Plasma 17β-estradiol Levels Research Articles

Histological, hormonal and biomolecular analysis of the pathogenesis of ovine Prolapsus vaginae ante partum

The objectives of the present study were to evaluate the hormonal profiles, histology of the vagina and biomolecular analysis of connective tissue of ewes with and without vaginal prolapse. Blood samples from the jugular vein and biopsies of the vaginal tissue were taken from five late term pregnant, unaffected animals, four sheep during parturition and six ewes suffering from vaginal prolapse ante partum. The blood samples were submitted for determining the concentration of the steroid hormones progesterone by automatic luminescence immunoassay and estradiol-17β by the sequence test. Investigations in the mRNA-expression including the estimation of the transcript levels of the α 2-chain of collagen I, the collagenolytic metalloproteinase 1 (MMP 1), the tissue inhibitor of MMP 1 (TIMP 1) and the estrogen receptor α were carried out by using semiquantitative reverse transcription-PCR. Additionally, the histology of the vaginal wall of ewes with and without vaginal prolapse and animals intra partum was assessed. Because of a right-skewed distribution, data were logarithmised and described using the geometric mean (x̄g) and the dispersion factor (DF). The average progesterone concentration of affected ewes (x̄g = 19.35 ng/ml, DF 1.33) was above those of control animals ante (x̄g = 10.44 ng/ml, DF 1.58) and intra partum (x̄g = 9.24 ng/ml, DF 1.92). Compared to the pregnant control group (x̄g = 20.13 pg/ml, DF 1.49) the plasma levels of 17β-estradiol in animals suffering from ante partum vaginal prolapse (x̄g = 27.81 pg/ml, DF 1.56) appeared to be slightly increased, but the difference was without statistical significance. The analysis of mRNA expression revealed a difference in the ante partum collagen metabolism in affected sheep. In prolapsed tissue the α2-chain of collagen I showed a decreased expression level in relation to the control animals in late-term pregnancy (P < 0.01). The average mRNA synthesis of MMP 1 or TIMP 1 in affected ewes was higher or lower, respectively, than the synthesis in healthy, late-term pregnant sheep. Significant differences were not observed. The production of transcripts of the estrogen receptor α was significantly decreased within the group of affected sheep compared to the unaffected pregnant ewes. Histological assessment showed that oedema was only detected in the subepithelial zone of the vaginal wall of intra partum sheep. There was no evidence for an inflammation of the prolapsed vaginal tissue since infiltration of leucocytes was present in all samples equally. The thickest vaginal epithelium due to hyperplasia of the epithelial cells was observed in sheep suffering from ante partum vaginal prolapse (x̄g = 83.95 μm, DF 1.21). This difference was statistically significant between the ante (x̄g = 31.12 μm, DF 1.22) and intra partum groups (x̄g = 33.27 μm, DF 1.24). Peripheral concentrations of progesterone and estradiol-17β seem to have no influence on the occurrence of vaginal prolapse in ewes. Regarding histology of the vaginal wall in combination with the expression of local estrogen receptors, it was determined that there is neither a pronounced oedema nor an overexpression of the estrogen receptor α in affected animals, which means that no local estrogenic effect provokes the prolapse of vaginal tissue. The biomolecular analysis led to the new result, that ewes suffering from vaginal prolapse show alterations in the antepartal metabolism of vaginal connective tissue.

Endocrine modulation, inhibition of ovarian development and hepatic alterations in rainbow trout exposed to polluted river water

Under laboratory conditions, female rainbow trout were exposed to graded concentrations of water from the River Lambro, a polluted tributary of the River Po, and to the effluent of a large wastewater treatment plant which flows into the River Lambro. In field exposures, trout were held in cages in the River Po upstream and downstream from the confluence of the River Lambro. After 10-day (laboratory) and 30-day (laboratory and field) exposures, trout were examined for several chemical, biochemical and histological endpoints. The results indicated that exposure to complex mixtures of chemicals, including estrogen receptor agonists, aryl-hydrocarbon receptor agonists, and probably antiandrogens, had occurred. Exposure altered the plasma levels of 17β-estradiol and testosterone, and some treatments also enhanced the activity of hepatic ethoxyresorufin O-deethylase. Gonadal histology showed varying levels of degenerative processes characterised by oocyte atresia, haemorrhages, melano-macrophage centres (MMCs), and oogonia proliferation. Liver histology showed less severe effects.

