Comparative effects of analgesics on pain threshold, respiratory frequency and gastrointestinal propulsion

One-year efficacy and safety of naloxegol on symptoms and quality of life related to opioid-induced constipation in patients with cancer: KYONAL study

OBJECTIVES

Naloxegol is a peripherally acting µ-opioid receptor antagonist (PAMORA) for treatment of opioid-induced constipation (OIC). The main objective was to analyse the long-term efficacy, quality of life (QOL) and safety of naloxegol in patients with cancer in a real-world study.

METHODS

This one-year prospective study included patients older than 18 years, with active oncological disease who were under treatment with opioids for pain control and Karnofsky≥50 and OIC with inadequate response to treatment with laxative (s). All the patients received treatment with naloxegol according to clinical criteria. The main efficacy objectives were measured by the patient assessment of constipation QOL questionnaire (PAC-QOL), the PAC symptoms (PAC-SYM), the response rate at day 15, and months 1-3-6-12, and global QOL (EuroQoL-5D-5L).

RESULTS

A total of 126 patients (58.7% males) with a mean age of 61.5 years (95% CI 59.4 to 63.7) were included. PAC-SYM and PAC-QOL total score and all their dimensions improved from baseline (p<0.0001). At 12 months, 77.8% of the patients were responders to naloxegol treatment. Global QOL was conserved from baseline. A total of 28 adverse reactions, mainly gastrointestinal were observed in 15.1% of the patients (19/126), being 75% (21) mild, 17.9% (5) moderate and 7.1% (2) severe. Most adverse reactions (67.9%) appeared the first 15 days of treatment.

CONCLUSION

The results of this first long-term and real-world-data study in patients with cancer, showed the sustained efficacy and safety of naloxegol for the treatment of OIC in this group of patients.

Overcoming barriers to opioid-induced constipation management in cancer patients

PURPOSE

Opioid-induced constipation (OIC) is a common adverse effect of opioid therapy. We aim to identify the main barriers hindering clinical recommendations implementation and propose consensus solutions to improve OIC control in cancer patients.

METHODS

Following collaborative and prioritization techniques, a scientific committee generated statements addressing possible barriers to optimal OIC management (related to patients, health providers and health care system), and potential interventions to overcome these barriers. An expert panel of 36 oncologists assessed the statements to reach a consensus.

RESULTS

The survey consisted of 70 statements. Consensus was reached on 12/45 items related to barriers (26.6%) and on 19/25 items about corrective interventions (76%). The panel considered that patients are unaware of the existence of a specific OIC treatment, and their information sources are highly variable and unreliable. Regarding health providers, the panel considered that the oncologists prioritize symptoms such as diarrhea, pain, anxiety, or other treatment toxicities, over constipation. Work overload and bureaucratic requirements were the main barriers related to health care system. Regarding potential interventions, best-rated proposals included specific training programs development for primary care physicians and nurses, and multiplatform informative resources development for patients and caregivers, including precisely written instructions about OIC recognition and management. Oncologists assessed positively measures aiming to improve coordination between primary care physicians and oncologists, and nursing consultations implementation. The panel considered useful the OIC treatment algorithms simplification.

CONCLUSIONS

The expert panel identified the main barriers to optimal OIC management and suggested some feasible approaches to overcome these barriers.

Can Naloxegol Therapy Improve Quality of Life in Patients with Advanced Cancer?

This observational study aims to evaluate the efficacy of naloxegol therapy in resolving opioid-induced constipation (OIC) and in improving the quality of life in a home palliative care cancer setting. Advanced cancer patients with OIC (Rome IV criteria) not relieved by laxatives started a naloxegol therapy 25 mg/day for 4 weeks. Quality of life was evaluated by Patient Assessment of Constipation Quality-of-Life (PAC-QoL) at day 0 and day 28; background pain by Numerical Rating Scale, number of weekly spontaneous bowel movements and Bowel Function Index (BFI) were evaluated at day 0 and every week. Seventy-eight patients who completed the 4-week study improved all four PAC-QoL dimensions (physical and psychological discomfort, worries/concerns and satisfaction level). Weekly spontaneous bowel movements increased and BFI improved. Background pain reduced after seven days and remained lower during the following weeks. Seventy-two patients dropped out the study before day 28 with a reduced survival compared to patients completing the study. Even in these patients, an improvement of bowel function was observed after two weeks. Naloxegol was effective in improving the quality of life, resolving OIC and reducing overall pain in patients with advanced cancer.

