Effects of κ- and μ-opioid agonists on cholinergic neurotransmission and contraction in isolated bovine trachealis

Interactions between glycopyrronium and indacaterol on cholinergic neurotransmission and contractile response in bovine trachealis

BACKGROUND

Muscarinic-receptor antagonists and β-adrenoceptor agonists are used, alone or in combination, as first-line treatment for chronic obstructive pulmonary disease. Both drugs decrease airway smooth muscle tone by post-junctional mechanisms but they may have opposing effects on pre-junctional acetylcholine (ACh)-release.

METHODS

We studied the effects of the muscarinic-receptor antagonist glycopyrronium (GLY), the β-adrenoceptor agonist indacaterol (IND) and their combination on electrically-induced ACh-release and contractile response in isolated bovine trachealis. Data were analyzed by paired t-test and analysis of variance for repeated or independent measures with Newmann-Keuls post-hoc test when appropriate.

RESULTS

GLY 10-8 M decreased contractile response by 19 ± 6% (p = 0.010) without altering ACh-release. GLY 10-7 M and 10-6 M almost abolished contractile responses even if the ACh-release was increased by 27 ± 19% (p < 0.001) and 20 ± 8% (p = 0.004), respectively. IND 10-7 M had no significant effects on contractile response and ACh-release, whereas IND 10-6 M reduced contractile response by 24 ± 12% (p = 0.002) without altering ACh-release. IND 10-5 M decreased contractile response by 51 ± 17% (p < 0.001) and ACh-release by 22 ± 11% (p = 0.004). Co-incubation with GLY 10-8 M and IND 10-7 M did not alter ACh-release but inhibited contractile response by 41 ± 8% (p < 0.001). The latter effect was greater than with GLY 10-8 M, or IND 10-7 M, or IND 10-6 M given separately (p < 0.001 for all). The increment of ACh-release caused by GLY was attenuated by IND 10-5 M, though this did not affect contractile response.

CONCLUSIONS

At equimolar concentration, GLY alone attenuates airway smooth muscle contraction more than IND, despite an increased ACh-release. Combination of GLY with IND at submaximal concentrations has more than additive effect suggesting a synergistic post-junctional effect. Adding GLY to IND provides a greater inhibitory effect on airway smooth muscle contraction than increasing IND concentration.

Does nebulized fentanyl relieve dyspnea during exercise in healthy man?

Few therapies exist for the relief of dyspnea in restrictive lung disorders. Accumulating evidence suggests that nebulized opioids selective for the mu-receptor subtype may relieve dyspnea by modulating intrapulmonary opioid receptor activity. Our respective primary and secondary objectives were to test the hypothesis that nebulized fentanyl (a mu-opioid receptor agonist) relieves dyspnea during exercise in the presence of abnormal restrictive ventilatory constraints and to identify the physiological mechanisms of this improvement. In a randomized, double-blind, placebo-controlled crossover study, we examined the effect of 250 μg nebulized fentanyl, chest wall strapping (CWS), and their interaction on detailed physiological and perceptual responses to constant work rate cycle exercise (85% of maximum incremental work rate) in 14 healthy, fit young men. By design, CWS decreased vital capacity by ∼20% and mimicked the negative consequences of a mild restrictive lung disorder on exercise endurance time and on dyspnea, breathing pattern, dynamic operating lung volumes, and diaphragmatic electromyographic and respiratory muscle function during exercise. Compared with placebo under both unrestricted control and CWS conditions, nebulized fentanyl had no effect on exercise endurance time, integrated physiological response to exercise, sensory intensity, unpleasantness ratings of exertional dyspnea. Our results do not support a role for intrapulmonary opioids in the neuromodulation of exertional dyspnea in health nor do they provide a physiological rationale for the use of nebulized fentanyl in the management of dyspnea due to mild restrictive lung disorders, specifically those arising from abnormalities of the chest wall and not affiliated with airway inflammation.

Endogenous opiates and behavior: 2013

This paper is the thirty-sixth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2013 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.