Leucine metabolism during fasting and exercise

Whole body leucine kinetics were examined in seven healthy young men while in a 14-h postabsorptive state (PAS) and after a 3.5-day fast (FS). Subjects received a primed constant intravenous infusion of L-[1-13C]leucine while resting for 3 h and then while exercising on a cycle ergometer at 45% maximal O2 uptake to exhaustion. Blood samples drawn during isotopic steady state were analyzed for 13C enrichment of leucine and alpha-ketoisocaproic acid, and expired gas samples were analyzed for 13CO2. Resting leucine flux was higher in the FS, and there was a slight increase in leucine oxidation. During exercise, leucine flux did not differ between PAS and FS but leucine oxidation rose markedly. In the FS, leucine oxidation was 25 +/- 7 (SD) mumol.kg-1.h-1 at rest and rose to 75 +/- 21 mumol.kg-1.h-1 during exercise; in the PAS, oxidation was 20 +/- 5 mumol.kg-1.h-1 at rest and 52 +/- 17 mumol.kg-1.h-1 during exercise. These data indicate that the high rate of leucine oxidation previously found during exercise was increased further by a 3.5-day fast.     

Lipid metabolism in the adipose tissues of a carnivore, the raccoon dog, during prolonged fasting

Previous studies on laboratory rodents, rabbits, and humans have demonstrated that adipose tissue fatty acid (FA) mobilization is selective, and its efficiency is related to the molecular structure of FAs. This study was undertaken to find out whether such preferences of FA mobilization are a general feature of mammalian white adipose tissue (WAT) and are also manifested in carnivores. Fractional mobilization of a wide spectrum of FAs was studied by gas-liquid chromatography from six subcutaneous (scapular, rump, ventral) and intra-abdominal (omental, mesenteric, retroperitoneal) WAT depots of raccoon dogs (Nyctereutes procyonoides) fed or fasted for 2 months. Fasting stimulated the mobilization of shorter-chain saturated, mono-unsaturated (MUFAs), and polyunsaturated FAs (PUFAs). The effects of unsaturation and the position of the first double bond from the methyl end were more inconsistent. The effect of double-bond position may be due to chain shortening of longer-chain MUFAs and preferential utilization of n-3 PUFAs over n-6 PUFAs. Moreover, there were site-specific differences in fractional mobilization, the omental adipose tissue being the most divergent. The in vivo FA mobilization from the regional WAT depots of a carnivore was selective, and the molecular structure of the FA affected its efficiency.     

Lipid metabolism and dynamics during phagocytosis

Phagocytosis, the engulfment of particles, mediates the elimination of invading pathogens as well as the clearance of apoptotic cells. Ingested particles reside within a vacuole or phagosome, where they are eventually destroyed and digested. The phagosomal lumen acquires microbicidal and digestive properties through interaction with various components of the endocytic pathway, a process known as maturation. Lipids are known to have numerous roles in phagosome formation and maturation; recent developments in the design of lipid-specific probes and in high-resolution imaging have revealed that lipids, notably phosphoinositides, are involved in signaling, actin assembly and the recruitment of molecular motors to sites of ingestion. In addition, phosphoinositides and other lipids also regulate multiple membrane budding, fission and fusion events required for maturation.     

Lipid metabolism during encystment of Azotobacter vinelandii.

The formation of cysts by Azotobacter vinelandii involves the synthesis of lipids as major metabolic products. Cells which encyst at low levels in aging glucose cultures undergo the same pattern of lipid synthesis as cells which undergo reasonably synchronous encystment in beta-hydroxybutyrate or n-butanol. The accumulation of poly-beta-hydroxybutyrate (PHB) precedes the synthesis of 5-n-heneicosylresorcinol and 5-n-tricosylresorcinol (AR1), which is then followed in about 6 h by the synthesis of the 5-n-alkylresorcinol galactosides (AR2). In the mature cyst, PHB, AR1, and AR2 account for 8, 5.6, and 4.5%, respectively, of the dry weight. Phospholipid formation levels off 4 h postinduction, which coincides with the final cell division, but fatty acids synthesis continues at a very low level throughout encystment, suggesting some turnover of fatty acid. Distribution studies show that AR1 and AR2 are found in roughly equal amounts in the exine and central body of the cysts, with only trace amounts recovered from the intine. Studies of cysts labeled during encystment with [14C]beta-hydroxybutyrate or during vegetative growth with [14C]glucose suggest that the exine structure is synthesized during encystment, but that the intine is composed largely of vegetative cell components.     

