Low Dose Of Estradiol Benzoate Research Articles

Interaction of age and chronic estradiol replacement on memory and markers of brain aging

The current study examined effects of chronic estradiol replacement on cognition and biomarkers of aging. Young, middle-aged, and aged rats were ovariectomized and implanted with blank capsules, or capsules containing high or low doses of estradiol benzoate (EB). Three weeks later, animals were tested on inhibitory avoidance and cue and spatial discrimination on the Morris water maze. High plasma estradiol levels were associated with slower swim speed and impaired retention of inhibitory avoidance. No effect of EB treatment was observed for acquisition of the spatial discrimination task, however, a dose by age interaction was observed for retention of spatial discrimination such that higher retention scores were observed for young, middle-aged and aged animals under blank, low and high dose conditions, respectively. EB treatment reversed several hippocampal markers of age-related memory impairment, blocking induction of long-term depression and decreasing cytosolic calcineurin activity. Results indicate that the level of chronic hormone replacement interacts with age to influence hippocampal function.

Effect of Gonadal Steroids on Proliferative Responses and Subset Alterations in Cultured Chicken Lymphocytes

The effect of gonadal steroids (GS) on proliferation of lymphocytes and distribution of lymphocyte subpopulations in cell culture was examined. The involvement of protein kinase C (PKC) and calcium ionophore in the proliferative response was tested. Estradiol benzoate (EB) or testosterone propionate (TP) had no significant influence on proliferation of peripheral blood lymphocytes (PBL) when cells were not stimulated by mitogen. At high concentration (10-6 M), EB and dihydrotestosterone (DHT) decreased lymphocyte proliferative response to concanavalin A (ConA) and lipopolysaccharide (LPS) at 24 and 72 h of incubation. However, at physiological doses (10-12 to 10-16M), EB significantly enhanced the proliferative response at 24 h of incubation, whereas DHT had no effect. The inhibitory effect of the high dose of EB or DHT on proliferation of T and B lymphocytes was independent of time of hormone presentation to the cells or age and gender of cell donor. In all cultures, pre-incubation of lymphocytes with 10-6 M of EB or DHT significantly reduced their proliferative responses to ConA, phytohemagglutinin (PHA), and LPS. The percentage of CD3+ cells was significantly reduced by EB, whereas DHT had no such effect. In contrast to inhibition of proliferation in response to mitogens, 10-6 M EB dramatically enhanced the proliferation of lymphocytes in response to the PKC activator, phorbol 12-myristate 13-acetate, and calcium ionophore, A23187. Results suggest that high doses of EB do not damage the viability or proliferation capability of lymphocytes and, therefore, suppress the proliferative response to mitogens in a different manner, perhaps by reducing gene transcription for receptors that recognize the mitogens, or suppressing some postreceptor events. The enhancement of proliferation in response to mitogens by low doses of EB may support this assumption, because the biphasic effects of steroids on gene transcription are well documented.

Dopamine release in the medial preoptic area of female rats in response to hormonal manipulation and sexual activity.

Dopamine (DA) is responsive to hormonal manipulations and has been implicated in the regulation of female rat sexual behavior. In the present studies, extracellular DA levels were assessed in the medial preoptic area (MPOA) of ovariectomized female rats in response to exogenous ovarian hormones and during sexual activity. In female rats primed with a low dose of estradiol benzoate (2 microg), but not with a higher dose (20 microg), a 500-microg progesterone injection increased extracellular DA and facilitated copulatory behavior. Extracellular DA levels in the MPOA were further augmented during sexual interactions with a male rat in a nonpacing copulatory chamber by either perineal or vaginal stimulation. However, in a pacing chamber, DA efflux did not increase, although the metabolites rose significantly during copulation. Together, these findings suggest that extracellular DA in the MPOA responds to the hormonal state of the female rat and may contribute to her expression of sexual behavior.

