Vitamin B6 status, MTHFR and hyperhomocysteinaemia.
Explore the source record for details and available documents.
Adult↗
Biomedical subjects
D L Harmon
Publications and source records attributed to D L Harmon.
The thermolabile variant of 5,10-methylenetetrahydrofolate reductase is not associated with Parkinson's disease.
Explore the source record for details and available documents.
5,10-Methylenetetrahydrofolate Reductase (FADH2)↗
A common genetic variant affecting folate metabolism is not over-represented in chronic fatigue syndrome.
Explore the source record for details and available documents.
5,10-Methylenetetrahydrofolate Reductase (FADH2)↗
Effects of exogenous somatostatin and cysteamine on net nutrient flux across the portal-drained viscera and liver of sheep during intraduodenal infusion of starch hydrolysate and casein.
We used eight Polypay wethers (36 +/- .6 kg BW) fitted with hepatic portal, hepatic venous, mesenteric arterial and venous, and duodenal catheters in a crossover design experiment to determine the influence of somatostatin (SRIF) on splanchnic metabolism. Each crossover period consisted of 14 d, with net flux of nutrients and hormones (venoarterial differences x blood flow) measured on d 14. Before flux measurements, wethers received an i.v. dose (0 h) of either 0 (vehicle) or 50 mg x kg BW(-1) x 10 min(-1) cysteamine (CSH, SRIF-depleting agent) followed by a continuous duodenal infusion (h 10 to 22) of a starch hydrolysate-casein solution. Six sets of arterial, portal, and hepatic blood samples were obtained (h 12 to 16), after which a primed (10 microg), continuous jugular infusion of SRIF-14 (5.0 microg x kg BW(-1) x h(-1)) was initiated and sampling protocol repeated (h 18 to 22). Cysteamine administration increased (P < .01, vs control) portal and hepatic blood flow in the absence of exogenous SRIF (CSH x SRIF, P < .01). Net portal-drained viscera (PDV) release of glucose, alpha-amino N, ammonia N, beta-hydroxybutyrate, and oxygen consumption were decreased (P < or = .10) and lactate release increased (P = .005) during SRIF infusion. The CSH increased (P < .05) PDV release of beta-hydroxybutyrate and insulin and increased (P = .09, CSH alone vs control) net release of glucose in the absence of exogenous SRIF. Exogenous SRIF increased (P = .10) and CSH decreased (P = .09) net hepatic glucose output, whereas liver oxygen consumption was decreased (P = .04) with exogenous SRIF and increased (P = .01) with CSH. Net total splanchnic alpha-amino N release and oxygen consumption were decreased (P < .10) with exogenous SRIF, but CSH increased (P < .05) insulin release and oxygen consumption. These data provide initial evidence for a regulatory involvement of SRIF in visceral metabolism in ruminants.
3-Hydroxybutyric Acid↗
The use of urea dilution for estimation of carcass composition of Holstein steers at 3, 6, 9, and 12 months of age.
Every 3 mo for a 2-yr period, two weaned Holstein steer calves (94.5 kg) were randomly assigned to each of four slaughter age groups (3, 6, 9, and 12 mo). Urea dilution was performed before slaughter, and urea space (US) was calculated as total volume and as a percentage of body weight (BW) and empty body weight (EBW). The relationships between US (kg, % EBW and % BW), BW, and EBW and carcass soft tissue composition (protein, fat, moisture, and ash) were studied. One- and two-pool models were fitted using the urea dilution data and the coefficients of those equations (zero time, A + B), and the intercepts of compartments A and B were used to estimate body volume. Body weight and EBW effectively predicted the amount of water, fat, and protein in the carcass soft tissue. Equations expressed in kilograms were more accurate than those expressed as percentages. Urea space overestimated body water, probably because of the fast rate of urea disappearance in plasma. Correlation coefficients between US and carcass soft tissue water (kg) based on the pooled data ranged from .74 at 6 min to .48 at 42 min after infusion. The biexponential models coefficients explained more of the variation of carcass soft tissue composition than US; correlation coefficients using volume B and the soft tissue composition (in kg) with pooled data were .78 (water), .68 (fat), .69 (ash), and .76 (protein). The relationships between A and soft tissue composition were weaker (water .59, fat .51, ash .58 and protein .59). The highest correlation coefficients were obtained when A + B was used for water, fat, ash, and protein (.83, .70, .74 and .81, respectively). Equations combining BW, EBW, and two-model coefficients (A, B, A + B) explained much of the variation of soft tissue composition. No significant benefit was found in using the urea space at various times after infusion over BW or EBW alone to estimate carcass soft tissue composition in Holstein steers.
