Production of free estrogens and estrogen conjugates by the preimplantation equine embryo

In vitro production of free estrogens and estrogen conjugates by intact Day 12.5, 13.5 and 14.5 equine embryos was measured at 2-h intervals over a 24-h culture period. Production of free estrogens was higher for Day 14.5 than Day 12.5 embryos. Differences in production of conjugated estrogens were not significant, but a trend toward increased production with increased age of embryo was apparent. No trend toward increased free and conjugated estrogen production per cell was observed with age. Embryo diameter and number of cells increased with age but varied considerably within groups. The amount of free and conjugated estrogens measured in blastocoelic fluid did not decrease over the 24-h culture period, suggesting that estrogens detected in culture medium were produced by the embryo and not the result of leakage of maternal estrogen from the blastocoele. The results of this study support previous results that estrogen production increases with development of equine embryos. This increase in estrogen production appears to be more closely associated with the diameter of the embryo, and hence its number of cells, than with increased intracellular steroidogenic activity.     

The induction of ovalbumin and conalbumin mRNA by estrogen and progesterone in chick oviduct explant cultures

Estrogen pretreated chick oviduct tissue can be restimulated in vitro by physiological concentrations of estrogen and progesterone. The rates of synthesis of the major egg white proteins, ovalbumin and conalbumin, as well as the cellular levels of their respective mRNAs, increase after characteristic lag periods; this confirms previously reported results in vivo and demonstrates that both the lag phenomena and the mRNA induction are a function of the direct interaction of steroids with oviduct cells.The antagonistic action of progesterone on an estrogen-mediated induction of conalbumin mRNA also occurs in vitro, and the kinetics of this response are examined. Progesterone terminates the estradiol-induced accumulation of conalbumin mRNA within 30 min after addition to the medium; progesterone alone or in combination with estrogen, however, is capable of inducing conalbumin mRNA after a 4 hr lag period. The temporary nature of this antagonism and the fact that it does not occur with ovalbumin induction indicate the complexity of the oviduct's response to steroids.The role of protein synthesis in the induction of both ovalbumin and conalbumin was examined by including protein synthesis inhibitors in the culture medium. Puromycin, cycloheximide, emetine, pactamycin and high salt all block the induction of both ovalbumin and conalbumin mRNA when added together with either estrogen or progesterone. The effect of puromycin is reversible. After the drug is removed from the medium, the mRNA accumulation begins with the same characteristic lag period seen when no inhibitors are added. When given 2 hr after estrogen, puromycin stops the accumulation of conalbumin mRNA within 30 min, whereas cycloheximide and emetine allow the mRNA to accumulate for another 2 hr before causing complete inhibition. There is no effect of protein synthesis inhibitors on the number of estrogen receptors localized in the nucleus. The data suggest a direct link between protein synthesis and the steroid-induced accumulation of specific mRNAs in this system.     

INDUCTION OF ENDOMETRIAL PEROXIDASE SYNTHESIS AND SECRETION BY ESTROGEN AND ESTROGEN ANTAGONIST

Synthesis of peroxidase was induced in the uterine epithelium of immature rats by multiple doses over a 24–96-h period of either 17 β-estradiol, the estrogen-antagonist Parke-Davis CI-628, or a combination of estradiol plus antagonist. Endogenous peroxidase activity first appeared in the cisternae of the rough endoplasmic reticulum of surface epithelial and glandular cells within 24–48 after the initial injection. Uterine peroxidase activity was also visible in the cisternae of the Golgi apparatus, in Golgi-derived secretory granules, and within the uterine and glandular lumen. Some cells of the epithelium produced little or no peroxidase, even after 96 h. Whereas the antagonist appeared to induce synthesis and secretion of peroxidase, neither the antagonist alone nor the combined treatment (estradiol plus antagonist) reproduced the estradiol-mediated growth in organ size and increased lumen diameter.     

