Endothelium-independent relaxation by 17-alpha-estradiol of pig coronary arteries

Perfusion Changes with Photic Stimulation During two Phases of the Menstrual Cycle: A Pilot Study Comparing Controls and True Menstrual Migraine Patients

This pilot study investigated the effect of menstrual cycle phase (late luteal and mid-follicular) on cerebral perfusion changes during photic stimulation in both controls ( n = 5) and true menstrual migraine patients ( n = 5). No significant differences in resting baseline perfusion were observed between the two groups during either phase of the menstrual cycle. During the late luteal phase, changes in perfusion within the occipital lobe due to photic stimulation were similar for both groups. However, during the mid-follicular phase, occipital perfusion during visual stimulation decreased for controls but significantly increased for true menstrual migraine patients ( P < 0.05). A two way repeated measures ANOVA also demonstrated a significant difference between menstrual migraine patients and controls for photic activation ( P < 0.05).

Rapid estrogen actions on ion channels: A survey in search for mechanisms

A survey of nearly two hundred reports shows that rapid estrogenic actions can be detected across a range of kinds of estrogens, a range of doses, on a wide range of tissue, cell and ion channel types. Striking is the fact that preparations of estrogenic agents that do not permeate the cell membrane almost always mimic the actions of the estrogenic agents that do permeate the membrane. All kinds of estrogens, ranging from natural ones, through receptor modulators, endocrine disruptors, phytoestrogens, agonists, and antagonists to novel G-1 and STX, have been reported to be effective. For actions on specific types of ion channels, the possibility of opposing actions, in different cases, is the rule, not the exception. With this variety there is no single, specific action mechanism for estrogens per se, although in some cases estrogens can act directly or via some signaling pathways to affect ion channels. We infer that estrogens can bind a large number of substrates/receptors at the membrane surface. As against the variety of subsequent routes of action, this initial step of the estrogen's binding action is the key.

Mifepristone is a Vasodilator Due to the Inhibition of Smooth Muscle Cells L-Type Ca2+ Channels

Derived from the estrane progestins, mifepristone was the first synthetic steroid of this class employed as abortifacient in the first months of pregnancy. Mifepristone reduces high potassium-induced contraction and prevents calcium-induced contraction. At the vascular level, mifepristone induces direct relaxation in rat and human arteries, and this effect seems to be endothelium- and NO independent, suggesting that the vascular smooth muscle is its target. Moreover, mifepristone's effect could involve the modulation of different calcium channels. The aim of the present study is to analyze the involvement of calcium channels in the relaxation induced by mifepristone on vascular smooth muscle cells (VSMCs). Planar cell surface area (PCSA) technique was used to analyze the effect of mifepristone on the VSMC contractility, and the whole cell configuration of patch-clamp technique to measure the activity of L-type Ca(2+) channels (LTCC) in A7r5 cells. Regarding the PCSA technique, mifepristone induced relaxation of the VSMC previously contracted by different agents. Also, a rapid inhibitory effect on basal and BAY K8644-stimulated calcium current was observed, which indicates that this drug has the ability to block LTCC. These results suggest that mifepristone induces relaxation on the VSMCs due to the inhibition of the calcium channels.

Vasodilation in response to the GPR30 agonist G-1 is not different from estradiol in the mRen2.Lewis female rat

Our studies in the mRen2.Lewis female rat, an angiotensin II- and estrogen-dependent model of hypertension, revealed that chronic activation of estrogen receptor GPR30 markedly reduces blood pressure in ovariectomized females. The present studies measured acute vasodilation to the selective GPR30 agonist G-1 and 17-β-estradiol (10(-9)-10(-5.5) M) in isolated aortic rings and mesenteric arteries from intact mRen2.Lewis females. Maximal relaxation was greater in mesenteric vessels versus the aorta for both G-1 (47% ± 8% vs 80% ± 5% of phenylephrine preconstriction, P < 0.001) and estradiol (42% ± 7% vs 83% ± 4% of phenylephrine preconstriction, P < 0.001). The GPR30 antagonist G15 attenuated the response to both estradiol and G-1. Removal of the endothelium or pretreatment with Nitro-L-arginine methyl ester (L-NAME) partially attenuated vasorelaxation. Responses were not altered in mesenteric vessels from ovariectomized females. Immunohistochemical analysis revealed GPR30 expression in mesenteric endothelial and smooth muscle cells, and smooth muscle expression was confirmed in cultured cells. We conclude that estradiol-induced relaxation in conduit and resistance vessels from mRen2.Lewis females may be mediated by the novel estrogen receptor GPR30. The direct vasodilatory response of G-1 in resistance vessels presents one mechanism for the reduction in blood pressure induced by chronic G-1 administration.

Vasorelaxant action of 17 -estradiol in rat uterine arteries: role of nitric oxide synthases and estrogen receptors

The uterine vasculature plays an important role during pregnancy by providing adequate perfusion of the maternal-fetal interface. To this end, substantial remodeling of the uterine vasculature occurs with consequent changes in responsiveness to contractile agents. The purpose of our study was to characterize the vasorelaxant effects of estrogens on vascular smooth muscles of the rat uterine artery during pregnancy and to evaluate the involvement of estrogen receptors (ESR) and nitric oxide synthases (NOS). To do so, we measured NOS expression in the whole uterine and mesenteric circulatory bed by Western blotting. Vasorelaxant effects of 17beta-estradiol (17beta-E(2)) were assessed on endothelium-denuded uterine arteries with wire myographs in the absence and presence of pharmacological modulators [nitro-L-arginine methyl ester (L-NAME), ICI-182780, tamoxifen]. All experiments were performed on arteries from nonpregnant (NP) and late pregnant (P) rats. In the uterine vasculature of the latter group, NOS3 (endothelial NOS) expression was increased, while NOS1 (neuronal NOS) was reduced compared with NP rats. Expression of the NOS2 (inducible NOS) isoform was undetectable in the two groups. Both 17beta-E(2) and 17alpha-E(2) induced uterine artery relaxation, but the latter evoked lower responses. Endothelium-denuded arteries from NP rats showed larger relaxation with 17beta-E(2) than P rats. This larger relaxation disappeared in the presence of L-NAME. The ESR antagonist ICI-182780 did not affect acute relaxation with 17beta-E(2) and 17alpha-E(2). Moreover, membrane-nonpermeant 17beta-E(2):BSA (estradiol conjugated to bovine serum albumin) did not induce any vasorelaxation. Our results indicate that estrogens exert direct acute vasorelaxant effects in smooth muscles of the rat uterine artery that are mediated by mechanisms independent of ESR activation, but with some stereospecificity. Part of this effect, in NP rats only, is due to nitric oxide produced from muscle NOS1.