Aging↗
Considerations for gastrointestinal cannulations in ruminants.
The complexity of ruminant digestion necessitates a greater variety and complexity of experimental methods than with any other species. The fact that dietary ingredients are first subjected to microbial fermentation requires elaborate measures to ascertain nutrients presented for absorption. Numerous approaches have been attempted to obtain representative samples of digesta at sites throughout the gastrointestinal tract. The choices of a researcher before an experiment include animal(s), site(s) for cannula placement, style of cannula, cannula material, and numerous other more subtle factors that may contribute to the success of an experiment. This review compares the advantages and disadvantages of various approaches, cannula types, and cannula materials that should be considered before experiments are conducted.
Animals↗
Evolution of hemopoietic ligands and their receptors. Influence of positive selection on correlated replacements throughout ligand and receptor proteins.
The rates of amino acid replacement in cytokines and their receptors are high and vary considerably. To determine whether this reflects the action of positive selection, rates of nonsynonymous DNA substitution were examined and found to exceed the synonymous substitution rate in certain exons of rodent IL-3, granulocyte-macrophage stimulating factor, and IL-4. To determine the extent to which positive selection could account for correlations between the amino acid replacement rates of hemopoietins and their receptors, rates were examined in various domains: the correlation with ligand rate was not confined to the ligand-binding domain of the receptor, but extended into the transmembrane and cytoplasmic domains and even to leader peptide domains of both ligand and receptor. As the majority of these replacements are unlikely to be strongly advantageous, different levels of both positive and purifying selection contribute to the extensive variation in hemopoietin/receptor evolutionary rates. Changes in a few residues critical for ligand-receptor interaction may be followed by changes of lesser selective importance in both molecules: replacements of growth hormone residues that form hydrogen or salt bridges with the receptor occur in lineages in which there are many concurrent replacements. A ligand/receptor rate correlation is not found between the seven-transmembrane receptors and their ligands, whose mature forms are often short and completely conserved. This study predicts that a minority of concurrent evolutionary changes in hemopoietins and their receptors reflect directly compensatory changes.
Amino Acids↗
The common 'thermolabile' variant of methylene tetrahydrofolate reductase is a major determinant of mild hyperhomocysteinaemia.
Mild hyperhomocysteinaemia is a major risk factor for vascular disease and neural tube defects (NTDs), conferring an approximately three-fold relative risk for each condition. It has several possible causes: heterozygosity for rare loss of function mutations in the genes for 5,10-methylene tetrahydrofolate reductase (MTHFR) or cystathionine-beta-synthase (CBS); dietary insufficiency of vitamin co-factors B6, B12 or folates; or homozygosity for a common 'thermolabile' mutation in the MTHFR gene which has also been associated with vascular disease and NTDs. We quantified the contribution of the thermolabile mutation to the hyperhomocysteinaemic phenotype in a working male population (625 individuals). Serum folate and vitamin B12 concentrations were also measured and their relationship with homocysteine status and MTHFR genotype assessed. The homozygous thermolabile genotype occurred in 48.4, 35.5, and 23.4% of the top 5, 10, and 20% of individuals (respectively) ranked by plasma homocysteine levels, compared with a frequency of 11.5% in the study population as a whole, establishing that the mutation is a major determinant of homocysteine levels at the upper end of the range. Serum folate concentrations also varied with genotype, being lowest in thermolabile homozygotes. The MTHFR thermolabile genotype should be considered when population studies are designed to determine the effective homocysteine-lowering dose of dietary folate supplements, and when prophylactic doses of folate are recommended for individuals.
5,10-Methylenetetrahydrofolate Reductase (FADH2)↗
Technical note: a simple, rapid assay for alpha-amylase in bovine pancreatic juice.
