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Biomedical subjects

C L Davis

Publications and source records attributed to C L Davis.

At least 145 records · Page 8Linked to original sources
PubMed1983

Unrelatedness of factor VIII-derived non-A/non-B hepatitis and hepatitis B virus.

A DNA hybridization assay was used to detect hepatitis B virus (HBV)-specific DNA sequences in extracted sera obtained from chimpanzees infected with HBV, hepatitis A virus (HAV), and a factor VIII-derived non-A/non-B (NANB) agent. The results did not reveal any HBV-DNA homology with sera obtained from animals infected with HAV or factor VIII-derived NANB. Sera obtained from two HBV-infected chimpanzees demonstrated that HBV-specific DNA could be detected during the acute phase of the disease. In addition, an HBV-specific DNA-dependent DNA polymerase assay did not demonstrate any statistically significant activity in 12 of 12 NANB acute-phase specimens or in 6 of 6 NANB chronic-phase specimens. These results suggest that the factor VIII-derived NANB agent is unrelated to HBV.

Animals↗
PubMed1983

Comparison of ultracentrifugation and gel filtration for the isolation of bovine lipoproteins.

Lipoproteins from the plasma of three nonlactating Holstein cows were isolated using either preparative ultracentrifugation or gel filtration chromatography. Lipoprotein classes obtained by ultracentrifugation were very low density plus chylomicra, less than 1.006 g/ml; low density, 1.007-1.039 g/ml; high density1, 1.040-1.063 g/ml; and high density, 1.064-1.22 g/ml. These lipoprotein classes were individually applied to an agarose gel column to determine at what volume they eluted in comparison to lipoproteins that were separated after applying total bovine lipoproteins to the column. Three major peaks corresponding to very low density lipoproteins plus chylomicra, low density, and high density lipoproteins resulted after gel filtration of total lipoproteins. Very low density lipoproteins plus chylomicra, obtained by ultracentrifugation, eluted as a single peak, as did low density and high density lipoproteins. However, high density1 lipoproteins eluted as two peaks. The first peak eluted at the same volume as low density lipoproteins, and the second peak eluted at a volume similar to that of the ascending slope of the high density lipoprotein peak. Results from disc polyacrylamide gel electrophoresis, immunoelectrophoresis and double immunodiffusion of lipoprotein fractions, and SDS polyacrylamide gel electrophoresis of their apoproteins, similarly indicated that the lipoproteins present in the 1.040-1.063 g/ml density interval are a mixture of low and high density lipoproteins rather than a unique class of lipoproteins.

Animals↗
PubMed1983

Future improvement of milk production; potential for nutritional improvement.

Milk production/cow has increased so dramatically in the past 30 yr that some people question the wisdom of attempting to further increase milk production for fear we will shorten the lives of our dairy cows. What is the limit to milk production? At least two cows have produced over 22,000 kg of milk in a single lactation and numerous cows consistently produce 9,000 to 14,000 kg of milk/lactation. Therefore, it is evident that there is room for great progress, but it is not possible to predict the limits to milk production by the cow because we cannot see beyond the horizon to tell us what lies ahead. However, we know that nothing in sight appears to be an obstacle to further progress.

Amino Acids↗
PubMed1983

Effect of source and particle size of supplemental phosphate on rumen function of steers fed high concentrate diets.

We examined effects of source and particle size of supplemental defluorinated rock phosphate, to meet phosphorus requirements, on rumen function of 195-kg Holstein steers fed high concentrate. Two sources and two particle sizes of each source were evaluated in a 5 X 5 Latin square with 14-day periods. There was no effect of source on ruminal mH [- log (mean (H+)]; however, ruminal mH was higher in animals fed supplements of larger particle size. This effect was also evident when rumen pH versus time curves were integrated below pH 6. Animals fed supplements of larger particle size had less area below pH 6 than those fed supplements of smaller size. Ruminal buffering capacity at pH 7 was affected by diet; however, orthogonal comparisons between treatment means were not significant. Neither source nor particle size of the supplement affected ruminal fluid osmolality, total volatile fatty acid concentration, or fecal starch. Water intake and ruminal dry matter on HyCal supplemented diets; however, there was also a trend toward increasing rumen fluid volume. The net effect was little change of dilution rate of ruminal fluid. This may explain why rumen fermentation was not affected greatly. Conventional phosphate supplements may have potential as rumen buffering agents, but higher levels of feeding should be studied.

Animals↗
PubMed1983

Experimental conditions affecting the sensitivity of enzyme-linked immunosorbent assay (ELISA) for detection of hepatitis B surface antigen (HBsAg).

