Attenuation of endothelium-mediated vasodilation by halothane

Modification of endothelium-dependent relaxation by propofol, ketamine, and midazolam

Since volatile anesthetics, barbiturates, and local anesthetics have been reported to inhibit endothelium-dependent relaxation, we hypothesized that any drug with anesthetic action would suppress this relaxation. In the present study, using rat thoracic aortae, we attempted to determine whether nonbarbiturate intravenous anesthetics, including midazolam, propofol, and ketamine, suppress endothelium-dependent relaxation, and to clarify the mechanism(s) involved. Acetylcholine-induced, endothelium-dependent relaxation was significantly attenuated by propofol and ketamine, but was unaffected by midazolam. Sodium nitroprusside (SNP)-induced relaxation was attenuated by propofol, but not by midazolam or ketamine. The acetylcholine-stimulated 3',5'-cyclic guanosine monophosphate (cGMP) level was reduced by pretreatment with propofol and ketamine but not by midazolam, and that stimulated by SNP was reduced by propofol but not by ketamine or midazolam. We conclude that propofol and ketamine suppress endothelium-dependent relaxation, whereas midazolam has no influence. Moreover, the suppressive effect of ketamine on endothelium-dependent relaxation is mediated by suppression of nitrous oxide (NO) formation, whereas that of propofol may be mediated at least partly by suppression of NO function.

Oxygen-derived free radicals mediate isoflurane-induced vasoconstriction of rabbit coronary resistance arteries

Isoflurane induces endothelium-dependent constriction of rabbit coronary resistance arteries in vitro. This effect is inhibited by the cyclooxygenase inhibitor indomethacin. To determine whether thromboxane or oxygen-derived free radicals, a byproduct in the cyclooxygenase pathway, mediate this effect, subepicardial coronary arterioles (103 +/- 21 mu) from New Zealand White rabbits were studied in vitro in a pressurized (40 mm Hg), no-flow state using videomicroscopy. The vessels were subjected to increasing concentrations of isoflurane, 0%-3%, in the presence of Dazmegrel (a specific inhibitor of thromboxane synthesis; Pfizer Ltd., Sandwich, UK) or SOD-Mn (manganese superoxide dismutase, a scavenger of superoxide radicals) or mannitol (hydroxyl radical scavenger) 20 or 100 mM or in their absence (control). The control vessels showed a concentration-dependent constriction to isoflurane (P < 0.0001), with reduction in internal diameter of 11.4% +/- 3.5% at isoflurane 3%. This response was unaffected by Dazmegrel (P = 0.78), but was abolished by SOD-Mn (P < 0.01) or mannitol (P < 0.01). We conclude that isoflurane causes concentration-dependent constriction of rabbit coronary resistance arteries and that this effect is mediated by oxygen-derived free radicals.

Inhibitory effect of sevoflurane on nitric oxide release from cultured endothelial cells

We investigated the effect of sevoflurane (fluoromethyl-2,2,2-trifluoro-1-(trifluoromethyl) ethylether) on intracellular calcium concentration ([Ca2+]i) and nitric oxide (NO) release from cultured porcine aortic endothelial cells using fura-2 fluorometry, and direct (ESR spectrometry with NO-trapping by 2-(4-carboxyphenyl)-4,4,5,5-tetramiethylimidazoline-1-oxyl 3-oxide) or indirect (nitrite accumulation measured by Greiss reaction) NO measurement. Sevoflurane alone did not change resting [Ca2+]i, but diminished bradykinin-induced transient increase in [Ca2+]i in a concentration-dependent manner. The inhibitory effect of sevoflurane on bradykinin-induced transient rise in [Ca2+]i was larger than that of a non-selective Ca2+ channel blocker (CO2+). Application of sevoflurane following bradykinin-evoked [Ca2+]i transient diminished [Ca2+]i significantly, while bradykinin B2 receptor antagonist (D-Arg-[Hyp3, Thi5,8, D-Phe7] bradykinin) or CO2+ abolished it. Sevoflurane impaired nitrite accumulation stimulated by bradykinin, and reduced the amount of NO released from endothelial cells. Our results indicate that the negative effect of sevoflurane appears to be due to the inhibition of bradykinin-induced Ca2+ efflux from endoplasmic stores and Ca2+ influx through membrane Ca2+ channels.

