Multiple opioid receptors in endotoxic shock: evidence for delta involvement and mu-delta interactions in vivo

δ opioid receptor antagonist, ICI 174,864, is suitable for the early treatment of uncontrolled hemorrhagic shock in rats

BACKGROUND

Fluid resuscitation is the essential step for early treatment of traumatic hemorrhagic shock. However, its implementation is greatly limited before hospital or during evacuation. The authors investigated whether δ opioid receptor antagonist ICI 174,864 was suitable for the early treatment of traumatic hemorrhagic shock.

METHODS

With uncontrolled hemorrhagic-shock rats, the antishock effects of six dosages of ICI 174,864 (0.1, 0.3, 0.5, 1, 3, and 5 mg/kg) infused with or without a small volume of lactated Ringer's solution (LR) before bleeding controlled or bleeding cessation at different times were observed.

RESULTS

ICI 174,864 (0.1-3 mg/kg) with or without 1/4 volume of LR infusion showed dose-dependent increase in the mean arterial blood pressure, and significantly prolonged the survival time and 8-h survival rate, as compared with ICI 174,864 plus 1/2 volume of LR infusion. The best effect was shown with 3 mg/kg of ICI 174,864. Bleeding cessation at 1, 2, or 3 h during infusion of ICI 174,864 (3 mg/kg) plus 1/4 volume of LR improved subsequent treatment (70% 24-h survival rate vs. 50 and 10% 24-h survival rate in hypotensive resuscitation and LR group, respectively). There was significant improvement in hemodynamic parameters, oxygen delivery, and tissue perfusion of hemorrhagic-shock rats with 3 mg/kg of ICI 174,864 plus 1/4 volume of LR infusion.

CONCLUSION

δ Opioid receptor antagonist ICI 174,864 alone or with small volume of fluid infusion has good beneficial effect on uncontrolled hemorrhagic shock. Its early application can "buy" time for subsequent treatment of traumatic shock.

Multiple opioid receptors mediate the hypotensive response induced by central 5-HT(3) receptor stimulation

The aim of the present work was to investigate the role of brain μ, κ and δ opioid receptors in the central serotonergic mechanisms regulating blood pressure in rats. The data obtained show that: (1) pharmacological activation of central 5-HT(3) receptors yields a significant decrease in blood pressure; (2) the blockade of those receptors by a selective antagonist induces an acute hypertensive response; (3) the pharmacological blockade of central opioid receptors by three different opioid antagonists exhibiting variable degrees of selectivity to μ, κ and δ opioid receptors always suppressed the hypotensive response induced by central 5-HT(3) receptor stimulation; (4) the blockade of opioid receptors by the same opioid antagonists that impaired the hypotensive effect of central 5-HT(3) receptor stimulation failed to modify blood pressure in animals not submitted to pharmacological manipulations of central 5-HT(3) receptor function. It is shown that a 5-HT(3) receptor-dependent mechanism seems to be part of the brain serotonergic system that contributes to cardiovascular regulation since the hypertensive response observed after ondansetron administration indicates that central 5-HT(3) receptors exert a tonic inhibitory drive on blood pressure. Furthermore, the data obtained here clearly indicate that the hypotensive response observed after pharmacological stimulation of central 5-HT(3) receptors depends on the functional integrity of brain μ, κ and δ opioid receptors, suggesting that a functional interaction between serotonergic and opiatergic pathways in the brain is part of the complex, multifactorial system that regulates blood pressure in the central nervous system.

Does naloxone alone increase resuscitation rate during cardiopulmonary resuscitation in a rat asphyxia model?

Cardiac arrest was induced with asphyxia to identify if naloxone alone increases resuscitation rate during cardiopulmonary resuscitation in a rat asphyxia model. The animals were randomized into either a saline group (Sal-gro, treated with normal saline 1 ml iv, n = 8), a low-dose naloxone group (treated with naloxone 0.5 mg/kg iv, n = 8), or a high-dose naloxone group (HN-gro, treated with naloxone 1 mg/kg iv, n = 8) in a blinded fashion during resuscitation. At the end of 10 minutes of asphyxia, cardiopulmonary resuscitation was started, and each drug was administered at the same time. The rate of restoration of spontaneous circulation was seen in 1 of 8, 3 of 8, and 7 of 8 animals in the Sal-gro, LN-gro, and HN-gro, respectively. The rate of restoration of spontaneous circulation in HN-gro was significantly higher than that in Sal-gro (P < .05). Naloxone (1 mg/kg) alone can increase resuscitation rate following asphyxial cardiac arrest in rats.

