Raloxifene relaxes rat cerebral arteries in vitro and inhibits L-type voltage-sensitive Ca2+ channels

Expanding the Toolbox: Novel Modulators of Endolysosomal Cation Channels

Functional characterization of endolysosomal ion channels is challenging due to their intracellular location. With recent advances in endolysosomal patch clamp technology, it has become possible to directly measure ion channel currents across endolysosomal membranes. Members of the transient receptor potential (TRP) cation channel family, namely the endolysosomal TRPML channels (TRPML1-3), also called mucolipins, as well as the distantly related two-pore channels (TPCs) have recently been characterized in more detail with endolysosomal patch clamp techniques. However, answers to many physiological questions require work in intact cells or animal models. One major obstacle thereby is that the known endogenous ligands of TRPMLs and TPCs are anionic in nature and thus impermeable for cell membranes. Microinjection, on the other hand, is technically demanding. There is also a risk of losing essential co-factors for channel activation or inhibition in isolated preparations. Therefore, lipophilic, membrane-permeable small-molecule activators and inhibitors for TRPMLs and TPCs are urgently needed. Here, we describe and discuss the currently available small-molecule modulators of TRPMLs and TPCs.

Evidence for G-Protein-Coupled Estrogen Receptor as a Pronatriuretic Factor

Background The novel estrogen receptor, G-protein-coupled estrogen receptor (GPER), is responsible for rapid estrogen signaling. GPER activation elicits cardiovascular and nephroprotective effects against salt-induced complications, yet there is no direct evidence for GPER control of renal Na+ handling. We hypothesized that GPER activation in the renal medulla facilitates Na+ excretion. Methods and Results Herein, we show that infusion of the GPER agonist, G1, to the renal medulla increased Na+ excretion in female Sprague Dawley rats, but not male rats. We found that GPER mRNA expression and protein abundance were markedly higher in outer medullary tissues from females relative to males. Blockade of GPER in the renal medulla attenuated Na+ excretion in females. Given that medullary endothelin 1 is a well-established natriuretic factor that is regulated by sex and sex steroids, we hypothesized that GPER activation promotes natriuresis via an endothelin 1-dependent pathway. To test this mechanism, we determined the effect of medullary infusion of G1 after blockade of endothelin receptors. Dual endothelin receptor subtype A and endothelin receptor subtype B antagonism attenuated G1-induced natriuresis in females. Unlike males, female mice with genetic deletion of GPER had reduced endothelin 1, endothelin receptor subtype A, and endothelin receptor subtype B mRNA expression compared with wild-type controls. More important, we found that systemic GPER activation ameliorates the increase in mean arterial pressure induced by ovariectomy. Conclusions Our data uncover a novel role for renal medullary GPER in promoting Na+ excretion via an endothelin 1-dependent pathway in female rats, but not in males. These results highlight GPER as a potential therapeutic target for salt-sensitive hypertension in postmenopausal women.

Bazedoxifene-induced vasodilation and inhibition of vasoconstriction is significantly greater than estradiol

OBJECTIVE

A new strategy for menopausal hormone therapy replaces medroxyprogesterone with the selective estrogen receptor modulator bazedoxifene. While the agonist or antagonist activity of bazedoxifene has been examined in other tissues, the current study explored the impact of bazedoxifene on resistance artery reactivity. We hypothesized that bazedoxifene may induce greater vasoprotective effects than estradiol due to enhanced activation of the G-protein-coupled estrogen receptor.

METHODS

We measured the vasodilation of mesenteric resistance arteries from adult male and female wild-type and G-protein-coupled estrogen receptor knockout mice (n = 58) in response to increasing concentrations of bazedoxifene, medroxyprogesterone, and estradiol, and also the impact of these compounds on the responses to phenylephrine and sodium nitroprusside.

RESULTS

Bazedoxifene-induced vasorelaxation was greater than estradiol and blunted phenylephrine-induced contraction-an effect not observed with estradiol. Neither estradiol nor bazedoxifene altered relaxation to sodium nitroprusside. The combination of bazedoxifene + estradiol promoted greater vasodilation than medroxyprogesterone + estradiol, and opposed phenylephrine-induced contraction, whereas medroxyprogesterone + estradiol failed to attenuate this response. Both bazedoxifene + estradiol and medroxyprogesterone + estradiol enhanced sodium nitroprusside-induced relaxation in females. Vascular responses were similar in both sexes in wild-type and G-protein-coupled estrogen receptor knockout mice.

CONCLUSION

Bazedoxifene and bazedoxifene + estradiol relaxed mesenteric arteries and opposed vasoconstriction to a greater degree than estradiol or medroxyprogesterone + estradiol. These effects were independent of sex and G-protein-coupled estrogen receptor expression. We conclude that bazedoxifene may provide vascular benefits over estrogen alone or estrogen plus progestogen combinations in postmenopausal women.

Role of inducible nitric oxide synthase in endothelium-independent relaxation to raloxifene in rat aorta

BACKGROUND AND PURPOSE

Raloxifene can induce both endothelium-dependent and -independent relaxation in different arteries. However, the underlying mechanisms by which raloxifene triggers endothelium-independent relaxation are still incompletely understood. The purpose of present study was to examine the roles of NOSs and Ca²⁺ channels in the relaxant response to raloxifene in the rat isolated, endothelium-denuded aorta.

EXPERIMENTAL APPROACH

Changes in isometric tension, cGMP, nitrite, inducible NOS protein expression and distribution in response to raloxifene in endothelium-denuded aortic rings were studied by organ baths, radioimmunoassay, Griess reaction, western blot and immunohistochemistry respectively.

KEY RESULTS

Raloxifene reduced the contraction to CaCl₂ in a Ca²⁺ -free, high K⁺ -containing solution in intact aortic rings. Raloxifene also acutely relaxed the aorta primarily through an endothelium-independent mechanism involving NO, mostly from inducible NOS (iNOS) in vascular smooth muscle layers. This effect of raloxifene involved the generation of cGMP and nitrite. Also, it was genomic in nature, as it was inhibited by a classical oestrogen receptor antagonist and inhibitors of RNA and protein synthesis. Raloxifene-induced stimulation of iNOS gene expression was partly mediated through activation of the NF-κB pathway. Raloxifene was more potent than 17β-estradiol or tamoxifen at relaxing endothelium-denuded aortic rings by stimulation of iNOS.

