Changes in bovine milk secretion following intramammary infusions of concanavalin A, oyster glycogen, or water

Effects of sterile intramammary infusion of Concanavalin A on milk secretion were contrasted with infusion of oyster glycogen or water. Twenty-four cows were infused intramammary with 100 mg Concanavalin A, oyster glycogen in 20 ml water, or with 20 ml water alone. Concentrations of lactose, somatic cells, immunoglobulins G and A, serum albumin, and activity of N-acetyl-B-D-glucosaminidase were determined in milk. Blood N-acetyl-B-D-glucosaminidase activity and concentrations of blood immunoglobulins G and A and serum albumin were determined. Oyster glycogen and concanavalin A caused inflammation in treated quarters; peak elevations of milk somatic cell counts, serum albumin, immunoglobulin G concentrations, and N-acetyl-B-D-glucosaminidase activity were at 12 to 36 h following treatment. Milk production and lactose concentration were reduced by oyster glycogen and Concanavalin A. Selective indices of relative accumulation of milk immunoglobulins decreased following Concanavalin A and oyster glycogen, whereas the N-acetyl-B-D-glucosaminidase activity selective index generally remained unchanged. Inflammation reduced the selective accumulation of immunoglobulins, and absence of change in the N-acetyl-B-D-glucosaminidase selective index indicated that blood is not a major source of milk N-acetyl-B-D-glucosaminidase.

Is thiocyanate peroxidation at equilibrium in vivo?

The peroxidase-catalyzed oxidation of SCN- by H2O2 is an important in vivo reaction because it limits the accumulation of toxic H2O2 and provides significant concentrations of the antimicrobial agents, HOSCN and OSCN-. Data presented in this report suggest that the reaction: (Formula: see text) is in a state of dynamic equilibrium in vivo. Since OSCN- can form the weak acid HOSCN (pKa = 5.3), the equilibrium constant expression (Kox) for thiocyanate peroxidation is dependent on the concentration of hydrogen ions as well as the concentrations of H2O2, SCN-, HOSCN, OSCN- and water, and on the HOSCN ionization constant, Ka: (Formula: see text). The concentration of water is assumed to be constant and unaffected by the other components and is omitted from the Kox equation. The value of Kox was estimated from in vitro data to be 3.7 X 10(3) M-1 (S.D. = 0.8 X 10(3) M-1, n = 8). Using this value for Kox and observations of salivary concentrations of SCN- and HOSCN + OSCN- from several previous reports, the equilibrium concentrations of H2O2 in whole saliva were calculated to range from 8 to 13 microM. This range is consistent with reported estimates of 10 microM as the hydrogen peroxide tolerance limit for human cells.

The effect of retinoids on the activity of the membrane form of galactosyltransferase, studied in an enzyme/liposome model system

In the present study the effect of retinoids on the membrane form of galactosyltransferase was tested. A model system consisting of pure bovine milk galactosyltransferase and phosphatidylserine vesicles was used for this investigation. Retinol, retinal and retinylphosphate were able to overcome the modulating effect of phosphatidylserine, that is, activated the enzyme. Retinoic acid and retinylpalmitate were ineffective in this system.

Effects of different skim milk fractions on activity of cow milk purified lipoprotein lipase

Hydrolysis of a long-chain triglyceride substrate by purified cow milk lipoprotein lipase, in the absence of blood serum, was changed by adding heated skim milks. Preincubation of the substrate with small amounts of several skim milks increased (+50 to 300%) lipoprotein lipase activity. By contrast, greater amounts of skim milk increased further or decreased lipoprotein lipase activity (+ 300 to -90%). The inhibitory effect was due to substrate surface protection. Results obtained after removal of casein (by isoelectric precipitation or by ultracentrifugation) and of whey proteins (by heat treatment) showed that the effect of skim milk was due to the proteose-peptone fraction. Fractionation of the proteose-peptone fraction into component 5-enriched fraction and component 3-enriched fractions suggested that the activating effect was due partially to proteose-peptone component 5, and the inhibitory effect resulted from component 3. These effects were overcome by blood serum.

