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Endocrinology Vol. 145, No. 8 3866-3872
Copyright © 2004 by The Endocrine Society

Orchidectomy, But Not Ovariectomy, Regulates Angiotensin II-Induced Vascular Diseases in Apolipoprotein E-Deficient Mice

Tracy A. Henriques, Jing Huang, Susan S. D’Souza, Alan Daugherty and Lisa A. Cassis

Graduate Center for Toxicology (T.A.H., J.H., A.D., L.A.C.), Division of Pharmaceutical Sciences (S.S.D., L.A.C.), Graduate Center for Nutritional Sciences (A.D., L.A.C.), and Departments of Medicine (A.D.) and Physiology (A.D.), University of Kentucky, Lexington, Kentucky 40536-0082

Address all correspondence and requests for reprints to: Lisa A. Cassis, Ph.D., Graduate Center for Nutritional Sciences, Room 521B, Wethington Building, University of Kentucky, Lexington, Kentucky 40536-0082. E-mail: lcassis{at}uky.edu.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Conclusions
 References
 
In humans, the incidence and severity of abdominal aortic aneurysms (AAA) are greater in males than in females. Chronic infusion of angiotensin II (AngII) into apolipoprotein E-deficient (apoE–/–) mice promotes atherosclerosis and causes the formation of AAAs. Just as human males are more susceptible to developing AAAs, male mice are more susceptible to AngII-induced AAAs. We hypothesized that sex steroid hormones mediate gender differences in AngII-induced AAA through regulation of the renin-angiotensin system. To define the role of ovarian hormones, female apoE–/– mice were subjected to ovariectomy or sham operation and infused with AngII (1000 ng/kg·min) for 28 d. Ovariectomy had no effect on AngII-induced atherosclerosis, nor did it influence the incidence or severity of AAA. To define the role of testicular hormones, male apoE–/– mice were subjected to orchidectomy (orx) or sham operation and infused with AngII (1000 ng/kg·min) for 28 d. Orx resulted in a profound reduction in AAA incidence (85% vs. 18%, sham vs. orx; P = 0.003) to the level observed in females (25%). However, orx had no effect on AngII-induced reductions in plasma renin concentration or spleen AngII receptor density. In contrast, orx resulted in an increase in atherosclerosis (0.46 ± 0.07 vs. 1.20 ± 0.21 mm2, sham vs. orx; P = 0.002). These results suggest that estrogen does not mediate gender differences in AngII-induced AAA. In contrast, androgens mediate a higher incidence of AngII- induced AAA, through mechanisms that do not appear to involve circulating renin or angiotensin receptor density.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Conclusions
 References
 
GENDER IS A POTENT modifier of a number of cardiovascular diseases (1). Males have an increased prevalence of atherosclerotic-based diseases, such as ischemic heart disease, stroke, and abdominal aortic aneurysms (AAA) (2, 3). Recent clinical trials, such as HOPE and SECURE, have implicated the renin-angiotensin system in the development of cardiovascular disease (4, 5). In accord with these clinical findings, we and others have demonstrated that the chronic infusion of angiotensin II (AngII) into either low density lipoprotein receptor-deficient (6) or apolipoprotein E-deficient (apoE–/–) mice (7, 8, 9) results in accelerated atherosclerosis and formation of AAAs. An analysis of pooled data from mice implicates a gender-based discrepancy in the severity of some of these AngII-based diseases (10). Currently, this comparison has not been formally investigated.

The incidence and severity of cardiovascular disease increases after the onset of menopause. This increase has been suggested to result from the loss of estrogen and its associated protection from cardiovascular diseases (11). The administration of estradiol has been reported to decrease the development of atherosclerosis in several animal models (12, 13, 14, 15, 16). Estradiol has recently been reported to attenuate the development of AngII-induced AAA when administered to male apoE–/– mice (17). However, the contribution of endogenous ovarian hormones to previously observed gender differences in AngII-induced vascular disease has not been examined.

Male gender is an independent risk factor in the development of cardiovascular diseases (2, 3). Although the use of exogenous androgens is associated with a significant increase in the risk of cardiovascular disease (18, 19, 20, 21), testosterone has been shown to reduce the extent of atherosclerosis in both male mice and rabbits (22, 23, 24). The reduced atherosclerosis during the administration of testosterone has been suggested to be through its conversion to estradiol (23). Male gender has consistently been identified as a risk factor for AAA, with population studies demonstrating a 1.97 or greater hazard ratio for AAA in males compared with females, larger than any other risk factor examined (2). Mechanisms for the higher prevalence of AAA in males are unknown.

