Exogenous Estradiol Research Articles

Impact of chronic treatment of ewes with estradiol-17beta or progesterone on oxytocin receptor gene transcription and ovarian oxytocin secretion.

Three experiments were conducted, the objectives of which were to 1) examine the effects of exogenous estradiol (E2) and progesterone (P4) on uterine concentrations of oxytocin receptors (OTR) and OTR mRNA, as well as the effect of exogenous P4 on progesterone receptors (PR) during the late luteal phase of the cycle, and 2) ascertain whether chronic E2 treatment of ewes during the cycle would alter prostaglandin F2alpha (PGF2alpha)-induced secretion of luteal oxytocin (OT). In experiment 1, 15 ewes were assigned to a control (n = 5; 2 ml corn oil [CO] s.c. on Days 4-14 of the estrous cycle) and two treatment groups (n = 5 each) receiving either 250 microg E2 s.c. (Days 4-14) or 10 mg P4 s.c. (CO on Days 4-10 and P4 on Days 11-14). Endometria and corpora lutea were removed on Day 15 of the cycle. Mean luteal weights were greater in treated than in control ewes (p < 0.05). Endometrial concentrations of OTR and OTR mRNA were significantly greater in control than in E2- or P4-treated ewes. In experiment 2, five ewes each were treated s.c. with CO or 10 mg P4 on Days 11-14 of the cycle; endometria were then removed on Day 15 for PR assay. Endometrial concentration of PR did not differ between groups. Experiment 3 consisted of 20 ewes assigned to four groups in a 2 x 2 factorial arrangement. Treatment consisted of two dosages of E2 (0 or 250 microg/day) in 2 ml CO and two dosages of PGF2alpha analogue (0 or 125 microg Estrumate). All ewes were injected s.c. with E2 or CO for 11 days as described for experiment 1. On Day 15, all ewes received an i.v. injection of PGF2alpha or saline (Time 0); then jugular blood was collected at frequent intervals for analysis of serum concentrations of OT. PGF2alpha induced a release of OT in control and E2-treated ewes (p < 0.05) compared to the value in saline-treated ewes. Collectively, these data suggest that in cycling ewes, exposure of the uterus to increased concentrations of E2 or P4 causes down-regulation of OTR as a consequence of suppression of the OTR gene. Chronic E2 treatment of ewes during the cycle does not act directly on the ovary to alter the stores of luteal OT.

Intraspecific Variation in the Induction of Female Sexual Receptivity in Prairie Voles

ROBERTS, R. L., B. S. CUSHING AND C. S. CARTER. Intraspecific variation in the induction of female sexual receptivity in prairie voles. Physiol Behav 64(2) 209–212, 1998. Prairie voles ( Microtus ochrogaster) are monogamous New World rodents which show geographic variation in social behavior. In this study, parameters of female reproduction which might be related to mating system were compared in prairie voles from eastern Kansas (KAN) versus central Illinois (ILL). KAN females showed a more rapid onset of natural estrus following exposure to a male and were more likely to respond to injections of a low dose (0.5 μg) of exogenous estradiol benzoate than ILL females. Neither mating duration nor pregnancy success after mate removal differed in KAN versus ILL females. These results suggest that ILL voles are less sensitive than KAN voles to the estrus-inducing effects of either endogenous or exogenous estrogen, supporting the hypothesis that variations in reproductive strategy occur among geographically discrete populations of prairie voles.

