Analysis of cardiovascular effects of morphine in the cat

Low-Dose Morphine Reduces Pain Perception and Blood Pressure, but Not Muscle Sympathetic Outflow, Responses During the Cold Pressor Test

Our knowledge about how low-dose (analgesic) morphine affects autonomic cardiovascular regulation is primarily limited to animal experiments. Notably, it is unknown if low-dose morphine affects human autonomic cardiovascular responses during painful stimuli in conscious humans. Therefore, we tested the hypothesis that low-dose morphine reduces perceived pain and subsequent sympathetic and cardiovascular responses in humans during an experimental noxious stimulus. Twenty-nine participants (14F/15M; 29±6 y; 26±4 kg•m^-2, mean ± SD) completed this randomized, crossover, placebo-controlled trial during two laboratory visits. During each visit, participants completed a cold pressor test (CPT; hand in ~0.4 °C ice bath for two minutes) before and ~35 minutes after drug/placebo administration (5 mg IV morphine or saline). We compared pain perception (100 mm visual analog scale), muscle sympathetic nerve activity (MSNA; microneurography; 14 paired recordings), and beat-to-beat blood pressure (BP; photoplethysmography) between trials (at both pre- and post-drug/placebo time points) using paired, two-tailed t-tests. Before drug/placebo infusion, perceived pain (p=0.92), Δ MSNA burst frequency (n=14, p=0.21), and Δ mean BP (p=0.39) during the CPT were not different between trials. After the drug/placebo infusion, morphine versus placebo attenuated perceived pain (morphine: 43±20 vs. placebo: 57±24 mm,p<0.001) and Δ mean BP (morphine: 10±7 vs. placebo: 13±8 mmHg,p=0.003), but not Δ MSNA burst frequency (morphine: 10±11 vs. placebo: 13±11 bursts/minute,p=0.12), during the CPT. Reductions in pain perception and Δ mean BP were only weakly related (r=0.34,p=0.07; post-morphine CPT minus post-placebo CPT). These data provide valuable information regarding how low-dose morphine affects autonomic cardiovascular responses during an experimental painful stimulus.

Assessment of hydromorphone and dexmedetomidine for emesis induction in cats

OBJECTIVE

To compare the efficacy of hydromorphone and dexmedetomidine at inducing emesis in cats.

DESIGN

Prospective, blinded, randomized crossover study.

SETTING

Veterinary university teaching hospital.

ANIMALS

12 healthy purpose-bred cats.

INTERVENTIONS

Cats were randomly assigned to receive hydromorphone (0.1 mg/kg, subcutaneously) or dexmedetomidine (7 μg/kg, IM). Following administration, the incidences of emesis, number of emetic events, signs of nausea (hypersalivation, lip licking), temperature, heart rate, respiratory rate, and sedation score were recorded for 6 hours.

MEASUREMENTS AND MAIN RESULTS

Emesis was successful in 9 of 12 (75%) cats when treated with hydromorphone and in 7 of 12 (58%) cats when treated with dexmedetomidine (P = 0.67). Dexmedetomidine was more likely to cause sedation than hydromorphone (P < 0.001). Heart rate in cats was significantly decreased at 1 and 2 hours post-hydromorphone (P = 0.003, 0.014, respectively) and at 1, 2, 3, 5, 6 hours post-dexmedetomidine (P = 0.001, 0.003, 0.038, 0.013, 0.001, respectively). Cats were more likely to develop an increase in body temperature with hydromorphone administration although this was not clinically significant.

CONCLUSIONS

Results of the present study indicate that hydromorphone is an effective alternative to dexmedetomidine for the induction of emesis in cats. Hydromorphone appears to cause less sedation and less decrease in heart rate. Further investigation into the most adequate dose of hydromorphone for optimizing emesis is warranted.

The Impact of Opium Consumption on Blood Glucose, Serum Lipids and Blood Pressure, and Related Mechanisms

Aim: Substance abuse has become a universal crisis in our modern age. Among illegal substances, opium and its derivatives have been ranked second in terms of usage after cannabis in the world. In many Asian regions, the use of opium enjoys a high social acceptance; hence, some common people and even medical practitioners believe that opium lowers blood glucose and pressure and treat dyslipidemia. How much this belief is scientifically justified?

Method: The results of available studies on both humans and animals searched in different search engines up to mid-2016 were integrated (78 articles). Upon the findings we try to offer a more transparent picture of the effects of opium on the mentioned factors along with the probable underlying mechanisms of its action.

