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The effects of edrophonium and choline have been compared with those of the depolarizing substances acetylcholine, decamethonium, and suxamethonium, in both innervated and chronically denervated tibialis anterior muscles of cats under chloralose anaesthesia. Both edrophonium and choline were more potent antagonists to paralysis by tubocurarine than could be accounted for by their ability to stimulate the motor end-plates directly. It appeared likely that direct depolarization of the end-plate played no part in the anti-curare action of edrophonium and only some part in the anti-curare action of choline. A paralysis produced by the neuromuscular blocking agent, benzoquinonium, was more readily antagonized by a tetanus or by acetylcholine, suxamethonium, and decamethonium than a similar paralysis produced by tubocurarine. The tetraethyl ammonium ion was also slightly more effective against a paralysis by benzoquinonium. On the other hand, edrophonium was about 300 times and choline about five times less potent as an antagonist to benzoquinonium than to tubocurarine. Furthermore, the previous administration of benzoquinonium abolished the antagonistic action to tubocurarine of normally effective doses of edrophonium and reduced that of choline. These results were similar to those previously obtained with neostigmine, physostigmine and ethyl pyrophosphate and suggested that there was some similarity in the mechanism of action of all of these substances. Benzoquinonium, therefore, showed promise as a useful pharmacological tool for distinguishing compounds with this particular type of action. These anti-curare compounds did not appear to act by cholinesterase inhibition, not by an increase in the sensitivity of the motor end-plates. In common with other workers, we suggest that there is a pre-synaptic mechanism of action.

1. Cholinomimetics, acetylcholine antagonists and some other compounds of pharmacological interest were administered electrophoretically near neurones within the vermal cerebellar cortex of anaesthetized (pentobarbitone) and unanaesthetized (cerveau isolé) cats.2. The neurones were identified by position within the cortex, spontaneous activity, and the responses to afferent and antidromic stimulation.3. Purkinje cells, but neither granule nor basket cells, were excited by cholinomimetics, and the acetylcholine receptors had muscarinic properties. Excitation was often preceded by depression of the spontaneous firing.4. Intravenously administered atropine and dihydro-beta-erythroidine did not depress the synaptic excitation of cerebellar neurones evoked by impulses in mossy, climbing or parallel fibres.5. Acetylcholine is thus unlikely to be an excitatory transmitter within the feline cerebellum, particularly at mossy fibre-granule cell synapses, despite the presence of relatively high levels of acetylcholinesterase within mossy fibre terminals.

Subthreshold concentrations of the depolarizing agents, acetylcholine and decamethonium, potentiated isotonic contractures of the isolated frog rectus abdominis muscle elicited by effective doses of either of these drugs or by choline in the absence of the anticholinesterases, sarin, or dyflos. Comparable potentiation of the contracture produced by decamethonium or choline could be obtained by alternate stimulation with acetylcholine in the absence of dyflos or sarin. Furthermore, dyflos alone did not effect potentiation in the absence of alternate stimulation with acetylcholine. Finally, the inhibitory action of tubocurarine, as measured by depression of the contracture elicited by decamethonium and acetylcholine, was not antagonized by sarin. It was concluded that the enhancement of the response to acetylcholine produced by dyflos and by sarin was brought about exclusively by their action as inhibitors of cholinesterase. The ability of dyflos and of sarin to potentiate contractures elicited by decamethonium or by choline may be attributed to a facilitation of the action of the depolarizing compounds by subthreshold concentrations of acetylcholine available in the presence of these anticholinesterases.

Bretylium inhibits the contractions of the longitudinal muscle caused by histamine and, to a lesser extent, those by acetylcholine, carbachol and nicotine. It is a very weak antagonist of 5-hydroxytryptamine and in concentrations of up to 190 mug/ml. does not inhibit the actions of bradykinin and substance P on the longitudinal muscle. The inhibitory effect of bretylium on the emptying phase of the peristaltic reflex is similar to that of ganglion blocking agents, while the much less pronounced effect on the contraction of the longitudinal muscle during the preparatory phase is assumed to be due to a weak atropine-like action.

