Relationship between estimated breeding value for somatic cell count and prevalence of intramammary infection in dairy goats

Abstract

AIM

The objective of the study was to determine if dairy goats selected as having either Low or High estimated breeding values for somatic cell count (EBV SCC) would differ in prevalence of intramammary infection (IMI).

METHODS

The EBV SCC for all does in two dairy goat herds were calculated based on the three or four herd test results for somatic cell count (SCC) from the preceding lactations. Within each herd does were categorised into six age groups (i.e. 2, 3, 4, 5, 6 and >6 years old) and ranked on EBV SCC. Approximately the top (High group; n=149) and bottom (Low group; n=148) 12.5% of the does within each age group within each herd had milk samples collected from each gland on one calendar day for subsequent microbiology. The presence of any IMI or IMI due to a major pathogen at goat level was modelled using a GLM with a binomial link function.

RESULTS

There was no difference between the High and Low groups in terms of age, days in milk at the time of sampling or in the proportion of the Saanen breed. Mean EBV SCC was -1.0 (SD 0.4) vs 0.8 (SD 0.4) for the Low and High groups, respectively, and there was no overlap in EBV SCC between groups. Goats in the Low group had lower prevalence of any IMI than those in the High group (0.67 (95% CI=0.58-0.76) vs 0.81 (95% CI=0.74-0.88); p=0.002). Goats in the High group were 8.4 (95% CI=1.9-38.0) times more likely to have IMI due to a major pathogen infection than goats in the Low group (p=0.006).

CONCLUSIONS

Does with a high EBV SCC had a higher prevalence of any IMI and were more likely to have an IMI due to a major pathogen than does with a low EBV SCC. Thus selection for EBV SCC is likely to result in a lower SCC and also lower prevalence of IMI.

Composition and distribution of fatty acids in triglycerides from goat infant formulas with milk fat

Most infant formulas use vegetable oils in place of milk fat to provide an overall fatty acid profile similar to that of breast milk. Vegetable oils have 5 to 20% saturated fatty acids in the sn-2 position of triglycerides unless they are modified by interesterification. Interesterification is increasingly used for the fat for infant formulas to raise the level of saturated fatty acids in the sn-2 position to 40 to 60%. The objective of this study was to verify an alternative approach to providing the appropriate fatty acid profile, including in the sn-2 position, for a goat infant formula. In this method, 55% of total fat was made from goat milk fat and 45% from a mixture of unmodified high oleic sunflower, canola, and sunflower oils in a ratio of 44:30:26. The fatty acid profile was measured by gas-liquid chromatography and the relative percentage of fatty acids in the sn-2 position of triglycerides was measured via partial deacylation with Grignard reagent using trimethylsilyl derivatives of monoacylglycerols. Mixing goat milk fat with vegetable oils produced a formula with a profile of essential fatty acids and a ratio of linoleic:alpha-linolenic fatty acids within the required interval of 5 to 15:1 recommended for infant formula. The proportion of palmitic acid in the sn-2 position was 31%.

Effects on adhesion molecule expression and lymphocytes in the bovine mammary gland following intra-mammary immunisation

Changes to adhesion molecule expression and lymphocyte populations were evaluated in alveolar mammary tissue collected from cows following an immunisation protocol that involved intra-mammary inoculation to induce an IgA response in mammary secretions. The right quarters of the udder were immunised; the left side acted as a control. Antibody titres in secretions showed that at least two animals responded with antigen-specific IgA. Numbers of T-lymphocytes were 4-fold higher in immunised glands compared with controls (P<0.05). IgA-, IgM- and IgG-positive cell numbers were significantly higher (P<0.01) in immunised glands compared with controls in three of the four cows. No mucosal addressin molecule-1 (MAdCAM-1), vascular cell-adhesion molecule-1 (VCAM-1) or peripheral node addressin (PNAd) protein expression was detected on smaller venules that stained positively for von Willebrand factor in alveolar mammary tissues, from either immunised or control glands. Both VCAM-1 and PNAd were detected on smaller venules in supramammary lymph nodes, however, there was no significant difference between immunised and control glands. Quantification of MAdCAM-1 mRNA showed very low expression in both immunised and control alveolar tissue compared with Peyer's patch positive-control tissue. These findings suggest that the bovine mammary gland is capable of a mucosal antibody response; however, MAdCAM-1 is not involved with lymphocyte homing to the mammary gland in this species.

Adhesion molecule expression in the bovine mammary gland

The bovine mammary gland requires lymphocytes for immune protection of the gland from foreign pathogens and, in addition, to transfer immune protection to the neonate via colostrum and milk. The process of homing primed lymphocytes to tissues is mediated by the interaction of cell-adhesion molecules displayed on the surface of lymphocytes and counter receptors displayed on the vascular endothelium. This study was conducted to identify the cell-adhesion molecules involved in homing lymphocytes to the bovine mammary gland at four different physiological stages; pregnant, colostral, lactation and involution. The expression and distribution of adhesion molecules in alveolar tissues and supramammary lymph nodes from the mammary glands of healthy cows was determined in situ by immunohistochemical analysis and compared with bovine Peyer's patch, used as a typical mucosal-associated lymphoid tissue and positive control. The mucosal addressin molecule, MAdCAM-1, was not detected in bovine mammary tissues at any of the four different physiological stages. Absence of MAdCAM-1 expression was verified by quantitative real-time RT-PCR analysis. Transcription levels of MAdCAM-1 mRNA were found to be more then 5 x 10(3)-fold lower in mammary alveolar tissues compared with bovine Peyer's patch tissues. In contrast to MAdCAM-1, phase-dependent protein expression of VCAM-1 was detected in both mammary alveolar tissues and the supramammary lymph nodes, with the highest expression observed in colostral phase cows. The protein expression in mammary alveolar tissues was limited to larger venules, although in colostral phase cows, VCAM-1 was also detected around the alveoli perimeter. In the supramammary lymph node, VCAM-1 protein was observed on both small and large venules. PNAd was detected in supramammary lymph nodes at all physiological stages of the mammary gland; however, it was not found in mammary alveolar tissues. Lymphocytes expressing beta7 were not detected in mammary tissues and lymphocytes expressing CD62L were only observed in the supramammary lymph nodes. Overall the data suggest that MAdCAM-1 and VCAM-1 are not involved in homing lymphocytes to the bovine mammary gland; whereas, VCAM-1 and PNAd may have this role in the supramammary lymph node.

Mineral Retention in Three-Week-Old Piglets Fed Goat and Cow Milk Infant Formulas

Goat milk and cow milk are commonly used in infant formula preparations and, as such, understanding the nutritional characteristics of infant formulas made from these milks is important. In this study, a goat milk infant formula was compared with an adapted (whey-enhanced) cow milk infant formula with respect to mineral absorption and deposition using the 3-wk-old piglet as a model for the 3-mo-old infant. Equal numbers of piglets (n = 8) were fed either the goat milk formula or the cow milk formula. The mineral composition of the prepared goat milk formula was higher than that of the prepared cow milk formula for most minerals, including calcium (75.1 vs. 56.7 mg/100 mL) but excluding iron, which was higher in the prepared cow milk formula (0.92 vs. 0.74 mg/100 mL). The amounts of calcium, phosphorus, and manganese absorbed by the piglets were significantly higher for the goat milk formula, whereas the amounts of zinc, iron, and magnesium absorbed were significantly higher for the cow milk formula. Apparent mineral absorption, relative to intake, was statistically higher in the cow milk formula for calcium and phosphorus, although the actual differences were very small (less than 1.3%). For copper, zinc, iron, and magnesium there was no significant difference between treatments in apparent mineral absorption, whereas for manganese, absorption was higher for the goat milk infant formula. The absolute mineral deposition was higher in piglets fed the goat milk formula for calcium, phosphorus, and manganese, whereas iron deposition was higher in the piglets fed cow milk formula. For all other minerals tested, there were no significant differences between treatments. The goat milk infant formula provided a pattern of mineral retention in the 3-wk-old piglet very similar to that of the adapted cow milk infant formula. The minor differences observed between the 2 appeared to be due to the different mineral contents of the 2 formulas.

