Estrogen withdrawal selectively increases serotonin reactivity in rabbit basilar artery

Estrogen, nitric oxide, and hypertension differentially modulate agonist-induced contractile responses in female transgenic (mRen2)27 hypertensive rats

Clinical trials revealed that estrogen may result in cardiovascular risk in patients with coronary heart disease, despite earlier studies demonstrating that estrogen provided cardiovascular protection. It is possible that the preexisting condition of hypertension and the ability of estrogen to activate the renin-angiotensin system could confound its beneficial effects. Our hypothesis is that the attenuation of estrogen to agonist-induced vasoconstrictor responses through the activation of nitric oxide (NO) synthase (NOS) is impaired by hypertension. We investigated the effects of 17β-estradiol (E2) replacement in normotensive Sprague-Dawley (SD) and (mRen2)27 hypertensive transgenic (TG) rats on contractile responses to three vasoconstrictors, angiotensin II (ANG II), serotonin (5-HT), and phenylephrine (PE), and on the modulatory role of vascular NO to these responses. The aorta was isolated from ovariectomized SD and TG rats treated chronically with 5 mg E2 or placebo (P). The isometric tension of the aortic rings was measured in organ chambers, and endothelial NOS (eNOS) in the rat aorta was detected using Western blot analysis. E2 treatment increased eNOS expression in the SD and TG aorta and reduced ANG II- and 5-HT- but not PE-induced contractions in SD and TG rats. The inhibition of NOS with Nω-nitro-l-arginine methyl ester enhanced ANG II-, 5-HT-, and PE-induced contractions in P-treated and ANG II and PE responses in E2-treated SD and TG rats. Only the responses to 5-HT were augmented in hypertensive rats. In conclusion, this study shows that the preexisting condition of hypertension augmented the vascular responsiveness of 5-HT, whereas the attenuation of estrogen by ANG II and 5-HT vascular responses was not impaired by hypertension. The adrenergic agonist was unresponsive to estrogen treatment. The contribution of NO as a factor contributing to the relative refractoriness of the vascular responses is dependent on the nature of the vasoconstrictor and/or the presence of estrogen.

Effects of female sex hormones on responses to CGRP, acetylcholine, and 5-HT in rat isolated arteries

BACKGROUND

Female sex hormones are implicated in the modulation of reactivity of a wide range of blood vessels under physiological as well as pathological conditions. Migraine, a neurovascular syndrome, is 3 times more prevalent in women during their reproductive period than in men.

OBJECTIVE

This study sets out to investigate the effects of the female sex steroids, 17beta-estradiol and progesterone (separately and in combination) on vasoactive responses to calcitonin gene-related peptide (CGRP), acetylcholine, and 5-hydroxytryptamine (5-HT) in rat isolated mesenteric, caudal, and basilar arteries.

METHODS

Female Sprague-Dawley rats were ovariectomized (Day 0) and 7 days later subcutaneously implanted with pellets releasing over a 21-day period 17beta-estradiol (0.25 mg), progesterone (50 mg), their combination, or placebo. On days 25-28, the animals were killed, arteries isolated and mounted in Mulvany myographs, and cumulative concentration response curves to CGRP, acetylcholine, and 5-HT were constructed.

RESULTS

The relaxant responses to CGRP were significantly potentiated in mesenteric and caudal arteries from rats treated with 17beta-estradiol as compared to the placebo-treated rats. Acetylcholine-induced relaxations were potentiated in the caudal artery from rats treated with the combination of 17beta-estradiol and progesterone, as compared to that from placebo-treated rats. The 5-HT-induced contractions in the 3 arteries were not significantly different in efficacy or potency.

CONCLUSION

Our results show that 17beta-estradiol potentiates CGRP-induced relaxations in the mesenteric and caudal arteries, while the combination treatment enhances acetylcholine-induced relaxations in the caudal artery. Although these in vitro experiments have been carried out in rats and a direct extrapolation to migraine in humans is not possible, our results may provide a new avenue to study the effects of sex steroids on vascular reactivity.

