Effect of centchroman on the uptake of tritiated estradiol-17beta and progesterone by different tissues of ovariectomized rats

Modulation of estrogen action during preimplantation period and in immature estradiol-primed rat uterus by anti-implantation agent, ormeloxifene

Studies were undertaken to evaluate the influence of estrogen antagonist-cum anti-implantation agent, ormeloxifene, on 17beta-hydroxysteroid dehydrogenase (17beta-HSD) activity and estrogen action in rat uterus during preimplantation period and to examine its ability to induce progesterone receptor (PR) in immature rat model. A group of female rats received orally a contraceptive dose of 1.25 mg/kg of ormeloxifene on Day 1 postcoitum (pc). Rats were sacrificed on Days 3, 4 and 5 pc, and uterine tissues were processed for enzymatic, estrogen receptor and estradiol (E(2)) estimations. Immature ovariectomized rats received ormeloxifene, subcutaneously for 3 days at various doses in the absence or presence of estradiol, and uterine PR levels were measured using (3)H-R5020 as radioligand. Results revealed that ormeloxifene treatment caused a marked increase in enzyme activity of 17beta-HSD on Days 3, 4 and 5 pc as compared to respective controls. Further, total uterine estrogen receptors as estimated by exchange assay showed a noticeable decrease on Days 4 (35%) and 5 (>80%) pc in ormeloxifene-treated groups. The results correlated well with a decrease in tissue E(2) levels. In immature rats, ormeloxifene caused a dose-dependent increase in cytosolic PR levels; ormeloxifene given along with E(2) (0.1 mug) for 3 days caused a significant reduction in concentration of PRs at 10 mug and higher doses. Ormeloxifene also induced (3)H-progesterone (P) uptake by immature rat uterus. However, in the presence of E(2), it significantly reduced (3)H-P uptake. The in vitro competitive binding experiments did not reveal any displacement of (3)H-R5020 either by ormeloxifene or by its hydroxy derivative from PR. The results suggest that in addition to its competitive antagonism at estrogen receptor level, ormeloxifene enhances the inactivation of intracellular E(2) to estrone, a biologically less active form, thus declining estrogen receptor pool. Moreover, it causes indirect anti-progestational effects in the uterus by virtue of its anti-estrogenic profile rather than by blocking the PRs.

Centchroman, a selective estrogen receptor modulator, as a contraceptive and for the management of hormone-related clinical disorders

DL-Centchroman (67/20; INN: Ormeloxifene) synthesized at the Central Drug Research Institute, Lucknow, is a nonsteroidal once-a-week oral contraceptive. It was introduced in Delhi in July, 1991, marketed in India in 1992 as Saheli and Choice-7 (Hindustan Latex Ltd., Thiruvananthapuram) and Centron (Torrent Pharmaceuticals India Ltd., Ahmedabad), and included in the National Family Welfare Programme in 1995.5 According to post-marketing surveillance, approximately 100,000 women were using this pill and approximately 1100,000 menstrual cycles were covered until 1996. It is a unique need-oriented contraceptive being effective when taken immediately after coitus or routinely as a weekly pill and has the advantage of less frequent administration. Its contraceptive action is quickly reversible. It has long terminal serum halflife of 168 hr in women and exhibits duration of anti-implantation/estrogen antagonistic action of 120 hr, despite a short (24.1 hr) serum halflife, in the rat. In lactating women, it is excreted in milk in quantities considered unlikely to cause any deleterious effect on suckling babies. In phase II and III multicentric trials as a contraceptive, children born of method-and-user failure pregnancies showed normal milestones, without any congenital anomaly. Reports of its promising action in the management of certain hormone-related clinical disorders are available. It has an excellent therapeutic index and is considered safe for chronic administration.