Results: Taken together, a variety of evidences suggest that the consumption of opium has no scientific justification for amendment of these biochemical variables. The mechanisms proposed so far for the action of opium in the three above disorders are summarized at the end of the article. Short term effects seems to be mostly mediated through central nervous system (neural and hormonal mechanisms), but long term effects are often due to the structural and functional alterations in some body organs.

Conclusion: Although opium may temporarily reduce blood pressure, but it increases blood glucose and most of blood lipids. Moreover its long term use has negative impacts and thus it aggravates diabetes, dyslipidemia and hypertension. Accordingly, it is necessary to inform societies about the potential disadvantages of unauthorized opium consumption.

Clinical evaluation of alfaxalone to induce and maintain anaesthesia in cats undergoing neutering procedures

This study looked at the use and efficacy of alfaxalone for total intravenous anaesthesia (TIVA) in cats. Following intramuscular medetomidine (20 μg/kg) and morphine (0.3 mg/kg) premedication, anaesthesia was induced and maintained with intravenous alfaxalone. Patients were breathing 100% oxygen. Heart rate (HR), respiratory rate (RR), end-tidal carbon dioxide, oxygen saturation of haemoglobin and indirect arterial blood pressure via Doppler (DAP) were recorded every 5 mins. Thirty-four cats (10 males and 24 females), between the age of 6 and 18 months, and weighing between 1.8 and 5.3 kg, and undergoing neutering procedures were included in this study. The results are presented as median (min, max) values. The time to first spontaneous movement (TS) was >30 mins in 19 cats, of which 12 received atipamezole for reversal of the effects of medetomidine. The TS was 53 (43, 130) mins in these 12 cats and 50 (40, 72) mins in the other seven cats. The body temperature in those 19 cats was significantly lower than the other cats ( P = 0.05). The alfaxalone induction dose and maintenance infusion rate were1.7 (0.7, 3.0) mg/kg and 0.18 (0.06, 0.25) mg/kg/min, respectively. The HR, RR and DAP were 145 (68, 235) beats/min, 17 (5, 40) breaths/min and 110 (58, 210) mmHg, respectively. Apnoea was not observed in any cat. In conclusion, alfaxalone TIVA in combination with medetomidine and morphine premedication was effective in feral and domestic cats for the performance of neutering surgery; low body temperature might have resulted in longer recoveries in some cats.

Cardiovascular manifestations of sedatives and analgesics in the critical care unit

There are numerous sedatives and analgesics used in critical care medicine today; these medications are used on critically ill patients, many of whom have heart disease, including coronary artery disease or congestive heart failure. The purpose of this review is to recognize the effects of these medications on the heart. Studies that evaluated the effects of sedatives and analgesics on normal individuals or on those with heart disease were reviewed. Current choices for sustained sedation in the critically ill include the benzodiazepines, morphine, propofol, and etomidate. Each of these medications has their particular advantages and disadvantages. Benzodiazepines provide the greatest amnesia and cardiovascular safety but they can cause significant hypotension in the hemodynamically unstable patient. Morphine provides analgesia and cardioprotective activity after ischemia, although the large observational study CRUSADE showed increased mortality rate in those patients with non-ST segment elevation myocardial infarction who received morphine. Propofol is the most easily titratable drug with cardioprotective features, but its use must be accompanied with great attention to possible development of propofol infusion syndrome, which is a deadly disease, especially in patients with head injury and those with septic shock receiving vasopressors. Etomidate has a rapid onset effect and short period of action with great hemodynamic stability even in patients with shock and hypovolemia, but the incidence of adrenal insufficiency during infusion, not bolus doses, may cause deterioration in the circulatory stability. In conclusion, the sedatives and analgesics mentioned here have characteristics that give them a cardiovascular safety profile useful in critically ill patients. However, use of these drugs on an individual basis is dependent on each agent's safety and efficacy.

