Identification and characterization of angiotensin II receptors in rat epididymal adipocyte membranes

Inhibition of the Renin-Angiotensin System Reduces Gene Expression of Inflammatory Mediators in Adipose Tissue Independent of Energy Balance

Obesity is a growing health problem worldwide. The renin-angiotensin system (RAS) is present in adipose tissue, and evidence suggests that it is involved in both diet-induced obesity and the inflammation associated with obesity. The present experiments determined the effect of (1) different angiotensin-converting enzyme (ACE) inhibitors (captopril, perindopril, enalapril) and angiotensin receptor blockers (ARBs: telmisartan, losartan) on adiposity of mice fed a high-fat diet for 28 days (2); acute treatment with the ACE-inhibitor captopril on gene expression of inflammatory markers in mice fed a high-fat diet (HFD); and (3) short-term (2 days) and chronic (28 days) treatment of ACE-inhibition on energy expenditure (EE) and energy balance in mice fed HFD ad libitum (AL), as well as receiving HFD limited to the amount of calories eaten by controls (pair-fed (PF) group). Body weight, food intake, adiposity and plasma leptin were lower in ACE inhibitor or ARB-treated groups over 28 days compared with HFD untreated mice. Short-term treatment with captopril led to increased EE relative to the level in the PF group. After 28 days, EE was lower in both captopril-treated and PF mice compared with AL, but the effect was greater in the captopril-treated group. Adiponectin was elevated in captopril-treated mice, but not in PF mice, after both 2 and 28 days. Additionally, acute RAS blockade in HFD-fed mice reduced mRNA expression for MCP-1, IL-6, TLR4, and leptin in adipose tissue relative to values in untreated groups. These data demonstrate that ACE inhibition and angiotensin receptor blockade reduce food intake to produce weight loss and suggest that the anti-inflammatory effects of ACE inhibition may be independent of weight loss.

Trelagliptin succinate: DPP-4 inhibitor to improve insulin resistance in adipocytes

Trelagliptin inhibits the enzyme dipeptidyl-4 (DPP-4) to treat type 2 diabetes and it may possess the potential to improve insulin resistance. However, the molecular mechanism is not known. In this study, the effect of trelagliptin succinate in improving insulin resistance was investigated. The differentiation system of 3T3-L1 mouse preadipocytes was used to determine the content of adipokines and the content of GLUT4 in the outer membrane. The expression of AKT, P-AKT, IRS-1 and P-IRS-1 in differentiated 3T3-L1 adipocytes was determined by western blotting. Our results demonstrated that trelagliptin succinate increased the expression of AKT, P-AKT, IRS-1 and P-IRS-1 in the PI-3K/AKT insulin signaling pathway. These events promote the trans-membrane function of GLUT4 and concomitant glucose intake in adipocytes. In addition, the secretion of free fatty acids and resistin were decreased. In conclusion, our study suggested that trelagliptin succinate improved insulin resistance in adipocytes via regulation of PI-3K/AKT/GLUT4 insulin signaling pathway.

Impact of Adrenal Steroids on Regulation of Adipose Tissue

Corticosteroids are secreted by the adrenal glands and control the functions of adipose tissue via the activation of mineralocorticoid receptor (MR) and glucocorticoid receptor (GR). In turn, adipocytes release a large variety of adipokines into the bloodstream, regulating the function of several organs and tissues, including the adrenal glands, hereby controlling corticosteroid production. In adipose tissue, the activation of the MR by glucocorticoids (GC) and aldosterone affects important processes such as adipocyte differentiation, oxidative stress, autophagic flux, adipokine expression as well as local production of GC through upregulation of the enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). Notably, the proinflammatory responses induced by the MR are counteracted by activation of the GR, whose activity inhibits the expression of inflammatory adipokines. Both GR and MR are deeply involved in adipogenesis and adipose expansion; hence pharmacological blockade of these two receptors has proven effective against adipose tissue dysfunction in experimental models of obesity and metabolic syndrome (MetS), suggesting a potential use for MR and GR antagonists in these clinical settings. Importantly, obesity and Cushing's syndrome (CS) share metabolic similarities and are characterized by high levels of circulating corticosteroids, which in turn are able to deeply affect adipose tissue. In addition, pharmacological approaches aimed at reducing aldosterone and GC levels, by means of the inhibition of CYP11B2 (aldosterone synthase) or 11β-HSD1, represent alternative strategies to counter the detrimental effects of excessive levels of corticosteroids, which are often observed in obesity and, more general, in MetS. © 2017 American Physiological Society. Compr Physiol 7:1425-1447, 2017.

