OVX-E2 Rats Research Articles

Estrogen dampens central cannabinoid receptor 1-mediated neuroexcitation and pressor response in conscious female rats

Activation of the rostral ventrolateral medulla (RVLM) cannabinoid receptor-1 (CB1R) causes neuronal nitric oxide synthase (nNOS)-dependent increases in sympathetic activity, blood pressure (BP) and heart rate (HR) in male rats. However, it remains unknown if the CB1R-mediated neurochemical and cardiovascular responses are influenced by the ovarian sex hormones, particularly estrogen (E2). Therefore, we studied the effects of intra-RVLM CB1R activation (WIN 55,212–2) on BP and HR in conscious female rats under the following hormonal states: (1) highest E2 level (proestrus sham-operated, SO); (2) E2-deprivation (ovariectomized, OVX); (3) OVX with E2 replacement (OVXE2). Intra-RVLM WIN55,212–2 elicited dose (100–400 pmol) dependent pressor and tachycardic responses, in OVX rats, which replicated the reported responses in male rats. However, in SO and OVXE2 rats, the CB1R-mediated pressor response was attenuated and the tachycardic response reverted to bradycardic response. The neurochemical findings suggested a key role for the upregulated RVLM sympathoexcitatory molecules phosphorated protein kinase B, phosphorated nNOS and reactive oxygen species in the exaggerated CB1R-mediated BP and HR responses in OVX rats, and an E2-dependent dampening of these responses. The intra-RVLM WIN55212-2-evoked cardiovascular and neurochemical responses were CB1R-mediated because they were attenuated by prior CB1R blockade (AM251). Our findings suggest that attenuation of RVLM neuroexcitation and oxidative stress underlies the protection conferred by E2, in female rats, against the CB1R-mediated adverse cardiovascular effects.

Lung oxidative stress and transcriptional regulations induced by estradiol and intermittent hypoxia

We determined the effects of chronic intermittent hypoxia (CIH) and estradiol (E2) on oxidative stress and gene expression in the lungs. Female Sprague-Dawley rats were left intact (sham) or ovariectomized (OVX) and implanted with pumps delivering vehicle or E2 (0.5 mg/kg/day). Two weeks following surgery, the rats were exposed to room air (RA) or CIH for 7 days (10% O2, 10 cycles/hour, 8 h/day). Lung samples were used to measure the activities of pro- (NADPH and xanthine oxidases) and antioxidant (superoxide dismutase, catalase and glutathione peroxidase) enzymes, and concentrations of advanced oxidation of protein products (AOPP). We determined gene expression with an RNA microarray and enrichment analysis of differentially expressed genes. In rats exposed to RA, OVX and E2 supplementation increased pro- and antioxidant activities and AOPP concentration. In rats exposed to CIH, AOPP concentration, pro- and antioxidant enzymes activities increased in sham, did not changed in OVX-Veh rats, and were reduced in OVX-E2 rats. In rats exposed to RA, genes involved in extracellular matrix were up-regulated by OVX and down-regulated by E2, while E2 up-regulated genes involved in cell mobility/adherence and leukocytes migration. OVX downregulated expression of roughly 200 olfactory receptor genes without effect of E2. CIH altered gene expression in sham and OVX-E2, but not in OVX-Veh rats. Enrichment analysis confirmed the antioxidant effects of E2 under CIH. There are important interactions between ovarian hormones and CIH that can be relevant to better understand the consequences of sleep apnea (i.e. CIH) on the occurrence of lung pathologies in women.

Estradiol promotes and progesterone reduces anxiety-like behavior produced by nicotine withdrawal in female rats