True Ileal Amino Acid Digestibility of Goat and Cow Milk Infant Formulas

Goat milk is used as an alternative to cow milk for the production of infant formulas. However, little is known about the protein quality and, specifically, about the digestible AA pattern of goat milk formulas compared with their cow milk counterparts. In this study, the true ileal AA digestibility of a goat milk infant formula was compared with a premium cow milk infant formula. The 3-wk-old piglet was used as a model for the 3-mo-old infant. Both milk formulas were prepared as described by the manufacturer, with titanium dioxide added as an indigestible marker. The formulas were fed to the piglets over a 2-wk trial period. Digesta from the terminal ileum were collected post euthanasia and analyzed for AA content, along with samples of the formulas. True AA digestibility was determined after correcting for endogenous AA loss at the terminal ileum of pigs fed an enzyme-hydrolyzed casein-based diet, followed by ultrafiltration (5,000 Da) of the digesta. Total urine and feces collection was also undertaken to determine the nitrogen retention from the diets. The true ileal AA digestibility was similar between the goat and cow milk infant formulas for all AA except Gly and Trp. There was no significant difference in the nitrogen retention of piglets fed the two different formulas. The goat milk infant formula and the premium cow milk infant formula were similar in terms of protein quality.

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.

Stat5 phosphorylation status and DNA-binding activity in the bovine and murine mammary glands

The transcription factors Stat5a and Stat5b are mediators of prolactin signalling in mammary epithelial cells, and are thought to play a role in lactogenesis. In cultured cells, activation of Stat5 activity through phosphorylation results in Stat5 binding to the promoters of at least some of the milk protein genes, thereby stimulating their transcription. However, the mammary biology of Stat5 differs between species, and the role of Stat5 in the bovine mammary gland is not fully understood. We have generated an antibody that specifically recognises the phosphorylated forms of Stat5a and Stat5b and used it to compare the levels of phosphorylated Stat5 with Stat5 DNA-binding activity in bovine and murine mammary tissue. Both Stat5 DNA-binding activity and phosphorylation status in the bovine mammary gland were at near-maximal levels at late pregnancy (27-35 days prior to calving), when at least three of the major milk proteins are not highly expressed. In addition, these studies revealed significant animal-to-animal variation in the level of Stat5 activity in both species. The results are consistent with a role in terminal differentiation of mammary epithelial cells. They also suggest that the stimulation of high-level expression of milk protein genes in the bovine mammary gland is not through activation of the prolactin receptor-Jak2-Stat5 pathway.

Effects of mammary engorgement and feed withdrawal on microvascular function in lactating goat mammary glands

The responses of the mammary microvasculature in lactating goats (n = 8) during feed withdrawal (18-20 h) and mammary engorgement (26-28 h of milk accumulation) were compared using an indicator-dilution technique with FITC-albumin and [(14)C]sucrose as the intravascular and diffusible indicators, respectively. Feed withdrawal and mammary engorgement caused a 50-60% decrease in mammary arterial flow and in the permeability-surface area product (PS) values for sucrose. Only feed withdrawal increased the mean transit time [from 17.3 to 30.0 s, SE of the difference (SED) = 2.16, P < 0.01] of FITC-albumin, whereas only mammary engorgement reduced sucrose extraction (0.63 to 0.51, SED = 0.04, P < 0.05). Mammary engorgement also caused a substantial reduction in the sucrose-accessible extravascular space from 92 to 44 ml (SED = 15.2, P < 0.01). In a separate experiment using five goats, milking after mammary engorgement did not immediately restore arterial flow or sucrose extraction, indicating that the effect of milk accumulation was not mediated simply via increased intramammary pressure. In conclusion, feed withdrawal resulted in slower flow in the capillary bed but apparently no change in capillary recruitment, whereas mammary engorgement caused capillary derecruitment.

Effects of pasture allowance on the yield and composition of milk from cows of different beta-lactoglobulin phenotypes

The objective of this study was to determine whether the differences in the composition of milk from cows of different beta-lactoglobulin beta-LG) phenotypes are affected by the amount of pasture available and, hence, pasture dry matter intake. Twenty-two Friesian cows of each of the AA and BB variants of the beta-LG phenotype were subjected to ad libitum grazing or restricted grazing in crossover experiments during spring (early lactation, approximately 60 d in milk) and summer (mid to late lactation, approximately 180 d in milk). Milk samples were collected from each cow at the end of each 8-d treatment period and analyzed for composition. Cows of the AA variant of the beta-LG phenotype had higher concentrations of whey protein and beta-LG, but lower concentrations of casein (CN), alpha-CN, kappa-CN (summer only), and BSA, than cows of the BB variant. Compared with cows with a restricted allowance, cows grazing ad libitum had higher milk yields and concentrations of protein, casein, whey protein, and all individual proteins except BSA and immunoglobulin. There were no interactions between effects of pasture allowance and phenotype on milk yield or composition. The data show that having adequate pasture for grazing cows is important not only to maximize milk yield, but also to optimize concentrations of protein and casein, and hence the manufacturing potential of milk. Further, the differences in composition of milk from cows of differing beta-LG phenotypes persisted during short-term restrictions in pasture allowance, and between spring and summer.

Milk whey protein concentration and mRNA associated with beta-lactoglobulin phenotype

Two common genetic variants of β-lactoglobulin (β-lg), A and B, exist as co- dominant alleles in dairy cattle (Aschaffenburg, 1968). Numerous studies have shown that cows homozygous for β-lg A have more β-lg and less α-lactalbumin (α-la) and casein in their milk than cows expressing only the B variant of β-lg (Ng-Kwai-Hang et al. 1987; Graml et al. 1989; Hill, 1993; Hill et al. 1995, 1997). These differences have a significant impact on the processing characteristics of the milk. For instance, the moisture-adjusted yield of Cheddar cheese is up to 10% higher using milk from cows of the β-lg BB phenotype compared with milk from cows expressing only the A variant (Hill et al. 1997). All these studies, however, describe compositional differences associated with β-lg phenotype in established lactation only. No information is available on the first few weeks of lactation, when there are marked changes in the concentrations of β-lg and α-la (Pérez et al. 1990).

Effect of milking frequency and pasture intake on milk yield and composition of late lactation cows

Twenty-four monozygous twinsets in late lactation (> 210 d in milk) were used to examine the effects of feed restriction and milking frequency prior to drying off on milk yield and composition in a pastoral dairying system. Cows were assigned to one of four treatment groups for 26 d and were milked either twice or once daily and given either unrestricted or restricted access to feed. Dry matter intakes averaged 16 or 8 kg per cow per day, and diets comprised ryegrass and white clover pasture supplemented with 15% pasture silage. Feed restriction and once daily milking reduced milk yield and increased concentrations of milk fat and protein. Somatic cell count was increased by feed restriction only. Production losses caused by feed restriction were nearly threefold higher than were those for once daily milking. Yields of components that were mammary synthesized and serum derived were reduced by feed restriction, in accordance with milk volume reduction. Plasma lactose concentration increased with once daily milking only and indicated enhanced permeability of mammary tight junctions. Both feed restriction and once daily milking compromised milk quality, but increased leakage of serum components into milk via mammary tight junctions was deemed to occur only for once daily milking.

