In vivo inhibition of aromatization by exemestane, a novel irreversible aromatase inhibitor, in postmenopausal breast cancer patients

The effect of exemestane (6-methylenandrosta-1,4-diene-3,17-dione) 25 mg p.o. once daily on in vivo aromatization was studied in 10 postmenopausal women with advanced breast cancer. Aromatization was determined before treatment and after 6-8 weeks on therapy by administering a bolus injection of [3H]androstenedione (500 microCi) and [14C]estrone (5 microCi) followed by measurement of the isotope ratio of urinary estrogens after high-performance liquid chromatography purification. In addition, plasma endogenous estrogens were measured with highly sensitive radioimmunoassays after separation with high-performance liquid chromatography. Treatment with exemestane suppressed whole body aromatization from a mean pretreatment value of 2.059% to 0.042% (mean suppression of 97.9%). Plasma levels of estrone, estradiol, and estrone sulfate were found to be suppressed by 94.5%, 92.2%, and 93.2%, respectively. This is the first study revealing near total aromatase inhibition in vivo with the use of a steroidal aromatase inhibitor. The observation that exemestane is a highly potent aromatase inhibitor, together with the fact that the drug is administered p.o. and causes limited side effects, suggests that exemestane is a promising new drug for the treatment of hormone sensitive breast cancer.     

Massive extranglandular aromatization of plasma androstenedione resulting in feminization of a prepubertal boy

This report describes the mechanism of origin and the quantity of estrogen produced in a prepubertal boy who developed severe feminization at 8 yr of age as the result of a heretofore undescribed metabolic abnormality. The clinical findings were gynecomastia and accelerated linear growth and bone maturation. At the time feminization developed, there were no signs of growth or development of the otherwise normal prepubertal male external genitalia or any increase of muscle mass that normally accompanies male puberty. The hyperestrogenism was found to be the consequence of massive extraglandular conversion of plasma androstenedione to estrone. During a 6-mo period of study, the plasma production rate of androstenedione ranged from 1.2 to 1.6 mg/day. More than 55% of plasma androstenedione was metabolized by aromatization to estrone which, in turn, was extensively sulfurylated in the tissue sites of aromatization before its entry into the blood. Thus, estrone sulfate was the final product in the aromatizing sites, and the plasma production rate of estrone sulfate derived from plasma androstenedione was 782 mug/24 h. The extent of extraglandular conversion of plasma androstenedione to estrone measured in this boy was 50 times that observed in two normal prepubertal boys. Moreover, 94% of the extraglandular aromatization occurred in extrahepatic sites. The metabolic clearance rate of plasma androstenedione, 2,380 liters/day per m(2), was markedly increased in this boy. Approximately 1,500 liters of plasma androstenedione clearance was accounted for by extrahepatic, extraglandular aromatization. The fractional conversion of testosterone to estradiol, 0.16, was 50 times greater in this boy than that observed in normal young adult men. The total extent of aromatization of plasma prehormones was even greater in this boy inasmuch as evidence was obtained that aromatization of 16-hydroxysteroids, e.g. 16alpha-hydroxy androstenedione and 16alpha-hydroxy dehydroisoandrosterone (sulfate), resulted in estriol formation independent of estrone formation. Thus, extensive extrahepatic, extraglandular aromatization resulted in advanced feminization in this prepubertal boy by a previously undescribed metabolic abnormality.     

Influence of dexaminoglutethimide, an optical isomer of aminoglutethimide, on the disposition of estrone sulfate in postmenopausal breast cancer patients