Subclass opioid receptors associated with the cardiovascular depression after traumatic shock and the antishock effects of its specific receptor antagonists

The present available opioid receptor antagonists such as naloxone and naltrexone are not highly receptor selective. They may antagonize mu opioid receptors to affect the pain threshold of the patients with traumatic shock while they exert antishock effects. Therefore, they are not suitable for traumatic shock. It is very important to elucidate the subclass of opioid receptors that are closely associated with cardiovascular depression of traumatic shock and then choose their specific receptor antagonists to treat it. Traumatic shock was used in pentobarbital-anesthetized Wistar rats by right femur fracture plus hemorrhage (fixed hemorrhage at a rate of 20 mL/kg in experiment 1 or hemorrhage to 40 mmHg mean arterial blood pressure for 60 min in experiments 2 and 3), and the changes of myocardial and brain opioid receptors after traumatic shock, the antagonizing effects of mu, delta, and kappa opioid receptor antagonists on the cardiovascular depression of traumatic shock and the antishock effects of delta and kappa opioid receptor antagonists ICI174,864 and Nor-binaltorphimine (Nor-BNI) were observed. The results indicate that after traumatic shock, the number of myocardial and brain delta and kappa opioid receptors were significantly increased that were significantly associated with the decreased cardiovascular functions. mu Opioid receptors in the heart and brain did not change significantly. Intracerebral ventricular administration of ICI174,864 and Nor-BNI significantly antagonized the decreased cardiovascular function after traumatic shock and increased the survival rate of traumatic shock rats, but mu opioid receptor antagonist beta-funaltrexamine did not. Meanwhile, intravenous administration of delta and kappa opioid receptor antagonists ICI174,864 and Nor-BNI also significantly increased the mean arterial blood pressure, improved the hemodynamic parameters, and prolonged the survival rate of traumatic shock rats. These findings suggest that opioid receptors are involved in the cardiovascular depression of traumatic shock, and the subclass receptors are mainly delta and kappa opioid receptors. delta and kappa opioid receptor antagonists have good beneficial effects on traumatic shock.

C1 adrenergic neurons are contacted by presynaptic profiles containing DELTA-opioid receptor immunoreactivity

Ligands of the delta-opioid receptor tonically influence sympathetic outflow. Some of the actions of delta-opioid receptor agonists may be mediated through C1 adrenergic neurons in the rostral ventrolateral medulla. The goal of this study was to determine whether C1 adrenergic neurons or their afferents contain delta-opioid receptors. Single sections through the rostral ventrolateral medulla were labeled for delta-opioid receptor using the immunoperoxidase method and the epinephrine synthesizing enzyme phenylethanolamine N-methyltransferase (PNMT) using the immunogold method, and examined at the light and electron microscopic level. Few ( approximately 5% of 903) profiles dually labeled for PNMT and delta-opioid receptor were detected; most of these were dendrites with diameters < 1.5 microm. delta-Opioid receptor immunoreactivity was affiliated with multivesicular bodies in dually labeled perikarya, whereas delta-opioid receptor immunoperoxidase labeling appeared as isolated clusters within both singly and dually labeled dendrites. The majority ( approximately 83% of 338) of delta-opioid receptor-immunoreactive profiles were axons and axon terminals. delta-Opioid receptor-immunoreactive terminals averaged 0.75 microm in diameter, contained numerous large dense-core vesicles and usually formed appositions or asymmetric (excitatory-type) synapses with their targets. The majority (>50% of 250) of delta-opioid receptor-immunoreactive axons and axon terminals contacted PNMT-immunoreactive profiles. Most of the contacts formed by delta-opioid receptor-immunoreactive profiles ( approximately 75% of 132) were on single-labeled PNMT-immunoreactive dendrites with diameters <1.5 microm. The prominent localization of delta-opioid receptors to dense-core vesicle-rich presynaptic profiles suggests that delta-opioid receptor activation by endogenous or exogenous agonists may modulate neuropeptide release. Furthermore, the presence of delta-opioid receptors on axon terminals that form excitatory-type synapses with PNMT-immunoreactive dendrites suggests that delta-opioid receptor ligands may modulate afferent activity to C1 adrenergic neurons. The observation that some PNMT-immunoreactive neurons contain delta-opioid receptor immunoreactivity associated with multivesicular bodies and other intracellular organelles suggests that some C1 adrenergic neurons may present, endocytose and/or recycle delta-opioid receptors.