A procedure is described for the determination of alpha-amylase activity in bovine pancreatic juice. Bovine pancreatic juice was incubated with potato amylopectin for 6 min, and then alkaline potassium ferricyanide was added to stop the enzymatic reaction. Tubes were placed in a boiling water bath for 10 min and then cooled, and 40 mL of distilled water was added. Optical density was read at 420 nm, and the amount of end product (reducing sugars) was determined by comparison with maltose standards. Ten dilutions of bovine pancreatic secretion were assayed to determine the intraassay precision of this method, resulting in a CV of 1.05%. A pooled sample was assayed five times over five separate days to determine the interassay precision, resulting in a CV of 7.3%. This alpha-amylase assay provides a repeatable, rapid, and economical determination of alpha-amylase activity from bovine pancreatic juice.
Animals↗
Effects of varying levels of duodenal or midjejunal glucose and 2-deoxyglucose infusion on small intestinal disappearance and net portal glucose flux in steers.
Six crossbred steers (261 +/- 18 kg BW) fitted with hepatic portal, mesenteric venous and arterial catheters, and duodenal, midjejunal, and ileal cannulas were used in a replicated 3 x 3 Latin square design to determine the effect of varying levels and site of glucose plus 2-deoxyglucose (2DG) infusion on net portal-drained visceral flux. Steers were fed chopped alfalfa in six equal portions daily at 1.5% of BW. Glucose (0, 9, or 18 g/h) and 2DG (0, 1, or 2 g/h) were infused continuously through the duodenal or midjejunal cannula (two infusion sites) at total glucose plus 2DG infusion rates of 0, 10, or 20 g/h. Arterial and portal blood samples were taken simultaneously at 20-min intervals from 5 to 9 h of infusion. Portal blood flow was determined by continuous infusion of p-aminohippurate and net flux was calculated as venous-arterial concentration (PA) difference times blood flow. Arterial concentration of glucose was not affected (P > .10) by glucose plus 2DG infusion, whereas arterial concentration of 2DG was greater (P < .05) when glucose plus 2DG was infused into the duodenum and increased (linear, P < .10) as amount of glucose plus 2DG infused into both the duodenum and midjejunum increased. Net portal flux and PA difference of glucose and 2DG were greater (P < .05) when glucose plus 2DG was infused into the duodenum. Although 2DG was infused at 10% of the total glucose plus 2DG infusion, it accounted for only 1.7 and .7% of the glucose plus 2DG appearing in portal blood when glucose plus 2DG was infused at 10 and 20 g/h, respectively. We conclude that glucose is more readily absorbed across the proximal-half than the distal-half of the small intestine, and that passive diffusion is a minor route of glucose absorption.
Animals↗
The evolution of haematopoietic cytokine/receptor complexes.
The evolutionary expansion of the haematopoietic cytokines and their receptors is characterized by the duplication of both cytokines and receptors. A systematic analysis of primary sequence homology indicates that receptors for gp130-associated cytokines group into signal transducing and non-signal transducing receptors. This observation is consistent with the evolution of the interleukins 6, 11 and 12, granulocyte colony stimulating factor (G-CSF), leukemia inhibitory factor (LIF), oncostatin M, and the ciliary neurotrophic factor complexes from a common ancestral complex which included a homodimer of gp130-like signalling receptors and an interleukin 6 receptor-like non-signalling receptor. Alterations in the components of the complex are proposed to have arisen by receptor duplication and divergence to allow signal transduction via a LIF receptor/gp130 heterodimer, and loss of the non-signalling receptor component in the G-CSF and the LIF lineage. The short-chain haematopoietins and their receptors do not group clearly, although interleukins 4 and 13 grouped together, as did 2 and 10. Internal duplication of the ligand-binding domain appears to have occurred independently in three separate lineages. These observations have implications for the classification of cytokines and receptors, and for the modelling by homology of their structures and interactions.
Amino Acid Sequence↗
Effects of cysteamine on pulsatile growth hormone release and plasma insulin concentrations in sheep.