Influence of sex steroid hormones on cerebrovascular function

The cerebral vasculature is a target tissue for sex steroid hormones. Estrogens, androgens, and progestins all influence the function and pathophysiology of the cerebral circulation. Estrogen decreases cerebral vascular tone and increases cerebral blood flow by enhancing endothelial-derived nitric oxide and prostacyclin pathways. Testosterone has opposite effects, increasing cerebral artery tone. Cerebrovascular inflammation is suppressed by estrogen but increased by testosterone and progesterone. Evidence suggests that sex steroids also modulate blood-brain barrier permeability. Estrogen has important protective effects on cerebral endothelial cells by increasing mitochondrial efficiency, decreasing free radical production, promoting cell survival, and stimulating angiogenesis. Although much has been learned regarding hormonal effects on brain blood vessels, most studies involve young, healthy animals. It is becoming apparent that hormonal effects may be modified by aging or disease states such as diabetes. Furthermore, effects of testosterone are complicated because this steroid is also converted to estrogen, systemically and possibly within the vessels themselves. Elucidating the impact of sex steroids on the cerebral vasculature is important for understanding male-female differences in stroke and conditions such as menstrual migraine and preeclampsia-related cerebral edema in pregnancy. Cerebrovascular effects of sex steroids also need to be considered in untangling current controversies regarding consequences of hormone replacement therapies and steroid abuse.

Fractal and noisy CBV dynamics in humans: influence of age and gender

The complexity of spontaneous cerebral blood volume (CBV) fluctuations can emerge from random, fractal, or chaotic processes. Our aims were to define the contribution of these patterns to the observed complexity and to evaluate the effect of age and gender on it. The total hemoglobin content as the measure of CBV was monitored by near-infrared spectroscopy on volunteers (men n = 19, age = 20 to 78 years; women n = 23, age = 21 to 79 years). Random and fractal patterns were distinguished by the spectral index (beta). Chaos was identified by surrogate analysis of the correlation dimension (a static chaotic parameter, the dimension of the correlation integral) and the largest Lyapunov exponent (a dynamic chaotic parameter, the rate of exponential divergence of the system states from a perturbed initial condition over the chaotic attractor). In spontaneous CBV fluctuations, both fast random and slow fractal dynamics are present separately in their spectra by a cutoff frequency, f'. Below f' the pattern is fractal, in that power rises inversely with frequency as 1/f(beta). f' decreases with age in men and women alike (F1: up to 0.12+/-0.06 Hz versus F2: up to 0.05+/-0.04 Hz at P = 0.015, and M1: up to 0.16+/-0.05 Hz versus M2: up to 0.11+/-0.04 Hz at P = 0.044). Neither pre- nor postmenopausal age groups (1 and 2, respectively) showed a (low)beta gender difference. Surrogate analysis showed that CBV dynamics cannot be characterized on the grounds of deterministic chaos. Cerebral blood volume fluctuates in a complex, bimodal manner in humans, in that the fast dynamics has no structure, while the slow dynamics exhibits a self-similar, that is, fractal temporal structure. The range of fluctuation amplitudes produced by fractal dynamics is always larger than that of random fluctuations, and it shrinks with an altered structuring in aging women only.

Effect of estrogen therapy on cerebral arteries during stroke in female rats

OBJECTIVE

To investigate the effect of estrogen therapy on the structural and functional properties of the middle cerebral artery during ischemia and reperfusion.

DESIGN

Ovariectomized (OVX; n = 8) and ovariectomized with estrogen therapy (OVX+EST; n = 8) female Sprague-Dawley rats were exposed to 1 hour of ischemia using a model of temporary focal ischemia of the middle cerebral artery with 24 hours of reperfusion and compared to sham controls (CTL; n = 8). After occlusion and reperfusion, right middle cerebral arteries were removed from the brain and mounted on glass cannulas in a chamber that allowed for control over transmural pressure and measurement of lumen diameter. Lumen diameter was measured in response to increased transmural pressure (myogenic tone) as well as response to nitro-L-arginine, serotonin, and nifedipine. Cerebrovascular reactivity was compared to other stroke outcome measures, including infarct volume (%) and neurologic deficit.

