Some pharmacological properties of the alpha-toxin of staphylococcus pyogenes

The alpha-toxin of Staphylococcus pyogenes produced a slowly developing contracture of isolated preparations of rabbit jejunum and of guinea-pig ileum which persisted after thorough washing and left the gut unresponsive to further doses of alpha-toxin or of acetylcholine. After incubation with antitoxin, the alpha-toxin no longer produced a contracture. Antitoxin only prevented the alpha-toxin response if added to the bath fluid before but not after the alpha-toxin. Certain drugs reduced the alpha-toxin contracture when added to the bath fluid before or after the alpha-toxin, but the contracture reappeared on washing. Papaverine abolished the contracture and pethidine was only slightly less active. Mepyramine, amyl nitrite, caffeine, aminophylline, adrenaline and ephedrine partly reduced the contracture. Hexamethonium, cocaine, tubocurarine and gallamine had no effect. The effect of atropine was only small. The gut-stimulant activity/haemolytic unit of two alpha-toxin samples differed greatly; this difference did not appear to be due to activity of impurities. The implications of these observations are discussed.

Action of acetylcholine, choline and D-tubocurarine on the membrane of frog sartorius muscle fibers

Resting potentials of frog sartorius muscle fibers were taken with microelectrodes at different distances along the length of muscles before and after adding acetylcholine or choline. The mean membrane potential drop and scatter of the potentials recorded in the relatively nerve-free, and in the more densely innervated parts of the muscle, were similar. The loss of direct excitability to electrical and mechanical stimulation was correlated with the concentration of choline or acetylcholine presented. d-tubocurarine added beforehand protected against the depolarizing effect of acetylcholine and choline everywhere along the length of the muscle. A generalized action of acetylcholine and choline and also of d-tubocurarine all along the muscle fibers was inferred. This generalized action at higher concentrations of acetylcholine and choline is believed to be additional to a more specific end plate action.

Increase in twitch force of the adductor pollicis muscle with stabilized preload at constant thumb abduction before and after administration of muscle relaxant

OBJECTIVE

To determine whether the twitch force of the adductor pollicis remains stable when 0.1 Hz single twitch stimulation is started after stabilization of the thumb preload at a constant degree of thumb abduction; also to study any possible increase in twitch force before the onset of and after the recovery from neuromuscular block.

METHODS

Measurements were performed in thirty patients under general anaesthesia. Twitch forces were first allowed to stabilize after allowing the preload to drift to its resting tension at a constant degree of thumb abduction. Three groups of ten patients then each received either vecuronium (2, 4, 8, 16 and 32 microg/kg(-1), successively at intervals of 2 min), d-tubocurarine (5, 10, 20, 40 and 80 microg/kg(-1), successively at intervals of 2 min), or suxamethonium (0.025, 0.05, 0.1, 0.2 and 0.4 mg/kg(-1), successively at intervals of 2 min). Measurements were continued until twitch forces had recovered from neuromuscular block and were stable.

RESULTS

Twitch forces stabilized at 114% (sd = 8.9) of the initial value after 10.9 (6.1) min of stimulation. Increase in twitch force before the onset of neuromuscular block was seen in two patients receiving vecuronium and in two patients receiving d-tubocurarine. Increase in twitch force after recovery from neuromuscular block was seen in all patients receiving suxamethonium.

CONCLUSIONS

Twitch forces may increase when stimulation is started after stabilization of thumb preload at a constant degree of thumb abduction. In some patients twitch forces may increase before the onset of neuromuscular block with vecuronium or d-tubocurarine; twitch forces increase after recovery from suxamethonium.

Supersensitivity to neostigmine and resistance to d-tubocurarine in mice with hereditary myopathy

Mice having a hereditary myopathy (dystrophia muscularis) and normal controls were injected with neostigmine and/or d-tubocurarine. Neostigmine (8–19 µg/kg, i.v.) either induced or increased tremors in 16 of a group of 18 myopathic mice. Only 1 of 27 normal mice showed any twitching after the same treatment. Neostigmine when given intraperitoneally in larger doses (21–37 µg/kg) failed to produce twitching in either myopathic or normal mice if the animals were less than 4 weeks old. However, in mice of ages >30 days intraperitoneally administered neostigmine (7 g-18 µg/kg) did produce twitching in dystrophics (12/12) but not in most normals (1/12). A dose of d-tubocurarine (200–250 µg/kg, i.v.), which caused death in 78% of nine normal mice, was lethal to only 22% of nine myopathic mice. The data suggest that muscle from the myopathic mice may share with denervated muscle the property of supersensitivity to acetylcholine.

The action of substances which block sympathetic postganglionic nervous transmission

The substances which block sympathetic postganglionic transmission, xylocholine, bretylium and guanethidine, also block neuromuscular and sympathetic ganglionic transmission. To see if these last properties were related to the sympathetic blocking property, phenyltrimethylammonium, which blocks the neuromuscular junction (Riker, 1953), was used. It blocked the inhibition of the rabbit ileum produced by stimulating the periarterial nerves in the mesentery, though with higher concentrations the effect of stimulation was initially increased. The action was not modified by the presence of hyoscine. The blocking action was exerted on the response to stimulation of the highest frequency first, and on the response to stimulation of the lowest frequency last. This relation of block to stimulus frequency is similar to that at the neuromuscular junction when tubocurarine is used. Nine compounds have now been shown to block responses to sympathetic postganglionic stimulation, and seven of these are onium compounds. They are, however, mon-onium compounds, and not bis-onium compounds like hexamethonium and decamethonium, so that they can probably enter the postganglionic fibre, which bis-onium compounds (having a charged group at each end of the molecule) may not be able to do. Since these mon-onium compounds have some blocking action at neuromuscular junctions and at sympathetic ganglia, their block of postganglionic transmission may be essentially similar to that by hexamethonium at ganglia and to that by decamethonium at neuromuscular junctions. It is known that acetylcholine releases noradrenaline from sympathetic postganglionic terminations, and xylocholine and bretylium block this release in the vessels of the rabbit ear and in the rabbit isolated atria.

Asynchronous postganglionic firing from the cat superior cervical sympathetic ganglion treated with neostigmine

Neostigmine injected intra-arterially to the superior cervical ganglion of the cat evoked an asynchronous postganglionic nervous discharge in both normal and denervated superior cervical ganglia. This asynchronous firing was enhanced by tubocurarine but blocked by small doses of atropine. In addition, the responses evoked by acetylcholine in ganglia treated with neostigmine were characterized by two components. The first was blocked by tubocurarine and the second by atropine. Asynchronous firing evoked by repetitive preganglionic nerve stimulation of ganglia treated with neostigmine was blocked by atropine but not tubocurarine. It is suggested that neostigmine (1) has actions on ganglia other than those attributable to inactivation of cholinesterase, (2) may possess both pre- and post-synaptic sites of action, and (3) may unmask a cholinoceptive site which can be blocked by atropine.