Exogenous Estradiol Benzoate Research Articles

Gut Microbiota and Acylcarnitine Metabolites Connect the Beneficial Association between Estrogen and Lipid Metabolism Disorders in Ovariectomized Mice.

Decreased estrogen level is one of the main causes of lipid metabolism disorders and coronary heart disease in women after menopause. Exogenous estradiol benzoate is effective to some extent in alleviating lipid metabolism disorders caused by estrogen deficiency. However, the role of gut microbes in the regulation process is not yet appreciated. The objective of this study was to investigate the effects of estradiol benzoate supplementation on lipid metabolism, gut microbiota, and metabolites in ovariectomized (OVX) mice and to reveal the importance of gut microbes and metabolites in the regulation of lipid metabolism disorders. This study found that high doses of estradiol benzoate supplementation effectively attenuated fat accumulation in OVX mice. There was a significant increase in the expression of genes enriched in hepatic cholesterol metabolism and a concomitant decrease in the expression of genes enriched in unsaturated fatty acid metabolism pathways. Further screening of the gut for characteristic metabolites associated with improved lipid metabolism revealed that estradiol benzoate supplementation influenced major subsets of acylcarnitine metabolites. Ovariectomy significantly increased the abundance of characteristic microbes that are significantly negatively associated with acylcarnitine synthesis, such as Lactobacillus and Eubacterium ruminantium group bacteria, while estradiol benzoate supplementation significantly increased the abundance of characteristic microbes that are significantly positively associated with acylcarnitine synthesis, such as Ileibacterium and Bifidobacterium spp. The use of pseudosterile mice with gut microbial deficiency greatly facilitated the synthesis of acylcarnitine due to estradiol benzoate supplementation and also alleviated lipid metabolism disorders to a greater extent in OVX mice. IMPORTANCE Our findings establish a role for gut microbes in the progression of estrogen deficiency-induced lipid metabolism disorders and reveal key target bacteria that may have the potential to regulate acylcarnitine synthesis. These findings suggest a possible route for the use of microbes or acylcarnitine to regulate disorders of lipid metabolism induced by estrogen deficiency.

Effects of administration of exogenous estradiol benzoate on follicular, luteal, and uterine hemodynamics in beef cows

Objectives of these two experiments were to determine if exogenous estradiol benzoate (EB) affects follicular, luteal, and uterine hemodynamics. In both experiments, 77 estrous-synchronized beef cows were assigned to one of two treatments: 1) Control (CON) or, 2) an injection of 1 mg EB the day before expected estrus (Day 0; Experiment 1) or on the day of estrus (Day 1; Experiment 2). There was transfer of an embryo (Day 7) into cows that expressed estrus. In Experiment 1, estradiol concentrations in circulation at Day 0 were greater in EB-treated cows (P = 0.003); however, concentrations of progesterone were only greater (P = 0.03) at Day 21 in cows of the EB-treated compared to those in the CON group. The follicular and luteal blood perfusion was similar, however, treatment with EB resulted in a greater uterine blood perfusion. In Experiment 2, treatment with EB did not affect size or blood perfusion of the corpus luteum (CL) on Day 7, 14, and 21. Only on Day 21, however, did pregnant cows have a larger CL than non-pregnant cows (P = 0.02). Blood perfusion to the CL was greater (P < 0.05) in all cows on Day 21 compared to 7 or 14 and those determined to be pregnant on Day 35 tended (P = 0.06) to have greater CL blood perfusion only on Day 21 compared to non-pregnant cows. In conclusion, EB treatment resulted in a greater blood perfusion of the uterus, and only affected the CL on Day 21 in Experiment 2.

Characterization of blood flow and the effects of exogenous estradiol benzoate on residual follicles formed after ultrasound-guided transvaginal follicle aspiration in cattle.

