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

Calcium signaling in endothelial and vascular smooth muscle cells: sex differences and the influence of estrogens and androgens

Calcium signaling in vascular endothelial cells (ECs) and smooth muscle cells (VSMCs) is essential for the regulation of vascular tone. However, the changes to intracellular Ca2+ concentrations are often influenced by sex differences. Furthermore, a large body of evidence shows that sex hormone imbalance leads to dysregulation of Ca2+ signaling and this is a key factor in the pathogenesis of cardiovascular diseases. In this review, the effects of estrogens and androgens on vascular calcium-handling proteins are discussed, with emphasis on the associated genomic or nongenomic molecular mechanisms. The experimental models from which data were collected were also considered. The review highlights 1) in female ECs, transient receptor potential vanilloid 4 (TRPV4) and mitochondrial Ca2+ uniporter (MCU) enhance Ca2+-dependent nitric oxide (NO) generation. In males, only transient receptor potential canonical 3 (TRPC3) plays a fundamental role in this effect. 2) Female VSMCs have lower cytosolic Ca2+ levels than males due to differences in the activity and expression of stromal interaction molecule 1 (STIM1), calcium release-activated calcium modulator 1 (Orai1), calcium voltage-gated channel subunit-α1C (CaV1.2), Na+-K+-2Cl- symporter (NKCC1), and the Na+/K+-ATPase. 3) When compared with androgens, the influence of estrogens on Ca2+ homeostasis, vascular tone, and incidence of vascular disease is better documented. 4) Many studies use supraphysiological concentrations of sex hormones, which may limit the physiological relevance of outcomes. 5) Sex-dependent differences in Ca2+ signaling mean both sexes ought to be included in experimental design.

Functions of Membrane Progesterone Receptors (mPRs, PAQRs) in Nonreproductive Tissues

Gender differences in a wide variety of physiological parameters have implicated the ovarian hormones, estrogens and progesterone, in the regulation of numerous nonreproductive tissue functions. Rapid, nongenomic (nonclassical) progesterone actions mediated by membrane progesterone receptors (mPRs), which belong to the progestin and adipoQ receptor family, have been extensively investigated in reproductive and nonreproductive tissues since their discovery in fish ovaries 20 years ago. The 5 mPR subtypes (α, β, γ, δ, ε) are widely distributed in vertebrate tissues and are often expressed in the same cells as the nuclear progesterone receptor (PR) and progesterone receptor membrane component 1, thereby complicating investigations of mPR-specific functions. Nevertheless, mPR-mediated progesterone actions have been identified in a wide range of reproductive and nonreproductive tissues and distinguished from nuclear PR-mediated ones by knockdown of these receptors with siRNA in combination with a pharmacological approach using mPR- and PR-specific agonists. There are several recent reviews on the roles of the mPRs in vertebrate reproduction and cancer, but there have been no comprehensive assessments of mPR functions in nonreproductive tissues. Therefore, this article briefly reviews mPR functions in a broad range of nonreproductive tissues. The evidence that mPRs mediate progesterone and progestogen effects on neuroprotection, lordosis behavior, respiratory control of apnea, olfactory responses to pheromones, peripheral nerve regeneration, regulation of prolactin secretion in prolactinoma, immune functions, and protective functions in vascular endothelial and smooth muscle cells is critically reviewed. The ubiquitous expression of mPRs in vertebrate tissues suggests mPRs regulate many additional nonreproductive functions that remain to be identified.

Involvement of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) in mPRα (PAQR7)-mediated progesterone induction of vascular smooth muscle relaxation

Progesterone acts directly on vascular smooth muscle cells (VSMCs) through activation of membrane progesterone receptor α (mPRα)-dependent signaling to rapidly decrease cytosolic Ca²⁺ concentrations and induce muscle relaxation. However, it is not known whether this progesterone action involves uptake of Ca²⁺ by the sarco/endoplasmic reticulum (SR) and increased sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) activity. The present results show that treatment of cultured human VSMCs with progesterone and the selective mPR agonist Org OD-02-0 (OD 02-0) but not with the nuclear PR agonist R5020 increased SERCA protein expression, which was blocked by knockdown of mPRα with siRNA. Moreover, treatments with progesterone and OD 02-0, but not with R5020, increased phospholamban (PLB) phosphorylation, which would result in disinhibition of SERCA function. Progesterone and OD 02-0 significantly increased Ca²⁺ levels in the SR and caused VSMC relaxation. These effects were blocked by pretreatment with cyclopiazonic acid (CPA), a SERCA inhibitor, and by knockdown of SERCA2 with siRNA, suggesting that SERCA2 plays a critical role in progesterone induction of VSMC relaxation. Treatment with inhibitors of inhibitory G proteins (Gi, NF023), MAP kinase (AZD 6244), Akt/Pi3k (wortmannin), and a Rho activator (calpeptin) blocked the progesterone- and OD 02-0-induced increase in Ca²⁺ levels in the SR and SERCA expressions. These results suggest that the rapid effects of progesterone on cytosolic Ca²⁺ levels and relaxation of VSMCs through mPRα involve regulation of the functions of SERCA2 and PLB through Gi, MAP kinase, and Akt signaling pathways and downregulation of RhoA activity.NEW & NOTEWORTHY The rapid effects of progesterone on cytosolic Ca²⁺ levels and relaxation of VSMCs through mPRα involve regulation of the functions of SERCA2 and PLB through Gi, MAP kinase, and Akt signaling pathways and downregulation of RhoA activity.

