Activity Of 17β-hydroxysteroid Oxidoreductase Research Articles

Reductase Activity of 17β-Hydroxysteroid Oxidoreductase in Prostatic Tumors of Different Histological Structure

Reductase activity of 17beta-hydroxysteroid oxidoreductase in biopsy specimens of prostatic cancer and benign hyperplasia, and prostatic intraepithelial neoplasia and serum concentrations of testosterone, 5alpha-dihydrotestosterone, 4-androstene-3,17-dione were compared in patients and healthy individuals. Reductase activities of 17beta-hydroxysteroid oxidoreductase in soluble fraction of prostatic biopsy specimens decreased in the following order: prostatic cancer>prostatic intraepithelial neoplasia>>benign prostatic hyperplasia. No differences in serum concentrations of testosterone, 5alpha-dihydrotestosterone, 4-androstene-3,17-dione between these three groups of patients were found, while the mean serum concentration of these androgens in patients with prostatic tumors did not surpass the threshold normal values for men. Hence, high reductase activity of 17beta-hydroxysteroid oxidoreductase can be associated with pathogenetic mechanisms of human malignant prostatic tumors.

Identification, quantitation and biological activity of phytoestrogens in a dietary supplement for breast enhancement

A hop-based dietary supplement, marketed for natural breast enhancement, was analysed to determine the identity and biological activity of active constituents and potential biological effects in man. Extracts of the dietary supplement were analysed by LC–MS n and phytoestrogens identified and quantitated by reference to appropriate standards. Only hop-associated phytoestrogens were found in the dietary supplement at significant concentrations as follows (mean±1 S.D.); 8-prenylnaringenin 10.9±0.3, 6-prenylnaringenin 27.4±1.2, 6,8-diprenylnaringenin 0.9±0.1, xanthohumol 321±17 and isoxanthohumol 81.1±1.6 μg/g of dietary supplement. The oestrogenic activity of extracts in an ERα reporter gene assay was equivalent to 48±6.3 ng 17β-oestradiol/g supplement and consistent with the 8-prenylnaringenin content. The dietary supplement extract also inhibited reductive 17β-hydroxysteroid oxidoreductase activity, but to a greater extent than a concentration matched reference mixture of hop phytoestrogens. However, the supplement was only weakly active in mouse uterotrophic assays following administration in feed or after subcutaneous injection of extract at doses of 8-PN up to 250 times higher than that recommended for women. These preliminary findings suggest that the dietary supplement is unlikely to produce oestrogenic effects in vivo at the level of the uterus; supporting evidence is still required to demonstrate efficacy.

Hepatic microsomal enzyme activity in the koala and tammar wallaby: high 17β-hydroxysteroid oxidoreductase activity in koala liver microsomes

We have studied the hepatic microsomal xenobiotic metabolising capacity of koala ( Phascolarctos cinereus) and tammar wallaby ( Macropus eugenii). Total cytochrome P450 content in hepatic microsomes from koala (0.87±0.18 nmol/mg protein, n=4, mean (S.D.) and rat were comparable while tammar wallaby displayed reduced P450 content (0.24±0.04 nmol/mg protein). Associated microsomal activities (NADPH cytochrome P450 reductase, aminopyrine N-demethylation, aniline hydroxylation, and androstenedione 6β- and 16α-hydroxylation) in koala liver were similar to or reduced relative to rat. Hepatic microsomal NADPH-supported 17β-hydroxysteroid oxidoreductase (17β-HSOR) activity was significantly higher in koala (9.99±3.08 nmol/mg protein/min) than in tammar wallaby liver (0.86±0.16 nmol/mg protein/min). However, when NADH was utilised as cofactor the activity was similar in both marsupial species (koala, 1.44±0.84 nmol/mg protein/min; tammar wallaby, 1.52±0.44 nmol/mg protein/min). Michaelis–Menten parameters for the kinetics of 17β-HSOR androstenedione reduction by NADPH and NADH were determined in the koala. The K m for androstenedione was of the order of 1.9–4 μM ( n=4) irrespective of the cofactor used, whilst the K m for NADPH was 0.04–0.05 μM ( n=2) and for NADH was 134–430 μM ( n=2). Potential inhibitors were evaluated for their effects on NADPH-mediated 17β-HSOR activity with menadione and, to lesser extents, menthone, benzaldehyde and metyrapone eliciting significant inhibition. From detailed kinetic studies menthone was found to be an uncompetitive inhibitor of the activity in koala liver ( K i 220 μM).

