Fibroblasts under pressure: cardiac fibroblast responses to hypertension and antihypertensive therapies

Approximately 50% of Americans have hypertension, which significantly increases the risk of heart failure. In response to increased peripheral resistance in hypertension, intensified mechanical stretch in the myocardium induces cardiomyocyte hypertrophy and fibroblast activation to withstand increased pressure overload. This changes the structure and function of the heart, leading to pathological cardiac remodeling and eventual progression to heart failure. In the presence of hypertensive stimuli, cardiac fibroblasts activate and differentiate to myofibroblast phenotype capable of enhanced extracellular matrix secretion in coordination with other cell types, mainly cardiomyocytes. Both systemic and local renin-angiotensin-aldosterone system activation lead to increased angiotensin II stimulation of fibroblasts. Angiotensin II directly activates fibrotic signaling such as transforming growth factor β/SMAD and mitogen-activated protein kinase (MAPK) signaling to produce extracellular matrix comprised of collagens and matricellular proteins. With the advent of single-cell RNA sequencing techniques, heterogeneity in fibroblast populations has been identified in the left ventricle in models of hypertension and pressure overload. The various clusters of fibroblasts reveal a range of phenotypes and activation states. Select antihypertensive therapies have been shown to be effective in limiting fibrosis, with some having direct actions on cardiac fibroblasts. The present review focuses on the fibroblast-specific changes that occur in response to hypertension and pressure overload, the knowledge gained from single-cell analyses, and the effect of antihypertensive therapies. Understanding the dynamics of hypertensive fibroblast populations and their similarities and differences by sex is crucial for the advent of new targets and personalized medicine.

Comparative Analysis of Hypertensive Tubulopathy in Animal Models of Hypertension and Its Relevance to Human Pathology

Assessment of hypertensive tubulopathy for more than fifty animal models of hypertension in experimental pathology employs criteria that do not correspond to lesional descriptors for tubular lesions in clinical pathology. We provide a critical appraisal of experimental hypertension with the same approach used to estimate hypertensive renal tubulopathy in humans. Four models with different pathogenesis of hypertension were analyzed-chronic angiotensin (Ang) II-infused and renin-overexpressing (TTRhRen) mice, spontaneously hypertensive (SHR), and Goldblatt two-kidney one-clip (2K1C) rats. Mouse models, SHR, and the nonclipped kidney in 2K1C rats had no regular signs of hypertensive tubulopathy. Histopathology in animals was mild and limited to variations in the volume density of tubular lumen and epithelium, interstitial space, and interstitial collagen. Affected kidneys in animals demonstrated lesion values that are significantly different compared with healthy controls but correspond to mild damage if compared with hypertensive humans. The most substantial human-like hypertensive tubulopathy was detected in the clipped kidney of 2K1C rats. For the first time, our study demonstrated the regular presence of chronic progressive nephropathy (CPN) in relatively young mice and rats with induced hypertension. Because CPN may confound the assessment of rodent models of hypertension, proliferative markers should be used to verify nonhypertensive tubulopathy.

Comparative analysis of hypertensive nephrosclerosis in animal models of hypertension and its relevance to human pathology. Glomerulopathy

Current research on hypertension utilizes more than fifty animal models that rely mainly on stable increases in systolic blood pressure. In experimental hypertension, grading or scoring of glomerulopathy in the majority of studies is based on a wide range of opinion-based histological changes that do not necessarily comply with lesional descriptors for glomerular injury that are well-established in clinical pathology. Here, we provide a critical appraisal of experimental hypertensive glomerulopathy with the same approach used to assess hypertensive glomerulopathy in humans. Four hypertensive models with varying pathogenesis were analyzed–chronic angiotensin II infused mice, mice expressing active human renin in the liver (TTRhRen), spontaneously hypertensive rats (SHR), and Goldblatt two-kidney one-clip rats (2K1C). Analysis of glomerulopathy utilized the same criteria applied in humans–hyalinosis, focal segmental glomerulosclerosis (FSGS), ischemic, hypertrophic and solidified glomeruli, or global glomerulosclerosis (GGS). Data from animal models were compared to human reference values. Kidneys in TTRhRen mice, SHR and the nonclipped kidneys in 2K1C rats had no sign of hyalinosis, FSGS or GGS. Glomerulopathy in these groups was limited to variations in mesangial and capillary compartment volumes, with mild increases in collagen deposition. Histopathology in angiotensin II infused mice corresponded to mesangioproliferative glomerulonephritis, but not hypertensive glomerulosclerosis. The number of nephrons was significantly reduced in TTRhRen mice and SHR, but did not correlate with severity of glomerulopathy. The most substantial human-like glomerulosclerotic lesions, including FSGS, ischemic obsolescent glomeruli and GGS, were found in the clipped kidneys of 2K1C rats. The comparison of affected kidneys to healthy control in animals produces lesion values that are numerically impressive but correspond to mild damage if compared to humans. Animal studies should be standardized by employing the criteria and classifications established in human pathology to make experimental and human data fully comparable for comprehensive analysis and model improvements.

Impact of Angiotensin II Antagonism on the Sex-Selective Dysregulation of Cardiovascular Function Induced by In Utero Dexamethasone Exposure

In utero exposure to glucocorticoids in late gestation programs changes in cardiovascular function. The objective of this study was to determine the degree to which angiotensin II mediates sex-biased changes in autonomic function as well as basal and stress-responsive cardiovascular function following in utero glucocorticoid exposure. Pregnant rats were administered the synthetic glucocorticoid dexamethasone (DEX 0.4mg/kg per day, s.c.) or vehicle on gestation days 18-21. Mean arterial pressure, heart rate, and heart rate variability (HRV) were measured via radiotelemetry in freely moving, conscious adult rats. To evaluate the impact of stress, rats were placed in a restraint tube for 20 minutes. In a separate cohort of rats, restraint stress was performed before and after chronic treatment with the angiotensin type 1 receptor antagonist, losartan (30mg/kg per day, i.p). Frequency domain analysis of HRV was evaluated, and data integrated into low frequency (LF: 0.20-0.75Hz) and high frequency (HF: 0.75-2.00Hz) bands. Prenatal DEX resulted in an exaggerated pressor and heart rate response to restraint in female offspring that was attenuated by prior losartan treatment. HF power was higher in vehicle-exposed female rats, compared to DEX females. Following losartan, HF power was equivalent between female vehicle and DEX-exposed rats. In utero exposure to DEX produced female-biased alterations in stress-responsive cardiovascular function which may be indicative of a reduction in parasympathetic activity. Moreover, these findings suggest this autonomic dysregulation may be mediated in part by long-term changes in renin-angiotensin signaling.