The Role of Sex in the Pathophysiology of Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease characterised by increased pulmonary vascular resistance and pulmonary artery remodelling as result of increased vascular tone and vascular cell proliferation, respectively. Eventually, this leads to right heart failure. Heritable PAH is caused by a mutation in the bone morphogenetic protein receptor-II (BMPR-II). Female susceptibility to PAH has been known for some time, and most recent figures show a female-to-male ratio of 4:1. Variations in the female sex hormone estrogen and estrogen metabolism modify FPAH risk, and penetrance of the disease in BMPR-II mutation carriers is increased in females. Several lines of evidence point towards estrogen being pathogenic in the pulmonary circulation, and thus increasing the risk of females developing PAH. Recent studies have also suggested that estrogen metabolism may be crucial in the development and progression of PAH with studies indicating that downstream metabolites such as 16α-hydroxyestrone are upregulated in several forms of experimental pulmonary hypertension (PH) and can cause pulmonary artery smooth muscle cell proliferation and subsequent vascular remodelling. Conversely, other estrogen metabolites such as 2-methoxyestradiol have been shown to be protective in the context of PAH. Estrogen may also upregulate the signalling pathways of other key mediators of PAH such as serotonin.

Progesterone induces relaxation of human umbilical cord vascular smooth muscle cells through mPRα (PAQR7)

Progesterone effects on vascular smooth muscle cell (VSMC) relaxation and the mechanism were investigated in cultured human umbilical vein VSMCs. Membrane progesterone receptors mPRα, mPRβ, and mPRγ were highly expressed in VSMCs, whereas nuclear progesterone receptor (nPR) had low expression. Progesterone (20 nM) and 02-0 (mPR-selective agonist), but not R5020 (nPR agonist), induced muscle relaxation in both a VSMC collagen gel disk contraction assay and an endothelium-denuded human umbilical artery ring tension assay. Progesterone and 02-0 increased ERK and Akt phosphorylation and decreased cAMP levels. These effects were blocked by preincubation with pertussis toxin. Progestin-induced muscle relaxation was blocked by pretreatment with mPRα, but not nPR, siRNAs, and by co-treatment with 8-Br-cAMP, AZD6244 (MAP kinase inhibitor), and wortmannin (PI3K inhibitor). Progestins reduced myosin light chain phosphorylation which was blocked with AZD6244 and wortmannin. These results demonstrate progesterone directly relaxes human VSMCs through mPRα/Gi and MAP kinase/ERK-, Akt/PI3K-, and cAMP-dependent pathways.

Progesterone suppressed vasoconstriction in human umbilical vein via reducing calcium entry

The aim of this study was to evaluate the actions of progesterone on human umbilical vein (HUV) from normal pregnancies and the possible underlying mechanisms involved. HUV rings were suspended in organ baths and exposed to progesterone followed by phenylephrine (PE) or serotonin (5-HT). Progesterone suppressed PE- or 5-HT-induced vasoconstriction in HUV rings. The inhibitory effect induced by progesterone was not influenced by nitric oxide syntheses inhibitor, prostaglandins syntheses blocker, the integrity of endothelium, selective progesterone receptor or potassium channel antagonists. Further testing showed that progesterone and nifedipine (a blocker for L-type calcium channels) produced similar inhibitory effects on PE-, 5-HT-, Bay-k8644-, KCl-induced vasoconstriction in Krebs solution as well as CaCl2-induced vasoconstriction in Ca(2+)-free Krebs solution. But the inhibitory effect of mibefradil (mibe, a blocker for L-type (CaV1.2) and T-type calcium channels (CaV3.2)) on PE-, 5-HT-induced vasoconstriction was significantly greater than progesterone or nifedipine in Krebs solution. Furthermore, progesterone did not affect the vasoconstriction caused by PE, 5-HT, or caffeine in Ca(2+)-free Krebs solution. In addition, incubation HUV with progesterone did not change CaV1.2 and progesterone receptor (PR) expressions. The results gained demonstrated that progesterone could suppress multiple agonist-induced vasoconstrictions in HUV, mainly due to a reduction of calcium entry through L-type calcium channels, not endothelium-dependent vascular relaxation pathways, potassium channels, or Ca(2+) release from intracellular stores, providing new information important to further understanding the contribution of progesterone in the regulation of the placental-fetal circulation.

Differential regulation of endothelium behavior by progesterone and medroxyprogesterone acetate

Medroxyprogesterone acetate (MPA) is a synthetic progestin commonly used in hormone replacement therapy (HRT). The aim of this research was to study and compare the effect of progesterone (Pg) and MPA on the regulation of cellular events associated with vascular homeostasis and disease. Platelet adhesion to endothelial cells (ECs), nitric oxide (NO) production, and cell migration were studied using murine ECs in vitro exposed to the progestins. After 7 min of treatment, MPA significantly inhibited NO synthesis with respect to control values; meanwhile, Pg markedly increased vasoactive production. In senile ECs, the stimulatory action of Pg decreases; meanwhile, MPA maintained its ability to inhibit NO synthesis. The presence of RU486 antagonized the action of each steroid. When ECs were preincubated with PD98059 (MAPK inhibitor) or chelerythrine (protein kinase C (PKC) inhibitor) before Pg or MPA treatment, the former totally suppressed the steroid action, but the PKC antagonist did not affect NO production. In the presence of a PI3K inhibitor (LY294002), a partial reduction in Pg effect and a reversal of MPA action were detected. Using indomethacin, the contribution of the cyclooxygenase (COX) pathway was also detected. On platelet adhesion assays, Pg inhibited and MPA stimulated platelet adhesion to ECs. Under inflammatory conditions, Pg prevented platelet adhesion induced by lipopolysaccharide (LPS); meanwhile, MPA potentiated the stimulatory action of LPS. Finally, although both steroids enhanced migration of ECs, MPA exhibited a greater effect. In conclusion, the data presented in this research provide evidence of a differential regulation of vascular function by Pg and MPA.

