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A comparative study has been made of the action of 3-methyl salicylic acid, a derivative which has a much longer half-life than salicylic acid in man, on free fatty acid mobilisation and plasma cholesterol in the rat, rabbit, baboon and man. 3-Methyl salicylic acid decreased plasma free fatty acids in rats exposed to conditions of increased mobilisation, such as fasting, cold, and treatment with noradrenaline and ACTH. Evidence was obtained that a dose equivalent to salicylic acid given shortly before test was more effective. As for salicylate, 3-methyl salicylate decreased the in vitro production of FFA and glycerol liberated in vitro by the incubated rat epididymal fat pad. Administration of 3-methyl salicylic acid (100 mg/kg, body weight) reduced plasma cholesterol from 7 to 45% in baboons given an atherogenic, cholesterol-containing diet for one month. In acute experiments, the drug caused a marked choleresis in which the volume and excretion of bile acids but not cholesterol was increased. In the rabbit, the drug (100 mg/kg) caused a decrease in fasting FFA for up to four hours, followed by a large elevation. Inclusion of the drug in the diet of animals given a semi-synthetic diet of low cholesterol content did not reduce hypercholesterolaemia or the extent and severity of atherosclerotic lesions in the aorta. Administration of 0.9 g orally to fasting patients caused a 50% reduction in elevated plasma FFA after four hours and even after twelve hours the values were still subnormal. A double-blind control trial of nine hypercholesterolaemic and eight normal patients was conducted over twelve to eighteen months. Subjects in the hypercholesterolaemic group on chronic dosage (0.9–1.8 g per day) showed a fall of 25% in the mean plasma cholesterol, but there was no change in normal patients. Side effects, the chief of which were drowsiness and vomiting precluded the use of 3-methyl salicylate as a therapeutic agent in man.

Summary Ethionine inhibits protein synthesis in the intestinal mucosa of female rats and interferes with the intestinal transport of triglycerides containing long-chain fatty acids presumably by reducing chylomicron formation. The absorption of triglycerides containing medium-chain fatty acids is unaffected. In contrast to its effects on the liver, ethionine does not lead to decreases in intestinal ATP levels and administration of ATP to the animals does not protect against the inhibitory effects of ethionine. The intestinal activity of methionine-activating enzyme is about one-sixth that of liver. This may account for the failure of ethionine to reduce intestinal ATP concentrations since with low activating enzyme levels in the intestine relatively little adenine would be trapped in the form of S -adenosythionine. It is suggested that the inhibitory effect of ethionine on intestinal protein synthesis must involve a mechanism unrelated to reductions in cellular ATP levels.