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1.
Our objective was to investigate the mitogenic response of primary mammary epithelial cells to extracts of mammary parenchyma from 24 prepubertal Friesian heifers treated with placebo or growth hormone at either a low or a high feeding level. The mitogenic responses to mammary extracts were tested by using primary mammary epithelial organoids obtained from prepubertal heifers cultured for 4 to 5 d in collagen gels in serum-free medium supplemented to 5% concentration of the mammary extracts. Cell proliferation was determined using [methyl-3H]thymidine incorporation as a measure of DNA synthesis. High feeding level reduced DNA synthesis in response to mammary extracts. At low feeding level, growth hormone treatment decreased DNA synthesis in response to mammary extracts whereas, at high feeding level, growth hormone increased DNA synthesis in response to mammary extracts. These results suggest that locally produced growth factors are involved in the regulation of mammary development when mammary growth is modulated by feeding level and growth hormone treatment. 相似文献
2.
The objective of this study was to determine the mechanism by which insulin-like growth factor-I (IGF1) stimulates proliferation of mammary epithelial cells, using the bovine mammary epithelial cell line MAC-T as a model. IGF1 significantly up- or down-regulated the expression of 155 genes in MAC-T cells. Among the most significantly suppressed was the gene for connective tissue growth factor (CTGF), a secretory protein that has both proliferative and apoptotic effects and is also a low-affinity binding protein of IGF1. IGF1 inhibited CTGF expression through the PI3K-Akt signaling pathway. Administration of growth hormone (GH), a strong stimulator of IGF1 production in vivo, decreased mammary CTGF mRNA in cattle; however, GH did not affect CTGF expression in MAC-T cells, suggesting that IGF1 may also inhibit CTGF expression in the mammary gland. Added alone CTGF stimulated proliferation of MAC-T cells, but in combination with IGF1 it attenuated IGF1's stimulation of proliferation of MAC-T cells. Excess IGF1 reversed this attenuating effect of CTGF. Despite being an IGF binding protein, CTGF did not affect IGF1-induced phosphorylation of IGF1 receptor (IGF1R) or IGF1R expression in MAC-T cells, indicating that the attenuating effect of CTGF on IGF1 stimulated proliferation of MAC-T cells was not mediated by decreasing IGF1's ability to bind to IGF1R or by decreasing IGF1R expression. Overall, these results suggest a novel biochemical and functional relationship between CTGF and IGF1 in the bovine mammary gland, where IGF1 may inhibit CTGF expression to reduce the attenuating effect of CTGF on IGF1 stimulated proliferation of epithelial cells. 相似文献
3.
Bovine mammary undifferentiated epithelial cells from young female calves, cultured in three-dimensional collagen gels in serum-free medium exhibited ultrastructural organization that resembled the in vivo situation. Extracts of bovine pituitary, kidney, uterus and mammary gland, stimulated cell proliferation in a dose-dependent manner. This mitogenic activity strongly synergised with the existant growth factors (GFs) in FCS and with IGF-I, while the addition of EGF had only minor effect. No synergistic manifestation was found with cholera toxin but pertussis toxin inhibited the growth-promoting activity of all four extracts. Other experiments indicated that this mitogenic activity does not result from prolactin, growth hormone or fibroblast growth factor. The present and former results, in which synergism between IGF-I and cholera toxin was demonstrated, suggest therefore, that the mitogenesis of normal mammary epithelial cells regulated by several tissue derived growth factors, consists of at least two pathways which are distinct from those activated by EGF and IGF-I. One of these pathways indicates involvement of pertussis toxin-sensitive GTP-binding proteins, and the other, activation of cholera toxin-sensitive adenylate cyclase. 相似文献
4.