The role of sex steroids on cellular events involved in vascular disease

In this work we checked the hypothesis whether estrone, progesterone, and testosterone are able to modulate the interactions between platelets, monocytes, and endothelial cells either under basal or inflammatory conditions. Using adhesion assays we demonstrated that pretreatment of endothelial cells with estrone, progesterone, or testosterone prevented monocytes and platelets adhesion induced by the proinflammatory agent bacterial lipopolysaccharide. The hormones reduced the expression of mRNA of ICAM-1, VCAM-1, and P-selectin, endothelial surface proteins that mediate monocytes and platelets adhesion respectively. Integrins are the main leukocyte proteins that allow firm adhesion. Using flow cytometry we showed that estrone treatment of monocytes reduced CD11b and CD11c expression, either under basal or injury (lipopolysaccharide) conditions. The three steroids inhibited platelet aggregation in a nitric oxide dependent manner. Platelet function was not affected by the steroid treatment. The molecular mechanisms of action exerted by the steroids included the participation of the intracellular signaling pathways PKC, MAPK, and PI3K, which selectively and differentially mediate the stimulation of nitric oxide release. We evidence that estrone, progesterone, and testosterone modulate monocyte and platelet adhesion to endothelial cells, events that play a major role in the initiation and progression of vascular lesions. The steroid action was evidenced under basal or inflammatory conditions. The mechanisms of action exerted by the steroids included stimulation of nitric oxide production and the participation of PKC, MAPK, and PI3K systems.

Non-genomic vasorelaxant effects of 17β-estradiol and progesterone in rat aorta are mediated by L-type Ca2+ current inhibition

AIM

The sex hormones 17β-estradiol (βES) and progesterone (PRG) induce rapid non-genomic vasodilator effects which could be protective for the cardiovascular system. The purpose of this study was to analyze the mechanisms underlying their vasodilator effect in rat aortic smooth muscle preparations.

METHODS

Endothelium-denuded aorta artery rings were prepared from male Wistar rats and incubated in an organ bath. The contractions of the preparation were recorded through isometric transducers. The effects of the hormones on K(+) current and L-type Ca(2+) current (LTCC) were analyzed by using the whole cell voltage-clamp technique in A7r5 cells.

RESULTS

Both βES and PRG (1-100 μmol/L) concentration-dependently relaxed the endothelium-denuded aortic rings contracted by (-)-Bay K8644 (0.1 μmol/L) or by KCl (60 mmol/L). The IC(50) values of the two hormones were not statistically different. The K(V) channel blocker 4-aminopyridine (2 mmol/L), BK(Ca) channel blocker tetraethylammonium (1 mmol/L) and K(ATP) channel blocker glibenclamide (10 μmol/L) did not significantly modify the relaxant effect of the hormones. On the other hand, the blockage of the intracellular βES and PRG receptors with estradiol receptor antagonists ICI 182,780 (1 μmol/L) and PRG receptor antagonist mifepristone (30 μmol/L), respectively, did not significantly modify the relaxant action of the hormones. In A7r5 cells, both the hormones (1-100 μmol/L) rapidly and reversibly inhibited the basal and BAY-stimulated LTCC. However, these hormones had no effect on the basal K(+) current.

CONCLUSION

The vasorelaxant effects of βES and PRG are due to the inhibition of LTCC. The K(+) channels are not involved in the effects.

Inhibition of diacylglycerol-sensitive TRPC channels by synthetic and natural steroids

TRPC channels are a family of nonselective cation channels that regulate ion homeostasis and intracellular Ca²⁺ signaling in numerous cell types. Important physiological functions such as vasoregulation, neuronal growth, and pheromone recognition have been assigned to this class of ion channels. Despite their physiological relevance, few selective pharmacological tools are available to study TRPC channel function. We, therefore, screened a selection of pharmacologically active compounds for TRPC modulating activity. We found that the synthetic gestagen norgestimate inhibited diacylglycerol-sensitive TRPC3 and TRPC6 with IC₅₀s of 3–5 µM, while half-maximal inhibition of TRPC5 required significantly higher compound concentrations (>10 µM). Norgestimate blocked TRPC-mediated vasopressin-induced cation currents in A7r5 smooth muscle cells and caused vasorelaxation of isolated rat aorta, indicating that norgestimate could be an interesting tool for the investigation of TRP channel function in native cells and tissues. The steroid hormone progesterone, which is structurally related to norgestimate, also inhibited TRPC channel activity with IC₅₀s ranging from 6 to 18 µM but showed little subtype selectivity. Thus, TRPC channel inhibition by high gestational levels of progesterone may contribute to the physiological decrease of uterine contractility and immunosuppression during pregnancy.

Cross-talk between rapid and long term effects of progesterone on vascular tissue

We tested the hypothesis whether; the non-genomic action of progesterone (Pg) on vascular tissue would be associated with hormonal long term effect on the modulation of cell growth. Using rat aortic strips, we showed that the stimulatory effect of Pg on nitric oxide synthesis involved both kinase and phosphatase pathways. The increase in the vasoactive production was prevented by the MAPK inhibitor (PD98059). In addition, preincubation with a phosphatase antagonist potentiated the hormonal effect. Pg increased PKC activity, but the inhibition of PKC did not alter the stimulatory action of the hormone on nitric oxide generation. In endothelial cell cultures (EC), 24h treatment with Pg significantly diminished cell proliferation. This antiproliferative effect was suppressed by the PKC inhibitor chelerythrine (chel) and l-NAME (nitric oxide synthase inhibitor). We also observed that Pg stimulates EC migration. In summary, the present findings provide evidence of an integration of genomic and non-genomic effects in the mechanism of action displayed by Pg in vascular tissue. The fast effects elicited by the hormone implies signal transduction activation required for the regulation of vasoactive production, but also necessary for the modulation of endothelial cells growth.

