Effects of chronic prednisolone treatment on bone resorption and bone composition in intact and ovariectomized rats and in ovariectomized rats receiving beta-estradiol

To examine the interactions between estrogen deficiency and glucocorticoid excess on bone metabolism the osteopenic effects of a standard dose of prednisolone (2 mg/kg BW.day) were studied in sham-ovariectomized (Sham-OVX), ovariectomized (OVX), and OVX rats given replacement beta-estradiol (OVX + E2). For 12 weeks six groups of female albino rats aged 4 months which had their skeletons labeled with 45Ca were fed matched amounts of low-calcium (0.1% Ca) hydroxyproline-free diet. The six treatment groups were: group 1, Sham-OVX; group 2, Sham-OVX + prednisolone; group 3, OVX; group 4, OVX + prednisolone; group 5, OVX + E2; group 6, OVX + E2 + prednisolone. Bone resorption was estimated by studying the urinary excretion of hydroxyproline and 45Ca. Parathyroid function was assessed indirectly from urinary cAMP excretion. Treatments did not influence parathyroid activity or serum levels of calcium or 1,25-dihydroxyvitamin D. However, ovariectomy increased bone resorption and induced osteopenia whereas prednisolone decreased bone resorption and formation and caused osteopenia. Ovariectomy increased the rate of bone resorption in prednisolone-treated rats; prednisolone lowered the rates of bone resorption and formation in OVX rats. The osteopenic effects of prednisolone and ovariectomy were additive and independent. E2 protected bone from the osteopenic effects of ovariectomy but did not affect bone loss induced by prednisolone. These results suggest prophylactic estrogen should help to avoid bone loss from estrogen deficiency in patients requiring chronic high dose glucocorticoid treatment.     

Tamoxifen inhibits osteoclast-mediated resorption of trabecular bone in ovarian hormone-deficient rats

The effects of the nonsteroidal antiestrogen tamoxifen were determined on trabecular bone mass in the proximal tibial metaphysis of intact and ovariectomized rats. Rats were ovariectomized at the beginning of the study. On day 7 of the study, 5-mg slow release pellets of tamoxifen or placebo were implanted sc. All of the rats were killed on day 28 of the experiment. Sections of the proximal tibial metaphysis were stained for acid phosphatase and evaluated histomorphometrically. Ovariectomy resulted in marked loss of bone. Compared to the values in sham-operated animals, the trabecular bone at a sampling site in the secondary spongiosa of ovariectomized rats was reduced by more than 60%, the length of trabecular bone surface covered by osteoclasts was increased by 563%, the percentage of trabecular bone surface covered by osteoclasts was increased by 567%, the mean osteoclast size was increased by 84%, and the number of nuclei per osteoclast was increased by 38%. In contrast, treatment of ovariectomized rats for 3 weeks with tamoxifen restored the histomorphometric measurements to values comparable to those in sham-operated animals. 17 beta-Estradiol increased trabecular bone fractional area in ovariectomized and sham-operated rats, and administration of tamoxifen to estrogen-treated, ovariectomized, and sham-operated animals produced a further increase in trabecular bone. In summary, 1) ovariectomy resulted in large increases in both the number and activity of osteoclasts, 2) the increased bone resorption associated with ovariectomy produced a net loss of trabecular bone, and 3) treatment of ovariectomized rats with tamoxifen prevented these skeletal changes. The results indicate that in the rat, tamoxifen mimics the effects of estrogen on trabecular bone at concentrations that are not uterotropic.     

Estrogen and tamoxifen modulate cerebrovascular tone in ovariectomized female rats