The intricacies of the renin-angiotensin-system in metabolic regulation

Over recent years, the renin-angiotensin-system (RAS), which is best-known as an endocrine system with established roles in hydromineral balance and blood pressure control, has emerged as a fundamental regulator of many additional physiological and pathophysiological processes. In this manuscript, we celebrate and honor Randall Sakai's commitment to his trainees, as well as his contribution to science. Scientifically, Randall made many notable contributions to the recognition of the RAS's roles in brain and behavior. His interests, in this regard, ranged from its traditionally-accepted roles in hydromineral balance, to its less-appreciated functions in stress responses and energy metabolism. Here we review the current understanding of the role of the RAS in the regulation of metabolism. In particular, the opposing actions of the RAS within adipose tissue vs. its actions within the brain are discussed.

Milk-derived tripeptides IPP (Ile-Pro-Pro) and VPP (Val-Pro-Pro) promote adipocyte differentiation and inhibit inflammation in 3T3-F442A cells

Milk derived tripeptides IPP (Ile-Pro-Pro) and VPP (Val-Pro-Pro) have shown promise as anti-hypertensive agents due to their inhibitory effects on angiotensin converting enzyme (ACE). Due to the key inter-related roles of hypertension, chronic inflammation and insulin resistance in the pathogenesis of metabolic syndrome, there is growing interest in investigating established anti-hypertensive agents for their effects on insulin sensitivity and inflammation. In this study, we examined the effects of IPP and VPP on 3T3-F442A murine pre-adipocytes, a widely used model for studying metabolic diseases. We found that both IPP and VPP induced beneficial adipogenic differentiation as manifested by intracellular lipid accumulation, upregulation of peroxisome proliferator-activated receptor gamma (PPARγ) and secretion of the protective lipid hormone adiponectin by these cells. The observed effects were similar to those induced by insulin, suggesting potential benefits in the presence of insulin resistance. IPP and VPP also inhibited cytokine induced pro-inflammatory changes such as reduction in adipokine levels and activation of the nuclear factor kappa B (NF-κB) pathway. Taken together, our findings suggest that IPP and VPP exert insulin-mimetic adipogenic effects and prevent inflammatory changes in adipocytes, which may offer protection against metabolic disease.

The renin-angiotensin system in adipose tissue and its metabolic consequences during obesity

Obesity is a worldwide disease that is accompanied by several metabolic abnormalities such as hypertension, hyperglycemia and dyslipidemia. The accelerated adipose tissue growth and fat cell hypertrophy during the onset of obesity precedes adipocyte dysfunction. One of the features of adipocyte dysfunction is dysregulated adipokine secretion, which leads to an imbalance of pro-inflammatory, pro-atherogenic versus anti-inflammatory, insulin-sensitizing adipokines. The production of renin-angiotensin system (RAS) components by adipocytes is exacerbated during obesity, contributing to the systemic RAS and its consequences. Increased adipose tissue RAS has been described in various models of diet-induced obesity (DIO) including fructose and high-fat feeding. Up-regulation of the adipose RAS by DIO promotes inflammation, lipogenesis and reactive oxygen species generation and impairs insulin signaling, all of which worsen the adipose environment. Consequently, the increase of circulating RAS, for which adipose tissue is partially responsible, represents a link between hypertension, insulin resistance in diabetes and inflammation during obesity. However, other nutrients and food components such as soy protein attenuate adipose RAS, decrease adiposity, and improve adipocyte functionality. Here, we review the molecular mechanisms by which adipose RAS modulates systemic RAS and how it is enhanced in obesity, which will explain the simultaneous development of metabolic syndrome alterations. Finally, dietary interventions that prevent obesity and adipocyte dysfunction will maintain normal RAS concentrations and effects, thus preventing metabolic diseases that are associated with RAS enhancement.

