Determination of free and conjugated oestrogens in peripheral blood plasma, feces and urine of cattle throughout pregnancy.

In order to further characterize oestrogen production and metabolism during bovine pregnancy, free (f) and conjugated (c) estrone (E1), total free and conjugated oestrogens (tfcOe) and total free oestrogens (tfOe) were determined as marker oestrogens in blood plasma respectively in urine and feces of 10 pregnant cows. For the determination of individual oestrogens blood, urine and feces samples of days 240, 200, 160, 100, 60, 30, 10 and 5 prior to parturition were pooled and the free, sulfo (sc)- and glucuconjugated (gc) forms of E1, 17 beta-estradiol (E2 beta) and 17 alpha-estradiol (E2 alpha) were obtained following differential enzyme hydrolysis and separation by HPLC; hormone assay was by established RIA-procedures. FE1 and cE1 concentration in blood plasma, tfOe in feces and tfcOe in urine showed a similar pattern. A first rise occurred between days 110 and 120 of pregnancy, an additional overproportional rise commenced at around days 230-250. Highest concentrations were measured in feces (tfOe ca. 500 ng/g 1 day a. p.), followed by urine (tfcOe ca. 3.5 ng/mosmol 2 days a. p.) and blood plasma (fE1 ca. 8 nmol/l and cE1 ca. 20 nmol/l 2 days a. p.). Determination of individual oestrogens in blood plasma revealed that fE2 beta and fE2 alpha could only be found 10 days a. p. while the conjugated forms could already be detected on days 100 and 160 a. p. With 62% E1 was the dominant oestrogen, followed by E2 alpha (37%) and E2 beta (1.0%); E1 occurred predominantly as sulfate, E2 alpha and E2 beta predominantly as glucuronide. Main metabloite in feces was fE2 alpha (56.7%), followed by fE2 beta (32%) and fE1 (11.3%); conjugated oestrogens were not detected. Main metabolite in urine was scE1 followed by gcE2 alpha and gcE2 beta. ScE2 alpha and scE2 beta were not detected or were present in small quantities only. Hormonal changes over time were highly significant. Main product of placental oestrogen synthesis is scE1, the concentrations of f and c E2 beta and E2 alpha in plasma largely result from oestrogen metabolism and enterohepatic circulation.