Induction of progestin receptors by estradiol in the forebrain of estrogen receptor-alpha gene-disrupted mice

Mice, rats, and humans have two types of estrogen receptors, estrogen receptor-alpha (ERalpha) and estrogen receptor-beta (ERbeta). Estrogen receptor-alpha gene-disrupted (ERalpha-disrupted) mice bear two nonfunctional copies of the ERalpha gene. This mutation blocks the synthesis of full-length ERalpha, renders the animals infertile, and inhibits the induction of female sexual behaviors by estradiol and progesterone. It is likely that many of the processes contributing to the regulation of sexual receptivity by estradiol and progesterone are compromised in ERalpha-disrupted mice. However, given the importance of progesterone in the regulation of sexual receptivity and given the importance of progestin receptors (PRs) in mediating the responses of females to progesterone, we investigated the effects of ERalpha disruption on the induction of PRs by estradiol in the forebrain. We hypothesized that estradiol would induce PRs in wild-type mice but not in ERalpha-disrupted mice. Ovariectomized wild-type and ERalpha-disrupted mice were implanted with either estradiol-filled capsules or empty capsules for 5 d, after which their brains were processed for the immunocytochemical detection of PR. Estradiol increased the number of PR-immunoreactive cells in both wild-type and ERalpha-disrupted mice. The residual responsiveness of ERalpha-disrupted mice to estradiol could be accounted for by an ERbeta-dependent mechanism or another as yet unidentified estrogen receptor; however, because ERalpha-immunoreactivity and PCR product representing the 3' end of ERalpha mRNA were found in at least one PR-containing region of the ERalpha-disrupted mice, an ERalpha splice variant may also mediate the induction of PR-immunoreactivity in ERalpha-disrupted mice.     

Characterization of mechanisms of interleukin-6 gene repression by estrogen receptor

Some prior reports have suggested that guided tissue regeneration (GTR) procedures achieve only partial regeneration and induces the ankylosis rather than true attachment. Accordingly, others have developed an alternative procedure employing gelatine membrane compounded with bovine cementum particles (CGM) which has proven effective in stimulating a more physiologic form of attachment. This study was undertaken to perform a direct comparison of histological results when CGM and GTR membrane were used at comparable sites in the same monkey. Three monkeys with no periodontal disease were used. Following flap surgery, recession type defects were created on the buccal side of the maxillary lateral incisors and second premolars, and the cementum was removed from the root surface at an area corresponding to the bone crest. The right and left lateral incisors and second premolars were covered with CGM and GTR membrane, respectively. The GTR membranes were removed after 4 weeks. At 6 wks, the animals were sacrificed, and specimens were prepared for histological examination. More coronally placed true new attachment was observed following application of CGM to the planed root surfaces. Application of the GTR membrane resulted in formation of bone-like cementum and ankylosis, whereas CGM established true periodontal regeneration.     

Requirements for repression of retinoid X receptor by the oncoprotein P75gag-v-erbA and the thyroid hormone receptors

Three major ionic currents, Ca2+-dependent K+ current (IK-Ca), delayed rectifier type K+ current (Ikd) and Ca2+ current (ICa), were activated by depolarization under whole-cell clamp in single smooth muscle cells isolated from guinea-pig urinary bladder. Externally applied ruthenium red (RuR) reduced the amplitude of IK-Ca and ICa at 0 mV (IC50 values were 4.2 and 5.6 muM, respectively), but did not affect IKd. Spontaneous transient outward currents (STOCs) and caffeine-induced outward currents (Icaf) at -30 mV were reduced by external 10 muM RuR. When 10 muM RuR was added to the pipette solution, IK-Ca during depolarization, STOCs and Icaf significantly decreased with time. RuR did not change the unitary current amplitude of the large-conductance Ca2+-dependent K+ (BK) channels, but reduced the open probability of the channel under excised patch-clamp recording mode. RuR reduced the channel activity more effectively from the cytosolic face than from the other. This inhibition decreased when the cytosolic Ca2+ concentration was increased. These results indicate that RuR blocks BK and Ca2+ channels in urinary bladder smooth muscle cells. The decrease in IK-Ca, STOCs and Icaf by RuR is attributable to the direct inhibition of BK channel activity, probably in addition to the inhibition of Ca2+ release from storage sites. The direct inhibition of BK channel activity by RuR may be related to the interaction of RuR with the Ca2+-binding sites of the channel protein.     

