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

Summary

In order to further characterize oestrogen production and metabolism during bovine pregnancy, free (f) and conjugated (c) estrone (El), 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 El, 17β-estradiol (E2β) and 17α-estradiol (E2α) were obtained following differential enzyme hydrolysis and separation by HPLC; hormone assay was by established RIA-procedures.

FEl and cEl 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 (fEl ca. 8 nmol/1 and cEl ca. 20 nmol/1 2 days a. p.). Determination of individual oestrogens in blood plasma revealed that fE2β and fE2α 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% El was the dominant oestrogen, followed

by E2α (37%) and E2β (1.0%); El occurred predominantly as sulfate, E2α and E2β predominantly as glucuronide. Main metabloite in feces was fE2α (56.7%), followed by fE2β (32%) and fEl (11.3%); conjugated oestrogens were not detected. Main metabolite in urine was scEl followed by gcE2α and gcE2β. ScE2α and scE2β were not detected or were present in small quantities only. Hormonal changes over time were highly significant. Main product of placental oestrogen synthesis is scEl, the concentrations of f and c E2β and E2α in plasma largely result from oestrogen metabolism and enterohepatic circulation.

Key words

Oestrogens - metabolism - pregnancy - cattle