Oestrogenic effects of neonatal administration of raloxifene on hypothalamic-pituitary-gonadal axis in male and female rats

The anti-androgenic effect of chronic exposure to semicarbazide on male Japanese flounder (Paralichthys olivaceus) and its potential mechanisms

Semicarbazide (SMC), a new marine pollutant, has anti-estrogenic effects on female Japanese flounder (Paralichthys olivaceus). However, whether SMC also affects the reproductive endocrine system of male marine organisms is currently unclear. In this study, Japanese flounder embryos were exposed to 1, 10, and 100 μg/L SMC for 130 days. Plasma testosterone (T) and 17β-estradiol (E₂) concentrations were significantly decreased in male flounders after SMC exposure. The expression of genes involved in T and E₂ synthesis, including steroidogenic acute regulatory protein, cytochrome P450 11A1, 17α-hydroxylase, 17β-hydroxysteroid dehydrogenase and cytochrome P450 19A, was down-regulated in the gonads, which may explain the decrease in plasma sex hormones levels. Moreover, SMC-mediated changes in the transcription of these steroidogenic genes were associated with reduced levels of follicle-stimulating hormone beta subunit (fshβ), luteinizing hormone beta subunit (lhβ), follicle-stimulating hormone receptor (fshr) and luteinizing hormone receptor (lhr) mRNA. In addition, down-regulated transcription of fshβ and lhβ in the SMC exposure groups was affected by reduced mRNA levels of seabream gonadotropin-releasing hormone (sbgnrh), g-protein-coupled receptor 54 (gpr54) in the kisspeptin/gpr54 system, as well as the gamma-aminobutyric acid (GABA) synthesis enzyme glutamic acid decarboxylase (gad). Overall, our results showed that environmentally relevant concentrations of SMC exerted anti-androgenic effects in male flounders via impacting HPG axis, kiss/gpr54 system and GABA synthesis, providing theoretical support for investigating reproductive toxicity of environmental pollutants that interfere with the neuroendocrine system.

Effect of ormeloxifene on ovariectomy-induced bone resorption, osteoclast differentiation and apoptosis and TGF beta-3 expression

Effect of ormeloxifene, a multifunctional selective estrogen receptor modulator, on prevention of ovariectomy-induced bone resorption in retired breeder female rats, osteoclastogenesis using bone marrow cells from adult Balb/c mice cultured in presence of M-CSF and RANKL, osteoclast apoptosis using terminal deoxynucleotidyl transferase fragment end labeling and TGF beta-3 expression were investigated. Raloxifene, a benzothiophene reported to mimic effects of estrogen in bone, and estradiol were used for comparison. Ormeloxifene (10(-6) and 10(-8)M) significantly inhibited osteoclastogenesis (P<0.001 versus vehicle control) as evidenced by lower number of TRAP-positive osteoclasts in bone marrow cultures and caused apoptosis of osteoclasts. The effect was almost equivalent to that observed in presence of estradiol-17 beta, except that significant number of cells undergoing apoptosis was evident even at 10(-9)M concentration of estradiol-17 beta (P<0.001). Raloxifene, though inhibited osteoclastogenesis at much lower concentrations (10(-8) to 10(-12)M; P<0.001), failed to cause apoptosis of osteoclasts at any of the concentrations used. While ormeloxifene, raloxifene and ethynylestradiol significantly prevented ovariectomy-induced bone loss in vivo in retired breeder female rats, prevention of ovariectomy-induced decrease in BMD and trabecular network of proximal tibia, calcium and phosphorus levels in femur and tibia and prevention of ovariectomy-induced down-regulation of TGF beta-3 expression in lumbar vertebrae was of lower order in raloxifene- than ormeloxifene- or ethynylestradiol-supplemented females. Both the SERMs, however, produced considerable estrogenic effects at the uterine level as evidenced by increase in weight, total and endometrial area and luminal epithelial cell height; the effect being generally greater in raloxifene- than ormeloxifene-treated rats. Findings demonstrate that inhibition of estrogen-deficiency osteoporosis by ormeloxifene, as in case of estradiol, was mediated via inhibition of osteoclastogenesis, apoptosis of osteoclasts and up-regulation of TGF beta-3 expression. Raloxifene, though effective in inhibiting osteoclastogenesis in vitro at much lower concentrations, was not only less potent in preventing ovariectomy-induced bone loss in retired breeder female rats in vivo but also appeared to have a different mechanism of action than ormeloxifene and estradiol.