Androgens and Their Role in Regulating Sex Differences in the Hypothalamic/Pituitary/Adrenal Axis Stress Response and Stress-Related Behaviors

Androgens play a pivotal role during development. These gonadal hormones and their receptors exert organizational actions that shape brain morphology in regions controlling the stress regulatory systems in a male-specific manner. Specifically, androgens drive sex differences in the hypothalamic/pituitary/adrenal (HPA) axis and corresponding hypothalamic neuropeptides. While studies have examined the role of estradiol and its receptors in sex differences in the HPA axis and associated behaviors, the role of androgens remains far less studied. Androgens are generally thought to modulate the HPA axis through the activation of androgen receptors (ARs). They can also impact the HPA axis through reduction to estrogenic metabolites that can bind estrogen receptors in the brain and periphery. Such regulation of the HPA axis stress response by androgens can often result in sex-biased risk factors for stress-related disorders, such as anxiety and depression. This review focuses on the biosynthesis pathways and molecular actions of androgens and their nuclear receptors. The impact of androgens on hypothalamic neuropeptide systems (corticotropin-releasing hormone, arginine vasopressin, oxytocin, dopamine, and serotonin) that control the stress response and stress-related disorders is discussed. Finally, this review discusses potential therapeutics involving androgens (androgen replacement therapies, selective AR modulator therapies) and ongoing clinical trials.

Abstract P504: Transient Angiotensin Converting Enzyme Inhibition Protects Against Future Fibrogenic Responses Via Sex-specific Mechanisms

Following washout of angiotensin converting enzyme inhibitor (ACEi) treatment in hypertensive rats (SHR), there is an increase in the proportion of homeostatic cardiac fibroblasts (CFs) characterized by a less fibrogenic gene profile. The present study investigated the impact of this shift in CFs on subsequent Ang II-induced oxidative stress and fibrogenic responses in the left ventricle (LV). Male and female SHRs (11 wk old) underwent a 6-week treatment scheme: 2-week ACEi (enalapril, 30mg/kg/day) or vehicle treatment, followed by a 2-week washout period, and then a 2-week Ang II (400ng/kg/min, s.c.) or vehicle infusion (n=5-11/group/sex). RT-qPCR for collagens and immunoblotting for LOX, Postn, OPN, NOX2, SOD2, and catalase was performed. In males, Ang II-induced increases in ColI, III, and IV expression were significantly attenuated by prior ACEi. While in females, Ang II significantly increased the expression of ColI and III similarly, regardless of prior ACEi treatment; highlighting a sex-specific impact of ACEi. After Ang II infusion, both Postn and LOX are reduced in LV of male and female SHR previously treated with an ACEi - suggesting reduced collagen cross-linking. Oxidative stress induced by NOX2 has been linked to OPN in fibrotic tissue. Ang II-induced increases in NOX2 are attenuated in LV of both sexes, while OPN is only reduced in females previously treated with an ACEi. NOX2 is significantly positively correlated with OPN in males only suggesting a sex-specific link between OPN and oxidative stress. Antioxidant (SOD2, catalase) levels were positively correlated to NOX2 in females, but not males. This suggests that females more efficiently neutralize oxidative stress than males - regardless of prior ACEi. Taken together, the persistent genomic and phenotypic changes in CFs following transient ACEi render the heart resistant to future fibrotic and oxidative effects of Ang II, but the mechanisms of protection may differ by sex. Collectively, these data reveal that there are sex-specific processes that govern collagen production vs. cross-linking and oxidative stress. Future studies will elucidate the mechanistic underpinnings of sex-specific cellular memory following transient ACEi with a goal of identifying novel therapeutic targets.

Cardiac fibrosis: Pathobiology and therapeutic targets

Cardiac fibrosis is characteristic of the end stage in nearly all forms of heart disease. Accumulation of extracellular matrix in the myocardium leads to increased risk of arrhythmia and impaired cardiac function, and ultimately progression to heart failure. Despite the critical need to slow or reverse development of cardiac fibrosis to maintain cardiac function, there are no approved therapies that directly target the extracellular matrix. Research into the underlying causes and therapeutic targets has been hampered, in part, by the lack of a clear marker for cardiac fibroblasts - the cells responsible for regulating extracellular matrix turnover. Lineage tracing studies as well as single-cell RNA sequencing studies have provided new insights into cardiac fibroblast origins and heterogeneity. Moreover, a greater understanding of pathways governing fibroblast activation during ischemic and non-ischemic cardiac remodeling and their communication with other inflammatory and cardiac cells may lead to novel therapeutic targets to slow or reverse fibrotic remodeling. The special issue of Cellular Signaling entitled "Cardiac Fibrosis: Pathobiology and Therapeutic Targets" is comprised of review articles in which these topics, as well as important open questions for future investigation, are discussed.

Transient ACE (Angiotensin-Converting Enzyme) Inhibition Suppresses Future Fibrogenic Capacity and Heterogeneity of Cardiac Fibroblast Subpopulations

Transient ACE (angiotensin-converting enzyme) inhibition in spontaneously hypertensive rats is known to protect against future injury-induced cardiac inflammation, fibrosis, and dysfunction; however, the mechanisms of protection have not been delineated. Here, we used single-cell RNA sequencing to test the hypothesis that transient ACE inhibitor treatment would induce a persistent shift in cardiac fibroblast subpopulations. Adult male spontaneously hypertensive rats (11 weeks old, hypertensive with cardiac hypertrophy) were treated for 2 weeks with an ACE inhibitor, enalapril (30 mg/kg per day, PO), or water (untreated spontaneously hypertensive rats) followed by a 2-week washout period (n=7/group). Cardiac fibroblasts were isolated from the left ventricle and subjected to single-cell RNA sequencing. Nine clusters of fibroblasts were identified, with 98% of cells in clusters 0 to 6. The transient treatment produced significant changes both within and across clusters. Cluster 1 depicted a highly fibrogenic gene profile, with cluster 6 serving as a gateway to cluster 1. Transient ACE inhibition depleted the gateway and expanded cluster 0, which was the least fibrogenic profile. Moreover, within cluster 1 fibroblasts, ACE inhibition reduced expression of individual fibrosis genes (eg, COL1A1, COL3A1, and FN1; all P<1×10-35). Clusters 2 to 5 reflected proliferative, moderately fibrogenic, translationally active, and less inflammatory subsets of fibroblasts, all of which exhibited attenuated fibrogenic gene expression after transient ACE inhibition. In conclusion, transient ACE inhibition shifts cardiac fibroblast subpopulations and degree of activation resulting in an overall reduced fibrogenic phenotype.