Postmenopausal estrogen deficiency increases the incidence of cerebrovascular disease. However, hormone replacement therapy is associated with an increased cardiovascular risk. Tamoxifen is a selective estrogen receptor modulator with estrogenic effects on cardiovascular risk factors, but its long-term impacts on cerebral vasculature are unknown. We hypothesized that chronic 17beta-estradiol or tamoxifen treatment exerted similar effects in reducing cerebrovascular tension in ovariectomized rats. We therefore determine whether (1) chronic 17beta-estradiol treatment could influence vasomotor activities, (2) chronic tamoxifen therapy could exert an estrogen-like or estrogen-antagonistic effect, and (3) acute exposure to estrogen could mimic the effect of 17beta-estradiol. Isometric tension was measured in cerebral arteries from female rat groups: control, ovariectomy, ovariectomy plus 17beta-estradiol treatment, ovariectomy plus tamoxifen treatment, and ovariectomized rats treated with tamoxifen and 17beta-estradiol. Ovariectomy enhanced cerebrovascular contractions to endothelin-1 or CaCl2, but not to U46619 or phenylephrine. 17beta-Estradiol therapy reversed these effects. Chronic tamoxifen treatment exerted estrogen-like actions by reversing ovariectomy-induced enhancement of vessel tone without antagonizing the effect of chronic 17beta-estradiol treatment. Ovariectomy enhanced the relaxing potency of nicardipine, and 17beta-estradiol treatment prevented this effect. Acute exposure to 10(-9) mol/L 17beta-estradiol or 10(-8) mol/L tamoxifen did not modulate contractions in rings from nonoperated female rats. In conclusion, ovariectomy differentially enhances agonist-induced cerebrovascular tone, an effect that was reversed by estrogen therapy. Tamoxifen does not act as an estrogen antagonist; instead, it functions as an estrogen agonist during estrogen deficiency. Thus, tamoxifen may confer beneficial effects similar to estrogen in cerebrovascular vessels.     

Estrogen replacement raises rat CRP without evidence of complement activation

Given current controversies regarding anti- and pro-inflammatory effects of estrogen, there is a need to explore relationships between gonadal hormones and inflammation using appropriate animal models. It has been proposed that rats are not appropriate for such research since, contrary to the effect of estrogen in humans, earlier animal studies had reported that estrogen downregulates serum C-reactive protein (rCRP) levels in the rat. With these considerations in mind, we re-examined the effects of estrogen withdrawal and replacement on CRP expression and complement activation in the rat. F-344 rats underwent bilateral ovariectomy or sham surgery at 9-10 months of age. Four months later, ovariectomized rats were treated with traditional high-dose 17beta-estradiol (Hi-E2) capsules, lower-dose (Lo-E2) 17beta-estradiol capsules, or placebo capsules for 7 days prior to sacrifice. Levels of plasma rat C-reactive protein (rCRP) were significantly lower in ovariectomized vs. sham-operated animals (415.5 +/- 10.6 vs. 626.6 +/- 23.0 mg/L, p < 0.001). Estrogen replacement significantly raised rCRP levels in ovariectomized animals (690.0 +/- 28.0 mg/L in Lo-E2 and 735.5 +/- 35.8 mg/L in Hi-E2, respectively, p < 0.001). Plasma rCRP levels correlated significantly with both hepatic rCRP (r = 0.79, p < 0.001) and serum estradiol (r = 0.70, p < 0.001) levels. However, no significant differences were observed in indices of complement activation (C4b/c) or CRP-complement complex generation (rCRP-C3 complex). In the mature female rat, ovariectomy reduces and estrogen replacement raises rCRP. Effects of estrogen on plasma rCRP induction are mediated, at least in part, through hepatic mechanisms and do not appear to require or be associated with complement activation.     

The effect of oral calcitonin on cartilage turnover and surface erosion in an ovariectomized rat model

OBJECTIVE: To investigate whether oral calcitonin treatment influences the increases in type II collagen (CII) degradation and related surface erosions of articular cartilage in ovariectomized rats. METHODS: Fifty rats were randomly allocated into 1 of the 5 following intervention groups: sham-operated, ovariectomy, ovariectomy plus subcutaneously implanted 17beta-estradiol pellet, ovariectomy plus 2 mg/kg salmon calcitonin plus 50 mg/kg 5CNAC (carrier), or ovariectomy plus 50 mg/kg 5CNAC. Each treatment was administered for 9 weeks after the ovariectomy. Blood samples for biochemical marker analysis were collected from fasting animals at baseline, on day 3, and after 1, 2, 4, 6, and 9 weeks. CII degradation was quantified by specific immunoassay, and the changes in severity scores of articular cartilage erosions were visualized and scored in histologic sections of the knees. RESULTS: Ovariectomy resulted in a marked increase in serum levels of C-telopeptide of type II collagen (CTX-II) (P < 0.001), which could be effectively reversed by 17beta-estradiol supplementation. Oral administration of calcitonin elicited similar decreases in serum levels of CTX-II (P < 0.001). Histologic scoring of cartilage erosion showed significantly less cartilage erosion in calcitonin-treated ovariectomized rats versus control ovariectomized rats that were untreated or treated with 5CNAC alone. (P < 0.01). CONCLUSION: The in vivo effects of calcitonin in rats suggest that calcitonin is able to counteract CII degradation and the accompanying structural disintegration of articular cartilage promoted by estrogen deficiency. Clinical assessment of the chondroprotective potential of calcitonin in postmenopausal women seems warranted.     

