Search PubMed⌕ Search

Biomedical subjects

J D Turner

Publications and source records attributed to J D Turner.

At least 73 records · Page 4Linked to original sources
PubMed1992

Proliferation of the MAC-T bovine mammary epithelial cell line in the presence of mammary secretion whey proteins.

Development of the MAC-T bovine mammary epithelial cell line by stable transfection with simian virus-40 large T-antigen should greatly assist study of possible intrinsic (local) and extrinsic (systemic) factors regulating bovine mammary epithelial cell development, differentiation, and function. This study evaluated the influence of mammary secretion whey proteins alpha-lactalbumin (ALA), beta-lactoglobulin (BLG), lactoferrin (LF), transferrin (TF) and serum albumin (SA) on MAC-T cell proliferation in the absence and presence of 10% fetal bovine serum (FBS). Concentration of whey proteins in culture ranged from 0 to 625 micrograms/ml. MAC-T cell proliferation in the absence of FBS was significantly lower than in the presence of 10% FBS. Alpha-lactalbumin and LF significantly decreased MAC-T proliferation in both the absence and presence of 10% FBS. Transferrin significantly increased MAC-T cell proliferation only in the absence of FBS. There were no significant differences in MAC-T cell proliferation cultured in the presence of BLG or SA. These experiments illustrate the potential usefulness of MAC-T cells for the study of factors involved in mammary cell proliferation. Results identified ALA, LF and TF as possible intrinsic factors associated with regulation of mammary epithelial cell proliferation.

Animals↗
PubMed1992

Overexpression of ovine insulin-like growth factor-I stimulates autonomous autocrine or paracrine growth in bovine mammary-derived epithelial cells.

To test the hypothesis that insulin-like growth factor-I (IGF-I) affects the growth of bovine mammary epithelial cells through an autocrine and/or paracrine pathway, a cell line (MD-IGF-I) was originated from MAC-T cells by cotransfection with a construct containing the cDNA for an ovine exon 2-encoded prepro-IGF-I under control of the mouse mammary tumor virus-long terminal repeat promoter. Clone MD-IGF-I contained multiple copies of the plasmid integrated into the genome, expressed the highest level of IGF-I mRNA, and secreted radioimmunoactive IGF-I into the medium. The mitogenic activity of MD-IGF-I cells was stimulated 80% by dexamethasone (DEX). The total DNA in MD-IGF-I cells was 2.5-fold higher than that in parental MAC-T cells in the presence of DEX. Conditioned medium from MD-IGF-I cells, induced with DEX, stimulated [3H]thymidine incorporation into DNA of MAC-T cells and uninduced MD-IGF-I cells. These data provide evidence that IGF-I was secreted into medium by MD-IGF-I cells. It is suggested that IGF-I can stimulate the growth of mammary epithelial cells by an autocrine and/or paracrine mode of action. The MD-IGF-I cell line may be a suitable system to study translational and posttranslational modifications of IGF-I peptides.

Animals↗
PubMed1992

Receptor binding and growth-promoting activity of insulin-like growth factor-I in a bovine mammary epithelial cell line (MAC-T3).

Insulin-like growth factor-I (IGF-I) has been known to be mitogenic to a variety of cell types, although a growth-regulatory role for IGF-I on bovine mammary epithelial cells has not been fully investigated. In the present study, we examined the receptor binding of IGF-I and its effect on growth in a bovine mammary epithelial cell line (MAC-T3). Specific receptors for IGF-I were detected on cultured bovine mammary epithelial cells. Competitive binding revealed that half-maximal inhibition of 125I-labelled IGF-I binding by IGF-I was approximately 3 micrograms/l. Dissociation rate constant of the IGF-I receptor was 3.10 +/- 0.06 nmol/l (S.E.M.) with a receptor site concentration of 366 +/- 8 fmol/mg protein for the average of three experiments. IGF-I exerted a positive mitogenic effect on MAC-T3 cells according to both direct DNA assay and thymidine incorporation assay. Moreover, the mitogenic effect of IGF-I on MAC-T3 cells was enhanced by the addition of fetal calf serum in the culture media. The present results suggest that the bovine mammary epithelial cell line (MAC-T3) provides a useful model system with which to study the biological actions of insulin-like growth factors on the bovine mammary secretory tissue in vitro.

Animals↗
PubMed1991

Establishment of bovine mammary epithelial cells (MAC-T): an in vitro model for bovine lactation.

