Estradiol Pulses Research Articles

Chronic stress and a cyclic regimen of estradiol administration separately facilitate spatial memory: Relationship with hippocampal CA1 spine density and dendritic complexity.

This study investigated the effects of chronic restraint stress and repeated cyclic estradiol pulses on hippocampal CA3 and CA1 dendritic and/or spine morphology and spatial memory in female rats. Sprague-Dawley adult female rats were ovariectomized and then injected over 2 days with 17β-estradiol (10 μg, s.c.), which was repeated every 4-5 days. While all rats received similar estradiol injection histories, half of the rats were chronically restrained and/or given a final cyclic pulse of estradiol prior to testing on a hippocampal-dependent object placement (OP) task to assess spatial memory. OP testing was performed 2 days after the last restraint session, as well as when the last 2 estradiol pulses best captured the maximal effect on hippocampal CA1 spine density. The data revealed several novel findings: (a) chronic stress or estradiol separately facilitated spatial memory, but did not have the same effects when coadministered, (b) CA1 spine densities negatively correlated with spatial memory, and (c) repeated estradiol pulses failed to prevent stress-induced CA3 dendritic retraction. We also corroborated previous studies showing increased CA1 spine density following estradiol, chronic stress, and behavioral manipulations. The present study uniquely combined chronic stress, repeated estradiol pulses, hippocampal morphology, and behavior within the same animals, allowing for correlational analyses to be performed between CA1 spine morphology and spatial memory. We demonstrate novel findings that chronic stress or estradiol pulses independently facilitate spatial memory, but not when coadministered, and that these effects may involve a balance of CA1 apical spine expression that is independent of CA3 dendritic complexity.

An enzyme linked immunosorbant assay (ELISA) for testosterone, estradiol, and 17,20β-dihydroxy-4-pregenen-3-one using acetylcholinesterase as tracer: application to measurement of diel patterns in rainbow trout (Oncorhynchus mykiss)

A simple and rapid Enzyme Linked ImmunoSorbant Assay (ELISA) is described and validated for testosterone, estradiol, and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP). A general procedure for preparation of the acetylcholinesterase labeled steroid is described which is applicable to any steroid. Use of acetylcholinesterase tracer increased the sensitivity of assay so that reliable measurements of each steroid could be achieved with only 10 μl of plasma. The ELISA was applied to measurement of all three steroids every hour for over 24 hours in a female trout using cannulation of the dorsal aorta. This high sampling frequency revealed several short-term (<2 h) episodic pulses of testosterone and estradiol.

Paced Mating Behavior in Female Rats in Response to Different Hormone Priming Regimens

A female rat will display a repertoire of behaviors during a sexual encounter with a male rat including sexually receptive (the lordosis response) and proceptive (hopping, darting) behaviors. In addition, when given the opportunity, a sexually receptive female rat will approach and withdraw from the male rat, controlling the timing of the receipt of mounts, intromissions, and ejaculations, a behavior known as paced mating behavior. The present experiments tested the hypotheses (1) that progesterone regulates paced mating behavior, and (2) that multiple hormone regimens used previously to induce sexual receptivity have the same effect on paced mating behavior. Paced mating behavior was assessed in sexually receptive ovariectomized female rats after treatment with: (1) estradiol benzoate (EB; 30.0 mg/kg) followed by a range of doses of progesterone (P; 1.0–8.0 mg/kg), (2) two pulses of unesterified estradiol (E2; 2.0 μg/rat) followed by 1.0 mg/rat of P, and (3) EB alone (5.0 μg/rat) for 6 days. No differences in sexual receptivity or in paced mating behavior were observed across doses of P (1.0–8.0 mg/kg). In contrast, the number of hops and darts per min increased with the dose of P administered. E2+ P administration resulted in slightly, but significantly, lower levels of sexual receptivity along with significantly longer contact-return latencies following an intromission in relation to the other treatment conditions. In addition, female rats exhibited fewer hops and darts per min in response to E2+ P than in response to EB + 8.0 mg/kg of P. The administration of EB alone for 6 days induced levels of receptivity and paced mating behavior indistinguishable from EB + P, while eliciting significantly fewer hops and darts per min than the EB + 8.0 mg/kg P treatment condition. Hormone priming regimen had no effect on the percentage of exits displayed during the paced mating tests in any experimental phase. Dose of P had no effect on paced mating behavior in sexually receptive rats. In addition, P does not appear to be necessary for the display of paced mating behavior following long-term treatment with EB. In contrast, the pulsatile administration of E2+ P induced a different pattern of paced mating behavior in sexually receptive rats.

