| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 Department of Physiology, Faculty of Medicine, University of Murcia, Spain
 |
Abstract |
|---|
 Top Abstract IntroductionMethodsResultsDiscussionReferences |
|---|
(Received 7 February 2006;
accepted after revision 10 April 2006; first published online 20 April 2006)
Corresponding author I. Hernández: Departamento de Fisiología, Facultad de Medicina, Universidad de Murcia, Campus de Espinardo, 30100, Murcia, Spain. Email: isabelhg{at}um.es
|
Introduction |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
After menopause, oestrogen deficiency promotes overexpression of AT1 receptors and increased angiotensin-converting enzyme (ACE) activity, which may contribute to increased hypertension and cardiovascular risk in postmenopausal women. In addition, the use of ACE inhibitors has been recently proposed as a preventive drug intervention in women with high risk of coronary heart disease (Mosca et al. 2004). Angiotensin-converting enzyme inhibitors reduce blood pressure, protect vessels against vascular injury, and exert a renoprotective action by blocking the formation of angiotensin II and increasing bradykinin levels, an effect is at least partly mediated through NO (Linz et al. 1999). Since oestrogens induce changes in the renin–angiotensin system (RAS; Tostes et al. 2003), NO bioavailability (Mendelsohn & Karas, 1999) and bradykinin action (Madeddu et al. 1996), a potential interaction between oestrogens and ACE inhibitors seems feasible. Consequently, the study of RAS inhibition in the presence or absence of oestrogen may be of particular interest.
Based on preliminary results from our laboratory, which showed a stronger chronic hypotensive effect of captopril in the presence of 17ß-oestradiol in female ovariectomized spontaneiously hypertensive rats (SHR), we hypothesized that 17ß-oestradiol would enhance the haemodynamic cardiovascular responses to captopril. To address this issue, in the present study we have examined the effect of chronic 17ß-oestradiol administration on acute systemic haemodynamic responses to captopril in SHR. We also evaluated whether bradykinin and/or NO play a role in oestrogen modulation of the antihypertensive effect of captopril.
|
Methods |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Experimental protocols
Three different protocols were designed to investigate whether 17ß-oestradiol was able to potentiate the systemic haemodynamic effects of blocking the RAS, and the possible mechanisms involved in such an effect.
Protocol I. This protocol was designed to determine the effects of 17ß-oestradiol on acute cardiovascular responses to administration of an ACE inhibitor. At 10 weeks of age, 22 virgin female SHR were anaesthetized with ketamine (30 mg kg–1 I.M.) and xylazine (20 mg kg–1 I.M.), after which the ovaries were exposed and removed in 15 rats and the ovaries exposed but left intact in the remaining seven animals, these latter being used as the intact group. Furthermore, during this same surgical procedure, pellets (Innovative Research of America, Sarasota, FL, USA) containing either placebo (n = 7) or 17ß-oestradiol (1.5 mg delivered over 8 weeks, n = 8) were subcutaneously implanted in ovariectomized animals. All rats were kept in their cages for 2 months until haemodynamic studies took place.
Haemodynamic measurements were performed on 18-week-old rats. The rats were anaesthetized with ketamine (30 mg kg–1 I.M.) and xylazine (20 mg kg–1 I.M.) for implantation of catheters. A catheter was placed into the left femoral artery to measure mean arterial pressure (MAP) and heart rate (HR). A right atrial catheter and a thoracic aortic thermocouple were implanted via the right external jugular vein and right carotid artery, respectively. The catheters were brought out through the skin on the dorsal side of the neck. Finally, the distal ends were threaded through a lightweight flexible spring connected to a swivel. All surgical procedures were performed under aseptic conditions. Rats were placed in individual plastic cages with the swivels mounted above, allowing them complete freedom of movement and free access to chow and tap water. Three full days were allowed for recovery from surgery before haemodynamic measurements.