Placental 17β-hydroxysteroid oxidoreductase, lactate dehydrogenase and malate dehydrogenase during the latter half of pregnancy in the mouse

The specific activity of 17β-hydroxysteroid oxidoreductase (17-HOR) with estradiol-17β (E2), estrone (E1) and testosterone (T), as well as that of lactate dehydrogenase (LDH) and malate dehydrogenase (MDH) were measured in homogenates of CF-1 mouse placenta during the latter half of pregnancy. 17-HOR activity with E2 and T increased over 100-fold between days 9 and 12, and 3- to 4-fold between days 15 and 19, with no further change to day 21. In contrast, activity with E1 increased 39-fold between days 9 and 12, 3.8-fold between days 15 and 9 but then decreased between days 19 and 21. The E2/T activity ratio was constant while the E2 E1 ratio increased between days 9 and 21. LDH increased 2-fold between days 9 and 12 with no further increase to day 19. MDH was constant from day 9 to 19. Activity with E2 was inhibited by T, 5α-dihydrotestosterone (5α-DHT) and DHA but not by E1, androstenedione (A) or 20α-dihydroprogesterone. Activity with T was inhibited by E2, 5α-DHT and DHA, but not by A. In contrast, activity with E1 was inhibited by A and DHA but not by E2, T or 5α-DHT. The results suggest placental 17-HOR is developmentally regulated. Although the results are also suggestive of multiple forms of 17-HOR, a single enzyme with an ordered kinetic mechanism cannot be ruled out.

Androstenedione is an important precursor of dihydrotestosterone in the genital skin of women and is metabolized via 5α-androstanedione

Androgen action is largely determined by the formation of dihydrotestosterone in target tissues. In women, androstenedione is the major precursor of dihydrotestosterone production in female genital skin. The present study was initiated to determine whether androstenedione is converted to dihydrotestosterone primarily via testosterone or 5α-adrostane-3,17-dione (5α-androstanedione), and to examine the pathway of androstenedione metabolism in genital skin. Genital skin was obtained from 9 normal premenopausal women and 2 normal men. Each tissue was incubated with [ 3H]androstenedione in RPMI-1640 medium for 1 h at 37°C in 95% O 2 5% CO 2. The metabolites were separated and purified by paper partition and thin-layer chromatography. The conversions of androstenedione to 5α-androstanedione and to androsterone were similar (10.45 ± 1.46 and 11.04 ± 2.04%/200 mg tissue), and were approx. 12, 8 and 23 times higher than the conversion of androstenedione to testosterone, dihydrotestosterone and 5α-androstane-3α,17β-diol, respectively. The male samples showed a similar pattern of metabolism. These data indicate that 5α-androstanedione is the most important intermediate in the conversion of androstenedione to dihydrotestosterone. The data also confirm the importance of 5α-reductase activity over that of 17β-hydroxysteroid oxidoreductase activity in the expression of androgen action in women.