Role of mineralocorticoid receptor and renin-angiotensin-aldosterone system in adipocyte dysfunction and obesity

The mineralocorticoid receptor (MR) classically mediates aldosterone effects on salt homeostasis and blood pressure regulation in epithelial target tissues. In recent years, functional MRs have been identified in non classical targets of aldosterone actions, in particular in adipose tissue, where they mediate the effects of aldosterone and glucocorticoids in the control of adipogenesis, adipose expansion and its pro-inflammatory capacity. In this context, inappropriate MR activation has been demonstrated to be a causal factor in several pathologic conditions such as vascular inflammation, endothelial dysfunction, insulin resistance and obesity. The aim of this review is to summarize the latest developments in this rapidly developing field, and will focus on the role of MR and renin-angiotensin-aldosterone system (RAAS) as potential leading characters in the early steps of adipocyte dysfunction and obesity. Indeed modulation of MR activity in adipose tissue has promise as a novel therapeutic approach to treat obesity and its related metabolic complications. This article is part of a Special Issue entitled 'CSR 2013'.

Role of the Renin-Angiotensin system and aldosterone on cardiometabolic syndrome

Aldosterone facilitates cardiovascular damage by increasing blood pressure and through different mechanisms that are independent of its effects on blood pressure. In this respect, recent evidence involves aldosterone in the pathogenesis of metabolic syndrome. Although this relationship is complex, there is some evidence suggesting that different factors may play an important role, such as insulin resistance, renin-angiotensin-aldosterone system, oxidative stress, sodium retention, increased sympathetic activity, levels of free fatty acids, or inflammatory cytokines and adipokines. In addition to the classical pathway by which aldosterone acts through the mineralocorticoid receptors leading to sodium retention, aldosterone also has other mechanisms that influence cardiovascular tissue remodelling. Finally, overweight and obesity promote the adrenal secretion of aldosterone, increasing the predisposition to type 2 diabetes mellitus. Further studies are needed to better establish therapeutic strategies that act on the blockade of mineralocorticoid receptor in the treatment and prevention of cardiovascular diseases related to the excess of aldosterone and the metabolic syndrome.

Angiotensin converting enzyme inhibition from birth reduces body weight and body fat in Sprague-Dawley rats

In vitro studies have demonstrated that angiotensin II (ANG II) induces adipocyte hyperplasia and hypertrophy. The aim of the present study was to determine the effect of angiotensin-converting enzyme inhibition on body weight, adiposity and blood pressure in Sprague-Dawley rats. From birth half of the animals (n=15) were given water to drink, while the remainder were administered perindopril in their drinking water (2 mg/kg/day). Food intake, water intake and body weight were measured weekly. Blood pressure was measured by tail cuff plethysmography at 11-weeks. Body fat content and distribution were assessed using dual energy X-ray absorptiometry and Magnetic Resonance Imaging at 12 weeks. Animals administered with perindopril had a body fat proportion that was half that of controls. This was consistent with, but disproportionately greater than the observed differences in food intake and body weight. Perindopril treatment completely removed hypertension. We conclude that the chronic inhibition of ANG II synthesis from birth specifically reduces the development of adiposity in the rat.

DOCA stimulates salt appetite in Zucker rats: effect of dose, synergistic action with central angiotensin II, and obesity

An enhanced sodium appetite is found in rats by the synergist interaction of peripheral mineralocorticoids, deoxycorticosterone acetate (DOCA), and central angiotensin II (AngII), the synergy theory. We used obese Zucker rats which have a predisposition to develop hypertension under appropriate salt conditions to examine this synergy response between AngII and different low doses of DOCA on 2% NaCl intake. Obese and lean Zucker rats on low sodium food were treated systemically with 0.5, 1 and 2 mg/kg/day of DOCA for 3 days, before receiving i.c.v. AngII (10 pmol) on the fourth day. Food, fluid intakes and urine outputs were measured daily throughout. Plasma aldosterone levels were also analysed. Results showed that AngII alone increased water but not salt intake, whereas all three doses of DOCA by themselves enhanced daily salt intake during the treatment period. The lowest dose of DOCA plus AngII did not stimulate an enhanced sodium consumption. The 1 mg/kg was the threshold dose of DOCA for a synergistic response, and with 2 mg/kg DOCA the obese rats consumed nearly 2-fold more hypertonic NaCl solution than the leans. Moreover, obese baseline plasma levels of aldosterone were more elevated than the lean rats. In conclusion, in adult Zucker rats a threshold level of mineralocorticoid is required for the salt stimulating action of central AngII. In the obese rat the synergistic effect is enhanced with higher doses of mineralocorticoid, suggesting that the plasma level of aldosterone could be a prominent factor, which may predispose the obese to salt-sensitivity and, possibly, subsequently to hypertension under appropriate conditions.