Acute, nongenomic actions of the neuroactive gonadal steroid, 3 alpha-hydroxy-4-pregnen-20-one (3 alpha HP), on FSH release in perifused rat anterior pituitary cells.

We have previously shown that the gonadal and neurosteroid, 3 alpha-hydroxy-4-pregnen-20-one (3 alpha HP), can selectively suppress gonadotrophin-releasing hormone (GnRH) induced follicle-stimulating hormone (FSH) release from static cultures of anterior pituitary cells during a 4-h incubation period. The actions appeared to be at the level of the gonadotroph membrane and the cell signaling pathway involving Ca2+ and protein kinase C (PKC). In order to investigate further if the effects of 3 alpha HP on FSH release are generated by nongenomic mechanisms, we monitored the short-term effects of 3 alpha HP using dispersed anterior pituitary cells in a low dead-volume perifusion system with short (< or = 5 min) exposures to the steroid. Pulses of GnRH (10(-8) or 10(-7) M) lasting 2-5 min resulted in marked peaks of FSH release, and the variation in FSH amounts released from the cells in a particular column were minimal if the interval between successive GnRH pulses was at least 3-4 h. A 5-min pulse of 3 alpha HP (10(-9) M) administered simultaneously with the GnRH pulse suppressed GnRH-induced FSH release. On the other hand, similar treatment with the stereoisomer 3 beta-hydroxy-4-pregnen-20-one (3 beta HP), had no effect, but progesterone and estradiol pulses augmented the GnRH-induced FSH release. Pretreatment of cells with a 5-min pulse of 3 alpha HP, at 120, 60, or 30 min prior to a GnRH pulse suppressed the GnRH-induced FSH release. The suppression of GnRH-induced FSH release by 3 alpha HP was only partial if the start of the 3 alpha HP pulse occurred 0.5 or 1.0 min after the start of the GnRH pulse, and no suppression occurred if the start of the 3 alpha HP pulse was delayed by 2-5 min. The FSH release elicited by 5-min pulses of the Ca2+ ionophore A23187, the Ca2+ agonist BAY K8644, the PKC activator phorbol 12-myristate 13-acetate (PMA), or phospholipase C (PLC) was suppressed by simultaneous pulses of 3 alpha HP. The suppression of FSH release by 3 alpha HP appeared to be stereospecific, since no suppression was observed with 5 alpha-pregnane-3,20-dione (5 alpha P) or 3 alpha-hydroxy-5 alpha-pregnan-20-one (5 alpha P3 alpha). In separate experiments, cells were treated with pulses of BSA conjugates of 3 alpha HP, 3 beta HP, or progesterone; the 3 alpha HP-BSA, but not the 3 beta HP-BSA or the progesterone-BSA, suppressed the GnRH-induced release of FSH. The results of this study provide the first evidence that 3 alpha HP exerts immediate (nongenomic) and direct effects on GnRH-induced FSH release by interacting at the level of the pituitary gonadotroph membrane and the phosphoinositol cell signaling cascade involving Ca2+.

A one minute pulse of estradiol to MCF-7 breast cancer cells changes estrogen receptor binding properties and commits cells to induce estrogenic responses.

Changes in estradiol (E2)-binding parameters can be detected within minutes, while the estrogenic responses are manifested after several hours or days of continuous exposure to the steroid. The goal of this study was to determine the time of commitment for the induction of transcription-dependent responses in the human breast cancer cell line MCF-7. In cultures grown in steroid-deprived serum, a pulse of 1 nM E2 as short as 1 min was sufficient to maximally increase the level of the progesterone receptor, as determined by binding of the progestin [3H]ORG.2058 after 2 days, and to partially stimulate cell proliferation for 5 days. From uptake experiments it was calculated that after 1 min about 7000 E2 molecules were bound per cell, enough to occupy 5% of the approx. 150,000 estrogen receptors per cell. Preincubating cells with unlabelled E2 for 1 min lead to a loss of [3H]E2-binding capacity. As analysed by Scatchard plot, this loss was due to a decrease in the number of exchangeable binding sites and, to a lesser extent, to an increase in the dissociation constant. For up to 30 min of E2-incubation the level of receptor protein remained constant as determined by immunoassay with the anti-ER monoclonal antibodies D547 and H222. The dissociation kinetics of [3H]E2 bound by MCF-7 cells after a 5 min pulse were biphasic, with the slower phase having a rate of 2.3 x 10(-3) min. This rate is characteristic of the activated ER. The estrogenic response is thus committed by E2 within less than 1 min and evoked by the activation of a small fraction of estrogen receptors.