Cutaneous postural vasoconstriction is modified by exogenous but not endogenous female hormones in young women

Previously reported attenuation of skin postural vasoconstriction in women during the luteal menstrual cycle phase may be due to a progesterone-mediated decrease in myogenic or veno-arteriolar (VAR) mechanisms. Skin perfusion was measured in the shin and foot dorsum by Laser Doppler Fluxometry during leg dependency that increased vascular transmural pressure below (myogenic constriction only) and above (myogenic and VAR) the 25 mmHg threshold for activation of the VAR, and during venous distension to activate the VAR alone (cuff inflation to 50 mmHg). In six young women with normal menstrual cycles, vasoconstrictor responses to all interventions did not differ between days 7-13 (follicular) and 18-23 (luteal) of the normal menstrual cycle when progesterone levels were low and at their peak respectively. In eight women taking combined oral contraceptives (OC) and tested during pill consumption days, reductions in foot skin perfusion were smaller (P = 0.05) than in the luteal phase of the normal cycle for leg dependency below (-36.9 +/- 5.2% OC vs. -52.5 +/- 7.8% luteal, mean +/- S.E.M.) and above (-43.7 +/- 3.4% OC vs. -55.1 +/- 4.8% luteal) the VAR threshold, and for venous distension (-53.1 +/- 2.6% OC vs. 66.4 +/- 5.5% luteal). In women with normal menstrual cycles, impaired postural vasoconstriction may be confined to those who experience pre-menstrual symptoms rather than a direct effect of endogenous hormones. Reduced vasoconstriction in the dependent foot during OC use is consistent with the known vasodilator action of exogenous hormones and its long-term effects.

Aqueous extract of Schizandra chinensis fruit causes endothelium-dependent and -independent relaxation of isolated rat thoracic aorta

An aqueous extract of Schizandra chinensis fruit (ScEx) has long been used to promote the vascular health of postmenopausal women in Korea. This study investigated the ability of ScEx to relax rat aorta constricted with norepinephrine (NE) and the mechanism(s) of such relaxation. ScEx induced partial, endothelium-dependent relaxation. In particular, the relaxation induced by lower concentrations of ScEx (0.1 and 0.3 mg/ml) was largely endothelium-dependent, and was essentially abolished by NG-nitro-L-arginine, methylene blue, 1H-[1,2,3] oxadiazole [4,4-a] quinoxalin-1-one, indomethacin, or ICI 182,780. The results indicate that the response to ScEx involves enhancement of the nitric oxide (NO)-cGMP system, and that it occurs via estrogen receptors. The magnitude of the inhibition with these treatments decreased with increasing ScEx concentration, however, indicating that other vasorelaxation mechanisms are involved, which depend on the ScEx concentration. Calcium concentration-dependent contraction curves in high potassium depolarization medium were shifted significantly to the right and downward after incubation with ScEx (0.3 and 1.0 mg/ml), implying that ScEx is also involved in inhibition of the extracellular calcium influx to vascular smooth muscle. These data demonstrate that ScEx caused both endothelium-dependent and -independent vasorelaxation, which may contribute to understanding the cardiovascular protective effect of ScEx.

Hormone therapy and cardiovascular risk markers and disease: focus on progestagens

Biological studies have demonstrated estrogen's beneficial effect on cardiovascular risk factors, including plasma lipoproteins, atherogenesis, vascular reactivity, inflammation and antioxidative activity. Additionally, observational studies have supported a cardioprotective effect of hormone therapy (HT), although an underlying healthy-user effect may account for these observations. Progestagens are added to protect against an increased risk of endometrial cancer observed with unopposed estrogen treatment. The inclusion of progestagen in HT has been associated with possible adverse cardiovascular outcomes. Recent, large-scale, randomized clinical studies did not confirm a beneficial cardiovascular effect of HT. On the contrary, an increased risk was found with continuous combined estrogen-progestagen regimens. The progestagen used in these trials was medroxyprogesterone acetate and other progestagen components have only been sparsely elucidated. The purpose of the present review is to outline some of the modifying effects of different progestagens on the actions of estrogen on cardiovascular risk markers and clinical end points observed in biological, observational and clinical studies.

17-Hydroxyprogesterone caproate reverses induced vasoconstriction of the fetoplacental arteries by the thromboxane mimetic U46619

OBJECTIVE

This study was undertaken to determine whether 17-hydroxyprogesterone caproate (17P) has a vasoactive effect on fetoplacental vasculature.

STUDY DESIGN

Two cotyledons were obtained from each of 5 placentas. Baseline perfusion was established with Hanks-based solution. One cotyledon from each pair was then infused with perfusate to which U46619 a thromboxane sympathomimetic had been added. After 30 minutes, a dose of 17P was then administered to each cotyledon. Finally, a vasoconstricting dose of angiotensin II was administered to each cotyledon. Perfusion pressures were recorded throughout. Statistical analysis of pressure change for a single cotyledon was performed by using a paired t test. Statistical analysis of mean perfusion pressure difference between U46619 exposed and nonexposed cotyledons was analyzed by using a students t test.

RESULTS

17P did not significantly alter the perfusion pressure of the control cotyledon. (30.6 +/- 8.3 mm Hg vs 30.1 +/- 7.8 mm Hg P = .48). 17P administration significantly lowered the perfusion pressure of the U46619 preconstricted vessels in comparison with preadministration. (60.1 +/- 13 mm Hg vs 27.3 +/- 7.1 mm Hg P = .03). Both groups of cotyledons responded with vasoconstriction to angiotension II with no difference in response between groups (38.3 +/- 12 mm Hg vs 45.8 +/- 8.2 mm Hg P = .63).

CONCLUSION

17P reverses induced vasoconstriction by U46619 in fetoplacental arteries.

Aortic function is compromised in a rat model of polycystic ovary syndrome

BACKGROUND

Arterial mechanical parameters are modified in women with polycystic ovary syndrome (PCOS), before and during pregnancy. This study tested the hypothesis that aortic mechanics and endothelial function are modified in the mifepristone-treated rat model of PCOS.

METHODS

Female rats injected daily with mifepristone or vehicle for 7-9 days were assessed by ultrasound to allow estimation of aortic stiffness index and compliance. The influence of acetylcholine (ACh) and sodium nitroprusside (SNP) on dissected phenylephrine-contracted aortic rings was assessed.

