The postnatal ontogeny of rat uterine ornithine decarboxylase: acquisition of a second peak of estrogen-induced enzyme activity

17beta-estradiol corrects hemostasis in uremic rats by limiting vascular expression of nitric oxide synthases

Conjugated estrogens shorten the prolonged bleeding time in uremic patients and are similarly effective in a rat model of uremia. We have previously demonstrated that the shortening effect of a conjugated estrogen mixture or 17beta-estradiol on bleeding time was abolished by the nitric oxide (NO) precursor L-arginine, suggesting that the effect of these drugs on hemostasis in uremia might be mediated by changes in the NO synthetic pathway. The present study investigated the biochemical mechanism(s) by which conjugated estrogens limit the excessive formation of NO. 17beta-estradiol (0.6 mg/kg), given to rats made uremic by reduction of renal mass, significantly reduced bleeding time within 24 h and completely normalized plasma concentrations of the NO metabolites, nitrites and nitrates, and of NO synthase (NOS) catalytic activity, determined by NADPH-diaphorase staining in the thoracic aorta. Endothelial NOS (ecNOS) and inducible NOS (iNOS) immunoperoxidase staining in the endothelium of uremic aortas of untreated rats was significantly more intense than in control rats, while in uremic rats receiving 17beta-estradiol staining was comparable to controls. Thus 17beta-estradiol corrected the prolonged bleeding time of uremic rats and fully normalized the formation of NO by reducing the expression of ecNOS and iNOS in vascular endothelium. These results provide a possible biochemical explanation of the well-known effect of estrogens on primary hemostasis in uremia, in experimental animals and humans.

Effect of nitrous oxide exposure on maternal and embryonic S-adenosylmethionine levels and ornithine decarboxylase activity

Nitrous oxide is suspected to be a developmental toxicant in humans. The anesthetic does produce increases in the resorption and malformation frequencies in rodents. The mechanism for the drug's developmental toxicant effects is unknown. Embryonic DNA synthesis is decreased; however, this decrease does not appear to be due to depressed levels of adenine or guanine. In this investigation, we examined the effect of N2O on maternal and embryonic S-adenosylmethionine (AdoMet) levels and ornithine decarboxylase (ODC) activity, and the effect of exogenous methionine (Met) on these parameters was also examined. AdoMet and ODC are involved in polyamine synthesis, and polyamines are involved in regulation of macromolecular synthesis. Pregnant rats were treated with N2O for 24 hours beginning on the morning of day 10 of gestation. There was no effect of N2O on maternal hepatic AdoMet or S-adenosylhomocysteine (AdoHcy) levels; there was also no effect on embryonic AdoMet. Embryonic AdoHcy could not be detected in many of the samples; however, N2O treatment did significantly increase the number of embryonic samples in which AdoHcy was detectable. ODC activity was not affected by either treatment in dams but was increased by N2O in embryos. It is possible that the embryotoxic effect of this anesthetic is mediated by alterations in the AdoMet to AdoHcy ratio or to changes in ODC activity and polyamine synthesis.

Differential effects of sex steroids on uterine and renal ODC activity in ovariectomized rats

Many hormones are known to induce the activity of ornithine decarboxylase (ODC), the first and rate-limiting enzyme for polyamine biosynthesis, in their target tissues. Using ovariectomized rats, we have compared the effects of sex hormones on ODC activity in the uterus and the kidney which contain estrogen and androgen receptors. The results show that 1) both estrogen and androgen stimulate renal ODC activity, 2) estrogen but not androgen effectively increases ODC activity in the uterus, 3) estrogen at higher dosage can stimulate renal ODC activity to an extent similar to that in the uterus, 4) daily treatment with estradiol for 5 days results in the desensitization of uterine ODC activity, but not that of renal ODC activity to the hormonal stimuli. Although both uterus and kidney are targets of sex hormones, our results indicate that estrogen and androgen have differential influences on the ODC activity in these two organs.