CONCLUSIONS AND IMPLICATIONS

Raloxifene-mediated vasorelaxation in rat aorta is independent of a functional endothelium and is mediated by oestrogen receptors and NF-κB. This effect is mainly mediated through an enhanced production of NO, cGMP and nitrite, via the induction of iNOS and inhibition of calcium influx through Ca²⁺ channels in rat aortic smooth muscle.

Glabridin-induced vasorelaxation: Evidence for a role of BKCa channels and cyclic GMP

Background and purpose

Glabridin is a major flavonoid in Glycyrrhiza glabra (licorice) root, a traditional Asian medicine. Glabridin is reported to have anti-atherogenic, anti-inflammatory and anti-nephritic properties; however its effects on vascular tone remain unexplored.

Experimental approach

We examined the effect of glabridin on rat main mesenteric artery using isometric myography and also ELISA to measure cGMP levels.

Key results

Glabridin (30 μM) relaxed arteries pre-constricted with the thromboxane A₂ analog U46619 (0.2 μM) by ~ 60% in an endothelium-independent manner. Relaxation to 30 μM glabridin was abolished by the guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (1 μM) and by the BK_Ca channel blocker tetraethyammonium (1 mM) but was unaffected by the estrogen receptor antagonist ICI182780. The concentration-response curve to glabridin (0.1 to 30 μM) was downshifted by the K_ATP channel blocker glibenclamide (10 μM), the K_V channel blocker 4-aminopyridine (300 μM), and the K_IR blocker BaCl₂ (30 μM). In U46619-contracted arteries partially relaxed by 0.1 μM sodium nitroprusside, application of 10 and 30 nM glabridin caused additional vasorelaxation. Glabridin (30 μM) approximately doubled tissue [cyclic GMP]. Application of the phosphodiesterase inhibitor isobutylmethylxanthine caused a much larger rise in [cyclic GMP], and glabridin failed to cause vasorelaxation or a further rise in [cGMP] when co-applied with IBMX.

Conclusions and implications

Vasorelaxation to glabridin is dependent on the opening of K⁺ channels, particularly BK_Ca, probably caused by a rise in cellular [cyclic GMP] owing to phosphodiesterase inhibition. In the presence of sodium nitroprusside an effect of glabridin is observed at nM concentrations, similar those measured in plasma following human ingestion of licorice flavonoid oil.

The G protein estrogen receptor (GPER) is regulated by endothelin-1 mediated signaling in cancer cells

Endothelin-1 (ET-1) is a potent endogenous vasoconstrictor involved in many diseases, including certain cardiovascular disorders and cancer. As previous studies have shown that the G protein estrogen receptor (GPER) may regulate ET-1 dependent effects on the vascular system, we evaluated whether GPER could contribute to the effects elicited by ET-1 in breast cancer and hepatocarcinoma cells. Here, we demonstrate that ET-1 increases GPER expression through endothelin receptor A (ETAR) and endothelin receptor B (ETBR) along with the activation of PI3K/ERK/c-Fos/AP1 transduction pathway. In addition, we show that GPER is involved in important biological responses observed upon ET-1 exposure, as the migration of the aforementioned tumor cells and the formation of tube-like structures in human umbilical vein endothelial cells (HUVECs). Our data suggest that GPER may contribute to ET-1 action toward the progression of some types of tumor.

Raloxifene inhibits cloned Kv4.3 channels in an estrogen receptor-independent manner

Raloxifene is widely used for the treatment and prevention of postmenopausal osteoporosis. We examined the effects of raloxifene on the Kv4.3 currents expressed in Chinese hamster ovary (CHO) cells using the whole-cell patch-clamp technique and on the long-term modulation of Kv4.3 messenger RNA (mRNA) by real-time PCR analysis. Raloxifene decreased the Kv4.3 currents with an IC50 of 2.0 μM and accelerated the inactivation and activation kinetics in a concentration-dependent manner. The inhibitory effects of raloxifene on Kv4.3 were time-dependent: the association and dissociation rate constants for raloxifene were 9.5 μM(-1) s(-1) and 23.0 s(-1), respectively. The inhibition by raloxifene was voltage-dependent (δ = 0.13). Raloxifene shifted the steady-state inactivation curves in a hyperpolarizing direction and accelerated the closed-state inactivation of Kv4.3. Raloxifene slowed the time course of recovery from inactivation, thus producing a use-dependent inhibition of Kv4.3. β-Estradiol and tamoxifen had little effect on Kv4.3. A preincubation of ICI 182,780, an estrogen receptor antagonist, for 1 h had no effect on the inhibitory effect of raloxifene on Kv4.3. The metabolites of raloxifene, raloxifene-4'-glucuronide and raloxifene-6'-glucuronide, had little or no effect on Kv4.3. Coexpression of KChIP2 subunits did not alter the drug potency and steady-state inactivation of Kv4.3 channels. Long-term exposure to raloxifene (24 h) significantly decreased the expression level of Kv4.3 mRNA. This effect was not abolished by the coincubation with ICI 182,780. Raloxifene inhibited Kv4.3 channels by interacting with their open state during depolarization and with the closed state at subthreshold potentials. This effect was not mediated via an estrogen receptor.

Effect of ranolazine on rat intrarenal arteries in vitro

Ranolazine is mainly used to treat patients with chronic stable angina in clinical practice. However, ranolazine does not lower significantly systemic blood pressure. The direct effect of ranolazine on vascular tone remains unknown. In the present study, we investigated the vascular effects and mechanisms of action of ranolazine in isolated rat intrarenal arteries. Rings of intrarenal arteries were mounted in a small vessel myography using two stainless steel wires for the measurement of isometric tension. L-type Ca²⁺ currents were recorded in isolated single renal arterial smooth muscle cells using patch clamp techniques in whole-cell mode. Ranolazine induced concentration-dependent relaxations in rings contracted with phenylephrine, but ranolazine failed to cause any relaxation in rings pre-contracted by U46619, 5-HT or endothelin-1. Ranolazine also induced relaxations in norepinephrine pre-contracted rings. Yohimbine failed to induce relaxation in rings pre-contracted by norepinephrine. Propranolol did not affect ranolazine-induced relaxation but the relaxant effect of ranolazine was much less than that of prazosin. Ranolazine-induced relaxations were slight but significantly attenuated by endothelial denudation. Partial inhibition was observed in endothelium-intact arteries exposed to a combination of iberiotoxin and apamin. Ranolazine at higher concentration (>30 μM) inhibited Ca²⁺-induced contraction in a noncompetitive manner. Ranolazine reduced L-type Ca²⁺ currents at potentials between -30 and 50 mV in isolated renal artery myocytes. Therefore it can be said that ranolazine has significant α₁-adrenergic receptor and weak calcium channel antagonistic effects in rat intrarenal arteries.