Activation of the systemic and adipose renin-angiotensin system in rats with diet-induced obesity and hypertension

In obesity-related hypertension, activation of the renin-angiotensin system (RAS) has been reported despite marked fluid volume expansion. Adipose tissue expresses components of the RAS and is markedly expanded in obesity. This study evaluated changes in components of the adipose and systemic RAS in diet-induced obese hypertensive rats. RAS was quantified in adipose tissue and compared with primary sources for the circulating RAS. Male Sprague-Dawley rats were fed either a low-fat (LF; 11% kcal as fat) or moderately high-fat (32% kcal as fat) diet for 11 wk. After 8 wk, rats fed the moderately high-fat diet segregated into obesity-prone (OP) and obesity-resistant (OR) groups based on their body weight gain (body weight: OR, 566 ± 10; OP, 702 ± 20 g; P < 0.05). Mean arterial blood pressure was increased in OP rats (LF: 97 ± 2; OR: 97 ± 2; OP: 105 ± 1 mmHg; P < 0.05). Quantification of mRNA expression by real-time PCR demonstrated a selective increase (2-fold) in angiotensinogen gene expression in retroperitoneal adipose tissue from OP vs. OR and LF rats. Similarly, plasma angiotensinogen concentration was increased in OP rats (LF: 390 ± 48; OR: 355 ± 24; OP: 530 ± 22 ng/ml; P < 0.05). In contrast, other components of the RAS were not altered in OP rats. Marked increases in the plasma concentrations of angiotensin peptides were observed in OP rats (angiotensin II: LF: 95 ± 31; OR: 59 ± 20; OP: 295 ± 118 pg/ml; P < 0.05). These results demonstrate increased activity of the adipose and systemic RAS in obesity-related hypertension.

The adipose-tissue renin-angiotensin-aldosterone system: role in the metabolic syndrome?

Overfeeding of rodents leads to increased local formation of angiotensin II due to increased secretion of angiotensinogen from adipocytes. Whereas angiotensin II promotes adipocyte growth and preadipocyte recruitment, increased secretion of angiotensinogen from adipocytes also directly contributes to the close relationship between adipose-tissue mass and blood pressure in mice. In contrast, angiotensin II acts as an antiadipogenic substance in human adipose tissue, and the total increase in adipose-tissue mass may be more important in determining human plasma angiotensinogen levels than changes within the single adipocyte. However, as increased local formation of angiotensin II in adipose tissue may be increased especially in obese hypertensive subjects, a contribution of the adipose-tissue renin-angiotensin system to the development of insulin resistance and hypertension is conceivable in humans, but not yet proven. Insulin resistance may be aggravated by the inhibition of preadipocyte recruitment, which results in the redistribution of triglycerides to the liver and skeletal muscle, and blood pressure may be influenced by local formation of angiotensin II in perivascular adipose tissue. Thus, although the mechanisms are still speculative, the beneficial effects of ACE-inhibition and angiotensin-receptor blockade on the development of type 2 diabetes in large clinical trials suggest a pathophysiological role of the adipose-tissue renin-angiotensin system in the metabolic syndrome.

Possible involvement of the adipose tissue renin-angiotensin system in the pathophysiology of obesity and obesity-related disorders

Angiotensin II (Ang II), acting on the AT1 and AT2 receptors in mammalian cells, is the vasoactive component of the renin-angiotensin system (RAS). Several components of the RAS have been demonstrated in different tissues, including adipose tissue. Although the effects of Ang II on metabolism have not been studied widely, it is intriguing to assume that components of the RAS produced by adipocytes may play an autocrine, a paracrine and/or an endocrine role in the pathophysiology of obesity and provide a potential pathway through which obesity leads to hypertension and type 2 diabetes mellitus. In the first part of this review, we will describe the production of Ang II, the different receptors through which Ang II exerts its effects and summarize the concomitant intracellular signalling cascades. Thereafter, potential Ang II-induced mechanisms, which may be associated with obesity and obesity-related disorders, will be considered. Finally, we will focus on the different pharmaceutical agents that interfere with the RAS and highlight the possible implications of these drugs in the treatment of obesity-related disorders.