The sensitivity of an enzyme-linked immunosorbent assay (ELISA) for the detection of hepatitis B surface antigen (HBsAg) was improved 16 to 32 times after examination of various solid-phase supports, different antibody preparations as capture antibody, and different conditions for adsorbing capture antibody to the solid-phase. Comparisons were made by checkerboard titration analysis and by sensitivity studies, both of which demonstrated essentially equivalent results. Endpoints were determined by visual inspection and by spectrophotometry using o-phenylenediamine as substrate. The assay was as sensitive as commercially available radioimmunoassays without the requirement of affinity chromatography purified reagents, expensive instrumentation, or radioisotopes.

Animals↗
PubMed1982

Phosphorylation of the receptor of immunoglobulin E.

Specific immune precipitation of immunoglobulin E(IgE)-receptor complexes from detergent extracts of 32P-labeled rat basophilic leukemia cells yielded a phosphoprotein of Mr approximately 35,000 on gel electrophoresis in sodium dodecyl sulfate. This phosphoprotein was shown by several criteria to be the beta chain of the receptor for IgE. Phosphorylation occurs at a serine residue (or residues) in a region (beta 2) of the beta chain that is thought to be exposed on the cytoplasmic face of the plasma membrane. Our results suggest that phosphorylation probably takes place after the insertion of the beta chain into the membrane. The IgE-binding alpha chain of the receptor and the IgE associated with it are not phosphorylated. We have so far been unable to detect any changes in the state of phosphorylation of either chain of the receptor or of IgE itself after IgE-mediated triggering of the cells.

Animals↗
PubMed1982

Estimation of the proportion of non-ammonia-nitrogen reaching the lower gut of the ruminant derived from bacterial and protozoal nitrogen.

1. A method for estimating the proportions of bacterial- and protozoal-N in the total non-ammonia-N reaching the lower gut of the ruminant under steady-state conditions was evaluated. Three trials using two different diets were conducted with a Holstein steer equipped with a rumen cannula and duodenal re-entrant cannulas. 2. An intraruminal primed infusion of (15NH4)2SO4 was administered for 68 h during each trial. Bacteria and protozoa samples were isolated from rumen fluid at approximately 6 h intervals during each infusion period. Total non-ammonia-N was isolated from duodenal digesta samples taken at approximately the same times. All of these samples were analysed for 15N enrichment. A computer program was used to fit equations to the 15N-enrichment curves of bacterial- and protozoal-N. Models of both bacterial- and protozoal-N kinetics consisted of a small pool which equilibrated rapidly with rumen NH3 and a large pool with a fractional turnover rate of 0.045-0.070/h for bacterial-N and 0.056-0.069/h for protozoal-N. 3. Abomasal fluid turnover was estimated by a single injection of polyethylene glycol (molecular weight 4000) into the rumen followed by sampling of rumen fluid and duodenal digesta. 4. Estimates of abomasal fluid turnover, bacterial-N turnover, and protozoal-N turnover were entered into an equation which was adjusted by computer iteration to fit the 15N-enrichment curve of duodenal digesta non-NH3-N generated from each (15NH4)2SO4 infusion period. The computer fit of this equation to the observed results gave estimates of 0:39-0.45 and 0.22-0.41 for the proportion of duodenal non-NH3-N derived from bacterial-N and protozoal-N respectively. 5. This method is potentially useful in estimating microbial protein passage to the lower gut in ruminants. Sampling digesta from the omasum rather than the duodenum would simplify the method and possibly increase the reliability of the estimates.

Abomasum↗
PubMed1982

Alteration of rumen fermentation, milk fat synthesis, and nutrient utilization with mineral salts in dairy cows.

The ability of mineral salts to alter rumen fermentation, rumen fluid dilution rate, milk fat synthesis, and nutrient utilization was investigated in dairy cows fed a high-concentrate, milk-fat depressing diet. Four rumen-fistulated Holstein cows were in a 4 X 4 Latin square design. Treatments consisted of: 1) basal (25% corn silage: 75% concentrate on a dry matter basis), 2) basal + 2.0% sodium chloride, 3) basal + 2.0% sodium bicarbonate, and 4) basal + 2.4% limestone. Addition of limestone to the basal diet reduced dry matter intake but increased efficiency of dietary nutrient utilization for milk synthesis. Sodium bicarbonate increased synthesis of milk fat. Sodium chloride also tended to increase milk fat synthesis whereas limestone had no effect. Milk yields (kg/day) and milk fat (%) for the four treatments were 1) 29.5, 2.40; 2) 29.3, 2.66; 3) 28.9, 3.26; and 4) 29.2, 2.32. Rumen fluid pH, dilution rate (%/hour), and molar percentage of acetate and propionate were: 1) 5.98, 10.3, 49 and 39; 2) 6.02, 12.4, 55 and 32; 3) 6.16, 12.2, 58 and 25; and 4) 5.92, 10.7, 51 and 38. Limestone was totally ineffective in altering ruminal pH, fluid dilution rate, molar percentages of acetate and propionate, and synthesis of milk fat. Improved feed efficiency for milk production after addition of limestone was related to an increase in starch digestion compared to the basal ration (95 versus 88%).

