Influence of temperature on vagal inhibition and liberation of acetylcholine in frog hearts

The effect of reserpine on the acetylcholine content of different areas of the central nervous system of the dog

The acetylcholine content of the frontal and temporal lobes, hippocampus, hypothalamus, cerebellum and spinal cord was estimated in 18 dogs 3 hr. after the intravenous administration of reserpine. Another group of 7 dogs served as control. After reserpine (0.5 mg./kg. body weight) there was an increase of acetylcholine in all the areas under study except in the hippocampus. The increase was specially marked in the hypothalamus. In the hippocampus, however, reserpine caused a significant decrease of acetylcholine.

Effect of reserpine on the acetylcholine content of the heart, the ileum and the hypothalamus of the dog

The effect of intravenous administration of reserpine in 10 dogs was studied on the acetylcholine content of the sino-atrial node, the right auricle and the right ventricle of the heart, the ileum and the hypothalamus of dog. The general sedation, the bradycardia, and the purgative effects of reserpine were also noted. Tissues were removed for estimation of acetylcholine when bradycardia was maximal. Reserpine increased the acetylcholine content of all the tissues studied. The increase in the peripheral tissues was greater than in the hypothalamus. The bradycardia and the purgative effects of reserpine may be related to the increase of the acetylcholine content of the sino-atrial node and the ileum.

Drug-induced changes in brain acetylcholine

In rats, drug-induced depression of the central nervous system has been shown generally to be associated with an elevation in level of total acetylcholine in the brain. This generalization held true for a wide variety of depressant drugs with one notable exception: the subacute administration of reserpine, with which there was an increase in cerebral acetylcholine after the first dose, but a return to normal levels after subsequent doses, despite continued depression of the animals. Reduction in the level of total acetylcholine in the brain followed the administration of certain convulsants (pentylenetetrazole and 3,5-dimethylbutylethylbarbiturate); but no change was seen after the administration of several mildly exciting agents. The notable exceptions to this generalization were atropine and scopolamine, which significantly lowered brain acetylcholine in doses producing mild excitation in only some of the animals and no gross manifestations in the rest.

THE EFFECT OF INTRA(CEREBRO)VENTRICULAR RESERPINE ON THE ACETYLCHOLINE CONTENT OF THE HEART, ILEUM AND HYPOTHALAMUS OF THE DOG

The effect of injection of reserpine into the cerebral ventricles on the acetylcholine contents of the sino-atrial node, ileum and hypothalamus of the dog was studied in ten dogs. Another group of five dogs served as a control. The effect of intravenous administration of reserpine, in the same dose as given intracerebroventricularly, was also studied on the acetylcholine content of these tissues in five dogs. General sedation, bradycardia, miosis, salivation, emesis and purgation were looked for. Tissues were removed 1 hr after administration of reserpine for estimation of acetylcholine content, which was increased in all the tissues studied. The increase in the peripheral tissues was greater than in the hypothalamus. The increase in the acetylcholine content was not quantitatively related to the other effects of reserpine. The increase in the acetylcholine content of the sino-atrial node and the ileum and also the peripheral effects observed on intracerebroventricular administration of reserpine can be attributed to its central action. With the same dose of reserpine given intravenously the acetylcholine content of the sino-atrial node was significantly increased, while that of the hypothalamus and ileum was not.

Effect of drugs on brain acetylcholine level in Gerbillus pyramidum

1. The quantitative estimation of total acetylcholine content in the whole brain tissue in normal Egyptian gerbil Gerbillus pyramidum, gives an average of 1.43 +/- 0.06 micrograms of acetylcholine chloride/g fresh brain tissue. 2. The brain acetylcholine level in Gerbillus pyramidum was generally found to vary with the changes induced in the brain activity by drugs. 3. Depressants caused a increase and convulsants a decrease in total brain acetylcholine level. 4. Phenytoin depressed the brain activity but lowered brain acetylcholine level.

Studies on the effect of physostigmine on experimental cardiac arrhythmias in dogs

1. Experimental cardiac arrhythmias were produced in dogs anaesthetized with pentobarbitone. Ventricular arrhythmias were induced by strophanthin-K, light petroleum plus adrenaline or coronary ligation procedures. Atrial flutter was induced by an injury-stimulation technique. The acetylcholine and glycogen concentrations of the atria and ventricles were estimated.2. Physostigmine pretreatment (0.1 mg/kg) significantly reduced the incidence of ventricular arrhythmias after myocardial ischaemia but had no effect on any of the other arrhythmias.3. Physostigmine markedly increased the acetylcholine concentrations of atria and ventricles in control dogs, to nearly the same extent. Physostigmine had no effect on ventricular acetylcholine concentrations in dogs treated with strophanthin-K and light petroleum plus adrenaline but in the coronary ligation group it caused a significant increase in the acetylcholine concentrations of both atria and ventricles, and of atrial acetylcholine only in the injury-stimulation group.4. All the arrhythmias produced marked glycogenolysis of both the atria and the ventricles, to nearly the same extent. Although physostigmine produced marked glycogenolysis in the control dogs it significantly inhibited cardiac glycogenolysis after light petroleum plus adrenaline, atrial glycogenolysis after strophanthin-K-induced arrhythmias and ventricular glycogenolysis after myocardial ischaemia.5. There appears to be a possible correlation between the increase in the acetylcholine concentration of the ventricles and anti-arrhythmic actions of physostigmine, but there is a less clear correlation between changes in the glycogen concentration of ventricles and the anti-arrhythmic action.

The effects of temperature on the release of material with acetylcholine-like activity from brain subcellular particles

It was observed that when rat brain subcellular particles were cooled to 0 °C, there was little or no release of materials with acetylcholine-like activity from within the particles into the incubation fluid. When these experiments were conducted at elevated temperatures, there was gradual enhancement of release of these materials, until at about 43 °C, there was a relatively large release. We suggest that extreme hypothermia (below 20 °C) in animals results in the failure of transmission in nerve and brain partly because of the concomitant failure of release of the transmitter substance(s).