17β-Hydroxysteroid oxidoreductase activity: Age-dependent profile in rat liver and kinetic properties of the hepatic microsomal enzyme in relation to cytochrome P450-dependent steroid hydroxylation

The functional relationship between the microsomal cytochrome P450 and 17 beta-hydroxysteroid oxidoreductase (HSOR) enzymes involved in steroid metabolism was investigated in rat liver. In male and female rat hepatic microsomes the NADPH-dependent conversion of androstenedione (AD) to testosterone (T) was approx. 4-fold greater at 6 weeks of age than in 1 week old animals. In hepatic microsomes from 15 week old rats the activity of the HSOR pathway was greater in males than in females (1.51 compared to 0.80 nmol T formed/min/mg protein). However, oestradiol administration to intact adult male rats did not decrease HSOR activity. Thus, androgen is not essential for maintenance of HSOR enzymes. Instead, it is likely that irreversible androgen imprinting of the HSOR enzyme occurs during the prepubertal period. The in vitro characteristics of HSOR activity were also assessed. The Km for NADH-dependent reduction of AD to T was 9.2 microM and the Vmax was 3.0 nmol/min/mg protein but the NAD-mediated formation of AD from T did not follow Michaelis-Menton kinetics. pH markedly influenced HSOR-mediated AD/T interconversion with 17-ketosteroid reduction facilitated at low pH, and 17 beta-hydroxysteroid dehydrogenation about 2-fold more efficient at pH 8.0 than at pH 5.5. Product steroid activation of HSOR activity was noted. 17 beta-Hydroxysteroids, including T and oestradiol, activated the rate of conversion of AD to T and 17-ketosteroids such as oestrone and AD activated the NAD-dependent dehydrogenation of T. Activation was not observed at low steroid substrate concentrations so that it was not possible to analyse this phenomenon by a conventional kinetic approach.

17β-Hydroxysteroid oxidoreductase activity in human maternal and umbilical cord sera

The specific activity of 17β-hydroxysteroid oxidoreductase (17β-HSOR) in human umbilical cord arterial serum has been reported to be similar to that of maternal serum and 5- to 15-times higher than that of cord venous serum. Based on these findings, it was proposed that 17β-HSOR in cord arterial serum arises from fetal tissue sources other than placenta. In the course of studies of the role of 17β-HSOR in the modulation of bioactive estrogen levels in the human fetus, we determined that: (i) the specific activity of 17β-HSOR in maternal serum is 2.1- to 55-times higher than that in either umbilical cord venous serum or cord arterial serum; (ii) the specific activity of 17β-HSOR in umbilical cord venous and cord arterial sera are similar; (iii) anti-human placental cytosolic 17β-HSOR antibody inactivates the 17β-HSOR in maternal, umbilical cord arterial, and cord venous sera but not in maternal or fetal erythrocytes; (iv) the specific activity of 17β-HSOR in maternal serum (expressed per mg protein) is higher than that in umbilical cord serum and maternal and fetal erythrocytes, and is approximately 700-times lower than that of the placental microsomal enzyme; (v) the preferred cofactor for maternal serum 17β-HSOR is NADP+; (vi) 17β-HSOR is associated with the high speed supernatant fraction of maternal serum rather than with the particulate fraction; and, (vii) the patterns of binding of [3H]estradiol-17β to proteins in maternal and umbilical cord arterial sera and those of 17β-HSOR activity, determined in corresponding fractions obtained after sucrose density gradient centrifugation, are approxi-mately coincidental at S20,ω, 4.6–5. The findings of higher 17β-HSOR levels in maternal serum compared with umbilical cord arterial serum and the inactivation of the cord arterial serum enzyme by an antibody that recognizes human placental cytosolic 17β-HSOR is suggestive that 17β-HSOR in cord arterial serum is of placental origin.