BackgroundRemoval of the follicular content by ultrasound-guided transvaginal follicle aspiration (TVFA) may fail to induce immediate atresia and loss of function, resulting in the occurrence of residual follicles (RF). The aims of this study were to characterize the blood flow in RF and to determine the effects of the treatment with estradiol benzoate on RF fate. Lactating, cyclic Holstein-Gir crossbred cows were used. In Experiment 1, follicular wave emergence (D0) was synchronized in cows (n = 10) and follicular growth was then monitored by transrectal ultrasonography from D0 to D8, followed by TVFA of the largest follicle present on the ovaries 24 h later. Color Doppler ultrasound imaging was used to examine blood flow on the follicular wall, which was recorded immediately before and every 12 h after TVFA, up to 72 h. In experiment 2, cows (n = 22) were randomly allocated to receive either 2 mL of saline i.m. (Control group, n = 11) or 2 mL estradiol benzoate i.m. (EB group, n = 11) immediately after TVFA. Ovaries were scanned every 12 h to confirm the presence and to measure the diameter of RF. The contents of the RF, if present, were collected 72 h after the first TVFA, using the same aspiration procedures. Follicular fluid from original follicles and RF were stored at -20 °C until hormonal assays.ResultsIn Experiment 1, there was no reduction (P > 0.05) of blood flow in the remaining follicle walls after TVFA and maximum blood flow values were observed at 49.5 ± 19.7 h post-TVFA. In Experiment 2, formation of RF after TVFA was proportionally similar between Controls (5/9) and EB (5/10) cows. Also, RF diameter did not differ between groups (P > 0.05). Nonetheless, the content of RF from cows in the EB group had lower (P = 0.0004) estradiol (E2) concentration and lower (P = 0.0005) E2:P4 ratio compared with Controls.ConclusionsIn conclusion, 1) the persistence of vascularization in the remaining follicle wall may contribute to the formation of RF after follicle aspiration, and 2) the treatment with estradiol benzoate does not prevent formation of RF, but does reduce their estradiol production.

Characterization of Neural Estrogen Signaling and Neurotrophic Changes in the Accelerated Ovarian Failure Mouse Model of Menopause

Accelerated ovarian failure (AOF) can be induced in young mice with low doses of 4-vinylcyclohexene diepoxide (VCD), modeling the hormone changes observed across menopause. We assessed markers of synaptic plasticity in the hippocampus, anxiety-like behavior, and spatial learning longitudinally at 4 time points across the AOF model: premenopause, early perimenopause, late perimenopause, and postmenopause (POST). As others have shown, VCD administration decreased ovarian follicle counts and increased acyclicity as the model progressed to POST but with no impact on organ or body weights. The morphology of Iba1 immunoreactive microglia did not differ between vehicle- and VCD-administered mice. Hippocampal postsynaptic density 95 levels were minimally altered across the AOF model but decreased at POST in CA3b 24 hours after exogenous estradiol benzoate (EB). In contrast, hippocampal phosphorylated AKT levels transiently decreased in premenopause but increased at POST after 24 hours of EB in select subregions. Electron microscopy revealed fewer estrogen receptor α containing dendritic spines and terminals in CA1 stratum radiatum at POST. mRNA levels of most brain-derived neurotrophic factor exons (except V and VI) were lower in POST compared with ovariectomized mice. Exon V was sensitive to 24 hours of EB administration in POST-VCD. Anxiety-like behavior was unaffected at any menopause phase. Spatial learning was unaffected in all groups, but POST-VCD mice performed below chance. Our results suggest that the AOF model is suitable for longitudinal studies of neurobiological changes across the menopause transition in mice. Our findings also point to complex interactions between estrogen receptors and pathways involved in synaptic plasticity.

Differential effects of estrogen exposure on arylsulfatase B, galactose-6-sulfatase, and steroid sulfatase in rat prostate development

Sulfatase enzymes remove sulfate groups from sulfated steroid hormones, including estrone-sulfate and dehydroepiandrosterone-sulfate, and from sulfated glycosaminoglycans (GAGs), including chondroitin sulfates and heparan sulfate. The enzymes N-acetylgalactosamine-4-sulfatase (arylsulfatase B; ARSB) and N-acetylgalactosamine-6-sulfatase (GALNS), which remove sulfate groups from the sulfated GAGs chondroitin 4-sulfate (C4S) and chondroitin 6-sulfate, respectively, have not been studied in prostate development previously. In this report, the endogenous variation and the impact of exogenous estradiol benzoate on the immunohistochemistry and activity of ARSB and GALNS in post-natal (days 1–30) ventral rat prostate are presented, as well as measurements of steroid sulfatase activity (STS), C4S, total sulfated GAGs, and versican, an extracellular matrix proteoglycan with chondroitin sulfate attachments on days 5 and 30. Findings demonstrate distinct and reciprocal localization of ARSB and GALNS, with ARSB predominant in the stroma and GALNS predominant in the epithelium. Control ARSB activity increased significantly between days 5 and 30, but following estrogen exposure (estradiol benzoate 25μg in 25μl sesame oil subcutaneously on days 1, 3, and 5), activity was reduced and the observed increase on day 30 was inhibited. However, estrogen treatment did not inhibit the increase in GALNS activity between days 5 and 30, and reduced STS activity by 50% on both days 5 and 30 compared to vehicle control. Sulfated GAGs, C4S, and the extracellular matrix proteoglycan versican declined between days 5 and 30 in the control, but these declines were inhibited following estrogen. Study findings indicate distinct variation in expression and activity of sulfatases, sulfated GAGs, C4S, and versican in the process of normal prostate development, and disruption of these events by exogenous estrogen.

