Ovariectomy Rats Research Articles

Effect of estrogen on calcium-handling proteins, β-adrenergic receptors, and function in rat heart

Regulation of cellular Ca 2+ cycling is central to myocardial contractile function. Loss of Ca 2+ regulation is associated with cardiac dysfunction and pathology. Estrogen has been shown to modify contractile function and to confer cardioprotection. Therefore, we investigated the effect of estrogen on expression of rat heart myocardial Ca 2+-handling proteins and beta-adrenergic receptor (β 1-AR) and examined functional correlates. Female rats were sham-operated (SHAM) or ovariectomized. Two weeks after ovariectomy rats were injected (i.p.) daily with estradiol benozoate (OVX + EB) or sesame oil (OVX) for 2 weeks. Protein abundance was measured by immunoblotting and mRNA was quantified by real-time RT-PCR. OVX significantly decreased estrogen and progesterone levels and EB replacement returned both estrogen and progesterone to physiological levels. OVX induced a 75% reduction of uterine weight and a gain in body weight. Replacement restored weights to SHAM level. OVX increased and estrogen-replacement normalized abundance of β 1-AR and L-type Ca 2+ channel (Cav1.2) protein. OVX decreased sodium–Ca 2+ exchange protein (NCX) and estrogen restored protein abundance to SHAM levels. Sarcoplasmic reticular ATPase (SERCA), phospholamban (PLB), and ryanodine receptor (RyR) abundance was not altered by hormone status. Levels of mRNA encoding for β 1-AR, Cav1.2, and NCX were not influenced by OVX or estrogen replacement. OVX had no effect on SERCA and PLB mRNA level but estrogen replacement elicited a significant increase compared to OVX and SHAM. Estrogen-dependent changes in Ca 2+-handling proteins and β 1-AR are theoretically consistent reduced myocellular Ca 2+ load. However, hormone-dependent alterations in protein were not associated with changes in contractile function.

Efeitos da ovariectomia experimental no metabolismo ósseo de ratas wistar adultas: um modelo para estudo da osteoporose

A privação dos hormônios ovarianos acarreta distúrbios endócrinos e funcionais, tais como disfunção sexual, perda da libido, maior risco de osteoporose e de doenças cardíacas, níveis alterados de lipoproteínas, ganho ponderal, entre outros. A osteoporose é uma patologia óssea sistêmica caracterizada por um desequilíbrio entre reabsorção e formação óssea, resultando em um aumento da fragilidade óssea. O objetivo do nosso estudo foi descrever os efeitos da ovariectomia (OVT) experimental no metabolismo ósseo e no ganho ponderal de ratas wistar adultas. Ratas adultas foram submetidas ao procedimento de OVT (G1) bilateralmente ou uma falsa castração (G2). Após 30 dias, foi coletado sangue para dosagem de estrogênio sérico e após 60 dias os animais foram sacrificados para a realização das análises séricas e ósseas. O consumo de ração e o ganho de peso foram monitorados duas e uma vez por semana, respectivamente. As ratas OVT apresentaram médias estatisticamente maiores (p < 0,05) para o consumo de dieta, ganho de peso e atividade sérica da fosfatase alcalina e, menores (p < 0,05) para concentração de estrogênio sérico, conteúdo de cálcio, radiodensidade e limite proporcional ósseo quando comparadas às ratas sham-operadas. Além das análises quantitativas, as ratas OVT apresentaram fêmures com superfície com fossas de reabsorção visivelmente profundas, confirmando que ratas ovariectomizadas são um bom modelo de estudo de osteoporose em mulheres na pós-menopausa.