Aminoglutethimide (AG) has been the most widely used aromatase inhibitor in breast cancer patients to date. Commercially, AG (Orimeten) is available as a racemate (DL-AG). Previous studies suggested the stereoisomers of AG (D-AG and L-AG) to differ considerably in their affinities and potencies to inhibit different cytochrome P-450-dependent enzymes, with D-AG being the potent aromatase inhibitor. DL-AG, apart from being an aromatase inhibitor, is known to enhance the metabolism of plasma estrone sulfate (E1S). In the present study we compared the effects of D-AG (500 mg daily) and DL-AG (1000 mg daily) on plasma estrogen levels and estrone (E1) and E1S clearance rates, determined after the injection of [14C]E1 and [3H]E1S, in a cross-over study involving 12 postmenopausal breast cancer patients. Treatment with DL-AG and D-AG suppressed plasma E1S to 18.6% and 15.0% of pretreatment levels, whereas E1 and estradiol E2 levels fell to 18.6% and 23.4% of their pretreatment levels during treatment with DL-AG and to 17.7% and 23.4% during treatment with D-AG, respectively. Thus, both treatment options suppressed all estrogens measured to a similar extent. The clearance rate of E1S increased from a mean pretreatment value of 5.9 to 14.0 and 10.0 L/h during treatment with DL-AG and D-AG, respectively (P < 0.05, comparing the two on-treatment situations), whereas the production rate of E1S decreased from a pretreatment value of 1.44 to 0.64 nmol/h with DL-AG and 0.36 nmol/h with D-AG (P < 0.05, comparing on-treatment values). These findings are consistent with the hypothesis that the D- as well as the L-form of AG may enhance the clearance rate of E1S. The finding of a higher estrogen production rate during treatment with DL-AG compared to D-AG probably reflects an increased plasma level of the estrogen precursor androstenedione (mean levels of androstenedione of 2.54 and 1.27 nmol/L during treatment with D-AG and DL-AG, respectively; P < 0.05).     

Inhibition of breast cancer tissue aromatase activity and estrogen concentrations by the third-generation aromatase inhibitor vorozole

In about one-third of advanced breast cancers, estrogen deprivation causes tumor regression. Estrogen concentrations in tumor tissue seem to depend largely on local production. The aromatase enzyme complex is thought to be the key enzyme in this respect. In the present study, the effect of the new third-generation nonsteroidal aromatase inhibitor vorozole (Rivizor) on tumor tissue aromatase activity and estrogen concentrations was evaluated. During 7 days preceding mastectomy, 11 postmenopausal breast cancer patients were treated with 2.5 mg of vorozole once daily. Eight patients could be evaluated. Intratumoral aromatase activity and estrone and estradiol levels were measured and compared to the values of nine untreated postmenopausal breast cancer patients. In treated patients, median tissue aromatase activity was 89% lower than that in controls (P < 0.001). Similarly, median tissue estrone and estradiol concentrations were 64 and 80% lower, respectively, in treated patients (P = 0.001 and P < 0.05, respectively). These results support the hypothesis that depleting the tumor of estrogens, thus impairing estrogenic stimulation, is an important mechanism in the antitumor activity of aromatase inhibitors.     

Anastrozole: a new selective nonsteroidal aromatase inhibitor

Aromatase (estrogen synthetase) is the enzyme complex responsible for the final step in estrogen synthesis--the conversion of androstenedione and testosterone to estrone and estradiol, respectively. Inhibitors of this enzyme have been shown to be clinically effective in the treatment of advanced breast cancer in postmenopausal women, in whom the major source of estrogen production derives from aromatization of adrenal androgens in peripheral tissues, such as muscle, liver, and fat. The most widely used aromatase inhibitor has been aminoglutethimide; however, it is nonselective and also inhibits adrenocorticosteroid synthesis, necessitating hydrocortisone supplementation. Aminoglutethimide is also associated with frequent and troublesome side effects. Formestane, the first selective aromatase inhibitor to be developed, has an improved safety profile and selectivity, but its use has been limited somewhat by its inconvenient administration via intramuscular injection. In this article, the preclinical and clinical data published to date on the new third-generation aromatase inhibitor anastrozole (Arimidex) are presented in the context of current endocrine therapies. Future applications of aromatase inhibitors, both as monotherapy and in combination with other endocrine therapies, are discussed. The use of aromatase inhibitors in advanced disease, the adjuvant setting, and as possible chemopreventive agents are examined.     

Th2 responses induce humorally mediated injury in experimental anti-glomerular basement membrane glomerulonephritis

