The direct action of 17 beta-estradiol in isolated omental artery from nonpregnant and pregnant women is related to calcium antagonism

Adaptive changes of mesenteric arteries in pregnancy: a meta-analysis

The vascular response to pregnancy has been frequently studied in mesenteric artery models by investigating endothelial cell (EC)- and smooth muscle cell (SMC)-dependent responses to mechanical (flow-mediated vasodilation, myogenic reactivity, and vascular compliance) and pharmacological stimuli (G protein-coupled receptor responses: Gq(EC), Gs(SMC), Gq(SMC)). It is unclear to what extent these pathways contribute to normal pregnancy-induced vasodilation across species, strains, and/or gestational age and at which receptor level pregnancy affects the pathways. We performed a meta-analysis on responses to mechanical and pharmacological stimuli associated with pregnancy-induced vasodilation of mesenteric arteries and included 55 (188 responses) out of 398 studies. Most included studies (84%) were performed in Wistar and Sprague-Dawley rats (SDRs) and compared late gestation versus nonpregnant controls (80%). Pregnancy promotes flow-mediated vasodilation in all investigated species. Only in SDRs, pregnancy additionally stimulates both vasodilator Gq(EC) sensitivity (EC(50) reduced by -0.76 [-0.92, -0.60] log[M]) and Gs(SMC) sensitivity (EC(50) reduced by -0.51 [-0.82, -0.20] log[M]), depresses vasopressor Gq(SMC) sensitivity (EC(50) increase in SDRs by 0.23 [0.16, 0.31] log[M]), and enhances arterial compliance. We conclude that 1) pregnancy facilitates flow-mediated vasodilation at term among all investigated species, and the contribution of additional vascular responses is species and strain specific, and 2) late pregnancy mediates vasodilation through changes at the receptor level for the substances tested. The initial steps of vasodilation in early pregnancy remain to be elucidated.

Endothelial dysfunction in uterine circulation in preeclampsia: can estrogens improve it?

OBJECTIVE

The purpose of this study was to evaluate whether a 3-hour incubation with 17beta-estradiol will enhance blood flow- and bradykinin-mediated dilatation and alter pressure-induced basal tone in myometrial resistance arteries from women with preeclampsia and to evaluate the role of nitric oxide in the responses that were observed.

STUDY DESIGN

Blood flow- and bradykinin-mediated dilatation and responses to intraluminal pressure of 60 and 80 mm Hg were compared before and after 3 hours of incubation with 17beta-estradiol (10(-8) mol/L) in isolated myometrial arteries with the pressure myography technique. In separate experiments, the role of nitric oxide on 17beta-estradiol-induced responses was evaluated in the presence of the nitric oxide synthase inhibitor (10(-4) mol/L). Endothelial morphologic condition was evaluated by scanning electron microscopy.

RESULTS

Incubation with 17beta-estradiol significantly improved blood flow-mediated dilatation compared with initial blood flow-mediated response in arteries from women with preeclampsia. This effect was nitric oxide mediated, because the nitric oxide synthase inhibitor abolished the response. Arteries from women with preeclampsia demonstrated impaired bradykinin-mediated dilatation compared with that obtained in arteries from normal pregnant women. The 17beta-estradiol had no effect on bradykinin-mediated dilatation in arteries from women with preeclampsia. The enhanced pressure-induced tone at 80 mm Hg compared with the tone that developed at 60 mm Hg in arteries from women with preeclampsia was reduced after incubation with 17beta-estradiol. This reduction was also nitric oxide mediated. Morphologic signs of endothelial dysfunction were evident in arteries from women with preeclampsia.

CONCLUSION

The 17beta-estradiol improved impaired blood flow-mediated dilatation and reduced basal tone through a nitric oxide-mediated pathway in isolated myometrial arteries from women with preeclampsia.

Flow rate-perfusion pressure relationships in situ in the uterine circulation of pregnant rats

OBJECTIVE

Our purpose was to study the effects of inhibition of nitric oxide synthesis on perfusion pressure and flow rate-perfusion pressure relationships in the rat uterine circulation in situ.

STUDY DESIGN

Nonpregnant, midpregnant (day 14), and late pregnant (day 21) Sprague-Dawley rats were studied. The vascular bed of the intact uterus and its contents were isolated and perfused with Krebs buffer (37 degrees C, pH approximately 7.4, 2% dextran and indomethacin, 10(-5) mol/L) through a cannula inserted into the abdominal aorta close to the iliac artery bifurcation, and perfusion pressure was monitored. After equilibration, the flow rate was increased from 1 mL/min to 8 or 16 mL/min, in the absence and presence of N(omega)-nitro-L-arginine methyl ester (L-NAME), phenylephrine, or both.

RESULTS

The flow rate-perfusion pressure relationship in midpregnant rats (n = 9) was not significantly different from that in late pregnant rats (n = 12), but the latter was significantly greater than the relationship in nonpregnant animals (n = 5). L-NAME did not influence perfusion pressure and flow rate-perfusion pressure relationships in any of the groups. However, L-NAME enhanced the phenylephrine-induced and flow rate-induced increase in perfusion pressure in the vascular beds from nonpregnant and midpregnant animals, and to a lesser extent in late pregnant rats. L-arginine did not influence perfusion pressure or the flow rate-perfusion pressure relationship in any group.