Morphine-Induced Analgesia, Hypotension, and Bradycardia Are Enhanced in Hypertensive Rats

Several studies have emphasized an opioidergic link between the central regulation of cardiovascular function and acute noninflammatory pain. By contrast, relatively few studies have investigated the relationships between opioids, hypertension, and inflammatory pain. We used the formalin model of acute inflammatory pain to compare morphine antinociception among spontaneously hypertensive (SHR) rats, their genetic normotensive controls, Wistar-Kyoto (WKY) rats, and Sprague-Dawley (SD) rats. Measures of nociception included both behavioral and cardiovascular end-points (increased mean arterial blood pressure and heart rate). Morphine (3.0 mg/kg subcutaneously) produced greater hypotension and bradycardia in SHR than in WKY or SD rats. We next administered formalin (5%; 50 microL) and observed greater nociception during both Phase 1 and Phase 2 in SHR controls than in WKY controls. The morphine-treated groups did not differ, suggesting that morphine attenuates hypersensitivity to formalin pain in the SHR. Morphine inhibited edema but not paw hyperthermia to a greater degree in SHR, whereas Phase 1 remifentanil produced a relatively shorter delay in the onset of Phase 2 in SHR. We suggest that the presentation of essential hypertension be considered when opioid regimens are planned both during surgery (to minimize cardiovascular complications) and during the postoperative period (to optimize analgesic effects).

IMPLICATIONS

Presentation of essential hypertension should be considered when opioid regimens are planned both during surgery (to minimize cardiovascular complications) and during the postoperative period (to optimize analgesic effects).

Effect of morphine on sympathetic nerve activity in humans

There are conflicting reports for the role of endogenous opioids on sympathetic and cardiovascular responses to exercise in humans. A number of studies have utilized naloxone (an opioid-receptor antagonist) to investigate the effect of opioids during exercise. In the present study, we examined the effect of morphine (an opioid-receptor agonist) on sympathetic and cardiovascular responses at rest and during isometric handgrip (IHG). Eleven subjects performed 2 min of IHG (30% maximum) followed by 2 min of postexercise muscle ischemia (PEMI) before and after systemic infusion of morphine (0.075 mg/kg loading dose + 1 mg/h maintenance) or placebo (saline) in double-blinded experiments on separate days. Morphine increased resting muscle sympathetic nerve activity (MSNA; 17 +/- 2 to 22 +/- 2 bursts/min; P < 0.01) and increased mean arterial pressure (MAP; 87 +/- 2 to 91 +/- 2 mmHg; P < 0.02), but it decreased heart rate (HR; 61 +/- 4 to 59 +/- 3; P < 0.01). However, IHG elicited similar increases for MSNA, MAP, and HR between the control and morphine trial (drug x exercise interaction = not significant). Moreover, responses to PEMI were not different. Placebo had no effect on resting, IHG, and PEMI responses. We conclude that morphine modulates cardiovascular and sympathetic responses at rest but not during isometric exercise.

Effects of mu-, delta- and kappa-agonists on isolated right atria of the rat

The present study examined the effects of morphine, DAMGO, DPDPE and U-50, 488H on auricular rate on isolated right atria of the rat. All the opioid agonists tested induced a decrease of auricular rate. The maximal effect obtained with U-50,488H (75 +/- 8.3%) was significantly (p < 0.001) higher than that obtained with morphine (12 +/- 2.7%), DAMGO (8 +/- 0.6%) or DPDPE (11 +/- 1.8%). The inhibitory effects of U-50,488H were not antagonized by the presence of naloxone (10(-7) or 5 x 10(-7) M) or MR-2266 (10(-7) or 5 x 10 (-7) M). Moreover, U-50,488H did not change the auricular chronotropism in the presence of atropine (5 x 10(-7) M). In this case the maximal inhibitory effect was 79 +/- 6.7%, similar to that obtained with the kappa-agonist alone (75 +/- 8.3%). Propranolol (10(-8) or 5 x 10(-8) M) modified the inhibitory effect of U-50,488H. The maximal effect obtained by the kappa-agonist in presence of propranolol was 100 +/- 0 significantly (p < 0.01) higher than that obtained with U-50,488H alone. These results demonstrated that the depressant action of U-50,488H was not blocked in the presence of opioid receptor antagonists and probably does not involve opioid receptors. Furthermore, propranolol caused a dose-dependent potentiation of the effects of the kappa-agonist supporting the conclusion that it is not mediated by opioid receptors.

Effects of morphine on isolated right atria of the rat

1. The present study describes the effects of morphine in the absence or presence of naloxone or atropine in the isolated right atria of the rat. 2. Morphine significantly decreased the auricular chronotropism. 3. The maximal effect was 10 +/- 1.0%. 4. Similar results were obtained in reserpinized animals (13 +/- 0.2% maximum). 5. Naloxone (5 x 10(-7) or 5 x 10(-6) M) did not change the inhibitory effects induced by morphine. 6. The maximal effect obtained with morphine in the presence of atropine (5 x 10(-7) M) was 9 +/- 0.1% similar to that obtained with morphine alone. 7. These results suggest that opioid or vagal mechanisms may not be involved in the cardiac inhibitory effects induced by morphine.

