Serum paraoxonase-1 activity in tail and mammary veins of ketotic dairy cows

The objective of this study was to evaluate the association between ketonemia and serum paraoxonase-1 (PON1), malondialdehyde (MDA), and other blood components in tail and mammary veins of dairy cows. Forty-two Holstein dairy cows with decreased feed intake were divided into HIGH (≥ 1.2 mM; n = 31) and LOW (< 1.2 mM; n = 11) groups based on the β-hydroxybutyrate concentration in plasma collected from the tail vein. The HIGH group had a significantly greater plasma non-esterified fatty acid (NEFA) concentration, but significantly lower serum PON1 activity and phospholipid concentration, and a tendency to have a lower cholesterol ester concentration than the LOW group. Serum PON1 activity was not correlated with the MDA concentration but was positively correlated with serum concentrations of cholesterol esters and phospholipids, and negatively correlated with the plasma NEFA concentration. These results suggest that serum PON1 activity is reduced by hyperketonemia and the relevance of PON1 to MDA seems to not be direct, though it is involved.

Regulation of fluid flow through the mammary gland of dairy cows and its effect on milk production: a systematic review

Dairy milk consists of more than 85% water. Therefore, understanding the regulation of fluid absorption in the mammary gland is relevant to improving milk production. In recent decades, studies using different approaches, including blood flow, transmembrane fluid flow, tight junction, fluid flow of the paracellular pathway and functional mammary epithelial cell state, have been conducted aiming to investigate how mammary gland fluid absorption is regulated. However, the relationship between regulation mechanisms of fluid flow and milk production has not been studied systematically. The present review summarizes a series of key milk yield regulatory factors mediated by whole-mammary fluid flow, including milk, mammary blood flow, blood/tissue fluid-cell fluid flow and cell-alveolus fluid flow. Whole-mammary fluid flow regulates milk production by altering transporter activity, ion channels, local microcirculation-related factors, driving force of fluid transport (osmotic pressure or electrochemical gradient), cellular connection state and a cell volume sensitive mechanism. In addition, whole-mammary fluid flow plays important roles in milk synthesis and secretion. Knowledge gained from fluid flow-mediated regulatory mechanisms of the dairy mammary gland will lead to a fundamental understanding of lactation biology and will be beneficial for the improvement of dairy productivity. © 2017 Society of Chemical Industry.

Phytoestrogens Weaken the Blood-Milk Barrier in Lactating Mammary Epithelial Cells by Affecting Tight Junctions and Cell Viability

During lactation, mammary epithelial cells (MECs) form the blood-milk barrier by less-permeable tight junctions (TJs) to prevent the leakage of milk components. Phytoestrogens affect the proliferation, differentiation, and apoptosis of MECs. However, it remains unclear whether phytoestrogens are involved in the blood-milk barrier. Therefore, we investigated the influence of phytoestrogens (coumestrol, genistein, and daidzein) by using an in vitro mouse-MEC-culture model. The results showed that coumestrol and genistein changed the expression of TJ proteins (claudins-3 and -4 and occludin), weakened barrier function, and reduced β-casein production. Daidzein also weakened barrier function without inhibiting β-casein production. Additionally, coumestrol and genistein induced apoptosis in MECs. These results indicate that phytoestrogens weaken the blood-milk barrier by directly affecting TJs and the cellular viability of lactating MECs in different ways.

A RhoA-FRET Biosensor Mouse for Intravital Imaging in Normal Tissue Homeostasis and Disease Contexts

The small GTPase RhoA is involved in a variety of fundamental processes in normal tissue. Spatiotemporal control of RhoA is thought to govern mechanosensing, growth, and motility of cells, while its deregulation is associated with disease development. Here, we describe the generation of a RhoA-fluorescence resonance energy transfer (FRET) biosensor mouse and its utility for monitoring real-time activity of RhoA in a variety of native tissues in vivo. We assess changes in RhoA activity during mechanosensing of osteocytes within the bone and during neutrophil migration. We also demonstrate spatiotemporal order of RhoA activity within crypt cells of the small intestine and during different stages of mammary gestation. Subsequently, we reveal co-option of RhoA activity in both invasive breast and pancreatic cancers, and we assess drug targeting in these disease settings, illustrating the potential for utilizing this mouse to study RhoA activity in vivo in real time.

Technical note: Measurement of mammary plasma flow in sows by downstream dilution of mammary vein infused -aminohippuric acid

The objectives of the present study were to design a method to estimate mammary plasma flow (MPF) in lactating sows using downstream dilution of -aminohippuric acid (AH) and to compare these estimates with MPF estimates based on specific AA as internal markers (MPF-AA). A permanent indwelling catheter was surgically implanted in the femoral artery, and another 2 were inserted in the right cranial mammary vein of 8 second- and third-parity sows on d 76 ± 2 SEM of gestation. On the 3rd and 17th days in milk, arterial and venous blood samples were drawn in hourly intervals from 0.5 h before until 6.5 h after feeding. The MPF in the right cranial mammary vein was measured by downstream dilution of infused AH (3.0 mmol/h). Total MPF-AH was calculated assuming that the measured flow constituted the flow from 5 out of 14 suckled glands on the basis of the anatomical structure of the mammary vascular system. Total MPF-AA was estimated on the basis of the output of the specific AA marker in milk and the arteriovenous differences of the marker as free AA in plasma, assuming a direct transfer of AA from plasma to milk protein. Total MPF-AH was 6,860 L/d in early lactation and increased to 8,953 L/d at peak lactation ( = 0.003). In early lactation, MPF-AA estimates were greater or tended to be greater (132% to 175%; < 0.10) than MPF-AH estimates for all internal markers, except Met (119%). Moreover, MPF-AH was correlated with MPF-AA only for MET as an internal marker ( = 0.74; = 0.03) in early lactation. In contrast, MPF-AH and MPF-AA estimates did not differ and were well correlated at peak lactation with the strongest correlation observed when Met ( = 0.84; = 0.009) and Phe + Tyr ( = 0.82; = 0.01) were used as the internal AA markers. Litter gain increased from d 3 to 17 of lactation (2.13 vs. 3.46 g/d; = 0.001) and was correlated with MPF-AH during lactation ( = 0.74; < 0.001), whereas no correlation between litter gain and MPF-AA was observed ( > 0.10). These results suggest that downstream dilution of infused AH and the AA methods are applicable methods to estimate MPF at peak lactation. The reason for the observed discrepancy in early lactation between MPF- AH and MPF-AA is not obvious but might be related to the rapid metabolic changes observed in early lactation. In conclusion, MPF measured by downstream dilution of mammary infused AH was higher at peak compared to early lactation, which the internal AA marker approach failed to show.

Regulation and localization of vascular endothelial growth factor within the mammary glands during the transition from late gestation to lactation

The vascular network within the developing mammary gland (MG) grows in concert with the epithelium to prepare for lactation, although the mechanisms coordinating this vascular development are unresolved. Vascular endothelial growth factor A (VEGF-A) mediates angiogenesis and vascular permeability in the MG during pregnancy and lactation, where its expression is upregulated by prolactin. Given our previous finding that late-gestational hyperprolactinemia induced by domperidone (DOM) increased subsequent milk yield from gilts, we sought to establish changes in vascular development during late gestation and lactation in the MGs of these pigs and determine whether DOM altered MG angiogenesis and the factors regulating it. Gilts received either no treatment (n = 6) or DOM (n = 6) during late gestation, then had their MG biopsied from late gestation through lactation to assess microvessel density, VEGF-A distribution and messenger RNA expression, and aquaporin (AQP) gene expression. Microvessel density in the MG was unchanged during gestation then increased between days 2 and 21 of lactation (P < 0.05). The local expression of messenger RNA for VEGF-A120, VEGF-A147, VEGF-A164, VEGF-A164b, VEGF-A188, VEGF receptors-1 and -2, and AQP1 and AQP3 all generally increased during the transition from gestation to lactation (P < 0.05). Immunostaining localized VEGF-A to the apical cytoplasm of secretory epithelial cells, consistent with a far greater concentration of VEGF-A in colostrum and/or milk vs plasma (P < 0.0001). There was no effect of DOM on any of the variables analyzed. In summary, we found that vascular development in the MG increases during lactation in first-parity gilts and that VEGF-A is a part of the mammary secretome. Although late-gestational hyperprolactinemia increases milk yield, there was no evidence that it altered vascular development.

