Chronic mu-opioid receptor stimulation alters cardiovascular regulation in humans: differential effects on muscle sympathetic and heart rate responses to arterial hypotension

Low-dose sufentanil does not affect tolerance to LBNP-induced central hypovolemia or blood pressure responses during a cold pressor test

Hemorrhage is a leading cause of death in the prehospital setting. Since trauma-induced pain often accompanies a hemorrhagic insult, the administered pain medication must not interfere with critical autonomic regulation of arterial blood pressure and vital organ perfusion. The purpose of this study was to test two unrelated hypotheses: 1) sublingual sufentanil (Dsuvia) impairs tolerance to progressive central hypovolemia and 2) sublingual sufentanil attenuates pain sensation and the accompanying cardiovascular responses to a noxious stimulus. Twenty-nine adults participated in this double-blinded, randomized, crossover, placebo-controlled trial. After sublingual administration of sufentanil (30 μg) or placebo, participants completed a progressive lower-body negative pressure (LBNP) challenge to tolerance (aim 1). After a recovery period, participants completed a cold pressor test (CPT; aim 2). Addressing the first aim, tolerance to LBNP was not different between trials (P = 0.495). Decreases in systolic blood pressure from baseline to the end of LBNP also did not differ between trials (time P < 0.001, trial P = 0.477, interaction P = 0.587). Finally, increases in heart rate from baseline to the end of LBNP did not differ between trials (time P < 0.001, trial P = 0.626, interaction P = 0.424). Addressing the second aim, sufentanil attenuated perceived pain (P < 0.001) in response to the CPT, though the magnitude of the change in mean blood pressure during the CPT (P = 0.078) was not different between trials. These data demonstrate that sublingual sufentanil does not impair tolerance to progressive central hypovolemia. Additionally, sublingual sufentanil attenuates perceived pain, but not the accompanying mean blood pressure responses to the CPT.NEW & NOTEWORTHY Addressing two unique aims, we observed that sublingual sufentanil administration does not impair tolerance or cardiovascular responses to lower-body negative pressure (LBNP)-induced progressive central hypovolemia. Second, despite pain perception being reduced, sublingual sufentanil did not attenuate mean blood pressure responses to a cold pressor test (CPT).

Low-dose morphine reduces tolerance to central hypovolemia in healthy adults without affecting muscle sympathetic outflow

Hemorrhage is a leading cause of preventable battlefield and civilian trauma deaths. Low-dose (i.e., an analgesic dose) morphine is recommended for use in the prehospital (i.e., field) setting. Morphine administration reduces hemorrhagic tolerance in rodents. However, it is unknown whether morphine impairs autonomic cardiovascular regulation and consequently reduces hemorrhagic tolerance in humans. Thus, the purpose of this study was to test the hypothesis that low-dose morphine reduces hemorrhagic tolerance in conscious humans. Thirty adults (15 women/15 men; 29 ± 6 yr; 26 ± 4 kg·m-2, means ± SD) completed this randomized, crossover, double-blinded, placebo-controlled trial. One minute after intravenous administration of morphine (5 mg) or placebo (saline), we used a presyncopal limited progressive lower-body negative pressure (LBNP) protocol to determine hemorrhagic tolerance. Hemorrhagic tolerance was quantified as a cumulative stress index (mmHg·min), which was compared between trials using a Wilcoxon matched-pairs signed-rank test. We also compared muscle sympathetic nerve activity (MSNA; microneurography) and beat-to-beat blood pressure (photoplethysmography) during the LBNP test using mixed-effects analyses [time (LBNP stage) × trial]. Median LBNP tolerance was lower during morphine trials (placebo: 692 [473-997] vs. morphine: 385 [251-728] mmHg·min, P < 0.001, CI: -394 to -128). Systolic blood pressure was 8 mmHg lower during moderate central hypovolemia during morphine trials (post hoc P = 0.02; time: P < 0.001, trial: P = 0.13, interaction: P = 0.006). MSNA burst frequency responses were not different between trials (time: P < 0.001, trial: P = 0.80, interaction: P = 0.51). These data demonstrate that low-dose morphine reduces hemorrhagic tolerance in conscious humans. Thus, morphine is not an ideal analgesic for a hemorrhaging individual in the prehospital setting.NEW & NOTEWORTHY In this randomized, crossover, placebo-controlled trial, we found that tolerance to simulated hemorrhage was lower after low-dose morphine administration. Such reductions in hemorrhagic tolerance were observed without differences in MSNA burst frequency responses between morphine and placebo trials. These data, the first to be obtained in conscious humans, demonstrate that low-dose morphine reduces hemorrhagic tolerance. Thus, morphine is not an ideal analgesic for a hemorrhaging individual in the prehospital setting.