Activity of 17β-hydroxysteroid oxidoreductase in tissues of the human fetus

The interconversion of oestrone and oestradiol, androstenedione and testosterone, and dehydroepiandrosterone and 5-androstene-3 beta,17 beta-diol in mammalian tissues is catalysed by 17 beta-hydroxysteroid oxidoreductase (17 beta-HSOR). To identify tissue sites of 17 beta-HSOR activity in the human fetus, microsomal fractions from 15 different fetal tissues obtained from first and second trimester pregnancies were used for evaluation of enzymatic activity by use of [17 alpha-3H] oestradiol as the substrate and NADP+ as the co-factor. With these reagents, the enzyme-catalysed reaction led to the production of both non-radiolabelled oestrone and NADP3H in equimolar amounts; the radioactivity associated with NADP3H was used to quantify 17 beta-HSOR activity. Activity of 17 beta-HSOR was present in microsomes of all the tissues evaluated. The specific activity of the enzyme was highest in liver and placental microsomes. The interconversion of oestradiol and oestrone in microsomal fractions of nine different fetal tissues was studied by the use of substrates labelled with tritium at stable nuclear positions ([6,7-3H]oestradiol and [6,7-3H]oestrone). The products, [3H]oestrone and [3H]oestradiol, were quantified by the use of established techniques; other metabolites formed in these incubations were not identified. The reductive pathway of metabolism (oestrone to oestradiol) appeared to be favoured in microsomal fractions prepared from placenta, fetal zone of the adrenal gland and, possibly, lung. The oxidative pathway (oestradiol to oestrone) appeared to be favoured in microsomes prepared from liver, intestine, stomach, kidney, brain and heart. 17 beta-HSOR activity in fetal liver also was assessed by the use of fresh and frozen-thawed tissue, homogenate, subcellular fractions, and, also, in primary hepatocytes maintained in culture; the specific activity of the enzyme was highest in the microsomal fraction of liver tissue and 17 beta-HSOR activity in liver microsomes was linear with time of incubation up to 1 h. In hepatocytes, the enzymatic activity was linear with time of incubation up to 2 h and with cell number up to 2.5 x 10(5) cells/ml; the apparent Michaelis constant of hepatocyte 17 beta-HSOR for oestradiol was 11 mumol/l. The specific activity of 17 beta-HSOR did not change after pretreatment of hepatocytes for 24 h with insulin, glucagon or dexamethasone.

17 beta-Hydroxysteroid oxidoreductase activity in the endometrium of normal women and patients with pelvic pain and polycystic ovaries.

17 beta-Hydroxysteroid oxidoreductase (17-OHSD) activity in the endometrium of women with pelvic pain syndrome (PPS) and/or polycystic ovaries (PCO) was compared with that of a control group. In both groups there was a 10-fold increase in 17-OHSD activity in secretory phase tissue compared with that of the proliferative phase, measured by both oxidative and reduction pathways, and a highly significant correlation between the two directions (P less than 0.001). In normal subjects, the ratio of activity measured under oxidative conditions: reducing conditions, at all stages of the cycle except late proliferative phase, was 2.1-2.9. In the late proliferative phase the ratio was 5.5 which was significantly different from other stages of the cycle. Similar ratios were found for the PPS/PCO group (proliferative phase 2.5, secretory phase 5.6); these were also significantly different (P less than 0.01). On the basis of this study oestrogen metabolism in the endometrium of women with PPS and/or PCO appears to be no different from that of normal subjects. Measurement of enzyme activity in high speed soluble and particulate fractions of endometrial homogenate indicated the presence of two activities with different cofactor requirements. Gel filtration chromatography of the soluble fraction revealed a single peak of activity coincident with a molecular weight of 30 kDa with a strong preference for NAD + as cofactor. These preliminary findings suggest the presence of both soluble and particulate forms of 17-OHSD activity in the endometrium.

