Cardiac and aortic structural alterations due to surgically-induced menopause associated with renovascular hypertension in rats

The effects of estrogen deficiency and aging on myocardial deformation and motion in normotensive female rats

OBJECTIVE

Estrogen deficiency is associated with left ventricular (LV) dysfunction in postmenopausal women and ovariectomized rats. Whether the relationship between estrogen deficiency and LV dysfunction is independent of cardiovascular disease (CVD) risk factors remains uncertain. This study assessed the effects of short-term and long-term estrogen deficiency on cardiac structure and function using conventional and speckle tracking echocardiography, independent of traditional CVD risk factors.

METHODS

Female Sprague-Dawley rats were divided into short-term (6 wks) ovariectomized (n = 9), short-term sham-operated (n = 10), long-term (6 mo) ovariectomized (n = 8), and long-term sham-operated (n = 9) groups. Cardiac geometry, systolic and diastolic function, and myocardial deformation and motion were measured using echocardiography.

RESULTS

Ovariectomy had no effect on conventional echocardiography measures of cardiac structure or function. Compared with short-term, long-term groups had reduced LV internal diameter (false discovery rate [FDR] adjusted P = 0.05) and impaired relaxation (e'; FDR adjusted P = 0.0005) independent of body mass and blood pressure (BP). Global longitudinal strain was impaired in ovariectomized compared with sham-operated rats (FDR adjusted P = 0.05), but not after adjusting for body mass and BP (FDR adjusted P = 0.16). Global longitudinal strain (FDR adjusted P = 0.05), strain rate (FDR adjusted P = 0.002), and velocity (FDR adjusted P = 0.04) were impaired in long-term compared with short-term groups. Global longitudinal strain rate remained impaired after adjustments for body mass and BP (FDR adjusted P = 0.02).

CONCLUSIONS

Estrogen deficiency does not independently cause cardiac remodeling, LV dysfunction, or impaired myocardial deformation. Traditional CVD risk factors accompanying estrogen deficiency may account for cardiac remodeling and dysfunction observed in postmenopausal women.

Orally active epoxyeicosatrienoic acid analog does not exhibit antihypertensive and reno- or cardioprotective actions in two-kidney, one-clip Goldblatt hypertensive rats

This study examined the effects of a novel orally active 14,15-epoxyeicosatrienoic acid analog (EET-A) on blood pressure (BP) and myocardial infarct size (IS) in two-kidney, one-clip (2K1C) Goldblatt hypertensive rats during sustained phase of hypertension. Between days 31 and 35 after clip placement the rats were treated with EET-A and BP was monitored by radiotelemetry; sham-operated normotensive rats were used as controls. Tissue concentrations of epoxyeicosatrienoic acids served as a marker of production of epoxygenase metabolites. The rats were subjected to acute myocardial ischemia/reperfusion (I/R) injury and IS was determined. We found that EET-A treatment did not lower BP in 2K1C rats and did not alter availability of biologically active epoxygenase metabolites in 2K1C or in sham-operated rats. The myocardial IS was significantly smaller in untreated 2K1C rats as compared with normotensive controls and EET-A reduced it in controls but not in 2K1C rats. Our findings suggest that during the phase of sustained hypertension 2K1C Goldblatt hypertensive rats exhibit increased cardiac tolerance to I/R injury as compared with normotensive controls, and that in this animal model of human renovascular hypertension short-term treatment with EET-A does not induce any antihypertensive and cardioprotective actions.

Gonadal hormones differently modulate cutaneous wound healing of chronically stressed mice

Gonadal hormones influence physiological responses to stress and cutaneous wound healing. The aim of this study was to investigate the role of gonadal hormones on cutaneous wound healing in chronically stressed mice. Male and female mice were gonadectomized, and after 25 days, they were spun daily at 115 rpm for 15 min every hour until euthanasia. Twenty-eight days after the gonadectomy, an excisional lesion was created. The animals were killed 7 or 14 days after wounding, and the lesions were collected. Myofibroblast density, macrophage number, catecholamine level, collagen deposition, and blood vessel number were evaluated. In the intact and gonadectomized groups, stress increased the plasma catecholamine levels in both genders. In intact groups, stress impaired wound contraction and re-epithelialization and increased the macrophage number in males but not in females. In addition, stress compromised myofibroblastic differentiation and blood vessel formation and decreased collagen deposition in males but not in females. In contrast to intact mice, wound healing in ovariectomized female mice was affected by stress, while wound healing in castrated male mice was not. In conclusion, gender differences contribute to the cutaneous wound healing of chronically stressed mice. In addition, androgens contribute to the stress-induced impairment of the healing of cutaneous wounds but estrogens inhibit it.