Effects of monocrotophos on the reproductive axis in the male goldfish ( Carassius auratus): Potential mechanisms underlying vitellogenin induction

Monocrotophos (MCP) is a highly toxic organophosphorus pesticide that has been banned in many countries. Both vitellogenin mRNA expression and secretion were significantly induced in male goldfish by exposure to an MCP-based pesticide, suggesting that MCP has significant estrogenic properties. To elucidate the mechanisms of action of MCP on vitellogenin induction, we used radioimmunoassay to examine the effect of MCP treatment on plasma 17β-estradiol and testosterone levels in male goldfish ( Carassius auratus). We also investigated the potential impacts of MCP treatment on aromatase expression, on the synthesis and secretion of pituitary gonadotropins and on the regulation of hypothalamic gonadotropin-releasing hormones by real-time PCR and radioimmunoassay. Experiments were carried out during the period of gonadal late recrudescence following a 21-day exposure to 0.01, 0.10 and 1.00 mg L −1 of a pesticide containing 40% MCP in a semi-static exposure system. The results indicated that males in each MCP treatment group had much higher plasma levels of 17β-estradiol, suggesting that the induction of VTG production by MCP was indirectly caused by elevated levels of endogenous 17β-estradiol. MCP-induced plasma 17β-estradiol levels via interference with the reproductive axis at multiple potential sites in male goldfish: (a) MCP exposure enhanced the mRNA expression of gonadal aromatase, the enzyme that converts androgens into estrogens, consequently reducing plasma levels of testosterone and increasing plasma concentrations of 17β-estradiol; (b) MCP treatment increased follicle-stimulating hormone β subunit mRNA expression and protein secretion and decreased luteinizing hormone β subunit mRNA expression and protein secretion, thus interfering with gonadotropin synthesis and secretion at the pituitary level and leading to the disruption of reproductive endocrine control and androgen and estrogen balance.

Annual sex steroid and other physiological profiles of Pacific lampreys ( Entosphenus tridentatus)

We documented changes in plasma levels of estradiol 17-β (E2), progesterone (P), 15α-hydroxytestosterone (15α-T), thyroxine (T4), triiodothyronine (T3), protein, triglycerides (TGs), and glucose in adult Pacific lampreys ( Entosphenus tridentatus) held in the laboratory in two different years. Levels of E2 in both sexes ranged from 0.5 to 2 ng/mL from September to March, peaked in late April (2–4 ng/mL), and decreased in May, with levels higher in males than in females. Levels of P were low from September through April, but then increased substantially during May (2–4 ng/mL), with levels again highest in males. Levels of 15α-T in males were around 0.75 ng/mL through the winter before exceeding 1 ng/mL in April and decreasing thereafter, whereas females showed a gradual increase from 0.25 ng/mL in November to 0.5 ng/mL in April before decreasing. Thyroxine concentrations differed between fish in each year, with most having levels ranging from 0.75 to 2.5 ng/mL in the fall and winter, and only fish in 2003 showing distinct peaks (3–4 ng/mL) in early April or May. Plasma T3 was undetectable from November through mid-March before surging dramatically in April (ca. 150 ng/mL) and decreasing thereafter. Levels of protein, TGs, and glucose decreased or were stable during the fall and winter with TGs and glucose surging in late April to early May for some fish. Our study is the first to document long-term physiological changes in Pacific lampreys during overwintering and sexual maturation and increases our understanding of the life history of this unique fish.

Local effect of progesterone infusion into the porcine ovarian artery on androgen and estrogen secretion during the middle luteal phase