Transplacental estrogen responses in the fetal rat: increased uterine weight and ornithine decarboxylase activity

The synthetic estrogens, diethylstilbestrol (DES) and ethynylestradiol (EE2), are more potent than 17 beta-estradiol (E2) in inducing uterine weight gain in the neonatal rat, due to the binding of E2 to serum alpha-fetoprotein (AFP). However, all three hormones are equipotent in inducing neonatal uterine ornithine decarboxylase (ODC) activity. The present study assessed estrogen potency in fetal rats. Pregnant CD rats were injected sc daily on gestation days (GD) 16-20 with DES, EE2, or E2 in sesame oil. Both DES and EE2, but not E2, significantly increased uterine weight at birth, to more than twice that of controls. In addition, implants which continuously release E2 only slightly increased uterine weight at birth. Alternatively, dams were given a single estrogen injection on GD 20 and were sacrificed at various times after injection. Peak fetal uterine ODC activity occurred at 6-8 hours after maternal injection for all three estrogens. E2 had a relative potency about tenfold less than either DES or EE2 in stimulating fetal ODC activity, in contrast to equal potencies of the three estrogens in the postnatal rat uterus. Similar patterns were found following direct fetal injection with E2 or DES. In summary, these data demonstrate a transplacental induction of fetal uterine ODC activity and uterine weight gain by both DES and EE2. In addition, the lack of correlation between these endpoints in response to E2 suggests that they may be useful as selective indicators of potential toxicity of both natural and synthetic estrogens.

Postnatal uterine development in the rat: estrogen and antiestrogen effects on luminal epithelium

We examined the effects of the synthetic estrogens, diethylstilbestrol (DES) and ethynylestradiol (EE), and the triphenylethylene antiestrogen, clomiphene citrate (CC), on uterine growth and development in the rat. These compounds, unlike estradiol, do not bind significantly to rat serum alphafetoprotein (AFP). Administration of DES or EE during the period of normal uterine gland genesis (postnatal days 10-14) induced luminal epithelium hypertrophy and increased uterine wet weight. The durations of these responses were dose-related. By day 26, luminal epithelium cell numbers were significantly depressed, compared to controls. Uterine gland development was delayed 6 to 9 days, depending upon estrogen dose, and the numbers of uterine glands ultimately achieved were generally less than in untreated control animals. While a daily dose of 0.1 micrograms CC/rat did not alter uterine development, 10 micrograms CC/rat caused prolonged luminal epithelium hypertrophy and inhibited uterine gland genesis without inducing the large increases in uterine weight or the decreases in luminal epithelium cell number seen after estrogen exposure. The number of stromal cells was significantly increased on day 26 after CC exposure. Together with previous studies, these data demonstrate the greater potency and developmental stage specificity of non-AFP-bound estrogens with respect to altering uterine gland development. In addition, these data suggest that the disruptive influence of antiestrogens on gland genesis may be mediated through an indirect influence on the uterine stroma.

Estrogen- and antiestrogen-induced ornithine decarboxylase activity and uterine growth in the rat

The estrogen antagonists tamoxifen and monohydroxytamoxifen are also classified as partial estrogen agonists. In infantile rats, estradiol induced a single peak of uterine ODC activity at 6h following injection regardless of the extent of induction by various estradiol doses. By contrast, the timing of the ODC activity peak induced by tamoxifen and monohydroxytamoxifen was highly dependent upon the dosing conditions and was delayed to 18 h at lower tamoxifen doses. In immature rats, tamoxifen and monohydroxytamoxifen induced two peaks of uterine ODC activity resembling those induced by estradiol. Both ODC activity peaks were delayed by 9 h, without decreases in peak heights, by a 50-fold tamoxifen dose reduction. In all experiments the initial appearance of antiestrogen- and estradiol-induced ODC activity corresponded to initial uterine wet weight gain regardless of dosing condition. Thus, when dose-related temporal shifts are taken into account, tamoxifen and monohydroxytamoxifen are complete agonists with respect to induction of uterine weight gain and ODC activity.

