Morphine and opioid peptides selectively inhibit the non-cholinergically mediated neurogenic contraction of guinea-pig isolated bronchial muscle

Current pharmacological strategies for symptomatic reduction of persistent breathlessness - a literature review

INTRODUCTION

Persistent breathlessness is a debilitating symptom that is prevalent in the community, particularly in people with chronic and life-limiting illnesses. Treatment includes different steps, including pharmacological treatment aiming to improve the symptom and optimize people's wellbeing.

AREAS COVERED

PubMed and Google Scholar were screened using 'chronic breathlessness' OR 'persistent breathlessness,' AND 'pharmacological treatment,' OR 'opioids.' This review focuses on pharmacological treatments to reduce persistent breathlessness and discusses possible mechanisms involved in the process of breathlessness reduction through pharmacotherapy. Research gaps in the field of persistent breathlessness research are outlined, and future research directions are suggested.

EXPERT OPINION

Regular, low-dose (≤30 mg/day), sustained-release morphine is recommended as the first-line pharmacological treatment for persistent breathlessness. Inter-individual variation in response needs to be investigated in future studies in order to optimize clinical outcomes. This includes 1) better understanding the centrally mediated mechanisms associated with persisting breathlessness and response to pharmacological therapies, 2) understanding benefit from the perspective of people experiencing persistent breathlessness, small and meaningful gains in physical activity.

Progress in understanding mechanisms of opioid-induced gastrointestinal adverse effects and respiratory depression

Opioids evoke analgesia through activation of opioid receptors (predominantly the μ opioid receptor) in the central nervous system. Opioid receptors are abundant in multiple regions of the central nervous system and the peripheral nervous system including enteric neurons. Opioid-related adverse effects such as constipation, nausea, and vomiting pose challenges for compliance and continuation of the therapy for chronic pain management. In the post-operative setting opioid-induced depression of respiration can be fatal. These critical limitations warrant a better understanding of their underpinning cellular and molecular mechanisms to inform the design of novel opioid analgesic molecules that are devoid of these unwanted side-effects. Research efforts on opioid receptor signalling in the past decade suggest that differential signalling pathways and downstream molecules preferentially mediate distinct pharmacological effects. Additionally, interaction among opioid receptors and, between opioid receptor and non-opioid receptors to form signalling complexes shows that opioid-induced receptor signalling is potentially more complicated than previously thought. This complexity provides an opportunity to identify and probe relationships between selective signalling pathway specificity and in vivo production of opioid-related adverse effects. In this review, we focus on current knowledge of the mechanisms thought to transduce opioid-induced gastrointestinal adverse effects (constipation, nausea, vomiting) and respiratory depression.

Central and peripheral mechanisms of narcotic antitussives: codeine-sensitive and -resistant coughs

Narcotic antitussives such as codeine reveal the antitussive effect primarily via the mu-opioid receptor in the central nervous system (CNS). The kappa-opioid receptor also seems to contribute partly to the production of the antitussive effect of the drugs. There is controversy as to whether delta-receptors are involved in promoting an antitussive effect. Peripheral opioid receptors seem to have certain limited roles. Although narcotic antitussives are the most potent antitussives at present, certain types of coughs, such as chronic cough, are particularly difficult to suppress even with codeine. In guinea pigs, coughs elicited by mechanical stimulation of the bifurcation of the trachea were not able to be suppressed by codeine. In gupigs with sub-acute bronchitis caused by SO2 gas exposure, coughing is difficult to inhibit with centrally acting antitussives such as codeine. Some studies suggest that neurokinins are involved in the development of codeine-resistant coughs. However, evidence supporting this claim is still insufficient. It is very important to characterize opiate-resistant coughs in experimental animals, and to determine which experimentally induced coughs correspond to which types of cough in humans. In this review, we describe the mechanisms of antitussive effects of narcotic antitussives, addressing codeine-sensitive and -resistant coughs, and including our own results.

Inhibitory effect of olopatadine hydrochloride on the sneezing response induced by intranasal capsaicin challenge in guinea pigs

To investigate the possible inhibitory effect of olopatadine hydrochloride (olopatadine), an antiallergic drug, on the tachykinin-mediated nasal responses, we examined the effect of olopatadine on the sneezing and the nasal rubbing responses induced by intranasal capsaicin challenge in guinea pigs. Olopatadine (10 mg/kg, p.o.) inhibited the sneezing response by 57% without affecting the nasal rubbing one. The antihistamines chlorpheniramine and clemastine did not affect the responses. Morphine caused the inhibition of both responses, which was antagonized by naloxone. These results suggest that olopatadine inhibits the sneezing response by the inhibition of the tachykinin release and not by its antihistaminic action.

