Rate Of Acetate Incorporation Research Articles

Effect of growth hormone on the differentiation of bovine preadipocytes into adipocytes and the role of the signal transducer and activator of transcription 5b1

We evaluated the effect of GH on the differentiation of primary bovine preadipocytes into adipocytes. Bovine preadipocytes, derived from adipose tissue explants, were induced to differentiate into adipocytes in the presence or absence of recombinant bovine GH. The differentiation status of adipocytes was assessed by Oil Red O staining and by measuring the activity of glycerol-3-phosphate dehydrogenase (G3PDH) and the rate of acetate incorporation. Fewer preadipocytes became adipocytes in the presence of GH than in the absence of GH; adipocytes formed in the presence of GH had lower G3PDH activity and lower rate of acetate incorporation than those formed without GH treatment (P < 0.05). These data suggest an inhibitory effect of GH on the differentiation of bovine preadipocytes into adipocytes. Growth hormone decreased the expression of C/EBPα and PPARγ mRNA in bovine adipocytes (P < 0.05). Because C/EBPα and PPARγ are the master regulators of adipocyte differentiation, this data suggests that GH might inhibit the differentiation of bovine preadipocytes into adipocytes by inhibiting the expression of C/EBPα and/or PPARγ. Because the signal transducer and activator of transcription 5 (STAT5) is a major component of signaling from the GH receptor, we next determined the potential role of STAT5 in GH inhibition of bovine adipocyte differentiation. Overexpression of a constitutively active form of STAT5b (STAT5bCA) in bovine preadipocytes through adenoviral transduction mimicked the effects of GH on the formation of lipid-containing adipocytes, G3PDH activity, and acetate incorporation rate. Overexpression of STAT5bCA was associated with decreased expression of C/EBPα mRNA (P < 0.05) but not that of PPARγ mRNA in bovine adipocytes. These results support a role of STAT5b in mediating GH inhibition of C/EBPα expression but not that of PPARγ expression in bovine preadipocytes. Overall, the present study suggests that GH may inhibit adipose growth in cattle in part by inhibiting adipogenesis and that GH inhibits the differentiation of bovine preadipocytes to adipocytes through STAT5b-dependent inhibition of C/EBPα expression and STAT5b-independent inhibition of PPARγ expression.

Influence of abomasal carbohydrates on subcutaneous, omental, and mesenteric adipose lipogenic and lipolytic rates in growing beef steers

To determine the response to alteration in site and form of carbohydrate delivery to the digestive tract, in vitro rates of lipogenesis and lipolysis in mesenteric (MESA), omental (OMA), and subcutaneous (SQA) adipose depots were compared. Forty crossbred beef steers (243 +/- 2 kg of BW) were fed 161 (LI) or 214 (HI) kcal of ME/(kg of BW(0.75) x d) or they were fed LI and infused for 35 d into the rumen (R) or abomasum (A) with starch hydrolysate (SH) or into the abomasum with glucose (G). Jugular blood samples were collected, steers were slaughtered, and adipose depots were sampled and prepared for assessment of lipogenesis and lipolysis in vitro. Blood concentrations of glucagon were increased (P = 0.04) in HI-H2O compared with LI-H2O steers, whereas A-SH tended to increase (P = 0.08) circulating IGF-I relative to R-SH, and A-G tended to have elevated (P = 0.09) T3 compared with A-SH. Lipolysis, as assessed by NEFA release, was unaffected by treatment. Glycerol release by the MESA and SQA was increased or tended to be increased (P < or = 0.08) in HI-H2O compared with LI-H2O steers. In A-G compared with A-SH steers, glycerol release from OMA increased (P = 0.008) and from SQA tended to be increased (P = 0.08). Acetate incorporation into total neutral lipids (TNL) increased or tended to increase with ME intake and SH infusion (P < or = 0.09) across all depots. Rates of acetate incorporation into fatty acids (FA) also increased or tended to be increased (P < or = 0.1) by SH infusion across all depots, but only that of SQA was increased with ME intake (HI-H2O vs. LI-H2O; P = 0.02). Rates of acetate incorporation into FA and TNL in MESA were increased (P < or = 0.03) by A-SH compared with R-SH, but site of SH infusion did not affect the rates in SQA or OMA. Glucose incorporation into TNL for MESA and SQA increased or tended to be increased (P < or = 0.1) by dietary and infused energy, whereas for OMA they tended to be increased (P = 0.1) only by SH infusion. In contrast, glucose incorporation into FA was unaffected by energy supply but tended to be increased (P = 0.07) by SH in MESA and tended to be greater (P = 0.08) for A-G than A-SH in OMA. The general across-depot pattern of acetate incorporation rate into FA and TNL was SQA > OMA > MESA, whereas, for glucose incorporation, rates across depots were equivalent. These data provide evidence that the postruminal supply of energy, specifically carbohydrate, stimulates lipogenesis from acetate and glucose and is more pronounced in abdominal depots relative to the subcutaneous depot.