Importance of estrogen receptors in hepatic LDL receptor regulation

Treatment with pharmacological doses of estrogen is the most potent way to stimulate hepatic LDL receptor expression in vivo. The mechanism for this effect is unclear, in part because of difficulties in inducing this stimulation in vitro. A fundamental question, whether estrogen receptors (ERs) mediate this stimulation, has not been addressed. The aim of the current study was to determine the involvement of ERs in the estrogen-induced stimulation of LDL receptors. Treatment of rats with high doses of ethynylestradiol for 7 days increased the hepatic LDL receptor protein and mRNA levels four- and threefold, respectively. LDL receptor stimulation in estrogen-treated rats was not due to their reduced food intake because hepatic LDL receptor expression did not increase in rats fasted for 72 hours. Treatment with antiestrogen (tamoxifen or clomiphene) abolished the LDL receptor stimulatory effect of ethynylestradiol at both the protein and mRNA levels. Antiestrogen alone had no effect on hepatic LDL receptor expression and did not influence the strong resistance to dietary cholesterol normally present in rats. It is concluded that ERs are critically involved in the induction of hepatic LDL receptor expression by ethynylestradiol. The known role of growth hormone for the expression of hepatic ERs may therefore play a role in the modulation of the effects of estrogen on cholesterol metabolism and hepatic LDL receptors in the rat.     

Effects of hysterectomy on sexual receptivity, food intake, running wheel activity, and hypothalamic estrogen and progestin receptors in rats.

Ovariectomized-hysterectomized (OH) CD rats given sequential treatments with 2 μg of estradiol benzoate (EB) and .5 mg of progesterone (P) showed significantly higher lordosis quotients than ovariectomized (OV) Ss in 2 tests, 1 and 2 wks after surgery. To test whether the effects of hysterectomy persist, 3 groups of OV and OH Ss received weekly injections of EB, EB?+?P, or sesame oil for 4 wks, were given 2 μg of EB followed 24 hrs later by .5 mg of P, and tested for receptivity. Only the OH Ss that had received hormones for 4 wks showed a significantly higher lordosis score than OV Ss. The effects of hysterectomy on food intake, weight gain, and running wheel activity were also tested. After 1 wk of 2 μg/day EB, OH Ss lost significantly more weight and consumed less food than OV Ss, but by 2 wks the effects of hysterectomy were no longer evident. Treatment with .5 μg/day EB resulted in a significant loss in weight and food intake in OH Ss throughout the experiment. OH Ss implanted with Silastic capsules containing EB were significantly more active in running wheels than OV Ss over the 1st 9 days, but by Day 23 the activity of both groups was similar. 24 hrs following a single injection of EB, hypothalamic-preoptic area cell nuclear estrogen receptors and cytoplasmic progestin receptors were significantly higher in OH than in OV Ss. Possible mechanisms by which hysterectomy might act to enhance hormone-dependent behaviors are discussed. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Up-regulation of estrogen receptor mRNA and estrogen receptor activity by estradiol in liver of rainbow trout and other teleostean fish

[125I]- and [123I]NNC 13-8241 were prepared from the trimethyltin precursor and radioactive iodide using the chloramine-T method. The total radiochemical yields of [125I]- and [123I]NNC 13-8241 were 60-70% and 40-50% respectively, with radiochemical purity higher than 98%. In binding studies with [125I]NNC 13-8241 in rats in vitro and in vivo a high uptake of radioactivity was demonstrated in brain regions known to have a high density of benzodiazepine (BZ) receptors such as the occipital and frontal cortex. SPECT examination with [123I]NNC 13-8241 in a Cynomolgus monkey demonstrated a high uptake of radioactivity in the occipital and frontal cortex. After displacement with flumazenil radioactivity in these brain regions was reduced to the level of a central region including the pons. Four hours after injection about 80% of the radioactivity in monkey plasma represented unchanged radioligand. This low degree of metabolism indicates that NNC 13-8241 is metabolically more stable than the radioligands hitherto developed for imaging of BZ-receptors in the primate brain.