GPER regulates endothelin-dependent vascular tone and intracellular calcium

AIMS

An increase in intracellular vascular smooth muscle cell calcium concentration (VSMC [Ca(2+)](i)) is essential for endothelin-1 (ET-1)-induced vasoconstriction. Based on previous findings that activation of the G protein-coupled estrogen receptor (GPER) inhibits vasoconstriction in response to ET-1 and regulates [Ca(2+)](i) in cultured VSMC, we investigated whether endogenous GPER regulates ET-1-induced changes in VSMC [Ca(2+)](i) and constriction of intact arteries.

MAIN METHODS

Pressurized carotid arteries of GPER-deficient (GPER(0)) and wildtype (WT) mice were loaded with the calcium indicator fura 2-AM. Arteries were stimulated with the GPER-selective agonist G-1 or solvent followed by exposure to ET-1. Changes in arterial diameter and VSMC [Ca(2+)](i) were recorded simultaneously. Vascular gene expression levels of ET(A) and ET(B) receptors were determined by qPCR.

KEY FINDINGS

ET-1-dependent vasoconstriction was increased in arteries from GPER(0) compared to arteries from WT mice. Despite the more potent vasoconstriction to ET-1, GPER deficiency was associated with a marked reduction in the ET-1-stimulated VSMC [Ca(2+)](i) increase, suggesting an increase in myofilament force sensitivity to [Ca(2+)](i). Activation of GPER by G-1 had no effect on vasoconstriction or VSMC [Ca(2+)](i) responses to ET-1, and expression levels of ET(A) or ET(B) receptor were unaffected by GPER deficiency.

SIGNIFICANCE

These results demonstrate that endogenous GPER inhibits ET-1-induced vasoconstriction, an effect that may be associated with reduced VSMC Ca(2+) sensitivity. This represents a potential mechanism through which GPER could contribute to protective effects of endogenous estrogen in the cardiovascular system.

Differential vasoactive effects of oestrogen, oestrogen receptor agonists and selective oestrogen receptor modulators in rat middle cerebral artery

Cerebrovascular disorders are less common in pre-menopausal than post-menopausal women and in females than males. This protection may be due, in part at least, to direct effects of oestrogens on blood vessels. Oestrogen's vasodilatory mechanisms have been reported to be via the endothelium, vascular smooth muscle and extracellular matrix, depending on the vascular bed studied. Herein we investigated the vasoactive effects of oestrogen, oestrogen receptor (ER) and GPR30 agonists and selective ER modulators (SERMs) in the rat middle cerebral artery(MCA), an artery affected in focal ischaemia. MCAs isolated from male Sprague Dawley rats were mounted on a wire myograph. Concentration response curves were constructed to 17β-oestradiol, ERα agonist-PPT, ERβ agonist-DPN, GPR30 agonist-G1 and novel SERMs (LY362321 and LY2120310) in pre-constricted vessels, in the presence and absence of endothelium, blocking agents for nitric oxide synthase (L-NAME), classic ER antagonist (ICI182,780) or plasma membrane specific ERα (ERα-36) antibody. 17β-oestradiol induced rapid vasorelaxation of the MCA which was not affected by endothelium removal, L-NAME or ICI182,780. Vasorelaxation was mimicked by PPT, DPN and G1 but not by the SERMs. Using ERα-36 antibody, effects of oestrogen were partially blocked. PPT had a greater vasorelaxation, while DPN and G1 had a lesser effect than 17β-oestradiol. These findings indicate that activation of plasma membrane bound ERα, β and GPR30 elicits rapid, endothelial-nitric oxide-independent relaxation of the rat MCA.

Raloxifene temporarily reduces arterial stiffness

AIM

Aortic stiffness is widely recognized as an important, independent determinant of cardiovascular risk. The cardio-ankle vascular index (CAVI) has been developed to estimate vascular wall stiffness which is theoretically less affected by varied blood pressure. The purpose of this paper was to evaluate the change of CAVI during one-year use of raloxifene (RLX).

MATERIAL & METHODS

Forty-eight women who visited the menopausal clinic in Tokyo Medical and Dental University were enrolled in this study. Twenty-two patients with osteopenia/osteoporosis (mean age 61.3 ± 1.1) out of 48 had RLX 60 mg/day (RLX group). The remaining 26 women (mean age 56.3 ± 1.0) had no medication and were recognized as younger, healthy control (control group). CAVI and ankle-brachial index were measured every 6 months, compared among 0, 6 and 12 months, in respective group.

RESULTS

CAVI showed a significant positive correlation to age by the single linear regression analysis. Control group indicated no change of age-adjusted CAVI through 12 months, but RLX group showed significant reduction of CAVI at 6 months and increased to the original level after 12 months. On the other hand, ankle-brachial index change showed significant increase in control group, but slight increase in RLX group, suggesting no increased risk of arterial stenosis. Furthermore, CAVI in the relatively younger group (50 to 59 years; n = 11) indicated stronger reduction at 6 months than older group, suggesting high sensitivity to RLX treatment in the younger group.

CONCLUSION

RLX treatment reduced CAVI value at 6 months which was superior in relatively younger group.

Therapeutically relevant concentrations of raloxifene dilate pressurized rat resistance arteries via calcium-dependent endothelial nitric oxide synthase activation

OBJECTIVE

Selective estrogen receptor modulators (SERMs) inhibit constriction of mammalian conduit arteries. However, it is unknown whether SERMs at therapeutically achievable concentrations could reduce vascular tone in resistance arteries. The present study aimed to examine roles of Ca(2+) influx in endothelium and endothelial nitric oxide synthase (eNOS) activation in dilatations induced by raloxifene, a second-generation SERM in myogenically active arteries.