Reduced lipolysis and increased lipogenesis in adipose tissue from pinealectomized rats adapted to training

The current study investigated the effects of chronic training and pinealectomy on the lipogenic and lipolytic activity of adipose tissue. Pinealectomized and sham-operated adult male Wistar rats were distributed in to four subgroups: pinealectomized untrained, pinealectomized trained, control untrained and control trained. At the end of the training period (8 wk) the rats were killed. Blood samples were collected for glucose, insulin and leptin determinations. Peri-epididymal adipocytes were isolated for measurement of in vitro rates of lipolysis and incorporation of substrates (D-[U-14C]-glucose, L-[U-14C]-lactate, [2-14C]-acetate and [1-14C]-palmitate) into lipids, and samples of epididymal adipose tissue were homogenized for evaluation of glucose-6-phosphate dehydrogenase maximal activity. Pinealectomy resulted in a significantly increased lipolytic capacity in response to isoproterenol and a decrease in circulating leptin levels without affecting the rates of incorporation of different substrates into lipids. However, only in the intact control group did training promote a higher basal and isoproterenol-stimulated lipolysis, increase the incorporation of palmitate (esterification), decrease the incorporation of acetate (lipogenesis) into lipids and diminish circulating leptin levels. These effects of exercise training were not seen in pinealectomized rats. However, pinealectomized trained animals showed a marked reduction in lipolysis and an increased rate of acetate incorporation. In conclusion, we demonstrated for the first time that the pineal gland plays an important role in the regulation of lipid metabolism in such a way that its absence caused a severe alteration in the balance between lipogenesis and lipolysis, which becomes evident with the adaptation to exercise training.

Fungal content and activities in standing-decaying leaf blades of plants of the Georgia Coastal Ecosystems research area

Change in salinity, including expansion or contraction of salt- and freshwater marshes, due to altered river outflow may influence a variety of ecosystem processes, and the literature to date suggests that fungal activity in standing-decaying blades of macrophytes may be lower in freshwater marshes than in saltmarshes. I measured living-fungal mass (as ergosterol), rate of CO2 evolution, and rate of fungal membrane synthesis (acetate incorporation into ergosterol) for standing-decaying blades from a series of macrophytes, including saltmarsh cordgrass in both saline and fresher-water sites. Three terrestrial plants with prominent standing-decaying leaf blades were included for com- parison. Species involved were: Spartina alterniflora, S. cynosuroides, Zizaniopsis miliacea, Typha angustifolia, Sabal palmetto, Uniola paniculata, and Panicum amarum. Although there was no differ- ence in fungal content of S. alterniflora blades from saltier and fresher sites, there was a significant trend downwards (from > 500 to <250 µg ergosterol g -1 system organic mass) in mean content of living-fungal mass moving from saltmarsh-adapted toward freshwater-adapted plants, and 2 of 3 ter- restrial plants were also low (ca. 100 µg g -1 ). The activity measurements (CO2, acetate incorporation) revealed an opposite pattern: blades from fresher-water plants had higher activities per unit living- fungal mass (range of about 4-fold for mean rate of acetate incorporation per unit ergosterol), and lower CO2 release per unit fungal membrane synthesis, than did more saline-adapted plants. It is pro- posed that this is perhaps largely a consequence of the microstructure (lignification, cuticular hydrophobicity) of the blades of the fresher-water plants (and 2 of the terrestrial plants) limiting dura- tion of fungal activity. Upon thorough wetting, such as eventually occurs when blades move to the marsh-sediment surface, fungi within the fresher-water blades would be permitted to grow quickly, which would explain reported increases in ergosterol content of fallen blades.

