Role of tissue remodeling in mammary epithelial cell proliferation and morphogenesis

miR-145 Modulates Fatty Acid Metabolism by Targeting FOXO1 to Affect SERBP1 Activity in Bovine Mammary Epithelial Cells

MicroRNA-mediated gene regulation is important for the regulation of fatty acid metabolism and synthesis. Our previous study uncovered that the miR-145 expression is higher in the lactating mammary gland of dairy cows than in the dry-period, but the underlying molecular mechanism is incompletely understood. In this study, we have investigated the potential role of miR-145 in bovine mammary epithelial cells (BMECs). We found that the expression of miR-145 gradually increased during lactation. CRISPR/Cas9-mediated knockout (KO) of miR-145 in BMECs results in the downregulated expression of fatty acid metabolism-associated genes. Further results revealed that miR-145 KO reduced total triacylglycerol (TAG) and cholesterol (TC) accumulation and altered the composition of intracellular fatty acids (C16:0, C18:0, and C18:1). Conversely, miR-145 overexpression had the opposite effect. Bioinformatics online program predicted that miR-145 targets the 3'-UTR of the Forkhead Box O1 (FOXO1) gene. Subsequently, FOXO1 was identified as a direct target of miR-145 by qRT-PCR, Western blot analysis, and luciferase reporter assay. Furthermore, siRNA-mediated silencing of FOXO1 promoted fatty acid metabolism and TAG synthesis in BMECs. Additionally, we observed the involvement of FOXO1 in the transcriptional activity of the sterol regulatory element-binding protein 1 (SREBP1) gene promoter. Overall, our findings indicated that miR-145 relieves the inhibitory effect of FOXO1 on SREBP1 expression by targeting FOXO1 and subsequently regulating fatty acid metabolism. Thus, our results provide valuable information on the molecular mechanisms for improving milk yield and quality from the perspective of miRNA-mRNA networks.

Evaluation of biological mechanisms of artemisinin on bovine mammary epithelial cells by integration of network pharmacology and TMT-based quantitative proteomics

The sesquiterpene lactone, artemisinin, is a primary component of the medicinal plant Artemisia annua L., which has anti-inflammatory, antibacterial and antioxidant activities. However, the potential effects of artemisinin on the mammary gland of dairy cows and the underlying molecular mechanisms remain unclear. Here, we utilized systematic network pharmacology and proteomics to elucidate the mechanism by which artemisinin affects milk production and the proliferation of bovine mammary epithelial cells (BMECs). Nineteen bioactive compounds and 56 key targets were identified through database mining. To delineate the mechanism of artemisia’s activity, a protein-protein interaction network and integrated visual display were generated from bioinformatics assays to explore the relationships and interactions among the bioactive molecules and their targets. The gene ontology (GO) terms and kyoto encyclopedia of genes and genomes annotation suggested that the apoptotic process, cell division, p53 pathway, prolactin and PI3K-Akt pathways played vital roles in mammary gland development. Using proteomics analysis, we identified 122 up-regulated and 96 down-regulated differentially significant expressed proteins (DSEPs). The differentially significant expressed proteins had multiple biological functions associated with cell division, apoptosis, differentiation, and migration. Gene ontology enrichment analysis suggested that differentially significant expressed proteins may promote cell proliferation and regulate apoptosis in bovine mammary epithelial cells. Kyoto encyclopedia of genes and genomes pathway analysis indicated that several biological pathways, such as those involved in antigen processing and presentation, cell adhesion molecules and ribosomes, played significant roles in the effects of artemisinin on bovine mammary epithelial cells. These findings contribute to a comprehensive understanding of the mechanism by which artemisinin affects bovine mammary epithelial cells to improve mammary gland turnover by inducing cell proliferation and mammary gland development.