Induction of Carbon Starvation-Induced Proteins in Vibrio vulnificus

By using two-dimensional polyacrylamide gel electrophoresis of pulse-labelled proteins, carbon starvation-induced (Sti) proteins produced by Vibrio vulnificus were identified. At least 34 proteins were induced over a 26-h period of carbon starvation. Although the total rate of protein synthesis over the 26-h starvation period suggests that there is a dramatic decrease in total protein synthesis within the first hour of starvation, at least 23 of the Sti proteins were induced within the first 20 min of carbon depletion. Six temporal classes of proteins could be identified, with class A(ii) encompassing the largest (21 proteins) group. All of the proteins in this group could be characterized by one of two patterns of protein synthesis. The addition of chloramphenicol at sequential times throughout starvation revealed that proteins required for starvation survival are made within the first 4 h of starvation.     

Recovery of maximal insulin responsiveness and insulin sensitivity after induction of insulin resistance in primary cultured adipocytes

Treatment of primary cultured adipocytes with 50 ng/ml insulin and 20 mM glucose for 0-6 h resulted in a loss of maximal insulin responsiveness (MIR) which was immediate (no lag period), rapid (t1/2 of 3 h), linear, and extensive (80% of that seen at 24 h), whereas loss of insulin sensitivity from 0-24 h was slow (t1/2 = 8 h), extensive (insulin ED50 of 0.3 and 1.45 ng/ml at 2 and 24 h, respectively), and was preceded by an initial 2-h lag. Recovery of MIR and insulin sensitivity was assessed by inducing desensitization for various times from 2-24 h, removing insulin and glucose, and then measuring MIR and insulin sensitivity over a subsequent 1-6-h period. After 2 h, recovery of MIR in desensitized cells was rapid (251 pmol of glucose/3 min/h), whereas after 24 h, recovery was much slower (35 pmol/3 min/h). In contrast, the opposite trend was seen for recovery of insulin sensitivity: at early times recovery of insulin sensitivity was slow (0.05 ng/ml/h) but was rapid after 24 h (0.12 ng/ml/h). Thus, it appears that MIR and insulin sensitivity can be independently regulated since recovery rates for MIR and insulin sensitivity diverged with the progression of insulin resistance. When the effects of insulin and glucose on recovery were examined, we found that insulin alone was unable to block recovery of MIR or insulin sensitivity. Glucose alone, however, was effective in preventing recovery of insulin sensitivity but not recovery of MIR. In the presence of 20 mM glucose, low doses of insulin (treatment EC50 = 0.22-0.46 ng/ml) effectively prevented recovery of both MIR and insulin sensitivity. De novo protein synthesis apparently is not involved in the development of insulin resistance or the reversal of desensitization since inhibition of protein synthesis by cycloheximide had no effect on the loss of MIR and insulin sensitivity or recovery.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of antigens and lymphokines on early activation of single hapten-specific B lymphocytes

An assay was developed to monitor early activation of single fluorescein-specific B cells obtained from the spleens of nonimmunized adult mice by prefractionation on hapten gelatin. Early activation was assessed as a significant increase in the diameter of individual B cells after 24 hr in vitro. Significant enlargement of the single B cells was induced within 24 hr by either T-independent antigens acting alone or a crude source of B cell growth and differentiation factors (EL-BGDF-pik) acting alone. In contrast, T-dependent antigens acting alone were ineffective. When selected T-independent antigens and EL-BGDF-pik acted together, a greater number of B cells were induced to enlarge. B cell stimulatory factor 1 (BSF 1) behaved in a similar manner as EL-BGDF-pik, inducing early B cell enlargement both in the absence and more so in the presence of antigen. Both EL-BGDF-pik and BSF 1 enhanced the survival of single hapten-specific B cells during the 24-hr period. Interleukin 1 was unable to cause B cell enlargement when acting alone, although it was able to augment B cell enlargement induced by antigen. Interleukin 2 did not induce cell enlargement in either the presence or absence of antigen. Activation was demonstrated among cells of all sizes, regardless of the stimulus, although a greater response was demonstrated amongst the larger cell population. The addition of 3T3 filler cells enhanced early B cell activation and cell survival during the 24-hr period. The 24-hr B cell enlargement assay as applied to isolated single cells provides an unequivocal approach to the analysis of early B cell activation, adding a further parameter for the dissection of the precise roles of antigen and the various factors in the B cell differentiation pathway.     

