Presynaptic muscarinic and adenosine receptors are involved in 2 Hz-induced train-of-four fade caused by antinicotinic neuromuscular relaxants in the rat

Recurarization with magnesium sulfate administered after two minutes sugammadex reversal: A randomized, double-blind, controlled trial

STUDY OBJECTIVE

The current study tested the hypothesis that magnesium sulfate after reversal with sugammadex causes recurarization.

DESIGN

A single-center, prospective, randomized, double-blind, controlled trial.

SETTING

Terciary care hospital in Rio de Janeiro, Brazil.

PATIENTS

Included 60 patients undergoing for elective otolaryngological surgery.

INTERVENTIONS

All patients received total intravenous anesthesia and a single dose of rocuronium (0.6 mg/kg). In 30 patients, the neuromuscular blockade was reversed with sugammadex (4 mg/kg) at the reappearance of one or two posttetanic counts (deep-blockade series). In 30 other patients, sugammadex (2 mg/kg) was administered at the reappearance of the second twitch of the train-of-four (moderate-blockade series). After the normalized train-of-four ratio recovered to ≥0.9, the patients in each series were randomized to receive intravenous magnesium sulfate (60 mg/kg) or placebo for 10 min. Neuromuscular function was measured by acceleromyography.

MEASUREMENTS

The primary outcome was the number of patients who exhibited recurarization (normalized train-of-four ratio < 0.9). The secondary outcome was rescue with an additional dose of sugammadex after 60 min.

MAIN RESULTS

In the deep-blockade series, a normalized train-of-four ratio < 0.9 occurred in 9/14 (64%) patients receiving magnesium sulfate and 1/14 (7%) receiving placebo, RR 9.0 (95% CI: 62-1.30), and (p = 0.002), with four rescues with sugammadex. In the moderate-blockade series, neuromuscular blockade recurred in 11/15 (73%) patients receiving magnesium sulfate and in 0/14 (0%) receiving placebo (p < 0.001), with two rescues. The absolute differences in recurarization were 57% and 73% in the deep-blockade and moderate-blockade, respectively.

CONCLUSIONS

Single-dose magnesium sulfate led to a normalized train-of-four ratio < 0.9, 2 min after recovery from rocuronium-induced deep and moderate neuromuscular blockade using sugammadex. Additional sugammadex reversed prolonged recurarization.

Purinergic Tuning of the Tripartite Neuromuscular Synapse

The vertebrate neuromuscular junction (NMJ) is a specialised chemical synapse involved in the transmission of bioelectric signals between a motor neuron and a skeletal muscle fiber, leading to muscle contraction. Typically, the NMJ is a tripartite synapse comprising (a) a presynaptic region represented by the motor nerve ending, (b) a postsynaptic skeletal motor endplate area, and (c) perisynaptic Schwann cells (PSCs) that shield the motor nerve terminal. Increasing evidence points towards the role of PSCs in the maintenance and control of neuromuscular integrity, transmission, and plasticity. Acetylcholine (ACh) is the main neurotransmitter at the vertebrate skeletal NMJ, and its role is fine-tuned by co-released purinergic neuromodulators, like adenosine 5'-triphosphate (ATP) and its metabolite adenosine (ADO). Adenine nucleotides modulate transmitter release and expression of postsynaptic ACh receptors at motor synapses via the activation of P2Y and P2X receptors. Endogenously generated ADO modulates ACh release by acting via co-localised inhibitory A₁ and facilitatory A_2A receptors on motor nerve terminals, whose tonic activation depends on the neuronal firing pattern and their interplay with cholinergic receptors and neuropeptides. Thus, the concerted action of adenine nucleotides, ADO, and ACh/neuropeptide co-transmitters is paramount to adapting the neuromuscular transmission to the working load under pathological conditions, like Myasthenia gravis. Unravelling these functional complexities prompted us to review our knowledge about the way purines orchestrate neuromuscular transmission and plasticity in light of the tripartite synapse concept, emphasising the often-forgotten role of PSCs in this context.

Effects of sevoflurane and adenosine receptor antagonist on the sugammadex-induced recovery from rocuronium-induced neuromuscular blockade in rodent phrenic nerve-hemidiaphragm tissue specimens

Sevoflurane affects on the A1 receptor in the central nervous system and potentiates the action of neuromuscular blocking agents. In the present study, we investigated whether sevoflurane (SEVO) has the ability to potentiate the neuromuscular blocking effect of rocuronium and if the specific antagonist of adenosine receptor (SLV320) can reverse this effect. In this study, phrenic nerve-hemidiaphragm tissue specimens were obtained from 40 Sprague-Dawley (SD) rats. The specimens were immersed in an organ bath filled with Krebs buffer and stimulated by a train-of-four (TOF) pattern using indirect supramaximal stimulation at 20 s intervals. The specimens were randomly allocated to control, 2-chloroadenosine (CADO), SEVO, or SLV320 + SEVO groups. In the CADO and SLV320 + SEVO groups, CADO and SLV320 were added to the organ bath from the start to a concentration of 10 μM and 10 nM, respectively. We then proceeded with rocuronium-induced blockade of >95% depression of the first twitch tension of TOF (T1) and TOF ratio (TOFR). In the SEVO and SLV320 + SEVO groups, SEVO was added to the Krebs buffer solution to concentration of 400-500 μM for 10 min. Sugammadex-induced T1 and TOFR recovery was monitored for 30 min until >95% of T1 and >0.9 of TOFR were confirmed, and the recovery pattern was compared by plotting these data. T1 recovery in the SEVO and CADO groups was significantly delayed compared with the control and SLV320 + SEVO groups (p < .05). In conclusion, sevoflurane affects on the A1 receptor at the neuromuscular junction and delays sugammadex-induced recovery from neuromuscular blockade.