Comparison of milk antitrypsin, albumin, n-acetyl-beta-D-glucosaminidase, somatic cells and bacteriological analysis as indicators of bovine subclinical mastitis

Thirty-two quarters, five of which harbored subclinical mastitis, were examined daily for one month. The usefulness of milk antitrypsin, BSA (bovine serum albumin), NAGase, somatic cells and bacteriological analysis in differentiating the inflamed quarters from the healthy control quarters was analysed. Inter-quarter evaluation clearly improved each indirect mastitis parameter; NAGase and antitrypsin were better indicators of differences between infected and non-infected quarters than BSA or the somatic cell count.

The hydrolysis of very low density lipoproteins and chylomicrons of intestinal origin by lipoprotein lipase in ruminants

The hydrolysis by lipoprotein lipase of a very low density lipoprotein/chylomicron fraction, obtained from the intestinal lymph of sheep, has been studied in vitro. Rapid hydrolysis of triacylglycerols, with an accumulation of free fatty acids, was observed. After an initial lag period, phosphatidylcholine also was hydrolyzed. No specificity for particular fatty acids in the triacylglycerols (or phosphatidylcholines) was observed.

Milk plasmin, N-acetyl-beta-D-glucosaminidase, and antitrypsin as determinants of bacterial replication rates in whey

Quarter milk samples were collected monthly on a selected herd of 80 Ayrshire cows having a high frequency of subclinical mastitis. Analysis of bacterial growth rates in milk showed that whey prepared from infected or inflamed quarters stimulated bacterial growth. Milk N-acetyl-beta-D-glucosaminidase, antitrypsin, and plasmin activities all showed positive correlations with bacterial replication rates (Staphylococcus aureus and Escherichia coli) in respective whey samples as determined by a turbidometric micro-technique. Increased bacterial replication rates in mastitic whey represent an increased yield of the key nutrients for bacteria. Bacterial growth enhancement can be partly explained by proteose-peptone originating from plasmin activation and casein degradation. However, as multiple regression analysis showed that a combination of the predictor variables: antitrypsin, N-acetyl-beta-D-glucosaminidase and plasmin explained enhancement of bacterial growth better than plasmin alone, other factors connected with inflammation should be sought when searching for growth-enhancing factors in whey. Milk plasmin activities showed increasing activities toward end of lactation (before drying off) as well as during later lactation (age of cow in years minus 2). Bacterial replication was enhanced in parallel with these changes in plasmin activities.

Lipolysis-induced degradation of apolipoproteins B and E of human very low density lipoproteins

We have found that in vitro lipolysis of human very low density lipoproteins (VLDL) by purified bovine milk lipoprotein lipase (LpL) promotes degradation of the apolipoprotein (apo) B moiety of VLDL. Analysis by sodium dodecyl sulfate-polyacrylamide gradient gel electrophoresis showed that lipolysis of VLDL by purified LpL for 1 h at 37 degrees C induced the selective degradation of the high Mr apo-B (apo-B-100) from most hypertriglyceridemic VLDL and from a few normolipidemic VLDL into several small fragments with molecular weights ranging from 90,000-490,000. No detectable degradation of apo-B occurred in control VLDL when incubated without LpL. The apo-E moiety of VLDL from certain individuals was also degraded following lipolysis of VLDL, and the extent of degradation of apo-B and -E in VLDL was varied among the individual VLDL. The major degradation products of apo-E, identified from the gel, were 31,000- and/or 28,000-Da species. In contrast to the apo-E moiety of VLDL, purified apo-E was not degraded when incubated with LpL. Incubation of low density lipoproteins (LDL) with LpL showed only a minimal effect on the apoproteins of LDL. When high density lipoprotein (HDL) was included in the lipolysis mixture as an acceptor of lipolytic surface remnants, the apoproteins of HDL remained unaltered, while the apo-B moiety of VLDL remnants in the mixture was degraded. Inclusion of protease inhibitors in the lipolysis mixture prevented the degradation of apo-B, but the hydrolysis of VLDL-triglyceride was minimally affected. A selective degradation of apo-B in VLDL also occurred during lipolysis of VLDL when VLDL was perfused through rat hearts. These results suggest that conformational changes in apo-B and apo-E caused by VLDL lipolysis may increase the susceptibility of apo-B and apo-E to degradation by the proteases co-isolated with VLDL. The consequences of the lipolysis-induced degradation of apo-B and apo-E on changes in metabolic properties of VLDL remnants remain to be determined.