Experimental evidence for a non-clock role of the circadian system in spider mite photoperiodism

In the spider mite Tetranychus urticae photoperiodic time measurement proceeds accurately in orange-red light of 580 nm and above in light/dark cycles with a period length of 20 h but not in 'natural' cycles with a period length of 24 h. To explain these results it is hypothesized that the photoperiodic clock in the spider mite is sensitive to orange-red light, but the Nanda-Hamner rhythm (a circadian rhythm with a free-running period tau of 20 h involved in the photoperiodic response) is not and consequently free runs in orange-red light. To test this hypothesis a zeitgeber was sought that could entrain the Nanda-Hamner rhythm to a 24-h cycle without inducing diapause itself, in order to manipulate the rhythm independently from the orange-red sensitive photoperiodic clock. A suitable zeitgeber was found to be a thermoperiod with a 12-h warm phase and a 12-h cold phase. Combining the thermoperiod with the long-night orange-red light/dark regime, both with a cycle length of 24 h, resulted in a high diapause incidence, although neither regime was capable of inducing diapause on its own. The conclusion is that the Nanda-Hamner rhythm is necessary for the realization of the photoperiodic response, but is not part of the photoperiodic clock, because photoperiodic time measurement takes place in orange-red light whereas the rhythm is not able to 'see' the orange-red light. It is speculated that the Nanda-Hamner rhythm is involved in the timely synthesis of a substrate for the photoperiodic clock in the spider mite.     

Keloid fibroblasts are refractory to inhibition of DNA synthesis by phorbol esters. Altered response is accompanied by reduced sensitivity to prostaglandin E2 and altered down-regulation of phorbol ester binding sites.

To investigate abnormal growth regulation in keloid fibroblasts, responses to phorbol esters were examined. Treatment of quiescent cultures with phorbol 12-myristate 13-acetate (PMA) blocked a normally occurring (20-24 h) peak of serum-stimulated thymidine incorporation in normal and keloid cells. In keloid fibroblasts PMA induced a delayed peak of DNA synthesis. When indomethacin was added with PMA the delayed peak appeared in normal fibroblasts. The ED50 for inhibition of the 20-24-h peak was 1 nM, whereas the delayed peak required a 50-fold-higher PMA concentration. In both cell types PMA induced prostaglandin E2 (PGE2) synthesis, and exogenous PGE2 caused 50% inhibition of the 20-24-h peak. When PMA and indomethacin were added with PGE2 the delayed peak was inhibited 90% in normal fibroblasts, whereas inhibition of keloid cells was the same as with PGE2 alone. Normal and keloid fibroblasts had the same number of phorbol ester binding sites. However, in normal cells, phorbol 12,13-dibutyrate bound with greater affinity, and down-regulation of phorbol ester binding occurred to a greater extent. These findings suggest that altered expression of protein kinase C isozymes or another molecule that binds phorbol esters may play a role in abnormal growth regulation of keloid cells.     

Protein synthesis in perfused rat hearts after in vivo hyperthermia and in vitro cold ischemia

Isolated and perfused rat hearts can be maintained for up to 2.5 h with minimal synthesis of a stress protein with a relative mass (Mr) of 71 kilodaltons (SP71). Isolated hearts, subjected to 17 h of cold (4 degrees C) ischemia, upon perfusion (37 degrees C) synthesize a large amount of SP71. In the present study, the effect of in vivo hyperthermia on protein synthesis in isolated and perfused hearts was examined. Hearts were excised from rats subjected to a 15-min episode of hyperthermia (42 degrees C), either immediately (no recovery) or after 24 h of recovery. The excised hearts were perfused either immediately or after 17 h of cold ischemia. Hyperthermia (no recovery) increased [3H]leucine incorporation into SP71, while hyperthermia with a 24-h recovery did not increase incorporation into SP71 during perfusion (no ischemia). Hyperthermia (no recovery) increased the incorporation of [3H]leucine into SP71 seen after cold ischemia. Hyperthermia with a 24-h recovery decreased the incorporation of [3H]leucine into SP71 seen after cold ischemia. This reduction in synthesis of SP71 after 24-h recovery from hyperthermia could be caused by the accumulation of SP71 suppressing its own synthesis or a measure of protection (tolerance) induced by the hyperthermia.     

