Effects of angiotensin II and angiotensin II antagonist saralasin on cell growth and renin in 3T3 and SV3T3 cells

Alterations in Gene Expression of Components of the Renin-Angiotensin System and Its Related Enzymes in Lung Cancer

Objectives

The study assessed the existence and significance of associations between the expression of fifteen renin-angiotensin system component genes and lung adenocarcinoma.

Materials and Methods

NCBI's built-in statistical tool, GEO2R, was used to calculate Student's t-tests for the associations found in a DNA expression study of adenocarcinoma and matched healthy lung tissue samples. The raw data was processed with GeneSpring™ and then used to generate figures with and without Sidak's multiple comparison correction.

Results

Ten genes were found to be significantly associated with adenocarcinoma. Seven of these associations remained statistically significant after correction for multiple comparisons. Notably, AGTR2, which encodes the AT₂ angiotensin II receptor subtype, was significantly underexpressed in adenocarcinoma tissue (p < 0.01). AGTR1, ACE, ENPEP, MME, and PRCP, which encode the AT₁ angiotensin II receptor, angiotensin-converting enzyme, aminopeptidase N, neprilysin, and prolylcarboxypeptidase, respectively, were also underexpressed. AGT, which encodes angiotensinogen, the angiotensin peptide precursor, was overexpressed in adenocarcinoma tissue.

Conclusion

The results suggest an association between the expression of the genes for renin-angiotensin system-related proteins and adenocarcinoma. While further research is necessary to conclusively demonstrate a link between the renin-angiotensin system and lung cancers, the results suggest that the renin-angiotensin system plays a role in the pathology of adenocarcinoma.

Update on tissue renin-angiotensin systems

Angiotensin (Ang) II is not only generated in the circulation by renin and angiotensin-converting enzyme (ACE) but also is produced locally in numerous organs including kidney, vessels, heart, adrenal gland, eye, testis, and brain. Furthermore, widely distributed mast cells have been shown to be a production site. Local Ang II production process is commonly termed the result of a "tissue" renin-angiotensin system (RAS). Because pharmacological experiments do not easily allow targeting of specific tissues, many novel findings about the functional importance of tissue RAS have been collected from transgenic rodent models. These animals either overexpress or lack RAS components in specific tissues and thereby elucidate their local functions. The data to date show that in most tissues local RAS amplify the actions of circulating Ang II with important implications for physiology and pathophysiology of cardiovascular diseases. This review summarizes the recent findings on the importance of tissue RAS in the most relevant cardiovascular organs.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

A novel function of angiotensin II in skin wound healing. Induction of fibroblast and keratinocyte migration by angiotensin II via heparin-binding epidermal growth factor (EGF)-like growth factor-mediated EGF receptor transactivation

The role of angiotensin II (Ang II) in the control of systemic blood pressure and volume homeostasis is well known and has been extensively studied. Recently, Ang II was suggested to also have a function in skin wound healing. In the present study, the in vivo function of Ang II in skin wound healing was investigated using Ang II type 1 receptor (AT1R) knock-out mice. Wound healing in these mice was found to be markedly delayed. Keratinocytes and fibroblasts play important roles in wound healing, and thus the effect of Ang II on the migration of these cells was examined. Ang II stimulated keratinocyte and fibroblast migration in a dose-dependent manner. It has been reported that G protein-coupled receptor (GPCR) activation induces epidermal growth factor (EGF) receptor (EGFR) transactivation through the shedding of heparin-binding EGF-like growth factor (HB-EGF). As AT1R is a GPCR, it was hypothesized that Ang II-induced keratinocyte and fibroblast migration is mediated by EGFR transactivation. Ang II induced EGFR phosphorylation, which was inhibited by an AT1R antagonist, HB-EGF neutralizing antibody, and an HB-EGF antagonist in both keratinocytes and in fibroblasts. Moreover, Ang II-induced migration of keratinocytes and fibroblasts was also prevented by these inhibitors. Taken together, these findings clearly demonstrate, for the first time, that Ang II plays an important role in skin wound healing and that it functions by accelerating keratinocyte and fibroblast migration in a process mediated by HB-EGF shedding.

From Left Ventricular Hypertrophy to Congestive Heart Failure: Management of Hypertensive Heart Disease

Other than age, left ventricular hypertrophy (LVH) is the most potent predictor of adverse cardiovascular outcomes in the hypertensive population, and is an independent risk factor for coronary heart disease, sudden death, heart failure and stroke. Although directly related to systolic blood pressure, other factors including age, sex, race, body mass index and stimulation of the renin-angiotensin-aldosterone and sympathetic nervous systems play an important role in the pathogenesis of LVH. LVH involves changes in myocardial tissue architecture consisting of perivascular and myocardial fibrosis and medial thickening of intramyocardial coronary arteries, in addition to myocyte hypertrophy. The physiologic alterations which occur as a result of these anatomical changes include disturbances of myocardial blood flow, the development of an arrhythmogenic myocardial substrate and diastolic dysfunction. The latter is directly related to the degree of myocardial fibrosis and is the hemodynamic hallmark of hypertensive heart disease. When diastolic dysfunction is present, left ventricular end-diastolic pressure increases out-of-proportion to volume and may be elevated at rest or with exertion leading to clinical heart failure. At least one third of heart failure patients in the United States can be considered to have heart failure related to diastolic dysfunction. Compared to heart failure patients with systolic dysfunction, diastolic heart failure patients are more likely to be older, female, and to be hypertensive at the time of presentation. Although it has been assumed that LVH may lead to systolic dysfunction, evidence is lacking that LVH resulting from hypertension is a major risk factor for systolic heart failure independent of coronary artery disease. Treatment of hypertension greatly attenuates the development of LVH and significantly decreases the incidence of heart failure. In patients with established LVH, regression is both possible and desirable and results in a significant reduction in adverse clinical endpoints.

Angiogenic protection from focal ischemia with angiotensin II type 1 receptor blockade in the rat

Angiogenesis within an ischemic region of the brain may increase tissue viability and act to limit the extent of an infarct. The ANG II pathway can both stimulate and inhibit angiogenesis depending on the tissue and the activated receptors. Previous work showed that 2-wk losartan administration (ANG II type 1 receptor blockade) initiates a significant cerebral angiogenic response. We hypothesized that administration of losartan in the drinking water of rats for 2 wk before initiation of focal ischemia would decrease the extent of the resulting infarct. Adult male Sprague-Dawley rats were given losartan (50 mg/day) in drinking water for 2 wk before initiation of cerebral focal ischemia produced by cauterization of cortical surface vessels. Controls received normal drinking water. In control animals, three main vessels feeding the whisker barrel cortex were cauterized, resulting in cessation of blood flow. The same protocol was followed for losartan-treated animals but did not result in cessation of blood flow in the whisker barrel cortex. Another group of losartan-treated animals received between 8 and 14 cauterizations of surface vessels feeding the whisker barrel cortex, and cessation of blood flow was verified. Rats were killed 72 h after surgery. Morphological examination revealed angiogenesis, maintained vascular delivery, and significantly decreased infarct size in losartan-treated animals compared with controls. These results demonstrate that pretreatment with losartan reduces infarct size after cerebral focal ischemia and support the hypothesis that cerebral angiogenesis may be one of the mechanisms responsible.