Actions of endotoxin and morphine

In summary, our current studies show that treatment with a bacterial endotoxin, lipopolysaccharide (LPS), induces the expression of mu opioid receptors in the rat mesentery. This induction may be mediated through IL-1's actions on mu opioid receptors. Morphine stimulates the expression of adhesion molecules in human brain microvascular endothelial cells (HBMEC) isolated from pathological tissues. Under pathological conditions, mu opioid receptor-dependent pathways may be modulated through the induction of mu opioid receptors, especially in endothelial cells. Treatment with morphine increases [14C]-inulin permeability of an in vitro microvascular endothelial cell barrier, and decreases endothelial cell viability. Morphine pre-treatment potentiates the effects of LPS on endothelial cell viability, and on LPS induction of IL-1beta secretion from 1alpha, 25-dihydroxy-vitamin D3-treated HL-60 human leukemia cells. Previously, it was suggested that an opioid-dependent pathway may be involved in the recovery from endotoxin shock (D'Amato and Holaday, 1984). Induction of mu opioid receptors by treatment with high doses of endotoxin suggests that mu opioid receptor-dependent pathways may be involved in mediating the response to endotoxins. Taken together, these data provide valid evidence for an association between endotoxins and opioid actions. These studies suggest that opioid-dependent pathways in disease or in endotoxin exposure may be modified by cytokine-induced expression of opioid receptors in endothelial cells. In a pathological condition, an alteration of the opioid-dependent pathway may be expected. When morphine is used for its therapeutic values, it may, indeed, potentiate LPS' effects in an adverse manner. From a clinical perspective, these data indicate that morphine and an endotoxin, such as LPS, may interact in a positive 'feedback type of reaction, and thereby modulate the body's immune responses with unexpected and detrimental results.

Naloxone improves arterial blood pressure and hypoxic ventilatory depression, but not survival, of rats during acute hypoxia

OBJECTIVE

To investigate the effects of naloxone and morphine during acute hypoxia.

DESIGN

Prospective, randomized animal study.

SETTING

University laboratory.

SUBJECTS

Twenty-eight adult male Sprague Dawley rats, weighing 300-350 g.

INTERVENTIONS

The rats were implanted with a femoral catheter and subcutaneous electrodes for electrocardiogram recording and were randomly assigned to receive morphine (5 mg/kg), naloxone (5 mg and 10 mg/kg), or normal saline (control) (n = 7 in each). Fifteen minutes after intraperitoneal injection of the drug, each rat was exposed to hypoxic gas (5% oxygen, 95% N2) for 70 mins. Hypoxic survival time was measured. Mean arterial pressure (MAP), arterial pH, Paco2, Pao2, and base excess were measured before injection (baseline), 14 mins after injection (H0), and 6 mins (H1), 33 mins (H2), and 48 mins (H3) after exposure to hypoxia.

MEASUREMENTS AND MAIN RESULTS

Hypoxic survival was similar between the naloxone 5 mg/kg and control groups (p = .183), significantly lower in the naloxone 10 mg/kg group (p < .01), and significantly higher in the morphine 5 mg/kg group (p < .05) compared with controls. MAP significantly decreased in all groups. However, at H2-H3, MAP was better preserved in both naloxone groups and was lower in the morphine group compared with controls. Paco2 was maintained higher at H0-H3 in the morphine group and lower at H2-H3 in both naloxone groups compared with controls.

CONCLUSION

During acute hypoxia, naloxone preserves arterial blood pressure and attenuates hypoxic ventilatory depression by antagonizing endogenous opiates, but it does not improve hypoxic survival. In contrast, morphine, which enhances the action of endogenous opiates, does improve hypoxic survival. The acute hypoxic tolerance of morphine may be partly attributable to a depression of oxygen consumption, increased cerebral blood flow secondary to high Paco2, and protective actions mediated by delta-opioid receptors.

Modulation of humoral immune responses in the rat by centrally applied Met-Enk and opioid receptor antagonists: functional interactions of brain OP1, OP2 and OP3 receptors