RESULTS

Aortic compliance was reduced by 67% in mifepristone-treated rats versus controls (P<0.05), while stiffness index was increased 2.3-fold (P<0.02). ACh-induced dilation was less in aortic rings from mifepristone-treated rats (P=0.022) and was less sensitive to the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) (P<0.001), while SNP-induced dilation was greater (P=0.001).

CONCLUSIONS

Aortic mechanics in vivo and endothelial function in vitro were consistently perturbed in mifepristone-treated rats. Aortic ring behaviour suggested that NO release was depressed or degradation elevated, with a compensatory increase in NO sensitivity and/or activation of a non-NO-mediated relaxation mechanism. The mifepristone-treated rat is a valid model for investigation of the vascular deficits seen in PCOS.

Effect of oral contraceptives on endothelial function in the peripheral microcirculation of healthy women

OBJECTIVES

We assessed whether third-generation oral contraceptive (OC) treatment (30 microg ethinylestradiol + 75 microg gestodene daily) could affect the endothelial function of healthy women.

METHODS

In 20 young healthy women (HW) and 10 hypercholesterolemic women (CW) we assessed forearm blood flow (strain-gauge plethysmography) changes induced by the intrabrachial infusion of acetylcholine (ACH) (0.15-15 microg/100 ml forearm tissue/min) and sodium nitroprusside (SNP) (1-4 microg/100 ml forearm tissue/min). ACH was repeated during the nitric oxide synthase inhibitor intra-arterial NG-monomethyl-L-arginine (L-NMMA) (100 microg/100 ml forearm tissue/min) or the antioxidant vitamin C (8 mg/100 ml forearm tissue/min). HW repeated the protocol after 6-month OC (n = 10) or placebo (n = 10) treatment.

RESULTS

In HW the maximal vasodilation to ACH, similar between placebo and OC subgroups, was significantly reduced in CW (P < 0.01). Vasodilation to ACH was blunted (P < 0.01) by L-NMMA and unaffected by vitamin C, in both OC and placebo groups. In CW the vasodilation to ACH, not modified by L-NMMA, was improved by vitamin C (P < 0.01). OC treatment raised (P < 0.01) plasma total and low-density lipoprotein cholesterol, and values were similar to those shown by CW. Both OC and placebo intake did not change the response to ACH and the modulation induced by L-NMMA or vitamin C. Vasodilation to SNP was similar in all groups.

CONCLUSIONS

In HW 6-month treatment with third-generation OC, although associated with an abnormal lipid profile, does not adversely affect endothelium-dependent vasodilation. This neutral effect could be the balance between a deleterious effect of hypercholesterolemia and a protective effect of OC on endothelial function.

Vasodilating effect of norethisterone and its 5 alpha metabolites: a novel nongenomic action

Estrogens are generally administered in hormone replacement therapy in combination with synthetic progestins. Studies of cardiovascular risk factors in postmenopausal women have shown a variety of responses according to the molecular structure of the progestin used in hormone replacement therapy schemes. The present study sets out to determine the vasoactive effects of norethisterone and its 5alpha-dihydro (5alpha-norethisterone) and -tetrahydro (3alpha,5alpha-norethisterone and 3beta,5alpha-norethisterone) metabolites in isolated precontracted rat thoracic aorta. The addition of norethisterone and 3alpha,5alpha-norethisterone in rat aorta exhibited a potent, concentration-response inhibition of noradrenaline-induced contraction, while 5alpha- and 3beta,5alpha-norethisterone had very little, if any, vasorelaxing effect. Relaxation to norethisterone and 3alpha,5alpha-norethisterone had very rapid time-courses and it was neither affected by the absence of endothelium nor by the inhibitor of nitric oxide synthase, Nomega-nitro-L-arginine methyl ester (L-NAME). The addition of specific anti-androgen, anti-progestin and anti-estrogen compounds and protein synthesis inhibitors did not preclude the vasorelaxing effect of norethisterone and its 3alpha,5alpha-reduced metabolite. The results strongly suggest that these effects are not mediated by nuclear sex steroid hormone receptors. The overall data document a novel nongenomic endothelium-independent vasorelaxing action of a 19-nor synthetic progestin and one of its A-ring-reduced derivatives.

The impact of estrogen and progesterone on asthma

OBJECTIVE

This paper describes evidence of a positive effect of both endogenous and exogenous estrogen and progesterone on lung function across the life span in women.

DATA SOURCES

Articles were identified using the keywords asthma, pulmonary function, menarche, menopause, estrogen, progesterone, hormone replacement therapy, oral contraceptives, and menstrual cycle from years 1966 to 2001 in MEDLINE. Additional studies were identified from article reference lists.

STUDY SELECTION

Relevant, peer-reviewed original research articles in the English language were selected.

RESULTS

Estrogen and/or progesterone may alter pulmonary function and asthma. Premenopausal women experience decreases in pulmonary function and increases in asthma exacerbations and hospitalizations during the premenstrual and menstrual phases. Oral contraceptives and hormone replacement therapy are associated with improved pulmonary function and decrease in asthma exacerbation. Some asthmatic patients experience improved pulmonary function and reduced asthma medication requirement during pregnancy.

CONCLUSIONS

Estrogen and progesterone modify airway responsiveness. Further research is needed to elucidate the clinical relevance of estrogen and progesterone in the pathophysiology and therapy of asthma.