Characterization of the relaxant response to N,N'-dipropyl-1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine in porcine coronary arteries

N,N'-Dialkyl-1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamines show structural analogy with estrogens and selective estrogen receptor modulators. Because the vasodilator properties of these compounds are unknown, we investigated their potential to relax porcine coronary arteries and determined the mechanism(s) of relaxation. Isolated porcine coronary arterial rings were suspended in organ chambers, precontracted with KCl (30 mM), and the relaxant response was determined by measurement of changes in isometric force. Dependent on the chemical structure, the drugs induced concentration-dependent relaxation in rings with and without endothelium. N,N'-Dipropyl-1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine (8) was most potent and showed a 12- to 15-fold higher vasodilatory effect than 17beta-estradiol (E2). The vasorelaxation was independent of endothelium. Calcium concentration-dependent contractions in high-potassium depolarizing medium were insurmountably inhibited by 8. The effect of the L-type Ca2+ channel activator (S)-(-)-Bay K 8644 [(S)-(-)-1,4-dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)phenyl]-3-pyridine-carboxylic acid methyl ester], which induced a leftward shift of Ca2+ contraction, was blocked by 8. The relaxant response to 8 was unaffected by the estrogen receptor antagonist ICI 182,780 (7alpha-[9-[(4,4,5,5,5-pentafluoropentyl]-sulfinyl]nonyl]-estra-1,3,5(10)-triene-3,17beta-diol) and K+ channel blockers, i.e., TEA, glibenclamide, and 4-aminopyridine. Furthermore, the vasodilatory effect of 8 was unaffected by the adenylyl cyclase inhibitor SQ 22536 [9-(tetrahydro-2-furanyl)-9H-purin-6-amine], the guanylyl cyclase inhibitor ODQ [1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one], the protein kinase A inhibitor KT 5720 [(9S,10S,12R)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg: 3',2',1'-kl]pyrrolo[3,4-i][1,6]benzodiazocine-10-carboxylic acid hexyl ester], the protein kinase G inhibitor KT 5823 [(9S,10R,12R)-2,3,9,10,11,12-hexahydro-10-methoxy-2,9-dimethyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-i][1,6]benzodiazocine-10-carboxylic acid methyl ester], and the p38 mitogen-activated protein kinase (MAPK) inhibitor SB 203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole]. Western blot analysis demonstrated that 8, unlike E2, raloxifene, and tamoxifen, failed to stimulate p38 MAPK. It is concluded that N,N'-dipropyl-1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine induces endothelium-independent relaxation of coronary arteries; the mechanism apparently involves inhibition of L-type Ca2+ channels. The drug may be protective against cardiovascular diseases.

Endocrine therapy--current benefits and limitations

Endocrine therapy is a valuable option for the treatment of postmenopausal women with estrogen receptor (ER)-positive breast cancer due to its demonstrated efficacy and favorable safety profile. Although tamoxifen has been the established treatment for more than 20 years its long-term use is associated with several tolerability concerns and may lead to increased risk of endometrial cancer and thromboembolic complications. In addition, many patients who initially respond to treatment with endocrine agents such as tamoxifen eventually relapse with resistant disease. Sequential use of endocrine therapies is often used in patients as resistance to individual agents develops. Several endocrine approaches have been developed that deprive the tumor of estrogen stimulation, either by directly modulating the ER-signaling pathway or by lowering serum or tumor concentrations of estrogen. In the classic pathway of estrogen signal transduction, the steroid hormone binds to its intracellular ER, triggering a cascade of events that ultimately leads to altered gene transcription. More recently, it has become apparent that ER activation can also occur via estrogen-independent receptor activation or by non-nuclear action through cell surface receptors. Consequently, molecular cross-talk exists between the ER and growth factor signaling cascades, which is a key factor in de novo and acquired resistance to endocrine therapy. Inappropriate activation of growth factor signaling can readily promote endocrine therapy failure in breast cancer cells, either by overriding the growth-inhibitory properties of antiestrogenic drugs or by establishment of a new self-propagating autocrine loop that efficiently drives resistant cell growth. Fulvestrant is a new type of ER antagonist with no agonist effects that binds, blocks and causes degradation of the ER. As multiple signaling pathways are involved in the activation of ER, the use of agents such as fulvestrant that directly target the ER and lead to both degradation of the receptor and abrogation of ER signaling may prevent or delay the development of absolute endocrine resistance. In addition, combining antiestrogenic drugs with inhibitors of cell signaling molecules to target both the ER and growth factor signaling pathways is likely to provide a means of delaying endocrine therapy resistance, leading the way to more effective breast cancer treatment.

Evidence that 17alpha-estradiol is biologically active in the uterine tissue: antiuterotonic and antiuterotrophic action

BACKGROUND

17alpha-Estradiol has been considered as the hormonally inactive isomer of 17beta-estradiol. Recently, nongenomic (smooth muscle relaxation) and genomic (light estrogenic activity) effects of 17alpha-estradiol have been reported, but no reports have yet determined its possible antiestrogenic activity. Therefore, this study investigated: the nongenomic action of 17alpha-estradiol on uterine contractile activity and its potential agonist-antagonist activity on uterine growth.

METHODS

Uterine rings from rats were isometrically recorded. Different concentrations (0.2-200 microM) of 17alpha-estradiol were tested on spontaneous contraction and equimolarly compared with 17beta-estradiol. To examine the mechanism of 17alpha-estradiol action, its effect was studied in presence of beta2-antagonist (propranolol), antiestrogens (tamoxifen and ICI 182,780) or inhibitors of protein synthesis (cycloheximide) and transcription (actinomycin D). Moreover, contractions induced by high potassium (KCl) solution or calcium in depolarized tissues by KCl-calcium free solution were exposed to 17alpha-estradiol. Collaterally, we performed an uterotrophic assay in adult ovariectomized rats measuring the uterine wet weight. The administration for three days of 0.3 microM/day/Kg 17beta-estradiol was equimolarly compared with the response produced by 17alpha-estradiol. Antiuterotrophic activity was assayed by administration of 0.3 microM/day/Kg 17beta-estradiol and various doses ratios (1:1, 1:3, 1:5, and 1:100) of 17alpha-estradiol.

RESULTS

The estradiol isomers elicited an immediate relaxation, concentration-dependent and reversible on spontaneous contraction. 17alpha-Estradiol presented lower potency than 17beta-estradiol although it did not antagonize 17beta-estradiol-induced relaxation. Relaxation to 17alpha-estradiol was not inhibited by propranolol, tamoxifen, ICI 182,780, cycloheximide or actinomycin D. The KCl contractions were also sensitive to 17alpha-estradiol-induced relaxation and calcium contractions in depolarized tissues were markedly prevented by 17alpha-estradiol, implying a reduction of extracellular calcium influx through voltage-operated calcium channels (VOCCs). Uterotrophic assay detected significant increase in uterine weight using 17alpha-estradiol, which was significantly minor as compared with 17beta-estradiol. 17alpha-Estradiol, at all doses ratios, significantly antagonized the hypertrophic response of 17beta-estradiol.

CONCLUSION

17alpha-Estradiol induces a relaxing effect, which may be independent of the classical estrogen receptor, nongenomic action, apparently mediated by inactivation of VOCCs. 17alpha-Estradiol is also a weak estrogen agonist (uterotrophic response); likewise, 17alpha-estradiol may act as an antiestrogen (antiuterotrophic response). The overall data document a nongenomic relaxing action and a novel antiestrogenic action of 17alpha-estradiol, which are relevant in estrogen-mediated uterine physiology.