This study assessed sex differences and the role of ovarian hormones in nicotine withdrawal. Study 1 compared physical signs, anxiety-like behavior, and corticosterone levels in male, intact female, and ovariectomized (OVX) female rats during nicotine withdrawal. Estradiol (E2) and progesterone levels were also assessed in intact females that were tested during different phases of the 4-day estrous cycle. Study 2 assessed the role of ovarian hormones in withdrawal by comparing the same measures in OVX rats that received vehicle, E2, or E2+progesterone prior to testing. Briefly, rats received a sham surgery or an ovariectomy procedure. Fifteen days later, rats were prepared with a pump that delivered nicotine for 14 days. On the test day, rats received saline or the nicotinic receptor antagonist, mecamylamine to precipitate withdrawal. Physical signs and anxiety-like behavior were assessed on the elevated plus maze (EPM) and light-dark transfer (LDT) tests. During withdrawal, intact females displayed greater anxiety-like behavior and increases in corticosterone levels as compared to male and OVX rats. Females tested in the estrus phase (when E2 is relatively low) displayed less anxiety-like behavior and had lower corticosterone levels versus all other phases. Anxiety-like behavior and corticosterone levels were positively correlated with E2 and negatively correlated with progesterone levels. Intact females displaying high E2/low progesterone showed greater anxiety-like behavior and corticosterone levels as compared to females displaying low E2/high progesterone. Lastly, OVX-E2 rats displayed greater anxiety-like behavior than OVX-E2+progesterone rats. These data suggest that E2 promotes and progesterone reduces anxiety-like behavior produced by nicotine withdrawal.

The Effect of Estrogen on Hepatic Fat Accumulation during Early Phase of Liver Regeneration after Partial Hepatectomy in Rats.

Fatty liver is common in men and post-menopausal women, suggesting that estrogen may be involved in liver lipid metabolism. The aim of this study is to be clear the role of estrogen and estrogen receptor alpha (ERα) in fat accumulation during liver regeneration using the 70% partial hepatectomy (PHX) model in male, female, ovariectomized (OVX) and E2-treated OVX (OVX-E2) rats. Liver tissues were sampled at 0–48 hr after PHX and fat accumulation, fatty acid translocase (FAT/CD36), sterol regulatory element-binding protein (SREBP1c), peroxisome proliferator-activated receptor α (PPARα), proliferative cell nuclear antigen (PCNA) and ERα were examined by Oil Red O, qRT-PCR and immunohistochemistry, respectively. Hepatic fat accumulation was abundant in female and OVX-E2 compared to male and OVX rats. FAT/CD36 expression was observed in female, OVX and OVX-E2 at 0–12 hr after PHX, but not in male rats. At 0 hr, SREBP1c and PPARα were elevated in female and male rats, respectively, but were decreased after PHX in all rats. The PCNA labeling index reached a maximum at 36 hr and 48 hr in OVX-E2 and OVX rats, respectively. ERα expression in OVX-E2 was higher than OVX at 0–36 hr after PHX. In conclusion, these results indicated that estrogen and ERα might play an important role in fat accumulation related to FAT/CD36 during early phase of rat liver regeneration.

Hemin blunts the depressant effect of chronic nicotine on reflex tachycardia via activation of central NOS/PI3K pathway in female rats.

Chronic nicotine administration impairs reflex chronotropic responses that follow arterial baroreceptor unloading in female rats with repleted, but not depleted (ovariectomized, OVX), estrogen (E2). This study investigated whether products of nitric oxide synthase (NOS) and/or heme oxygenase (HO) and related soluble guanylate cyclase (sGC)/phosphatidylinositol 3-kinase (PI3K)/mitogen-activated protein kinases (MAPKs) signaling mediate the E2-sensitive depressant effect of nicotine on reflex tachycardia. Baroreflex curves relating reflex tachycardic responses to falls in blood pressure (BP) generated by sodium nitroprusside (SNP) were established in conscious female rats and slopes of the curves were taken as measures of baroreflex sensitivity (BRS). Nicotine (2 mg/kg/day ip, 14 days) reduced BRS in OVX rats treated with E2 but not vehicle. Baroreceptor dysfunction in nicotine-treated OVXE2 rats was abolished after iv treatment with hemin (HO inducer) but not l-arginine (NOS substrate) denoting the importance of reduced availability of carbon monoxide, but not NO, in the nicotine effect. The favorable BRS effect of hemin was abolished after intracisternal (ic) administration of L-NAME (NOS inhibitor) or wortmannin (PI3 K inhibitor). Central circuits of MAPKs do not seem to contribute to the baroreflex facilitatory effect of hemin because the latter was preserved after central inhibition of MAPKERK (PD98059), MAPKp38 (SB203580) or MAPKJNK (SP600125). Likewise, sGC inhibition (ODQ) or E2 receptor blockade (ICI182780) failed to alter the hemin effect. The activation of central NOS/PI3K signaling following HO upregulation improves the E2-dependent depressant effect of nicotine on reflex tachycardia.

