypotensive state. Group C had less blood loss (761 +/- 199 mL) than Group N (1297.5 +/- 264, P < or = .05). Time to restoration of baseline MAP was longer with Group C (26.8 +/- 4.0 min) than Group N (7.3 +/- 1.1 min, P < or = 0.001). Both drugs rapidly achieved a stable, controlled hypotensive state and an acceptable operating field. There was no statistically significant difference between groups with respect to the amount of crystalloid administered or urine output. These results suggest that nicardipine is a safe, effective drug for controlled hypotension in this population and that it may offer the significant advantage of reduced blood loss in these patients.     

Melagatran, a low molecular weight thrombin inhibitor, counteracts endotoxin-induced haemodynamic and renal dysfunctions in the pig

Coagulation and fibrinolysis are crucial in septic shock and inhibition of thrombin may be beneficial in this circumstance. Since porcine endotoxaemia has been found to replicate severe septic shock, a low molecular weight thrombin inhibitor, melagatran, was infused during the first 3 out of 6 h of endotoxaemia in pigs. Plasma creatinine (p <0.01) and urinary output (p <0.05) were less affected in the melagtran + endotoxin group (n=6) as compared to endotoxaemic controls (n=9). The left ventricular stroke work index, systemic vascular resistance index and oxygen extraction were all less affected (p <0.05) by endotoxin during the infusion of melagatran. The plasma concentration of melagatran declined with an apparent plasma half-life of 5 h as soon as the infusion was stopped. APTT, however, continued to increase after the infusion of melagatran had stopped and reached a maximum of 113 s at 5 h (baseline 17 s). APTT in endotoxaemic control pigs reached a maximum of 22 s. Thus, melagatran may counteract some consequences of endotoxaemia.