Clinical and endocrinological effects of exemestane (6-methylenandrosta-1,4-diene-3,17-dione; PNU 155971) were evaluated in an open Phase I study. Thirteen postmenopausal women suffering from advanced breast cancer received exemestane in escalating doses over a 12-week period. Starting on 5 mg once daily (o.d.), exemestane was subsequently escalated at 2-week intervals to 10, 25, 50, 100, and 200 mg o.d. Each patient subsequently continued treatment on the highest tolerated dose until time of progression. One patient terminated treatment after 6 days due to diarrhea that was probably not related to drug therapy, although a relationship could not be excluded. Apart from this, no serious side effects were seen during the dose escalation period. Exemestane (10 mg o.d.) caused maximal suppression of plasma estradiol (E2) and estrone (E1) to a mean of 14.6 and 5.8% of pretreatment levels, respectively, whereas 25 mg of exemestane o.d. suppressed estrone sulfate (E1S) to 8.9% of pretreatment levels. No fall in adrenal steroid levels was recorded. Exemestane (5 mg o.d.) suppressed urinary E2 and E1 to a mean of 11.9 and 12.2% of pretreatment levels, respectively. Administering exemestane at doses of 50-200 mg o.d. caused no further suppression of urinary E1, whereas urinary E2 fell to 6-7% of pretreatment levels. Median time to progression was 63 weeks. We conclude that exemestane is a well-tolerated aromatase inhibitor that effectively suppresses plasma and urinary estrogens in postmenopausal patients with breast cancer.     

Safety, activity and estrogen inhibition by exemestane in postmenopausal women with advanced breast cancer: a phase I study

Exemestane is an irreversible, steroidal, oral aromatase inhibitor under evaluation in postmenopausal women with advanced breast cancer. A phase I study was conducted in 27 postmenopausal patients who were candidates for hormone therapy because they had advanced breast cancer and estrogen receptor-positive or unknown status. Most patients were moderately or heavily pretreated. Cohorts of at least three patients received sequentially escalating daily oral doses of 5-600 mg. The median duration of exemestane treatment was 13 weeks (range: 3-166 weeks). The maximal tolerated dose was not reached because of lack of treatment-related grade 3 or 4 toxicity. The most common adverse events, including those not related to treatment, were mild to moderate headache (44% of patients), dizziness (33%), nausea (33%), hot flushes (30%) and tumor-related pain (30%). There were three complete and four partial responses for an objective response rate of 26% (95% CI: 11.1-46.3%) in the intent-to-treat population; the median duration of response was 74 weeks (95% CI: 48-99 weeks). Exemestane, at the dose of 25 mg, maximally suppressed estradiol, estrone and estrone sulfate serum levels to 13, 5 and 10% of baseline, respectively. Exemestane appears to suppress estrogen, be well tolerated and have antitumor activity in postmenopausal women with advanced breast cancer. A large, safe therapeutic window of up to 600 mg was defined. In view of its safety and estrogen-suppression profiles, the most favorable effects were observed at the 25 mg daily dose.     

Effect of soymilk consumption on serum estrogen concentrations in premenopausal Japanese women

BACKGROUND: Estrogens have been implicated in the development of breast cancer. Preliminary evidence suggests that consumption of soy products, which contain isoflavones (phytoestrogens), can reduce serum estrogen levels. Our purpose was to determine the effect of soy consumption on serum estrogen levels in premenopausal women by use of a dietary intervention approach. METHODS: Premenopausal Japanese women were randomly assigned to receive either a soymilk-supplemented diet (n = 31) or a normal (control) diet (n = 29). The women in the soymilk-supplemented group were asked to consume about 400 mL of soymilk (containing about 109 mg of isoflavones) daily during a study period that involved three consecutive menstrual cycles. Follicular-phase blood samples were to be obtained in the menstrual cycles preceding (cycle 1) and following (cycle 3) the 2-month dietary intervention. All statistical tests were two-sided. RESULTS: At the end of the study period, estrone and estradiol levels were decreased by 23% and 27%, respectively, in the soymilk-supplemented group and were increased by 0.6% and 4%, respectively, in the control group. The changes for each hormone between the two groups were not statistically significantly different. In the soymilk-supplemented group, menstrual cycle length was increased by nearly 2 days, and, in the control group, it was decreased by approximately 1 day, a difference that was not statistically significant. A subgroup analysis restricted to subjects who provided follicular-phase blood samples on the same day or 1 day apart in menstrual cycles 1 and 3 showed a reduction in serum estrone levels in the soymilk-supplemented group that was of borderline statistical significance (P = .07 for change in serum estrone level in soymilk-supplemented group versus control group). CONCLUSION: Much larger studies will be required to confirm the ability of soy products to reduce serum estrogen levels.     