We have previously demonstrated that central application of leucine-enkephalin (Leu-Enk) elicits potentiation and suppression of humoral immune responses through OP(1) (delta) and OP(2) (kappa) receptors, respectively. Interestingly, both effects were found to be additionally dependent on OP(3) (mu) receptor function. In the present study, we have further investigated whether opioid receptor interactions underlie the immunomodulatory effects of endogenous opioids as well as exogenously applied methionine-enkephalin (Met-Enk). For that purpose, the plaque-forming cell (PFC) response was determined in rats injected intracerebroventricularly (i.c.v.) with opioid receptor-selective antagonists and Met-Enk. Application of the OP(1) antagonist ICI 174864, but not naltrindole, resulted in suppression of the PFC response. In contrast, i.c.v. injection of the OP(2) selective antagonist nor-binaltorphimine (nor-BNI) significantly potentiated the PFC response. Both effects, presumably mediated by endogenous opioid peptides, were antagonized by the OP(3) receptor antagonist beta-funaltrexamine (beta-FNA) at a dose that was devoid of immunomodulatory activity. The immunopotentiation of the PFC response induced by Met-Enk was reversed by OP(1) receptor antagonists, naltrindole and ICI 174864, but not by beta-FNA or nor-BNI. On the basis of these and previous findings, it may be concluded that central OP(3) receptors are permissive for the central immunomodulatory action of endogenous opioid peptides and Leu-Enk. In contrast, the central immunoenhancing effect of Met-Enk appears to be mediated through OP(3)-independent OP(1) receptors.

Opiates and infection

This review on the effects of opiate use on infectious diseases discusses the complete spectrum of infections in the opiate user, including those of the lung, the GI tract, the skin, the skeletal system, and the CNS. There is both increased prevalence and increased severity of bacterial and viral infections in injection drug users with the outcome of increased morbidity and mortality. The experimental administration of opiates has lead to a greater understanding of the effects on susceptibility to and progression of infectious diseases. Animal models of opiate dependence and infection are reviewed with specific attention to cases in which the opiate-mediated effects are harmful and in which cases they are beneficial.

Cardiovascular effects of central choline during endotoxin shock in the rat

The cardiovascular effects of intracerebroventricular (i.c.v.) administration of choline were studied in endotoxin-treated rats. Intravenous (i.v.) endotoxin (20 mg/kg) caused a moderate hypotension and tachycardia within 10 min of treatment. Choline (50, 100, and 150 microg; i.c.v.) increased blood pressure and decreased heart rate in this condition in a dose-dependent manner. Mecamylamine (50 microg; i.c.v.) pretreatment prevented the pressor and bradycardic responses to choline, whereas atropine (10 microg; i.c.v.) failed to alter both responses. Atropine pretreatment, alone, inhibited endotoxin-induced hypotension. The pressor responses to choline in endotoxin-treated rats were attenuated by pretreatment with hemicholinium-3 (20 microg; i.c.v.), a high-affinity neuronal choline-uptake inhibitor. Plasma vasopressin levels of endotoxin-treated rats were severalfold higher than those of control animals, and choline (50-150 microg; i.c.v.) produced further increases in plasma vasopressin in this condition. Mecamylamine abolished vasopressin response to endotoxin as well as to choline. The vasopressin receptor antagonist, (beta-mercapto-beta,beta-cyclopentamethylene-propionyl(1)-O-Me-Tyr2,Arg8 )-vasopressin (10 microg/kg; i.v.) administered 5 min after choline decreased blood pressure from the increased level to the precholine levels but did not alter bradycardia. These results indicate that, in rats treated with endotoxin, choline increases blood pressure and decreases heart rate by a presynaptic mechanism leading to the activation of central nicotinic cholinergic pathways. An increase in plasma vasopressin levels seems to be involved in the pressor, but not in the bradycardic response, to choline.

Effects of neuropeptide FF on intestinal motility and temperature changes induced by endotoxin and platelet-activating factor

Several effects of bacterial endotoxins involve an opioid pathway and neuropeptide FF is an endogenous peptide known to modulate opioid activity, mainly in the central nervous system. The aim of this study was to investigate in rats the role of central neuropeptide FF receptors in intestinal motor disturbances and body temperature changes induced by endotoxins and platelet-activating factor (PAF), a major endotoxin mediator. Rats were fitted with intestinal electrodes, an intraperitoneal thermistor probe and an intracerebroventricular (i.c.v.) cannula for long-term use. E. coli endotoxin (100 microg/kg, i.v.) disrupted the cyclic pattern of intestinal migrating myoelectric complexes and induced a biphasic increase in body temperature while PAF (25 microg/kg, i.p.) disrupted the migrating myoelectric complexes and induced hypothermia for about 2 h. The neuropeptide FF analog, (1 DME)Y8Fa (D-Tyr-D-Leu[N-Me]-Phe-Gln-Pro-Gln-Arg-Phe-NH2) administered i.c.v. 40 and 100 microg/kg reduced the duration of migrating myoelectric complex disruption induced by endotoxin and PAF and abolished the PAF-induced hypothermia. Only at the dose of 100 microg/kg did (1 DME)Y8Fa change the biphasic endotoxin-induced hyperthermia into a monophasic increase. Naloxone (1 mg/kg, s.c.) reduced only the duration of migrating myoelectric complex disruption induced by endotoxin. These results indicate that central neuropeptide FF modulates the intestinal motor disturbances and changes in body temperature induced by endotoxin and PAF. Its action against endotoxin may involve an anti-opioid pathway whereas its action against PAF does not.