Estrogen increases the density of 5-Hydroxytryptamine2A receptors in cerebral cortex and nucleus accumbens in the female rat

Estrogen exerts a profound effect on mood and mental function in man. Based on our finding that estradiol selectively stimulates the expression of 5-hydroxytryptamine(2A) (5-HT2A) receptor mRNA in the dorsal raphe nucleus of the female rat, we investigated the effects of estradiol on the density of 5-HT2A receptors in brain. The distribution and density of 5-HT2A receptors were determined by in vitro binding of [3H]ketanserin in the presence of prazosin to exclude binding to alpha 1-adrenoreceptors. Brains were collected, processed and analysed in pairs from six estradiol- and six vehicle-treated animals. Our results show that a single pulse of estradiol induces a significant increase in the density of 5-HT2A receptors in female rat forebrain, particularly the anterior frontal, anterior cingulate and primary olfactory cortex and the nucleus accumbens. Since these brain regions play a pivotal role in cognition and emotion, as well as neuroendocrine and motor control, our findings provide the first experimental evidence for the fact that estrogen could alter mood and mental state by increasing the density of 5-HT2A receptors in cerebral cortex and nucleus accumbens.

Progestin receptors in substance P-immunoreactive neurons in the hypothalamus of male guinea pigs after behaviorally effective estradiol pulse treatment.

Pulsatile administration of estradiol effectively primes orchidectomized (ORCH) male guinea pigs to display progesterone-facilitated lordosis. In contrast, a single injection of estradiol benzoate (EB) is not behaviorally effective. In ovariectomized female guinea pigs, estradiol pulses induce progestin receptors selectively in substance P neurons in the ventrolateral hypothalamus (VLH), a site at which estradiol primes females to respond behaviorally to progesterone. To test the hypothesis that behaviorally effective estradiol pulses induce progestin receptors selectively in substance P neurons in the VLH in males, ORCH animals received a single injection of EB 40 h before, or two pulses of estradiol-17 beta, 39 and 11 h before perfusion. Colchicine was administered intracerebroventricularly prior to perfusion. The only difference found between the two estradiol treatment groups was a higher number of progestin receptor-immunoreactive (PR-IR) cells in the rostral VLH of estradiol pulse-treated males. There were no significant differences in the number of PR-IR cells in the mid- or caudal VLH, nor in the number of substance P-immunoreactive (SP-IR) neurons in the VLH/ventromedial hypothalamus (VMH) of animals receiving the two estradiol treatments. Furthermore, the percentage of PR-IR cells in the VLH also immunoreactive for SP did not differ between the estradiol pulse- (22%-25%) and the EB-injected animals (22%-32%). These data do not support the hypothesis that administration of behaviorally effective estradiol pulses, as compared to behaviorally ineffective EB injections, induce progestin receptors selectively in substance P neurons in the VLH of male guinea pigs.

Sex differences in estrogen receptor binding in the rat hypothalamus: effects of subsaturating pulses of estradiol