Melatonin increases oestradiol-induced bone formation in ovariectomized rats

To assess the effect of melatonin on bone metabolism in ovariectomized rats, receiving oestradiol therapy or not, melatonin was administered in the drinking water (25 microg/mL water) and oestradiol (10 microg/kg body weight) or vehicle was given subcutaneously 5 days/week for up to 60 days after surgery. Urinary deoxypyridinoline (a marker of bone resorption) and circulating levels of bone alkaline phosphatase activity (a marker of bone formation), as well as serum calcium and phosphorus levels, were measured every 15 days. Bone area (BA), bone mineral content (BMC), bone mineral density (BMD) and total body fat (expressed as 100 g body weight) were measured by dual-energy X-ray absorptiometry at the end of the experiment. Body weight and total body fat were augmented after ovariectomy, and decreased after melatonin or oestradiol treatment. The effect of melatonin on body weight was seen in sham-operated rats only. Ovariectomy augmented, and melatonin or oestradiol lowered, urinary deoxypyridinoline excretion. This effect of melatonin and oestradiol was seen mainly in ovariectomized rats. The efficacy of oestradiol to counteract ovariectomy-induced bone resorption was increased by melatonin. Melatonin or oestradiol lowered serum bone alkaline phosphatase activity. Melatonin inhibition was seen mainly on the increase of bone alkaline phosphatase activity that followed ovariectomy. Serum phosphorus levels decreased after melatonin administration and were augmented after oestradiol injection; overall, melatonin impaired the increase of serum phosphorus caused by oestradiol. Ovariectomy decreased, and oestradiol increased, serum calcium levels while melatonin augmented serum calcium in sham-operated rats only. On day 60 after surgery, BMD and content decreased after ovariectomy and were increased after oestradiol injection. Melatonin augmented BA of spine and BMC of whole of the skeleton and tibia. The highest values observed were those of rats treated concurrently with oestradiol and melatonin. The present results indicate that: (i) melatonin treatment restrained bone remodelling after ovariectomy; (ii) the effect of melatonin required adequate concentrations of oestradiol; (iii) melatonin augmented oestradiol effects on bone in ovariectomized rats; (iv) a counter-regulation by melatonin of the increase in body fat caused by ovariectomy was uncovered. The melatonin doses employed were pharmacological in terms of circulating melatonin levels but not necessarily for some other fluids or tissues.     

Aging reduces the efficacy of estrogen substitution to attenuate cardiac hypertrophy in female spontaneously hypertensive rats

Clinical trials failed to show a beneficial effect of postmenopausal hormone replacement therapy, whereas experimental studies in young animals reported a protective function of estrogen replacement in cardiovascular disease. Because these diverging results could in part be explained by aging effects, we compared the efficacy of estrogen substitution to modulate cardiac hypertrophy and cardiac gene expression among young (age 3 months) and senescent (age 24 months) spontaneously hypertensive rats (SHRs), which were sham operated or ovariectomized and injected with placebo or identical doses of 17beta-estradiol (E2; 2 microg/kg body weight per day) for 6 weeks (n=10/group). Blood pressure was comparable among sham-operated senescent and young SHRs and not altered by ovariectomy or E2 treatment among young or among senescent rats. Estrogen substitution inhibited uterus atrophy and gain of body weight in young and senescent ovariectomized SHRs, but cardiac hypertrophy was attenuated only in young rats. Cardiac estrogen receptor-alpha expression was lower in intact and in ovariectomized senescent compared with young SHRs and increased with estradiol substitution in aged rats. Plasma estradiol and estrone levels were lower not only in sham-operated but surprisingly also in E2-substituted senescent SHRs and associated with a reduction of hepatic 17beta-hydroxysteroid dehydrogenase type 1 enzyme activity, which converts weak (ie, estrone) into potent estrogens, such as E2. Aging attenuates the antihypertrophic effect of estradiol in female SHRs and is associated with profound alterations in cardiac estrogen receptor-alpha expression and estradiol metabolism. These observations contribute to explain the lower efficiency of estrogen substitution in senescent SHRs.     