The effects of cysteamine (CSH; 0, 50, or 100 mg/kg BW), a somatostatin depleting agent, on growth hormone (GH) and insulin (INS) secretion were studied in sheep (Ovis aries). Cysteamine was administered as a single intragastric bolus on day 0 (0900). Jugular blood samples were collected at 15-min (GH) and 2-hr (INS) intervals over an 8-hr period (1100-1900) on day 0, 3, and 7. Intragastric administration of CSH at 50 mg/kg BW augmented (quadratic, P = .04) mean plasma GH concentration, with the greatest response occurring on day 3. Baseline GH concentrations were elevated in wethers dosed with 50 mg/kg BW CSH on day 3, whereas wethers dosed with 100 mg/kg BW CSH had lower baseline GH concentrations on day 0 (CSH x day interaction, P = .02). Cysteamine administration increased GH pulse amplitude (quadratic, P = .15), with the greatest magnigtude of change occurring with 50 mg/kg BW CSH on day 0 and 3. Frequency of GH pulses was increased (quadratic, P = .10) following CSH treatment. Administration of 100 mg/kg BW CSH augmented plasma INS on day 0 (CSH x day interaction, P = .09). These findings indicate that CSH alters GH and INS secretion in a dose-dependent and temporal manner. The observed changes in mean and baseline plasma GH concentrations associated with 50 mg/kg BW CSH are consistent with somatostatin depletion; however, higher doses of CSH appear to disrupt GH secretion by an alternative mechanism.
Animals↗
Abomasal glucose, maize starch and maize dextrin infusions in cattle: small-intestinal disappearance, net portal glucose flux and ileal oligosaccharide flow.
Three castrated male Holstein cattle (423 (SD 19)kg live weight) fitted with elevated carotid artery, portal, and mesenteric venous catheters, and abomasal and ileal cannulas were used to study small-intestinal starch digestion. The cattle were infused abomasally with water (275 ml/h), glucose (66 g/h), maize dextrin (66 g/h) or maize starch (66 g/h) in an incomplete Latin square design, with eight infusion periods. Infusion with carbohydrate resulted in higher arterial glucose concentrations and greater net portal glucose flux than when cattle were infused with water. Arterial glucose concentration and net portal glucose flux were highest when glucose was infused. In the small intestine, 85% of abomasally-infused glucose, 78% of infused dextrin, and 66% of infused starch disappeared. Of the carbohydrate that disappeared in the small intestine, that which could be accounted for as net portal glucose flux was 73% for glucose, 60% for dextrin, and 57% for starch. Ileal digesta contained unpolymerized glucose, and short-chain soluble alpha-glucoside. Of the infused dextrin flowing past the ileum (14 g/h), 0.3 g/h was glucose, 6.2 g/h was soluble alpha-glucoside, and 7.5 g/h was insoluble alpha-glucoside. Of the infused starch flowing at the ileum (22.2 g/h), 0.9 g/h was glucose, 5.3 g/h was soluble alpha-glucoside, and 15.9 g/h was insoluble alpha-glucoside. The average chain lengths of the soluble alpha-glucosides in ileal digesta were 2.07 and 2.36 for dextrin and starch infusions respectively, indicating mostly di- and to a lesser extent trisaccharides. We conclude that (1) when 66 g raw starch is presented to the small intestine per h, about half of the intestinal disappearance appears as glucose in the portal vasculature, and (2) alpha-1,4 glucosidase (EC 3.2.1.20) activity at the brush border is the rate-limiting step to small-intestinal starch digestion in cattle.
Abomasum↗
The effects of ruminal acidosis on volatile fatty acid absorption and plasma activities of pancreatic enzymes in lambs.
Twenty crossbred wethers (41.9 +/- 4.0 kg BW), each fitted with a ruminal cannula and a jugular catheter, were used in a completely randomized design to examine the effects of ruminal acidosis on plasma activities of pancreatic enzymes and fractional rates of VFA absorption. Lambs had ad libitum access to a 50% concentrate diet. Acidosis was induced by an intraruminal dose of glucose at 0, 6, 12, or 18 g/kg BW via the ruminal cannula. Ruminal fluid and plasma were collected 0, 4, 8, 12, 18, 24, 36, 48, and 72 h after dosing. Ruminal fluid pH was reduced (linear, P < .001) with increasing ruminal glucose. Total ruminal VFA concentration decreased (linear, P < .01) and D(-)-lactate (linear, P < .01) and L(+)- lactate (linear, P = .07) concentrations increased with increasing ruminal glucose. Activities of amylase and lipase in plasma were not affected by ruminal glucose (P > .10). Ten days after the acidosis insult, rumens were evacuated and contents were replaced with an isotonic Cr:VFA solution to measure ruminal VFA absorption. Ruminal fluid was collected hourly from 0 to 6 h. Fractional rate of acetate absorption was 13% lower for lambs receiving 18 g/kg BW glucose than for control lambs. In addition, fractional liquid passage rate was lower (P < .05) in lambs receiving 18 g/kg BW glucose 6 mo after the insult of acidosis. These data suggest that a short-term, severe insult of acute acidosis does not result in pancreatic tissue damage but may result in reduced ruminal VFA absorption for an extended period of time.