The present study was undertaken to elucidate whether an increased, but physiological, amount of progesterone (P(4)) supplied to the porcine corpus luteum (CL) affects luteal secretion of androgens and estrogens in freely moving gilts. On day 9 of the estrous cycle, the jugular veins as well as both ovarian arteries and both ovarian veins of gilts were cannulated. Progesterone was infused into the right ovarian arteries of experimental gilts (n=5) on days 10, 11 and 12 of the estrous cycle at a rate adequate to physiological retrograde transfer found during the middle luteal phase of the cycle. The left ovarian arteries of the experimental gilts were infused with saline. Both ovarian arteries of the control gilts (n=5) were infused with saline. The P(4) infusion rate was 0.62 microg/min (10 day), 2x0.62 microg/min (11 day) and 3x0.62 microg/min (12 day). Blood samples were collected from the jugular vein and both ovarian veins of the experimental and control gilts on days 10-12 of the estrous cycle before and after P(4) or saline infusion. The mean plasma androstenedione (A(4)) level in the ovarian vein ipsilateral to the P(4)-infused ovary was higher (p<0.01) on days 10-12 of the estrous cycle than those found in the contralateral ovarian vein of the experimental gilts as well as the control gilts. The ovarian venous level of testosterone (T) in the ovarian vein ipsilateral to the P(4)-infused ovary on days 10-12 of the estrous cycle was not significantly different (p>0.05) from those found in the contralateral ovarian vein of the experimental gilts and ovarian vein of the control gilts. However, on day 12, a decrease in T concentration was demonstrated in the ovarian vein ipsilateral to the P4-infused ovary in comparison to those of the contralateral and control ovarian veins. The mean plasma 17beta-estradiol (E(2)) level in the ovarian vein ipsilateral to the P(4)-infused ovary was lower on days 10-12 than those found in the contralateral ovarian vein of the experimental gilts and in the ovarian vein of the control gilts (p<0.001). The results of the present paper indicate that local elevation of P4 concentration in blood supplying the ovary during the middle luteal phase of the porcine estrous cycle affected local secretion of androgens and estrogens. The effect of P(4) on the secretion of androgens and estrogens suggested the existence of a short regulatory loop of a positive feedback for A(4) secretion and a negative feedback for E(2) secretion.

Individual, temporal, and population-level variations in circulating 11-ketotestosterone and 17β-estradiol concentrations in the oyster toadfish Opsanus tau

Sex steroid hormones are important for reproduction in all vertebrates, but few studies examine inter-individual, temporal, and population-level variations, as well as environmental influences on circulating steroid levels within the same species. In this study we analyzed plasma 11-ketotoestosterone (11-KT) and 17β-estradiol (E 2) levels in the oyster toadfish to test for 1) individual and temporal variations by serially sampling the same individuals during the reproductive and post-reproductive period, 2) variations in steroid levels among toadfish obtained from different sources or maintained under different holding conditions, and 3) correlations with environmental parameters. Results from serial sampling showed marked inter-individual variations in male 11-KT levels in two separate groups of toadfish, but no temporal differences from June to September. Females also showed inter-individual variations in E 2 concentrations, but most had elevated levels late in the reproductive season coincident with oocyte growth prior to winter quiescence. E 2 concentration, but not 11-KT, was positively correlated with water temperature, and negatively correlated with daylength and lunar phase. Maricultured toadfish held under constant conditions had elevated levels of E 2 and 11-KT that should be considered when using these fish for experimentation. This study provides important comparative information on the relationship between individual variations in steroid levels, and how they relate to physiological and environmental correlates in a model marine teleost.

Milk Inhibits the Regression of 7,12-Dimethylbenz(a)anthracene-Induced Mammary Tumors in Ovariectomized Rats

Epidemiological studies have yielded inconsistent results regarding the relation between the milk consumption and breast cancer risk. In this study, rats were induced mammary tumors by 7,12-dimethylbenz(a)anthracene. When tumors developed to acceptable levels, rats were placed into 1 of 3 treatment groups. Those in the negative control group and the milk group were ovariectomized, whereas those in the positive control group were sham operated. After grouping, tumor incidence remained 100%, and tumor number and volume increased in the positive control group. However, tumors in the 2 ovariectomized groups regressed. Compared with the negative control group, tumor incidence and tumor number and volume per rat in the milk group became significantly higher from Week 6 and Week 4, respectively. Insulin-like growth factor-I levels were borderline significantly higher in the milk group than in the negative control group at autopsy. Although plasma 17β-estradiol levels did not differ significantly, estrogenicity was found in the milk group because uterine weight was significantly heavier in the milk group than in the negative control group. In conclusion, commercial milk inhibited the regression of carcinogen-induced mammary tumors in ovariectomized rats.