Inhibition of progesterone-induced development of giant mitochondria in uterine glandular epithelial cells by an antiestrogen in rat

Effect of antiestrogen ormeloxifene on progesterone-induced development of giant mitochondria in uterine glandular epithelial cells in ovariectomized adult Sprague-Dawley rats was investigated. Antiestrogen tamoxifen and antiprogestin onapristone were used for comparison. Well-formed giant mitochondria were observed in uterine glandular epithelial cells in rats treated with progesterone (20 mg/kg, subcutaneous [SC] per se for three consecutive days. In rats primed with estradiol-17 beta (0.5 micrograms/day, s.c.) on days-2 and -1 before progesterone treatment, there was, in addition, a marked increase and distension of smooth endoplasmic reticulum (SER) and Golgi complex, in comparison to extensive rough endoplasmic reticulum (RER) and polyribosomes in progesterone per se treated rats. Cytological picture in rats receiving single (1.25 mg/kg, day 1, p.o.) or multiple (0.25 mg/kg, days 1-3, p.o.) anti-implantation doses of ormeloxifene showed marked reduction in glandular epithelial cell height, luminal surface microvilli, RER, polyribosomes and cytoplasm:nucleus ratio, straightening of intercellular membranes, and interdigitation of basement membrane. Mitochondria were of normal size and nuclei were heterochromatic. Inhibition in the case of tamoxifen (0.1 mg/kg, days 1-3, p.o.) appeared partial and rare giant mitochondria with degenerating cristae and outer membranes were apparent. Onapristone (10 mg/kg, day 1, s.c.), in addition to inhibiting development of giant mitochondria, caused extensive vacuolization and distension of intercellular membranes in glandular epithelial cells.

Uterine estradiol and progesterone receptor concentration, activities of certain antioxidant enzymes and dehydrogenases and histoarchitecture in relation to time of secretion of nidatory estrogen and high endometrial sensitivity in rat

Alterations in uterine nuclear and cytosolic estradiol (ER) and progesterone (PR) receptor concentration, activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glucose-6-phosphate dehydrogenase (G-6-PDH) and lactate dehydrogenase (LDH), surface and transmission electron microscopy and histology in relation to the time of secretion of nidatory estrogen and the onset of endometrial sensitivity in the rat were investigated. A significant increase in plasma estradiol (E2) concentration in control rats was observed at 22.00 h on day 4 post-coitum, whereas progesterone (P) concentration increased at 17.00 h on day 4 and was maintained until 17.00 h on day 5. The period of high endometrial sensitivity (10.00 h on day 5) was characterized by elevated uterine cytosolic ER and nuclear and cytosolic PR concentration and POD activity, low columnar luminal epithelium with undulating surface and intercellular membranes, covered with short microvilli and pinopods, and containing numerous electron-transparent apical vesicles, mitochondria, polyribosomes, rough (RER) and smooth (SER) endoplasmic reticulum, well developed Golgi, few lysosomes and lipid droplets and loose edematous antimesometrial stroma. Inhibition in endometrial sensitivity by post-coital centchroman was associated with a marked depletion in uterine cytosolic ER and an increase in nuclear ER concentration, a decrease in POD and G-6-PDH activities, compact fibroblastic stroma, an increase in luminal epithelial cell height with decreased RER, SER, polyribosomes, Golgi, straightening of intercellular membranes, reduced surface undulations and absence of pinopods. Electron-transparent vesicles appeared flattened and clumped in the apical portion of cells, tight junctions were more prominent and lipid droplets were translucent. Nuclear and cytosolic PR and the pattern of secretion or plasma E2 and P remained unaffected. CAT, SOD and LDH activities, although high throughout pre-implantation, did not vary in relation to the secretion of nidatory estrogen, endometrial sensitivity or centchroman treatment.

Contraceptive efficacy of tamoxifen in female hamsters

Systemic administration of tamoxifen (trans-1-(4-B-dimethylaminoethoxyphenyl)-1,2-diphenyl-but-1-ene), an antiestrogen, at a dose level of 2 mg/kg body weight on days 1, 2 and 3 post-coitum (p.c.) intercepts pregnancy during the peri-implantation period in 70-80% of hamsters. Significant alterations in the circulating levels of estradiol and progesterone were accompanied by the abolition of peak activities of various uterine lysosomal enzymes in the treated animals. The present study, therefore, suggests that estrogen plays a crucial role during the process of ovum-implantation in hamsters, and tamoxifen displays an interceptive role in this species.