The hallmark of differentiated mammary epithelial cells is a copious secretion of milk-specific components regulated by lactogenic hormones. We describe an established clonal cell line produced from primary bovine mammary alveolar cells (MAC-T) by stable transfection with SV-40 large T-antigen. MAC-T cells show a population doubling time of approximately 17 h and have been cultured more than 350 passages without showing any sign of senescence. They show the characteristic "cobblestone" morphology of epithelial cells when grown on plastic substratum. Differentiation was induced by augmenting cell-cell interaction on a floating collagen gel in the presence of prolactin. The differentiated phenotype was characterized to include (1) increased abundance in beta-casein mRNA, (2) increased number and size of indirect immunofluorescent casein secretory vesicles in each cell and (3) alpha s- and beta-casein protein secretion. The clonal nature of the cells, their immortality, and their ability to uniformly differentiate and secrete casein proteins make this cell line unique.

Animals↗
PubMed1991

Role of tissue remodeling in mammary epithelial cell proliferation and morphogenesis.

Lactation is a physiological process characterized by the secretion of large quantities of protein, carbohydrate, and lipid. To achieve the production, the mammary gland must grow and then differentiate; both processes require extensive tissue remodeling. Remodeling begins with a carefully controlled proteolysis of the extracellular matrix and cell-cell adhesion proteins. Plasmin is a serine protease that has been implicated in the tissue remodeling associated with the declining phase of lactation and mammary involution. As lactation progresses, the quantity of plasmin activity increases within the mammary tissue and milk. This has led to the hypothesis that gradual involution results from progressive tissue remodeling. Hormonal attenuation of gradual involution by bST would slow tissue remodeling and would be permissive for lactation. In vitro results indicate that insulin-like growth factor-I impairs the secretion of plasminogen activator by bovine mammary epithelial cells. As such, a mechanism of action for bST exists.

Animals↗
PubMed1991

Secretion of interleukin-1 by bovine milk macrophages.

The relative sensitivity of bovine blood monocytes and macrophages isolated from milk to lipopolysaccharide, with respect to interleukin 1 (IL-1) production, was evaluated. Addition of lipopolysaccharide (0 to 30 microgram/ml) to the culture medium resulted in increases in secreted and intracellular IL-1 activity for monocytes and milk macrophages, with maximal stimulation achieved at 30 micrograms of lipopolysaccharide/ml of medium. At this concentration of lipopolysaccharide, monocytes released 76% of the total IL-1, whereas milk macrophages released only 26% of the total IL-1 produced within the cell. Secretion of a small quantity of IL-1 was a common property of macrophages isolated from healthy and mastitic quarters. We concluded that limited secretion of IL-1 may render the milk macrophages less efficient in promoting lymphocyte activation.

Animals↗
PubMed1991

Plasminogen activator production by bovine milk macrophages and blood monocytes.

The type of plasminogen activator (PA) produced by bovine milk macrophages has been determined. Macrophages produce a PA protein with molecular weight of 28,000 and isoelectric point of 8.5, and with enzymatic activity independent of fibrin. These characteristics are identical to those reported for bovine urokinase-PA. Although blood monocytes and milk macrophages produce PA after stimulation with lipopolysaccharide, mammary macrophages are clearly limited in their ability to release PA. At maximal stimulation, 78% of the PA produced by milk macrophages remained cell-associated. In marked contrast, blood monocytes released 76% of the PA produced into the culture medium. Macrophages isolated from mastitic quarters produced higher (2.5 times) amounts of PA, compared with those produced by macrophages isolated from healthy quarters. However, in both cases, macrophages were unable to secrete the protein already produced. The limited PA secretion by milk macrophages might be a residual function of a differentiated macrophage population.

Animals↗
PubMed1990

Changes in and partial identification of the plasminogen activator and plasminogen activator inhibitor systems during ovarian follicular maturation in the pig.

Plasminogen, plasmin, and plasminogen activator (PA) activities and PA and PA inhibitor (PAI) contents were measured in granulosa (GC) and theca interna cell extracts and follicular fluid (FF) obtained from preovulatory follicles of prepubertal gilts treated with eCG and hCG to induce follicular growth and ovulation. Plasmin activity in FF increased just before the time of expected ovulation. This increase was not attributable to changes in plasminogen levels, which remained relatively constant during preovulatory follicular development. The increase in follicular plasmin levels was associated with significant (p less than 0.01) increases in PA activity and content and decreases in PAI content in GC and FF. Western blot analysis suggested that follicular PA activity was represented principally by two forms of tissue type PA (t-PA) each with a pI of 7.8 and with molecular masses of 72,000 and 78,000 daltons, respectively. Two PA-PAI complexes of 126,000 and 130,000 daltons were observed. These complexes were partially dissociated with nucleophilic agents into two t-PA-like forms and a 52,000-dalton PAI protein with a pI of 4.8. Biochemical characteristics of the PAI protein suggest that it belongs to the same class of inhibitors as bovine and human PAI-1. These data indicate that rupture of the porcine ovarian follicle is temporally associated with a net increase in PA activity and an increase in plasmin activity. The increase in PA activity appears to be regulated by changes in PA and PAI content.

