Free and Conjugated Steroids in Maternal and Fetal Plasma in the Cow Near Term

Abstract

Plasma samples were collected in 5 pregnant cows (between Days 247 and 273 postconception) via indwelling catheters from the maternal jugular and uterine veins, umbilical artery and vein and the fetal vena cava caudalis. Four fetuses died within four days and the fifth was born alive on Day 3 postsurgery. Progesterone (P), Testosterone (T) as well as free and conjugated (enzyme hydrolysis) cortisol (F), corticosterone (B), estrone (E5), estradiol-17α and -17β (E2α, E2β) were determined by CPB and RIA respectively. Steroid concentrations showed a distinct separation between maternal and fetal circulation. Fetal P was low (x̄ = 0.20 ng/ml) but maternal P was high as anticipated for the stage of pregnancy, while T values were low in all sampling sites (0.08 – 0.55 ng/ml). Corticoids were higher in the maternal than fetal compartment except in one cow which was cannulated post Day 270 where F increased in the fetus within 4 days from 71 to 102 ng/ml on the day of parturition. No significant changes in F/B-ratios occurred in maternal samples while fetal plasma F/B ratios increased during the sampling period. Conjugated F and B were 5 percent and 10 – 20 percent of the free, respectively, while conjugated estrogens could exceed the free estrogens by a factor of 10 to 100 reaching concentrations above 100 ng E2α/ml in 2 samples in the fetus. Free and conjugated E1 was the major maternal estrogen while it was Esa in the fetus. In both compartments lowest concentrations were found for E2β (free: 0.007 – 0.060 ng/ml, conjugated 0.04 – 1.69 ng/ml, depending on the sampling site). Except for E2β and based on paired samples, estrogen levels in the uterine vein were higher than in the jugular vein, and in the fetus they were highest in the vena cava and lowest in the umbilical artery.