The effect of photoperiod and temperature on growth and frost resistance of winter rye root systems

Root growth, development and frost resistance were examined in winter rye ( Secale cereale L. cv. Puma) plants grown under 6 combinations of temperature and photoperiod (20/16°C or 5/3°C, day/night; 8, 16- or 24-h days). Overall root system growth is influenced by the interaction of temperature and photoperiod. Maximum shoot growth occurs at a 24-h photoperiod in 20°C plants and at a 16-h photoperiod in 5°C plants, and is correlated in both treatments with a high root:shoot ratio. Frost resistance of rye roots is affected by short photoperiods in 2 ways. First, short photoperiod and low temperature delay production of new adventitious roots so that newly developing roots are not exposed to freezing temperatures. Second, short photoperiod alone can induce several degrees of frost tolerance in existing roots during the lag phase of growth. Low temperature alone does not decrease the rate of dry weight accumulation in rye root systems, but cold temperature does retard developmental processes within the roots. Rye roots grown at 5°C develop first order lateral roots, differentiate metaxylem vessels and suberize endodermal cell walls more slowly than roots grown at 20°C.     

Effect of PGF2alpha, indomethacin, tamoxifen, or estradiol-17beta on incidence of abortion, progesterone, and pregnancy-specific protein B (PSPB) secretion in 88- to 90-day pregnant sheep

One objective of this experiment was to evaluate our hypotheses that estradiol-17beta regulates secretion of pregnancy specific protein B (PSPB) and that secretion of progesterone during pregnancy is regulated by a prostanoid by examining the effects of prostaglandin F2alpha (PGF2alpha), a luteolyic agent; indomethacin, a prostanoid synthesis inhibitor; tamoxifen, an estrogen receptor antagonist; estradiol 17-beta; and interaction of these factors on the incidence of abortion and progesterone and PSPB secretion. Another objective was to determine if there is a luteal source of PSPB. Weights of corpora lutea were decreased (P < or = 0.05) by PGF2alpha, indomethacin, PGF2alpha + tamoxifen, PGF2alpha + indomethacin, and PGF2alpha + estradiol-17beta but not (P > or = 0.05) by tamoxifen or estradiol-17beta alone. No ewe treated with PGF2alpha alone aborted (P > or = 0.05). Forty percent of ewes treated with PGF2alpha + estradiol-17beta aborted (P < or = 0.05), but ewes were not aborted by any other treatment within the 72-h sampling period. Profiles of progesterone in jugular venous blood differed (P < or = 0.05) among control, indomethacin-, tamoxifen-, and PGF2alpha + indomethacin-treated ewes. Progesterone in jugular venous blood of control ewes decreased (P < or = 0.05) by 24 h, followed by a quadratic increase (P < or = 0.05) from 24 to 62 h. Progesterone in jugular venous blood of indomethacin-, PGF2alpha-, PGF2alpha- + tamoxifen-, PGF2alpha + indomethacin-, PGF2alpha + estradiol-17beta-, and tamoxifen-treated ewes was reduced (P < or = 0.05) by 18 h and did not vary (P > or = 0.05) for the remainder of the 72-h sampling period. Progesterone in vena cava and in uterine venous blood was reduced (P < or = 0.05) at 72 h in PGF2alpha-, indomethacin-, tamoxifen-, PGF2alpha + indomethacin-, PGF2alpha + tamoxifen-, and PGF2alpha + estradiol-17beta-treated ewes. Weights of placentomes did not differ among treatment groups (P > or = 0.05). Profiles of PSPB in inferior vena cava blood differed (P < or = 0.05) among control, estradiol-17beta-, indomethacin-, tamoxifen-, PGF2alpha + indomethacin-, and PGF2alpha + tamoxifen-treated 88- to 90-day pregnant ewes. Concentrations of PSPB in inferior vena cava blood were increased (P < or = 0.05) in indomethacin-, estradiol-17beta-, tamoxifen-, PGF2alpha + tamoxifen-, and PGF2alpha + indomethacin-treated 88- to 90-day pregnant ewes within 6 h and did not vary (P > or = 0.05) for the remainder of the 72-h sampling period. Concentrations of PSPB in uterine venous blood of indomethacin-, tamoxifen-, PGF2alpha + tamoxifen-, and PGF2alpha + indomethacin-treated ewes were greater (P < or = 0.05) at 72 h than at 0 h. PSPB in ovarian venous blood did not differ (P > or = 0.05) adjacent or opposite to the ovary with the corpus luteum. It is concluded from these data that estrogen regulates placental secretion of PSPB and that a prostanoid, presumably prostaglandin E, regulates placental secretion of progesterone during 88-90 days of gestation in sheep and that there is no luteal source of PSPB.     