Suppressive effect of oestradiol on chemical hepatocarcinogenesis in rats

Aims —To examine the effects of oestradiol and testosterone on the early carcinogenic changes expressed in rat liver from the diethylnitrosamine (DEN), 2-acetylaminofluorene (AAF), partial hepatectomy (PH) model of hepatocarcinogenesis. Methods —Preneoplastic liver lesions were evaluated using immunohistochemical analysis of glutathione-S-transferase placental form (GST-P) expression; oestrogen and androgen receptor levels were measured by radioimmunoassay. Results—Oestradiol administration to non-castrated DEN-AAF-PH treated males resulted in a decrease in the area of GST-P positive foci, while testosterone increased the serum oestradiol level and reduced the area. In males, castration alone and castration with oestradiol replacement significantly reduced the GST-P positive area, and increased the hepatic oestrogen receptor level. In DEN-AAF-PH treated females, castration with testosterone replacement was associated with a significant increase in the GST-P positive area and the hepatic androgen receptor level. Conclusion —These findings suggest that exogenous and endogenous oestradiol can suppress chemical hepatocarcinogenesis. It appears that oestrogen receptors may be involved in the inhibition of malignant transformation of preneoplastic liver cells, while androgens and androgen receptors are involved in hepatocarcinogenesis.

Synchronization of endogenous and exogenous FSH stimuli in controlled ovarian hyperstimulation (COH).

We have previously observed that exogenous oestradiol can delay the intercycle increase in plasma follicle stimulating hormone (FSH). The increase in plasma FSH that follows discontinuation of exogenous oestradiol peaks after 3 days. We have now studied the possibility of using exogenous oestradiol to synchronize the increase in endogenous FSH with the onset of human menopausal gonadotrophin (HMG) treatment in controlled ovarian hyperstimulation (COH). A total of 30 women aged 35.1+/-6.3 years (mean+/-SD) undergoing ovarian stimulation received 2 mg of oestradiol valerate twice daily starting on day 25 of the previous menstrual cycle until the first Tuesday following menses. Ovarian stimulation was initiated 3 days later. On the last day of oestradiol treatment, plasma oestradiol, FSH and luteinizing hormone (LH) (mean+/-SEM) were 566+/-53 (pmol/l), 3.8+/-0.4 (IU/l) and 5.5+/-0.8 (IU/l) respectively. After 3 days, the FSH and LH (mean+/-SEM) had increased to 6.7+/-0.7 and 6.9+/-0.7 (IU/l) respectively while oestradiol decreased to 251+/-29 (pmol/l). The mean number (+/-SEM) of HMG ampoules used was 25.1+/-2.7 and treatment lasted 11.3+/-0.9 days. Five women became pregnant for a pregnancy rate (ongoing) of 19 (15)%. If all women aged >40 years (six women who did not become pregnant) were excluded from analysis the pregnancy rate (ongoing) was 24 (19%). These results indicate that exogenous oestradiol can safely be used for the synchronization of endogenous and exogenous FSH stimuli in COH. This approach provides the practical advantage of permitting an advanced timing of the onset of COH treatments when gonadotrophin-releasing hormone (GnRH) agonists are not used, which improves treatment convenience for patients and team members alike. Further development of this model may enable control of the onset of natural cycles which may find practical applications for timing assisted reproductive techniques (intrauterine insemination or in-vitro fertilization) in the natural cycle.

Glucoprivic induction of Fos immunoreactivity in hypothalamic dopaminergic neurons.

The hypothalamic neurotransmitter dopamine (DA) regulates pituitary secretion of the glucoregulatory hormones, growth hormone (GH) and adrenocorticotropin (ACTH). The glucose antimetabolite, 2-deoxy-D-glucose (2DG), elicits expression of the proto-oncogene product Fos, which is expressed in hypothalamic structures where DA is synthesized. These studies utilized dual-label immunocytochemistry to determine whether discrete DA neuron populations in this region of the brain exhibit Fos immunoreactivity (-ir) in response to glucopenia. Ovariectomized female rats implanted s.c. with exogenous estradiol or vehicle were injected with 2DG (400 mg/kg, i.p.) or saline, and sacrificed 2 h later. Whereas Fos-ir was negligible after saline administration, 2DG induced expression of Fos-ir by TH-ir neurons in the paraventricular (PVN), periventricular (Pe) and arcuate nuclei (ARC), and in the anterior hypothalamic area (AHA). TH-ir neurons in the zona incerta did not express Fos-ir following 2DG. Although mean numbers of co-labeled neurons in the Pe, PVN and AHA did not differ between estradiol- and non-steroid-treated rats, the former group exhibited significantly higher numbers of TH-positive plus Fos-positive neurons in the ARC in response to 2DG. These results reveal the functional responsiveness of discrete DA neuron populations to glucoprivation, and indicate that estradiol enhances cellular accumulation of Fos-ir by ARC DA neurons during this metabolic challenge.