Activity of angiotensin-converting enzyme after treatment with L-arginine in renovascular hypertension

The renin-angiotensin system plays a role in the pathophysiology of renovascular hypertension. In addition, some studies have demonstrated a beneficial effect of L-arginine (L-Arg), the precursor of nitric oxide (NO), in this model of hypertension. This study was designed to investigate the effects of L-Arg on cardiovascular parameters and on the activity of the angiotensin-converting enzyme (ACE), after 14 days of renovascular hypertension. The experiments were performed on conscious male Wistar rats. Two-kidney, one-clip renovascular hypertension (2KIC) was initiated in rats by clipping the left renal artery during 14 days, while control rats were sham-operated. One group was submitted to a similar procedure and treated with L-Arg (10 mg/ml; average intake of 300mg/day) from the 7th to the 14th day after surgery, whereas the respective control group received water instead. At the end of the treatment period, the mean arterial pressure (MAP) was measured in conscious animals. The rats were sacrificed and the ACE activity was assayed in heart and kidneys, using Hip-His-Leu as substrate. In a separate group, the heart was removed, the left ventricle (LV) was weighed and the LV/body weight ratios (LV/BW) were determined. We observed significant differences in MAP between the L-Arg-treated and untreated groups (129 +/- 7 vs. 168 +/- 6 mmHg; P< 0.01). The cardiac hypertrophy described for this model of hypertension was attenuated in the 2K1C-L-Arg-treated group (14th day, wet LV/BW: 2K1C-L-Arg = 1.88 +/- 0.1; 2K1C = 2.20 +/- 0.1 mg/g; P < 0.05). L-Arg administration caused an important decrease in cardiac ACE activity (2K1C-L-Arg: 118 +/- 15; 2K1C: 266 +/- 34 micromol/min/mg; P < 0.01). L-Arg also decreased the ACE activity in the clipped kidney by 47% (P < 0.01), but not in the nonclipped kidney. These data suggest that increased NO formation and reduced angiotensin II formation are involved in the anthihypertensive effect of orally administered L-arginine.

Human skin: source of and target organ for angiotensin II

The present study examined the expression of angiotensin receptors in human skin, the potential synthesis of angiotensin II (Ang II) in this location and looked for a first insight into physiological functions. AT1 and AT2 receptors were found within the epidermis and in dermal vessel walls. The same expression pattern was found for angiotensinogen, renin and angiotensin-converting enzyme (ACE). All components could additionally be demonstrated at mRNA level in cultured primary keratinocytes, melanocytes, dermal fibroblasts and dermal microvascular endothelial cells, except for AT2 receptors in melanocytes. The ability of cutaneous cells to synthesize Ang II was proved by identifying the molecule in cultured keratinocytes. Furthermore, in artificially wounded keratinocyte monolayers, ACE-mRNA expression was rapidly increased, and enhanced ACE expression was still found in cutaneous human scars 3 months after wounding. These findings suggest that the complete renin-angiotensin system is present in human skin and plays a role in normal cutaneous homeostasis as well as in human cutaneous wound healing.

Synergistic effects of co-administration of angiotensin 1–7 and Neupogen on hematopoietic recovery in mice

PURPOSE

Angiotensin 1-7 [A(1-7)] is a seven amino acid peptide that has been shown to increase the proliferation of epidermal stem cells after dermal injury and the number of hematopoietic progenitors in the bone marrow of myelosuppressed mice. In this study, the effect of combining A(1-7) with Neupogen on hematopoietic recovery and bone marrow progenitors was evaluated.

MATERIALS AND METHODS

Intravenous 5-fluorouracil (5FU) was administered to induce myelosuppression. Administration of A(1-7) and/or Neupogen was initiated 2 days after chemotherapy. Angiotensin II (AII) and A(1-7) binding were assessed by flow cytometric analysis. Hematopoietic progenitors were counted by colony forming assays. Recovery of formed elements in the blood was evaluated by hemocytometer.

RESULTS

Flow cytometric analysis indicated that the number of early hematopoietic progenitors (Lin(-)Sca1(+)cKit(+)) that bind AII or A(1-7) increased 5-7 days after intravenous injection of 150 mg/kg 5FU. Further, administration of A(1-7) led to a slight increase in the number of circulating leukocytes and platelets after this chemotherapeutic regimen. When given in combination with a subclinical dose of Neupogen, a synergistic effect on the number of circulating leukocytes was observed, but there was no further effect on the number of circulating platelets. In myelosuppressed mice, A(1-7) had its most profound effect on the number of hematopoietic progenitors in the bone marrow. The progenitors evaluated in the study included BFU-E, CFU-Meg, CFU-GM and CFU-GEMM. There was an increase in the number of these progenitors in the bone marrow, indicating an effect on all hematopoietic lineages. When given in combination with Neupogen, these effects were synergistic for the numbers of BFU-E and CFU-Meg (Neupogen by itself had no effect) and for the myeloid progenitors at lower doses of A(1-7).

CONCLUSIONS

These results suggest that these hematopoietic agents act at different sites within the hematopoietic cascade and that combining these two agents may be of benefit in the treatment of hematopoietic disorders.

Protection against ischemia: a physiological function of the renin-angiotensin system

The renin-angiotensin system (RAS) is involved in a complex mechanism that serves to preserve the blood supply to organs so that they can maintain cellular function. Angiotensin II exerts this effect, independently of the blood pressure generated, through two time-related events: a fast opening of the reserve collateral circulation and a much slower response of new vessel formation or angiogenesis. This effect is observed in rats with ligation of the abdominal aorta and in gerbils with abrupt or progressive unilateral carotid artery ligation. Inhibition of the angiotensin-converting enzyme (ACE) or the angiotensin II receptor represses this effect, and it appears that it is mediated through a non-AT1 receptor site of angiotensin II. Many tumors, both benign and malignant, express renin and angiotensin. It seems that the stimulating action of angiotensin II on angiogenesis could also be involved in preserving the blood supply to tumor cells. Administration of converting enzyme inhibitors increases survival and decreases tumor size in tumor-bearing rats. These observations support the hypothesis that the RAS, directly or indirectly, is involved in situations in which the restoration of blood supply is critical for the viability of cells and that it is present not only in normal but also in pathological conditions such as tumors. In view of the ubiquitous presence of renins and angiotensins, it is also likely to be involved in other conditions, such as inflammation, arthritis, diabetic retinopathy, and retrolental fibroplasia, among others in which angiogenesis is prominent. In addition, angiotensin II could be involved, through the counterbalance of the AT1 and AT2 receptors, in the rarefaction of blood vessels as an etiologic component of essential hypertension.

