Low-dose Estradiol Research Articles

Selective release of luteinizing hormone by 3 alpha-hydroxy-5 alpha-pregnan-20-one in immature ovariectomized estrogen-primed rats.

This study investigated the role of 3 alpha-hydroxy-5 alpha-pregnan-20-one (3 alpha,5 alpha-THP) in the modulation of gonadotropin secretion using the immature ovariectomized (OVX) rat primed with a low dose of estradiol. A treatment regimen of either 0.2 or 0.4 mg/kg of 3 alpha,5 alpha-THP given in conjunction with estradiol for 4 days significantly increased levels of serum luteinizing hormone (LH) but had no effect on serum follicle-stimulating hormone (FSH). Estrogen-primed rats receiving a single injection of 3 alpha,5 alpha-THP at 0930 h showed an increase in serum and pituitary LH levels at 1200 h and 1500 h. At 1800 h, only pituitary levels of LH remained significantly higher than controls. An injection of 3 alpha,5 alpha-THP at 1230 h in estrogen-primed rats resulted in enhanced levels of pituitary LH at 1500 h and elevated levels of both serum and pituitary LH at 1800 h. When 3 alpha,5 alpha-THP was given at 0930 h and 1230 h, elevated serum levels of LH were maintained for over 6 h. The administration of pentobarbital (Pb) 30 min after an injection of 3 alpha,5 alpha-THP at 0930 h or 1230 h prevented the increases in serum LH at 1200 h, 1500 h or 1800 h. This suggests that LH-releasing hormone (LHRH) is involved in mediating the LH response by 3 alpha,5 alpha-THP. There was no change in the sensitivity of the pituitary to LHRH following 3 alpha,5 alpha-THP treatment, indicating the absence of a pituitary effect of this steroid.

Selective release of follicle-stimulating hormone by 5 alpha-dihydroprogesterone in immature ovariectomized estrogen-primed rats.

The effect of 5 alpha-dihydroprogesterone (5 alpha-DHP) on gonadotropin release was examined in the immature acutely ovariectomized (OVX) rat primed with a low dose of estradiol (E2). Treatment with various doses of 5 alpha-DHP given in combination with E2 increased levels of follicle-stimulating hormone (FSH) but had no effect on serum luteinizing hormone (LH). A single injection of a maximally stimulating dose of 5 alpha-DHP (0.4 mg/kg) stimulated increases in serum FSH at 1200 h and, 6 h later, at 1800 h. Pituitary LH and FSH content was dramatically enhanced by 1600 h and levels remained elevated at 1800 h. The administration of pentobarbital at 1200 h, versus 1400 h or 1600 h, prevented the increase in basal serum FSH levels at 1800 h, implying that the release of hypothalamic LH releasing hormone (LHRH) is modulated by 5 alpha-DHP. In addition, changes in pituitary sensitivity to LHRH as a result of 5 alpha-DHP were measured and a significant increase in the magnitude of FSH release was observed at 1200 h and 1800 h. Although the LH response to LHRH in 5 alpha-DHP-treated rats was not different from controls, the duration of LH release was lengthened. These results suggest that 5 alpha-DHP may stimulate FSH release by a direct action at the pituitary level. Together, these observations support the theory that 5 alpha-DHP mediates the facilitative effect of progesterone on FSH secretion and further suggests an action of 5 alpha-DHP in this phenomenon at both pituitary and hypothalamic sites.

Estrogen-stimulated uptake of plasminogen by the mouse uterus.

Administration of a single low dose of estradiol to the immature (4- to 5-week-old) female mouse caused a rapid, uterine-specific increase in the uptake of radiolabeled plasminogen from plasma. A significant increase in uptake was detectable within 30 min and reached a maximum 2-4 h after administration of the hormone. After 4 h, a substantial amount (42%) of the newly taken up plasminogen was found in the uterine lumen. Half-maximal stimulation of uptake occurred at a dose of 0.20 microgram estradiol/animal. Estrogen stimulation of uptake was not blocked by puromycin, indicating that new protein synthesis was not required. Similar results were obtained with mouse plasma albumin. Estrogen-stimulated uptake was not blocked by indomethacin (10 micrograms/g BW, iv), but was blocked by prednisolone. Approximately 50% inhibition of the stimulation induced by 0.5 microgram estradiol in these 10-g animals was accomplished with 50 micrograms prednisolone. This study extends our initial findings on the estrogen-stimulated uptake of plasma proteins by the mouse uterus and provides a mechanism by which uterine plasminogen levels can be elevated before implantation.

