Oestrogen synthesis by bovine foetal placenta at normal parturition

Abstract

Abstract. In vitro conversion of C 19 -[ 3 H]androstenedione and C 21 -[ 3 H]pregnenolone steroids to oestrogens 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 labour. At collection of tissues, blood samples were drawn from the cows and peripheral plasma oestrogen levels were determined by radioimmunoassay. Percentage conversion to unconjugated and conjugated oestrogens 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 Oe 1 > conjugated Oe 1 > unconjugated Oe 2 > conjugated Oe 2 . 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 labour when compared to cultures from normally calving cows. The sire of the foetus had an influence on conversion rate in the tissue cultures. The plasma oestrogen concentrations of the cows decreased significantly with an increased interval from parturition to blood-sampling. With the exception of one cow, the tissue culture conversion rates and the plasma oestrogen levels of the cows were significantly correlated.