Effects of halothane and isoflurane on carbon monoxide-induced relaxations in the rat aorta

Efficacy of wearable vibration dressings on full-thickness wound healing in a hyperglycemic rat model

Local low-frequency vibration promotes blood flow and wound healing in hard-to-heal diabetic foot ulcers (DFUs). However, vibration treatment is challenging in patients with DFUs due to wound management difficulties and low adherence. Consequently, developing wearable self-care devices becomes imperative for effective wound healing. This study introduces a wearable vibration dressing and assesses its impact on wound healing in hyperglycemic rats. Low-frequency vibration at 52 Hz was applied to the wound for 40 min/day in awake rats. Relative wound areas on post-wounding days (PWDs) 4-7 were significantly smaller and the wound closure rate was significantly higher in the vibration group than in the control group (p < 0.05, respectively). The total haemoglobin at baseline and after vibration on post-wounding day 7 was significantly larger in the vibration group than in the control group (p < 0.05). On PWD 7, the thickness of the granulation tissue was significantly higher in the vibration group than in the control group (p < 0.05). Moreover, the number of blood vessels at the wound site and vascular endothelial growth factor A protein expression were significantly higher in the vibration group than in the control group (p < 0.05, respectively). The ratio of (CD68+ /iNOS+ )/(CD163+ ) macrophages in the vibration group was significantly lower than that in the control group (p < 0.05). These results indicate the potential of wearable vibration dressings as new self-care devices that can promote angiogenesis and blood flow, improve inflammation, and enhance wound healing in DFUs.

[Vasoreactivity changes during extracorporeal circulation: effects of halogenated agents]

During cardiopulmonary bypass (CPB), endothelium is exposed to multiple disturbances leading to significant vasomotor tone and vascular systemic resistances (VSR) level modifications. Properties of endothelial function on vascular tone were summarized herein. According bibliographic findings, physiological and clinical impacts of respectively halogenated agents and CPB concerning vasomotor tone were reported. Main effects of halogenated agents administered through oxygenator during CPB were also identified. Usually when administered above one MAC, halogenated agents decreased VSR during hypothermic bypass. Once those mechanisms summarized, increase of halogenated agent's effects on VSR during normothermic CPB was postulated. Assuming that decrease of VSR could be deleterious favoring severe vasoplegia event, clinical experience of administration of isoflurane during CPB among more 4000 patients was retrospectively reported. Incidence of severe vasoplegia was established to 9.5 % in the studied population and this result was similar as others. More over predicting factors of severe vasoplegia were the same as previously reported : severity of preoperative clinical status according Euroscore, hemodynamical instability before induction of anesthesia, surgical procedure complexity and CPB duration. Absence of deleterious effects in SVR decrease when administering isoflurane during normothermic CPB was assumed but prospective comparative studies comparing effects of halogenated agents and other anesthetic agents are needed in order to confirm these findings.

Effect of isoflurane on the beta-adrenergic and endothelium-dependent relaxation of pig cerebral microvessels after cardiopulmonary bypass

We examined the direct vasomotor effect of isoflurane as well as its effect on endothelium-dependent and beta-adrenergic vasodilation of cerebral microcirculation following either normothermic cardiopulmonary bypass (CPB) or profoundly hypothermic CPB with circulatory arrest. Pigs were placed on CPB; the systemic temperature was either maintained at 37 degrees C or lowered to 15 degrees C with 60 minutes of circulatory arrest. After 2 hours of CPB, the animals were separated from CPB; 15 minutes later the brain was quickly harvested in cold Krebs solution. Control animals were not instrumented and their brains were similarly harvested. Arteries of approximately 100 microm were dissected and changes in diameter monitored by in vitro videomicroscopy. Following preconstriction with the thromboxane analogue U46619 1 micromol/L, percent relaxation to the endothelium-dependent dilator adenosine diphosphate (ADP) 10(-9) to 10(-4) mol/L, the endothelium-independent dilator sodium nitroprusside (SNP) 10(-9) to 10(-4) mol/L, or the beta-adrenergic agonist isoproterenol 10(-12) to 10(-4) mol/L was measured either in the presence or absence of isoflurane 2%. Additionally, with or without preconstriction with U46619 1 micromol/L, vessel diameter changes were monitored with increasing concentrations of isoflurane 0-3%. Dose-response curves were compared by two-way analysis of variance. Vasodilation to ADP or isoproterenol, but not SNP, was attenuated after normothermic CPB (N-CPB) or profoundly hypothermic CPB (PH-CPB). Although isoflurane attenuated vasodilation of control vessels to ADP or isoproterenol, isoflurane did not further attenuate vasodilation to ADP or isoproterenol after N-CPB or PH-CPB. The direct vasomotor effect of isoflurane depended on the preexisting tone of the vessels, constricting vessels without preconstriction and dilating them after preconstriction. These findings may have implications on the incidence of neuropsychological dysfunction after CPB and use of isoflurane.