An evaluation of the involvement of polyamines in modulating MCF-7 human breast cancer cell proliferation and progesterone receptor levels by estrogen and antiestrogen

The present studies were undertaken to determine the importance of the polyamine biosynthetic pathway in cellular proliferation and hormone-regulated progesterone receptor synthesis in estrogen receptor-containing breast cancer cells. Treatment of MCF-7 cells with difluoromethylornithine (DFMO), the irreversible inhibitor of the enzyme ornithine decarboxylase (ODC), prevented estradiol-induced cell proliferation in a dose-dependent fashion. DFMO inhibition of estradiol-induced cell proliferation was completely recoverable by the addition of exogenous putrescine while putrescine alone did not stimulate proliferation of control cells. ODC activity was 4-fold greater in estrogen-treated cells and DFMO (5 mM) fully inhibited ODC activity. DFMO was able to suppress only slightly further the proliferation of antiestrogen (tamoxifen) treated cells and putrescine was able to recover this DFMO inhibition. In contrast to the suppressive effect of DFMO on cell proliferation, DFMO had no effect on the ability of estrogen to stimulate increased (4-fold elevated) levels of progesterone receptor. Hence, while ODC activity appears important for estrogen-induced cell proliferation, inhibition of the activity of this enzyme has no effect on the ability of estradiol to increase cellular progesterone receptor content.

Gonadotropin- and estrogen-induced increase of peripheral-type benzodiazepine binding sites in the hypophyseal-genital axis of rats

Peripheral-type benzodiazepine binding sites (PBS) were demonstrated in the cell membranes of various organs (ovary, uterus, oviduct, pituitary and kidney) of mature and immature female rats by using the PBS-specific ligand [3H]PK 11195. The equilibrium dissociation constants of [3H]PK 11195 for PBS in mature rats ranged from 3 to 4 nM. The specific binding of [3H]PK 11195 (2 nM) in the hypophyseal-genital axis of immature (19-27 days old) female rats was found to be significantly increased in the ovary and uterus, concurrently with the increase in age. Administration of pregnant mare serum gonadotropin or diethylstilbestrol to immature rats increased the density of PBS in the ovary and uterus 2- to 3-fold but no change was found in the kidney. The affinity of [3H]PK 11195 to these tissues did not change following hormonal treatment. These results suggest that gonadotropin and estrogen are involved in the induction of PBS in the organs of the hypophyseal-genital axis in female rats.

The polyamines putrescine, spermidine and spermine in human gingival crevicular fluid

In human periodontal disease, there may be periods of exacerbation and remission. Definition of the homeostatic mechanisms in the periodontium may therefore be important in understanding the natural history of this disorder. The polyamines are biologically active amines involved in the regulation of cell growth, regeneration of tissue and modulation of inflammation. Their occurrence was examined in gingival crevicular fluid (GCF). Fifteen sites were evaluated in four patients with moderately advanced periodontitis before and after root planing and scaling, and 15 sites were evaluated in four patients with mild inflammatory gingivitis and no attachment loss. Polyamine analysis was by high-performance liquid chromatography. GCF from untreated sites in periodontitis patients contained the highest concentration of putrescine (10(4) greater than serum). This polyamine was detected in all periodontitis samples and 12 of 15 gingivitis samples. Significant differences were seen when the amount of putrescine/30 s sample was compared: periodontitis sites before treatment 1005.7 +/- 106.1 pmol; periodontitis sites after treatment 504.7 +/- 89.2 pmol; gingivitis sites 186.7 +/- 40.1 pmol. In contrast, spermidine and spermine were detected only occasionally. Thus putrescine may play an important homeostatic role in the periodontium.

Dissociation of estrogen-induced uterine growth and ornithine decarboxylase activity in the postnatal rat

Estrogens are teratogens and developmental carcinogens in several species. We have used uterine growth to quantitate the potency of three estrogens [estradiol (E2), diethylstilbestrol (DES), ethynylestradiol (EE2)] during four postnatal periods (days 1-5, 10-14, 20-24, and 60-64) in the rat. Alphafetoprotein (AFP), present at high levels in neonatal serum, is thought to regulate estrogen bioavailability. Association constants for DES and EE2 were 2.7% and 4.9% of that for E2 binding to AFP, determined in a batch Sephadex equilibrium binding assay. On days 1-5, DES and EE2 were about 80-fold more potent than E2 in increasing uterine weight. As AFP levels fell, potency differences between E2 and the synthetic estrogens decreased. In the adult, which essentially lacks AFP, the three estrogens were nearly equipotent. These data are consistent with AFP regulation of estrogen potency. On days 10-14, uterine growth was less sensitive than at other ages to all three estrogens, perhaps related to uterine differentiation and/or the high endogenous serum E2 levels reported at this age. However, when we examined another uterine estrogen response, ornithine decarboxylase (ODC) induction at 6 h following estrogen injection, all three hormones were about equipotent in both neonatal and adult animals. This apparently AFP-independent event shows dissociation of ODC induction and uterine growth, which could be due to separate mechanisms for hormone entry to target tissue or subsequent intracellular events.

