Morphine blocks the bradycardia associated with severe hemorrhage in the anesthetized rat

Effect of opioid receptors of the cuneiform nucleus on cardiovascular responses in normotensive and hypotensive hemorrhagic rats

The presence of opioid receptors in the cuneiform nucleus (CnF), which is a mesencephalic area, and their involvement in the central cardiovascular responses have been shown. Therefore, this study is designed to examine the possible role of mu- (μ) and delta- (δ) opioid receptors in the CnF in the cardiovascular responses in normotensive and hemorrhagic hypotensive rats. Following anesthesia and the recording of the blood pressure, the agonist and antagonist of μ- (morphine and naloxone) and δ- (D-Pen 2, 5]-Enkephalin hydrate (DPDPE) and naltridole) receptors were microinjected into the CnF. In the hemorrhagic groups, the drugs were microinjected into the nucleus 2 min after withdrawing 15 % of the total blood volume (TBV). Time-course changes (Δ) in the mean arterial pressure (MAP), systolic blood pressure (SBP), and heart rate (HR) were obtained and compared with the control and hemorrhage groups. Microinjecting morphine in both normotensive and hemorrhagic rats significantly decreased ΔSBP, ΔMAP, and ΔHR; also, naloxone significantly increased all these parameters. The cardiovascular effects of DPDPE and naltridole were not significant in the normotensive rats; however, DPDPE attenuated only the tachycardia induced by the hypotensive hemorrhage. The findings of this study revealed that the opioid receptors in the CnF had an inhibitory effect on the cardiovascular parameters in both normotensive and hypotensive hemorrhagic conditions and these effects were mostly mediated by μ-opioid receptors.

Haemodynamic changes in trauma

Trauma is the leading cause of death during the first four decades of life in the developed countries. Its haemodynamic response underpins the patient's initial ability to survive, and the response to treatment and subsequent morbidity and resolution. Trauma causes a number of insults including haemorrhage, tissue injury (nociception) and, predominantly, in military casualties, blast from explosions. This article discusses aspects of the haemodynamic responses to these insults and subsequent treatment. 'Simple' haemorrhage (blood loss without significant volume of tissue damage) causes a biphasic response: mean arterial blood pressure (MBP) is initially maintained by the baroreflex (tachycardia and increased vascular resistance, Phase 1), followed by a sudden decrease in MAP initiated by a second reflex (decrease in vascular resistance and bradycardia, Phase 2). Phase 2 may be protective. The response to tissue injury attenuates Phase 2 and may cause a deleterious haemodynamic redistribution that compromises blood flow to some vital organs. In contrast, thoracic blast exposure augments Phase 2 of the response to haemorrhage. However, hypoxaemia from lung injury limits the effectiveness of hypotensive resuscitation by augmenting the attendant shock state. An alternative strategy ('hybrid resuscitation') whereby tissue perfusion is increased after the first hour of hypotensive resuscitation by adopting a revised normotensive target may ameliorate these problems. Finally, morphine also attenuates Phase 2 of the response to haemorrhage in some, but not all, species and this is associated with poor outcome. The impact on human patients is currently unknown and is the subject of a current physiological investigation.

Combat Casualty Care research programme

The Combat Casualty Care research programme is an integrated suite of projects designed to address Defence Medical Services' research needs for casualty care. The programme covers a broad spectrum of topics ranging from the pathophysiological and immunological impact of military relevant injuries to the effects of these disturbances on the response to early treatment. Dstl Porton Down has a long history of studying military injuries and has developed models, both in vivo and physical, to address the research needs. The work is conducted in close collaboration with clinical colleagues at the Royal Centre for Defence Medicine who have direct experience of the clinical issues faced by combat casualties and insights into the potential clinical implications of emerging strategies. This article reviews progress in research areas spanning forward resuscitation, with a particular focus on blast-related injuries, trauma coagulopathy, effects of drugs on the response to haemorrhage and deployed research. A significant 'value added' component has been the underpinning of higher degrees for seconded military clinicians at Dstl Porton Down who have made a valuable contribution to the overall programme.

Modification of acute cardiovascular homeostatic responses to hemorrhage following mild to moderate traumatic brain injury

OBJECTIVES

The cardiovascular homeostatic responses to hemorrhage are coordinated in the central nervous system. Coincidental brain injury, which is present in 64% of trauma patients, could impair these responses. Our objective was to test the hypothesis that mild to moderate traumatic brain injury alters cardiovascular reflex responses to acute hemorrhage.

