Masakazu Yamaguchi

Propofol Attenuates Ovalbumin-induced Smooth Muscle Contraction of the Sensitized Rat Trachea: Inhibition of Serotonergic and Cholinergic Signaling

Propofol is considered suitable for induction of anesthesia in patients with bronchial asthma. However, the mechanisms of its action on bronchi are not fully understood. We examined the effects of propofol on ovalbumin (OA)-induced contraction of OA-sensitized rat trachea. Male Wistar rats were sensitized by a single intraperitoneal injection of OA 10 &mgr;g mixed with aluminum hydroxide, 10 mg, as adjuvant. Fourteen days later, the experiment was performed using the tracheal rings. We observed the effects of ketanserin, a 5-HT2 receptor antagonist, and atropine on OA-induced contraction. Next, the effects of propofol on OA-, serotonin (5-HT)-, acetylcholine-, or electrical field stimulation-induced contractions were observed. OA-induced contraction was 90% attenuated by the combination of ketanserin and atropine. Propofol significantly attenuated OA-induced contraction in a dose-dependent manner. Propofol abolished 5-HT-induced contraction, attenuated acetylcholine-induced contraction, and also almost completely attenuated the enhancement by 5-HT of electrical field stimulation-induced contraction. These results suggest that the mechanism involved in the attenuation by propofol of OA-induced contraction is inhibition of the actions of 5-HT. Propofol should be a useful anesthetic in patients with immunoglobulin E-related asthma.

Effects of propofol and ketamine on ATP-induced contraction of the rat trachea

PurposeATP causes airway smooth-muscle contraction in patients with asthma and chronic obstructive pulmonary disease. Propofol and ketamine attenuate the airway smooth-muscle contraction induced by histamine and acetylcholine. However, it is not clear whether propofol and ketamine affect the ATP-induced airway smooth-muscle contraction.MethodsWe examined the effects of propofol and ketamine on the ATP-induced contraction and ATP-P2-purinoceptor binding.ResultsPropofol attenuated the ATP-induced contraction in a dose-dependent manner, with a 50% inhibitory concentration of 54 ± 22 µM. Ketamine at 300 µM attenuated the ATP-induced contraction. In the binding study, propofol attenuated the binding of the P2-purinoceptor with [3H]-ATP in a dose-dependent manner, while ketamine did not attenuate this binding.ConclusionPropofol attenuates ATP-induced contraction through the inhibition of ATP-P2-purinoceptor binding.

The effects of fentanyl on the contractile response of ovalbumin-sensitized rat trachea

BACKGROUND: It is not clear whether fentanyl affects a hyperresponsive airway. We examined the effects of fentanyl on the contractile response of ovalbumin (OA)-sensitized rat tracheas. METHODS: Rats were sensitized with a single intraperitoneal injection of 10 &mgr;g of OA mixed with adjuvant. Fourteen days later, the trachea was cut into 3-mm-wide rings. The OA-induced tension was measured, and the effects of fentanyl were studied in the presence of naloxone. Second, the role of cholinergic nerves and serotonin in the contraction and the effects of fentanyl were examined using tetrodotoxin and ketanserin. Third, lungs of sensitized rats were ventilated, and respiratory system resistance was calculated before and after the administration of OA in the presence of fentanyl. RESULTS: Fentanyl dose-dependently attenuated the OA-induced contraction, and naloxone partly reversed it. Both tetrodotoxin and ketanserin attenuated the contraction. Fentanyl had no further effect on the contraction in the presence of tetrodotoxin, whereas the contraction was nearly abolished by fentanyl in the presence of ketanserin. OA increased respiratory system resistance in sensitized rats, and this effect was attenuated by fentanyl. CONCLUSIONS: Fentanyl attenuates the airway hyperresponsiveness of sensitized rat trachea through the inhibition of cholinergic nerves on the smooth muscle.

Anticholinesterase drugs stimulate smooth muscle contraction of the rat trachea through the Rho-kinase pathway.

We performed this study to determine the effects of Rho-kinase inhibitors, Y-27632 and fasudil, on the anticholinesterase (anti-ChE)-induced contractile and phosphatidylinositol responses of the rat trachea. In vitro measurements of isometric tension and [3H] inositol monophosphate (IP1) that was formed were conducted by using rat tracheal rings or slices. Neostigmine- and pyridostigmine-induced contractions were almost completely inhibited by Y-27632 and fasudil at 30 &mgr;M each, whereas acetylcholine-induced contraction was inhibited incompletely, i.e., by 56% by Y-27632 and by 51% by fasudil, at 100 &mgr;M for each, respectively. The inhibitory effects of fasudil on neostigmine- and acetylcholine-induced contractions were completely reversed by calyculin-A, a myosin phosphatase inhibitor. Neostigmine-induced IP1 accumulation was attenuated by fasudil at 100 &mgr;M. The results suggest that anti-ChEs cause airway smooth muscle contraction, in part, through activation of the Rho-kinase pathway.