Although much is known about the endocrine control of bovine mammary development, most heifer work has focused on periods near the time of puberty or during gestation. However, we have found that ovariectomy in the prepubertal period also markedly impacts mammary development well before the onset of estrus would have normally occurred. Interactions between the pituitary and ovary to control udder development are mediated at least in part via alteration in concentrations of local IGF-I axis molecules within the developing mammary gland. For example, in heifers treated with growth hormone or estrogen, expression of IGF-I binding proteins (IGFBP-3) protein was reduced, thus effecting an increase in free IGF-I. Ovariectomized heifers had reduced rates of epithelial cell proliferation, fewer IGF-I receptors, and less local IGF-I. Mammary tissue expression of fibronectin was increased in ovariectomized heifers, but laminin expression was higher in controls. Thus, alterations in specific extracellular matrix proteins likely impact heifer mammary development. As a result, we have initiated calfhood studies. At 30 days of age, it is difficult to detect parenchymal tissue in the udder. Only a thin cord of parenchymal tissue (150 mg per gland) is discernible. By 75 days of age, a rounded, walnut-like mass of mammary parenchymal tissue becomes very evident and at 90 days of age, this mass of tissue has grown to approximately 10 g, a approximately 60-fold increase. At 2 months of age, most proliferating epithelial cells (>92%) are confined to a population of light and intermediate-staining parenchymal cells. Between 2 and 5 months of age, a dark-staining cell population markedly emerges, but these dark cells were rarely labeled with bromodeoxyuridine (BrdU) and are likely to represent a more differentiated or committed cell lineage. The coordinated change in the proportions of each cell type suggests a progression from light-, to intermediate-, to dark-staining cell phenotypes. We are currently focusing on the importance of the ovary and mammary tissue synthesis of estrogens on emergence of specific populations of putative mammary stem cells. 相似文献
5.
Sixteen Hereford and 16 Holstein heifers were used to study the relationship of milk production potential to mammary development and differentiation. Heifers were slaughtered 150, 180, and 260 days of first gestation and at 49 days of first lactation. Prolactin binding capacity of mammary tissue was 2.5 fold higher in dairy than beef heifers at day 260 of gestation (27.2 vs 11.0 fmols/mg protein). In both breeds, maximal growth hormone binding in liver coincided with the beginning of the rapid phase of mammary growth at 180 days. Mammary tissue from dairy heifers released more casein and alpha-lactalbumin during in vitro incubations than tissue from beef heifers. No differences were observed between breeds with respect to incorporation of [14C]acetate into lipids. Mass of dairy mammary tissue at 49 days of lactation was 3.3 times greater (16.4 vs 4.9 kg) and produced 5.7 times more milk (20.3 vs 3.5 kg/day) than its beef counterpart. The total DNA content and the RNA/DNA ratio of lactating dairy mammary tissue was approximately twice that of lactating beef mammary tissue. The data suggested that the higher milk production observed in dairy cattle is a result of a greater number of secretory cells and greater activity per cell. 相似文献
6.
OBJECTIVE: To determine cytotoxic effects of activated polymorphonuclear neutrophils (PMN) and peroxynitrite on bovine mammary secretory epithelial cells before and after addition of nitric oxide synthase inhibitors, myeloperoxidase (MPO) inhibitors, and free-radical scavengers. SAMPLE POPULATION: Polymorphonuclear neutrophils from 3 lactating cows. PROCEDURE: Cells from the bovine mammary epithelial cell line MAC-T were cultured. Monolayers were treated with activated bovine PMN, lipopolysaccharide (LPS), phorbol 12-myristate 13-acetate (PMA), 3-morpholino-sydnonimine (SIN-1), 4-amino-benzoic acid hydrazide (ABAH), NG-monomethyl-L-arginine, histidine, and superoxide dismutase (SOD). At 24 hours, activity of lactate dehydrogenase in culture medium was used as a relative index of cell death. Tyrosine nitration of proteins in MAC-T cell lysates was determined by visual examination of immunoblots. RESULTS: Lipopolysaccharide, PMA, and < or = 0.1 mM SIN-1 were not toxic to MAC-T cells. Activated PMN, > or = 6 mg of histidine/ml, and 0.5 mM SIN-1 were toxic. Together, histidine and 500,000 activated PMN/ml also were toxic. NG-monomethyl-L-arginine did not have an effect, but ABAH decreased PMN-mediated cytotoxicity. Ten and 50 U of SOD/ml protected MAC-T cells from cytotoxic effects of 0.5 mM SIN-1. Compared with control samples, nitration of MAC-T tyrosine residues decreased after addition of 500,000 PMN/ml or > or = 6 mg of histidine/ml. Superoxide dismutase increased and SIN-1 decreased tyrosine nitration of MAC-T cell proteins in a dose-responsive manner. CONCLUSIONS AND CLINICAL RELEVANCE: Peroxynitrite, MPO, and histidine are toxic to mammary secretory epithelial cells. Superoxide dismutase and inhibition of MPO activity mitigate these effects. Nitration of MAC-T cell tyrosine residues may be positively associated with viability. 相似文献
7.