Impacts of Maternal Nutrition on Vascularity of Nutrient Transferring Tissues during Gestation and Lactation

As the demand for food increases with exponential growth in the world population, it is imperative that we understand how to make livestock production as efficient as possible in the face of decreasing available natural resources. Moreover, it is important that livestock are able to meet their metabolic demands and supply adequate nutrition to developing offspring both during pregnancy and lactation. Specific nutrient supplementation programs that are designed to offset deficiencies, enhance efficiency, and improve nutrient supply during pregnancy can alter tissue vascular responses, fetal growth, and postnatal offspring outcomes. This review outlines how vascularity in nutrient transferring tissues, namely the maternal gastrointestinal tract, the utero-placental tissue, and the mammary gland, respond to differing nutritional planes and other specific nutrient supplementation regimes.

Vasoinhibins, N-terminal mouse prolactin fragments, participate in mammary gland involution

Vasoinhibins are a family of peptides that act on endothelial cells to suppress angiogenesis and promote apoptosis-mediated vascular regression. Vasoinhibins include the N-terminal fragments from prolactin (PRL), GH, and placental lactogen. One of the vasoinhibins, the N-terminal PRL fragment of 16 kDa, is generated by the lysosomal representative protease cathepsin D (Cath D). Because the normal growth and involution of the mammary gland (MG) are profoundly affected by the expansion and regression of blood vessels and also because PRL stimulates the growth and differentiation of MG, we proposed that intact PRL produced during lactation contributes to MG angiogenesis and increased blood flow, whereas during involution, the N-terminal PRL fragment would have proapoptotic effects on mammary epithelial cells (MECs). Therefore, we investigated the production of the N-terminal PRL fragment and its direct effect on the MG. Mouse PRL (mPRL) was proteolytically cleaved by Cath D between amino acids 148 and 149. N-terminal PRL fragment and Cath D expression increased during MG involution. Furthermore, incubation of MG fragments and MCF7 with recombinant 16 kDa mPRL revealed a proapoptotic effect in MECs. Ectopic mPRL in MECs was cleaved to 16 kDa PRL by Cath D in the MG lysosomal fraction. The majority of PRL derived from pituitary gland was cleaved to 16 kDa PRL in culture medium. Therefore, N-terminal PRL fragment increases during the involution period, has a proapoptotic effect on MECs, and is mainly generated by secreted Cath D in the extracellular space of MG.

In vivo fluorescence imaging reveals the promotion of mammary tumorigenesis by mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) are multipotent adult stem cells which are recruited to the tumor microenvironment (TME) and influence tumor progression through multiple mechanisms. In this study, we examined the effects of MSCs on the tunmorigenic capacity of 4T1 murine mammary cancer cells. It was found that MSC-conditioned medium increased the proliferation, migration, and efficiency of mammosphere formation of 4T1 cells in vitro. When co-injected with MSCs into the mouse mammary fat pad, 4T1 cells showed enhanced tumor growth and generated increased spontaneous lung metastasis. Using in vivo fluorescence color-coded imaging, the interaction between GFP-expressing MSCs and RFP-expressing 4T1 cells was monitored. As few as five 4T1 cells could give rise to tumor formation when co-injected with MSCs into the mouse mammary fat pad, but no tumor was formed when five or ten 4T1 cells were implanted alone. The elevation of tumorigenic potential was further supported by gene expression analysis, which showed that when 4T1 cells were in contact with MSCs, several oncogenes, cancer markers, and tumor promoters were upregulated. Moreover, in vivo longitudinal fluorescence imaging of tumorigenesis revealed that MSCs created a vascularized environment which enhances the ability of 4T1 cells to colonize and proliferate. In conclusion, this study demonstrates that the promotion of mammary cancer progression by MSCs was achieved through the generation of a cancer-enhancing microenvironment to increase tumorigenic potential. These findings also suggest the potential risk of enhancing tumor progression in clinical cell therapy using MSCs. Attention has to be paid to patients with high risk of breast cancer when considering cell therapy with MSCs.

Development and initial application of a fully integrated photoacoustic micro-ultrasound system

Photoacoustic (PA) imaging for biomedical applications has been under development for many years. Based on the many advances over the past decade, a new photoacoustic imaging system has been integrated into a micro-ultrasound platform for co-registered PA-ultrasound (US) imaging. The design and implementation of the new scanner is described and its performance quantified. Beamforming techniques and signal processing are described, in conjunction with in vivo PA images of normal subcutaneous mouse tissue and selected tumor models. In particular, the use of the system to estimate the spatial distribution of oxygen saturation (sO2) in blood and co-registered with B-mode images of the surrounding anatomy are investigated. The system was validated in vivo against a complementary technique for measuring partial pressure of oxygen in blood (pO2). The pO2 estimates were converted to sO2 values based on a standard dissociation curve found in the literature. Preliminary studies of oxygenation effects were performed in a mouse model of breast cancer (MDA-MB-231) in which control mice were compared with mice treated with a targeted antiangiogenic agent over a 3 d period. Treated mice exhibited a >90% decrease in blood volume, an 85% reduction in blood wash-in rate, and a 60% decrease in relative tissue oxygenation.

[Comparative examination of selected blood parameters from different sampling sites in high yielding cows. Practical usability of blood sampling from the udder vein for metabolic analyses]

OBJECTIVE

The aim of the present study was to evaluate different statements in the literature on the influence of the sampling site on various blood parameters in a larger amount of animals. In addition, the practical usability of blood sampling from the udder vein or other accessible veins (e. g. saphenous vein or tail vein) in comparison to the jugular vein for metabolic analyses should be verified.

MATERIAL AND METHODS

For this purpose blood samples from 92 cows and heifers were taken from the jugular vein, the udder vein and the saphenous vein of the left and right hind limb at four different time points (from 3 weeks ante partum until 8 weeks post partum) and comparatively investigated.

RESULTS

For five of the 16 investigated parameters (free fatty acids, beta-hydroxybutyrate, glucose, creatine kinase, and calcium) partially high significant differences between the sampling sites became apparent, dependant on the moment of analysis.

CONCLUSION AND CLINICAL RELEVANCE

In metabolic analyses, which comprise the aforementioned parameters, the blood sampling site has decisively influence and has to be considered in the interpretation. The udder vein represents no alternative for blood sampling in high yielding cows for metabolic analyses. For obtaining meaningful results, the jugular vein has to be used for blood sampling, despite the higher procedural effort. An exception is the determination of the creatine kinase activity. Since defence movements of the animal's neck seem to have an influence on the local activity, the udder vein should be preferred as sampling site.

Fibroblast growth factor receptor 1 activation in mammary tumor cells promotes macrophage recruitment in a CX3CL1-dependent manner

Tumor formation is an extensive process requiring complex interactions that involve both tumor cell-intrinsic pathways and soluble mediators within the microenvironment. Tumor cells exploit the intrinsic functions of many soluble molecules, including chemokines and their receptors, to regulate pro-tumorigenic phenotypes that are required for growth and progression of the primary tumor. Previous studies have shown that activation of inducible FGFR1 (iFGFR1) in mammary epithelial cells resulted in increased proliferation, migration, and invasion in vitro and tumor formation in vivo. These studies also demonstrated that iFGFR1 activation stimulated recruitment of macrophages to the epithelium where macrophages contributed to iFGFR1-mediated epithelial cell proliferation and angiogenesis. The studies presented here further utilize this model to identify the mechanisms that regulate FGFR1-induced macrophage recruitment. Results from this study elucidate a novel role for the inflammatory chemokine CX3CL1 in FGFR1-induced macrophage migration. Specifically, we illustrate that activation of both the inducible FGFR1 construct in mouse mammary epithelial cells and endogenous FGFR in the triple negative breast cancer cell line, HS578T, leads to expression of the chemokine CX3CL1. Furthermore, we demonstrate that FGFR-induced CX3CL1 is sufficient to recruit CX3CR1-expressing macrophages in vitro. Finally, blocking CX3CR1 in vivo leads to decreased iFGFR1-induced macrophage recruitment, which correlates with decreased angiogenesis. While CX3CL1 is a known target of FGF signaling in the wound healing environment, these studies demonstrate that FGFR activation also leads to induction of CX3CL1 in a tumor setting. Furthermore, these results define a novel role for CX3CL1 in promoting macrophage recruitment during mammary tumor formation, suggesting that the CX3CL1/CX3CR1 axis may represent a potential therapeutic approach for targeting breast cancers associated with high levels of tumor-associated macrophages.