DESIGN

Experimental prospective, randomized study in terminally anesthetized rats.

SETTING

Experimental laboratory of university.

SUBJECTS

Twenty-four male Wistar rats weighing 240-260 g.

INTERVENTIONS

Brain injury was induced using the lateral fluid percussion injury model in anesthetized rats. The fluid percussion device delivered an applied cortical pressure of 1.2 atm and 1.8 atm, producing mild and moderate injury, respectively. Control animals underwent identical surgical procedures but with no applied cortical pressure. Hemorrhage was carried out 10 mins after brain injury, at a rate of 2% of blood volume per minute until 40% blood volume was withdrawn.

MEASUREMENTS AND MAIN RESULTS

The effects of acute traumatic brain injury on the biphasic heart rate and mean arterial blood pressure response to hemorrhage were studied. Traumatic brain injury attenuated the normal bradycardic response and delayed the hypotensive response to hemorrhage. This effect was graded according to the severity of brain injury. In mild injury, the depressor phase was delayed, but the biphasic pattern of heart rate response was maintained. No mortality was observed in this group. Following moderate brain injury, marked attenuation of the biphasic heart rate and mean arterial blood pressure response (p < .001 and p = .0007) was observed. Fifty percent of this group died within 90 mins of hemorrhage completion. Significant differences in the biphasic response were observed between survivors and nonsurvivors (p = .013, p = .001, respectively). In nonsurvivors, the biphasic response was abolished.

CONCLUSIONS

Acute mild and moderate traumatic brain injury disrupts cardiovascular homeostatic responses to extracranial hemorrhage; this disruption is graded according to the severity of traumatic brain injury. Severe disruption is associated with an increase in early mortality.

Central inhibition of opioid receptor subtypes and its effect on haemorrhagic hypotension in conscious sheep

AIM

To investigate the contribution of cerebral mu-, kappa- and delta-opioid receptors in causing the hypotension, bradycardia and renal hypoperfusion evoked by haemorrhage.

METHODS

Adult conscious ewes were bled continuously from a jugular vein until mean arterial blood pressure (MAP) was reduced to below 50 mmHg. Starting 30 min before and continuing until 60 min after haemorrhage either artificial cerebrospinal fluid (control), d-Phe-Cys-Tyr-d-Trp-Orn-Thr-Pen-Thr-NH(2) (CTOP micro-receptor antagonist), ICI 174,864 (delta-receptor antagonist) or nor-binaltorphimine dihydrochloride (nor-BNI, kappa-receptor antagonist) were infused intracerebroventricularly. In a randomized crossover fashion the effect of antagonizing one central opioid receptor subtype was compared to control experiments in the same animal (n = 6 in all groups).

RESULTS

Compared to corresponding controls, nor-BNI and ICI 174,864 significantly increased the haemorrhage volume needed to reduce MAP to below 50 mmHg (+4.7 mL kg(-1), SD 1.8 and +3.1 mL kg(-1), SD 3.0 respectively). In the nor-BNI group this was accompanied by a significantly augmented tachycardia before MAP fell. Both nor-BNI and ICI 174,864 also postponed haemorrhagic bradycardia and prolonged adequate blood flow to the kidney. The infusions did not affect the circulation per se or the recovery after haemorrhage. The micro-opioid receptor blockade had no effect on baseline circulation or the response to haemorrhage.

CONCLUSION

Activation of kappa- and delta-opioid receptors adjacent to the ventricular compartment contributes to initiating haemorrhagic hypotension and bradycardia in conscious sheep. However, other parts of the brain and different receptors are likely to play a role as well.