C. Le Jan 《Research in veterinary science》1993,55(3):237
Secretory component (SC) and IgA expression of epithelial cells were studied in the mammary tissue and mammary secretions of sows. In mammary tissue, SC was not detected until day 105 of gestation. From the time of delivery (day 115) to the time of established lactation, the proportion of epithelial cells containing sc rose from 20 per cent to nearly 100 per cent. There was no IgA in alveolar epithelial cells until day 105 of gestation; on day 115, IgA positive epithelial cells were present in 10 per cent of the alveoli, which increased to 80 per cent during lactation. Epithelial cells represented more than 20 per cent of the total cells in colostrum, and predominated over leucocytes in milk. In colostrum, these epithelial cells (9 to 15 μm) showed weakly positive membrane, sc, contained cytoplasmic SC and had a limited capacity for in vitro proliferation. Ten per cent of epithelial cells contained intracytroplasmic IgA. In milk, the epithelial cells were larger (15 to 40 μm) with a higher expression of both membrane and intracytoplasmic sc; 66 per cent of these cells expressed intracytoplasmic IgA. These data showed that the capacity of mammary epithelium to process IgA to secretory IgA was complete at the end of mammary gland organisation, and established that the epithelial cells of milk contribute to the transfer of IgA to neonates. 相似文献
8.
A E Fekry J E Keys A V Capuco J Bitman D L Wood R H Miller 《Domestic animal endocrinology》1989,6(2):87-94
Incorporation of [14C]acetate into lipids was measured in 24 hr co-cultures of mammary, liver and adipose tissue from Holstein cows at 53, 210 and 318 d of lactation in the presence or absence of bovine growth hormone. Little (less than 1%) of the labeled lipids appeared in the media relative to that incorporated into the tissue. In mammary tissue, incorporation of [14C]acetate was highest into triglycerides (16,298 cpm/mg mammary tissue), followed by phospholipids (1,887 cpm), free fatty acids (1,252 cpm), diglycerides (708 cpm), free cholesterol (360 cpm) and monoglycerides (93 cpm). Bovine growth hormone did not increase incorporation of [14C]acetate when mammary or adipose tissue were incubated separately. However, in the presence of liver and adipose tissue, bovine growth hormone significantly increased the incorporation of [14C]acetate into triglycerides, diglycerides, free fatty acids and free cholesterol by mammary tissue. These results suggest that bovine growth hormone acts on mammary tissue indirectly through liver and adipose tissue to increase lipid synthesis. This mechanism may play a role in the action of bovine growth hormone in vivo to increase milk and milk fat production. 相似文献
9.
We have examined the in vitro growth-promoting properties and growth factor content of porcine mammary secretions. Defatted, porcine colostrum stimulated the proliferation of fibroblast and epithelial-like cell lines of diverse species origins in serum-free medium and cellular DNA synthesis (4- to 119-fold) as monitored by uptake of 3H-thymidine into DNA of quiescent cells in culture. Porcine milk, although mitogenic, had reduced activity when compared with colostrum on an equivalent-volume basis. Furthermore, the relative mitogenic activity of milk, although still detectable at 3 wk, continued to decline with length of the lactation period. Fractionation of pig colostrum on gel-filtration columns revealed multiple peaks of (AKR-2B) fibroblast mitogenic activity (208, 66 and 4.6 kdaltons) and a heterogenous profile of epithelial cell mitogenicity. Polyclonal antibodies (IgG) specific for murine epidermal growth factor (EGF; the major mitogen in human and murine milk) or human platelet-derived growth factor (PDGF) did not inhibit the mitogenic activity of pig colostrum or milk, demonstrating lack of antigenic relatedness between the contributing porcine factors and mEGF or hPDGF. Also, we were unable to demonstrate similarity of the small Mr colostral factor with EGF by use of EGF radioreceptor assay. These results identify porcine colostrum and milk as sources of potentially important in vitro growth-promoting factors. The enhanced expression of these factors in early mammary secretions suggests their possible in vivo involvement in mammary and neonatal tissue growth processes. 相似文献
10.
