17β-Estradioi and Endotheilal Nitric Oxide Synthase

Impaired cardiac response to exercise in post-menopausal women: relationship with peripheral vascular function

Endothelial dysfunction has been demonstrated in post-menopausal women. To assess the relationship between peripheral vascular reserve and cardiac function during exercise in post-menopausal women, 91 subjects, who had no ischaemic findings on myocardial SPECT, were assigned to four groups: pre-menopausal women (n=13), post-menopausal women (n=33), younger men aged < or =50 years (n=10), and older men aged >50 years (n=35). First-pass radionuclide angiography was performed before and during bicycle exercise to calculate ejection fraction (EF) and peripheral vascular resistance (VR). There were no differences in haemodynamic variables among the groups at baseline. The per cent increase in EF=(exercise EF - resting EF)x100/resting EF, and the per cent decrease in VR=(resting VR - exercise VR)x100/resting VR were depressed in the post-menopausal women (0.4+/-2% and 35+/-3%, respectively) compared to the pre-menopausal women (10+/-3% and 47+/-3%, respectively; P<0.05 each). Although the age dependent impairment is thought to cause this depression, neither the per cent increase in EF nor the per cent decrease in VR in the older men was significantly different from that in the younger men. Post-menopausal women exhibited depressed cardiac function during exercise, which may be related to the impairment of peripheral vascular function after menopause.

Effect of estrogen on endothelial function and angiogenesis

Animal studies evaluating gender difference, the effects of gonadectomy and estrogen replacement and clinical studies in post-menopausal women with and without estrogen replacement therapy (ERT) proved that estrogen exerts significant benefits on the cardiovascular system. Since effects on the plasma lipoprotein profile is responsible for only approximately 25-40% of the cardiovascular protection exerted by estrogens, it is postulated that direct effects of estrogen on the vascular wall must play an important role. Indeed, experimental and clinical evidence accumulated over the past decade, and reviewed briefly here, indicate that at least a part of cardiovascular benefits of 17 beta-estradiol can be attributed to the direct effect of the ovarian sex steroid hormone on vascular endothelial cells. Maintenance and upregulation of endothelial nitric oxide production and suppression of EDCF generation by 17 beta-estradiol may play an important role in preventing or reversing endothelial dysfunction, associated with atherosclerosis, hypertension and other cardiovascular diseases. Stimulation of angiogenesis (especially collateral vessel formation in ischemic tissues) by the ovarian steroid hormone could be beneficial in coronary artery disease, peripheral vascular disease, cerebral ischemia (stroke) and congestive heart failure. Despite these indisputable beneficial effects, several key questions remain to be answered in the future, including the better understanding of the apparently opposite effects of estrogen on prevention of cardiovascular disease vs. treatment of existing disease.

Effect of two oral contraceptives with different ethinyl estradiol and levonorgestrel concentrations on the urinary excretion of biochemical vasoactive markers

In the present study the effect on the urinary excretion of vasoactive markers of two oral contraceptives (OCs), i.e., Leios, containing 0.02 mg ethinyl estradiol and 0.1 mg levonorgestrel, and Stediril 30, containing 0.03 mg ethinyl estradiol and 0.15 mg levonorgestrel, was investigated. cGMP, prostacyclin and its antagonist thromboxane, serotonin, and urodilatin, a natriuretic and diuretic peptide formed in the kidney, were measured as markers. In a comparative, double-blind, randomized, parallel group study, 34 women received Leios and 33 women Stediril 30. Nocturnal urine was collected before treatment and during cyclic treatment after 3 and 12 cycles. Both contraceptives significantly enhanced cGMP excretion after 12 cycles. The prostacyclin metabolite remained unchanged for both formulations, but the excretion of the thromboxane metabolite was significantly decreased after 12 cycles. Thus, the ratio of prostacyclin to thromboxane, crucial for the resulting effect on vascular tone, increased significantly. For the serotonin metabolite, no changes were observed for both contraceptives. The excretion of urodilatin significantly increased for both preparations after 12 cycles compared to the pretreatment values. These results indicate that the low-dose OCs Leios and Stediril 30 may stimulate the production of some vasoactive markers, at least after 12 cycles of treatment. The positive influence of these contraceptives on the various markers investigated may improve vascular tone, impede development of atherosclerosis and arterial thrombosis, and improve water and electrolyte homeostasis. These effects most likely can be attributed to the estrogenic component. Levonorgestrel may elicit no impact on these estrogen-induced changes that, however, seem only to be manifested after a longer treatment period.

Effect of oral contraceptives on the urinary excretion of biochemical markers indicating vasoactive action

OBJECTIVE

In the present study the effect of two contraceptive pills, i.e. Neorlest, containing ethinylestradiol and norethisterone acetate, and Valette, containing ethinylestradiol and the new progestin dienogest, was investigated on the urinary excretion of vasoactive markers. As markers prostacyclin and its antagonist thromboxane, cGMP, serotonin, and the vasorelaxing mediators relaxin and urodilatin were measured.