To investigate mechanisms for gender differences in AngII-induced vascular disease, we used gonadectomy to remove endogenous sex hormones from apoE–/– male and female mice. We hypothesized that the relative susceptibility to AngII-induced vascular disease is due to sex steroid hormones through regulation of the renin-angiotensin system. Results from these studies demonstrate that the removal of ovarian hormones does not influence AngII-induced vascular disease. In contrast, orchidectomy (orx) resulted in a striking reduction in AngII-induced AAA formation to the incidence observed in female mice, but increased the extent of atherosclerosis.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Conclusions
 References
 
Animals
Male and female apoE–/– mice (12 wk old, backcrossed 10 times onto a C57BL/6J background) used in studies examining the effect of ovariectomy (ovx) were bred in-house. ApoE–/– male mice used in the orx studies were obtained from Taconic Farms (Germantown, PA). All mice were maintained under barrier conditions. Water and normal laboratory diet were available ad libitum. AngII (500 or 1000 ng/kg·min) or saline was administered sc by minipumps (model 2004, Alzet, Cupertino, CA) as described previously (7, 25). All procedures were approved by the animal care and use committee at the University of Kentucky.

Ovx and orx
Ovx was performed on 3-month-old female apoE–/– mice. Mice were anesthetized with ketamine/xylazine, bilateral incisions were made into the abdominal cavity, and the uterus was exposed. Circulation to the fallopian tubes was cut off to minimize bleeding when dissecting the ovaries. Once the ovaries were excised, the cut end of the fallopian tubes was cauterized and placed back under the muscle. The muscle was then sutured, and the skin was closed using surgical glue. Sham controls were subject to a similar procedure without removing the ovaries. Orx surgeries were performed by Taconic Farms on 3-month-old male apoE–/– mice.

Blood pressure measurements
Systolic blood pressure was measured on conscious mice using a computerized tail-cuff method (BP-2000; Visitech Systems, Apex, NC). Mice were acclimated to the blood pressure machine for 1 wk, and baseline measurements were obtained before implantation of osmotic minipumps. Blood pressure measurements were recorded at the same time of day, 5 d/wk, throughout the study as described previously (10).

Measurements of plasma and serum components
Total serum cholesterol concentrations were determined on each mouse using enzymatic assay kits (Wako Pure Chemical, Richmond, VA). Lipoprotein cholesterol distributions were evaluated in individual serum samples (50 µl) from four mice in each group after fractionation by size exclusion chromatography on a single Superose 6 column (7). Fractions were collected, and cholesterol concentrations were determined with enzymatic kits. The individual lipoprotein fractions were quantified using Peak Fit (SPSS, Inc., Chicago, IL) as described previously (26).

The renin concentration in plasma (4 µl) was measured by incubation with an excess of porcine angiotensinogen (0.4 µM; Sigma-Aldrich Corp., St. Louis, MO) in the presence of EDTA (0.02 M) for 60 min at 37 C. AngI generated in samples was quantified by RIA using a commercially available kit (NEN Life Science Products, Boston, MA).

Serum testosterone concentrations were assayed using Active Testosterone RIA DSL-4000 kits (Diagnostic Systems, Inc., Webster, TX), previously used for measurements of circulating testosterone in rodents (27). The lower limit of detection for this assay was 0.08 ng/ml, and the intra- and interassay coefficients of variation were 10% and 9%, respectively.

Receptor autoradiography
Receptor autoradiography was performed on spleen sections (16 µm) as described previously (28). The spleen was chosen for examination because it is a rich source of AT1 receptors and macrophages. Analysis of angiotensin receptor density and localization was performed by incubating duplicate tissue sections in phosphate buffer containing 400 pM [125I]Sar1,Ile8-AngII (Peptide Radioiodination Center, Washington State University, Pullman, WA). Sets of adjacent sections were used to determine total binding, nonspecific binding (incubation in the presence of 10 µM unlabeled AngII), and AT1 receptors (binding displaced by 10 µM losartan). Binding results were quantified by video densitometry using public domain NIH Image 5.2 software. A standard curve was generated for each set of films from a set of radioactive standards by plotting ODs vs. nanocuries of standards. Results are presented as nanocuries specifically bound.

