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

Effect of dexamethasone on milk yield and composition in dairy cows

Dexamethasone was injected in dairy cows in order to get a better insight into the effects of corticosteroids on milk secretion and composition. A single intramuscular dose of 40 mg dexamethasone caused a 45% reduction in milk yield after 24 h; full recovery took 5 d. The secretion of fat, casein and magnesium was not affected by the treatment. Consequently, the concentration of fat, total protein, total casein, magnesium and phosphorus increased then decreased in direct proportion to the changes in milk yield. The secretion of total protein, calcium and phosphorus decreased as a result of the treatment. The concentration of lactose and the monovalent ions (sodium, potassium, and chlorine) was unaffected, and as a result their secretion decreased and returned to pretreatment level in direct inverse proportion to the changes in milk yield. Whey protein secretion decreased for 48 h and was responsible for the decrease in total protein secretion for 48 h. The most profound effect of dexamethasone is the reduction in the secretion of the osmotic components.Effet de la dexaméthasone sur la production et la composition du lait chez les vaches laitières. La dexaméthasone a été injectée à des vaches laitières afin de mieux comprendre les effets des corticostéroïdes sur la sécrétion et la composition du lait. Une dose unique intramusculaire de 40 mg de dexaméthasone a réduit de 45 % la production de lait après 24 h ; le retour total à la production antérieure a pris 5 jours. La sécrétion des lipides, des caséines et du magnésium n'a pas été affectée par le traitement. En conséquence, la concentration des lipides, des protéines totales, des caséines totales, du magnésium et du phosphore a augmenté puis a diminué proportionnellement aux changements de production laitière. La sécrétion des protéines totales, du calcium et du phosphore a diminué à la suite du traitement. La concentration du lactose et des ions monovalents (sodium, potassium et chlore) est restée inchangée ; leur sécrétion a diminué et est revenue au niveau initial dans une proportion inverse aux modifications de la production laitière. La sécrétion des protéines du lactoserum a diminué pendant 48 h et a été responsable de la diminution de la sécrétion des protéines totales pendant 4 h. L'effet le plus important de la dexaméthasone est la réduction de la sécrétion des composés à pouvoir osmotique

Triglyceride (Tg) secretion from mammary epithelial cells is altered in the presence of specific free fatty acids (FFAs).

<p>Mammary epithelial cells were treated with 100 μM FFA (palmitic or oleic acid) or with FFA-free medium (control) for 24 h, then the medium was collected and Tg content was determined. Data are presented as mean ± SEM. Different letters indicate significant differences between treatment groups (<i>P</i> < 0.05).</p

Specific free fatty acids (FFA) influence the amount and composition of phospholipid in mammary epithelial cells.

<p>Mammary epithelial cells were treated with 100 μM FFA (capric, palmitic or oleic acid) or with FFA-free medium (control) for 24 h; lipids were extracted and analyzed by HPLC-ELSD. (A) Membrane lipid amounts. (B) Phospholipid weight %. The percent of the amount of an individual phospholipid out of the summed phospholipids amounts. (C) Weight ratio between phosphatidylcholine and phosphatidylethanolamine. All data are presented as mean ± SEM. Different letters indicate significant differences between treatment groups (<i>P</i> < 0.05). PI: phosphatidylinositol; PE: phosphotidylethanolamine; PS: phosphatidylserine; PC: phosphotidylcholine; SM: sphingomyelin.</p

Specific free fatty acids (FFAs) influence amounts and ratio between polar and neutral lipids in mammary epithelial cells.

<p>Mammary epithelial cells were treated with 100 μM FFA (capric, palmitic or oleic acid) or with FFA-free medium (control) for 24 h; lipids were then extracted and analyzed by HPLC-ELSD. (A) Total lipid amount. (B) Triglyceride amount. (C) Total phospholipid amount. (D) Triglyceride-to-phospholipid ratio. All data are presented as mean ± SEM. Different letters indicate significant differences between treatment groups (<i>P</i> < 0.05).</p

Different size distribution of lipid droplets in the medium induced by specific free fatty acids (FFAs).

<p>After cultivating mammary epithelial cells with 100 μM FFA (palmitic or oleic acid) or with FFA-free medium (control) for 24 h, medium was collected and lipid droplets were stained with Nile red. Representative images of lipid droplets in the medium collected from palmitate and oleate treatments (A and B, respectively). Droplets were measured and divided into three size groups: 0 > X < 3, 3 > X < 5, and ≤5 μm. Size distribution of lipid droplets in the medium was compared by chi-square test (C). Scale bar = 20 μm.</p

Intracellular lipid droplet size is altered by the presence of various free fatty acids (FFAs) in the culture medium.

<p>After cultivating mammary epithelial cells with 100 μM FFA (palmitic or oleic acid) or with FFA-free medium (control) for 24 h, lipid droplets were stained with Nile red. (A) Representative images showing the cellular phenotype according to the presence and size of cytoplasmic lipid droplets. Cells were categorized into three groups according to their lipid droplet phenotype: without lipid droplets, with small lipid droplets, or with large lipid droplets. Scale bar = 10 μm. (B) Distribution of mammary epithelial cells with different lipid droplet phenotypes was analyzed by chi-square test (<i>P</i>> 0.05). (C) Number of lipid droplets, by size categories. (D) Maximal lipid droplet diameter. In C and D, data are presented as mean ± SEM and different letters indicate significant differences between treatment groups (<i>P</i> < 0.05).</p