Increased lh pulse frequency and estrogen secretion associated with termination of anestrus followed by enhancement of uterine estrogen receptor gene expression in the beagle bitch

The relationships among pulsatile LH secretion pattern, estrogen secretion, and expression of the uterine estrogen receptor gene were examined throughout the estrous cycle in beagle bitches. In Experiment 1, blood samples were collected from 30 bitches every 10 min for 8 h from a cephalic vein during different phases of the estrous cycle. An increase in the mean plasma levels of LH occurred from mid to late anestrus (P < 0.01). The LH pulse frequency increased (P < 0.01) from late anestrus to proestrus, and was strongly correlated (r = 0.96, P < 0.001) with the mean plasma level of estradiol-17β (E 2). In Experiment 2, middle uterine samples, including the myometrium and endometrium, from 18 bitches were taken at 6 stages of the estrous cycle. The total number of estrogen receptors and nuclear estrogen receptor and its mRNA levels in the uterus also increased (P < 0.01) from late anestrus to proestrus. Mean plasma E 2 level and the number of uterine estrogen receptor were positively correlated (r = 0.81, P < 0.05). In Experiment 3, nine bitches were ovariectomized in mid anestrus. Two weeks later they received a single injection of 10 or 50 μg/kg, im,estradiol benzoate. The number of uterine estrogen receptor and their mRNA levels for ovariectomized bitches were low, but increased (P < 0.05) after treatment with a low dose of estradiol benzoate. These results suggest that increases in LH pulse frequency and estrogen secretion are associated with termination of anestrus and that subsequent enhancement of uterine estrogen receptor expression may be up-regulated by estradiol.

Enhancement of estrogen receptor gene expression in the mediobasal hypothalamus during anestrus in the beagle bitch

Estrogen receptor mRNA (ER mRNA) levels were measured in the mediobasal hypothalamus (MBH) of beagle bitches at different stages of the estrous cycle, and compared with levels in ovariectomized (OVX) estrogen-treated bitches. In cyclic bitches, the level of hypothalamic ER mRNA increased during the progression of anestrus and declined thereafter. Hypothalamic ER mRNA and plasma luteinizing hormone (LH) levels during anestrus and proestrus were positively correlated ( r=0.94, P<0.001). In OVX bitches, levels of hypothalamic ER mRNA were low, and increased significantly after treatment with a low dose of estradiol benzoate. These results suggest that, during the course of anestrus in the bitch, hypothalamic ER mRNA expression increases, and may be up-regulated by estradiol.

Effects of hormonal treatment and history on scopolamine inhibition of lordosis

The muscarinic receptor blocker, scopolamine, inhibits the display of lordosis behavior in female rats but its effectiveness depends on hormonal conditions. In these experiments, systemic administration of scopolamine (0.031–4 mg/kg) inhibited lordosis in ovariectomized rats brought into receptivity by treatment with a low dose of estradiol benzoate (EB, 0.25 μg for 3 days) with progesterone (P, 500 μg for 1 day), or a high dose of EB (25 μg for 3 days) with and without P. However, the effectiveness of scopolamine was reduced at the high dose of EB and with the addition of P. Furthermore, scopolamine failed to inhibit lordosis in females treated on a second week with the high dose of EB with or without P, unless an interval of at least 3 weeks separated the two sets of steroid treatments. The reduced effectiveness of scopolamine cannot be explained by peripheral mechanisms because its inhibitory effect on lordosis also was reduced following repeated hormonal exposure even when scopolamine was infused directly into the lateral ventricles.

Sex differences in the rapid and acute effects of estrogen on striatal D 2 dopamine receptor binding

Regional changes in striatal D 2 dopamine (DA) receptor binding in castrated (CAST) or ovariectomized (OVX) rats were investigated following administration of a low dose of estradiol benzoate (EB), repeated treatment with EB followed by progesterone, or vehicle. In two separate experiments, there was a significant decrease in striatal D 2 DA receptor binding in caudal striatum from OVX, but not CAST rats 30 min after a single injection of EB. In CAST rats, there was a significant increase in striatal D 2 DA receptor binding in rostral striatum 4 h after injection of EB. There was no effect of EB plus progesterone treatment in either OVX or CAST rats. In addition, CAST rats had significantly lower D 2 DA receptor binding in the lateral region of the rostral striatum than did OVX rats. These results show sexually dimorphic and regionally specific effects of estrogen on striatal D 2 DA receptor binding, and a significant sex difference in striatal D 2 DA receptor binding in the absence of circulating gonadal hormones. The present findings are discussed in light of previous reports of sex differences in gonadal hormone influences on striatal DA mediated behaviors.