Estimation of fungal growth rates in soil using 14C-acetate incorporation into ergosterol

A technique to estimate fungal growth rates in field samples was tested in soil. The technique is based on the addition of 14C-acetate to a soil slurry and the subsequent uptake and incorporation of the labelled acetate into the fungus specific substance ergosterol by the fungi. The addition of fungal inhibitors decreased acetate incorporation rates, while bacterial inhibitors did not. Fungus-free soil exhibited no incorporation of acetate into ergosterol, indicating that the method was specific for measuring fungal activity. Incorporation rates were linear up to 18 h after the addition of acetate indicating that changing the conditions (adding acetate as a solution to a soil slurry) did not affect the incorporation rate. Problems associated with saturation of the incorporation of the added acetate were encountered, which together with uncertain conversion factors made calculations of absolute growth rates difficult. However, for relative comparisons the technique worked well. This was exemplified by measuring the relationship between temperature and growth rate of the soil fungal community, where an optimum temperature between 25 and 30°C and an apparent minimum temperature for fungal growth of −11°C were found. The technique was also used to indicate which nutrients limited instantaneous fungal growth in soil by adding carbon, nitrogen and phosphorus in different combinations and measuring the rate of acetate incorporation into ergosterol 2 days later. Carbon appeared to be the limiting nutrient for fungal growth in both an agricultural soil and a forest humus soil.

Estimating production of litter-decomposing fungi in streams from rates of acetate incorporation into ergosterol

Estimating production of litter-decomposing fungi in streams from rates of acetate incorporation into ergosterol

In vivo and in vitro lipogenesis and aspects of metabolism in ovines: Effect of environmental temperature and dietary lipid supplementation

Twenty-four wether lambs were randomly allocated to six treatments to investigate the effect of temperature and dietary lipid supplements on fatty acid synthesis and metabolic activity in sheep. The treatments consisted of four groups exposed to either cold (0 °C) or warm temperature (+23 °C) and given ad libitum access to either a control barley-based diet or with lipid supplementation. Two other groups were placed on the dietary regimen at 0 °C, but pair-fed to intake of animals in the +23 °C environment. At 5 wk, fatty acid synthesis was measured by [1-14C]acetate incorporation into tissue lipids. Cold exposure and dietary lipid supplementation had no effect (P &gt; 0.05) on in vivo fatty acid synthesis rates in either longissimus dorsi or the liver. In both subcutaneous and mesenteric adipose tissue depots, the rate of acetate incorporation into tissue lipid was not significantly affected by cold exposure. In the perirenal fat depot, cold exposure increased (P &lt; 0.05) the rate of fatty acid synthesis, while lipid supplementation decreased (P &lt; 0.05) the rate in all tissue adipose depots. In vitro, mesenteric and perirenal adipose tissues from cold pair-fed animals had higher (P &lt; 0.05) rates of fatty acid synthesis compared to tissues from animals in the warm environment. However, there was no effect of dietary lipid supplementation in these two fat depots. Metabolic heat production, and energy and nitrogen excretion by animals were increased (P &lt; 0.05) by cold exposure while lipid supplementation had the opposite effect (P &lt; 0.05). The relationship between average daily gain and feed intake was linear at both warm and cold environments, but with higher (P &lt; 0.05) average daily gain at all levels of intake in the cold compared to the warm environment. Results indicate that both environment and diet regulate metabolic activity in sheep. However, there were differences in lipogenic response by tissues to the treatments. Key words: Environmental temperature, dietary lipid, fatty acid synthesis, metabolic rate, sheep