Interaction of beta-funaltrexamine with [3H]cycloFOXY binding in rat brain: further evidence that beta-FNA alkylates the opioid receptor complex

beta-Funaltrexamine (beta-FNA) is an alkylating derivative of naltrexone. In addition to acting as an irreversible inhibitor of mu-receptor-mediated physiological effects, intracerebroventricular (i.c.v.) administration of beta-FNA to rat attenuates the ability of selective delta receptor antagonists and naloxone to reverse delta receptor-mediated effects. Moreover, recent work demonstrated that i.c.v. administration of beta-FNA alters the conformation of the opioid receptor complex, as inferred by a decrease in the Bmax of the lower affinity [3H][D-ala2,D-leu5]enkephalin binding site. Consistent with the decreased potency of naloxone as an inhibitor of delta receptor mediated effects, beta-FNA doubled the naloxone IC50 for displacing [3H][D-ala2,D-leu5]enkephalin from its lower affinity binding site. These data collectively support the hypothesis that the opioid receptor complex postulated to mediate mu-delta interactions in vivo is identical to the opioid receptor complex as defined by vitro ligand binding studies. A direct prediction of this hypothesis is that beta-FNA should increase the Kd of antagonists for the mu binding site (mu cx) of the receptor complex. The data reported in this paper demonstrate that beta-FNA doubled the IC50 of the potent narcotic antagonist, 6-desoxy-6 beta-fluoronaltrexone (cycloFOXY) for displacing [3H][D-ala2,D-leu5]enkephalin from its lower affinity binding site, and doubled the Kd of [3H]cycloFOXY for its mu binding site, providing additional data that the mu binding site labeled by [3H]cycloFOXY is the mu binding site of the opioid receptor complex. beta-FNA also altered the kappa binding site labeled by [3H]cycloFOXY, and when administered intrathecally to mice, beta-FNA produced a longlasting antinociception in the acetic acid writhing test.

Opioid-induced respiratory depression and analgesia may be mediated by different subreceptors

Use of selective delta opioid antagonists provide evidence that the delta receptor within the brain seems an integrated part in the mediation of respiratory depression induced by a potent analgesic like fentanyl. Low doses of the delta antagonists RX-8008M (3-6 micrograms/kg) as well as ICI 174,864 (3-6 micrograms/kg) reversed fentanyl-related respiratory depression (arterial blood gases) in the unanesthetized canine. Opioid-induced blockade of afferent sensory nerve volleys (amplitude height of the somatosensory-evoked potential) could be reversed only by a high dose (9 micrograms/kg) of RX-8008M. Depression of amplitude height of the SEP could not be reversed by ICI 174,864 over the whole dose range (3-6-9 micrograms/kg). In comparison, naloxone (1-5-10 micrograms/kg) not only reversed depression of PaO2, it also reversed the blockade of afferent sensory nerve impulses in the low (5-micrograms/kg)-dose range. A highly selective delta antagonist may have a therapeutic value in reversing opioid-related respiratory depression, resulting in little or no attenuation of analgesia.

Effects of mu-opioid receptor agonists on circulatory responses to simulated haemorrhage in conscious rabbits