Novel human metabolites of the angiotensin-II antagonist tasosartan and their pharmacological effects

Three novel metabolites of the angiotensin-II (A-II) receptor antagonist tasosartan have been identified in humans, and the syntheses and pharmacologic profiling of these metabolites are reported. Each metabolite bound the human A-II receptor with IC(50)s between 20 and 45nM. The in vivo effects of these compounds in attenuating the pressor response to angiotensin-II challenge in anesthetized rats were also investigated. An unsaturated diol metabolite exhibited in vivo efficacy at intravenous doses of 1 and 3mg/kg, while the other metabolites, both carboxylic acids, had no significant effect at the same doses.

Angiotensin II regulates oxygen consumption

Previous studies demonstrated that angiotensin II (ANG II) decreases body weight. This study examined whether ANG II regulates body weight through energy expenditure. Acute ANG II administration decreased oxygen consumption. To determine whether this effect was maintained, rats were infused with ANG II or saline for 14 days. Oxygen consumption was transiently decreased on day 1 of ANG II infusion; however, body weight and food intake were reduced for 14 days. In pair-feeding studies, reductions in food intake accounted for 63% of the effect of ANG II on body weight but did not influence systolic pressure, water intake, or oxygen consumption. With 28 days of ANG II infusion, differences in body weight between ANG II and control rats were of greater magnitude. An initial decrease in oxygen consumption was followed by a rebound increase. Coadministration of losartan prevented the effect of ANG II on body weight, food intake, blood pressure, and water intake. However, losartan only partially prevented ANG II reductions in oxygen consumption. These results demonstrate that ANG II transiently decreases oxygen consumption through mechanisms unrelated to food intake. With chronic ANG II exposure, energy expenditure may contribute to sustained reductions in body weight.

Characterization of a G protein-coupled receptor for nicotinic acid

Nicotinic acid is a lipid-lowering agent widely used to treat hypertriglyceridemia and to elevate low high density lipoprotein levels. However, the underlying mechanisms are poorly understood. In this study, G protein activation by nicotinic acid and derivatives was assessed as stimulation of guanosine 5'-(gamma-[(35)S]-thio)triphosphate ([(35)S]GTPgammaS) binding, and [(3)H]nicotinic acid was used for specific labeling of binding sites. Nicotinic acid (EC(50) approximately 1 microM) stimulated [(35)S]GTPgammaS binding in membranes from rat adipocytes and spleen, but not from other tissues. G protein activation in adipocyte membranes in the presence of maximally activating concentrations of the selective A(1) adenosine receptor agonist 2-chloro-N(6)-cyclopentyladenosine and nicotinic acid was almost additive, indicating that G proteins of mostly distinct pools were activated by these agonists. G protein activation by nicotinic acid and related substances in spleen and adipocytes revealed identical pharmacological profiles. [(3)H]Nicotinic acid specifically detected guanine nucleotide-sensitive binding sites of identical pharmacology in adipocyte and spleen membranes. The site of action of nicotinic acid is distinct from other G protein-coupled receptors. These data indicate that nicotinic acid most probably acts on a specific G protein-coupled receptor.

Physiology and pathophysiology of the adipose tissue renin-angiotensin system

The renin-angiotensin system has long been recognized as an important regulator of systemic blood pressure and renal electrolyte homeostasis, and local renin-angiotensin systems have also been implicated in pathological changes of organ structure and function by modulation of gene expression, growth, fibrosis, and inflammatory response. Recently, substantial data have been accumulated in support of the notion that adipose tissue, besides other endocrine functions, also hosts a local renin-angiotensin system. In the first part of this review, we describe the components of the adipose tissue renin-angiotensin system in human and rodent animal models with respect to regulation of angiotensinogen expression and secretion, formation of angiotensin peptides, and the existence of angiotensin II receptors. In the second part, we describe the role of the adipose tissue renin-angiotensin system in the process of adipogenic differentiation and in the regulation of body weight. We also detail the differential regulation of the adipose tissue renin-angiotensin system in obesity and hypertension and thereby also speculate on its possible role in the development of obesity-associated hypertension. Although some findings on the adipose tissue renin-angiotensin system appear to be confusing, its involvement in the physiology and pathophysiology of adipose tissue has been confirmed by several functional studies. Nevertheless, future studies with more carefully described phenotypes are necessary to conclude whether obesity (by stimulation of adipogenic differentiation) and hypertension are associated with changes of renin-angiotensin system activity in adipose tissue. If so, the physiological relevance of this system in animal models and humans may warrant further interest.