METHOD

30 women received Neorlest and 33 women Valette in a randomized, open, parallel-group study design. Nocturnal urine was collected before treatment and during cyclic treatment after 6 and 11 weeks.

RESULTS

For prostacyclin, the ratio of prostacyclin to thromboxane, relaxin and urodilatin significant increases compared to the pretreatment values were observed with Valette within 11 weeks treatment. For the markers cGMP and serotonin both contraceptive pills showed a tendency to an increase of the renal excretion after 11 weeks treatment. No significant differences between the two pills were observed, except in the case of the ratio of prostacyclin to thromboxane, which showed a significant, clear-cut enhancement with Valette.

CONCLUSION

These results indicate that contraceptive pills may stimulate the production of vasodilative markers, an effect which can be attributed most likely to the oestrogenic component of the pill. The progestogenic component of the pill may elicit an impact on this oestrogen-induced vasodilation, which, however, seems to be minimized in the case of the new compound dienogest, a C-19 progestin with antiandrogenic properties.

17beta-estradiol restores endothelial nitric oxide release to shear stress in arterioles of male hypertensive rats

BACKGROUND

Endothelial nitric oxide (NO)-mediated responses are impaired in arterioles of male spontaneously hypertensive rats (SHR), but they are still present in female SHR. We hypothesized that in vitro incubation of arterioles of male SHR with estrogen will restore NO-mediated responses by upregulation of endothelial NO synthase.

METHODS AND RESULTS

Responses to increases in perfusate flow (from 0 to 25 microL/min) and to the calcium ionophore A23187 (5 x 10(-8) to 10(-6) mol/L), norepinephrine (NE; 10(-7) to 3 x 10(-7) mol/L), sodium nitroprusside (SNP; 10(-8) to 10(-6) mol/L), and adenosine (ADO; 10(-6) to 5 x 10(-5) mol/L) were studied in cannulated and pressurized gracilis muscle arterioles ( approximately 75 microm in diameter) isolated from 12-week-old male SHR before and after incubation with 10(-9) mol/L 17beta-estradiol (17beta-E(2)) for 16 to 18 hours. After incubation with 17beta-E(2), basal diameter of arterioles was significantly increased (by approximately 10%), and flow-induced dilation was significantly enhanced (79.8+/-2.9 versus 103.7+/-3.7 microm at 25 microL/min), resulting in a lowered shear stress (62.0+/-9.1 versus 32.5+/-4.2 dyne/cm(2)). Also, vasoconstrictions to A23187 were reversed to dilations (-18.7+/-2.2 versus 18.8+/-1.7 microm), and constrictions to NE were significantly attenuated (-30.7+/-3.0 versus -21.2+/-2.8 microm). These alterations were eliminated by ICI 182,780 (10(-7) mol/L), an estrogen receptor antagonist; 5, 6-dichloro-1-beta-D-ribofuranosylbenzimidazole (10(-5) mol/L), a transcription inhibitor; or N(omega)-nitro-L-arginine methyl ester (10(-4) mol/L), an inhibitor of NO synthase, whereas they were not affected by aminoguanidine (5 x 10(-5) mol/L), a specific inhibitor of inducible NO synthase. Arteriolar responses were not altered by incubation with 17alpha-estradiol.

CONCLUSIONS

Estrogen, via a receptor-mediated pathway, upregulates endothelial NO synthase gene expression, leading to increased NO production, and restores the regulation of wall shear stress in arterioles of male SHR.

Effect of 17-beta estradiol on pre-existing atherosclerotic lesions: role of the endothelium

The atheroprotective effects of estrogen during the process of atherogenesis is well documented, whereas limited information is available about the effect of estrogen on pre-existing atherosclerotic lesions. After bilateral ovariectomy, 24 New Zealand White rabbits were randomized into three groups of eight animals each and subsequently fed a 0.5% cholesterol diet. In group I, the vessels were excised at day 84, whereas in group II, the cholesterol diet was continued for a total of 168 days. In group III, the animals were first fed with a cholesterol diet for 84 days; in the second phase of the experiment, the cholesterol diet was continued for a further 84 days with a combined estrogen treatment (1 mg estradiol valerate per kg body weight per week intramuscularly). At the end of the experiment, the proximal aortic arch, right carotid artery, thoracical aorta and abdominal aorta of each animal were excised and prepared for histological and immunohistological examination. By day 168, morphometrical analysis displayed a significantly lower plaque development under estrogen therapy in the carotid artery (0.08+/-0.18 mm(2) vs. 0.60+/-0.39 mm(2)), the thoracic aorta (0.56+/-0.94 mm(2) vs. 3.63+/-2.06 mm(2)), and in the abdominal aorta (0.55+/-0.70 mm(2) vs. 1.71+/-1.05 mm(2)) in comparison with the corresponding 168 day control group. However, estrogen treatment has failed to reduce further atherosclerotic plaque development in the aortic arch (9.42+/-1.79 mm(2) vs. 11. 64+/-3.29 mm(2)). Immunohistological detection of the 'anti-human factor VIII related antigen', i.e. the 'von Willebrand factor' (vWF), showed a significantly lower number of luminal cells positive for vWF in the aortic arch in the 84-day cholesterol group, compared with the corresponding controls of normocholesterolemic rabbits (65. 9+/-12.4% vs. 83.1+/-6.2%; P<0.05). Estradiol was able to inhibit the further progression of atherosclerosis when moderate vessel wall alterations were present, whereas pre-existing severe atherosclerosis was associated with a failure of the anti-atherosclerotic estrogen action. As suggested by the in situ detection of vWF as a morphological marker for endothelial cells, an intact endothelial layer might play an important role in mediating the beneficial effect of estrogen in the process of atherosclerosis.