1. Cardiac output, arterial pressure, heart rate, systemic vascular conductance, respiratory rate and arterial blood PO2 and PCO2 were measured in unanaesthetized rabbits. Haemorrhage was simulated by inflating a cuff placed around the inferior vena cava so that cardiac output fell at a constant rate of about 8% of its resting value per min. 2. The effects of drug treatments on resting haemodynamic and respiratory variables, and on the haemodynamic response to simulated haemorrhage, were tested. The treatments were; 4th ventricular (-)-naloxone HCl (10-100 nmol), 4th ventricular H-Tyr-D-Ala-Gly-MePhe-NH(CH2)2OH (DAMGO; 30-300 pmol), and i.v. morphine sulphate (0.5-5.0 mumol kg-1). The interactions of graded 4th ventricular doses of naloxone (3-100 nmol) with the actions of DAMGO (100-300 pmol) on these responses were also assessed. 3. After sham treatments, the circulatory response to simulated haemorrhage had two phases. During the first compensatory phase, systemic vascular conductance fell, heart rate rose, and mean arterial pressure fell by only about 7 mmHg. A second decompensatory phase supervened when cardiac output had fallen by about 50%. At this point systemic vascular conductance rose abruptly and arterial pressure fell to less than or equal to 40 mmHg. 4. Low 4th ventricular doses of naloxone (10-30 nmol) and DAMGO (30-100 pmol) had no discernible effect on the circulatory response to simulated haemorrhage. Higher doses of naloxone (30-100 nmol) and DAMGO (100-300 pmol) prevented the decompensatory phase. These high doses of naloxone and DAMGO lowered resting heart rate without affecting the other haemodynamic or respiratory variables. 5. Low doses of i.v. morphine (0.5-1.Spumolkg-1) also had no discernible effect on the circulatory response to simulated haemorrhage. Higher doses of morphine (1.5-5.Opmol kg 1) abolished the decompensatory phase. These high doses caused respiratory depression without affecting the resting haemodynamic variables. 6. The prevention of circulatory decompensation by high doses of DAMGO was reversed by 3-10nmol of naloxone in 3 out of 4 rabbits and by 10-30 nmol of naloxone in all 4 rabbits. The decompensatory phase was, however, prevented by the combined high doses of DAMGO (100-300pmol) and naloxone (30-100 nmol). 7. These findings provide strong evidence that activation of mu-opioid receptors in the central nervous system abolishes circulatory decompensation during acute reduction of central blood volume in conscious rabbits. This effect does not appear to be due to activation of arterial chemoreceptors or to a non-specific increase in sympathetic vasoconstrictor drive, since respiratory depression and hypertension were not observed after 4th ventricular doses of DAMGO which abolished circulatory decompensation. Our results also provide indirect confirmation of our previous finding that naloxone acts to prevent circulatory decompensation by an antagonist action at central delta-receptors.

Role of central opiate receptor subtypes in the circulatory responses of awake rabbits to graded caval occlusions

1. In unanaesthetized rabbits, haemorrhage was simulated by inflating a cuff placed round the inferior vena cava so that cardiac output fell at a constant rate of approximately 8% of its resting value per minute. The circulatory responses were measured after injections into the fourth ventricle of saline vehicle, selective opioid antagonists, selective opioid agonists, and agonist-antagonist mixtures. Three sets of experiments were done to determine if a specific subtype of opiate receptor within the central nervous system is responsible for the circulatory decompensation that occurs during simulated haemorrhage. 2. In six rabbits the effects of ascending doses of the antagonists naloxone (mu-selective), Mr 2266 (kappa- and mu-selective), ICI 174864 (delta-selective) and nor-binaltorphimine (kappa-selective) were tested. In three rabbits the effects of the antagonist naloxone, the agonists HTyr-D-Ala-Gly-MePhe-NH(CH2)2OH (DAGO, mu-selective), U 50488H (kappa-selective), and [D-Pen2,D-Pen5]-enkephalin (DPDPE, delta-selective), and combinations of these agonists with naloxone were tested. In four rabbits the dose-related effects of DAGO on respiratory, as well as circulatory, functions were examined. 3. After injecting saline vehicle, the circulatory response to simulated haemorrhage had two phases. During the first phase, systemic vascular conductance fell, heart rate rose, and mean arterial pressure fell by only approximately 10 mmHg. A second, decompensatory, phase began when cardiac output had fallen to approximately 50% of its resting level. At this point, there was an abrupt rise in systemic vascular conductance and a fall in mean arterial pressure to less than or equal to 40 mmHg. 4. The lower range of doses of naloxone (3-30 nmol), Mr 2266 (10-100 nmol), ICI 174864 (10-30 nmol), and all doses of nor-binaltorphimine (1-100 nmol), were without effect on the circulatory response to stimulated haemorrhage. Higher doses of naloxone (30-100 nmol), Mr 2266 (100-300 nmol) and ICI 174864 (30-100 nmol) abolished the decompensatory phase. The relative order of antagonist potency was ICI 174864 greater than or equal to naloxone greater than Mr 2266 greater than or equal to nor-binaltorphimine. 5. In the second set of experiments, the critical dose of naloxone necessary to prevent circulatory decompensation during simulated haemorrhage was 30-150 nmol. The delta-agonist DPDPE (50 nmol) did not affect the haemodynamic response to simulated haemorrhage, but it did block the effect of naloxone on the response.(ABSTRACT TRUNCATED AT 400 WORDS)