Three lactation-related hormones: Regulation of hypothalamus-pituitary axis and function on lactation

The endocrine system plays a central role in many aspects of lactation, including mammogenesis (mammary gland development), lactogenesis (onset of lactation), and galactopoiesis (maintenance of milk secretion). Many hormones of the endocrine system directly or indirectly regulate lactation process. The secretion of prolactin (PRL), one of the most important lactation-related hormones, is inhibited by hypothalamus-pituitary dopaminergic system and stimulated by hypothalamus-pituitary oxytocinergic system. This hormone is essential in all stages of lactation. The growth hormone (GH) regulates metabolism and the distribution of nutrients between tissues mammary glands, and stimulates the production of IGF-I from the liver which binds to IGF-IR of mammary epithelial cells (MECs) to indirectly promote lactation. The synthesis and secretion of estrogen (E) are affected by the hypothalamus-pituitary axis. The hormone regulates duct morphogenesis and MECs proliferation. It also modulates the synthesis and secretion of PRL and GH, which together regulate the lactation in female animals. In this article, we reviewed the three main lactation-related hormones (PRL, GH, and E), summarize their regulation by the hypothalamus-pituitary axis and how they influence lactation.

MiR-21-3p Centric Regulatory Network in Dairy Cow Mammary Epithelial Cell Proliferation

MicroRNA-mediated gene regulation is important for the development of the mammary gland and the lactating process. A previous study has shown that the expression of microRNA-21 (miR-21) is different in the dry and early lactation period of the dairy cow mammary gland, but the molecular mechanisms underlying the lactation cycle are not fully understood. Here, the function of miR-21-3p on bovine mammary gland epithelial cells (BMECs) was detected by MTT assay and flow cytometry analysis, which showed that miR-21-3p significantly promoted the cell viability and proliferation. Then, the regulating mechanism of miR-21-3p on cell viability and proliferation was elucidated. Dual luciferase assay, RT-qPCR, and Western blot results revealed that IGFBP5 was a target gene of miR-21-3p. It was known that lncRNA could act as a competing endogenous RNA to sequester miRNAs and reduce the regulatory effect of miRNA-targeted genes. Based on our previous lncRNA-seq data and bioinformatics analysis, lncRNA NONBTAT017009.2 was potentially associated with miR-21-3p, and its expression was specifically inhibited with the transfection of miR-21-3p mimic into BMECs. Inversely, the overexpression of NONBTAT017009.2 significantly decreased the expression level of miR-21-3p in BMECs, while the expression of IGFBP5, the target gene of miR-21-3p, was significantly upregulated. In addition, the promoter region of miR-21 contained two STAT3 binding sites, and the dual luciferase reporter assays revealed that the overexpression of STAT3 significantly reduced the promoter activity of miR-21, implying that the transcription factor STAT3 may act as an upstream regulator affecting the regulation process of miR-21-3p. The overexpression of STAT3 significantly inhibited the expression of miR-21-3p, while the mRNA expression of IGFBP5 was significantly increased compared with the control group. Besides, there are no STAT3 binding sites in the promoter region of IGFBP5 as we predicted by gene-regulation and JASPAR software. Therefore, it could infer that STAT3 might regulate the expression of IGFBP5 by miR-21-3p. Taken together, these results established a regulatory network of miR-21-3p to illustrate the regulating mechanism on promoting cow mammary epithelial cell proliferation.

Evidence for a Role of Prolactin in Mediating Effects of Photoperiod during the Dry Period

Photoperiod manipulation during the lactation cycle alters milk yield, with long days (LDPP) increasing yield in lactation and short days (SDPP) in the dry period improving subsequent yield. Circulating prolactin (PRL) is directly related to day length, with LDPP increasing and SDPP decreasing PRL, respectively. Two blocks of 24 multiparous Holstein cows were used during two consecutive years to test the hypothesis that the mammary response to SDPP is the result of decreased concentrations of PRL in the circulation relative to LDPP. Cows were randomly assigned to one of three treatment groups during the dry period: SDPP, LDPP, or SDPP+PRL. Cows were returned to ambient photoperiod at calving and milk yield and DMI recorded for 120 d and 42 d, respectively. Mammary biopsies were obtained to determine rates of [³H]-thymidine incorporation into DNA in vitro. Treatment of SDPP cows with PRL caused a rapid increase in systemic PRL that reached concentrations similar to cows under LDPP. The periparturient PRL surge was similar for LDPP and SDPP+PRL cows, but those groups had greater surge concentrations versus SDPP. Cows exposed to SDPP produced more milk than LDPP cows, and there was a trend for SDPP+PRL cows to produce more milk than LDPP cows. Milk production was inversely related to the periparturient PRL surge. There was a trend for a treatment effect on mammary cell proliferation with greater proliferation in mammary tissue of SDPP cows relative to LDPP or SDPP+PRL on day −20 relative to parturition. Replacement of PRL to cows on SDPP when dry resulted in milk yield intermediate to cows on SDPP or LDPP, supporting the concept of a link between dry period PRL and yield.