Nongenomic steroid action: controversies, questions, and answers

Steroids may exert their action in living cells by several ways: 1). the well-known genomic pathway, involving hormone binding to cytosolic (classic) receptors and subsequent modulation of gene expression followed by protein synthesis. 2). Alternatively, pathways are operating that do not act on the genome, therefore indicating nongenomic action. Although it is comparatively easy to confirm the nongenomic nature of a particular phenomenon observed, e.g., by using inhibitors of transcription or translation, considerable controversy exists about the identity of receptors that mediate these responses. Many different approaches have been employed to answer this question, including pharmacology, knock-out animals, and numerous biochemical studies. Evidence is presented for and against both the participation of classic receptors, or proteins closely related to them, as well as for the involvement of yet poorly understood, novel membrane steroid receptors. In addition, clinical implications for a wide array of nongenomic steroid actions are outlined.

Nongenomic actions of steroid hormones

Steroid hormones modulate many physiological processes. The effects of steroids that are mediated by the modulation of gene expression are known to occur with a time lag of hours or even days. Research that has been carried out mainly in the past decade has identified other responses to steroids that are much more rapid and take place in seconds or minutes. These responses follow nongenomic pathways, and they are not rare.

Acute effects of 17beta -estradiol on femoral veins from adult gonadally intact and ovariectomized female pigs

Our experiments were designed to determine the acute effects of 17beta-estradiol on femoral veins from intact and ovariectomized female pigs. Rings of femoral veins with or without endothelium were suspended in organ chambers for measurement of isometric force. Concentration-response curves to 17beta-estradiol (10(-9) to 10(-5) M) were obtained in veins contracted with prostaglandin F(2alpha) in the absence and presence of inhibitors of either estrogen receptors (ICI-182780; 10(-5) M), nitric oxide synthase [N(G)-monomethyl-l-arginine (l-NMMA); 10(-4) M], soluble guanylate cyclase (1-H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one; 10(-5) M), or potassium channels (tetraethylammonium; 10(-2) M). Estrogen receptors were identified with the use of Western blotting and immunostaining in veins of both groups. 17beta-Estradiol caused acute endothelium-dependent relaxations in both groups. Relaxations to 17beta-estradiol were inhibited by l-NMMA and 1-H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one but not ICI-182780. Tetraethylammonium inhibited relaxations only in veins with endothelium from intact females. Results indicate that 17beta-estradiol causes acute endothelium-dependent relaxations in femoral veins. The relative contribution of nitric oxide and K(+) channels as mechanisms involved in relaxations to 17beta-estradiol in femoral veins is modulated by ovarian status.

17beta-estradiol increases nitric oxide-dependent dilation in rat pulmonary arteries and thoracic aorta

Past studies have demonstrated that 17beta-estradiol (E(2)beta) increases endothelial nitric oxide (NO) synthase (eNOS) activity in uterine, heart, and skeletal muscle and in cultured human endothelial cells. However, little is known about E(2)beta regulation of NO synthesis in the pulmonary vasculature. The present study evaluated E(2)beta regulation of eNOS function in pulmonary arteries and thoracic aortas. We hypothesized that E(2)beta upregulates vascular NO release by increasing eNOS expression. To test this, NO-dependent vasodilation was assessed in isolated perfused lungs and aortic rings from ovariectomized Sprague-Dawley rats treated for 1 wk with 20 microg/24 h of E(2)beta or vehicle. Expression of eNOS was evaluated by Western blot and immunohistochemistry. Also, a RNase protection assay determined eNOS mRNA levels in lung and aortic homogenates from control and treated rats. Vasodilation to ionomycin in lungs from the E(2)beta-treated group was enhanced compared with that in control animals. Endothelium-intact aortic rings from E(2)beta-treated animals also demonstrated augmented endothelium-dependent dilation. Both responses were blocked with NOS inhibition. Immunostaining for eNOS was greater in pulmonary arteries and aortas from E(2)beta-treated compared with control rats. However, mRNA levels did not differ between groups. Thus we conclude that in vivo E(2)beta treatment augments endothelium-dependent dilation in aorta and lung, increasing expression of eNOS independently of sustained augmented gene transcription.

Involvement of K(ATP) channels in diethylstilbestrol-induced relaxation in rat aorta

The estrogens prevent cardiovascular diseases that among other effects could be related to the modulation of the vascular tone via modifying ionic channel permeability. ATP-sensitive K(+) (K(ATP)) channels seem to be involved in diethylstilbestrol-induced relaxation in isolated rat aorta precontracted by noradrenaline (30 nM), since the effect is inhibited by glibenclamide (1--10 microM), and 1 mM tetraethylammonium, but not by 30 mM tetraethylammonium or paxilline. The antiestrogen tamoxifen, the inhibitor of protein kinase A, Rp-cAMPS, and the inhibitor of ornithine decarboxylase, difluoromethylornithine, antagonized diethylstilbestrol-induced relaxation. The association of glibenclamide with these compounds separately did not modify the effect of glibenclamide alone on diethylstilbestrol-induced relaxation. Functional K(ATP) channels are present in rat aorta, since diazoxide induced relaxation sensitive to glibenclamide. Papaverine, dibutyryl cyclic AMP and spermine relaxed isolated rat aorta although this was not sensitive to glibenclamide. The relaxation to forskolin was antagonized by glibenclamide. We conclude that diethylstilbestrol-induced relaxation in rat aorta is related to the modulation of K(ATP) channels. Cyclic AMP-dependent mechanisms and polyamine synthesis may mediate this modulation.

Venous endothelial function in postmenopausal women who are receiving long-term estrogen and progestagen therapy

OBJECTIVE

To test venous endothelial function during long-term hormone replacement therapy (HRT) and after treatment withdrawal.

DESIGN

Measurement of dorsal hand-vein diameter by venous occlusion plethysmography during infusion of norepinephrine, bradykinin, NG-monomethyl L-arginine, and sodium nitroprusside.

SETTING

Plethysmography and menopause units, University Hospital Marqués de Valdecilla, Santander, Spain.

PATIENT(S)

Twenty postmenopausal women, of whom 10 were assigned to receive no hormone replacement therapy (HRT) for 6 months after plethysmography (group A) and 10 were assigned to receive HRT for 6 months (group B). After 6 months, HRT was administered to group A and withdrawn from group B for another 6 months.

INTERVENTION(S)

Plethysmography at baseline and at 6 and 12 months.

MAIN OUTCOME MEASURE(S)

Dorsal hand-vein diameter measured by venous occlusion plethysmography during infusion of norepinephrine, bradykinin, NG-monomethyl L-arginine, or sodium nitroprusside.

RESULT(S)

At 6 months, the maximum dilation obtained with bradykinin was 48.8 +/- 7.58% in group A and 76.7 +/- 12.9% in group B. At 12 months, maximum bradykinin dilation increased to 74.3 +/- 14.2% in group A and decreased to 54.0 +/- 15.9% in group B.

CONCLUSION(S)

Long-term HRT with estrogen plus progestin improves endothelium-dependent vasodilation, but this effect is lost in a relatively short time. Endothelial function in dorsal hand veins is an easy-to-use plethysmography model that can be used in serial studies.

Mechanism of mifepristone-induced spasmolytic effect on isolated rat uterus

Mifepristone, a synthetic 19-norsteroid, relaxed the KCl-induced tonic contraction in isolated rat uterus in a concentration-dependent way and CaCl2 (0.1 to 10 mM) counteracted it. This effect was similar to other steroids although the mechanisms involved are unclear. Before adding the contracturant, tissue was incubated with actinomycin D (10 microM), cycloheximide (300 microM), TPCK (3 and 10 microM), Rp-cAMPS (30 microM), DDA (100 microM) and H-7 (1 microM). None of these modified the relaxing effect of mifepristone. Incubation with drugs that interfere with cGMP such as a nucleotide analogue DDG (100 microM), a soluble guanylyl cyclase inhibitor ODQ (1 microM) and an inhibitor of protein kinase G 8pCPTcGMPS (1 microM) significantly modified the effect of mifepristone, increasing its IC50.