In conscious, freeling moving rats, cardiac output was measured using thermodilution, as previously described (Hernandez et al. 1991), by rapidly injecting 200 µl of 0.9% saline at room temperature (20°C) through the jugular catheter, using a spring-loaded, constant-rate, constant-volume syringe (Hamilton CR 700-200). The thermodilution curve and the pressure signal were processed with a microcomputer system (Cardiomax IIR, Columbus Instruments, Ohio, US). Haemodynamic values were taken as the mean of three determinations. Cardiac output and vascular resistance were corrected for body weight and expressed as cardiac index (CI, in ml min–1 (100 g body weight)–1) and vascular resistance index (VRI, in mmHg ml–1 min–1 (100 g body weight)–1), respectively. On the day of the experiment, basal cardiovascular parameters (MAP, HR, CI and VRI) were first determined following an equilibration period of 30 min. An intravenous bolus of captopril (10 mg kg–1, Sigma) was then given to the animals (Cachofeiro et al. 1992; Ruiz et al. 1994), and haemodynamic measurements performed again 15 and 30 min after captopril administration.
Protocol II. This protocol was designed to determine the role of bradykinin on 17ß-oestradiol potentiation of the cardiovascular effects of captopril. Ten-week-old rats were randomized into groups of six intact, six ovariectomized and six ovariectomized rats treated with 17ß-oestradiol, and catheters were implanted at 18 weeks of age using the same procedures as described for protocol I. All three groups were intravenously administered a bradykinin B2 receptor blocker (HOE140 (Sigma-Aldrich, Madrid, Spain), 1 mg kg–1) 30 min prior to captopril administration (10 mg kg–1, I.V.). Haemodynamic measurements were performed 30 min after both HOE140 (basal values, time 0) and captopril administration. To test for inhibition of B2 receptors in the presence of HOE140, 1 mg kg–1 of bradykinin (250 ng I.V., Sigma, Madrid, Spain) was administered as a bolus 15 min before and 40 min after HOE140 administration. HOE140 blocked over 80% of the blood pressure response to bradykinin.
Protocol III.
This protocol was designed to evaluate the role of NO in 17ß-oestradiol potentiation of the cardiovascular effect of captopril. Ten-week-old rats were randomized into groups of six intact, six ovariectomized and six ovariectomized rats treated with 17ß-oestradiol, and catheters implanted at 18 weeks of age using the same procedures as described for protocol I. All three groups were administered N
-nitro-L-arginine methyl ester (L-NAME, 3 mg kg–1
I.V.) 60 min before captopril (10 mg kg–1
I.V.). Haemodynamic measurements were performed 60 min after L-NAME (basal values, time 0) and 30 min after captopril administration.
Plasma levels of 17ß-oestradiol
As a control, plasma levels of 17ß-oestradiol were measured by microparticle enzyme immunoassay (IMx estradiol assay, Abbot Laboratories, North Chicago, IL, USA) on three different SHR groups (6 sham surgery intact; 6 ovariectomized plus placebo; and 6 ovariectomized + 17ß-oestradiol treatment) at 18 weeks of age, 8 weeks following treatment.
Data analysis
All values are reported as means ± S.E.M. One-way ANOVA for randomized measures, followed by a post hoc Fisher's least-significant difference test, was used to determine differences in baseline haemodynamic parameters from protocol I, and also differences between groups within protocols II and III. Changes between groups within protocols II and II and between groups from protocol I where analysed using a two-way ANOVA for repeated measures, and group means compared by post hoc Fisher's least-significant difference test. Differences were considered significant at P < 0.05.