Efficacy of naloxegol on symptoms and quality of life related to opioid-induced constipation in patients with cancer: a 3-month follow-up analysis

Objectives

Opioid-induced constipation (OIC) can affect up to 63% of all patients with cancer. The objectives of this study were to assess quality of life as well as efficacy and safety of naloxegol, in patients with cancer with OIC.

Methods

An observational study was made of a cohort of patients with cancer and with OIC exhibiting an inadequate response to laxatives and treated with naloxegol. The sample consisted of adult outpatients with a Karnofsky performance status score ≥50. The Patient Assessment of Constipation Quality of Life Questionnaire (PAC-QOL) and the Patient Assessment of Constipation Symptoms (PAC-SYM) were applied for 3 months.

Results

A total of 126 patients (58.2% males) with a mean age of 61.3 years (range 34–89) were included. Clinically relevant improvements (>0.5 points) were recorded in the PAC-QOL and PAC-SYM questionnaires (p<0.0001) from 15 days of treatment. The number of days a week with complete spontaneous bowel movements increased significantly (p<0.0001) from 2.4 to 4.6 on day 15, 4.7 after 1 month and 5 after 3 months. Pain control significantly improved (p<0.0001) during follow-up. A total of 13.5% of the patients (17/126) presented some gastrointestinal adverse reaction, mostly of mild (62.5%) or moderate intensity (25%).

Conclusions

Clinically relevant improvements in OIC-related quality of life, number of bowel movements and constipation-related symptoms were recorded as early as after 15 days of treatment with naloxegol in patients with cancer and OIC, with a good safety profile.

Anaesthesia and changes in parameters that reflect glucose metabolism in pigs – a pilot study

Pigs are commonly used in diabetes research due to their many physiological similarities to humans. They are especially useful in imaging procedures because of their large size. However, to achieve imaging procedures the pig must lie completely still, and thus needs to be anaesthetized. Most anaesthetic drugs used in laboratory animals affect carbohydrate metabolism by the inhibition of insulin release. The aim of this pilot study was primarily to develop an anaesthetic protocol for pigs that did not have an effect on blood glucose levels throughout the 3 h of anaesthesia; and secondly, to evaluate the most promising protocol in combination with an oral glucose tolerance test (OGTT). Two anaesthetic protocols were used in four growing pigs. Intravenous propofol infusion caused hyperglycaemia in three out of four pigs within 5–10 min after induction and was therefore excluded. Intravenous infusion with tiletamine, zolazepam and butorphanol (TZB) for 3 h did not affect blood glucose levels. The pigs underwent OGTT twice, once without anaesthesia and once with TZB induction after glucose intake. Anaesthesia during OGTT resulted in a lower area under the curve (AUC) of glucose ( P < 0.05), higher AUC of glucagon ( P < 0.05) and an insulin response less than 10% of that during OGTT without anaesthesia. In conclusion, long-term infusion anaesthesia with TZB does not affect glucose homeostasis in pigs. However, the protocol is not effective when combined with OGTT, as glucose, insulin and glucagon levels are affected.

Ultraviolet-A irradiation to the eye modulates intestinal mucosal functions and properties of mast cells in the mouse

We previously reported that topical irradiation of the eye by ultraviolet-B (UVB) activated hypothalamo-pituitary-adrenal axis (HPA-A) of the mouse to increase 3, 4-dihydroxyphenylalanine (DOPA)-positive melanocytes in the skin by an inducible nitric oxide synthase (iNOS)-dependent mechanism. This work demonstrates that irradiation of the eye by ultraviolet-A (UVA) specifically increased DOPA-positive cells in the mucosa of the jejunum and colon of C57BL/6J mice by some HPA- and iNOS-independent mechanism. UVA-induced increase in DOPA-positive cells in the intestine was inhibited by the administration of hexamethonium or prazosin plus propranolol, blockers for the sympathetic nervous system. UVA irradiation of the eye increased DOPA- and histidine decarboxylase (HDC)-positive cells in the intestinal mucosa of both C57BL/6J and WBB6F1/J mice but not in the mutant strain W/Wv of the latter that lack mast cells. UVA irradiation of the eye suppressed the intestinal peristalsis of control, hypophysectomized or iNOS(-/-) C57BL/6J mice by the mechanism that was inhibited by hexamethonium or prazosin plus propranolol. These observations suggest that UVA irradiation of the eye stimulated the sympathetic nervous system to increase the mucosal DOPA- and HDC-positive mast cells and suppressed the peristalsis of the small intestine of the mouse.