Interaction of lipoprotein lipase with phospholipid vesicles: effect on protein and lipid structure

The interaction of lipoprotein lipase (LpL) and a nonhydrolyzable phosphatidylcholine, 1,2-ditetradecyl-rac-glycero-3-phosphocholine (C14-ether-PC), has been studied by several physical methods. Analysis of the circular dichroic spectrum of LpL gave the following fractional conformation: 35% alpha-helix, 30% beta-pleated sheet, and 45% remaining structure. No significant change in the circular dichroic spectrum of LpL was observed on addition of C14-ether-PC vesicles. The quenching of LpL fluorescence by acrylamide and iodide ion was decreased only slightly by addition of C14-ether-PC vesicles. Addition of LpL to sonicated C14-ether-PC vesicles containing entrapped carboxyfluorescein caused the release of less than 15% of the vesicle contents in 20 min, indicating that the enzyme did not disrupt the structure of the lipid. In contrast, greater than 80% of the vesicle contents were released with the addition of apolipoprotein A-I to an identical vesicle preparation. The temperature dependence of the fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene incorporated into C14-ether-PC vesicles was not significantly altered by the addition of LpL. When LpL is added to vesicles, the bilayer structure of the vesicles is not disrupted as observed by freeze-fracture electron microscopy. However, at low ionic strength (0.1-0.25 M NaCl) significant aggregation of intact vesicles is observed by light scattering and electron microscopy. Vesicle aggregation is prevented and reversed by 1 M NaCl and by heparin. These data demonstrate that LpL binds to the surface of a lipid interface, without dramatic changes in lipid bilayer or protein structure.

Interaction of synthetic peptides of apolipoprotein C-II and lipoprotein lipase at monomolecular lipid films

The triacylglycerol hydrolyase and phospholipase A1 activities of bovine milk lipoprotein lipase toward long-chain fatty acyl ester substrates were investigated with monomolecular lipid films containing trioleoylglycerol and phosphatidylcholine. In a monolayer of egg phosphatidylcholine containing 3 mol% [14C]trioleoylglycerol, and in the presence of apolipoprotein C-II, a 79 amino acid activator protein for lipoprotein lipase, enzyme activity was maximal at a surface pressure of 21-22 mN X m-1 (37 mumol oleic acid released/h per mg enzyme); enzyme activity was enhanced 9-fold by apolipoprotein C-II. At surface pressures between 22 and 30 mN X m-1, lipoprotein lipase activity decreased over a broad range and was nearly zero at 30 mN X m-1. Apolipoprotein C-II and the synthetic fragments of the activator protein containing residues 56-79, 51-79 and 44-79 were equally effective at 20 mN X m-1 in enhancing lipoprotein lipase catalysis. However, at surface pressures between 25 and 29 mN X m-1, only apolipoprotein C-II and the phospholipid-associating fragment containing residues 44-79 enhanced enzyme catalysis. The effect of apolipoprotein C-II and synthetic peptides on the phospholipase A1 activity of lipoprotein lipase was examined in sphingomyelin:cholesterol (2:1) monolayers containing 5 mol% di[14C]myristoylphosphatidylcholine. At 22 mN X m-1, apolipoprotein C-II and the synthetic fragments containing residues 44-79 or 56-79 enhanced lipoprotein lipase activity (70-80 nmol/h per mg enzyme). In contrast to trioleoylglycerol hydrolysis, the synthetic fragments were not as effective as apolipoprotein C-II enhancing enzyme activity towards di[14C]myristoylphosphatidylcholine at higher surface pressures. We conclude that the minimal amino acid sequence of apolipoprotein C-II required for activation of lipoprotein lipase is dependent both on the lipid substrate and the packing density of the monolayer.