Body fat, resting and exercise blood pressure and the angiotensinogen M235T polymorphism: the heritage family study

OBJECTIVE

The association of resting and exercise blood pressure (BP) and fat mass with the angiotensinogen (AGT) M235T polymorphism was investigated in 522 sedentary Caucasian subjects from 99 families.

RESEARCH METHODS AND PROCEDURES

Resting BP was measured on two separate days, three times each day, and the mean of six valid measurements was used. Exercise BP was measured during a cycle ergometer test at a constant power output (50 W). Body composition was derived from under-water weighing and the AGT M235T polymorphism was typed with a polymerase chain reaction-based method.

RESULTS

Neither resting nor exercise BP was associated with the AGT genotypes. In mothers, the homozygotes for the T allele showed 8.8 kg and 7.1 kg greater (p=0.017) age-adjusted body fat mass (FM) than the MM homozygotes and heterozygotes, respectively. Sixty-nine percent of all TT homozygotes were found in the highest FM tertile, whereas only 16% of the MM homozygotes fell in the same tertile (p = 0.008). Moreover, a significant interaction was seen between FM and T-allele carrier status in women with regard to resting diastolic BP (p = 0.002). Among women with a FM> or =24 kg, carriers of the T allele showed a 6.3 mmHg higher diastolic blood pressure (DBP) than non-carriers whereas no difference was found in women with a FM less than 24 kg. A similar trend toward an interaction term was evident with resting systolic blood pressure (p = 0.011) and exercise DBP (p = 0.012). Body fat was not associated with the AGT polymorphism in fathers or in offspring.

DISCUSSION

These data suggest that the AGT M235T polymorphism is associated with body fatness in women, and that the relationship between DBP and AGT M235T polymorphism is dependent on FM in middle-aged sedentary normotensive women.

Co-expression of renin-angiotensin system genes in human adipose tissue

OBJECTIVE

The renin-angiotensin system plays a central role in blood pressure regulation, both by affecting renal function and by modulating vascular tone and structure. Recent studies in rodents demonstrated the existence of several components of this system in adipose tissue. The activity of the renin-angiotensin system appears to be regulated by food intake, suggesting that it may be involved in obesity-associated hypertension. Few data are available on the presence of renin-angiotensin system components in human adipose tissue.

MATERIALS AND METHODS

In order to explore the expression of renin-angiotensin system genes in human adipose tissue and adipocytes, total RNA was isolated from whole adipose tissue (subcutaneous and omental) or cultured adipocytes (mammary) and subjected to reverse-transcriptase polymerase chain reaction with primers specific for human angiotensinogen, renin, renin-binding protein, angiotensin converting enzyme, chymase and type 1 and type 2 angiotensin receptors.

RESULTS

Angiotensinogen, angiotensin converting enzyme and type 1 angiotensin receptor genes were widely expressed, both in human adipose tissue and in cultured human adipocytes. Furthermore, we found expression of the chymase and renin-binding protein genes in these samples.

CONCLUSIONS

Our findings suggest the presence of a local renin -angiotensin system in human adipose tissue, with adipocytes being an important part of this system, and prompt speculation that this local renin-angiotensin system may be involved in obesity-related disorders, including hypertension and the metabolic syndrome.

Angiotensin II receptors in human preadipocytes: role in cell cycle regulation

The role of angiotensin II (AII) in human preadipocyte physiology has been investigated in primary cultures from human adipose tissue. Receptor binding studies indicated that human preadipocytes express a high affinity AII binding site of the AT1 subtype, as binding of 125I-labeled [Sar1,Ile8]AII was rapid, saturable, and specific. As AII has previously been demonstrated to affect the cell cycle in adrenal and cardiac cells, the effect of AII on regulation of cycle progression was examined in human preadipocytes. Stimulation of preadipocytes with AII resulted in G1 phase progression of the cell cycle, as determined by flow cytometric analysis. AII treatment was associated with induction of expression of the messenger RNA for the cell cycle regulatory protein cyclin D1 in a dose-dependent manner. Pretreatment of cells with subtype-selective AT receptor ligands before AII stimulation indicated that the cyclin response was mediated via the AT1 receptor. The identity of the cells as preadipocyte was verified by culture in a defined differentiation medium, observing both leptin message expression and triglyceride accumulation by flow cytometry. These findings indicate that AII has early, receptor-mediated effects on cell cycle progression in human preadipocytes that may contribute to differentiation to the adipocyte phenotype.