The Expression Pattern of MicroRNAs and the Associated Pathways Involved in the Development of Porcine Placental Folds That Contribute to the Expansion of the Exchange Surface Area

The development of the microscopically folded structure of the diffuse epitheliochorial placenta in pigs is important because it expands the surface area for maternal-fetal exchange, resulting in an increase in placental efficiency. To better understand the regulatory mechanisms involved in this process, we characterized miRNA expression profiles in porcine placentas during the initiation and establishment of placental fold development. A total of 42 miRNAs were found to be differentially expressed, and their putative target genes were predicted using four target prediction programs. Following a comparative analysis with published gene expression pattern data obtained from porcine placentas in the corresponding stages of placental fold development, only those genes that were negatively correlated with miRNA expression were retained for further function and pathway enrichment analysis. The results showed that the up-regulated miRNAs were associated mainly with extracellular matrix remodeling and tissue morphogenesis, while the down-regulated miRNAs were related to cell proliferation and signal transduction. Furthermore, we provide evidence that miR-130b may facilitate the expression of HPSE, which has been reported to be a regulator of the folding of the pig placenta, by suppressing the expression of PPARG. In addition, we also reveal that the miRNA-target pairs expressed in the pig placenta may trigger the degradation of the stromal matrix and basement membrane (miR-29a-COL1A2, COL3A1, and LAMC1) and regulate trophoblast epithelial cell adherens junctions (the miR-200 family and miR-205-ZEB2-CDH1) and proliferation (miR-17-92 cluster-HBP1 and ULK1). Taken together, these results indicate that miRNAs and related pathways may have potential roles in porcine placental fold development.

Morphogenesis of Mammary Glands in Buffalo (Bubalus bubalis)

The present research was elucidated on the morphogenesis of mammary gland of buffalo during prenatal development. Total of 16 foetuses ranging from 1.2 cm (34 days) to 108 cm CVRL (curved crown rump length) (317 days) were used for study. The study revealed that mammary line was first observed at 1.2 cm CVRL (34 days), mammary hillock at 1.7 cm (37 days), and mammary bud at 2.6 cm CVRL (41 days) foetuses. Epidermal cone was found at 6.7 cm CVRL (58 days) whereas primary and secondary ducts were observed at 7.4 cm CVRL (62 days) and 15 cm CVRL (96 days), respectively. Connective tissue whorls were reported at 18.2 cm CVRL (110 days) and internal elastic lamina and muscle layers at 24.1 cm CVRL (129 days). Lobules were observed at 29.3 cm CVRL (140 days), rosette of furstenberg at 39.5 cm CVRL (163 days), and keratin plug at 45.5 cm CVRL (176 days) foetus. Primordia of sweat and sebaceous glands around hair follicle were seen at 21.2 cm CVRL (122 days) of foetal life. Differentiation of all the skin layers along with cornification was observed at 69 cm (229 days) in group III foetuses.

Target Gene and Function Prediction of Differentially Expressed MicroRNAs in Lactating Mammary Glands of Dairy Goats

MicroRNAs are small noncoding RNAs that can regulate gene expression, and they can be involved in the regulation of mammary gland development. The differential expression of miRNAs during mammary gland development is expected to provide insight into their roles in regulating the homeostasis of mammary gland tissues. To screen out miRNAs that should have important regulatory function in the development of mammary gland from miRNA expression profiles and to predict their function, in this study, the target genes of differentially expressed miRNAs in the lactating mammary glands of Laoshan dairy goats are predicted, and then the functions of these miRNAs are analyzed via bioinformatics. First, we screen the expression patterns of 25 miRNAs that had shown significant differences during the different lactation stages in the mammary gland. Then, these miRNAs are clustered according to their expression patterns. Computational methods were used to obtain 215 target genes for 22 of these miRNAs. Combining gene ontology annotation, Fisher's exact test, and KEGG analysis with the target prediction for these miRNAs, the regulatory functions of miRNAs belonging to different clusters are predicted.

