In Vitro Conversion of [4-14c] Dehydroepiandrosterone and Androstenedione to Oestrogens by the Microsomes of Placentas From Normal, Toxaemic, Diabetic and Postmature Pregnancies

Abstract

The placental oestrogen precursors [4-14C]dehydroepiandrosterone (DHA) and [4-14C]androstenedione (AD) were incubated with microsomal fractions of human placentas from normal and pathological pregnancies at different stages of gestation, in order to evaluate the rate of conversion of the substrates to oestrogens. In placentas from normal pregnancies the capability to convert C19-steroids (DHA and AD) to C18-steroids (oestrone and oestradiol017β) increased with the age of gestation. The placenta at term metabolizes [4-14C]DHA and [4-14C]AD into oestrogens (oestrone and oestradiol-17β) with a four times greater aromatisation rate than the placenta at midpregnancy. The concentration of protein in the placental microsomal fraction also increased with the age of gestation. In our aromatisation studies it was found that the conversion rate of DHA and AD to oestrogens (oestrone and oestradiol-17β) by placental microsomes was significantly lowered in toxaemic and diabetic placentas and in placentas of postmaturity cases as compared to normal placentas at term. The relationship between placental insufficiency and a lowered capacity of Δ5-Δ4-isomerase, 3β-hydroxysteriod-dehydrogenase and the aromatizing enzyme systems is discussed with regard to the main causes of a low oestriol excretion and a low aromatisation rate of injected DHA-S in pathological pregnancies. Finally it is shown, that the parameters of the hormonal investigations correlate with the degree of pathological microscopic alterations of the placentas.

Regionally different stetoid-biosynthesis within materno-fetal circulation units (placentones) of mature human placentas

“…I, (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) Q J 4 -androstendione was incubated with microsomal fraction (equivalent to 0.5 g fresh weight) from 12 placentones of 8 placentas. Each incubation took place with a subcellular fraction from the center and then from the periphery of the placentones, so that a direct comparison was possible in each placenta.…”

“…Tissue was then homogenized in 0.25 M sucrose in a glass homogenisator. (The method has been described elsewhere [5].) Remains of connective tissue which coüld not be homogenized were * Investigations were supported by the Forschungsgemeinschaft".…”

“…All incubations took place in SOERENSON phosphate buffer (pH 7.35) at 37°C, open to the air in a shaking thermostat. In every case 250 nC (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) Q A f Androstendione (specific activity 60mC/mMol) was dissolved with 0.5 ml microsomal fraction (equivalent to 0.5 g fresh weight placenta) or with 0.5 mg of microsomal fraction and with an NADPH-generating System in 3 ml of 0.15 M SOERENSON phosphate buffer. After 5 minutes incubation, extraction of Solutions was performed 3 times with ether/chloroform (3:1).…”

“…(The method has been described elsewhere [5].) Quantitative analysis: Quantitative analysis of steroids took place on paper chromatograms after measurement of radioactivity with a PACKARD lladiochromatograph Scanner, model 7201.…”

Estrogens in maternal plasma following intraamniotic injection of (3H)-dehydroepiandrosterone-sulfate in midpregnancy

“…The DHEA-S induced increase in urinary or plasma estrogens provides Information about the reservecapacity of the placenta. Using incubation studies with placental tissue we could demonstrate in vitro that the conversion of DHEA to estrogens by the placental aromatising enzyme-system is significantly reduced in pathological pregnancies (preeclampsia, diabetes, postmaturity) s compared to normal pregnancies [10,12,13]. These studies demonstrated that in complicated pregnancies the diminished capacity of the aromatizing enzymesystem can occur and may result in a reduced estrogen production which is of great clinical importance.…”