Metabolic effects of amylin in lactating goats

The objective of this study was to investigate the role of amylin (a pancreatic hormone) in regulating metabolism in support of lactation. Rat amylin was infused (320 pmol.kg LW(-1).h(-1)) for 6 h via an external pudic (mammary) artery into six lactating goats. This dose of amylin led to a sixfold increase in plasma concentrations of amylin relative to baseline. Amylin infusion increased plasma concentrations (jugular) of glucose and NEFA up to 16 and 168%, respectively, relative to saline infusion. In contrast, plasma concentrations of Ca and PO4 during amylin infusion were reduced by 18 and 30%, respectively, relative to saline infusion. Plasma concentrations of IGF-I, insulin, and Mg were not different between the two treatments, although IGF-I concentrations in the amylin-infused group, 1 and 6 h postinfusion, were significantly higher than those in the saline-infused group. Similarly, amylin infusion failed to affect milk yield and major constituents of milk except protein; milk protein content decreased progressively until the end of amylin infusion and remained low thereafter. Amylin also had no effect on minerals in milk (Ca, PO4, Mg, Fe, Sr, S, K, or Na) except Zn, which was significantly decreased from 56.8+/-5.8 micromol/L at 0 h to 44.5+/-2.4 micromol/L at 6 h postinfusion. Mammary blood flow (measured with a transit-time blood flow probe) increased up to 26% during amylin infusion, although this effect lasted only for the first 3 h. In conclusion, amylin increased plasma concentrations of glucose and NEFA, and mammary blood flow, while decreasing plasma concentrations of Ca and PO4. Despite these metabolic changes, amylin infusion did not increase milk yield of lactating goats.

No evidence for basolateral secretion of milk protein in the mammary gland of lactating goats

Recent research suggests that a small percentage of milk proteins may be secreted basolaterally, which would have implications for our work on the permeability of tight junctions in the mammary epithelium. In our work, the presence of alpha-lactalbumin (LA) or lactose in plasma is used as an indicator of permeability. The aim of this study was to examine basolateral secretion by determining the presence of milk proteins in efferent mammary lymph. Five Saanen goats were fitted with mammary lymph catheters and were administered intramammary isosmotic bolus infusions of sucrose control solutions or ethylene glycolbis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid to induce leaky tight junctions. Lymph samples were collected before and approximately 5 h after infusion. Lymph was analyzed by Western blotting for the presence of alpha-casein (CN), beta-CN, and alpha-LA No alpha-CN or beta-CN was detected in lymph, but alpha-LA was detected in all lymph samples. Moreover, the signal was much stronger in samples from goats that were treated with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, and concentrations of alpha-LA in lymph were significantly increased with this treatment. These changes and the absence of casein in lymph suggest increased permeability of tight junctions rather than basolateral secretion. In summary, these data do not support basolateral secretion.

Effect of atropine on milk protein yield by dairy cows with different beta-lactoglobulin phenotypes

The objective of this study was to determine the response of individual milk proteins to a reduction in amino acid (AA) availability induced by atropine and to determine whether the response was different in cows with different beta-lactoglobulin (LG) phenotypes. Six cows that were homozygous for the A variant of beta-LG and six cows that were homozygous for the B variant of beta-LG were each given a single subcutaneous injection of saline or 20 mg of atropine. In both groups of cows, atropine decreased milk yield by 30% and reduced the concentration of alpha-lactalbumin (LA) by 25 to 30% at 8 h following injection. Eight hours after atropine injection, yield of beta-LG was 41% lower than it was following saline injection, and yield of beta-casein (CN) after atropine injection declined 16% relative to saline. Concentrations of BSA and the ratio of gamma-CN to beta-CN, which reflects plasmin activity in milk, were significantly increased after administration of atropine. Although the response to atropine tended to be more pronounced in cows that were homozygous for beta-LG B, they were not significantly different from the response of cows that were homozygous for beta-LG B, they were not significantly different from the response of cows that were homozygous for beta-LG A. The differential response of individual proteins to a reduction in AA concentrations in whole blood suggested that susceptibility to restriction in substrate availability differed for individual proteins. The concentration of lactose in plasma did not change, which implied that the integrity of the mammary epithelial barrier was not compromised when AA derived from blood were diminished. The consistent concentration of lactose combined with the minimal increase in total yield of BSA in milk following atropine treatment indicated that the increased concentration in milk of proteins derived from serum was due to the concentrating effect of lower milk volume.

Time course of milk accumulation-induced opening of mammary tight junctions, and blood clearance of milk components

Eight cows in early lactation were used to study the effect of milk accumulation on the state of mammary tight junctions and to examine alpha-lactalbumin as an indicator of tight junction permeability in vivo. During three successive periods, the cows were milked twice (4 days), once (6 days), and twice daily (4 days). Plasma lactose, alpha-lactalbumin, and milk sodium concentrations were used as indicators of tight junction permeability. Furthermore, four cows were used to study the clearance of lactose and alpha-lactalbumin from the blood. Milk yield during once-daily milking decreased by 15.4% (P < 0.001). All indicators of mammary tight junction patency increased (P < 0.05) transiently during once-daily milking and indicated that tight junctions opened after approximately 18 h. Plasma alpha-lactalbumin and lactose were highly correlated (r = 0.82, P < 0.001), indicating the suitability of plasma alpha-lactalbumin as an indicator of tight junction status in vivo. Clearance of alpha-lactalbumin and lactose from the blood was best described by a biexponential model. Elimination half-lives for lactose and alpha-lactalbumin were 44 and 40 min, respectively. This study showed that milk stasis during early established lactation induces tight junctions to switch to a leaky state after approximately 18 h and to revert to the closed state shortly after milking.

The effect of bovine somatotropin and diet on somatotropin binding sites in hepatic tissue of lactating dairy cows

In the lactating cow, galactopoiesis is stimulated by treatment with recombinant bovine somatotropin (bST) and by an improved plane of nutrition. The present study determined the interaction between these variables and examined whether a positive galactopoietic effect was accompanied by a change in hepatic binding sites for bST. Lactating dairy cows received one of three diets with increasing nutrient density; diet 1, 150 g/kg of dry matter (DM) of crude protein (CP) and 10.5 MJ/kg of DM of metabolizable energy; diet 2, 170 g/kg of DM of CP and 11.3 MJ/kg of DM of metabolizable energy; and diet 3, 190 g/kg of DM of CP and 12.1 MJ/kg of DM of metabolizable energy. At 90 d after calving, half of the cows in each dietary group were treated with bST every 14 d for the rest of the lactation. Both nutrient density and administration of bST increased milk yield significantly in mid and late lactation; there was no significant treatment by diet interaction. Treatment with bST significantly increased plasma concentrations of insulin-like growth factor (IGF)-I compared with IGF-I concentrations in controls in both mid and late lactation. Comparisons within diet revealed that concentrations of IGF-I were significantly higher in cows fed diet 3 than in cows fed diets 1 and 2 at both stages of lactation. Increases in plasma insulin were confined to cows in late lactation, and no changes were observed for nonesterified fatty acids. Liver biopsies showed that concentrations of hepatic binding sites for bST were not affected significantly by bST treatment but were increased in midlactation for cows fed diet 3. Concentration of hepatic binding sites per unit weight of tissue were greater for cows in midlactation than for cows in late lactation. In summary, exogenous bST treatment and increased nutrient density were associated with elevated plasma IGF-I concentrations and increased milk yield; however, only nutrient density in midlactation increased the number of hepatic binding sites for bST. Exogenous bST treatment had relatively little effect on the concentration of hepatic bST receptors compared with nutrient density.