Selegiline, an MAO-B inhibitor, attenuates airway smooth muscle contraction in the rat trachea

Selegiline is widely used for Parkinsons disease and sometimes for Alzheimers disease. It is reported to affect intracellular Ca2+ concentration. Since intracellular Ca2+ is partly regulated by phosphatidylinositol (PI) response and is important for smooth muscle contraction, selegiline may affect airway smooth muscle tension. We examined the effects of selegiline on acetylcholine (ACh)‐ and KCl‐induced contractile and PI responses in rat trachea. The trachea was cut into 3‐mm‐wide ring segments or 1‐mm‐wide slices. ACh (3 μM, 50% effective dose) or KCl (40mM) was added, and ring relaxation was induced by the addition of selegiline. Tracheal slices were incubated with [3H]myo‐inositol and 3 μM ACh in the presence of selegiline, and [3H]inositol monophosphate (IP1) was measured. Selegiline dose‐dependently attenuated ACh‐ and KCl‐induced tracheal ring contractions. Fifty‐percent inhibitory doses (ID50) of selegiline against ACh‐ and KCl‐induced contraction were 120±30 μM and 80±20 μM, respectively. Basal and ACh‐induced IP1 accumulation were 2.20±0.20 Bq and 7.88±0.23 Bq, respectively, and selegiline at a dose of 1000 μM attenuated ACh‐induced IP1 accumulation (5.44±0.30 Bq). These results suggest that selegiline inhibits contractile responses through the inhibition of voltage‐operated Ca2+ channels and the PI response.

High concentrations of landiolol, a β1-adrenoceptor antagonist, stimulate smooth muscle contraction of the rat trachea through the Rho-kinase pathway

PurposeGradually progressing contraction of airway smooth muscle is suggested to be due to the Rho-kinase signaling pathway. In our preliminary study in rat tracheas, landiolol, a β1-adrenoceptor antagonist, at high doses caused gradually progressing contraction, and this contraction reached a plateau after 20 min. Therefore, this study was carried out to clarify whether landiolol could stimulate the Rho-kinase pathway or the phosphatidylinositol (PI) response in the rat trachea.MethodsSeventy-eight male Wistar rats weighing 250–350 g were used for the experiments. Their tracheas were cut into 3-mm-wide ring segments or 1-mm-wide slices. Measurements of isometric tension and [3H] inositol monophosphate (IP1) production were conducted, using these tracheal rings or slices. Data values are expressed as means ± SD, and statistical significance (P < 0.05) was determined using analysis of variance (ANOVA).ResultsLandiolol (700 μM)-induced contraction was completely inhibited by fasudil at 30 μM, while the landiolol-induced contraction was not inhibited by 4-diphenylacetoxy-N-methyl-piperidine methobromide (4-DAMP), ketanserin, or nicardipine. Landiolol did not stimulate IP1 production.ConclusionThese results suggest that high concentrations of landiolol could cause airway smooth muscle contraction through the Rho-kinase pathway, but not through the PI response coupled with muscarinic M3 receptors, 5-HT receptors or the activation of L-type Ca2+ channels.

Succinylcholine potentiates acetylcholine-induced contractile and phosphatidylinositol responses of rat trachea

PurposeAlthough succinylcholine (SCh) is often used as a muscle relaxant in electroconvulsive therapy, its influence on airway reactivity has not been fully investigated. We examined the effects of SCh on acetylcholine (ACh)-, carbachol (CCh)-, and electrical field stimulation (EFS)-induced contractions, and on the ACh-induced phosphatidylinositol (PI) response of rat trachea.MethodsThirty-two male Wistar rats weighing 250–350 g were used. The trachea was rapidly isolated and cut into 3-mm-wide rings. The resting tension was adjusted periodically to 1.0 g during the equilibration period. ACh, 1 µM; carbachol (CCh), 0.05 µM; or neither of them, was added, and SCh was then added at 1–300 µM final concentrations, and ring tension was examined. Contractions were elicited by EFS in the presence or absence of 100 µM SCh. Tracheal slices were incubated with [3H] myo-inositol, 1 µM ACh, and various concentrations of SCh. The accumulation of [3H] inositol monophosphate (IP1) was measured.ResultsSCh did not affect the tension by itself without ACh, or with CCh, but SCh potentiated the ACh-induced contraction of rat trachea at concentrations of 10 µM or more (50% effective concentration [EC50]; 43.6 µM). SCh produced a significant increase in the amplitude and duration of EFS-induced contractions. SCh, at concentrations of 10 µM and 100 µM, potentiated ACh-induced IP1 accumulation.ConclusionSCh potentiated ACh-induced, but not CCh-induced, contractile and PI responses, and enhanced EFS-induced contraction of rat trachea, suggesting that competition for butyrylcholinesterase (BChE) in airway smooth muscle could be involved in the potentiation by SCh of ACh-induced airway smooth muscle contraction.

Effects of ketamine on neostigmine-induced contractile and phosphatidylinositol responses of the rat trachea.

AbstractPurpose. Neostigmine causes airway smooth muscle contraction through the direct stimulation of muscarinic receptors and the activation of phosphatidylinositol (PI) responses. Ketamine attenuates airway smooth muscle contraction. It is not clear whether ketamine attenuates neostigmine-induced airway smooth muscle contraction by inhibiting the PI response. This study was designed to examine the effects of ketamine on neostigmine-induced contractile and PI responses of the rat trachea. Methods. Thirty male Wistar rats weighing 250–350 g were used. In the experiment on the contractile response, active contraction was induced with 1 μM neostigmine in the presence or absence of ketamine. In the experiment on the phosphatidylinositol response, the trachea slices were incubated with [3H]myo-inositol, 1 μM neostigmine, or 100 μM aluminum fluoride, and ketamine. The formation of [3H]inositol monophosphate (IP1), a degradation product of the phosphatidylinositol response, was measured with a liquid scintillation counter. Statistical significance (P < 0.05) was determined by analysis of variance. Results. Neostigmine 1 μM caused tracheal ring contraction. This contraction was attenuated by ketamine dose-dependently and reached resting tension at 100 μM. Neostigmine- and aluminum fluoride-induced IP1 accumulation was also attenuated by ketamine. Conclusion. The results suggest that ketamine attenuates neostigmine-induced contractile responses, at least in part, through the inhibition of phospholipase C coupled with G protein in the PI response.