Nitric oxide-related agents alter alcohol withdrawal in male rats

Evidence has been reported supporting the hypothesis that nitric oxide (NO) partially mediates the expression of morphine dependence. To examine whether NO-related agents also affect the expression of alcohol dependence, adult male rats were treated chronically with alcohol. Upon withdrawal of alcohol administration, abstinence signs were observed after treatment with a NO synthase (NOS) inhibitor, NG-nitro-L-arginine methyl ester (NAME), or a NO donor, isosorbide dinitrate (ISDN). Withdrawal severity was based primarily on the presence and intensity of tremors, rigidity, hyperactivity, and spontaneous and audiogenic convulsions. The NOS inhibitor, NAME (10-100 mg/kg), injected during alcohol withdrawal significantly inhibited withdrawal severity decreasing the intensity of signs of hyperactivity, tremors, and rigidity, but not affecting the occurrence of convulsions. The NO donor, ISDN (30 mg/kg), administered during alcohol withdrawal significantly increased the severity of most withdrawal signs. These results suggest that NO mediates some aspects of the expression of alcohol dependence.

Effects of halogenated and non-halogenated anesthetics on diaspirin cross-linked hemoglobin induced contractions of porcine pulmonary veins

Diaspirin crosslinked hemoglobin (DCLHb) is a resuscitative fluid presently undergoing clinical trials. Administration of DCLHb is associated with an elevation of mean arterial pressure in vivo and contraction of isolated blood vessels in vitro. The mechanisms for the vascular actions are unknown but may be due to inhibition of nitric oxide (NO). Halothane has been reported to inhibit NO induced relaxation. We examined the effect of anesthetics on DCLHb induced contraction of blood vessels. Porcine pulmonary veins were excised, cut into rings and placed in organ chambers filled with 25 ml Krebs-Ringer solution (37 degrees C). Following equilibration at their optimal length the rings were exposed to increasing concentrations of serotonin(10(-8)M-10(-5)M). Endothelial activity was confirmed by relaxation greater than 80% with ACh (10(-6)M). DCLHb (1.5 x 10(-8)M to 6 x 10(-7)M) contracted porcine pulmonary veins (1.04 +/- 0.17g to 3.45 +/- 0.22g), and halothane (0.5% and 1%) significantly inhibited these DCLHb induced contractions in a dose-related manner (-41.6 +/- 8.1% and -73.3 +/- 8.2%, respectively). At equi-molar concentrations, isoflurane had no inhibitory activity. The relative effect of these volatile anesthetics is consistent with their inhibitory actions on other heme containing proteins. Propofol (10(-5)M) only has inhibitory effects on lower concentrations of DCLHb. Fentanyl did not have inhibitory effects. These results suggest that halogenated anesthetics may interact with the heme iron of DCLHb and inhibit its binding with NO.

Effects of preanesthetic and anesthetic drugs on endothelium-dependent responses in the rat aorta

1. Acetylcholine often fails to induce endothelium-dependent relaxation in human vessels in vitro. Due to the fact that most of these vessels come from surgery, we examined the influence of drugs used in anesthesia on endothelium-dependent responses in rat aorta. 2. Groups of male Wistar rats of the following treatments were utilized: P group, diazepam+promethazine+atropine; I group, pentothal+succinylcholine; IG group, halothane+nitrous oxide; M group, morphine+pancuronium; C group, untreated rats. Dose-response curves to noradrenaline and acetylcholine were determined in rat aorta in vitro, in the presence and absence of endothelium. 3. Acetylcholine induced more relaxation (P < 0.05) in the rat aorta of IG group compared with that of the C group. 4. In the rat aorta from P and IG groups, the contractions produced by several concentrations of noradrenaline were significantly smaller (P < 0.05) when the endothelium was removed. Similar effects occurred in aorta strips of animals previously treated with either atropine, promethazine, cimetidine or halothane. 5. Our results suggest that drugs currently used in anesthesia interfere with some endothelium-dependent effects on isolated rat aorta but according to these results they do not seem to be responsible for the lack of acetylcholine relaxation sometimes described in human vessels in vitro.