去卵巢大鼠血清乳铁蛋白与骨密度的相关性研究

目的 探讨去卵巢大鼠血清乳铁蛋白(LF)水平与骨密度(BMD)的关系,为临床应用乳铁蛋白提供实验依据.方法 采用4月龄Wistar雌性大鼠,随机分为假手术组(sham,20只)与去卵巢模型组(ovariectomy,OVX,40只,分为OVX I组与OVX Ⅱ组,各20只),分别于术后14与18周处死OVX I组与OV...     

Effects of the Japanese herbal medicine Keishi-bukuryo-gan and 17beta-estradiol on calcitonin gene-related peptide-induced elevation of skin temperature in ovariectomized rats

The effects of a Japanese herbal medicine, Keishi-bukuryo-gan, and 17beta-estradiol on calcitonin gene-related peptide (CGRP)-induced elevation of skin temperature were investigated in ovariectomized (OVX) rats. Ovariectomy not only potentiated CGRP-induced elevation of skin temperature and arterial vasorelaxation but also induced a lower concentration of endogenous CGRP in plasma and up-regulation of arterial CGRP receptors, suggesting that lowered CGRP in plasma due to ovarian hormone deficiency increases the number of CGRP receptors and consequently amplifies the stimulatory effects of CGRP to elevate skin temperature. Oral Keishi-bukuryo-gan (100-1000 mg/kg, once a day for 7 days) restored a series of CGRP-related responses observed in OVX rats by normalizing plasma CGRP levels in a dose-dependent manner as effectively as s.c. injection. 17Beta-estradiol (0.010 mg/kg, once a day for 7 days). However, Keishi-bukuryo-gan did not affect the lower concentration of plasma estradiol and the decreased uterine weight due to ovariectomy, although the hormone replacement of 17beta-estradiol restored them. These results suggest that Keishi-bukuryo-gan, which does not confer estrogen activity on plasma, may be useful for the treatment of hot flashes in patients for whom estrogen replacement therapy is contraindicated, as well as menopausal women.     

Effects of estrogen on muscarinic acetylcholine receptors in the rat hippocampus

The aim of the present study was to investigate whether different estrogen manipulations have effects on the expression of muscarinic acetylcholine receptors (mAChRs) in the adult female rat hippocampus. Hippocampus was obtained from rats in proestrus (control), ovariectomized for 2, 10 and 15 days, ovariectomized for 15 days and treated with 17beta-estradiol for 7 days, and treated with 17beta-estradiol immediately after ovariectomy for 21 days. Rats' estrogen status was monitored by measuring estradiol plasma levels and uterus relative weight. [3H]quinuclidinyl benzilate ([3H]QNB) binding studies indicated that ovariectomy time-dependently increases the number of mAChRs in hippocampus when compared to those obtained from control rats. Estradiol treatments for 21 days avoid the effect of ovariectomy. However, the estradiol treatments for 7 days after 15 days of ovariectomy slightly change the number of mAChRs. In conclusion, these results showed that ovariectomy time-dependently increases mAChRs number in the rat hippocampus. In addition, these data suggest that treatment with estradiol initiated within a specific period of time after the loss of ovarian function may be effective at preventing specific effects of hormone deprivation on hippocampus.     

