Effect of lignocaine on the responses produced by depolarizing agents at the chick neuromuscular junction

Epidurally administered mepivacaine delays recovery of train-of-four ratio from vecuronium-induced neuromuscular block

BACKGROUND

The aim of this study was to examine the efficacy of epidurally administered mepivacaine on recovery from vecuronium-induced neuromuscular block.

METHODS

Eighty patients were randomly assigned to one of two study groups. They were either given epidurally a bolus of 0.15 ml kg(-1) of mepivacaine 2%, followed by repetitive injections of 0.1 ml kg(-1) h(-1) throughout the study, or were not given epidurally. General anaesthesia was induced and maintained with fentanyl, propofol and nitrous oxide. Neuromuscular block was induced with vecuronium 0.1 mg kg(-1) and monitored using acceleromyographic train-of-four (TOF) at the adductor pollicis. Patients in each treatment group were randomized to receive neostigmine 0.04 mg kg(-1) at 25% recovery of the first twitch of TOF or to recover spontaneously to a TOF ratio of 0.9. The effect of epidural mepivacaine on speed of spontaneous and facilitated recovery of neuromuscular function was evaluated.

RESULTS

The time from administration of vecuronium to spontaneous recovery to a TOF ratio of 0.9 was significantly longer in the epidural mepivacaine group [105.4 (14.2) min] as compared with the control group [78.5 (9.1) min, P < 0.01]. Neostigmine administered at 25% of control in T1 shortened recovery from neuromuscular block, however the time required for facilitated recovery to a TOF ratio of 0.9 in the epidural group was significantly longer than that in the control group [7.6 (1.6) min vs 5.8 (2.1) min, P < 0.01].

CONCLUSIONS

In clinical anaesthesia, it should be recognized that epidurally administered mepivacaine delays considerably the TOF recovery from neuromuscular block.

Local anaesthetics inhibit influx of calcium, sodium and potassium into rat ileum, diaphragm and human isolated saphenous vein

The effects of 5 different local anaesthetics, lignocaine, prilocaine, etidocaine, mepivacaine, bupivacaine, on uptake of Ca2+, Na+ and K+ were studied, using a Kone Microlyte Analyzer, into 3 different types of muscle fibres, the rat ileum, rat diaphragm and human isolated saphenous vein. The aim of the present experiments was to see if local anaesthetics had a calcium antagonistic activity, like that produced by calcium antagonists, e.g. verapamil. The results showed that local anaesthetics in moderate and high concentrations (more than 100 microM) depressed uptake of Ca2+, as well as the Na+ and K+, although the depression of the uptake of Ca2+ was 7 and 2 times less than those of Na+ and K+. In low concentrations (1-10 microM), the local anaesthetics had no or little effect on Ca2+ uptake, although they still significantly reduced Na+ and K+ uptake. It was concluded that the effect of local anaesthetics on uptake of Ca2+, Na+ and K+ into rat ileum, diaphragm and human saphenous vein, is concentration-dependent, and that only at high concentrations do they have a calcium antagonistic activity in muscle. Furthermore, there was no clear evidence that the effect of local anaesthetics was species-dependent, since the uptake of Ca2+ was depressed by only about 17% more in smooth muscle than in skeletal muscle.

Verapamil intensifies neuromuscular blockade produced by gallamine and pancuronium at the chick neuromuscular junction

Experiments were performed to study the effect of verapamil on neuromuscular transmission and muscle contraction at a chick skeletal muscle-nerve preparation. In addition, the effects and interactions of verapamil with some muscle relaxants were studied in the same preparation. These effects were explored by studying the effects of verapamil on: directly-and indirectly-elicited twitch contractions, and neuromuscular blockade produced by gallamine and pancuronium. The results showed that verapamil (2-200 microM) had a differential effect on the twitch responses; more reductions occurred in the indirectly-elicited twitch tension, whereas the directly-elicited twitch response was reduced only by 20-30% of maximum indirectly-elicited twitch tension. Furthermore, in low concentrations (1-20 microM), verapamil significantly increased the neuromuscular blockade produced by gallamine (28-1280 nM) and pancuronium (18-573 nM). In high concentrations (greater than 200 microM), verapamil completely blocked the indirectly-elicited twitch response and produced a marked contracture in the chick skeletal muscle (1.0 +/- 0.1 g, n = 6). It was concluded that by reducing twitch tension and inhibiting neuromuscular transmission, verapamil increases (intensifies) neuromuscular blockade produced by muscle relaxants, e.g. gallamine and pancuronium.

Effect of lignocaine on chick biventer cervicis skeletal muscle

The effect of lignocaine (0.01-100 micrograms.ml-1) on amplitude of indirectly and directly-elicited twitch contractions and on contractures produced by acetylcholine (ACh) (0.1-10 mM) and tetraethylammonium (TEA) (1.2-12 mM) was studied in isolated biventer cervicis skeletal muscle of the chick. Lignocaine (0.01-0.9 microgram.ml-1) increased the amplitude of the indirectly-elicited twitch contractions. At high concentrations (10-100 micrograms.ml-1), lignocaine decreased or blocked the twitch tension and produced a contracture in the chick skeletal muscle. Lignocaine also reduced or blocked the directly-elicited twitch contractions in a dose-dependent manner. Lignocaine (10 micrograms.ml-1) reduced the ACh-induced contracture whereas it increased that produced by TEA. Physostigmine (2 micrograms.ml-1) increased the stimulating effect of lignocaine, at low concentrations. However, repeated exposures to lignocaine followed by physostigmine resulted in both increase and decrease in the indirectly-elicited twitch contractions. It was concluded that lignocaine had a dual action at the neuromuscular junction. In low concentrations, lignocaine increases the twitch tension, possibly by an anticholinesterase action, and in high concentrations it reduces or blocks the twitch tension, produces a contracture in the muscle, and reduces the ACh-induced contractures, whereas it increases the TEA-induced responses. Some of these effects of lignocaine may be interpreted in terms of effects on excitation-contraction coupling in muscle.