METHODS AND RESULTS

Small mesenteric arteries from Sprague-Dawley rats were isolated and mounted in a pressure myograph for measurement of changes in vessel diameter. [Ca(2+)](i) images on native endothelial cells of intact arteries were determined by the fluorescence imaging technique, and phosphorylation of eNOS was assayed by Western blotting. Raloxifene (0.3 to 10 nmol/L) produced dilatations on established steady myogenic constriction. Female rat arteries dilated significantly more in response to raloxifene than male arteries. Raloxifene-induced dilatations of female arteries were blunted by N(G)-nitro-l-arginine methyl ester but unaffected by 1400W, charybdotoxin plus apamin, wortmannin, or LY294002. Raloxifene (3 nmol/L) triggered rises in endothelial cell [Ca(2+)](i) and increased eNOS phosphorylation at Ser1177. Both effects were greater in arteries from female rats than in arteries from male rats. Increases in endothelial cell [Ca(2+)](i) and in eNOS phosphorylation were prevented by removal of extracellular Ca(2+) ions. Finally, ICI 182,780 did not affect the raloxifene-stimulated rise in endothelial cell [Ca(2+)](i), eNOS phosphorylation, and vasodilatations. Chronic raloxifene treatment reduced myogenic constriction in arteries from female but not male rats.

CONCLUSION

Raloxifene at therapeutically relevant concentrations inhibits myogenic constriction by an NO-dependent mechanism that causally involves the elevated [Ca(2+)](i) in endothelial cells and subsequent eNOS activation. Raloxifene dilates resistance arteries more effectively in female rats, indicating its significant gender-related action on endothelial cells in microcirculation.

Effects of raloxifene on cerebral vasospasm after experimental Subarachnoid Hemorrhage in rabbits

BACKGROUND

The aim of this study was to investigate the ability of a SERM, RLX, to prevent vasospasm in a rabbit model of SAH.

METHODS

Thirty-four New Zealand white rabbits were allocated into 3 groups randomly. Subarachnoid hemorrhage was induced by injecting autologous blood into the cisterna magna. The treatment groups were as follows: (1) sham operated (no SAH [n = 12]), (2) SAH only (n = 12), and (3) SAH plus RLX (n = 10). Basilar artery lumen areas and arterial wall thickness were measured to assess vasospams in all groups.

RESULTS

There was a statistically significant difference between the mean basilar artery cross-sectional areas and the mean arterial wall thickness measurements of the control and SAH-only groups (P < .05). The difference between the mean basilar artery cross-sectional areas and the mean arterial wall thickness measurements in the RLX-treated group was statistically significant (P < .05). The difference between the SAH group and the SAH + RLX group was also statistically significant (P < .05).

CONCLUSIONS

These findings demonstrate that RLX has marked vasodilatatory effect in an experimental model of SAH in rabbits. This observation may have clinical implications suggesting that this SERM drug could be used as possible anti-vasospastic agent in patients without major adverse effects.

Evidence-based pharmacotherapy for cerebral vasospasm

INTRODUCTION

The vast amount of literature on the pharmaceutical treatment of cerebral vasospasm after aneurysmal subarachnoid hemorrhage remains daunting. Optimal treatment regimens for patients can be obscured by studies not statistically powered to draw evidenced-based conclusions.

METHODS

In this chapter, we reviewed the English literature using the National Library of Medicine for studies regarding pharmacotherapies for the treatment of cerebral vasospasm. These studies were then categorized according to the US Preventative Services Task Force ranking system for evidence based medicine and reviewed each pharmacotherapy for its efficacy in the treatment of cerebral vasospasm.

RESULTS

Nimodipine (Nimotop), HMG Co-A reductase inhibitor (statins) and enoxaparin (Lovenox) were the only drugs with level-1 evidence available for the treatment of vasospasm from aneurysmal subarachnoid hemorrhage as defined by the US Preventative Services Task Force.

CONCLUSION

As the understanding of the pathophysiological mechanisms of vasospasm after aneurysmal subarachnoid hemorrhage evolves in the basic science laboratory, novel medications are being trialed in humans. However, significantly more work must be carried out in this area before we have an effective medical treatment that can prevent or reverse the devastating events of cerebral vasospasm.

Raloxifene protects endothelial cell function against oxidative stress

BACKGROUND AND PURPOSE

Maintaining a delicate balance between the generation of nitric oxide (NO) and removal of reactive oxygen species (ROS) within the vascular wall is crucial to the physiological regulation of vascular tone. Increased production of ROS reduces the effect and/or bioavailability of NO, leading to an impaired endothelial function. This study tested the hypothesis that raloxifene, a selective oestrogen receptor modulator, can prevent endothelial dysfunction under oxidative stress.

EXPERIMENTAL APPROACH

Changes in isometric tension were measured in rat aortic rings. The content of cyclic GMP in aortic tissue was determined by radioimmunoassay. Phosphorylation of endothelial NOS (eNOS) and Akt was assayed by Western blot analysis.

KEY RESULTS

In rings with endothelium, ACh-induced relaxations were attenuated by a ROS-generating reaction (hypoxanthine plus xanthine oxidase, HXXO). The impaired relaxations were ameliorated by acute treatment with raloxifene. HXXO suppressed the ACh-stimulated increase in cyclic GMP levels; this effect was antagonized by raloxifene. The improved endothelial function by raloxifene was abolished by ICI 182,780, and by wortmannin or LY294002. Raloxifene also protected endothelial cell function against H2O2. Raloxifene increased the phosphorylation of eNOS at Ser-1177 and Akt at Ser-473; this effect was blocked by ICI 182,780. Finally, raloxifene was not directly involved in scavenging ROS, and neither inhibited the activity of xanthine oxidase nor stimulated that of superoxide dismutase.

CONCLUSION AND IMPLICATIONS

Raloxifene is effective against oxidative stress-induced endothelial dysfunction in vitro through an ICI 182,780-sensitive mechanism that involves the increased phosphorylation and activity of Akt and eNOS in rat aortae.