Characterization of renin activity in brown adipose tissue

Angiotensin (ANG) II plays a vital role in blood pressure regulation and body fluid homeostasis. Although many peripheral tissues synthesize components of the renin-ANG system, very few synthesize all of the major components involved in the generation ofANG II. This study used interscapular brown adipose tissue (ISBAT) as a model system to evaluate the mechanism of ANG II generation in an extrarenal tissue. Polymerase chain reaction analysis of DNA from ISBAT demonstrated angiotensinogen gene expression; however, renin gene expression was not detected. Renin activity that was not completely derived from the residual blood pool was detected in ISBAT homogenates. Kinetic parameters for renin activity were similar in ISBAT and adrenal gland. Renin activity was partially inhibited by anti-renin antibody and completely inhibited by a specific rat renin inhibitor. Bilateral nephrectomy did not decrease renin activity in ISBAT. Western blot analysis, employing two species-specific renin antibodies, indicated the presence of a variety of isoforms of renin in ISBAT. The presence of renin activity in isolated brown adipocytes demonstrated that the enzyme is localized to adipocytes. The release of immunoreactive ANG peptides from ISBAT slices over 3 h indicated de novo synthesis. These studies support the existence of a local renin-ANG system in ISBAT and suggest involvement of renin in the formation of ANG II.

Angiotensin II causes weight loss and decreases circulating insulin-like growth factor I in rats through a pressor-independent mechanism

The renin-angiotensin system regulates normal cardiovascular homeostasis and is activated in certain forms of hypertension and in heart failure. Angiotensin II has multiple physiological effects and we have shown recently that its growth-promoting effects on vascular smooth muscle require autocrine activation of the IGF I receptor. To study the effect of angiotensin II on circulating IGF I, we infused rats with 500 ng/kg/min angiotensin II for up to 14 d. Angiotensin II markedly reduced plasma IGF I levels (56 and 41% decrease at 1 and 2 wk, respectively) and IGF binding protein-3 levels, and increased IGF binding protein-2 levels, a pattern suggestive of dietary restriction. Compared with sham, angiotensin II-infused hypertensive rats lost 18-26% of body weight by 1 wk, and pair-feeding experiments indicated that 74% of this loss was attributable to a reduction in food intake. The vasodilator hydralazine and the AT1 receptor antagonist losartan had comparable effects to reverse angiotensin II-induced hypertension, but only losartan blocked the changes in body weight and in circulating IGF I and its binding proteins produced by angiotensin II. Moreover, in Dahl rats that were hypertensive in response to a high-salt diet, none of these changes occurred. Thus, angiotensin II produces weight loss through a pressor-independent mechanism that includes a marked anorexigenic effect and an additional (likely metabolic) effect. These findings have profound implications for understanding the pathophysiology of conditions, such as congestive heart failure, in which the renin-angiotensin system is activated.

Characterization and regulation of angiotensin II receptors in rat adipose tissue. Angiotensin receptors in adipose tissue

Characterization and regulation of angiotensin II (AII) receptor binding sites was performed in rat membrane preparations from nonadipose (liver, lung) and adipose (interscapular (ISBAT) and periaortic (PA) brown adipose tissue; epididymal (EF) and retroperitoneal (RPF) white adipose tissue). In membrane preparations from brown and white adipose sources, [125I]AII saturation binding revealed a single, high affinity (Kd range of 0.3 -0.6 nM) binding site with a modest AII receptor density (Bmax range of 17-120 fmol/mg protein) comparable to rat lung (130 fmol/mg protein). White adipose tissue contained a greater number of AII receptor sites than brown adipose tissue. Competition displacement studies demonstrated the AT1 receptor is the only angiotensin receptor subtype localized in adipose tissue, with the rank order for competition of [125I]AII binding in all adipose tissues examined AIII > AII > losartan > angiotensin I (AI) > PD123319. The AT2 specific receptor antagonist, PD123319, was ineffective at displacing [125I]AII binding in all adipose tissues examined. Since components of the renin-angiotensin system are regulated in adipose tissue, we determined if the AII receptor is also regulated in the obese state. AII receptor binding characteristics were determined in liver, lung, ISBAT and EF membrane preparations from adult Zucker obese (fa/fa) and lean (Fa/?) rats. AII receptor density was decreased in liver from obese rats. In contrast, the affinity for [125I]AII binding was not altered in tissues from obese rats. In a separate group of obese and lean rats, regulation of the AII receptor by phenobarbital (PB) was examined. Administration of PB restored AII receptor density in liver from obese rats to levels obtained in lean rats. In summary, these results demonstrate the presence of AT1 receptor sites in brown and white adipose tissue. Moreover, AII receptor density is decreased in tissues from obese rats, with restoration of receptor density by administration of PB. Future studies will determine if PB regulates the AT1 receptor at the level of gene expression.