The effect of estrogen treatment on scopolamine inhibition of lordosis

Previous evidence indicates that the cholinergic muscarinic antagonist, scopolamine, inhibits lordosis in female rats. In the experiments reported here, the effects of various doses and repeated administrations of estrogen on the scopolamine inhibition of lordosis were examined. In the first experiment, intraperitoneal injections of scopolamine (1 mg/rat) completely inhibited lordosis in ovariectomized rats primed with low doses of estradiol benzoate (0.25 or 0.5 μg for 3 days) and progesterone (500 μg). However, scopolamine was significantly less effective in inhibiting lordosis in females primed with a higher dose of estradiol benzoate (25 μg for 3 days) and progesterone (500 μg). When hormone priming was repeated on subsequent weeks, scopolamine continued to inhibit lordosis in females that received 0.25 μg estradiol benzoate but was less effective in females primed with 0.5 μg. Scopolamine failed to inhibit lordosis in females treated with 25 μg estradiol benzoate on these later tests. In the second experiment, various doses of scopolamine (1, 2, or 4 mg/rat) were administered intraperitoneally to females primed with the highest dose of estradiol benzoate (25 μg) and progesterone (500 μg). Lordosis was inhibited equally by all scopolamine doses during the first week. As in the first experiment, scopolamine failed to inhibit lordosis at all doses on subsequent weeks of testing. These results indicate that the ability of scopolamine to inhibit lordosis is reduced by increasing the dose or the number of estrogen exposures. Because higher doses of scopolamine failed to restore its inhibitory effect on lordosis an upregulation of muscarinic receptors by estrogen cannot account for the reduced effectiveness of scopolamine.

Light^dark differences in behavioral sensitivity to oxytocin.

Ovariectomized female rats treated with estradiol benzoate (EB) and progesterone (P) were infused intracerebroventricularly with a low (200 ng) or high (1 microgram) dose of oxytocin (OT). The low dose of OT facilitated lordosis behavior only during the dark phase of the light-dark cycle in females that were pretreated with low doses of EB (2 micrograms) and P (250 micrograms). In contrast, the high dose of OT facilitated lordosis behavior during both the light and the dark phases but only in long-term ovariectomized females that were primed with large amounts of EB (2 x 10 micrograms) and P (500 micrograms). In females that were primed with lower amounts of ovarian steroids, the high dose of OT failed to increase levels of lordosis responding in either the dark or light phase. Thus, when female rats are treated with physiological amounts of ovarian hormones and OT, they are more sensitive to the facilitative effects of the OT on lordosis behavior during the dark phase.

Cytosol and nuclear estrogen receptor binding in the preoptic area and hypothalamus of female rats during pregnancy and ovariectomized, nulliparous rats after steroid priming: Correlation with maternal behavior

In a previous study, high nuclear estrogen receptor concentrations in the preoptic area (POA) were found on Day 16 of pregnancy to prime females to respond to a subsequent low dose of estradiol benzoate (EB) after hysterectomyovariectomy by exhibiting maternal behavior in 48 hr. Receptor concentrations in the POA were found to be higher than those in the hypothalamus (HYP). The present study investigated when nuclear estrogen receptors increase during pregnancy in POA and when the difference in receptor concentrations between POA and HYP occurs. An attempt was made to reproduce these pregnancy changes with a 16-day treatment of estrogen and progesterone in Ovariectomized (OVX), nulliparous rats. In Experiment 1, we measured cytosol and nuclear estrogen receptor concentrations in the POA and HYP of female rats during pregnancy. Nuclear receptor concentrations in the POA increased beginning on Day 10, increased again on Day 16, and continued at this high level for the remainder of pregnancy. Nuclear estrogen receptor concentrations in the HYP remained at a lower level throughout most of pregnancy until Day 22 when they increased significantly. In Experiment 2, we tested the maternal behavior and measured estrogen receptor concentrations in OVX, steroid-primed, nulliparous rats after hysterectomy (H) and EB treatment. While 90% of estradiol (E) + progesterone (P)-primed females displayed short-latency maternal behavior 48 hr after H and EB treatment, 46% of E + vehicle (V)-treated controls were maternal. At 0 hr (prior to H and EB treatment), there was a significantly larger nuclear receptor accumulation in the POA but significantly attenuated receptor binding in the HYP. P treatment significantly affected cytosol and nuclear estrogen receptor dynamics. Differences in nuclear estrogen receptor concentrations were shown to be based on the number of available binding sites and not to changes in receptor affinity for estradiol.