Development of angiotensin (1-7) as an agent to accelerate dermal repair

Angiotensin II has been shown to be a potent agent in the acceleration of wound repair. Angiotensin (1-7), a fragment of angiotensin II that is not hypertensive, was found to be comparable to angiotensin II in accelerating dermal healing. This activity was evaluated in four models: rat and diabetic mouse full-thickness excisional wounds; rat random flap; and guinea pig partial thickness thermal injury. In all models, angiotensin (1-7) was comparable to angiotensin II. Angiotensin (1-7) accelerated the closure of wounds in diabetic mice and rats. In diabetic mice the resultant tissue at day 25 after injury was more comparable to normal tissue than the fibrotic scar observed in placebo-treated wounds. In the random flap model, angiotensin (1-7) was comparable to angiotensin II in maintaining flap viability (approximately 82%) and flap survival (40%). Finally, angiotensin (1-7) increased proliferation in the hair follicles at the edge of the wound and site of thermal injury, and the number of patent blood vessels on day 7 after partial thickness thermal injury. These data may be partially explained by the effect of angiotensin II and angiotensin (1-7) on keratinocyte proliferation. While platelet-derived growth factor had no effect on keratinocyte proliferation, angiotensin II and angiotensin (1-7) significantly increased keratinocyte proliferation. These data show that angiotensin(1-7) is comparable to angiotensin II in accelerating skin repair. Furthermore, the hypertensive and wound healing effects can be separated within the family of angiotensin peptides.

The angiotensin type 2 receptor: variations on an enigmatic theme

Since its discovery and molecular characterization, the angiotensin AT2.receptor has been enigmatic with respect to signalling pathways and function. Evidence now emerges that angiotensin II exerts actions through the AT2 receptor which are directly opposed to those mediated by the AT1 receptor. This can be exemplified e.g. by mutually antagonizing effects on cell growth. Upregulated by the endogenous agonist itself, as well as by several growth- and differentiating factors in development and tissue injury, the AT2 receptor appears to act as a modulator of complex biological programmes involved in embryonic development, cell differentiation, tissue protection and regeneration, as well as in programmed cell death. Research on the AT2 receptor has thus unveiled hitherto unknown functions of the renin-angiotensin system extending far beyond the classical role of this old hormonal system in cardiovascular control.

Effects of angiotensin II on bone cells in vitro

Other than its known effects on the cardiovascular system, angiotensin II (Ang II) stimulates cell growth in several cell types. In this study, we examined whether it also might affect bone cell metabolism. Ang II stimulated DNA and collagen synthesis and decreased alkaline phosphatase (AP) activity in bone cell populations derived from the periosteum of fetal rat calvariae. Similar effects of Ang II were observed on human adult bone cells obtained by collagenase digestion from trabecular bone. Clonal cell analysis, autoradiographic studies, and receptor subtype analysis suggested the presence of specific Ang II receptor subtype 1 (AT1) binding sites on AP+ osteoblastic precursor cells. Ang II had no direct effects on osteoblastic cells with a mature phenotype, but paracrine effects of Ang II on mature osteoblasts could be observed upon coculture with Ang II-responsive bone cell populations. Because Ang II is known to be locally generated by endothelial cells, Ang II might play an important role in coordinating capillary cell growth and osteoblastic bone formation during bone remodeling.

Effects of angiotensin-converting enzyme inhibition and angiotensin II AT1 receptor antagonism on cardiac parameters in left ventricular hypertrophy

Left ventricular hypertrophy (LVH) is considered to be an independent risk factor giving rise to ischemia, arrhythmia, and left ventricular dysfunction. In this article, we summarize recent studies performed in our laboratory to investigate (1) the contribution of the renin-angiotensin system to the cardiac remodeling process, which is triggered by myocardial infarction (MI) or hypertension-induced cardiac hypertrophy; (2) the effects of angiotensin-converting enzyme (ACE) inhibition and angiotensin AT1 receptor antagonism on cardiac parameters, such as myocardial infarct size, cardiac hypertrophy, heart function, and myocardial metabolism; (3) the mechanism of an ACE inhibitor-induced increase in cardiac capillary density in spontaneously hypertensive rats (SHR) and stroke prone SHR (SHR-SP). We observed that AT1 receptor gene expression in rat vascular smooth muscle cells (but not in rat coronary endothelial cells) was markedly enhanced after an ischemic insult in vitro. In a rat model in which MI was induced by coronary artery ligation, the AT1 receptor mRNA levels were transiently increased after MI and reached a peak level 24 hours post-MI. The AT2 receptor gene expression increased in a pattern similar to that of the AT1 receptor. ACE expression at the protein level in the repairing scar, which was demonstrated by monoclonal antibody staining, started to increase 2 weeks after MI and reached a peak level 3 weeks post-MI. Furthermore, long-term treatment with an ACE inhibitor limited infarct size, prevented cardiac hypertrophy, and improved heart function in the rat MI model. In SHR-SP, long-term treatment with either an ACE inhibitor or an AT1 receptor antagonist improved cardiac function and metabolism. Cardiac metabolism was even improved after low-dose ACE inhibitor treatment, which did not prevent hypertension and cardiac hypertrophy. In both SHR and SHR-SP, we found that the ACE inhibitor ramipril significantly increased capillary length density independently of its antihypertensive and antihypertrophic actions. Most of the cardiac effects of the ACE inhibitor could be abolished by a bradykinin B2 receptor antagonist. Thus, these cardiac effects of ACE inhibitors can be ascribed, at least under our experimental conditions, to ACE inhibitor-induced bradykinin potentiation.

Renin-angiotensin system and cell communication in the failing heart

The influence of heart failure on the process of cell communication was investigated in cell pairs isolated from the ventricle of cardiomyopathic hamsters (11 months old) and the results compared with age-matched normal hamsters. The gap junctional conductance (gj) was measured with two voltage-clamp amplifiers. The results showed two major populations of cell pairs with respect to gj values: one with very low values (0.8 to 2.5 nS) and the other with higher values (7 to 35 nS). In normal hamsters, the most frequent gj values were in the range of 40 to 100 nS. Angiotensin II (Ang 11, 1 microg/mL) caused cell uncoupling in myopathic myocytes with low gj but reduced gj by 53 +/- 6.6 percent (+/- SE) in cell pairs with higher gj values (7 to 35 nS). The effect of Ang II on gj of myopathic cell pairs was suppressed by losartan (10(-7) mol/L). In cardiomyopathic cell pairs with low gj (0.8 to 2.5 nS), enalapril (1 microg/mL) caused an appreciable increase in gj (219 +/- 20.3 percent), whereas in cell pairs with higher gj (7 to 35 nS), the gj increment was smaller (80 +/- 10.8 percent) but still larger than that seen in controls (33 +/- 5.4 percent). Intracellular dialysis of Ang I (10(-8) mol/L) abolished cell communication in myopathic cell pairs with low gj (0.8 to 2.5 nS) and reduced gj by 66 +/- 1.7 percent in the other pairs (7 to 35 nS). The effect of Ang I on gj was greatly reduced by enalaprilat (10(-9) mol/L) added to the cytosol. Dialysis of Ang II (10(-8) mol/L) into the myopathic cell reduced gj by 48 +/- 4.2 percent, an effect abolished by losartan (10(-8) mol/L). The results indicate that the decline in gj seen in the ventricle of cardiomyopathic hamsters is in part due to activation of the cardiac renin-angiotensin system.

Angiotensin II type 1 receptor induced signal-transduction pathways as new targets for pharmacological treatment of the renin-angiotensin system

The peptide hormone angiotensin II is the main effector of the renin angiotensin system and may be involved in the pathogenesis of several cardiovascular disease such as congestive heart failure and hypertension. Drugs developed to inhibit angiotensin II effects such as angiotensin-converting enzyme (ACE) inhibitors or receptor antagonists helped to detect the cardiovascular and cellular mechanisms of angiotensin II effects. ACE inhibitor effects are complex and include indirect as well as direct mechanisms. Indirect effects are mediated by unloading the heart via prevention of aldosterone release and modulation of sympathetic nervous system activity. Direct actions include the inhibition of cardiac fibroblast proliferation and collagen synthesis as well as hypertrophy of cardiomyocytes. Recent work has focused on uncovering the biochemical and molecular mechanisms of angiotensin II induced cell growth.