Profound suppression of plasma estrogens by megestrol acetate in postmenopausal breast cancer patients

Twelve postmenopausal women suffering from advanced breast cancer had plasma estrogens, androgens, cortisol, and gonadotropins determined before therapy and during treatment with megestrol acetate (MA) in oral doses escalated from 40 to 160 mg. The plasma clearance and production rate of estrone and estrone sulfate were determined before treatment and after 4 weeks of therapy with 160 mg MA. Treatment with MA suppressed plasma levels of dehydroepiandrosterone sulfate, androstenedione, and cortisol in a dose-dependent manner to <10% of pretreatment values. Plasma testosterone, estradiol, estrone, and estrone sulfate were suppressed to 18-29% of pretreatment values, whereas the gonadotropins were suppressed to 35-52%. The plasma clearance rates of estrone and estrone sulfate were increased by a mean value of 23.7% (P < 0.01) and 23.5% (P < 0.025), whereas the production rates were reduced by 76.7% (P < 0.0005) and 76.1% (P < 0.0005), respectively. Our findings indicate that MA causes profound suppression of adrenal steroid production but in addition suppresses ovarian secretion of androgens in postmenopausal breast cancer patients. The reduction in plasma estrogens is comparable to values obtained with commonly used aromatase inhibitors and may be responsible for its antitumor effects in breast cancer.     

Aromatase inhibitors--new possibilities in treatment of breast carcinoma

Aromatase inhibition is now an acknowledged second line treatment modality for advanced breast cancer in postmenopausal women. Aminoglutethimide is an inhibitor of adrenal steroid biosynthesis and blocks the conversion of cholesterol to pregnenolone, and therefore reduces levels of adrenal androgens, which are a source of estrogens in both premenopausal and postmenopausal women. Aminoglutethimide has produced antitumor response rates of 35% in unselected patients, most of whom have undergone prior therapy with either chemotherapy or hormonal manipulation. As is true of other hormonal responses, high response rates of up to 70% are observed in patients who are ER and/or PR positive. The reason why these drugs are currently used after tamoxifen is mainly due to the side effects of aminoglutethimide, which impairs the mineralocorticoid and glucocorticoid synthesis. New, less toxic compounds appear, which block the conversion of androstenedione to estrone and efficiently suppress plasma estrogen levels., e.g. formestane, anastrozole and letrozole. Aromatase inhibitors are now being compared to tamoxifen as first-line endocrine treatment in relapsing patients. If these trials confirm a similar or better response rate to new aromatase inhibitors compared to tamoxifen, the time will come to study them as the first line adjuvant treatment in non-metastatic disease.     

Inhibitory effect of combined treatment with the aromatase inhibitor exemestane and tamoxifen on DMBA-induced mammary tumors in rats

The antitumor effect of exemestane (FCE 24304), an irreversible aromatase inhibitor, given alone or in combination with tamoxifen, was investigated in rats with 7,12-dimethylbenzanthracene (DMBA)-induced mammary tumors. The compounds were given once daily, 6 days a week for 4 weeks. Exemestane, given at the dose of 20 mg/kg/day s.c., induced 26% complete (CR) and 18% partial (PR) tumor regressions, compared to 0% CR and 6% PR observed in controls. Tamoxifen, given at 1 mg/kg/day p.o., induced 16% CR and 13% PR. The combined treatment caused 41% CR and 16% PR, thus resulting in a higher antitumor effect than either single treatment. The appearance of new tumors was reduced by each single treatment and almost totally prevented by the combined treatment. Serum prolactin (PRL) levels, assayed 4 h after the last dose, were unchanged in the group treated with the combination, whereas tamoxifen alone caused a slight increase of serum PRL. These results indicate that estrogen deprivation through aromatase inhibition and estrogen receptor antagonism causes a better inhibition of DMBA-induced mammary tumors than either treatment modality alone.     

Pneumocystis carinii infections in patients with neoplasms and AIDS--clinical-pathologic changes in the lungs