Overriding the blockade of antinociceptive actions of opioids in rats treated with extended-release naltrexone

A monthly extended-release formulation of the opioid antagonist naltrexone (XR-NTX) is approved for treatment of alcohol dependence. There is little research regarding overriding chronic (>21 days) competitive opioid receptor blockade with opioids for acute pain. Using the hot plate test after XR-NTX or placebo microsphere administration, rats were treated with an opioid analgesic to determine the dose required to produce the maximum response latency (MRL; 60 s). Rats were later treated with the same opioid to determine any potential effects on respiration rate or locomotor activity. In naïve rats, 15 mg/kg morphine, 0.1 mg/kg fentanyl and 8 mg/kg hydrocodone produced MRL. In XR-NTX treated rats, morphine produced 36% and 46% MRL at 90 mg/kg on days 4 and 19 and 96% MRL at 45 mg/kg on day 39. Fentanyl produced 100% MRL at 2.0 mg/kg on days 4 and 19 and at 0.5 mg/kg on day 39. Hydrocodone (80 mg/kg) produced 69%, 80% and 100% MRL on days 4, 19 and 39. Compared to placebo, these doses did not further depress respiration or alter locomotor activity. Thus, opioid receptor blockade with XR-NTX can be overcome in rats with higher doses of opioids without further affecting respiration or locomotor activity.

Methylnaltrexone mechanisms of action and effects on opioid bowel dysfunction and other opioid adverse effects

OBJECTIVE

To review the mechanisms of action of methylnaltrexone and its effects on opioid bowel dysfunction, as well as its effects on other opioid-induced adverse effects (ADEs), and its potential roles in clinical practice.

DATA SOURCES

A literature search using the MEDLINE and Cochrane Collaboration databases for articles published between 1966 and March 2007 was performed. Additional data sources were obtained from manual searches of recent journal articles, book chapters, and monographs. An updated literature search showed no additional publications.

STUDY SELECTION AND DATA EXTRACTION

Abstracts and original preclinical and clinical research reports published in the English language were identified for review. Review articles, commentaries, and news reports of this compound were excluded. Literature related to opioids, opioid receptors, opioid antagonists, methylnaltrexone, opioid-induced bowel dysfunction, constipation, nausea, and vomiting was evaluated and selected based on consideration of the support shown for the proof of concept, mechanistic findings, and timeliness. Fifty-eight original articles from preclinical studies and clinical trials using methylnaltrexone were identified. Pharmacologic action, benefits, and ADEs of methylnaltrexone were reviewed, with a focus on its effects on bowel dysfunction after opioids. Emphases were placed on its receptor binding activities and therapeutically relevant sites of action (peripheral vs central), in which peripheral opioid receptors in the body contribute to physiological and drug-induced effects.

DATA SYNTHESIS

Morphine and related opioids are associated with a number of limiting ADEs, including opioid-induced bowel dysfunction. Methylnaltrexone, a quaternary derivative of naltrexone, blocks peripheral effects of opioids while sparing central analgesic effects. It is currently under late-stage clinical investigation for the treatment of opioid-induced constipation in patients with advanced illness. Reported results showed the drug to be generally well-tolerated. The rapid reversal of constipation is very encouraging. Hastening postoperative discharge may also be possible.

CONCLUSIONS

Methylnaltrexone has the potential to prevent or treat opioid-induced peripherally mediated ADEs on bowel dysfunction without interfering with central analgesia. The study of methylnaltrexone leads to a greater understanding of the mechanisms of action of opioid pharmacology.

