Ordered synthesis and mobilization of glycogen in the perfused heart.

The molecular order of synthesis and mobilization of glycogen in the perfused heart was studied by 13C NMR. By varying the glucose isotopomer ([1-13C]glucose or [2-13C]glucose) supplied to the heart, glycogen synthesized at different times during the perfusion was labeled at different carbon sites. Subsequently, the in situ mobilization of glycogen during ischemia was observed by detection of labeled lactate derived from glycolysis of the glucosyl monomers. When [1-13C]glucose was given initially in the perfusion and [2-13C]glucose was given second, [2-13C]lactate was detected first during ischemia and [3-13C]lactate second. This result, and the equivalent result when the glucose labels were given in the reverse order, demonstrates that glycogen synthesis and mobilization are ordered in the heart, where glycogen is found morphologically only as beta particles. Previous studies of glycogen synthesis and mobilization in liver and adipocytes [Devos, P., & Hers, H.-G. (1979) Eur. J. Biochem. 99, 161-167; Devos, P., & Hers, H.-G. (1980) Biochem. Biophys. Res. Commun. 95, 1031-1036] have suggested that the organization of beta particles into alpha particles was partially responsible for ordered synthesis and mobilization. The observations reported here for cardiac glycogen suggest that another mechanism is responsible. In addition to examining the ordered synthesis and mobilization of cardiac glycogen, we have selectively monitored the NMR properties of 13C-labeled glycogen synthesized early in the perfusion during further glycogen synthesis from a second, differently labeled substrate. During synthesis from the second labeled glucose monomer, the glycogen resonance from the first label decreased in integrated intensity and increased in line width.(ABSTRACT TRUNCATED AT 250 WORDS)

Rates of glycolysis and glycogenolysis during ischemia in glucose-insulin-potassium-treated perfused hearts: A 13C, 31P nuclear magnetic resonance study.

The effects of 11.7 mM glucose, insulin, and potassium (GIK) on metabolism during ischemia were investigated in the perfused guinea pig heart using magnetic resonance spectroscopy. Intracellular metabolites, primarily glycogen and glutamate, were labeled with 13C by addition of [1-13C]glucose to the perfusate during a normoxic, preischemic period. 13C and 31P NMR spectroscopy was used to observe the metabolism of 13C-labeled metabolites simultaneously with high-energy phosphorus metabolites and pH. The extent of acidosis and the rate and amount of labeled lactate accumulation during ischemia were the same in control (3 mM glucose + insulin) and GIK-treated hearts. In contrast, the rate of labeled glycogen mobilization during ischemia in GIK-treated hearts was one third the rate observed in control hearts. These observations suggest that GIK decreased the rate of glycogenolysis during ischemia without affecting the rate of glycolysis. We propose that glucose contributed as a glycolytic substrate to a greater extent during ischemia in GIK-treated hearts than in hearts perfused with 3 mM glucose and insulin. The glycogen-sparing effect of GIK demonstrated in these studies could delay the onset of ischemic damage in a clinical setting by prolonging the availability of glycolytic substrate necessary for production of high-energy phosphate.

Metabolic consequences of anoxia in the isolated, perfused guinea pig heart: anaerobic metabolism of endogenous amino acids.

The metabolic consequences of anoxia in the isolated, perfused guinea pig heart were examined by 13C NMR spectroscopy of 13C-labeled metabolites in situ. Upon addition of [3-13C]pyruvate to the perfusate during normoxic conditions, label is detected in several metabolites, including alanine (C3), glutamate (C2, C3, and C4), and aspartate (C2 and C3), reaching steady state levels 10-15 min after the labeled precursor reaches the heart. During anoxia, the label in glutamate and aspartate decreases and label appears in C2(3) of succinate. This real-time observation demonstrates that in the isolated intact heart, anaerobic metabolism of the amino acids aspartate and glutamate to succinate occurs. These pathways, which were first noted to occur in skeletal muscle of diving mammals, may provide a mechanism supplemental to glycolysis for the production of nucleoside triphosphates during periods of anoxia.

Prenatal toxicology of shale oil retort water in mice.

Shale oil retort water, a by-product of the production of oil from shale, potentially amounts to tens of millions of gallons per year and must be treated or recycled with regard for public health. Such retort water was given to 98 female ICR/DUB mice in their drinking water at concentrations of 0, 0.1, 0.3, and 1.0% for periods up to 203 d. Seven of 75 treated animals developed adenomalike lesions that were not seen in the control animals. These ranged from adenomas and an adenomatoid nodule in the lung to the rectal adenocarcinoma. Although the incidence of adenomalike lesions was not statistically significant, this appearance of neoplasia requires further investigation. Eighty-five animals became pregnant. The proportion of animals pregnant, weights of nonpregnant animals, weight gain during pregnancy, average fetal weight, number of live fetuses per liter, and proportion of male fetuses were unaffected by drinking retort water. Early and late fetal deaths and preimplantation losses were likewise unaffected, except for a significant increase in preimplantation losses in animals consuming 1.0% retort water. A variety of palatal defects were seen in treated animals, however, including single and multiple cleft palates and a defect, to our knowledge not previously reported, in which the posterior portion of one or both palatal shelves appeared not to have formed. The palatal defects, as a group, were dose-dependent and statistically significant.

Pyrimidine biosynthesis in Lactobacillus leichmannii.

Tracer studies of pyrimidine biosynthesis in Lactobacillus leichmannii (ATCC 7830) indicated that, while aspartate is utilized in the usual manner, the guanido carbon of arginine, rather than carbon dioxide, is utilized as a pyrimidine precursor. The guanido carbon of arginine also contributes, to some extent, to the carbon dioxide pool utilized for purine biosynthesis. The enzyme of the first reaction leading from arginine to pyrimidines, arginine deiminase, was investigated in crude bacterial extracts. It was inhibited by thymidylic acid and purine ribonucleotides, and to a lesser extent by purine deoxynucleotides and deoxycytidylic acid. Under the assay conditions employed, a number of nucleotides had no effect on the enzyme activity of the aspartate transcarbamylase of L. leichmannii. Growth of the cells in media containing uracil, compared to growth in media without uracil, resulted in a four- to fivefold decrease in the concentrations of aspartate transcar-bamylase and dihydroorotase and a twofold increase in the concentration of arginine deiminase, as estimated from specific enzyme activity in crude extracts of the cells. A small increase in specific enzyme activity of ornithine transcarbamylase and carbamate kinase was also observed in extracts obtained from cells grown on uracil. No appreciable change in concentration of any of the five enzymes studied was detected when the cells were grown in media containing thymidine or guanylic acid. A hypothetical scheme which suggests a relationship between the control of purine and pyrimidine biosynthesis in this bacterium and which is consistent with the experimental results obtained is presented.