Quantification of atherosclerosis and aneurysms
Atherosclerotic lesions were quantified in the arch and thoracic aorta as described previously (7, 29). Data are expressed as the percentage of the intimal surface covered by grossly discernible atherosclerotic lesions. Atherosclerotic lesions were verified by at least two independent observers. There was routinely less than a 5% difference between the determinations of the two observers, as described previously (7). The incidence of AAA was determined by three independent observers, and the weight of the abdominal aorta was determined as an index of severity. A modest AAA was defined as a dilation of greater than 50% of the normal diameter of the abdominal aorta.

Statistics
Data are presented as the mean and SEM. Data were initially analyzed using ANOVA. If differences existed between groups, post hoc analyses were performed using parametric tests if these data conformed to the constraints of equivalence in variance and distribution. If these constrains were not satisfied, nonparametric analysis was used. The incidence of aneurysm formation was analyzed by Fisher’s exact test. P < 0.05 was considered statistically significant. All statistical analyses were performed with SigmaStat (SPSS, Inc.).


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Conclusions
 References
 
Gender difference in AngII-induced atherosclerosis and AAAs
AngII infusion has been described previously to augment atherosclerotic lesion development in both male and female apoE–/– mice (7, 10). To define the role of ovarian hormones in gender differences in AngII-induced vascular disease, female apoE–/– mice were subjected to ovx or sham operation and infused with saline or AngII. We included age-matched male apoE–/– mice infused with saline or AngII in this study to determine the effect of gender on baseline and AngII-induced atherosclerosis. We did not observe a gender difference in baseline atherosclerosis in saline-infused male vs. female mice (Fig. 1Go). Moreover, AngII increased atherosclerosis to the same extent in both genders (Fig. 1Go). AngII infusion also promoted an equivalent increase (~20 mm Hg) in systolic blood pressure in sham females (Table 1Go) and males (data not shown).



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  		FIG. 1. Quantification of atherosclerosis in male, ovx, and sham-operated female apoE–/– mice. The atherosclerotic lesion area was determined by en face analysis of the thoracic aorta. An intimal surface covered by grossly discernible lesions was determined and is expressed as a percentage of the total intimal area. Symbols represent the values from individual mice, with the mean and SEM adjacent to each group. The percentage of thoracic intima covered by atherosclerotic lesions was similar in male, ovx, and sham-operated female mice infused with saline (A). AngII significantly increased atherosclerotic lesion area to a similar extent in all three groups (B) (*, P < 0.05).

 

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  		TABLE 1. Effects of saline and AngII (1000 ng/kg·min) infusions on vascular disease in sham and ovx mice

 
Although there was no difference in the extent of AngII-induced atherosclerosis between male and female mice, there were striking differences in the development of AAAs (Fig. 2Go). AngII infusion induced a higher incidence of AAAs in males compared with sham-operated females (82% vs. 25% respectively; P < 0.05). Furthermore, the AAAs that developed were significantly larger in male mice (P < 0.05; Fig. 2Go).



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  		FIG. 2. AAA formation during AngII infusion in male apoE–/– mice and female apoE–/– mice that were either sham operated or ovx. A, Abdominal aorta tissue weights were measured for mice in each group as an indication of AAA severity. Abdominal aorta tissue weights were not different between sham and ovx mice. Abdominal aorta tissue weights of male mice were significantly increased compared with those of sham females (*, P < 0.05). Triangles represent the individual mice, circles are group means, bars are SEMs. B, Representative photographs of AAA from mice in each group, illustrating that male AAAs were larger than those in sham and ovx females.

 
Ovx fails to modify AngII-induced vascular diseases
Surgical ovx was well tolerated by all mice, and its success was indicated by marked uterine atrophy (Table 1Go). Ovx resulted in an initial increase in the rate of body weight gain, although there was no significant difference at the termination of the study (Table 1Go). Ovx did not influence systolic blood pressure during the infusion of saline or AngII (Table 1Go). The procedure did produce a modest, but statistically significant, increase in serum total cholesterol concentrations during AngII infusion (P < 0.01; Table 1Go). Ovx did not influence spleen AngII receptor density in saline-infused mice (data not shown). The infusion of AngII resulted in an equivalent decrease (17%) in specific binding in spleen from sham-operated and ovx mice (saline, 1.18 ± 0.01 nCi; AngII, 0.98 ± 0.02 nCi; P = 0.01).