The actions of both reversible and irreversible anticholinesterase drugs on the nerve-free smooth muscle of the chick amnion are described. The tertiary compound physostigmine and the irreversible inhibitor diisopropylfluorophosphonate were found to be active in causing contractions, whereas the quaternary compound neostigmine and the irreversible inhibitor Mipafox were only slightly active in this respect. Manometric studies showed that all four compounds were highly active, however, in inhibiting the cholinesterase found in the chick amnion. The effects produced by these compounds in the organ bath are thought to be due to the accumulation of endogenously produced acetylcholine within the tissue. Evidence for an intracellular action of endogenously produced acetylcholine in the smooth muscle of the chick amnion is discussed.

The sensitivity of completely denervated and the innervated end-plate regions of partially denervated frog's sartorius muscles to stimulation by drugs has been investigated. The drugs were tested on muscles isolated 12 to 39 days following denervation. On the basis of the results obtained most of the drugs could be put into one of two main groups. The first group included choline, tetramethylammonium, carbachol and decamethonium; these drugs readily stimulated non-denervated muscles, and chronic denervation, either partial or complete, greatly increased the sensitivity of the muscles. The second group included pilocarpine and carbamate of (2-hydroxypropyl) trimethyl ammonium chloride (Bethanechol, U.S.P.). The muscles were relatively insensitive to stimulation by these two drugs. They could stimulate the muscles if applied in high enough concentrations, but the responses thus obtained could not be distinguished from responses produced by similar concentrations of sucrose and chronic denervation did not increase the sensitivity of the muscles to stimulation by these two drugs. Methacholine, like the drugs in the second group, was unable to stimulate the muscles in low concentrations, but chronic denervation rendered the muscles sensitive to stimulation by this drug. Tetraethylammonium presented a completely different pattern of activity which was consistent with a hypothesis that in low doses this drug stimulates skeletal muscle by causing a release of acetylcholine from nerve endings in the muscle.

The methoxy analogs of epinephrine, norepinephrine, and dopamine manifest some activity on smooth muscle and blood pressure. Metanephrine is as potent as epinephrine on rabbit aortic strips. The same compounds demonstrate a lesser potency on rabbit duodenum preparation, while 3-methoxy-dopamine produces a slight contraction of the duodenum. Both metanephrine and 3-methoxy-dopamine have 15 to 25 percent of the pressor activity of the original nonmethylated catecholamines. Normetanephrine is 1/600 as active as norepinephrine on the blood pressure of the cat.

A protein-like constituent of scorpion venom produced effects on the skeletal muscle fibre resembling those of citrate, lack of calcium or veratrine. These effects could be diminished by the addition of calcium. They do not appear to be due to the formation of a non-ionized complex with calcium.

1. The rat isolated anterior mesenteric artery was perfused at a constant rate with a calcium-free depolarizing solution. Injection close to the cannula of 0.05-0.1 ml. of solutions of CaCl(2) (117 mM) or BaCl(2) (100 mM) caused a rise in perfusion pressure.2. The responses to injected CaCl(2) solution could be obtained repeatedly but those to successive injections of BaCl(2) solution slowly declined. When the responsiveness to barium had almost disappeared, it could be restored by the addition to the perfusing fluid of a small amount of calcium (0.05 mM).3. The contractile effects of calcium or barium were antagonized by the addition to the perfusing fluid of several anti-inflammatory substances, certain local anaesthetics and certain spasmolytic drugs.4. Perfusion of the mesenteric artery with a depolarizing solution containing 0.2 mM-CaCl(2) caused a persistent rise of the perfusion pressure. This was rapidly and completely reversed by the addition of indomethacin (4 mg/100 ml.) or cinchocaine hydrochloride (2 mg/100 ml.) to the perfusing fluid.5. The uptake of (45)Ca by rat aorta depleted of calcium was reduced by amethocaine hydrochloride (10 mg/100 ml.) or cinchocaine hydrochloride (2 mg/100 ml.) but not by indomethacin (10 mg/100 ml.) or desipramine hydrochloride (1 mg/100 ml.).

The slow contraction of smooth muscle produced by human plasma becomes less potent after storage of the plasma for six months at room temperature and after processing of the plasma with kaolin. These observations fall into line with the fact that 40% of the initial smooth-muscle-contracting activity of the plasma can be accounted for in the deposit which is formed during the six-months period of storage, and also with the fact that the recovery of G acid from human plasma treated with kaolin is about 50% of the yield which is obtained from the same plasma before kaolin treatment.