RESULTS

Serum estrogen was increased in OVX+EST rats (60.5 +/- 18.2 pg/mL) compared to OVX (0.2 +/- 0.2 pg/mL P < 0.05 vs OVX+EST) and CTL animals (1.3 +/- 1.0 pg/mL P > 0.05 vs OVX). OVX showed significantly less myogenic tone at 75 mm Hg (13.8 +/- 3.6%, P < 0.05 vs CTL) than CTL (29.8 +/- 4.7%) that was partially restored by estrogen therapy (21.2 +/- 4.5; P > 0.05). At serotonin concentrations of 10(-7) M, 3 x 10(-7) M, and 10(-6) M, the vessels from ischemic OVX rats showed significantly greater constriction (20.9 +/- 2.1%, 35.0 +/- 3.9%, and 39.4 +/- 3.4%, respectively) compared to nonischemic CTL rats (6.3 +/- 1.1%, 11.3 +/- 1.8%, and 16.8 +/- 2.5%, respectively P < 0.05). Estrogen therapy resulted in intermediate responses (18.2 +/- 5.3%, 25.2 +/- 6.6%, and 28.2 +/- 6.5%, respectively) that were not significantly different from the other groups. In addition, ischemia resulted in significantly greater dilation in response to 0.01 microM nifedipine in vessels from OVX animals (51.1 +/- 8.0%) compared to nonischemic CTL (18.0 +/- 3.8%; P < 0.05) and estrogen therapy resulted in an intermediate response (38.0 +/- 10.6; P > 0.05). Both reactivity to nitro-L-arginine and passive distensibility were not different among groups. There were no differences in percent infarct or neurologic deficit between ischemic groups.

CONCLUSIONS

The influence of ischemia and reperfusion on vessel function was more dominant than that of estrogen therapy. However, estrogen therapy seemed to partially restore vessel function to similar levels as nonischemic vessels.

Effects of estrogen therapy on hearing in postmenopausal women

OBJECTIVE

This study was undertaken to investigate how hormone therapy affects hearing in postmenopausal women.

STUDY DESIGN

This prospective study involved 109 postmenopausal women. Twenty of the women were using estrogen therapy (ET group), 30 women were using hormone therapy (HT group), and 59 had not received hormone therapy of any kind (control group). Otoscopic examination revealed normal tympanic membranes in all 109 subjects. Each individual was tested with low- (250-2000 Hz) and high-frequency audiometry (4000-16000 Hz). Duration of hormone therapy was recorded, and patient characteristics (age, type of menopause, time since onset of menopause), body mass index (BMI), and hearing test results in the ET, HT, and control groups were compared.

RESULTS

There were no statistically significant differences between the treatment (ET and HT group) and control groups with respect to age, BMI, or time since onset of menopause. The mean time on HT and ET was 4.13+/-2.41 years and 3.35+/-2.20 years, respectively. The mean air conduction results at low frequencies (250, 500, 1000, and 2000 Hz) in the ET group were significantly higher than the corresponding findings in the control group (P<.001) and than the HT group (P<.001). When the same comparisons were made between the HT group and the control group, none of the differences was statistically significant (P>.05). The mean air-conduction results at high frequencies (4, 6, 8, 10, 12, 14, and 16 kHz) in the ET group were significantly higher than the corresponding results in the HT group (P<.008). ET versus controls and HT versus controls at high frequencies revealed no significant differences (P>.05). The mean bone conduction results in the ET group were significantly higher than the corresponding findings in the control group (P<.016). Analysis of the same comparisons between the HT-ET and HT-control groups revealed no significant differences (P>.05).

CONCLUSION

Estrogen therapy may slow down hearing loss in aging postmenopausal women; however, further studies of larger series are needed to confirm this, and the sites of hormonal action must also be explored.

Estradiol exerts neuroprotective effects when administered after ischemic insult

BACKGROUND AND PURPOSE

17beta-Estradiol (E2) has been reported to exert neuroprotective effects when administered before an ischemic insult. This study was designed to determine whether E2 treatment after ischemia exerts the same effects and, if so, how long this therapeutic window remains open, and whether the effects are related to changes in cerebral blood flow (CBF).

METHODS

Female Sprague-Dawley rats were subjected to permanent middle cerebral artery occlusion (MCAO). In protocol 1, E2 was administered (100 microg/kg IV followed immediately by subcutaneous implantation of crystalline E2 in a silicone elastomer tube) to ovariectomized females (OVX+E2) at 0.5 (n=8), 1 (n=6), 2 (n=7), 3 (n=6), or 4 (n=9) hours after MCAO. Intact (INT; n=6) and ovariectomized females (OVX; n=12) were subjected to MCAO and received vehicle instead of E2. Two days after MCAO the animals were killed, and ischemic lesion volume was determined by 2,3,5-triphenyltetrazolium chloride staining. In protocol 2, CBF was monitored before and at 1, 24, and 48 hours in a group of animals receiving E2 or vehicle 0.5 hour after ischemia induction (INT, n=6; OVX, n=8; OVX+E2, n=6).