The effects of morphine administered into the vertebral artery on the somatosympathetic A- and C-reflexes in anesthetized cats

The effects of morphine (0.2-200 micrograms/kg) administered into the brain stem via a vertebral artery on the somatosympathetic A- and C-reflexes evoked in a cardiac sympathetic nerve by electrical stimulation of somatic myelinated (A) and unmyelinated (C) afferent nerve fibers in anesthetized cats were examined. The intravertebral arterial administration of 20-200 micrograms/kg morphine depressed dose-dependently both the somatosympathetic A- and C-reflexes. Following the administration of 200 micrograms/kg morphine, the amplitudes of the sympathetic A- and C-reflexes were depressed to 71 +/- 8% and 80 +/- 8% of the control magnitude, respectively. Injection of 2-200 micrograms/kg morphine caused hypotension in a dose-dependent manner. It is concluded that morphine administered in the brain stem via the vertebral artery produced a nonselective and slight depression of both the somatosympathetic A- and C-reflexes by acting at the level of brain stem.

Evidence for involvement of catecholamines in the effect of morphine on ventricular automaticity in the rat

1. The present study examined the effects of morphine on ectopic automaticity induced by local injury in the isolated right ventricle of the rat. 2. Morphine (10(-7)-5 x 10(-5) M) induced a significant increase of ventricular rate similar to that produced by noradrenaline. The excitatory effect of morphine was not modified by the presence of naloxone (5 x 10(-5) M). The maximal effect obtained with morphine in the presence of naloxone was 60 +/- 7%, similar to that obtained with morphine alone (67 +/- 15%). The EC50 values for morphine in the absence (0.89 x 10(-7) M) and presence of naloxone (0.87 x 10(-7) M) were also similar. Apparently this effect is not mediated by postsynaptic opioid receptors. 3. The ventricular automaticity induced in isolated right ventricle of the rat was significantly decreased by the highest concentrations of naloxone (5 x 10(-5) and 10(-7) M). 4. Morphine (10(-9)-5 x 10(-5) M) did not significantly change ventricular automaticity in the presence of propranolol (5 x 10(-8) M) or in reserpinized rats (5 mg kg-1 i.p. 24 h before the experiments). The maximal increases induced by morphine in the presence of propranolol or in reserpinized rats were 5 +/- 0.8% and 16 +/- 14.7% respectively. These results were significantly different from the maximal increase obtained without propranolol or with non-reserpinized animals. It is possible that the effects of morphine on ventricular automaticity could be mediated by an indirect effect located presynaptically at the adrenergic nerve terminals through the release of catecholamines.

Morphine and (D-Ala2, NMe-Phe4, Gly-ol)-enkephalin increase the intracellular free calcium in isolated rat myocytes--effect of naloxone or pretreatment with morphine

The purpose of the present study was firstly to determine whether morphine and (D-Ala2, NMe-Phe4, Gly-ol)-enkephalin (DAGO), a highly selective mu-agonist, increased intracellular free calcium of rat myocytes and secondly to determine whether opioid receptors were involved. Two series of experiments were performed. In the first, the effect of morphine and DAGO on intracellular free calcium (Cai) of cultured isolated myocytes was studied with a spectrophotometric method using fura2-AM as the fluorescent Ca2+ indicator. In the second, the effect of morphine on Cai of isolated ventricular myocytes from rats which had received chronic daily injection of morphine for two weeks or myocytes which had been incubated in a solution with morphine for 12 hr was studied. It was found that both morphine at 100-250 microM and DAGO at 23-75 microM increased Cai dose-dependently and that the effect was significantly antagonized by naloxone at a concentration of 50 microM, which itself did not cause any significant alteration in Cai. Pretreatment with morphine also abolished the morphine-induced increase in Cai of isolated myocytes. The results suggest that morphine increases Cai by directly activating the cardiac receptors (most likely micro-receptors) on the membrane of ventricular myocytes.

Interaction between morphine and noradrenaline on isolated heart muscle

1. We evaluated the interaction between morphine and noradrenaline on the right atria. 2. Noradrenaline significantly increased atrial contraction rate, with an effective concentration 16 (EC16) of 85 +/- 0.8 x 10(-9) M. 3. The EC16 of noradrenaline significantly decreased in the presence of morphine. 4. These results demonstrate that morphine increases the potency of noradrenaline on the isolated right atria.