The effects of subsaturating pulses of estradiol on cell nuclear retention of estrogen receptors in brain regions of male and female rats was determined. In the first experiment, age-matched adrenalectomized/gonadectomized (ADX/GDX) rats were killed 1 h after i.v. injection of a subsaturating dose of free estradiol (1.0 μg/kg b. wt.) and cell nuclear estrogen receptor binding was measured in microdissected brain areas by an in vitro exchange assay. As we have previously reported with saturating doses of estradiol (3.6–36.0 μg/kg b. wt.), a greater concentration of receptors was measured in the ventromedial nucleus (VMN), periventricular preoptic area (PVPOA), and medial preoptic area (mPOA) of the female than in the same regions of the male brain. Binding levels did not differ between the sexes in the bed nucleus of the stria terminalis, arcuate nucleus, or the corticomedial amygdala. In the second experiment, GDX/ADX male and female rats received either a single or double pulse of 0.5 μg estradiol/kg b. wt. administered 6 h apart. Rats were killed 1 h after the second pulse. In animals treated with a single pulse of estradiol 1 h before sacrifice, higher concentrations of estrogen binding were measured in the female VMN and PVPOA than in the male. Except in the mPOA, the concentration of estrogen receptor binding measured was not different from that measured in animals that had received an additional, earlier pulse of estradiol. In this area, receptor concentrations were lower in male rats treated with two pulses than in males treated with one pulse. Thus, receptor dynamics in the mPOA of the male may differ from that of the female and from that of other brain regions. In the third experiment, cytosol estrogen receptor concentrations measured in untreated male and female GDX/ADX rats were compared. Consistent with our data on cell nuclear binding after exposure to estradiol, cytosol receptor concentrations in the female VMN, PVPOA and mPOA were greater than those in the male. These results extend our previous findings of regional sex differences in maximal cell nuclear estrogen binding capacity by demonstrating that these differences exist in the presence of subsaturating pulses of estradiol and that they reflect differences in cytosol estrogen receptors.

Estradiol pulses induce progestin receptors selectively in substance P-immunoreactive neurons in the ventrolateral hypothalamus of female guinea pigs.

Low doses of estradiol, administered as pulses, are as effective as higher doses for priming ovariectomized (OVX) guinea pigs to display progesterone-facilitated lordosis. High doses of estradiol, administered by constant-release implants, induce progestin receptors in many substance P-immunoreactive (SP-IR) neurons in the ventrolateral hypothalamus (VLH), a site at which estradiol primes OVX guinea pigs to respond behaviorally to progesterone. To test the hypothesis that behaviorally effective estradiol pulses induce progestin receptors selectively in substance P-containing neurons in the VLH, OVX females received estradiol implants 1 week prior to perfusion, or two pulses of estradiol-17 beta, injected 39 and 11 h before perfusion. Colchicine was administered intracerebroventricularly prior to perfusion. No significant differences were observed in the total number of progestin receptor-immunoreactive (PR-IR) or substance P-immunoreactive cells in the VLH and VLH/ventromedial hypothalamus (VMH), respectively, of females receiving the two estradiol treatments. However, the percentage of PR-IR cells in the VLH also immunoreactive for SP was significantly higher in the estradiol pulse-treated (53%), than in the estradiol capsule-implanted animals (36%). These data suggest that behaviorally effective estradiol pulses induce progestin receptors selectively in substance P-containing neurons in the VLH and are consistent with the hypothesis that substance P is involved in progesterone-facilitated lordosis in guinea pigs.

Progesterone facilitates lordosis, but not LH release, in estradiol pulse-primed male rats

Gonadectomized (GDX) male and female rats received repeated cycles of estradiol pulses, which prime animals of both sexes to display progesterone-facilitated lordosis. One, three and six treatment cycles of estradiol pulses followed by progesterone induced progressively higher luteinizing hormone (LH) surges in GDX females. Six treatment cycles of estradiol pulses alone (i.e., without subsequent progesterone treatment) induced a small but significant (∼4 ng/ml) increase in LH levels in GDX females. In contrast, GDX males never produced LH surges in response to estradiol pulses alone or estradiol pulses followed by progesterone, regardless of the number of hormone treatment cycles. Thus, female patterns of steroid-induced sexual receptivity and LH release are not inextricably linked, as steroid treatments sufficient for induction of lordosis do not stimulate LH secretion in adult male rats. These data also suggest that the neural system governing the LH surge might be more firmly sexually differentiated than that responsible for sexual receptivity in rats.

Pulsatile Cosecretion of Estradiol and Progesterone by the Midluteal Phase Corpus Luteum: Temporal Link to Luteinizing Hormone Pulses*

Using recently defined analytical tools that permit quantitative and integrated assessments of pulsatile activities of two or more hormones, we have examined the coincidence of pulses of estradiol (E2), progesterone (P4), and LH determined in blood withdrawn at 15-min sampling intervals for a duration of 24 h in each of 15 women during the midluteal phase of the human menstrual cycle. The occurrence of E2 and P4 pulses is simultaneous, as their peaks were maximally correlated at zero time lag (P less than 10(-4], and there were comparable periodicities for E2 (13.5 +/- 0.7 pulses/24 h) and P4 (11.2 +/- 0.7 pulses/24 h). This coupling of E2 and P4 pulses suggests cosecretion by the mature corpus luteum. These E2 and P4 pulses are significantly coupled with LH pulses, with a lag time of about 30 min and/or 45 min for P4 (P = 0.029) and 0 min and/or 15 min for E2 (P = 0.032). Further, when considered together, LH, E2, and P4 are found to be triply copulsatile (P = 0.0066). However, significant numbers of discrete pulses of P4 and E2 are observed without antecedent LH pulses, suggesting some degree of corpus luteum autonomy. In conclusion, orchestrated synchrony of pulsatile pituitary and ovarian (corpus luteum) signaling can be demonstrated by the coordinated temporal release of LH, E2, and P4 in normal cycling women.