Annual production of leaf‐decaying fungi in a woodland stream

1. Fungi are thought to be important mediators of energy flow in the detritus‐based food webs of woodland streams. However, until recently, quantitative methods to assess their contribution have been lacking. Growth rates of leaf‐decaying fungi can be estimated from rates of acetate incorporation into ergosterol which, together with estimates of fungal biomass from ergosterol concentrations, enables calculation of fungal production. In this study, I used this method to estimate total production of leaf‐decaying fungi over an annual cycle in a small woodland stream, Walker Branch, Tennessee, U.S.A. To calculate fungal biomass and production on an areal basis, I determined the amount of leaf litter occurring in the stream by sampling transects randomly selected in each of ten 10‐m sections every 20–50 days. Subsamples of leaves chosen from five of the transects were used to determine ergosterol concentrations and in situ rates of acetate incorporation into ergosterol.2. Leaf litter, fungal biomass m–2, and fungal production m–2 were highly seasonal. Leaf litter ranged from 249 g m–2 in November to less than 5 g m–2 during the summer. Fungal biomass as percentage of leaf litter ranged from 4.4 to 8.8% during the year, but on an areal basis ranged from 11 to 13 g m–2 during November to January to 0.25 g m–2 in June, primarily due to the seasonal variation in amount of leaf litter present. Fungal growth rates averaged 2.6% day–1 (0.9–7.0% day–1) during the year. Daily production of leaf‐decaying fungi ranged from 0.49 g m–2 in November, when the amount of leaf litter was at its maximum, to 0.006 g m–2 during the summer when the amount of leaf litter was low. Annual production of leaf‐decaying fungi was 34 g m–2, with an annual production to biomass ratio (P/B) of 8.2.3. Fungal spore concentrations in the stream were also seasonal and were correlated with amount of leaf litter m–2 and fungal biomass m–2. Spore concentrations varied between one and four spores ml–1 throughout most of the year, but increased to eighteen spores ml–1 shortly after the greatest amount of leaf litter was present in the stream during November.

Application of fungal and bacterial production methodologies to decomposing leaves in streams

As leaves enter woodland streams, they are colonized by both fungi and bacteria. To determine the contribution of each of these microbial groups to the decomposition process, comparisons of fungal and bacterial production are needed. Recently, a new method for estimating fungal production based on rates of [(sup14)C]acetate incorporation into ergosterol was described. Bacterial production in environmental samples has been determined from rates of [(sup3)H]leucine incorporation into protein. In this study, we evaluated conditions necessary to use these methods for estimating fungal and bacterial production associated with leaves decomposing in a stream. During incubation of leaf disks with radiolabeled substrates, aeration increased rates of fungal incorporation but decreased bacterial production. Incorporation of both radiolabeled substrates by microorganisms associated with leaf litter was linear over the time periods examined (2 h for bacteria and 4 h for fungi). Incorporation of radiolabeled substrates present at different concentrations indicated that 400 nM leucine and 5 mM acetate maximized uptake for bacteria and fungi, respectively. Growth rates and rates of acetate incorporation into ergosterol followed similar patterns when fungi were grown on leaf disks in the laboratory. Three species of stream fungi exhibited similar ratios of rates of biomass increase to rates of acetate incorporation into ergosterol, with a mean of 19.3 (mu)g of biomass per nmol of acetate incorporated. Both bacterial and fungal production increased exponentially with increasing temperature. In the stream that we examined, fungal carbon production was 11 to 26 times greater than bacterial carbon production on leaves colonized for 21 days.

Influence of nitrogen and phosphorus on thein situ bioremediation of trichloroethylene