Administration of 0.5 or 1% lyophilized green tea (5 or 10 mg tea solids per ml, respectively) as the sole source of drinking fluid to female Long-Evans rats for 18 days stimulated liver microsomal glucuronidation of estrone, estradiol and 4-nitrophenol by 30-37%, 15-27% and 26-60%, respectively. Oral administration of 0.5% lyophilized green tea to female CD-1 mice for 18 days stimulated liver microsomal glucuronidation of estrone, estradiol and 4-nitrophenol by 33-37%, 12-22% and 172-191%, respectively. The in vitro addition of a green tea polyphenol mixture, a black tea polyphenol mixture or (-)-epigallocatechin gallate inhibited rat liver microsomal glucuronidation of estrone and estradiol in a concentration-dependent manner and their IC50 values for inhibition of estrogen metabolism were approximately 12.5, 50 and 10 microg/ml, respectively. Enzyme kinetic analysis indicates that the inhibition of estrone glucuronidation by 10 microM (-)-epigallocatechin gallate was competitive while inhibition by 50 microM (-)-epigallocatechin gallate was noncompetitive. Similarly, several flavonoids (naringenin, hesperetin, kaempferol, quercetin, rutin, flavone, alpha-naphthoflavone and beta-naphthoflavone) also inhibited rat liver microsomal glucuronidation of estrone and estradiol to varying degrees. Naringenin and hesperetin displayed the strongest inhibitory effects (IC50 value of approximately 25 microM). These two hydroxylated flavonoids had a competitive mechanism of enzyme inhibition for estrone glucuronidation at a 10 microM inhibitor concentration and a predominantly noncompetitive mechanism of inhibition at a 50 microM inhibitor concentration.     

The regulation of gonadotropin-releasing hormone-induced calcium signals in male rat gonadotrophs by testosterone is mediated by dihydrotestosterone

The biological effects of testosterone (T) may be mediated directly by T or indirectly by its metabolites, dihydrotestosterone (DHT) and estradiol. The present study examined whether the metabolism of T is involved in the regulation of GnRH-induced Ca2+ signaling at the pituitary. In gonadotrophs from castrated rats, a significantly greater percentage of gonadotrophs demonstrated oscillatory Ca2+ responses to 100 nM GnRH than cells from intact rats (72% vs. 24%; P < 0.05). This increase was prevented by the administration of T propionate (0.1 mg/kg x day), DHT benzoate (2 mg/kg x day,), estradiol benzoate (EB; 5 microg/kg x day), or the combination of the above doses of DHT benzoate and EB. In all cases the proportion of gonadotrophs from the steroid-treated rats having oscillatory Ca2+ responses to 100 nM GnRH was between 21-25% (P > 0.05, compared with intact rats). To assess the importance of T metabolism, intact male rats were treated with the aromatase inhibitor letrozole (1 mg/kg x day), the 5alpha-reductase inhibitor finasteride (50 mg/kg x day), or their respective vehicles for 7 days. Letrozole had no effect on GnRH-induced Ca2+ signals, serum LH concentrations, or ventral prostate or testes weight. Finasteride treatment, however, mimicked the effects of castration, with significantly more gonadotrophs exhibiting Ca2+ oscillations in response to 100 nM GnRH than gonadotrophs from the vehicle-treated group (71% vs. 20% respectively; P < 0.05). Finasteride also caused a significant (P < 0.05) decrease in prostatic weight and DHT concentration, but had no significant effect on either prostatic T or serum LH concentrations. These findings suggest that in the intact male rat, the effects of T on GnRH-induced Ca2+ signaling are preferentially mediated via DHT. The results of this study also show that in the absence of androgens, estradiol may regulate GnRH-induced Ca2+ signaling in the male rat pituitary.     

Tennis elbow. Current concepts of treatment and rehabilitation

OBJECTIVE: Estrogens are known to exhibit antioxidative effects. At present little information exists on the influence of co-administered progestins upon this effect. Therefore we investigated the influence of levonorgestrel, a potent antiestrogenic progestin, on the inhibition of the low-density lipoprotein (LDL) oxidation by 17 beta-estradiol or 17 beta-estradiol valerate in vitro and ex vivo. METHODS: After isolation from blood, the in vitro oxidation of LDL was induced by copper ions and measured continuously by monitoring the formation of conjugated dienes. In 21 female ovariectomized White New Zealand rabbits the antioxidative action of 17 beta-estradiol alone or in combination with levonorgestrel after subcutaneous infusion for 3 days was determined using the copper-induced LDL-oxidation as an endpoint. Eleven postmenopausal women were exposed to sequential estrogen-progestin replacement therapy (day 1-21:2 mg estradiol valerate/day, day 10-21: 0.15 mg levonorgestrel/day). Blood samples were collected at three times: on day 1, on day 10, on day 22 (after the combination phase). The lag time of ex vivo oxidation of LDL, the plasma estradiol and estrone levels were estimated. RESULTS: In the chosen cell-free system, 17 beta-estradiol increased the lag time of the LDL-oxidation in a dose-dependent manner. Levonorgestrel showed neither pro-oxidative nor antioxidative effects when administered alone in different concentrations. Co-administration of different doses of levonorgestrel did not modify the antioxidative action of estrogen either. The two ex-vivo models confirmed these results. In rabbits the co-administered 19-nortestosterone derivative levonorgestrel did not impair or reverse the estradiol-dependent effect. In postmenopausal women the daily oral administration of levonorgestrel in conjunction with 17 beta-estradiol valerate did not diminish the antioxidative action of this estrogen given for the first 9 days. CONCLUSION: The antioxidative potential of estradiol and estradiol valerate is maintained in the presence of levonorgestrel.     

