Avi Shamay

A High‐Fat Diet Has a Tissue‐Specific Effect on Adiponectin and Related Enzyme Expression

Objective: This study was designed to test whether adiponectin plays a role in diet‐induced obesity and insulin resistance and acts as a mediator to induce or inhibit specific metabolic pathways involved in lipid metabolism

Stress down regulates milk yield in cows by plasmin induced β-casein product that blocks K+ channels on the apical membranes

Stress and stress related hormones such as glucocorticoids inhibit lactation in cows. In the present study we propose a novel mechanism connecting stress with plasminogen-plasmin system (PPS) (an enzymatic mechanism in milk, which leads to the breakdown of the major milk protein casein). We show that stress activates the PPS leading to an increase in plasmin activity, and that a distinct plasmin-induced beta-casein breakdown product (fraction 1-28) is a potent blocker of potassium channels in mammary epithelia apical membranes. The reduction in milk production due to dehydration stress or glucocorticoid (dexamethsone) was correlated with the activities of plasmin and channel blocking activity in the milk of the tested cows. The notion that the axis Stress-PPS-beta-casein fraction 1-28 is responsible for the reduction in milk yield is supported by the results of experiments showing that injecting solution composed of casein digest enriched with beta-casein fraction 1-28 to the udder lumen leads to a transient reduction in milk production. Furthermore, injecting a pure beta-casein fraction 1-28 to the udder lumen of goats lead also to a transient reduction in milk production with kinetics that was similar to the kinetics observed in cows.

Casein-derived phosphopeptides disrupt tight junction integrity, and precipitously dry up milk secretion in goats

Mammary involution is triggered by local stimuli, but the precise mechanism has not been defined. Milk stasis accumulate local signals, which makes the tight junctions (TJ) leaky. The aim of the study was to check the hypothesis that casein hydrolyzates (CNH) compromise TJ integrity and dry up milk secretion. A single dose of CNH transiently (12 to 24 h) compromised TJ integrity in the treatedudder. This was associated by a transient (12 to 96 h) decline in milk secretion. No such changes were recorded in the contralateral gland that served as a control. Four repeated doses of CNH after each milking caused drastic changes in mammary secretion and composition, which were associated with irreversible cessation of milk secretion within 96 h. No such changes were recorded in goats treated with de-phosphorylated casein (control). We conclude that CNH are the milk-borne factors that cause the disruption of TJ integrity and induction of involution, and that the serine-Ps in the CNHs are essential for the excretion of biological activity.

Increased serum leptin and insulin concentrations in canine hypothyroidism

Serum concentrations of leptin and insulin were compared between gender-matched hypothyroid (n=25) and healthy (n=25) client-owned dogs within comparable age and body condition score (BCS) ranges. Fasted blood samples were collected from each dog and analysed for glucose, cholesterol, triglyceride, leptin and insulin concentrations. Leptin and insulin concentrations were significantly higher in the hypothyroid compared to normal dogs (P=0.006 and P=0.001, respectively) following adjustment for potential confounders. A nearly significant (P=0.051) interaction with BCS was found in the association between hypothyroidism and leptin. Leptin concentrations were significantly higher in hypothyroid dogs compared to normal dogs, in separate analyses for BCS 6 (P=0.036) and 7 (P=0.049). There was no significant difference in glucose concentration between the hypothyroid and normal groups (P=0.84) following adjustment for BCS. This study showed that canine hypothyroidism is associated with increased serum leptin and insulin concentrations, neither of which may be attributed to obesity alone.

Adrenocorticotrophic hormone and dexamethasone failed to affect milk yield in dairy goats: comparative aspects.

The ability of adrenocorticotrophic hormone (ACTH; single i.v. injection of 2.5IU/kg BW) and dexamethasone (single i.m. injection of 36mg/kg BW) to affect milk production was studied in mid-lactating Israeli Saanen goats. None of these treatments produced changes in milk yield and composition of the goats. The effects of ACTH on blood cortisol levels, and the effects of ACTH and dexamethasone on blood plasma concentrations of glucose, however, were consistent with previous reports in goats and cows. These responses suggest that ACTH and dexamethasone treatments produced their expected glucocorticoid effects. It is suggested that obstructing the axis: stress-ACTH-glucocorticoid-down regulation of milk yield, which was demonstrated in dairy cows, reflects the adaptation of goats to harsh conditions, and the selection pressure to produce milk under conditions which are considered stressful for other ruminants.

Use of an ion-selective electrode to determine free Ca ion concentration in the milk of various mammals

Milk is a heterogeneous fluid in which the colloidal phase is homogeneously dispersed in the aqueous phase. Calcium is partitioned between the colloidal and aqueous phases and is in complex electrochemical equilibrium with several major milk components. In human and bovine milk, calcium is mainly distributed between the aqueous and casein micelle in the colloidal phases (Holt & Jenness, 1984; Neville et al. 1994). Caseins form a complex micelle structure that contains approximately 25000 phosphorylated monomers that react with calcium phosphate complexes in the milk to bind 20–40 mole calcium per mole casein (Holt & Jenness, 1984; Neville et al.