1. Summit metabolism of lambs declined steadily from about 3.5 l. O(2)/kg.hr during the first day of life, to about 2.0 l. O(2)/kg.hr at 2 months of age.2. The contributions of shivering and non-shivering thermogenesis to these changes were estimated by three independent methods; non-shivering thermogenesis was stimulated by catecholamines in a thermoneutral environment, shivering was suppressed by curariform drugs during summit metabolism, and an attempt was made to suppress non-shivering thermogenesis during summit metabolism by use of the sympatholytic drugs phentolamine and propranolol. Drugs were given by intravenous infusion during measurement of oxygen consumption in a closed circuit respiration chamber.3. ;Resting' metabolic rate of lambs during the first day of life was increased two to three-fold, from 1 l. O(2)/kg.hr, by either adrenaline or noradrenaline infused at 1-10 mug/kg.min. The increase declined with increasing age of lamb and was virtually absent by 3 weeks. The response to catecholamines appeared maximal at the dose levels used.4. Muscular paralysis induced by suxamethonium or gallamine reduced summit metabolism by about 2 l. O(2)/kg.hr in all lambs examined within the first 2 months of life. The residual metabolic rate, and the metabolic response to catecholamines under thermoneutral conditions, declined with age in the same manner, and their magnitudes were similar.5. Summit metabolism in lambs aged up to 2 months was depressed to varying degrees by the sympathetic inhibitors phentolamine, propranolol and hexamethonium. The depression with propranolol was greater, and the decline with age clearer, than with phentolamine. Hexamethonium and phentolamine depressed blood pressure, propranolol decreased heart rate and phentolamine and propranolol each suppressed shivering in some experiments.6. In 1 day-old lambs estimates of non-shivering thermogenesis, by the various methods, ranged from 0.8 to 1.4 l. O(2)/kg.hr (mean 1.1 l. or 31% of summit metabolism), and the estimates of shivering ranged from 1.3 to 1.9 l. O(2)/kg.hr (mean 1.6 l. or 46% of summit metabolism). However, in lambs 1-month old, estimates of non-shivering thermogenesis from sympathetic inhibition (0.6 and 0.8 l. O(2)/kg.hr) were considerably higher than estimates from muscular paralysis or stimulation by catecholamines (0.2 and 0.1 l. O(2)/kg.hr). It is suggested that the depression of summit metabolism by the sympathetic inhibitors is not solely due to specific inhibition of non-shivering thermogenesis, at least in the older lambs.7. The possession of a non-shivering thermogenic mechanism in addition to shivering is of clear survival value to new-born lambs.

1. Neuromuscular blocking agents have been shown to be powerful inhibitors of choline transport in human erythrocytes. Ganglionic blocking agents were weaker inhibitors.2. The affinity of the choline transport site for alkyltrimethylammonium compounds was considerably higher than its affinity for alkyl-bis-(trimethylammonium) compounds of similar chain length. The affinity increases with increasing length of the alkyl chain in both series.3. Tetramethylammonium (TMA), ethyl- and propyltrimethylammonium appear to enter the cells on the choline carrier while the larger monoquaternary compounds, and the bisquaternary compounds, bind to the carrier but are unable to cross the cell membrane.4. Radioactively labelled carbachol, acetylcholine and decamethonium do not enter the cells on the choline carrier.5. Choline transport in erythrocytes from patients with myasthenia gravis is normal, suggesting that this disorder is not associated with a generalized defect of choline transport.

1. ACh was measured in the effluent from the perfused lumbosacral cord of the cat with or without stimulation of the central ends of the cut left sciatic and femoral nerves after section of the left dorsal roots.2. In about 30% of the preparations ACh was obtained in the samples collected at rest (average 3.3 ng/min); the amount of ACh release was increased 1.3-9 times by stimulation of the peripheral nerves. The average amount of ACh collected during stimulation of the peripheral nerves at 5/sec was 6.9 ng/min. Antidromic motor nerve impulses responsible for the ACh release were likely to be only those in alpha motor fibres.3. There was a depression in ACh release/stimulus as the stimulus frequency was increased more than 10/sec. Such changes in ACh release with various stimulus frequencies were correlated with depression in the response of Renshaw cells to excitation through motor-axon collaterals.4. Amounts of ACh release during stimulation of the peripheral nerves at 5/sec were significantly increased for 1 or 2 min after a short tetanic stimulation of the nerves.5. Intravenous injection of dihydro-beta-erythroidine did not reduce the amount of ACh release produced by stimulation of the peripheral nerves.6. It is concluded that antidromic impulses in alpha motor fibres liberate ACh from the presynaptic terminals at the central synapses on Renshaw cells.