Acetylcholine-mediated relaxation in rat thoracic aorta is enhanced following acute exposure to physiological concentrations of 17beta-estradiol

We investigated the effects of short-term exposure to low concentrations of 17beta-estradiol on vasorelaxation using an in vitro rat thoracic aortic ring preparation. Supraphysiological levels of 17beta-estradiol directly relaxed phenylephrine-contracted rings. Although acute incubation (20 min) with 1-100 nM of the female sex hormone did not have any significant effect on phenylephrine-contracted rings, relaxation evoked by acetylcholine was significantly potentiated. In contrast, calcium ionophore A23187-elicited endothelium-dependent relaxation as well as cromakalim- and sodium nitroprusside-mediated endothelium-independent relaxation was unchanged following the same regime with 17beta-estradiol. These results demonstrate that short-term treatment with physiologically relevant levels of 17beta-estradiol, which on their own have no effect, enhances endothelium-dependent relaxation by acetylcholine. The vascular effects observed herein may partly account for some of the improved acute vasodilatory responses reported with 17beta-estradiol on blood flow in humans.

Rapid, nongenomic steroid actions: A new age?

In the traditional theory of steroid action, steroids bind to intracellular receptors and modulate nuclear transcription after translocation of steroid-receptor complexes into the nucleus. Due to similarities of molecular structure, specific receptors for steroids, vitamin D(3) derivatives, and thyroid hormone are considered to represent a superfamily of steroid receptors. While genomic steroid effects characterized by their delayed onset of action and their sensitivity to blockers of transcription and protein synthesis have been known for several decades, rapid actions of steroids have been more widely recognized and characterized in detail only recently. Rapid effects of steroids, thyroid hormones, and the steroid hormone metabolite of vitamin D(3), 1alpha, 25-dihydroxyvitamin D(3), on cellular signaling and function may be transmitted by specific membrane receptors. Binding sites in membranes have been characterized, exposing binding features compatible with an involvement in rapid steroid signaling. Characteristics of putative membrane receptors are completely distinct from intracellular steroid receptors, a fact which is further supported by the inability of classic steroid receptor antagonists to block nongenomic steroid actions. A putative progesterone membrane receptor has been cloned and functionally expressed with regard to progesterone binding. Development of drugs that specifically affect nongenomic action alone or even both modes of action may find applications in various, areas such as in the cardiovascular and central nervous systems and treatment of preterm labor, infertility, and electrolyte abnormalities.

Nongenomic steroid actions: fact or fantasy?

In the common theory of steroid action, steroids bind to intracellular receptors and modulate nuclear transcription after translocation of steroid--receptor complexes into the nucleus. Due to homologies of molecular structure, specific receptors for steroids, vitamin D3, and thyroid hormone are considered to represent a superfamily of steroid receptors. While genomic steroid effects being characterized by their delayed onset of action and their sensitivity to blockers of transcription and protein synthesis have been known for several decades, very rapid actions of steroids have been more widely recognized and characterized in detail only recently. Rapid effects of steroids, vitamin D3, and thyroid hormones on cellular signaling and function may be transmitted by specific membrane receptors. Although no receptor of this kind has been cloned up to now, binding sites in membranes have been characterized exposing binding features compatible with an involvement in rapid steroid signaling. Characteristics of putative membrane receptors were completely different from those of intracellular steroid receptors, which was further supported by the inability of classic steroid receptor antagonists to inhibit nongenomic steroid actions. Development of drugs that specifically affect nongenomic action alone or even both modes of actions may find applications in various areas such as the cardiovascular and central nervous systems and treatment of preterm labor, infertility, and electrolyte homeostasis. To acquaint the reader with major aspects of nongenomic steroid actions, these effects on cellular function will be summarized, potentially related binding sites in membranes discussed, and the physiological or pathophysiological relevance of nonclassic actions exemplified.

Estrogen increases Ca2+ efflux from female porcine coronary arterial smooth muscle

Acute estrogen administration relaxes vascular smooth muscle by decreasing intracellular Ca2+ concentration ([Ca2+]i). In the present study, we examined the hypothesis that this reduction in [Ca2+]i is mediated in part by enhanced Ca2+ efflux. Coronary artery smooth muscle cells were isolated from gonad-intact, sexually mature female pigs. The [Ca2+]i response to endothelin-1 was measured using fluo 3 and confocal microscopy. 17beta-Estradiol (E2beta), but not 17alpha-estradiol or triamcinolone acetonide, caused a concentration-dependent (IC50 = 10 nM) decrease in the [Ca2+]i response to endothelin-1. This decrease was blocked by the specific estrogen receptor antagonist ICI-182780. Under conditions in which Ca2+ influx and sarcoplasmic reticulum Ca2+ reuptake were blocked, E2beta still decreased [Ca2+]i. The response was blocked by extracellular lanthanum. These data indicate that E2beta decreases [Ca2+]i in coronary artery smooth muscle by affecting Ca2+ efflux via a receptor-mediated mechanism.

Gender differences in coronary artery diameter reflect changes in both endothelial Ca2+ and ecNOS activity

Elevation of nitric oxide (NO) release from the vascular endothelium may contribute to some of the gender-associated differences in coronary artery function. The mechanisms by which gender affects NO release from the endothelium of coronary arteries are not known. In this study, endothelial function was examined in pressurized coronary arteries from female and male rats. Diameter and endothelial cell intracellular Ca2+ concentration ([Ca2+]i) in intact arteries, as well as enzymatic activity of endothelial constitutive nitric oxide synthase (ecNOS) in arterial lysates, was measured. Elevation of intravascular pressure to 60 mmHg constricted coronary arteries from female animals less than coronary arteries from male animals (18% and 31% constriction, respectively). The increased arterial diameter of coronary arteries from females was associated with elevated endothelial [Ca2+]i (female 174 nM, male 90 nM; P < 0.001). Elevation of Ca2+ activated ecNOS with a similar slope and half-activation constant ( approximately 160 nM) for both female and male coronary arteries. However, at [Ca2+] > 100 nM, ecNOS activity was significantly higher in coronary arteries from female rats compared with their male equivalents (P < 0.01). Maximal activity for ecNOS at saturating Ca2+ (300 nM) was 37% higher in coronary arteries from female animals compared with male animals (P < 0.05). Thus elevated [Ca2+]i in the endothelium of female coronary arteries alone is predicted to increase the production of NO (by nearly 2-fold). This gender difference combined with increased ecNOS activity at a given [Ca2+] in females indicates that tonic NO production should be nearly threefold greater in female coronary arteries compared with male coronary arteries. We conclude that, in the regulation of endothelial Ca2+ and ecNOS, gender differences contribute significantly to the overall decrease in myogenic tone observed in coronary arteries of females.