Estradiol does not directly regulate adipose lipolysis

ABSTRACTThe mechanisms by which estradiol modulates adipose lipolysis are poorly understood. We sought to measure basal and β3-stimulated indices of lipoysis (FFAs, glycerol) in vivo in E2 deficient or supplemented rats, and ex vivo with direct acute E2 exposure. For 2 weeks, ovariectomized (OVX) and OVX rats treated with a daily oral dose of E2 (OVX E2) were pairfed to SHAM controls (n = 12 per group). Adipocyte size was modestly (∼40%) increased in OVX rats, but did not reach significance (p = 0.2). After 2 weeks, half of the animals in each group received an in vivo injection of saline or 1 mg/kg of the β3 agonist CL 316, 243. Serum FFA concentrations, but not glycerol, were lower in OVX and OVX E2 rats compared with SHAM controls (p = 0.02). A significant CL response was present in all groups (p<0.001) and HSL activation was unaffected by OVX or OVX E2 in retroperitoneal (r.p.) or inguinal (iWAT) adipose depots in vivo. Ex vivo, CL increased FFA and glycerol accumulation in the media as well as HSL phosphorylation by several fold in r.p. and iWAT explants, but responses from OVX and OVX E2 rats were comparable to SHAMs. To assess whether E2 can directly affect lipolysis, r.p. and iWAT tissue was treated with E2, CL or E2 + CL for 2, 4 or 8 hours using adipose tissue organ culture. CL stimulated FFA release (p<0.001), but was unaffected by E2. Overall, our results indicate that E2 does not directly regulate adipose tissue lipolysis.

The estrogen-dependent baroreflex dysfunction caused by nicotine in female rats is mediated via NOS/HO inhibition: Role of sGC/PI3K/MAPKERK

We have previously reported that estrogen (E2) exacerbates the depressant effect of chronic nicotine on arterial baroreceptor activity in female rats. Here, we tested the hypothesis that this nicotine effect is modulated by nitric oxide synthase (NOS) and/or heme oxygenase (HO) and their downstream soluble guanylate cyclase (sGC)/phosphatidylinositol 3-kinase (PI3K)/mitogen-activated protein kinases (MAPKs) signaling. We investigated the effects of (i) inhibition or facilitation of NOS or HO on the interaction of nicotine (2mg/kg/dayi.p., 2weeks) with reflex bradycardic responses to phenylephrine in ovariectomized (OVX) rats treated with E2 or vehicle, and (ii) central pharmacologic inhibition of sGC, PI3K, or MAPKs on the interaction. The data showed that the attenuation by nicotine of reflex bradycardia in OVXE2 rats was abolished after treatment with hemin (HO inducer) or l-arginine (NOS substrate). The hemin or l-arginine effect disappeared after inhibition of NOS (Nω-Nitro-l-arginine methyl ester hydrochloride, L-NAME) and HO (zinc protoporphyrin IX, ZnPP), respectively, denoting the interaction between the two enzymatic pathways. E2-receptor blockade (ICI 182,780) reduced baroreflexes in OVXE2 rats but had no effect on baroreflex improvement induced by hemin or l-arginine. Moreover, baroreflex enhancement by hemin was eliminated following intracisternal (i.c.) administration of wortmannin, ODQ, or PD98059 (inhibitors of PI3K, sGC, and extracellular signal-regulated kinases, MAPKERK, respectively). In contrast, the hemin effect was preserved after inhibition of MAPKp38 (SB203580) or MAPKJNK (SP600125). Overall, NOS/HO interruption underlies baroreflex dysfunction caused by nicotine in female rats and the facilitation of NOS/HO-coupled sGC/PI3K/MAPKERK signaling might rectify the nicotine effect.

Activation of Brainstem and Hypothalamic Areas Related to Increased Tail Skin Temperature in Ovariectomized Rats