Mutagenicity studies on paracetamol in human volunteers. II. Unscheduled DNA synthesis and micronucleus test

The possible genotoxic effect of paracetamol (PC) was studied in a group of 11 healthy volunteers. PC was administered in the form of tablets 3 x 1000 mg in the course of 8 h. Blood samples and buccal mucosa cells were taken 0, 24, 72 and 168 h after the first administration of the drug. Each blood sample was used for the termination of the unscheduled DNA synthesis (UDS) in peripheral lymphocytes and ascorbemia in plasma. Buccal mucosa cells were analysed for micronuclei. After PC administration the level of UDS induced by MNNG was decreased to T/C = 4.11 +/- 0.56 after 24 h vs. T/C = 5.02 +/- 0.47 (p less than 0.01) at 0 h. The frequency of micronucleated cells in the buccal mucosa was increased after 72 h to 0.38 +/- 0.07% vs. 0.19 +/- 0.06% (p less than 0.01) before PC administration. If PC was administered simultaneously with ascorbic acid (AA), also in a dose of 3 X 1000 mg, a decreased level of UDS was observed after 24, 72 and 168 h and the increased number of micronuclei was qualitatively the same as the PC alone: 0.38 +/- 0.09% after 72 h vs. 0.20 +/- 0.05% at 0 h AA did not decrease the genotoxic effect of PC, but prolonged the influence of PC on UDS.     

Sulfide induction of synthesis of a periplasmic protein in the cyanobacterium Oscillatoria limnetica.

Two proteins which may play a role in the induction of anoxygenic photosynthesis in Oscillatoria limnetica have been demonstrated by comparing the pattern of labeling during pulses of [35S]methionine of cells incubated under inducing conditions [anaerobic conditions plus 3-(3,4-dichlorophenyl)-1,1-dimethylurea, light, and sulfide) with that of cells incubated under noninducing conditions (without sulfide). The major inducible protein has an apparent molecular mass of 11.5 kilodaltons and is associated with a less strongly labeled 12.5-kilodalton protein. The synthesis of both proteins commences within the first 30 min of induction and continues throughout the 2-h induction period. Since these proteins are not synthesized in the presence of dithionite without sulfide, low redox potential alone is insufficient as an inducer of these proteins. Lysozyme treatment and/or osmotic shock of intact cells results in the release of the sulfide-induced proteins. Our data thus indicate that these proteins are located in the periplasmic space of the cells.     