Ornithine decarboxylase activity in human endometrium and endometrial cancer cells

Ornithine decarboxylase (ODC) activities were significantly higher in proliferative endometrium during the estrogen-dominated follicular phase of the menstrual cycle than in secretory endometrium after the formation of the progesterone-secreting corpus luteum. The enzymatic activity was increased about fivefold by renewal of the medium during incubations of endometrial fragments or isolated endometrial glands. Endometrial adenocarcinoma cells (HEC-1, HEC-50), both in monolayers and suspension, also responded to medium renewal by increasing ODC activity about 10-fold after 4 h, with subsequent reduction to control levels after 7 h. These effects were blocked by actinomycin D and cycloheximide. Endometrial stromal cells exhibited highly variable ODC activities at different passages. Difluoromethylornithine (DFMO) and sodium molybdate had marked antiproliferative effects in HEC-50 cultures, reducing cell numbers to 10 to 20% of control values 11 d after plating and inhibiting ODC activity by approximately 80% on Day 7. The antiproliferative effect of DFMO, but not that of molybdate, was reversed by 10 microM putrescine, the product of ODC activity. In contrast to DFMO, molybdate had no effect on ODC activity of cell homogenates. Molybdate did not elicit antizyme formation in HEC-50 cells under conditions in which putrescine did. These results indicate that ODC activity, present in both epithelial and stromal cells, as shown analytically and also by autoradiography after labeling with [3H]DFMO, may be related to cell proliferation in vivo and that proliferation of human endometrial cancer cells in culture can be arrested by DFMO and by molybdate.

Rat luminal cell nuclear area changes correlated with uterine growth responses induced by a low dose infusion or injection of estradiol-17 beta

Rat uterine luminal epithelial cells (LEC) responded differently when exposed to an injection of 1.0 microgram estradiol-17 beta (E2) compared to a continuous infusion of E2 at the rate of 1.0 microgram/24 hours. After injection or beginning infusion, LEC mean nuclear area significantly decreased by 4 h, then increased thereafter. After injection, nuclear area distributions were determined at each time point. The percentage of large nuclei (greater than 40 mu 2) decreased by 4h postinjection and remained a relatively small proportion of the population, while the percentage of nuclei of 20-30 mu 2 areas increased throughout the experiment. During infusion, the percentage of large nuclei decreased by 4h after pump implantation, then increased. Only infusion induced sustained, increased uterine protein content, DNA synthesis and ornithine decarboxylase activity. This study suggests that E2 treatment modality induces differences in nuclear size in target cells as well as in biochemical parameters.

Relationships among uterine growth, ornithine decarboxylase activity and polyamine levels: studies with estradiol and antiestrogens

We have examined the effects of estradiol (E2) and antiestrogen (AE) on ornithine decarboxylase (ODC) activity and uterine polyamine concentrations as an aid to understanding the dissimilar effects of E2 and AE on uterine growth. ODC activity rises rapidly from very low levels in immature (day 20-23) rat uteri, showing two markedly (approximately 500-fold) increased peaks of activity at 5 h and 16 h after E2 (2 micrograms) injection. After AE (50 micrograms CI628 or U23469) treatment, the temporal increase in ODC activity is slow and only one major peak is found at 24 h. Daily injections of E2 over a 3-day period evoke continued stimulation of uterine ODC activity; however, the same daily treatment regimen with AE results in stimulation of ODC activity only during the first day. After pretreatment with AE, E2 can still elicit the early (5 h) peak of ODC activity, but the later (16 h) peak of ODC activity is blocked. Quantitation of uterine polyamines by high performance liquid chromatography reveals a 1.5-2-fold increase in the concentration of spermidine after 1 day of E2 or AE exposure, with little change in putrescine or spermine levels. After 3 days of E2, AE, or E2 plus AE treatment, spermidine concentrations are elevated 2-2.5-fold and spermine concentrations are elevated 1.5-fold. Putrescine concentrations are unchanged. Hence, regardless of the different degree to which the uterus is stimulated to grow in response to E2 and/or AE, there are corresponding changes in uterine ODC activity, such that polyamine concentrations are elevated to a similar extent in the E2- or AE-treated uterus.