Rapid inhibition of the contraction of rat tail artery by progesterone is mediated by inhibition of calcium currents

Progesterone induced rapid relaxation of KCl-contracted tail artery helical strips from rats. The effect was dose dependent, with an IC50 (inhibitory concentration which produces 50% of the maximal response) of 8.9 microM progesterone. The actions of progesterone were not blocked by bicuculline, indicating that in this tissue the non-genomic actions of progesterone were not mediated via a gamma-aminobutyric acid (GABA)-A receptor. Fura-2 was used to measure intracellular calcium levels ([Ca(2+)](i)) in isolated vascular smooth muscle cells (VSMC). Incubation of cultured VSMC for 15 min with progesterone (10 microM) resulted in an inhibition of the KCl-induced [Ca(2+)](i )increase. The whole-cell patch-clamp technique was used to examine Ca(2+)-channel currents in the membrane of isolated VSMC. Progesterone suppressed the L-type Ca(2+)-channel currents in cells held at a potential of -40 mV. The effects of progesterone were quickly reversed by washout in all three experimental protocols suggesting that these effects on vascular tissues are non-genomic. The correlation of the effects on all these preparations, their time course and reversibility suggested that the rapid relaxation of the rat tail artery induced by progesterone is mediated at least in part by inhibition of L-type calcium channels, leading to inhibition of calcium responses in the VSMC of this tissue.

Rapid effect of progesterone on the contraction of rat aorta in-vitro

Progesterone induced rapid relaxation of KCl-induced contraction of rat aortic rings. The relaxant effect of progesterone on aortic rings was concentration-dependent (over the range of 10(-10) to 10(-5) M) and partially dependent on the endothelium. Application of a nitric oxide (NO) synthase antagonist N(G)-monomethyl-L-arginine (L-NMMA, 10(-5) M) after progesterone treatment partially inhibited the relaxant effects of progesterone. This suggested that part of the effect was through the production of nitric oxide. Washing out the steroid hormone in the bath solutions could quickly reverse the inhibitory effects of progesterone on phasic tension generation in aortic rings. Five minutes after washout, the tension generation in aortic rings was completely restored. Cultured endothelial cells from rat aorta increased release of NO into culture media in response to a 60-min exposure to progesterone. Aldosterone and dexamethasone were also tested, and failed to relax KCl-induced contraction of aortic rings. These data suggest that the vascular effects of progesterone are not mediated by a genomic action of this steroid, and that the vascular effects are mediated partially through endothelial NO production.

Nongenomic action of progesterone in rat aorta: role of nitric oxide and prostaglandins

The mechanism of action of progesterone (Pg) on rat vascular tissue was investigated. We obtained evidence that 10-nM Pg inhibited platelet aggregation at 1-5 min. Previously, we reported that nitric oxide (NO) mediated this antiaggregatory effect. Rat aortic strips (RAS) NO synthase (NOS) activity in response to "in vitro" treatment with other sex steroids hormones was measured. The stimulatory action of Pg on NO production was specific for ovarian hormones and depends on sex. The effect was nongenomic since cycloheximide did not suppress the increment in NO induced by Pg. Finally, we demonstrated that Pg (5 min) increased prostacyclin release (42-182% above control) in a dose-dependent manner (1-100 nM). Indeed, indomethacin (10 microM) completely suppressed the increment in citrulline levels induced by the hormone. These results suggest that Pg exerts a direct nongenomic action on rat aortic metabolism, which involves NOS and cyclooxygenase (COX) activation and a cross-talk between NO- and prostacyclin (PGI(2))-dependent pathways.

Hormone replacement in postmenopausal women: impact of progestogens on autonomic tone and blood pressure regulation

OBJECTIVE

Depressed heart rate variability (HRV) reflects an imbalance of autonomic tone and independently predicts increased cardiovascular risk in patients with congestive heart failure or after acute myocardial infarction. While hormone replacement therapy (HRT) with estrogens beneficially modulates autonomic tone and blood pressure (BP) regulation in postmenopausal women, the impact of concomitant treatment with progestogens remains unclear.

DESIGN

In this cross-sectional study, HRV and BP were examined in 62 healthy women (ages 48-71 years) using digital beat-to-beat interval recordings of heart rate and 24-hour ambulatory BP measurements.

RESULTS

Demographic parameters did not differ among women without HRT (n = 23), on estrogen (n = 17; ERT), or on progestogen-estrogen containing HRT (n = 22; PERT). Total power of HRV was significantly lower, whereas mean heart rate (HR) was significantly higher among women on PERT group versus controls and ERT (total power: 1611 +/- 146 vs. 2497 +/- 308 and 2472 +/- 348 ms(2); heart rate: 80.7 +/- 1.2 vs. 75.0 +/- 1.4 and 74.0 +/- 2.2 bpm; p < 0.05). In addition, low-frequency power and time-dependent parameters of HRV were lower among women on PERT group versus controls and ERT (p < 0.05). ERT use was associated with reduced systolic and diastolic daytime BP, whereas no significant differences were evident PERT users compared with controls.

CONCLUSIONS

Progestogen-containing replacement therapy was associated with increased HR and an attenuation of HRV in postmenopausal women. BP was lower in women on ERT, whereas this effect was offset in the PERT group. These observations could at least partially explain the ambiguous results of progestogen-containing HRT on cardiovascular risk in the Heart and Estrogen/Progestin Replacement Study (HERS).

Women exhibit a greater age-related increase in proximal aortic stiffness than men

BACKGROUND

Large artery mechanical properties are a major determinant of pulse pressure and cardiovascular outcome. Sex differences in these properties may underlie the variation in cardiovascular risk profile between men and women, in relation to age.

OBJECTIVE

To investigate sex differences in the age-related stiffening of large arteries.

DESIGN

Cross-sectional.

METHODS

One hundred and twenty healthy men and women were recruited and divided equally into tertiles by age: young (mean +/- SD, 23 +/- 5 years), middle-age (47 +/- 3 years) and older (62 +/- 7 years). Lipids, mean arterial pressure and heart rate were matched within each tertile. Carotid tonometry and Doppler velocimetry were used to measure indices of large artery stiffness.