Vascular effects of halothane and isoflurane: cGMP dependent and independent actions

This study investigated the effects of halothane and isoflurane on cGMP-dependent and independent regulation of vascular contraction of the isolated rat aorta and on NO-stimulated soluble guanylate cyclase (sGC) isolated from the perfused rat liver. For the studies of the aorta, isometric tension of isolated rings, with and without, endothelium was recorded and cGMP content measured. ACh was used to initiate endothelial-dependent relaxation of norepinephrine (NE)-contracted rings while NO was used to directly stimulate isolated aortic ring sGC which catalyzes the isolated aortic ring formation of cGMP. Both halothane and isoflurane interfered with ACh and NO relaxations and with NO-stimulated increases in cGMP. Halothane was more potent, having significant attenuating effects at 0.34 mM (1 MAC) and 0.72 mM (2 MAC) while isoflurane had effects only at 0.53 mM (2 MAC). For the isolated sGC studies, a soluble liver fraction was prepared from perfused rat livers. In the absence of NO stimulation, neither halothane nor isoflurane modified the activity of the sGC. However, during NO-stimulation halothane produced significant, concentration-dependent, inhibition of sGC activity over a wide range of NO concentrations. Isoflurane also inhibited sGC activity, but to a lesser extent than halothane. The mechanism whereby the anesthetics could interfere with sGC from liver and blood vessels is unknown. It could result from anesthetic interaction at hydrophobic sites that may exist in GC. However, the results of both the aorta and liver sGC enzyme studies support the suggestion that these anesthetics can compete with NO for its binding site on the ferrous heme of sGC, with chemical structural differences accounting for the potency variations. Both anesthetics also had cGMP independent effects, causing concentration dependent relaxations of NE-contracted vessels without endothelium. Isoflurane was about 5 times more effective at 1 MAC than halothane. Therefore, the net effects of these anesthetics involve the sum of two opposite effects on tension of vessels with intact endothelium: 1) interference with NO-stimulated cGMP relaxation and 2) direct stimulation of relaxation (not dependent on changes in cGMP).

Effects of nitric oxide-related agents on alcohol narcosis

To examine whether nitric oxide (NO) affects alcohol (ethanol) narcosis, adult male rats were pretreated with a NO synthase (NOS) inhibitor, NG-nitro-l-arginine methyl ester (NAME); a NOS substrate, l-arginine methyl ester (AME); or a NO donor, isosorbide dinitrate (ISDN); then treated with anesthetic doses (3-5 g/kg, ip) of alcohol. Pretreatment with NAME (30-100 mg/kg, sc) 40 min before alcohol treatment delayed the onset of alcohol-induced loss of the righting reflex (LORR) and increased the duration of the LORR. NAME (100 mg/kg) pretreatment combined with high doses of alcohol (4-5 g/kg) exerted significant lethal effects, even though treatment with either agent alone or NAME combined with lower doses of alcohol (3-3.5 g/kg) was not lethal. Simultaneous treatment with the NOS substrate AME (100 mg/kg, subcutaneous) blocked the effects of NAME on LORR duration times, but did not alter LORR onset times. The NO donor ISDN (30 mg/kg) given by oral gavage 2 hr before alcohol decreased LORR duration times without affecting the onset of LORR. In addition, ISDN dose-dependently inhibited NAME-induced LORR duration increases during alcohol narcosis without significantly altering LORR onset times. Neither ISDN nor NAME significantly altered blood alcohol concentrations. These results suggest that NOS inhibition and subsequent decreases in NO production enhance alcohol-induced narcosis and that increases in NO concentrations inhibit alcohol narcosis, supporting the hypothesis that inhibition of arginine-NOS-NO systems mediates part of the sedative-hypnotic effect of alcohol.