Gonadotropin-releasing hormone messenger ribonucleic acid expression changes before the onset of the estradiol-induced luteinizing hormone surge in the ewe.

The preovulatory LH surge in the ewe is stimulated by the massive and sustained release of GnRH into the pituitary portal vessels. This study has examined the temporal relationship between changes in LH secretion and GnRH messenger RNA (mRNA) expression at the time of the estradiol-induced LH surge. Ovariectomized Clun Forest ewes were treated with exogenous progesterone and estradiol (E) to mimic estrous cycle concentrations of these gonadal steroids and to induce the LH surge. Ewes were killed at five time points relative to the time of onset of the LH surge: pre-E, before E insertion (n = 6); presurge, after E insertion and 8-10 h before surge onset (n = 5); ascending limb, 2-6 h after surge onset (n = 5); midpeak, 9-12 h after surge onset (n = 5); and postsurge, 21-27 h after surge onset (n = 5). Control animals (n = 5/group), which received no E, were killed at identical time intervals alongside the E-treated ewes. Coronal sections containing the diagonal band of Broca through to the anterior hypothalamus were processed for cellular in situ hybridization using an 35S-labeled oligonucleotide probe complementary to ovine GnRH. No changes were found in the number of GnRH mRNA-expressing cells detected in the rostral preoptic area or the medial septum in either gonadal steroid-treated or control ewes. In contrast, cellular GnRH mRNA expression (as assessed by silver grain density) decreased significantly (P < 0.05) between presurge and ascending limb groups within both the rostral preoptic area (0.64 +/- 0.06 vs. 0.43 +/- 0.05 silver grain density/microm2) and medial septum cells (1.08 +/- 0.09 vs. 0.77 +/- 0.07). No significant changes were detected in control ewes. These results show that the estradiol-induced LH surge in the ewe is associated with a decrease in GnRH mRNA expression that occurs in advance of the onset of the GnRH surge. This suggests that neural mechanisms controlling GnRH biosynthesis may be distinct from those regulating GnRH secretion.

Suppressive effect of oestradiol on chemical hepatocarcinogenesis in rats

Aims—To examine the effects of oestradiol and testosterone on the early carcinogenic changes expressed in rat liver from the diethylnitrosamine (DEN), 2-acetylaminofluorene (AAF), partial hepatectomy (PH) model of hepatocarcinogenesis.Methods—Preneoplastic liver...

Effect of exogenous estradiol on plasma concentrations of somatotropin, insulin-like growth factor-I, insulin-like growth factor binding protein activity, and metabolites in ovariectomized angus and braham cows