The US Department of Energy, Office of Technology Development, has supported a field-scalein situ demonstration of trichloroethylene (TCE) bioremediation at the Westinghouse Savannah River Site (WSRS). Several methods were used to examine the influence of nitrogen and phosphorus species on TCE degradation during methane (CH4) injection into contaminated sediments. Laboratory experiments using WSRS ground water revealed that the rate of acetate incorporation into microbial lipids was stimulated when triethyl-phosphate (TEP) or nitrous oxide (N2O) was added. The trend was: CH4+N2O>CH4 +TEP>CH4+N2O+TEP>CH4 alone. The degree of stimulation of14C-TCE mineralization in ground water incubated for 30 d in the laboratory with added methane and nutrients increased in the order: OP=TEP>NH3+TEP=NH3>N2O (OP, orthophosphate; NH3, ammonia). Monitoring of WSRS ground water revealed significant differences among sampling wells over time in nutrient concentrations, nitrogen uptake, and urease activity during operations of the bioremediation demonstration. In the field, the addition of TEP+N2O to the pulsed injection of CH4 resulted in dramatic stimulation of TCE-degrading potentials observed in ground water enrichments. The potential to mineralize14C-TCE in ground water enriched with nutrients in the laboratory increased from 90% of the samples taken during the injection of CH4+TEP+N2O treatment. These results demonstrated the dramatic impacts of nitrogen and phosphorus supplements during thein situ bioremediation of chlorinated solvents.

Factors influencing the abundance and metabolic capacities of microorganisms in Eastern Coastal Plain sediments

The abundance and metabolic capacities of microorganisms residing in 49 sediment samples from 4 boreholes in Atlantic Coastal Plain sediments were examined. Radiolabeled time-course experiments assessing in situ mirobial capacities were initiated within 30 min of core recovery. Acetate (1-(14)C- and(3)H-) incorporation into lipids, microbial colony forming units, and nutrient limitations were examined in aliquots of subsurface sediments. Water-saturated sands exhibited activity and numbers of viable microorganisms that were orders of magnitude greater than those of the low permeability dense clays. Increased radioisotope utilization rates were observed after 6-24-h incubation times when sediments were amended with additional water and/or nutrients. Supplements of water, phosphate, nitrate, sulfate, glucose, or minerals resulted in the stimulation of microbial activities, as evidenced by the rate of acetate incorporation into microbial lipids. Additions of water or phosphate resulted in the greatest stimulation of microbial activities. Regardless of depth, sediments that contained >20% clay particles exhibited lower activities and biomass densities, and greater stimulation with abundant water supplementation than did sediments containing >66% sands and hydraulic conductivities > 200 μm sec.(-1).

Duodenal Rapeseed Oil Infusion in Early and Midlactation Cows. 5. Milk Fatty Acids and Adipose Tissue Lipogenic Activities

Lipogenic activities of perirenal adipose tissue were investigated in early (wk 3) and midlactation (wk 19 to 26) cows that received a duodenal rapeseed oil infusion (1.0 to 1.1 kg/d). In midlactation, oil infusion resulted in a decreased rate of fatty acid synthesis from acetate and a decreased rate of the activities of fatty acid synthetase and glucose-6-phosphate dehydrogenase, whereas lipoprotein lipase activity tended to increase. The rate of glucose incorporation into glyceride-glycerol and the activities of glycerol-3-phosphate dehydrogenase and malic enzyme were not significantly affected. Fatty acid C14:0 content of perirenal adipose tissue was decreased, and fatty acid C18:2 and C18:3 contents were increased in oil-infused cows. In early lactation, rates of acetate incorporation into fatty acids and activities of fatty acid synthetase and lipoprotein lipase were very low. Activities of glucose-6-phosphate dehydrogenase and glycerol-3-phosphate dehydrogenase were lower in the early than in the midlactation trial. Oil infusion did not change the measured parameters. In both trials, percentages and yields of milk fatty acids C18:1, C18:2, and C18:3 were increased, whereas those of C14:0. and C16:0 were decreased by oil. Calculated transfer rates of absorbed fatty acid C18:2 from oil to milk fat were 16 to 26%. Results suggested that oil fatty acids affected adipose and mammary de novo lipogenesis in a direct way without affecting fatty acid esterification in adipose tissue or total fat secretion in mammary tissue.