Effects of sex steroids on expression of adenylyl cyclase messenger RNA in rat uterus

The aim of our study was to investigate the effects of estradiol (E2) and/or progesterone (P4) bilateral ovariectomized rats on gene expressions of adenylyl cyclases (AC2, AC4, AC6, AC9). Non-pregnant (NP) Wister rats (between post-natal 10 and 12 weeks) and normal pregnant rats (between postnatal 10 and 14 weeks) were used. NP rats were divided into five groups: 1) control NP rats, 2) ovariectomy rats (OVX), 3) OVX injected with E2 (6 microg) for 4 days (E2), 4) OVX injected with P4 (5 mg) for 4 days (P4), 5) ovariectomy rats injected with E2 (6 microg) and P4 (5 mg) for 4 days (E2/P4). The ovariectomized rats were sacrificed by anesthesia of diethyl ether after 24 h from the last injection. The pregnant group was sacrificed in the same way on 14 (P14), 17 (P17) and 21 (P21) of pregnancy, because the days between P14 and P17 were the second trimester of pregnancy and P21 was the third trimester. Total RNA were prepared from the uteri of each subject, and expression of ACs was analyzed by reverse transcription-polymerase chain reaction (RT-PCR). Expression of mRNAs for AC2, AC4, AC6 and AC9 were maximally increased on P17 and then decreased on P21. In OVX rats, expression of mRNAs for AC2, AC4, and AC9 were decreased as compared to NP. AC2 mRNA was significantly increased by E2 treatment. AC4 and AC9 mRNA was significantly increased by injection of E2 or P4. AC6 mRNA level was not affected by E2 and/or P4. In conclusion, AC2, AC4 and AC9 gene expression is affected by estrogen and/or P4. On the contrary, AC6 gene expression was not changed by OVX or hormone treatment. Since, all ACs mRNA examined here are increased during pregnancy, AC6 may be affected by other factor(s) other than estrogen and P4.

Ovariectomy increases Na +, K +-ATPase, acetylcholinesterase and catalase in rat hippocampus

In the present work we investigated the effect of ovariectomy on Na +, K +-ATPase and acetylcholinesterase (AChE) activities in rat hippocampus. We also studied some parameters of oxidative stress, namely total radical-trapping antioxidant potential (TRAP), thiobarbituric acid-reactive substances (TBA-RS), as well as the antioxidant enzyme activities superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) activities. Our hypothesis is that ovariectomy might cause alterations in essential enzyme activities necessary to brain normal functioning and that these chances could be caused by oxidative stress. Female adult Wistar rats were divided into three groups: (1) naïve (control); (2) sham-operated; and (3) ovariectomized. Thirty days after ovariectomy rats were sacrificed. Results showed that rats subjected to ovariectomy presented a significant increase in Na +, K +-ATPase, AChE and CAT activities, but did not change the oxidative stress parameters studied when compared to sham or naïve rats. Since ovariectomy mimics postmenopausal changes, our findings showing alteration in the activities of brain Na +, K +-ATPase, AChE and CAT may be related to problems in postmenopausal women.

Do sex steroids regulate glutamine synthesis with age?

Glutamine synthetase, a key enzyme in the production of glutamine, is known to be induced by glucocorticoids and preserved in skeletal muscle during aging, but the effect of other steroids, such as sex steroids (progesterone, estradiol), is unknown in vivo. The aim of this study was to determine whether progesterone or estradiol plays a role in the regulation of glutamine synthetase (GS) with aging. The effects of glucocorticoids and sex steroids on muscle GS activity and mRNA expression were measured in adult (6-8 mo; n = 7 in each group) and aged (26 mo; n = 10 in each group) female Wistar rats after adrenalectomy (ADX), ovariectomy (OV), or both (ADXOV) and were compared with those in sham-operated (Sham) control rats. In tibialis anterior muscle, ADX noticeably decreased both GS activity and expression irrespective of age (50-60%; P < 0.05), whereas OV had no effect at either age. Progesterone and estradiol replacement had no effect on the recovery of muscle GS response in either ADX or OV rats, regardless of age. In contrast, heart GS activity was decreased by ADX in aged animals only. These results suggest that the reproductive endocrine status of female rats does not affect muscle GS activity either in muscle or in heart, in young or aged animals, and that the heart GS response to steroids may be differently regulated in aged rats.

Effect of in vivo estradiol administration to bilaterally ovariectomized rats on in vitro myometrial responsiveness to prostaglandin F2alpha and oxytocin.