Adrenergic neurone blockade and other acute effects caused by N-benzyl-N'N"-dimethylguanidine and its ortho-chloro derivative

N-Benzyl-N'N"-dimethylguanidine sulphate (BW 467C60) and its ortho-chloro derivative (BW 392C60) had adrenergic neurone blocking and sympathomimetic effects resembling those of bretylium and guanethidine in cats, dogs and monkeys, but they were more potent in blocking adrenergic mechanisms in the cat. BW 467C60 was more active than its chloro derivative. Each compound inhibited release of noradrenaline during stimulation of the splenic nerve of cats, and increased smooth muscle responses to adrenaline and noradrenaline. Pressor responses to standard doses of tyramine were also increased except when large doses of BW 467C60 or BW 392C60 were given. The adrenergic neurone block by BW 467C60 was inhibited by dopamine, cocaine and amphetamine in situations in which these amines inhibit the effects of bretylium and guanethidine. In contrast to guanethidine, BW 467C60 and BW 392C60 did not lower the pressor amine content of the iris of cats 24 hr after administration of single doses of the compounds. BW 467C60 depressed the slope of curves relating the frequency of stimuli applied to the cervical sympathetic nerves and the resulting contraction of the nictitating membrane, but the effects of the lower rates of stimulation were preferentially inhibited. Large intravenous doses of BW 467C60 and BW 392C60 blocked autonomic cholinergic mechanisms and caused neuromuscular paralysis of voluntary muscle. These effects were brief, in contrast to the adrenergic neurone blockade. Both BW 467C60 and BW 392C60 were well absorbed from the alimentary tract. In contrast to guanethidine, BW 467C60 did not cause diarrhoea in guinea-pigs.

The actions of bretylium: adrenergic neurone blocking and other effects. 1959

Bretylium caused a specific and lasting depression of many excitatory and inhibitory responses evoked by electrical stimulation of the peripheral sympathetic nervous system, probably by impairing conduction of impulses in adrenergic neurones with consequent failure of noradrenaline and adrenaline release. This effect, which will be referred to as the adrenergic neurone blocking action, was preceded by weak sympathomimetic effects. In the presence of bretylium the effects of adrenaline and noradrenaline were increased, as after sympathectomy. Concentrations producing blocking of adrenergic neurones did not prevent the release of adrenaline and noradrenaline from the adrenal medulla by splanchnic nerve stimulation or by the injection of dimethylphenylpiperazinium iodide, nor did they cause antiparasympathetic or parasympathomimetic effects. No action on the central nervous system has been detected. Curare-like neuromuscular block occurred with 10 to 30 times the amount required to block the response to adrenergic nerve stimulation alone and was accompanied by signs of temporary synaptic block in autonomic ganglia. A drenergic. nerve trunks and sensory nerves in the skin were readily blocked for long periods by topical application of bretylium, whereas the phrenic nerve of the rat was not. Bretylium had little effect on gastrointestinal propulsion or on the sensitivity of smooth muscle to acetylcholine, 5-hydroxytryptamine, adrenaline, or noradrenaline, but moderate amounts depressed the peristaltic reflex and the sensitivity of the guinea-pig ileum to histamine. Bretylium caused postural hypotension in the cat in doses which had little effect on the supine blood pressure. Experiments on the nictitating membrane indicated that compensation for the effects of bretylium on low rates of stimulation of postganglionic sympathetic nerves could be attained by a small increase in the rate of stimulation, whereas compensation for its effects on high rates required an increase in the rate of stimulation beyond physiological limits.

[Oral papaverine prevents morphine-induced constipation without interfering with analgesia achieved with oral morphine]