Mechanisms of inhibition of endothelium-dependent relaxation by halothane, isoflurane, and sevoflurane

Volatile anaesthetics inhibit endothelium-dependent relaxation, but the underlying mechanism(s) have not been clarified. In an attempt to elucidate the mechanism(s), we determined the effects of halothane, isoflurane and sevoflurane on relaxation induced by acetylcholine and sodium nitroprusside (SNP) and the cGMP formation elicited by exogenous nitric oxide (NO) and SNP in rat aortas. Acetylcholine (10(-7)-10(-5) M)-induced relaxation was attenuated by halothane (2%), isoflurane (2%) and sevoflurane (4%). SNP (10(-8) M)-induced relaxation was reduced by halothane (2%), but not by isoflurane (2%) or sevoflurane (4%). The cGMP level of NO-stimulated aorta was reduced by halothane (2%) and sevoflurane (4%), but not by isoflurane (2%). The cGMP level of SNP (10(-7) M)-stimulated aorta was reduced by halothane (2%), but not by isoflurane (2%) and sevoflurane (4%). We conclude that the mechanisms responsible for the inhibition of endothelium-dependent relaxation differ among anaesthetics. Isoflurane inhibits the relaxation mainly by inhibiting the formation of NO in the endothelium. In contrast, the effect of halothane on endothelium-dependent relaxation may be largely due to the inhibition of action of NO in the vascular smooth muscle and the effect of sevoflurane may be to inactivate NO or to inhibit the action of NO.

Diminished effect of inhibition of nitric oxide synthase on regional cerebral vascular resistance in conscious and in isoflurane anesthetized rats during hemorrhage

Effects of a nitric oxide (NO) synthase inhibitor on regional cerebral vascular resistance (rCVR) and regional cerebral blood flow (rCBF) were studied during a severe hemorrhage in conscious and in isoflurane anesthetized groups of rats. Half of each group was infused with NG-nitro-L-arginine-methyl ester (L-NAME), a NO synthase inhibitor, at a rate of 2 mg.kg-1.min-1 for 30 min. Half of the L-NAME infused and half of the normal saline infused rats were bled to reduce the mean arterial blood pressure (MAP) to 44-49 mmHg. rCBF was measured using [14C]iodoantipyrine. rCVR was calculated as the ratio of MAP to rCBF. In the conscious non-hemorrhagic rats, L-NAME markedly increased rCVR in all the brain regions that we studied. In the conscious rats without L-NAME treatment, hemorrhage decreased rCVR in most of the brain regions. With L-NAME treatment in this group, hemorrhage increased rCVR only in the rostral part of the brain. Isoflurane decreased rCVR in most of the brain regions except the cortical area. L-NAME markedly increased rCVR in all the brain regions that we studied in the isoflurane anesthetized rats. In the isoflurane anesthetized rats, hemorrhage did not reduce rCVR in any of the brain regions. In the isoflurane anesthetized hemorrhagic rats, L-NAME did not significantly affect rCVR in any of the brain regions that we studied. We found that L-NAME increased rCVR to a greater extent in the non-hemorrhagic rats than in the hemorrhagic rats in both the conscious and in the isoflurane anesthetized rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Halothane inhibits the pressor effect of diphenyleneiodonium