The Hypothalamic-Pituitary-Adrenal Axis: Development, Programming Actions of Hormones, and Maternal-Fetal Interactions

The hypothalamic-pituitary-adrenal axis is a complex system of neuroendocrine pathways and feedback loops that function to maintain physiological homeostasis. Abnormal development of the hypothalamic-pituitary-adrenal (HPA) axis can further result in long-term alterations in neuropeptide and neurotransmitter synthesis in the central nervous system, as well as glucocorticoid hormone synthesis in the periphery. Together, these changes can potentially lead to a disruption in neuroendocrine, behavioral, autonomic, and metabolic functions in adulthood. In this review, we will discuss the regulation of the HPA axis and its development. We will also examine the maternal-fetal hypothalamic-pituitary-adrenal axis and disruption of the normal fetal environment which becomes a major risk factor for many neurodevelopmental pathologies in adulthood, such as major depressive disorder, anxiety, schizophrenia, and others.

RAS inhibition in resident fibroblast biology

Angiotensin II (Ang II) is a primary mediator of profibrotic signaling in the heart and more specifically, the cardiac fibroblast. Ang II-mediated cardiomyocyte hypertrophy in combination with cardiac fibroblast proliferation, activation, and extracellular matrix production compromise cardiac function and increase mortality in humans. Profibrotic actions of Ang II are mediated by increasing production of fibrogenic mediators (e.g. transforming growth factor beta, scleraxis, osteopontin, and periostin), recruitment of immune cells, and via increased reactive oxygen species generation. Drugs that inhibit Ang II production or action, collectively referred to as renin angiotensin system (RAS) inhibitors, are first line therapeutics for heart failure. Moreover, transient RAS inhibition has been found to persistently alter hypertensive cardiac fibroblast responses to injury providing a useful tool to identify novel therapeutic targets. This review summarizes the profibrotic actions of Ang II and the known impact of RAS inhibition on cardiac fibroblast phenotype and cardiac remodeling.

Targeting the renin-angiotensin-aldosterone system in fibrosis

Fibrosis is characterized by excessive deposition of extracellular matrix components such as collagen in tissues or organs. Fibrosis can develop in the heart, kidneys, liver, skin or any other body organ in response to injury or maladaptive reparative processes, reducing overall function and leading eventually to organ failure. A variety of cellular and molecular signaling mechanisms are involved in the pathogenesis of fibrosis. The renin-angiotensin-aldosterone system (RAAS) interacts with the potent Transforming Growth Factor β (TGFβ) pro-fibrotic pathway to mediate fibrosis in many cell and tissue types. RAAS consists of both classical and alternative pathways, which act to potentiate or antagonize fibrotic signaling mechanisms, respectively. This review provides an overview of recent literature describing the roles of RAAS in the pathogenesis of fibrosis, particularly in the liver, heart, kidney and skin, and with a focus on RAAS interactions with TGFβ signaling. Targeting RAAS to combat fibrosis represents a promising therapeutic approach, particularly given the lack of strategies for treating fibrosis as its own entity, thus animal and clinical studies to examine the impact of natural and synthetic substances to alter RAAS signaling as a means to treat fibrosis are reviewed as well.

The Impact of Genistein Supplementation on Tendon Functional Properties and Gene Expression in Estrogen-Deficient Rats

Tendinopathy risk increases with menopause. The phytoestrogen genistein prevents collagen loss during estrogen deficiency (ovariectomy [OVX]). The influence of genistein on tendon function and extracellular matrix (ECM) regulation is not well known. We determined the impact of genistein on tendon function and the expression of several genes important for the regulation of tendon ECM. Eight-week-old rats (n = 42) were divided into three groups: intact, OVX, or OVX-genistein (6 mg/kg/day) for 6 weeks. Tail fascicles were assessed with a Deben tensile stage. Achilles tendon mRNA expression was determined with digital droplet polymerase chain reaction. Compared to intact, fascicle stress tended to be lower in untreated OVX rats (P = .022). Furthermore, fascicle modulus and energy density were greater in genistein-treated rats (P < .05) compared to intact. Neither OVX nor genistein altered expression of Col1a1, Col3a1, Casp3, Casp8, Mmp1a, Mmp2, or Mmp9 (P > .05). Compared to intact, Tnmd and Esr1 expression were greater and Pcna and Timp1 expression were lower in OVX rats (P < .05). Genistein treatment returned Tnmd, Pcna, and Timp1 to levels of intact-vehicle (P < .05), but did not alter Scx or Esr1 (P > .05). Several β-catenin/Wnt signaling-related molecules were not altered by OVX or genistein (P > .05). Our findings demonstrate that genistein improves tendon function in estrogen-deficient rats. The effect of genistein in vivo was predominately on genes related to cell proliferation rather than collagen remodeling.

Chronic doxorubicin administration impacts satellite cell and capillary abundance in a muscle-specific manner

Anthracycline chemotherapies are effective at reducing disease recurrence and mortality in cancer patients. However, these drugs also contribute to skeletal muscle wasting and dysfunction. The purpose of this study was to assess the impact of chronic doxorubicin (DOX) administration on satellite cell and capillary densities in different skeletal muscles. We hypothesized that DOX would reduce satellite cell and capillary densities of the soleus (SOL) and extensor digitorum longus (EDL) muscles, along with muscle fiber size. Ovariectomized female Sprague-Dawley rats were randomized to receive three bi-weekly intraperitoneal injections of DOX (4 mg∙kg-1 ; cumulative dose 12 mg∙kg-1 ) or vehicle (VEH; saline). Animals were euthanized 5d following the last injection and the SOL and EDL were dissected and prepared for immunohistochemical and RT-qPCR analyses. Relative to VEH, CSA of the SOL and EDL fibers were 26% and 33% smaller, respectively, in DOX (P < 0.05). In the SOL, satellite cell and capillary densities were 39% and 35% lower, respectively, in DOX (P < 0.05), whereas in the EDL satellite cell and capillary densities were unaffected by DOX administration (P > 0.05). Proliferating satellite cells were unaffected by DOX in the SOL (P > 0.05). In the SOL, MYF5 mRNA expression was increased in DOX (P < 0.05), while in the EDL MGF mRNA expression was reduced in DOX (P < 0.05). Chronic DOX administration is associated with reduced fiber size in the SOL and EDL; however, DOX appeared to reduce satellite cell and capillary densities only in the SOL. These findings highlight that therapeutic targets to protect skeletal muscle from DOX may vary across muscles.