Structure-activity relationships of the inhibition of human placental aromatase by imidazole drugs including ketoconazole

The aim of the present study was to investigate the effectiveness of several imidazole drugs to inhibit human placental aromatase compared with the known inhibitors of aromatase, 4-hydroxyandrostenedione (4-OHA) and aminoglutethimide (AG). Inhibition was similar with both androstenedione and testosterone as substrates. The order of decreasing inhibitory effect (determined from ID 50 values) was: 4-OHA > tioconazole > econazole > bifonazole > clotrimazole > micomazole > isoconazole > ketoconazole > AG > nimorazole. The imidazole drugs and AG were reversible inhibitors of aromatase activity, in contrast 4-OHA was an irreversible inhibitor. Astemizole inhibited less than 40% whereas metronidazole, carbimazole, mebendazole, tinidazole and thiabendazole inhibited less than 20% of aromatase activity at 100 μmol/1. The imidazole drugs and AG were without effect on 3β -hydroxy steroid dehydrogenase-isomerase (3β-HSD-I) and 17β-hydroxysteroid oxidoreductase activity. In contrast 4-OHA was found to be a potent, reversible inhibitor of 3β-HSD-I with an ID 50 value of 2.15μmol/l. A common structural feature of the imidazole drugs having an inhibitory effect was the presence of one or more aromatic rings on the N-1 substituent. In contrast, the imidazole drugs having the imidazole ring fused to a benzene ring, i.e. benzimidazoles (astemizole, mebendazole, thiabendazole) and those having an aliphatic side chain on the N-1 of the imidazole ring (carbimazole, metronidazole, nimorazole, tinidazole) were only weak inhibitors of aromatase.

17β-Hydroxysteroid oxidoreductase: A ubiquitous enzyme. Interconversion of estrone and estradiol-17β in [formula omitted] mouse tissues

A survey was conducted to define the sites of 17β-hydroxysteroid oxidoreductase activity in organs and tissues of male and female BALB c mice, as well as the favored direction of the oxidoreductase reaction in intact tissues. The enzyme activity was assayed by use of radiolabeled estrone and estradiol-17β as substrates. Estrone formation from estradiol-17β was demonstrated in all tissues. The formation of estradiol-17β from estrone was demonstrated in most tissues, however, it was barely detected or was undetectable in the glandular stomach, small intestine, cecum, and large intestine. Thus, 17β-hydroxysteroid oxidoreductase activity is expressed in all BALB c mouse organs and tissues. Approximately two-thirds of the tissues and organs examined, including those of the reproductive tracts, favored the conversion of estrone to estradiol-17β rather than the reverse reaction. The results of this study, however, represent qualitative estimates of 17β-hydroxysteroid oxidoreductase activity in BALB c mouse tissues that are uncorrected for conversion to hydroxylated metabolites. These in vitro findings suggest that the 17β-hydroxysteroid oxidoreductase catalyzed reduction of estrone may contribute to the maintenance of physiologic levels of estradiol-17β in estrogen responsive tissues.

Steroid sulfatase and 17β-hydroxysteroid oxidoreductase activities in mouse tissues

The metabolism of estrone sulfate and dehydroisoandrosterone sulfate to the free, unconjugated steroids, estrone and dehydroisoandrosterone, was demonstrated in more than thirty different tissues from male and female BALB/c mice. The activity of steroid sulfatase, when expressed per mg tissue, was greatest in both the pituitary gland and the adrenal glands. The pituitary gland, however, had the lowest capacity for hydrolysis of steroid sulfates while the liver had the greatest capacity. 17β-Hydroxysteroid oxidoreductase activity also was demonstrated in all mouse tissues by the formation of estradiol-17β when using estrone sulfate as the substrate. The highest apparent activity for 17β-hydroxysteroid oxidoreductase was found in lung tissue, and the greatest capacity to form estradiol-17β from estrone sulfate was found in liver, lungs, kidneys and testes. This study demonstrates that the majority of mouse tissues have steroid sulfatase and l 7β -hydroxysteroid oxidoreductase activities.