|
Results |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Basal values of MAP, VRI, CI and HR were not significantly different among experimental groups (Table 1). The effects of captopril on the haemodynamic parameters of intact ovariectomized SHR and ovariectomized SHR treated with 17ß-oestradiol are illustrated in Fig. 1. In all three groups, captopril administration significantly decreased MAP at both time points examined (15 and 30 min after the captopril bolus). The decrease in MAP at the 30 min time point was significantly smaller in OVX versus intact rats (P < 0.05), whereas chronic treatment with 17ß-oestradiol significantly increased the hypotensive effect of captopril with respect to non-treated OVX rats at both time points. Vascular resistance index was also significantly less reduced in OVX versus intact SHR (P < 0.05) 30 min after captopril administration. In addition, VRI reduction was more pronounced in OVX + E2 SHR compared to both intact and OVX SHR (P < 0.05). In contrast, captopril administration significantly increased cardiac index at both time points in OVX + E2 SHR (P < 0.01), whereas it reduced cardiac index after 30 min in OVX animals (P < 0.05). The administration of captopril increased HR in all three experimental groups.
|
|
Figure 2 illustrates the effects of the bradykinin inhibitor HOE140 on the systemic haemodynamic effects of captopril in intact, OVX and OVX + E2 SHR. Basal values of MAP, VRI, CI and HR are given in Table 1, where it can be seen that none of these parameters was significantly affected by HOE140 administration. As shown in Fig. 2, pretreatment with HOE140 partly blocked the captopril-induced MAP decrease in intact rats, thus abolishing the difference between intact and OVX SHR that had been observed in the previous experiment, but was not able to counteract the reduction in MAP in OVX + E2 SHR, which was more pronounced than that in OVX SHR (P < 0.05). HOE140 partly blocked the more pronounced fall in VRI induced by captopril in OVX + E2 SHR. In contrast, in the OVX group, in the presence of bradykinin receptor blockade, captopril resulted in a less pronounced tachycardia, but a greater decrease in VRI, and an increase in CI. As a result, the effect of captopril after B2 receptor blockade was similar in all three experimental groups. After HOE140 pretreatment, captopril administration slightly increased CI and HR to similar extents in all three groups.
|
Basal haemodynamic values in intact, OVX and OVX + E2 rats after L-NAME and before captopril administration are given in Table 1. L-NAME administration induced a significant increase in MAP and VRI in all three groups and a significant decrease in CI in the intact group only. A marked significant attenuation of MAP response to captopril in the L-NAME-treated intact rats is shown in Fig. 3. Also, the captopril-induced decrease in MAP was partly blocked by the presence of L-NAME in OVX + E2 SHR, so that the effect of captopril similar on all these three groups (compare with Fig. 1). Compared to protocol I results, the VRI fall induced by captopril was partly blocked in OVX + E2 rats after pretreatment with L-NAME, but it was more pronounced in OVX rats. L-NAME pretreatment also blocked both the CI increase previously seen in OVX + E2 SHR and the HR increase observed in OVX and OVX + E2 SHR in response to captopril administration, abolishing in the case of HR the differences between all experimental groups.
|
The plasma concentration of 17ß-oestradiol in intact animals was 97.4 ± 4.3 pg ml–1. Ovariectomy significantly reduced this concentration to 6.9 ± 0.4 pg ml–1, whereas treatment with 17ß-oestradiol significantly increased plasma levels to 164.6 ± 4.2 pg ml–1.
|
Discussion |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
This synergistic action of oestradiol and captopril was partly suppressed when bradykinin B2 receptors were blocked with HOE140, and completely blocked when NO synthesis was inhibited by L-NAME. Angiotensin-converting enzyme inhibitors are effective antihypertensive drugs because they reduce blood pressure not only in renin-dependent models of hypertension but also in forms of hypertension that are less clearly related to the RAS, such as SHR (Wu & Berecek, 1993) and essential hypertension in humans (Williams, 1988). The antihypertensive effect of ACE inhibitors has been mainly attributed to reduced formation of angiotensin II in both plasma and tissues (Dzau, 1990), and accumulation of the endogenous vasodilator kinin, since ACE catalyses the degradation of bradykinin and related kinins (Carretero et al. 1981; Erdos, 1990). When bradykinin B2 receptors were blocked, the differential effect of captopril on ovariectomized rats treated versus non-treated with 17ß-oestradiol disappeared, suggesting that the kallikrein–kinin system may be involved in this effect. In contrast, it should be noted that in ovariectomized animals in the presence of bradykinin blockade, captopril did not cause more reduction in MAP, but resulted in a greater decrease in VRI and CI and less tachycardia. Thus, in ovariectomized rats the captopril effect cannot be explained solely by an increase in bradykinin.