Although ovx resulted in discernable physiological changes, the low level of atherosclerosis in young saline-infused apoE–/– mice used in this study was not significantly influenced by ovx (Fig. 1Go). In the present study AngII infusion increased the extent of atherosclerosis compared with saline infusion in both sham and ovx mice (Fig. 1Go). Under the constraints of the present study design, we did not observe a statistically significant difference in the extent of thoracic aortic intima surface that was covered by atherosclerotic lesions between sham-operated and ovx mice. Furthermore, ovx failed to significantly modify either the incidence (sham, 25%; ovx, 52%; not significant) or the severity of AngII-induced AAA formation (Fig. 2Go).

Orx differentially influences AngII-induced vascular diseases
The success of surgical orx was demonstrated by decreased serum concentrations of testosterone in castrated male mice [sham, 7.43 ± 0.92 ng/ml; orchidectomized (orx), 0.85 ± 0.13 ng/ml; P < 0.001]. In addition, orx mice exhibited a reduction in body weight compared with sham controls (29.1 ± 0.5 vs. 32.2 ± 0.5 g, respectively; P < 0.001). The infusion of AngII (1000 ng/kg·min) resulted in a distinct hypertensive response that was evident by d 3 and maintained throughout the study (Fig. 3Go). The hypertensive response induced by AngII was not influenced by orx.



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  		FIG. 3. Systolic blood pressure during AngII infusion in male apoE–/– mice that were with sham operated or orx. Systolic blood pressure was measured by a computerized tail-cuff technique before and during AngII infusion. Baseline blood pressure did not differ between sham or orx mice. The infusion of AngII (d 0) resulted in a distinct hypertensive response that was evident by d 3 of infusion. Points represent means, and bars are SEMs.

 
The incidence of AngII-induced AAA was strikingly reduced in orx mice compared with sham controls (18% vs. 85%, respectively; P = 0.003; Fig. 4Go), similar to the incidence observed in female mice infused with AngII (25%). The few orx mice that developed AAAs died early in the study due to ruptured AAA. Atherosclerosis was not determined due to the high incidence of death from ruptured AAA in sham-operated mice at the dose of 1000 ng/kg·min.



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  		FIG. 4. Incidence of AngII-induced (1000 ng/kg·min) AAA in sham-operated and orx apoE–/– mice. Orx decreased AAA incidence from 85% to 18%. Histobars represent the percent incidence. *, P < 0.003.

 
As high doses of AngII infusion can cause mortality due to aneurysmal rupture, a subsequent study was performed in orx and sham-operated mice that were infused with either saline or a lower dose of AngII (500 ng/kg·min). This dose of AngII did not change systolic blood pressure, as reported previously (25). Orx had no effect on the plasma renin concentration in saline-infused mice (Table 2Go). Moreover, the infusion of AngII decreased the plasma renin concentration to the same extent in sham and orx mice. Orx did not significantly influence AngII receptor binding density in the spleen of saline-infused mice (Table 2Go). Furthermore, chronic infusion of AngII decreased the number of AngII-binding sites to the same extent in sham and orx mice (Table 2Go). Losartan displaced 99% of the binding in all groups (data not shown).


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  		TABLE 2. Effects of saline and AngII (500 ng/kg·min) infusions on plasma renin concentration and AngII receptor density

 
At the termination of the experiment, serum total cholesterol concentrations were not significantly changed by either infusion or surgical procedure (data not shown). However, orx promoted a pronounced decrease in high density lipoprotein (HDL) cholesterol concentrations in both AngII-infused (sham, 50 ± 6 mg/dl; orx, 33 ± 6 mg/dl; P < 0.05; Fig. 5Go) and saline-infused (data not shown) mice.



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  		FIG. 5. Serum lipoprotein cholesterol distribution in sham-operated and orx apoE–/– mice infused with AngII (500 ng/kg·min). Orx decreased HDL cholesterol concentrations in saline-infused (data not shown) and AngII-infused mice. {bullet}, Sham-operated mice; {circ}, orx mice. The values shown are the mean ± SEM of four individual mice per group. *, P < 0.05 in comparison of area under the curve for HDL-cholesterol.

 
Atherosclerosis was quantified by en face analysis in the aortic arch and was expressed as the percent lesion covering the intimal area. Orx significantly increased the severity of atherosclerosis in saline-infused mice (Fig. 6Go). AngII infusion also promoted increases in the extent of lesions in both sham-operated and orx mice (Fig. 6Go).