To determine the effect of breed and estradiol-17β on selected hormones and metabolites, ovariectomized (⪖3 mo) Angus ( n = 14) and Brahman ( n = 12) cows were paired by age and body weight and randomly assigned as either nonimplanted controls (CON) or implanted with estradiol (E2) for 45 d. After Day 7 and through Day 42, plasma concentration of somatotropin was greater for E2 than CON cows (treatment X day, P < 0.05). During an intensive blood sampling on Day 36, E2 cows tended (P < 0.10) to have greater somatotropin pulse amplitudes than CON cows, but other parameters of somatotropin release were not affected (P > 0.10) by E2 treatment. The effect of breed was apparent on Day 36 as Brahman cows had greater (P < 0.05) somatotropin pulse amplitude, basal secretion, and mean concentration than Angus cows. Overall, plasma concentration of IGF-I was greater (P < 0.01) for E2 than CON cows (158.3 vs. 104.2 ng/ml) and was greater for Brahman than Angus cows (164.1 vs. 98.4 ng/ml). However, there was a trend (P < 0.10) for a treatment X breed X day interaction for IGF-I (i.e., the magnitude of increase in IGF-I concentration was greater in E2-Angus than E2-Brahman cows). After Day 7 and through Day 42, total plasma IGF binding protein (IGFBP) activity was greater (P < 0.01) for E2 than CON cows. Ligand blotting revealed at least five forms of IGFBP activity, and E2 cows had greater (P < 0.05) binding activity of IGFBP-3 and the 30- and 32-kDa IGFBP than CON cows. Brahman cows had greater (P < 0.05) IGFBP-3 and the 32-kDa IGFBP than Angus cows. After Day 14 and through Day 42, concentration of urea nitrogen (PUN) was greater (P < 0.001) for CON than E2 cows (treatment X day, P < 0.001). Brahman had greater (P < 0.01) PUN than Angus cows (16.6 vs. 14.2 mg/dl). Plasma concentration of glucose was greater (P < 0.01) for E2 than CON cows (78.9 vs. 76.4 mg/dl) but was not affected (P > 0.10) by breed. In summary, these data suggest that some, but not all, of the positive effects of estradiol on peripheral concentration of IGF-I and IGFBP activity can be attributed to increased somatotropin. Moreover, breed influenced basal and E2-induced secretion of somatotropin and IGF-I such that differences between Brahman and Angus cows in plasma IGF-I concentrations were abated within 3 wk of estradiol implantation. Thus, breed influences the metabolite and hormonal response of cattle to estrogenic implants.

Stimulation of LH secretion in sheep by central administration of corticotrophin-releasing hormone.

Corticotrophin-releasing hormone (CRH) has been proposed as a mediator of the antireproductive effects of stress through an action within the hypothalamus to inhibit GnRH secretion. This hypothesis was tested in sheep by studying the responses to central administration of CRH in both sexes and in both seasons. Sexually mature, Ile-de-France ewes and Romanov rams that had been gonadectomized and implanted with a permanent guide cannula into the third cerebral ventricle were used. Ewes were studied in the presence and absence of exogenous oestradiol plus progesterone, in both the breeding and anoestrous seasons. All rams were treated with testosterone and were studied only during the breeding season. Each observation involved serial samples (every 10 min) of jugular blood for 5 h before (control) and 5 h after an intracerebroventricular (i.c.v.) injection of either saline (vehicle) or 5 nmoles CRH in 20 microliters vehicle. The saline injections did not affect any of the endocrine variables measured; however, CRH always increased cortisol concentrations in jugular plasma. In the absence of treatment with replacement sex steroids, icv injection of CRH had no effect on pulsatile LH secretion in females either during the breeding season or during anoestrus. However, LH pulse frequency and mean LH concentrations increased significantly on every occasion on which animals were treated with sex steroids. Treatment with CRH also increased LH secretion in the testosterone-treated rams. It is concluded that, contrary to the hypothesized role of CRH as an inhibitor of reproductive activity, this neuropeptide stimulates pulsatile LH (and thus GnRH) secretion, at least in this species. The fact that gonadal steroids seem to be obligatory for the expression of this effect suggests that the protocols used in past studies need to be reassessed.

The incidence of renal anomalies at full term in fetal rats is synergistically increased by estradiol (but not testosterone) supplementation on day 18 of alcoholic gestation