Orthostatic intolerance after fast-track knee arthroplasty: Incidence and hemodynamic pathophysiology

BACKGROUND

Early postoperative mobilization can be hindered by orthostatic intolerance (OI) due to failed orthostatic cardiovascular regulation. The underlying mechanisms are not fully understood and specific data after total knee arthroplasty (TKA) are lacking. Therefore, we evaluated the incidence of OI and the cardiovascular response to mobilization in fast-track TKA.

METHODS

This prospective observational cohort study included 45 patients scheduled for primary TKA in spinal anesthesia with a multimodal opioid-sparing analgesic regime. OI and the cardiovascular response to sitting and standing were evaluated with a standardized mobilization procedure preoperatively, and at 6h and 24h postoperatively. Hemodynamic variables were measured non-invasively (LiDCO™ Rapid). Perioperative bleeding, fluid balance, surgery duration, postoperative hemoglobin, opioid use and pain during mobilization were recorded.

RESULTS

Eighteen (44%) and 8 (22%) patients demonstrated OI at 6 and 24h after surgery respectively. Four (10%) and 2 (5%) patients experienced severe OI and terminated the mobilization procedure prematurely. Dizziness was the most common OI symptom during mobilization at 6h. OI was associated with decreased orthostatic responses in systolic, diastolic, mean arterial pressures and heart rate (all p<0.05), while severe OI patients demonstrated impaired diastolic, mean arterial pressures, heart rate and cardiac output responses (all p<0.05). No statistically significant differences in perioperative bleeding, fluid balance, surgery duration, postoperative hemoglobin, pain or opioid use were observed between orthostatic tolerant and intolerant patients.

CONCLUSION

Early postoperative OI is common following fast-track TKA. Pathophysiologic mechanisms include impaired orthostatic cardiovascular responses. The progression to severe OI symptoms appears to be primarily due to inadequate heart rate response.

Cardiac Protective Role of Heat Shock Protein 27 in the Stress Induced by Drugs of Abuse

Heat shock proteins (HSP) are induced after different stress situations. Some of these proteins, particularly HSP-27, function as markers to indicate cellular stress or damage and protect the heart during addictive processes. Morphine withdrawal induces an enhancement of sympathetic activity in parallel with an increased HSP-27 expression and phosphorylation, indicating a severe situation of stress. HSP-27 can interact with different intracellular signaling pathways. Propranolol and SL-327 were able to antagonize the activation of hypothalamic-pituitary adrenal (HPA) axis and the phosphorylation of HSP-27 observed during morphine withdrawal. Therefore, β-adrenergic receptors and the extracellular signal-regulated kinase (ERK) pathway would be involved in HPA axis activity, and consequently, in HSP-27 activation. Finally, selective blockade of corticotrophin releasing factor (CRF)-1 receptor and the genetic deletion of CRF1 receptors antagonize cardiac adaptive changes. These changes are increased noradrenaline (NA) turnover, HPA axis activation and decreased HSP-27 expression and phosphorylation. This suggests a link between the HPA axis and HSP-27. On the other hand, morphine withdrawal increases µ-calpain expression, which in turn degrades cardiac troponin T (cTnT). This fact, together with a co-localization between cTnT and HSP-27, suggests that this chaperone avoids the degradation of cTnT by µ-calpain, correcting the cardiac contractility abnormalities observed during addictive processes. The aim of our research is to review the possible role of HSP-27 in the cardiac changes observed during morphine withdrawal and to understand the mechanisms implicated in its cardiac protective functions.

Effects of anesthetic and sedative agents on sympathetic nerve activity

BACKGROUND

The effects of sedative and anesthetic agents on sympathetic nerve activity (SNA) are poorly understood.

OBJECTIVE

The purpose of this study was to determine the effects of commonly used sedative and anesthetic agents on SNA in ambulatory dogs and humans.

METHODS

We implanted radiotransmitters in 6 dogs to record stellate ganglion nerve activity (SGNA), subcutaneous nerve activity (ScNA), and blood pressure (BP). After recovery, we injected dexmedetomidine (3 μg/kg), morphine (0.1 mg/kg), hydromorphone (0.05 mg/kg), and midazolam (0.1 mg/kg) on different days. We also studied 12 human patients (10 male; age 68.0 ± 9.1 years old) undergoing cardioversion for atrial fibrillation with propofol (0.77 ± 0.18 mg/kg) or methohexital (0.65 mg/kg) anesthesia. Skin sympathetic nerve activity (SKNA) and electrocardiogram were recorded during the study.