Sex and estrogen receptor expression influence opioid peptide levels in the mouse hippocampal mossy fiber pathway

The opioid peptides, dynorphin (DYN) and enkephalin (L-ENK) are contained in the hippocampal mossy fiber pathway where they modulate synaptic plasticity. In rats, the levels of DYN and L-ENK immunoreactivity (-ir) are increased when estrogen levels are elevated (Torres-Reveron et al., 2008, 2009). Here, we used quantitative immunocytochemistry to examine whether opioid levels are similarly regulated in wildtype (WT) mice over the estrous cycle, and how these compared to males. Moreover, using estrogen receptor (ER) alpha and beta knock-out mice (AERKO and BERKO, respectively), the present study examined the role of ERs in rapid, membrane-initiated (6h), or slower, nucleus-initiated (48h) estradiol effects on mossy fiber opioid levels. Unlike rats, the levels of DYN and L-ENK-ir did not change over the estrous cycle. However, compared to males, females had higher levels of DYN-ir in CA3a and L-ENK-ir in CA3b. In WT and BERKO ovariectomized (OVX) mice, neither DYN- nor L-ENK-ir changed following 6 or 48h estradiol benzoate (EB) administration. However, DYN-ir significantly increased 48h after EB in the dentate gyrus (DG) and CA3b of AERKO mice only. These findings suggest that cyclic hormone levels regulate neither DYN nor L-ENK levels in the mouse mossy fiber pathway as they do in the rat. This may be due to species-specific differences in the mossy fiber pathway. However, in the mouse, DYN levels are regulated by exogenous EB in the absence of ERα possibly via an ERβ-mediated pathway requiring new gene transcription.

Evaluation of the hypothalamus–pituitary axis response to exogenous GnRH, estradiol benzoate, and LH during the postpartum period in Nellore cows

The objective was to evaluate when the LH reserve was re-established in postpartum Nellore (Bos indicus) cows by evaluating the response of the hypothalamic–pituitary axis responsiveness to exogenous GnRH or estradiol benzoate (EB). Additionally, we tested the influence of dietary supplementation (SUPL) and calf removal (CR) on the duration of postpartum anestrus. Ninety multiparous lactating Nellore cows were randomly assigned to eight groups. The EB and GnRH groups received 1.0 mg EB (N = 7), and 50 μg lecireline (N = 16), respectively. Additional cows were given the same hormones, and subjected to either nutritional supplementation (EB-SUPL, N = 9; GnRH-SUPL, N = 16), or calf removal at 72 hours after calving (EB-CR, N = 4; GnRH-CR, N = 13). The remaining two groups were the LH (12.5 mg, N = 14) and control groups (saline, N = 11). Hormones were administered weekly from 7 (±5) days postpartum to first ovulation (detection of a CL during a weekly ultrasonographic examination). Blood samples were collected just before and 2 hours (GnRH, LH, and control groups) or 18 hours (EB groups) after hormone or saline (control) administration. Ovulation occurred as early as 15 days postpartum in the GnRH group. The mean ± SEM intervals (days) from calving to first ovulation were EB, 87.7 ± 4.2; EB-CR, 20.3 ± 1.2; EB-SUPL, 60.3 ± 3.2; GnRH, 40.4 ± 2.1; GnRH-CR, 21.0 ± 1.1; GnRH-SUPL, 26.4 ± 1.1; LH, 35.6 ± 1.1; and control, 60.9 ± 2.1. We concluded that there was sufficient LH in the pituitary gland (of Nellore cows) from the second week postpartum to induce ovulation in response to exogenous GnRH. Additionally, calf removal and nutritional supplementation reduced, by 2 to 4 weeks, the interval from calving to an LH increase and ovulation induced by GnRH or EB.