Animals↗
PubMed1990

Effect of somatotropin on the plasminogen and plasmin system in the mammary gland: proposed mechanism of action for somatotropin on the mammary gland.

Somatotropin exerts a powerful galactopoietic effect when it is administered to dairy cattle. The mechanism by which somatotropin increases milk yield is currently unknown. This study describes the relationship between long-term exogenous somatotropin injections, milk plasmin concentrations, and milk yield. Plasmin is a serine-protease involved in rodent mammary gland involution. Thirty-five control cows were shown to increase milk plasmin concentrations and decrease milk yield as their lactation period advanced past the 2nd mo. In 42 somatotropin injected cows, milk plasmin was maintained at low concentrations, and milking performance was enhanced. Cessation of somatotropin injections at drying off led to a rapid elevation of milk plasmin to control values. Our hypothesis is that somatotropin suppresses plasmin production within the mammary gland, thereby suppressing involution and allowing a persistence of milk production. During a normal lactation, gradually increasing amounts of plasmin within the mammary gland results in the gradual involution process.

Animals↗
PubMed1990

Abecarnil, a metabolically stable, anxioselective beta-carboline acting at benzodiazepine receptors.

Abecarnil (isopropyl 6-benzyloxy-4-methoxymethyl-beta-carboline-3-carboxylate) is a novel ligand for central benzodiazepine (BZ) receptors, possessing anxiolytic and anticonvulsant properties, but with considerably reduced muscle relaxant effects in comparison to diazepam (DZP). In vitro, abecarnil inhibited the binding of the BZ [3H]lormetazepam to rat cerebral cortex membranes with an IC50 value of 0.82 nM in comparison to 56 nM for DZP. The ability of abecarnil to displace [3H]lormetazepam was enhanced 1.24-fold in the presence of 30 microM gamma-aminobutyric acid; the corresponding value for DZP was 2.8-fold. DZP and abecarnil were equally effective in enhancing the binding of t-[35S]butylbicyclophosphorothionate to rat cortical membranes. In vivo, abecarnil exhibited a 3- to 6-fold higher affinity to forebrain BZ receptors than DZP. Abecarnil was from 2 to 10 times more potent than DZP in most rodent tests of anxiolytic activity, and in reducing locomotor activity in mice and rats thoroughly habituated to the test chamber. However, in rats newly exposed to a novel cage, abecarnil was less potent than DZP in reducing locomotor activity. In tests of motor coordination, abecarnil, in contrast to DZP, showed no or only weak activity, and in potentiating the effects of ethanol and hexobarbital on motor performance abecarnil was 4 to 25 times less potent than DZP. Abecarnil antagonized the effects of BZs in the chimney and loss of righting reflex tests, but not in the rotarod test.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Plasmin and plasminogen in bovine milk: a relationship with involution?

A total of 774 individual milk samples were collected from 66 Holstein cows between October 1987 and April 1988. Samples were analyzed for plasmin, plasminogen, and SCC. An increase in SCC from less than 250,000/ml to more than 1,000,000/ml resulted in an increase of plasmin, plasminogen, and serum albumin by 105, 74, and 140%, respectively. Plasminogen, plasmin, and serum albumin followed similar trends that are expected for components from blood that gain access to the alveolar lumen through ruptured epithelium caused by mastitis. Increased plasmin is the direct result of this process rather than an increase in activation of plasminogen to plasmin. The plasminogen to plasmin ratio supports this interpretation, being 4.7 at 250,000 SCC/ml and 4.0 when SCC exceeded 1 million/ml. Plasmin and plasminogen concentrations were also increased during lactation to reach peak values immediately before the dry period. However, in this case, ratio of plasminogen to plasmin was 6.55 during early lactation and decreased by half to 3.29 during the latest stage, indicating that considerable activation of plasminogen to plasmin occurred during the latter part of lactation. Mammary epithelium is not compromised at this stage, as shown by low (.8 mg/ml) serum albumin concentration in milk. Two mechanisms responsible for increased milk plasmin include influx of plasmin from blood during mastitis and increased activation of plasminogen as lactation progresses.

Animals↗
PubMed1988

Induction of mRNA for IGF-I and -II during growth hormone-stimulated muscle hypertrophy.