Rapid inhibition of rat brain mitochondrial proton F0F1-ATPase activity by estrogens: comparison with Na+, K+ -ATPase of porcine cortex

Our earlier studies have identified oligomycin sensitivity-conferring protein (OSCP), a subunit of proton F0F1-ATPase/ATP synthase in the mitochondrial inner membranes, as a new estradiol binding protein. This finding suggests that mitochondrial ATPase/ATP synthase could be a potential target for estradiol or compounds with similar structures. Here, we report that estradiol and several other compounds inhibited F0F1-ATPase activity of detergent-solubilized rat brain mitochondrial preparations in a following decreasing order: diethylstilbestrol (half-inhibition concentration, IC50 of 10-25 microM) > alpha-zearalenol, 4-hydroxyestradiol (1C50 of 55 microM) >2-hydroxyestradiol (IC50 of 110 microM), 17beta-estradiol, 17alpha-estradiol > beta-zearalanol > estriol, testosterone, 16alpha-hydroxyestrone > corticosterone, progesterone, dehydroepiandrosterone, dehydroepiandrosterone 3-sulfate, cholesterol (less than 10% inhibition at 140 microM). On the other hand, Na+, K+ -ATPase of porcine cortex showed different sensitivity to the compounds tested above. At 70 microM, the rank of inhibitory potency in decreasing order was as follows: 2-hydroxyestradiol (IC50 of 70 microM) > diethylstilbestrol> 4-hydroxyestradiol > progesterone > alpha-zearalenol, while other compounds had little effect (less than 5%). The data indicate that the ubiquitous mitochondrial F0F1-ATPase is a specific target site for estradiol and related estrogenic compounds; however, under this in vitro condition, the effect seems to require pharmacological concentrations.

Effect of acute and long-term treatment with 17-beta-estradiol on the vasomotor responses in the rat aorta

1. This study sought to evaluate whether the effects of acute and long-term treatment with 17-beta-estradiol on the vasomotor responses in rat aortic rings are mediated through the same mechanism. 2. Ovariectomized rats were treated daily with either 17-beta-estradiol-3-benzoate (100 microg kg(-1)) or vehicle for 1 week. 3. The effect of long-term 17-beta-estradiol treatment on the responses to cumulative doses of phenylephrine, 5-HT, calcium, potassium and 17-beta-estradiol was determined in aortic rings. In the same rings, the effect of acute exposure to 17-beta-estradiol (5 and 10 microM) on the dose response curves for phenylephrine, 5-HT, calcium, potassium and acetylcholine were estimated. The measurements were made in rings with and without intact endothelium. The tone-related basal release of nitric oxide (NO) was measured in rings with intact endothelium. 4. Long-term 17-beta-estradiol treatment reduced the maximum developed contraction to all contracting agents studied. This effect was abolished in endothelium denuded vessels. Acute 17-beta-estradiol treatment also reduced maximal contraction. This effect, however, was independent of the endothelium. 5. Long-term 17-beta-estradiol treatment significantly increased the ability of the rings to dilate in response to acetylcholine whereas acute exposure to 17-beta-estradiol had no effect. The tone-related release of NO was significantly increased after long-term exposure to 17-beta-estradiol. 6. In conclusion, this study indicate that the acute and long-term effects of 17-beta-estradiol in the rat aorta are mediated through different mechanisms. The long-term effect is mediated through the endothelium most likely by increasing NO release. In contrast, the acute effect of 17-beta-estradiol seems to be through an effect on the vascular smooth muscle cells.

Plant derived estrogens relax rat mesenteric artery in vitro

The aim of this study was to investigate whether plant derived estrogens have the same relaxing effects in vitro as estradiol-17beta on arterial smooth muscle. The mesenteric arterial rings of female and male Wistar rats were studied. The relaxing effects of estradiol-17beta, genistein, daidzein and beta-sitosterol were determined, with particular focus on the role of endothelium. B-sitosterol had no relaxing effect on the arteries. Estradiol-17beta, genistein and daidzein relaxed noradrenaline, potassium chloride and calcium chloride precontracted arterial rings endothelium-independently. The relaxation responses were also independent of gender. Neither the removal of endothelium, nor the inhibition prostacyclin or nitric oxide synthesis, had any effect on the relaxation responses. The exact mechanism of these findings is still unclear.

Effects of 17beta-oestradiol on rat isolated coronary and mesenteric artery tone: involvement of nitric oxide

Pre- and post-menopausal women receiving oestrogen replacement therapy have a significantly reduced risk of cardiovascular disorders. It has been suggested that this protection might be partly a result of a direct relaxant effect of oestrogens on coronary arteries. This study examines and directly compares the effects of 17beta-oestradiol on rat isolated coronary and mesenteric vessels. The influence of nitric oxide on these responses was also investigated. 17Beta-oestradiol caused similar concentration-dependent relaxation of isolated coronary and mesenteric resistance arteries pre-contracted with either KCl (60 mM) or 9,11-dideoxy-11alpha,9alpha-epoxymethanoprostaglandin (U46619; 1 microM). The relaxation responses to 17beta-oestradiol were significantly reduced, but not totally inhibited, in the presence of N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase; they were not altered by indomethacin, an inhibitor of prostaglandin synthesis. The responses to 17beta-oestradiol in the presence of L-NAME were not dependent on the vessel studied or the pre-contracting agent used. These results suggest that nitric oxide might contribute to the vasodilatory effects of 17beta-oestradiol in rat isolated coronary and mesenteric resistance arteries.

17Beta-oestradiol enhances nitric oxide synthase activity in endothelium-denuded rat aorta

1. It has been suggested that oestrogen-produced vasodilatation is due to induction of endothelial nitric oxide synthase (NOS), but there are many reports of direct effects on vascular smooth muscle. In the present study, these processes were investigated in rat aorta isolated from ovariectomized rats. 2. Short-term treatment (10 min) with 17beta-oestradiol (10 micromol/L) produced a small attenuation of the phenylephrine (PE)-induced constriction, which was unaffected by the nitric oxide synthase inhibitor L-N5(-1-iminoethyl)ornithine (NIO; 100 micromol/L). Long-term treatment (6 h) with 17beta-oestradiol (10 micromol/L) did not affect acetylcholine-mediated vasorelaxation in endothelium-intact aortic rings, but did attenuate PE-induced constriction. This attenuation was also observed in endothelium-denuded preparations after 17beta-oestradiol (10 micromol/L for 6 h) and was far greater than the acute effect of 17beta-oestradiol (10 micromol/L). 3. The attenuation produced by 17beta-oestradiol (10 micromol/L for 6 h) was significantly inhibited by concomitant treatment with cycloheximide (1 micromol/L), suggesting that protein synthesis was involved. NIO (100 micromol/L) also attenuated the effect, which suggests that the anti-constrictor effect of 17beta-oestradiol occurs through the increased production of nitric oxide (NO). 17Beta-oestradiol increased NO production, as assessed by the conversion of [3H]-arginine to [3H]-citrulline in rat aorta. These effects were prevented by cycloheximide and NIO. The anti-constrictor effect of oestrogen was blocked by the oestrogen receptor antagonist ICI 182 780 (100 nmol/L). 4. Western blotting using an antibody specific for inducible nitric oxide synthase (NOS) revealed that 17beta-oestradiol (10 micromol/L for 24 h) treatment induced the formation of inducible NOS protein in the aorta, an effect blocked by cycloheximide. The results indicate that 17beta-oestradiol can attenuate the vasoconstrictor effect of PE by a specific receptor-mediated process that involves induction of inducible NOS.