Studies on the protective effects of pollen-originated phytoestrogens on the growth and development of ovary in rats

This present study was undertaken to investigate the effects of pollen extracts on the development of ovary in the presence of exogenous estradiol benzoate. 45-day old female Wistar rats were administered with estradiol benzoate to induce the pathological status of the ovary. Histological observation of ovarian paraffin sections revealed that interruption of the maturation of follicles was associated with massive follicular atresia. Significantly increased serum FSH level was characteristic of the rats. Exposing to estradiol benzoate also resulted in severe lesion of the liver. Abnormally elevated levels of alanine aminotransferase and aspartate aminotransferase were accompanied by increased liver weight and hepatosomatic index. Extracts of phytoestrogens from pollen exhibited protective effects on ovary and liver tissues. Histological evaluation showed that the inhibition of follicular development was markedly diminished after receiving treatment for 28 days. Serum FSH concentration was restored to the normal level. No significant difference in ovarian weight and ovary-somatic index could be detected between treated groups and the control group. The liver tissue displayed normal morphology and function. Taken together, our results demonstrated pollen-originated phytoestrogens were helpful in re-establishing the hormonal milieu and attenuating the adverse influences of estradiol benzoate on the ovary and liver tissues. Key words: Estradiol benzoate, phytoestogen, pollen, ovary, liver.

Brain estradiol content in newborn rats: sex differences, regional heterogeneity, and possible de novo synthesis by the female telencephalon.

Accurate assessment of gonadal steroid levels in the developing brain is critical for understanding naturally occurring steroid-mediated sexual differentiation as well as determining the physiological relevance of exogenous steroid treatments commonly used in the study of this phenomenon. Using RIA, we measured the estradiol (E(2)) content of six regions of the developing brain immediately post partum, 1 d post partum, and after injection of exogenous estradiol benzoate, testosterone propionate, or the aromatase inhibitor formestane. We found sexually dimorphic E(2) content in several regions of the newborn brain. At 2 h of life, there was significantly higher E(2) content in males vs. females in the frontal cortex, hypothalamus and preoptic area but not in the hippocampus, brainstem, or cerebellum. Surprisingly, the female hippocampus had significantly higher E(2) content than all other female regions examined. By d 1 post partum, E(2) levels had decreased precipitously in most brain regions, and only the hypothalamus maintained a sex difference. Injection of female pups with estradiol benzoate raised tissue levels to that of the male in the hypothalamus but 2- to 3-fold higher in the other five regions. Testosterone administration increased E(2) content exclusively in the preoptic area, suggesting local variation in aromatase activity and/or substrate availability. Central administration of formestane decreased estrogen content in the male cortex, hypothalamus, and preoptic area. Formestane treatment also decreased endogenous E(2) in female cortex and hippocampus, suggesting de novo synthesis selectively in these brain regions. These data corroborate and extend previous findings of sex differences in brain E(2) levels perinatally and reveal an unexpected regional heterogeneity in E(2) synthesis and/or metabolism.

The effect of exogenous estradiol benzoate and altrenogest on uterine and ovarian blood flow during the estrous cycle in mares