Gradual hypertension induction in middle-aged Cyp1a1-Ren2 transgenic rats produces significant impairments in spatial learning

Hypertension is a major health concern in the developed world, and its prevalence increases with advancing age. The impact of hypertension on the function of the renal and cardiovascular systems is well studied; however, its influence on the brain regions important for cognition has garnered less attention. We utilized the Cyp1a1-Ren2 xenobiotic-inducible transgenic rat model to mimic both the age of onset and rate of induction of hypertension observed in humans. Male, 15-month-old transgenic rats were fed 0.15% indole-3-carbinol (I3C) chow to slowly induce renin-dependent hypertension over a 6-week period. Systolic blood pressure significantly increased, eventually reaching 200 mmHg by the end of the study period. In contrast, transgenic rats fed a control diet without I3C did not show significant changes in blood pressure (145 mmHg at the end of study). Hypertension was associated with cardiac, aortic, and renal hypertrophy as well as increased collagen deposition in the left ventricle and kidney of the I3C-treated rats. Additionally, rats with hypertension showed reduced savings from prior spatial memory training when tested on the hippocampus-dependent Morris swim task. Motor and sensory functions were found to be unaffected by induction of hypertension. Taken together, these data indicate a profound effect of hypertension not only on the cardiovascular-renal axis but also on brain systems critically important for learning and memory. Future use of this model and approach may empower a more accurate investigation of the influence of aging on the systems responsible for cardiovascular, renal, and neurological health.

Exercise Protects Skeletal Muscle during Chronic Doxorubicin Administration

PURPOSE

This study aimed to assess the ability for exercise training performed before and during biweekly doxorubicin (DOX) administration to attenuate adverse effects of DOX on skeletal muscle. We hypothesized that DOX treatment would increase REDD1, impair mammalian target of rapamycin (mTOR) signaling, and reduce muscle fiber size, and that exercise training would attenuate these responses.

METHODS

Eight-week-old ovariectomized female Sprague-Dawley rats were randomized to one of four treatments: exercise + DOX (Ex-Dox), Ex + vehicle (Ex-Veh), sedentary + DOX (Sed-Dox), and Sed + Veh (Sed-Veh). DOX (4 mg·kg) or vehicle (saline) intraperitoneal injections were performed biweekly for a total of three injections (cumulative dose, 12 mg·kg). Ex animals performed interval exercise (4 × 4 min, 85%-90% V˙O2peak) 5 d·wk starting 1 wk before the first injection and continued throughout study duration. Animals were euthanized ~5 d after the last injection, during which the soleus muscle was dissected and prepared for immunoblot and immunohistochemical analyses.

RESULTS

REDD1 mRNA and protein were increased only in Sed-Dox (P < 0.05). The phosphorylation of mTOR and 4E-BP1 and MHC I and MHC IIa fiber size were lower in Sed-Dox versus Sed-Veh (P < 0.05). By contrast, REDD1 mRNA and protein, mTOR, 4E-BP1, and MHC I fiber size were not different between Ex-Dox and Ex-Veh (P > 0.05). LC3BI was higher, and the LC3BII/I ratio was lower in Sed-Dox versus Sed-Veh (P < 0.05) but not between Ex-Dox and Ex-Veh (P > 0.05).

CONCLUSION

These data suggest that DOX may inhibit mTORC1 activity and reduce MHCI and MHCIIa fiber size, potentially through elevated REDD1, and that exercise may provide a therapeutic strategy to preserve skeletal muscle size during chronic DOX treatment.

Prenatal stress-immune programming of sex differences in comorbidity of depression and obesity/metabolic syndrome

Major depressive disorder (MDD) is the number one cause of disability worldwide and is comorbid with many chronic diseases, including obesity/metabolic syndrome (MetS). Women have twice as much risk for MDD and comorbidity with obesity/MetS as men, although pathways for understanding this association remain unclear. On the basis of clinical and preclinical studies, we argue that prenatal maternal stress (ie, excess glucocorticoid expression and associated immune responses) that occurs during the sexual differentiation of the fetal brain has sex-dependent effects on brain development within highly sexually dimorphic regions that regulate mood, stress, metabolic function, the autonomic nervous system, and the vasculature. Furthermore, these effects have lifelong consequences for shared sex-dependent risk of MDD and obesity/MetS. Thus, we propose that there are shared biologic substrates at the anatomical, molecular, and/or genetic levels that produce the comorbid risk for MDD-MetS through sex-dependent fetal origins.

Impact of TGF-β inhibition during acute exercise on Achilles tendon extracellular matrix

The purpose of this study was to evaluate the role of TGF-β₁ in regulating tendon extracellular matrix after acute exercise. Wistar rats exercised (n = 15) on a treadmill for four consecutive days (60 min/day) or maintained normal cage activity. After each exercise bout, the peritendinous space of each Achilles tendon was injected with a TGF-β₁ receptor inhibitor or sham. Independent of group, tendons injected with inhibitor exhibited ~50% lower Smad 3 (Ser^423/425) (P < 0.05) and 2.5-fold greater ERK1/2 phosphorylation (P < 0.05) when compared with sham (P < 0.05). Injection of the inhibitor did not alter collagen content in either group (P > 0.05). In exercised rats, hydroxylyslpyridinoline content and collagen III expression were lower (P < 0.05) in tendons injected with inhibitor when compared with sham. In nonexercised rats, collagen I and lysyl oxidase (LOX) expression was lower (P < 0.05) in tendons injected with inhibitor when compared with sham. Decorin expression was not altered by inhibitor in either group (P > 0.05). On the basis of evaluation of hematoxylin and eosin (H&E) stained cross sections, cell numbers were not altered by inhibitor treatment in either group (P > 0.05). Evaluation of H&E-stained sections revealed no effect of inhibitor on collagen fibril morphology. In contrast, scores for regional variation in cellularity decreased in exercised rats (P < 0.05). No differences in fiber arrangement, structure, and nuclei form were noted in either group (P > 0.05). Our findings suggest that TGF-β₁ signaling is necessary for the regulation of tendon cross-link formation, as well as collagen and LOX gene transcription in an exercise-dependent manner.

