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Biomedical subjects

C L Davis

Publications and source records attributed to C L Davis.

At least 163 records · Page 9Linked to original sources
PubMed1980

gamma-Glutamyl transpeptidase activity along the small intestine of sheep: potential areas of amino acid and peptide transport.

Total homogenates of small intestinal sections (10 cm) from 16 wethers and ewes were used to investigate the distribution of gamma-glutamyl transpeptidase activity along the small intestine. gamma-Glutamyl transpeptidase activity was assayed per gram wet tissue, per milligram protein, and total units of enzyme activity per section. Additionally, glutathione was measured. The small intestine had areas of relatively high and low gamma-glutamyl transpeptidase activity, regardless of activity expression (high/low ratio = 5) and corresponding glutathione. Variation of enzyme activity was related to intestinal mucosa, with higher activity resulting from more enzyme activity per milligram of mucosal microvillus-membrane. The comparison of all high gamma-glutamyl transpeptidase activity from all animals showed small intestine of sheep had a region with high activity closest to the pylorus and other high activity locations between 3.75 m and 12.5 m (upper- to mid-jejunum) and between 21 m and 25 m (terminal ileum) from the pylorus. The latter two areas of high activity correspond to areas previously identified as being active in amino acid absorption.

Amino Acids↗
PubMed1980

Amino acid nutrition of the young calf. Estimation of methionine and lysine requirements.

A semipurified diet containing 14 crystalline amino acids as the sole source of nitrogen was used qualitatively and quantitatively to determine dietary needs of the young calf for lysine and methionine. Body weight gain, nitrogen balance, and concentrations of free amino acids in plasma were the criteria to assess the response of young calves to the experimental diets containing graded amounts of lysine and methionine. By these methods the methionine requirement as D-L methionine in the absence of cystine ranged from .17 to .23 g/day/kg body weight (.65 g/kg weight.75).

Animals↗
PubMed1980

Ammonia saturation constants for predominant species of rumen bacteria.

Ammonia saturation constants were determined for representative pure cultures of predominant, anaerobic, fermentative rumen bacteria. Based on growth experiments with ammonia limited continuous cultures, average estimates for ammonia saturation constants of Bacteroides amylophillus and Bacteroides ruminicola were 10.5 and 23.5 microM ammonia-nitrogen, respectively. With ammonia-limited linear-growth cultures, the estimates for the ammonia saturation constants of B. amylophilus, B. ruminicola, and Selenomonas ruminantium were, respectively, 6, 33.5, and 18 microM ammonia nitrogen. By a third method, which involved estimation of ammonia concentration in the medium when the growth rate of ammonia-limited batch cultures reached half maximal, the ammonia saturation constant was determined for the species mentioned as well as Megaspaera elsdenii and Ruminococcus flavefaciens. Except for M. elsdenii, saturation constants of the other bacteria were less than 50 microM ammonia nitrogen. An organism with a saturation constant for ammonia of 50 microM growing in a medium containing 1 mM ammonia should achieve 95% of its maximum specific growth rate. Many of the predominant species of rumen bacteria are efficient scavengers of ammonia.

Ammonia↗
PubMed1979

Endogenous production of immunoglobulin IgG1 in newborn calves.

There is a decrease in the specific activity of labeled IgG1 of serum over 3 wk following the feeding of iodine-125 labeled immunoglobulin IgG1 in colostrum to calves at birth. This decrease indicated the appearance of new IgG1 from some source. To determine if this new IgG1 came from endogenous production in the calf or from continued small amount of intestinal absorption from milk, labeled IgG1 was added to normal milk and fed to calves of various ages up to 3 wk after an initial feeding of colostrum at birth. Labeled IgG1 was also added to colostrum fed to calves at birth, and the calves were maintained on a normal milk diet or fed a synthetic milk diet. Determination of iodine-125 in the serum protein fractions of these calves indicated that there was no apparent intestinal absorption of labeled IgG1 from the milk in the period from 2 days to 3 wk. Furthermore, comparable decreases occurred in the specific activity of labeled IgG1 in serum in the calves fed the labeled IgG1 in colostrum at birth and subsequently maintained either on a diet including milk or on the synthetic milk diet devoid of IgG1. The results support the conclusion that the origin of new IgG1 in the calf after about 36 h and up to about 3 wk of age arises from endogenous production at a rate of about 1 g of IgG1 per day.

Age Factors↗
PubMed1978

Purification and partial characterization of hepatitis e antigen (HBeAg).

Purification of hepatitis e antigen (HBeAg) from 200 ml of chimpanzee plasma was accomplished by a combination of ion-exchange chromatography on diethylaminoethyl-cellulose followed by gel filtration. High-resolution sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified HBeAg demonstrated two major polypeptides with estimated molecular weights of 22,000 and 55,000. HBeAg labeled with 125I showed a high affinity for protein A-conjugated Sepharose CL-4B. The precipitation reaction between HBeAg and anti-HBe was inhibited by preincubating the purified antigen with rabbit anti-human immunoglobulin G (IgG). These data show that HBeAg is associated with a serum fraction with the biophysical and antigenic properties of an immunoblobulin of the IgG class. Sedimentation coefficient analysis of purified HbeAg resulted in an S20w value of 11.6 and a molecular weight value of 324,000. These findings, supported by gel filitration and polyacrylamide gradient gel electrophoresis, revealed that HBeAg has properties analogous to those of a dimer of IgG.