Effects of exercise on monocrotaline-induced changes in right heart function and pulmonary artery remodeling in rats

Pulmonary arterial hypertension (PAH) induced by monocrotaline (MCT) is an experimental protocol of right heart failure. We analyzed the role of exercise training on the right ventricle structure and function, pulmonary artery remodeling, and GSK-3β expression. Rats were divided among the following groups: sedentary control (SC), sedentary monocrotaline (SM), trained control (TC), and trained monocrotaline (TM). Rats underwent exercise training for a period of 5 weeks, with 3 weeks post-MCT injection. Rats in the SM and TM groups presented with an increase in right ventricle hypertrophy indexes and lung congestion. The right ventricular end diastolic pressure (RVEDP), right ventricular systolic pressure (RVSP), and its minimum and maximal pressure derivates were increased in the SM and TM groups. The right ventricle interstitial volume pulmonary artery thickness and p-GSK-3β/GSK-3β were increased in the MCT groups as compared with the control groups. The TM group had a reduction in interstitial volume, p-GSK-3β/GSK-3β ratio, pulmonary artery thickness, RVEDP, and an increase in intramyocardial vessels volume as compared with the SM group. The overall results have shown that the exercise protocol used promoted positive changes in right ventricle and pulmonary artery remodeling. These observations also suggest that structural remodeling may be influenced by signaling proteins, such as GSK-3β.

Influence of ovariectomy on cardiac oxidative stress in a renovascular hypertension model

The aim of this study was to evaluate the potential influence of endogenous ovarian hormones on cardiac oxidative stress in renovascular hypertension. Female Wistar rats (N = 10 per group) were divided among 4 groups: (i) normotensive control; (ii) hypertensive control; (iii) normotensive ovariectomized; and (iv) hypertensive ovariectomized rats. To induce hypertension, 2-kidney 1-clip (2K1C) Goldblatt's method was followed. Blood pressure (BP) was enhanced (25%) in 2K1C and it was not further altered in hypertensive ovariectomized animals. Lipid peroxidation (measured by thiobarbituric acid reactive substances; TBARS) increased in heart homogenates after ovariectomy (253%) and was additionally augmented when associated with hypertension (by 28%). Superoxide dismutase and catalase activities were similar in both hypertensive groups. Hypertension enhanced glutathione peroxidase activity (75%), but the association with ovariectomy prevented this change. Total radical trapping antioxidant potential (TRAP) decreased in hypertensive rats (34%) and was recovered when associated with ovariectomy. However, this adaptation seems not to be sufficient to avoid the increased oxidative damage in ovariectomized hypertensive animals. These results suggest a protective role for physiological ovarian hormones in the cardiac oxidative stress induced by 2K1C hypertension.

White spotting variant mouse as an experimental model for ovarian aging and menopausal biology

OBJECTIVE

Menopause is a unique phenomenon in modern women, as most mammalian species possess a reproductive period comparable with their life span. Menopause is caused by the depletion of germ cell-containing ovarian follicles and in laboratory studies is usually modeled in animals in which the ovarian function is removed through ovariectomy or chemical poisoning of the germ cells. Our objective was to explore and characterize the white spotting variant (Wv) mice that have reduced ovarian germ cell abundance, a result of a point mutation in the c-kit gene that decreases kinase activity, as a genetic model for use in menopause studies.

METHODS

Physiological and morphological features associated with menopause were determined in female Wv/Wv mice compared with age-matched wildtype controls. Immunohistochemistry was used to evaluate the presence and number of follicles in paraffin-embedded ovaries. Bone density and body composition were evaluated using the PIXImus x-ray densitometer, and lipids, calcium, and hormone levels were determined in serum using antigen-specific enzyme immunoassays. Heart and body weight were measured, and cardiac function was evaluated using transthoracic echocardiography.