IBC’s 5th Annual Conference on Blood Substitutes

IBC's 5(th) Annual Conference on Blood Substitutes was held on November 20-21, 1997. Approximately 100 medical researchers, academic scientists, blood substitute company speakers and representatives from major pharmaceutical companies with an interest or partner in the field attended. The papers presented focused on the progress in clinical trials for those compounds in human study, on preclinical models for predicting efficacy in humans, and on novel approaches and agents for the delivery of oxygen. Both perfluorocarbons (PFC) and haemoglobin-based oxygen carriers were described. Several lectures addressed the history of the field and future directions for laboratory and clinical investigation. The following is a summary of some of the presentations. This summary is divided into 3 sections. The first section provides a historical overview and discusses the changes in the perceived need for a blood substitute. Section 2 comprises an update of company activities. The final section focuses on likely future directions for laboratory and human clinical study.

Effect of isoflurane on skin-pressure-induced vasodilation

Since general anesthesia has been shown to attenuate endothelium-dependent vasodilation, it was of interest to verify whether general anesthesia would modify skin vasodilation in response to local pressure application, which is endothelium dependent. To study the effect of general anesthesia on pressure-induced vasodilation development, we examined the effects of low- and high-dose isoflurane. Skin blood flow was measured by laser Doppler flowmetry during 11.1 Pa s(-1) increases in locally applied pressure in anesthetized rats treated with low or high doses of isoflurane. Following the administration of low doses of isoflurane, skin blood flow increased from baseline, with increasing local pressure application (+37 +/- 10% at 2.0 kPa). The increase in skin blood flow was absent in rats treated with high doses (-20 +/- 5% at 2.0 kPa), even when the anesthesia-induced hypotension was corrected by gelofusine infusion (-20 +/- 10% at 2.0 kPa). Whereas sodium-nitroprusside-induced vasodilation developed following low and high doses of isoflurane, acetylcholine-induced vasodilation was impaired with high doses compared to low doses. These data show that pressure-induced vasodilation is abolished with high doses of anesthetics. It is not the anesthesia-induced hypotension, but the depth of anesthesia, which can lead to the disappearance of pressure-induced vasodilation by an alteration in endothelial function.

Fluid resuscitation of the patient with major trauma

Current reviews and consensus documents now recommend a more discriminating approach to the traditional practices of delivering liberal infusions of intravenous fluid to all major trauma patients with suspected or known major hemorrhage. The evolving evidence suggests that aggressive fluid resuscitation prior to hemostasis leads to additional bleeding through hydraulic acceleration of hemorrhage, soft clot dissolution, and dilution of clotting factors. Aggressive preoperative fluid infusion is still considered appropriate for unconscious patients without palpable blood pressure or for those with controllable hemorrhage (e.g. isolated extremity or head injury), However, the latest recommendations are to limit or delay intravenous fluid resuscitation preoperatively in those with uncontrollable hemorrhage (e.g. those with penetrating torso injuries), even if they are hypo-perfusing. Although most clinicians still generally support fluid resuscitation for multisystem blunt trauma, particularly with head injury, the most recent experimental data have begun to challenge this traditional practice as well, suggesting a 'slow infusion' approach when there is risk for uncontrolled internal bleeding. By providing oxygen delivery with slow, limited infusion, new hemoglobin-based oxygen carriers might help to resolve the current dilemma of having to limit preoperative resuscitation when there is risk of uncontrolled hemorrhage.