Moreover, many reports support the notion that sex hormones may contribute to regulation of the kallikrein–kinin system. Madeddu et al. (1997) found that replacement of oestrogens reversed the attenuated vasodepressor response to bradykinin associated with ovariectomy, and also prevented reduction of bradykinin B2 receptor mRNA expression in the aorta and kidney of ovariectomized Wistar rats, indicating that oestrogens regulate B2 receptor gene expression and function (Madeddu et al. 1997). Furthermore, hormone replacement therapy has been reported to increase circulating plasma levels of bradykinin in postmenopausal women with essential hypertension (Sumino et al. 1999). All these reports suggest that the cardioprotective effects of oestrogen might be at least partly mediated by the kallikrein–kinin system, and that ACE inhibitors may be more effective in the presence of oestrogen. In SHR, inhibition of NO synthesis has been found to attenuate the acute blood pressure-lowering effect of captopril (Ruiz et al. 1994) and the hypotensive effect of 1 week oral administration of ramipril (Cachofeiro et al. 1992). Since ACE inhibitors increase the endogenous levels of kinins, and NO mediates the vasodilatory effects of bradykinin (Margolius, 1995), the possibility exists that oestradiol may increase the haemodynamic effect of captopril by increasing bradykinin and then NO.
Furthermore, additional mechanisms appear to be involved in the hypotensive action of ACE inhibitors in the presence of oestradiol. As previously described, 17ß-oestradiol increases NO bioavailability (Mendelsohn & Karas, 1999), and inhibition of NO synthesis has been shown to attenuate the antihypertensive effect of ACE inhibitors (Carretero et al. 1981; Cachofeiro et al. 1992). In these conditions, 17ß-oestradiol could improve the action of captopril by increasing NO bioavailability. Here we have shown that blocking NO synthesis with L-NAME reduces the antihypertensive effect of captopril in intact and 17ß-oestradiol-treated ovariectomized SHR, with no effect on ovariectomized SHR. L-NAME alone increased MAP and VRI in all groups as a result of a vasoconstriction derived from the absence of the endothelial vasodilator NO, which regulates vascular tone. Furthermore, following L-NAME administration, the decrease in MAP and VRI in response to captopril was very similar for all experimental groups. These results suggest that NO could contribute to the more potent antihypertensive action of captopril in ovariectomized rats treated with 17ß-oestradiol. This statement is supported by several reports showing that 17ß-oestradiol increases endothelial-derived NO in a variety of experimental models (Mendelsohn, 2002). Thus, when administered directly into a coronary artery of a non-human primate or a human, oestradiol causes rapid vasodilatation by activating endothelial NO production (Mendelsohn & Karas, 1999). Caulin-Glaser et al. (1997) demonstrated a rapid rise in the release of nitric oxide from female human endothelial cells from the umbilical vein in response to 17ß-oestradiol. Other studies attribute this increase in nitric oxide release to increased endothelial NO synthase activity and NO synthase gene expression (Mendelsohn & Karas, 1999). In male SHR, 17ß-oestradiol upregulated endothelial NO synthase gene expression, leading to increased NO production and restoring the regulation of wall shear stress in arterioles (Huang et al. 2000). In contrast, recent studies suggest that oestradiol reduces superoxide anion bioavailability in microvessels of SHR (Dantas et al. 2002), and prevents oxidative stress in ovariectomized rats (Hernández et al. 2000) by improving NO–O2 balance (Wagner et al. 2001). This mechanism of action of 17ß-oestradiol could lower NO degradation which, together with the increase in NO synthesis and release, would lead to higher NO bioavailability.