Milk composition of rats feeding restricted litters

Milk samples were taken from rats feeding ten pups and from both the suckled and non-suckled glands of rats feeding two pups. The lipid, protein and lactose concentrations were similar in the milks from the secreting glands, but the fluid from the non-suckled glands contained less lactose and lipid but significantly higher total protein and transferrin concentrations. The fatty acid compositions of the milk from the three sources were very similar. The mammary tissue from the rats feeding ten pups had a higher DNA content/g wet wt. than either the suckled or non-suckled mammary tissue of the rats feeding two pups. The specific activities of several lipogenic enzymes were significantly lower in the non-suckled mammary tissue.

Carryover of preformed staphylococcal enterotoxins and thermostable deoxyribonuclease from raw cow milk to Khoa--a heat-concentrated Indian milk product

Preformation of enterotoxins and thermostable deoxyribonuclease by Staphylococcus aureus in raw cow milk and their carryover to Khoa--a heat-concentrated (98 degrees C for 15 to 20 min) Indian milk product--was evaluated. Detectable enterotoxins and deoxyribonuclease, as evidenced in the zone diameters of 10 to 16 mm, were performed in 10 h incubation of milk samples inoculated with strains of Staphylococcus aureus at 1 X 10(6) cfu/ml of milk. Both preformed enterotoxins and thermostable deoxyribonuclease were carried over to Khoa from raw milk. The study implies the use of good quality raw milk free from pathogenic organisms for preparation of milk products such as Khoa.

Effects on mastitis of overmilking in conjunction with pulsation failure

Half-udder comparisons were made using 56 cows for 2 months, in an experiment involving high bacterial challenge, to assess the combined effects of 5 min overmilking and pulsation failure (resulting from the use of shortened teacup liners) on teat condition and mastitis. Only three new infections were confirmed in over 12500 quarter milkings in quarters milked with control liners (of 148 mm effective length) indicating little or no effect of prolonged overmilking in these quarters. A 3.5-fold increase in the new infection rate (NIR) based on bacteriological diagnosis alone (P less than 0.01), or a 9-fold increase in NIR based on bacteriological diagnosis plus raised cell count and/or N-acetyl-beta-D-glucosaminidase (P less than 0.01), occurred in quarters milked with the same liners shortened to an effective length of 120-130 mm. The mean interval to infection or teat canal colonization (41 v. 60 milkings), and for a quarter infection to be confirmed by other diagnostic tests (45 v. 79 milkings) was significantly less in quarters overmilked with short liners. The results confirm that NIR increases whenever pulsation fails. Overmilking may increase NIR when it is associated with pulsation failure.

Immunologic and enzymatic comparisons between human and bovine lipoprotein lipase

Studies were conducted to compare human and bovine lipoprotein lipase (LPL) preparations with regard to immunological cross-reactivity and substrate specificity. LPL was partially purified from human milk. An antiserum against the human LPL preparation was produced in a goat. This antiserum inhibited LPL enzymatic activity in human milk and in human post-heparin plasma. Neither bovine milk nor bovine post-heparin plasma LPL enzymatic activity was inhibited by this antiserum. These findings suggest that there are significant structural differences between the human and bovine enzymes in domains that are involved in enzymatic activity. Human and bovine post-heparin plasma and partially purified preparations of LPL from human and bovine milk were compared with regard to substrate specificity, by comparing their lipolytic activities against triglyceride, cholesteryl esters, and retinyl esters. Only the partially purified bovine milk LPL preparation possessed retinyl palmitate hydrolase activity. The results suggest that this latter activity may be the result of a previously unrecognized contaminant in the commonly used LPL preparations from bovine milk.