Background/Purpose: Fetal alcohol syndrome is characterized by facial dysmorphology, mental and growth retardation, and somatic anomalies including hydronephrosis. The authors sought to determine the influence of exogenous testosterone or estradiol on the incidence of hydronephrosis in a rodent model of fetal alcohol syndrome (FAS). Methods: Pregnant rats were fed a liquid diet containing 35% ethanol-derived calories from gestation day 6 through 15, with exogenous testosterone or estradiol supplementation on day 18. On day 20, fetal kidneys were examined for evidence of hydronephrosis, and fetal serum estradiol concentrations were determined by radioimmunoassay. Results: Maternal estrogen supplementation resulted in very high fetal serum estradiol levels that were not additionally increased by alcoholism. Despite this fact, the expression of renal malformations was highest in the alcoholic, estradiol-supplemented offspring. Additionally, the rate of renal malformations was significantly higher in the estrogen-supplemented alcoholic group than in the strictly estradiol animals, yet the fetal serum estradiol concentrations did not differ between the two groups. Conclusions: This suggests that ethanol may act synergistically with estradiol to increase the rate of renal anomalies including hydronephrosis. Such damage may persist via a suppression of normal testosterone-stimulated renal growth and development. FAS includes significant renal anomalies characterized by hydronephrosis in both animal models and affected children. Although the long-term functional sequelae of hydronephrosis and reflux are well known, the progression of renal disease in FAS children remains to be documented.

Correlation among Thermosensitive Period, Estradiol Response, and Gonad Differentiation in the Sea TurtleLepidochelys olivacea

Reptile embryos with temperature sex determination have a thermosensitive period (TSP). The finding that exogenous estradiol (E2) overcomes the effect of male-promoting temperature led to the idea that temperature may regulate estrogen concentration in the gonad during TSP. Since interspecific variations in TSP and in the effect of exogenous E2 exist, we undertook a study in the olive ridleyLepidochelys olivacea.Four parameters were correlated: the TSP (time dimension), the thermosensitive stages (rate of development), gonad development (histological aspect), and the estradiol response. Two kinds of experiments were performed: (1) Eggs were shifted once, at different stages of development, from a male-promoting temperature to a female-temperature (or vice versa) for the remainder of development. (2) Eggs at male-promoting temperature were treated once with 6 or 12 μg of estradiol (E2) at various times of incubation. Sex ratio was established around hatching in each experimental series. We found that the temporal dimension of the TSP was around 7 days (Days 20–27 of incubation) at a male-promoting or a female-promoting temperature. The rate of development of the whole embryo and gonadal growth was faster at female-promoting temperature than at male-promoting temperature. Formation of the genital ridge began at stage 21–22 and histological differentiation of the gonads occurred around stage 26–27. Although these stages coincided with the TSP, at male-promoting temperature the thermosensitive stages occurred earlier (from stages 20–21 to stages 23–24) than at female-promoting temperature (from stages 23–24 to stages 26–27). Thus, at male promoting-temperature, sex was determined in embryos with incipient or undifferentiated gonads. In contrast, E2 treatment continued to feminize the gonads of embryos at a male-promoting temperature beyond the TSP up to stage 25–26, but the E2-induced ovaries were significantly smaller than temperature-induced ovaries. It is suggested that the doses of E2 used were higher than the concentration of endogenous E2 required for normal sex determination. The lack of correlation between sex determination and gonad differentiation suggests that irreversible molecular processes underlying sex determination occur earlier at male- than at female-promoting temperature. Results suggest that the male sex may be the default state and that the female condition must be imposed upon it.

Estradiol Dosage and the Solicitation Display Assay in Red-Winged Blackbirds

The majority of female Red-winged Blackbirds (Agelaius phoeniceus) given exogenous estradiol responded to playback of male song with copulation solicitation. Nine females given no exogenous estradiol all failed to give any displays in response to playback. We conclude that estradiol treatment is necessary to elicit response to playback in captive female Red-winged Blackbirds. Given the task of discriminating full conspecific song from a partial song, females treated with a double dose of estradiol showed a degree of discrimination nearly identical to that shown by females treated with a single dose. Variation in estradiol dosage appears not to have a strong effect on discrimination.