A single epithelium-free mammary fat pad was surgically prepared in each of twenty-five one-month-old, Friesian heifers. At 18 mo of age, heifers were randomly assigned to one of four treatment groups. Treatments were: control (C), growth hormone (GH), estrogen (E) or growth hormone + estrogen (GE). Hormones were administered for 40 hr before the animals were sacrificed to provide mammary samples of parenchyma (PAR), intact fat pad (MFP), and epithelium-free or "cleared" fat pad (CFP). IGF-1 and IGF binding protein-3 (IGFBP-3) mRNA was highest in CFP and MFP whereas the protein products were highest in PAR. IGFBP-2, a 28-kDa IGFBP and a 24-kDa IGFBP were more abundant in CFP and MFP. E and GH increased incorporation of [(3)H]thymidine into DNA of PAR. Incorporation of [(3)H]thymidine into the DNA of MFP or CFP was minimal. Coincident with the changes observed in mammary epithelial proliferation, E increased IGF-1 protein in MFP and PAR, and to a lesser extent in CFP. E tended to increase IGF-1 mRNA levels in MFP, but not CFP implying that the regulation of IGF-1 expression is modulated by adjacent epithelium. GH and E reduced IGFBP-3 protein in PAR and increased the 24-kDa IGFBP in CFP and MFP. Increased proliferation of mammary parenchymal cells was associated with increased IGF-1 and reduced IGFBP-3 protein in mammary tissue. An increase in the ratio of mammary IGF-1: IGFBP-3 likely increases the proportion of the mammary IGF-1 available to stimulate proliferation. These data also indicate that stromal: epithelial interactions regulate the IGF-1 axis in mammary tissue. 相似文献
11.
Quantitative histology of mammary parenchymal tissue from 16 Hereford and 16 Holstein heifers was determined for tissue obtained on day 150, 180, and 280 of gestation and on day 49 of lactation. Percent area occupied by stromal tissue was progressively decreased on each consecutive sample day during gestation in Herefords and was lower in both breeds during lactation. Overall, area occupied by stromal tissue elements was also greater in Herefords. Percent lumenal space and number of cells per alveolar cross section was consistently greater for Holsteins and increased across sample periods in both breeds. During lactation more than 40% of the alveolar cells in Herefords were characterized as poorly differentiated, but in Holstein heifers nearly all of the cells were classified as either intermediate or fully differentiated. These data provide additional evidence to support the idea that much of the difference in milk production between beef and dairy animals depends on increased mammary function. Whether differences in milk production within dairy breeds are also explained by altered cellular differentiation remains to be determined. 相似文献
12.
13.
Z. Wicik M. Gajewska A. Majewska D. Walkiewicz E. Osińska T. Motyl 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2016,133(1):31-42
MicroRNAs (miRNAs) are small non‐coding RNAs that participate in the regulation of gene expression. Their role during mammary gland development is still largely unknown. In this study, we performed a microarray analysis to identify miRNAs associated with high mammogenic potential of the bovine mammary gland. We identified 54 significantly differentially expressed miRNAs between the mammary tissue of dairy (Holstein‐Friesian, HF) and beef (Limousin, LM) postpubertal heifers. Fifty‐two miRNAs had higher expression in the mammary tissue of LM heifers. The expression of the top candidate miRNAs (bta‐miR‐10b, bta‐miR‐29b, bta‐miR‐101, bta‐miR‐375, bta‐miR‐2285t, bta‐miR‐146b, bta‐let7b, bta‐miR‐107, bta‐miR‐1434‐3p) identified in the microarray experiment was additionally evaluated by qPCR. Enrichment analyses for targeted genes revealed that the major differences between miRNA expression in the mammary gland of HF versus LM were associated with the regulation of signalling pathways that are crucial for mammary gland development, such as TGF‐beta, insulin, WNT and inflammatory pathways. Moreover, a number of genes potentially targeted by significantly differentially expressed miRNAs were associated with the activity of mammary stem cells. These data indicate that the high developmental potential of the mammary gland in dairy cattle, leading to high milk productivity, depends also on a specific miRNA expression pattern. 相似文献
14.