Bilaterally ovariectomized, nonpregnant female CD rats were studied to investigate the effect of estradiol treatment on in vitro myometrial responsiveness to oxytocin and prostaglandin F2alpha. The first study investigated dose-dependent effects. Seven days after ovariectomy rats were given a single s.c. dose of corn oil (n = 4) or estradiol (5 microg, n = 5; 15 microg, n = 5; 50 microg, n = 4). A second identical injection of corn oil or estradiol was administered 24 h after the initial injection. Rats were killed 48 h after the first injection. A second study investigated time-dependent effects of estradiol treatment. A second group of ovariectomized rats received s.c. estradiol (50 microg) seven days after ovariectomy. These rats were killed either 12 h (n = 5) or 24 h (n = 4) after injection. Full-thickness cross-sections of uteri were suspended in vitro in the longitudinal direction in a superfusion system. Cumulative concentration-response curves were constructed to oxytocin and prostaglandin F2alpha. Both the duration and dose of estradiol treatment significantly (p < 0.05) attenuated baseline contractile activity, and the maximum myometrial response to oxytocin and prostaglandin F2alpha. Estradiol, in a dose-dependent manner, significantly reduced myometrial sensitivity (p < 0.05) for oxytocin and prostaglandin F2alpha.

Effects of 17β-estradiol administration on cortical and cancellous bone of ovariectomized rats with and without hypophysectomy

Pituitary hormones are essential for bone growth and bone turnover. Hypophysectomy (HX) diminishes mitogenesis and abolishes the high bone turnover rate induced by ovariectomy (OV). It is not known whether the suppressive effect of estrogen on bone resorption is diminished or abolished by HX. The present study investigates the effects of 17β-estradiol (E 2) (20 μg/wk) on cortical and cancellous bone mass and bone turnover as measured by histomorphometry in HX + OV (HO) rats. Sprague-Dawley rats at 2 months of age were OV or HO and the experiment was performed over a 6 week period. Hypophysectomy + OV (HO) resulted in a cessation of periosteal bone formation, and longitudinal bone growth and a decrease in cancellous bone volume. The tibial dry weight and tibial density were significantly lower in the HO than in the intact or OV groups. Administration of E 2 to HO rats partially prevented cancellous bone loss, whereas the same dosage of E 2 fully prevented cancellous bone loss in rats with OV alone. Nevertheless, cancellous bone volume was higher in the HO + E 2 than in the HO-alone groups. Estradiol administration in HO rats did not suppress cancellous bone formation rate or the eroded surface as much as it did in the OV rats. The suppressive effect of E 2 on periosteal bone formation rate and mineral apposition rate was also diminished in HO rats. However, factorial ANOVA showed that the effects of E 2 on increasing cancellous bone volume and decreasing periosteal bone formation rate and mineral apposition rate were still significant in the HO rats. Tibial dry weight and tibial density did not differ between HO and HO + E 2 groups. In conclusion, we have demonstrated that the estrogen-induced effects of preventing cancellous bone loss, of suppressing bone formation, and resorption as seen in OV rats was diminished but not abolished in HO rats.

Modulation of Glomerular ECTO-ADPase Expression by Oestradiol

The effect of 17-beta-oestradiol (OE2) upon the activity of the glomerular anti-thrombotic ecto-enzyme ADPase was studied in cyclic and ovariectomized (OVX) Wistar rats. On day 0 (i.e. at the time of ovariectomy or 11 days after ovariectomy) rats received OE2-releasing Silastic implants or empty implants and were sacrificed on day 3, 10 or 21. Cryostat kidney sections were histochemically stained for ecto-ADPase activity using enzyme-histochemistry and glomerular reaction product was quantitatively evaluated by computerized image analysis. Both the histological distribution of reaction product in each glomerulus, as reflected by the relative glomerular area covered with reaction product, as well as enzyme activity, as reflected by staining intensity of the reaction product, were scored. The results show significantly decreased histological distribution after OVX; OVX, however, did not change enzyme activity. It further appeared that OE2 (partly) prevented the decrease of histological distribution in OVX rats, while the enzyme activity was significantly increased by exogenous OE2. In cyclic rats, OE2 did not change histological distribution, although OE2 significantly increased enzyme activity in these rats. It is concluded that glomerular ecto-ADPase expression in the rat kidney is influenced by one or more ovarian factor(s), a very likely candidate being oestradiol. These results may thus point to a dual action of OE2 upon haemostasis: In addition to the known enhancement of procoagulatory plasma factors by OE2, also anti-aggregatory effects may be stimulated by OE2 as reflected by upregulation of vessel wall associated ecto-ADPase activity.