Long-term administration of morphine for the treatment of chronic pain produces constipation; this requires the use of laxatives, which impair water absorption and upset the electrolyte balance. Morphine-induced constipation is mainly due to inhibition of the propulsive movement of the gastrointestinal tract combined with spastic contraction of smooth circular muscles as a result of drug binding to opioid receptors in the tract. Since papaverine lacks affinity for opioid receptors but relaxes smooth muscle, it seemed possible that oral papaverine might be capable of diminishing constipation without impairing the analgesia achieved with morphine. For this purpose, experiments were carried out on rats: constipation was checked for by measuring the intestinal transit time, and analgesia was assessed by measuring the latency of the tail-flick response to radiant heat or nociceptive activity in single neurons of the thalamus evoked by supramaximal electrical stimulation of afferent C fibres in the sural nerve. Morphine and papaverine were administered by the oral route. Control animals received saline. To measure the intestinal transit time, India ink solution was given orally. Morphine (2.5 and 5 mg/kg orally) prolonged the transit time from approx. 420 min in the controls to more than 600 min, a dose of 2.5 mg/kg producing the maximum effect. Papaverine (0.5, 1, and 2 mg/kg) administered orally together with morphine significantly reduced morphine-induced constipation (Tables 1, 2). Papaverine given alone at a dose of 2 mg/kg caused no change in transit time, while 5 mg/kg significantly increased it (Table 2). The latency of the tail-flick response was increased by oral morphine (2.5 and 5 mg/kg) at 1, 2, and 3 h after administration. Papaverine (0.5, 1 and 2 mg/kg) given in combination with morphine left the antinociceptive effect of morphine unchanged (Figs. 1-3). A study of the nociceptive activity evoked in thalamus neurons of rats under urethane anaesthesia indicated that intestinal absorption of morphine was blocked. Therefore, metoclopramide (0.15 mg/kg) was injected i. v. 10 min before oral administration of morphine or the combination of morphine plus papaverine. Subsequently, morphine produced a dose-dependent depression of evoked nociceptive activity (Fig. 4), the mean effect amounting to 60 % of the control activity and being produced by 2.5 mg/kg (Fig. 5). Since in former experiments on nociceptive activity evoked in thalamus neurones it has been found that the ED(50) of i. v. morphine is 0.05 mg/kg, it is very likely that the presystemic elimination of orally administered morphine is very high and, in addition, that the efficiency of its active metabolite, morphine-6-glucuronide, is rather poor. When morphine 2.5 mg/kg was given together with papaverine 0.5 mg/kg, and morphine 5 mg/kg was administered in combination with papaverine 2 mg/kg, there was no significant reduction in the depressant effect of morphine on nociceptive activity evoked in thalamus neurons (Figs. 6, 7). The results suggest that papaverine given by the oral route may reduce morphine-induced constipation without impairment of the analgesic action of morphine in patients suffering from pain.

A method for simultaneous measurement of intragastric, intraduodenal, and intracolonic pressures in the bilaterally vagotomized spinal rat

A method has been developed where quantitative evaluation of intragastric (IGP), intraduodenal (IDP), and intracolonic (ICP) pressures (cm H2O) can be obtained in the bilaterally vagotomized spinal rat. The preparation is very sensitive to 5-hydroxytryptamine (5-HT) and 5-HT-agonists, carbachol, histamine, dopamine, and/or noradrenaline. The effects of drugs on IGP, IDP, and ICP (increase or decrease) can be assessed and a dose-response curve before and after antagonists can be computed. The described experimental model is simple, reliable, reproducible, and appropriate to study and differentiate the different gastrointestinal system receptors that seem to be involved in the modulation of gastrointestinal motility. The additional advantage in using this method is that drug effects on the motility of stomach, duodenum, and colon can be investigated simultaneously.

Buprenorphine and gastrointestinal transit in rats: effect of naloxone on the biphasic dose-response curve

1. Buprenorphine (0.01-10 mg/kg, subcutaneous [s.c.]) slowed the passage of a charcoal meal along the gastrointestinal tract in rats. The dose-response relationship was U-shaped. 2. When rats were pretreated with naloxone (0.30 mg/kg, s.c.), both the descending and ascending components of the buprenorphine dose-response curve were displaced to the right. 3. Buprenorphine-induced delay of transit was maximal at a dose of 0.10 mg/kg. In rats pretreated with naloxone, a 30-fold higher dose of buprenorphine was required for a comparable peak effect. 4. Moderate-high doses of buprenorphine may be acting on a functionally related binding site which non-competitively inhibits the usual buprenorphine-mu opioid receptor interaction.

Stress effects on gastrointestinal transit in the rat

Previous investigations of stress effects on gastric emptying, orocaecal, and colonic transit in rats have produced conflicting results. Here one type of stressor, a 'passive avoidance' situation, was used to investigate its effects on gastric emptying, orocaecal and colonic transit. After the rats had been trained to eat a standard amount of semisolid food, gastric emptying was determined (n = 12) by the food remaining in the stomach after various periods of rest, or stress exposure. Orocaecal transit (n = 14) was determined by breath hydrogen measurements after the food had been labelled with 1 g lactose. Colonic transit (n = 18) was measured as the arrival time of coloured faeces after infusion of a carmine red solution into the caecum through a chronically implanted catheter. The stressor had differential effects on transit through the stomach, small bowel and colon: gastric emptying was delayed (p less than 0.05) after stress (t1/2 = 2.66 h after stress, 1.97 h at rest). Orocaecal transit was accelerated (p less than 0.05) after stress; transit time decreased from 124.3 min at rest to 86.2 min after stress. Colonic transit was accelerated (p less than 0.01) under stress, from 15.5 h to 1.29 h. It is concluded that gastrointestinal transit in different parts of the gastrointestinal tract is differently affected by central nervous stimuli.