In recent years, a positive relationship between genital perfusion and fertility has been established; in species other than horses, uterine and ovarian perfusion was improved by exogenous estrogen but impaired by exogenous progestin. The goal of the present study was to investigate the effect of exogenous estrogen and progestin on uterine and ovarian blood flow in cycling mares. Five Trotter mares were examined daily during three estrous cycles. Mares were given no treatment, altrenogest (0.044 mg/kg BW) orally from Day 0 (ovulation) to Day 14 and estradiol benzoate (5 mg i.m.) on Days 0, 5, and 10, in three cycles, respectively. There was no difference ( P>0.05) in the length of untreated versus estrogen-treated cycles (22.8±1.3 days and 23.2±1.5 days, respectively), but cycle length was increased ( P<0.05) in progestin-treated cycles (26.0±1.2 days). To facilitate comparisons among cycles with different lengths, data from Days 0 to 15 (diestrus) and from Days −6 to −1 (estrus) were analyzed. Transrectal Doppler sonography was used to evaluate blood flow in both uterine arteries and in the ovarian artery ipsilateral to the preovulatory follicle during estrus and ipsilateral to the corpus luteum during diestrus. Blood flow was assessed semiquantitatively using the pulsatility index (PI); high PI values indicated high resistance and a low perfusion and vice versa. An immediate effect of treatments occurred only after the administration of estradiol benzoate on Day 0; uterine PI values decreased ( P<0.05) between Days 0 and 1 and estrogen-treated mares but increased ( P<0.05) at the corresponding time in untreated cycles. Mean PI values for the uterine and ovarian arteries during both diestrus and estrus were higher ( P<0.05) in estrogen-treated versus untreated mares. Furthermore, mean uterine PI values during diestrus and estrus were higher ( P<0.05) in altrenogest-treated versus untreated mares. Neither estrogen nor altrenogest treatments had a significant immediate effect on ovarian PI values. Compared to untreated cycles, mean ovarian PI values were elevated ( P<0.05) only in the estrus following altrenogest administration. In conclusion, exogenous estrogen and progestin both decreased genital perfusion in cycling mares.

Secretion of estradiol-17β by porcine mammary gland of ovariectomized steroid-treated sows

Although the mammary gland of many species secretes estradiol (E 2), nothing is known of E 2 secretion in the porcine gland. The present study was designed to investigate whether porcine mammary gland was a source of E 2, and to test the influence of individual and combined effects of exogenous progesterone and estradiol benzoate (EB) on the secretion of E 2. Immature crossbred gilts were ovariectomized at 7 months of age followed by 4 weeks later by steroid hormone replacement therapy to produce estradiol and progesterone (P 4) blood concentrations similar to those observed during a normal estrous cycle. Arterial and venous blood plasma (from carotid artery and anterior mammary vein, respectively) were sampled for 2 h at 10 min intervals. Plasma concentrations of progesterone, androstenedione (A 4), testosterone (T), estrone (E 1) and estradiol were determined by RIA. In all gilts treated with progesterone alone or in combination with EB, concentrations of P 4, A 4 and E 1 in blood collected from venous outflow were lower compared to concentrations in arterial blood, whereas concentrations of E 2 were higher in blood plasma from the anterior mammary vein compared to plasma from the carotid artery. The results indicated that the porcine mammary gland secreted E 2. Increased concentrations of plasma E 2 collected only from P 4-treated animals suggested that progesterone activated enzymes involved in steroidogenesis in porcine mammary gland, or those utilized in its metabolism.

The modulatory effect of estradiol benzoate on superoxide dismutase activity in the developing rat brain.

The sensitivity of copper,zinc (CuZn)- and manganese (Mn)-superoxide dismutase (SOD) to exogenous estradiol benzoate (EB) was investigated in Wistar rats during postnatal brain development. Enzyme activities were measured in samples prepared from brains of rats of both sexes and various ages between 0 and 75 days, treated sc with 0.5 micro g EB/100 g body weight in 0.1 ml olive oil/100 g body weight, 48 and 24 h before sacrifice. In females, EB treatment stimulated MnSOD activity on days 0 (66.1%), 8 (72.7%) and 15 (81.7%). In males, the stimulatory effect of EB on MnSOD activity on day 0 (113.6%) disappeared on day 8 and on days 15 and 45 it became inhibitory (40.3 and 30.5%, respectively). EB had no effect on the other age groups. The stimulatory effect of EB on CuZnSOD activity in newborn females (51.8%) changed to an inhibitory effect on day 8 (38.4%) and disappeared by day 45 when inhibition was detected again (48.7%). In males, the inhibitory effect on this enzyme was observed on days 0 (45.0%) and 15 (28.9%), and then disappeared until day 60 when a stimulatory effect was observed (38.4%). EB treatment had no effect on the other age groups. The sensitivity of MnSOD to estradiol differed significantly between sexes during the neonatal and prepubertal period, whereas it followed a similar pattern thereafter. The sensitivity of CuZnSOD to estradiol differed significantly between sexes during most of the study period. Regression analysis showed that the sensitivity of MnSOD to this estrogen tended to decrease similarly in both sexes, whereas the sensitivity of CuZnSOD showed a significantly different opposite tendency in female and male rats. These are the first reports indicating hormonal modulation of antioxidant enzyme activities related to the developmental process.