Prenatal exposure to bisphenol A promotes angiogenesis and alters steroid-mediated responses in the mammary glands of cycling rats

Prenatal exposure to BPA disturbs mammary gland histoarchitecture and increases the carcinogenic susceptibility to chemical challenges administered long after BPA exposure. Our aim was to assess the effect of prenatal BPA exposure on mammary gland angiogenesis and steroid hormone pathways in virgin cycling rats. Pregnant Wistar rats were exposed to either 25 or 250 g/kg/day (25 and 250 BPA, respectively) or to vehicle. Female offspring were autopsied on postnatal day (PND) 50 or 110. Ovarian steroid serum levels, the expression of steroid receptors and their co-regulators SRC-3 and SMRT in the mammary gland, and angiogenesis were evaluated. At PND 50, all BPA-treated animals had lower serum levels of progesterone, while estradiol levels remained unchanged. The higher dose of BPA increased mammary ERα and decreased SRC-3 expression at PND 50 and PND 110. SMRT protein levels were similar among groups at PND 50, whereas at PND 110, animals exposed to 250 BPA showed a lower SMRT expression. Interestingly, in the control and 25 BPA groups, SMRT increased from PND 50 to PND 110. At PND 50, an increased vascular area associated with higher VEGF expression was observed in the 250 BPA-treated rats. At PND 110, the vascular area was still increased, but VEGF expression was similar to that of control rats. The present results demonstrate that prenatal exposure to BPA alters the endocrine environment of the mammary gland and its angiogenic process. Increased angiogenesis and altered steroid hormone signals could explain the higher frequency of pre-neoplastic lesions found later in life. This article is part of a Special Issue entitled 'Endocrine disruptors'.

Conditional knockout of fibronectin abrogates mouse mammary gland lobuloalveolar differentiation

Fibronectin (Fn) plays an important part in the branching morphogenesis of salivary gland, lung, and kidney. Here, we examine the effect of the conditional knockout of Fn in the mammary epithelium [Fn(MEp-/-)] on postnatal mammary gland development, using Cre-loxP-mediated gene knockout technology. Our data show that Fn deletion causes a moderate retardation in outgrowth and branching of the ductal tree in 5-week-old mice. These defects are partially compensated in virgin 16-week-old mice. However, mammary glands consisting of Fn-deficient epithelial cells fail to undergo normal lobuloalveolar differentiation during pregnancy. The severity of lobuloalveolar impairment ranged from lobular hypoplasia to aplasia in some cases and was associated with the amount of Fn protein recovered from these glands. Decreased rates of mammary epithelial cell proliferation accounted for delayed ductal outgrowth in virgin and lack of alveologenesis in pregnant Fn(MEp-/-) mice. Concomitant decreased expression of integrin beta(1) (Itgb1) and lack of autophosphorylation of focal adhesion kinase (Fak) suggest that this pathology might, at least in part, be mediated by disruption of the Fn/Itgb1/Fak signaling pathway.

The mammary gland vasculature revisited

Concomitant with the extensive growth and differentiation of the mammary epithelium during pregnancy and lactation, and epithelial involution after weaning, the vasculature of the mammary gland undergoes repeated cycles of expansion and regression. Vascular expansion is effected by sprouting angiogenesis, intussusception and conceivably also vasculogenesis. The capacity of the epithelial cells to stimulate vascular growth and differentiation is dependent on the constellation of systemic and local hormones and growth factors as well as the changing demands for oxygenation and nutrient supply. This results in the release of angiogenic factors which stimulate endothelial cell growth and regulate vascular architecture. In contrast to the angiogenic phase of the mammary gland cycle, little is known about the control of vascular regression although this would possibly offer new insights into therapeutic possibilities against breast cancer. In this review we summarize knowledge regarding the mechanisms regulating the vasculature of the mammary gland and delineate the importance of the vasculature in the attainment of organ function. In addition, we discuss the angiogenic mechanisms observed during mammary carcinogenesis and their consequences for breast cancer therapy.

Vascular Robo4 restricts proangiogenic VEGF signaling in breast

Formation of the vascular system within organs requires the balanced action of numerous positive and negative factors secreted by stromal and epithelial cells. Here, we used a genetic approach to determine the role of SLITs in regulating the growth and organization of blood vessels in the mammary gland. We demonstrate that vascularization of the gland is not affected by loss of Slit expression in the epithelial compartment. Instead, we identify a stromal source of SLIT, mural cells encircling blood vessels, and show that loss of Slit in the stroma leads to elevated blood vessel density and complexity. We examine candidate SLIT receptors, Robo1 and Robo4, and find that increased vessel angiogenesis is phenocopied by loss of endothelial-specific Robo4, as long as it is combined with the presence of an angiogenic stimulus such as preneoplasia or pregnancy. In contrast, loss of Robo1 does not affect blood vessel growth. The enhanced growth of blood vessels in Robo4(-/-) endothelium is due to activation of vascular endothelial growth factor (VEGF)-R2 signaling through the Src and FAK kinases. Thus, our studies present a genetic dissection of SLIT/ROBO signaling during organ development. We identify a stromal, rather than epithelial, source of SLITs that inhibits blood vessel growth by signaling through endothelial ROBO4 to down-regulate VEGF/VEGFR2 signaling.

Lactation: some cardiovascular and metabolic consequences, and the mechanisms of lactose and ion secretion into milk

Lactation causes increases in mammary blood flow, gastrointestinal blood flow and cardiac output in the rat, and the suckling-induced release of lactogenic anterior pituitary hormones probably causes these changes, directly or indirectly. Metabolic requirements of lactation in women are similar to those in other animals not artificially selected for a high milk yield but the physiological control of the relationship between milk secretion and nutrient availability is not well understood. The unusual composition of the aqueous phase of human milk (rich in lactose but poor in sodium and potassium ions) can be explained by the same basic mechanisms for secretion of lactose and ions as operate in other animals but with quantitative differences.

Role of prolactin and vasoinhibins in the regulation of vascular function in mammary gland

The formation of new blood vessels has become a major focus of mammary gland research stimulated by the therapeutic opportunities of controlling angiogenesis in breast cancer. Normal growth and involution of the mammary gland are profoundly affected by the expansion and regression of blood vessels, whereas dysregulation of angiogenesis is characteristic of breast cancer growth and metastasis. Prolactin stimulates the growth and differentiation of the mammary gland under normal conditions, but its role in breast cancer is controversial. Its action is complicated by the fact that prolactin itself is angiogenic, but proteases cleave prolactin to generate vasoinhibins, a family of peptides that act on endothelial cells to suppress angiogenesis and vasodilation and to promote apoptosis-mediated vascular regression. This review summarizes our current knowledge about the vascular effects of prolactin and the generation and action of vasoinhibins, and discusses their possible contribution to the regulation of blood vessels in the normal and malignant mammary gland.

Mammary arteriovenous differences of glucose, insulin, prolactin and IGF-I in lactating sows under different protein intake levels

Mammary uptake of nutrients is dependent on their availability in the circulation but the role of hormones in that process is not known. Arteriovenous differences (AVD) of glucose and key hormones across the mammary glands were therefore determined in sows fed varying levels of protein. Sixteen lactating sows (four/dietary treatment) were fed a 7.8, 13.0, 18.2 or 23.5% crude protein (CP) isocaloric diet throughout lactation and their litters were standardized to 11 pigs within 48 h of birth. The anterior main mammary vein and a carotid artery were cannulated on day 4+/-1 of lactation and blood samples were collected every 30 min over 6h on days 10, 14, 18 and 22 of lactation to measure glucose, insulin, IGF-I, and prolactin (PRL) concentrations. Amino acid data from these sows were previously published and used here to determine residual correlations. Dietary treatments had no effect on any of the insulin or PRL variables measured (P>0.1) and, on day 18 only, IGF-I AVD was greater (P=0.05) for sows on the 23.5% compared to the 18.2% diet. On days 18 and 22, sows fed the 13% CP diet had greater arterial, venous and AVD glucose concentrations than sows fed other diets (P<0.05). Total arterial amino acid concentrations were correlated to arterial insulin (P<0.001) and PRL (P<0.05) concentrations, but not to those of IGF-I (P>0.1). Mammary AVD for total (P<0.001) and essential amino acids (P<0.05) were correlated to arterial concentrations of insulin, but not to those of IGF-I (P>0.1) or PRL (P>0.1). Mammary AVD of both total (P<0.01) and essential (P<0.05) amino acids were also correlated to mammary PRL AVD. In conclusion, dietary protein level did not affect mammary AVD and circulating lactogenic hormone concentrations. Yet, amino acid utilization by the sow mammary gland seems to be regulated via both circulating insulin concentrations and PRL binding to and uptake by porcine mammary cells.