Antinociceptive effects of the novel opioid peptide BW443C compared with classical opiates; peripheral versus central actions

1. To investigate peripherally mediated antinociceptive effects of opioids, the activity of a novel polar enkephalin analogue H-Tyr-D-Arg-Gly-Phe (4-NO2)-Pro-NH2 (BW443C) has been compared with those of classical tertiary opiates against different nociceptive stimuli in the mouse. 2. In chemically-induced writhing models BW443C, administered subcutaneously, demonstrated dose-related antinociceptive effects less potent than morphine and of a similar order to pethidine and D-propoxyphene. In assays using heat as the noxious stimulus BW443C was markedly less potent than any of the opiates tested. 3. In heat-induced assays, but not in chemically-induced writhing assays, BW443C demonstrated a 'U'-shaped dose-time response relationship. Morphine, pethidine and D-propoxyphene showed simple, approximately linear, dose-time effects in all assays. 4. When given subcutaneously, the inhibitory effects of BW443C and morphine in chemically-induced writhing were antagonized by naloxone given intraperitoneally. The inhibitory effects on writhing of BW443C, but not those of morphine, were also antagonized by prior intraperitoneal administration of the quaternary opioid antagonist N-methyl nalorphine. When this antagonist was administered intracerebroventricularly, the antinociceptive effects in writhing of both BW443C and morphine were antagonized. 5. It is concluded that BW443C, being only poorly able to cross the blood brain barrier, demonstrates peripherally mediated opioid antinociceptive effects in chemically-induced writhing models. In heat-induced models, that detect centrally acting opioids, BW443C is effective only at high doses and at time intervals after dosing sufficient to allow slow penetration of drug into the CNS. It is suggested that the peripheral antinociceptive actions of BW443C are mediated by inhibition of sensory neurones.

Effect of substance P on rat gastrointestinal transit

The in vivo effect of substance P and related peptide analogs on gastrointestinal transit in unanesthetized rats was studied. Fasted male rats were given intragastrically 0.5 ml of a powdered charcoal (BaSo4.H2O) meal and were concomitantly injected intraperitoneally with 8 micrograms/kg of substance P or a related peptide. In control rats, the percentage of small intestine traversed by the meal 15 min after feeding was 44.9 +/- 1.4 (N = 12). Substance P, [pGlu6]SP, [pGlu6, gPhe8, mGly9]SP and [pGlu5, N-MePhe8, N-MeGly9]SP significantly accelerated intestinal transit: 59.5 +/- 3.1% (N = 7); 66.0 +/- 3.8% (N = 14), 66.8 +/- 2.4% (N = 25), and 58.4 +/- 4.4% (N = 4), respectively. Concomitant injection of [pGlu6]SP and BOC-Phe-Phe-Gly-NHOH, an inhibitor of enzyme degradation at a dose of 800 micrograms/kg lowered by 10-fold the dose of [pGlu6]SP needed to induce the same degree of intestinal transit acceleration. These results indicate that in rats, substance P and related peptides accelerate gastrointestinal transit.

Antagonism by N-methyl levallorphan-methane sulphonate (SR 58002 C) of morphine-elicited acute and chronic central and peripheral effects

The peripheral activity of the quaternary narcotic antagonist N-methyl levallorphan-methane sulphonate (SR 58002 C) at opioid sites located in the periphery and in the central nervous system (CNS), was studied by different approaches in rats after subcutaneous injection (s.c.). Pretreatment with SR 58002 C 2,8 or 32 mg/kg s.c. 10, 50 or 110 min before buprenorphine consistently reduced buprenorphine in vivo binding only in the small intestinal longitudinal muscle with attached myenteric plexus (MP), whereas naloxone (1 mg/kg s.c.) 10 min before buprenorphine lowered buprenorphine binding in MP and brain (without cerebellum). Plasma levels were not altered by SR 58002 C or naloxone. The same doses of SR 58002 C injected 10, 50 or 110 min before morphine selectively antagonized the inhibition of transit of a charcoal meal along the small intestine (mainly a peripheral effect) induced by the agonist, but did not antagonize morphine-elicited analgesia in the hot-plate test (central effect). Naloxone (1 mg/kg s.c.) injected 10 min before morphine antagonized both agonist effects simultaneously. In morphine-dependent rats SR 58002 C (0.25, 1, 4 and 32 mg/kg s.c.) induced diarrhea, dose-dependently, in most animals within the first 30 min, while jumping, measured in the same rats, occurred in some animals, not dose-dependently, from 60 min on. Naloxone (1 mg/kg s.c.) induced both effects in most rats. These findings suggest that, although SR 58002 C probably penetrates the blood-brain barrier in some morphine-dependent rats, it discriminates peripheral and CNS opioid effects.