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.

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.

A Comparison of LH Secretion and Brain Estradiol Receptors in Heterosexual and Homosexual Rams and Female Sheep

This study examined endocrine components of sexual orientation of male sheep. Sexual orientation of adult rams was identified through standardized sexual performance tests. Four rams that copulated with ewes, four rams that never mounted females and copulated with males, and eight ewes were used in the experiments. Exogenous estradiol benzoate (50 μg, i.m.) stimulated (P < .05) a preovulatory-like LH surge 16-22 hr after administration to females. Estradiol did not (P > .05) affect LH release of heterosexual or homosexual rams. Thirty days after the estradiol challenge, sheep were euthanized and areas of the amygdala (AMY), hypothalamus (HYP), anterior pituitary (AP), and preoptic area (POA) of the hypothalamus were collected. Occupied and unoccupied content of estradiol receptors (ER) was determined. The content of ER in the amygdala of both homosexual rams and ewes was similar, but less than (P < .05) the content of ER in heterosexual rams. The ER content measured in other brain regions did not differ by sex or orientation. In summary, results from these data show that the preovulatory LH surge mechanism that is a characteristic of the female does not occur in either homosexual or heterosexual rams. Conversely, the ER content of the AMY of homosexual rams is similar to that of ewes and differs from the heterosexual male. Differences in ER content between heterosexual and homosexual rams imply that the amygdala serves as a link for input from potential mates. These data suggest that the amygdala not only plays a role in sexual behavior but may be involved in sexual orientation of rams.

Estrogen and sex reversal in turtles: A dose-dependent phenomenon

Exogenous estradiol benzoate (EB) or estradiol-17β (E2) caused dose-dependent gonadal feminization of slider turtle ( Trachemys scripta) embryos incubated at a male-producing temperature (26°), suggesting that sex reversal requires a threshold dosage of these hormones. Even at dosages resulting in mixtures of males and females, nearly all hatchlings had normal-appearing ovaries or testes. Only 7 of 241 hatchlings had gonads that had not differentiated fully into ovaries or testes. Thus, with rare exception, estrogens exerted an “all or none” effect. The transport of hormone into the embryo varied with mode of administration and E2 was more effective than was EB at the lowest dosage used. These studies suggest either that exogenous estrogen is capable of coordinating cortical/medullary development in the gonad so that intersexes are prevented or that estrogen acts “upstream” of the developmental processes responsible for coordinating gonadal development.

Action of sex steroid hormones on temperature-induced sex determination in the snapping turtle ( Chelydra serpentina)

Administration of exogenous estradiol benzoate (EB) or an estrogen agonist, R2858, into eggs of snapping turtles caused all embryos incubated at male-producing temperatures to develop as females, whereas testosterone propionate (TP) caused 42% of the embryos to develop as females. Some of the embryos treated with EB, R2858, or TP also had hypertrophied oviducts. Neither dihydrotestosterone (DHT) nor cholesterol had any apparent effect on the sex determination of embryos incubated at male-producing temperatures. Injections of TP, DHT, the androgen agonist R1881, or cholesterol had no apparent effect on sex determination of embryos incubated at female-producing temperatures. Administration of estradiol antiserum or testosterone antiserum resulted in some individuals having undifferentiated or ambiguous gonads. Although both exogenous estrogens and androgens can induce embryonic gonads to develop as ovaries, the findings of this study indicate that estrogen is the female-inducing hormone and that androgens may feminize gonads via aromatization to estrogen. Furthermore, the results of the antisera injections suggest that endogenous steroid hormones may have a natural role in gonadal differentiation of reptiles with environmental sex determination.

Steroids induce hypothalamic progestin receptors and facilitate female sexual behavior in neonatal rats

This report provides the first evidence that two activational actions of estrogen can occur within the first week of life in the rat. Priming 4-day-old rats with exogenous estradiol benzoate facilitates lordosis and ear wiggling-like behavior, and induces cytosol progestin receptors in the medial basal hypothalamus and preoptic region (Hyp-PoA) 44 h later. Moreover, unprimed male infants show more intense lordosis and higher concentrations of cytosol progestin receptors in Hyp-PoA than infant females. Neonatal castration of male infants decreases their concentration of cytosol progestin receptors in Hyp-PoA to the levels normally seen in infant females. In addition, priming 6-day-old infants with progesterone alone facilitates lordosis in male but not female infants. Together, these data demonstrate that in the male infant, endogenous steroids of testicular origin have activational as well as organizational actions.