Physicochemical properties of proteinases from selected psychrotrophic bacteria

The physicochemical properties of eight extracellular proteinases secreted by psychrotrophic bacteria of dairy origin have been studied. Seven of these proteinases were able to withstand ultra heat treatment (UHT) with D values at 140 degrees C ranging from 2 to 300 s. The six Pseudomonas fluorescens proteinases were glycoproteins of mol. wt 47000-49500. The two Serratia marcescens proteinases, of mol. wt of 51000, did not contain carbohydrate but in other respects were similar to the Pseudomonas proteinases. The proteinases were inhibited by various metal chelators and all contained Ca and Zn in similar proportions. Their amino acid compositions were similar, with alanine as the N-terminal group, cysteine completely absent and very low levels of methionine. Isoelectric points ranged from 5.10 to 8.25. Their physical and chemical properties enabled them to be classified as alkaline metalloendopeptidases. A similarity index (S delta n) was used to predict sequence homology between ten proteinases of known amino acid composition. Comparisons of S delta n of these proteinases showed only minor sequence differences except for those of Ps. fluorescens MC60. Heat resistance could not be related wholly to similarities in protein sequence, but could be related both to the strength of stabilizing Ca2+-protein interactions and to the randomness inherent within the folding of the peptide chain.

The equilibration of reducing equivalents within milk xanthine oxidase

The rate at which reducing equivalents equilibrate among the several oxidation-reduction active sites in xanthine oxidase has been investigated using a pH-jump technique in which partially reduced enzyme in dilute buffer is mixed with concentrated anaerobic buffer at a different pH in a conventional stopped flow apparatus. It is found that the rate constant associated with the observed spectral change varies with pH, doubling from 155 s-1 at pH 6 to 330 s-1 at pH 8.5, but is always found to be approximately 10-fold greater than kcat at the same pH. The observation of fast rates for the equilibration of reducing equivalents within xanthine oxidase is consistent with a great deal of indirect evidence from conventional kinetic studies of both the oxidative and reductive half-reactions of xanthine oxidase and lends support to the rapid equilibrium model that has been proposed for the oxidation-reduction interactions of the several centers in xanthine oxidase (Olson, J. S., Ballou, D. P., Palmer, G., and Massey, V. (1974) J. Biol. Chem. 249, 4363-4382). The present conclusions are in conflict, however, with the interpretation of recent flash photolysis experiments with xanthine oxidase (Battacharyya, A., Tollin, G., Davis, M. D., and Edmondson, D. E. (1983) Biochemistry 22, 5270-5279). Possible sources for the apparent inconsistencies between the flash photolysis results and those of the present experiments are discussed.

Fatty acids in the milk of goats after cessation of lactation

Regular hand milking of six goats was discontinued after 32-35 weeks of lactation. A few days after milking out ceased, the concentration of triglyceride in peripheral blood plasma increased. Over a period of weeks, the concentration of triglyceride in small samples of fluid taken from the teat canal fell gradually. Lipase activity of the milk fluid was temporarily reduced shortly after milking out ended, but, despite this, its concentration of free fatty acids increased. It is suggested that free fatty acids are released during clearance of milk triglyceride from residual fluid in the mammary gland after cessation of lactation.

Effect of extracellularly generated free radicals on the plasma membrane permeability of isolated pancreatic B-cells

Previous experiments on alloxan diabetogenicity suggest that alloxan increases the permeability of B-cell plasma membranes by generation of noxious free radicals. Whether the radicals are generated intra- or extracellularly has however been disputed. To test if extracellularly generated free radicals could decrease trypan blue exclusion of dispersed islet cells, a radical-generating solution of xanthine oxidase/hypoxanthine was employed. The solution increased dye uptake by cells in the cell suspension. Superoxide dismutase and catalase but not scavengers of hydroxyl radicals protected against the increase in dye uptake. Both L- and D-glucose protected the cells from injury. It is concluded that extracellularly generated free radicals induce damage to the plasma membrane of islet cells. The result strengthens the hypothesis of plasma membrane damage by extracellularly generated free radicals as the primary event in alloxan diabetogenicity and may provide a link for explanation of damage caused by islet inflammation in juvenile diabetes.