A tachykinin antagonist inhibits gastric emptying and gastrointestinal transit in the rat

The effect of a substance P antagonist, [D-Pro2, D-Trp7,9]-substance P (SPA), on gastric emptying and gastrointestinal transit in the rat was studied in order to elucidate a possible physiological role of endogenous substance P and other tachykinins in gastrointestinal motility. SPA was given by intraperitoneal injection concurrently with the intragastric administration of a test meal containing charcoal and 51Cr. Examination 15 min after the test meal showed that SPA (0.13-1.3 mumol kg-1) inhibited gastric emptying and gastrointestinal transit in a dose-dependent manner. The inhibitory effect of SPA on gastric emptying and gastrointestinal transit remained unchanged after pretreatment of rats with mepyramine (8.7 mumol kg-1) plus cimetidine (19.8 mumol kg-1) or with guanethidine (67 mumol kg-1). Since a full examination of SPA as a specific tachykinin antagonist was not possible in vivo, SPA was also tested on circular muscle strips from the rat gastric corpus in vitro. Submaximal contractions in response to bombesin or bethanechol were not reduced by SPA (50 microM), whereas those in response to substance P were inhibited. The results suggest that SPA inhibits gastric emptying and gastrointestinal transit by interfering with the action of tachykinins released from enteric nerves and that endogenous tachykinins are involved in the regulation of gastrointestinal motility.

Intrathecal morphine slows gastrointestinal transit in rats

Intrathecal (i.th.) (by direct lumbar puncture) and intraperitoneal (i.p.) administration of morphine (30-100 micrograms/rat) caused a dose-related inhibition of gastrointestinal transit in the rat. Pretreatment with i.th. naloxone (5 micrograms at -5 min) reversed the effects of i.th., but not i.p., morphine. These results suggest that the spinal cord appears to be a target site for the inhibitory effects of morphine on gastrointestinal transit in the rat.

Pituitary-adrenal mediation of bombesin-induced inhibition of gastrointestinal transit in rats

Centrally administered bombesin (0.1-3.5 micrograms, i.c.v.) inhibits gastrointestinal transit of a charcoal meal in a dose-related manner in rats. The roles of pituitary and adrenal glands in the mediation of this effect were assessed. The inhibition of gastrointestinal transit associated with bombesin (0.5 microgram, i.c.v.) was prevented by either hypophysectomy or adrenalectomy. Bombesin-induced inhibition of gastrointestinal transit is therefore mediated through the pituitary-adrenal axis. This is in contrast to bombesin-induced scratching and inhibition of gastric acid secretion which are not markedly influenced by either hypophysectomy or adrenalectomy.

A species difference in the slowing effect of intrathecal morphine on gastrointestinal transit

Intrathecal administration of morphine, levorphanol, bremazocine, ethylketocyclazocine or [D-Ser2,Leu5,Thr6]enkephalin to rats, at doses 10-50 times greater than that necessary to elicit analgesia in the tail flick test, had no marked effect on gastrointestinal transit as determined by the charcoal meal test. In contrast, intrathecal administration of various doses of morphine to mice significantly antagonized transit (A50 (that dose which inhibited transit to 50% of controls) = 14.7 (0.71-2.89) micrograms/mouse). These results suggest (1) a lack of involvement of opioid sensitive spinal structures in the control of gastrointestinal transit in rats, and (2) a species difference in the slowing effect of intrathecal morphine on gastrointestinal transit.

Intrathecal bombesin in rats: effects on behaviour and gastrointestinal transit

When bombesin is given intracerebroventricularly to rats, it is known to cause excessive scratching and inhibit gastrointestinal transit. We have administered bombesin via a permanent indwelling cannula into the subarachnoid space of the lumbar spinal cord of rats. By this route, bombesin elicited immediate excessive scratching and rapidly inhibited passage of a charcoal meal along the gastrointestinal tract. The A50 values for these effects were 0.004 (0.001-0.018) micrograms/rat and 0.34 (0.22-0.55) micrograms/rat, respectively. Bombesin-induced scratching and inhibition of transit are therefore mediated at spinal, as well as supraspinal, levels.