Proliferation of bovine undifferentiated mammary epithelial cells in vitro is modulated by G-proteins

Several cAMP-elevating agents such as cholera toxin (CT), forskolin and 3-isobutyl-1-methylxanthine (IBMX) exhibited weak mitogenic activity on bovine undifferentiated mammary epithelial cells in three-dimensional collagen culture. CT and IBMX strongly synergized with epidermal growth factor (EGF), insulin-like growth factor I (IGF-I) or both, but not with 10% fetal calf serum (FCS). Permeable cAMP analogs also synergized with IGF-I. Other hormones such as ovine prolactin, bovine growth hormone, estrogen or progesterone were not mitogenic and not synergistic with EGF, IGF-I, CT and FCS. Pertussis toxin (PT) reduced the DNA synthesis in cells cultured in the basal medium and attenuated 40-90% of the mitogenic activity stimulated by 10% FCS. PT inhibition of DNA synthesis was accompanied by ADP-ribosylation of 40 kDa and 41 kDa membrane proteins. The 41 kDa protein cross-reacted with antibodies that recognize the Gi-protein of the adenylate cyclase system, indicating the involvement of the latter in the mitogenic process. The nature of the second protein remains unknown. The present results suggest that the mitogenesis of normal mammary epithelial cells which is stimulated by IGF-I, EGF and other factors found in FCS is mediated through both cAMP-dependent and independent pathways. These pathways include PT-sensitive GTP-binding proteins.

Mammary Fat Can Adjust Prolactin Effect on Mammary Epithelial Cells via Leptin and Estrogen.

Leptin, like estrogen, is one of the endo/paracrine factors, which are synthesized in and secreted from mature adipocytes. The roles of the mammary fat pad and mammary adipocytes in the initiation of lactation are not clear. In this study, we showed that combination of prolactin, leptin and estrogen elevated the expression of the milk protein beta-lactoglobulin. We also showed that after prolactin stimulate the secretion of leptin from the mammary fat, leptin upregulated the expression of estrogen receptor alpha in the mammary epithelial cells. Also, prolactin affected aromatase mRNA expression in the bovine mammary fat and we demonstrated that leptin and prolactin can affect cholesterol secretion from explants in culture to the medium. Therefore, we suggest that prolactin initiates estrogen expression (as represented by aromatase mRNA) in the mammary fat pad, whereas leptin stimulates estrogen receptor alpha expression in the mammary epithelial cells. We hypothesize that leptin and estrogen, secreted from the mammary fat regulate lactation after stimulation of prolactin.

Regulation of Lipid Droplet Size in Mammary Epithelial Cells by Remodeling of Membrane Lipid Composition—A Potential Mechanism

Milk fat globule size is determined by the size of its precursors—intracellular lipid droplets—and is tightly associated with its composition. We examined the relationship between phospholipid composition of mammary epithelial cells and the size of both intracellular and secreted milk fat globules. Primary culture of mammary epithelial cells was cultured in medium without free fatty acids (control) or with 0.1 mM free capric, palmitic or oleic acid for 24 h. The amount and composition of the cellular lipids and the size of the lipid droplets were determined in the cells and medium. Mitochondrial quantity and expression levels of genes associated with mitochondrial biogenesis and polar lipid composition were determined. Cells cultured with oleic and palmitic acids contained similar quantities of triglycerides, 3.1- and 3.8-fold higher than in controls, respectively (P < 0.0001). When cultured with oleic acid, 22% of the cells contained large lipid droplets (>3 μm) and phosphatidylethanolamine concentration was higher by 23 and 63% compared with that in the control and palmitic acid treatments, respectively (P < 0.0001). In the presence of palmitic acid, only 4% of the cells contained large lipid droplets and the membrane phosphatidylcholine concentration was 22% and 16% higher than that in the control and oleic acid treatments, respectively (P < 0.0001). In the oleic acid treatment, approximately 40% of the lipid droplets were larger than 5 μm whereas in that of the palmitic acid treatment, only 16% of the droplets were in this size range. Triglyceride secretion in the oleic acid treatment was 2- and 12-fold higher compared with that in the palmitic acid and control treatments, respectively. Results imply that membrane composition of bovine mammary epithelial cells plays a role in controlling intracellular and secreted lipid droplets size, and that this process is not associated with cellular triglyceride content.

Determination of lactose and D-galactose using thio-NAD+ instead of NAD+

Replacement of NAD by thio-NAD and measurement at 405 rather than 340 nm can be used in the determination of lactose and galactose. These modifications allow microplate-readers rather than UV spectrophotometers to be used in the assays.