Comparison of phagocytosis and chemiluminescence by blood and mammary gland neutrophils from multiparous and nulliparous cows 总被引：3，自引：0，他引：3
Neutrophils were isolated from the blood and mammary gland of 3 multiparous lactating cows and 3 nulliparous heifers. Neutrophil function was evaluated by phagocytosis and luminol-dependent chemiluminescence. Peroxidase activity was detected by use of transmission electron microscopy. Compared with that for blood neutrophils, percentage of phagocytosis was 9.6% lower for neutrophils isolated from the mammary gland of lactating cows, but this difference was not observed between neutrophils isolated from the mammary gland and from the blood heifers. Similarly, after subtraction of chemiluminescence values in the absence of zymosan, phagocytosing neutrophils from the mammary gland of lactating cows had lower chemiluminescence than did those from the blood of such cows. For heifers, however, chemiluminescent activity by phagocytosing neutrophils obtained from the mammary gland was similar to that of blood neutrophils. Chemiluminescent activity of resting neutrophils from the mammary gland of lactating cows pretreated with cytochalasin B was not inhibited, compared with that of nontreated resting neutrophils (controls). This was attributed to xanthine oxidase activity. Transmission electron microscopy of mammary gland neutrophils from lactating cows revealed peroxidase-positive material associated with milk-fat globule membranes and with phagosomes containing zymosan. Results indicated that ingestion of fat and casein by neutrophils isolated from milk caused a decrease in phagocytic and chemiluminescent activity. Also, luminol-dependent chemiluminescence was not a reliable measure of milk neutrophil function, because of interference by xanthine oxidase. 相似文献
15.
Neumann JL Lazaris A Huang YJ Karatzas C Ryan PL Bagnell CA 《Domestic animal endocrinology》2006,31(2):173-185
Relaxin is a peptide hormone produced by a wide variety of mammals. In the horse, the placenta is the major source of relaxin. Since pure equine relaxin is difficult to obtain to study its role in the pregnant mare, the objectives of this study were to produce recombinant equine prorelaxin and characterize its immunological and biological activity. First, an equine relaxin gene cassette was transfected into immortalized bovine mammary epithelial (MAC-T) cells. Second, immunological activity of media conditioned by transfected MAC-T cells was tested by Western blotting and quantified using a homologous equine radioimmunoassay. Finally, bioactivity of the conditioned media was tested using the human monocyte cell line, THP-1, which exhibits a rapid and dose-dependent increase in the accumulation of cAMP upon binding relaxin. The results showed that conditioned media, concentrated 5x, yielded 4.11 +/- 0.81 ng/ml recombinant equine prorelaxin. In addition, a 19 kDa immunoreactive band, corresponding to the expected size of equine prorelaxin, was visualized by SDS-PAGE. THP-1 cells incubated with conditioned media (5x) from transfected cells, in the presence of forskolin (1 microM) and isobutylmethylxanthine (50 microM), showed an increase in cAMP production over media from mock-transfected cells alone. In conclusion, recombinant equine prorelaxin secreted by MAC-T cells was both immunologically and biologically active. This study demonstrates the first attempt to produce recombinant equine prorelaxin, important for further study of the role of relaxin in the mare. 相似文献
16.