Endogenous peroxidase: specific marker enzyme for tissues displaying growth dependency on estrogen

Data derived from a correlated morphological and biochemical study suggest the following: (a) estradiol-17beta, diethylstilbestrol, the estrogen antagonists nafoxidine (Upjohn 11,000), and Parke Davis C1628 induce synthesis of an endogenous peroxidase in the epithelium of target tissues like the vagina, the cervix, the uterus, and in the acinar cells of the estrogen-dependent rat mammary tumor; (b) peroxidase is a "specific" secretory protein of the estrogen-sensitized uterine endometrium; (c) peroxidase synthesis is not a nonspecific response to steroid hormone action, since progesterone and testosterone do not induce its synthesis; (d) endogenous peroxidase is a possible diagnositc protein for the detection of estrogen-dependent growing tissues, including breast cancer; (e) movement of exogenous horseradish peroxidase from the interstitium to the uterine lumina is restricted by tight junctions located at the apices of epithelial cells. Estrogen and antagonists do not appear to influence the transepithelial movement of exogenous peroxidase into the lumen.     

Estrogen and antagonist-induced changes in endometrial topography of immature and cycling rats

The topographical changes of the luminal surface of the endometrium of immature and ovariectomized rats treated with estrogen, antagonists to estrogen, and progesterone. and during various stages of the estrous cycle and in pregnancy were examined by scanning electron microscopy. Massive increases in numbers and length of endometrial cell microvilli were observed at estrus, after injection of estradiol-17beta, diethylstilbestrol, estrogen plus progesterone. or the inhibitor C1628 to immature and ovariectomized rats. Withdrawal of the estrogen stimulus results in diminution of microvilli, producing a state identical to diestrus, during pregnancy, and after injection of progesterone, The estrogen antagonist appears to have both estrogenic and progestogenic properties, stimulating endometrial cell hypertrophy, secretion of protein, and production of numerous apical microvilli.     

Proteoglycans and glycosaminoglycans induce gap junction synthesis and function in primary liver cultures

Intercellular communication via gap junctions, as measured by dye and electrical coupling, disappears within 12 h in primary rat hepatocytes cultured in serum-supplemented media or within 24 h in cells in a serum-free, hormonally defined medium (HDM) designed for hepatocytes. Glucagon and linoleic acid/BSA were the primary factors in the HDM responsible for the extended life span of the electrical coupling. After 24 h of culture, no hormone or growth factor tested could restore the expression of gap junctions. After 4-5 d of culture, the incidence of coupling was undetectable in a serum-supplemented medium and was only 4-5% in HDM alone. However, treatment with glycosaminoglycans or proteoglycans of 24-h cultures, having no detectable gap junction protein, resulted in synthesis of gap junction protein and of reexpression of electrical and dye coupling within 48 h. Most glycosaminoglycans were inactive (heparan sulfates, chondroitin-6 sulfates) or only weakly active (dermatan sulfates, chondroitin 4-sulfates, hyaluronates), the weakly active group increasing the incidence of coupling to 10-30% with the addition of 50-100 micrograms/ml of the factor. Treatment of the cells with 50-100 micrograms/ml of heparins derived from lung or intestine resulted in cells with intermediate levels of coupling (30-50%). By contrast, 10-20 micrograms/ml of chondroitin sulfate proteoglycan, dermatan sulfate proteoglycan, or liver-derived heparin resulted in dye coupling in 80-100% of the cells, with numerous cells showing dye spread from a single injected cell. Sulfated polysaccharides of glucose (dextran sulfates) or of galactose (carrageenans) were inactive or only weakly active except for lambda-carrageenan, which induced up to 70% coupling (albeit no multiple coupling in the cultures). The abundance of mRNA (Northern blots) encoding gap junction protein and the amounts of the 27-kD gap junction polypeptide (Western blots) correlated with the degree of electrical and dye coupling indicating that the active glycosaminoglycans and proteoglycans are inducing synthesis and expression of gap junctions. Thus, proteoglycans and glycosaminoglycans, especially those found in abundance in the extracellular matrix of liver cells, are important in the regulation of expression of gap junctions and, thereby, in the regulation of intercellular communication in the liver. The relative potencies of heparins from different tissue sources at inducing gap junction expression are suggestive of functional tissue specificity for these glycosaminoglycans.     

