Administration of transdermal estrogen without progestin increases the capacity of plasma and serum to stimulate prostacyclin production in human vascular endothelial cells

Differential effects of oral and transdermal menopausal hormone therapy on prostacyclin and thromboxane in platelets

Abstract Menopausal hormone therapies (MHT) may increase thrombotic risk but modulate endothelial function and reduce development of vascular lesions. This study compared effects of MHT on prostanoid-modulated adenosine triphosphate (ATP) secretion from platelets in relationship with endothelial reactive hyperemia (RH) index and carotid intima medial thickness (CIMT). Participants were healthy, recently menopausal women of the Kronos Early Estrogen Prevention Study (KEEPS) randomized to one of three treatments: oral conjugated equine estrogen (oCEE, 0.45 mg/day), transdermal 17β-estradiol (tE2, 50 μg/day) each with intermittent oral progesterone or placebo pills and patch (PL). Prostacyclin and thromboxane A2 were assessed by quantification of their stable metabolites (6-keto-prostaglandin F1α, 6-k-PGF1α; thromboxane B2, TXB2), using ELISA. Dense granule ATP secretion from activated platelets was determined by bioluminescence; RH and CIMT were determined by fingertip tonometry and ultrasound, respectively. After 48 months of treatment, platelet content of 6-k-PGF1α and TXB2 was significantly lower in oCEE compared to the PL. Inhibition of ATP secretion by exogenous activation of cAMP associated with platelet 6-k-PGF1α (r = -0.41, P = 0.04) and TXB2 (r = 0.71, P = 0.0005) only in the oCEE group. Serum and platelet content of 6-k-PGF1α and TXB2 associated positively in the PL and tE2 groups. Serum 6-k-PGF1α positively associated with RH in the oCEE group (r = 0.73, P = 0.02), while serum TXB2 positively associated with CIMT in the tE2 group (r = 0.64, P = 0.01). Thus, oCEE and tE2 differentially affect prostanoid-mediated platelet secretory pathways but alone would not account for an increased thrombotic risk for oral MHT. Furthermore, platelet-derived prostanoids may contribute to RH and vascular remodeling in healthy menopausal women.

Endothelial function across an oral contraceptive cycle in women using levonorgestrel and ethinyl estradiol

Oral contraceptive pills (OCPs) are a popular contraception method. Currently, lower-dose ethinyl estradiol formulations are most commonly prescribed, although they have been linked to increased arterial vascular risk. The aim of this study was to investigate endothelial function in healthy young women using lower-dose ethinyl estradiol OCPs. We examined flow-mediated, endothelium-dependent and nitroglycerin-mediated, endothelium-independent vasodilation of the brachial artery, comparing two doses of ethinyl estradiol/levonorgestrel OCPs in 15 healthy young women on two study days: once during the active phase and once during the placebo phase of an OCP cycle. Group low dose (LD) ( n = 7) active pills contained 150 μg levonorgestrel/30 μg ethinyl estradiol versus Group very low dose (VLD) ( n = 8) with 100 μg levonorgestrel/20 μg ethinyl estradiol. Endothelium-dependent vasodilation was lower during the active phase in Group VLD (5.33 ± 1.77% vs. 7.23 ± 2.60%; P = 0.024). This phase difference was not observed in Group LD (8.00 ± 0.970% vs. 7.61 ± 1.07%; P = 0.647). Endothelium-independent vasodilation did not differ between phases in either group. Finally, we measured endothelium-dependent vasodilation in two additional women who received 10 μg of unopposed ethinyl estradiol. Endothelium-dependent vasodilation was increased by unopposed ethinyl estradiol compared with the placebo phase (10.88 ± 2.34% vs. 6.97 ± 1.83%). These results suggest that levonorgestrel may antagonize the activity of ethinyl estradiol. Thus both the progestin type and estradiol dose need to be considered when assessing arterial vascular risk of OCP use in women.