Low dietary folate impairs glucose tolerance and plasma lipid profile in oral contraceptive-treated rats

Estrogen–progestogen oral contraceptive (OC) use is associated with abnormal lipid metabolism, impaired glucose tolerance and high prevalence of vascular complications. OC use has been shown to alter the requirements for folic acid. Therefore, the aim of the present study was to clarify the influence of dietary folic acid on OC-induced impaired glucose tolerance and abnormal plasma lipid profile in female Sprague– Dawley rats. Vehicle-treated and OC-treated rats were fed for 6 weeks with a control diet (750 μg folic acid/kg diet) while OC-treated folic acid deficient (FD) rats were fed for 6 weeks with a folic acid-deficient diet (250 μg folic acid/kg diet). OC receiving rats were treated with a combination of OC steroids (ethinyl estradiol and norgestrel) by oral gavage. OC treatment resulted in rats receiving folic acid deficient diet in impaired glucose tolerance, decreased high-density lipoprotein (HDL)-cholesterol and increased low-density lipoprotein (LDL)-cholesterol when compared with control rats. However, OC treatment did not result in impaired glucose tolerance or disturbed plasma lipid profile in rats receiving the same folic acid level as the controls. OC treatment led to significant decreases in plasma levels of 17β-estradiol and testosterone in both groups. OC administration in rats with folic acid deficient diet significantly lower HDL-cholesterol and higher LDL-cholesterol levels while plasma levels of 17β-estradiol and testosterone were similar in both OC-treated groups. Conclusion: These results demonstrate impaired glucose tolerance and disturbed plasma lipid profile induced by OC treatment in folic acid deficient rats and suggest that inadequate folic acid intake might contribute to increased cardiovascular risk during OC use that could be prevented by proper oral folic acid intake.

Exogenous leptin promotes the recovery of regressed ovary in fasted ducks

The present study was undertaken to examine the effect of administered recombinant mouse leptin on the recovery of regressed ovary in fasted ducks. Twenty-eight ducks were divided into five groups: fed ad libitum (control; n = 5), fasted control (FC; n = 5), fasted + low dose of leptin (F + L; n = 5), fasted + medium dose of leptin (F + M; n = 5) and fasted + high dose of leptin (F + H; n = 3). All four fasted groups were fasted for 2 days and then ad libitum and the ducks were treated with leptin at doses of 0 (control and FC), 50 (F + L), 250 (F + M) and 1000 (F + H) μg/kg body weight/day on day 3–5. Results showed that a moderate dose of leptin (250 μg/kg body weight/day) injected during the re-feeding period: (i) promoted the recovery of the regressed ovary as evidenced by an increase in ovary weight and recovery of yellow hierarchical follicles; (ii) elevated the plasma 17β-estradiol (E 2) level; (iii) increased the mRNA levels of ovary follicle-stimulating hormone receptor (FSHR), luteinizing hormone receptor (LHR) and estrogen receptor-β (ER-β). Furthermore, the results also showed that a high dose of leptin (1000 μg/kg body weight/day) may have a negative effect on the recovery of the regressed ovary. In conclusion, this study indicates that, in ducks, leptin may be involved in the recovery of the regressed ovary caused by 2 days of fasting. This effect may be related to increased plasma E 2 levels and stimulation of the mRNA levels of ovarian FSHR, LHR and especially ER-β.

Additive effects of advanced temperature and photoperiod regimes and LHRHa injection on ovulation in Atlantic salmon (Salmo salar)

In order to evaluate manipulation of spawning time as a potential means to extend 0+ Atlantic salmon (Salmo salar) smolt production in Tasmania, Australia, female salmon were exposed to a natural/simulated natural (42°S) photoperiod or an advanced (L:D 9:15) photoperiod from the austral summer solstice (20 December) under natural or advanced (~6 °C below natural temperature) temperature conditions. In late summer (26 February) injections of a commercial LHRHa preparation or vehicle (propylene glycol) commenced. Regular ovulation checks were conducted and ova were fertilised using milt from LHRHa-injected males held under matching photo-thermal conditions. Plasma levels of 17β-estradiol (E2) and testosterone (T) were monitored and reproductive success (cumulative % ovulation, % fertilisation and % survival to the eyed-egg stage) was recorded. Ovulations commenced first (09 March) in LHRHa-treated fish that experienced advanced photoperiod and thermal regimes whereas sham-treated fish exposed to natural photoperiod and temperature conditions where the last to ovulate (22 May–08 June). Treatment-related sequential changes in the timing of ovulations were reflected by sequential advances in the timing of peaks in plasma levels of E2 and T. The fertilisation of ova from LHRHa-treated fish that experienced advanced photoperiod and thermal regimes was significantly reduced (~52%) relative to all other treatments (>80%) but there were no significant treatment-related differences in the survivals of eggs to the eyed stage (~50–90%). Consequently, a maximum advance in the timing of median ovulation of 71 days and commercially acceptable eyed-egg yields were generated, demonstrating that combinations of photoperiod, thermal and hormone treatments may be employed to significantly extend spawning and thereafter increase the availability of 0+ smolts for grow-out.