Persistent phenotypic shift in cardiac fibroblasts: impact of transient renin angiotensin system inhibition

Fibrotic cardiac remodeling ultimately leads to heart failure - a debilitating and costly condition. Select antihypertensive agents have been effective in reducing or slowing the development of cardiac fibrosis. Moreover, some experimental studies have shown that the reduction in fibrosis induced by these agents persists long after stopping treatment. What has not been as well investigated is whether this transient treatment results in a protection against future fibrotic cardiac remodeling. In the present review, previously published studies are re-examined to assess whether the relative percent increase in collagen deposition over an off-treatment period is attenuated, relative to control, following transient antihypertensive treatment in young or adult rats. Present findings suggest that transient inhibition of the renin angiotensin system (RAS) not only produces a sustained reduction in cardiac fibrosis, but also results in a degree of protection against future collagen deposition. In addition, prior transient RAS inhibition appears to alter the cardiac fibroblast phenotype such that these cells show a muted response to myocardial injury - namely reduced proliferation, chemokine release, and collagen deposition. This review puts forth several potential mechanisms underlying this long-term cardiac protection that is afforded by transient RAS inhibition. Specifically, fibroblast phenotypic change, cardiac fibroblast apoptosis, sustained suppression of the RAS, persistent reduction in left ventricular hypertrophy, and persistent reduction in arterial pressure are each discussed. Identifying the mechanisms ultimately responsible for this change in cardiac fibroblast response to injury, hypertension, and aging may reveal novel targets for therapy.

Time course of cardiac inflammation during nitric oxide synthase inhibition in SHR: impact of prior transient ACE inhibition

We have previously demonstrated that angiotensin-converting enzyme (ACE) inhibition with enalapril produces persistent effects that protect against future nitric oxide synthase (NOS) inhibitor (L-arginine methyl ester, L-NAME)-induced cardiac dysfunction and outer wall collagen deposition in spontaneously hypertensive rats (SHR). In the present study, we dissect the cytokine/chemokine release profile during NOS inhibition, its correlation to pathological cardiac remodeling and the impact of transient ACE inhibition on these effects. Adult male SHR were treated with enalapril (E+L) or tap water (C+L) for 2 weeks followed by a 2-week washout period. Rats were then subjected to 0, 3, 7 or 10 days of L-NAME treatment. The temporal response to NOS inhibition was evaluated by measuring arterial pressure, cardiac remodeling and cytokine/chemokine levels. L-NAME equivalently increased blood pressure and myocardial and vascular injury in C+L and E+L rats. However, pulse pressure (PP) was only transiently altered in C+L rats. The levels of several inflammatory mediators were increased during L-NAME treatment. However, interleukin-6 (IL-6) and IL-10 and monocyte chemoattractant protein-1 were uniquely increased in C+L hearts; whereas IL-4 and fractalkine were only elevated in E+L hearts. By days 7 and 10 of L-NAME treatment, there was a significant increase in the cardiac density of macrophages and proliferating cells, respectively only in C+L rats. Although myocardial injury was similar in both treatment groups, PP was not changed and there was a distinct cardiac chemokine/cytokine signature in rats previously treated with enalapril that may be related to the lack of proliferative response and macrophage infiltration in these hearts.

Persistent change in cardiac fibroblast physiology after transient ACE inhibition

Transient angiotensin-converting enzyme (ACE) inhibition induces persistent changes that protect against future nitric oxide synthase (NOS) inhibitor-induced cardiac fibrosis and inflammation. Given the role of fibroblasts in mediating these effects, the present study investigates whether prior ACE inhibition produced persistent changes in cardiac fibroblast physiology. Adult male spontaneously hypertensive rats (SHRs) were treated with vehicle (C+L) or the ACE inhibitor, enalapril (E+L) for 2 wk followed by a 2-wk washout period and a subsequent 7-day challenge with the NOS inhibitor N(ω)-nitro-l-arginine methyl ester. A third set of untreated SHRs served as controls. At the end of the study period, cardiac fibroblasts were isolated from control, C+L, and E+L left ventricles to assess proliferation rate, collagen expression, and chemokine release in vitro. After 7 days of NOS inhibition, there were areas of myocardial injury but no significant change in collagen deposition in E+L and C+L hearts in vivo. In vitro, cardiac fibroblasts isolated from C+L but not E+L hearts were hyperproliferative, demonstrated increased collagen type I gene expression, and an elevated secretion of the macrophage-recruiting chemokines monocyte chemoattractant protein-1 and granulocyte macrophage-colony stimulating factor. These findings demonstrate that in vivo N(ω)-nitro-l-arginine methyl ester treatment produces phenotypic changes in fibroblasts that persist in vitro. Moreover, this is the first demonstration that transient ACE inhibition can produce a persistent modification of the cardiac fibroblast phenotype to one that is less inflammatory and fibrogenic. It may be that the cardioprotective effects of ACE inhibition are related in part to beneficial changes in cardiac fibroblast physiology.

Influence of acute and chronic streptozotocin-induced diabetes on the rat tendon extracellular matrix and mechanical properties