Glucose transport in a murine mammary epithelial cell line

The glucose transport systems of the COMMA-D cell line (a murine mammary epithelial cell line) were examined using 2-deoxyglucose as substrate. The kinetics and inhibition studies with other sugars including xylose suggested that the transport system had properties of both GLUT-1 and Glut-3. Subsequent analysis of mRNA transcripts using cDNAs for GLUT-1 to 4 showed that only GLUT-1 was expressed in the COMMA-D cells. The results highlight the fact that kinetic and substrate specificity are not sufficient, by themselves, for the identification and characterisation of GLUT isoforms in cultured cells.

Interaction of interferon-gamma and epidermal growth factor in the regulation of nitric oxide production and cellular proliferation in a cultured murine mammary cell line, COMMA-D

The regulation of nitric oxide synthase (NOS) activity and gene expression by cytokines and growth factors has been studied using the murine mammary epithelial cell line, COMMA-D. NOS activity was stimulated by exposure to interferon-gamma (IFN-gamma) and could be further stimulated by tumour necrosis factor-alpha (TNF-alpha) and epidermal growth factor (EGF) although neither was affective alone. The maximal activity observed in the presence of IFN-gamma and EGF was not affected by the order in which cells were exposed. Messenger RNA levels for the inducible NOS isoform were increased by IFN-gamma and TNF-alpha in a manner consistent with the elevation of NOS activity. EGF also stimulated thymidine incorporation into DNA which was attenuated by coexposure with IFN-gamma in a manner that appeared to be largely NO-independent.

Local secretion of nitric oxide and the control of mammary blood flow

Our objective was to test the hypothesis that local production of the vasorelaxant nitric oxide could regulate mammary blood flow. In four lactating Saanen goats, the response of mammary blood flow to intraarterial infusion of the nitric oxide donor diethylamine NONOate and the inhibitor of nitric oxide synthesis N omega-nitro-arginine was measured. Diethylamine NONOate induced a rapid and sustained increase of mammary blood flow in the infused gland only, suggesting a direct effect on vasculature of the mammary gland. In contrast, infusion of N omega-nitro-arginine decreased mammary blood flow by up to 35%, and the coinfusion of arginine, the nitric oxide precursor, with N omega-nitro-arginine markedly reduced its ability to decrease mammary blood flow. The distribution of nitric oxide synthase was investigated in cryosections of caprine and bovine mammary tissue by histochemical staining for NADPH-diaphorase activity and by immunocytochemistry using specific antibodies against two nitric oxide synthase isoforms. Both techniques revealed nitric oxide synthase in the vascular endothelium and secretory epithelium of the two species. Only antibodies against nitric oxide synthase-III showed specific staining. These results suggest that the mammary gland produces and responds to nitric oxide and, further, raise the possibility that the epithelium may control its own blood supply by secreting nitric oxide.

Regulation of blood flow in the mammary microvasculature

Although milk yield of cows and goats is known to be closely related to the total flow of blood through the udder, a number of studies suggest that milk yield can vary independently. No studies have attempted to measure the proportion of total flow that is nutritive. Within the mammary gland, capillary networks form a basket-like architecture surrounding each alveolus. Notably, flow in individual capillaries is not constant and varies among capillaries. Capillary flow (measured by intravital microscopy) was decreased by oxytocin, which generally increased total flow in the mammary artery, suggesting that the proportion of total flow that is nutritive can vary. In addition to classic metabolic regulators (e.g., carbon dioxide and oxygen) of tissue blood flow, the mammary gland produces a number of vasodilatory compounds, including parathyroid hormone-related protein, insulin-like growth factor-I, prostacyclin, nitric oxide, and endothelin. All of these compounds have been shown to alter mammary blood flow. Mammary tissue also contains kallikrein and angiotensin-converting enzyme, which convert circulating kinins and angiotensin, respectively, into potent vasoactive compounds. A number of these compounds are produced by epithelial cells themselves, providing a mechanism for the functioning epithelium to control its own blood supply and, hence, nutrient flow for milk synthesis. In this review, we examine the nature of the mammary microcirculation, its behavior under different conditions, and some of the regulatory features of the mammary microvasculature.

Influence of insulin-like growth factor-binding protein-2 on plasma clearance and transfer of insulin-like growth factors-I and -II from plasma into mammary-derived lymph and milk of goats

Plasma clearance of insulin-like growth factors-I and -II (IGF-I and -II) and insulin-like growth factor-binding protein-2 (IGFBP-2) from lactating goats (n = 4) was determined following a single intravenous injection of the corresponding 125I-labelled human protein. Transfer of these proteins out of the vascular space was monitored by their subsequent appearance in mammary-derived lymph and milk. Clearance of 125I-IGFBP-2 from circulation was 0.37 +/- 0.06 ml/min/kg, which is markedly greater than that of 125I-IGF-I or -II (0.11 +/- 0.01 and 0.12 +/- 0.01 ml/min/kg respectively). This was also reflected in longer elimination half-lives for IGF-I (353 +/- 6 min) and -II (254 +/- 8 min) compared with IGFBP-2 (110 +/- 9 min). Three hours after injection of the 125I-labelled protein, the plasma:lymph ratio of trichloroacetic acid-precipitable radioactivity was 1.54 +/- 0.04, 3.3 +/- 0.6 and 4.1 +/- 0.4 for IGFBP-2, IGF-I and -II respectively. The form of 125I-IGFBP-2 in lymph was not different from that of plasma. Elevation of plasma concentrations of IGFBP-2 by its intravenous infusion significantly decreased plasma half-life of both IGF-I and -II (251 +/- 8 and 198 +/- 7 min respectively). Although the amount and rate of transfer of IGF into mammary-derived lymph was decreased slightly by IGFBP-2, concentrations eventually obtained were not different from control. However, secretion of IGFs into milk was significantly reduced by IGFBP-2, particularly in the case of IGF-I. These results are consistent with the ability of all three compounds to cross the vascular endothelium intact and of IGFBP-2 to decrease the uptake of IGF by mammary epithelium and subsequent secretion into milk. IGFBP-2 may well have acted to target plasma IGF towards non-mammary tissues, thus explaining the more rapid plasma clearance of IGFs in the presence of elevated IGFBP-2.

Insulin-like growth factors in milk and mammary gland

Milk contains insulin-like growth factor I and II (IGF-I and IGF-II) and four IGF binding proteins (IGFBP). Their concentrations are highest prepartum and early postpartum, coinciding with maximal proliferation of mammary cells and the time when the infant gut is the least developed. This has lead to the suggestion that IGFs may be important for the growth and development of the mammary gland and that IGFs in milk play a role in promoting development of the gastrointestinal tract of the newborn. IGF-I and, to a lesser extent, IGF-II can stimulate milk yield and blood flow in goats when infused directly into the mammary gland, suggesting they may also be important in supporting established lactation. Thus IGFs may have a dual function in the mammary gland, establishing and maintaining the maternal mammary system and, once secreted into milk, supporting gastrointestinal development in the newborn.

Continuous versus single drainage of milk from the bovine mammary gland during a 24 hour period

Five primiparous and five multiparous cows were used to determine if mammary cisternal storage of milk during a 24 h period of milk accumulation limited milk secretion. In addition, we investigated if there is a parity effect for the capacity of the mammary cisternal compartment to hold a 24 h accumulation of milk secretion, and studied the movement of milk from the alveolar compartment into the cisternal compartment. All cows were fitted with catheters in all teats in order to collect cisternal and alveolar milk fractions separately. For a 24 h period of milk accumulation, the milk was drained once (after 24 h) from one side of the udder (OD), and continuously from the other side of the udder (CD). There was no significant parity effect for cisternal, alveolar and total milk volumes at 24 h. Therefore, data from primi- and multiparous cows were pooled for subsequent analyses. Cisternal milk volume from CD glands was higher than that from OD glands (P < 0.01), indicating that cisternal storage of milk in the mammary gland may be limiting to milk secretion during 24 h milking intervals. Alveolar volumes did not differ between OD and CD, but, as a result of the higher cisternal milk volume, total milk volume was highest in the CD glands (P = 0.05). Movement of milk from the alveolar into the cisternal compartment was intermittent. Moreover, analyses of the slopes of individual milk accumulation profiles of the first 6 h of accumulation revealed that the cisternal compartment starts filling immediately following milking, although the rate of filling is relatively low until 7-8 h postmilking.