In summary, ovariectomy blunted the decrease in blood pressure and vascular resistance index induced by captopril in intact rats. Treatment with 17ß-oestradiol prevented the blunted response and enhanced the acute hypotensive action of captopril in ovariectomized rats. However, this effect of 17ß-oestradiol was prevented by blocking bradykinin B2 receptors or NO synthesis, which suggests that the synergy between 17ß-oestradiol and captopril is dependent, at least in part, on the kallikrein–kinin system and NO.
|
References |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Cachofeiro
V, Sakakibara
T
&
Nasjletti
A (1992). Kinins, nitric oxide, and the hypotensive effect of captopril and ramiprilat in hypertension. Hypertension
19, 138–145.
Carretero
OA, Miyazaki
S
&
Scicli
AG (1981). Role of kinins in the acute antihypertensive effect of the converting enzyme inhibitor, captopril. Hypertension
3, 18–22.
Caulin-Glaser
T, García-Cardeña
G, Sarrel
P, Sessa
WC
&
Bender
JR (1997). Estradiol regulation of human endothelial cell basal nitric oxide release, independent of cytosolic Ca2+ mobilization. Circ Res
81, 885–892.
Dantas
AP, Tostes
RC, Fortes
ZB, Costa
SG, Nigro
D
&
Carvalho
MH (2002). In vivo evidence for antioxidant potential of estrogen in microvessels of female spontaneously hypertensive rats. Hypertension
39, 405–411.
Dzau VJ (1990). Mechanism of action of angiotensin-converting enzyme (ACE) inhibitors in hypertension and heart failure: role of plasma versus tissue ACE. Drugs 39, 11–16.
Erdos
EG (1990). Angiotensin I converting enzyme and the changes in our concept through the years. Hypertension
16, 363–370.
Hernández
I, Delgado
JL, Díaz
J, Quesada
T, Teruel
MJ
et al. (2000). 17ß-Estradiol prevents oxidative stress and decreases blood pressure in ovariectomized rats. Am J Physiol Regul Integr Comp Physiol
279, R1599–R1605.
Hernandez I, Ingles AC, Pinilla JM, Quesada T & Carbonell LF (1991). Cardiocirculatory responses to AII and AVP in conscious rats. J Cardiovasc Pharmacol 17, 916–922.[Medline]
Higashi
Y, Sanada
M, Sasaki
S, Nakagawa
K, Goto
C
et al. (2001). Effect of estrogen replacement therapy on endothelial function in peripheral resistance arteries in normotensive and hypertensive postmenopausal women. Hypertension
37, 651–657.
Liu
HW, Iwai
M, Takeda-Matsubara
Y, Wu
L, Li
JM, Okumura
M
et al. (2002). Effect of estrogen and AT1 receptor blocker on neointima formation. Hypertension
40, 451–457.
Huang
A, Sun
D, Koller
A
&
Kaley
G (2000). 17ß-Estradiol restores endothelial nitric oxide release to shear stress in arterioles of male hypertensive rats. Circulation
101, 94–100.
Linz
W, Wohlfart
P, Scholkens
BA, Malinski
T
&
Wiemer
G (1999). Interactions among ACE, kinins and NO. Cardiovasc Res
43, 549–561.
Madeddu P, Emanueli C, Song Q, Varoni MV, Demontis MP, Anania V et al. (1997). Regulation of bradykinin B2-receptor expression by oestrogen. Br J Pharmacol 121, 1763–1769.[CrossRef][Medline]
Madeddu
P, Parpaglia
PP, Anania
V, Glorioso
N, Chao
C
et al. (1996). Sexual dimorphism of cardiovascular responses to early blockade of bradykinin receptors. Hypertension
27, 746–751.
Margolius
HS (1995). Kallikrein and kinins. Hypertension
26, 221–229.
Mendelsohn ME (2002). Genomic and nongenomic effects of estrogen in the vasculature. Am J Cardiol 90, 3F–6F.[CrossRef][Medline]
Mendelsohn
M
&
Karas
R (1999). The protective effects of estrogen on the cardiovascular system. New Engl J Med
340, 1801–1811.