Rysánek D Babák V Sládek Z Toman M 《Journal of veterinary medicine. B, Infectious diseases and veterinary public health》2001,48(1):31-41
The phenotypic characteristics are described for the activity of polymorphonuclear leucocytes NMN) obtained by either lavage of the cavity system of juvenile mammary glands stimulated with a synthetic muramyl dipeptide analogue or isolation from the peripheral blood. Attention was paid to the variability of characteristics and its sources, and to correlations among them. The following characteristics were investigated in 27 clinically healthy, unbred Bohemian Red Pied x Holstein heifers: migration activity in situ, number of phagocytosing PMN, phagocytotic index, bactericidal activity of PMN and unstimulated and zymosan-stimulated luminol-dependent chemiluminescence. Considerable individual variation was found in the characteristics. Significant differences between blood PMN and PMN from lavages after influx induction were found for bactericidal activity (P < 0.05) and chemiluminescence (P < 0.01). A significant correlation between blood PMN and mammary gland PMN was found only for the number of phagocytosing cells (r = 0.329; P < 0.01). Highly significant positive correlations (P < 0.01) were demonstrated between the number of phagocytosing PMN [a], phagocytotic index [b], and bactericidal activity [c] in both blood PMN (r(ab) = 0.602; r(ac) = 0.565; r(bc) = 0.529) and mammary gland PMN (r(ab) = 0.730, r(ac) = 0.618, r(bc) = 0.589). No significant correlation was demonstrated for non-stimulated (NS), zymosan-stimulated (ZS), or opsonized zymosan-stimulated (OZS) chemiluminescence with any of the other characteristics of phagocytotic activity, in either blood PMN or mammary gland PMN (P > 0.05). The animal was a highly significant source of variability for all the phagocytotic activity characteristics (P < 0.01). Udder quarter was a non-significant source of variability for all the characteristics of phagocytotic activity except for NS chemiluminescence (P < 0.05) and ZS or OZS chemiluminescence (P < 0.01). However, udder quarter was a non-significant source of variability of chemiluminescence indices ZS/NS and OZS/NS (P > 0.05). It has been demonstrated that in situ migration activity, the number of phagocytosing PMN, phagocytotic index, bactericidal activity of PMN and chemiluminescence indices of PMN collected from juvenile mammary glands of unbred heifers after influx induction can be regarded as candidate early markers of resistance to mammary infections. 相似文献
17.
The aim of this study was to evaluate the effect of a dopamine antagonist, domperidone, in nonpregnant, reproductively cycling heifers consuming endophyte-infected (EI) fescue diets. Thirty crossbred heifers (Angus x Holstein or Hereford x Holstein) were assigned to one of three treatment groups (n = 10); endophyte-free (EF) fescue diet, EI fescue diet, or endophyte-infected diet and treated with domperidone (EID). Heifers fed EI diets had decreased weight gains compared with heifers fed EF or EID (P < 0.05) during a 21-d treatment period. Ovarian structures were monitored via transrectal ultrasound to determine follicle size and day of ovulation. Blood plasma samples were collected daily and analyzed for progesterone concentration to determine luteal function. Heifers ingesting EI diets had estrous cycles of shorter duration and lower mid-cycle progesterone concentrations than heifers in the EF or EID treatments (P < 0.05). Ovaries from a subset of heifers in each group (n = 3 per group) were harvested and in vitro secretion of progesterone from luteal tissue extracts was determined. No differences in progesterone concentrations were detected among luteal tissue incubates (P > 0.05). These results suggest that domperidone supplementation of heifers consuming EI fescue may ameliorate certain symptoms of fescue toxicosis. 相似文献
18.
Several experimental parameters were examined to determine optimal conditions for proliferative responses of mammary mononuclear cells (MMC) obtained from six nonlactating dairy cows. These parameters were: pre-incubation of cells in medium prior to assay, mitogen concentration, assay incubation time, and type of culture medium. Response variables included viability of cells and the rate of proliferation as assessed by tritiated thymidine incorporation. Pre-incubation of cells in medium had no effect on the proliferative response of MMC. Whereas Concanavalin A (ConA; 3.3 or 6.6 micrograms/ml) and phytohemagglutinin (PHA; 1, 5, 10 micrograms/ml) did stimulate proliferation of MMC, the higher doses did not stimulate greater proliferation than the lower doses of mitogens. The greatest mitogenic response was obtained on days 2 and 3 of incubation. Proliferative responses were significantly higher at all mitogen levels tested in a 50-50 mixture of Rosewell Park Memorial Institute medium 1640 and Liebovitz-15 medium (RPMI/L-15) than in RPMI alone. Viability of MMC was also significantly higher in the RPMI/L-15 medium. To test whether the significant effect of media on blastogenesis was specific for mononuclear cells from the bovine mammary gland, peripheral blood lymphocytes (PBL) from four dairy cows were cultured with ConA and PHA in a mitogen assay in both RPMI and RPMI/L-15. Viability was measured on day of collection and on all culture days. PBL were stimulated equally in both media. PBL viability decreased significantly on day 1 in both RPMI and RPMI/L-15. These results suggest that the optimal culture conditions for blastogenic responses of mammary mononuclear cells and peripheral blood lymphocytes may differ. 相似文献
19.