The expression of insulin-like growth factor (IGF) genes during skeletal and cardiac muscle hypertrophy was examined using skeletal and cardiac muscle hypertrophy was examined using adult 5-mo-old female Wistar-Furth rats implanted with growth hormone-secreting GH3 cells. Control and treated animals were killed at 40, 60, and 80 days after initiation of the experiment. From the time of injection to day 80, body, heart, skeletal muscle, and liver weights increased 112, 93, 55, and 314%, respectively. RNA was extracted and steady-state levels of IGF-I and IGF-II mRNAs were quantitated using a solution-hybridization nuclease-protection assay. Low levels of mRNA for both growth factors were detected in control tissues. By day 80 IGF-I mRNA had increased eightfold and IGF-II mRNA sixfold in skeletal muscle from treated rats. In cardiac muscle the levels of mRNA for both growth factors rose three- to fourfold. Although growth hormone induced an increase in hepatic IGF-I mRNA, IGF-II mRNA remained nearly undetectable. This study shows that during growth hormone-stimulated muscle growth mRNAs for both IGF-I and IGF-II accumulate, supporting other observations implicating the IGFs as paracrine or autocrine factors involved in skeletal muscle growth.

Animals↗
PubMed1987

Involvement of endopeptidase 24.15 in the inactivation of bradykinin by rat brain slices.

The effect of peptidase inhibitors on the degradation of [3H]-bradykinin by rat hypothalamic slices was studied using HPLC to separate and identify the products. The degradation appears to be mainly mediated by an enzyme which cleaves the peptide at the Phe5-Ser6 bond and is inhibited by 1,10-phenanthroline, dynorphin(1-13) and carboxyphenylethyl-Ala-Ala-Phe-p-aminobenzoate. This suggest the involvement of a membrane bound variant of the soluble metalloendopeptidase (EC3.4.24.15) isolated from rat brain which degrades neurotensin, angiotensin and other neuropeptides as well as bradykinin.

4-Aminobenzoic Acid↗
PubMed1987

Efflux of putative transmitters from superfused rat brain slices induced by low chloride ion concentrations.

Slices of rat cerebral cortex, preloaded with [14C]gamma-aminobutyric acid (GABA) and either [3H]5-hydroxytryptamine (5-HT) or [3H]noradrenaline, were superfused with media in which varying concentrations of Cl- had been replaced with other monovalent anions. Rapid reduction of [Cl-], by superfusion with media containing instead the impermeant anions propionate, isethionate, gluconate, or methyl sulphate, caused increases in the efflux of tritiated biogenic amines, but the increase in that of [14C]-GABA was not significant. The increased efflux of [3H]5-HT evoked by superfusion with low Cl- levels when propionate was the replacement anion, was transient and was linearly related to the log[Cl-]-1. It was not affected by removal of Ca2+ or by addition of 10 mM Mg2+ and was delayed but not abolished by tetrodotoxin. The low Cl(-)-evoked efflux of [3H]5-HT was not affected by pretreatment with neuronal reuptake blockers but was inhibited by picrotoxin, strychnine, and 4-acetamido-4-isothiocyanostilbene-2,2-disulphonic acid and was enhanced by glycine. Muscimol and GABA were without effect. These observations are taken to indicate that the efflux of biogenic amines is brought about by terminal depolarisation due to outward movement of Cl- in low chloride-containing media. They are of relevance to other physiological and pharmacological studies in which anion concentrations are manipulated and suggest that the anion-evoked release phenomenon may provide a model for the analysis of Cl(-)-dependent mechanisms in nerve terminals.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1986

Interaction between hypersomatotropism and age in the Wistar-Furth rat.

The purpose of this study was to examine body growth parameters and serum somatomedin levels in progressively older rats exposed to high levels of circulating growth hormone (GH). The effects of growth hormone secreting tumors arising from GH3 cell injection were evaluated in 3, 5, 9, 18 and 24 month old female Wistar-Furth rats. In all tumor-bearing rat age groups, body weights were in excess of 70% of age-matched controls. Contributing to these body weight gains were significant increases in heart, liver, kidney and hind limb muscle weights. Fat pads from the tumored groups were similar to controls in the young (3, 5, 9 month) rats but were significantly smaller in the older groups at 18 and 24 months. Elevated GH predictably increased somatomedin levels in young rats while in the 18 and 24 month old groups, smaller increases were noted. These results show that old rats respond to GH in a mechanism involving somatomedin and that significant increases in somatic growth can be obtained, even at advanced age.

Adipose Tissue↗