Influence of lindane on the fluidity of the rat ventral prostate membranes

The influence of lindane upon the dynamic properties of plasma membranes from rat ventral prostate has been investigated using a fluorescence polarization technique. Preincubation with lindane decreased the fluorescence polarization in a dose dependent manner. This effect, which is associated with an increased membrane fluidity, occurred in a very short period of time. Lindane also provoked a number of changes in lipid biosynthesis from acetate in the membrane. Less [1-14C]acetate was incorporated into cholesterol and more into phospholipids when this liposoluble toxicant was added to the preincubation medium. However, not all phospholipid classes were equally increased, because while the rate of acetate incorporation was greater into choline glycerophospholipids than into ethanolamine glycerophospholipids, both were higher than the rates of acetate incorporation into serine glycerophospholipids and sphingomyelin.

LIPID SYNTHESIS AND FATTY ACID COMPOSITION IN NANNOCHLOROPSIS SP. (EUSTIGMATOPHYCEAE) GROWN IN A LIGHT‐DARK CYCLE1

ABSTRACTChemical composition and lipid biosynthesis were studied in the marine eustigmatophyte Nannochloropsis sp. Grown under a 12:12 h light‐dark regime. Cellular division occurred in the dark and was associated with a reduction in cell volume. The cellular content of chlorophyll a and carotenoids increased during the light period and decreased during the dark period. Other cellular components, such as proteins, carbohydrates and lipids, followed a similar pattern. Nannochloropsis sp. Incorporated acetate, mostly into lipids during the light period, whereas a low rate of acetate incorporation was observed during the dark period, mostly into nonlipid compounds. Neutral lipids such as triacylglycerol were synthesized and accumulated in the light and showed a rapid turnover in the dark. Polar structural lipids such as monogalactosyl diacylglycerol were synthesized during the light period and hardly turned over during the dark period. Changes in lipid content were associated with variations in cellular fatty acid composition. The light period was characterized by an increase in the percentage of C16:0 and 16:1 fatty acids associated with triacylglycerols. However, in the dark period, as triglycerides were consumed for cellular maintenance, the relative distribution of the C20:5 fatty acid associated with the galactolipids increased.

Mineralization of linear alkylbenzene sulfonate (las) and linear alcohol ethoxylate (lae) in 11 contrasting soils

AbstractThe microbial mineralization of [U‐14C‐ring] linear alkylbenzene sulfonate (LAS) and [U‐14C‐ethoxylate] linear alcohol ethoxylate (LAE) was examined in 11 soils. These soils differed in their physical‐chemical properties and were obtained from geographically distinct locations. With one exception, they had no previous exposure to synthetic surfactants. Soil samples were amended with trace levels (50 ng/g soil) of each 14C surfactant, and evolution of 14CO2 was measured over time. When appropriate, the data were fitted to a first‐order production equation, and first order rate constants and asymptotic yields of 14CO2 were estimated using nonlinear regression. Both surfactants were mineralized without a lag period in every soil tested. Yields ranged from 16 to 71% and 30 to 69% for LAS and LAE respectively. First‐order rate constants ranged from 0.14 to 0.63 for LAS and 0.07 to 0.62 for LAE. Mean half‐life (across all soils) was 2 d for both surfactants. Community microbial activity, measured as the rate of acetate incorporation into lipids, did not correlate with either the rate or extent of surfactant mineralization. Subjecting these soils to cycles of wetting and drying in the laboratory prior to testing in most cases resulted in more rapid and extensive mineralization. These results indicate that microbial communities in soils have an indigenous ability to degrade low concentrations of LAS and LAE. This ability appears to be ubiquitous since it is present in a wide array of soil types from various locations. In addition, laboratory experiments involving wetting and drying of soils indicated that both the rate and extent of mineralization may be affected by climatological events.