Effects of estradiol and raloxifene on arterial thrombosis in ovariectomized mice

OBJECTIVE

The effects of estrogen and selective estrogen receptor modulators (eg, raloxifene) on arterial thrombosis are not well defined. This study assessed the manner and mechanism by which estrogen and raloxifene affect homeostatic pathways in ovariectomized mice after acute arterial injury.

DESIGN

Female mice (3 weeks old) underwent ovariectomy or sham operation. Five days after surgery, mice were assigned to treatment with estradiol (5.3 nmol/kg), raloxifene (2.7 micromol/kg), or placebo (n = 10-12/group). The biological effects of both treatments were assessed by measurements of bone mass and the degree of uterine atrophy. After 4 months of therapy, carotid artery thrombosis was induced by photochemical injury, and the time to vascular occlusion was measured.

RESULTS

Both treatments increased bone mineral density (4.1%-7.85%). Reversal of macroscopic uterine atrophy was observed only in estrogen-treated mice. Ovariectomized mice had a shorter time to occlusion compared with sham-operated mice (70.8 +/- 7.4 vs 103 +/- 11.3 min), suggesting accelerated thrombosis. Both estradiol and raloxifene significantly inhibited intra-arterial thrombosis in ovariectomized mice, prolonging the time to occlusion to 136.33 +/- 13.5 and 141.43 +/- 9.26 min, respectively. Cyclooxygenase-2 levels in the lung tissue were significantly increased by both raloxifene and estradiol with endothelial nitric oxide synthase expression being unaltered. Platelet adhesion (measured by surface coverage under a shear rate of 1,800 s for 2 min) was significantly reduced in ovariectomized animals, being 4.63% +/- 1.47%, 5.78% +/- 1.58%, and 10.04% +/- 1.33% for raloxifene, estradiol, and placebo, respectively.

CONCLUSIONS

Ovariectomy amplifies thrombosis. We found that 4 months of treatment with both estradiol and raloxifene attenuates intravascular thrombosis. The antithrombotic effect was accompanied by increased expression of cyclooxygenase-2 and suppression of platelet surface adhesion.

Effect of raloxifene on cerebral vasospasm following experimental subarachnoid hemorrhage in rats

The effect of raloxifene on cerebral vasospasm following experimental subarachnoid hemorrhage (SAH) was investigated in a rat model. Seven groups of seven rats underwent no SAH, no treatment; SAH only; SAH plus vehicle; SAH plus 3 days intraperitoneal raloxifene treatment; SAH plus 4 days intraperitoneal raloxifene treatment; SAH plus 3 days intrathecal raloxifene treatment; and SAH plus 4 days intrathecal raloxifene treatment. The basilar artery cross-sectional areas were measured at 72 or 96 hours following SAH. The results showed raloxifene decreased SAH-induced cerebral vasospasm in all treatment groups, and suggested no difference between intraperitoneal and intrathecal application, or between 3 days and 4 days of raloxifene treatment. The present study demonstrates that raloxifene is a potential therapeutic agent against cerebral vasospasm after SAH.

Raloxifene, tamoxifen and vascular tone

1. Oestrogen deficiency causes progressive reduction in endothelial function. Despite the benefits of hormone-replacement therapy (HRT) evident in earlier epidemiological studies, recent randomized trials of HRT for the prevention of heart disease found no overall benefit. Instead, HRT users had higher incidences of stroke and heart attack. Most women discontinue HRT because of its many side-effects and/or the increased risk of breast and uterine cancer. This has contributed to the development of selective oestrogen receptor modulators (SERMs), such as tamoxifen and raloxifene, as alternative oestrogenic agents. 2. A SERM is a molecule that binds with high affinity to oestrogen receptors but has tissue-specific effects distinct from oestrogen, acting as an oestrogen agonist in some tissues and as an antagonist in others. Clinical and animal studies suggest multiple cardiovascular effects of SERMs. For example, raloxifene lowers serum levels of cholesterol and homocysteine, attenuates oxidation of low-density lipoprotein, inhibits endothelial-leucocyte interaction, improves endothelial function and reduces vascular smooth muscle tone. 3. Available evidence suggests that raloxifene and tamoxifen are capable of acting directly on both endothelial cells and the underlying vascular smooth muscle cells and cause a multitude of favourable modifications of the vascular wall, which jointly contribute to improved local blood flow. The outcome of the Raloxifene Use for the Heart (RUTH) trial will determine whether raloxifene, currently approved for the treatment of post-menopausal osteoporosis, could substitute for HRT in alleviating cardiovascular symptoms in post-menopausal women.

Therapeutic concentrations of raloxifene augment nitric oxide-dependent coronary artery dilatation in vitro

BACKGROUND AND PURPOSE

Raloxifene improves cardiovascular function. This study examines the hypothesis that therapeutic concentrations of raloxifene augment endothelium-dependent relaxation via up-regulation of eNOS expression and activity in porcine coronary arteries.

EXPERIMENTAL APPROACH

Isometric tension was measured in rings from isolated arteries. Intracellular Ca(2+) concentrations ([Ca(2+)](i)) in arterial endothelial cells were detected by Ca(2+) fluorescence imaging. Phosphorylation of eNOS at Ser-1177 was assayed by Western blot analysis.

KEY RESULTS

In arterial rings pre-contracted with 9,11-dideoxy-11alpha,9alpha-epoxy-methano-prostaglandin F(2alpha) (U46619), treatment with raloxifene (1-3 nM) augmented bradykinin- or substance P-induced relaxation and this effect was antagonized by ICI 182,780, an estrogen receptor antagonist. The enhanced relaxation was abolished in rings treated with inhibitors of nitric oxide/cyclic GMP-dependent dilation, N(G)-nitro-L-arginine methyl ester (L-NAME) plus 1H-[1,2,4]oxadizolo[4,3-a]quinoxalin-1-one (ODQ). In contrast, effects of raloxifene were unaffected after inhibition of endothelium-derived hyperpolarizing factors by charybdotoxin plus apamin. Raloxifene (3 nM) did not influence endothelium-independent relaxation to sodium nitroprusside. 17beta-Estradiol (3-10 nM) also enhanced bradykinin-induced relaxation, which was inhibited by ICI 182,780. Treatment with raloxifene (3 nM) did not affect bradykinin-stimulated rise in endothelial cell [Ca(2+)](i). Raloxifene, 17beta-estradiol, and bradykinin increased eNOS phosphorylation at Ser-1177 and ICI 182,780 prevented effects of raloxifene or 17beta-estradiol but not that of bradykinin. Raloxifene had neither additive nor antagonistic effects on 17beta-estradiol-induced eNOS phosphorylation.