Opiate receptor inhibition improves the blunted baroreflex function in conscious dogs with right-sided congestive heart failure

The endogenous opiate system is activated in congestive heart failure. because endogenous opioids are known to depress the baroreflex function, we conducted studies to determine whether the increased endogenous opioids play a role in causing the reduced baroreflex function that occurs in heart failure. Right-sided congestive heart failure was produced in 16 dogs by tricuspid avulsion and progressive pulmonary artery constriction. Seven sham-operated dogs were included for comparison. Baroreflex function was measured in the conscious dogs after pretreatment with either normal saline or an opiate-receptor antagonist by bolus administration of phenylephrine. The slope of the regression line relating systolic blood pressure to cardiac cycle (R-R) interval was taken as an index of baroreflex sensitivity. Plasma beta-endorphin was elevated in the dogs with heart failure (15.3 +/- 2.5 pmol/l) compared with the sham-operated dogs (4.2 +/- 0.4 pmol/l, p less than 0.001). The dogs with heart failure also exhibited a reduced baroreflex sensitivity (3.84 +/- 0.19 msec/mm Hg) after saline pretreatment when compared with the sham-operated dogs (10.86 +/- 1.20 msec/mm Hg, p less than 0.001). Administration of naloxone hydrochloride increased the baroreflex sensitivity of dogs with heart failure to 5.16 +/- 0.26 msec/mm Hg (p less than 0.01) but produced no significant effects in sham-operated dogs (11.36 +/- 1.42 msec/mm Hg). To further study the site of action for the effect of naloxone, we measured baroreflex sensitivity in the dogs with heart failure after pretreatment with naloxonazine, a selective mu-receptor antagonist, with ICI 154,129, a selective delta-receptor antagonist, or with naloxone methobromide, a quaternary analogue of naloxone that does not penetrate the blood-brain barrier.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphine-like discriminative stimulus effects of opioid peptides: possible modulatory role of D-Ala2-D-Leu5-enkephalin (DADL) and dynorphin A (1-13)

The role of the different opioid receptors was studied in rats trained to discriminate SC injections of 3.0 mg/kg morphine from saline by tests for generalization to graded doses of morphine and receptor-selective peptides administered into the lateral cerebral ventricle. Dose-dependent morphine-like stimulus effects were produced over a wide range of doses (0.001-30 micrograms), depending upon ligand and animal, by morphine, by the mu-selective peptides DAGO[D-Ala2-NMePhe4-Gly(ol)-enkephalin] and FK33824[D-Ala2,NMePhe4-Met(O)5-(ol)-enkephalin], and by the delta-selective peptide, DADL[D-Ala2,D-Leu5)enkephalin]. The order of relative potency of these substances was: FK33824 greater than DAGO greater than morphine greater than DADL. In contrast, DPLPE[D-Pen2,L-Pen5)enkephalin], which has much greater delta receptor selectivity than does DADL, and dynorphin A(1-13) (0.1-10 micrograms), a kappa-receptor agonist, engendered choice responding appropriate for saline. When 1.0 micrograms DADL, a dose lacking morphine-like discriminative effects, was administered concurrently with SC morphine, the stimulus effects of morphine were potentiated. Concurrent administration of 10 micrograms dynorphin A(1-13) and morphine attenuated the stimulus effects of morphine inconsistently. These results support previous findings that mu-opioid receptors are of primary importance in mediating the morphine-like discriminative effects of opioid peptides. They also suggest that morphine-like discriminative effects can be modulated by other types of opioid receptors.

Opiate receptors and the endorphin-mediated cardiovascular effects of clonidine in rats: evidence for hypertension-induced mu-subtype to delta-subtype changes