Novel aspects of endothelium-dependent regulation of vascular tone

The vascular endothelium plays a crucial role in the regulation of vascular homeostasis and in preventing the initiation and progress of cardiovascular disease by controlling mechanical functions of the underlying vascular smooth muscle. Three vasodilators: nitric oxide (NO), prostacyclin, and endothelium-derived hyperpolarizing factor, produced by the endothelium, underlie this activity. These substances act in a co-ordinated interactive manner to maintain normal endothelial function and operate as support mechanisms when one pathway malfunctions. In this review, we discuss recent advances in our understanding of how gender influences the interaction of these factors resulting in the vascular protective effects seen in pre-menopausal women. We also discuss how endothelial NO synthase (NOS) can act in both a pro- and anti-inflammatory action and therefore is likely to be pivotal in the initiation and time course of an inflammatory response, particularly with respect to inflammatory cardiovascular disorders. Finally, we review recent evidence demonstrating that it is not solely NOS-derived NO that mediates many of the beneficial effects of the endothelium, in particular, nitrite acts as a store of NO released during pathological episodes associated with NOS inactivity (ischemia/hypoxia). Each of these more recent findings has emphasized new pathways involved in endothelial biology, and following further research and understanding of the significance and mechanisms of these systems, it is likely that new and improved treatments for cardiovascular disease will result.

Estrogen and hypertension

Menopause is accompanied by a dramatic rise in the prevalence of hypertension in women, suggesting a protective role of endogenous estradiol on blood pressure (BP). Both animal experimental and human clinical investigations suggest that estrogen engages several mechanisms that protect against hypertension, such as activation of the vasodilator pathway mediated by nitric oxide and prostacyclin and inhibition of the vasoconstrictor pathway mediated by the sympathetic nervous system and angiotensin. However, emerging evidence from recent clinical trials indicates a small increase, rather than decrease, in systolic BP with oral estrogen administration in postmenopausal women, without any detectable effect on diastolic BP. Mechanisms underlying this selective rise in systolic BP in postmenopausal women and oral contraceptive-induced hypertension in premenopausal women remain unknown, but the rise may be related to supraphysiologic concentration of estrogen in the liver. To date, transdermal delivery of estrogen, which avoids the first-pass hepatic metabolism of estradiol, appears to have a small BP-lowering effect in postmenopausal women and may be a safer alternative in hypertensive women.

Pharmacology of estrogens and progestogens: influence of different routes of administration

This review comprises the pharmacokinetics and pharmacodynamics of natural and synthetic estrogens and progestogens used in contraception and therapy, with special consideration of hormone replacement therapy. The paper describes the mechanisms of action, the relation between structure and hormonal activity, differences in hormonal pattern and potency, peculiarities in the properties of certain steroids, tissue-specific effects, and the metabolism of the available estrogens and progestogens. The influence of the route of administration on pharmacokinetics, hormonal activity and metabolism is presented, and the effects of oral and transdermal treatment with estrogens on tissues, clinical and serum parameters are compared. The effects of oral, transdermal (patch and gel), intranasal, sublingual, buccal, vaginal, subcutaneous and intramuscular administration of estrogens, as well as of oral, vaginal, transdermal, intranasal, buccal, intramuscular and intrauterine application of progestogens are discussed. The various types of progestogens, their receptor interaction, hormonal pattern and the hormonal activity of certain metabolites are described in detail. The structural formulae, serum concentrations, binding affinities to steroid receptors and serum binding globulins, and the relative potencies of the available estrogens and progestins are presented. Differences in the tissue-specific effects of the various compounds and regimens and their potential implications with the risks and benefits of hormone replacement therapy are discussed.

Progestogens stimulate prostacyclin production by human endothelial cells

BACKGROUND

The effects of progestogens on endothelial physiology are poorly studied. Prostacyclin is a potent vasodilator synthesized by two isoforms of cyclooxygenase (COX) in endothelium. We examined the effects of two clinically used progestogens, progesterone and medroxyprogesterone acetate (MPA), on prostacyclin production by cultured human umbilical vein endothelial cells (HUVEC) and the possible role of progesterone receptors and both COX enzymes.

METHODS

Cells were exposed to 1-100 nmol/l of either progesterone or MPA and prostacyclin production was measured in culture medium.