Biochemical and Immunocytochemical Assessment of Neural Progestin Receptors Following Estradiol Treatments that Eliminate the Sex Difference in Progesterone‐Facilitated Lordosis in Guinea‐Pigs

Abstract A single injection of estradiol benzoate (10 mug), while highly effective in ovariectomized female guinea-pigs, does not prime castrated males to display progesterone-facilitated lordosis. In contrast, adult males and females exhibit the same, high degree of progesterone-facilitated lordosis when primed with two, 2.0 mug injections of free estradiol-17ss (pulse regimen). We compared neural progestin receptor induction after these different estradiol treatments by in vitro radioligand binding assays and immunocyto-chemistry. Binding assays confirmed previous observations of lower concentrations of cytosol progestin receptors in the mediobasal hypothalamus-preoptic area in estradiol benzoate-treated males than in females. No such sex difference was observed in animals that had been exposed to the behaviorally effective estradiol pulse regimen; rather, hypothalamic-preoptic area progestin receptor concentrations in these animals did not differ from the low levels observed in males treated with the behaviorally ineffective estradiol benzoate regimen. Immunocytochemical analysis revealed progestin receptor-immunoreactivity in fewer cells in the medial preoptic nucleus-anterior hypothalamic nucleus, periventricular preoptic area and arcuate nucleus of estradiol pulse- as compared to estradiol benzoate-treated males and females. Estradiol benzoate treatment induced progestin receptor-immunoreactivity in more cells in the medial preoptic area and ventrolateral hypothalamus than estradiol pulses in males, but not in females. Surprisingly, in these regions estradiol benzoate-treated males had significantly more progestin receptor-immunoreactive cells than females. These experiments yield two major findings: First, as has been shown in rats, the display of progesterone-facilitated lordosis is not inflexibly differentiated according to sex in guinea-pigs. Furthermore, reduced concentrations of estradiol-induced progestin receptors in the hypothalamus and preoptic area cannot account for the lack of progesterone-facilitated lordosis that is observed following priming with estradiol benzoate in males. Secondly, in the medial preoptic area and ventrolateral hypothalamus of female guinea-pigs, estradiol pulses are as effective as estradiol benzoate in inducing progestin receptors. These observations, taken together with the finding of equal behavioral efficacy of the two estradiol treatments, are consistent with the hypothesis that estradiol-induced progestin receptors in these regions of the brain are involved in progesterone-facilitated lordosis in female guinea-pigs.

Pulsatile Secretion of Ovarian Steroids in the Mid-luteal Phase of the Menstrual Cycle