In vitro anti-resorptive activity and prevention of ovariectomy-induced osteoporosis in female Sprague-Dawley rats by ormeloxifene, a selective estrogen receptor modulator

Antiosteoporotic activity of ormeloxifene, a multifunctional SERM, using inhibition in parathyroid hormone (PTH) induced resorption of 45Ca from prelabeled chick and rat fetal limb bones in chase cultures and modulation of certain biochemical markers of bone turnover and bone mineral density (BMD) in ovariectomized adult female rats, was investigated. Ormeloxifene concentration-dependently inhibited PTH-induced resorption of 45Ca from chick fetal femora with treated/control (T/C) ratio of 0.71, 0.32 and 0.20 at 50, 100 and 200 microM concentration, in comparison to 0.49, 0.53 and 0.95 in case of CDRI-85/287 (a pure antiestrogen), tamoxifen and ethynylestradiol (100 microM), respectively. Using rat fetal limb bones, ormeloxifene (100 microM) exhibited T/C ratio of 0.67, in comparison to 1.43 with PTH alone. Heat-killed bones exhibited negligible resorption (2.9%; T/C: 0.098) in response to PTH. In adult female rats, ormeloxifene (1.25 and 12.5 mg/kg per day) inhibited ovariectomy-induced increase in serum total and bone-specific alkaline phosphatase and osteocalcin and urine calcium/creatinine ratio to almost intact control level. Ovariectomy was accompanied by marked decrease in bone mineral density of isolated femur and tibia, being maximum in femur neck (28.3%; P < 0.01) and midshaft (23.7%; P < 0.01), but only marginal (6.7%; P > 0.05) in region proximal to tibio-fibular separation point. Decrease in BMD based on T-/Z-score, too, was >2.5 S.D. than mean value of normal young adult/age-matched females. This was prevented by ormeloxifene and the effect, though apparently more in females supplemented with higher dose of ormeloxifene, was not always significantly different and clear dose-response was not evident until BMD data was evaluated on T-/Z-score basis. The analysis also demonstrated much higher threshold level of tibia than femur and more so for their mid-shafts. Increase in BMD of isolated bones was also observed in ormeloxifene-treated intact females, without significantly altering biochemical markers of bone turnover or uterine weight. Findings suggest potential of ormeloxifene in management of post-menopausal osteoporosis and beneficial effect on BMD in women taking this SERM for contraception or any hormone-related clinical disorder.

Regulation of Estrogen Receptor (ER) Isoform Messenger RNA Expression by Different ER Ligands in Female Rat Pituitary1

Net estrogen sensitivity in target tissues critically depends on the regulated expression of full-length and alternately processed estrogen receptor (ER) isoforms. However, the molecular mechanisms for the control of pituitary responsiveness to estrogen remain partially unknown. In the present communication, we report the ability of different ligands, with distinct agonistic or antagonistic properties at the ER, to modulate the expression of the transcripts encoding ERalpha and ERbeta isoforms, as well as those for the truncated ERalpha product (TERP), and the variant ERbeta2, in pituitaries from ovariectomized rats, i.e., a background devoid of endogenous estrogen. Compared with expression levels at the morning of proestrus, ovariectomy (OVX) resulted in increased pituitary expression of ERbeta and ERbeta2 mRNAs, whereas it decreased TERP-1 and -2 levels without affecting those of ERalpha. Administration of estradiol benzoate (as potent agonist for alpha and beta forms of ER) or the selective ERalpha agonist, propyl pyrazole triol, fully reversed the responses to OVX, while the ERbeta ligand, diarylpropionitrile, failed to induce any significant effect except for a partial stimulation of TERP-1 and -2 mRNA expression levels. To note, the ERbeta agonist was also ineffective in altering pituitary expression of progesterone receptor-B mRNA, i.e., a major estrogen-responsive target. In all parameters tested, tamoxifen, a selective ER modulator with mixed agonist/antagonist activity, behaved as ERalpha agonist, although the magnitude of tamoxifen effects was significantly lower than those of the ERalpha ligand, except for TERP induction. In contrast, the pure antiestrogen RU-58668 did not modify the expression of any of the targets under analysis. Overall, our results indicate that endogenous estrogen differentially regulates pituitary expression of the mRNAs encoding several ER isoforms with distinct functional properties, by a mechanism that is mostly conducted through ERalpha. Differential regulation of ER isoforms may represent a relevant system for the self-tuning of estrogen responsiveness in female pituitary.