RESULTS

There was no sex difference in systemic arterial compliance (SAC) in the young group (mean +/- SEM, 0.61 +/- 0.05 arbitrary compliance units (ACU) in women compared with 0.67 +/- 0.04 ACU in men), but in the older population women had lower SAC than men (0.27 +/- 0.03 ACU compared with 0.57 +/- 0.04 ACU respectively; P < 0.001). Measures independent of aortic geometry (distensibility index and aortic impedance) indicated that stiffness was lower in young women than in men (P < 0.05), but the reverse was true in the older population (P < 0.01). This paralleled the brachial and carotid pulse pressures, which were lower in young (P < 0.01) and higher in older women compared with those in men (P < 0.05). Follicle stimulating hormone concentrations correlated strongly (r values 0.39-0.65) with all indices of central, but not peripheral, arterial function, whereas concentrations of luteinizing hormone, progesterone and oestradiol correlated less strongly.

CONCLUSIONS

In men and women matched for mean pressures, the age-related stiffening of large arteries is more pronounced in women, which is consistent with changes in female hormonal status.

Effect of progesterone on the contractile response of isolated pulmonary artery in rabbits

The purpose of this study was to assess the direct effect of progesterone on rabbit pulmonary arteries and to examine the mechanism of its action. Rings of pulmonary artery from male rabbits were suspended in organ baths containing Krebs solution, and isometric tension was measured. The response to progesterone was investigated in arterial rings contracted with noradrenaline (NA), KCl, and CaCl2. The effects of endothelium, nitric oxide(NO), prostaglandins, cyclic GMP(cGMP), and the adrenergic β-receptor on progesterone-induced relaxation were also assessed. Progesterone inhibited the vasocontractivity to NA, KCl, and CaCl2, and relaxed rabbit pulmonary artery. The relaxing response of progesterone in pulmonary artery was significantly reduced by removal of endothelium, inhibitors of nitric oxide synthase and guanylate cyclase, but not by prostaglandin synthase inhibitor and blockage of the adrenergic β-receptor. In Ca2+-free (0.1 mM EGTA) Krebs solution, progesterone inhibited NA-induced contraction that was intracellular Ca2+-dependent, but didn't affect the contraction of extracellular Ca2+-dependent component. Our results suggest that progesterone induces relaxation of isolated rabbit pulmonary arteries partially via NO and cGMP. Progesterone may also inhibit Ca2+ influx through potential-dependent calcium channels (PDCs) and Ca2+ release from intracellular stores.Key words: progesterone, pulmonary artery, Ca2+ channel, endothelium.

Temporal changes in cardiac function and cerebral blood flow during sequential postmenopausal hormone replacement

OBJECTIVE

The purpose was to assess the temporal changes in cardiac function and cerebral blood flow during postmenopausal administration of estrogen with and without progestogen.

STUDY DESIGN

Sixteen postmenopausal volunteers were assessed during estradiol plus sequential norethindrone acetate and placebo in two 12-week periods. Temporal changes were measured by magnetic resonance flow mapping 8 times.

RESULTS

Systemic vascular resistance was reduced during estradiol (-6.9%; P <.05), declined further during the addition of norethindrone acetate, and was accompanied by an increase in stroke volume (maximum increase, 5.2%; P <.05) without fluid retention. Both systolic (-5 mm Hg; P =.03) and diastolic (-3 mm Hg; P =.03) blood pressure were reduced during estradiol. Cerebral blood flow was reduced after 9 weeks of hormone replacement therapy (-37 mL/min; P =.01) but increased to baseline after the addition of norethindrone acetate.

CONCLUSIONS

Sequential hormone replacement therapy is associated with changes in cardiac function, which are of therapeutic potential in cardiovascular disorders. Sequential hormone replacement therapy exhibits an overall neutral effect on cerebral blood flow.

Differential effects of progesterone and 17beta-estradiol on the Ca(2+) entry induced by thapsigargin and endothelin-1 in in situ endothelial cells

The effects of progesterone and 17beta-estradiol on Ca(2+) signaling in in situ endothelial cells were investigated using front-surface fluorometry of fura-2-loaded strips of porcine aortic valve. Progesterone inhibited the thapsigargin-induced sustained [Ca(2+)](i) elevation (IC(50)=33.9 microM, n=4), while 17beta-estradiol added a transient [Ca(2+)](i) elevation. Progesterone and 17beta-estradiol had no significant effect on the thapsigargin-induced [Ca(2+)](i) elevations in the absence of extracellular Ca(2+). A Mn(2+)-induced decline of fluorescent intensity at 360 nm excitation was accelerated by thapsigargin. This acceleration was completely reversed by progesterone, but not by 17beta-estradiol. Progesterone inhibited, and 17beta-estradiol enhanced the endothelin-1 (ET-1)-induced [Ca(2+)](i) elevation, while both had no effect on the ET-1-induced Ca(2+) release observed in the absence of extracellular Ca(2+) or in the pertussis toxin-treated strips. Progesterone and 17beta-estradiol thus had different effects on Ca(2+) signaling, especially on Ca(2+) influx, in endothelial cells.

Temporal changes in clinic and ambulatory blood pressure during cyclic post-menopausal hormone replacement therapy

OBJECTIVE

Post-menopausal hormone replacement (HRT) might protect against cardiovascular disease, possibly by arterial vasodilation and reduced blood pressure. Progestogens are needed to avoid endometrial disease but vascular effects are controversial. The objective was to assess temporal changes in blood pressure (BP) by two measurement techniques during a cyclic hormone replacement regimen.

DESIGN AND METHODS

Sixteen healthy and normotensive post-menopausal women (age 55 +/- 3 years) were studied in a placebo-controlled, randomized crossover study, and were randomized to 17beta-oestradiol plus cyclic norethisterone acetate (NETA) or placebo in two 12-week periods separated by a 3-month washout Clinic blood pressure was measured sitting by the same observer with a mercury manometer at four visits in each period. Twenty-four hour ambulatory blood pressure was measured at baseline and in the ninth weeks of treatment in both periods.