Can autologous vascular endothelial cell seeding increase the patency rate of small-diameter No-React-treated bovine internal mammary arteries? An in vivo study in juvenile sheep

BACKGROUND

This study was performed to evaluate the possibility of seeding No-React-treated bovine small-diameter internal mammary arteries (SIMAs) and to record any improvement in patency rate.

MATERIAL/METHODS

During the in vitro study, 12 seeded SIMAs were divided into two groups; group I (n=6) was endothelial cell (EC) seeded and group II (n=6) EC seeded after pre-coating with fibrin glue to evaluate the binding capacity. During the in vivo part of the study, eight juvenile sheep received either a seeded or a non-seeded SIMA. In the seeded group (n=3), a piece of jugular vein was harvested to culture autologous ECs. SIMA grafts were coated and seeded in a special bioreactor. In the control group (n=5), non-seeded SIMA grafts were implanted. No anti-coagulation was administered. Explantation was performed at three and six months post-implantation. Grafts were evaluated by gross examination, histology, and immunohistochemistry.

RESULTS

By inserting two million ECs in the in vitro study, the seeding density in group I was 1.29+/-0.09 x 10(5) cells/cm(2) and 2.27+/-0.17 x 10(5) cells/cm(2) in group II (p<0.003). In the in vivo study the mean EC density of the implanted seeded grafts was 2.35+/-0.04 x 10(5) cells/cm(2). At explantation, the seeded grafts showed less inflammatory reaction and a higher patency rate compared with the non-seeded grafts. Histology showed a monolayer of ECs on the inner surface of seeded SIMAs at follow-up.

CONCLUSIONS

Seeding of No-React-treated SIMA arterial grafts with autologous ECs increases the patency rate.

Innervation of the canine mammary gland: an immunohistochemical study

The distribution of peptidergic nerves in canine mammary tissues was studied by immunohistochemical techniques. In addition, the general and the noradrenergic innervations were demonstrated using protein gene product 9.5 and tyrosine hydroxylase immunoreactivities as markers, respectively. Tissue specimens from the caudal mammary glands were obtained from adult, non-lactating, female dogs. The overall innervation of the mammary gland tissue was sparse and primarily associated with the arterial vasculature. Nerve fibres positive for protein gene product 9.5 were rarely found in the secretory parenchyma. The nipple was not richly innervated, although it displayed a greater amount of nerve fibres than the mammary parenchyma. Nerve fibres supplying nonvascular structures of the nipple expressed immunoreactivity for the sensory neuropeptides calcitonin gene-related peptide, substance P and neuropeptide K, but not for vasoactive intestinal peptide, peptide histidine isoleucine and C-flanking peptide of neuropeptide Y. Somatostatin immunoreactivity was not detected in mammary gland tissue. Our results indicate that the innervation of the canine mammary gland is mainly affiliated with the vasculature and comprises peptidergic nerves which may be involved in the regulation of local blood flow. The presence of sensory neuropeptides in nerves supplying the mammary nipple suggest that these peptides may play a role in the afferent pathway of the milk ejection reflex.

[Lactogenic effects of hyperinsulinemic-euglycaemic clamp in goats]

In the experiment performed on lactating goats, insulin was infused into the jugular vein over during 2 days every day at the rate 2 mg/kg/hour during 6 hour synchronously with glucose at variable rate to maintain euglycaemia; the transport activity (T, in clearance units) was estimated using the equation: T = Q x E/ (1-E), where Q is plasma flow and E is extraction efficiency. At the end of infusion of the 1st and 2nd days, insulin level in the blood was increased by 63 and 82%, mammary plasma flow by 38 and 78%, milk secretion rate by 23.7 and 31.3 %, milk protein yield by 21.4 and 40%, transport activity of glucose by 63 %, and amino acids by 18% (all p < 0.05) compared to control, respectively. The data obtained suggest that productive effect resulted from elevated metabolic activity of secretory cells and increased mammary blood flow.

[The conjugate regulation of mammary blood flow and secretory cell metabolism: analysis of problem]

In the review the essential features of system regulation of mammary blood flow, substrate supply, uptake and utilization by cellular metabolism and for milk component synthesis are considered, with emphasis on productive ruminants (cows and goats). The conception of local control of regional vascular resistance in described. in which the criterion of maintenance of energetic balance in secretory cells is used. The some steps of substrates utilization and their regulation are described (glucose, acetate, free amino acids, triacylglycerols, free fatty acids). The secretory cell is considered as control unit equilibrating the extraction of substrates from blood with the rate of milk components synthesis. The role of hormonal factors in these processes is discussed.

Mammary gland macrophages: pleiotropic functions in mammary development

Mammary gland development is a complex process involving epithelial cells and supporting stromal cells. Macrophages (MØs) are an important component of the mammary gland stroma and are critical for normal mammary gland development; however, the mechanisms by which macrophages regulate these processes are not well understood. MØs are known to interact with numerous cell types, including epithelial cells, fibroblasts, adipocytes, and endothelial cells, all of which are significant components of mammary gland development. Therefore, the purpose of this review is to describe the interactions between MØs and these various cell types and use this knowledge to identify potential functions of MØs in the mammary gland.

Increasing Milking Intervals Decreases the Mammary Blood Flow and Mammary Uptake of Nutrients in Dairy Cows

Increasing the milking intervals reduces milk yield. The aims of this study were to determine whether the reduction in milk yield could be explained by a decrease in mammary uptake of the nutrients or a decrease in the efficiency of the mammary gland in using the milk precursors to synthesize milk components, or both. In a Latin square design with 5 periods, 4 multiparous lactating dairy cows in midlactation were milked at 8-, 12-, 16-, or 24-h intervals over a period of 7 d. The cows were surgically prepared to estimate the net mammary balance of nutrient precursors of milk components (glucose, alpha-amino nitrogen, acetate, beta-hydroxybutyrate, and total glycerol). The efficiency of the mammary gland in synthesizing milk components was estimated by the mammary uptake:milk output ratio. After 7 d of treatment, the decrease in milk yield of 6.1 kg/d between 8- and 24-h milking intervals was associated with a reduction in the uptake of nutrients by the mammary gland, whereas the efficiency of the mammary gland in synthesizing milk components remained relatively unchanged. The mammary uptake decreased by 26% for glucose, 32% for alpha-amino nitrogen, 18% for acetate, 24% for total glycerol, and 24% for beta-hydroxybutyrate, respectively. These reductions in nutrient uptake were due to a decrease in the mammary blood flow (1.23 +/- 0.24 L/min). For milk fat precursors (acetate, beta-hydroxybutyrate, and total glycerol), the decrease in mammary blood flow explained the entire reduction in the mammary uptake. For glucose and the milk protein precursors, the reduction in the mammary blood flow explained 60% of the decrease in the mammary uptake, with the other 40% being accounted for by a reduction in the mammary extraction of nutrients. The nutrient uptake was altered as milk yield decreased. These decreases began with the 16-h milking interval and were higher at the 24-h milking interval.