Partial contribution of polyamines to the relaxant effect of 17 alpha-estradiol in rat uterine smooth muscle

1. The effects of 17 alpha-estradiol on KCl (60 mM), CaCl2 (30 microM to 10 mM) and vanadate (0.3 mM)-induced contractions in rat uterus have been assayed. Furthermore, the effect of 17 alpha-estradiol on calmodulin-stimulated cAMP-phosphodiesterase activity was also studied. 2. 17 alpha-estradiol relaxed the tonic contraction induced by KCl (60 mM) in a concentration-dependent way (IC50, 8.3 +/- 0.7 microM), and CaCl2 (0.1 to 10 mM) counteracted it. 3. CaCl2 (30 microM to 10 mM) produced concentration-dependent contraction of rat uterus in a calcium-free medium supplemented with 60 mM of KCl (EC50: 0.2 +/- 0.01 mM). 17 alpha-estradiol (8 microM) antagonized the contraction induced by CaCl2, increasing the EC50 value up to 0.7 +/- 0.1 mM (P < 0.01). 4. 17 alpha-estradiol (0.1 to 1 mM) relaxed in a concentration-dependent way the tonic contraction induced by vanadate in rat uterus incubated in a calcium-free medium and EDTA supplemented. The maximal relaxation achieved with 1 mM of 17 alpha-estradiol was 52.2 +/- 2.8%. 5. 17 alpha-estradiol (1 to 100 microM) did not modify the basal activity of cAMP-phosphodiesterase but inhibited the calcium plus calmodulin stimulated activity. The maximal inhibition achieved was 43 +/- 5.4%. 6. The relaxing effect of 17 alpha-estradiol on KCl (60 mM)-induced tonic contraction was unmodified with the antioestrogen tamoxifen (0.1 and 1 microM), the inhibitor of tirosine kinase (genistein, 10 microM) and the cAMP-dependent protein kinase inhibitor (Rp-adenosine 3',5'-monophosphothioate, triethylamine salt, 100 microM). However, the effect was antagonized with the inhibitor of transcription (actinomycin D, 5 micrograms/ml,), the inhibitor of protein synthesis (cycloheximide, 10 and 100 micrograms/ml), and the inhibitor of ornithine decarboxilase (alpha-difluoromethyl-ornithine, 10 mM). 7. Our results suggest that polyamines contribute to the relaxant effect of 17 alpha-estradiol in rat uterine smooth muscle behaving, presumably, as mediators of the transcriptional component involved in the effect of 17 alpha-estradiol.

Mechanisms of relaxation of rat aorta in response to progesterone and synthetic progestins

OBJECTIVE

To compare the acute effects of progesterone, chlormadinone acetate (CMA), norethisterone acetate (NETA) and dienogest (DNG) with those of 17 beta-estradiol (17 beta-E2) on the vascular reactivity of male rat thoracic aorta.

METHODS

Aortic rings with or without endothelium were placed in an organ bath for isometric tension recording. The integrity of the endothelium was assessed by the relaxant response of precontracted rings to acetylcholine (1 and 10 microM), which was diminished after mechanical removal of the endothelium. The concentrations of the steroid hormones were 0.01-10 microM.

RESULTS

In vessels precontracted with phenylephrine (1 microM), CaCl2 (3 mM) or KCl (30 mM), progesterone, CMA and NETA (10 microM each) an endothelium-independent relaxation of 20-35% resulted, with a maximum response after 20-30 min, while DNG had a negligible effect in all experiments. The same concentration of 17 beta-E2 was twice as potent as the progestins. Indomethacin, the cyclooxygenase inhibitor and glibenclamide, an inhibitor of the ATP-sensitive potassium channels, did not affect the relaxant responses. The antagonists of progesterone receptors J 867 (1 microM) as well as of estrogen receptors ICI 182780 (1 microM) did not counteract the relaxation induced by progesterone and 17 beta-E2, respectively. Progesterone (10 microM) did not interfere with endothelium-dependent acetylcholine-induced relaxation of precontracted aortic rings. Pretreatment of the vessels with the hormones attenuated the maximal contractile response to phenylephrine. In the presence of verapamil (1 microM) or progesterone (10 microM) or 17 beta-E2 (1 and 10 microM) the concentration-response curves for calcium-induced contractions in K(+)-depolarized vessels were shifted to the right, with suppression of the maximum response.

CONCLUSIONS

These studies suggest that in addition to 17 beta-E2 the progestins, progesterone, CMA and NETA caused a reduction of vascular tone, probably due to blockade of voltage-dependent and/or receptor-operated calcium channels.

In vitro administration of 17 beta-estradiol inhibits drug-induced contractions of the rat isolated seminal vesicle

1. The rat isolated seminal vesicle responded to noradrenaline (NA), acetylcholine (ACh), potassium chloride (KCl) and barium chloride (BaCl2) with reproducible contractions. 2. 17 beta-estradiol (17 beta E) cumulatively added in the isolated organ bath reduced the number of contractions with all agonists used in the rank order of potency: BaCl2 > or = KCl > ACh > NA. The dose-response curves constructed in the presence of 17 beta E (2 x 10(-5) mol/l) produced a rightward shift and a reduction in the maximum response showing inhibitory activity. 3. When the calcium content in the normal Krebs medium (2.5 mmol/l) was reduced to half, the inhibitory activity of 17 beta E was potentiated. The maximum inhibition rates to KCl (phasic and tonic), BaCl2 and ACh were significantly (P < 0.05) different from each other. 4. The inhibitory effects of 17 beta E against all agonists tested were found to be similar in their responses to verapamil, but were much lower in potency. 5. The inhibitory effects of 17 beta E was seen only when the hormone was present in the tissue environment and was readily reversible as soon as the tissue was washed with the Krebs medium, suggesting that the effect of 17 beta E is localized. 6. It is suggested that the in vitro application of 17 beta E on the rat isolated seminal vesicle interferes with the process of translocation of calcium ions from the extracellular medium.

Nitric oxide mediates LDL uptake in the artery wall in response to high concentrations of 17 beta-estradiol

Female sex hormones are known to affect lipoprotein flux in the artery wall and atherosclerosis. However, the mechanisms of these artery wall effects are unclear. To examine the effect of 17 beta-estradiol (estradiol) on LDL uptake in the artery wall, we developed an isolated perfused rat carotid artery model from ovariectomized rats. LDL flux in the artery wall was measured by quantitative fluorescence microscopy before and after treatment with estradiol (0.001 to 10,000 nmol/L). Dose-response experiments showed no significant difference in the rate of LDL uptake when arteries were perfused with estradiol at physiological concentrations (0.001 to 1 nmol/L) compared with control perfusions. However, higher concentrations of estradiol (10 to 10,000 nmol/L) significantly increased the rate of LDL uptake in isolated arteries. Artery lumen volume significantly increased with perfusion of estradiol (1 to 100 nmol/L) but decreased after perfusions of higher concentrations of estradiol (1000 to 10,000 nmol/L). Additional studies were performed to examine mechanisms of estradiol-mediated increases in LDL uptake. The effect of estradiol (10 nmol/L) on the rate of LDL uptake was blocked by nitric oxide synthase inhibitors. However, the estrogen receptor antagonist tamoxifen did not block the effects of estradiol on the rate of LDL uptake. Our study indicates that modulation of LDL uptake in the artery wall by estradiol is concentration dependent. High concentrations of estradiol increase LDL uptake by production of endothelium-derived nitric oxide. These observations suggest that increased nitric oxide production compromises endothelial layer barrier function to increase LDL uptake in the artery wall.