Activation of central opioid receptors determines the timing of hypotension during acute hemorrhage-induced hypovolemia in conscious sheep

After an initial compensatory phase, hemorrhage reduces blood pressure due to a widespread reduction of sympathetic nerve activity (decompensatory phase). Here, we investigate the influence of intracerebroventricular naloxone (opioid-receptor antagonist) and morphine (opioid-receptor agonist) on the two phases of hemorrhage, central and peripheral hemodynamics, and release of vasopressin and renin in chronically instrumented conscious sheep. Adult ewes were bled (0.7 ml x kg(-1) x min(-1)) from a jugular vein until mean arterial blood pressure (MAP) reached 50 mmHg. Starting 30 min before and continuing until 60 min after hemorrhage, either artificial cerebrospinal fluid (aCSF), naloxone, or morphine was infused intracerebroventricularly. Naloxone (200 microg/min but not 20 or 2.0 microg/min) significantly increased the hemorrhage volume compared with aCSF (19.5 +/- 3.2 vs. 13.9 +/- 1.1 ml/kg). Naloxone also increased heart rate and cardiac index. Morphine (2.0 microg/min) increased femoral blood flow and decreased hemorrhage volume needed to reduce MAP to 50 mmHg (8.9 +/- 1.5 vs. 13.9 +/- 1.1 ml/kg). The effects of morphine were abolished by naloxone at 20 microg/min. It is concluded that the commencement of the decompensatory phase of hemorrhage in conscious sheep involves endogenous activation of central opioid receptors. The effective dose of morphine most likely activated mu-opioid receptors, but they appear not to have been responsible for initiating decompensation as 1) naloxone only inhibited an endogenous mechanism at a dose much higher than the effective dose of morphine, and 2) the effects of morphine were blocked by a dose of naloxone, which, by itself, did not delay the decompensatory phase.

Tramadol enhances hepatic insulin sensitivity via enhancing insulin signaling cascade in the cerebral cortex and hypothalamus of 90% pancreatectomized rats

Clinical observation found that tramadol, mu opioid receptor (MOR) agonist and serotonin (5-HT) reuptake inhibitor, has a hypoglycemic effect in type 2 diabetes patients. The mechanism of its hypoglycemic effect has not been fully defined. This study showed that tramadol activated a neuronal insulin signaling cascade by increasing the induction of insulin receptor substrate-2 expression in primary cultured neuronal cells while this activation was suppressed by naloxone (MOR inhibitor) and dexamethasone (non-specific inhibitor of MOR and 5-HT receptor, DEX). Glucose utilization of the cerebral cortex and hypothalamus was enhanced by a 4-week-tramadol administration in 90% pancreatectomized rats, in vivo, as assessed by measurement of glucokinase expression and glycogen deposition via activating insulin signaling cascade such as neuronal cells in vitro. This improvement was almost completely suppressed by naloxone as well as DEX. Tramadol decreased fasted serum glucose levels, favored an increase in the glucose infusion rate and reduced endogeneous hepatic glucose production after 4 weeks of treatment. However, tramadol did not modulate hepatic glucose output directly, as exhibited by liver perfusion, suggesting tramadol altered hepatic glucose utilization through the effect of organs other than the liver, possibly the central nervous system. The data suggest that tramadol ameliorates peripheral glucose metabolism through central activation of MOR, and that central and peripheral glucose metabolism are therefore likely to be interrelated.

HEMODYNAMIC AND IMMUNE CONSEQUENCES OF OPIATE ANALGESIA AFTER TRAUMA/HEMORRHAGE

The regulation of compensatory hemodynamic, inflammatory, and metabolic counter-regulatory responses to traumatic injury (trauma/hemorrhage [tx/hem]) and subsequent inflammatory challenges during the post-tx/hem period relies on balanced activation of neuroendocrine and opioid pathways. Pharmacological interventions during the rescue period as well as during the early post-tx/hem period that target these regulatory pathways can potentially affect the activation or efficacy of compensatory mechanisms. Their impact on mechanisms involved in these responses has not been well defined. We examined the impact of morphine and ketamine on immediate hemodynamic responses to tx/hem as well as on the integrity of host defense mechanisms at day 5 post-tx/hem. Morphine (10 mg/kg), ketamine (18 mg/kg), or saline (0.3 ml) were injected intraperitoneally at 15 min post-tx/hem (soft tissue injury and fixed pressure hemorrhage, 40 mmHg, 60 min) and 15 min before lactated Ringer's fluid resuscitation (LRFR, 2.4x total blood volume removed). Morphine, but not ketamine, produced effective and sustained analgesia. Morphine and ketamine impaired the rise in mean arterial blood pressure (MABP) during LRFR and increased 48-h mortality (2- to 3-fold). Morphine and ketamine markedly (40%-80%) attenuated the systemic LPS- (100 microg/100 g body weight) induced TNF response at day 5 post-tx/hem. Morphine attenuated LPS-induced lung and spleen TNF expression, whereas ketamine enhanced spleen TNF expression but did not alter lung responses. Subsequent studies demonstrated that the morphine-induced impairment of the response was not due to altered cytokine responses during the early post-tx/hem period but that they could be restored and 24 h mortality could be reduced by increasing the volume of LRFR (2-fold). These results indicate that morphine and ketamine analgesia compromise the hemodynamic and host defense responses after tx/hem, directly affecting mortality and morbidity during the recovery period.