Effect of Mastitis on Milk Perchlorate Concentrations in Dairy Cows

Recent surveys have identified the presence of perchlorate, a natural compound and environmental contaminant, in forages and dairy milk. The ingestion of perchlorate is of concern because of its ability to competitively inhibit iodide uptake by the thyroid and to impair synthesis of thyroid hormones. A recent study established that milk perchlorate concentrations in cattle highly correlate with perchlorate intake. However, there is evidence that up to 80% of dietary perchlorate is metabolized in clinically healthy cows, thereby restricting the available transfer of ingested perchlorate into milk. The influence of mastitis on milk perchlorate levels, where there is an increase in mammary vascular permeability and an influx of blood-derived components into milk, remains unknown. The present study examined the effect of experimentally induced mastitis on milk perchlorate levels in cows receiving normal and perchlorate-supplemented diets. Over a 12-d period, cows were ruminally infused with 1 L/d of water or water containing 8 mg of perchlorate. Five days after the initiation of ruminal infusions, experimental mastitis was induced by the intramammary infusion of 100 microg of bacterial lipopolysaccharide (LPS). Contralateral quarters infused with phosphate-buffered saline served as controls. A significant reduction in milk perchlorate concentration was observed in the LPS-challenged glands of animals ruminally infused with either water or perchlorate. In control glands, milk perchlorate concentrations remained constant throughout the study. A strong negative correlation was identified between mammary vascular permeability and milk perchlorate concentrations in LPS-infused glands. These findings, in the context of a recently published study, suggest that an active transport process is operative in the establishment of a perchlorate concentration gradient across the blood-mammary gland interface, and that increases in mammary epithelial and vascular endothelial permeability lead to a net outflow of milk perchlorate. The overall finding that mastitis results in lower milk perchlorate concentrations suggests that changes in udder health do not necessitate increased screening of milk for perchlorate.

Ascorbic acid-independent synthesis of collagen in mice

The mouse has become the most important model organism for the study of human physiology and disease. However, until the recent generation of mice lacking the enzyme gulanolactone oxidase (Gulo), the final enzyme in the ascorbic acid biosynthesis pathway, examination of the role of ascorbic acid in various biochemical processes using this model organism has not been possible. In the mouse, similar to most mammals but unlike humans who carry a mutant copy of this gene, Gulo produces ascorbic acid from glucose. We report here that, although ascorbic acid is essential for survival, its absence does not lead to measurable changes in proline hydroxylation. Vitamin C deficiency had no significant effect on the hydroxylation of proline and collagen production during tumor growth or in angiogenesis associated with tumor or mammary gland growth. This suggests that factors other than ascorbic acid can support proline hydroxylation and collagen synthesis in vivo. Furthermore, the failure of Gulo-/- mice to thrive on a vitamin C-deficient diet therefore suggests that ascorbic acid plays a critical role in survival other than the maintenance of the vasculature.

Regulation of genes encoding proteolytic enzymes during mammary gland development

The mammary gland undergoes extensive tissue remodelling during each lactation cycle. During pregnancy, the epithelial compartment of the gland is vastly expanded (Benaud et al. 1998). At the end of lactation the epithelial cells undergo apoptosis and adipocyte differentiation is induced (Lilla et al. 2002). Ductal and alveolar growth during puberty and pregnancy, and the involution process require the action of proteolytic enzymes (including matrix metalloproteinases, plasminogen and membrane-peptidases) and the corresponding genes are activated during these periods (Benaud et al. 1998; Alexander et al. 2001). Matrix metalloproteinases (MMP) are expressed in several cell types of the mammary gland including stromal fibroblasts (e.g., MMP3, MMP2), epithelial cells (e.g., MMP7 or MMP9), adipocytes (e.g., MMP2) and lymphoid cells (e.g., MMP9) (Crawford et al. 1996; Lund et al. 1996; Wiseman et al. 2003). A number of knock-out mice, which are deficient for individual MMP genes (e.g., MMP2, MMP3) or plasminogen, display alterations to mammary gland structure and impairment of lactation (Lund et al. 1999; Wiseman et al. 2003).

Endocrinology of milk production

The physiology of lactation includes development of the mammary gland from the foetal to the adult stage, further development during pregnancy and onset of lactation, with the accompanying metabolic and behavioural adaptation. At the onset of pregnancy the endocrine system undergoes dramatic changes. The growth of the mammary gland is stimulated by growth hormone and prolactin, adrenocortical steroids, oestrogens and progesterone, and that of the gastrointestinal (GI) tract by gastrin, CCK and secretin. The onset of lactation is accompanied by increases in the blood volume, cardiac output, mammary blood flow and blood flow through the GI-tract and liver, aiming to provide the udder with nutrients and hormones for regulation of milk synthesis. Food intake and distribution of nutrients to the mammary gland are partially regulated by hormones as well as the repartitioning of nutrients away from body stores towards the udder. To improve milk production, administration of growth hormone has been practised, but also much discussed. Besides central mechanisms, local mechanisms within the mammary gland regulate initiation of lactation, maintenance, regulation of blood flow and mammary gland cell apoptosis. Most of the milk in a filled dairy cow udder is stored in the alveolar compartments. The milk ejection reflex must be activated to gain access to the udder milk, i.e. oxytocin contracts the myoepithelial cells. Recent studies show that vasopressin may also elicit milk ejection. More efficient oxytocin release is achieved if the cows are fed during milking. Beyond milk let down, oxytocin influences maternal behaviour and metabolism. Furthermore, it has been indicated that suckling or milking activates a vagal reflex, which may link the milk production to the endocrine system of the GI-tract. The question has been raised whether the mammary gland is a supporting or consuming organ.

Cancer growth and spread are saltatory and phase-locked to the reproductive cycle through mediators of angiogenesis

The frequency of breast cancer metastatic spread is affected by the menstrual cycle phase of its resection. Breast cancer growth, post-resection spread, and cure frequency are each modulated by the estrous cycle in C(3)HeB/FeJ mice. Tumor metastases are 2- to 3-fold more frequent when the resection is done during diestrus as compared with estrus. Tumor angiogenesis is essential for both cancer growth and lethal metastatic cancer spread. The balance between vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) modulates new blood vessel formation and blood vessel permeability. Sex hormones modulate the expression of these key angiogenesis regulators in the endometrium and uterus. We, therefore, asked whether the estrous cycle modulates the density of CD31-positive vessels within the tumor, the permeability of tumor blood vessels, levels of VEGF and bFGF immunoreactive protein in normal breast and breast cancer, and whether expression of these genes are modulated by the estrous cycle stage in C(3)HeB/FeJ mice. We find that tumor blood vessel density and blood volume do not vary throughout the cycle; however, tumor capillary permeability is regulated by the estrous cycle being highest in diestrus, the cycle stage associated with the highest cancer growth rate and the highest frequency of post-resection cancer metastasis. VEGF protein levels in breast cancer are >100-fold higher than in normal breast. VEGF protein in this mammary tumor varies with the estrus cycle with highest levels in proestrus. In a non-breast tumor, methylcholantrenene A sarcoma, from CD(2)F(1) mice, tumor VEGF protein also varies with the estrus cycle with highest levels in proestrus and diestrus. VEGF gene expression in the mammary tumor does not change significantly across the cycle, but is modulated by the cycle in normal breast tissue. bFGF protein concentration is 6-fold higher in normal breast than in breast cancer. bFGF protein pattern in both tumor and breast are similar, opposite to VEGF, and affected by oophorectomy. bFGF message is modulated by the cycle in both breast cancer and normal breast. The changes in breast cancer capillary permeability, VEGF, and bFGF that occur during each fertility cycle, in breast tissue and breast cancer, putatively in response to cyclical changes in sex hormones, might contribute, at least in part, to both the modulation of cancer growth and post-resection breast cancer spread by the fertility cycle. These fertility cycle-induced effects on tumor biology also seem to extend to non-breast cancer biology.

Innate immune response to intramammary infection with Serratia marcescens and Streptococcus uberis

Streptococcus uberis and Serratia marcescens are Gram-positive and Gram-negative bacteria, respectively, that induce clinical mastitis. Once initial host barrier systems have been breached by these pathogens, the innate immune system provides the next level of defense against these infectious agents. The innate immune response is characterized by the induction of pro-inflammatory cytokines, as well as increases in other accessory proteins that facilitate host recognition and elimination of the pathogens. The objective of the current study was to characterize the innate immune response during clinical mastitis elicited by these two important, yet less well-studied, Gram-positive and Gram-negative organisms. The pro-inflammatory cytokine response and changes in the levels of the innate immune accessory recognition proteins, soluble CD14 (sCD14) and lipopolysaccharide (LPS)-binding protein (LBP), were studied. Decreased milk output, induction of a febrile response, and increased acute phase synthesis of LBP were all characteristic of the systemic response to intramammary infection with either organism. Infection with either bacteria similarly resulted in increased milk levels of IL-1 beta, IL-8, IL-10, IL-12, IFN-gamma, TNF-alpha, sCD14, LBP, and the complement component, C5a. However, the duration of and/or maximal changes in the increased levels of these inflammatory markers were significantly different for several of the inflammatory parameters assayed. In particular, S. uberis infection was characterized by the sustained elevation of higher milk levels of IL-1 beta, IL-10, IL-12, IFN-gamma, and C5a, relative to S. marcescens infection. Together, these data demonstrate the variability of the innate immune response to two distinct mastitis pathogens.