Animals↗
PubMed1978

Blood metabolic profiles: their use and relation to nutritional status of dairy cows.

Profiles of blood metabolites have been used widely to identify problem herds and to indicate dietary causes of disease or low production. Related herd survey studies and designed experiments are reviewed. An initial study of profiles and estimated nutrient intake of five "normal" and four "problem" herds was conducted between 1972 and 1974 to establish baseline values for blood metabolites. Profiles of blood metabolites for additional problem herds were obtained during 1974 through 1977. Variation due to herd of origin, production, stage of lactation, and season of year are important causes of variation in concentrations of metabolites in jugular blood of dairy cows. They need to be considered carefully in interpreting profiles of blood metabolites. Several relationships between dietary intake of nutrients and concentrations of associated components in jugular blood are significant. Concentrations of metabolites are of almost no practical use for individual cows because of extreme variations in diet required to generate abnormal concentrations of blood metabolites. Averages of glucose of blood and nitrogen in urea on seven to ten cows, adjusted for the factors mentioned above, have limited practical value in detecting inadequate energy and protein intake, respectively.

Animal Nutritional Physiological Phenomena↗
PubMed1978

Radioimmunoassay for the detection of hepatitis e antigen (HBeAG) and antibody (anti-HBe).

A solid phase micro-immunoradiometric assay (micro-SPIRA) for the detection of hepatitis e antigen (HBeAg) and antibody has been developed. Chimpanzee anti-HBe/2 was developed by repeated immunizations with purified antigen containing HBeAg/1 and HBeAg/2. An anti-HBe/2 titer of 1:4 was determined by immunodiffusion (ID) analysis. Anti-HBe/1 was not detected. The anti-HBe IgG used in the assay was purified from plasma by a combination of DEAE-cellulose and affinity chromatography. The sensitivity of the micro-SPIRA for antigen and antibody was 193 ng/ml and 65 ng/ml, respectively. By comparing relative endpoint titers obtained by ID to micro-SPIRA, it was determined that micro-SPIRA for antigen and antibody is 320 and greater than 1300 times more sensitive, respectively, than ID. The specificity of the assay was ascertained by the examination of various non-B specimens. The application of the assay to a panel of 50 hepatitis B surface antigen (HBsAg)-positive specimens resulted in an increase in positivity of 18% for antigen and 22% for antibody.

Animals↗
PubMed1977

Immunoglobulin IgG1 metabolism in new born calves.

The half-life of IgG1 immunoglobulin was measured in six neonatal calves following a meal of iodine-125 labeled IgG1 in colostrum derived from their dams. The half-life as measured by the decrease in plasma concentration of IgG1 was 19.9 +/- 1.9 days. However, the half-life as measured by the disappearance of [iodine-125]IgG1 from the plasma was 11.5 +/- .6 days. The latter value is closer to the true half-life because it is not affected by endogenous production of IgG1 by the tissues of the young calf. A decrease in the specific activity of plasma [iodine-125]IgG1 with time representing the body "pool" of IgG1 (half-life 25.8 +/- 6.1 days) suggests that the calf from birth to about 20 days of age is capable of synthesizing a significant amount of IgG1 immunoglobulin.

Animals↗
PubMed1977

Valine, leucine, and isoleucine metabolism by lactating bovine mammary tissue.

Valine, leucine, and isoleucine were extracted by the lactating bovine mammary gland in excess of outputs in milk protein. Carbon-14 uniformly labeled L-valine, L-leucine or L-isoleucine were catabolized when incubated in vitro with lactating bovine mammary tissue slices. The pathways of degradation of these amino acids by mammary tissue appear to be those common to other tissues. These amino acids represent a potential source of energy to the mammary gland as well as a source of carbon and alpha-amino nitrogen for synthesis of nonessential amino acids.

Acetates↗
PubMed1976

Characterization of fatty acid synthesis by cow mammary subcellular fractions.

Cellular site of fatty acid synthesis was investigated with mammary tissue from lactating cows. Cytosol, mitochondrial, and microsomal fractions were obtained by differential centrifugation and characterized by measurement of marker enzymes. Two incubation media were utilized to quantitate acetate incorporation into fatty acids by the subcellular fractions. The cytosol fraction synthesized fatty acids from 4 to 16-carbons in chain length with the pattern similar to those synthesized in vivo. No significant acetate incorporation into fatty acids was obtained with mitochondria or microsomal incubations. The malonyl-CoA pathway was the predominant pathway of fatty acid synthesis in cow mammary cytosol as evidenced by inhibitory studies with avidin.

Acetates↗
PubMed1976

Production and turnover of IgG1 and IgG2 immunoglobulins in the bovine around parturition.