EGTA-induced disruption of epithelial cell tight junctions in the lactating caprine mammary gland

The suitability of the Ca2+ chelator ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) to induce disruption of mammary tight junctions (TJ) and its effect on milk secretion were investigated in six goats. EGTA was administered via the teat of one gland as an isosmotic (300 mosmol/l) K-EGTA solution (68 mM EGTA), whereas the control gland received an isosmotic sucrose solution. Lactose, Na, K, and Cl in milk, blood lactose, and the presence of Evans blue (EB) in mammary lymph were used as indicators of TJ disruption. EGTA caused transient (approximately 60 h) changes (P < 0.05) in the concentration of lactose, K, Na, and Cl in milk, consistent with loss of TJ integrity. This was confirmed by a rapid (< 1 h) increase (P < 0.05) in blood lactose levels. Moreover, EB appeared in lymph < 1 h after EGTA+EB treatment. Milk secretion declined unilaterally by 15% (P < 0.05) after EGTA and did not return to baseline until approximately 60 h after EGTA. EGTA caused a unilateral, temporary (first 7 h) increase in mammary blood flow. This study shows that a rapid temporary disruption of mammary TJ can be successfully induced in vivo and that such disruption compromises milk secretion.

Isolation of cDNAs and tissue specific expression of ovine glucose transporters

The facilitative glucose transporters are a family of proteins responsible for the transmembrane transport of glucose and other hexose sugars (1,2). In mammals, the seven glucose transporter isoforms display a characteristic tissue distribution reflecting the physiological requirement and metabolism of glucose. This report describes the isolation and sequencing of the full length ovine GLUT-3 cDNA and the tissue distribution of ovine GLUT-1 and GLUT-3 mRNA. The ovine GLUT-3 cDNA is 3854 base pairs and the coding nucleotides show 82% and 79% homology with the human and mouse GLUT-3 sequences respectively. In addition, a reverse transcriptase-polymerase chain reaction strategy is described for the rapid isolation of mammalian cDNA subclones for GLUT-1, GLUT-2 and GLUT-4. This method has been used to isolate the corresponding ovine subclones.

Metabolic response of sheep skin to a chronic infusion of a variant of insulin-like growth factor I

The effects of a chronic (21-day) skin infusion of a variant of insulin-like growth factor I (IGF-I) (long-Arg3-IGF-I; LR3IGF-I) on short-term (48 h) responses of skin metabolism and 21-day plasma hormone concentration, wool-follicle characteristics and wool production were investigated in well-fed castrated Romney sheep. A bilateral arteriovenous preparation was used to infuse LR3IGF-I continuously into the skin on one abdominal flank and saline into the other abdominal flank of six sheep; a further six sheep had one flank infused with saline (controls). LR3IGF-I caused an initial (4-24 h) reduction in the plasma concentrations of amino acids, especially tyrosine, valine and lysine, and, after 24 h, significant (P < 0.05) reductions in blood oxygen and plasma glucose concentrations. After 4 h of LR3IGF-I infusion, there was a significant increase in blood flow (P < 0.05) and oxygen uptake (P < 0.05), and net uptake of amino acids [which was significant (P < 0.05) for valine and phenylalanine] by the LR3IGF-I-infused skin was increased. Total uptake of phenylalanine for skin protein synthesis, measured using [3H]phenylalanine uptake, was also significantly increased after 4 and 24 h of infusion. After 48 h of infusion all LR3IGF-I-dependent measurements of metabolic parameters had fallen to preinfusion values. By day 7 of the 21-day infusion there was a significant (P < 0.05) decrease in circulating endogenous IGF-I in plasma of treated sheep compared with that of control sheep, followed by a significant (P < 0.05) increase between day 7 and 21. Plasma insulin levels followed a similar pattern. There was no change at any stage of infusion in IGF-binding proteins in the plasma of the two LR3IGF-I-infused sheep tested, and it is concluded that LR3IGF-I caused a down-regulation of the type-I IGF-I receptors followed by a rise in endogenous IGF-I concentration consequent on lack of feedback regulation. After 21 days of infusion there was no effect of LR3IGF-I on wool-follicle-bulb-cell mitotic rate, bulb diameter or wool production.(ABSTRACT TRUNCATED AT 400 WORDS)

Milk protein synthesis, gene expression, and hormonal responsiveness in primary cultures of mammary cells from lactating sheep

A ruminant mammary cell culture that accurately reproduces mammary function in vitro would be a valuable tool in studies of ruminant lactation. With this in mind, we have examined milk protein synthesis and secretion, milk protein mRNA abundance, and hormonal responsiveness in primary cultures of mammary acini from lactating sheep. alpha- and beta-casein protein synthesis, beta-lactoglobulin synthesis, and alpha-casein, beta-casein, and beta-lactoglobulin secretion are maintained at high levels for 8 h in culture, but then decline to approximately 25% of maximal rates between 8 and 24 h in culture, whereas synthesis of other proteins remains unaltered. The relative abundance of alpha-S1-casein, beta-lactoglobulin, and alpha-lactalbumin mRNAs similarly decline between 8 and 24 h in culture. Extracellular labeled alpha-casein is increased fourfold in the presence of fetal calf serum (FCS). In total, FCS alters the abundance of 47 of 68 secreted proteins detected by two-dimensional electrophoresis. However, FCS and lactogenic/galactopoietic hormones had no effect on the rate of decline of mammary function and did not promote any regaining of function when present for up to 9 days in culture. These results suggest that providing its limitations are recognized, this primary cell culture system may be useful in studying some aspects of ruminant mammary function in vitro.

Pharmacokinetics and bioactivity of intact versus truncated IGF-I during a 24-h infusion into lactating goats

The aim of this study was to compare the plasma concentration profile, mammary blood flow response and transfer into milk of intact IGF-I with that of its truncated analogue, des(1-3)IGF-I (des-IGF-I). Each peptide was infused for 24 h into the pudic artery supplying one mammary gland of lactating goats (n = 5). Concentrations of IGF-I in plasma (from the jugular vein) rose rapidly during infusion of IGF-I or des-IGF-I to reach 510 +/- 62 and 640 +/- 32 ng/ml (mean +/- S.E.M.) respectively, compared with 262 +/- 35 ng/ml after a similar infusion of saline. Ligand blotting analysis indicated a significant increase in the intensity of [125I]IGF-I binding to the 40-43 kDa doublet (binding protein-3 (BP-3), P < 0.01) and the band at 31 kDa (P < 0.05) during infusion of either IGF-I or des-IGF-I, as compared with saline. Furthermore des-IGF-I induced a significant increase in intensity of binding to the 35 and 24 kDa bands, but IGF-I did not. Whereas [125I]IGF-I was distributed between BP-3 and the other binding proteins, [125I]des-IGF-I bound exclusively to BP-3. Mammary blood flow (MBF) increased 48 +/- 6% after 12 h of infusion of des-IGF-I, compared with an increase of 22 +/- 6% during IGF-I. The difference in response was significant at P < 0.05. In addition, more IGF-I was secreted into the milk of the infused than the non-infused gland during either infusion of IGF-I or des-IGF-I.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of caprylic acid for the extraction of the immunoglobulin fraction from egg yolk of chickens immunised with ovine alpha-lactalbumin

The extraction and purification of serum-derived immunoglobulin fraction in the egg yolk of hens by the combined treatment of the raw egg yolk with caprylic (octanoic) acid and ammonium sulphate is described. This simple two-step method proved to be both rapid, reproducible and suitable for batch processing of pooled egg yolk. The method recovered in excess of 130 mg of immunoglobulin per egg yolk. Two chickens were inoculated at two weekly intervals with 100 micrograms each of ovine alpha-lactalbumin over a ten week period. The alpha-lactalbumin antigen was purified by a hydrophobic-interaction chromatographic procedure and further purified by a gel excision-elution process. No precipitating antibodies could be demonstrated in gel diffusion techniques with this antibody. The specificity and specific activity of the antibody were monitored by western blotting and demonstrated the presence of highly specific antibodies to ovine alpha-lactalbumin in the treated egg yolk. The extraction procedure had no adverse effects on antibody titre. We concluded, and confirmed previous reports, that the use of chickens for the production of highly specific antibodies to mammalian proteins with particular reference to milk proteins presented numerous advantages over conventional procedures.