Origin of estrogen in a postmenopausal woman with a nonendocrine tumor of the ovary and endometrial hyperplasia

The origin and quantity of estrogen and androgen were measured in a postmenopausal woman with clinical signs of estrogen excess and a nonendocrine tumor of the ovary. The plasma androstenedione production rate was elevated 5-fold. The estrone production rate was also five times that normally expected for a postmenopausal women and could be accounted for totally by the extraglandular conversion of plasma and androstenedione. Following removal of the tumor, the concentration of plasma androstenedione and the estrone production rate fell dramatically to normal postmenopausal levels. It is concluded that this markedly increased androstenedione production was the result of excessive secretion of androstenedione by the hyperplastic stromal cells of the ovary containing the mucinous cystadenocarcinoma. The excessive prehormone production together with its normal extraglandular conversion to estrone resulted in the massive increase in endogenous estrogen formation.     

Steroid binding and metabolism in the luteinizing hormone-releasing hormone-producing neuronal cell line GT1-1

LHRH synthesis and release are modulated in vivo by gonadal steroids. Although immunocytochemical and autoradiographic studies failed to detect appreciable amounts of estrogen or androgen receptor in LHRH-producing neurons, the recent finding that the promoter region of the LHRH gene contains several steroid hormone-responsive elements indicates a possible direct effect of sex steroids on these specialized neurons. The immortalized LHRH-producing neuronal cell line, GT1, which became recently available, may allow the study of LHRH dynamics. The presence of specific binding sites for estrogen and androgens as well as the presence of the two major enzymatic pathways involved in modulation of androgen action (the 5 alpha-reductase/3 alpha-hydroxysteroid dehydrogenase and the aromatase) have been studied in the GT1-1 clone. High affinity, low capacity binding sites for [3H]estradiol (Kd, 0.11 nM; binding capacity, 6.2 fmol/mg protein) and for a ligand of the androgen receptor, [3H]R1881 (Kd, 0.054 nM; binding capacity, 9.58 fmol/mg protein), have been identified in this cell line. A 2-fold induction of androgen-binding sites has been observed after 3 days of treatment of GT1-1 cells with estradiol (1 microM), indicating that the estradiol binding is probably linked to a functional estrogen receptor. Aromatase and 5 alpha-reductase/3 alpha-hydroxysteroid dehydrogenase activities have been also tested in GT1-1 cells. Under the culture conditions adopted, no detectable aromatization of [1 beta 3H]delta 4-androstenedione to estrone was observed using the tritiated water method. On the other hand, GT1-1 cells efficiently converted testosterone into dihydrotestosterone and subsequently into 5 alpha-androstan-3 alpha,17 beta-diol. In conclusion, GT1-1 cells possess several elements of the machinery through which sex steroids may influence LHRH dynamics.     

Nuclear estradiol receptor in the adult rat uterus: a new exchange assay

A protamine exchange assay has been developed to measure uterine nuclear estrogen receptor in mature rats exposed to estradiol (E). After ovariectomized-adrenalectomized mature rats are injected with E, estrogen receptor (RnE) is extracted from uterine nuclei with 0.6 M potassium chloride, diluted, and quantitatively precipitated with protamine sulfate. The precipitate is subjected to a ligand exchange with radiolabeled estradiol (E), with or without unlabeled diethylstilbesterol, to determine nonspecific binding. At 37 degrees C complete exchange of E for E in RnE is observed at 2.5 h; virtually no receptor degradation occurs up to at least 5 h. Exchange does not occur at 4 degrees C. Using the protamine assay, the depletion of cytoplasmic estrogen receptor (Rc) and the accumulation of RnE were studied at various doses of E at specific time points. Increasing doses of E result in a decrease of Rc with an equal increase of RnE. At the highest dose of E (10 mug) Rc is completely depleted within 10 min, by 6 h it is 25% replenished, and by 24 h returns to slightly above control levels. Within 10 min after the injection, RnE increases to 80-90% of the original cytoplasmic level of receptor (approximately 2-3 pmol/mg of DNA or approximately 1.5 pmol/100 mg of uterus). At 6 h RnE is 75% depleted and it is completely absent at 24 h. The protamine assay permits precise quantitative studies of nuclear estrogen receptor and avoids the problems of receptor degradation and excessive nonspecific binding often found in exchange reactions at elevated temperatures.     