Heat pretreatment differentially affects cardiac fatty acid accumulation during ischemia and postischemic reperfusion

We investigated whether the cardioprotection induced by heat stress (HS) pretreatment is associated with mitigation of phospholipid degradation during the ischemic and/or postischemic period. The hearts, isolated from control rats and from heat-pretreated rats (42 degrees C for 15 min) either 30 min (HS0.5-h) or 24 h (HS24-h) earlier, were subjected to 45 min of no-flow ischemia, followed by 45 min of reperfusion. Unesterified arachidonic acid (AA) accumulation was taken as a measure for phospholipid degradation. Significantly improved postischemic ventricular functional recovery was only found in the HS24-h group. During ischemia, AA accumulated comparably in control and both HS groups. During reperfusion in control and HS0.5-h hearts, AA further accumulated (control hearts from 82 +/- 33 to 109 +/- 51 nmol/g dry wt, not significant; HS-0.5h hearts from 52 +/- 22 to 120 +/- 53 nmol/g dry wt; P < 0.05). In contrast, AA was lower at the end of the reperfusion phase in HS24-h hearts than at the end of the preceding ischemic period (74 +/- 18 vs. 46 +/- 23 nmol/g dry wt; P < 0.05). Thus accelerated reperfusion-induced degradation of phospholipids in control hearts is completely absent in HS24-h hearts. Furthermore, the lack of functional improvement in HS0.5-h hearts is also associated with a lack of beneficial effect on lipid homeostasis. Therefore, it is proposed that enhanced membrane stability during reperfusion is a key mediator in the heat-induced cardioprotection.     

The role of estradiol 17β in the activation of the uterus during premature labor and the effect of naproxen,an inhibitor of prostaglandin synthesis

Fifty-two pregnant rats were ovariectomized on day 16 of gestation to induce estrogen and progesterone deficiencies and the animals were divided into four Groups. Ovariectomy alone (Group A) resulted in the premature delivery of 21% of the fetuses. When ovariectomy was followed by estrogen treatment restoring normal estrogen levels (Group B), premature delivery of the fetuses increased to 96%. Daily injections of 25mg/kg b.w. Naproxen (Group C), given from the day of ovariectomy to reduce prostaglandin synthesis, completely prevented premature delivery if the animals received no estradiol treatment and reduced prematurity to 50% if estradiol had been administered (Group D).It is concluded that the estrogen and progesterone deficiency, induced by ovariectomy, provokes a regulatory imbalance which promotes premature delivery. This imbalance is enhanced when the estradiol levels are restored to normal values, probably because estradiol increases the synthesis of prostaglandin, the intrinsic myometrial stimulant. Naproxen, an inhibitor of prostaglandin synthesis, restores the regulatory balance, partially or completely, depending on the estrogen levels.     

Effects of long-term estrogen replacement on social investigation and social memory in ovariectomized C57BL/6 mice

Estrogen has been shown to play a role in modulating social recognition memory. However, the literature regarding the influence of estrogen on social memory is sparse and only covers two experimental manipulations: acute injections and receptor knockout. Long-term effects of estrogen replacement on social investigation and social recognition are unknown. Furthermore, existing social recognition protocols focus on memory of very short durations (<2 h). In the present study, we examined long-term effects of estrogen replacement on both short- (<30 min) and long-term (24 h) social recognition in ovariectomized female C57BL/6 mice by implanting 60-day time-release pellets containing physiological doses of estradiol (0, 0.18, or 0.72 mg of 17beta-estradiol). After 55 days of treatment, evidence of social recognition memory, measured by 24-h habituation, was found only in mice receiving the 0.72-mg pellet. This result is remarkable as previous reports indicate that individually-housed untreated rats and mice do not show habituation beyond 2 h. Our study further revealed that estrogen also increased frequencies of baseline social investigation without affecting general activity levels and decreased delayed post-swim-stress serum corticosterone concentration. Thus, these results suggest that long-term estrogen replacement increased the interest in social interaction as well as decreased stress responses. It is likely that the 24-h habituation observed in the estrogen replacement group is mediated jointly by the non-mnemonic effects of estrogen on the behavior displayed during the stage of memory encoding as well as mnemonic effects during the stage of memory consolidation.