Hot flushes are usually treated with estrogen replacement in postmenopausal women but the neural pathways involved are poorly understood. We investigated the activation of brain areas associated with the increase in tail skin temperature in an animal model of menopause. Female Wistar rats were ovariectomized (OVX) and implanted with subcutaneous capsules containing 17ß‐estradiol (E2) (OVX+E2) or corn oil (OVX). Tail skin temperature (TST) was recorded during two hours at ambient temperature at 3, 7 and 14 days after surgery. On day 15th, rats were perfused and the brains were processed for immunohistochemistry. Neuronal activity was evaluated by counting the number of Fos‐immunoreactive (ir) cells. On day 14 after ovariectomy, the TST in OVX rats was higher than in OVX+E2 rats. All the brain areas examined exhibited significantly more Fos‐ir cells in OVX than OVX E2 rats. In the brainstem, OVX rats displayed more Fos/tyrosine hydroxylase doubled‐labeled neurons in the A1, A2 and locus coeruleus compared with OVX+E2 rats. OVX rats exhibited more Fos‐ir neurons than OVX+E2 rats in the rostral preoptic area (POA), anteroventral periventricular nucleus (AVPV), and median preoptic nucleus (MnPO) in the preoptic area and in the paraventricular nucleus (PVN) and arcuate nucleus (ARC) of the hypothalamus. Moreover, there was a high correlation between the TST and Fos expression in the A1, A2, AVPV and POA. Thus, ovariectomy gradually increases TST and induces neuronal activation in the brainstem, preoptic area and hypothalamus. Fos expression in neurons of the A1, A2, AVPV, and POA is directly correlated with TST, suggesting these brain areas are associated with the thermoregulatory effects of estrogen. &#x0D; Financial support: CNPQ, FAPEMIG, CAPES

The interplay between heme oxygenase and nitric oxide synthase and downstream PI3K/sGC/ERK signaling ameliorates the estrogen‐dependent depressant effect of chronic nicotine on reflex bradycardia (837.2)

Chronic nicotine impairs reflex bradycardia in estrogen (E2)‐replaced, but not depleted, female rats. We tested the hypothesis that nitric oxide synthase (NOS) and/or heme oxygenase (HO) and their downstream mitogen‐activated protein kinases mediate the nicotine‐baroreflex interaction. The depressant effect of nicotine (2 mg/kg/day i.p., 2 weeks) on reflex bradycardic responsiveness to phenylephrine in E2‐replaced ovariectomized (OVXE2) rats was abolished after treatment with hemin (HO inducer) or L‐arginine (NOS substrate), denoting the importance of reduced availability of their respective gaseous products, CO and NO, in the nicotine effect. The roles of CO and NO appear to be mutually facilitated because the hemin and L‐arginine effect was abolished after NOS (L‐NAME) and HO inhibition (ZnPP), respectively. Estrogen receptor blockade (ICI 182,780) reduced baroreflexes in OVXE2 rats but failed to abolish the improved baroreflex gain caused by hemin or L‐arginine in OVXE2/nicotine rats. Baroreflex facilitation by hemin was eliminated after inhibition of PI3K (wortmannin), sGC (ODQ) or ERK (PD98059) in central neurons, in contrast to no effect for the inhibition of p38 (SB203580) or JNK (SP600125). Together, the upregulation of NOS/HO‐coupled PI3K/sGC/ERK signaling downstream of E2 receptors rectifies the E2‐dependent, nicotine‐evoked impairment of reflex bradycardia in female rats.Grant Funding Source: Supported by Grant STDF ID 502, Egypt

Nongenomic effects of estrogen mediate the dose‐related myocardial oxidative stress and dysfunction caused by acute ethanol in female rats (652.19)

Acute ethanol lowers blood pressure (BP) and cardiac output in proestrus and after chronic estrogen (E2) replacement in ovariectomized (OVX) female rats. However, whether rapid nongenomic effects of E2 mediate these hemodynamic effects of ethanol remained unanswered. To test this hypothesis, we investigated the effect of ethanol (0.5, 1 or 1.5 g/kg; i.v.) on left ventricular (LV) function and oxidative markers in OVX rats pretreated 30 min earlier with 1 μg/kg E2 (OVXE2) or vehicle (OVX) and in proestrus sham‐operated (SO) rats. In SO rats, ethanol caused significant and dose‐ related reductions in BP, rate of rise in LV pressure (LV dP/dtmax), and LV developed pressure (LVDP). The ethanol effects disappeared in OVX rats and were restored in OVXE2 rats suggesting rapid estrogen receptor signaling mediates the detrimental LV effects of ethanol. The E2‐dependent LV dysfunction caused by ethanol was associated with higher LV: (i) generation of reactive oxygen species, (ii) expression of the malondialdehyde and 4‐hydroxynonenal protein adducts, (iii) Akt and ERK1/2, and (iv) catalase activity. Collectively, it is concluded that rapid estrogen receptor signaling is implicated in the cellular events that lead to the generation of aldehyde protein adducts and Akt/ERK1/2 phosphorylation, which ultimately mediate the estrogen‐dependent LV oxidative stress and dysfunction caused by ethanol in female rats. Grant Funding Source: Supported by NIAAA [2R01 AA014441‐07]