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  		FIG. 6. Development of atherosclerosis. Atherosclerotic lesion area was determined by en face analysis in the aortic arch. The intimal surface covered by grossly discernible lesions was determined and is expressed as a percentage of the total intimal area. Symbols represent the values from individual mice, with the mean and SEM adjacent to each group. Orx increased the extent of atherosclerosis in the arch compared with sham controls (*, P = 0.001; A). AngII (500 ng/kg·min; B) significantly increased the percent lesion area in the arch of the aorta of both sham and orx mice (**, P = 0.014). However, there was no interaction between surgery and AngII infusion.

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Conclusions
 References
 
Gender effects on AngII-induced vascular diseases
Previous studies in diet and genetically manipulated mice have quantified the effect of gender on the extent of atherosclerosis. Although there are some studies that have noted increased atherosclerosis in female mice (30), the majority of studies demonstrate that gender does not affect hypercholesterolemia-induced lesion formation (14, 31, 32, 33, 34). In agreement with hypercholesterolemia-mediated atherosclerosis, we found no difference in the size of the lesions caused by chronic infusion of AngII into male or female apoE–/– mice.

Despite the lack of a gender effect in AngII-induced atherosclerosis, there were large gender differences in the development of AAAs. We have previously speculated an enhanced incidence and severity of AngII-induced AAAs in males based on analysis of pooled data (10) and literature comparisons (9, 10). This speculation was confirmed in the present study in which male and female mice were studied simultaneously. This enhanced susceptibility of male mice to develop AAAs is consistent with the enhanced prevalence of AAAs in human males.

Lack of effect of ovx on AngII-induced atherosclerosis and AAA
Administration of estradiol has been reported to protect against the development of atherosclerosis in hyperlipidemic mouse models (13, 14, 16, 35). In the majority of previous studies that have examined the effect of ovx on lesion formation, ovx was performed on young mice, and atherosclerotic lesion formation was quantified after waiting a considerably longer time (>2 months) than in the present study design (14, 16, 35). The current study design examined the effect of ovx after a relatively brief 28-d infusion of saline or AngII. Moreover, in contrast to the design of previous studies, we chose to ovariectomize older mice because of the critical effects that estrogens have on development (36, 37). Even with these differences in experimental design, our results are in agreement with previous studies demonstrating a lack of effect of ovx (<60 d) on the extent of atherosclerosis (13, 14). Moreover, results from this study extend previous findings by demonstrating that ovx does not markedly influence AngII-induced atherosclerosis.

A recent study demonstrated that administration of estradiol to male apoE–/– mice infused with AngII decreased the extent of atherosclerosis and AAA formation (17). These findings suggest that removal of ovarian hormones would have detrimental effects on AngII-induced vascular diseases. Potential differences related to the administration of exogenous hormones vs. removal of endogenous hormones may contribute to disparate results across studies. For example, administration of exogenous estradiol would result in steady, supraphysiological levels of the hormone in the circulation, as opposed to the cyclic secretion of estradiol that is seen endogenously. Moreover, administration of estradiol to intact male mice may exert beneficial effects on AngII-induced vascular diseases through a variety of pharmacological mechanisms. Our results demonstrate that endogenous ovarian hormones in female mice are not the primary mediators of gender differences in AngII-induced AAA.

Orx increases AngII-induced atherosclerosis
Androgens are believed to be associated with a higher risk of cardiovascular disease in men (22, 38, 39 ; for review, see Ref. 18). However, our results demonstrate that orx of apoE–/– mice increased the extent of atherosclerosis in both saline- and AngII-infused mice, suggesting that male gonadal hormones exert beneficial effects on the cardiovascular system. Similarly, in previous studies castration of male apoE–/– mice increased the extent of atherosclerosis (40). Moreover, castration of male low density lipoprotein receptor-deficient mice increased early fatty lesions, which were reversed by administration of testosterone (23). Protective effects of testosterone were attributed to conversion to estradiol (23, 24). In the present study increases in atherosclerosis in orx mice were accompanied by a significant decrease in HDL cholesterol. The influence of androgens on serum lipids and lipoprotein concentrations in men remains controversial (22). Some studies have reported a negative relationship between testosterone and HDL cholesterol (22, 41), whereas others have reported the opposite effect (42, 43). Reductions in HDL may have contributed to the negative effect of orx on atherosclerosis in this study. To determine whether orx altered the renin-angiotensin system, we measured AngII receptor binding in the spleen, a tissue rich in macrophages and previously demonstrated to exhibit high AngII receptor density (28). Moreover, we determined the plasma renin concentration as an index of the systemic renin-angiotensin system. Our results suggest that the effect of orx on baseline atherosclerosis does not involve marked changes in these components of the renin-angiotensin system.