Influence of Estrus of Dairy Goats on Somatic Cell Count, Milk Traits, and Sex Steroid Receptors in the Mammary Gland

Two experiments were conducted to study the effect of the stage of a spontaneous estrus cycle on milk yield and constituents [somatic cell count (SCC), fat, protein, caseins, lactose, and urea content] and on estrogen receptor-α (ERα) and progesterone receptor (PR) immunostaining in the mammary gland. In experiment I, the major components of milk and SCC were monitored weekly in 80 lactating Saanen goats for 6 wk, whereas detection of estrus was daily. In experiment II, milk samples were collected daily for SCC determination during 1 spontaneous estrus (d 0) until the second spontaneous estrus in 14 Saanen goats. The day of the estrous cycle was confirmed by plasma progesterone and 17β-estradiol levels. Immunoreactivity of ERα and PR was analyzed in mammary gland samples of 8 Saanen goats (d 0, n=4; d 10, n=4) and the number of positive nuclei and intensity of the staining were evaluated in 1,000 cells. In experiment I, milk casein and protein percentages were significantly affected by the stage of estrous cycle; during proestrus and estrus, these variables were higher (3.32±0.06 and 4.44±0.08) than during metestrus (3.03±0.07 and 4.07±0.10), but not higher than during diestrus (3.23±0.06 and 4.35±0.09, respectively). In experiment II, daily measurement of SCC revealed higher levels at estrus (7,195±672×103 cells/mL) and a decline toward the luteal phase (1,694±672±103 cells/mL). Estrogen receptor-α and PR immunostaining were exclusively detected on epithelial cells. The percentage of positive nuclei to ERα was higher on d 0 than on d 10 (75.4±8.8 vs. 68.3±8.8%), but no change was observed for PR (4.0±0.3 vs. 3.5±0.4%). The average immunostaining intensity for both receptors was greater on d 0 than on d 10 (ERα : 1.44±0.02 vs. 1.35±0.02; PR: 0.079±0.008 vs. 0.057±0.008). The high SCC at estrus in experiment II was associated with high plasma estradiol and low progesterone, suggesting that the increased SCC could be brought about by the estrogen-induced proliferation and exfoliation of epithelial cells. In addition, this action may be supported by the higher sensitivity to estrogens (ERα content) found at d 0.

Disruption of gonadal maturation in cultured Senegalese sole Solea senegalensis Kaup by continuous light and/or constant temperature regimes

A major problem in the development of Senegalese sole Solea senegalensis intensive culture is the poor control on reproduction, in part due to the lack of knowledge on the precise role of photoperiod and temperature. Thus, gonadal maturation was evaluated by assessing the sequential changes in plasma levels of 17β-estradiol (E 2), 11-ketotestosterone (11-KT), and testosterone (T) in both female and male cultured Senegalese sole (F1 generation) exposed to various combinations of constant or naturally-fluctuating daylength and water temperature. Under natural photoperiod (NP; 36° N), exposure to constant temperature (t0; 18–20 °C) disrupted gonadal development, as indicated by a lower incidence (in comparison with naturally-fluctuating water temperature; 14–24 °C) of females at advanced maturation (from February to April: 12 vs. 33%) and running males (from February to May: 46% vs. 57%), and the reduced mean (± S.E.M.) sex steroid plasma levels (female peak E 2 levels: 2.9 ± 0.28 vs. 1.8 ± 0.3 ng ml − 1 ; male peak T levels: 1.5 ± 0.14 vs. 0.9 ± 0.06 ng ml − 1 ). Therefore, the onset and progression of gonadal development in this species seem to be strongly (“proximally”) influenced by fluctuating water temperature. When compared to NP and t0, exposure to continuous light (LL) under t0 significantly reduced steroid production (female peak E 2 levels: 1.8 ± 0.28 vs. 0.5 ± 0.05 ng ml − 1 ; male peak 11-KT levels: 9.4 ± 1.06 vs. 5.4 ± 1.33 ng ml − 1 ) and subsequently gonadal development (lower proportions of females at intermediate [46 vs. 6%] and advanced maturation [12 vs. 0%] from February to April and of RM [46 vs. 33%] from February to May). Thus, the seasonal changes of daylength would be crucial for normal gonadal development, being its cueing effects of higher magnitude than those of water temperature. The present report constitutes the first systematic study focused on the environmental control of reproductive events in Senegalese sole.