The cellular perspective on mammary gland development: stem/progenitor cells and beyond

Study of the mammary gland at the stem cell level is necessary for understanding mammary gland development. Knowledge of mammary gland development and growth is the first step toward formulating strategies to improve milk production. The success of these strategies requires an understanding of the dynamics of adult stem cells and their progeny in the development of the bovine mammary gland. The stem cell lineage pathway begins with adult stem cells and ends with the production of terminally differentiated cells. The progression of adult stem cells along the mammary gland stem cell lineage pathway requires the coordination of many events. One important event in this process is cell differentiation. This differentiation process evolves with a gradient appearance of cell organelles progressing from stem cells to terminally differentiated cells. To dissect differentiation, mechanisms that regulate stem cells to differentiate toward a particular cell fate must be identified. Ultrastructural characteristics assist in distinguishing cells in various stages of differentiation in the mammary gland cell lineage pathway. Cells in the lineage pathway can become either epithelial cells or myoepithelial cells. Epithelial cells function in the production and secretion of milk, whereas myoepithelial cells assist epithelial cells in milk secretion. This review focuses on current concepts regarding adult stem cells and the recent progress on bovine mammary gland stem/progenitor cell development and differentiation. Multistep strategies that incorporate manipulation of the mechanisms influencing lineage choices in the mammary gland will produce beneficial effects on mammary gland development and milk production.

Exposure to Short Day Photoperiod During the Dry Period Enhances Mammary Growth in Dairy Cows

Exposure to short day photoperiod (SD; 8 h light:16 h dark) during the dry period increased milk yield of cows in the subsequent lactation. We hypothesized that this effect is due to increased growth of mammary cells in response to enhanced prolactin signaling to influence the insulin-like growth factor (IGF) axis. Multiparous Holstein cows were dried off 60 d before parturition and assigned to long day photoperiod (LD; 16 h light:8 h dark) or SD during the dry period. Mammary biopsies were obtained at approximately -40, -20, -10 and +10 d relative to expected calving. Expression of IGF-I, IGF-II, and IGF binding protein-5 mRNA was assessed by real time reverse transcription-polymerase chain reaction. In SD cows, incorporation of [3H]-thymidine in vitro increased from -40 d to -20 d and was greater at -20 d than in LD cows. A later increase in proliferation was observed at -10 d in LD cows. For both groups, cell proliferation decreased during lactation. Analysis by terminal deoxynucleotidyl transferase dUTP nick end labeling revealed that the apoptotic index in mammary epithelial cells was less in SD cows than in LD cows. Expression of IGF-II mRNA increased during the dry period and into lactation and was greater in SD cows. Expression of IGF binding protein-5 mRNA increased during lactation, but was unaffected by day length. Expression of IGF-I did not differ over time or between treatments. We concluded that exposure to SD during the dry period enhanced mammary growth relative to LD, and this may be related to increased expression of IGF-II. Treatment differences in the temporal pattern of proliferation indicated the existence of a critical period wherein photoperiod affects mammary gland development during the dry period.

Correlation of blood and milk components with the milk yield response to bovine somatotropin in dairy cows

Our aim was to correlate the individual variation in the milk yield response (MYR) of Holstein dairy cows to bovine somatotropin (bST), with changes in milk plasmin and plasminogen activities as well as with plasma hormone and metabolite levels. Thirty-two housed multiparous Holstein cows (90 +/- 3.8 days post partum) received daily subcutaneous injections of saline for 1 week followed by subcutaneous injections of 20 mg/day of bST for 2 weeks. Blood samples were taken at approximately 4h intervals over 24 h at the end of the saline and bST treatment periods. Milk samples were also taken at the end of the saline and bST treatment periods. The difference in milk yield between the saline and the second week of bST treatment (MYR) varied considerably between animals (from -0.2 to +8.6 kg/day, relative to the saline treatment week). Low milk yield before bST treatment was associated with a high MYR. The plasma growth hormone response to treatment was negatively correlated with MYR. Plasma insulin-like growth factor-1 response to treatment was positively correlated with MYR. Furthermore, a high MYR to bST was associated with a lower milk plasminogen level before treatment and a greater reduction in the level of plasminogen in milk following treatment.

