Effects of estradiol-17 beta and estriol on their binding sites in the rabbit uterus

1. Receptors for estradiol-17 beta (E2) and estriol (E3) were detected in the rabbit uterus. 2. Saturation analysis of estrogen binding sites in the cytosol showed that the dissociation constants of E2 and E3 for the high affinity binding sites were 1.8 +/- 0.5 nM and 2.3 +/- 0.3 nM, respectively, when dextran-coated charcoal was used to isolate free and bound ligands. 3. To eliminate non-specific (cross) bindings to their receptors, effects of unlabeled E2 and E3 on [3H]E3 and [3H]E2 bindings was examined. 4. [3H]E2 cytosol binding was observed to be specific for E2 and [3H]E3 cytosol binding was more specific for E3. 5. E2 priming to rabbits increased the binding sites for both E2 and E3, which was also more potent than E3 priming. 6. Moreover, the increase in E2 binding sites was greater than that in E3 binding sites. 7. These findings may suggest that there are separate binding sites for E2 and E3 in rabbit uterus and that synthesis of their binding sites is regulated by E2 but not E3.     

The effect of estradiol-17beta and estrone administration on GnRH-induced LH release during the early postpartum in dairy cattle

The effect of high plasma concentrations of estradiol-17beta or estrone, similar to those observed in late gestation, on the gonadotropin releasing hormone (GnRH)-induced luteinizing hormone (LH) release was studied in early postpartum dairy cows. Twenty dairy cows in late gestation were assigned to four groups of five cows each. Treatment groups were 1) no exogenous estrogens, 2) 20 mg estradiol-17beta (E(2)beta) daily, 3) 30 mg estrone (E(1)) daily and 4) 20 mg E(2)beta and 30 mg E(1) daily. Steroids were dissolved in ethanol (vehicle). Injections of the vehicle or steroids were given in two daily subcutaneous injections for seven consecutive days starting immediately following parturition. All cows (Groups 1-4) were given 100 mug GnRH intramuscularly on days 2, 10, 18 and 26 postpartum. Blood for plasma determination of E(2)beta, E(1), progesterone (P) and LH was collected daily from parturition to completion of vehicle or steroid injection and on alternate days thereafter. In addition, blood was collected on GnRH treatment days prior to GnRH and at 30-min intervals thereafter for four hours. Concentrations of hormones were determined by validated radioimmunoassays (RIA's). Effects of treatment (T), days postpartum (D) and the interaction between T and D (T x D) on the amount of LH released (area under the curve) in response to GnRH were significant (P < 0.01). More LH was released over all days combined in Group 1 compared to the other groups. LH release to GnRH increased as time postpartum increased in Groups 1 and 3, but at a ratelower for Group 3 than Group 1 (P < 0.05). In contrast, LH release to GnRH was greater (P < 0.05) on day 2 postpartum for Groups 2 and 4 compared to Groups 1 and 3, but less on days 10 and 18 postpartum. Average LH release was less (P < 0.05) on day 10 for Groups 2 and 4 than for day 2 postpartum. By day 26 postpartum, however, LH release in Groups 2 and 4 was greater than in Group 3. In summary, E(2)beta appeared to stimulate LH release early postpartum with a subsequent inhibition of LH release after prolonged E(2)beta administration, and E(1) administration did not stimulate LH release early postpartum.     

In vivo studies on the metabolism of estrone and estradiol-17beta by the brain

³H-Estrone and H-estradiol-17β were infused in separate experiments into the jugular veins of each of 4 ewes. During the infusions blood samples were obtained from the ipsilateral jugular vein and common carotid artery. The blood samples were analyzed for radioactivity as free estrone and estradiol-17β and the conversion of infused precursor to product steroid by brain tissue, the transtissue conversion (ρ^PRE-PRO_AV) and the extraction by brain tissue of infused precursor, the transtissue extraction (1-ρ^PRE-PRE_AV) and the metabolic clearance rates were calculated.The mean ± SE for ρ_AV^1,2 (precursor, estrone = 1; product, estradiol = 2) was 0.09 ±0.03 and the mean ± SE for ρ_AV^2,1 (precursor, estradiol = 2; product, estrone = 1) was 0.08 ±0.02. The mean trans-tissue extraction of estrone was 0.13 ± 0.02 and of estradiol-17β was 0.14- ± 0.02. The transtissue extractions of estrone and estradiol-17β were greater than ρ_AV^1,2 ρ_AV^2,1 respectively in 2 of the 4 ewes.Brain metabolism of estrogens can account for only 2–4% of the total metabolism of these free estrogens from the blood pool.     

The rate of estrone production by mouse blastocysts increases with estradiol-17 beta concentration in medium

Following the finding of 17 beta-hydroxysteroid dehydrogenase activity in mouse blastocysts, the present study examined the relation of estrone (E1) production rate to estradiol-17 beta (E2) concentration in the medium. When Day 5 blastocysts were cultured in 107-6,860 ng E2/ml medium, the amount of E1 formed during the first 5 hours (y) was found to increase linearly with the logarithm of E2 concentration (x), as represented by the equation y = 2,161x - 3,947. However, there was a sharp decline during the next 5 hours of culture except for the 107 ng E2 culture. The E1 production then remained steady for up to 46-58 hours. There was a tendency for further decline during the 46-70-hour period. The results indicate that (1) E2 may be metabolized to E1 and, probably, another unknown steroid; (2) E1 production rate is E2-dose dependent; and (3) the blastocyst possesses the enzymatic capability to change the steroid milieu to suit its own needs and/or to cause local effects in the uterus for its proper implantation.     