RESULTS

SGNA and ScNA were significantly suppressed immediately after administration of dexmedetomidine (P = .000 and P = .000, respectively), morphine (P = .011 and P = .014, respectively), and hydromorphone (P = .000 and P = .012, respectively), along with decreased BP and heart rate (HR) (P <.001 for each). Midazolam had no significant effect on SGNA and ScNA (P = .248 and P = .149, respectively) but increased HR (P = .015) and decreased BP (P = .004) in ambulatory dogs. In patients undergoing cardioversion, bolus propofol administration significantly suppressed SKNA (from 1.11 ± 0.25 μV to 0.77 ± 0.15 μV; P = .001), and the effects lasted for at least 10 minutes after the final cardioversion shock. Methohexital decreased chest SKNA from 1.59 ± 0.45 μV to 1.22 ± 0.58 μV (P = .000) and arm SKNA from 0.76 ± 0.43 μV to 0.55 ± 0.07 μV (P = .001). The effects lasted for at least 10 minutes after the cardioversion shock.

CONCLUSION

Propofol, methohexital, dexmedetomidine, morphine, and hydromorphone suppressed, but midazolam had no significant effects on, SNA.

Evaluation of the Effects of a Monthly Buprenorphine Depot Subcutaneous Injection on QT Interval During Treatment for Opioid Use Disorder

Extensive 12‐lead electrocardiogram monitoring and drug concentrations were obtained during development of BUP‐XR, a monthly subcutaneous injection for the treatment of opioid use disorder (OUD). Matched QT and plasma drug concentrations (11,925) from 1,114 subjects were pooled from 5 studies in OUD. A concentration‐QT model was developed, which accounted for confounding factors (e.g., comedications) affecting heart rate and heart rate‐corrected QT interval (QTc). Bias‐corrected nonparametric two‐sided 90% confidence intervals (CIs) were derived for the mean predicted effect of BUP‐XR on QTc (ΔQTc) at therapeutic and supratherapeutic doses. Changes in QTc were associated with age, central vs. noncentral reading, sex, methadone, and barbiturates. The upper 90% CI of ΔQTc was 0.29, 0.67, and 1.34 ms at the steady‐state peak concentration (C_max) for 100, 300, and 2 × 300 mg doses, respectively. An effect of BUP‐XR on QT can be ruled out at therapeutic and supratherapeutic doses of BUP‐XR, after accounting for covariates that may influence heart rate and QT interval in OUD.

Adverse Drug Reactions in the Intensive Care Unit

Adverse drug reactions (ADRs) are undesirable effects of medications used in normal doses [1]. ADRs can occur during treatment in an intensive care unit (ICU) or result in ICU admissions. A meta-analysis of 4139 studies suggests the incidence of ADRs among hospitalized patients is 17% [2]. Because of underreporting and misdiagnosis, the incidence of ADRs may be much higher and has been reported to be as high as 36% [3]. Critically ill patients are at especially high risk because of medical complexity, numerous high-alert medications, complex and often challenging drug dosing and medication regimens, and opportunity for error related to the distractions of the ICU environment [4]. Table 1 summarizes the ADRs included in this chapter.

Decreased heart rate variability responses during early postoperative mobilization--an observational study

BACKGROUND

Intact orthostatic blood pressure regulation is essential for early mobilization after surgery. However, postoperative orthostatic hypotension and intolerance (OI) may delay early ambulation. The mechanisms of postoperative OI include impaired vasopressor responses relating to postoperative autonomic dysfunction. Thus, based on a previous study on haemodynamic responses during mobilization before and after elective total hip arthroplasty (THA), we performed secondary analyses of heart rate variability (HRV) and aimed to identify possible abnormal postoperative autonomic responses in relation to postural change.

METHODS

A standardized mobilization protocol before, 6 and 24 h after surgery was performed in 23 patients scheduled for elective THA. Beat-to-beat arterial blood pressure was measured by photoplethysmography and HRV was derived from pulse wave interbeat intervals and analysed in the time and frequency domain as well as by non-linear analysis using sample entropy

RESULTS

Before surgery, arterial pressures and HR increased upon standing, while HRV low (LF) and high frequency (HF) components remained unchanged. At 6 and 24 h after surgery, resting total HRV power, sample entropy and postural responses in arterial pressures decreased compared to preoperative conditions. During standing HF variation increased by 16.7 (95 % CI 8.0-25.0) normalized units (nu) at 6 h and 10.7 (2.0-19.4) nu at 24 h compared to the preoperative evaluation. At 24 h the LF/HF ratio decreased from 1.8 (1.2-2.6) nu when supine to 1.2 (0.8-1.8) nu when standing.