Role of the nongravid part of the uterus in the luteolytic effects of estrogen in pregnant rats.

Effects of a low dose of estradiol on the luteal function were studied in intact pregnant rats. The pregnant rats received daily sc injections of 0.1 microgram estradiol or sesame oil from day 7 to 14 of pregnancy (day 1 = day of insemination). Serum progesterone levels on day 15 were significantly lower in the estrogen-treated group than in the oil-treated group. In order to study how estrogen induced luteolysis, the pregnant rats received each of the following treatments on day 7 of pregnancy: (1) The uterus except that containing a single conceptus was removed by hysterectomy (hysterectomy group); (2) All but a single conceptus were removed by aspiration, so that rats carried only a single conceptus with the whole part of the nongravid uterus (aspiration group). Each group of rats received also sc injections of 0.1 microgram estradiol or sesame oil from day 7 to 14 of pregnancy. Estradiol treatment caused a significant decline in serum progesterone levels in the aspiration group on day 15, but this was not the case in the hysterectomy group. There was no significant difference in serum LH levels among any of the groups on day 15 of pregnancy. These results indicated that estradiol induced luteolysis in the intact pregnant rats, which would, at least in part, be mediated through the uterus.

Effects of sex steroids on brain β-endorphin

Brain β-endorphin was measured by radioimmunoassay in female rats during different stages of the estrous cycle, during pregnancy, 3 weeks after ovariectomy, and 3 weeks after ovariectomy plus estradiol or estradiol and progesterone replacement. No change in hypothalamic β-endorphin content was noted on the afternoon of diestrus, proestrus, or estrus. However, in 9 rats studied between days 8–20 of pregnancy the mean hypothalamic β-endorphin concentration of41.6 ± 2.24ng/mg protein was significantly higher than the concentration of32.7 ± 1.01 in 21 non-pregnant animals (P < 0.001). Although hypothalamic β-endorphin content did not change 3 weeks after ovariectomy, when ovariectomized rats were treated iwth silastic estradiol capsules for 3 weeks, hypothalami β-endorphin decreased significantly from25.5 ± 1.2to18.3 ± 1.3and15.5 ± 0.94ng/mg protein after low and high dose estradiol treatment respectively (P < 0.001). In a second experiment hypothalamic β-endorphin in ovariectomized rats decreased from27.1 ± 1.5to20.7 ± 1.9ng/mg protein after 3 weeks of estradiol treatment (P < 0.02); the β-endorphin content of the thalamus and midbrain also decreased from8.95 ± 1.5and4.11 ± 0.70to5.24 ± 0.39and2.42 ± 0.25ng/mg protein, respectively (P < 0.025). When progesterone was administered together with estradiol, the decrease in β-endorphin induced in the hypothalamus, thalamus and midbrain by estradiol treatment was partially blocked and β-endorphin concentrations in the latter two regions were no longer significantly different from controls. We conclude that physiologic concentrations of estradiol and progesterone can alter the content of brain β-endorphin and suggest that ovarian steroids may be important regulators of this brain peptide.

Estrogen-stimulated uptake of alpha 1-protease inhibitor and other plasma proteins by the mouse uterus.