CONCLUSIONS AND IMPLICATIONS

Raloxifene in therapeutically relevant concentrations augmented endothelial function in porcine coronary arteries in vitro through ICI 182,780-sensitive mechanisms that were associated with increased phosphorylation of eNOS but independent of changes in endothelial cell [Ca(2+)](i).

Selective estrogen receptor modulators and risk for coronary heart disease

Coronary heart disease (CHD) is the leading cause of death in women in most countries. Atherosclerosis is the main biological process determining CHD. Clinical data support the notion that CHD is sensitive to estrogens, but debate exists concerning the effects of the hormone on atherosclerosis and its complications. Selective estrogen receptor modulators (SERMs) are compounds capable of binding the estrogen receptor to induce a functional profile distinct from estrogens. The possibility that SERMs may shift the estrogenic balance on cardiovascular risk towards a more beneficial profile has generated interest in recent years. There is considerable information on the effects of SERMs on distinct areas that are crucial in atherogenesis. The complexity derived from the diversity of variables affecting their mechanism of action plus the differences between compounds make it difficult to delineate one uniform trend for SERMs. The present picture, nonetheless, is one where SERMs seem less powerful than estrogens in atherosclerosis protection, but more gentle with advanced forms of the disease. The recent publication of the Raloxifene Use for The Heart (RUTH) study has confirmed a neutral effect for raloxifene. Prothrombotic states may favor occlusive thrombi at sites occupied by atheromatous plaques. Platelet activation has received attention as an important determinant of arterial thrombogenesis. Although still sparse, available evidence globally suggests neutral or beneficial effects for SERMs.

Raloxifene Modulates Pulmonary Vascular Reactivity in Spontaneously Hypertensive Rats

Selective estrogen receptor modulators (SERMs) reduce vascular tone in the systemic circulation. Their effects on the pulmonary circulation are unknown. The present study examined the effect of oral treatment with raloxifene (a second-generation SERM) on vasomotor reactivity in pulmonary arteries from normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Pulmonary arterial rings were suspended in a multi-channel myograph, and changes in isometric tension were measured. WKY rings constricted less to U46619 than SHR rings, and the difference was eliminated after chronic treatment with raloxifene. More contraction to U46619 was obtained after inhibition of nitric oxide synthase (NOS) by L-NAME (as an index of basal NO release) in raloxifene-treated than in control SHR rings. Less U46619-induced contraction after raloxifene treatment occurred only in SHR rings with endothelium, and this effect was abolished upon removal of the endothelium. Raloxifene treatment did not enhance the contribution of basal NO to U46619-induced constriction in WKY rings. Raloxifene treatment did not modify endothelium-dependent relaxation to acetylcholine and endothelium-independent relaxation to nifedipine. The reduced relaxing sensitivity to sodium nitroprusside (SNP) in SHR rings was normalized by raloxifene treatment. Raloxifene treatment reduced CaCl2-induced tone in SHR but not in WKY rings. The results show that chronic treatment with raloxifene could improve pulmonary vascular function in hypertensive animals by (1) increasing basal NO release, (2) reducing vascular smooth muscle tone, and (3) improving the effect of NO on vascular smooth muscle in SHR. In contrast, raloxifene has little effect on vascular reactivity in pulmonary arteries from normotensive WKY rats.

Raloxifene inhibits transient outward and ultra-rapid delayed rectifier potassium currents in human atrial myocytes

The selective estrogen receptor modulator raloxifene is widely used in the treatment of postmenopausal osteoporosis, and has cardioprotective properties. However, effects of raloxifene on cardiac ion channels are unclear. The present study was designed to investigate the effects of raloxifene and beta-estradiol on transient outward and ultra-rapid delayed rectifier potassium currents (Ito1 and IKur) in human atrial myocytes with a whole cell patch-clamp technique. Ito1 was inhibited by raloxifene in a concentration-dependent manner with an IC50 of 0.9 microM. Raloxifene at 1 microM decreased Ito1 by 40.2+/-1.9% (at +50 mV, n=14, P<0.01 vs control). Time-dependent recovery from inactivation was slowed, and time to peak and time-dependent inactivation of Ito1 were significantly accelerated, while steady-state voltage dependent activation and inactivation of Ito1 were not affected by raloxifene. In addition, raloxifene remarkably suppressed IKur (IC50=0.7 microM). Raloxifene at 1 microM decreased IKur by 57.3+/-3.3% (at +50 mV, n=10, P<0.01 vs control). However, beta-estradiol inhibited Ito1 (IC50=10.3 microM) without affecting IKur. The inhibitory effects of raloxifene and beta-estradiol on Ito1 and/or IKur were unaffected by the estrogen receptor antagonist ICI 182,780. Our results indicate that raloxifene directly inhibits the human atrial repolarization potassium currents Ito1 and IKur. Whether raloxifene is beneficial for supraventricular arrhythmias remains to be studied.

