Oestrogen synthesis by bovine foetal placenta at normal parturition

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Abstract
In vitro conversion of C19-[3H]androstenedione and C21-[3H]pregnenolone steroids to estrogens was studied in tissue cultures prepared from bovine cotyledons collected 10-240 min after natural parturition. A total of 17 cows was used; 15 had normal parturitions and 2 cows required assistance due to weak and prolonged labor. At collection of tissues, blood samples were drawn from the cows and peripheral plasma estrogen levels were determined by radioimmunoassay. Percentage conversion to unconjugated and conjugated estrogens was estimated for each cow from 6 tissue culture replicates for each precursor. The steroids were extracted with toluene and separated by phenolic extraction and column chromatography. The repeatability of conversion rate was very high. Incubation with androstenedione yielded consistently higher conversion rates than incubation with pregnenolone. Independent of precursor the conversion rates, within cows, ranked unconjugated E1 [estrone] > conjugated E1 > unconjugated E2 [estradiol] > conjugated E2. The conversion rates decreased significantly with increasing intervals from parturition to collection of material. Lower conversion rates were found for cultures of tissues from the 2 cows with weak labor when compared to cultures from normally calving cows. The sire of the fetus had an influence on conversion rate in the tissue cultures. The plasma estrogen concentrations of the cows decreased significantly with an increased interval from parturition to blood-sampling. With the exception of 1 cow, the tissue culture conversion rates and the plasma estrogen levels of the cows were significantly correlated.