Estrogen receptor-related receptor alpha impinges on the estrogen axis in bone: potential function in osteoporosis

The orphan nuclear estrogen receptor-related receptor alpha (ERRalpha) is expressed by osteoblastic cells and plays a functional role in osteoprogenitor proliferation and differentiation. To dissect further the role of ERRalpha in bone, we investigated the effects of estrogen (E2) on ERRalpha both in vitro and in vivo. Chronic treatment of fetal rat calvaria cells with E2-stimulated bone nodule formation and up-regulated ERRalpha mRNA expression at early (10 h and d 8) but not later times in culture, suggesting a link between ERRalpha and E2 during osteoprogenitor proliferation. ERRalpha mRNA levels were significantly lower in ovariectomized adult rat bones vs. those of sham-operated rats early (1 d and 1 wk) post surgery, but levels returned to control levels thereafter. ERRalpha is also expressed in osteoclasts (tartrate-resistant acid phosphatase + multinucleated cells) in vivo and in vitro (RAW 264.7 cells) and ovariectomization lowered the OPG/receptor activator of nuclear factor kappaB ligand expression ratio. Down-regulation of ERRalpha expression via antisense treatment of rat calvaria cells not only inhibited osteogenesis but also increased adipocyte colony formation and changed the OPG/receptor activator of nuclear factor kappaB ligand ratio. These data suggest that ERRalpha is regulated by estrogen in bone in which it may play a functional role at several levels (osteoblasts, adipocytes, and osteoclasts) in E2 deficiency diseases such as osteoporosis.     

Cadmium accelerates bone loss in ovariectomized mice and fetal rat limb bones in culture.

Loss of bone mineral after ovariectomy was studied in mice exposed to dietary cadmium at 0.25, 5, or 50 ppm. Results show that dietary cadmium at 50 ppm increased bone mineral loss to a significantly greater extent in ovariectomized mice than in sham-operated controls. These results were obtained from two studies, one in which skeletal calcium content was determined 6 months after ovariectomy and a second in which 45Ca release from 45Ca-prelabeled bones was measured immediately after the start of dietary cadmium exposure. Furthermore, experiments with 45Ca-prelabeled fetal rat limb bones in culture demonstrated that Cd at 10 nM in the medium, a concentration estimated to be in the plasma of mice exposed to 50 ppm dietary Cd, strikingly increased bone resorption, from 27 +/- 2% (mean +/- SEM) 45Ca release in cultures with no added cadmium to 68 +/- 6% release in cultures containing cadmium (n = 4). These in vitro results indicate that cadmium may enhance bone mineral loss by a direct action on bone. Results of the in vivo studies are consistent with a significant role of cadmium in the etiology of Itai-Itai disease among postmenopausal women in Japan and may in part explain the increased risk of postmenopausal osteoporosis among women who smoke.     

雌激素缺乏引起雌性SD大鼠血小板激活

目的 研究雌激素缺乏对雌性SD大鼠血小板聚集功能的影响及其与一氧化氮相关的作用机制.方法 雌性SD大鼠随机分为假手术组、卵巢切除组以及卵巢切除补充雌激素组,分别施行假手术、卵巢切除术以及在卵巢切除术后第3天开始皮下注射补充雌激素,药物补充4周后处死动物,提取血清检测血清雌激素水平,提取富小板血浆测定血小板聚集功能,并用ELISA方法测定血浆中一氧化氮生物活性指标环磷酸鸟苷的水平.结果 卵巢切除组雌性SD大鼠血清雌激素水平明显降低,雌激素补充使卵巢切除补充雌激素组动物的雌激素水平回复到假手术组状态.卵巢切除组雌性SD大鼠血小板聚集率显著升高;卵巢切除补充雌激素后血小板聚集率较前者明显回落,但仍高于假手术组聚集水平;血浆中环磷酸鸟苷水平在卵巢切除组显著下降,补充雌激素后血浆中环磷酸鸟苷水平与假手术组差异无显著性.结论 雌激素缺乏会促进雌性SD大鼠的血小板聚集,其机制可能与血浆中一氧化氮/环磷酸鸟苷水平下降有关.     

