Bovine colostrum: determination of naturally occurring steroid hormones by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS).

The aim of this study was to collect further data about levels of endogenous hormones in foodstuffs derived from animal production. Because of expected higher concentrations of especially estrogens in colostrum compared to other foodstuffs, our investigation focused on this matrix. For evaluation of endogenous steroid hormones in separated colostrum (fat and defatted fraction) and colostrum powder, the relevant free and conjugated estrogens (estradiol-17ß, estradiol-17α, estrone, and estriol) androgens (androstendione, 19nor-androstendione, 19nor-testosterone-17ß, 19nor-testosterone-17α, testosterone-17ß, and testosterone-17α), and progesterone were determined by means of liquid chromatography-tandem mass spectrometry (LC-MS/MS). Upmost determined concentrations were found in the fat fraction, with 25.56 and 7.59 µg/L for estrone and androstendione, respectively. In defatted milk and colostrum powder, conjugated estrogens dominated, whereas total (free and conjugated) estrone (5.51 µg/L; 15.0 µg/kg) exceeded estradiol-17α (2.66 µg/L; 7.5 µg/kg) and estradiol-17ß (2.28 µg/L; 3.3 µg/kg). Neither 19nor-steroids nor estriol were detected in colostrum fractions or processed colostrum.

Differential expression of ABC transporters and their regulatory genes during lactation and dry period in bovine mammary tissue.

ATP-binding cassette (ABC) transporters play a pivotal role in human physiology, and mutations in these genes often result in severe hereditary diseases. ABC transporters are expressed in the bovine mammary gland but their physiological role in this organ remains elusive. Based on findings in the context of human disorders we speculated that candidate ABC transporters are implicated in lipid and cholesterol transport in the mammary gland. Therefore we investigated the expression pattern of selected genes that are associated with sterol transport in lactating and nonlactating mammary glands of dairy cows. mRNA levels from mammary gland biopsies taken during lactation and in the first and second week of the dry period were analysed using quantitative PCR. Five ABC transporter genes, namely ABCA1, ABCA7, ABCG1, ABCG2 and ABCG5, their regulating genes LXRalpha, PPARgamma, SREBP1 and the milk proteins lactoferrin and alpha-lactalbumin were assessed. A significantly enhanced expression in the dry period was observed for ABCA1 while a significant decrease of expression in this period was detected for ABCA7, ABCG2, SREBP1 and alpha-lactalbumin. ABCG1, ABCG5, LXRalpha, PPARgamma and lactoferrin expression was not altered between lactation and dry period. These results indicate that candidate ABC transporters involved in lipid and cholesterol transport show differential mRNA expression between lactation and the dry period. This may be due to physiological changes in the mammary gland such as immigration of macrophages or the accumulation of fat due to the loss of liquid in the involuting mammary gland. The current mRNA expression analysis of transporters in the mammary gland is the prerequisite for elucidating novel molecular mechanisms underlying cholesterol and lipid transfer into milk.