The cardiac renin-angiotensin-aldosterone system and hypertensive cardiac hypertrophy

Angiotensin-converting enzyme inhibitors have proven to be uniquely effective in inducing regression, or preventing the occurrence, of ventricular hypertrophy associated with systemic hypertension. This has pointed, for many years, to a possible direct involvement of the renin-angiotensin system in the pathogenesis of cardiac hypertrophy. Over the last 10 years further supporting evidence has been forthcoming about direct trophic effects of angiotensin II in several experimental systems. Additionally, we now have rather conclusive evidence for the existence of a local, intracardiac renin-angiotensin system, which is capable of synthesis of all components of the system, and of cleaving, via the classic pathway, angiotensin peptides from the precursor, angiotensinogen. Moreover, a number of studies have demonstrated the capacity of regulatory response and modulation of activity of the local system in response to a variety of pharmacologic perturbations as well as differential expression of specific components under pathologic conditions, including compensatory hypertrophy and remodeling after myocardial infarction, pressure overload hypertrophy, and volume overload hypertrophy. Continued research into the role of the cardiac renin-angiotensin system in the pathogenesis of cardiac hypertrophy and failure will provide us with the tools to devise more specific, targeted strategies for therapeutic intervention or prevention.

Altered angiotensinogen amino acid sequence and plasma angiotensin II levels in genetically hypertensive rats. A study on cause and effect

The components of the renin-angiotensin system have been implicated in the development of primary hypertension in humans and genetically hypertensive rats. In humans a mutation in the angiotensinogen gene and elevated plasma angiotensinogen levels have been linked to primary hypertension. Although we had previously excluded a linkage of blood pressure to the angiotensinogen gene in the stroke-prone spontaneously hypertensive rat (SHRSP), elevated angiotensin II (Ang II) levels in this strain compared with the normotensive reference, the Wistar-Kyoto rat (WKY), prompted us to investigate further into the origins and effects of altered Ang II regulation using a range of physiological, biochemical, molecular, and genetic approaches. Ang II plasma levels determined by radioimmunoassay were confirmed to be significantly elevated in SHRSP compared with WKY. Sequence comparison among the two rat strains revealed a mutation in the coding region of the angiotensinogen gene that results in an isoleucine-to-valine substitution in SHRSP at amino acid position 154 (I154V). We performed a cosegregation analysis in an F2 intercross cohort bred from SHRSP and WKY from the University of Heidelberg (SHRSPHD and WKYHD) to address the following questions: (1) whether this or another mutation of the angiotensinogen gene may be casually related to the observed differential Ang II plasma levels, (2) whether Ang II plasma levels may be correlated with blood pressure or organ hypertrophy, and (3) whether genetic linkage to the renin or angiotensin-converting enzyme (ACE) gene loci (the two classic regulatory enzymes of the renin-angiotensin system) may provide an explanation for elevated Ang II plasma levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein synthesis in the hypertrophied heart of spontaneously hypertensive rats and a comparison of the effects of an ACE-inhibitor and a calcium channel antagonist

The aim of the investigation was to assess and compare the effects of a calcium channel antagonist, (i.e. amlodipine) and an ACE-inhibitor (i.e. lisinopril) in reducing chronic left ventricular hypertrophy in 15-week old spontaneously hypertensive rats (SHR). Changes in cardiac hypertrophy were assessed after 8 weeks by measuring the fractional rates of protein synthesis using a 'flooding dose' of [3H]-phenylalanine for 10 min. Blood pressure was monitored throughout the treatment period in both SHR and Wistar-Kyoto control rats (WKY). The results showed a decrease in blood pressure by amlodipine after 1 week of treatment which was further reduced at 4 to 8 weeks. Lisinopril caused immediate and sustained reductions in blood pressure (190 mmHg to 130 mmHg, P < 0.001). After 8 weeks of treatment in SHR rats, amlodipine had no significant effect on left ventricular weight (P > 0.05), whereas lisinopril caused a marked reduction. The protein content and RNA were also not changed by amlodipine. In contrast, lisinopril significantly lowered the tissue protein, RNA and DNA content (P < 0.001). The changes in the left ventricles of lisinopril-treated SHR rats were accompanied by an increase in the fractional synthesis rate of left ventricular myofibrillar proteins (+12 per cent, P < 0.025). The synthesis rate per unit RNA was also increased in right ventricular tissue of lisinopril-treated SHR rats. However, amlodipine had no effect on the fractional synthesis rates of any of the left-ventricular fractions of SHR rats (P > 0.05). The cellular efficiency in the right ventricle was also increased in amlodipine-treated SHR rats, indicating a moderate effect on protein metabolism. In conclusion, amlodipine had minimal effects in the reduction of established left ventricular hypertrophy (LVH), despite reducing the blood pressure, whereas lisinopril caused regression of LVH. These events were associated with small changes in protein synthesis rates, with the contractile protein showing an increase.

Angiotensin II induces fibronectin expression associated with cardiac fibrosis in the rat

Fibronectin expression was studied in the heart of rats given a continuous infusion of angiotensin II (Ang II). Northern blot analysis showed that left ventricular fibronectin steady-state mRNA increased fivefold to eightfold in response to pressor doses of Ang II after 24 hours. Accumulation of immunodetectable fibronectin in the ventricles occurred after the mRNA levels increased. The changes in fibronectin expression were reversible when Ang II treatment was withdrawn. The Ang II-induced increase in fibronectin mRNA accompanied similar increases for collagen type I, collagen type IV, and atrial natriuretic factor steady-state mRNA. Interstitial and perivascular fibrosis was identified in both ventricles of angiotensin-treated rats within 3 days. In situ hybridization identified cells associated with areas of fibrosis as the principal site of fibronectin mRNA accumulation in treated animals. By comparison, normal hearts showed fibronectin expression primarily within ventricular vascular tissue and the atrial endocardium. A dose-dependent reduction of fibronectin expression followed treatment with losartan, indicating an Ang II type 1 receptor-mediated effect. Normalization of blood pressure during Ang II infusion by either hydralazine or prazosin had different effects on the level of fibronectin steady-state mRNA, indicating that blood pressure elevation was not the principal factor responsible for fibronectin induction. Concurrent administration of angiotensin-converting enzyme inhibitors with Ang II attenuated the increased fibronectin expression. Our data indicate that Ang II induces an acute fibrotic response within the heart and suggests that Ang II stimulates fibronectin expression within nonmyocytic cardiac cells by a direct action.