Administration of a single low dose of estradiol to the immature female mouse resulted in a rapid increase in uterine trypsin inhibitory capacity. The increase was apparent within 1 h, reached a maximum in 3--4 h, and returned to base line after 18 h. No corresponding increases were observed in liver or heart. The properties of the uterine inhibitor were found to be essentially the same as those of plasma alpha 1-protease inhibitor (alpha 1-PI). When 125I-labeled mouse plasma alpha 1-PI was given iv to immature mice the administration of estradiol caused a specific stimulation of uterine uptake of the labeled protein that closely matched the estrogen-stimulated increase in uterine trypsin inhibitory capacity. Half-maximal stimulation of uptake occurred at a dose of 0.15 microgram estradiol/animal. After 3 h 97% of the labeled alpha 1-PI taken up by the uterus was in the soluble (105,000 x g) fraction of which 50% was in the lumen. Estradiol also stimulated the uptake of soybean trypsin inhibitor, bovine serum albumin, porcine fibrinogen, and human alpha 2-macroglobulin. Under conditions where puromycin blocked the synthesis of an estrogen-stimulated uterine-specific hydrolase, puromycin had no effect on the estrogen-stimulated uptake of either mouse alpha 1-PI or mouse albumin. These results suggest that the estrogen-stimulated uptake of plasma proteins by the uterus does not require new protein synthesis.

Altered ovarian regulation of wound healing during aging.

AbstractThe healing rate of full-thickness skin lesions is slower in senescent female rats (22-23 months) than in their young adult (5-6 months) counterparts. Fifty percent wound closure times were 9.46 ± 0.31 and 6.45 ± 0.40 days, respectively (P < 0.001). Ovariectomy significantly slows the healing process in the mature group but not in the senescent animals. Treatment of ovariectomized rats with low-dose estradiol (0.3 μg/kg body wt) restores the healing rate to nearly normal in mature rats and accelerates the healing rate relative to sham-operated controls in senescent rats. Thus, decreased healing rates in senescent female rats may be due in part to reduced estrogenic potentiation of healing.

Ovarian hormones act early in development to feminize adult open-field behavior in the rat

Three experiments were done to investigate the feminizing effect of prepubertal ovarian hormones on the development of adult sex differences in open-field behavior in the rat. Gonadectomy at either 1 or 8 days of age, but not at 23 days or later, disrupted the normally high levels of activity found in adult females. Exposure of Day 1 gonadectomized female and male rats to low doses of exogenous estradiol between Days 10 and 20 led to higher levels of adult activity than did oil treatment. Finally it was shown that low doses of estradiol had similar effects on open-field scores whether given between Days 10 and 20 or between Days 30 and 40, whereas exposure of Day 1 gonadectomized females to a high dose of estradiol as late as 10 days of life appeared to suppress adult open-field activity. It was concluded that estrogens given during the period prior to weaning can have a feminizing effect on adult open-field behavior and that the sex difference normally observed in adult rats is dependent in part on the presence of the ovaries during a period after birth.

Pharmacokinetic studies on low dose estradiol 17 beta administered orally to postmenopausal women.

Peripheral plasma from four postmenopausal women was analysed for estrone, estradiol, lutenizing hormone and follicle stimulating hormone during 24 hours following an oral intake of a single dose of 1.0 mg micronized estradiol, on the first day of therapy and after one month. A similar study was carried out with another four postmenopausal patients, who received 0.2 mg estradiol three times daily. The measurements were performed by radioimmunoassay (RIA). It is concluded that the plasma concentrations of estrone and estradiol are higher and those of FSH lower after one month of therapy than on the first treatment day, while plasma LH remains unchanged. Micronized estradiol is rapidly absorbed from the gastrointestinal tract and converted to estrone, and the plasma profiles of estrone during the day are more constant with a divided daily dose than with a single higher dose. The divided daily dose results in an equally good clinical effect even though the total administration of estradiol is lower.

The Peroxidase Activity of Rat Uterus

The peroxidase activity in the uterine extract of rats previously given a low dose of oestradiol has been examined. From sexually mature rats, two peroxidases of apparent molecular weights of 92 000 (peroxidase I) and 40 000 (peroxidase II) and of different mobilities in polyacrylamide disc gel electrophoresis were found. The two peroxidases were separated and characterized in terms of their substrate specificities, kinetics, pH optima for activity, inhibitors and stabilities. Both enzymes appeared to be classic haemoprotein peroxidases of very similar properties. Peroxidase II was further purified.

Fertility in ewes receiving low doses of estradiol during synchronized estrus.

