Colostrogenesis: Role and Mechanism of the Bovine Fc Receptor of the Neonate (FcRn).

Colostrogenesis is a separate and unique phase of mammary epithelial cell activity occurring in the weeks before parturition and rather abruptly ending after birth in the bovine. It has been the focus of research to define what controls this process and how it produces high concentrations of specific biologically active components important for the neonate. In this review we consider colostrum composition and focus upon components that appear in first milked colostrum in concentrations exceeding that in blood serum. The Fc Receptor of the Neonate (FcRn) is recognized as the major immunoglobulin G (IgG) and albumin binding protein that accounts for the proteins' long half-lives. We integrate the action of the pinocytotic (fluid phase) uptake of extracellular components and merge them with FcRn in sorting endosomes. We define and explore the means of binding, sorting, and the transcytotic delivery of IgG1 while recycling IgG2 and albumin. We consider the means of releasing the ligands from the receptor within the endosome and describe a new secretion mechanism of cargo release into colostrum without the appearance of FcRn itself in colostrum. We integrate the insulin-like growth factor family, some of which are highly concentrated bioactive components of colostrum, with the mechanisms related to FcRn endosome action. In addition to secretion, we highlight the recent findings of a role of the FcRn in phagocytosis and antigen presentation and relate its significant and abrupt change in cellular location after parturition to a role in the prevention and resistance to mastitis infections.

Estrone and estrone sulfate concentrations in milk and milk fractions.

Dairy products naturally contain estrogens, and some consumer groups contend these estrogens cause adverse health effects. The objectives of this research were to characterize estrone (E(1)) and estrone sulfate (E(1)S) concentrations in milk from a large number of individual cows, in skim and fat fractions of milk, and in retail milk to provide food and nutrition practitioners with information to estimate potential consumption. Milk was from Holstein cows. Data are presented as means and standard deviations. Analysis of variance was used to determine differences in E(1) and E(1)S content of whole milk and its skim and fat fractions. Mean E(1) and E(1)S concentrations (n=173 cows) were 7.0±12.7 and 46.7±62.1 pg/mL (25.89±46.96 and 172.74±229.71 pmol/L), respectively. Analysis of milk fractions (n=50 samples) demonstrated that 55% of E(1) and 14% of E(1)S were associated with the fat fraction with the remainder associated with the skim fraction. Concentrations of E(1) and E(1)S in pasteurized-homogenized whole milk (n=8) averaged 10.3±0.6 and 85.9±7.3 pg/mL (38.09±2.22 and 317.74±27.00 pmol/L), respectively. Production rates of E(1) plus estradiol in human beings range from 54,000 to 630,000 ng/day. US Food and Drug administration guidelines state that no physiologic effects occur when consumption is ≤1% of the endogenous quantities produced by the segment of the population with the lowest daily production. This threshold value for intake would be 540 ng/day. Estimated total E(1) intake from three servings of whole milk was 68 ng/day, which represents 0.01% to 0.1% of daily production rates in human beings. These findings support levels below the current guidelines for safe consumption.