Bovine somatotropin administration to dairy goats in late lactation: effects on mammary gland function, composition and morphology

We investigated the effects of bovine somatotropin (bST) on mammary gland function and composition in the declining phase of lactation in goats. Sixteen Saanen goats, 180 +/- 11 days in milk (DIM), were divided equally into control and treated groups. The treated group received 120 mg/2 wk of slow-release bST for three cycles. Milk yield, milk composition, milk clotting measures, and plasmin-plasminogen activator activities were recorded weekly. Milk Na and K were determined in individual milk samples collected weekly during the third cycle. Blood samples were collected weekly during the second cycle and the plasma analyzed for nonesterified fatty acids (NEFA), glucose, and urea. At the end of the 6 wk, three goats from each group were slaughtered, and the udders were removed. Mammary gland weight, composition, and total DNA content were determined. The histological effects of bST on mammary tissue were investigated. The analyzed parameters included numbers of alveoli, corpora amylacea, apoptotic cells, and laminin fibronectin distribution and localization. An extensive morphological analysis on the epithelial and stromal components was performed. Milk yield was significantly higher in the treated group, fat content was not affected, but protein and nonprotein nitrogen were lower in treated goats milk. Treatment with bST did not influence milk pH but reduced coagulation time. Plasmin and plasminogen activator activities were not affected. Milk K levels were higher and the Na/K ratio was lower in treated animals. Plasma glucose, NEFA, and urea were unaffected. Mammary gland weight and total DNA were higher in treated than control animals, suggesting that with advancing lactation bST treatment maintains cells. Fat, protein, and collagen content of the mammary tissue did not differ between the groups. Treatment with bST significantly increased the number of lactating alveoli (LA) and significantly reduced the number of regressing alveoli (RA) and corpora amylacea, both within and outside the alveolar lumen. Laminin and fibronectin localization were not affected, and very few apoptotic cells were found in both treated and control samples. Our findings suggest that bST administration to dairy goats in late lactation can modulate mammary gland activity and improve lactation persistency; this is associated with maintained total mammary parenchyma weight and lactating alveoli.

Immunohistochemical expression of nm23 in primary invasive malignant melanoma is predictive of survival outcome

The objective of this study was to determine the utility of nm23 as an immunohistochemical indicator of prognosis in a large series (157 cases) of malignant melanoma and also in two subsets within this group: stage 1 tumours, whether in radial or vertical growth phase (140 cases); and stage 1 tumours in which a vertical growth phase component was positively identified (123 cases). A secondary objective was to explore the relationship between the immunohistochemical expression of nm23 and established clinical and histological indicators of prognosis in each of these three groups. In all groups it was found that strong immunoreactivity correlated positively with survival and inversely with indicators of poor prognosis, in keeping with transfection and mRNA studies and also with many immunohistochemical studies of other tumour types. That these findings are at variance with earlier reported immunohistochemical studies of melanoma highlights the importance of large case numbers of primary invasive tumours in studies which set out to explore the relationship between immunoreactivity and survival.

Temporal expression of urokinase plasminogen activator, plasminogen activator inhibitor and gelatinase-B in chronic wound fluid switches from a chronic to acute wound profile with progression to healing