Action of κ and Δ opioid agonists on premotor cardiac vagal neurons in the nucleus ambiguus

Both enkephalin and dynorphin containing fibers are in close proximity to neurons in the nucleus ambiguus, including cardiac vagal neurons. Microinjection of Delta and kappa agonists into the nucleus ambiguus have been shown to evoke decreases in heart rate. Yet little is known about the mechanisms by which Delta and kappa opioid receptors alter the activity of cardiac vagal neurons. This study tests whether kappa and Delta opioid agonists can alter the activity of cardiac vagal neurons by modulating likely opioid targets including voltage gated calcium currents, and both glycinergic and GABA) neurotransmission to cardiac vagal neurons. Cardiac vagal neurons were identified in vitro by a fluorescent tracer and studied using patch clamp techniques. Neither the kappa agonist spiradoline or the Delta agonist [D-Pen(2), D-Pen(5)]enkephalin (DPDPE) modulated the voltage gated calcium currents in cardiac vagal neurons. DPDPE also did not alter either glycinergic or GABAergic synaptic neurotransmission. Spiradoline did not change GABAergic synaptic inputs, but did significantly inhibit glycinergic synaptic inputs to cardiac vagal neurons. At a concentration of 1 microM, spiradoline inhibited the amplitude of glycinergic events, and at a concentration of 5 microM, spiradoline inhibited both glycinergic amplitude and frequency. Spiradoline also inhibited both the amplitude and frequency of glycinergic miniature inhibitory post-synaptic currents, indicating kappa agonists likely act at both presynaptic and postsynaptic sites to inhibit glycinergic neurotransmission to cardiac vagal neurons.

Mu-opioid receptors are located postsynaptically and endomorphin-1 inhibits voltage-gated calcium currents in premotor cardiac parasympathetic neurons in the rat nucleus ambiguus

Activation of opioid receptors in the CNS evokes a dramatic decrease in heart rate which is mediated by increases in inhibitory parasympathetic activity to the heart. Injection of opiates into the nucleus ambiguus, where premotor cardiac parasympathetic nucleus ambiguus neurons are located elicits an increase in parasympathetic cardiac activity and bradycardia. However, the mechanisms responsible for altering the activity of premotor cardiac parasympathetic nucleus ambiguus neurons is unknown. This study examined at the electron microscopic level whether premotor cardiac parasympathetic nucleus ambiguus neurons possess postsynaptic opioid receptors and whether mu-opioid receptor agonists alter voltage-gated calcium currents in these neurons. Premotor cardiac parasympathetic nucleus ambiguus neurons were identified in the rat using retrograde fluorescent tracers. One series of experiments utilized dual-labeling immunocytochemical methods combined with electron microscopic analysis to determine if premotor cardiac parasympathetic nucleus ambiguus neurons contain mu-opioid receptors. In a second series of experiments whole cell patch clamp methodologies were used to determine whether activation of postsynaptic opioid receptors altered voltage-gated calcium currents in premotor cardiac parasympathetic nucleus ambiguus neurons in brainstem slices. The perikarya and 78% of the dendrites of premotor cardiac parasympathetic nucleus ambiguus neurons contain mu-opioid receptors. Voltage-gated calcium currents in premotor cardiac parasympathetic nucleus ambiguus neurons were comprised nearly entirely of omega-agatoxin-sensitive P/Q-type voltage-gated calcium currents. Activation of mu-opioid receptors inhibited these voltage-gated calcium currents and this inhibition was blocked by pretreatment with pertusis toxin. The mu-opioid receptor agonist endomorphin-1, but not the mu-opioid receptor agonist endomorphin-2, inhibited the calcium currents. In summary, mu-opioid receptors are located postsynaptically on premotor cardiac parasympathetic nucleus ambiguus neurons. The mu-opioid receptor agonist endomorphin1 inhibited the omega-agatoxin-sensitive P/Q-type voltage-gated calcium currents in premotor cardiac vagal nucleus ambiguus neurons. This inhibition is mediated via a G-protein mediated pathway which was blocked by pretreatment with pertusis toxin. It is possible that the inhibition of calcium currents may act to indirectly facilitate the activity of premotor cardiac parasympathetic nucleus ambiguus neurons by disinhibition, such as by a reduction in inhibitory calcium activated potassium currents.