Activation of brainstem endorphinergic neurons causes cardiovascular depression and facilitates baroreflex bradycardia

The effects of electrical stimulation of the arcuate nucleus on blood pressure, heart rate and baroreflex sensitivity were studied in urethane-anesthetized Sprague-Dawley rats. Stimulation of the mid-anterior parts of the arcuate nucleus at 80 Hz, 0.8 ms and 50-200 microA caused a biphasic, depressor/pressor, response and moderate bradycardia. Intravenous administration of a vasopressin V1-receptor antagonist eliminated the pressor component and unmasked a pure depressor response. This depressor response could be inhibited by naltrexone, 2 mg/kg i.v., by an antiserum against beta-endorphin, 100 nl injected directly into the ipsilateral nucleus tractus solitarii, or by deafferentation of the dorsal vagal complex (nucleus tractus solitarii and dorsal vagal nucleus) by an ipsilateral, dorsolateral knife-cut of the medulla oblongata. Stimulation of the arcuate nucleus at currents of 20-40 microA did not influence basal blood pressure or heart rate but potentiated the reflex bradycardia induced by phenylephrine, and this effect was completely blocked by naltrexone. It is concluded that a beta-endorphin-containing pathway projecting from the arcuate nucleus to the ipsilateral dorsal vagal complex is involved in depressor cardiovascular regulation and in the facilitation of baroreflex bradycardia.

Opiate receptor subtypes in the nucleus tractus solitarii of the cat: the effect of vagal section

The distribution of mu, delta and kappa opioid receptors in the lower brainstem of the cat has been determined autoradiographically by studying the binding of tritiated [D-Ala2,MePhe4,Glyol5][tyrosyl-3,5-3H]enkephalin (DAGO), [D-Pen2,D-Pen5][tyrosyl-3,5-(n)-3H]enkephalin (DPDPE) and [9-3H]ethylketazocine (EKC), respectively. General opiate receptor binding was established using [3H]naloxone (NX). High densities of [3H]NX and DAGO binding sites were found most prominently in the nucleus tractus solitarii. There was no DPDPE and very weak EKC binding within this nucleus, although both these ligands bound to the cerebellum. The effect of unilateral vagotomy on receptor density was examined. Sectioning the cervical vagus had no effect on the density of mu receptors in the brainstem. Sectioning the vagus, accompanied by nodose ganglion excision, led to a marked depletion of mu receptors which was restricted to dorsal and medial regions of the ipsilateral nucleus tractus solitarii at, and rostral to, the obex. These results suggest that mu opiate receptors are located presynaptically on vagal afferents terminating within a restricted region of the nucleus tractus solitarii.

Sympathetic stimulating effects of sufentanil in the cat are mediated centrally

The hemodynamic and adrenal secretory response to sufentanil (25 micrograms/kg i.v.) was evaluated during halothane anesthesia in 3 groups of cats: group I, n = 5, control; group II, n = 4, naloxone pretreatment (3 mg/kg i.v.); and group III, n = 5, acute spinal transection at T3-4. Administration of sufentanil in intact cats (group I), caused a significant increase in mean arterial blood pressure and adrenal vein plasma levels of norepinephrine, epinephrine, dopamine, and Met-enkephalin. These effects were abolished in naloxone-pretreated cats (group II). Following spinal transection (group III), sufentanil evoked a significant increase in blood pressure and heart rate, but no change in adrenal hormone levels. Intraventricular injections of sufentanil suggest that these sympathetic stimulating effects are mediated at central sites in proximity to the lateral and third ventricle.

Enkephalin-immunoreactive neurons in the nucleus tractus solitarius project to the parabrachial nucleus of the cat

Enkephalin immunoreactive neurons within the nucleus tractus solitarius (NTS) were found to project to the parabrachial nucleus of the cat with the use of a combination of immunohistochemistry and retrograde transport of horseradish peroxidase. Double labelled neurons were located in the medial, parvocellular and commissural subdivisions of the NTS and were present predominantly ipsilateral to the injection site within the parabrachial nucleus. Only a few double labelled neurons were found in the contralateral NTS. The presence of neurons containing enkephalin immunoreactivity suggests that the role of enkephalin in the regulation of autonomic functions may be, in part, by circuits between the NTS and the parabrachial nucleus.

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.