Mechanism of vascular smooth muscle relaxation by estrogen in depolarized rat and mouse aorta. Role of nuclear estrogen receptor and Ca2+ uptake

17 beta-Estradiol induces vasodilation in vitro and in vivo, which has been suggested to contribute to the cardiovascular protection by this ovarian steroid hormone. However, the exact mechanism of vasorelaxation by estrogens remains to be elucidated. In this study, we analyzed the potential role of genomic mechanisms involving the nuclear estrogen receptor and inhibition of entry of extracellular Ca2+ in 17 beta-estradiol-induced vasorelaxation in depolarized aortic rings, isolated from male and female rats and male mice. In both male and female rat aortic rings without endothelium and in intact male mouse aortic rings treated with NG-nitro-L-arginine, 17 beta-estradiol caused dose-dependent (0.3 to 30 mumol/L) relaxation of contraction evoked by high-K+ depolarization (30 and 45 mmol/L KCl, respectively). The estrogen receptor antagonist ICI 164384 had no effect on 17 beta-estradiol-induced relaxations. 125I-17 beta-estradiol binding studies showed the presence of high-affinity cytosolic-nuclear estrogen receptors in control male mouse aortas. Comparable relaxations of aortic rings isolated from control and estrogen receptor-deficient transgenic mice provided direct evidence that the nuclear estrogen receptor is not involved in this response. 17 beta-Estradiol-induced relaxation of rat aortic rings could not be prevented by cycloheximide or actinomycin D, suggesting that the response was not mediated by de novo protein synthesis or gene transcription. In rat aortic rings, 17 beta-estradiol inhibited the increase of 45Ca uptake by 30 mmol/L KCl at concentrations (10 and 30 mumol/L) that caused vasorelaxation in the same tissue, suggesting that inhibition of Ca2+ entry contributes to the response. 17 alpha-Estradiol was less effective, and estrone was devoid of vasorelaxing activity. Vasorelaxation by estrogens in female and male rat aortas was similar, indicating no gender difference in vascular responses under these conditions.

Calcifying subpopulation of bovine aortic smooth muscle cells is responsive to 17 beta-estradiol

BACKGROUND

Arterial calcification, common in atherosclerosis, is associated with an increased risk of clinical events such as myocardial infarction. We previously identified a subpopulation of bovine aortic medial cells, calcifying vascular cells (CVCs), that have osteoblastic characteristics and form bone mineral in vitro in the form of calcified nodules. To assess whether estrogen modulates arterial calcification as well as bone calcification, we tested CVCs for estrogen receptors and for the effect of 17 beta-estradiol on formation of calcified nodules, calcium content, alkaline phosphatase activity, and osteocalcin concentration in the culture medium.

METHODS AND RESULTS

Estrogen receptor immunoreactivity was identified in the cytoplasm and the perinuclear region of CVCs by immunocytochemistry. CVCs were treated with 17 beta-estradiol at concentrations of 0, 5, and 10 nmol/L. Twenty-one days of 17 beta-estradiol treatment resulted in a significantly increased number of calcified nodules, visualized by von Kossa staining, as well as increased calcium content of the cultures. Increases in alkaline phosphatase activity, a marker for early osteoblastic differentiation, and secreted osteocalcin, a marker for late osteoblastic differentiation, were enhanced in cells treated with 17 beta-estradiol compared with control cells.

CONCLUSIONS

These results suggest that 17 beta-estradiol promotes osteoblastic differentiation and calcification in vascular cells and that estrogen may play a regulatory role in arterial calcification.

Non-genomic mechanism of 17 beta-oestradiol-induced inhibition of contraction in mammalian vascular smooth muscle

17 beta-Oestradiol (E2) at 0.1-10 microM directly inhibited various tonic and phasic smooth muscle contractions. The mechanism(s) of oestrogen-induced inhibition of contraction was studied using intact and permeabilized strips and isolated single cells of smooth muscle. 2. In endothelium-denuded vascular smooth muscle, E2 attenuated high K(+)-induced force development and myosin light chain phosphorylation, and produced rapid and reversible relaxation. There were no significant differences in these inhibitory effects between tissue types (femoral artery vs. portal vein), species (rat vs. rabbit) or sexes. 3. The inhibitory potencies of several steroidal and non-steroidal oestrogen analogues were examined and their effects were for the most part stereo-specific. However, two steroids with negligible affinities for the nuclear oestrogen receptor also strongly inhibited high K(+)-induced contraction. 4. Genomic modulators including a protein synthesis inhibitor, an RNA synthesis inhibitor, and oestrogen receptor antagonists did not affect the inhibitory actions of E2. Inhibitors of cyclic nucleotide-dependent protein kinases did not reduce the E2 effect. 5. Ca2+ release from intracellular stores by agonists and by inositol 1,4,5-trisphosphate (IP3) does not appear to be modulated by E2. Neither pretreatment with ryanodine nor with thapsigargin affected the E2-induced inhibition of high K(+)-induced contraction. 6. E2 had no effect on either normal or GTP gamma S-increased Ca2+ sensitivity of the regulatory and contractile apparatus. 7. E2 and its analogues rapidly inhibited voltage-dependent L-type Ca2+ channel currents in isolated smooth muscle cells. Repetitive stimulation was not required for E2-induced inhibition of the currents. 8. This study strongly suggests that at pharmacological concentrations oestrogen primarily reduces Ca2+ influx through inhibition of L-type Ca2+ channels in a non-genomic manner and decreases myosin light chain phosphorylation and contraction of smooth muscle.

Estradiol, Administered Acutely, Protects Ischemic Myocardium in Both Female and Male Rabbits

BACKGROUND: The benefits of chronic administration of estrogen to postmenopausal women are well documented; however, the acute effects of exogenous estradiol on myocardium after coronary artery occlusion and reperfusion in male and female animal models are unknown. We tested the influence of acute pretreatment with estradiol on the development of myocardial necrosis in two protocols, studying intact anesthetized female and male rabbits. METHODS AND RESULTS: 17beta-estradiol (1 mg) was given 15 minutes before coronary artery occlusion in the treated groups (n = 10 females, 10 males); control rabbits (n = 11 females, 10 males) received water. All rabbits underwent 30 minutes of coronary artery occlusion and 4 hours of reperfusion. Myocardial blood flow was similar between groups at 10 minutes after treatment and during coronary artery occlusion and reperfusion. Thus estradiol did not increase blood flow. Heart rate and systemic pressure were also similar between groups. Estradiol levels during coronary artery occlusion were 1-8 pg/mL in untreated female and male rabbits and 66 +/- 28 (male) and 352 +/- 273 (female) in treated rabbits. Although the size of the ischemic risk zones was similar in both groups in both protocols, estradiol-treated rabbits of both sexes developed significantly less necrosis. Infarct size as a percent of the risk region was 10 +/- 1% in female estradiol-treated rabbits compared with 23 +/- 5% in controls (P <.03) and 16 +/- 4% in estradiol-treated male rabbits compared with 31 +/- 5% in control males (P =.03). Although male rabbits had larger infarcts than female rabbits, sex was not a significant covariate for infarct size. CONCLUSIONS: Estradiol exerts a protective effect on ischemic myocardium that is not associated with an increase in myocardial blood flow or alteration in hemodynamics. This study shows that acute administration of estrogen before coronary artery occlusion reduces infarct size in both male and female rabbits.