Animals↗
PubMed1982

Rumen volatile fatty acid production and nutrient utilization in steers fed a diet supplemented with sodium bicarbonate and monensin.

Effects of feeding dietary supplements of monensin and sodium bicarbonate singly or in combination on production of rumen volatile fatty acids, nitrogen balance, and rumen water kinetics were studied. Four rumen fistulated steers were fed a diet (50% concentrate mix and 50% corn silage) ad libitum in a 4 X 4 Latin square design (21-day periods) with a 2 X 2 factorial arrangement of treatments. Sodium bicarbonate increased feed intake, water intake, rumen pH, fluid dilution rate, and decreased both molar proportion and production rate of propionate in the rumen. Alteration of the ratio of acetate to propionate reflects the large decrease in propionate production relative to the small increase in acetate production. In contrast, monensin did not alter significantly rumen fluid dilution rate or ruminal pH but did decrease the molar proportion of acetate and increase that of propionate. Monensin increased production of both acetate and propionate in the rumen; however, the large increase in propionate production appears to account for more of the increase in molar proportion of propionate in the rumen. Increases in total volatile fatty acid production per kilogram of dry matter consumed with monensin supplementation appears to result from decrease in feed intake, thereby increasing ruminal retention time of dry matter and potentially the extent of digestion. Efficiency of nitrogen utilization was not altered by either sodium bicarbonate or monensin.

Animals↗
PubMed1982

Effects of intraruminal infusions of mineral salts on volatile fatty acid production in steers fed high-grain and high-roughage diets.

Four rumen fistulated Holstein steers were used to assess the effects of intraruminal salt infusions on various rumen characteristics including volatile fatty acid production rates. In the first experiment, the basal diet consisted of 75% concentrate and 25% corn silage (high-grain diet). The experimental design was a 4 X 4 Latin square in which the four treatments were: 1) intraruminal infusion of 8 liters of water (control) or 8 liters of water plus 2) 288 g sodium bicarbonate, 3) 200 g sodium chloride, or 4) 600 g sodium chloride. In the second experiment, procedures were the same except the basal diet consisted of 64% alfalfa hay and 18% each of corn silage and concentrate (high-roughage diet). When the high-grain basal diet was fed, intraruminal infusions of mineral salts increased dilution rate of rumen fluid. Total fluid flow from the rumen also was increased by salt infusions with sodium bicarbonate and the most sodium chloride from (600 g/day) exerting greatest effects for both dietary regimens. Salt infusions reduced the molar percentage of rumen propionate and increased the molar percentage of acetate when the high-grain diet was fed. These same treatments were without effect on molar percentages of rumen acids when the high-roughage diet was fed. The change in the molar percentages of acetate and propionate on the high-grain ration was solely from reduction in propionate production. The lower production of propionate, from salt infusions, may have occurred because of the washout of readily fermentable materials. Dry matter disappearance from feeds placed in dacron bags and suspended in the rumen was unaffected by infusion of mineral salts.

Animals↗
PubMed1981

Enzyme potentiated radioimmunoassay (EPRIA): a sensitive third-generation test for the detection of hepatitis B surface antigen.

A sensitive, specific immunoassay for detection of hepatitis B surface antigen (HBsAg) is described. The assay combined enzyme-linked immunosorbent assay and solid-phase radioimmunoassay and is termed enzyme potentiated radioimmunoassay (EPRIA). HBsAg was quantitated by enzymatic conversion of L[14C]glutamic acid to 14CO2 and gamma-aminobutyric acid by glutamate decarboxylase (GDC) conjugated wih goat anti-HGs IgG. Conjugation of IgG and GDC was by a thiol-disulfide bond exchange reaction after reacting N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP) with each reagent. A positive/negative ratio of 2.2 was established as significant by examination of 40 normal sera negative for HBsAg. This value was the mean cpm plus 3 standard deviations. By an identical statistical analysis of sensitivity, EPRIA was found to be approximately 100-fold more sensitive than Ausria II (Abbott Laboratories, North Chicago, IL).

Animals↗
PubMed1981

Features of rumen and sewage sludge strains of Eubacterium limosum, a methanol- and H2-CO2-utilizing species.