Mosca
L, Appel
LJ, Benjamin
EJ, Berra
K, Chandra-Strobos
N, Fabunmi
RP
et al. (2004). Evidence-based guidelines for cardiovascular disease prevention in women. Circulation
109, 672–693.
Nickenig
G, Baumer
AT, Grohe
C, Kahlert
S, Strehlow
K, Rosenkranz
S
et al. (1998). Estrogen modulates AT1 receptor gene expression in vitro and in vivo. Circulation
97, 2197–2201.
Nickenig
G, Strehlow
K, Wassmann
S, Baumer
AT, Ahlbory
K
et al. (2000). Differential effects of estrogen and progesterone on AT1 receptor gene expression in vascular smooth muscle cells. Circulation
102, 1828–1833.
Nigro D, Fortes ZB, Scivoletto R, Barbeiro HV & Carvalho MH (1997). Sex-related differences in the response of spontaneously hypertensive rats to angiotensin-converting enzyme inhibitor. Endothelium 5, 63–71.[Medline]
Pinto
S, Virdis
A, Ghiadoni
L, Bernini
G, Lombardo
M
et al. (1997). Endogenous estrogen and acetylcholine-induced vasodilation in normotensive women. Hypertension
29, 268–273.
Preston RA, Alonso A, Panzitta D, Zhang P & Karara AH (2002). Additive effect of drospirenone/17-beta-estradiol in hypertensive postmenopausal women receiving enalapril. Am J Hypertens 15, 816–822.[CrossRef][Medline]
Ruiz FJ, Salom MG, Ingles AC, Quesada T, Vicente E & Carbonell LF (1994). N-Acetyl-1-cysteine potentiates depressor response to captopril and enalaprilat in SHRs. Am J Physiol 267, R767–R772.
Safar ME, Myers MG, Leenen F & Asmar R (2002). Gender influence on the dose-ranging of a low-dose perindopril-indapamide combination in hypertension: effect on systolic and pulse pressure. J Hypertens 20, 1653–1661.[CrossRef][Medline]
Saitta
A, Altavilla
D, Cucinotta
D, Morabito
N, Frisina
N
et al. (2001). Randomized, double-blind, placebo-controlled study on effects of raloxifene and hormone replacement therapy on plasma NO concentrations, endothelin-1 levels, and endothelium-dependent vasodilation in postmenopausal women. Arterioscler Thromb Vasc Biol
21, 1512–1519.
Sumino H, Ichikawa S, Kanda T, Sakamaki T, Nakamura T, Sato K et al. (1999). Hormone replacement therapy in postmenopausal women with essential hypertension increases circulating plasma levels of bradykinin. Am J Hypertens 12, 1044–1047.[CrossRef][Medline]
Tostes RC, Nigro D, Fortes ZB & Carvalho MH (2003). Effects of estrogen on the vascular system. Braz J Med Biol Res 36, 1143–1158.[Medline]
Virdis
A, Ghiadoni
L, Pinto
S, Lombardo
M, Petraglia
F
et al. (2000). Mechanisms responsible for endothelial dysfunction associated with acute estrogen deprivation in normotensive women. Circulation
101, 2258–2263.
Wagner
AH, Schroeter
MR
&
Hecker
M (2001). 17beta-Estradiol inhibition of NADPH oxidase expression in human endothelial cells. FASEB J
15, 2121–2130.
Williams GH (1988). Converting-enzyme inhibitors in the treatment of hypertension. N Engl J Med 319, 1517–1525.[Medline]
Wu
JN
&
Berecek
KH (1993). Prevention of genetic hypertension by early treatment of spontaneously hypertensive rats with the angiotensin converting enzyme inhibitor captopril. Hypertension
22, 139–146.
|
Acknowledgements |
|---|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
), OVX (•) and OVX + E2 SHR (
) 15 and 30 min after captopril administration (10 mg kg–1, I.V.) 
significant differences from basal values (P < 0.05); 
significant differences from intact SHR (P < 0.05).