Influence of dexamethasone on the lipid distribution of newly synthesized fatty acids in fetal rat lung

There is a developmental increase in fatty acid biosynthesis and surfactant production in late-gestation fetal lung and both are accelerated by glucocorticoids. We have examined the distribution of the newly synthesized fatty acids to determine whether they are preferentially incorporated into surfactant. Explants of 18 day fetal rat lung were cultured with and without dexamethasone for 48 h and then with [ 3H]acetate for 4 h after which labeled fatty acids were measured. Incorporation of radioactivity from acetate was considered a measure of newly synthesized fatty acids. Phospholipids contained 86% of the newly synthesized fatty acids of which approx. 80% were in phosphatidylcholine. Phosphatidylcholine and disaturated phosphatidylcholine contained a much greater percentage of the labeled fatty acids than of the phospholipid mass determined by phosphorus assay while phosphatidylethanolamine, phosphatidylserine and sphingomyelin contained less. Dexamethasone increased the rate of acetate incorporation into total lipid fatty acids but it had little effect on fatty acid distribution, except that it increased the percentages in phosphatidylglycerol and disaturated phosphatidylcholine. The hormone also increased the mass of these two phospholipids to a greater extent than that of the total. These data suggested that the newly synthesized fatty acids are preferentially incorporated into surfactant phospholipids and that this process is accelerated by dexamethasone. However, since phosphatidylcholine and phosphatidylglycerol are not exclusive to surfactant, we compared isolated lamellar bodies with a residual fraction not enriched in surfactant. The rate of acetate incorporation into fatty acids in lamellar body phosphatidylcholine as well as its specific activity (radioactivity per unit phosphorus) were both increased by dexamethasone. Specific activity, however, was no greater in the lamellar bodies than in the residual fraction in both control and dexamethasone-treated cultures. Therefore, there is no preferential incorporation of newly synthesized fatty acids into phospholipids in surfactant as opposed to those in other components of the lung.

Alveolar type II cells, surfactant protein A (SP-A), and the phospholipid components of surfactant in acute silicosis in the rat.

Silica instillation causes a massive accumulation of surfactant phospholipids and the appearance of hypertrophic type II cells in the rat. We have examined the metabolic consequences of silica instillation with a special emphasis on surfactant protein A (SP-A), the major glycoprotein of surfactant. Fourteen days after instillation of 10 mg of silica, the amount of phospholipids in lavage increased 14-fold and the amount of SP-A increased 10-fold. The phospholipid composition of lavage material from silica-treated animals was altered by a reduction in the percentage of phosphatidylglycerol and an increase in phosphatidylinositol. The percentage of saturated phosphatidylcholine did not change. Type II cells isolated from rats treated with silica could be separated into cells of normal size and of increased size by centrifugal elutriation. There was an increase in phospholipid and SP-A content in the larger type II cells isolated from silica-treated rats relative to type II cells from control rats (by 45% and 70%, respectively, when expressed per micrograms protein; p less than 0.01). Activities of the phospholipid biosynthetic enzymes cholinephosphate cytidyltransferase, lysophosphatidylcholine acyltransferase, and phosphatidylglycerol phosphate synthetase increased (nmol/min/mg cell protein) in the hypertrophic type II cells relative to type II cells from control rats (by 40%, 112%, and 95%, respectively, p less than 0.05). Incorporation of (1-14C)-acetate was also increased in hypertrophic type II cells relative to type II cells from control rats (by 43%, p less than 0.05). The only difference in the distribution of acetate incorporated into individual lipids was a slight increase in the percentage incorporated into phosphatidylinositol. Although the increase in phosphatidylcholine found in the lavage could be due to increased synthesis as reflected by the changes in enzymatic activity and rate of acetate incorporation, the reduction in phosphatidylglycerol in lavage and in type II cells could not be explained simply by a reduction in synthesis on the basis of available data. There was a marked increase in SP-A content in lavage and in type II cells isolated from silica-treated rats without a significant change in the relative abundance of SP-A mRNA. This dissociation of SP-A mRNA abundance and apoprotein content suggests that factors other than transcription may be important for the observed accumulation of SP-A in silica-treated rats. We conclude that the phospholipidosis and proteinosis that occur subsequent to silica instillation in the rat lung are not solely attributable to increase in the rates of synthesis of these components.