Raloxifene effects upon the neuronal system controlling sexual receptivity in female rats

Selective estrogen receptor modulators (SERMs) constitute a new family of drugs with growing interest in the management of estrogen-associated pathology. Raloxifene is a SERM that mimics estrogen action on bone and blood lipid concentration but whether it acts as estrogen in the central nervous system remains to be fully established. In the present communication, we aimed at evaluating the estrogenic/antiestrogenic effects of raloxifene upon organization and activation of sexual receptivity, an estrogen-dependent event, in female rats. To this end, the effects of raloxifene, administered during the neonatal period, were compared with those of estrogen in terms of disruption of sexual receptivity in estrogen-progesterone-primed ovariectomized (OVX) female rats. In addition, the ability of raloxifene to induce sexual receptivity in progesterone-primed OVX females was analyzed. Similarly, the effects of the combined administration of estrogen and raloxifene were studied. Our results suggest that raloxifene does not act as estrogen upon the organization of the neuronal system involved in the control of sexual receptivity in female rats and exerted an antiestrogenic action in adult OVX estrogen-primed female rats.

Selective estrogen receptor modulators: tissue actions and potential for CNS protection

Significant physiologic changes occur during menopause. Evidence exists to suggest that estrogen may be neuroprotective under specific conditions. However, there are limitations in the neuroprotection afforded by standard hormone therapy. Accordingly, alternative agents with selected estrogenic effects may hold even greater promise rather than conventional hormone replacement therapy for the prevention and treatment of CNS injury. Recently, a variety of selective estrogen receptor modulators (SERMs) have been developed to retain the favorable and minimize the adverse side effects of estrogens. This review focuses on the CNS and known neuroprotective effects of two specific SERMs, raloxifene and arzoxifene. Recent studies hint that raloxifene and arzoxifene are neuroprotective and may preserve some elements of cognitive function. However, the mechanism of action is not well described and it is unclear if the beneficial effects of SERMs rely on activation of estrogen receptors.

Evidence for an estrogen-like action of raloxifene upon the hypothalamic-pituitary unit: raloxifene inhibits luteinizing hormone secretion and stimulates prolactin secretion in ovariectomized female rats

Selective estrogen receptor modulators (SERMs) constitute a new family of drugs with growing interest in the management of estrogen-associated pathology. Raloxifene is a SERM that is used to treat and prevent osteoporosis in postmenopausal women. The actions of raloxifene on bone, breast, uterus and serum cholesterol have been widely analyzed, but very few studies have been carried out to evaluate whether raloxifene has an estrogenic activity upon the hypothalamic-pituitary axis in the rat. For this purpose, adult female rats were ovariectomized or sham ovariectomized. One week later, the rats were implanted with intracardiac canullae and 24 h after injected daily with raloxifene (500 microg/rat/day) or vehicle for 5 days. One hour after the last injection, blood samples were obtained at 5 min intervals for a 3 h. period (10:00-13:00 h). Our results indicate that raloxifene inhibits the pulsatile nature of the post-ovariectomy hypersecretion of luteinizing hormone (LH) and increases prolactin (PRL) secretion in ovariectomized animals. These effects are suggestive of an estrogenic activity of raloxifene on LH and PRL secretion in ovariectomized females.