Fertility in ewes receiving low doses of estradiol during synchronized estrus.

Dimethystilbestrol is not antiestrogenic for rat sexual behavior or gonadotropin secretion.

Antiestrogens have been used recently to elucidate the critical steps in the mechanism of action of estrogen (E). The present study was designed to assess the actions of the presumably potent antiestrogen dimethylstilbestrol (DMS) on E-induced sexual behavior. gonadotropin secretion regulation and uterine growth. DMS failed to block estradiol bencoate (EB)-induced lordosis behavior in rats and, when given concurrently with a low dose of EB, acted synergistically to facilitate receptivity. When given in combination with progesterone (P). DMS induced lordotic behavior in a dose-dependent manner. When given in combination with a low dose of estradiol (E2), DMS also facilitated the inhibitory effect of E2 on compensatory ovarian hypertrophy. When tested for its ability to block E2-stimulated uterine growth. DMS neither stimulated nor inhibited the action of E2. When given alone. DMS again induced sexual receptivity, while having no significant effect on uterine growth in the same animals. The antiestrogenic effects of DMS, as revealed by studies of uterine growth and vaginal cornification in mice, were not evident in the rat where DMS acted as an estrogen with respect to CNS functions, while having few or no estrogenic or antiestrogenic effects on peripheral target tissues.

Effect of oestradiol infusion on plasma gonadotrophins and ovarian activity in progesterone-primed and unprimed anoestrous ewes.

Plasma gonadotrophin and ovarian responses to physiological infusions of oestradiol were examined in anoestrous ewes with and without progesterone priming. Intravenous infusion of oestradiol (1 microgram/h) for 24 h followed at 96 h by a second infusion for 12 h (low dose) resulted in simultaneous increases in LH and FSH of magnitude and duration similar to those of ewes at natural oestrus. Infusions of 3 microgram/h for 16 h, and again at 96 h for 4 h (high dose) resulted in similar gonadotrophin peaks. Endoscopy revealed that only two out of eight ewes had ovulated despite increased ovarian activity and surges of plasma gonadotrophins. Other anoestrous ewes were primed with 25 mg progesterone daily for 12.5 days before similar infusions of oestradiol on day 15. In the presence of very low plasma progesterone concentrations (less than 1.0 ng/ml) at the onset of infusion, there was no pituitary response to the infusion of a low dose of oestradiol but the gonadotrophins were released after the second high-dose infusion. Progesterone inhibited the positive feedback on both gonadotrophins but not the negative feedback on FSH. Ovulation occurred in all four ewes which had been progesterone-primed and infused with a high dose of oestradiol.

Serum LH suppression by estradiol but not by testosterone or progesterone in wethers.

The objective of this experiment was to determine the effect of steroids, previously shown to depress serum luteinizing hormone (LH) in rams, upon serum LH in orchiecto-mized sheep. Accordingly serum LH concentration was monitored during the intravenous injection of testosterone, progesterone or estradiol. Neither testosterone at rates of 12.5, 125 or 1,250 jug/hr nor progesterone at 125, 1,250 or 12,500 Aig/hr significantly depressed LH during an 8-hr injection period. Estradiol, however, injected for 12 hr at only 1 jUg/hr, depressed LH from 22 ng/ml to 11 ng/ml within 4 hours. Although the temporal response to this low dose of estradiol may have been slower, the depression in serum LH concentration appeared to be as great with 1 jUg/hr as with 12 Mg/hr indicating an all or none response. Two of the three steroids reported to depress serum LH in rams failed to do so in wethers. Thus, the steroid signals available for acute control of LH in this animal model are more limited.

Serum FSH, LH, and prolactin in adult ovariectomized mice bearing silastic implants of estradiol: responses to social cues.