Endothelial and neuronal nitric oxide synthases variably modulate the oestrogen-mediated control of blood pressure and cardiovascular autonomic control

1. We have shown previously that long-term oestrogen (E2) replacement lowers blood pressure (BP) and improves cardiovascular autonomic control in ovariectomized (OVX) rats. In the present study, we investigated whether constitutive and/or inducible (i) nitric oxide synthase (NOS) modulate these E2 effects. 2. We evaluated changes in BP, myocardial contractility index (dP/dtmax ) and power spectral indices of haemodynamic variability following selective inhibition of endothelial (e) NOS with N(5)-(1-iminoethyl)-L-ornithine (L-NIO), neuronal (n) NOS with N(ω)-propyl-L-arginine (NPLA) or iNOS with 1400W in telemetered OVX rats treated for 16 weeks with (OVXE2) or without (control; OVXC) E2. 3. The OVXE2 rats exhibited: (i) reduced BP and increased dP/dtmax ; (ii) cardiac parasympathetic dominance, as reflected by the reduced low-frequency (LF; 0.25-0.75 Hz)/high-frequency (HF; 0.75-3 Hz) ratio of interbeat intervals (IBI(LF/HF)); and (iii) reduced LF oscillations of systolic BP, suggesting a reduced vasomotor sympathetic tone. Inhibition of eNOS (L-NIO; 20 mg/kg, i.p.) elicited a shorter-lived pressor response in OVXE2 than OVXC, rats along with reductions in dP/dtmax and increases in the spectral index of spontaneous baroreflex sensitivity (index α). Treatment with 1 mg/kg, i.p., NPLA reduced BP and increased the IBI(LF/HF) ratio in OVXE2 but not OVXC rats. The iNOS inhibitor 1400W (5 mg/kg, i.p.) caused no haemodynamic changes in OVXC or OVXE2 rats. 4. Overall, constitutive NOS isoforms exert restraining tonic modulatory BP effects that encompass eNOS-mediated reductions and nNOS-mediated elevations in BP in OVXE2 rats. Baroreflex facilitation and dP/dtmax reductions may account for the shorter pressor action of L-NIO in E2-treated, compared with untreated, OVX rats.

Nongenomic effects of estrogen mediate the dose-related myocardial oxidative stress and dysfunction caused by acute ethanol in female rats

Acute ethanol lowers blood pressure (BP) and cardiac output in proestrus and after chronic estrogen (E2) replacement in ovariectomized (OVX) female rats. However, whether rapid nongenomic effects of estrogen mediate these hemodynamic effects of ethanol remains unanswered. To test this hypothesis, we investigated the effect of ethanol (0.5 or 1.5 g/kg iv) on left ventricular (LV) function and oxidative markers in OVX rats pretreated 30 min earlier with 1 μg/kg E2 (OVXE2) or vehicle (OVX) and in proestrus sham-operated (SO) rats. In SO rats, ethanol caused significant and dose-related reductions in BP, rate of rise in LV pressure (LV dP/dtmax), and LV developed pressure (LVDP). These effects of ethanol disappeared in OVX rats and were restored in OVXE2 rats, suggesting rapid estrogen receptor signaling mediates the detrimental effects of ethanol on LV function. Ex vivo studies revealed that the estrogen-dependent myocardial dysfunction caused by ethanol was coupled with higher LV 1) generation of reactive oxygen species (ROS), 2) expression of malondialdehyde and 4-hydroxynonenal protein adducts, 3) phosphorylation of protein kinase B (Akt) and extracellular signal-regulated kinases (ERK1/2), and 4) catalase activity. ERK1/2 inhibition by PD-98059 (1 mg/kg iv) abrogated the myocardial dysfunction, hypotension, and the elevation in myocardial ROS generation caused by ethanol. We conclude that rapid estrogen receptor signaling is implicated in cellular events that lead to the generation of aldehyde protein adducts and Akt/ERK1/2 phosphorylation, which ultimately mediate the estrogen-dependent LV oxidative stress and dysfunction caused by ethanol in female rats.