O-206. Exogenous oestradiol treatment during breast feeding suppresses ovarian activity as measured by plasma inhibin B

O-206. Exogenous oestradiol treatment during breast feeding suppresses ovarian activity as measured by plasma inhibin B

The luteal phase of cycles utilizing controlled ovarian hyperstimulation and the possible impact of this hyperstimulation on embryo implantation

OBJECTIVE: Our purpose was to evaluate the early luteal phase of assisted reproductive cycles utilizing controlled ovarian hyperstimulation and to compare these results with those obtained in unstimulated cycles. STUDY DESIGN: We undertook a descriptive study analyzing luteal phase serum progesterone levels, endometrial histologic features, and endometrial surface ultrastructure by scanning electron microscopy of cycles utilizing controlled ovarian hyperstimulation. Study samples were obtained from 7 oocyte donors undergoing controlled ovarian hyperstimulation for the purpose of follicle aspiration in oocyte donation. Control (unstimulated) serum progesterone samples were obtained from 19 patients undergoing in vitro fertilization in unstimulated cycles. Prospective recipients of oocyte donation ( n = 20) undergoing mock cycles of exogenous estradiol and progesterone acted as controls for the endometrial biopsies. RESULTS: Serum progesterone levels on the day of human chorionic gonadotropin administration were twofold higher in the study group than in the unstimulated group (1.1 ± 0.6 vs 0.5 ± 0.2 ng/ml, mean ± SD, p < 0.01). On the day of follicle aspiration, progesterone levels were much higher in the study group (8.5 ± 2.2 vs 0.5 ± 0.1 ng/ml, p < 0.001). Histologic dating of endometrial biopsies revealed that the study group was advanced by nearly 2 days as compared with the group having artificial cycles. Pinopods, ultrastructural markers of the implantation window, were present in only one of seven study cycles as compared with all of the four artificial cycles. CONCLUSIONS: The early luteal phase of cycles undergoing controlled ovarian hyperstimulation is characterized by markedly elevated serum progesterone levels during the periovulatory period, advanced endometrial histologic features, and an absence of endometrial pinopods at the time of embryo implantation. We speculate that these high levels of progesterone in the early luteal phase cause premature endometrial luteinization and a premature appearance of the implantation window, thus providing an explanation for the observed decrease in endometrial receptivity. (Am J Obstet Gynecol 1997;176:1262-9.)

Ovulatory responses and plasma luteinizing hormone concentrations in dairy heifers after treatment with exogenous progesterone and estradiol benzoate

The objectives of this experiment were to determine the effects of 0.5 mg estradiol benzoate, administered intramuscularly 24 h after removal of CIDR-B progesterone containing intravaginal devices, on the time to estrus, ovulation and peak LH concentration in dairy heifers. Ovulatory responses and plasma LH concentrations were examined using 14 Friesian dairy heifers in 2 separate treatment periods. All heifers received a CIDR-B progesterone-containing intravaginal device with an attached 10-mg estradiol benzoate capsule for 12 d. Within each period, 24 h after CIDR-B removal, 7 heifers received an intramuscular injection of 0.5 mg estradiol benzoate while the remaining 7 heifers received an intramuscular injection of a placebo. Blood samples for LH assay were collected at 0, 6 and 12 h, and then every 4 h for 60 h after estradiol injection. Detection of estrus was conducted at 4-h intervals, and ultrasonographical examination to detect ovulation was conducted every 8 h for 88 h after removal of the CIDR-B device. Treatment with estradiol benzoate tended to reduce the time from device removal to the LH peak in Period 1 (median time to LH peak 40.1 vs 63.9 h; P = 6.07). In Period 2, treatment with estradiol had no significant effect on the time to the LH peak, standing estrus or ovulation. We hypothesize that the period effect was due to the stage of cycle at the time of treatment. For heifers treated in Period 1, the stage of cycle was random. However, because of the prior synchronization of estrus, which was implicit in the experimental design, heifers in Period 2 tended to be in late diestrus. The administration of estradiol benzoate after treatment with exogenous progesterone appears to overcome the variability in timing of LH peaks typically occurring in a herd of synchronized heifers due to different stages of follicular development.

Estradiol, Administered Acutely, Protects Ischemic Myocardium in Both Female and Male Rabbits.