Production rates (entry rate into blood plasma) and other metabolic parameters for the IgG1 and IgG2 subclasses of immunoglobulins in mammary secretions (ratio of about 7 to 1) were determined in cows around the time of parturition by both single-injection and continuous-infusion isotope-dilution techniques. Four cows were given a single dose of 150 to 200 muCi of iodine-125 labeled IgG1 and 100 to 250 muCi of iodine-131 labeled IgG2 at 2 to 1 wk before parturition. Four cows, including two of the above, were infused continuously with constant amounts of the labeled immunoglobulins starting at 11 to 4 days before parturition. All cows were maintained until 4 to 6 days after parturition for monitoring the specific activities of iodine-125 labeled IgG1 and iodine-131 labeled IgG2 in the plasma and mammary secretions. Maximum entry rates of IgG1 and IgG2 were between 3 and 1 day prepartum with means of 125 and 60 g/500 kg body weight per day. The exchangeable pool means for IgG1 and IgG2 were 619 and 643 g/500 kg body weight, and both immunoglobulins were divided almost equally between the intra- and extravascular pools. A greatly increased production and a shortened half-life or greater turnover for plasma IgG1 occurs around the time of parturition which can account for the large accumulation of IgG1 in colostrum.

Animals↗
PubMed1975

Milk production and nitrogen utilization in response to postruminal infusion of sodium caseinate in lactating cows.

Five lactating, rumen-fistulated Holstein cows were used to obtain additional information concerning the effects of postruminal infusion of sodium caseinate on milk production and amino acid utilization. A 7-day continuous abomasal infusion of approximately 450 g/day of sodium caseinate was preceded and followed by 7-day infusions of an isonitrogenous-isocaloric solution of glucose, monosodium glutamate, and urea. Total collections of milk, urine, and feces were obtained during the last 5 days of each infusion period. On the last day of each period, arterial and mammary venous blood samples were obtained for analysis of plasma free amino acids. During infusion of sodium caseinate, milk production, milk protein (N times 6.38) production, and efficiency of nitrogen utilization for milk crude protein production were increased. Arterial plasma concentrations of free histidine, isoleucine, phenylalanine, valine, and total essential amino acids were elevated above control levels during infusion of sodium caseinate, while ornithine and tryrosine were decreased. Calculation of the relative concentration of essential amino acids in arterial plasma and in milk protein indicated that methionine and lysine were least abundant in plasma relative to their requirement for milk protein synthesis. A high precentage extraction from arterial plasma by the mammary gland also suggested that methionine and lysine may have been the essential amino acids in most critical supply for milk protein synthesis. Calculation of uptake to output ratios of individual plasma amino acids by the mammary gland suggested that significant quantities of extracted arginine, isoleucine, leucine, threonine, and valine were utilized in pathways other than direct incorporation into milk protein.

Amino Acids↗
PubMed1975

Effects of intraruminal and intra-abomasal additions of cod-liver oil on milk fat production in the cow.

Four Holstein cows were used in a modified switchback design to show the effect on milk-fat synthesis of (1) control diet, (2) 29.23, 3.92, 6.48, 30.65, 3.44 control diet plus 255 g/day of cod-liver oil in rumen, and (3) control diet plus 225 g/day of cod-liver oil in abomasum. Mean milk yield (kg/day), fat production (kg/day), and milk-fat percentage were (1) 21.87, .79, 3.63; (2) 22.99, .70, 3.05; and (3) 23.02, .75, 3.28. Compared to the post-treatment control period, only one cow decreased in milk-fat percentage on 3 while all cows decreased in milk-fat percentage on 2. Proportions of carbons 16:0, 16:1, 18:0, 18:1, 18:2, and trans-monoene fatty acids of the milk fat were (1) 30.31, 3.24, 10.15, 30.48, 2.59, 7.91; (2) 26.37; and (3) 26.30, 3.72, 10.56, 30.10, 2.96, 9.84. Proportions of rumen volatile fatty acids were not significantly affected by treatment. Proportions of carbons 16:0, 18:0, 18:1, 18:2, and 18:3 fatty acids in the rumen ingesta were (1) 17.28, 47.92, 21.71, 10.59, 2.46; (2) 19.55, 25.90, 37.21, 11.97, 5.39; and (3) 16.90, 50.80, 19.66, 9.11, and 3.23. Fatty acid composition of blood-serum phospholipids were affected by treatment.

Abomasum↗
PubMed1975

Metabolism of arginine and ornithine in the cow and rabbit mammary tissue.

Amino acid uptake by the bovine mammary gland was determined by arteriovenous difference. Extraction of arginine from the plasma by the lactating bovine mammary gland was in excess of requirements for milk protein synthesis. Ornithine and citrulline also were extracted by the gland but are not in milk protein. Incubations of slices of lactating mammary tissue from cows and rabbits indicate that nonessential amino acids, especially proline and glutamate, are the major end products of arginine and ornithine metabolism in the lactating mammary gland.

Abdomen↗