Brain angiotensin receptor subtypes in the control of physiological and behavioral responses

This review summarizes emerging evidence that supports the notion of a separate brain renin-angiotensin system (RAS) complete with the necessary precursors and enzymes for the formation and degradation of biologically active forms of angiotensins, and several binding subtypes that may mediate their diverse functions. Of these subtypes the most is known about the AT1 site which preferentially binds angiotensin II (AII) and angiotensin III (AIII). The AT1 site appears to mediate the classic angiotensin responses concerned with body water balance and the maintenance of blood pressure. Less is known about the AT2 site which also binds AII and AIII and may play a role in vascular growth. Recently, an AT3 site was discovered in cultured neoblastoma cells, and an AT4 site which preferentially binds AII(3-8), a fragment of AII now referred to as angiotensin IV (AIV). The AT4 site has been implicated in memory acquisition and retrieval, and the regulation of blood flow. In addition to the more well-studied functions of the brain RAS, we review additional less well investigated responses including regulation of cellular function, the modulation of sensory and motor systems, long term potentiation, and stress related mechanisms. Although the receptor subtypes responsible for mediating these physiologies and behaviors have not been definitively identified research efforts are ongoing. We also suggest potential contributions by the RAS to clinically relevant syndromes such as dysfunctions in the regulation of blood flow and ischemia, changes in cognitive affect and memory in clinical depressed and Alzheimer's patients, and angiotensin's contribution to alcohol consumption.

Regulation of cell proliferation and growth by angiotensin II

The peptide hormone angiotensin II (AngII) has clearly defined physiologic roles as a regulator of vasomotor tone and fluid homeostasis. In addition AngII has trophic or mitogenic effects on a variety of target tissues, including vascular smooth muscle and adrenal cells. More recent data indicate that AngII exhibits many characteristics of the 'classical' peptide growth factors such as EGF/TGF alpha, PDGF and IGF-1. These include the capacity for local generation ('autocrine or paracrine' action) and the ability to stimulate tyrosine phosphorylation, to activate MAP kinases and to increase expression of nuclear proto-oncogenes. The type 1 AngII receptor, which is responsible for all known physiologic actions of AngII, has been cloned. Activation of this receptor leads to elevated phosphoinositide hydrolysis, mobilization of intracellular Ca2+ and diacylglycerol, and activation of Ca2+/calmodulin and Ca2+/phospholipid-dependent Ser/Thr kinases, as well as Ca2+ regulated tyrosine kinases. The existence of other AngII receptor subtypes has been postulated, but the function(s) of these sites remains unclear. In vascular smooth muscle, AngII can promote cellular hypertrophy and/or hyperplasia, depending in part on the patterns of induction of secondary factors that are known to stimulate (PDGF, IGF-1, basic FGF) or inhibit (TGF-beta) mitosis. Together, these findings have suggested that AngII plays important roles in both the normal development and pathophysiology of vascular, cardiac, renal and central nervous system tissues.

Angiotensin I and II exert inotropic effects in atrial but not in ventricular human myocardium. An in vitro study under physiological experimental conditions

BACKGROUND

The renin-angiotensin system with its renal-humoral and local myocardial components plays an important role in the development and progression of chronic heart failure. Whereas angiotensin receptors have been found in atrial and ventricular myocardium of different species including humans, its influence on myocardial contractility is not yet defined in human failing myocardium and especially in human nonfailing myocardium.

METHODS AND RESULTS

We measured force development of right atrial and right and left ventricular myocardial preparations of patients with a variety of cardiac diseases. To evaluate the physiological effects of angiotensin, experimental temperature and stimulation rates were 37 degrees C and 60 beats per minute, respectively. Angiotensin I and II increased peak developed force in atrial myocardial preparations obtained from patients without heart failure in a concentration-dependent manner. At optimal concentrations, peak developed force is increased from 10.2 +/- 1.8 to 12.3 +/- 1.9 mN/mm2 by angiotensin I (P < .05) and from 15.4 +/- 2.1 to 20.5 +/- 3.3 mN/mm2 by angiotensin II (P < .05). This effect was not influenced by pretreatment with propranolol (10(-6) mol/L) and prazosin (10(-5) mol/L) but was completely blocked by saralasin (10(-6) mol/L). The positive inotropic effect of angiotensin I could be blocked by enalaprilate (10(-5) mol/L). Neither angiotensin I nor angiotensin II had any effect in preparations of the left ventricle from patients with idiopathic dilated cardiomyopathy, mitral valve stenosis, and incompetence or in patients with no significant heart disease. Additionally, no effect could be seen when angiotensin II was applied to right ventricular preparations from infants undergoing reconstructive heart surgery for tetralogy of Fallot.

CONCLUSIONS

Angiotensin I and II exert positive inotropic effects via angiotensin receptors in atrial preparations but not in right or left ventricular preparations. Furthermore, the existence of a local myocardial angiotensin converting enzyme with functional importance is shown.

Molecular characterization of angiotensin II--induced hypertrophy of cardiac myocytes and hyperplasia of cardiac fibroblasts. Critical role of the AT1 receptor subtype

Increasing evidence suggests that angiotensin II (Ang II) may act as a growth factor for the heart. However, direct effects of Ang II on mammalian cardiac cells (myocytes and nonmyocytes), independent of secondary hemodynamic and neurohumoral effects, have not been well characterized. Therefore, we analyzed the molecular phenotype of cultured cardiac cells from neonatal rats in response to Ang II. In addition, we examined the effects of selective Ang II receptor subtype antagonists in mediating the biological effects of Ang II. In myocyte culture, Ang II caused an increase in protein synthesis without changing the rate of DNA synthesis. In contrast, Ang II induced increases in protein synthesis, DNA synthesis, and cell number in nonmyocyte cultures (mostly cardiac fibroblasts). The Ang II-induced hypertrophic response of myocytes and mitogenic response of fibroblasts were mediated primarily by the AT1 receptor. Ang II caused a rapid induction of many immediate-early genes (c-fos, c-jun, jun B, Egr-1, and c-myc) in myocyte and nonmyocyte cultures. Ang II induced "late" markers for cardiac hypertrophy, skeletal alpha-actin and atrial natriuretic factor expression, within 6 hours in myocytes. Ang II also caused upregulation of the angiotensinogen gene and transforming growth factor-beta 1 gene within 6 hours. Induction of immediate-early genes, late genes, and growth factor genes by Ang II was fully blocked by an AT1 receptor antagonist but not by an AT2 receptor antagonist. These results indicate that: (1) Ang II causes hypertrophy of cardiac myocytes and mitogenesis of cardiac fibroblasts, (2) the phenotypic changes of cardiac cells in response to Ang II in vitro closely mimic those of growth factor response in vitro and of load-induced hypertrophy in vivo, (3) all biological effects of Ang II examined here are mediated primarily by the AT1 receptor subtype, and (4) Ang II may initiate a positive-feedback regulation of cardiac hypertrophic response by inducing the angiotensinogen gene and transforming growth factor-beta 1 gene.