Diabetes is a major risk factor for tendinopathy, and tendon abnormalities are common in diabetic patients. The purpose of the present study was to evaluate the effect of streptozotocin (60 mg/kg)-induced diabetes and insulin therapy on tendon mechanical and cellular properties. Sprague-Dawley rats (n = 40) were divided into the following four groups: nondiabetic (control), 1 wk of diabetes (acute), 10 wk of diabetes (chronic), and 10 wk of diabetes with insulin treatment (insulin). After 10 wk, Achilles tendon and tail fascicle mechanical properties were similar between groups (P > 0.05). Cell density in the Achilles tendon was greater in the chronic group compared with the control and acute groups (control group: 7.8 ± 0.5 cells/100 μm(2), acute group: 8.3 ± 0.4 cells/100 μm(2), chronic group: 10.9 ± 0.9 cells/100 μm(2), and insulin group: 9.2 ± 0.8 cells/100 μm(2), P < 0.05). The density of proliferating cells in the Achilles tendon was greater in the chronic group compared with all other groups (control group: 0.025 ± 0.009 cells/100 μm(2), acute group: 0.019 ± 0.005 cells/100 μm(2), chronic group: 0.067 ± 0.015, and insulin group: 0.004 ± 0.004 cells/100 μm(2), P < 0.05). Patellar tendon collagen content was ∼32% greater in the chronic and acute groups compared with the control or insulin groups (control group: 681 ± 63 μg collagen/mg dry wt, acute group: 938 ± 21 μg collagen/mg dry wt, chronic: 951 ± 52 μg collagen/mg dry wt, and insulin group: 596 ± 84 μg collagen/mg dry wt, P < 0.05). In contrast, patellar tendon hydroxylysyl pyridinoline cross linking and collagen fibril organization were unchanged by diabetes or insulin (P > 0.05). Our findings suggest that 10 wk of streptozotocin-induced diabetes does not alter rat tendon mechanical properties even with an increase in collagen content. Future studies could attempt to further address the mechanisms contributing to the increase in tendon problems noted in diabetic patients, especially since our data suggest that hyperglycemia per se does not alter tendon mechanical properties.

Abstract 310: Role of Cardiac Fibroblast in Cardioprotective Effects of Prior Transient ACE Inhibition

Prior treatment with the ACE inhibitor enalapril followed by washout protects against nitric oxide synthase inhibitor (L-NAME) induced fibrosis, cellular proliferation, and cardiac dysfunction. The present study investigated i) whether in vivo L-NAME administration induces a change in cardiac fibroblast phenotype that persists in vitro, ii) whether prior ACE inhibition protects against L-NAME induced changes in cardiac fibroblasts. SHR were divided into 3 groups: Control, L-NAME (C+L: 7d), enalapril+L-NAME (E+L: 14d enalapril + 14d washout + 7d L-NAME). MAP was measured by radiotelemetry (n=5-9), injury assessed by histology (n=6-10), and heart weight to body weight (HW/BW) was determined after 0 or 7 days of L-NAME in C+L and E+L (n=6-10). In separate rats cardiac fibroblasts were isolated after 7 days of L-NAME (C+L, E+L) or placebo (Con) and cultured to passage 1 (n=10-12). Gene expression was measured by quantitative real-time PCR. L-NAME increased MAP in C+L (22±4.1%) and E+L (21±3.6%) rats. Prior enalapril induced a persistent 13% reduction in HW/BW. L-NAME increased heart mass in E+L (7%) but not C+L; however, HW/BW remained 8% lower than C+L at sacrifice. L-NAME induced infarct in 70% of C+L and 40% of E+L hearts. Cardiac fibroblasts demonstrated a significant increase in proliferation rate in C+L, but not E+L, relative to control (C+L: 1.75-fold vs. con; E+L 1.09-fold vs. con). Fibroblasts from C+L hearts tended to have increased Collagen I and III gene expression. Despite hypertension, cardiac injury, and increased HW/BW; fibroblasts isolated from E+L proliferated at the same rate as those from control. In contrast, those isolated from C+L were hyperproliferative with a tendency toward increased capacity for collagen production. It may be that the fibroblast phenotype from E+L hearts would protect against infarct expansion and account, in part, for the previously reported cardioprotection in these rats.

Role of angiotensin II type 2 receptor during regression of cardiac hypertrophy in spontaneously hypertensive rats

We previously reported that the AT1 receptor antagonist valsartan and the angiotensin converting enzyme (ACE) inhibitor enalapril decrease DNA synthesis and stimulate apoptosis in interstitial fibroblasts and epicardial mesothelial cells during regression of ventricular hypertrophy in spontaneously hypertensive rats (SHR). To examine the role of the AT2 receptor in this model, we studied hearts from SHR treated with valsartan or enalapril either alone or combined with the AT2 antagonist PD123319 for 1 or 2 weeks. Apoptosis was evaluated by quantification of DNA fragmentation or by TUNEL labeling. At 1 week, valsartan significantly increased ventricular DNA fragmentation, increased apoptosis in epicardial mesothelial cells, and decreased DNA synthesis. At 2 weeks, ventricular DNA content and cardiomyocyte cross-sectional area were significantly reduced. These valsartan-induced changes were attenuated by PD123319 co-administration. However, valsartan-induced increases in apoptosis of left ventricular interstitial non-cardiomyocytes was unaffected by the AT2 blocker. Enalapril-induced changes were similar to those observed with valsartan but were not affected by co-treatment with PD123319. These results demonstrate that AT1 and AT2 receptors act in a coordinated yet cell-specific manner to regulate cell growth and apoptosis in the left ventricle of SHR during AT1 receptor blockade but not ACE inhibition.

Evaluating a theory-based health education intervention to improve awareness of prostate cancer among men in Western Jamaica

OBJECTIVE

To evaluate the impact of a theory-based health education intervention on awareness of prostate cancer and intention to screen among men in Western Jamaica.

METHODS

One hundred and eighty-eight men attending outpatient clinics in a hospital in Western Jamaica completed an interviewer-administered pretest survey. Following the pretest, participants received a health education intervention related to prostate cancer and an immediate post-test survey

RESULTS

There were statistically significant increases in the percentage of correct responses between the pretest and post-test (p < 0.05). The greatest improvement was among items measuring knowledge of prostate cancer screening tests. Participants moved across the Stages of Change theoretical constructs indicating intention to screen.

CONCLUSION

The sample was receptive to information about prostate cancer and the use of a theory-based educational intervention positively influenced knowledge of prostate cancer risk factors, symptoms, and types of screenings.

PRACTICE IMPLICATIONS

This theory-based patient education programme can be replicated to promote awareness of prostate cancer and informed screening methods including potential risk associated with screening behaviours.