The plasminogen activator/plasmin system is known to initiate a proteolytic cascade resulting in the activation of matrix metalloproteinases in vitro leading to the degradation of extracellular matrix. To investigate whether or not this cascade is present during delayed wound healing and contributes to the pathophysiological basis of impaired healing we examined the temporal expression of urokinase plasminogen activator, plasminogen activator inhibitor-1 and gelatinase-B in fluid collected from chronic venous leg ulcers compared to acute surgical mastectomy wounds. Using a chromogenic substrate assay, levels of active urokinase plasminogen activator in chronic wounds were found to be about five fold higher compared to sera and two fold higher compared to mastectomy wounds. Levels of active plasminogen activator inhibitor-1 in chronic wounds were four times higher than those found in sera and two times higher than those found in mastectomy wound fluid. Using a fibrin overlay system and reverse zymography, we found that when the wound was not healing, the expression of urokinase plasminogen activator in chronic wound fluid was initially detected in the active forms (50 and 33 kDa), but that as the wound healed and decreased in size, was detected as an inhibitor- bound urokinase plasminogen activator-plasminogen activator inhibitor-1 complex ( congruent with 80-116 kDa). When the expression of active urokinase plasminogen activator was highest, no plasminogen activator inhibitor-1 was detectable. In contrast, urokinase plasminogen activator was always detected in the inhibitor bound form as a urokinase plasminogen activator-plasminogen activator inhibitor-1 complex in blood- and plasma-derived serum and mastectomy wound fluid. Plasminogen activator inhibitor-1 was detected in blood-derived serum and mastectomy wound fluid but not in plasma derived serum. Expression of matrix metalloproteinase-9 in chronic wound fluids, analyzed by gelatin zymography, showed that when urokinase plasminogen activator was detected in the active forms, matrix metalloproteinase-9 was overexpressed by approximately twice that found in mastectomy wounds and approximately 30 times that detected in blood-derived sera. When urokinase plasminogen activator appeared almost entirely as an enzyme- inhibitor complex, the level of expression of matrix metalloproteinase-9 was similar to that seen in mastectomy wound fluid. We conclude that the switch in urokinase plasminogen activator expression from an active to inhibitor bound form correlates with the decrease seen in matrix metalloproteinase-9 expression suggesting the presence of a proteolytic cascade initiated by the plasminogen activator/plasmin system during wound healing leading to the activation of matrix metalloproteinase-9. In addition, expression of urokinase plasminogen activator and matrix metalloproteinase-9 appear to be useful biomarkers to determine clinical wound healing status.

Milk plasmin during bovine mammary involution that has been accelerated by estrogen

The purpose of this study was to evaluate whether the plasminogen and plasmin system within bovine mammary secretions was influenced by an estrogen treatment that was used to accelerate mammary tissue involution. Holstein cows were injected with 4 ml of ethanol excipient (n = 21) or 15 mg of estradiol-17 beta (n = 23) on each of the 4 d that preceded final milk removal. Dates of final milk removal (d 0) were designated as 60 d prior to expected dates of calving. Each mammary quarter was sampled once to collect secretions that corresponded to d 0, 3, 11, and 25 or d 1, 7, 18, and 30 of the dry period. Concentrations of plasminogen, plasmin, and somatic cells in secretions increased earlier for treated cows than for control cows. The ratio of plasminogen to plasmin in secretions decreased earlier for treated cows than for control cows. These responses support the suggestion that the plasminogen and plasmin system is involved in the involution of bovine mammary tissue. Estrogen treatment increased the activation of plasminogen, which was evidenced by a precipitous decrease in the ratio of plasminogen to plasmin that occurred as concentrations of plasminogen and plasmin increased. The activation of plasminogen likely contributed to the increased rate of mammary tissue involution that was effected by exogenous estrogen. Endogenous estrogen secreted by the developing fetal and placental unit might mediate, in part, the gradual involution that occurs during lactation.

Plasminogen activator system: implications for mammary cell growth and involution

Several tissue remodeling events that require extracellular proteolysis are thought to be mediated by plasminogen activators that convert the inactive proenzyme plasminogen to active plasmin. The involvement of plasminogen activator in many biological phenomena reflects the ubiquitous presence of plasminogen and the ability of numerous cell types to synthesize plasminogen activator in a highly regulated manner. Increased plasmin and plasminogen activator in bovine milk are correlated with gradual involution (the declining phase of lactation). Treatment with bST prevented the increase in plasmin during gradual involution, indicating that bST interferes with conversion of plasminogen to plasmin. Concentrations of plasminogen activator in mammary tissue are high after cessation of milking. These results reinforce the association of the plasmin-plasminogen system with gradual involution postlactation. Recently, a role has been proposed for plasminogen activator in cell proliferation in several cellular systems. Insulin and IGF-I increased synthesis of urokinase plasminogen activator and enhanced proliferation of cultured bovine mammary epithelial cells. In contrast, phorbol myristate acetate, which increased expression of urokinase plasminogen activator mRNA by mammary epithelial and myoepithelial cells, stimulated proliferation of myoepithelial cells, but not epithelial cells. Thus, expression of plasminogen activator is not simply related to mitogenesis but is likely to serve multiple functions in bovine mammary epithelial cells.