RESULTS

Lesion volume was 20.9+/-2.2% and 21.8+/-1.2% in the INT and OVX groups, respectively. E2 was found to decrease lesion volume significantly when administered within 3 hours after MCAO. The lesion volumes were 6.3+/-0.5%, 10.3+/-2.1%, 11.8+/-1.8%, 13.5+/-1.6%, and 17.9+/-2.8% when E2 was administered at 0.5, 1, 2, 3, or 4 hours after MCAO, respectively. CBF decreased to 43.1+/-2.2% and 25.4+/-1.0% in the INT and OVX animals, respectively, at 5 minutes after MCAO. In comparison to OVX rats, CBF was not different at 1 hour after E2 administration but was increased significantly in the OVX+E2 group 1 and 2 days after E2 administration.

CONCLUSIONS

E2 exerts neuroprotective effects when administered after ischemia, with a therapeutic window in a permanent focal cerebral ischemia model of approximately 3 hours. This effect of estradiol was associated with no immediate change in blood flow but with a delayed increase in CBF.

A proposed role for nerve growth factor in the etiology of multiple sclerosis

It is proposed that, in addition to genetic factors involved in immune attack on myelin, higher concentrations of nerve growth factor in certain tissues during development determine susceptibility to multiple sclerosis. High early nerve growth factor in some vasculature of spontaneously hypertensive rats increases sympathetic innervation and catecholamine production in these vessels. They become more sensitive than controls to noradrenaline after chemical sympathectomy. Continued exposure to high noradrenaline can result in sympathectomy-like effects, heightening sensitivity to constricting neurotransmitters. Vasoresponses of spontaneously hypertensive rats are impaired with submaximal but not maximal hypoxia. Such a situation in multiple sclerosis patients could result in insufficient blood flow by vasoconstriction until it becomes maximal. Glutamate increase by ischemia and hyperemic release of free radicals could injure neurons, prompting an immune response to myelin proteins in susceptible people. Developmental adaptation to situations requiring lower sympathetic activity might help counteract these effects.

Supersensitivity to serotonin- and histamine-induced arterial contraction following ovariectomy

The modulating role of estrogens and ovariectomy on coronary artery and thoracic aortic rings was examined in female rabbits. Three treatment groups were studied: (1) control, (2) ovariectomy, and (3) ovariectomy + 17beta-estradiol acetate (40 microg/kg per day, i.m. for 7 days). Coronary artery reactivity was studied in the isolated retrogradely perfused heart. Aortic reactivity was studied using endothelium intact and denuded aortic rings. Concentration-response curves were performed to serotonin (5-HT) and histamine. A 21-fold, a 4.7-fold, and a 5.2-fold increase in sensitivity to 5-HT-induced contraction were observed in the ovariectomy group compared to the control group for coronary artery, intact aortic, and denuded aortic preparations, respectively (P < 0.05 for each comparison). Similarly, 34-fold, 4.9-fold, and 5.0-fold increases in sensitivity to histamine-induced contraction were observed in the ovariectomy group compared to control group for coronary artery, intact aortic, and denuded aortic preparations, respectively (P < 0.05 for each comparison). 17beta-Estradiol administration reversed the supersensitivity to serotonin- and histamine-induced vascular contraction observed following ovariectomy. No differences in EC50 or maximal contraction were noted between control and ovariectomy + estrogen groups. Baseline nitric oxide release and maximal 5-HT- and histamine-induced nitric oxide release from the perfused heart were decreased (P < 0.05) in ovariectomy rabbits compared to control and ovariectomy + estrogen treatment groups. The data demonstrate that (1) reduced autacoid-induced nitrous oxide release following ovariectomy and (2) direct effects upon the vascular smooth muscle contractility, which are probably mediated by altered receptor sensitivity by ovariectomy and estrogen replacement therapy. The information obtained from this study provides additional information regarding possible beneficial actions of estrogen replacement therapy in post-menopausal women.