Gender-related differences of serum thyroxine-binding proteins in the rat

Because little information is available, studies were performed to determine the relationship between gender and sex steroid status on serum T4 binding proteins in the rat. The binding capacity of serum thyroxine-binding globulin was greater in female rats than in male rats (27 +/- 1.3 vs 18.0 +/- 1.3 nmol/l, p less than 0.01) and in fasted female rats than in fasted male rats (64.4 +/- 2.6 vs 30.8 +/- 2.7 nmol/l, p less than 0.01). The binding capacity of serum transthyretin was lower in female rats than in male rats (2.1 +/- 0.1 vs 3.1 +/- 0.1 mumol/l, p less than 0.01). Neither ovariectomy or orchidectomy affected the binding capacity of serum thyroxine-binding globulin and it was not increased in ovariectomized rats treated with estrogen. Orchidectomy did not cause a decrease in the binding capacity of serum transthyretin and testosterone administration did not increase it. In contrast, ovariectomy caused an increase in the binding capacity of serum transthyretin (Intact = 2.2 +/- 0.1 vs ovariectomized = 2.8 +/- 0.1 mumol/l, p less than 0.01) and estrogen administration caused a decrease (ovariectomized = 2.8 +/- 0.1 vs ovariectomized + E2 = 1.9 +/- 0.1 mumol/l, p less than 0.05). The results indicate that the binding capacity of serum thyroxine-binding globulin is higher in female rats than in male rats but this difference is not due to differences in the secretion of gonadal hormones. The binding capacity of transthyretin is lower in female rats than in male rats. This is probably due to the higher circulating levels of estrogen in the female compared to the male.     

Selective effects of genistein, a soybean isoflavone, on B-lymphopoiesis and bone loss caused by estrogen deficiency

Genistein, an isoflavone abundantly present in soybeans, has structural similarity to estrogen, suggesting that genistein may act as a phytoestrogen. To examine the possible role of genistein in hemopoiesis and bone metabolism, female mice were either sham-operated or ovariectomized (OVX), and selected OVX mice were administered genistein for 2-4 weeks (0.1-0.7 mg/day) or 17beta-estradiol (E2; 0.01-0.1 microg/day) s.c., using a miniosmotic pump (Alza Corp., Palo Alto, CA). In OVX mice, uterine weight declined but was completely restored by E2 administration. In contrast, genistein did not demonstrate a reversal of the OVX-induced uterine atrophy. The number of bone marrow cells markedly increased, 2-4 weeks after OVX, and most of these were B220-weakly positive pre-B cells. The increased B-lymphopoiesis was completely restored, not only by E2 but also by genistein administration. In OVX mice, the trabecular bone volume of the femoral distal metaphysis, measured by microcomputed tomography scanning and dual-energy x-ray absorptiometry, was markedly reduced; and genistein restored this, as did E2. These results indicate that genistein exhibits estrogenic action in bone and bone marrow, to regulate B-lymphopoiesis and prevent bone loss, without exhibiting estrogenic action in the uterus. Phytoestrogens may be useful for preventing bone loss caused by estrogen deficiency in females.     

Ovariectomy leads to a rapid increase in rat placental lactogen secretion

Serum placental lactogen (rPL) levels were measured by RIA in late pregnant rats subjected to a number of endocrine ablations. Adrenalectomy or unilateral ovariectomy had no significant effect on serum rPL levels. Hypophysectomy of the dam at midpregnancy resulted in a significant increase in serum rPL at late pregnancy. Bilateral ovariectomy of day-14 or -16 pregnant rats led to a rapid increase in serum rPL levels for 2 days followed by a gradual decrease as fetuses were reabsorbed or aborted. Adrenalectomy combined with ovariectomy led to sustained, elevated levels of serum rPL which were greater than those seen with bilateral ovariectomy alone. When progesterone (4 mg/rat X day) and estrone (500 ng/rat X day) or 17 beta-estradiol (100 or 200 ng/rat X day) were administered to ovariectomized pregnant rats, serum rPL remained elevated and the conceptuses were retained. In conclusion our studies have shown that ovarian and adrenal factors influence rPL secretion.     