RESULTS

The ovaries of the Wv/Wv females have a greatly reduced number of normal germ cells at birth compared with wildtype mice. The remaining follicles are depleted by around 2 months, and the ovaries develop benign epithelial lesions that resemble morphological changes that occur during ovarian aging, whereas a normal mouse ovary has numerous follicles at all stages of development and retains some follicles even in advanced age. Wv mice have elevated plasma gonadotropins and reduced estrogen and progesterone levels, a significant reduction in bone mass density, and elevated serum cholesterol and lipoprotein levels. Moreover, the Wv female mice have enlarged hearts and reduced cardiac function.

CONCLUSIONS

The reduction of c-kit activity in Wv mice leads to a substantially diminished follicular endowment in newborn mice and premature depletion of follicles in young mice, although mutant females have a normal life span after cessation of ovarian function. The Wv female mice exhibit consistent physiological changes that resemble common features of postmenopausal women. These alterations include follicle depletion, morphological aging of the ovary, altered serum levels of cholesterol, gonadotropins and steroid hormones, decreased bone density, and reduced cardiac function. These changes were not observed in male mice, either age-matched male Wv/Wv or wildtype mice, and are improbably caused by global loss of c-kit function. The Wv mouse may be a genetic, intact-ovary model that mimics closely the phenotypes of human menopause to be used for further studies to understand the mechanisms of menopausal biology.

Dehydroepiandrosterone protects against oxidative stress-induced endothelial dysfunction in ovariectomized rats

Cardiovascular disease is less frequent in premenopausal women than in age-matched men or postmenopausal women. Moreover, the marked age-related decline in serum dehydroepiandrosterone (DHEA) level has been associated to cardiovascular disease. The aim of this study was to evaluate the effects of DHEA treatment on vascular function in ovariectomized rats. At 8 weeks of age, female Wistar rats were ovariectomized (OVX) or sham (SHAM) operated and 8 weeks after surgery both groups were treated with vehicle or DHEA (10mg kg⁻¹ week⁻¹) for 3 weeks. Aortic rings were used to evaluate the vasoconstrictor response to phenylephrine (PHE) and the relaxation responses to acetylcholine (ACh) and sodium nitroprusside (SNP). Tissue reactive oxygen species (ROS) production and SOD, NADPH oxidase and eNOS protein expression were analysed. PHE-induced contraction was increased in aortic rings from OVX compared to SHAM, associated with a reduction in NO bioavailability. Furthermore, the relaxation induced by ACh was reduced in arteries from OVX, while SNP relaxation did not change. The incubation of aortic rings with SOD or apocynin restored the enhanced PHE-contraction and the impaired ACh-relaxation only in OVX. DHEA treatment corrected the increased PHE contraction and the impaired ACh-induced relaxation observed in OVX by an increment in NO bioavailability and decrease in ROS production. Besides, DHEA treatment restores the reduced Cu/Zn-SOD protein expression and eNOS phosphorylation and the increased NADPH oxidase protein expression in the aorta of OVX rats. The present results suggest an important action of DHEA, improving endothelial function in OVX rats by acting as an antioxidant and enhancing the NO bioavailability.

Vimentin and laminin are altered on cheek pouch microvessels of streptozotocin-induced diabetic hamsters

OBJECTIVE

Normal endothelial cells respond to shear stress by elongating and aligning in the direction of fluid flow. Hyperglycemia impairs this response and contributes to microvascular complications, which result in deleterious effects to the endothelium. This work aimed to evaluate cheek pouch microvessel morphological characteristics, reactivity, permeability, and expression of cytoskeleton and extracellular matrix components in hamsters after the induction of diabetes with streptozotocin.

METHODS

Syrian golden hamsters (90-130 g) were injected with streptozotocin (50 mg/kg, i.p.) or vehicle either 6 (the diabetes mellitus 6 group) or 15 (the diabetes mellitus 15 group) days before the experiment. Vascular dimensions and density per area of vessels were determined by morphometric and stereological measurements. Changes in blood flow were measured in response to acetylcholine, and plasma extravasation was measured by the number of leakage sites. Actin, talin, α-smooth muscle actin, vimentin, type IV collagen, and laminin were detected by immunohistochemistry and assessed through a semiquantitative scoring system.