Mammary metabolism in the goat during normal or hormonally-induced lactation

Mammary metabolism was studied in 4 normal lactating goats (group N) and in 4 non-pregnant goats induced to lactate by hormonal treatment (group 1). Tissue was sampled by biopsy after 3, 9 and 18 weeks of lactation. Although milk potential was the same in both groups, group 1 produced 45% less milk than group N. The RNA-DNA ratio, activities of lipoprotein lipase (LPL), glucose-6-phosphate dehydrogenase and acetyl-CoA carboxylase, and the beta-casein % of in vitro protein synthesis were not significantly lower in the 1 than in the N goat mammary tissue. This suggests that differences in mammary cell hyperplasia during hormonal treatment, and not potential metabolic activities, partially accounted for the difference in milk yield levels. Milk composition was comparable in the two groups. However, milk fat in group N had a higher long-chain fatty acid content (stearic and oleic acids) during the first month of lactation due to the higher mobilization of body lipids in high-yielding animals. Another qualitative difference was the delayed increase in milk LPL secretion during the first 3 months of lactation in induced goats.

N-acetyl-beta-D-glucosaminidase and antitrypsin in subclinically infected quarter-milk samples: effect of bacteria and hemolysins, lactation stage, and lactation number

Interrelationships between N-acetyl-beta-D-glucosaminidase (indicating cellular damage) and antitrypsin (indicating increased permeability between the blood and milk compartments) were evaluated in 1,411 quarter-milk samples collected during routine herd surveys. N-Acetyl-beta-D-glucosaminidase was antitrypsin, whereas, in more severe mastitis, antitrypsin had a more constant deflection. The sensitivity of both determinants was associated with the virulence of bacteria. Production of bacterial hemolytic toxins was associated with a significant increase in both determinants. Penicillinase production by staphylococci was associated with selective increases of antitrypsin.

Significance of the presence of bovine milk beta-glucuronidase in mastitis detection

The presence of beta-glucuronidase enzyme in bovine milk was related both to the existence of major and minor pathogens and to somatic cell counts. The detection of this enzyme in whole milk was made possible by the use of p-nitrophenyl-beta-glucuronide as a substrate. This detection allowed us to determine abnormal udder secretions with a high degree of specificity and sensitivity. The particular method of enzyme determination was considered important for mastitis detection because beta-D-glucuronidase, the most significant enzyme in inflammatory processes, is released selectively. The relationship between enzyme, presence of pathogens, and somatic cell counts was established in 220 milk samples obtained at random from individual quarters of apparently healthy udders of cows from four local dairy farms (Santiago del Estero and Tucuman, Argentina). Four of these samples were from cows of recent parturition and two from cows with severe clinical mastitis. Only 17% of the milk samples were normal with somatic cell counts 500,000 cells/ml or less. This ratio is the usual one throughout the area, and the remaining 83% showed higher somatic cell counts. Taking the latter as 100%, the presence of beta-glucuronidase and the positive bacteriological analyses represented 76 and 74%, respectively.

Tissue specific deficiency of lysozyme in ruminants

The distribution of lysozyme in tissues and fluids of ruminants was examined and it was determined that, except for a few tissues, ruminants were deficient in lysozyme activity compared with other species. The prominent exception was the abomasum of cattle, which had high levels of lysozyme activity. Mixing and extraction studies indicated that the lysozyme deficiency of ruminants was due neither to the presence of inhibitors of lysozyme in ruminant tissue nor to the binding of lysozyme in a manner that interfered with its enzymatic activity or assay. Other investigations have indicated that isozymes of lysozyme are present in ruminants and this study suggests that ruminants have only low levels of the isozyme that is the major isozyme of lysozyme in non-ruminants.

[Isolation and purification of lactoperoxidase from cow's milk]

A procedure is described for isolation and purification of lactoperoxidase from cow milk. The procedure involved the following steps: isolation of casein from milk, sorption of lactoperoxidase on CM-Sephadex, concentration of the eluate using ultrafiltration, salting out with ammonium sulfate; isoelectric focusing was carried out in the borate-polyol system. Highly purified, active preparation of lactoperoxidase was obtained within a relatively short period by means of the procedure, where the available reagents were used.