The possibility of the pulsatile secretion of pituitary gonadotropins (LH and FSH) and ovarian steroids (estradiol and progesterone) was studied. In addition, an evaluation was made of the regulatory factors for steroid secretion of corpus luteum in view of the response behavior of the secretion of LH, FSH, estradiol and progesterone when loaded with hCG and gonadotropin releasing hormone (Gn-RH). The study was performed on 9 cases of infertile women in the mid-luteal phase of a normal menstrual cycle. In 5 cases, blood was collected every 30 minutes and over 24 hours. Thereafter, 2,500 iu of hCG was given twice to another subject at 8 hour intervals, and blood was collected every 30 minutes from immediately after the 1st administration over 16 hours. In the other 3 cases, 15 micrograms of Gn-RH was given at an interval of 90 minutes, and blood was collected every 20 minutes for 16-24 hours. Then, the frequency and amplitude of each pulse for LH, FSH, estradiol and progesterone were calculated under the modified Santen's rule in situ and when loaded with Gn-RH, and the relationship between pulses of gonadotropins and those of estradiol and progesterone was analysed by determining the number of concomitant pulses. The hormone dynamics when loaded with hCG were also assessed. The pulse frequency and amplitude in situ of each hormone were 10.6 +/- 0.8 times/24 h and 4.9 +/- 0.6 miu/ml for LH, 9.9 +/- 9.9 times/24h and 1.3 +/- 0.1 miu/ml for FSH, 9.2 +/- 0.9 times/24h and 34.3 +/- 2.7 pg/ml for estradiol, 7.4 +/- 0.5 times/24 and 3.7 +/- 0.4 ng/ml for progesterone. The coincidence of estradiol pulses and LH pulses was 37 times, and the concomitant ratio of LH pulse to estradiol pulse was 81%. The coincidence of progesterone pulses and LH pulses was 31 times, and the concomitant ratio of LH pulse to progesterone pulse was 84%. Furthermore, the concomitant ratio of FSH pulse to estradiol pulse or progesterone pulse was 61% or 70%, respectively. The mean plasma concentration of LH, estradiol and progesterone during 8 hours after the 1st administration and 2nd administration of hCG changed from 29.9 +/- 2.3 to 41.8 +/- 1.6 miu/ml, from 140.3 +/- 3.0 to 160.6 +/- 3.6 pg/ml and from 19.2 +/- 1.0 to 25.7 +/- 0.6 ng/ml, respectively. These values increased significantly after the second injection (P less than 0.001).(ABSTRACT TRUNCATED AT 400 WORDS)

Modulation by Norepinephrine of Neural Responses to Estradiol

Pharmacological studies have suggested that neurotransmitter activity impinging on steroid-concentrating cells can affect the steroid receptor system within those cells, modifying behavioral responses to the hormone. The present experiments revealed that the alpha 1-noradrenergic antagonist prazosin, administered to ovariectomized rats at the time of each of two pulses of estradiol, inhibited the appearance of sexual receptivity. Prazosin also substantially reduced the levels of estrogen receptors within hypothalamic cell nuclei following an injection of estradiol. Manipulation of noradrenergic inputs into the hypothalamus by lesioning brain stem norepinephrine cell groups with 6-hydroxydopamine (6OHDA) also reduced the level of nuclear estrogen receptors following an injection of estradiol. Although this effect of 6OHDA lesions was observed in two separate experiments, in other experiments 6OHDA had no effect on estrogen receptors. In some instances, there was a positive correlation between nuclear estrogen receptor levels in the hypothalamus and the levels of norepinephrine. The results are consistent with the hypothesis that brain stem inputs to the hypothalamus are able to modulate neural responses to steroids and specifically that noradrenergic inputs are able to modulate neural responses to estradiol. However, there are additional undiscovered variables that preclude statements of a simple relationship between norepinephrine levels and estrogen receptor levels.

Progesterone facilitation of lordosis in male and female Sprague-Dawley rats following priming with estradiol pulses

Adult male Sprague-Dawley rats rarely exhibit progesterone-facilitated lordosis following steroid treatments which are effective in females. In contrast, progesterone-facilitated lordosis has been observed following priming with estradiol pulses in another strain. The aim of this study was to compare progesterone-facilitated feminine sexual behavior in adult male and female Sprague-Dawley rats following priming with estradiol benzoate (EB) or estradiol pulses. Female sexual behavior was measured in adult, gonadectomized males and females treated as follows: Two pulses of estradiol followed by progesterone or oil the next day; EB (two doses) for 3 days, and progesterone or oil the next day. These protocols were repeated at 4- or 6-day intervals, respectively. Progesterone-facilitated lordosis was observed consistently in both sexes treated with estradiol pulses. By the fifth test, lordosis quotients did not differ between the sexes, but the lordosis ratings in progesterone-treated males remained lower than those observed in females. Proceptivity (hop-darting) was facilitated by progesterone in females, but was never observed in males. Lordosis was induced in both sexes by 15 μg EB, but was not reliably facilitated by progesterone. Treatment with the lower dose of EB (1.5 μg) induced high levels of receptivity in females (occasionally facilitated by progesterone), but not in males regardless of subsequent treatment (i.e, progesterone or oil). These data suggest that progesterone-facilitated lordosis can be induced in male Sprague-Dawley rats, if a regimen of estradiol pulses is used. Thus, the brain of the adult male is not inflexibly differentiated with regard to progesterone facilitation of feminine receptive behavior.

Characterization and therapeutic use of hormone dependency of breast cancer.