RESULTS

There were no major alterations in the lumen, wall diameters, or densities of the examined vessels. Likewise, vascular reactivity and permeability were not altered by diabetes. The arterioles demonstrated increased immunoreactivity to vimentin and laminin in the diabetes mellitus 6 and diabetes mellitus 15 groups.

DISCUSSION

Antibodies against laminin and vimentin inhibit branching morphogenesis in vitro. Therefore, laminin and vimentin participating in the structure of the focal adhesion may play a role in angiogenesis.

CONCLUSIONS

Our results indicated the existence of changes related to cell-matrix interactions, which may contribute to the pathological remodeling that was already underway one week after induction of experimental diabetes.

Exercise training enhances elastin, fibrillin and nitric oxide in the aorta wall of spontaneously hypertensive rats

This work aimed to analyze the effect of low-intensity exercise training on ultrastructural and molecular aortic remodeling. Male Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were allocated into four groups: sedentary WKY (SED-WKY), exercised WKY (EX-WKY, 1 h/day, 5 days/week treadmill exercise training), sedentary SHR (SED-SHR), and exercised SHR (EX-SHR). EX-SHR showed blood pressure reduction of 26% in comparison to SED-SHR after 1 month of exercise (P<0.05). At the 20th week, BP level was not different between EX-SHRs and WKYs. Circumferential wall tension (CWT) was higher by 77% in SED-SHRs than in SED-WKYs (P<0.001). Exercise training reduced CWT by 30% in EX- vs. SED-SHR (P<0.001). In SED-SHRs, endothelial cells showed large and numerous cytoplasmatic vacuoles, fragmented inner elastic lamina and scarce elastin and fibrillin, while exercise training ameliorated it in EX-SHR group. The highest eNOS immunodensity was observed in EX-SHR, which was 50% higher than EX-WKY (P<0.01) and 120% higher than SED-SHR (P<0.0001). In conclusion, present findings indicate beneficial effects of exercise training in hypertensive rats since it increased elastin, fibrillin and eNOS content in the aortic wall.

Rosiglitazone (peroxisome proliferator-activated receptor-gamma) counters hypertension and adverse cardiac and vascular remodeling in 2K1C hypertensive rats

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists have been shown controlling blood pressure (BP) in spontaneously hypertensive rats and salt-sensitive hypertensive rats. The present study aims to test the hypothesis that PPAR-gamma agonist rosiglitazone has beneficial effects on cardiac and vascular adverse remodeling in a model of renovascular hypertension (two-kidneys-one-clip, 2K1C model). Wistar rats were divided into four groups (n=6): SHAM group, 2K1C, 2K1C+HYD (treated with hydralazine for 5 weeks) and 2K1C+ROSI (treated with rosiglitazone for 5 weeks). The left ventricle (LV), thoracic aorta (Ao) and common carotid artery (CCA) were analyzed. The BP did not show significant difference at the end of the experiment in groups 2K1C+ROSI, 2K1C+HYD and SHAM. The LV mass was smaller in 2K1C+ROSI compared with the other groups. The intima-media thickness was smaller in 2K1C+ROSI compared with untreated 2K1C ones, but not in 2K1C+HYD; 2K1C and 2K1C+HYD showed smaller Ao and CCA density of smooth muscle cell nuclei, and smaller surface density of the elastic lamellae than SHAM. The Ao and CCA circumferential wall tension and tensile stress were greater in 2K1C than in SHAM. Hypertrophied cardiomyocytes were seen in 2K1C, but not in 2K1C+ROSI and SHAM; 2K1C+ROSI had enhanced volume and length densities of intramyocardial arteries than 2K1C. The volume density of cardiac interstitium was greater in 2K1C and 2K1C+HYD than in SHAM. In conclusion, PPAR-gamma agonist rosiglitazone has beneficial effects controlling BP, reducing vascular adverse remodeling, and preserving intramyocardial vascularization in renovascular hypertensive rats (2K1C model).