Reduced estradiol production by a substituted triazole results in delayed ovulation in rats

Ovulation in the rat is delayed by a single administration of the substituted triazole R151885 (1,1-di(4-fluorophenyl)-2-(1,2,4-triazol-1-yl)-ethanol). This delay results from a 24-hr shift in the preovulatory luteinizing hormone (LH) surge since administration of chorionic gonadotrophin on proestrus restores ovulation. Plasma levels of estradiol are markedly reduced (42–45%) 6–12 hr after administration of R151885. The restoration of ovulation in R151885-pretreated rats, by administration of exogenous estradiol benzoate, indicates that the reduced estradiol levels play a pivotal role in the delay of ovulation. Granulosa cells isolated from rat ovaries produce estradiol and progesterone in vitro in the presence of both follicle-stimulating hormone and testosterone. The addition of R151885 to such cultures results in a dose-dependent inhibition of estradiol production (69% by 1 μ m) without a significant effect on progesterone production. This inhibition occurs at concentrations of R151885 similar to those measured in vivo. R151885 is a competitive inhibitor of human placental aromatase (apparent K i with androstenedione substrate of 410 n m) and produces a type II spectral perturbation of cytochrome P-450 from placental microsomes. Pituitaries isolated from R151885-treated rats have reduced LH output in response to gonadotrophin-releasing hormone stimulation compared with those of controls. It is proposed that R151885 competitively inhibits aromatase activity in developing ovarian follicles. The resultant temporary reduction of plasma estradiol levels at a critical time in the estrous cycle, and consequent inadequate pituitary sensitization, produces a 24-hr delay in the preovulatory LH surge and hence ovulation is delayed by 24 hr.

Induction of parturition in swine with prostaglandin F 2α, estradiol benzoate and oxytocin

Pregnant sows and gilts were administered either 0, 2.5, 5, 10 or 20 mg prostaglandin F 2α (PGF 2α) intramuscularly on Day 112 or 113 of gestation at 0800 h in an effort to induce parturition. The average interval from PGF 2α injection to farrowing was 55.1 ± 5.7, 29.4 ± 3.1, 32.1 ± 4.6, 27.8 ± 1.8 and 26.9 ± 1.1 h for 0, 2.5, 5, 10 and 20 mg, respectively. All PGF 2α treatments increased (P < 0.01) over controls the number of sows farrowing 23 to 33 h after injection. The average gestation length was significantly shorter in treated gilts; however, no detrimental effect on pig performance or pig survivability was observed. A second trial evaluated the effect of a 10-mg dose of PGF 2α on the induction of parturition in sows in order to obtain a majority of sows farrowing within normal working hours (0700 to 1700 h). The interval from injection to farrowing was decreased (P < 0.05) by PGF 2α treatment (66.2 ± 5.3 vs 28.1 ± 2.2 h). Fifty-seven percent (P < 0.05) of PGF 2α-treated sows farrowed between 0700 and 1700 h as compared to 13.6% for control sows. A third trial was conducted to examine a sequential treatment of PGF 2α and oxytocin to control the time of parturition more precisely. Sows receiving only 10 mg of PGF 2α farrowed on an average 31.1 ± 1.4 h after injection. The injection of 40 IU oxytocin 24 to 28 h after PGF 2α decreased (P < 0.05) the interval from PGF 2α to farrowing (28.1 ± 0.9 h). The addition of oxytocin increased (P < 0.05) the number of sows farrowing within 3 h of injection (33 vs 86% for PGF 2α and PGF 2α + oxytocin treatments, respectively). A fourth trial was designed to determine if the addition of exogenous estradiol benzoate (EB) to a sequential treatment of PGF 2α and oxytocin would improve the predictability and synchronization of the induced parturition. Sows were assigned to receive either saline, 10 mg PGF 2α + 40 IU oxytocin or 10 mg PGF 2α + 5 mg EB + 40 IU oxytocin. The addition of EB reduced (P < 0.01) the variance in the interval from oxytocin to farrowing and added precision to the predicted time of induced parturition.