1. We have recently found that diphenyleneiodonium (DPI), a novel inhibitor of nitric oxide (NO) synthase, causes pressor and tachycardic responses in pentobarbitone- but not halothane-anaesthetized rats. The present study investigated the mechanism by which halothane suppresses the pressor response of DPI. The effects of halothane on the pressor response of DPI were also compared with those of other anaesthetic agents. 2. In conscious rats, i.v. bolus injections of DPI (0.025- 1.6 mg kg-1) caused dose-dependent increases in mean arterial pressure (MAP), with ED90 of 0.07 +/- 0.01 mg kg-1 and maximal rise of MAP (Emax) of 59 +/- 2 mmHg. While ketamine potentiated Emax without altering the ED50 and pentobarbitone increased the ED50 without changing Emax of the pressor response to DPI, chloralose, urethane and ethanol displaced the curve to the right and potentiated Emax. In contrast, halothane (0.5-1.25%) dose-dependently and non-competitively reduced the pressor responses to DPI. 3. Intravenous bolus injection of a single dose of DPI (1.6 mg kg-1) caused immediate and large increases in plasma noradrenaline and adrenaline, as well as MAP in conscious rats. Halothane (1.25%) almost completely inhibited these increases. 4. The results suggest that DPI causes a pressor response in conscious rats by activating the sympathetic nervous system and halothane abolishes this pressor response by inhibiting activities of the sympathetic nervous system. The results also show that influences of anaesthetics must be taken into consideration when evaluating pressor response of vasoactive agents.

Alteration of calcium mobilization in endothelial cells by volatile anesthetics

Halothane and isoflurane have different effects on the peripheral vasculature. Halothane decreases blood pressure primarily by decreasing cardiac contractility, whereas isoflurane acts primarily as a peripheral vasodilator. These peripheral vascular actions may result from different effects of the anesthetics on endothelial cell function and the release of endothelium-derived vasoactive mediators. The ability of these agents at clinically relevant concentrations to alter agonist-induced calcium mobilization in single cultured bovine aortic endothelial cells was tested using the fluorescent indicator fura-2. Neither halothane (0.3, 0.5, and 2 mM) or isoflurane (0.5 and 2 mM) altered basal calcium ([Ca]i = 49 +/- 5 nM); however, the calcium transient normally elicited by 10 nM bradykinin (peak [Ca]i = 307 +/- 22 nM) was inhibited significantly by halothane but not isoflurane. Neither anesthetic altered the calcium response to ATP (10 microM). These findings suggest that anesthetics may have specific effects on receptor-mediated endothelial cell functions that could influence hemodynamics.

Endothelial vasomotor regulation in health and disease

The purpose of this review is to provide the anaesthetists with a comprehensive update on the endothelial-cell control of local blood flow. This single cell layer was originally thought to represent only a passive barrier. It is now evident that it plays an active role in a broad variety of biological functions. Since the discovery of the endothelial-derived relaxing factor (EDRF), it has been the subject of a considerable amount of research. It is established that EDRF is secreted continuously at a basal state and that many physical stimuli as well as vasoactive substances can modulate its secretion. Evidence presented indicates that the endogenous vasodilatation produced by EDRF is similar to that of the exogenous nitrovasodilator nitroglycerin and nitroprusside (i.e., nitric oxide). Aside from EDRF, the endothelium produces other vasodilating as well as vasoconstricting factors. A review of the physiology of the endothelium regarding the local control of blood flow is provided along with its influence upon several pathophysiological states. Also included is an overview of the influence of anaesthetic agents on endothelial function. These findings linking vasomotor control to endothelial function will help to explain pathophysiological process and may lead to new therapeutic modalities.

Cerebrovascular responses to carbon dioxide in children anaesthetized with halothane and isoflurane

