Lipoate effect on carbohydrate and lipid metabolism and gastric H+ secretion

Substrate-level energy dependence of acid secretion in the isolated human gastric mucosa

The substrate-level energy dependence of acid secretion was investigated in the human gastric mucosa in vitro using biopsy specimens obtained during fiberoptic gastroscopy in symptomatic patients. The oxygen consumption and the accumulation of aminopyrine were used as indexes of secretory activity. Basal and histamine-stimulated oxygen uptake by fundic biopsy specimens were not affected by medications (pethidine and diazepam) administered during gastroscopy. Under substrate-depleted conditions, the oxygen consumption and the aminopyrine accumulation of fundic mucosa were not significantly increased by histamine. Stimulation of functional activities by gastric secretagogues was observed only in the presence of exogenous substrates. The ability of various substrates to support acid formation in the presence of gastric secretagogues was evaluated. Carbohydrates were found to be effective substrates in supporting the functional responses of the tissue, with glucose being the most effective. Propionate, butyrate, beta-hydroxybutyrate, and octanoate were ineffective as substrates. Glucose by itself, but not butyrate, significantly increased oxygen uptake and aminopyrine accumulation. The results suggest that the human gastric mucosa, in vitro, has an absolute requirement for metabolic substrates to support secretory responses and that carbohydrates seem to be the preferential substrates.

Stimulation of pyruvate carboxylation by gastric secretagogues

Pyruvate carboxylation was stimulated by 2 gastric secretagogues, histamine and dibutyryl cyclic AMP, and by butyrate. Thiocyanate, an inhibitor of acid secretion, produced a slight decrease. Avidin significantly reduced acid secretion and this effect was overcome by biotin and oxalacetate. The results suggest that carboxylation of pyruvate is one of the reactions controlling oxidative metabolism and acid secretion in toad gastric mucosa.

Effect of Krebs cycle intermediates and inhibitors on toad gastric mucosa

An attempt to increase the permeability of gastric mucosa to exogenous Krebs cycle intermediates seemed advisable for a better understanding their relationship with acid secretion. At pH 7.4, citrate, oxoglutarate, fumarate, and malate had no significant effect on oxygen uptake (QO2) nor on acid secretion (QH+) by toad gastric mucosa; succinate increased QO2 slightly and had no effect on QH+; but at pH 5.0, oxoglutarate and succinate increased QO2 by 18 and 21%, respectively. 14CO2 evolved by gastric mucosa incubated with [14C]oxoglutarate, succinate, malate, or citrate was 155, 92, 128, and 353%, respectively, greater at pH 5. Citrate, oxoglutarate, succinate, fumarate, and malate increased QH+ by theophylline-stimulated mucosa at pH 5.0 by 25, 39, 35, 17 and 28%, respectively. Oxoglutarate-dependent respiration was shown to correlate with oxoglutarate oxidation. Malonate and arsenite inhibited QO2 and QH+; malonate inhibition was reversed by washout or by succinate. Arsenite was reversed by washout and accelerated by addition of lipoate immediately after washout. The results suggest that the Krebs cycle has concomitant roles in the regulation of QH+ and oxidative metabolism in the toad gastric mucosa.