Mammary uptake and excretion of prostanoids in relation to mammary blood flow and milk yield during pregnancy-lactation and somatotropin treatment in dairy goats

Mammary arterious-venous differences (A-V) and excretion into milk of four prostanoids were related to changes in milk yield and milk vein blood velocity (MBV) in goats at different stages of pregnancy and lactation, and during somatotropin (ST) treatment in mid-lactation. Arterial concentrations and mammary A-V for the vasodilators prostacyclin (PGI(2)) and prostaglandin (PG) E(2) (measured as 6-keto-PGF(1 alpha) and bicyclic PGE(2), respectively) decreased from late pregnancy to lactation. A-V were negatively correlated to MBV (r = -0.32 to -0.34). Arterial concentrations of the vasoconstrictors PGF(2 alpha) and TXA(2) (measured as TXB(2)) changed similarly, but no A-V across the mammary gland were found. The vasodilator to vasoconstrictor ratio in plasma was around 1:1, and in skimmed milk around 0.29-0.49 due to significantly higher TXB(2) levels in milk compared to plasma. Close linear correlations were established between milk yield and excretion of TXB(2) into milk (r = 0.80, P < 0.001), and between MBV and PGE(2) excretion into milk (r = 0.69, P < 0.001). ST treatment stimulated MBV and mammary prostanoid supply, and decreased prostanoid concentration in milk vein plasma. The high arterial levels of prostaglandins during pregnancy most likely reflected uterine synthesis. Our results support a role for PGI(2) and PGE(2) in local mammary blood flow regulation during lactation. Increased mammary uptake of these two prostanoids may be involved in the mammary blood flow response to ST. TXA(2) may be synthesized by mammary epithelial as well as vascular cells, and TXA(2) may be an important factor in regulation of mammary function.

The amino acid need for milk synthesis is defined by the maximal uptake of plasma amino acids by porcine mammary glands

To define dietary indispensable amino acid (IAA) needs for milk synthesis by the mammary glands (MG), 16 lactating sows were fed 1 of 4 isocaloric diets varying in protein concentrations (from 78 to 235 g/kg) with an ideal amino acid (AA) pattern. On d 9, 13, 17, and 21 of lactation, blood samples were obtained simultaneously from a carotid artery and the main mammary vein every 30 min over 6 h. A quadratic regression model of the log mammary arteriovenous difference (AVD) of plasma IAA (ŷ) against daily intake of dietary IAA (X) was established. First, the reverse log intercept, defined as the mammary AVD at zero dietary AA supply, was used to quantify the contribution of endogenous IAA. The quantification was validated by body N balance coupled with AA composition analysis. Then, the estimated vertex (ŷ(max), X(i)) was used in 2 aspects: 1) The maximal mammary uptake of plasma IAA, quantified by multiplying the maximal mammary AVD and plasma flow rate, was considered the physiological IAA need for milk synthesis. 2) Corresponding to the ŷ(max), dietary IAA intake (X(i)) would represent the total dietary IAA requirement, i.e., the sum of maintenance need and milk synthesis need after adjustment for body weight loss. Thus, dietary IAA needs for milk synthesis were derived. Moreover, the estimate of lysine need for milk synthesis in this study was identical to an estimate obtained from multiple regression analysis of feeding trial data. We conclude that dietary IAA needs for milk synthesis can be quantified by the maximal uptakes of plasma IAA by porcine MG.

Effect of Dietary Energy Restriction on Vascular Density during Mammary Carcinogenesis

Inhibition of mammary carcinogenesis by dietary energy restriction is associated with a decrease in cell proliferation and the induction of apoptosis. Although changes in the metabolism of insulin-like growth factor I and glucocorticoids have been proposed to modulate these cellular processes, limitations in blood supply could induce similar effects. To investigate this possibility, female Sprague Dawley rats were given an injection of 1-methyl-1-nitrosourea and fed purified diets ad libitum or at 60% ad libitum intake, i.e., 40% dietary energy restriction. Premalignant mammary pathologies and mammary adenocarcinomas obtained from these rats were processed for vascular density analysis via CD-31 immunostaining. Vascular density, measured as vessels/unit area, of premalignant mammary pathologies and adenocarcinomas from dietary energy restriction rats was reduced 31 and 39%, respectively (P < 0.01). This effect, which was observed in a 50-microm wide band of tissue surrounding each pathology, was exerted on blood vessels > 25 microm2. Conversely, intratumoral vascular density was unaffected by dietary energy restriction. cDNA microarray and Western blot analyses of adenocarcinomas for evidence of dietary energy restriction-mediated effects on vascularization revealed that only the level of vascular endothelial growth factor receptor protein Flk-1 was significantly reduced (P < 0.001). It appears that dietary energy restriction imposes limitations in the supply of blood to developing pathologies, an effect that could directly inhibit the carcinogenic process. The vascular density data imply that dietary energy restriction inhibited the growth of endothelial cells but leave unresolved the question of whether dietary energy restriction had a specific effect on angiogenesis. The factors that account for the failure of dietary energy restriction to limit intratumoral vascularization are not obvious and merit additional investigation.

Targeting angiogenesis for mammary cancer prevention: factors to consider in experimental design and analysis

An experimental model developed to investigate premalignant stages of breast cancer was used to establish a rationale for designing experiments that target angiogenesis for cancer prevention. Blood vessels were identified via CD31 immunostaining, and all vessels that occurred in a 50 microm wide region circumscribing each pathology were counted using a digital imaging technique. The blood vessel density associated with terminal end buds was unaffected by carcinogen treatment, whereas vessel density was higher in intraductal proliferations and ductal carcinoma in situ than in terminal end buds (P < 0.001) and total vascularity increased with morphologic progression. In comparison with intraductal proliferation or ductal carcinoma in situ, mammary carcinomas had higher vascular density in the tissue surrounding the cancer with a marked increase in the number of blood vessels <25 microm(2). These data suggest that antiangiogenic chemopreventive agents would inhibit cancer occurrence if initiated at any premalignant stage of the carcinogenic process. Because increased vascular density observed during premalignancy could be explained by the size expansion of the lesion and its encroachment on a preexisting blood supply, by pathology-associated vessel expansion, and/or by angiogenesis, it remains to be determined if antiangiogenic agents will reduce the prevalence of premalignant lesions or cause their accumulation by blocking conversion to carcinomas. Failure to recognize the patterns of vascularization that accompany morphologic progression could limit the success of efforts to target angiogenesis for cancer prevention and lead to misinformation about how agents that affect blood vessel formation or growth inhibit the carcinogenic process.

Transgenic expression of mammalian heparanase uncovers physiological functions of heparan sulfate in tissue morphogenesis, vascularization, and feeding behavior

We have generated homozygous transgenic mice (hpa-tg) overexpressing human heparanase (endo-beta-D-glucuronidase) in all tissues and characterized the involvement of the enzyme in tissue morphogenesis, vascularization, and energy metabolism. Biochemical analysis of heparan sulfate (HS) isolated from newborn mice and adult tissues revealed a profound decrease in the size of HS chains derived from hpa-tg vs. control mice. Despite this, the mice appeared normal, were fertile, and exhibited a normal life span. A significant increase in the number of implanted embryos was noted in the hpa-tg vs. control mice. Overexpression of heparanase resulted in increased levels of urinary protein and creatinine, suggesting an effect on kidney function, reflected also by electron microscopy examination of the kidney tissue. The hpa-tg mice exhibited a reduced food consumption and body weight compared with control mice. The effect of heparanase on tissue remodeling and morphogenesis was best demonstrated by the phenotype of the hpa-tg mammary glands, showing excess branching and widening of ducts associated with enhanced neovascularization and disruption of the epithelial basement membrane. The hpa-tg mice exhibited an accelerated rate of hair growth, correlated with high expression of heparanase in hair follicle keratinocytes and increased vascularization. Altogether, characterization of the hpa-tg mice emphasizes the involvement of heparanase and HS in processes such as embryonic implantation, food consumption, tissue remodeling, and vascularization.