Estrogen treatment prevents osteopenia and depresses bone turnover in ovariectomized rats

Female Sprague-Dawley rats were subjected to bilateral ovariectomy (OVX) or sham surgery (control). Groups of ovariectomized (OVX) and control rats were injected daily with low, medium, or high doses of 17 beta-estradiol (10, 25, or 50 micrograms/kg BW, respectively). An additional group of OVX and control rats was injected daily with vehicle alone. All rats were killed 35 days after OVX, and their proximal tibiae were processed undecalcified for quantitative bone histomorphometry. Trabecular bone volume was markedly reduced in vehicle-treated OVX rats relative to that in control rats (12.1% vs. 26.7%). This bone loss was associated with a 2-fold increase in osteoclast surface and a 4-fold increase in osteoblast surface. The bone formation rate, studied with fluorochrome labeling, was also significantly elevated in vehicle-treated OVX rats (0.111 vs. 0.026 micron3/micron2.day). In contrast, treatment of OVX rats with the three doses of estradiol resulted in normalization of tibial trabecular bone volume and a decline in histomorphometric indices of bone resorption and formation. Our results indicate that estrogen treatment provides complete protection against osteopenia in OVX rats. The protective mechanism involves estrogenic suppression of bone turnover. These findings are consistent with the skeletal effects of estrogen therapy in postmenopausal women.     

Oestrogen attenuates the increases in blood pressure and platelet aggregation in ovariectomized and salt-loaded Dahl salt-sensitive rats

OBJECTIVE: To investigate the effects of oestrogen supplementation after ovariectomy on systolic blood pressure and platelet aggregation on different sodium content diet in the female Dahl salt-sensitive rats. METHODS: At 12 weeks of age, rats were ovariectomized or sham-operated and were fed either a high NaCl (8%) or low NaCl (0.3%) diet Ovariectomized rats were treated with either 17beta-oestradiol or placebo for 8 weeks, whereas sham-operated rats received placebo alone. After 8 weeks, the systolic blood pressure and platelet aggregation were measured and analysed by two-way analysis of variance. RESULTS: The systolic blood pressure of ovariectomized rats was significantly higher than that of sham-operated rats, and this increase in systolic blood pressure was suppressed by oestrogen supplementation. Systolic blood pressure was inversely correlated with plasma 17beta-oestradiol levels (r= -0.77, P< 0.01) and with the uterus weight to body weight ratio (r = -0.47, P < 0.01). Platelet aggregation was significantly enhanced by salt loading. Salt loading and female hormonal manipulation significantly interacted on platelet aggregation. Only in Dahl salt-sensitive rats fed a low sodium diet, ovariectomy increased platelet aggregation, whereas hormone replacement did not improve it. In Dahl salt-sensitive rats fed a high sodium diet, hormone replacement reduced platelet aggregation. CONCLUSIONS: Oestrogen replacement suppresses the development of hypertension and attenuates platelet aggregatory function in the salt-loaded ovariectomized Dahl salt-sensitive rats. It has a potential to inhibit the atherosclerotic process in postmenopausal hypertension.     

Failure of DHEA to modulate ovariectomy induced osteopenia in rats

As a result of reports indicating that dehydroepiandrosterone (DHEA) has bone anabolic properties, studies were carried out to determine whether DHEA will prevent osteopenia due to ovarian hormone deficiency. Female Sprague Dawley rats were randomized into four groups: Group 1 rats were ovariectomized; Group 2 rats were sham-operated upon; and Group 3 rats were ovariectomized and given subcutaneous injections of DHEA five times per week. Groups 1 and 2 rats were injected similar volume of solvent vehicle, and Group 4 rats were killed at the beginning of the study to serve as baseline controls. Six months after ovariectomy, Groups 1, 2 and 3 rats were bled, killed and their femurs dissected out. The following observations were made. The mean food intake of the rats over the experimental period was 20.9 gm per rat per day for the control, ovariectomized and DHEA-treated animals. Compared to age-matched controls, ovariectomy resulted in an increase in body weight, and in a decrease in: plasma calcium (P<0.005), serum calcitonin (P<0.01), femur density (P<0.005), femur calcium (P<0.01) and the ratio of cortical to periosteal area (P<0.03). None of these changes was reversed by DHEA administration. When the changes in cross-sectional areas at the midpoint of the femoral diaphysis were expressed as percentage of the baseline levels, the medullary and cortical areas were increased 32% and 11% respectively in ovariectomized animals, and 14% and 17% respectively in the sham-operated controls. The changes in cross-sectional areas induced by ovariectomy were slightly augmented by DHEA administration: medullary area (32% vs. 35%), and cortical area (11% vs. 15%). Although we have confirmed that ovariectomy induces osteopenia in rats, our findings indicate that dehydroepiandrosterone does not prevent the bone loss.