Developmental regulation of nitric oxide synthase expression in rat skeletal bone

Nitric oxide (NO) has been implicated in bone growth and remodeling by studies showing that inhibition of NO-synthase (NOS) activity retards normal gain in bone mineral density both during skeletal development and after sexual maturity. In the present study, we aimed to assess the level of expression and cellular localization of the three NOS isoforms during skeletal bone development from neonatal to sexual maturity in female Wistar rats. Reverse transcription polymerase chain reaction (RT-PCR) was used to analyze the presence of NOS1 (neuronal), NOS2 (inducible), and NOS3 (endothelial) transcripts in femoral bone from neonatal, 4-, 8-, and 12-week-old rats. RT-PCR amplified NOS1, NOS2, and NOS3 transcripts of 472-, 807-, and 289-bp, respectively. There were no detectable differences in the levels of NOS1 mRNA between the groups; however, NOS2 mRNA was more abundant in the neonatal group compared with 4-, 8-, and 12-week groups. Expression of NOS1 protein could not be detected in bones by either Western blotting or immunocytochemistry in any of the age groups investigated. Western blots for NOS2 revealed expression in the neonatal group only and it was not detected in any of the older age groups. Immunostaining for NOS2 was also most evident in the neonatal group and was localized specifically to trabecular osteoblasts and osteoclasts. In all age groups studied, NOS3 mRNA and protein were found in bone-resorbing osteoclasts, cuboidal active osteoblasts, and osteocytes. Semiquantitative RT-PCR provided evidence of down-regulation of NOS3 transcripts during the skeletal development. This was confirmed using in situ hybridization, which showed higher expression in neonatal and 4-week groups than in other groups. Western blots and counting the ratio of trabecular osteoblasts that were NOS3 immunoreactive showed parallel down-regulation of NOS3 protein during skeletal development. Taken together, these data show that there is regulation of NOS2 and in particular NOS3 expression during skeletal development and this may be significant to trabecular bone growth and remodeling.

Effect of 17beta-oestradiol on cytokine-induced nitric oxide production in rat isolated aorta

1. Studies were performed on isolated aortic rings without endothelium to investigate the effect of 17beta-oestradiol on cytokine-induced nitric oxide production by the inducible nitric oxide synthase (iNOS). 2. Treatment of the isolated aortic rings with interleukin-1beta (IL-1beta, 20 micro ml(-1)) led to the expression of iNOS mRNA and protein, as well as significant nitrite accumulation in the incubation media and suppression of phenylephrine (1 nM-10 microM)-evoked contraction. 3. Cycloheximide (1 microM), a protein synthesis inhibitor, prevented iNOS protein expression, nitrite accumulation and the suppression of contractility by IL-1beta on the isolated aortic rings. 17Beta-oestradiol (1 nM-10 microM) and the partial oestrogen receptor agonist 4-OH-tamoxifen (1 nM-10 microM) produced concentration-dependent inhibition of IL-1beta-induced nitrite accumulation and restored vasoconstrictor responsiveness to phenylephrine, similar to the iNOS inhibitor aminoguanidine (100 microM). 4. Semiquantitative PCR demonstrated decreased iNOS mRNA in the IL-1beta-induced and 17beta-oestradiol-treated rings. Western blot analysis of rat aorta homogenates revealed that 17beta-oestradiol treatment resulted in a reduction in IL-1beta-induced iNOS protein level. 5. Incubation with tumour necrosis factor alpha (TNF alpha, 1 ng ml(-1)) resulted in significant nitrite accumulation in the incubation media and suppression of the smooth muscle contractile response to phenylephrine, similar to IL-1beta. The effects of TNF alpha were also inhibited by co-incubation of the rings with 17beta-oestradiol and 4-OH-tamoxifen (1 microM). 6. The anti-transforming growth factor-beta1 (TGF-beta1) antibody, which inhibited TGF-beta1-induced suppression of nitrite production from IL-1beta-treated vascular rings, did not affect the inhibitory action of 17beta-oestradiol, suggesting that the effect of oestrogen on iNOS inhibition was not mediated by TGF-beta1. 7. These results show that the ovarian sex steroid, 17beta-oestradiol is a modulator of cytokine-induced iNOS activity in rat vascular smooth muscle and its mechanism of action involves decrease of iNOS mRNA and protein.