Nuclear estrogen receptor binding in the preoptic area and hypothalamus of pregnancy-terminated rats: correlation with the onset of maternal behavior.

Terminating the pregnancies of female rats on day 16 (D 16) by hysterectomy and ovariectomy (HO) and administering estradiol benzoate (EB) systemically or centrally into the medial preoptic area (MPOA) stimulates the onset of maternal behavior 48 h later. Since estrogen's effects are mediated through its intracellular receptors, the present studies measured nuclear and cytosol estrogen receptor concentrations in the POA and hypothalamus (HYP) of female rats during the 48 h when estrogen is active in stimulating maternal behavior. A low dose of EB (5 micrograms/kg) was used which was effective in stimulating maternal behavior in D16HO females but not in nonpregnant HO females of two types. In D16 animals there was a significantly higher concentration of nuclear receptors in the POA than in the HYP at time 0 (before HO and EB) but thereafter levels were similar in the two areas: nuclear receptor levels rose between 6 and 24 h after which they declined. In nonpregnant females, nuclear receptor levels at time 0 were low in both brain regions, rose significantly between 0 and 24 h, and significantly declined between 24 and 48 h similar to the D16 females. There were minimal differences in cytosol receptor levels among all groups at any time. Results from additional groups, nonpregnant HO females given 100 micrograms/kg EB and D16H animals (females whose pregnancies were terminated by hysterectomy only and their ovaries left intact), both of which exhibit maternal behavior at 48 h, support the idea that a high level of nuclear estrogen receptors in the POA followed by a sustained high level is necessary for estrogen stimulation of maternal behavior.

Hypothalamic nuclear estrogen receptors and lordosis behavior in hamsters

These experiments examined the effects of a high and a low dose of estradiol benzoate (EB) in enhancing lordosis behavior and correlated these effects with the retention of hypothalamic nuclear estrogen receptors (NER) in female hamsters. Ten μg EB was significantly more effective in facilitating sexual receptivity in hamsters when it was followed 36 or 48 hr later by 0.5 mg progesterone (P), but not when P was given 24 hr after EB. Low levels of behavioral responses were observed in animals that received P at 24, 36 or 48 hr after 2 μg EB. Correspondingly, although the hypothalamic NER levels were equally elevated 24 hr after either a low or a high dose of EB, these receptor concentrations remained high at 36 and 48 hr post EB, only in those animals that received the high estrogen dose. The results of these experiments suggest that the long-term retention of NERs (which is maintained by a single high EB dose) may play an important role in the enhancement of sexual receptivity in hamsters.

Specificity and neural sites of action of anisomycin in the reduction or facilitation of female sexual behavior in rats

