Oestrogens in Bovine Fetal and Maternal Plasma Near Term

Abstract

turition, little is known of the source of this oestrogen rise in the cow. It seemed pertinent, therefore, to determine the levels of oestrogens in fetal and maternal plasma over the last 3 weeks of gestation. In the present paper, the levels of free oestrone and oestradiol-17\g=b\ in the maternal jugular and utero-ovarian vein plasma and in fetal vena cava plasma in relation to the initiation of parturition in the cow were determined by radioimmunoassay.Catheters were implanted surgically into the maternal utero-ovarian and jugular veins and into the fetal posterior vena cava through the fetal saphenous vein in three cows during the last third of gestation. Fetal and maternal blood samples were taken twice daily until parturition; when calving was imminent, maternal utero-ovarian samples were taken more frequently. Blood was collected into ice-cold, heparinized syringes, centrifuged immediately and the plasma was stored at -15\s=deg\C until analysis. The plasma was extracted with 10 vols redistilled diethyl ether and chromatographed on micro-columns of Sephadex (Wu & Lundy, 1971). The oestrone and oestradiol fractions thus separated were subjected to radioimmunoassay by the method of Peterson & Common (1972), using antisera against oestradiol-17ß-17-BSA and oestradiol-17/J-6-rBSA, respectively. Oestrone cross-reacted 56% with the oestradiol-17ß-17-BSA antiserum and oestradiol-17a cross-reacted 1-9% with the antiserum against oestradiol-17/Í-6-BSA. Over the range of 0-01 to 1-0 ng, recoveries of oestrone and oestradiol-17 ß were of the order of 70 to 80% and the within-assay coefficient of variation was 10 to 12%. The between-assay coefficient of varia¬ tion, calculated from control samples run in duplicate with each assay was 15%. The sensitivity of the method, determined from the variability of the reagent blanks, was 5 pg/ml for oestrone and 4 pg/ml for oestradiol-17ß. The results in this paper have been corrected for procedural losses.The mean values for three cows are presented in Text-fig.

Gonadotrophins and ovarian steroids in cattle II. Pulsatile changes of concentrations in the jugular vein throughout pregnancy

“…Blood flow to the pregnant uterus horn is controlled by the conceptus (Ford et al 1979) and might be triggered by oestradiol-17ß. The decrease in pro¬ gesterone during the last 2 months before term and the pronounced increase in oestradiol-17ß towards end-pregnancy confirm earlier data of Henricks et al (1972), Edqvist & Johansson (1972), Hoffmann et al (1973b, 1977, Peterson et al (1975), and Mosti et al (1981). Relatively constant oestradiol-17ß concentrations during mid-preg¬ nancy were reported by Robertson & King (1979) what is in agreement with our findings.…”

Role of the adrenals in the maintenance of pregnancy in cows

“…A fetal contribution to maternal progesterone or oestrogen has not been found either by analysis of hormones in fetal and maternal blood (Hunter, Fairclough, Peterson & Welch, 1977) or by assay of maternal hormones after fetectomy (Hoffmann et al, 1979). The bovine placenta at this time does not contain detectable amounts of progesterone (Erb, Randel & Callahan, 1971 ;Peterson, Hunter, Welch & Fairclough, 1975). However, when incubated in vitro it can release progesterone into the medium, but the amounts are small compared to those produced by the placentas of other species (Ainsworth & Ryan, 1967).…”

Effect of Labor Induction on the Expression of Oxytocin Receptor, Cytochrome P450 Aromatase, and Estradiol Receptor in the Reproductive Tract of the Late-Pregnant Ewe1

“…At this stage of pregnancy, estrone sulphate is the predominant estrogen produced [16]. Free estradiol, which is the major biologically active estrogen in the sheep, does not increase significantly until approximately 24 h before parturition [16,17,18,33]. This suggests that the regulation of aromatase expression is probably at the transcriptional level.…”