Steroidogenesis in the monkey testis: Relationship of enzyme organization to endogenous steroids, steroidogenesis and gonadotropin treatment

To explore testicular factors which determine steroidogenesis, circulating and intratesticular steroid levels were measured and in vitro steroidogenesis in testicular minces and microsomes was investigated using adult rhesus monkeys before and after treatment with pharmacological doses of hCG or hCG together with hMG. After gonadotropin treatment serum and intratesticular levels of 17α-hydroxyprogesterone as well as end product testosterone were markedly elevated. Dynamic studies revealed that 17α-hydroxyprogesterone produced from pregnenolone was partly metabolized to C 19-steroids but almost no 17α-hydroxyprogesterone produced from progesterone was utilized by C 17–20 lyase. Androstenedione levels increased in serum after both treatments and were elevated in testis tissue after hCG treatment. Androstenedione accumulated in vitro during incubation of untreated and hCG-treated testes with [ 3H]pregnenolone and [ 14C]progesterone. The major portion of the accumulated androstenedione was produced from pregnenolone through dehydroepiandrosterone rather than through 17α-hydroxyprogesterone, indicating differential availability of androstenedione to 17β-hydroxy steroid oxidoreductase according to its origin. The 3H/ 14C ratio in product androstenedione was much greater than the ratio in product testosterone in both untreated and hCG-treated testis; in testes of animals treated with hCG together with hMG, the ratios in both products were closely linked. Among the enzymes examined, 17α-hydroxylase and C17–20 lyase activities for 5-ene-C 21-steroids were increased and 17β-hydroxysteroid oxidoreductase activity were decreased by gonadotropin treatment. Our findings confirm the phenomenon of unequal substrate availability to enzymes depending upon the provenance of the substrate and demonstrate that gonadotropin(s) change substrate availability as do direct changes in enzyme activities. The unequal substrate availability validates the assumption, previously proposed by others, that microsome enzymes have an organized arrangement as enzyme complexes.

Human Ovarian 17β-Hydroxysteroid Oxidoreductase Activity: A Comparison of Normal and Polycystic Ovarian Tissues*

Ovarian tissue and ovarian venous blood were obtained from women undergoing wedge resection, and ovarian tissue was obtained from normally menstruating women who had an oophorectomy for medical reasons. A morphological evaluation was made of the wedged tissue. 17 beta-Hydroxysteroid oxidoreductase levels were determined as the 17-ketoreductase (17-KR) and 17 beta-dehydrogenase activities in both normal and wedged tissue. Plasma androstenedione (A) and testosterone (T) levels were measured in the ovarian venous blood. Low, but measurable, 17 beta-hydroxysteroid oxidoreductase activity was found in the mitochondria, microsomes, and cytosol. With whole, cell-free homogenates, mean 17-KR activity was not significantly different in normal tissues and polycystic tissues; mean 17-KR activity of corpora lutea was significantly greater than that of the other tissues. Mean 17 beta-dehydrogenase activity was not significantly different from 17-KR activity in the tissues studied. Ovarian venous A levels were higher than the reported mean ovarian venous A levels of normal women with only one exception; approximately half of the ovarian venous T levels were higher than reported mean ovarian venous T levels of normal women. The morphology of the wedge sections did not correlate well with the biochemical data.

Metabolism of 1,4-androstadiene-3,17-dione by human placental microsomes. enzyme properties and kinetic parameters in the formation of estrogens and 17β-hydroxy-1,4-androstadien-3-one