Specific, nongenomic actions of steroid hormones

Traditionally, steroid hormone action has been described as the modulation of nuclear transcription, thus triggering genomic events that are responsible for physiological effects. Despite early observations of rapid steroid effects that were incompatible with this theory, nongenomic steroid action has been widely recognized only recently. Evidence for these rapid effects is available for steroids of all clones and for a multitude of species and tissues. Examples of nongenomic steroid action include rapid aldosterone effects in lymphocytes and vascular smooth muscle cells, vitamin D3 effects in epithelial cells, progesterone action in human sperm, neurosteroid effects on neuronal function, and vascular effects of estrogens. Mechanisms of action are being studied with regard to signal perception and transduction, and researchers have developed a patchy sketch of a membrane receptor-second messenger cascade similar to those involved in catecholamine and peptide hormone action. Many of these effects appear to involve phospholipase C, phosphoinositide turnover, intracellular pH and calcium, protein kinase C, and tyrosine kinases. The physiological and pathophysiological relevance of these effects is unclear, but rapid steroid effects on cardiovascular, central nervous, and reproductive functions may occur in vivo. The cloning of the cDNA for the first membrane receptor for steroids should be achieved in the near future, and the physiological and clinical relevance of these rapid steroid effects can then be established.

beta-Estradiol, but not alpha-estradiol, reduced myocardial necrosis in rabbits after ischemia and reperfusion

Recent studies in several animal models have suggested that estrogen, given for the short term, may protect ischemic myocardium. Our objective was to test the effect of exogenous estradiol on the development of myocardial necrosis. Twenty minutes before coronary occlusion, rabbits were given an IV bolus of either 17 beta-estradiol, a form of the hormone that stimulates the estrogen receptor (10 micrograms) or 17 alpha-estradiol, a natural form of the hormone lacking estrogenic effects (1 mg), or vehicle. Regional myocardial blood flow (RMBF) was measured after treatment and during occlusion and reperfusion, and heart rate and blood pressure were monitored throughout. All rabbits underwent 30 minutes of coronary artery occlusion and 4 hours of reperfusion. Estradiol levels were 6 +/- 2 pg/ml in untreated rabbits, 392 +/- 78 pg/ml in rabbits given 17 beta-estradiol, and 413 +/- 68 pg/ml in rabbits given 17 alpha-estradiol. The size of the ischemic region was similar in all groups, but rabbits treated with 17 beta-estradiol developed significantly less necrosis than did control rabbits (0.33 +/- 0.04 vs 0.53 +/- 0.05 of the area at risk; p < 0.05), whereas rabbits treated with 17 alpha-estradiol did not (0.43 +/- 0.03; p = NS vs control group). Heart rate, systemic pressure, and RMBF were comparable among groups throughout the protocol. In conclusion, 17 beta-estradiol exerts a protective effect on ischemic myocardium, reducing infarct size. This beneficial effect is not associated with an increase in myocardial blood flow or alteration in hemodynamics. Because 17 alpha-estradiol did not affect infarct size, the cardioprotective effect of 17 beta-estradiol is probably receptor mediated.

Calcium and depolarization-dependent effect of pregnenolone derivatives on uterine smooth muscle

1. The effects of several gestagens (pregnenolone [1 to 30 microM], 20 alpha-hydroxy-pregnenolone [1 to 30 microM], and 20 beta-hydroxypregnenolone [1 to 30 micro M]) on rat uterine contraction induced by KCl (60 mM) and CaCl2 (30 microM to 6 mM) have been assayed. 2. The three drugs relaxed the tonic contraction induced by KCl in a concentration-dependent way. The respective EC50 values were: 27.6 +/- 1.58 microM (pregnenolone), 4.1 +/- 0.12 microM (20 alpha-hydroxy-pregnenolone), and 11.2 +/- 1.04 microM (20 beta-hydroxypregnenolone). CaCl2 (1 to 10 mM) totally counteracted the relaxing effect of pregnenolone but only partially compared to that of 20 alpha- or 20 beta-hydroxy-pregnenolone. 3. CaCl2 (30 microM to 6 mM) produced concentration-dependent contraction of rat uterus in medium lacking calcium plus 30, 60, or 90 mM of KCl. The EC50 values of CaCl2 were: 0.38 +/- 0.072, 0.183 +/- 0.015, and 0.183 +/- 0.015 mM in a medium with 30, 60, or 90 mM of KCl, respectively. 4. Pregnenolone (10 microM) did not significantly modify the EC50 of CaCl2 in a medium with 30, 60, or 90 mM of KCl. However, 20 beta-hydroxypregnenolone (10 microM) antagonized, in a noncompetitive manner, the concentration-response curve to CaCl2. 5. 20 alpha-Hydroxypregnenolone (4 microM) antagonized the concentration-response curve to CaCl2 in a competitive manner. This antagonism was directly related to the concentration of KCl in the medium. 6. Our results suggest a different calcium antagonist effect of the three gestagens assayed.

Non-genomic effects of estrogen and the vessel wall

Estrogen, like other steroids, is now believed to possess rapid membrane effects independent of the classical gene activation pathway of steroid action. The presence of membrane estrogen receptors has been demonstrated in different cell types, but not yet in vascular tissue. In vivo, estrogen administration rapidly promotes acetylcholine-induced vasodilation of the coronary and peripheral vascular beds of postmenopausal women. Estrogen also causes relaxation of precontracted isolated arterial segments and perfused organ preparations, within minutes of administration of the hormone. These rapid vasomotor effects of estrogen may be related to blockade of the cell membrane voltage-dependent calcium channels, resulting in inhibition of extracellular Ca2+ mobilization and flux. Recently, estradiol has been shown to rapidly affect cyclic nucleotide turnover in vascular segments, smooth muscle, and epithelial cell cultures, suggesting the possibility of a "cross-talk" between membrane-mediated events and nuclear receptor activation.

Mechanisms involved in the relaxant effect of estrogens on rat aorta strips

The effects of estrogens 17beta-estradiol (17beta-E2), 17alpha-estradiol (17alpha-E2) and diethylstilbestrol (DES) on CaCl2 (3mM)-induced contractions on rat aorta strips have been assayed. Both 17alpha-E2 and DES, but not the 17beta-E2 relaxed and inhibited the contraction induced by CaCl2. The antiestrogen tamoxifen (0.1, 1 and 3 microM) antagonizes, in a concentration-dependent way, the relaxant effect of 17alpha-E2 but the relaxation induced by DES is only significantly antagonized with 3 microM of tamoxifen. Cycloheximide (0.1 and 0.3 mM) does not modify the 17alpha-E2 or DES effects. However, the inhibitors of cAMP-dependent protein kinase TPCK (1 microM) and Rp-cAMPS (10 microM) inhibit the relaxation induced by 17alpha-E2 and DES. The elimination of endothelium by rubbing, significantly inhibits the effect of DES but does not modify the effect of 17alpha-E2. Our results suggest that estrogen-induced relaxation is a non-genomic effect possibly or presumably produced by activation of estrogenic receptors and mediated by cAMP. The DES-effect is partially endothelium-dependent but the effect of 17alpha-E2 is independent of endothelium.