Isoflurane does not further impair microvascular vasomotion in a rat model of subarachnoid hemorrhage

PURPOSE

Since isoflurane is known to attenuate endothelium-dependent dilation (EDD) in normal cerebral arterioles, we examined whether the anesthetic has a similar effect and further impairs EDD in vessels exposed to SAH.

METHODS

Autologous blood was introduced in the subarachnoid space and the parietal lobe harvested. Control animals were sacrificed without introduction of blood. The response of microvessles to the endothelium-dependent dilator adenosine diphosphate (ADP) 10(-9)-10(-4) M, the endothelium-independent dilator nitroprusside 10(-9)-10(-4) M, and ET-1 10(-13)-10(-8) M was measured by videomicroscopy in the presence of 0-2 minimum alveolar concentration (MAC) of isoflurane.

RESULTS

Isoflurane attenuated EDD to ADP in control vessels [66 +/- 5% (control) vs 27 +/- 11% (2 MAC) dilation to ADP 10(-4) M, P < 0.05]. Although SAH was associated with reduced dilation to ADP, exposure to isoflurane did not further impair dilation to ADP after SAH [26 +/- 3% (SAH) vs 21 +/- 5% (SAH/2 MAC) dilation to ADP 10(-4) M, P = NS]. Dilation to nitroprusside was not affected by isoflurane or SAH. Constriction to ET-1 was reduced by 2 MAC of isoflurane [21 +/- 1% (control) vs 13 +/- 5% (2 MAC) constriction to ET-1 10(-8) M, P < 0.05], but not by 1 MAC of isoflurane in control vessels. Constriction to ET-1 was greatly attenuated by 1 or 2 MAC of isoflurane after SAH [32 +/- 5% (SAH) vs 18 +/- 4% (SAH/2 MAC) constriction to ET-1 10(-8) M, P < 0.05].

CONCLUSION

In rats, isoflurane does not further impair EDD after SAH and modulates the constrictive response to ET-1. Such an effect of isoflurane would not predispose the SAH-exposed vessels to vasospasm.

Halogenated volatile anesthetics inhibit carbon monoxide-stimulated soluble guanylyl cyclase activity in rat brain

BACKGROUND

Because of halogen contents, halogenated volatile anesthetics (HVA) have a similarity to nitric oxide (NO) in terms of great affinity for the ferrous ion. Interactions between HVA and NO at the ferrous ion of soluble guanylyl cyclase (sGC) have been reported in different tissues. Carbon monoxide (CO), a more stable gas than NO, activates sGC by the same mechanism as NO. This study was undertaken to examine the effect of HVA on CO-stimulated sGC activity in rat brain.

METHODS

Sprague-Dawley rat brain was homogenized and ultracentrifuged. The resulting supernatant was used as sGC fraction. The fraction was incubated with CO and HVA, and the activity of sGC was determined by measuring cyclic guanosine monophosphate (cGMP) production using an enzyme immunoassay in aliquots of the supernatant.

RESULTS

CO clearly increased cGMP production in a dose-dependent manner. Sevoflurane and isoflurane produced significant and dose-dependent inhibition of CO-stimulated sGC activity. There was no difference in the inhibitory effect between the two anesthetics. GTP dose-dependently increased CO-stimulated cGMP production. Both anesthetics decreased GTP production, but the inhibition by the anesthetics was not significant at higher GTP concentrations.

CONCLUSIONS

These results suggest that HVA can compete with CO at the ferrous ion of sGC and inhibit the activity of this enzyme.