Neointimal-specific induction of apoptosis by losartan results in regression of vascular lesion in rat aorta

We previously reported that initiating treatment with the angiotensin II receptor antagonist losartan, prior to and immediately after balloon injury, attenuates neointimal hyperplasia via induction of smooth muscle cell (SMC) apoptosis in the aorta of spontaneously hypertensive rats (SHR). The present study examines whether losartan can induce regression of an established neointima. Balloon angioplasty was performed in the aorta of 1 1 week-old SHR. Five weeks were allowed for neointima formation before rats received placebo or losartan (30 mg/kg/day) for 1 to 4 weeks. Blood pressure was measured by tail cuff plethysmography. Losartan significantly reduced blood pressure (16%) versus placebo within 2 weeks of treatment. In situ labeling with terminal deoxynucleotidyl transferase among neointimal SMC was transiently increased with losartan (10-fold at 2 weeks; P=0.004) in correlation with internucleosomal fragmentation of vascular DNA. Accordingly, losartan reversed neointimal hyperplasia by 43% (P=0.002) and 61% (P=0.007) at weeks 2 and 4, respectively, and neointimal mass by 63% (P<0.001) and 75% (P<0.001) at weeks 2 and 4, respectively, as compared to pre-treatment values. No change in aortic medial hyperplasia or mass was observed during losartan treatment. Taken together, endothelial denudation rendered the underlying media resistant to drug-induced remodeling, while losartan treatment induced vascular lesion regression by inducing apoptosis selectively in neointimal SMC, an effect that may contribute to the reduction of cardiovascular complications in hypertension.

Restoration of female genital vasocongestive arousal responses in young and aged rats

INTRODUCTION

Treatments of aged, male hypertensive rats that induce vascular remodeling or that normalize endothelial function are known to produce sustained improvements in erectile function. Whether the treatments targeting these processes benefit female genital vasocongestive arousal (GVA) responses is currently not known.

AIM

To determine whether the actions of nitric oxide (NO) are critical to the apomorphine (APO)-generated GVA responses in both intact and ovariectomized OVX young adult female rats (before any aging-associated decreases in the responses). In addition, we also investigated whether the diminished GVA responses in aged rats could be restored, at least in part, using an antihypertensive treatment, which is known to enhance erectile responses and improve general vascular function in male rats.

METHODS

In female Wistar rats, APO-induced GVA responses (80 microg/kg, subcutaneously [sc], 30 minutes) were assessed by videomonitoring following various treatments. Young adult females were ovariectomized or were treated with the nitric oxide synthase (NOS) inhibitor N-nitro-L-arginine methyl ester (30 mg/kg, iv), followed by an NO mimetic, sodium nitroprusside (10 microg/kg/minute, intravenous). Aged females (18 months) were treated for 2 weeks with the angiotensin converting enzyme (ACE) inhibitor, enalapril (30 mg/kg/day, orally) plus low sodium (0.04%).

MAIN OUTCOME MEASURES

APO-induced GVA responses in female rats.

RESULTS

There was an age-associated reduction in sexual responses in normotensive rats that was greatly enhanced (fourfold) by brief, aggressive antihypertensive treatment. The enhanced vasocongestive responses persisted for a 5-week off-treatment. Both OVX and NOS inhibition significantly decreased sexual responses by approximately 80% in young female rats. Systemic administration of an NO mimetic recovered vasocongestive responses in the NOS-blocked rats, but not in OVX animals.

CONCLUSIONS

Although mechanisms were not established, the major findings were that brief aggressive ACE inhibitor treatment markedly improved sexual responses in aged female rats, and systemic delivery of an NO mimetic recovered sexual responses in globally NOS-blocked animals.

Chondroitin sulfate inhibits the nuclear translocation of nuclear factor-kappaB in interleukin-1beta-stimulated chondrocytes

Chondroitin sulfate is referred as a symptomatic slow-acting drug for osteoarthritis because it improves articular function, and reduces joint swelling and effusion. In addition, chondroitin sulfate prevents joint space narrowing of the knee. We hypothesized that the anti-inflammatory effect of chondroitin sulfate is associated to a decrease in the activation of mitogen-activated protein kinases (MAPK) and of the transcription factors nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1). Cultured rabbit chondrocytes were stimulated with interleukin-1beta (IL-1beta) in presence of chondroitin sulfate. Nuclear translocation of NF-kappaB and AP-1, and nitrite concentrations (as an index for nitric oxide) was assessed 48 hr later. The effect of chondroitin sulfate on IL-1beta activation of extracellular signal-regulated kinase 1/2 (Erk1/2) and p38MAPK was documented by immunoblot. The effect of chondroitin sulfate on sodium nitroprusside-induced apoptosis was evaluated with the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling assay. Chondroitin sulfate reduced IL-1beta-induced NF-kappaB nuclear translocation, but not AP-1 translocation, it decreased IL-1beta-induced phosphorylation of Erk1/2 and abrogated p38MAPK phosphorylation, but did not prevent IL-1beta-induced increase in nitrite. Finally, chondroitin sulfate decreased nitroprusside-induced apoptosis of the chondrocytes. These results suggest that some of the biological activities of chondroitin sulfate may be associated to the reduction in Erk1/2 and p38MAPK phosphorylation and nuclear transactivation of NF-kappaB.

Impact of antihypertensive treatments on erectile responses in aging spontaneously hypertensive rats

OBJECTIVE

We previously demonstrated that brief, aggressive antihypertensive therapy recovered erectile function in 40-week-old spontaneously hypertensive rats (SHR). The present study examined the impact of antihypertensive and testosterone treatments on erectile function in aging SHR.

DESIGN AND METHODS

Centrally initiated erections were determined in response to apomorphine throughout. At 30 and 49 weeks, SHR were treated for 2 weeks with enalapril or hydralazine. A third more aggressive treatment (68 weeks) involved enalapril or losartan plus a low salt diet or a triple therapy (hydralazine, nifedipine, hydrochlorothiazide). In a separate study, cross-over kidney transplantations were performed between untreated and losartan-treated SHR. Arterial pressure was assessed post-transplantation using radio-telemetric transducers.

RESULTS

There was an age-related decrease in erections between 30 and 68 weeks (3.1 +/- 0.79 versus 0.2 +/- 0.38) that was not improved by testosterone administration. Early treatment with enalapril or hydralazine did not prevent this decline, although the second treatment resulted in significant improvements (enalapril, 0.8 +/- 0.70; hydralazine, 0.8 +/- 0.41 versus control, 0.3 +/- 0.60). A 2-week aggressive antihypertensive treatment at 68 weeks increased erections approximately two-fold, with the previously treated rats receiving triple therapy having markedly improved erectile responses (0.2 +/- 0.53 versus 1.1 +/- 1.67). In the transplantation study, previously losartan-treated SHR given an untreated kidney had higher arterial pressure but twice the number of erections in comparison with the SHR with lower arterial pressure resulting from transplanting a treated kidney.