The Estrogen‐Mediated Control Of Blood Pressure And Cardiovascular Autonomic Control Are Differentially Modulated By Endothelial And Neuronal Nitric Oxide Synthases

Estrogen (E2) replacement lowers blood pressure (BP) and improves the cardiovascular autonomic control in ovariectomized (OVX) rats. We investigated whether constitutive and/or inducible nitric oxide synthase (NOS) modulate these E2 effects. We evaluated changes in BP, myocardial contractility (dP/dtmax), and power spectral indices of hemodynamic variability following inhibition of eNOS (L‐NIO), nNOS (NPLA), or iNOS (1400W) in telemetered OVX rats treated for 16 weeks with (OVXE2) or without (control, OVXC) E2. OVXE2 rats exhibited (i) reduced BP, and increased dP/dtmax, (ii) enhanced cardiac parasympathetic influence as reflected by decreases in low‐frequency/high‐frequency ratio of interbeat intervals (IBILF/HF), and (iii) reduced LF oscillations of systolic BP, suggesting a reduced vasomotor sympathetic tone. L‐NIO elicited a shorter‐lived pressor response in OVXE2, than in OVXC, rats along with reductions in dP/dtmax and increases in the spectral index of spontaneous baroreflex sensitivity (index α). NPLA reduced BP and increased IBILF/HF ratio in OVXE2 but not in OVXC rats. No hemodynamic changes were caused by 1400W. Overall, eNOS and nNOS exert contrasting tonic modulatory BP effects, which comprise induction of hypotension and hypertension, respectively, in OVXE2 rats. Baroreflex facilitation and dP/dtmax reductions might explain the shorter pressor action of L‐NIO in OVXE2 rats.

Exacerbation of myocardial dysfunction and autonomic imbalance contributes to the estrogen-dependent chronic hypotensive effect of ethanol in female rats

Our previous studies showed that the hypotensive effect of chronic ethanol in female rats is reduced by ovariectomy (OVX) rats and was restored after estrogen replacement (OVXE2). Further, in randomly cycling rats, chronic ethanol increased cardiac parasympathetic dominance and subsequently reduced myocardial contractility and blood pressure (BP). In this study, we tested the hypothesis that alterations in myocardial contractility and sympathovagal control account for the E2 exacerbation of the hemodynamic effects of ethanol. BP, myocardial contractility (+dP/dtmax), and spectral cardiovascular autonomic profiles were evaluated in radiotelemetered OVX, and OVXE2 rats receiving liquid diet with or without ethanol (5%, w/v) for 13weeks. In OVX rats, ethanol caused modest hypotension along with significant increases in +dP/dtmax during weeks 2–5. The high-frequency (IBIHF, 0.75–3Hz) and low-frequency (IBILF, 0.25–0.75Hz) bands of interbeat intervals were briefly increased and decreased, respectively, by ethanol. Compared with its effects in OVX rats, chronic treatment of OVXE2 rats with ethanol elicited significantly greater and more sustained reductions in systolic (SBP) and diastolic (DBP) blood pressures and +dP/dtmax. Altered sympathovagal balance and parasympathetic overactivity were more evident in ethanol-treated OVXE2 rats as suggested by the sustained: (i) increases in high-frequency bands of interbeat intervals (IBIHF, 0.75–3Hz), and (ii) decreases in low-frequency IBI bands (IBILF, 0.25–0.75Hz), IBILF/HF ratio and +dP/dtmax. The plasma ethanol concentration was not affected by changes in the hormonal milieu. These findings suggest that estrogen exacerbates the ethanol-evoked reductions in myocardial contractility and BP and the associated parasympathetic overactivity in female rats.

Estrogen Protects Female Rats Against The Nicotine‐Induced Attenuation Of Reflex Tachycardia: Role Of Central Estrogen Receptors

Our preliminary studies showed that nicotine attenuates reflex tachycardia in male and not female rats. Here, the hypothesis was tested that the resistance of female rats to the nicotine effect is estrogen‐dependent. Baroreflex curves relating reflex tachycardic responses to decreases in blood pressure evoked by sodium nitroprusside (1–16 μg/kg) were constructed in proestrus, ovarictomized (OVX), and estrogen (50 μg/kg s.c., 5 days)‐replaced OVX (OVXE2) rats. Slopes of the curves were taken as a measure of baroreflex sensitivity (BRS). Nicotine (100 μg/kg) reduced BRS in OVX rats but not in proestrus or OVXE2 rats. The attenuation of reflex tachycardia by nicotine was also evident in diestrus rats, which exhibit low plasma estrogen, and in OVX rats treated simultaneously with E2 and the estrogen receptor antagonist tamoxifen. Experiments were then extended to determine whether central estrogenic pathways modulate the nicotine‐BRS interaction. Intracisteral (i.c.) treatment of OVX rats with E2 (0.2 μg/rat) abolished the BRS attenuating effect of nicotine. This protective effect of E2 disappeared when OVX rats were pretreated with i.c. ICI 182,780, a selective estrogen receptor antagonist. Together, central pathways of estrogen receptors seem to play integral role in the protection offered by E2 against nicotine‐induced barorecetor dysfunction.