Effects of ovariectomy on cerebral flow of rats

Recent reports suggest that estrogens may enhance cognitive function in postmenopausal women and women suffering from dementia of the Alzheimer's type. One of several proposed mechanisms of action of estrogen has been an improvement in cerebral blood flow (CBF). The current study examined the effects of estrogen deprivation resulting from ovariectomy on the CBF of rats using the quantitative autoradiographic 14C-iodoantipyrine technique. CBF was assessed in passively restrained, awake adult rats at 6 weeks following ovariectomy (n = 10) or sham surgery (n = 10). Rats demonstrated marked endometrial atrophy and a decrease in uterine weight (mean 78%) in response to ovariectomy. Ovariectomized animals did not differ from control animals both in the magnitude and the topography of cortical or subcortical CBF, including the medial preoptic area, amygdala, arcuate nucleus and anterior hypothalamus, areas previously associated with high estrogen binding. These results suggest that in young, surgically ovariectomized animals, hormonal factors do not significantly contribute to changes in basal CBF.

Effect of estrogen on nitric oxide-induced relaxation of the rabbit urethra

We evaluated the effect of estrogen on nitric oxide (NO)-mediated urethral relaxation in rabbits. Female New Zealand white rabbits, 4-5 weeks old, were treated with 5 mg/kg estradiol dipropionate (estrogen group) or saline (control group) injected intramuscularly weekly for 2 weeks. Electrical field stimulation (supramaximum voltage, 2 ms pulse duration, 0.3-15 Hz and 3 s train) caused frequency-dependent relaxation of urethral strips in both groups, which was inhibited by Nomega-nitro-L-arginine (L.-NNA). This inhibition was overcome by addition of L-arginine. The relaxation induced by nitrergic nerve stimulation was significantly lower in the estrogen group than in the control group. There was no significant difference in sodium nitroprusside-induced urethral relaxation between the two groups. The production of NO in urethral strips during nitrergic nerve stimulation was evaluated by measuring nitrite/nitrate (NO2-/NO3-) levels in both groups, using microdialysis. The NO2-/NO3- production during electrical field stimulation in the estrogen group was significantly less than that in the control group. The NADPH diaphorase-positive reaction in the control group was greater than that in the estrogen group. The results suggest that estrogen treatment may reduce NO synthase activity, and inhibit the relaxation induced by nitrergic nerve stimulation in rabbit urethral smooth muscle.

Headache induced by serotonergic agonists--a key to the interpretation of migraine pathogenesis?

Serotonergic agonists such as m-chlorophenylpiperazine (m-CPP) and fenfluramine may induce migraine attacks. This has led to opposing theories concerning the role of 5-hydroxytryptamine (5HT) in triggering migraine attacks; is there hyperfunction or hypofunction of the central serotonergic system. Our review of the literature strongly suggests that m-CPP and fenfluramine provoke migraine attacks by stimulating, directly or indirectly, the 5HT2C/5HT2B receptors, although there is no total agreement with this interpretation. Central 5HT hypersensitivity in migraine patients, probably due to 5HT neuronal depletion, is proposed on the basis of review of electrophysiological tests and neuroendocrine challenge paradigms.

The menopause and the cardiovascular system

Combining the wealth of epidemiological, metabolic and recent mechanistic data, it would appear biologically plausible that HRT, either oestrogen alone or in combination with progestogen, is cardioprotective. Further research is required, as information is lacking on cardiovascular effects of HRT instigated at an older age. There is a need to identify cardiovascular benefit, indirect and/or direct, of combined oestrogen/progestogen therapy using randomized trials. The various progestogen types and doses also need to be investigated. Studies are also required to investigate the effect of HRT use in higher risk patients with established CVD. There is scant information on the effect of HRT on blood pressure of patients with hypertension. Cardiovascular risk factor profiles and incidence surveys need to be conducted in developing countries to characterize their female population and to identify the prevalence of CVD; this needs to be undertaken before widespread recommendations on CVD prevention and the role of HRT can be made. If HRT is to be used effectively in the future treatment of heart disease in women these questions need to be addressed. At present HRT is indicated for the relief of menopausal symptoms and the prevention of osteoporosis. In women without these indications, ORT may be recommended in those who have had a premature menopause, and possibly in those who have established CHD or who are at high risk of developing CHD. It is too early to suggest a blanket recommendation for the use of HRT in the treatment of the symptoms of women with established CVD, but HRT after the menopause may at least be safely used in the secondary prevention of CHD.