CONCLUSIONS

This study observed postoperative autonomic cardiovascular dysregulation that may contribute to limited HRV responses during early postoperative mobilization.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01089946.

Corticotropin-releasing factor (CRF) receptor-1 is involved in cardiac noradrenergic activity observed during naloxone-precipitated morphine withdrawal

BACKGROUND AND PURPOSE

The negative affective states of withdrawal involve the recruitment of brain and peripheral stress circuitry [noradrenergic activity, induction of the hypothalamic-pituitary-adrenocortical (HPA) axis and activation of heat shock proteins (Hsps)]. Corticotropin-releasing factor (CRF) pathways are important mediators in the negative symptoms of opioid withdrawal. We performed a series of experiments to characterize the role of the CRF₁ receptor in the response of stress systems to morphine withdrawal and its effect in the heart using genetically engineered mice lacking functional CRF₁ receptors.

EXPERIMENTAL APPROACH

Wild-type and CRF₁ receptor-knockout mice were treated with increasing doses of morphine. Precipitated withdrawal was induced by naloxone. Plasma adrenocorticotropic hormone (ACTH) and corticosterone levels, the expression of myocardial Hsp27, Hsp27 phosphorylated at Ser⁸², membrane (MB)- COMT, soluble (S)-COMT protein and NA turnover were evaluated by RIA, immunoblotting and HPLC.

KEY RESULTS

During morphine withdrawal we observed an enhancement of NA turnover in parallel with an increase in mean arterial blood pressure (MAP) and heart rate (HR) in wild-type mice. In addition, naloxone-precipitated morphine withdrawal induced an activation of HPA axis and Hsp27. The principal finding of the present study was that plasma ACTH and corticosterone levels, MB-COMT, S-COMT, NA turnover, and Hsp27 expression and activation observed during morphine withdrawal were significantly inhibited in the CRF₁ receptor-knockout mice.

CONCLUSION AND IMPLICATIONS

Our results demonstrate that CRF/CRF₁ receptor activation may contribute to stress-induced cardiovascular dysfunction after naloxone-precipitated morphine withdrawal and suggest that CRF/CRF₁ receptor pathways could contribute to cardiovascular disease associated with opioid addiction.

Crosstalk between G protein-coupled receptors (GPCRs) and tyrosine kinase receptor (TXR) in the heart after morphine withdrawal

G protein-coupled receptors (GPCRs) comprise a large family of membrane receptors involved in signal transduction. These receptors are linked to a variety of physiological and biological processes such as regulation of neurotransmission, growth, and cell differentiation among others. Some of the effects of GPCRs are known to be mediated by the activation of mitogen-activated extracellular kinase (MAPK) pathways. Cross-talk among various signal pathways plays an important role in activation of intracellular and intranuclear signal transduction cascades. Naloxone-induced morphine withdrawal leads to an up-regulation of adenyl cyclase-mediated signaling, resulting in high expression of protein kinase (PK) A. In addition, there is also an increased expression of extracellular signal regulated kinase (ERK), one member of MAPK. For this reason, the crosstalk between these GPCRs and receptors with tyrosine kinase activity (TKR) can be considered a possible mechanism for adaptive changes that occurs after morphine withdrawal. Morphine withdrawal activates ERK1/2 and phosphorylated tyrosine hydroxylase (TH) at Ser31 in the right and left ventricle. When N-(2-guanidinoethyl)-5-isoquinolinesulfonamide (HA-1004), a PKA inhibitor was infused, the ability of morphine withdrawal to activate ERK, which phosphorylates TH at Ser31, was reduced. The present finding demonstrated that the enhancement of ERK1/2 expression and the phosphorylation state of TH at Ser31 during morphine withdrawal are dependent on PKA and suggest cross-talk between PKA and ERK1/2 transduction pathway mediating morphine withdrawal-induced activation of TH. Increasing understanding of the mechanisms that interconnect the two pathway regulated by GPCRs and TKRs may facilitate the design of new therapeutic strategies.