Distribution of mu-opioid receptors in rat visceral premotor neurons

Agonists of the mu-opioid receptor (MOR) can modulate the activity of visceral premotor neurons, including cardiac premotor neurons. Neurons in brainstem regions containing these premotor neurons also contain dense concentrations of the MOR1. This study examined the distribution of MOR1 within two populations of visceral premotor neurons: one located in the dorsal motor nucleus of the vagus and the other in the nucleus ambiguus. Visceral premotor neurons contained the retrograde tracer Fluoro-Gold following injections of the tracer into the pericardiac region of the thoracic cavity. MOR1 was localized using immunogold detection of an anti-peptide antibody. Visceral premotor neurons in both regions contained MOR1 at somatic and dendritic sites, although smaller dendrites were less likely to contain the receptor than larger dendrites, suggesting there may be selective trafficking of MOR1 within these neurons. MOR1 labeling in nucleus ambiguus neurons was more likely to be localized to plasma membrane sites, suggesting that ambiguus neurons may be more responsive to opioid ligands than neurons in the dorsal motor nucleus of the vagus. In addition, many of the dendrites of visceral premotor neurons were in direct apposition to other dendrites. MOR1 was often detected at these dendro-dendritic appositions that may be gap junctions. Together these findings indicate that the activity of individual visceral premotor neurons, as well as the coupling between neurons, may be regulated by ligands of the MOR.

Cellular relations between mu-opioid receptive, GABAergic and reticulospinal neurons in the rostral ventrolateral medulla

Physiological studies have suggested that mu-opioid receptor (MOR) activation can both excite and inhibit reticulospinal neurons in the rostral ventrolateral medulla (RVL), possibly via influences on GABAergic neurons. Thus, to determine the cellular relationships of MORs to GABAergic neurons in the RVL, two experimental approaches were used. First, single sections through the RVL were labeled for MOR using immunoperoxidase detection and for GABA using immunogold detection and examined by electron microscopy. These studies revealed that MOR-immunoreactive (IR) terminals were smaller on average than GABA-IR terminals and formed both asymmetric and symmetric synapses, whereas GABA-IR terminals formed exclusively symmetric synapses. MOR and GABA immunoreactivities rarely co-localized. Interactions between axons and terminals containing MOR or GABA immunoreactivity were primarily: (1) direct appositions with each other; or (2) convergence onto a common dendritic target that sometimes contained either MOR or GABA immunoreactivity. Since the identity of these target dendrites mostly was unknown, a second study was designed to determine if they might be reticulospinal neurons. For this study, reticulospinal neurons were identified with a retrograde tracer and both MOR and GABA were localized in the same sections of the RVL. These studies revealed that numerous GABA-IR terminals formed symmetric synapses on the perikarya and proximal dendrites of reticulospinal neurons. In contrast, few MOR-IR terminals contacted reticulospinal perikarya and large dendrites although they were often found nearby. These results provide anatomical evidence that MOR activation by endogenous or exogenous agonists may indirectly alter GABAergic neurotransmission in the RVL either through presynaptic interactions between cells or through competing influences on postsynaptic targets.

Selective distribution of mu-opioid receptors in C1 adrenergic neurons and their afferents

