Enhanced Lactate Production Research Articles

Intracellular accumulation of isoproterenol enhances the lactate production in the perfused rat heart

Effects of intracellular accumulation of isoproterenol (ISO) on lactate production were examined in perfused rat heart. The lactate production during ISO perfusion in rat heart was increased and subsequent addition of an inhibitor of catechol-O-methyl transferase (COMT) further enhanced the production, and the enhanced production was significantly reduced by uptake 2 inhibitor. The perfusion with ISO free-medium in the heart with high intracellular accumulation of ISO produced lactate more than that in the low intracellular accumulation. The present experiments demonstrated that the enhanced lactate production is accompanied by intracellular accumulation of ISO in the perfused rat heart, and suggested that the accumulated ISO may activate intracellular β-adrenoceptors in the rat heart.

Effects of muscle stimulation in situ in pregnant rats.

Effects of muscle stimulation were studied in the perfused hindleg of late pregnant and age-matched control rats. Muscle stimulation increased tissue glucose uptake in both groups with a tendency towards higher values in the pregnant rats. The stimulation-induced lactate production was markedly larger in pregnant than in control rats. In the pregnant rats muscle tension output decreased more rapidly and vascular resistance was greater than in non-pregnant group. The decline of tension, accompanied by the enhanced lactate production of contracting muscles, may suggest a reduced muscle oxidative potential in late pregnancy and/or delayed adaptation of the local blood flow. The greater vascular resistance found during muscle stimulation in pregnant animals might have been due to the persistent local action of estrogens. The data obtained indicate that pregnancy modifies skeletal muscle function during stimulation in situ.

Metabolism in the hypothermically perfused kidney. Production and utilization of lactate and utilization of acetate in the dog kidney.

The mechanism for the high lactate production during hypothermic kidney perfusion has not been clarified previously. The metabolism of lactate and acetate was studied in 23 dog kidneys during continuous hypothermic perfusion. The perfusions were performed in a Gambro machine with a perfusate based on human serum albumin. With a perfusate containing fatty acid extracted albumin, which was almost free of fatty acids, the glucose uptake of the kidney was more pronounced than during perfusion with a fatty acid-rich perfusate. The high glucose uptake under this perfusion condition was associated with a lower lactate production and a higher glucose oxidation rate. In perfusions with a perfusate containing lactate at a concentration of 2.5 mmol/l a considerable lactate uptake of the kidney was shown. By isotope dilution technique the production and uptake rate of lactate was estimated at 4.4 and 8.0 mumol/g kidney and day in two experiments. The labeled lactate carbon was recovered in CO2, and glucose in the perfusate indicating a continuous oxidation and gluconeogenesis. Acetate was used by the kidney both for oxidation and for gluconeogenesis. Addition of acetate to the ordinary fatty acid-rich perfusate caused an enhanced lactate production from the perfused kidney. The results indicate that the high lactate production during hypothermic perfusion of kidneys is mainly dependent on a metabolic blockade at the level of pyruvate dehydrogenase.

Effect of insulin on the performance of the hypoxic rat heart

The effect of insulin (0.1 mU/ml) on peak systolic aortic pressure, heart rate, glucose uptake and lactate production was studied in the isolated hypoxic working rat heart. Without insulin, hypoxia lowered heart rate ( P < 0.01) and peak systolic aortic pressure ( P < 0.01), and increased glucose uptake ( P < 0.005) and lactate production ( P < 0.001). Insulin stimulated glucose uptake under aerobic ( P < 0.02) and hypoxic conditions ( P < 0.05), leading to enhanced lactate production aerobically ( P < 0.05). Hypoxic lactate production was not changed significantly by the presence of insulin. Heart rate and peak systolic aortic pressure remained unchanged by insulin regardless of oxygen supply. Our experiments show that in moderate hypoxia insulin does not enhance anaerobic glycolysis (lactate production) despite increased glucose uptake and does not improve cardiac performance.

Glucose Metabolism of the Isolated Eccrine Sweat Gland. I. The Effects of Mecholyl, Epinephrine and Ouabain

The effects of mecholyl, epinephrine and ouabain on glucose metabolism were studied in freshly dissected human and monkey paw eccrine sweat glands. Both showed active glycolytic activity which was further stimulated by mecholyl and epinephrine. Ouabain inhibited unstimulated as well as mecholyl or epinephrine-stimulated glycolysis and mecholyl-stimulated 14 CO 2 production. Anaerobic incubation and the addition of KCN markedly enhanced lactate production. Mecholyl and lower concentrations of epinephrine stimulated both 14 CO 2 and lactate production. Higher concentrations of epinephrine stimulated lactate production but markedly suppressed 14 CO 2 production. A possible link between energy production and glandular secretion was discussed.

Influence of puromycin and anoxia on the effect of gonadotrophins on ovarian carbohydrate metabolism.

AbstractAn analysis of certain requirements for the gonadotrophic stimulation of ovarian carbohydrate metabolism has been performed. Whole ovaries from prepubertal and hypophysectomized rats were incubated in bicarbonate or Tris‐HCl buffer at 37° C. Puromycin, injected to the rats either before removal of the ovaries or added directly to the incubation medium, blocked the protein synthesis in the ovaries and caused a decrease in the rate of glucose uptake and lactic acid production. The stimulatory effects, however, of both LH and FSH on carbohydrate metabolism, which have been reported in detail previously (Hamberger and Ahrkn 1967) were not blocked by puromycin. Furthermore, this effect of FSH in vitro on carbohydrate metabolism could not be explained as due to a contamination by LH in the FSH preparation used. Ovaries incubated under anaerobic conditions showed increased rates of glucose uptake and lactate production. LH had no stimulatory effect on lactate production under these experimental conditions while puromycin still caused a significant decrease of this parameter. Addition of 2,4‐dinitrophenol to the medium markedly enhanced lactate production by the ovaries. Possible mechanisms for the gonadotrophic stimulation of carbohydrate metabolism in the ovary are discussed.