To determine the effects of isoflurane and halothane on cerebrovascular reactivity to CO2, 30 children aged one to six years were anaesthetized with isoflurane or halothane in an air and oxygen mixture with an FIO2 of 0.3. The end-tidal concentrations (0.5 minimum alveolar concentration (MAC) or 1.0 MAC) of isoflurane or halothane were age-adjusted. After achieving a steady-state at both 0.5 MAC and 1.0 MAC isoflurane and halothane, the end-tidal carbon dioxide tension (PETCO2) was randomly adjusted to 20, 40, or 60 mmHg. Cerebral blood flow velocity (CBFV) and the cerebrovascular resistance index (RI+) in the middle cerebral artery (MCA) were measured by a transcranial Doppler monitor. Three measurements of CBFV and RI+ were obtained at each PETCO2 and isoflurane or halothane concentration. Any rise in the PETCO2 caused an increase in CBFV during both 0.5 MAC (r2 = 0.99 and 0.99) and 1.0 MAC (r2 = 0.96 and 0.95) isoflurane and halothane anaesthesia, respectively (P less than 0.05). The CBFV for isoflurane increased as PETCO2 increased from 20 to 60 mmHg for both 0.5 MAC and 1.0 MAC (P less than 0.05). The CBFV for halothane increased as PETCO2 increased from 20 to 40 mmHg for both 0.5 MAC and 1.0 MAC halothane (P less than 0.05), but did not change as PETCO2 increased from 40 to 60 mmHg for both 0.5 MAC and 1.0 MAC halothane. The RI+ showed an inverse relationship with CBFV at each PETCO2 for 0.5 MAC (r2 = 0.98 and 0.99) and 1.0 MAC (r2 = 0.76 and 0.53) isoflurane and halothane, respectively (P less than 0.05). The CBFV did not differ significantly between 0.5 and 1.0 MAC isoflurane and halothane at corresponding PETCO2 values. The cerebrovascular response to CO2 at 20 mmHg between 0.5 MAC and 1.0 MAC halothane was not significantly different. These data strongly suggest that isoflurane and halothane in doses up to 1.0 MAC do not affect the cerebrovascular reactivity of the MCA to CO2 in anaesthetized, healthy children.

Endothelium-derived relaxing factor: basic review and clinical implications

EDRF is a potent, endogenous vasodilator that is produced and released from endothelial cells and subsequently causes the relaxation of VSM through the activation of soluble guanylate cyclase and an increase in VSM cyclic GMP. Structurally, EDRF is likely to be NO or a related nitrogen oxide-containing compound. It is synthesized in endothelial and other cell types from L-arginine by a calcium-calmodulin and NADPH-dependent enzyme. Its action is very similar to the nitrovasodilators that act directly on VSM. EDRF is present in all vascular beds, large and small vessels, and in a wide range of species. Its role in human vascular physiology and pathophysiology is just beginning to be understood. EDRF is a potent endogenous vasodilator and inhibitor of platelet aggregation and adhesion. Its activity is impaired in hypertension and atherosclerosis, and its absence due to endothelial damage may play a role in cerebral and coronary vasospasm. It is a mediator of flow-dependent vasodilation, and its inhibition by hypoxia may contribute to the hypoxic pulmonary vasoconstrictor response. Endothelial cell damage and impairment of EDRF production may also contribute to acute and chronic pulmonary hypertension. A further understanding of the chemical nature and synthetic pathways of EDRF should lead to the production of analogs and antagonists, which may play an important role in future treatments for atherosclerosis, myocardial infarction, angina, hypertension, and other vascular diseases. The recent realization that EDRF serves as the second messenger for guanylate cyclase activation and cyclic GMP production in a variety of cell types outside of the cardiovascular system, including renal and respiratory epithelium, cerebellar neurons, macrophages, and adrenocytes, suggests even broader implications. The importance of EDRF to the anesthesiologist may go beyond an understanding of its role in cardiovascular physiological and pathophysiological states. Initial studies have shown that the endothelium may play a role in mediating the vascular actions of anesthetics, and that anesthetics can inhibit the production, release, or action of EDRF. How are these interactions mediated? Are there significant differences between anesthetics with regard to their effects on EDRF? Is there a clinically significant effect of anesthetics on basal activity of EDRF, or only in response to exogenous stimulation? Conversely, it is important to determine if alterations in endothelial cell function by various disease states such as hypertension, atherosclerosis, adult respiratory distress syndrome, cerebral vasospasm, and others cause changes in the vascular actions of anesthetics. The potential interactions of anesthetics with EDRF production and action in cell types other than the endothelium have not yet been explored.(ABSTRACT TRUNCATED AT 400 WORDS)