Risedronate pretreatment does not hamper the anabolic effects of prostaglandin E2 in ovx rats.

Pretreatment of an anti-resorptive agent on the anabolic effects of prostaglandin E2 (PGE2) was studied on the proximal tibia and tibial shaft of ovariectomy (ovx) rats. Two days after ovx, rats were treated with either risedronate (Ris, 5 micrograms/kg twice weekly) or vehicle (V) for 60 days and then switched to 3 or 6 mg/kg/d PGE2 for 21 or 90 days. Bone area of both proximal tibial metaphysis (PTM) and tibial shaft (TX) were measured. Pretreatment with Ris increased the bone mass in PTM but not in TX of ovx rats. In the PTM, PGE2 produced the same percentage of new bone mass in both V- and Ris-pretreated ovx rats. The amount of new bone was almost the same after 3 weeks and 12 weeks of PGE2 treatment. There was no difference in the anabolic effects of 3 and 6 mg PGE2/kg/d in V-pretreated rats; however, the effects in Ris-pretreated groups were greater with 6 mg PGE2/kg/d than with 3 mg PGE2/kg/d. In TX, only the 6mg PGE2/kg/d administration added new bone on endocortical surfaces of both V- or Ris-pretreatment rats which leads to thickening the minimal cortical width, decreasing the marrow cavity and increasing total bone area. Both doses of PGE2 created new trabecular bone in the marrow cavity of tibial shaft in both vehicle- and Ris-pretreated ovx rats. These results suggest that Ris-pretreatment did not hamper the anabolic effects of PGE2 on either PTM or TX in ovx rats.

Effect of ovariectomy on cancellous bone in the hypophysectomized rat.

This experiment studied the effects of hypophysectomy (HX) and ovariectomy (OV) on cancellous bone in the proximal tibia and distal 5th lumbar vertebra by dynamic histomorphometry. Forty-eight female Sprague-Dawley rats, 3 months of age, were divided into age-matched control, HX, OV, and HX + OV (HO) groups. Ten rats were sacrificed at 3 months of age as baseline controls, and the rest of the animals were sacrificed 5 weeks after the surgery. While the age-matched controls, and the OV rats significantly increased in body weight compared with the baseline control rats, cancellous bone volumes in the proximal tibia and distal 5th lumbar vertebra increased in the age-matched controls and decreased in the OV rats. In the HX and HO rats, body weight equaled baseline control values, and their cancellous bone volumes were decreased with a poorer trabecular architecture in both bone sites. In all HX, OV, and HO rats, uterine weight and serum estradiol were significantly decreased. OV significantly increased longitudinal bone growth and the tissue- and surface-based bone formation and bone resorption parameters in both the proximal tibia and 5th lumbar vertebra (p < 0.05). HX alone or HO significantly decreased longitudinal bone growth and the tissue-based bone formation rate without significantly affecting surface-based bone formation and bone resorption parameters when compared with the age-matched controls. No significant differences were detected in any variables between the HX alone and HO rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of estradiol on the secretion of LH in the GnRH-pretreated rat after treatment with the GnRH-antagonist, Org 30093.