These experiments were designed to investigate the role of neuronal protein synthesis in the hormonal activation of female sexual behavior using intracranial implants of the protein synthesis inhibitor, anisomycin. In the first experiment, female rats receiving bilateral cannulae implants in the medial preoptic area (POA), septal region (SEPT), ventromedial hypothalamus (VMH), or midbrain central gray (CG) were injected with 2.5 μg estradiol benzoate (EB), followed 48 hr later by 500 μg progesterone (P). Females receiving anisomycin in the VMH at the time of EB injection had lower levels of lordosis and darting compared to tests without anisomycin. Sexual behavior was unaffected in females receiving anisomycin implants in the POA, SEPT, or CG. In a second experiment, we replicated the finding that anisomycin could attenuate lordotic responsivity when placed in the VMH of female rats injected with 2.5 μg EB and 500 μg P. In addition, we found that POA implants of anisomycin could facilitate lordosis in females given a low dose of EB (1.25 μg) plus 500 μg P. In a third experiment, we assessed the effects of anisomycin application to the VMH or POA of female rats receiving estradiol (E; diluted 1:250 with cholesterol) implants in the VMH and systemic P. Treatment of the VMH with anisomycin prior to E in the VMH suppressed lordotic responding, whereas anisomycin application to the POA prior to E in the VMH had no effect on lordosis. The results of these experiments suggest that reducing protein synthesis in the region of the VMH disrupts the action of estrogen on the VMH, and that the facilitative action of anisomycin in the POA of female rats requires more estrogen treatment than threshold stimulation of the VMH alone.

Estradiol and progesterone influence l-5-hydroxytryptophan-induced myoclonus in male guinea pigs: Sex differences in serotonin-steroid interactions

The effects of castration in males and sex differences in the effects of estradiol and progesterone on l-5-hydroxytryptophan ( l-5-HTP)-induced myoclonus in guinea pigs were examined. Castration had no effect on l-5-HTP-induced myoclonus in males. There were sex differences in sensitivity to l-5-HTP. In the absence of steroids, l-5-HTP-induced myoclonus was higher in gonadectomized males than females. A low dose of estradiol benzoate (EB; 3.5 μg) given 46 h before l-5-HTP (100 mg/kg) enhanced myoclonus in gonadectomized females but not males. However, at a higher dose of EB (10 μg) and a lower dose of l-5-HTP (80 mg/kg), myoclonic responding was enhanced in males. These findings indicate that estradiol has a similar effect on l-5-HTP-induced myoclonus in males and females, but do not rule out the possibility of sex differences in sensitivity to l-5-HTP when both sexes are given estradiol priming. When l-5-HTP was given 6 h after 0.5 mg progesterone in estradiol-primed males, myoclonus was enhanced. Progesterone treatment reverses the facilitative effect of EB on l-5-HTP-induced myoclonus in females. Therefore, progesterone has opposite effects on l-5-HTP-induced myoclonus in males and females. These findings were discussed with respect to the interaction of steroids and 5-HT transmission in the regulation of steroid-dependent reproductive behavior.

Positive Feedback Effect of Progesterone on Luteinizing Hormone (LH) Release in Cyclic Female Rhesus Monkeys

The synergistic effects of progesterone (P) and estrogen on LH release were examined in nine monkeys with regular menstrual cycles. During six menstrual cycles, animals were subjected, in alternate cycles, to each of the following treatments in random order beginning at 0830 on the third day of the cycle: 1) 30 <g estradiol benzoate (EB) sc, 2) 30 jug EB sc, followed by 2.5 mg P sc 24 h later, or 3) 330 <g EB sc. During the seventh menstrual cycle, all animals were assigned again to either treatment 1 or 2. Blood samples were obtained at 3- to 24-h intervals, and serum concentrations of LH, estradiol, and P were determined by RIA. The high dose of EB induced the characteristic negative feedback response of serum LH, followed by the positive feedback response which peaked 36–54 h after EB, while the low dose of EB induced initial small decreases of LH within 24 h after EB, followed by slight increases of LH during the second and third days after EB. P administration after the low dose of EB induced two dis...

Age-dependent participation of the adenohypophysis and adrenal cortex in the estrogenic response of the quail oviduct.

The purpose of this work was to study the role played by the pituitary in the overall estrogenic response of the quail oviduct during the first 30 days of life. The oviduct response (weight, soluble protein, and DNA content) was measured in castrated and castrated-hypophysectomized quails 24 h after a single im dose of 0.1 or 1 mg estradiol benzoate (EB)/kg BW. The effect of ACTH (0.5 mg/kg) and corticosterone (1 mg/kg) alone or in combination with EB has been investigated as well. The monitored parameters show different patterns as a function of age whether the castrated quails were injected with 0.1 mg or 1 mg EB/kg. These patterns are linear in quails treated with low doses of EB and nonlinear in animals treated with high doses of EB. In this latter group, the oviduct responses to EB, regardless of parameter measured, are constant from days 8-18, increase progressively from days 18-22, and are constant again from days 22-30. Hypophysectomy, ACTH administration, or corticosterone administration does not...