Agonists of the mu-opioid receptor (MOR) have profound effects on blood pressure, heart rate, and respiration that may be mediated by C1 adrenergic neurons in the rostral ventrolateral medulla (RVL). C1 neurons are sympathoexcitatory and are involved in both tonic and reflex regulation of sympathetic outflow. This study was designed to determine whether C1 neurons, or their afferents, contain MOR. C1 neurons were identified by using an antibody against the epinephrine synthesizing enzyme phenylethanolamine-N-methyl transferase (PNMT), whereas MOR was localized by using an antipeptide antibody that recognizes the cloned MOR, MOR1. Combined immunoperoxidase and immunogold methods were used to examine the cellular distribution of MOR1 relative to PNMT-containing neurons in the RVL. MOR1 was found in 22% of PNMT-containing dendrites (n = 392), whereas MOR1-containing axons or axon terminals contacted 14% of PNMT-containing dendrites. This distribution was heterogenous with regard to dendritic size: PNMT-labeled dendrites containing MOR1 were usually large (60% were >1.2 microm), whereas PNMT-containing dendrites that received MOR1-labeled afferents were usually small (79% were <1.2 microm). Individual dendrites rarely contained MOR1 at both pre- and postsynaptic sites. Together these results suggest that MOR agonists may directly influence the activity of C1 neurons, as well as the activity of select afferents to these cells. Plasmalemmal membrane labeling for MOR1 was more frequent in smaller PNMT-containing dendrites, suggesting that postsynaptic receptors are more readily available for ligand binding in small dendrites, although the receptor was more frequently detected in larger PNMT dendrites. The selective distribution of MORs to specific pre- and postsynaptic sites suggests the receptor may be selectively trafficked to positions where it may regulate afferent activity that is heterogeneously distributed along the dendritic tree of C1 neurons.

Mu-opioid receptors are present in functionally identified sympathoexcitatory neurons in the rat rostral ventrolateral medulla

Agonists of the mu-opioid receptor (MOR) produce profound hypotension and sympathoinhibition when microinjected into the rostral ventrolateral medulla (RVL). These effects are likely to be mediated by the inhibition of adrenergic and other presympathetic vasomotor neurons located in the RVL. The present ultrastructural studies were designed to determine whether these vasomotor neurons, or their afferents, contain MORs. RVL bulbospinal barosensitive neurons were recorded in anesthetized rats and filled individually with biotinamide by using a juxtacellular labeling method. Biotinamide was visualized by using a peroxidase method and MOR was identified by using immunogold localization of an antipeptide antibody that recognizes the cloned MOR, MOR1. The subcellular relationship of MOR1 to RVL neurons with fast- or slow-conducting spinal axons was examined by electron microscopy. Fast- and slow-conducting cells were not morphologically distinguishable. Immunogold-labeling for MOR1 was found in all RVL bulbospinal barosensitive neurons examined (9 of 9). MOR1 was present in 52% of the dendrites from both types of cells and in approximately half of these dendrites the MOR1 was at nonsynaptic plasmalemmal sites. A smaller portion of biotinamide-labeled dendrites (16%) from both types of cells were contacted by MOR1-containing axons or axon terminals. Together, these results suggest that MOR agonists can directly influence the activity of all types of RVL sympathoexcitatory neurons and that MOR agonists may also influence the activity of afferent inputs to these cells. The heterogenous distribution of MORs within individual RVL neurons indicates that the receptor is selectively targeted to specific pre- and postsynaptic sites.

Bradycardia and hypotension associated with severe hemorrhage are reversed by morphine given centrally or peripherally in anesthetized rats

BACKGROUND

Severe simple hemorrhage (blood loss in the absence of tissue damage and nociception) leads to a reflex bradycardia and hypotension. Earlier studies showed that this reflex can be attenuated by prior administration of morphine. However, some patients may receive morphine, e.g., for analgesia after they have suffered severe hemorrhage. The aim of this study was to determine whether an established bradycardia and hypotension could be reversed by morphine.

METHODS

Four groups of male Wistar rats (236-258 g) were anesthetized with alphadolone/alphaxalone (16-19 mg x hg x h(-1) intravenously). All groups received a hemorrhage of 40% total blood volume (BV) at 2% BV x min(-1). After the loss of 27% BV, bradycardia and hypotension were established equally in groups I and II and III and IV. Groups I (n=8) and III (n=10) received 0.9% saline (20 microL intracerebroventricularly or 1 mL x kg(-1) intravenously, respectively), whereas groups II (n=10) and IV (n=10) received morphine (10 microg intracerebroventricularly or 0.5 mg x kg(-1) intravenously, respectively).

RESULTS

In groups I and III, heart rate and mean arterial blood pressure continued to fall, whereas the bradycardia was completely reversed and the hypotension partly reversed in groups II and IV after treatment with morphine.

CONCLUSION

Morphine, administered centrally or peripherally, can reverse the bradycardia and markedly can attenuate the hypotension associated with severe hemorrhage. However, any benefit may be more apparent than real because other studies suggest that mortality may be increased.