Maintenance of lung myeloperoxidase activity in proestrus females after trauma-hemorrhage: upregulation of heme oxygenase-1

Previous studies showed that females in the proestrus stage of the reproductive cycle maintain organ functions after trauma-hemorrhage. However, it remains unknown whether the female reproductive cycle is an important variable in the regulation of lung injury after trauma-hemorrhage and, if so, whether the effect is mediated via upregulation of heme oxygenase (HO)-1. To examine this, female Sprague-Dawley rats during diestrus, proestrus, estrus, and metestrus phases of the reproductive cycle or 14 days after ovariectomy underwent soft tissue trauma and then hemorrhage (mean blood pressure 40 mmHg for 90 min followed by fluid resuscitation). At 2 h after trauma-hemorrhage or sham operation, lung myeloperoxidase (MPO) activity and intercellular adhesion molecule (ICAM)-1, cytokine-induced neutrophil chemoattractant (CINC)-1, CINC-3, and HO-1 protein levels were measured. Plasma 17beta-estradiol concentration was also determined. The results indicated that trauma-hemorrhage increased lung MPO activity and ICAM-1, CINC-1, and CINC-3 levels in ovariectomized females. These parameters were found to be similar to sham-operated animals in proestrus female rats subjected to trauma-hemorrhage. Lung HO-1 protein level in proestrus females was increased significantly compared with female rats subjected to trauma-hemorrhage during diestrus, estrus, and metestrus phases of the reproductive cycle and ovariectomized rats. Furthermore, plasma 17beta-estradiol level was highest in proestrus females. Administration of the HO inhibitor chromium mesoporphyrin prevented the attenuation of shock-induced lung damage in proestrus females. Thus these findings suggest that the female reproductive cycle is an important variable in the regulation of lung injury following trauma-hemorrhage and that the protective effect in proestrus females is likely mediated via upregulation of HO-1.

Induction of spawning of captive-reared Senegal sole (Solea senegalensis) using different administration methods for gonadotropin-releasing hormone agonist

Captive-reared Senegal sole were treated with intramuscular injection or sustained-release implants of gonadotropin-releasing hormone agonist [D-Ala6, Pro9, NEt] GnRHa (GnRHa) to induce spermiation and spawning. Fish were treated with GnRHa during spring (April–May) or autumn (October), the natural spawning seasons known to occur in wild Senegal sole. During spring, females injected with a dose of 5μg GnRHa kg−1 three times a week, or treated with a single GnRHa-loaded implant (50μg kg−1) showed multiple ovulations and spawns within a period of approximately 30 days. Plasma levels of 17β-estradiol (E2) were elevated at 7days post-treatment, preceding the spawns with the highest fecundity, concomitant with a decrease in the levels of plasma testosterone (T). During autumn, however, females changed their responsiveness to GnRHa treatment, a dose of 5μg kg−1 being ineffective in inducing spawning, while a dose of 1μg kg−1 induced a few spawns. Accordingly, plasma E2 levels showed a small increase after injection of 1μg kg−1 GnRHa. In contrast to females, GnRHa injection or implantation in males was ineffective in enhancing spermiation or milt production, regardless of the season when the treatments were applied. However, GnRHa treatment in males increased plasma levels of T and 11-ketotestosterone (11-KT) during spring, while in autumn the levels of plasma androgens decreased after GnRHa injection. These results show that administration of GnRHa during spring either by injection or sustained-release implants induces multiple spawns in captive Senegal sole, although these treatments were ineffective in inducing or enhancing sperm production in males.

Cyclic estradiol replacement attenuates stress-induced c-Fos expression in the PVN of ovariectomized rats

Estradiol modulates stress reactions in female rats. Several studies showed anxiolytic effects of estradiol in behavioral tests, but the underlying mechanisms are still unclear. The aim of the current study was to explore how estradiol-treated rats respond to acute and chronic stress compared to ovariectomized rats. Ovariectomized rats received vehicle or 17β-estradiol injections (10 μg/250 g) once every 4 days, which induced alternating high and low plasma 17β-estradiol levels. Stress was presented by daily exposure to an adverse environment in which the animals received five footshocks for either 3 or 22 days. Under control conditions no differences were observed, but as soon as stress was applied, reactions of ovariectomized and estradiol-treated rats diverged. Both acute and chronic stress increased the c-Fos protein expression in the paraventricular nucleus (PVN) of the hypothalamus. Cyclic estradiol treatment reduced this stress-induced activation of the PVN, an effect that seems to be dependent on the plasma estradiol levels. No differences in stress-induced corticosterone responses were revealed between the treatment groups. An increase in the number of ERβ-expressing cells in the PVN of ovariectomized and estradiol-treated rats during chronic stress implied increased ERβ-mediated mechanisms during these conditions. The dampening effect of estradiol on the excessive stress-induced activity in the PVN may be beneficial for the animal in its response to chronic recurrent stress by reducing the output of the PVN.