CONCLUSIONS

Aggressive antihypertensive treatments may be more beneficial in improving erectile function in aged SHR, via an effect that appears to be tissue specific, and not based on changes in blood pressure.

Common therapeutic strategies in the management of sexual dysfunction and cardiovascular disease

Sexual dysfunction is a frequent complication of treated and untreated cardiovascular disease. In fact, approximately 30% of hypertensives have been found to suffer from erectile dysfunction (ED) resulting from arterial dysfunction. Recent evidence has suggested that ED may be an early indicator of subclinical cardiovascular disease. In women, the evidence is similar, but more limited, showing that in hypertensive patients there is an increased prevalence of sexual dysfunction involving decreased vaginal lubrication, decreased orgasm, and increased pain. Clouding the issue, however, is that some antihypertensive agents may induce sexual dysfunction in hypertensives with normal sexual function. In contrast to the chronic treatments used in hypertension, therapies for ED involve acute treatments (none currently approved for women) targeting vasodilation of penile arteries, resulting in erection. Common to the treatment of hypertension and ED is that the current therapies were not designed to target underlying disorders of local, neural, vascular, or endocrine origin. In fact, while blood pressure is lowered, and erectile responses are improved with the respective therapies, the causal abnormalities may progress thereby limiting the long-term effectiveness of the medication. Some antihypertensive agents have been shown to have additional effects beyond blood pressure reduction and their impact on sexual function is a key focus of this review. This review examines the current and future strategies for treatments of male and female sexual dysfunction and the potential for therapeutic modalities that go beyond the recovery of the responses by targeting the fundamental mechanisms common to both sexual dysfunction and cardiovascular disease.

Persistent Lowering of Pressure by Transplanting Kidneys From Adult Spontaneously Hypertensive Rats Treated With Brief Antihypertensive Therapy

Kidney function is critical in determining the level of arterial pressure and in the pathogenesis of hypertension. Important evidence comes from studies in which the level of blood pressure is dictated by the donor when kidneys are transplanted between genetically hypertensive and normotensive rats. We have hypothesized that pharmacotherapy modifies specific properties of the kidney, particularly the vasculature, such that after kidney transplantation, there are persistent changes in the level of arterial pressure. Consistent with previous studies, a 2-week aggressive treatment of adult (15 weeks) spontaneously hypertensive rats with an angiotensin-converting enzyme inhibitor (enalapril) combined with a low-salt diet induced a persistent change in the kidney and a decrease in arterial pressure (18%). These persistent changes in arterial pressure could be completely transferred to untreated adult spontaneously hypertensive rats by kidney transplantation (ie, pressure in untreated rats was decreased after transplantation of a kidney donated from a previously treated rat). Further, the importance of kidney-specific changes was demonstrated by finding that the treatment-induced lowering of arterial pressure was completely reversed by transferring an untreated kidney into a previously treated rat. The specific treatment-induced changes to the kidney included a decrease in structurally based renal vascular resistance that was similar to the persistent lowering of arterial pressure. These data provide evidence for a link between the treatment-induced changes in kidney vascular structure and the persistent lowering of arterial pressure. The findings also suggest that a key pharmacotherapeutic target in hypertension should be kidney-specific changes, such as renal vascular structure.

A framework for the present and future development of experimental models of female sexual dysfunction

Female sexual dysfunction (FSD) is currently categorized according to disorders of (i). desire, (ii). arousal, (iii). orgasm and (iv). sexual pain. The advancement of research defining the physiological, pathophysiological and psychological mechanisms of these disorders, and to develop treatments for FSD, has been hampered by the paucity of experimental paradigms and animal models. It may be that animal models of FSD are best suited to address arousal disorders that include persistent or routine inability to attain or maintain genital lubrication or engorgement. Although still limited in scope, experimental models of FSD have involved a range of in vitro to in vivo methodologies. Specifically, the in vitro and in situ models include vaginal or clitoral smooth muscle preparations, histological evaluation and vaginal blood flow assessments. Previously, in vivo studies of sexual responses focussed on behavioral paradigms involving lordotic posturing and receptivity, as well as indices of motivation using a dual chamber pacing method. Recently, a new model of female sexual arousal was developed using pharmacological CNS stimulation; responses that were found to be sensitive to cardiovascular status, aging and hormonal conditions. It is important that a wide variety of animal models continue to be developed to reflect the multifactorial basis of the condition.

Time course of vascular structural changes during and after short-term antihypertensive treatment

The present study characterized the persistent changes (ie, off-treatment) resulting from short-term antihypertensive treatments on mean arterial pressure (MAP) and structurally based vascular resistance. Rats were treated for 14 days with enalapril (30 mg x kg(-1) x d(-1)) with regular (ENAL, 0.4%) or low salt (ELS, 0.04%) diets, or a triple therapy (Triple: hydralazine 45 mg x kg(-1) x d(-1), hydrochlorothiazide 100 mg/L, and nifedipine 200 mg/d). MAP was continuously recorded via radiotelemetry. Structurally based hindlimb vascular resistance properties (resistance at maximum dilation [Max Dil]; resistance at maximum constriction [Max Con]) were assessed after 14-day enalapril treatment and 2 to 3 weeks after all drugs were withdrawn. Aortic urokinase plasminogen activator (uPA) activity was measured by zymography after 14 days of ELS. All treatments induced a significant, persistent decrease in the off-treatment MAP (ENAL downward arrow 12+/-4.6%, ELS downward arrow 16+/-2.6%, Triple downward arrow 5+/-4.17%). During treatment (14 days) the enalapril group had significant changes in the index of medial bulk (Max Con downward arrow 15+/-2.6%), but only minimal changes in lumen properties (Max Dil downward arrow 3+/-6.5%, NS). After stopping therapy, vascular properties at Max Dil were significantly decreased only in the 2 enalapril groups (ENAL downward arrow 15+/-7.9%, P<0.05; ELS downward arrow 9+/-6.0%, P<0.05; Triple downward arrow 2+/-9.8%, NS), whereas Max Con was significantly decreased in all groups (ENAL downward arrow 12+/-8.0%, ELS downward arrow 16+/-6.1%, Triple downward arrow 7+/-5.4%). At 14 days of ELS treatment, there was increased aortic uPA activity (1.6-fold). The findings reveal that various short-term antihypertensive treatments can produce persistent long-term changes in MAP and vascular structure. Further, the magnitude of the depressor response may be as important in inducing persistent changes as is the removal of angiotensin II.