Endothelium-independent relaxation to raloxifene in porcine coronary artery

Although the vascular action of raloxifene has been studied in several vascular beds, the underlying mechanisms are still incompletely understood. The role of endothelium in raloxifene-induced vascular responses was controversial. The present study was designed to examine endothelium-independent effects of raloxifene in isolated porcine left circumflex coronary arteries. Arterial rings were suspended in organ baths and changes in isometric tension were measured. The large-conductance Ca2+-activated K+(BK(Ca)) currents were recorded using a whole-cell patch-clamp technique. Treatment with raloxifene (1-10 micromol/l) reduced the contractions to 9,11-dideoxy-11alpha,9alpha-epoxy-methanoprostaglandin F2alpha (U46619), serotonin (5-HT), endothelin-1 in normal Krebs solution and to CaCl2 in a Ca2+-free, high K+-containing solution. In endothelin-1-contracted rings, raloxifene (0.3 to 50 micromol/l) caused relaxations which were comparable in rings with and without endothelium. The raloxifene-induced relaxation was reduced by putative K+ channel blockers, iberiotoxin and tetraethyl ammonium chloride (TEA+) in rings with and without endothelium, or by elevated extracellular K+ ions (30 mmol/l K+ and 60 mmol/l K+). 13-methyl-7-[9-(4,4,5,5,5-pentafluoropentylsulfinyl)nonyl]-7,8,9,11,12,13,14,15,16, 17-decahydro-6H-cyclopenta[a] phenanthrene-3,17-diol (ICI 182,780) did not affect raloxifene-induced relaxation. Raloxifene enhanced the outward BK(Ca) currents, which were sensitive to inhibition by iberiotoxin. In summary, the present study shows that raloxifene acutely relaxes porcine coronary arteries via an endothelium-independent mechanism without involving the ICI 182,780-sensitive estrogen receptors. Raloxifene mainly acts on the vascular smooth muscle cells to induce vasorelaxation by the inhibition of Ca2+ channels and the activation of BK(Ca) channels. The former mechanism appears to play a more significant role.

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.

Characterisation of the relaxant response to raloxifene in porcine coronary arteries

The present study characterises the vasorelaxant response to raloxifene in isolated rings of porcine coronary artery. Tissues precontracted either with KCl (30 mM) or prostaglandin F(2alpha) (PGF(2alpha); 3 microM) were concentration-dependently relaxed by raloxifene (0.1-10 microM). Relaxation was not inhibited by the estrogen receptor antagonist 7alpha-[9-[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]-estra-1,3,5(10)-triene-3,17beta-diol (ICI 182,780; 1 microM). Preincubation with raloxifene (1-3 microM) caused an inhibition of the KCl or PGF(2alpha)-induced contraction. The effects of raloxifene were independent of the endothelium. The relaxant response to raloxifene was slow in the onset and could not be reversed after repeated washings. Raloxifene did not affect Ca(2+) release from intracellular stores since it failed to inhibit a transient contraction induced by caffeine (10 mM). Raloxifene-induced relaxation was not influenced by the intracellular calcium chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester) (BAPTA-AM; 10-20 microM). Calcium-induced contractions in Ca(2+)-free high K(+) (60 mM) depolarising medium were concentration-dependently inhibited by raloxifene (0.3-3 microM). If arterial rings were incubated with the L-type Ca(2+) channel activator (S)-(-)-1,4-dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)phenyl]-3-pyridine carboxylic acid methyl ester ((S)-(-)-Bay K 8644; 0.1 microM), cumulative concentration-response curves to Ca(2+) were shifted to the left. Raloxifene (0.3-3 microM) inhibited the effect of (S)-(-)-Bay K 8644 in a concentration-dependent manner. 4-(4-Fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole (SB 203580; 10 microM), an inhibitor of p38 mitogen-activated protein kinase (MAPK), diminished raloxifene-induced relaxation in endothelium-denuded arterial rings. Western blot analysis demonstrated that raloxifene stimulated p38 MAPK. It is concluded that raloxifene has an inhibitory effect on voltage-gated and receptor-operated L-type Ca(2+) channels in porcine coronary arteries, thus inducing vascular relaxation independent of the endothelium. p38 MAPK is, at least in part, involved in the relaxant response to raloxifene.

Raloxifene elicits combined rapid vasorelaxation and long-term anti-inflammatory actions in rat aorta

Previous studies reported the ability of raloxifene to acutely relax arterial and venous vessels, but the underlying mechanisms are controversial. Anti-inflammatory effects of the drug have been reported in nonvascular tissues. Therefore, the aim of this study was to investigate the nature of short- and long-term effects of raloxifene on selected aspects of vascular function in rat aorta. Isometric tension changes in response to raloxifene were recorded in aortic rings from ovariectomized female rats that underwent estrogen replacement, whereas long-term experiments were performed in isolated aortic smooth muscle cells (SMCs). Raloxifene (0.1 pM-0.1 microM) induced acute vasorelaxation through endothelium- and nitric oxide (NO)-dependent, prostanoid-independent mechanisms. The relaxant response to raloxifene was significantly weaker than that to 17beta-estradiol and was sensitive to neither the nonselective estrogen receptor antagonist ICI 182,780 [7,17-[9[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]estra-1,3,5(10)-triene-3,17-diol] nor a selective estrogen receptor (ER) alpha antagonist. This rapid vasorelaxant effect was retained in aortic rings from rats treated with 0.1 mg/kg, but not 1 mg/kg, lipopolysaccharide, 4 h before sacrifice. In cultured aortic SMCs, raloxifene treatment (1 nM-1 microM) for 24 h reduced inducible NO synthase activation in response to cytokines. This effect was prevented by the selective ERalpha antagonist and was associated with up-regulation of ERalpha protein levels, which dropped markedly upon cytokine stimulation. These findings illustrate the relevance of classic ER-dependent pathways to the vascular anti-inflammatory effects rather than to the nongenomic vasorelaxation induced by raloxifene and may assist in the design of novel ER isoform-selective estrogen-receptor modulators targeted to the vascular system.

Endothelial mediators of the acetylcholine-induced relaxation of the rat femoral artery