Absorption↗
Influence of ruminal or abomasal starch hydrolysate infusion on pancreatic exocrine secretion and blood glucose and insulin concentrations in steers.
Seven Holstein steers (234 +/- 6.4 kg) surgically fitted with pancreatic cannulas, ruminal and abomasal infusion cannulas, and hepatic-portal vein catheters were used in a 4 x 7 incomplete Latin square design experiment to examine the influence of ruminal and abomasal carbohydrate infusion on enzyme secretion and composition of pancreatic juice. Four treatments were arranged in a 2 x 2 factorial: 1) ruminal starch hydrolysate (SH; 34.2 g/[h.site]) or abomasal water and 2) abomasal SH or ruminal water. Starch hydrolysate is raw cornstarch that has been partially digested by a heat-stable alpha-amylase. Experimental periods were 14 d with 9 to 10 d of adaptation, 4 d of pancreatic collection, and blood collection on d 14. Abomasal SH infusion tended (P < .10) to increase pancreatic fluid secretion. The pH of pancreatic juice was higher (P < .01) for ruminal SH infusion, and abomasal SH infusion tended (P < .10) to result in lower pH of pancreatic juice. alpha-Amylase concentrations (units/milliliter and units/milligram of protein) and secretion (units/hour) were less (P < .002) for abomasal SH infusion. Chymotrypsin concentration (units/liter; P < .01) and secretion (units/hour; P < .10) were less for abomasal SH infusion; however, a rumen x abomasal interaction was found (P < .05). Chloride concentration (milligrams/deciliter) and secretion (milligrams/hour) were increased (P < .01) for abomasal SH infusion. Abomasal SH infusion resulted in increased (P < .01) portal blood glucose concentrations; however, portal plasma insulin concentration was not affected (P > .10). Abomasal SH infusion altered alpha-amylase secretion in steers, but ruminal SH infusion had minimal effect on alpha-amylase secretion. These changes suggest abosamal infusion of SH may negatively impact secretion of pancreatic alpha-amylase.
Abomasum↗
Cysteamine-induced depletion of somatostatin in sheep: time course of depletion and changes in plasma metabolites, insulin, and growth hormone.
Eight crossbred wethers (51 +/- 2 kg BW), surgically fitted with abomasal cannulas, were used to determine the extent and time course of cysteamine (CSH)-induced depletion of somatostatin (SRIF) in abomasal tissue and associated changes in plasma metabolites, insulin, and growth hormone (GH). Cysteamine was administered as a single i.v. bolus (50 mg.kg BW-1 x 10 min-1) on d 0. Abomasal biopsies were obtained on d -7, -3, 0, 1, 3, and 10. On d 0, additional biopsies were taken at 2, 4, and 8 h after CSH administration. Jugular blood samples were collected over 8 h at 15-min intervals on d -2, 0, and 1. Cysteamine administration decreased (P < .05) tissue SRIF on d 0 (2, 4, and 8 h), 1, and 3; maximal depletion (42 to 55% of Pre-treatment; Pre-trt) occurred during the initial 24 h, returning to Pre-trt by d 10. Gel chromatography of pooled -7 d abomasal tissue extracts showed five peaks of SRIF immunoreactivity; the predominate peak eluted in the same position as synthetic SRIF-14. Plasma glucose, lactate, and NEFA concentrations increased (P = .001) after CSH administration and reached peak at 2 h after treatment and declined to Pre-trt concentrations by 24 h. Insulin increased (P = .001) to a maximum at h 4 and returned to Pre-trt by 24 h. Mean and baseline GH were higher (P < .07) on day of CSH administration, and pulse amplitude was lower (P < .10) on d 0 and 1. These data show that CSH rapidly reduces SRIF in abomasal tissue in a reversible manner; suggesting that CSH-treated sheep may provide a SRIF-deficient model for studying the physiological role of SRIF in ruminants.