Nicotinic α7 receptor-induced adenosine release from perisynaptic Schwann cells controls acetylcholine spillover from motor endplates

Acetylcholine (ACh) spillover from motor endplates occurs after neuronal firing bursts being potentiated by cholinesterase inhibitors (e.g., neostigmine). Nicotinic α7 receptors (α7nAChR) on perisynaptic Schwann cells (PSCs) can control ACh spillover by unknown mechanisms. We hypothesized that adenosine might be the gliotransmitter underlying PSCs-nerve terminal communication. Rat isolated hemidiaphragm preparations were used to measure (1) the outflow of [³ H]ACh, (2) real-time transmitter exocytosis by video-microscopy with the FM4-64 fluorescent dye, and (3) skeletal muscle contractions during high-frequency (50 Hz) nerve stimulation bursts in the presence of a selective α7nAChR agonist, PNU 282987, or upon inhibition of cholinesterase activity with neostigmine. To confirm our prediction that α7nAChR-mediated effects require direct activation of PSCs, we used fluorescence video-microscopy in the real-time mode to measure PNU 282987-induced [Ca²⁺ ]_i transients from Fluo-4 NW loaded PSCs in non-stimulated preparations. The α7nAChR agonist, PNU 282987, decreased nerve-evoked diaphragm tetanic contractions. PNU 282987-induced inhibition was mimicked by neostigmine and results from the reduction of ACh exocytosis measured as decreases in [³ H]ACh release and FM4-64 fluorescent dye unloading. Methyllycaconitine blockage of α7nAChR and the fluoroacetate gliotoxin both prevented inhibition of nerve-evoked ACh release and PSCs [Ca²⁺ ]_i transients triggered by PNU 282987 and neostigmine. Adenosine deamination, inhibition of the ENT1 nucleoside outflow, and blockage of A₁ receptors prevented PNU 282987-induced inhibition of transmitter release. Data suggest that α7nAChR controls tetanic-induced ACh spillover from the neuromuscular synapse by promoting adenosine outflow from PSCs via ENT1 transporters and retrograde activation of presynaptic A₁ inhibitory receptors.

Effects of neuromuscular presynaptic muscarinic M1 receptor blockade on rocuronium-induced neuromuscular blockade in immobilized tibialis anterior muscles

This in vivo study tested the hypothesis that the modulation of acetylcholine (ACh) release by the M₁ muscarinic receptor (mAChR) in the neuromuscular junction of disused muscles may affect the tensions of the muscles during the neuromuscular monitoring of a rocuronium‐induced neuromuscular block and compared the results with those obtained from normal muscles. A total of 20 C57BL/6 (wild‐type) and 10 α7 knock out (α7KO) mice were used in this experiment. As a pre‐experimental procedure, knee and ankle joints of right hind limbs were fixed by needle pinning at the 90° flexed position. After 2 weeks, the main experiment was performed. Both tendons of the tibialis anterior (TA) muscles were obtained, and the muscle tensions were recorded while the dose‐responses of rocuronium were measured three times in the same mouse by the serial administration of pirenzepine (0, 0.001 and 0.01 μg/g). Weight losses were observed after 2 weeks of immobilization in both groups, and a decrease in the mass of TA muscles at the immobilized side was observed compared to those of the contralateral nonimmobilized side. Tension depression of the TA muscles at immobilized side of the α7KO group was faster than those of the wild‐type group, but these differences decreased after the administration of pirenzepine. The tension depressions were similar regardless of the pirenzepine doses at the same side in the group. Tension depression may become more rapid in the α7 AChR‐expressed disused muscles by the decreased release of ACh release upon neuronal firing by the blockade of facilitatory M₁mAChR

Effects of adenosine receptor agonist on the rocuroniuminduced neuromuscular block and sugammadex-induced recovery

Background

Several types of receptors are found at neuromuscular presynaptic membranes. Presynaptic inhibitory A₁ and facilitatory A_2A receptors mediate different modulatory functions on acetylcholine release. This study investigated whether adenosine A₁ receptor agonist contributes to the first twitch tension (T1) of train-of-four (TOF) stimulation depression and TOF fade during rocuronium-induced neuromuscular blockade, and sugammadex-induced recovery.

