Metabolism of oestradiol-17beta in the human myometrium

Further characterization of 17 beta-hydroxysteroid dehydrogenase activity in cultured myometrial cells: cofactor dependency and subcellular localization

To further characterize 17 beta-hydroxysteroid dehydrogenase (17 beta-SDH) from cultured ovine myometrial cells, an assay was established in whole cell homogenates and cell subfractions. Tritiated estradiol (E2) was incubated in the presence of an excess of cofactor and estrone (E1) formed purified by thin-layer chromatography. The enzyme activity was linear with time up to 2 hours and with protein concentration up to 0.7 mg/ml at the substrate concentration used (5 X 10(-9) M). The routine assay was for 30 min in the presence of 0.5 mg/ml of protein. Both NAD+ or NADP+ could sustain enzyme activity but NAD+ was twice as much efficient. Most of the enzyme activity was associated with the microsome and mitochondrial membranes. The addition of an excess (1000 microM) of NAD+ to the incubation medium prevented the progressive decline observed with time in a given subculture in the intact cell monolayer assay, supporting our previous hypothesis that this decline was due to cofactor depletion. In contrast, the slow and irreversible decline of enzyme activity observed in successive subcultures was not prevented by the addition of cofactor to the homogenate and thus reflects another phenomenon, probably a change in metabolism with age.

17 beta-hydroxysteroid dehydrogenase activity in cultured myometrial cells: effect of serial subcultures

17 beta-Hydroxysteroid dehydrogenase (17 beta-SDH) activity was studied in culture ovine myometrial cells. After primary culture, cells were routinely subcultured (every 7th day), seeded at 5 x 10(5) cells per dish and grown in a medium with 2% of serum. 17 beta-SDH activity was measured by incubating intact cell monolayers with [3H]-estradiol (5 x 10(-9) M) in serum-free medium. Metabolites were extracted from both cells and medium, and separated by thin-layer chromatography. 17 beta-SDH was expressed as total E1 formed (cells + medium) in fmol/mg of protein as a function of time. 17 beta-SDH has an approximate Km of 5 x 10(-6) M. After 3 min of incubation, all measurable E1 is within the cells; it is progressively released but after 1 h only 40% of E1 is found in the medium. 17 beta-SDH decreases from day 2 to day 8 of each subculture, whereas total proteins increase. Subculture partially restores 17 beta-SDH activity so that it is always higher on day 2 of any subculture than on day 8 of the previous one, however a progressive decline occurs with successive subcultures. This decline parallels the slowing of cell growth and overall protein synthesis and probably reflects cell ageing.

Synthesis of catechol estrogens by human uterus and leiomyoma

Homogenates of human endometrial, myometrial and leiomyoma tissues were incubated with (2,4,6,7-3H)-estradiol and tritiated catechol estrogens were isolated and identified. Though 2- and 4-hydroxylations were about the same in endometrium, 4-hydroxylation was two to four fold higher than 2-hydroxylation in myometrium and leiomyoma. However, endometrium showed greater capacity to form both 2- and 4-hydroxyestrogens than the other two tissues. Both 2- and 4-hydroxylations were significantly less than in myometrium. In view of the reports indicating that inhibitors of catechol 0-methyl transferase (COMT) might act as antineoplastic agents due to their interference with t-RNA methylases and since catechol estrogens inhibit COMT, the present results suggest that endogenous synthesis of catechol estrogens may play an important role in the pathophysiology of uterine leiomyoma.

In vitro conversion of estradiol-17beta into estrone in normal human myometrium and leiomyoma

The specific activity of 17beta-hydroxysteroid dehydrogenase was measured in normal human myometrium, and in leiomyoma specimens obtained from the same tumor-bearing uterus. In all cases the normal tissue showed greater conversion of estradiol-17beta into estrone than the neoplastic tissues. In normal myometrium of fertile women, the specific enzyme activity depended on the phase of the menstrual cycle, the highest values of 17beta-hydroxysteroid dehydrogenase activity being found in the early secretory phase. To determine the intracellular distribution of the 17beta-hydroxysteroid dehydrogenase, purified microsomes, mitochondria, nuclei and cytosol fractions were prepared. The purity of each fraction was monitored by marker enzymes. It was found that the enzyme was mainly located in mitochondria and microsomes. Furthermore it was demonstrated that the microsomal enzyme was bound tightly to the membranes of the endoplasmic reticulum, while the mitochondrial 17beta-hydroxysteroid dehydrogenase was mainly associated with the outer membranes of the organelle. Kinetic parameters (Km-values, coenzyme requirements, temperature and pH-optima) of the cytoplasmic, nuclear, mitochondrial and microsomal enzyme of normal and neoplastic tissue were compared.

Subcellular progesterone in human myometrium during late pregnancy

Samples of myometrium were obtained from twenty-two patients undergoing caesarian sections for various obstetric indications. The myometrium was homogenized and divided into four subcellular fractions (crude nuclear, mitochondrial, microsomal and cytosol). The concentration of endogenous progesterone in these fractions was determined by radioimmunoassay. In addition the concentration of oestrone and oestradiol of fifteen cytosolic fractions was determined. The subcellular concentration of progesterone (pg/mg protein) in human myometrium was higher in samples taken during labour than in samples taken at elective caesarian sections. This finding was statistically significant in the crude nuclear (P less than 0.005) and the microsomal (P less than 0.05) fractions. The absolute concentration of progesterone was lowest in the nuclear and highest in the microsomal fraction. The relative progesterone concentrations in the four subcellular fractions were the same in both groups. The data show that there is no significant decrease in myometrial progesterone associated with labour in man. The mean concentration of oestrone was higher than the mean oestradiol concentration in the cytosol fraction of human myometrium in late pregnancy. This study shows that a completely different oestrogen ratio exists in myometrium than in plasma.

Metabolism of [4-14C] testosterone in the rat uterus in vitro

In view of the uterine action of androgens we have investigated in vitro the metabolism of [4-14C]-testosterone in uterine tissue of ovariectomized rats. After purification of the extracts on Amberlite XAD-2 the metabolites have been isolated by gel. Five metabolites were isolated and identified during these incubation studies: 4-androstene 3,17-dione, 17beta-hydroxy-5alpha-androstan-3-one, 5 alpha-androstane-3alpha17beta-diol, 4-androstene-3 beta, 17beta-diol and 4-androstene-3alpha, 17beta-diol. Furthermore, two polar C19O3-metabolites and one isopolar to 5 alpha-androstane-3, 17-dione have also been detected. The metabolites were characterized by radioactive gas chromatogrphy, and determination of the relative specific activity in the eluates of Sephadex column chromatography. The identification of allylic alcohols was complemented by their oxidation to 4-androstene-3,17-dione. The present data show that activity of 17beta,3alpha- and 3beta-hydroxysteroid-oxidoreductase and 5alpha-ring-reductase are involved in the metabolism of testosterone in vitro in the rat uterus. The very low 5 alpha-reductase activity under the experimental conditions used in this work explains the formation of allylalcohols as the principal metabolites of testosterone in the rat uterus.