BACKGROUND: The benefits of chronic administration of estrogen to postmenopausal women are well documented; however, the acute effects of exogenous estradiol on myocardium after coronary artery occlusion and reperfusion in male and female animal models are unknown. We tested the influence of acute pretreatment with estradiol on the development of myocardial necrosis in two protocols, studying intact anesthetized female and male rabbits. METHODS AND RESULTS: 17beta-estradiol (1 mg) was given 15 minutes before coronary artery occlusion in the treated groups (n = 10 females, 10 males); control rabbits (n = 11 females, 10 males) received water. All rabbits underwent 30 minutes of coronary artery occlusion and 4 hours of reperfusion. Myocardial blood flow was similar between groups at 10 minutes after treatment and during coronary artery occlusion and reperfusion. Thus estradiol did not increase blood flow. Heart rate and systemic pressure were also similar between groups. Estradiol levels during coronary artery occlusion were 1-8 pg/mL in untreated female and male rabbits and 66 +/- 28 (male) and 352 +/- 273 (female) in treated rabbits. Although the size of the ischemic risk zones was similar in both groups in both protocols, estradiol-treated rabbits of both sexes developed significantly less necrosis. Infarct size as a percent of the risk region was 10 +/- 1% in female estradiol-treated rabbits compared with 23 +/- 5% in controls (P <.03) and 16 +/- 4% in estradiol-treated male rabbits compared with 31 +/- 5% in control males (P =.03). Although male rabbits had larger infarcts than female rabbits, sex was not a significant covariate for infarct size. CONCLUSIONS: Estradiol exerts a protective effect on ischemic myocardium that is not associated with an increase in myocardial blood flow or alteration in hemodynamics. This study shows that acute administration of estrogen before coronary artery occlusion reduces infarct size in both male and female rabbits.

Neutrophil migration into the uterine lumen of the cow: The influence of endogenous and exogenous sex steroid hormones using two intrauterine chemoattractants

Neutrophil migration into the uterine lumen in response to the intrauterine infusion of both an oyster glycogen suspension and a bacteria-free filtrate obtained after incubation of Actinomyces pyogenes in cooked meat medium was studied in 4 cows at estrus (Day 0) and at diestrus (Day 10). In addition, the same chemoattractants were used in 5 other cows following bilateral ovariectomy and after parenteral treatment with exogenous estradiol 17β and progesterone in oil. Large numbers of cells (average viability >85%, purity 95%) were obtained with both chemoattractants. In cyclic and bilaterally ovariectomized cows bacteria-free filtrate produced a greater migratory response than oyster glycogen, and the differences were significant (P < 0.01 and P < 0.002, respectively). On Day 10 of the estrous cycle a higher number of neutrophils was recovered than on Day 0 following infusion of oyster glycogen and bacteria-free filtrate, and again the differences were significant (P < 0.003 and P < 0.001, respectively). Following treatment of ovariectomized cows with estradiol and progesterone, greater response was observed for progesterone than for estradiol after oyster glycogen and bacteria-free filtrate treatment with significant differences (P < 0.002 and P < 0.003, respectively). Both chemoattractants produced adequate numbers of viable neutrophils suitable for subsequent evaluation of their function in vitro. The increased neutrophil response induced by progesterone, both in normal cyclic cows and after ovariectomy following progesterone treatment, may be a compensatory one due to reduced neutrophil phagocytosis and bactericidal activity or to the suppression of other uterine defense mechanisms, since this response is inconsistent with the long-recognized observation that the uterus of the cow is more susceptible to infection in diestrus than in estrus.

Expression of the steroidogenic acute regulatory protein in the corpus luteum of the rabbit: dependence upon the luteotropic hormone, estradiol-17 beta.