Portal Drained Visceral Flux, Hepatic Metabolism, and Mammary Uptake of Free and Peptide-Bound Amino Acids and Milk Amino Acid Output in Dairy Cows Fed Diets Containing Corn Grain Steam Flaked at 360 or Steam Rolled at 490 g/L

Objectives were to measure net fluxes of free (FAA) and peptide bound amino acids (AA) (PBAA) across portal-drained viscera (PDV), liver, splanchnic, and mammary tissues, and of milk AA output of lactating Holstein cows (n = 6, 109 +/- 9 d in milk) as influenced by flaking density of corn grain. Cows were fed alfalfa-based total mixed ration (TMR) containing 40% steam-flaked (SFC) or steam-rolled corn (SRC) grain. The TMR were offered at 12-h intervals in a crossover design. Six sets of blood samples were obtained from indwelling catheters in portal, hepatic, and mammary veins and mesenteric or costoabdominal arteries every 2 h from each cow and diet. Intake of dry matter (18.4 +/- 0.4 kg/d), N, and net energy for lactation were not altered by corn processing. Milk and milk crude protein yields (kg/12-h sampling) were 14.2 vs. 13.5 and 0.43 vs. 0.39 for cows fed SFC or SRC, respectively. The PDV flux of total essential FAA was greater (571.2 vs. 366.4 g/12 h, SEM 51.4) in cows fed SFC. The PDV flux of total essential PBAA was 69.3 +/- 10.8 and 51.5 +/- 13.2 g/12 h for cows fed SFC and SRC, respectively, and differed from zero, but fluxes of individual PBAA rarely differed between treatments. Liver flux of essential FAA was greater in cows fed SRC, but only the PBAA flux in cows fed SRC differed from zero. Splanchnic flux of FAA and PBAA followed the pattern of PDV flux, but variation was greater. Mammary uptake (g/12 h) of total essential FAA was greater in cows fed SFC than SRC (224.6 vs. 198.3, SEM 7.03). Mammary uptake of essential PBAA was 25.0 vs. 15.1, SEM 5.2, g/12 h for cows fed SFC or SRC, respectively, and differed from zero in half of the PBAA. Milk output of EAA was 187.8 vs 175.4, SEM 4.4 g/12 h in cows fed SFC and SRC, respectively, and output of most essential AA consistently tended to be greater in cows fed SFC. It is apparent that PBAA comprise a portion of total AA flux across PDV and are affected by grain processing. Further, this pool supplies an important component of AA taken up by the mammary gland. Quantifying the contribution of PBAA may improve diet formulation with respect to intestinal absorption and mammary uptake of AA.

Infusion of Glucose Directs Circulating Amino Acids to the Mammary Gland in Well-Fed Dairy Cows

The effect of intestinal glucose supply on mammary utilization of amino acids (AA) was studied in four lactating dairy cows. Glucose (0, 443, 963, and 2398 g/d) was continuously infused in the duodenum over 14-d periods using a Latin square design. A grass silage-based diet was formulated so that treatments (diet + infusions) were isoenergetic and isonitrogenous and met 100 and 110% of energy and protein requirements, respectively. Mammary AA uptake was determined by arteriovenous difference and continuous blood flow measurement. The milk protein yield tended to be quadratically increased (to +88 g/d for 963 g of glucose) by glucose infusion, but milk protein content was not significantly affected. Treatments did not change significantly arterial concentrations of urea and glucogenic AA. Mammary arterial fluxes of essential AA increased linearly with glucose infusion, whereas fluxes of nonessential and glucogenic AA were not significantly affected. Mammary arteriovenous differences and extraction rates were roughly unchanged by treatments. Mammary uptake of all essential AA, excluding Arg and Val, increased linearly with increasing supply of glucose. Ratio of blood AA uptake to milk protein output increased significantly for His, Met, and Leu. For the highest infused dose of glucose, all AA except for His were taken up in excess relative to their secretion in milk. Based on evolution of extraction rate and ratio of uptake to output, His and Leu could have limited the milk protein yield response to glucose infusions.

Isomers of conjugated linoleic acid differ in their effects on angiogenesis and survival of mouse mammary adipose vasculature

Dietary conjugated linoleic acid (CLA) is a cancer chemopreventive agent that has been shown to inhibit angiogenesis in vivo and in vitro, and to decrease vascular endothelial growth factor (VEGF) and Flk-1 concentrations in the mouse mammary gland. To determine which isomer mediates the antiangiogenic effects of CLA in vivo, the effects of diets supplemented with 5 or 10 g/kg c9,t11- or t10,c12-CLA isomers were compared in CD2F1Cr mice. Both isomers inhibited functional vascularization of a matrigel pellet in vivo and decreased serum VEGF concentrations; the t10,c12 isomer also decreased the proangiogenic hormone leptin (P < 0.05). Additionally, the t10,c12 isomer, but not c9,t11-CLA, rapidly induced apoptosis of the white and brown adipocytes as well as the preexisting supporting vasculature of the mammary fat pad (P < 0.05). Independent of this isomer-specific adipose apoptotic effect, both isomers induced a rapid and reversible decrease in the diameter of the unilocular adipocytes (P < 0.05). The ability of both CLA isomers to inhibit angiogenesis in vivo may contribute to their ability to inhibit carcinogenesis. Moreover, we propose that each CLA isomer uniquely modifies the mammary stromal "soil" in a manner that is useful for chemoprevention of breast cancer.

Eph and ephrin signaling in mammary gland morphogenesis and cancer

The Eph family of receptor tyrosine kinases and their membrane-bound ligands, the ephrins, play a central role in pattern formation during embryonic development and there is growing evidence that they are also instrumental in the control of tissue dynamics in the adult. The mammary gland is a paradigm for morphogenic processes occurring in the adult, since the gland develops predominantly postnatally and is subjected to continuous cyclic remodeling according to functional demands. Thus, pattern formation and the establishment of a functional organ structure are permanent themes in the mammary gland life cycle. In this paper we summarize the experimental evidence and discuss possible mechanisms by which Ephs and ephrins are modulating mammary epithelial cell adhesion, communication, and migration. Furthermore, we speculate on the different aspects of their influence on normal mammary gland development, function, and carcinogenesis.

[Correlation between the organ blood flow, substrate absorption from blood, the activity of transport into mammary gland secretory cells and formation milk components in cow]

Epithelial cells of mammary alveoles may he considered as a bioreactor that works being monitored by regulatory system maintaining balance between blood substrate supply and rate of macromolecular synthesis. In the trial performed on lactating cows assigned to feeding regimen with temporally altered level of nutrition, functioning of this system in the course of a transition period was studied. The earliest sign of adaptation was a decrease in volume blood flow through mammary gland provoking decline in uptake of water soluble substrates (glucose, amino N, P-hydroxybutyrate) with increase in arterio-venous difference across mammary gland and extraction efficiency. At the end of deprivation period, an activity of transport into the cell decreased for amino N from 7.5 to 4.5; l/min (p < 0.05), for P-hydroxyhutyrate from 16.0 to 13.8 l/min; activity of glucose transport was not changed. The data obtained indicate existence of defined points in the system monitoring organ blood supply and transport of substrates into the cell being adjusted during adaptation to alteration in the level of nutrition.

Effects of amino acid nutrition on the responses of dairy cows to milking more frequently with or without injection of growth hormone

The influence of amino acid nutrition on the response to milking more frequently, with or without injection of growth hormone, was examined in eight dairy cows in two 4 x 4 Latin squares with 28-d periods. The four treatments were a diet adequate in amino acids with or without injection of growth hormone and a diet inadequate in amino acids with or without injection of growth hormone. For all four treatments, during the last 14 d of each period, one half of the mammary gland was milked three times a day (3x), while the other half remained on twice-daily milking (2x). Both diets were based on grass silage given ad libitum and 4 kg/d of sugar beet pulp together with a supplement containing either fish meal (adequate diet) or feather meal (inadequate diet) as the only protein feeds. The diet containing feather meal is known to be deficient in His, Met, and Lys. On the fish meal diet, the cows responded positively to growth hormone and to milking more frequently and the responses to both treatments were additive. On the feather meal diet, however, even though injection of growth hormone increased the yield of milk protein by around 10%, milking more frequently did not affect milk production. It is concluded that milking more frequently has a weaker effect on the partitioning of amino acid use between body and udder than does growth hormone treatment.