RESULTS

Both progestogens significantly increased prostacyclin release in a time- and dose-dependent manner, being higher than control after 24 h. Progesterone and MPA, both at 10 nmol/l, increased mRNA expression and protein content of both COX. All these effects were mediated through progesterone receptor activation, since they were abolished by treatment of cells with the progesterone receptor antagonist RU-486. Selective inhibitors of COX-1 and -2 (SC-560 and NS-398 respectively) reduced basal prostacyclin release, and eliminated increased production in response to progestogens. In combination with estradiol, progestogens had an additive effect without eliminating estradiol-induced prostacyclin production.

CONCLUSIONS

Our results support the hypothesis that progesterone and MPA increased HUVEC prostacyclin production in a progesterone receptor-dependent manner, by enhancing COX-1 and COX-2 expression and activities.

Raloxifene increases the capacity of serum to promote prostacyclin release in human endothelial cells: implication of COX-1 and COX-2

OBJECTIVE

Prostacyclin is a potent vasodilator synthesized by two isoforms of cyclooxygenase in endothelium. The aim of this study was to investigate the effect of serum from postmenopausal women treated with raloxifene on prostacyclin production by human umbilical vein endothelial cells and on cyclooxygenases-1 and -2.

DESIGN

Serum was collected from 21 women receiving 60 mg/day of raloxifene, at baseline and at 3 and 6 months. Human umbilical vein endothelial cells were exposed to serum for 24 hours, and prostacyclin production was evaluated in supernatants. Selective inhibitors of cyclooxygenases-1 and -2 (SC-560 and NS-398) were used to investigate the relative contribution of each enzyme. Protein expression for each enzyme was determined using Western blot assays.

RESULTS

Prostacyclin production was increased by 30% (P < or = 0.001) when serum from women treated for 3 and 6 months was added. SC-560 reversed prostacyclin production but did not change baseline values. NS-398, in turn, reduced prostacyclin production using sera from baseline, 3 and 6 months. Cyclooxygenases-1 and -2 protein expression remained unaltered at each treatment step.

CONCLUSIONS

Serum from women treated with raloxifene stimulated prostacyclin release from human umbilical vein endothelial cells in culture, an effect that seems mediated by increased cyclooxygenase-1 activity.

Gender, sex hormones, and vascular tone

The greater incidence of hypertension and coronary artery disease in men and postmenopausal women compared with premenopausal women has been related, in part, to gender differences in vascular tone and possible vascular protective effects of the female sex hormones estrogen and progesterone. However, vascular effects of the male sex hormone testosterone have also been suggested. Estrogen, progesterone, and testosterone receptors have been identified in blood vessels of human and other mammals and have been localized in the plasmalemma, cytosol, and nuclear compartments of various vascular cells, including the endothelium and the smooth muscle. The interaction of sex hormones with cytosolic/nuclear receptors triggers long-term genomic effects that could stimulate endothelial cell growth while inhibiting smooth muscle proliferation. Activation of plasmalemmal sex hormone receptors may trigger acute nongenomic responses that could stimulate endothelium-dependent mechanisms of vascular relaxation such as the nitric oxide-cGMP, prostacyclin-cAMP, and hyperpolarization pathways. Additional endothelium-independent effects of sex hormones may involve inhibition of the signaling mechanisms of vascular smooth muscle contraction such as intracellular Ca2+ concentration and protein kinase C. The sex hormone-induced stimulation of the endothelium-dependent mechanisms of vascular relaxation and inhibition of the mechanisms of vascular smooth muscle contraction may contribute to the gender differences in vascular tone and may represent potential beneficial vascular effects of hormone replacement therapy during natural and surgically induced deficiencies of gonadal hormones.