In this investigation the metabolism of 1,4-androstadiene-3,17-dione by human placental microsomes was evaluated. The experiments were conducted with the substrate [ 3H]-1,4-androstadiene-3,17-dione, which was synthesized using a tritium-hydrogen keto-enol exchange technique. [4- 14C]-l,4-Androstadiene-3, 17-dione and [4- 14C]-17β-hydroxy-1,4-androstadien-3-one also were synthesized and used, together with [ 14C]-estrone and [ 14C]-estradiol-17β, as internal recovery standards for quantification. The radiolabeled metabolites identified from incubation mixtures with placental microsomes were estrone, estradiol-17β and 17β-hydroxy-1,4-androstadien-3-one; two other metabolites, one less polar than the substrate and the other more polar than estradiol-17β, were observed but not investigated further. The enzymatic conversions required either NADPH or NADH as cofactor and there was no apparent tritium loss in the transformation of substrate to products. The rates of formation of metabolites were linear with time for at least 30 min and with the amount of microsomal protein up to 15 mg. Tbe apparent pH optimum for placental microsomal estrogen synthetase was 7.5, and the apparent optimum pH for the 17β-hydroxysteroid oxidoreductase ranged from pH6.0 to pH7.4. The apparent optimal temperature for the estrogen synthetase activity was 37°C and for 17β-hydroxysteroid oxidoreductase it ranged from 37°C to 58°C. The apparent K m of estrogen synthetase for 1,4-androstadiene-3,17-dione was 1.3μM, and the apparent K m of 17β-hydroxysteroid oxidoreductase for 1,4-androstadiene-3, 17-dione was 24 μM. The apparent K m of estrogen synthetase for NADPH and NADH were 0.24 mM and 1.0mM, respectively; the apparent K m of placental microsomal 17β-hydroxysteroid oxidoreductase for NADH was 0.5 mM and that for NADPH was 0.67 mM. Androstenedione was found to be a competitive inhibitor of [ 3H]-1,4-androstadiene-3,17-dione aromatization ( K i ) = 0.75 μM androstenedione) and of 17β-hydroxysteroid oxidoreduction ( K i ) = 17μM androstenedione). Fifty per cent inhibition of estrogen synthetase and of 17β-hydroxysteroid oxidoreductase activities were obtained with an androstenedione concentration of 80 μM. The specific activity of NADPH-dependent cytochrome c reductase of placental microsomes was 22 nmol × mg −1 protein × min −1. The dependency of placental microsomal [ 3H]-1,4-androstadiene-3,17-dione aromatization on cytochrome P-450 and upon NADPH-dependent cytochrome c reductase was demonstrated using both anti-human and anti-porcine hepatic microsomal NADPH-dependent cytochrome c (P-450) reductase antibodies. The estrogen synthetase and NADPH-dependent cytochrome c reductase activities were inhibited greatly by the microsomal specific antibodies, whereas non-immune γ-globulin had little effect on enzyme activity. The 17β-hydroxysteroid oxidoreductase activity was affected only slightly by these antibodies.

Oestrogen receptors and metabolism of oestrone sulphate in human mammary carcinoma

The conversion of [ 3 H] oestrone sulphate into [ 3 H] oestrone and [ 3 H] oestradiol- 17β by homogenates of mammary carcinoma tissue in vitro and the oestrogen receptor levels in the tumor cytosol was studied in 23 breast cancer patients with low peripheral serum levels of oestradiol- 17β (< 150 pM). Sixteen of the patients had cytosol oestrogen receptor values above 0.3 fmole/μg of DNA (receptor rich) and seven patients receptor values below this level (receptor poor). [ 3 H] oesterone sulphate was converted into [ 3H ] oestrone and [ 3 H] oestradiol- 17β by all tumor homogenates. No significant difference between the receptor poor and receptor rich groups were found in the total hydrolysis of [ 3 H] oesterone sulphate. The transformation of [ 3 H] oesterone sulphate into [ 3 H] oestradiol- 17β was significantly higher in the receptor poor group than in the receptor rich group (35.95 ± 11.06 vs 5.33 ± 1.37 fmole [ 3 H] oestradiol- 17β formed per min and per mg of protein, P<0.001). The mean age of the receptor poor group was significantly lower than that of the receptor rich group (58.0 ± 5.5 vs 73.1 ± 2.1 yr, P < 0.01). No significant difference was found in the peripheral serum levels of oestradiol- 17β in the two groups. The results indicate that the ability of the tumour tissue to convert oestrone sulphate into oestradiol- 17β significantly influences the cytosol oestrogen receptor level in patients with low peripheral oestrogen levels. An age-related decrease in the 17β-hydroxysteroid oxidoreductase activity in the tumour was also noted. We conclude that a high rate of formation of oestradiol- 17β may lead to high intracellular levels of this steroid, resulting in blockade of the hormone binding site, increased nuclear translocation of the receptor and low cytosol oestrogen receptor values.