Orx markedly attenuates AngII-induced AAA formation
Male gender is a risk factor for the development of AAA (2, 3). However, mechanisms contributing to the increased risk of AAA in males have not been defined. In this study orx markedly decreased the incidence of AngII-induced AAA to the level of an intact female. These results suggest a primary role for androgens in mediating gender differences in AngII-induced AAA. A variety of potential mechanisms may contribute to deleterious effects from male androgens on AAA formation. For example, recent results demonstrated that doxycycline decreased AngII-induced AAA formation through inhibition of matrix metalloproteinases (MMPs) (44). Furthermore, androgens have the ability to stimulate MMP-2 expression (45). Taken together, these results suggest that androgens may increase AngII-induced AAA formation through stimulation of MMPs. Alternative mechanisms potentially contributing to deleterious effects of androgens on AngII-induced AAA formation include stimulation of components of the renin-angiotensin system (46), producing either increased synthesis or responsiveness to AngII. In the present study we found that orx did not influence the plasma renin concentration. Orx did result in a modest, yet significant, decrease in AngII receptor density in the spleen. However, AngII receptor density in the spleen was similar in sham and orx mice infused with AngII despite striking differences in AAA incidence between these groups. These results suggest that regulation of spleen AngII receptor density by orx is not the primary mechanism for gender differences in AngII-induced AAA. Further studies are necessary to determine the effect of orx on circulating plasma angiotensin peptide concentrations and other components of the renin-angiotensin system. In addition, the effect of ox to decrease AngII-induced AAA could be exerted locally on the vascular wall renin-angiotensin system.

Differential effects of orx on atherosclerosis and AAA
Atherosclerosis is considered a risk factor for AAA; however, it is debatable whether an atherosclerotic lesion is a strict requirement for subsequent formation of an aneurysm (47). We have found that orx has differential effects on AngII-induced AAA and atherosclerosis. Opposite to the protective effect that orx had on development of AngII-induced AAA, this procedure increased the extent of atherosclerosis. This differential effect was unexpected, because AAA is a disease typically associated with atherosclerosis (30, 48). Recent data from our laboratories demonstrated that atherosclerotic lesions were detected subsequent to the formation of AAAs, suggesting that atherosclerosis was not contributing to the development of AngII-induced AAA (49). Moreover, recent results demonstrate that normolipidemic C57BL/6 mice can also develop AngII-induced AAA, although at a lower incidence than is seen in hyperlipidemic apoE–/– mice (50). This further supports the idea that AngII-induced AAA and atherosclerosis are formed through different mechanisms, and that atherosclerosis is not a strict requirement for developing AAA.


   Conclusions
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusions
References
 
The results of these studies demonstrate that the removal of ovarian hormones does not markedly influence the development of AngII-induced vascular diseases in apoE–/– mice. Furthermore, we have shown that orx has differential effects on AngII-induced AAA and atherosclerosis, which do not appear to involve regulation of the plasma renin concentration or spleen AngII receptor density. Although orx resulted in a striking decrease in AAA formation, the atherosclerotic lesion area was increased. Importantly, orx decreased AngII-induced AAA in males to the level observed in female mice. These results demonstrate that the mechanism for gender differences in AngII-induced AAA resides in male sex hormones.


   Acknowledgments
 
We thank Marc Helton, Delana Hopkins, Deborah Howatt, Debra Rateri, and Wei Qiu for their technical assistance.


   Footnotes
 
This work was supported by National Institutes of Health Heart, Lung, and Blood Institute Grant HL-62846 and American Heart Association (Ohio Valley Affiliate) Grant AHA-0315062B.

Abbreviations: AAA, Abdominal aortic aneurysm; AngII, angiotensin II; apoE, apolipoprotein E; HDL, high-density lipoprotein; MMP, matrix metalloproteinase; orx, orchidectomy, orchidectomized; ovx, ovariectomy, ovariectomized.

Received December 1, 2003.

Accepted for publication April 12, 2004.


   References
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 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusions
 References
 

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