Effects of opiate receptor antagonists on centrally mediated cardiovascular responses to clonidine and beta-endorphin were studied in urethane-anesthetized spontaneously hypertensive Okamoto-Aoki rats (SHR), normotensive Sprague-Dawley rats, and Sprague-Dawley rats made hypertensive with deoxycorticosterone pivalate/salt. Microinjection of 270 pmol of naloxone into the nucleus tractus solitarii (NTS) significantly inhibited the hypotensive and bradycardic response to 5 nmol of similarly administered clonidine in both SHR and normotensive Sprague-Dawley rats. In SHR, a similar inhibition was observed after the delta-opiate receptor antagonist ICI 174864, but not after the mu-receptor antagonist beta-funaltrexamine (both at 270 pmol, intra-NTS), whereas in normotensive Sprague-Dawley rats, beta-funaltrexamine, but not ICI 174864, was an effective inhibitor. The same pattern of differential inhibition was seen when clonidine was given i.v. and the opiate antagonists were given intracisternally in SHR and Sprague-Dawley rats. Intra-NTS microinjection of 280 fmol of beta-endorphin caused hypotension and bradycardia, and these effects were similarly inhibited by ICI 174864 in SHR and by beta-funaltrexamine in Sprague-Dawley rats. In Sprague-Dawley rats made hypertensive by chronic administration of deoxycorticosterone pivalate and salt, the hypotensive and bradycardic effects of intra-NTS clonidine were inhibited by ICI 174864, but not by beta-funaltrexamine, a pattern similar to that in SHR, but different from that in normotensive Sprague-Dawley rats. These results support the hypothesis that beta-endorphin release and subsequent stimulation of opiate receptors in the NTS are involved in the cardiovascular effects of clonidine in rats. These results further suggest, however, that hypertension regulates the subtype of opiate receptors mediating these effects.

Current perspectives on septic shock

Although septic shock may be initiated by invading microbes, it is the metabolic and immunologic host responses that determine the true pathophysiology of this common critical care illness. Currently, septic shock therapeutics emphasize empiric and symptomatic treatment. Biochemical elucidation of the septic process will ultimately result in specific interventions for this ominous intensive care syndrome.

Central delta-opioid receptor interactions and the inhibition of reflex urinary bladder contractions in the rat

The in vivo effects of a number of opioid agonists and antagonists were studied on the spontaneous reflex contractions of the urinary bladder recorded isometrically in the rat anesthetized with urethane. All substances were administered into the central nervous system by the intracereboventricular (i.c.v.) or spinal intrathecal (i.t.) route. The conformationally restricted enkephalin analogues [2-D-penicillamine, 5-L-cysteine] enkephalin (DPLCE), [2-D-penicillamine, 5-L-penicillamine] enkephalin (DPLPE) and [2-D-penicillamine, 5-D-penicillamine] enkephalin (DPDPE) produced dose-related inhibition of reflex bladder contractions when administered by the i.c.v. or i.t. route. Both the novel delta-opioid receptor antagonist ICI 154,129 (200-600 micrograms) [N,N-bisallyl-Tyr-Gly-Gly-Psi-(CH2S)-Phe-Leu-OH) and ICI 174,864 (1-3 micrograms) [N,N-dially-Tyr-Aib-Aib-Phe-Leu-OH: Aib = alpha-aminoisobutyric acid] attenuated or abolished the effects of DPLCE, DPLPE and DPDPE when administered by the i.c.v. or i.t. route. The antagonism observed was selective since the equipotent inhibition produced by the mu-opioid receptor agonist [D-Ala2, Me-Phe4, Gly(ol)5] enkephalin (DAGO) was unaffected. Overall, ICI 154,129 was considerably weaker than ICI 174,864 and both antagonists inhibited bladder activity at doses higher than those required to demonstrate delta-receptor antagonism. Further studies of the agonistic effect of ICI 174,864 showed that it was insensitive to low doses of naloxone (2 micrograms, i.c.v. or i.t.) but could be abolished by higher (10-15 micrograms) doses of naloxone. These observations suggested that the agonistic effect of ICI 174,864 was not mediated by mu-opioid receptor. beta-Endorphin (0.2-1.0 micrograms, i.c.v.) inhibited bladder contractions but following recovery from this effect, appeared to prevent the expression of delta-receptor antagonism by ICI 174,864. In addition a previously subthreshold dose of ICI 174,864 now exhibited marked agonistic activity. The inhibitory effect of a submaximal dose of DPDPE was also potentiated by beta-endorphin under these circumstances. These observations suggest that supra-spinal and spinal delta-opioid receptors are involved in the opioid-mediated inhibition of reflex bladder contractions in the rat. Moreover beta-endorphin may be important in regulating central delta-opioid receptors.

Effect of beta-FNA on opiate delta receptor binding

beta-FNA, the beta-fumaramate methyl ester of naltrexone, has been shown to antagonize irreversibly the actions of morphine on the guinea pig ileum and mouse vas deferens bioassays but does not affect the actions of delta-receptor ligands on the mouse vas deferens bioassay, suggesting that the compound does not irreversibly bind to the delta receptor. In this paper we examine the effect of beta-FNA on the binding of the prototypic delta agonists, Leu-enkephalin and D-Ala2-D-Leu5-enkephalin, its metabolically stable analogue, and show that treatment of membranes with beta-FNA does lead to alterations in the in vitro properties of delta receptors.