Bovine mammary tissue obtained from midpregnant Holstein heifers by surgical biopsy was transplanted subcutaneously to ovariectomized athymic nude mice (n = 5 heifers). After 3 weeks recovery, mice were either sham operated or sialoadenectomized (submandibular salivary glands removed). After an additional week, mice were injected with saline or 17 beta-estradiol + progesterone (1 microgram + 1 mg/day) for 2 days. In addition, half of the sialoadenectomized mice were injected with epidermal growth factor (5 micrograms/day). Grafted tissue was removed and rate of deoxyribonucleic acid (DNA) synthesis estimated by incorporation of 3H thymidine. Estradiol + progesterone increased the incorporation of 3H thymidine from 77 +/- 20 dpm/micrograms DNA to 472 +/- 53 dpm/micrograms DNA. In sialoadenectomized mice, DNA synthesis was increased from 88 +/- 16 dpm/micrograms DNA (saline treated) to 360 +/- 29 dpm/micrograms DNA (estradiol + progesterone treated). In sialoadenectomized mice treated with epidermal growth factor, DNA synthesis in estradiol + progesterone treated mice was 529 +/- 36 dpm/micrograms DNA, compared to 112 +/- 30 dpm/micrograms DNA in sialoadenectomized mice treated with epidermal growth factor. These data indicate that sialoadenectomy of athymic nude mice decreased the ability of transplanted bovine mammary tissue to increase DNA synthesis in response to estradiol and progesterone. This inhibition was removed by epidermal growth factor treatment. These data suggest a physiological role of epidermal growth factor in regulating development and hormone responsiveness of bovine mammary tissue. 相似文献
20.
Capuco AV Ellis SE Hale SA Long E Erdman RA Zhao X Paape MJ 《Journal of animal science》2003,81(Z3):18-31
A persistent lactation is dependent on maintaining the number and activity of milk secreting cells with advancing lactation. When dairy cows are milked twice daily, the increase in milk yield from parturition to peak lactation is due to increased secretory activity per cell rather than to accretion of additional epithelial cells. After peak lactation, declining milk yield is due to loss of mammary epithelial cells by apoptosis. During lactation, only 0.3% of mammary cells proliferate in a 24-h period. Yet this proliferative rate is sufficient to replace most mammary epithelial cells by the end of lactation. Management practices can influence lactation persistency. Administration of bovine somatotropin may enhance persistency by increasing cell proliferation and turnover, or by reducing the rate of apoptosis. Increased photoperiod may also increase persistency of lactation by mechanisms that are as yet undefined. Increased milking frequency during the first weeks of lactation increases milk yield, even after return to less frequent milking, with increases of approximately 8% over the entire lactation. A mammary cell proliferation response to frequent milking during early lactation appears to be involved. Conversely, advanced pregnancy, infrequent milking, and mastitis increase death of epithelial cells by apoptosis. Regulation of mammary cell renewal provides a key to increasing persistency. Investigations to characterize epithelial cells that serve as the proliferative population in the bovine mammary gland have been initiated. Epithelial cells that stain lightly in histological sections are evident through all phases of mammary development and secretion and account for nearly all proliferation in the prepubertal gland. Characterization of these cells may provide a means to regulate mammary cell proliferation and thus to enhance persistency, reduce the effects of mastitis, and decrease the necessity for a dry period. 相似文献