SummaryOur work, centered on hormone dependency hreast cancer, has therapeutic and fundament al implications in two main domains:1. Characterization of hormonal responsiveness by receptor assays:Among clinical, biochemical and pathological data, estrogen receptors (ER) are the best barkers of responsiveness to hormonal treatments. The quantitative assay is particularly informative, and a model linking ER concentration to the probability of response has been created, nich guides the clinician for the treatment of indual patients. It is also helpful for the Prospective study of new treatments on groups of Patients.2. Use of interactions between hormones and Wotoxic drugsOn a murine model, it was shown that one single pulse of estradiol exerts a transient vmitogenic effect. This manipulation allows, under very stringent conditions, to amplify the an titumioral action of a cycle-active cytotoxic drug.The concept is now under study in a randomized clinical trial in which patients receive chmotherapy preceeded ...

Effective intervals for the administration of estradiol pulses and the induction of sexual behavior in female rats

The interval between two pulses of estradiol was varied and subsequent progesterone-facilitated female sexual behavior was observed. The total dose of estradiol (2 μg free estradiol) has been shown previously to elicit little receptivity when administered in a single pulse. In the present study, two pulses of 1.0 μg free estradiol separated by anywhere from 3–36 hours induced high levels of progesterone-facilitated receptivity when observed 18 hours after the second estrogen pulse. Various intervals between the second estrogen pulse and the time of testing were also evaluated. Female rats tested at 18, 24 and 36 hours after the second estrogen pulse (plus progesterone) were highly receptive. These results raise new possibilities about the time course of cellular events underlying the estrogen induction of feminine sexual behavior.

Incorporation of amino acids into proteins of the hypothalamus of prepuberal female rats after estradiol treatment.

The arcuate nucleus-median eminence complex (AM) undergoes major structural and functional changes during normal puberty or if exposed to a pulse of estradiol in the prepuberal period. Those changes are expressed by increased synaptogenesis and by a drastic alteration in the feedback control of anterior pituitary gland hormone release. In this study we investigated the effects of estradiol benzoate (EB) on specific proteins in this hypothalamic area. Prepuberal, 25-day-old female rats were administered 10 micrograms of EB s.c. in oil or sesame oil vehicle. The animals were decapitated either 17 or 42 h after treatment. The brains were removed, blocked and serially sections at 300 micron using a Vibratome. The AM was dissected out and incubated for 6 h in a medium containing 35S-methionine and 35S-cysteine. Proteins from the AM were separated by two-dimensional gel electrophoresis, and the gels were exposed to X-ray film. The resulting autofluorographs were analyzed by scanning densitometry. The results show that the incorporation of labeled amino acids was increased in 10 proteins and decreased in 2 proteins in rats killed 17 h after EB. At 42 h after EB, 6 proteins showed an increased incorporation of amino acids and two proteins showed a decrease. Our results suggest that one or several of these proteins might be involved in the neuroendocrine and structural changes observed in the AM during puberty.

Sensitivity of the hormone dependent MXT-mouse mammary carcinoma to estradiol during tumoral growth. An autoradiographic study

The MXT transplantable mammary tumor is an ovarian sensitive carcinoma of the B6D2F1 mouse strain. The present work documents the mitogenic effect of a single near-physiological dose (pulse) of estradiol (E2) in castrated mice bearing MXT neoplasms 2–7 weeks after their inoculation. Histological sections of tumors and uteri (as control E2 target organs) were processed and nuclear thymidine labeling indices (TLI) were determined by autoradiography. Tumor estrogen receptors contents were evaluated in parallel. The results indicate that the MXT tumor keeps a constant sensitivity to E2 6 weeks after implantation.

Pulsatile versus continuous estradiol exposure in inducing proliferation of cultured ZR-75.1 Human breast cancer cells

Estradiol induces proliferation of ZR-75.1 human breast cancer cells cultured as a monolayer using minimum essential medium supplemented with 10% charcoal treated fetal bovine serum. Comparing continuous and pulsatile estradiol treatment we could not observe any amplification or limitation of growth effects when we corrected for the different time of exposure. We could perfectly predict cell number by summarizing growth effects of all estradiol pulses and therefore conclude that estrogen receptor is a “sensor” that measures the time of estradiol exposure in a linear manner whereas the estradiol concentration is recognized in a non-linear fashion as predicted by the law of mass action which governs steroid-receptor interaction.