Perturbation in the 240Pu/239Pu global fallout ratio in local sediments following the nuclear accidents at Thule (Greenland) and Palomares (Spain)

Diabetes complicates 2-3% of all pregnancies and is associated with an increase in both perinatal morbidity and mortality, though reasons for these adverse outcomes are unknown. Estrogen biosynthesis is a critical factor during pregnancy and is carried out in the placenta via aromatase (cytochrome P450 19A1), which catalyzes the conversion of C-19 androgens to C-18 estrogens. Previous studies have shown that hormones such as insulin-like growth factors and insulin regulate aromatase activity when studied in vitro. Interestingly, levels of these hormones are altered in patients with diabetes. Thus, we hypothesized that the presence of maternal diabetes may alter placental aromatase activity and thus estrogen biosynthesis, possibly serving as one factor in the adverse outcomes of babies born to mothers with diabetes. To this end, we measured the production of 19-hydroxyandrostenedione, 19-oxoadrostenedione and estrone in 30 placental tissues from diabetic patients, using [7-3H]androst-4-ene-3,17-dione as a model substrate for aromatase (P450 19A1). A statistical difference was detected in the percentage of 19-oxoandrostenedione formed between the overt and control groups (P < 0.05). Additionally, NADPH P450-reductase levels were measured in these same tissues to determine whether alterations in this enzyme necessary for aromatase activity could be affected by diabetes. No differences in reductase levels were detected among the patient groups. However, a statistical correlation was found between NADPH P450-reductase activity and the formation velocities of all three estrogen products (P < 0.05). Thus, it appears that the presence of diabetes does not affect placental aromatase activity.     

Sex differences in the regulation of embryonic brain aromatase

Oestrogen formed from androgen by aromatization plays a critical role in the sexual differentiation of the male brain and behaviour. A question which has still to be answered is what regulates the gender-specific changes in aromatase activity forming oestrogen during sensitive periods of brain growth. Using a primary cell culture technique and sexed embryos, we have shown that in the fetal mouse brain, oestrogen formation in the male is neuronal rather than glial and aromatase activity is regionally localized, being higher in the hypothalamus than in the cortex. The aromatase activity measured from cells in culture has the same enzyme binding affinity (apparent Km approximately 40 nM) as intact brain samples. Neurones developing in the embryonic male brain (embryonic day (ED) 15) contain higher aromatase activity (Vmax, 895 fmol/h/mg protein) than the female (Vmax, 604). Although a sex difference exists at early stages of embryonic development (ED 13), the embryonic aromatase system is regulated by steroids later in fetal development. The developing aromatase-containing neuroblasts probably form processes which connect to other aromatase neurones. Immunoreactive staining with an aromatase polyclonal antibody identifies an increase in numbers of aromatase-immunoreactive hypothalamic neuronal cell bodies following testosterone treatment. Testosterone treatment also causes both stimulation of neurite growth and branching as well as functional maturation of aromatase neurones. In particular, there is an increase in aromatase activity per neurone as well as a dramatic increase in the number of neurones expressing the enzyme. Both the functional and morphological changes depend on androgen receptor stimulation for several days in vitro. This conclusion is supported by colocalization studies which reveal a high number of fetal hypothalamic aromatase neurones co-expressing androgen receptor. We conclude that testosterone influences the growth of male hypothalamic neurones containing aromatase at a sensitive period of brain development. Endogenous steroid inhibitors of aromatase, probably formed within the neuroglia, also play a role in the control of oestrogen production. An endogenous 5alpha-reduced metabolite of testosterone, 5alpha-androstanedione, is almost as potent in inhibiting neuronal hypothalamic aromatase activity (Ki = 23 nM) as the synthetic non-steroidal inhibitors such as the imidazole, fadrozole, and the triazoles, arimidex and letrozole. It is clear that the oestrogen-forming capacity of the male hypothalamus has the special characteristics and plasticity of regulation which could affect brain differentiation at specific steroid-sensitive stages in ontogeny.