Effect of milking frequency and somatotropin on the activity of plasminogen activator, plasminogen, and plasmin in bovine milk

Six pairs of identical twin cows during late lactation (213 d) were used to study the effect of milking frequency (twice vs. once daily) and bST during once daily milking on the activity of plasminogen activator, plasminogen, and plasmin in milk. Less frequent milking increased the activity of plasminogen, plasmin, and plasminogen activator in milk. The ratio of plasminogen to plasmin, a measure that is independent of milk volume, decreased during less frequent milking, suggesting that at least part of the increase in activity of plasmin was due to the accelerated conversion of plasminogen to plasmin. Changes in the activity of plasminogen and plasmin in milk were positively correlated with increases in the concentrations of milk BSA and plasma lactose, both of which are indicators of disruption of tight junctions between mammary epithelial cells, indicating that paracellular leakage may have contributed to increased protease activity in milk during less frequent milking. No correlation existed between changes in plasminogen activator and indicators of tight junction disruption, suggesting that increased activity of plasminogen activator in milk was not due to leakage across the mammary epithelium, but rather to increased local production in the mammary gland. Administration of bST during once daily milking did not significantly affect milk protease activity.

Effects of close-arterial (external pudic) infusion of insulin-like growth factor-II on milk yield and mammary blood flow in lactating goats

Five lactating goats were infused, via an external pudic arterial catheter, directly into the mammary gland with 0.9% (w/v) NaCl (20 ml/h), recombinant human insulin-like growth factor-I (IGF-I; 80 nmol/h), recombinant human IGF-II (133 nmol/h) or IGF-I and IGF-II combined. The infusion was for 6 h and milk yield was determined every 2 h. The ratio of milk yield in the infused relative to the non-infused gland was changed only slightly by saline (2%), but increased to 9% (P < 0.05) in response to IGF-I and 8% (P < 0.05) in response to IGF-II. When combined, both peptides increased this ratio by 6%. These effects were elicited within 2-4 h of the beginning of infusion. Mammary blood flow increased 50-80% (P < 0.05) during all IGF infusions, but only 28% during saline treatment. Plasma insulin decreased 50% (P < 0.01) during the infusion of IGF-I alone or in combination with IGF-II and 25% in response to IGF-II alone. Whereas plasma glucose increased by approximately 10% during infusion of IGF-I alone or with IGF-II, it was not altered by infusion of IGF-II only. The rapidity and unilateral nature of the milk-yield response to IGF-I and IGF-II is consistent with their acting directly on mammary tissue itself. Thus, the present results demonstrate similar local and systemic actions induced by intramammary infusion of IGF-II and IGF-I, although the magnitude of the response to IGF-II tends to be less than that to IGF-I.

Increased mammary blood flow in the lactating goat induced by parathyroid hormone-related protein

Human synthetic parathyroid hormone-related protein (PTHrP) increased mammary blood flow (MBF) following close-arterial infusion via the external pudic artery in goats during mid-lactation. MBF increased 74 +/- 8% within 30 min of the start of continuous infusion of PTHrP compared with 10 +/- 3% in controls. MBF decreased by 90 min, however, and was not different from control values for the remainder of the infusion. The increase in plasma concentrations of calcium and decrease in phosphate during PTHrP suggests that this was not due to altered activity of PTHrP, but may relate to downregulation of response or production of counter-regulatory vasoconstrictive agents within the gland. This problem was alleviated when PTHrP was infused in a pulsatile fashion. An average 14-40% increase in MBF was achieved over 6 h, but this did not alter the rate of milk secretion, suggesting that mammary hyperaemia is not sufficient by itself to increase milk yield in the normally lactating goat. MBF increased in a dose-dependent fashion, although the lowest dose used to give a detectable response was approximately 40-fold higher than the concentration normally present in the mammary venous circulation. Thus, endogenous PTHrP may not be an important regulator of MBF during lactation in the goat.

Mammary epithelial cell tight junction integrity and mammary blood flow during an extended milking interval in goats

The timing and relation of changes in mammary epithelial cell tight junction integrity and mammary blood flow during a 36-h milking interval were studied in six lactating Saanen goats. An increase in lactose concentration in plasma, a decrease in transepithelial potential difference, and changes in ionic milk composition were used to indicate tight junction patency. After 36 h of milk accumulation, mammary tight junctions had become disrupted. Further analyses indicated that this disruption began after 21 h of milk accumulation and that mammary blood flow also started to decline after 21 h. The time when both events occurred was not significantly different from the time when milk secretion began to decline (19 h). Moreover, positive but nonsignificant correlations existed between these events. Mammary tight junctions became disrupted when milk secretion declined, suggesting that impairment of mammary tight junction integrity is associated with decreased milk secretion during an extended milking interval. The decline in mammary blood flow may be the result of a negative feedback response to a reduced demand for metabolites, which is due to a reduced rate of milk secretion.

Insulin-like growth factor binding proteins of equine serum

Ligand blotting analysis of serum from the horse using radiolabelled IGF-I revealed a protein at 96 kDa which was not present in serum from goat, cow, sheep, deer or donkey. These latter species all displayed five labelled bands in the range 24 to 41 kDa. Conversely, these were only weakly labelled in serum from the horse. Size exclusion chromatography of horse serum pre-incubated with radiolabelled IGF-I revealed reduced binding in the 130-kDa peak compared with goat plasma, and ligand blotting analysis indicated the 96-kDa protein was present in this peak. The 96-kDa protein from horse serum binds IGF-I and IGF-II specifically and appears to be unique to this species. The nature of this protein is at present unknown.

Milking frequency alters the milk yield and mammary blood flow response to intra-mammary infusion of insulin-like growth factor-I in the goat

The milk yield and mammary blood flow responses to close-arterial, intra-mammary infusion of IGF-I were investigated in five Saanen goats milked frequently or normally the day before. Animals were infused for 6 h with recombinant human IGF-I (1.3 nmol/min) and milked hourly following i.v. injection of oxytocin beginning 2 h before infusion and then every 2 h. On one occasion animals were milked five times (after i.v. injection of oxytocin) on the day before infusion and on the other they were milked twice, without oxytocin. The ratio of milk yield from the infused to that from non-infused gland increased by 17 +/- 4% (mean +/- S.E.M.) in goats milked twice the day before infusion and by 6 +/- 2% when the infusion was preceded by frequent milking. Maximal responses were obtained 4 h after the start of the infusion and differed significantly (P < 0.05), according to pretreatment milking. Blood flow through the infused gland rose in parallel to the milk yield response. At 5 h, when maximal levels were achieved, blood flow was 182 +/- 23% of the pre-infusion flow rate following twice-daily milking and 139 +/- 3% of the pre-infusion flow rate following more frequent milk removal. Thus, more frequent milk removal on the day before close-arterial infusion of IGF-I attenuated both the milk yield and mammary blood-flow response to the infusion of IGF-I.