Longitudinal assessment of the effects of oestrogen on blood pressure and cardiovascular autonomic activity in female rats

1. Published data concerning the effects of ovarian hormones on haemodynamic variability are contradictory. For the first time, the present study used radiotelemetric haemodynamic monitoring to investigate the long-term effects of chronic oestrogen depletion and repletion on cardiovascular autonomic control and arterial baroreflex sensitivity (BRS) in female rats. 2. Blood pressure (BP), heart rate (HR) and +dP/dt(max) of arterial pressure (an estimate of myocardial contractility) were monitored in sham-operated (SO), ovariectomized (OVX) and oestrogen-replaced OVX rats (OVXE2) for 16 weeks. Cardiovascular autonomic control and baroreflexes were assessed by frequency domain analysis of interbeat intervals (IBI) and systolic BP (SBP). 3. Compared with SO rats, OVX rats exhibited no changes in BP, short-lived decreases in HR and sustained reductions in +dP/dt(max) of arterial pressure. The high- (HF; 0.75-3 Hz) and low-frequency (LF; 0.25-0.75 Hz) components of spectral power of IBI were significantly decreased and increased, respectively, by ovariectomy. An increase in the IBI(LF/HF) ratio in OVX rats suggests a shift in the cardiac sympathovagal balance towards sympathetic dominance. Index alpha, the spectral index of spontaneous BRS, was reduced by OVX. 4. Oestrogen replacement caused significant reductions in BP and HR and reversed OVX-induced changes in +dP/dt(max) of arterial pressure and cardiac autonomic activity. The LF oscillations of SBP were reduced in OVXE2 rats, suggesting a reduction in vascular sympathetic tone by oestrogen. 5. These findings highlight the importance of long-term oestrogen therapy in rectifying the detrimental effects of depletion of ovarian hormones on the cardiovascular system and baroreflex.

Longitudinal Assessment Of The Modulatory Effect Of Estrogen On Blood Pressure And Cardiac Autonomic Activity In Female Rats

Reported findings on the effect of ovarian hormones on hemodynamic variability are contradictory. In this study we employed radiotelemetric hemodynamic monitoring to investigate the long‐term effect of estrogen depletion and repletion on cardiac autonomic control and baroreflex sensitivity (BRS). Blood pressure (BP), heart rate (HR), and +dP/dtmax (index of myocardial contractility) were monitored in sham‐operated (SO), ovariectomized (OVX), and estrogen‐treated OVX (OVXE2) rats for 16 weeks. Cardiovascular autonomic control was assessed by frequency analysis of interbeat intervals (IBI) and systolic BP (SBP). Compared with SO, OVX rats exhibited sustained reductions in dP/dtmax despite similar BP and HR. High‐frequency (HF, 0.75‐3 Hz), but not low‐frequency (LF, 0.25‐0.75 Hz), bands of IBI were reduced in OVX rats, suggesting attenuated cardiac vagal activity. OVX increased IBILF/HF ratio, indicating increased sympathetic dominance. Indexα, spectral index of BRS, was reduced in OVX rats. E2 replacement decreased BP and HR and reversed the effects of OVX on dP/dtmax and cardiac autonomic activity. LF oscillations of SBP were reduced in OVXE2 rats, highlighting a reduction in vascular sympathetic tone.Conclusionslong‐term estrogen therapy rectifies the detrimental cardiovascular and baroreflex influences caused by depletion of ovarian hormones.Supported by Grant R01 AA014441 from NIAAA.