Methylene blue, a soluble guanylyl cyclase inhibitor, reduces the sevoflurane minimum alveolar anesthetic concentration and decreases the brain cyclic guanosine monophosphate content in rats

The nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signal pathway plays an important role in anesthetic and analgesic effects. We sought to determine the involvement of inhibition of soluble guanylyl cyclase (sGC) in the anesthetic mechanism and site of action of volatile anesthetics. We examined the effect of intracerebroventricular (ICV) administration of methylene blue (MB), a sGC inhibitor, on the minimum alveolar anesthetic concentration (MAC) of sevoflurane and the brain cGMP content in rats in vivo. We also investigated the effect of sevoflurane on NO-stimulated sGC activity in vitro. The rats were divided into three groups. After the ICV administration of MB, sevoflurane MAC and brain cGMP contents were measured in the first group and the second group, respectively. In the third group, brain cGMP contents were determined after sevoflurane anesthesia without the ICV administration of MB to examine the direct effect of sevoflurane on brain cGMP contents. MB significantly decreased sevoflurane MAC and brain cGMP content in a dose-dependent manner. Sevoflurane itself also dose-dependently decreased cGMP contents in brain in vivo and inhibited the NO-stimulated sGC activity in vitro. These results suggest that the inhibition of the NO-cGMP signal pathway at the sGC level could be involved in anesthetic or analgesic effects, and the inhibitory effect of sevoflurane on sGC would be one of the sites of action of this anesthetic.

IMPLICATIONS

Because the nitric oxide-cyclic guanosine monophosphate signal pathway mediates nociception and the site of action of halogenated volatile anesthetics in uncertain, we examined the possible involvement of inhibition of soluble guanylyl cyclase in the anesthetic mechanism. The inhibitory effect of sevoflurane on soluble guanylyl cyclase could be one of sites of this anesthetic.

[Effects of anesthetic agents on arterial reactivity]

OBJECTIVE

To review the effects of halogenated and intravenous anaesthetics on arterial vasoreactivity.

DATA SOURCE

Articles were obtained from a MEDLINE review (search terms: 'vascular smooth muscle, endothelium' used separately or associated with following anaesthetic agents: 'halothane, isoflurane, enflurane, desflurane, sevoflurane, thiopentone, propofol, ketamine, etomidate'. Other sources included review articles and textbooks.

STUDY SELECTION AND DATA EXTRACTION

All experimental studies published since 1975 were analysed and pertinent data extracted.

DATA SYNTHESIS

Within the vascular wall, arterial vasoreactivity involves the endothelium and the vascular smooth muscle. In vivo, arterial vasoreactivity is regulated by neuronal, hormonal, and metabolic factors. In vitro, the direct action of anaesthetic agents on the vessel can be studied in the absence of such factors. In vitro studies with arterial rings have shown that inhalational anaesthetics directly decrease endothelium-independent contraction induced by various pharmacological agents. This direct effect of anaesthetics results from a decrease in intracellular calcium, mainly caused by an inhibition of transsarcoplasmic calcium influx. Volatile anaesthetics decrease endothelium-dependent vasorelaxation at a site(s) within the nitric oxide (NO) signalling pathway, located downstream from the NO-related receptors and upstream from guanylyl cyclase. They may also decrease endothelium-independent vasorelaxation by inhibiting NO activation of guanylate cyclase. Intravenous anaesthetics, such as propofol, barbiturates, ketamine and etomidate also decrease vasoconstriction by various degrees. Propofol is the most potent inhibitor of vasoconstriction and thiopental the least one. All these IV anaesthetics have been shown to inhibit in some circumstances both endothelium-dependent and -independent vasorelaxation. Further studies are required to enable a better understanding of the mechanism and the site of action of these vascular effects of anaesthetics. For example, the investigation of the effects of anaesthetic agents on vascular reactivity in diseases associated with endothelial dysfunction may indirectly provide insight into the role of endothelium.

Halothane attenuates nitric oxide relaxation of rat aortas by competition for the nitric oxide receptor site on soluble guanylyl cyclase