Effect of colostrum intake on alpha-lactalbumin concentrations in serum of calves

Seven Friesian calves were fed colostrum for four days beginning within 24 hours of birth, and milk thereafter. The concentration of alpha-lactalbumin in serum was measured by specific radioimmunoassay and compared to IgG assayed by electroimmunodiffusion. Serum concentrations of alpha-lactalbumin peaked at 387 +/- 85 ng ml-1 within eight hours of initial intake of colostrum, declining to 12 +/- 3 ng ml-1 by day 6. IgG rose steadily to 17 mg ml-1 by 48 hours of birth and remained relatively constant thereafter. The temporal pattern of alpha-lactalbumin in serum following colostrum intake confirms previous studies suggesting reduced absorption of colostral proteins between 24 and 36 hours. The presence of variable amounts of alpha-lactalbumin in serum even after 17 days, however, indicates limited transfer of milk-derived proteins across the gut at this time. The data further show that cessation of maximal gut transfer does not relate to molecular weight of transferred protein.

Transfer of insulin-like growth factors I and II from plasma to lymph in young goats

The plasma clearance of intravenously injected 125I-labelled insulin-like growth factor I (IGF-I, n = 13) and IGF-II (n = 12) and their transfer into lymph draining the foreleg of 3.5- to 8-week-old British Saanen goats was studied. Both peptides were initially distributed into a volume equivalent to the plasma volume, while the final distribution spaces for IGF-I and IGF-II were 90 +/- 9.8 and 125 +/- 12 ml/kg live weight respectively. There were two phases to the plasma clearance of both IGF-I and IGF-II, with the half-lives of both phases for IGF-I (9.6 +/- 0.9 and 287 +/- 23 min, first and second phase respectively) being significantly (P less than 0.001) longer than those of IGF-II (4.2 +/- 0.6 and 172 +/- 18 min, respectively). The radioactivity transferred into lymph originated from intact IGF-I and IGF-II as well as degraded products of these compounds, as assessed by precipitation with trichloroacetic acid and gel filtration. Levels of undegraded IGF-I in lymph were 50% greater than IGF-II. While more than 90% of either peptide was bound to specific IGF-binding proteins in plasma, in lymph 34 +/- 2% of IGF-I and 23 +/- 3% of IGF-II remained in the free form 60-80 min after injection. The plasma: lymph ratio for free IGF-I was 2:1 and for bound IGF-I, 8:1. The corresponding values for IGF-II were 3:2 and 8:1 respectively. These results provide direct experimental evidence for transfer of undegraded IGF-I and IGF-II from blood into lymph of the foreleg, consistent with the ability of these factors to act in an endocrine role in growing tissues. Differences between plasma clearance and transfer of IGF-II into lymph compared with IGF-I may be due to its greater cellular uptake and/or degradation in vivo.

Secretion of insulin-like growth factor II into milk

125I-labeled insulin-like growth factor II (IGF-II) was infused directly into the pudic artery supplying one gland of lactating goats (n = 4). Maximum specific activity for [125I]IGF-II transferred into milk from the infused gland was reached 60 min after that in plasma and was 2.5 fold greater than in milk from the non-infused gland. Inclusion of either 67.5 nmoles unlabeled IGF-II or IGF-I had no influence on the amount or pattern of secretion of [125I]IGF-II into milk from either gland. While the temporal pattern of secretion of [125I]IGF-II into milk was consistent with a transcellular mechanism of transfer, the lack of competition by unlabeled IGF-II or IGF-I suggests a non-specific mechanism is operable, which contrasts to secretion of IGF-I.

Effect of growth hormone treatment on the distribution of insulin-like growth factor-I between plasma and lymph of lactating sheep

Plasma and mammary efferent lymph concentrations of insulin-like growth factor I (IGF-I) were determined in lactating ewes before and after treatment with GH (10 mg/day) for 3 days. The lymph:plasma ratio of IGF-I increased from 0.34 to 0.47 after GH treatment when the IGF-I content of plasma increased by 19.4 nmol/l (from 32.1 nmol/l) and lymph by 13.7 nmol/l (from 10.7 nmol/l). This increase in the relative content of IGF-I in lymph was associated with increased lymph content of IGF-I in a lower molecular mass pool (nominally 50 kDa) derived by size exclusion chromatography. GH treatment increased the total binding capacity for IGF-I in both high (150 kDa) and low (50 kDa) molecular mass pools of plasma and the 150 kDa pool in lymph but there was a proportionally greater increase in 50 kDa total binding in lymph relative to plasma. Further, GH treatment increased the 'saturation' of the 50 kDa binding proteins but decreased the 'saturation' of the 150 kDa fraction, in both plasma and lymph. Ligand blot analysis of IGF-binding proteins (IGFBPs) in plasma and lymph showed that GH treatment of lactating sheep increased IGFBP-3 and decreased IGFBP-2 in plasma and lymph. Radioimmunoassay of IGFBP-2 showed that while GH treatment reduced the plasma content of IGFBP-2 by about half, the lymph:plasma ratio was increased from 0.68 to 0.87. GH treatment of lactating ewes not only increased the IGF-I content of plasma but increased the apparent efficiency of transfer of IGF-I across capillary endothelium to mammary efferent lymph.

Mechanism of secretion of plasma insulin-like growth factor-I into milk of lactating goats

125I-Labelled insulin-like growth factor-I (IGF-I) was infused as the free form directly into the pudic artery supplying one gland of lactating goats (n = 6). The infusion was for 60 min and 0.4 +/- 0.09% (S.E.M.) of the infusate was secreted into milk from the infused gland during its first passage through that gland. A large proportion of the 125I-labelled IGF-I escaped into the systematic circulation and was secreted into milk of both glands. A total of 5.2 +/- 0.4% of infused radioactivity was recovered in milk from both glands from 0 to 720 min. Radioactivity consisted of trichloroacetic acid (TCA)-precipitable and -soluble counts which were shown by gel filtration to be authentic IGF-I and degraded products of the peptide. The amount and time course of TCA-soluble radioactivity in milk from both glands was similar, suggesting degradation of 125I-labelled IGF-I at extramammary sites. Maximum specific activity for 125I-labelled IGF-I in milk from the infused gland was reached 80-120 min after the start of infusion and was 2.5-fold greater than milk from the non-infused gland. The time course of appearance of 125I-labelled IGF-I in milk suggests that transfer was via the transcellular pathway and this was further supported by comparing the pattern of transfer of [14C]sucrose and [14C]amino acids. When excess unlabelled IGF-I was included in the infusate, specific activity in milk from the infused gland was reduced to that of the non-infused gland, indicating a competitive and saturable mechanism of secretion for 125I-labelled IGF-I.(ABSTRACT TRUNCATED AT 250 WORDS)

The galactopoietic effect of bovine growth hormone in goats is associated with increased concentrations of insulin-like growth factor-I in milk and mammary tissue