CONCLUSIONS

Vasoconstriction produced by phenylephrine uncovers basal release of endothelium derived nitric oxide. Vasoconstriction increases perfusion pressure responses to increases in flow rate in the uterine vascular beds of nonpregnant, midpregnant, and late pregnant rats. The release of endothelial nitric oxide in the uterine vascular beds depends on the basal contractile state of the vasculature.

Inhibition of cyclooxygenase but not nitric oxide synthase influences effects on the human omental artery of the thromboxane A2 mimetic U46619 and 17beta-estradiol

OBJECTIVE

These experiments were performed to study the influence of endothelial factors on the contractile effect of the thromboxane A(2) analog U46619 and on the relaxant action of 17beta-estradiol on isolated human omental arteries from nonpregnant women, women with normal pregnancies, and women with preeclampsia.

STUDY DESIGN

Arterial rings (3 mm) with or without endothelium were suspended in organ chambers filled with Krebs buffer, 37 degrees C, aerated with 5% carbon dioxide in air, pH approximately 7.4, for isometric tension recording. Rings were incubated with indomethacin, N(omega)-nitro-L -arginine, or 17beta-estradiol, alone or in combination. The concentration that produced 50% of maximal effect, the area under the curve, and the maximal effect of U46619, normalized with respect to a reference contraction in response to potassium chloride, were compared.

RESULTS

Neither indomethacin nor N(omega)-nitro-L -arginine changed the basal tone of omental artery rings. Neither N(omega)-nitro-L -arginine nor removal of the endothelium affected either the contractile action of U46619 or the relaxant action of 17beta-estradiol. In contrast, indomethacin potentiated the contractile effect of U46619 and abolished the inhibitory effect of 17beta-estradiol in rings from all three groups. The effects of U46619 and 17beta-estradiol were significantly less in rings from women with normal pregnancy than in those from women with preeclampsia. Tissues from women with preeclampsia demonstrated the highest contractile response to U46619.

CONCLUSION

The inhibitory effect of 17beta-estradiol is not due to increased production of endothelial nitric oxide but rather involves inhibitory products of the cyclooxygenase pathway. The effect of indomethacin may result from inhibited production or release of eicosanoids or from sensitization of thromboxane A(2) receptors.

The effect of 17beta-estradiol on isolated omental arteries from preeclamptic women

OBJECTIVE

To study the effect of 17beta-estradiol on isolated omental arteries from preeclamptic women.

STUDY DESIGN

Rings of omental artery with intact endothelium were mounted in organ chambers for isometric tension recording. We studied the effect of pharmacological concentrations of 17beta-estradiol on potassium chloride-induced tension and the concentration-contraction relationships for norepinephrine and calcium.

RESULTS

Cumulative application of 17beta-estradiol, in a concentration-dependent manner, relaxed potassium chloride contracted rings. Sixty minutes of incubation with 17beta-estradiol (10(-5)mol/l) attenuated the tension developed in response to potassium chloride, norepinephrine and calcium. Tamoxifen (10(-6)mol/l) did not antagonize the inhibitory actions of 17beta-estradiol.

CONCLUSIONS

Pharmacological concentrations of 17beta-estradiol retain the capability for relaxing omental artery rings from preeclamptic women. The loss of refractoriness to norepinephrine, increased responsiveness to calcium ions and decreased ability of 17beta-estradiol to inhibit calcium-induced tension may be responsible for increased vascular reactivity in preeclampsia.

The effect of ovariectomy and oestrogen replacement on small artery biomechanics in the rat

OBJECTIVE

To determine the effects of oestrogen deficiency and hormone replacement therapy on the biomechanical properties of a small artery.

SAMPLE

Thirty non-pregnant female Sprague-Dawley rats.

METHODS

Twenty animals were pharmacologically ovariectomised by triptorelin and received either oestradiol propionate or its vehicle. Ten other animals received only the vehicle for the same period of time (control group). After 12 weeks of treatment, cylindrical segments of the saphenous artery were isolated and cannulated at both ends. Pressure-diameter curves were recorded from segments in normal Krebs-Ringer, using norepinephrine, and then with papaverine. The vessel segment close to the examined one was histologically evaluated. Serum levels of oestradiol and cortisol were determined.

MAIN OUTCOME MEASURES

Biomechanical parameters based on the pressure-diameter curves.

RESULTS

Pharmacological ovariectomy decreased the passive diameter of the arteries and oestrogen replacement therapy prevented this. Decreased reactivity to norepinephrine was also restored by oestrogen treatment. Pressure induced myogenic tone was decreased significantly by oophorectomy and increased after oestradiol treatment. No significant changes were found in wall thickness, distensibility, elastic modulus or tangential stress. No significant histological alterations were seen in the vessel wall. Oestradiol levels were significantly decreased in the castrated animals compared with the other two groups.

CONCLUSIONS

These results suggest that oestrogen deficiency decreases and oestrogen replacement increases the passive diameter of small peripheral arteries, and that oestrogen enhances the reactivity of vascular smooth muscle. These responses may provide the background mechanisms for the increased incidence of arterial hypertension and hot flushes during the menopause and the ability of oestrogen substitution to prevent them.