Lipid metabolism during aging of high-alpha-linolenate-phenotype potato tubers

Previous studies demonstrated that high levels of alpha-linolenate in cell membranes of potato tubers (achieved by overexpressing fatty acid desaturases) enhances lipid peroxidation, oxidative stress, and tuber metabolic rate, effectively accelerating the physiological age of tubers. This study details the changes in lipid molecular species of microsomal and mitochondrial membranes from wild-type (WT) and high-alpha-linolenate tubers during aging. The microsomal and mitochondrial polar lipids of high-alpha-linolenate tubers were dominated by 18:3/18:3 and 16:0/18:3 molecular species. Relative to WT tubers, high-alpha-linolenate tubers had a substantially higher 16:0/18:n to 18:n/18:n molecular species ratio in mitochondria and microsomes, potentially reflecting a compensatory response to maintain membrane biophysical properties in the face of increased unsaturation. Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) accounted for 53 and 37% of polar lipids, respectively, in mitochondria from younger WT and high-alpha-linolenate tubers. The relative proportions of these phospholipids (PL) did not change during aging of WT tubers. In contrast, PE increased to dominate the PL pool of mitochondria during aging of high-alpha-linolenate tubers. While aging effected an increase in mitochondrial 18:3-bearing PCs and PEs in WT tubers, the concentration of 18:3-bearing PCs fell with a concomitant increase in 18:3-bearing PEs during aging of high-alpha-linolenate tubers. These age- and high-alpha-linolenate-induced changes had no effect on the respiration rate and functional integrity of isolated mitochondria. Differential increases in the respiration rates of WT and high-alpha-linolenate tubers during aging were therefore a consequence of unsaturation-dependent alterations in the microenvironments of cells. Microsomal 18:3-bearing PCs, PEs, digalactosyldiacylglycerols (DGDG), and monogalactosyldiacylglycerols all increased in WT tubers during aging. In contrast, a selective loss of 18:3-bearing PCs and DGDGs from microsomes of high-alpha-linolenate tubers likely reflects a greater susceptibility of membranes to peroxidative catabolism during aging. Aging resulted in an increase in sterol/PL ratio in microsomes from WT tubers, due primarily to a decline in PL. In high-alpha-linolenate tubers, the increase in sterol/PL ratio during aging was due to increases in Delta 5-avenasterol and stigmasterol, indicating membrane rigidification and likely contributing to increased membrane permeability. Age-induced changes in 18:3-bearing lipids in membranes of transformed tubers are discussed relative to the development of oxidative stress and accelerated aging.     

Ultrastructural demonstration of rabbit heart myocyte metabolism during fasting]

Thirty mature rabbits were completely deprived of food but water ad libitum for 10 days, then half of the animals were decapitated. The remaining animals were sacrificed 10 days after a sound diet. Histological, histochemical (estimation of glycogen, lipids, acid glycosamineglicans) and electron microscopic investigation of the myocardium was carried out. Degenerative and necrobiotic alterations were not revealed in muscular cells of the heart. At fasting accumulation of lipids and glycogen in the cardiac myocytes was evident. In fasting animals ultrastructure of the muscular cells of the heart demonstrated a certain decrease in synthetic processes. After a 10-day sound diet, the cardiac myocytes were actively involved into the process of intracellular regeneration. Increased lipid content in the rabbit myocardium, occurring at fasting, is connected with the necessity to provide the heart with an effective energy substrate required to preserve its contractile function and in this way adaptive-compensatory processes are demonstrated.