Comparison of growth hormone-releasing factor and somatotropin: body growth and lactation of primiparous cows

Growth hormone-releasing factor is the main endogenous stimulator of somatotropin secretion. Our objective was to compare the effects of recombinant growth hormone-releasing factor and recombinant bST on somatotropin secretion, mammary function, and body composition of lactating, primiparous dairy cows. Cows (118 d of lactation) served as uninfused controls or were infused for 63 d with 12 mg/d of releasing factor or with 29 mg/d of bST. These doses elevated somatotropin in serum to concentrations of similar magnitude. The releasing factor and bST each similarly increased milk yield, yield of milk components, weight of most organs, mobilization of adipose tissue, accretion of lean tissue in the carcass, and metabolic activity (RNA) of mammary tissue. Relative to controls, neither releasing factor nor bST significantly affected cell numbers (DNA) in mammary glands or concentrations of plasmin in milk. None of the variables measured provided evidence for galactopoietic effects of releasing factor independent of somatotropin.

Production of various forms of plasminogen activator and plasminogen activator inhibitor by cultured mammary epithelial cells

We examined amounts and types of plasminogen activator and plasminogen activator inhibitor produced by cultured bovine mammary epithelial cells. The MAC-T and two other mammary epithelial cell lines, MACT-UV1 and MACT-UV2 derived from the parental MAC-T cells by subcloning, were used as model systems. Cells were cultured in a medium free of serum and protein. Data showed that MACT-UV2 cells produced 6.2 and 17.2% more plasminogen activator than MACT-UV1 and parental MAC-T cells, respectively. Addition of amiloride, a specific urokinase-plasminogen activator inhibitor, dramatically decreased the activity in the culture medium of parental and subclonal lines, indicating that urokinase-plasminogen activator was present. Zymography revealed the presence of urokinase-plasminogen activator with an approximate molecular mass of 50,000 kDa in the culture medium of parental MAC-T cells. The culture medium of the subclonal lines contained urokinase-plasminogen activator and tissue-plasminogen activator with approximate molecular masses of 50,000 and 75,000 kDa, respectively. Complexes of both types of plasminogen activators with plasminogen activator-inhibitor-1 were detected in the culture medium of subclonal lines.

The effect of lactogenic hormones on protein synthesis and amino acid uptake in rat mammary acinar cell culture at various physiological stages

1. The activities of protein synthesis and amino acid uptake at various physiological stages were determined by the incorporation of radioactive materials ([3H]-lysine, [14C]-cycloleucine) in rat mammary epithelial cell cultures. The activity of protein synthesis and amino acid uptake was higher in early lactation than in virgin, pregnant and late lactation stages. 2. Lactogenic hormones (prolactin, hydrocortisone and insulin) treatment related with mammary growth and differentiation increased the activities of protein synthesis and amino acid uptake. But increase of these activities was different at each physiological stage. 3. The effect of prolactin and hydrocortisone on the activities were greater in virgin, pregnant and late lactation than in early lactation. And effect of insulin was greater in pregnant and early lactation than in virgin and weanling.

The effects of daily oxytocin injections before and after milking on milk production, milk plasmin, and milk composition

Exogenous daily oxytocin injections given immediately before milking increase milk production. To investigate the mechanism by which oxytocin increases milk production, oxytocin injections were given before and after milking, and saline injection was given before milking as a control. The experimental design was a replicated Latin square; two complete trials were performed: one with 12 cows (45 d) and another with 15 cows (95 d). In the first trial, the least squares means of milk production were 29.2, 29.3, and 28.3 kg for oxytocin injection before milking, oxytocin injection after milking, and saline injection before milking, respectively. In the second trial, the least squares means of milk production were 33.3, 32.9, and 32.4 kg for oxytocin injection before milking, oxytocin injection after milking, and saline injection before milking, respectively. Oxytocin before and after milking significantly increased milk production by 3%. The results suggest that increases in milk production may not be caused by removal of residual milk but by increased gland output of milk. The effect on milk plasmin activity, fat, protein, SCC, and lactose was nonsignificant and may indicate that effect of oxytocin is not manifested through an effect on cell remodeling.