Effect of Exogenous Bovine Somatotropin on Mammary Lipid Metabolism and Milk Yield in Lactating Dairy Cows

Eight lactating Holstein cows were used to study the effect of bovine somatotropin on mammary lipid metabolism, milk production, and milk composition. Eight cows were injected with either ex-cipient (n=4) or 50 IU somatotropin/d (n=4). A 2-wk adjustment period preceded a 10-d period when treatments were administered. On d 9, serial blood samples were collected from 2 to 5h post-injection to determine concentrations of somatotropin and metabolites in plasma. Mammary tissue biopsies were obtained 2 to 3h after a.m. milking on d 10 to determine lipoprotein lipase activity and in vitro rates of acetate incorporation into fatty acids and acetate oxidation by mammary tissue slices. Activity of lipoprotein lipase in milk and mammary tissue and rate of acetate metabolism by mammary tissue were not affected by treatment. The following means for placebo and somatotropin, respectively, were: milk production (21.5 and 24.8kg/d), milk fat (3.8 and 4.0%), and 4% FCM (20.7 and 25.1kg/d). Plasma concentrations of somatotropin (3.0 and 43.4ng/ml) and free fatty acids (105.6 and 219.5μeq/L) were significantly elevated with somatotropin. The injection of somatotropin into lactating dairy cows did not affect the mechanisms of fatty acid synthesis or metabolism evaluated in this study.

Influence of coal source and treatment upon indigenous microbial communities

The leaching of six Eastern coals was investigated using experimental coal columns subjected to simulated leaching events. Measurements of CO2 assimilation and specific enrichment cultures indicated that the microbial communities of all leachates were dominated by iron- and sulfur-oxidizing chemoautotrophic bacteria. Comparison of CO2 assimilation rates in leachates and core samples of leached coal indicated that most chemoautotrophs remained within coal columns during leaching. Mean numbers of chemoautotrophic bacteria in leachate samples were correlated with concentrations of dissolved iron and sulfate. Leachates from unwashed, run-of-mine coals contained more chemoautotrophs and more iron and sulfate than did leachates from washed, final product coals. After several leachings, the ratio of sulfur oxidizers to iron oxidizers tended to increase. These data suggest that the chemoautotrophic community of final product coals may be pyritelimited. Aerobic heterotrophs constituted a minor component of the microbial community in leachates from the six coals and their abundance and metabolic activity were apparently not influenced by the beneficiation history of the coal. Changes in rates of acetate metabolism may have been related to microbial succession within the heterotrophic community of coal columns. In all leachates, rates of tritiated methylthymidine assimilation were correlated with rates of acetate incorporation but not with CO2 assimilation, even though autotrophs dominated the microflora. Thus, thymidine assimilation rates appear to reflect activities or growth of mainly heterotrophic microorganisms in leachate.

Incorporation of acetate into acetylcholine, acetylcarnitine, and amino acids in the Torpedo electric organ.

The metabolism of acetate was investigated in the nerve-electroplaque system of Torpedo marmorata. In intact fragments of electric organ, radiolabeled acetate was incorporated into acetylcholine (ACh), acetylcarnitine (ACar), and three amino acids: aspartate, glutamate, and glutamine. These compounds were identified by TLC, high-voltage electrophoresis, column chromatography, and enzymic tests. The system responsible for acetate transport and incorporation into ACh displayed a higher affinity but a lower Vmax than that involved in the synthesis of ACar and amino acids. Choline, when added to the medium, increased the rate of acetate incorporation into ACh but decreased (at concentrations greater than 10(-5) M) that into ACar and amino acids. Monofluoroacetate slightly depressed ACh and ACar synthesis from external acetate but inhibited much more the synthesis of amino acids. During repetitive nerve stimulation, the level of the newly synthetized [14C]ACh was found to oscillate together with that of endogenous ACh, but the level of neither [14C]ACar nor the 14C-labeled amino acids exhibited any significant change as a function of time. This means that there is probably no periodic transfer of acetyl groups between ACh and the investigated metabolites in the course of activity. Acetate metabolism was also tested in the electric lobe (which contains the cell bodies of the neurons innervating the electric organ) and in Torpedo synaptosomes (which are nerve terminals isolated from the same neurons). Radioactive pyruvate and glutamine were also assayed in some experiments for comparison with acetate. These observations are discussed in connection with ACh metabolism under resting and active conditions in tissues where acetate is the preferred precursor of the neurotransmitter.