Dissociated regulation of growth and ornithine decarboxylase activity by estrogen in the rat uterus

To evaluate the role of polyamines in mediating the effect of estrogen on growth of the rat uterus, we examined the effect of an irreversible inhibitor of ornithine decarboxylase (ODC), 5 alpha-difluoromethylornithine (DFMO), on estrogen-stimulated uterine growth. Estradiol alone evoked two major surges of ODC activity at 5 h and at 16 h, and 2-fold increases in the concentration of spermidine in the uterus. When DFMO was administered to either intact or ovariectomized immature (20 day-old) rats for 2 or 6 days prior to and then during the 1 or 3 days of estradiol treatment, uterine ODC activity was completely suppressed as was the associated increase in spermidine concentration, but the magnitude of uterine growth stimulated by estradiol was equally great in the presence or absence of DFMO. These observations suggest that although uterine growth stimulation by estrogen is normally accompanied by marked increases in ODC activity and spermidine accumulation, these changes are not essential for hormonally regulated uterine cell proliferation in vivo.

Uterine growth responses of the mature castrate rat to estradiol-17B

To examine estrogen-stimulated uterine growth we have monitored changes in uterine DNA synthesis, ornithine decarboxylase (ODC) activity and protein content as well as luminal epithelial (LE) cell mitotic index and ultrastructural changes. We have utilized this model to examine castrate mature rat uterine growth as a function of time between 18 and 40 hours following a single injection of 25.0 ug of estradiol-17B. LE cell mitotic index and protein content increases were maximally elevated as early as 18 hours postinjection while uterine ODC activity was maximal at 28 hours; uterine DNA synthesis increases continued throughout the experiment. In addition, the infusion of either 1 or 2 ug E2 plus progesterone over a 24 hour period, stimulated elevated ODC activity under both treatment regimens and LE cell mitotic index which was inversely related to E2 dose.

Estrogenic activity of zearalenone and zearalanol in the neonatal rat uterus

Fusarium sp. contaminated feedstuffs elicit adverse estrogenic effects in several commercially important animal species via the mycotoxin zearalenone. An estrogenically active synthetic derivative, zearalanol, is used as an anabolic agent in cattle. Since estrogens can irreversibly alter target tissue development, we investigated the estrogenic activity of these compounds in the neonatal rat uterus. Both induced dose-dependent premature uterine growth when injected daily on postnatal days 1-5 (ED50 = 1.3 mg/kg BW). Nuclear estrogen receptor levels dramatically increased 1 hour after either a single injection on day 5 or after five daily injections. In 5-day-old animals, the translocated nuclear receptor was characterized as a single class of binding sites with a dissociation constant (KD) for estradiol (E2) of 1 nM. At 15 days, zearalanol-treated animals showed greater uterine nuclear receptor retention than zearalenone-treated animals. In 5-day-old animals, single mycotoxin doses induced five fold elevations of ornithine decarboxylase (ODC) at 6 hours. Unlike the growth response, ODC dose-response studies showed zearalanol to be about 20-fold more effective than zearalenone. Time course studies revealed that a low dose of zearalenone, but not of zearalanol, resulted in a shift in peak activity from 6 to 8 hours. These data suggest that metabolism of zearalenone may be important in short-term pharmacodynamics. In a competitive binding assay, neither compound competed [3H]E2 from the E2 binding site on alpha-fetoprotein. We conclude that the uterine growth response and ODC induction demonstrate the neonatal estrogenic action of these mycotoxins, apparently mediated via the estrogen receptor. The greater effectiveness of zearalanol in inducing ODC may be related to nuclear retention and/or zearalenone metabolism.