Gender and estrogen specificity of the renal vasodilatory effect of nicotine in rats

This study investigated whether the renal vasodilatory response to acute nicotine exposure is sexually dimorphic and the role of estrogen in modulating the nicotine effect. Nicotine vasodilation was evaluated in phenylephrine‐preconstricted perfused kidneys of male, proestrus female, ovariectomized (OVX) and estrogen‐replaced OVX (OVXE2) rats. Nicotine infusion (5×10−4 M) produced significantly greater decreases in the renal perfusion pressure (RPP) in proestrus female compared with male kidneys. Inhibition of NOS by NG‐nitro‐L‐arginine abolished nicotine vasodilation in the two genders and brought the RPP of male and female kidneys to similar levels. Surgical (OVX) or physiological (diestrus phase) estrogen depletion almost abolished nicotine vasodilation. Further, estrogen or L‐arginine supplementation of OVX rats largely restored the renal vasodilatory response to nicotine. Blockade of estrogen receptors by tamoxifen attenuated the increase in nicotine vasodilation demonstrated in OVXE2 rats. Together, these findings suggest that the renal vasodilator activity of nicotine is entirely dependent on NOS activation and is more pronounced in female than in male kidneys. Also, estrogen mediates, at least partly, the renal vasodilatory effect of nicotine probably via facilitation of NOS‐NO signaling.Supported by Faculty of Pharmacy, Univ. of Alexandria, Egypt.

Time course of liver lipid infiltration in ovariectomized rats: Impact of a high-fat diet

Objectives The present study was undertaken to determine the time course of liver lipid infiltration in ovariectomized (Ovx) rats and the impact of high-fat (HF; 42% kJ) feeding on this response. Methods In a first step, Ovx rats were compared to Sham-operated (Sham) and Ovx rats supplemented with 17β-estradiol (OvxE2) to evaluate the effect of estrogen removal. In a second time, Ovx rats fed a HF diet (OvxHf) were compared with normally fed Ovx rats. Animals were killed after 3, 8, and 13 weeks of their respective treatment ( n = 8 rats/group). We measured liver triacylglycerol (TAG) content, fat pad mass, and several other plasma parameters. Results Ovariectomy resulted in the typical increase in energy intake and body weight. Liver TAG accumulation was 35, 43, and 99% higher in Ovx than in Sham rats after 3, 8, and 13 weeks, respectively. The ovariectomy-induced liver lipid infiltration was completely prevented by estrogen replacement. On the opposite, plasma TAG concentrations were lower in Ovx than in Sham and OvxE2 rats. HF feeding in Ovx rats resulted in a significant ( P < 0.05; 38 versus 22 mg/g at 13-week) accumulation of fat in liver as compared to normally fed Ovx rats. Conclusions Ovariectomy results in a progressive accumulation of fat in liver over a 13-week period. In addition, HF feeding in Ovx rats lead to an even more severe liver lipid infiltration. These data indicate that the absence of estrogens in rat favours fat accretion in liver, which is highly amplified by a HF diet.

Effects of ethinyl estradiol, estradiol, and testosterone on hindlimb endothelial function in vivo.

This study was designed to evaluate the effects of chronic treatment with estrogen and testosterone on hindlimb vascular function. Spontaneously hypertensive rats (SHR) were sham-operated (SHAM) or ovariectomized and treated with vehicle (OVX), ethinyl estradiol (OVX-EE2), estradiol (OVX-E2), or testosterone (OVX-TESTO) for 3 weeks. Anesthetized SHR were instrumented for the measurement of arterial blood pressure and hindlimb blood flow. Ovariectomy had no significant effect on hindlimb resistance. Resting blood pressure (mm Hg) and hindlimb resistance (mm Hg/ml/min/kg) were higher in OVX-TESTO (158 +/- 4 and 4.7 +/- 0.3) than SHAM control (130 +/- 6 and 3.3 +/- 0.4), OVX (139 +/- 6 and 3.4 +/- 0.3), OVX-EE2 (130 +/- 4 and 3.0 +/- 0.3), and OVX-E2 (120 +/- 4 and 3.3 +/- 0.4). The hemodynamic responses to the endothelium-dependent vasodilator acetylcholine (ACh) were similar in SHAM, OVX, OVX-EE2, and OVX-E2. The hindlimb vasodilatory effects of ACh were consistently greater in OVX-TESTO compared with OVX, OVX-EE2, OVX-E2, and SHAM control rats. The hemodynamic responses to the nitric oxide donor, sodium nitroprusside, were similar in all groups. Our results provide evidence of modulatory influence of testosterone on vasomotor function. It is suggested that the enhanced hindlimb endothelial function represents a compensatory mechanism for testosterone-induced hypertension.