This study examined endothelium-derived mediators of acetylcholine-induced relaxation in male rat femoral arteries. Arterial rings were suspended in a myograph for the measurement of isometric force. The generation of hydrogen peroxide (H2O2) in endothelial cells was detected using the fluorescent probe, 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate acetyl ester. N(G)-nitro-L-arginine methyl ester (L-NAME, NOS inhibitor) and 1H-[1,2,4]oxadiazolo[4,2-alpha]quinoxalin-1-one (ODQ, guanylate cyclase inhibitor) alone or in combination with indomethacin (cycloxygenase inhibitor) diminished acetylcholine-induced endothelium-dependent relaxation to a similar extent. A small relaxation to acetylcholine in 60 mM KCl-constricted rings was abolished by L-NAME. Acetylcholine-induced relaxation was reduced by charybdotoxin plus apamin (intermediate- and small-conductance Ca2+-activated K+ channel blockers, respectively) or by 30 mM KCl. Both ouabain (Na+/K+ ATPase inhibitor) and BaCl2 (K(IR) channel blocker) also inhibited the relaxation albeit to a lesser degree. In the presence of L-NAME, ODQ plus indomethacin, charybdotoxin plus apamin or ouabain plus BaCl2 produced further inhibition. Catalase attenuated acetylcholine-induced relaxations and this attenuation was prevented by 3-amino-1,2,4-triazole (catalase inhibitor). Catalase did not affect acetylcholine-induced relaxations in rings treated with L-NAME or ODQ. Acetylcholine increased the dichlorofluorescein fluorescence intensity in native endothelial cells and this effect was abolished by catalase and by L-NAME. Exogenous H2O2 caused endothelium-independent relaxation that was slightly inhibited by iberiotoxin, ODQ or significantly reduced by elevated KCl, and abolished by catalase. The present results indicate that in addition to nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF, sensitive to charybdotoxin plus apamin, ouabain, and BaCl2), the endothelium of rat femoral artery can release H2O2 in response to acetylcholine, which was sensitive to L-NAME. Thus, the eNOS-dependent H2O2 is likely to be the third mediator of acetylcholine-mediated relaxations in rat femoral arteries.

Modulatory effect of interleukin-1β on rat isolated basilar artery contraction

An increased level of cytokine interleukin-1 (IL-1) has been detected around the site of stroke. However, the effect of IL-1beta on the basilar artery has received little attention. We evaluated the effects of IL-1beta on the contractile response of rat isolated basilar artery by measuring isometric tension change. IL-1beta (10 ng/ml) and phenylephrine (0.1 nM) markedly enhanced U46619 (30 and 100 nM)-induced basilar artery contraction. The IL-1beta-mediated potentiation was partly suppressed by zinc protoporphyrin (3 microM) and was abolished by tetrodotoxin (TTX, 100 nM), (-)-perillic acid (1 microM), PD98059 (0.3 microM), SB203580 (1 microM) and prazosin (1 microM). Our data suggest that IL-1beta (10 ng/ml) causes an enhancement of U46619-mediated basilar artery contraction that probably involves TTX-sensitive neuronal release of an alpha1-adrenoceptor agonist and activation of p42/p44 and p38 mitogen-activated protein kinases/p21(ras) pathways.

Raloxifene relaxes rat intrarenal arteries by inhibiting Ca2+ influx

Raloxifene may confer vascular benefits without causing estrogen-related side effects. However, its action on renal vascular circulation is unknown. This study aimed to examine the sex difference and roles of the endothelium and Ca2+ channels in rat renovascular relaxation to raloxifene. On isolated intralobar renal artery rings mounted in a myograph and contracted by U-46619, concentration-relaxation curves were constructed for raloxifene and contractions to CaCl2 were studied. Changes in intracellular Ca2+ concentration levels ([Ca2+]i) of vascular smooth muscle (VSM) were measured by fura 2 fluorescence. Raloxifene or 17β-estradiol was equally effective in relaxing renal arteries from both sexes, with raloxifene being more potent than 17β-estradiol. Endothelial denudation did not affect raloxifene- or 17β-estradiol-induced relaxation. NG-nitro-l-arginine methyl ester, charybdotoxin plus apamin, indomethacin, or ICI-182, 780 did not modify the effect of raloxifene. Raloxifene caused similar relaxations in rings contracted by U-46619 and high K+. Nifedipine attenuated the potency of raloxifene. Raloxifene reduced CaCl2-induced contractions. K+ (80 mM) stimulated an increase in VSM [Ca2+]i, and raloxifene attenuated this effect. Raloxifene-induced reduction of contraction and increase in VSM [Ca2+]i were insensitive to ICI-182, 780. In summary, raloxifene causes relaxation in rat renal arteries; this effect is independent of a functional endothelium and is not mediated by ICI 182, 780-sensitive estrogen receptors. Raloxifene inhibited both contractions and VSM [Ca2+]i in response to CaCl2, indicating that raloxifene relaxes rat renal arteries primarily through inhibiting Ca2+ influx via Ca2+ channels. There is little sex difference in raloxifene-induced relaxation.

Raloxifene Relaxes Rat Pulmonary Arteries and Veins: Roles of Gender, Endothelium, and Antagonism of Ca2+ Influx

Effects of raloxifene have been documented in the systemic circulation. However, its impact on the pulmonary circulation is unclear. The present study investigated the role of gender, endothelial modulation, and Ca(2+) channel in relaxations evoked by raloxifene in rat pulmonary arteries and veins. Vascular responses were studied on isolated pulmonary blood vessels mounted in a myograph and constricted by U46619 (9,11-dideoxy-11alpha,9alpha-epoxymethanoprostaglandin F(2alpha)). Constrictions to CaCl(2) were studied in Ca(2+)-free, 60 mM K(+) solution. Changes in the intracellular calcium ion concentration ([Ca(2+)](i)) in vascular smooth muscle were measured using a calcium fluorescence imaging method. Raloxifene was more effective in relaxing U46619-constricted pulmonary arteries from male than female rats. Raloxifene-induced relaxation was unaffected by ICI 182,780 [7alpha-[9-[(4,4,5,5,5,-pentafluoropentyl)-sulfinyl]nonyl]-estra-1,3,5(10)-triene-3,17beta-diol], inhibition of the nitric oxide (NO) pathway, or removal of the endothelium. In arteries without endothelium, raloxifene attenuated CaCl(2)-induced constriction and CaCl(2)-stimulated increase in [Ca(2+)](i) with similar potencies. Raloxifene caused endothelium-independent relaxations in pulmonary veins, albeit to a lesser degree than in pulmonary arteries. The venous responses showed a gender difference because raloxifene was more potent in male veins. In summary, raloxifene relaxed rat pulmonary arteries, and this effect did not involve the endothelium/NO or ICI 182,780-sensitive estrogen receptors. Raloxifene, like nifedipine, reduced constriction and [Ca(2+)](i) increase in response to CaCl(2) in high K(+) solution. Raloxifene also relaxed high K(+)-constricted pulmonary veins. Our data indicate that raloxifene acutely relaxes rat pulmonary blood vessels primarily via inhibition of Ca(2+) influx through voltage-sensitive Ca(2+) channels. Finally, raloxifene induced more relaxation in blood vessels isolated from male than female rats.