Methods

Phrenic nerve-diaphragm tissues were obtained from 30 adult Sprague-Dawley rats. Each tissue specimen was randomly allocated to either control group or 2-chloroadenosine (CADO, 10 μM) group. One hour of reaction time was allowed before initiating main experimental data collection. Loading and boost doses of rocuronium were sequentially administered until > 95% depression of the T1 was achieved. After confirming that there was no T1 twitch tension response, 15 min of resting time was allowed, after which sugammadex was administered. Recovery profiles (T1, TOF ratio [TOFR], and recovery index) were collected for 1 h and compared between groups.

Results

There were statistically significant differences on amount of rocuronium (actually used during experiment), TOFR changes during concentration-response of rocuronium (P = 0.04), and recovery profiles (P < 0.01) of CADO group comparing with the control group. However, at the initial phase of this experiment, dose-response of rocuronium in each group demonstrated no statistically significant differences (P = 0.12).

Conclusions

The adenosine A₁ receptor agonist (CADO) influenced the TOFR and the recovery profile. After activating adenosine receptor, sugammadex-induced recovery from rocuronium-induced neuromuscular block was delayed.

Effects of presynaptic muscarinic cholinoreceptor blockade on neuromuscular transmission as assessed by the train-of-four and the tetanic fade response to rocuronium

This study investigated the effect of muscarinic M₁ and M₂ receptor antagonists on the rocuronium‐induced train of four (TOF) fade and tetanic fade, respectively. Ex‐vivo phrenic nerves and diaphragms were obtained from adult Sprague‐Dawley rats and stabilized in Krebs buffer; the nerve‐stimulated muscle TOF fade was observed at 20 s intervals. For the TOF study, phrenic nerves and diaphragms were incubated with pirenzepine (an M₁ blocker) at concentrations of 0 nmol L⁻¹ (control), 10 nmol L⁻¹ (PZP10), or 100 nmol L⁻¹ (PZP100). Rocuronium was then administered incrementally until the first twitch tension had depressed by >95% during TOF stimulation. The mean TOF ratios were compared when the first twitch tensions were depressed by 40%‐50%. For the tetanic fade study, 50 Hz/5 s tetani was applied initially, 30 min after the administration of a loading dose of rocuronium and methoctramine (an M₂ receptor blocker, loaded at 0 μmol L⁻¹ [control], 1 μmol L⁻¹ [MET1], or 10 μmol L⁻¹ [MET10]). The EC₉₅ of rocuronium was significantly lower in the PZP10 group than in the control group. In the PZP10 group, the TOF ratios at 50% and first twitch tension depression were significantly lower than those in the control group (P=.02). During tetanic stimulation, the tetanic fade was significantly enhanced in the MET10 group compared to the other groups. This study shows that antagonists of muscarinic M₁ and M₂ receptors affect the rocuronium‐induced neuromuscular block as demonstrated by the reduced EC₉₅ and TOF ratios (M₁ antagonist, pirenzepine) or the enhanced 50‐Hz tetanic fade (M₂ antagonist, methoctramine).

Adenosine A(2A) receptor antagonists are broad facilitators of antinicotinic neuromuscular blockade monitored either with 2 Hz train-of-four or 50 Hz tetanic stimuli

1. The 2 Hz train-of-four ratio (TOF(ratio)) is used to monitor the degree of patient curarization. Using a rat phrenic nerve-hemidiaphragm preparation, we showed that antinicotinic agents, such as hexamethonium, d-tubocurarine and pancuronium, but not cisatracurium, decreased contractions produced by physiological nerve activity patterns (50 Hz) more efficiently than those caused by 2 Hz trains. Uncertainty about the usefulness of the TOF(ratio) to control safe recovery from curarization prompted us to investigate the muscarinic and adenosine neuromodulation of tetanic (50 Hz) fade induced by antinicotinic agents at concentrations that cause a 25% reduction in the TOF(ratio) (TOF(fade)). 2. Tetanic fade caused by d-tubocurarine (1.1 μmol/L), pancuronium (3 μmol/L) and hexamethonium (5.47 mmol/L) was attenuated by blocking presynaptic inhibitory muscarinic M(2) and adenosine A(1) receptors with methoctramine (1 μmol/L) and 1,3-dipropyl-8-cyclopentylxanthine (2.5 nmol/L), respectively. These compounds enhanced rather than decreased tetanic fade induced by cisatracurium (2.2 μmol/L), but they consistently attenuated cisatracurium-induced TOF(fade). The effect of the M(1) receptor antagonist pirenzepine (10 nmol/L) on fade produced by antinicotinic agents at 50 Hz was opposite to that observed with TOF stimulation. Blockade of adenosine A(2A) receptors with ZM 241385 (10 nmol/L) attenuated TOF(fade) caused by all antinicotinic drugs tested, with the exception of the 'pure' presynaptic nicotinic antagonist hexamethonium. ZM 241385 was the only compound tested in this series that facilitated recovery from tetanic fade produced by cisatracurium. 3. The data suggest that distinct antinicotinic relaxants interfere with fine-tuning neuromuscular adaptations to motor nerve stimulation patterns via activation of presynaptic muscarinic and adenosine receptors. These results support the use of A(2A) receptor antagonists together with atropine to facilitate recovery from antinicotinic neuromuscular blockade.