Differential expression of largemouth bass ( Micropterus salmoides) estrogen receptor isotypes alpha, beta, and gamma by estradiol

The expression levels of three estrogen receptor (ER) isotypes alpha, beta, and gamma were quantified in female largemouth bass ( Micropterus salmoides) (LMB) liver, ovary, brain, and pituitary tissues. ER alpha and beta expression predominated in the liver, while ERs beta and gamma predominated in the other tissues. Temporally in females, ER alpha was highly up-regulated, ER gamma was slightly up-regulated, and ER beta levels remained unchanged in the liver when plasma 17-β estradiol (E 2) and vitellogenin (Vtg) levels were elevated in the spring. In ovarian tissue from these same fish, all three ERs were maximally expressed in the fall, during early oocyte development and prior to peak plasma E 2 levels. When males were injected with E 2, ER alpha was highly inducible, ER gamma was moderately up-regulated, and ER beta levels were not affected. None of the ER isotypes were induced by E 2 in gonadal tissues. These results combined suggest that the ERs themselves are not regulated in the same manner by E 2, and furthermore, do not contribute equally to the transcriptional regulation of genes involved in fish reproduction such as Vtg.

Differential effects of 17beta-estradiol upon stroke damage in stroke prone and normotensive rats.

We previously reported that during pro-estrus (high endogenous estrogen levels), brain damage after middle cerebral artery occlusion (MCAO) was reduced in stroke-prone spontaneously hypertensive rats (SHRSP) but not in normotensive Wistar Kyoto rat (WKY). In the present study, we examined the effect of exogenous estrogen on brain damage after MCAO in SHRSP and WKY. A 17beta-estradiol (0.025 mg or 0.25 mg, 21 day release) or matching placebo pellet was implanted into ovariectomized WKY and SHRSP (3 to 4 months old) who then underwent distal diathermy-induced MCAO 2 weeks later. Plasma 17beta-estradiol levels for placebo and 17beta-estradiol groups were as follows: WKY 0.025 mg 16.4 +/- 8.5 (pg/mL, mean +/- SD) and 25.85 +/- 12.6; WKY 0.25 mg 18.2 +/- 9.0 and 69.8 +/- 27.4; SHRSP 0.25 mg 20.7 +/- 8.8 and 81.0 +/- 16.9. In SHRSP, infarct volumes at 24 hours after MCAO were similar in placebo and 17beta-estradiol groups: SHRSP 0.025 mg 126.7 +/- 15.3 mm (n = 6) and 114.0 +/- 14.1 mm (n = 8) (not significant); SHRSP 0.25 mg 113.5 +/- 22.3 mm (n = 8) and 129.7 +/- 26.2 mm (n = 7) (not significant), respectively. In WKY, 17beta-estradiol significantly increased infarct volume by 65% with 0.025 mg dose [36.1 +/- 20.7 mm (n = 8) and 59.7 +/- 19.3 mm (n = 8) (P = 0.033, unpaired t-test)] and by 96% with 0.25 mg dose [55.9 +/- 36.4 mm (n = 8) and 109.7 +/- 6.7 mm (n = 4) (P = 0.017)]. Thus, 17beta-estradiol increased stroke damage in normotensive rats with no significant effect in stroke-prone rats. Despite being contrary to our hypothesis, our findings add substance to the recently reported negative effects of 17beta-estradiol in clinical studies.