The effect of silastic implants containing 0-5000 mcg of 17beta-estr adiol on serum concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin and their relationship to social cues was studied in adult, ovariectomized mice. The normal variation in serum LH levels that is observed during the estrus cycle was established by this range of doses. However, the high levels of prolactin observed during the peri-ovulatory stage of the cycle were absent, and the treatment fialed to suppress FSH levels to the extent that they correlated with any stage characteristic of the estrus cycle. Serum gonadotropin levels were not markedly altered by housing in isolation, in isolation and exposed to the odor of male urine, and in groups of 6 in animals receiving the high dose of estradiol. However, those receiving the low dose responded to the presence of male urine by exhibiting a marked increase in serum LH levels, but with no marked effect on FSH and prolactin, and to grouping with an increase in prolactin levels, a decrease in LH, and no change in FSH. The results suggest that animals receiving the low dose of estradiol show a normal r esponse to social cues.

Influence of estrogen-progesterone combinations on gonadotropin secretion in castrate female rats(1).

In order to study the effect of progesterone in modulating the secretion of gonadotropins, various doses of progesterone were administered to castrated immature and mature female rats. Progesterone did not prevent the postcastration rise of FSH and LH in these animals. Various amounts of progesterone were then administered to castrated rats that were treated with a constant low dose of estradiol. In animals given doses of estradiol that were able to decrease serum FSH and LH below castrate levels, but not to prevent the post-castration rise, the effect of progesterone was dose-dependent. A very low dose of progesterone lowered serum gonadotropins, an intermediate dose brought about an increase in secretion, and high doses were suppressive. The modifying action of progesterone appears to be dependent upon the level of estrogen, the dose of progesterone, and the time of administration.

The Effects of Estrogen and Progesterone on the Volume and Electrolyte Content of the Uterine Luminal Fluid of the Rat

Rat uterine luminal fluid sodium and potassium contents have been studied by an uterine washing method and the volume of uterine fluid in each washing has been calculated by use of a molar electrolyte dilution factor: Three daily intramuscular injections of 10 μg estradiol-17² in 0.1 ml of an inert vehicle (ethyl laurate) in 10-day spayed rats, caused a 3-fold increase in the empty uterine horn weight (from 58 to 168 mg) and a 400-fold increase in the uterine luminal fluid volume (from 1.2 μl to 550 μl). Progesterone, 5 mg daily, given with the estradiol, gave an uterine weight (158 mg) almost as great as estradiol alone, but the progesterone completely blocked the accumulation of uterine luminal fluid (2.5 μl). A fall in the Na/K molar ratio of the uterine fluid from 3.5 in spayed controls to 1.8 was observed following low dose estradiol (0.01 μg) which did not cause an increase in uterine fluid volume. A higher dose of estradiol (0.1 μg) caused a marked rise in the Na/K ratio to 9.3 with the onset of ut...

WATER AND ELECTROLYTE ALTERATIONS IN PLASMA, BRAIN AND LIVER OF RATS AFTER CASTRATION AND SEX HORMONE ADMINISTRATION.

ABSTRACT Ovariectomy, hypophysectomy and administration of oestradiol, progesterone, testosterone or methylandrostenediol altered water or electrolyte concentrations in plasma, liver, cerebral cortex, brain stem and cerebellum in the rat. High daily doses of the steroids (500 μg/100 g body weight) increased plasma sodium levels. Oestradiol, followed by progesterone, then testosterone and methylandrostenediol, was most effective in producing hypernatraemia. Lower doses of oestradiol (10–200 μg/100 g body weight) did not change plasma sodium concentrations. Plasma potassium was increased by ovariectomy and decreased by low doses of oestradiol in ovariectomized, but not in hypophysectomized, rats. All doses of oestradiol lowered per cent plasma water in intact adult male rats and ovariectomized adult females, but not in hypophysectomized rats. High doses of the steroids, especially of oestradiol plus progesterone, raised concentrations of water, sodium, potassium and chloride in the liver, whereas water, sodium and potassium concentrations remained constant in brain. Each of the steroids elevated brain chloride concentrations. Of the brain areas analyzed, the cerebral cortex most consistently showed increased chloride after injections. Testosterone and progesterone, followed by oestradiol and then methylandrostenediol, were most potent in increasing brain chloride concentrations. Because the sex hormones have previously been shown to alter brain excitability, it is postulated that some of these alterations may be correlated with concomitant changes in brain anionic concentrations.