Manipulation of the radiosensitivity of pig epidermis by changing the concentration of oxygen and halothane in the anaesthetic gas mixture

A gas mixture of halothane, oxygen and nitrous oxide has been used to anesthetize pigs for irradiation. The effects of various concentrations of halothane and oxygen on the radiosensitivity of the epidermis were examined after irradiation with single doses of beta-rays from strontium-90 plaques. The incidence of moist desquamation was used as an endpoint, and experiments were compared on the basis of the dose associated with a 50 per cent incidence of moist desquamation (ED50 +/- SE). For pigs inspiring an anaesthetic gas mixture of 2 per cent halothane, approximately 70 per cent oxygen and approximately 30 per cent nitrous oxide the ED50 for moist desquamation was 27.32 +/- 0.52 Gy. A similar ED50 value of 27.39 +/- 1.20 Gy was obtained when 4 per cent halothane was used in place of 2 per cent. When the pigs were breathing air (approximately 21 per cent oxygen) in place of oxygen and nitrous oxide the ED50 values were increased significantly to 31.25 +/- 0.94 Gy and 33.72 +/- 1.08 Gy for 2, and 4 per cent halothane, respectively. This change in the radiosensitivity of the epidermis was represented by dose modification factors of approximately 1.13 and approximately 1.23 for 2 and 4 per cent halothane, respectively. Irradiation with a high oxygen concentration in the inspired gas mixture did not result in any significant variation of the dose required to produce moist desquamation in 50 per cent of the fields irradiated for dorsal, lateral and ventral positioned skin fields on the flank. However, pigs breathing air and halothane during irradiation showed marked differences in the radiosensitivity of the various sites on the flank, with ED50 values for moist desquamation of approximately 37 Gy and 26-30 Gy for dorsal and ventral positioned fields, respectively. This marked difference in radiosensitivity suggests variations in the physiological compensation over the flank when pigs are breathing oxygen at low concentrations under anaesthesia.

Neurogenic vasodilation in the rat hairy skin measured using a laser Doppler flowmeter

Intradermal stimulation of the saphenous nerve of anesthetized rats at C-fiber strength elicited stimulus-dependent vasodilator responses in saphenous-innervated hairy skin. A laser Doppler flowmeter (Periflux, Pf1d) was used to measure these neurovascular responses non-invasively. Capsaicin pretreatment significantly attenuated the vasodilator response. Furthermore, intraperitoneal administration of atropine or mepyramine significantly reduced the skin vascular responses. The responses of halothane-anesthetized rats were significantly attenuated when compared with rats anesthetized with pentobarbitone. Results of this study suggest the presence of endothelium-dependent vasodilator peptidergic, cholinergic and histaminergic contributions to electrically-evoked axon reflex vasodilation in the rat hairy skin.

Endothelium-dependent vascular smooth muscle control

Recent pharmacologic evidence supports the importance of the integrity of the endothelium in modulating vascular reactivity. The endothelial cells produce one or more endothelium derived relaxing factor(s) or EDRF that cause relaxation of vascular smooth muscle cells through production of cyclic guanosine monophosphate (GMP) and subsequent activation of protein kinase. While the molecular pharmacology of vascular relaxation is now well defined and numerous factors have been identified that inhibit or stabilize EDRF, the chemical identity of EDRF still is uncertain. Nitric oxide appears to be one such EDRF. Alterations in vasoreactivity observed during surgical manipulation, trauma, inhalational anesthesia, atherosclerosis, and other disease states can now be explained by their influence on the endothelial cells and EDRF. Further, it is now clear that nitrovasodilators act directly on the vascular smooth muscle cell to produce biological intermediates that mimic the endogenous factors. While anesthesiologists and critical care physicians have traditionally focused on hormonal and nervous system control of vascular reactivity, the effects of various drugs and manipulations on EDRF appear to be of clinical importance. In this manuscript we review the pharmacology of EDRF and of exogenous nitrovasodilators with particular reference to factors that can modulate vasoreactivity.