Morphine withdrawal activates hypothalamic-pituitary-adrenal axis and heat shock protein 27 in the left ventricle: the role of extracellular signal-regulated kinase

The negative affective states of withdrawal involve the recruitment of brain and peripheral stress circuitry [e.g., noradrenergic activity, induction of the hypothalamo-pituitary-adrenocortical (HPA) axis, and the expression and activation of heat shock proteins (Hsps)]. The present study investigated the role of extracellular signal-regulated protein kinase (ERK) and β-adrenoceptor on the response of stress systems to morphine withdrawal by the administration of [amino[(4-aminophenyl)thio]methylene]-2-(trifluoromethyl)benzeneacetonitrile (SL327), a selective inhibitor of ERK activation, or propranolol (a β-adrenoceptor antagonist). Dependence on morphine was induced by a 7-day subcutaneous implantation of morphine pellets. Morphine withdrawal was precipitated on day 8 by the injection of naloxone (2 mg/kg s.c.). Plasma concentrations of adrenocorticotropin and corticosterone were determined by radioimmunoassay; noradrenaline (NA) turnover in left ventricle was determined by high-performance liquid chromatography; and catechol-O-methyl transferase (COMT) and Hsp27 expression and phosphorylation at Ser82 were determined by quantitative blot immunolabeling. Morphine-withdrawn rats showed an increase of NA turnover and COMT expression in parallel with an enhancement of adrenocorticotropin and plasma corticosterone concentrations. In addition, we observed an enhancement of Hsp27 expression and phosphorylation. Pretreatment with SL327 or propranolol significantly reduced morphine withdrawal-induced increases of plasma adrenocorticotropin and Hsp27 phosphorylation at Ser82 without any changes in plasma corticosterone levels. The present findings demonstrate that morphine withdrawal is capable of inducing the activation of HPA axis in parallel with an enhancement of Hsp27 expression and Hsp27 phosphorylation at Ser82 and suggest a role for β-adrenoceptors and ERK pathways in mediating morphine-withdrawal activation of the HPA axis and cellular stress response.

Preparation and radiosynthesis of [18F]FE@CFN (2-[18F]fluoroethyl 4-[N-(1-oxopropyl)-N-phenylamino]-1-(2-phenylethyl)-4-piperidinecarboxylate): a potential μ-opioid receptor imaging agent

PET imaging of the μ-opioid receptor (OR) is still restricted to [11C]carfentanil ([11C]CFN) but its use is limited due to its short half-life and high agonistic potency. Recently, the radiosynthesis of [18F]fluoroalkyl esters of CFN was proposed, unfortunately yielding products not suitable for human PET due to their low specific activities. Therefore, our rationale was to develop a reliable radiosynthesis of a [18F]fluoroethylated CFN derivative overcoming these drawbacks.

The [18F]fluoroethyl ester of carfentanil, [18F]FE@CFN (2-[18F]fluoroethyl 4-[N-(1-oxopropyl)-N-phenylamino]-1-(2-phenylethyl)-4-piperidinecarboxylate), and its corresponding inactive standard compound were prepared. Purification of [18F]FE@CFN was achieved via a simple solid phase extraction method. [18F]FE@CFN was prepared with excellent purity (> 98%) and sufficient yields. Specific activity surpassed the level required for safe administration. We therefore conclude that our simplified synthesis of [18F]FE@CFN, for the first time, overcomes the shortcomings of [11C]CFN and the previously suggested alternatives, namely, (1) longer half-life; (2) easy production and (3) adequate specific activity, should make a wider application possible. Hence, [18F]FE@CFN may become a valuable PET tracer for the imaging of the μ-OR in human brain and heart.

Punishment induces risky decision-making in methadone-maintained opiate users but not in heroin users or healthy volunteers

Reinforcing properties of psychoactive substances are considered to be critically involved in the development and maintenance of substance dependence. While accumulating evidence suggests that the sensitivity to reinforcement values may generally be altered in chronic substance users, relatively little is known about the influence reinforcing feedback exerts on ongoing decision-making in these individuals. Decision-making was investigated using the Cambridge Risk Task, in which there is a conflict between an unlikely large reward option and a likely small reward option. Responses on a given trial were analyzed with respect to the outcome on the previous trial, providing a measure of the impact of prior feedback in modulating behavior. Five different groups were compared: (i) chronic amphetamine users, (ii) chronic opiate users in methadone maintenance treatment (MMT), (iii) chronic users of illicit heroin, (iv) ex-drug users who had been long-term amphetamine / opiate users but were abstinent from all drugs of abuse for at least 1 year and (v) matched controls without a history of illicit substance use. Contrary to our predictions, choice preference was modified in response to feedback only in opiate users enrolled in MMT. Following a loss, the MMT opiate group chose the likely small reward option significantly less frequently than controls and heroin users. Our results suggest that different opiates are associated with distinctive behavioral responses to feedback. These findings are discussed with respect to the different mechanisms of action of heroin and methadone. Neuropsychopharmacology (2005) 30, 2115-2124. doi:10.1038/sj.npp.1300812; published online 6 July 2005.

Endogenous opiates and behavior: 2002

This paper is the twenty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2002 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).