Pyrimidine nucleotide synthesis in the rat mammary gland: changes in the lactation cycle and effects of diabetes

Measurements have been made of the activities of the enzymes of the de novo and salvage pathways of pyrimidine synthesis (carbamoyl phosphate synthetase II (glutamine) (EC 6.3.5.5); dihydroorotate dehydrogenase (EC 1.3.99.11); the overall activity of Complex II (orotate phosphoribosyl pyrophosphate transferase (EC 2.4.2.10) and orotidine 5-phosphate decarboxylase (EC 4.1.1.23); uracil phosphoribosyltransferase (EC 2.4.2.9)) in the mammary gland of rats at different stages of the lactation cycle and the effects of diabetes on the activity of these enzymes in lactation have been studied. From a consideration of the changes in enzyme activities and the changes in the tissue concentration of phosphoribosyl pyrophosphate, an activator of the de novo pathway and substrate for both the de novo and salvage routes, it is concluded that the de novo pathway is the major route of pyrimidine synthesis in mammary tissue. Diabetes decreases the activity of the enzymes of the de novo pathway; the effects are particularly marked for Complex II. The present results on pyrimidine synthesis are compared to the pattern for purine synthesis previously published.

Active cell death in hormone-dependent tissues

Active cell death (ACD) in hormone-dependent tissues such as the prostate and mammary gland is readily induced by hormone ablation and by treatment with anti-androgens or anti-estrogens, calcium channel agonists and TGF beta. These agents induce a variety of genes within the hormone-dependent epithelial cells including TRPM-2, transglutaminase, poly(ADP-ribose) polymerase, Hsp27 and several other unidentified genes. Not all epithelial cells in the glands are equally sensitive to the induction of ACD. In the prostate, the secretory epithelial cells that are sensitive to hormone ablation are localized in the distal region of the prostatic ducts, and are in direct contact with the neighboring stroma. In contrast, the epithelial cells in the proximal regions of the ducts are more resistant to hormone ablation, probably because the permissive effects of the stroma are attenuated by the presence of the basal epithelial cells, which are intercalated between the epithelium and stroma. The underlying biology of ACD in prostate and mammary glands, and its relevance to hormone resistance, is discussed in this review.

Milk yields and hormone concentrations of Holstein cows in response to sometribove (somatotropin) treatment during the dry period

Holstein cows (n = 135) under commercial management were used to determine whether sometribove (recombinant methionyl bST, 25 mg/d) administered during the dry period affected milk yield during the ensuing lactation. Cows scheduled to begin lactations (greater than or equal to 2) during January to March were assigned randomly to treatments of sodium bicarbonate excipient (n = 67) or bST (25 mg/d, n = 68). Subcutaneous injections were given for 14 d, corresponding to d -21 to -7 relative to expected calving date. Days dry prior to first injection (64.0, 60.2) and number of injections received (13.9, 13.8) were similar for control and treatment groups, but days from last injection to calving (8.8, 7.1) differed. No differences in incidence of dystocia or udder edema were detected. Previous lactation yields were 8251 and 7952 kg, and yields for lactations following treatment were 8328 and 7852 kg, based on complete lactation data. Mean test date 3.5% FCM yields for control and treated groups during experimental lactation differed before (30.3 vs. 28.1 kg) but not after (29.5 vs. 28.4 kg) covariance adjustment for previous total lactation milk yield. Test of heterogeneity of regression provided no evidence that respective curves for FCM yield during lactation were not parallel or of different magnitude. Elevation of serum bST during 2 wk of the dry period resulted in no apparent increase in extent of mammogenesis or lactogenesis that was translated into an increase in milk yield.