Angiotensin II is mitogenic in neonatal rat cardiac fibroblasts

Angiotensin II has been reported to be a hormonal stimulus of cardiac growth, a response that may involve myocyte hypertrophy as well as growth of nonmyocytes. This study was designed to determine whether neonatal rat cardiac fibroblasts have an angiotensin II receptor that is coupled with hypertrophic and/or proliferative growth. Competitive radioligand binding studies showed that cardiac fibroblasts have a single class of high-affinity (IC50, 1.0 nM) angiotensin II binding sites (Bmax, 778 fmol/mg protein) that are sensitive to the competitive nonpeptide AT1 receptor antagonist losartan (IC50, 13 nM). Other angiotensin peptides competed for [125I]angiotensin II binding in the following rank order: angiotensin II > angiotensin III > angiotensin I > > [des-Asp1-des-Arg2]angiotensin II. A nonhydrolyzable analogue of guanosine triphosphate increased the dissociation rate of bound [125I]angiotensin II and decreased hormone binding to the receptor at equilibrium. The angiotensin II receptor was coupled with increases in intracellular calcium. Incorporation of precursors into protein, DNA, and RNA in response to angiotensin II was determined. In serum-deprived cultures, a 24-hour exposure to 1 microM [Sar1]angiotensin II increased rates of phenylalanine, thymidine, and uridine incorporation by 58%, 103%, and 118%, respectively. These increases were blocked by the noncompetitive AT1 receptor antagonist EXP3174. After 48 hours, [Sar1]angiotensin II increased total protein and DNA of cardiac fibroblasts by 23% and 15%, respectively, with no change in the protein/DNA ratio. [Sar1]Angiotensin II increased cell number by 138% after a 24-hour exposure, without affecting cell area. In summary, cardiac fibroblasts have G protein-linked AT1 receptors that are coupled with proliferative growth. These results suggest that angiotensin II-induced cardiac hypertrophy is, in part, secondary to stimulated increases in nonmyocyte cellular growth.

Differences in structure of angiotensin-converting enzyme inhibitors might predict differences in action

Angiotensin-converting enzyme (ACE) inhibitors probably work by inhibition of tissue-located ACE, and they differ with regard to their relative ability to inhibit ACE in different organs. This apparent tissue selectivity may stem from either differences in tissue bioavailability or from a different affinity for the enzyme. The affinity of the ACE inhibitor for a particular enzyme is not only determined by the structure of the inhibitor, but also by the structure of the enzyme. ACE enzymes from different tissues may be slightly different, and this may have some bearing on the relative affinities of different ACE inhibitors for ACE from different tissues. The duration of inhibition in a particular tissue reflects not only the affinity of that inhibitor for the tissue enzyme, but also reflects the ease or difficulty with which the active ACE inhibitor is released from that tissue. Whether the beneficial effects of ACE inhibitors on experimentally induced myocardial infarction and reperfusion arrhythmias are due to the presence of a sulfhydryl group or are mainly related to the ACE inhibitor-mediated bradykinin potentiation remains a matter of controversy.

Effects of angiotensin-converting enzyme inhibitors on tissue renin-angiotensin systems

The renin-angiotensin system (RAS) plays a major role in the control of blood pressure and cardiovascular homeostasis and is involved in the pathogenesis of a number of cardiovascular disorders. The efficacy of angiotensin-converting enzyme (ACE) inhibitors in the treatment of hypertension and congestive heart failure has led to the widespread clinical use of ACE inhibitors in primary or secondary prevention of heart disease. The demonstration of the expression of the components of the RAS in several extrarenal tissues, as well as local generation of angiotensin II, has confirmed the existence of a tissue RAS that may serve organ-specific functions and act independently from the plasma RAS. The concept of paracrine/autocrine functions of the local RAS has changed our understanding of the functions of the RAS and suggests that tissue ACE inhibition may be of greater importance than inhibition of circulating ACE in the treatment of congestive heart failure and other cardiovascular disorders. Whereas the circulating endocrine RAS appears to be responsible for mediation of acute effects, the tissue RAS seems to be involved in more chronic situations, such as secondary structural changes of the cardiovascular system, and therefore could contribute to the pathogenesis of hypertension as well as other cardiovascular disorders, such as cardiac hypertrophy, coronary artery disease, and atherosclerosis. Several experimental and clinical findings suggest that reversal of cardiovascular structural changes secondary to cardiovascular disease and enhancement of renal sodium excretion by ACE inhibitors are important long-term antihypertensive actions possibly mediated by inhibition of the tissue RAS.

Prospects for cardioreparation

The structure of the myocardium has 2 principal components, a myocytic compartment and a non-myocytic compartment that consists primarily of interstitial tissue. It appears that increased collagen production is mainly responsible for the functional consequences of structural remodelling. The concept of cardioreparation implies both a restoration of structural abnormalities and a return of cardiac function to or toward normal. In spontaneously hypertensive rats with left ventricular hypertrophy and adverse structural remodeling of the cardiac interstitium, angiotensin-converting enzyme inhibition has resulted in restoration of myocardial integrity and stiffness toward normal. Further research needs to be undertaken to identify the molecular mechanisms involved in the development of interstitial myocardial fibrosis, and reliable methods for assessing the interstitium and the changes that occur within it in clinical practice need to be developed.

Trandolapril inhibits atherosclerosis in the Watanabe heritable hyperlipidemic rabbit

The effects of trandolapril (0.25 mg/kg body wt per 48 hours) on aortic atherosclerosis were examined in the Watanabe heritable hyperlipidemic rabbit treated from 3 to 12 months of age. Trandolapril caused a significant decrease in atherosclerotic involvement of the intimal surface of total aorta from 56.3 +/- 5.0% in control Watanabe rabbits to 35.0 +/- 4.1% with treatment (p less than 0.01). The largest reductions were observed in descending thoracic aorta where 21.8 +/- 5.7% of intimal surface was involved in the trandolapril-treated animals versus 54.4 +/- 7.7% in the control group (p less than 0.01). Significant decreases also occurred in ascending aorta/arch and abdominal aortic segments. Cholesterol content of descending thoracic aorta was also significantly reduced in the trandolapril-treated rabbits. The atherosclerotic plaques in aorta from trandolapril-treated rabbits appeared to contain less foam cells and relatively greater amounts of connective tissue than those from control animals. These studies indicate that trandolapril inhibits aortic atherosclerosis in the Watanabe heritable hyperlipidemic rabbit. The similarity in results between the current study and that using captopril suggests that the antiatherosclerotic action of trandolapril and captopril represents a class effect related to angiotensin converting enzyme inhibition.

Synthesis of renin by tubulocystic epithelium in autosomal-dominant polycystic kidney disease

Evidence suggests an important role for the renin-angiotensin system in the pathogenesis of autosomal-dominant polycystic kidney disease (ADPKD). Therefore, we studied the presence of immunoreactive renin in renal biopsies and measured the concentrations of renin in cyst fluids. Normal kidneys and kidneys with renal artery stenosis were used for comparison. In ADPKD, immunoreactive renin was present in juxtaglomerular apparatus, associated arterioles, and in some cells within the connective tissue surrounding the cysts. Vascular immunoreactive renin was less prominent than in renal artery stenosis. Increased amounts of tubular immunoreactive renin were noted in polycystic kidneys, as compared to normal kidneys and kidneys with renal artery stenosis. Cyst fluids contained renin detected by Western analysis and enzymatic activity; concentrations were greater in gradient cysts than in nongradient cysts. Seventy-four percent of the renin in gradient cysts was active as compared to 23% in nongradient cysts and 15% in plasma. To determine whether cyst epithelial cells are capable of synthesizing renin, these cells were isolated in tissue culture. Enzymatic assay of extracts from these cells revealed the presence of renin-like enzymatic activity (1.3 +/- 0.8 ng AI/mg protein/hr). The synthesis of renin by tubulocystic epithelium was confirmed by [35S]-methionine radiolabeling of cyst-derived cells, followed by immunoprecipitation and SDS-PAGE and by detection of renin mRNA by the polymerase chain reaction. These results indicate that the tubulocystic epithelium has the potential to synthesize renin. Elevated levels of active renin in renal cysts may be linked to the pathogenesis of hypertension in ADPKD. The occurrence of renin in the lining epithelium of cyst walls raises the possibility that abnormal expression of the renin-angiotensin system may, by a paracrine or autocrine mechanism, regulate epithelial hyperplasia in growing renal cysts.