Animals↗
Portal and hepatic fluxes in sheep and concentrations in cattle ruminal fluid of 3-(4-hydroxyphenyl)propionic, benzoic, 3-phenylpropionic, and trans-cinnamic acids.
Extraction methods and HPLC procedures were developed for analysis of potential ruminal metabolites of dietary phenolics (reduced phenolics). Hepatic portal venous blood from wethers fed bromegrass, bermudagrass, ryegrass-wheat, and alfalfa hays also was analyzed for hippuric (HA), 3-(4-hydroxyphenyl)propionic (4OHPPA), benzoic (BA), 3-phenylpropionic (PPA), and t-cinnamic (CA) acids. Additionally, mesenteric arterial and hepatic venous blood was analyzed and, in conjunction with blood flow measurements, fluxes for portal-drained viscera (PDV) and liver were calculated. Ruminal fluid from four steers fed two levels of forage and two forage particle sizes in a Latin square design was analyzed for PPA and CA. 3-Phenylpropionic and benzoic acids were the most concentrated reduced phenolics identified in hepatic portal venous blood. Concentrations of PPA in ruminal fluid varied with ruminal disappearance of p-coumaric and ferulic acids. Additionally, hepatic portal venous concentrations of PPA were correlated (P < .05) with p-coumaric acid (r = .57) and ferulic acid (r = .67) intakes. Net release of PPA from PDV was observed, suggesting absorption of PPA from the gut. The liver removed PPA and BA with less efficiency. Given the relatively high concentrations of PPA in blood of ruminants, specific effects of this reduced phenolic on liver metabolism of ruminants should be assessed.
Animals↗
Adaptation to small intestinal starch assimilation and glucose transport in ruminants.
Four crossbred steers (380 +/- 6 kg) and seven Polypay wethers (40.3 +/- 6 kg) fitted with hepatic venous, hepatic portal, mesenteric venous and arterial, ruminal, and abomasal (steers) or duodenal (wethers) catheters were used in two crossover design experiments to evaluate adaptation to small intestinal starch and glucose transport. Steers were fed 8.6 kg/d and sheep were fed .9 kg/d of alfalfa hay in 12 equal portions and infused with an alpha-amylase partial starch hydrolysate (SH) either postruminally (adapted) or ruminally (unadapted) for 4 (steers; 40 g/h) or 5 (sheep; 6 g/h) days before measuring splanchnic flux of metabolites. On the day of flux measurements, ruminal SH infusion was switched to the postruminal site in unadapted animals. Flux measurements were made 3 to 6 h after switching infusion site for steers and 2 to 5 h for sheep. Phlorizin, a competitive inhibitor of Na/glucose cotransport, was then postruminally infused (550 and 500 mumol/h for steers and sheep, respectively) and flux measurements repeated from h 9 to 12 (steers) and h 7 to 10 (sheep). In the steers, adaptation increased (P < or = .09) portal-drained visceral (PDV) glucose release 26 mmol/h and decreased hepatic uptake of lactate 20 mmol/h. Abomasal infusion of phlorizin decreased (P = .01) net PDV glucose flux 40 mmol/h and concomitantly increased (P = .05) hepatic release of glucose by 47 mmol/h. In sheep, duodenal infusion of phlorizin increased (P < or = .005) portal and hepatic blood flow and decreased (P < or = .02) PDV release of glucose and lactate by 9 and .4 mmol/h, respectively. The liver released 4.2 mmol/h more (P = .09) glucose and removed 3.2 mmol/h more lactate (P = .09) glucose and removed 3.2 mmol/h more lactate (P = .001); arterial glucose decreased (P = .003) .75 mM in response to phlorizin. Phlorizin also caused loss of glucose in the urine of sheep (.09 mmol/h). Adaptation did not alter net splanchnic flux of glucose, lactate, oxygen, or alpha-amino N. These studies indicate that ruminants maintain the Na/glucose cotransporter when consuming little preformed alpha-glucosidic polymers and that the liver increases glucose release to compensate for reduced PDV delivery of glucose to maintain glucose homeostasis. In addition, the steers maintain at least 960 mmol/d and the sheep maintain at least 216 mmol/d of glucose transport capability regardless of adaptation.(ABSTRACT TRUNCATED AT 400 WORDS)
Adaptation, Physiological↗