The recent characterization of the mitochondrial protein, Steroidogenic Acute Regulatory (StAR) protein, as a rate-limiting protein in steroidogenesis prompted us to investigate whether StAR is expressed in the rabbit corpus luteum and whether the expression of StAR is responsive to estradiol-17 beta, the luteotropic hormone in the rabbit. In rabbits treated continuously with exogenous estradiol through Day 13 of pseudopregnancy (n = 9), immunoblot analysis revealed that luteal expression of StAR was stable, ranging from 8.5 to 9.7 U of corrected integrated optical density. Plasma progesterone concentration (mean +/- SEM) remained elevated in these rabbits (14.3 +/- 2.1 ng/ml). In contrast, expression of StAR decreased in corpora lutea of rabbits deprived of estradiol for the last 48 and 72 h of the experiment (4.9 +/- 2.2 and 0.3 +/- 0.2 U, respectively, n = 3 per group), and was associated with a decline in plasma progesterone (0.8 +/- 0.1 and 0.5 +/- 0.3 ng/ml, respectively). Replacement of estradiol after 48 h of estradiol deprivation (n = 3) stimulated the reappearance of StAR (10.3 +/- 2.6 U) and the restoration of plasma progesterone (10.4 +/- 4.9 ng/ml). [35S]Methionine labeling of proteins in rabbit corpora lutea revealed that several isoforms of StAR protein were specifically synthesized in response to estradiol treatment. Collectively, these observations are consistent with a proposed role for StAR in the mediation of the luteotropic effect of estrogen to promote the synthesis of progesterone in the rabbit.

Estrogen reduces atherosclerotic lesion development in apolipoprotein E-deficient mice.

We have studied the effects of endogenous and exogenous estrogen on atherosclerotic lesions in apolipoprotein E-deficient mice. Female mice ovariectomized (OVX) at weaning displayed increases (P < 0.01) in fatty streak lesions in the proximal aorta and aortic sinus compared with female mice with intact ovarian function. These differences between the OVX and sham controls were apparent in both chow- and "Western-type" diet-fed mice. Moreover, increases in lesion size following OVX occurred without changes in plasma cholesterol. Hormone replacement with subdermal 17-beta-estradiol pellets releasing either 6, 14, or 28 micrograms/day significantly decreased (P < 0.001) atherosclerotic lesion area in both male and OVX female mice. In contrast, neither 17-alpha-estradiol (28 micrograms/day) or tamoxifen (85 micrograms/day) affected lesion progression in OVX female mice. In the Western diet-fed group, exogenous estradiol markedly reduced plasma cholesterol and triglycerides, whereas, in animals fed the chow diet, exogenous estrogen and tamoxifen treatment only decreased plasma and very low density lipoprotein triglycerides. However, lesion area was only weakly correlated with plasma cholesterol and triglycerides, 0.35 and 0.44 tau values, respectively (P < 0.01). In summary, in the apolipoprotein E-deficient mouse 17-beta-estradiol protects against atherosclerotic lesion formation, and this can only be partially explained through effects on plasma lipoprotein levels.

Effects of estradiol on sexual receptivity, wheel-running behavior, and vaginal estrus in virgin prairie voles

This study examined the effects of estradiol on sexual receptivity and vaginal estrus in experienced and virgin female prairie voles, and running wheel activity in virgin females. Because prairie voles undergo induced ovulation, we predicted that exogenous estradiol would not affect activity patterns nor stimulate lordosis in virgins. Females were SC injected with estradiol benzoate (EB) and placed with males, and sexual receptivity was monitored. In experienced females 0.5 pg of EB resulted in 100% of the females displaying lordosis after 48 h. In contrast, only 20% of the females receiving 0.05 pg displayed lordosis. Less than 20% of virgin females receiving EB displayed lordosis. Virgins displayed no change in wheel-running activity after EB treatments, indicating that behaviors that are influenced by estradiol and regulated by the brain may require previous exposure to males to develop. Although all females receiving the 0.5 μg of EB displayed vaginal estrus, virgin females achieved vaginal estrus later than experienced females, suggesting that exposure to males has a priming effect resulting in a reduced period to vaginal estrus.