Effect of puberty on coronary arteries from female pigs

Vascular function changes following loss of ovarian hormones in women at menopause and in experimental animals following surgical ovariectomy. Little is known about changes in vascular function during hormonal transition from sexual immaturity (juvenile) to sexual maturity. Therefore, experiments were designed to determine effects of natural puberty on vascular function in female pigs. Tissue was studied from eight juvenile (2-3 mo) and eight adult (5-6 mo) female pigs. Plasma nitric oxide (NO) was measured, and mRNA for endothelium-derived NO synthase (eNOS) and eNOS protein were determined in aortic endothelial cells. Rings of coronary arteries were suspended for measurement of isometric force in organ chambers. Serum 17beta-estradiol levels were comparable in the two groups, whereas the arithmetic mean of progesterone levels was about two-thirds lower in adults compared with juvenile pigs. Plasma NO was significantly higher in juveniles compared with adults, but mRNA and protein for eNOS were comparable. In coronary arteries, an alpha2-adrenergic agonist caused greater endothelium-dependent relaxations in rings from juvenile compared with adult pigs. Relaxations to bradykinin were similar in arteries from both groups, but inhibition of NO reduced relaxations only in arteries from juvenile pigs. Relaxations from NO were greater in arteries from adult compared with juvenile female pigs. In conclusion, coronary arterial endothelial and smooth muscle responses are selectively modulated at puberty in female pigs. At maturity, plasma NO is reduced and sensitivity of the smooth muscle to exogenous NO is increased. Posttranscriptional regulation of eNOS protein may explain differences in NO bioavailability in juvenile pigs.

Changes in proinflammatory cytokine activity after menopause

There is now a large body of evidence suggesting that the decline in ovarian function with menopause is associated with spontaneous increases in proinflammatory cytokines. The cytokines that have obtained the most attention are IL-1, IL-6, and TNF-alpha. The exact mechanisms by which estrogen interferes with cytokine activity are still incompletely known but may potentially include interactions of the ER with other transcription factors, modulation of nitric oxide activity, antioxidative effects, plasma membrane actions, and changes in immune cell function. Experimental and clinical studies strongly support a link between the increased state of proinflammatory cytokine activity and postmenopausal bone loss. Preliminary evidence suggests that these changes also might be relevant to vascular homeostasis and the development of atherosclerosis. Better knowledge of the mechanisms and the time course of these interactions may open new avenues for the prevention and treatment of some of the most prevalent and important disorders in postmenopausal women.

Hormone replacement therapy at the threshold of 21st century

The management of postmenopausal women has become a major focus for the medical profession. The menopause era should progress from a period of "chaos" to an orderly understanding of the many issues related to the menopause and hormone replacement therapy (HRT). Although HRT has beneficial clinical effect and positive benefit/risk ratio, understanding of the side effects and weight gain, and, especially, a fear of cancer limit compliance. New data from long-term, controlled, prospective studies on the effects of different HRT schedules on cancer, cardiovascular disease and osteoporotic fracture risk are needed. HRT should be considered either as for prevention or for individualized care since women experience menopause as individuals, care should be taken not to make inappropriate generalizations. The priority should be the administration of appropriate medication to women with the best result in order to improve health care and quality of life. New therapeutic options will offer substantial medical advancement for the treatment of postmenopausal women.

Estrogen and cerebrovascular physiology and pathophysiology

Numerous studies have uncovered a wide variety of estrogen effects with apparent cardiovascular benefits, the most recognized ones being vasodilation, anti-atherogenesis, diminished post-ischemic inflammation and anti-oxidant effects. This article provides an overview of the influence of estrogen on the cerebral vasculature, under physiologic and pathophysiologic conditions, and covers both acute and chronic effects. The discussion is primarily focused on the vasodilatory and anti-inflammatory actions of estrogen, since those particular estrogen influences have received the greatest attention in studies published to date. With respect to vasodilation, although some consideration is given to the role of other vasodilating mechanisms and factors, the emphasis is mostly placed on the endothelial isoform of nitric oxide synthase, eNOS, which has emerged as a clear target of estrogen. Some consideration is given to recent findings that suggest that estrogen can stimulate eNOS activity by decreasing the expression of the eNOS inhibitor caveolin-1. With regard to the ability of estrogen to counteract inflammation, potential mechanisms by which estrogen limits the post-ischemic leukocyte adhesion, and the expression of the inducible NOS, are discussed.