Near-infrared spectroscopy evaluated as a technique for estimating udder haemodynamics in the lactating cow

Near-infrared spectroscopy (NIRS) that requires few compact instruments is a non-invasive and continuous method of monitoring haemodynamics in living organs. To assess the feasibility of using NIRS in evaluating the udder haemodynamics in six dairy cows, a probe component consisting of a light-emitting diode and a phototransistor was attached to the left side of the udder surface. Real-time variation of tissue haemodynamics was analysed and the data were transferred to the computer by way of a radiotelemetry system. On induction of temporary congestion by applying pressure with the hand pressed firmly against the left milk vein for 20 s, concentration of oxyhaemoglobin decreased throughout the 20-s duration of congestion, and concentration of deoxyhaemoglobin increased. A surge in blood volume was also observed from the beginning of congestion, then the volume attenuated to baseline. The data demonstrated that the reading seen on the monitor reflects the real-time status of the mammary gland. NIRS shows promise as a useful approach to physiological studies.

Mammary blood flow does not limit milk yield in lactating goats

There is a close relationship between mammary blood flow (MBF) and milk production, but whether MBF is limiting milk yield has not been determined. Five lactating goats received close arterial (external pudic) infusion of PBS or the nitric oxide donor diethylamine NONOate (0.5 mg/h; NONate) for 6 h, according to a crossover design. Goats were hand milked (with oxytocin) every 2 h starting 2 h before and ending 6 h after the end of the infusion. In one goat, a transit time flow probe was implanted around the infused and noninfused artery, whilst in another goat a flow probe was implanted around the infused artery only. Infusion of PBS did not affect MBF or milk production. As with previous results (Lacasse et al., 1996), NONate induced a rapid increase (up to 250% of preinfusion level) in MBF in the infused gland only. Mammary blood flow was still above the preinfusion level at the end of the infusion period. Despite this increase in MBF, NONate did not affect milk production. Milk yield ratio (infused/noninfused gland) averaged 1.20, 1.12, and 1.17 for the preinfusion, infusion and post infusion periods, respectively. Similarly, protein, fat and lactose yields were not affected by PBS or NONate infusion. These results provide no support to the contention that increasing MBF can enhance milk production.

Effect of ambient temperature on mammary gland metabolism in lactating sows

Two groups of three multiparous Large White x Landrace sows were used to investigate the direct effect of ambient temperature on mammary gland metabolism. Sows from the first group were exposed to temperatures of 28 degrees C between d 8 and 14 of lactation, and 20 degrees C between d 15 and 21; treatments were reversed in the second group. Four to six d after farrowing, an ultrasonic blood flow probe was implanted around the right external pudic artery and catheters were fitted in the right anterior mammary vein and in the carotid artery. After surgery all sows were fed 3.8 kg/d of a lactation diet. The arteriovenous (AV, mg/L) plasma samples were obtained every 30 min between 0915 and 1545 on d 5 of exposure to ambient temperature; the same day, milk samples were collected at 1630. Additional arterial samples were obtained between 1000 and 1100 on d 1, 4, and 6 of exposure. Milk yield was estimated from the body weight gain of the litter. Elevated temperature tended to reduce BW loss (2.44 vs 1.82 kg/d, P < 0.10), but did not affect milk yield (11.0 kg/d). Glucagon and leptin arterial concentrations increased (12 and 8%, respectively; P < 0.10), but thyroxin and triiodothyronine concentrations decreased (26 and 16%, respectively; P < 0.01) between 20 and 28 degrees C. Expressed as a percentage of total nutrients, AV difference, glucose, amino acids, triglycerides (TG), free fatty acids, and lactate A-V differences represented 60, 20, 11, 8, and 1%, respectively. Exposure to 28 degrees C increased the extraction rate of glucose, TG, and a-amino acid N (13, 8, and 2.5%, respectively; P < 0.10). The extraction rates of essential and nonessential amino acids were not affected by temperature. The right pudic artery mammary blood flow increased (872 vs 945 mL/min, P < 0.05) between 20 and 28 degrees C, whereas milk yield was unaffected by temperature. It is suggested that this apparent inefficiency of the sow mammary gland in hot conditions could be related to an increase of proportion of blood flow irrigating skin capillaries in order to dissipate body heat.

Differential effects of selective estrogen receptor modulators and estrogens on mammary blood flow in the ovine

OBJECTIVE

Hormone replacement therapy has been implicated in the increased incidence of breast cancer, although selective estrogen receptor modulators have been shown to be effective in the prevention of breast cancer. Breast cancers are associated with increased mammary blood flow compared to benign breast lesions. However, few studies have examined the hemodynamic effects of hormonal agents on the mammary circulation that promote or reduce the risk of breast cancers. Although estradiol-17beta has been shown to increase mammary blood flow, the effect of selective estrogen receptor modulators remains undetermined. We therefore compared the vascular effects of selective estrogen receptor modulators and estrogens on mammary blood flow.

STUDY DESIGN

Fourteen nonpregnant ovariectomized ewes were instrumented to measure mean arterial pressure, heart rate, and uterine and mammary blood flows. Compounds were administered intravenously on separate days, and responses were monitored up to 4 hours. Compounds that were studied included estradiol-17beta (1 microg/kg), conjugated equine estrogens (0.625 and 1.25 mg), tibolone (2.5 and 5 mg), raloxifene (10 microg/kg), and tamoxifen (300 microg/kg).

RESULTS

None of these compounds significantly affected mean arterial pressure or heart rate, but all of the compounds significantly increased uterine blood flow. Estradiol-17beta increased mammary blood flow by 98% +/- 25%; conjugated equine estrogen increased mammary blood flow by 46% +/- 6% and 68% +/- 13% at the 0.625 and 1.25 mg doses, respectively. Tibolone increased mammary blood flow by 37% +/- 13% at the 2.5-mg dose and by only 14% +/- 4% at the 5-mg dose. Neither raloxifene nor tamoxifen significantly altered mammary blood flow.

CONCLUSION

Although estrogens and selective estrogen receptor modulators induced similar increases in uterine blood flow, they had differential effects on mammary blood flow.

Effect of protein source on amino acid supply, milk production, and metabolism of plasma nutrients in dairy cows fed grass silage

This study conducted according to a 4 x 4 Latin square with 28 d periods and four ruminally cannulated Finnish Ayrshire cows investigated the effect of protein supplements differing in amino acid (AA) profile and rumen undegradable protein content on postruminal AA supply and milk production. Mammary metabolism of plasma AA and other nutrients were also studied. The basal diet (Control; 13.4% crude protein) consisted of grass silage and barley in a ratio of 55:45 on a dry matter basis. The other three isonitrogenous diets (17.0% crude protein) were control + fishmeal (FM), control + soybean meal (SBM), and control + corn gluten meal (CGM). The protein supplements replaced portions of dry matter of the control diet maintaining the silage to barley ratio constant for all diets. Dry matter intake was limited to 95% of the preexperimental ad libitum intake and was similar (mean 19.8 kg/d dry matter) across the diets. Protein supplements increased milk, lactose, and protein yields but did not affect yields of energy-corrected milk or milk fat. Milk protein yield response was numerically lowest for diet SBM. Protein supplements increased milk protein concentration but decreased milk fat and lactose concentrations. Microbial protein synthesis and rumen fermentation parameters were similar across the diets, except for an increased rumen ammonia concentration for diets supplemented with protein feeds. Protein supplements increased N intake, ruminal organic matter and N, and total tract organic matter, N, and neutral detergent fiber digestibilities. Protein supplements also increased N and AA flows into the omasum, with SBM giving the lowest and CGM the highest flows. This was associated with an unchanged microbial N flow and a higher undegraded dietary N flow. The omasal flows of individual AA reflected differences in total N flow and AA profile of the experimental diets. Differences in AA flows did not always reflect plasma AA concentrations. The results indicated that AA supply of dairy cows fed a grass silage-cereal diet can be manipulated using protein supplements differing in ruminal protein degradability and AA profile. Lower milk production response to SBM than that to FM and CGM appeared to be related mainly to lower N and AA supplies arising from a high ruminal protein degradability of SBM. Histidine appeared to be the first limiting AA for milk protein synthesis on the control diet. Mammary gland may regulate AA uptake according to requirements.