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The effects of methylenecyclopropylglycine (MCPG), the lower homologue of hypoglycin A, on starved rats are described. Upon oral ingestion of MCPG (43 mg/kg), a 50% decrease in blood glucose compared with controls was observed after 4 h. The plasma concentrations of lactate and non-esterified fatty acids were substantially increased during this period. The activity of general acyl-CoA dehydrogenase from isolated rat liver mitochondria was not significantly changed. By contrast, the activity of 2-methyl-(branched-chain)-acyl-CoA dehydrogenase decreased by over 80%. The enzyme activity of enoyl-CoA hydratase (crotonase) from pig kidneys decreased by 80% on incubation with the hypothetically toxic metabolite of MCPG, methylenecyclopropylformyl-CoA. These results suggest that the inhibition spectrum of MCPG is quite different from that of hypoglycin A and that similar physiological effects might result from inhibition of different enzymes of beta-oxidation, e.g. hypoglycaemia and lacticacidemia. Accumulation of medium-chain acyl-CoA thioesters is probably at the origin of disturbances in pyruvate metabolism.

Summary.Phenylalkyloxirane carboxylic acids and esters are a new class of potent hypoglycaemic substances. Sodium 2-[5-(4-chlorophenyl)-pentyl]-oxirane-2-carboxylate (B 807-27) produces a dosedependent hypoglycaemic effect when administered orally or intravenously to several fasted laboratory animals, i.e. rats (with and without adrenalectomy), guinea pigs, dogs, streptozotocin-treated diabetic pigs and db/db-mice. In addition, the substances have a more pronounced lowering effect on ketone bodies in the blood than any other known substance. The minimal dose for lowering blood glucose significantly in rats is 15 gmol/kg. The corresponding dose for a significant lowering of ketone bodies in the blood is < 2.4 lxmol/kg. Hence, the substance B 807-27 is approximately five times more potent than tolbutamide and 30 times more potent than the biguanide buformin with respect to lowering blood glucose levels. B 807-27 differs from the sulphonylureas in that it fails to stimulate insulin secretion. In contrast to the biguanides, the substance decreases rather than increases blood lactate concentration and blocks both fatty acid oxidation and gluconeogenesis. The therapeutic usefulness of these compounds in diabetic man remains to be elucidated.

Sodium 2-[5-(4-chlorophenyl)-pentyl]-oxirane-2-carboxylate (B 807-27 or POCA) inhibits ketogenesis from endogenous and exogenous long-chain fatty acids and 14C02 production from [U-'4C]palmitate, but not from [U-'4C]palmitoylcarnitine or octanoate, and inhibits gluconeogenesis from lactate and pyruvate in perfused livers of starved rats.2. Inhibition of ketogenesis, 14C02 production and gluconeogenesis was complete at concentrations of 10 pmol/l POCA, but onset was more rapid for inhibition of ketogenesis and C 0 2 production than for gluconeogenesis. Infusion of octanoate abolished inhibition of all three processes.3. Experiments with isolated rat liver mitochondria showed that carnitine palmitoyltransferase I (EC 2.3.1.21) is inhibited by POCA-CoA.The inhibitory process is dependent on time and concentration, and more pronounced in mitochondria from fed than from fasted rats. Concentrations required for 50% inhibition after 20 min preincubation with POCACoA are 0.02, 0.06 and 0.1 pmol/l in liver mitochondria from fed, 24-h-fasted and 48-h-fasted rats, respectively. The inhibitor appears to be tightly bound to the enzyme.4. The extent of inhibition of carnitine palmitoyltransferase I correlates well with the hypoglycaemic and hypoketonaemic effects of the compounds in fasted rats. We conclude that specific inhibition of the enzyme leads, due to inhibition of long-chain fatty acid utilization, to depressed ketogenesis and gluconeogenesis and, in consequence, to hypoglycaemic and hypoketonaemia in vivo under gluconeogenic and ketogenic conditions.Several cr-modified fatty acids are able to inhibit fatty acid oxidation, ketogenesis and gluconeogenesis [l -71. Since the consequence of these effects are a lowering of glucose and ketone body concentrations in the blood, the compounds were discussed as potential drugs in antidiabetic therapy [7].A few years ago, 2-tetradecylglycidate (McN-3802) was shown to exert these effects via a specific inhibition of carnitine palmitoyltransferase I (CPT I) [8], an enzyme located at the outer side of the inner mitochondria1 membrane which is involved in the transport of long-chain acyl-CoA into the mitochondria [9]. More recently, we found a new class of hypoglycaeimc compounds which shows similarities to McN-3802 as well as to the physiological inhibitor of CPT I, malonyl-CoA [lo, 1 I]. , inhibits oxidation of long-chain fatty acids in rat hepatocytes [12], rat liver and muscle mitochondria [13], perfused rat hearts [14, 151 and human fibroblasts [16]. A specific inhibition of CPT I has been shown in mitochondria of several rat organs [14,17, 181. The purpose of the present study was to provide further experimental evidence that POCA inhibits long-chain fatty acid oxidation at the site of CPT I and to investigate how this affects ketogenesis and gluconeogenesis in isolated perfused rat liver as well as blood concentrations of ketones and glucose in vivo. Sodium-2-[5-(4-chlorophenyl)-pentyl]-oxirane-2-carboxylate MATERIALS AND METHODSSodium-2-[ 5-(4-chlorophenyl)-pentyl]-oxirane...