Nociceptin effects in the airways

The opioid-like heptadecapeptide nociceptin (NC) has the following effects in the airways (investigated in isolated tracheae and bronchi from guinea pig or rat): the electric field stimulation (EFS)-induces release of acetylcholine (ACh), the tachykinin substance P (SP) and calcitonin gene-related peptide (CGRP) is reduced after pretreatment with NC, and EFS-induced tachykinergic nonadrenergic-noncholinergic (NANC) bronchoconstriction is inhibited by NC. Both the NC-mediated inhibition of neurotransmission and of smooth muscle contraction occurred in a concentration-dependent manner. Because these effects were naloxone-insensitive, were blocked by the NC receptor antagonist [F/G]NC(1-13)NH(2), and could be mimicked by the NC analogs, NCNH(2) and NC(1-13)NH(2), it is thought that they are distinct from the classic opioid receptors. That these pharmacological actions of NC are of relevance for airway physiology is highly probable given the presence of NC-immunoreactivity in the nerve fibers of the airways and of opioid-like receptor (ORL-1) transcripts in the jugular ganglia, from where the tachykinin-containing afferents arise.

Nociceptin inhibits non-adrenergic non-cholinergic contraction in guinea-pig airway

1. Electrical field stimulation (EFS) of guinea-pig isolated main bronchi induced a non-adrenergic non-cholinergic (NANC) contractile response. Nociceptin (0.01-1 microm) significantly inhibited the contractile response to EFS (P<0.01), but not to capsaicin (P>0.05). 2. The mu-, delta- and kappa-opioid receptor antagonists, naloxone (0.3 microM), naltrindole (3 microM) and norbinaltorphimine (1 microm), respectively, did not significantly affect the inhibitory effect of nociceptin (0.03 microM; P>0.05). 3. The novel nociceptin antagonist, [Phe1psi(CH2-NH)Gly2]nociceptin(1-13)NH2 (0.03-1 microM); the sigma ligands, carbetapentane (30 microM), 3-phenylpiperidine (30-100 microM) and (+)-cyclazocine (10-100 microM) significantly reversed the inhibitory effect of nociceptin (0.03 microM, P<0.05). In contrast, rimcazole, did not significantly reverse the inhibitory effect of nociceptin (0.03 microM) at any concentration tested (P>0.05). 4. EFS of guinea-pig bronchial preparations significantly increased SP-LI release above basal SP-LI (P<0.05). In the presence of nociceptin (1 microM), EFS induced a significant increase in SP-LI release above basal SP-LI release (P<0.05). Nociceptin caused a 59+11% (n=5) inhibition of EFS-induced release of SP-LI. 5. Nociceptin reduces the release of sensory neuropeptides induced by EFS, but not capsaicin, from guinea-pig airways. These experiments provide further evidence for a role for nociceptin in regulating the release of sensory neuropeptides in response to EFS.

SR 48968, a novel non-peptide tachykinin NK-2-receptor antagonist, selectively inhibits the non-cholinergically mediated neurogenic contraction of guinea-pig isolated bronchial muscle

We have examined the actions of SR 48968 ((S)-N-methyl-N-[4-(4-acetylamino-4-phenyl piperidino)-2-(3,4-dichlorophenyl)butyl]benzamide), a novel non-peptide tachykinin NK-2-receptor antagonist, on the response evoked by electrical field stimulation or by acetylcholine and neurokinin A on guinea-pig isolated airway smooth muscle. Electrical field stimulation (1-32 Hz, 0.3 ms, 30 V for 20 s) evoked a biphasic response in a frequency-dependent manner, consisting of a cholinergically-mediated fast contraction followed by a non-adrenergically-mediated relaxation in tracheal muscle and by a non-cholinergically-mediated slow contraction in bronchial muscle. SR 48968 (0.01-1 microM) caused a concentration-dependent inhibition of non-cholinergically mediated contraction of bronchial muscle, without significant influence on cholinergically and non-adrenergically-mediated responses. Submaximal contractions of tracheal and bronchial muscles evoked by exogenous neurokinin A (10-300 nM) were markedly inhibited by SR 48968 (0.1-1 microM), but those by exogenous acetylcholine (1-3 microM) were slightly inhibited by the antagonist. The results indicate that in guinea-pig isolated bronchial muscle, SR 48968 selectively inhibited non-cholinergically mediated neurogenic contraction via antagonism of NK-2 receptors.

Modulating effects of antiasthmatic and antitussive drugs on autonomic neurotransmission in guinea-pig bronchial muscle in vitro

Electrical field stimulation evoked a biphasic contraction of the guinea-pig isolated bronchi, consisting of a cholinergically mediated fast contraction followed by a non-cholinergically mediated slow contraction. Catecholamines, beta 2-stimulants, methylxanthines, antiallergic drugs, narcotic and non-narcotic antitussive drugs inhibited the neurogenic contractions not only by postjunctional depression of the response but also by prejunctional reduction of the transmitter release.