Ketazocines and morphine: effects on gastrointestinal transit after central and peripheral administration

The mu agonist, morphine, and the prototype kappa agonists, ketocyclazocine and ethylketocyclazocine (EK), were studied for their effects on gastrointestinal transit. Following s.c. administration, both morphine (0.3-3 mg/kg) and ketocyclazocine (0.3-10 mg/kg) antagonized transit of an opaque marker through the small intestines of mice. Morphine (0.1-1 microgram) was also effective after intracerebroventricular (icv) administration in mice whereas ketocyclazocine (0.3-30 micrograms) was not. Similarly, while both morphine (0.3-5 mg/kg) and EK (0.6-10 mg/kg) slowed transit after s.c. injection to rats, only morphine (1-10 micrograms), but not EK (0.3-300 micrograms), was active following icv administration. Icv infusion of the mu benzomorphan, phenazocine (10-100 micrograms), slowed transit in a dose-related manner. These results indicate that there may be an anatomically distinct distribution of receptors for benzomorphan kappa agonists in both the mouse and rat, with these opiate receptors not being located near the lateral cerebral ventricles. The difference in efficacy between morphine and ketazocines in slowing gastrointestinal transit after icv administration to rodents suggests that (a) inactivity in this endpoint is a characteristic of benzomorphan kappa compounds and (b) the model may serve as a useful screen when establishing in vivo profiles of kappa agonists in mice and rats.

A comparison of the receptor constants of morphine and ethylketocyclazocine for analgesia and inhibition of gastrointestinal transit in the rat

The efficacies and dissociation constants of proposed mu and kappa receptor agonists (morphine and ethylketocyclazocine, respectively) were compared using the method of partial irreversible blockade (with buprenorphine) and Stephenson's theory of drug action. While there was good agreement between the dissociation constant (KA) of morphine in analgesia (3.3 x 10(-5) M) and in inhibition of gastrointestinal transit (1.1 x 10(-5) M), the KA of ethylketocyclazocine differed by an order of magnitude in these endpoints (3.2 x 10(-6) M and 6.7 x 10(-5) M, respectively). The efficacies of morphine were found to be similar for the two effects studied (4.23 and 5.26), while those for ethylketocyclazocine differed markedly (2.06 and 10.39). The fraction of receptors remaining unblocked after buprenorphine was consistent for the test but not for the agonist, indicating a different distribution of receptors for the two endpoints. Our results strongly suggest that morphine induces analgesia, and slows transit in the small intestine, through the same type of receptor. The same conclusion cannot be drawn for ethylketocyclazocine.

The animal pharmacology of buprenorphine, an oripavine analgesic agent

1. The general pharmacology of buprenorphine, a potent analgesic agent derived from oripavine, is described. 2. After cute administration of buprenorphine, the spontaneous locomotor activity of mice was increased; rats displayed stereotyped licking and biting movements; behavioural depression was marked in guinea-pigs but mild in rhesus monkeys. The behaviour of cats was unchanged. 3. In general, buprenorphine reduced heart rate but had no significant effect on arterial blood pressure in conscious rats and dogs. 4. In anaesthetized, open-chest cats buprenorphine (0.10 and 1.0 mg/kg, i.v.) caused no major haemodynamic changes. 5. Buprenorphine (0.01-10 mg/kg i.a.) and morphine (0.30-30 mg/kg, i.a.) increased arterial PCO2 values and reduced PO2 values in conscious rats. With doses of buprenorphine greater than 0.10 mg/kg (a) the duration of respiratory depression became less, (b) ceiling effects occurred such that the maximum effects produced were less than those obtained with morphine. 6. Buprenorphine was a potent and long-lasting antagonist of citric acid-induced coughing in guinea-pigs. 7. At a dose level 20 times greater than the ED50 for antinociception (tail pressure), morphine suppressed urine output to a greater extent than the corresponding dose of buprenorphine in rats. 8. Over the range 0.01-1.0 mg/kg (s.c.), buprenorphine slowed the passage of a charcoal meal along the gastrointestinal tract in rats. After doses in excess of 1 mg/kg, the meal travelled increasingly further such that the distances measured at 10 and 30 mg/kg did not differ significantly from control values. In contrast, the morphine dose-response relationship was linear.