Mechanisms of cardiac growth. The role of the renin-angiotensin system

Hypertension is associated with cardiac hypertrophy, which is a structural adaptation of the heart in order to attenuate the systolic stress on the left ventricle. As cardiac myocytes cannot divide, they increase in mass and volume, probably by activating second messengers and proto-oncogenes involved in cellular differentiation and proliferation. Various mechanisms, such as pressure overload and angiotensin II (Ang II), have been proposed to trigger cardiocyte growth and left-ventricular hypertrophy (LVH). In both cases, activation of second messenger routes which increase the intracellular calcium concentration, protooncogene expression, and protein synthesis have been demonstrated. Ang II also facilitates the action of another trophic agent for cardiocytes, which is noradrenaline (NA). In addition, the prevention and reversal of LVH by inhibitors of angiotensin-converting enzyme (ACE) suggests a key role for Ang II. However, no conclusive evidence has demonstrated the role of a single pathophysiologic factor in LVH. Therefore, it is more attractive to suggest a link between high blood pressure, renin-angiotensin and other vasoactive systems, such as the adrenergic system, which might together lead in a synergistic way to cardiac hypertrophy.

Angiotensin II stimulates protein-tyrosine phosphorylation in a calcium-dependent manner

Cellular responses to epidermal growth factor (EGF) are dependent on the tyrosine-specific protein kinase activity of the cell-surface EGF receptor. Previous studies using WB rat liver epithelial cells have detected at least 10 proteins whose phosphotyrosine (P-Tyr) content is increased by EGF. In this study, we have examined alternate modes of activating tyrosine phosphorylation. Treatment of WB cells with hormones linked to Ca2+ mobilization and protein kinase C (PKC) activation, including angiotensin II, [Arg8]vasopressin, or epinephrine, stimulated rapid (less than or equal to 15-s) and transient increases in the P-Tyr content of several proteins (p120/125, p75/78, and p66). These proteins, detected by anti-P-Tyr immunoblotting, were similar in molecular weight to a subset of EGF-sensitive P-Tyr-containing proteins (P-Tyr-proteins). The increased P-Tyr content was confirmed by [32P]phosphoamino acid analysis of proteins recovered by anti-P-Tyr immunoprecipitation. Elevating intracellular [Ca2+] with the ionophore A23187 or ionomycin or with the tumor promoter thapsigargin mimicked the effects of hormones on tyrosine phosphorylation, whereas treatment with a PKC-activating phorbol ester did not. In addition, responses to angiotensin II were not diminished in PKC-depleted cells. Ca2+ mobilization, measured by fura-2 fluorescence, was coincident with the increase in tyrosine phosphorylation in response to angiotensin II or thapsigargin. Loading cells with the intracellular Ca2+ chelator bis-(o-aminophenoxy)ethane-N ,N ,N' , N'-tetraacetic acid (BAPTA) inhibited the appearance of all P-Tyr-proteins in response to angiotensin II, thapsigargin, or ionophores, as well as two EGF-stimulated P-Tyr-proteins. The majority of EGF-stimulated P-Tyr-proteins were not affected by BAPTA. These studies indicate that angiotensin II can alter protein-tyrosine phosphorylation in a manner that is secondary to, and apparently dependent on, Ca2+ mobilization. Thus, ligands such as EGF and angiotensin II, which act through distinct types of receptors, may activate secondary pathways involving tyrosine phosphorylation. These results also raise the possibility that certain growth-promoting effects of Ca2+ -mobilizing agents such as angiotensin II may be mediated via tyrosine phosphorylation.

Angiotensin II stimulates protein-tyrosine phosphorylation in a calcium-dependent manner

Cellular responses to epidermal growth factor (EGF) are dependent on the tyrosine-specific protein kinase activity of the cell-surface EGF receptor. Previous studies using WB rat liver epithelial cells have detected at least 10 proteins whose phosphotyrosine (P-Tyr) content is increased by EGF. In this study, we have examined alternate modes of activating tyrosine phosphorylation. Treatment of WB cells with hormones linked to Ca2+ mobilization and protein kinase C (PKC) activation, including angiotensin II, [Arg8]vasopressin, or epinephrine, stimulated rapid (less than or equal to 15-s) and transient increases in the P-Tyr content of several proteins (p120/125, p75/78, and p66). These proteins, detected by anti-P-Tyr immunoblotting, were similar in molecular weight to a subset of EGF-sensitive P-Tyr-containing proteins (P-Tyr-proteins). The increased P-Tyr content was confirmed by [32P]phosphoamino acid analysis of proteins recovered by anti-P-Tyr immunoprecipitation. Elevating intracellular [Ca2+] with the ionophore A23187 or ionomycin or with the tumor promoter thapsigargin mimicked the effects of hormones on tyrosine phosphorylation, whereas treatment with a PKC-activating phorbol ester did not. In addition, responses to angiotensin II were not diminished in PKC-depleted cells. Ca2+ mobilization, measured by fura-2 fluorescence, was coincident with the increase in tyrosine phosphorylation in response to angiotensin II or thapsigargin. Loading cells with the intracellular Ca2+ chelator bis-(o-aminophenoxy)ethane-N ,N ,N' , N'-tetraacetic acid (BAPTA) inhibited the appearance of all P-Tyr-proteins in response to angiotensin II, thapsigargin, or ionophores, as well as two EGF-stimulated P-Tyr-proteins. The majority of EGF-stimulated P-Tyr-proteins were not affected by BAPTA. These studies indicate that angiotensin II can alter protein-tyrosine phosphorylation in a manner that is secondary to, and apparently dependent on, Ca2+ mobilization. Thus, ligands such as EGF and angiotensin II, which act through distinct types of receptors, may activate secondary pathways involving tyrosine phosphorylation. These results also raise the possibility that certain growth-promoting effects of Ca2+ -mobilizing agents such as angiotensin II may be mediated via tyrosine phosphorylation.

Changes in angiotensinogen messenger RNA in differentiating 3T3-F442A adipocytes

Angiotensinogen messenger RNA (mRNA) has been identified in both brown and white adipose tissue. Recently we have shown that when 3T3-L1 cells were treated with isobutylmethylxanthine (IBMX) to accelerate differentiation, angiotensinogen mRNA increased markedly in adipocytes as compared with preadipocytes. To determine if a correlation existed between the regulatory events associated with the differentiation process, we compared the change in angiotensinogen mRNA in spontaneously differentiating 3T3-F442A cells with two established parameters of differentiation in adipocyte cell lines. Differentiation was assessed by visual examination of cells for lipid droplets, fluorescent staining of the F-actin fibers, and increases in glycerol phosphate dehydrogenase mRNA. F-actin fibers were highly structured in preadipocytes, becoming disassembled and very disorganized as cells differentiated into adipocytes. The quantity of angiotensinogen mRNA increased as the number of lipid-containing cells increased within a culture. Glycerol phosphate dehydrogenase mRNA accumulated in differentiated adipocytes to about the same extent as angiotensinogen mRNA. Thus, increases in angiotensinogen mRNA were associated with the morphological and biochemical changes that occur during the phenotypic modulation of 3T3-F442A cells.

