Endometrial estradiol-17 beta-dehydrogenase activity in women wearing Cu-IUD

In order to determine whether inhibition of the endometrial estradiol-17 beta-dehydrogenase activity by Cu++ could be one of the factors accounting for the enhanced contraceptive efficacy of copper intrauterine devices (Cu-IUD), the activity of the enzyme was measured in endometrial biopsies from women wearing this device. The levels of enzymatic activity found in these specimens were within the range of controls (women without IUD), e.g. 0.1--0.8 and 7--27 nmol E1 formed/mg protein/h in the follicular and luteal phases of the menstrual cycle, respectively. It is concluded that Cu-IUD does not modify significantly either the activity of endometrial-17 beta-dehydrogenase, an enzyme known to regulate the tissular concentration of estradiol, or its response to the inductive effect of progesterone.

Aryl hydrocarbon hydroxylase activity and microsomal cytochrome content of human fetal tissues

Aryl hydrocarbon hydroxylase (AHH) and microsomal cytochromes were measured in tissues of human features aborted by prostaglandins. Cytochrome P-450 concentrations and AHH activity were about 4 times higher in adrenal glands than in liver. AHH was present in testes, ovaries, and vagina and uterus at levels equal to or greater than those in the liver. In lung, kidney, and intestines it was present at levels lower than those in the liver. Mean hepatic AHH and hepatic and adrenal cytochromes P-450 and b5 were not significantly different in prostaglandin and hysterotomy abortuses; mean adrenal AHH was significantly lower in prostaglandin abortuses, but the ranges in both groups were overlapping. Neither fetal sex nor maternal cigarette smoking affected hepatic or adrenal AHH activity or microsomal cytochrome concentrations or difference spectra. Hepatic and adrenal AHH activities were concentrated in microsomes and were correlated with microsomal P-450 content. These findings are constant with P-450 mediation of AHH in human fetal tissues. The data demonstrate the utility of prostaglandin abortuses for studies of fetal tissue mixed-function oxidase activity and point to the endocrine glands and target tissues in addition to the liver as potential sites for activating chemical carcinogens and cytotoxins in the human fetus.

Estrogen metabolism in normal and neoplastic endometrium

Studies on normal endometrium at different phases of the menstrual cycle have shown that progesterone and synthetic progestins reduce the levels of estradiol receptors in the tissue and increase the activity of estradiol-17beta-dehydrogenase, an enzyme that converts estradiol to estrone. These effects may account for the antiestrogenic characteristics of the progestins. Similar effects were obtained in some postmenopausal patients with endometrial adenocarcinoma treated for two to 10 days with oral medroxyprogesterone acetate. These results point to the potential usefulness of a short-term, in vivo biochemical test which, combined with histologic observations, may identify patients who are likely to respond to treatment with progestins.

Comparison of results from in situ and in vitro perfusions of rabbit uterus with labeled estrone and estradiol

The interconversion of labeled estrone (E1) and estradiol (E2) in rabbit uterus was studied in vivo and in vitro, in order to evaluate the influence of incubation conditions upon the preferred direction of the reversible conversion of E2 to E1. In a typical experiment, one uterine horn was perfused intraluminally in situ with a mixture of [3H]E2 and [14C]E1, while the other horn was dissected and used for in vitro perfusions with the same tracers, both intraluminally and on tissue slices. The ratios of rate constants corresponding to the oxidative and reductive reactions were found to be similar under the three perfusion conditions, as calculated from the isotopic data. The rate constant of conversion of E1 to E2 was 10-20 times larger than the rate constant of the opposite reaction. Equal E2 nuclear saturation levels were obtained by perfusion of the uterine tissue with excess [3H]E2 in situ and in vitro after slicing.

Induction of human endometrial estradiol dehydrogenase by progestins

Estradiol-17beta dehydrogenase activity in proliferative human endometrium (average of 1.5 nmole of estrone formed from estradiol/mg protein/h) was stimulated as much as as 6-fold during incubations of tissue slices in culture medium containing progesterone. Stimulation was already detectable at 7 h and the highest activity values were reached at 48-72 h of incubation in the presence of excess progesterone. Maximal stimulation was achieved with concentrations of the hormone of 0.25 mug/ml or higher. At concentrations approximately equal to midluteal plasma levels (20 ng/ml) more than 50% of the maximal response was observed. Norgestrel (17alpha-ethynyl-18-methyl-19-nortestosterone) was also effective in inducing enzymatic activity. The similarity of the effects obtained with progesterone (a possible substrate for estradiol dehydrogenase) and the synthetic progestin indicates that the stimulation of enzymatic activity was not due to substrate induction. Addition of estradiol to the culture medium had no influence on the activity of the enzyme. The induction of estradiol dehydrogenase by progesterone was inhibited by puromycin or actinomycin D. These observations indicate that progestational agents increase the rate of de novo synthesis of the enzyme. Stimulation of endometrial estradiol dehydrogenase was also observed after 2-3 day oral administration of medroxyprogesterone acetate to women in the follicular phase. In contrast, the enzymatic activity in endometrium obtained from women taking estrogens was found to be as low as in normal proliferative tissue. These in vitro and in vivo results point to progesterone as the agent responsible for the 10-fold increase in endometrial estradiol dehydrogenase activity observed during the luteal phase in menstruating women. Data obtained from superfusion studies of estrogen dynamics in endometrium indicate that changes in enzyme concentrations may play a physiologic role in the regulation of tissue levels of estradiol.

Effects of progestins on estradiol receptor levels in human endometrium

Medroxyprogesterone acetate (Provera) was administered orally during 2-4 days to women undergoing endometrial curettage during the follicular phase of the menstrual cycle. Estradiol (E2) receptor levels were estimated from the amounts of 2H-E2 tightly bound in nuclei after incubation of endometrial tissue with an excess of the labeled hormone. An average value (9 subjects) of 1.5 pmole E2/mg DNA +/- 0.7 (mean +1- SD) was found. This value is significantly lower than the average E2 receptor levels in proliferative endometrium of untreated subjects (3.2 +/- 1.3, n = 33) and equals the level observed in the early secretory phase (1.5 +/- 0.5, n = 5). These results indicate that one of the progestin effects on human endometrium is the reduction of E2 receptor levels.

Quantitative studies of tissue uptake and disposition of hormones

A two-tracer continuous flow perfusion experimental design has been used to measure the entry of steroids (oestradiol, oestrone, progesterone, 20α-dihydroprogesterone, testosterone, androstenedione, cortisol, cortisone) and nucleic acid precursors (uridine, cytidine, UMP) into several tissues, using slices (human endometrium, endometrial adenocarcinoma, placenta, foetal membranes, rat and rabbit liver) or cell suspensions (chorion, amnion, liver, choriocarcinoma Be/Wo). Rates of interconversion between the perfused compounds and rates of release into the medium were also measured. The response of the system to additions of hormones, drugs and plasma proteins was evaluated by measuring rates and concentrations. The entry of oestrogen sulphates and UMP into tissues was compared with the entry of the corresponding unesterified compounds.