Lactating goats exhibiting widely divergent responses to short-term (4 days) treatment with bovine GH (bGH) were retrospectively divided into two groups based on the magnitude of this response. There was no difference between groups in terms of the pretreatment milk yield, but by day 4 of treatment milk secretion had increased by 4.99 +/- 2.5 (S.E.M.) ml/h (P greater than 0.05 compared with pretreatment) for group 1 and 22.9 +/- 2.4 ml/h (P less than 0.001) for group 2. Plasma GH increased in both groups, but concentrations were significantly higher both before and during treatment in group 1 compared with group 2. Plasma concentrations of insulin-like growth factor-I (IGF-I) increased significantly during bGH treatment for both groups and there was no significant difference between the two until day 4 of treatment when levels of IGF-I in group 1 began to decline, whereas those from group 2 were maintained. Concentrations of IGF-I in milk from goats in group 1 were not significantly altered by GH administration, whereas those in goats in group 2 were increased by 40% (P less than 0.01 compared with pretreatment). Levels of IGF-I in mammary secretory tissue from four animals from group 1 were not altered by bGH (2.8 +/- 0.2 and 2.77 +/- 0.08 nmol/kg tissue before and after treatment respectively), but were significantly (P less than 0.05) increased in four animals from group 2 (2.80 +/- 0.2 and 9.9 +/- 1.1 nmol/kg tissue).(ABSTRACT TRUNCATED AT 250 WORDS)

Increase in milk secretion and mammary blood flow by intra-arterial infusion of insulin-like growth factor-I into the mammary gland of the goat

The close-arterial infusion of free insulin-like growth factor-I (IGF-I; 1.1 nmol/min) for 6 h into the pudic artery supplying one mammary gland of lactating goats caused a 25 +/- 6% (mean +/- S.E.M., n = 6) increase in the rate of milk secretion of that gland. The increase in the rate of milk secretion in the adjacent noninfused gland (14 +/- 4%) was not significantly different from that observed during saline infusion (4 +/- 5%). Blood flow to the infused gland was increased from 378 +/- 26 ml/min 1 h before to 487 +/- 56 ml/min approximately 5 h after the start of the infusion of IGF-I, declining to 420 +/- 44 ml/min approximately 2 h after the end of the infusion. The total concentration of IGF-I (free and bound) in milk of the infused gland was significantly higher than that of the non-infused gland. The concentrations of IGF-I in carotid arterial plasma samples increased during IGF-I infusion from a mean value of 32 +/- 2 nmol/l before to a maximum of 49 +/- 3 nmol/l 5 h after the infusion commenced. Circulating concentrations of total IGF-I declined slowly after the infusion with an estimated half-life of 5 h. Infusion of saline alone did not alter mammary blood flow or the concentration of total IGF-I in milk or plasma. The results indicate that the infusion of free IGF-I into the mammary arterial supply enhances milk secretion and mammary blood flow in intact, conscious goats.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased secretion of insulin-like growth factor I into milk of cows treated with recombinantly derived bovine growth hormone

Six lactating, non-pregnant Jersey cows were given subcutaneous injections of recombinantly derived bovine growth hormone for 7 d. Milk yield was increased by 4.5 kg/d on d 7, compared with the average yield of 10.7 +/- 0.4 kg/d (mean +/- s.e.m.) for the 7 d preceding treatment. Concentrations of insulin-like growth factor I (IGF-I) in the milk increased from 0.44 +/- 0.04 nmol/l (mean +/- s.e.m.) during the 7 d preceding treatment to 1.6 +/- 0.2 nmol/l on d 7 of treatment. Taking the increase in milk yield into account the total increase in the secretion of IGF-I into milk of one udder half was 6-fold. Plasma concentrations of total IGF-I rose from 15.5 +/- 1.3 nmol/l (mean +/- s.e.m.) on the day preceding treatment to 56.9 +/- 3.6 nmol/l (mean +/- s.e.m.) on d 7 of treatment. Mammary plasma flow increased from 1.6 +/- 0.09 to 2.2 +/- 0.06 l/min.udder half over the same time. Estimates of the amount of IGF-I that reached the mammary gland gave values of 24 and 116 nmol/min.udder half before and during treatment respectively. IGF-I in milk of treated cows was associated predominantly with proteins ranging from 40,000 to 150,000 mol.wt, but a significant proportion (19%) of the total IGF-I was present in the free unbound form. IGF-I crosslinking studies revealed the presence in milk of one specifically labelled band at 31,000 mol.wt.

From animal to molecule: aspects of the biology of insulin-like growth factors

The synthesis of IGF-II mRNA in sheep foetal tissues is considerably higher than IGF-I. IGF-II probably has a paracrine role in the foetus; however it is likely that IGF-I originates mainly from the foetal liver and has an endocrine function. Although in the adult system IGF-I is tightly bound to serum carrier proteins it is potentially biologically active. Galactopoiesis in the goat mammary gland provides a useful model for demonstrating the importance of circulating IGF-I as a mediator of GH action. Ligand-receptor interactions involved in the stimulation of Swiss 3T3 fibroblasts by IGF-I, II and insulin were examined. It was found that the potency of binding to type I receptors was IGF-I greater than IGF-II much greater than insulin by competitive binding assays and chemical cross-linking studies, and that some cell lines secrete an IGF binding protein which is specific for IGF-I and II and which acts as an inhibitor in cellular binding assays. Maximal stimulation of DNA synthesis induced by IGF-I, II and insulin in the presence of synergising mitogens were similar. While the actions of the IGFs were consistent with type I receptor binding insulin appeared to act through its own receptor. The reduction of EGF receptor affinity following the addition of IGF-I and insulin to 3T3 cells may involve a protein kinase that is not sensitive to phorbol esters. 3T3 cell nuclei contain endogenous inositol phospholipids and their corresponding kinases and monoesterases.(ABSTRACT TRUNCATED AT 250 WORDS)

The insulin-like growth factor I content in human milk increases between early and full lactation

The concentration of immunoreactive insulin-like growth factor I (IGF-I) in human mammary secretions, assayed after acid-ethanol extraction, was high [mean, 4.1 +/- 0.5 (+/- SE) nmol/L; n = 13] for several weeks prepartum. It then decreased during the first 3 days postpartum to 1.3 +/- 0.1 nmol/L (n = 28), in parallel with changes in epidermal growth factor (EGF) and protein concentrations. However, between the first and sixth weeks postpartum, the IGF-I concentration increased to 2.5 +/- 0.2 nmol/L (n = 18), while levels of EGF and protein decreased further. Given that the volume of milk produced increases during this period, the total IGF-I output rose by up to 4-fold, while EGF output remained constant. The increase in IGF-I and decrease in EGF in milk suggest that different regulatory mechanisms control the output of different growth factors by the mammary gland.

Mechanism of the decrease in hexose transport by mouse mammary epithelial cells caused by fasting

The basal carrier-mediated uptake of 0.5 mM-3-O-methylglucose by mammary epithelial cells from lactating mice was calculated to be 227 +/- 9 pmol/min per microgram of DNA (mean +/- S.E.M., n = 11). Fasting the mice for 16 h overnight resulted in a decrease in this rate to 65 +/- 4 pmol/min per microgram of DNA (n = 10). Refeeding the fasted mouse for 3 h before isolation of the cells restored the transport activity to 230 +/- 12 pmol/min per microgram of DNA (n = 12). The Vmax. for equilibrium exchange entry of 3-O-methylglucose by intact cells was decreased from 6.6 +/- 0.4 to 0.9 +/- 0.2 nmol/min per microgram of DNA (mean +/- S.E.M., n = 3) by fasting. The number of D-glucose-inhibitable cytochalasin-B-binding sites in a plasma-membrane-enriched fraction of the cells was also decreased from 5.7 +/- 1.5 to 1.7 +/- 0.1 pmol/mg of membrane protein (mean +/- S.E.M., n = 3). Again, refeeding the fasted mouse for 3 h reversed both these effects. These results are consistent with a decrease in the number of functional glucose carriers in the plasma membrane of the mammary epithelial cells. Since the restoration of transporter activity after refeeding does not appear to require the synthesis of new protein, the effect of fasting probably involves not a loss of transporters, but a change in their orientation within the plasma membrane or a redistribution within the cell.