Estradiol and progesterone receptors in human endometrium: Normal and abnormal menstrual cycles and early pregnancy

Estradiol and progesterone receptor sites (empty or filled with endogenous hormone) have been measured in the cytoplasm and nuclei of human endometrium. Receptor changes have been observed throughout the normal menstrual cycle. During the preovulatory phase the cytoplasmic estradiol receptor sites do not change while the nuclear receptor sites more than double. Cytoplasmic estradiol receptor sites decrease very early in the secretory phase, whereas the decrease in nuclear sites occurs later. Cytoplasmic progesterone receptor sites more than double during the preovulatory phase and show a large decrease immediately after ovulation, when the concentration of nuclear receptor is at its highest. Thus the total cellular concentrations of both estradiol and progesterone receptors are lowest in the late secretory phase. It was found that they are positively correlated with the concentration of plasma estradiol only during the proliferative phase. The concentration of cytoplasmic progesterone receptor is negatively correlated with 17β-hydroxysteroid oxidoreductase activity during the secretory phase. In anovulatory cycles the concentrations of estradiol and progesterone receptors are high, similar to those of the late proliferative phase. “Luteal insufficiency” is characterized by a very low concentration of estradiol receptor. Early pregnancy endometrium (8 to 10 weeks' gestation) is characterized by a large concentration of progesterone receptor, exceeding those of any period of the menstrual cycle.

61. Influence of SHBG on activity of 17β-hydroxysteroid oxidoreductase in human erythrocytes

61. Influence of SHBG on activity of 17β-hydroxysteroid oxidoreductase in human erythrocytes

Relationship between serum concentration of gonadotropins and testosterone in heat-exposed ageing male rats

Serum follicle stimulating hormone (FSH), luteinizing hormone (LH) and testosterone of control rats (20–22°C, 30–50% relative humidity) did not vary at 4, 6 and 10 months of age. Prolonged maintenance of rats in a hot environment (33–35°C, 25–40% relative humidity) was accompanied by a significant decrease in testosterone concentration, irrespective of the animal's age or duration of exposure to heat (1, 2 and 7 months), whereas the concentration of FSH and LH remained relatively unaffected. Activity of 17β-hydroxysteroid oxidoreductase (17β-HSD) in the testes of control rats was inversely related to the animals' age. In most cases prolonged exposure to heat augmented the decline in activity of 17β-HSD associated with ageing. These data suggest that increasing in age is accompanied by a decrease in the activity of testicular 17β-HSD without affecting the concentration of FSH, LH and testosterone in blood serum. It is concluded that, within the age limits used in the present experiment, the significant drop in serum testosterone concentration characterizing rats exposed to heat is independent of serum gonadotropin concentration and testicular acitivity of 17β-HSD, as well as the animal's age.

40. Testosterone production by testicular tissue of the camel ( Camelus dromedarius) during the breeding season

Enzymatic reactions involved in androgen biosynthesis in Gerbillus dasyurus were investigated in vitro using testicular homogenates. The activity of 20α-hydroxysteroid oxidoreductase was significantly high, but that of the 17,20-lyase and 17β-hydroxysteroid oxidoreductase appeared relatively low. Double label experiments where [3H]5-ene 3β-hydroxysteroids and [14C]4-en-3-oxosteroids were incubated simultancously as substrates, indicated that testosterone is preferentially synthesized via the 4-ene route. The activity of 17β-hydroxysteroid oxidoreductase observed in testes of Gerbillus was the lowest of all the rodents compared. The activity of this enzyme decreased after laboratory rodents were acclimatized to an elevated ambient temperature (35°C, 30–50% relative humidity). The relevance of the enhanced activity of 20α-hydroxysteroid oxidoreductase associated with the low biosynthetic rate of testosterone in desert rodents is discussed.