Eubacterium limosum was isolated as the most numerous methanol-utilizing bacterium in the rumen fluid of sheep fed a diet in which molasses was a major component (mean most probable number of 6.3 X 10(8) viable cells per ml). It was also isolated from sewage sludge at 9.5 X 10(4) cells per ml. It was not detected in the rumen fluid of a steer on a normal hay-grain diet, although Methanosarcina, as expected, was found at 9.5 X 10(5) cells per ml. The doubling time of E. limosum in basal medium (5% rumen fluid) with methanol as the energy source (37 degree C) was 7 h. Acetate, cysteine, carbon dioxide, and the vitamins biotin, calcium-D-pantothenate, and lipoic acid were required for growth on a chemically defined methanol medium. Acetate, butyrate, and caproate were produced from methanol. Ammonia or each of several amino acids served as the main nitrogen source. Other energy sources included adonitol, arabitol, erythritol, fructose, glucose, isoleucine, lactate, mannitol, ribose, valine, and H2-CO2. The doubling time for growth on H2-CO2 (5% rumen fluid, 37 degree C) was 14 h as compared with 5.2 h for isoleucine and 3.5 h for glucose. The vitamin requirements for growth on H2-CO2 were the same as those for methanol; however, acetate was not required for growth on H2-CO2, although it was necessary for growth on valine, isoleucine, and lactate and was stimulatory to growth on glucose. Acetate and butyrate were formed during growth on H2-CO2, whereas branched-chain fatty acids and ammonia were fermentation products from the amino acids. Heat tolerance was detected, but spores were not observed. The type strain of E. limosum (ATCC 8486) and strain L34, which was isolated from the rumen of a young calf, grew on methanol, H2-CO2, valine, and isoleucine and showed the same requirements for acetate as the freshly isolated strains.

Animals↗
PubMed1981

Hyperreninemic hypoaldosteronism in the critically ill: a new entity.

To define the changes in adrenal gland function during critical illness, we evaluated 28 severely ill patients with persistent hypotension who were hospitalized in a medical intensive care unit. The patients had increased plasma cortisol (mean +/- SE, 40.1 +/- 10.1 micrograms/dl). PRA was increased in all subjects (21.6 +/- 7.2 ng/ml.h); however, the plasma aldosterone concentration was inappropriately low in 18 of the subjects, with values ranging from 1-9 ng/dl, despite normal serum potassium concentrations (4.3 +/- 0.1 meq/liter) and increased concentrations of the aldosterone percursor, 18-hydroxycorticosterone. These 18 patients had hypotension associated with major infections and a high mortality rate (78%). Infusions of ACTH or angiotensin II were associated with a normal aldosterone response in only 2 of the 14 patients tested, also suggesting that the defect was probably at the level of the zone glomerulosa cell. Although infection was a common underlying illness, no other factors, such as dopamine administration, decreased angiotensin-converting enzyme activity, or increased aldosterone clearance, could be implicated as the cause of the phenomena. Thus, selective hypoaldosteronism in the presence of high renin levels exists in a substantial percentage of hypotensive critically ill patients.

Acute Disease↗
PubMed1981

Effect of monensin on breakdown of protein by ruminal microorganisms in vitro.

The effects of monensin on N metabolism by ruminal microorganisms in a semicontinuous culture system were determined. Rumen fluid inoculum was obtained from steers fed a hay-concentrate diet (60:40 ratio on a dry matter basis) containing 33 ppm monensin. Treatments were 0, 1 and 4 mg monensin/kg of incubation mixture, with starch, glucose, cellulose and casein used as the energy and protein sources. Casein degradation decreased linearly (P less than .01) with increasing levels of monensin, as did production of ammonia-N (P less than .05) and microbial N (P less than .01). Increases were observed in nonammonia, nonmicrobial N (P less than .01), alpha-amino N (P less than .10) an total peptides (P less than .001). The culture supernatant was fractionated on a Sephadex G-10 column to separate peptides. With the 4 mg/kg treatment, the percentage of the total ninhydrin positive material eluted at an elution volume:void volume ratio of 1.5 or less was greater than the percentage eluted with the 0 or 1 mg/kg treatments (P less than .025). Acetate production and molar proportion decreased (P less than .001), while propionate production was unchanged. Methane production decreased slightly (P less than .10). Cellulose degradation was markedly inhibited (P less than .001) by monensin treatment.

Ammonia↗
PubMed1981

Methylmalonic acid in low-fat milk syndrome.

The possible association between low-fat milk syndrome and methylmalonic acid accumulation in blood was investigated. Blood was sampled from the internal iliac artery of nine lactating dairy cows fed ad libitum roughage plus grain or high grain, restricted roughage diets. Daily milk fat percent and milk fat production were decreased 44% and 47% on the high grain, restricted roughage diet. No differences in blood methylmalonate concentrations could be detected in the cows fed the two diets. The effect of methylmalonate and its metabolic precursor, propionate, on mammary rates of fatty acid synthesis was determined with bovine mammary tissue slices. Neither of these metabolites affected acetate incorporation into fatty acids. Methylmalonate and propionate were incorporated into fatty acids at extremely low rates. Low-fat milk syndrome is not caused by accumulation of methylmalonic acid.

Acetates↗