Studies on fatty acid oxidation. 8. The effects of fatty acids on metabolism of rat-brain cortex in vitro

Acute metabolic encephalopathy: a review of causes, mechanisms and treatment

Acute encephalopathy is a relatively common problem: one of the causes is metabolic disorders. A detailed history, examination and investigations performed during the acute illness (blood sugar, blood gases, plasma ammonia, blood lactate, plasma ketones, plasma amino acids, liver function tests, and urinary organic acids) should identify those patients in whom a metabolic disorder is likely. More detailed studies may be needed to establish a precise diagnosis. The mechanism of the acute brain dysfunction is multifactorial. Factors that contribute include changes in blood flow and, initially, a disturbance in neurotransmitter function followed by failure of energy metabolism and cellular depolarization. Treatment of these conditions is largely supportive, with special attention to the management of cerebral perfusion pressure.

On the effects of propionate and other short-chain fatty acids on sodium transport by the toad bladder

1. Propionate and other unbranched short-chain fatty acids, butyrate, pentanoate, hexanoate and octanoate were found to both stimulate and inhibit active sodium transport by the toad bladder, as measured by the short-circuit current (s.c.c.). 2. Stimulation alone followed addition of low concentrations of fatty acids (0.1-1.0 mM) to either the serosal or mucosal bathing medium; stimulation was also seen after an initial period of inhibition in response to higher concentrations (approx. 5 mM) of some compounds. 3. Inhibition alone followed addition of high concentrations (5-20 mM) of these compounds. The duration and magnitude of the inhibition varied with increasing concentration and chain length of the fatty acid, and was greater following mucosal addition than serosal addition. 4. The inhibitory effect of mucosal propionate increased with decreasing pH of the mucosal bathing medium. 5. Inhibition by the fatty acids was completely reversed upon removing the compound from the bathing medium, and stimulation characteristically followed. 6. In studies designed to evaluate the role of metabolism of the fatty acids in their mucosal inhibitory effects it was found that 14-c-labelled propionate, when added to the mucosal surface of the bladder, was converted to 14-CO2, and mucosal succinate and alpha-oxoglutaric acid at 20 mM inhibited the s.c.c. slightly. However, malonate did not interfere with inhibition by mucosal propionate and two non-metabolizable acids, dimethylpropionate and benzoate, induced inhibition (and no stimulation) of the s.c.c. 7. In the presence of an inhibitory concentration of fatty acid, the ability of the bladder to respond to added pyruvate was reduced in proportion to the reduction in the level of the s.c.c., whereas the natriferic response to vasopressin was largely intact. 8. We conclude that stimulation of sodium transport by propionate and other short-chain fatty acids is due to metabolism of the compounds and provision of energy to the sodium transport mechanism. The basis of the inhibition appears complex. It may in part depend on metabolism of the fatty acids and/or uncoupling of oxidative phosphorylation, with resultant reduction in net ATP production for the sodium transport mechanism. However, the inhibition may also be caused in part by a direct effect on the mucosal entry of sodium into the transporting epithelial cells.

AMINO ACID TRANSPORT IN BRAIN CORTEX SLICES: III. THE UTILIZATION OF ENERGY FOR TRANSPORT

When rat brain cortex slices are incubated with amino acids in the presence of various sugars, the ratio of amino acid transported to the steady-state level of ATP (termed the transport quotient) is constant. The actual amount of ATP maintained is greatest with glucose and mannose but somewhat less with fructose and galactose. Certain α-keto acids (pyruvate, oxalacetate, α-ketoglutarate, or glutamate which can give rise to α-ketoglutarate) also support glycine transport but with a lesser efficiency. Fumarate, malate, and succinate have little ability to support amino acid transport.The transport supported by pyruvate is particularly resistant to the action of agents which markedly reduce the transport supported by glucose as substrate. These agents include dinitrophenol, digoxin, and uranyl ions. Inhibitory effects are obtained with high concentrations of potassium ions whether the substrate is glucose or pyruvate.These results are interpreted in terms of pyruvate dismutation and acetate thiokinase leading to ATP production and in terms of intracellular localization of ATP.