Endothelial cells play an important role in the regulation of vascular activity through the release of endothelium derived relaxing factor (EDRF) now believed to be nitric oxide (NO). NO and the NO donor drug nitroglycerin relax vascular smooth muscle by stimulating soluble guanylyl cyclase leading to elevation of intracellular levels of cyclic guanosine 3',5'-monophosphate (cGMP). Halothane has been shown to inhibit the action of NO on blood vessels. This study was designed to further investigate the mechanisms by which halothane attenuates NO-induced vascular relaxations. This was done by examining the effects of halothane on nitroglycerin and NO-induced relaxations in the presence and absence of the inhibitors of soluble guanylyl cyclase, methylene blue and 6-anilino-5,8-quinolinedione (LY 83583). Thoracic aortas from anesthetized male Sprague-Dawley rats were excised and cut into rings and the endothelium was removed. The aortic rings were suspended in organ baths containing Krebs solution and equilibrated at their optimal passive tension. When a stable plateau of contraction was produced by EC60 concentrations of norepinephrine, increasing concentrations of nitroglycerin or NO were added to the baths to relax the rings. This contraction-relaxation procedure was repeated three or four times. In some baths halothane was administered by a calibrated vaporizer 10 min before beginning the second procedure. Either methylene blue or LY 83583 was added to the baths 20 min before the third procedure. The combination of halothane, methylene blue or LY 83583 was added before the fourth procedure. Halothane, methylene blue or LY 83583 significantly inhibited nitroglycerin-induced relaxation individually. Halothane and LY 83583 also significantly inhibited NO-induced relaxations (5 x 10(-9)-3 x 10(-8) M and 5 x 10(-9)-3 x 10(-5) M, respectively) individually. The combination of halothane and methylene blue or halothane and LY 83583 significantly inhibited nitroglycerin-induced relaxation, also, the combination of halothane and LY 83583 significantly inhibited NO-induced relaxations. Halothane, methylene blue and LY 83583 treatment led to rightward shift in the concentration-effect curves. Halothane, in combination with methylene blue or LY 83583, produced inhibition equivalent to the sum of their individual effects. The present study demonstrates that the halothane, methylene blue and LY 83583 attenuate nitroglycerin and NO-induced relaxations of endothelium-denuded rat aortic rings. This suggests that halothane, methylene blue and LY 83583 may act through competitive antagonism at a common site of action on soluble guanylyl cyclase in the EDRF/NO relaxation pathway.

The current status of haemoglobin-based blood substitutes

Haemoglobin-based red cell substitutes have recently passed a myriad of safety studies and are now undergoing efficacy evaluation. There are numerous potential benefits with use of these solutions: they are readily available and have a long shelf-life; do not require typing and cross-matching; are free of viral or bacterial contamination; lack the immunosuppressive effects of blood; and have a much lower viscosity than blood. One-third of the 10 million units of blood transfused in the United States each year is utilized in the emergency setting. Therefore, a safe, effective substitute for blood should have significant impact upon the way we resuscitate bleeding patients. In this article, the current status of the various haemoglobin-based red cell substitutes is reviewed.

Isoflurane and halothane attenuate endothelium-dependent vasodilation in rat coronary microvessels

Volatile anesthetics attenuate endothelium-dependent vasodilation but the mechanism of attenuation remains controversial. The present study examines the mechanism of isoflurane- and halothane-mediated attenuation of endothelium-dependent vasodilation in Wistar rat coronary microvessels of about 100 microns internal diameter. The vessels were studied in vitro in a pressurized (40 mm Hg), no-flow state using video microscopy. After preconstriction of the vessels with the thromboxane analog U46619 1 microM, concentration response curves to acetylcholine (ACh), the calcium ionophore A23187, sodium nitroprusside (SNP), or the stable cyclic guanosine monophosphate (cGMP) analog 8-bromo-cGMP (Br-cGMP) were obtained in the presence of 0% (control), 1% or 2% isoflurane, or 1% or 2% halothane. Isoflurane 1% and 2% significantly attenuated vasodilation to ACh and A23187. Isoflurane 2%, but not 1%, attenuated vasodilation to SNP. Vasodilation to Br-cGMP was not affected by isoflurane. Halothane attenuated vasodilation to ACh, but had no effect on vasodilation to A23187, SNP, or Br-cGMP. We conclude that isoflurane attenuates endothelium-dependent vasodilation by impairing at least two distinct steps in the nitric oxide (NO)-cGMP pathway, the first being between endothelial increase of calcium and smooth muscle guanylate cyclase and the second being inhibition of soluble guanylate cyclase activity. These two steps appear to have different sensitivities to the effect of isoflurane. Halothane has an effect at the endothelial receptor level, but not any distal steps in the NO-cGMP pathway.