RESULTS

Clinic systolic and diastolic BP were reduced after 10 days of oestradiol (-5.1 and -3.2 mmHg respectively, P < or = 0.05). After 9 weeks of cyclic HRT, prior to progestogen addition, clinic BP returned to baseline. During addition of NETA, diastolic blood pressure was again reduced (-3.6 mmHg, P= 0.037). Mean 24 h ambulatory systolic and diastolic blood pressures were significantly lower than clinic measurements (-15.7 and -5.9 mmHg, P < 0.001) but were unaffected by HRT.

CONCLUSIONS

Clinic blood pressure is reduced during a cyclic HRT regimen but the reduction varies with the HRT regimen, which might explain the diversity in previous BP findings during HRT. Norethisterone acetate might possess additive blood pressure-lowering effects in postmenopausal women.

The progestin levonorgestrel induces endothelium-independent relaxation of rabbit jugular vein via inhibition of calcium entry and protein kinase C: role of cyclic AMP

The progestin and oestrogen component of oral contraceptives have been involved in the development of venous thromboembolic events in women. In the present study we determined the vasoactive effects of sex steroids used in oral contraceptives in isolated preconstricted rabbit jugular veins in the presence of diclofenac and examined the underlying mechanisms. The natural hormone progesterone, the synthetic progestins levonorgestrel, 3-keto-desogestrel, gestodene and chlormadinone acetate, and the synthetic estrogen 17 alpha-ethinyloestradiol induced concentration-dependent relaxations of endothelium-intact veins constricted with U46619. Levonorgestrel also inhibited constrictions evoked by either a high potassium (K(+)) solution or phorbol myristate acetate (PMA) in the absence and presence of extracellular calcium (Ca(2+)). In addition, levonorgestrel depressed contractions evoked by Ca(2+) and reduced (45)Ca(2+) influx in depolarized veins. Relaxations to levonorgestrel in U46619-constricted veins were neither affected by the presence of the endothelium nor by the inhibitor of soluble guanylyl cyclase, NS2028, but were significantly improved either by the selective cyclic AMP phosphodiesterase inhibitor rolipram or in the absence of diclofenac, and decreased by the protein kinase A inhibitor, Rp-8-CPT-cAMPS. Rolipram also potentiated relaxations to levonorgestrel in PMA-constricted veins in the presence, but not in the absence of extracellular Ca(2+). Levonorgestrel increased levels of cyclic AMP and inhibited PMA-induced activation of protein kinase C in veins. These findings indicate that levonorgestrel caused endothelium-independent relaxations of jugular veins via inhibition of Ca(2+) entry and of protein kinase C activation. In addition, the cyclic AMP effector pathway contributes to the levonorgestrel-induced relaxation possibly by depressing Ca(2+) entry.

The effects of potassium channel blockers on progesterone-induced suppression of rat portal vein contractility

The suppression of contractility of rat portal vein caused by progesterone appears to be due to the potassium (K+) channel opening effect of this hormone. The identity of the specific K+ channels involved has been investigated using a variety of K+ channel blockers. Incubation with 100 nM iberiotoxin antagonised the progesterone-induced inhibition of spontaneous and 20 mM K+-induced phasic activity of the portal vein such that the contractions resembled those of the non-progesterone, non-iberiotoxin control tissues treated with the corresponding solvent vehicles. Incubation with barium chloride (20 and 100 microM), 4-aminopyridine (1 mM), tetraethylammonium chloride (1 mM), glibenclamide (1 microM) or apamin (1 microM) did not, however, have the same antagonistic effect. These results suggest that progesterone's selective suppression of rat portal vein contractility is mediated by the opening of BKCa channels.

The effect of progesterone on spontaneous and agonist-evoked contractions of the rat aorta and portal vein

The mechanisms underlying the suppression of vasocontractility caused by progesterone were investigated by studying changes in the contractile force of rat isolated aorta and portal vein, induced by altering extracellular concentrations of noradrenaline (NA) potassium ions (K+) and calcium ions (Ca2+). In the aorta, progesterone (10 microM) had a general suppressive effect on NA-, Ca2+- and K+-induced contractions. In contrast, in the portal vein a more selective suppression of contractions was observed. Both tonic and phasic components of contractions induced by cumulative addition of Ca2+ to tissues equilibrated in Ca2+-free saline were suppressed. The phasic but not tonic components of contractions induced by NA addition were suppressed. There was no significant effect on tonic contractions induced by elevated (40-120 mM) K+, but a concentration-dependent suppression of the phasic component of contractions was observed during depolarisation with smaller elevations of K+ concentrations (5-20 mM). These results suggest that on the portal vein the suppressive effect of progesterone is due to a potassium channel opening action, whilst on the aorta a different or additional mechanism of suppression exists.

Progesterone modulates estradiol actions: acute effects at physiological concentrations

The progestin element of hormone replacement therapy may reduce the cardioprotective actions of the estrogen component. Only high concentrations (microM) of progesterone directly relaxed U46619 (9,11-dideoxy-9alpha, 11alpha-methanoepoxy prostaglandin F2alpha)-pre-contracted porcine coronary artery rings. A low concentration of progesterone (1 nM), with no effects of its own, shifted the relaxation curves of bradykinin and calcium ionophore A23187 to the right while not affecting those of sodium nitroprusside and levcromakalim. The negative influence that 1 nM progesterone exerted on bradykinin- and A23187-mediated relaxation was diminished when 1 nM 17beta-estradiol was concomitantly added to the bathing medium. Conversely, the potentiating actions of 1 nM 17beta-estradiol on relaxations elicited by sodium nitroprusside and levcromakalim were reduced following simultaneous treatment with the same concentrations of progesterone. These findings represent the first evidence for an acute in vitro vascular effect of progesterone at a physiologically relevant concentration and concur with previous in vivo reports demonstrating that progesterone may diminish the beneficial effects of estrogens.