Positive and negative effects of estradiol-17 beta in the rat uterus

Estrogens could act as effectors or inhibitors of protein synthesis in the rat uterus, depending on the doses given to animals. A single injection of estradiol-17 beta to immature female rats led to the increase in protein synthesis and in enzyme activities involved in DNA synthesis. Four injections, given once daily, resulted in the inhibition of enzyme activity and synthesis of all proteins but one. The 105 kD protein which showed a gradual increase with the duration of estrogen treatment could be responsible for the negative action of estrogens on uterine growth.     

Metabolism of estrogens by rabbit blastocysts: formation of estrogen glucosides and preferential conversion of estrone to estradiol-17 beta

When day 6 rabbit blastocysts were cultured (3 embryos/mL) in medium 199 containing 3.68 microM estradiol-17 beta (E2), 40% of E2 was metabolized in 24 h, at a rate of 18 pmol/embryo(b)/h, yielding 4 major metabolite fractions. Two of them were identified to be estrogen glucosides: 17 beta-hydroxyestra-1,3,5(10)-trien-3-yl beta-D-glucopyranoside (E(2)3G) (12 pmol/b/h) and 17-oxoestra-1,3,5(10)-trien-3-yl beta-D-glucopyranoside (E(1)3G) (0.5 pmol/b/h). If the blastocysts were cultured in 3.68 microM E1 medium, 75% of E1 was metabolized in 24 h (34.1 pmol/b/h); most of it appears as E2 (8 pmol/b/h), E(1)3G (16 pmol/b/h), and E(2)3G (6 pmol/b/h). Thus, the 17 beta-hydroxysteroid dehydrogenase activity in the rabbit blastocysts catalyzes mainly in the direction of the E1----E2 conversion, with little or no E2----E1. This may be responsible in part for the faster metabolism of E1 than E2 by the rabbit blastocyst. In comparison with the rat, mouse, and hamster blastocyst, the rabbit embryo shows an additional capability to conjugate large amounts of estrogens into glucosides by steroid glucosyltransferase.     

Corpus luteal function in nonpregnant mares following intrauterine administration of prostaglandin E(2) or estradiol-17beta

The objective of this study was to test the hypothesis that intrauterine administration of prostaglandin E(2) (PGE(2)) or estradiol-17beta (E-17beta) would prolong CL function in nonpregnant mares. Nonpregnant mares were continuously infused with 240 mug/d of PGE(2), 6 mug/d of E-17beta, or vehicle (sham-treated) on Days 10 to 16 post ovulation (ovulation = Day 0), using osmotic minipumps surgically placed into the uterine lumen on Day 10 (n = 11 per group). Nonpregnant and pregnant mares served as negative and positive controls, respectively (n = 11 per group). Mares were defined as having prolonged CL function if plasma progesterone remained > 2.5 ng/ml and if ovulation did not occur on Days 9 to 30. Corpus luteal function was prolonged until Day 30 in 1 11 nonpregnant mares, 4 11 sham-treated mares, 6 11 E-17beta-treated mares, 8 11 PGE(2)-treated mares, and 11 11 pregnant mares. The incidence of prolonged CL function was similar (P=0.16) in the sham-treated and nonpregnant mares. The hypothesis that PGE(2) would prolong CL function in nonpregnant mares was supported, since the incidence of prolonged CL function was higher (P=0.003) in PGE(2)-treated versus nonpregnant mares, tended to be higher (P=0.09) in PGE(2)-versus sham-treated mares, and was not lower (P=0.11) in PGE(2)-treated versus pregnant mares. The hypothesis that E-17beta would prolong CL function in nonpregnant mares was not supported, since the incidence of prolonged CL function was not higher (P=0.34) in E-17beta-versus sham-treated mares, and was lower (P=0.02) in E-17beta-treated versus pregnant mares. These results demonstrate that intrauterine administration of a pharmacologic dose of PGE(2) initiated prolonged CL function in nonpregnant mares. Further experiments are needed to confirm the role of conceptus secretion of PGE(2) in CL maintenance, and to determine the mechanism of action of PGE(2) within the equine reproductive tract.     

Radioautographic study of the effect of estradiol-17 , estrone, estriol, progesterone, testosterone and corticosterone on the in vitro uptake of 2,4,6,7- 3 H estradiol-17 by uterine eosinophils of the rat

The in vitro uptake of 2,4,6,7-tritiated estradiol-17beta in uterine eosinophils of the rat was inhibited by the presence of nonradioactive estradiol-17beta, estrone, and estriol, but not by progesterone, testosterone, or corticosterone. This action is attributed to competition between tritiated estradiol and the various estrogenic compounds for the same binding site. Compounds without any estrogenic activity do not compete. The proposal is made that the eosinophil binding system and the 8S-5S binding system are involved in different mechanisms of estrogen action. The parallelism between the doses of estradiol and estriol needed to promote certain estrogenic early effects in the uterus, and the affinity of these steroids for the eosinophil uptake sites, suggests that uterine eosinophils might be responsible for some of these early effects, such as water imbibition, histamine releasing activity, and estrogen priming effect.