Seasonal steroid hormone levels and their relation to reproduction in the Western Diamond-backed Rattlesnake, Crotalus atrox (Serpentes: Viperidae)

We report seasonal variation in steroid hormone levels in blood samples from free-ranging Western Diamond-backed Rattlesnakes ( Crotalus atrox), and the relationship between these hormones and events in the reproductive cycle. At a field site in the Sonoran Desert of south-central Arizona, we collected monthly blood samples over the course of two active seasons from 17 radiotelemetered females, and over three active seasons from 103 randomly encountered males. We used radioimmunoassay to measure plasma levels of 17β-estradiol, progesterone, corticosterone, and testosterone in samples from females, and corticosterone and testosterone in samples from males. Non-reproductive females have consistently low levels of circulating 17β-estradiol, progesterone, and testosterone throughout the year. In reproductive females, 17β-estradiol levels increase dramatically and testosterone levels increase modestly during vitellogenesis in April and May, while progesterone levels increase dramatically at ovulation in June and then steadily decline until parturition in August. Corticosterone levels appear relatively constant in non-reproductive females, whereas reproductive females show increased levels at the end of gestation. Plasma testosterone levels in males are low in early summer and are elevated during spring and late summer, corresponding to the two mating periods of C. atrox. Plasma corticosterone levels in males did not vary seasonally and were not related to testosterone levels.

Mechanisms of lipopolysaccharide-induced changes in effects of contractile agonists on pregnant rat myometrium

ObjectiveThe study was undertaken to investigate the mechanisms underlying enhanced uterine contractility induced by lipopolysaccharide (LPS) in pregnant rats. Study designWistar rats were administered intrauterine either LPS (50 μg) or normal saline solution (0.05 mL) on day 17 of gestation. On day 19, the animals were killed and uterus was isolated for isometric recording, 45Ca++ influx measurement, and determination of plasma membrane Na+-K+-ATPase. ResultsUterine strips, taken from LPS-treated rats, displayed a marked increase in amplitude of spontaneous rhythmic contractions compared with controls. Enhancement in the sensitivity of uterine strips to agonists such as oxytocin, 5-hydroxytryptamine (5-HT), and BAY K8644 was also observed in rats treated with LPS. Cyclo-oxygenase-2 inhibitor, nimesulide (10 μmol/L) had no significant effect on the LPS-induced increase in spontaneous rhythmic contractions. On the other hand, nimesulide attenuated the increased sensitivity of uterine strips to oxytocin induced by LPS. Nimesulide significantly inhibited 5-HT–induced uterine contractions in both control and LPS-treated rats. However, the enhanced sensitivity of uterine strips to 5-HT was evident even in the presence of nimesulide in rats treated with LPS. Nifedipine-sensitive 45Ca++-influx into uterine strips both in the basal state as well as those stimulated by high K+ (80 mmol/L) and 5-HT (1 μmol/L) was greater in LPS-treated group compared with the controls. LPS treatment caused a marked inhibition in the Na+-K+-ATPase activity of the uterine plasma membrane compared with controls. LPS had no effect on plasma 17β-estradiol levels. ConclusionLPS appears to increase uterine contractility of pregnant rats both through the release of endogenous prostaglandins and increased influx of Ca++ through L-type Ca++ channels. Inhibition of sodium pump by LPS may be an additional mechanism in augmentation of uterine excitability.

Maintenance of Atlantic salmon ( Salmo salar) at elevated temperature inhibits cytochrome P450 aromatase activity in isolated ovarian follicles

Atlantic salmon ( Salmo salar) broodstock were transferred from natural (12–16 °C) to controlled temperatures of 14, 18 or 22 °C for 3 months during vitellogenesis. Fertility and survival were significantly reduced in eggs from broodstock held at 22 °C relative to 14 or 18 °C. Endocrine mechanisms were disrupted after only one month at 22 °C, as evidenced by decreased plasma vitellogenin (Vtg) and increased plasma testosterone (T) levels and, at later stages, decreased levels of plasma 17β-estradiol (E 2). In vitro incubations of isolated ovarian follicles were carried out at monthly intervals, with follicles exposed to human chorionic gonadotropin, N-2-0-dibutyryladenosine 3,5-cyclic monophosphate, and the gonadal steroid precursors 17-hydroxyprogesterone, androstenedione, and T. After one month of exposure to controlled temperature, T synthesis was generally enhanced in response to all treatments at all temperatures, but E 2 synthesis was inhibited at 22 °C, suggesting temperature impairment of cytochrome P450 aromatase (P450 arom) synthesis or activity. The effect became less marked as follicles matured suggesting that temperature sensitivity is stage dependent. The results of this study suggest that the inhibitory effects of elevated temperature on E 2 and Vtg synthesis, and subsequent egg development found in the present and earlier studies, arise at least partly, from temperature modulation of P450 arom.