Angiotensinogen gene expression in 3T3-L1 cells

It has previously been established that angiotensinogen mRNA is present in brown and white adipose tissue of the rat. To determine whether angiotensinogen gene expression is present in adipocytes as compared with other cell elements, we have examined angiotensinogen mRNA in 3T3-L1 cells. These cells undergo adipocyte differentiation when the culture reaches confluence. To accelerate the differentiation process, cells were treated with dexamethasone and isobutylmethylxanthine for 3 days. On the 7th day after drug treatment, RNA was extracted from cells and was examined for angiotensinogen mRNA using a full-length rat angiotensinogen cDNA. Angiotensinogen mRNA was readily detected in differentiated 3T3-L1 cells. To determine when the gene is expressed, a 7-day time course from day 0 (before drug treatment) to day 7 was examined for the presence of angiotensinogen mRNA. In addition, C2 cells, a clonal cell line that does not differentiate into adipocytes, were examined. Angiotensinogen mRNA was detected on days 2-7 after drug treatment in 3T3-L1 cells, with no detectable levels in untreated 3T3-C2 cells. When 3T3-C2 cells were subjected to the same drug regimen, angiotensinogen mRNA levels increased in the same time course as 3T3-L1 cells. However, the increase in angiotensinogen message was greater in differentiating 3T3-L1 cells than in the nondifferentiating 3T3-C2 cells. Thus angiotensinogen mRNA is present in both adipocytes and in fibroblast-like cells and appears to be regulated by steroids.

Converting enzyme inhibition specifically prevents the development and induces regression of cardiac hypertrophy in rats

Antihypertensive agents have been shown to differ markedly in their effects on the development and regression of cardiac hypertrophy. In view of possible trophic properties of angiotensin II (ANG II), we compared the effects of equipotent antihypertensive doses of the converting enzyme (CE) inhibitor ramipril (1 mg/kg), the calcium antagonist nifedipine (30 mg/kg), and the arterial vasodilator dihydralazine (30 mg/kg) on cardiac mass in rats subjected to banding of the abdominal aorta. Treatment was started either immediately after banding ("prevention experiments") or after hypertension and hypertrophy had already developed ("regression experiments"). Groups of untreated animals with aortic constriction and sham-operated animals served as controls. In the prevention experiments heart weight, myocardial protein content and ANG II plasma levels were significantly increased in untreated animals and in those receiving nifedipine and dihydralazine. In contrast, values obtained in animals treated with ramipril were not different from those seen in normotensive, sham operated controls with the exception of plasma ANG II levels which were lower. Similar results were observed in the second series of studies which examined the effect of antihypertensive agents on the "regression" of cardiac hypertrophy. Treatment was started 6 weeks after aortic banding and continued for another 6 weeks. While all three drugs lowered blood pressure equally well, only ramipril induced a significant and complete regression of cardiac hypertrophy to values not different from sham-operated controls. In addition we studied a group of animals treated with a nonantihypertensive low dose of ramipril (10 micrograms/kg). Remarkably, these animals showed the same complete regression of cardiac hypertrophy as seen in the group receiving the antihypertensive dose of CE inhibitor. Our study indicates a selective advantage of CE inhibitors over other antihypertensive drugs in the prevention and regression of hypertensive cardiac hypertrophy. Importantly, the dissociation between effects on blood pressure and cardiac mass demonstrated in the experiments with a low dose of ramipril stresses the role of factors other than blood pressure and afterload on the development of hypertensive cardiac hypertrophy. One such peptide, thus, may be ANG with its known potential as a growth factor.

The role of antihypertensive pharmacologic treatment in countering adverse pathophysiological profiles: influence on small arteries

Usually, when antihypertensive therapy is considered in the hypertensive patient, structural cardiovascular changes are already well established and the structure of the cardiovascular system is redesigned to maintain higher than normal pressure. Left ventricular hypertrophy has been shown to be an independent risk factor for all manifestations of coronary heart disease. In hypertension, the increased pressure load over a long period of time induces degenerative changes in, for example, cerebral, renal, and coronary vessels, with well-known clinical consequences. Independent of the primary cause of hypertension, full reversal to normotension will probably occur only when the structurally reset cardiovascular system has been returned to normal dimensions by regression of structural vascular changes. In animal models several forms of antihypertensive treatment have prevented the development of or induced regression of left ventricular hypertrophy as well as medial hypertrophy of the vessels. These effects have been related both to the extent of blood pressure reduction and to the degree of inhibition of neurohormonal trophic influences. In humans the results have been somewhat contradictory. Plethysmography has demonstrated a reduction of resistance at maximal dilatation with either combination therapy or pindolol but not with mefruside or atenolol. There may be several explanations for the difficulties in showing regression of structural vascular changes in humans: (1) inadequate treatment of high blood pressure, (2) reflexogenic activation of neurohormonal trophic factors, (3) investigation of an unsuitable vascular bed, or (4) treatment started too late. The ultimate goal in the treatment of hypertension is, of course, reduction of cardiovascular morbidity and mortality, but normalization of structural cardiovascular changes is clearly the second most important therapeutic goal.

Analysis of angiotensin-stimulated sodium transport in cultured smooth muscle cells from rat aorta

Angiotensin peptides (AI, AII, AIII) increased the rate of Na+ accumulation by smooth muscle cells (SMC) cultured from rat aorta. The stimulatory effect of AII on Na+ uptake was observed when Na+ exodus via the Na+/K+ pump was blocked either by ouabain or by the removal of extracellular K+. AII was at least ten times more potent than AIII and about 100 times more potent than AI in stimulating Na+ uptake. Saralasin had little effect on Na+ uptake by itself but almost completely blocked the increase caused by AII. The stimulation of net Na+ entry by AI, but not AII, was prevented by protease inhibitors. The stimulation of Na+ uptake was almost completely blocked by amiloride. Tetrodotoxin, which prevented veratridine from increasing Na+ uptake, had no effect on the response to AII. Angiotensin increased the rate of ouabain-sensitive 86Rb+ uptake (Na+/K+ pump activity) but had no effect on ouabain-sensitive ATPase activity in frozen-thawed SMC or in microsomal membranes isolated from cultured SMC. The stimulation of ouabain-sensitive 86Rb+ uptake by AII was blocked by saralasin. Omitting Na+ from the external medium prevented AII from increasing 86Rb+ uptake. AII had no effect on cell volume or cyclic AMP levels in the cultured SMC. These results suggest that angiotensin peptides activate an amiloride-sensitive Na+ transporter which supplies the Na+/K+ pump with more Na+, its rate-limiting substrate.

Effects of angiotensin II and of an angiotensin II receptor antagonist on simian virus 40-induced tumor growth in vivo

The effects of angiotensin II and of the competitive angiotensin II receptor antagonist saralasin on in vivo tumor growth were investigated in hamsters. Angiotensin II strongly inhibited tumor growth while saralasin stimulated it, though the high dose used had partial agonistic angiotensin II-like actions. Lower doses of saralasin were without significant effect on tumor weights.