LH responses induced in the long-term ovariectomized rat by GnRH or GnRH agonistic analogue are augmented by E2. The augmentation by E2 does not occur during, but after termination of GnRH pretreatment. In this study it was investigated whether the augmenting effect of E2 develops also in the GnRH-pretreated rat when the animals were treated with GnRH antagonistic analogue. Two weeks after ovariectomy rats were treated for 10 days with 250 ng GnRH/h (GnRH-rats), released by sc implanted osmotic minipumps. Control rats received a Silastic 'sham pump'. Rats were simultaneously treated with solvent (oil) or estradiol benzoate (EB, 3 micrograms, sc). Each group of rats was divided into two subgroups, one receiving solvent, the other the GnRH antagonist, Org 30093 (ANT, 100 micrograms/injection) on 3 consecutive days. In Experiment 1, the pituitary LH content and the LH secretion following stimulation with the agonistic GnRH analogue buserelin, were measured, in Experiment 2, the plasma concentrations of LH before and after cessation of ANT treatment. The effects of treatment with GnRH, EB and ANT were studied on the basis of 1) the height of the maximal LH response and 2) the half-maximally effective dose (ED50) of buserelin. Experiment 1 revealed that GnRH depleted the pituitary gland to about 42% of its original LH content. In EB-treated GnRH-rats the depletion was even stronger (to 14%). After ANT treatment, the pituitary glands of the GnRH-rats were (partly) repleted (oil: to 65%; EB: to 31%).(ABSTRACT TRUNCATED AT 250 WORDS)

Short- and long-term effects of ovariectomy on food intake, body weight, carcass composition, and brown adipose tissue in rats

This experiment examined both the short-term and the long-term effects of ovariectomy on brown adipose tissue growth and function in rats to determine if reduced brown adipose tissue thermogenesis might contribute to the weight gain and adiposity. Brown adipose tissue function was assessed by measuring sympathetic nervous system activity (estimated by the rate of norepinephrine turnover) and mitochondrial proton conductance (estimated by specific GDP binding) in interscapular brown adipose tissue. Rats ( n=12 per group) were killed 0 (sham), 1, 2, 4, and 12 weeks after ovariectomy. During the first five weeks after ovariectomy rats overate and rapidly gained weight. The weight gain was due to increases in all carcass components. Five weeks after ovariectomy food intake returned to control levels, and body weights stabilized 12–16% above sham-operated control weights for the duration of the experiment. Between week 4 and week 12 after surgery there was a redistribution of carcass composition, with decreases in carcass water and fat-free dry weights offset by a further increase in total carcass lipid. Brown adipose tissue pads were heavier in the 1-, 2-, and 4-week ovariectomy groups, but only in the 4-week group was the increase statistically significant. Brown adipose tissue protein, DNA, and norepinephrine content was unchanged 1-, 2-, 4-, or 12-weeks after ovariectomy. There was no difference in either the rate of norepinephrine turnover or specific mitochondrial GDP binding between sham-operated and 1-, 2-, 4-, or 12-week ovariectomized rats. These results indicate that the dynamic phase of ovariectomy-induced weight gain in rats cannot, even in part, be explained by a reduction in brown adipose tissue thermogenesis.

Influence of age, ovariectomy and submandibular-sublingual sialoadenectomy on submandibular gland metabolism in sexually mature and immature female rats

The effects of age, ovariectomy (OV), sialoadenectomy (SA) and diet intake on compensatory hypertrophy and on protein and sialic acid levels were investigated. Differences in diet intake and body weight gain were related to both age and animal treatment, the effects being greatest with the younger rats. The OV rats showed the largest body weight gains, but the SMG weight index was the smallest in these animals. The SA rats exhibited the same level of diet intake, but had smaller body weight gains than the control rats. Compensatory hypertrophy of the SMG was observed only with SA rats of both age groups. Protein and sialic acid levels were unchanged in the SMG of SA rats, but were increased in the mature OV animals. The influence of OV on SMG metabolism appeared to be related to both age and energy utilization by these rats. The mechanism of SMG compensatory hypertrophy in female rats was both age and sex hormone independent and must thereby differ from the age and androgen-dependent mechanism previously demonstrated in male rats.