Concurrent inhibition of sexual behavior, but not brain [3H]estradiol uptake, by progesterone in female rats.

Chronic injections of high doses of progesterone (5 mg) and low doses of estradiol benzoate (EB; 2 microgram) resulted in less sexual behavior than did low doses of progesterone (.5 mg) and low doses of EB. In a typical procedure for inducing sexual behavior, EB and progesterone were given sequentially, separated by 42 hr. High levels of progesterone (2.5 and 5 mg) administered concurrently with EB inhibited the induction of sexual receptivity. Increasing the dose of EB from 2 microgram to 6 microgram or 10 microgram offset this inhibition. High doses of progesterone (5 mg) administered simultaneously or 2-16 hr prior to EB inhibited the induction of sexual behavior, but the inhibition waned when progesterone was administered 48 hr prior to EB. A single injection of progesterone (1 mg) that did not inhibit the induction of sexual behavior when administered concurrently with EB did inhibit lordosis when distributed into five injections (.2 mg) every 4 hr. The results of two experiments in which progesterone did not inhibit the uptake or retention of [3H]estradiol by brain cell nuclei suggest that the antiestrogenic action of progesterone in the central nervous system is not to interfere with the binding of estradiol.

Effects of septal lesions on behavioral sensitivity of female rats to gonadal hormones

Spayed female rats were given bilateral septal lesions or a sham operation and 3 wk later tested for hormone-induced female sexual behavior. When primed with 0.5, 1.0, or 2.0 μg of estradiol benzoate (EB) per day for 3 days and tested for lordosis behavior on the fourth day, animals with septal lesions showed a positive dose-related increase in mean lordosis quotient (LQ), whereas control animals showed a low mean LQ for all doses of EB. After priming with a low dose of EB (0.5 μg/day for 3 days), progesterone administration prior to behavior testing on day 4 produced a comparable facilitation in LQ for both septal-lesioned and sham-operated animals. When treated for 3 days with either 50 or 150 μg of testosterone propionate (TP) and given progesterone prior to behavior testing on day 4, female rats with septal lesions showed a higher mean LQ than sham-operated rats. Thus, septal lesions increase the behavioral sensitivity of female rats to both EB and TP as measured by female sexual behavior, but do not appear to alter the responsiveness of animals to progesterone.

Intranuclear inclusions in mammotrophs of the Mongolian gerbil: Effect of low doses of estradiol benzoate and a study of females before weaning

The effect of dose of estrogen on induction of intranuclear inclusions was studied in mammotrophs of the Mongolian gerbil. The number of inclusions per high power field increased significantly with 0.5 and 1.0 μg/day of estradiol benzoate but not with the 0.05 μg dose. A form of inclusion was seen in young female gerbils before weaning which suggests that inclusions arise from the cytoplasm. Intranuclear inclusions develop soon after weaning of gerbils (0.06 ± 0.01 vs. 0.19 ± 0.03 for young mature females).

The role of estrogen in the regulation of erythropoietin production.

Low doses of estradiol benzoate (2.5-10.0 μg/day X 5) inhibited the production of erythropoietin (Ep) in female rats exposed to various intensities of hypoxia. This was not attributable to the presence of either residual estradiol, or an inhibitor of Ep in plasma samples, since these plasmas had no inhibitory effect on Ep simultaneously injected into assay mice. Although normal females produced less Ep in response to hypoxia than normal males, ovariectomized rats showed a response equal to males. Estradiol treatment of ovariectomized animals lowered their Ep response to hypoxia down to the level of intact females. Only the largest dose employed (10.0 μ/day) had some inhibitory effect on Ep production in hypoxic males. (Endocrinology 92: 358, 1973)