Localization of atrial natriuretic factor receptors in the mesenteric arterial bed. Comparison with angiotensin II and endothelin receptors

Although receptors for atrial natriuretic factor (ANF) and angiotensin II (Ang II) have been reported in rat mesenteric arteries, both peptides induce weak biological responses. Endothelin-1 (ET-1) evokes a potent vasoconstriction in the mesenteric artery. To identify the tissue localization of ANF, Ang II, and ET-1 receptors, radioligand binding experiments with 125I-ANF, 125I-[Sar1,Ile8]Ang II, and 125I-ET-1 were performed in defatted mesenteric arteries and in the surrounding adipose tissue. 125I-ANF binding assays in adipose tissue showed a single class of high-affinity binding sites (Bmax, 420 +/- 16 fmol/mg protein; Kd, 343 +/- 16 pmol/L). In vascular membranes, most 125I-ANF binding was nonspecific. The majority of receptors present in adipose tissue recognized ANF, C-type natriuretic peptide (CNP), and des-[Gln18,Ser19,Gly20,Leu21,Gly22]ANF-(4- 23) (C-ANF) with close affinities, with C-ANF competing for > 98% of the binding sites. In adipocytes, ANF and CNP stimulated cGMP generation. cGMP production by mesenteric arteries was stimulated by sodium nitroprusside but not by ANF or CNP. Autoradiographic localization of 125I-ANF and 125I-ET-1 showed that in the case of ANF, most specific binding occurred in adipocytes, whereas for ET-1, specific binding was present in both adipose tissue and mesenteric arteries. Cross-linking of 125I-ANF followed by SDS-PAGE revealed two receptor species of 130 and 70 kD in adipose membranes and none in vascular tissue. Both were completely displaced by ANF, CNP, and C-ANF. 125I-[Sar1,Ile8]Ang II binding assays in adipose tissue exhibited a single class of binding sites (Bmax, 211 +/- 4 fmol/mg protein; Kd, 520 +/- 10 pmol/L.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II stimulates macrophage-mediated oxidation of low density lipoproteins

Increased incidence of myocardial infarction was found in hypertensive patients with high plasma renin activity and increased susceptibility to oxidation was demonstrated in low density lipoprotein (LDL) that was obtained from hypertensive patients. As lipid peroxidation was demonstrated in areas of the atherosclerotic lesion, we sought to analyze the effect of angiotensin II (AN-II) on LDL oxidation, both in vitro and in vivo. Preincubation of J-774 A.1 macrophage-like cell line or mouse peritoneal macrophages (MPM) with AN-II (10(-7) M) for 1 h at 37 degrees C, followed by the addition of LDL for a further 18 h of incubation, resulted in a substantial increase in macrophage-mediated oxidation of LDL (by 55% and 19%, respectively). Similarly, incubation of LDL with MPM harvested from AN-II-injected mice resulted in a substantially increased oxidation of the lipoprotein by up to 90% in comparison to saline-injected mice. Analysis of cellular lipid peroxidation in the MPM themselves, in both the in vitro and the in vivo studies, revealed a 25% or 90% increased macrophage lipid peroxidation, respectively. The mechanism of AN-II-mediated cellular lipid peroxidation involved AN-II binding to its receptor on macrophages as saralasin, an AN-II receptor antagonist, completely inhibited this effect. Inhibitors of phospholipases A2, C and D substantially reduced macrophage lipid peroxidation, suggesting the involvement of phospholipases A2, C and D substantially reduced macrophage lipid peroxidation, suggesting the involvement of phospholipid metabolites in AN-II-mediated macrophage lipid peroxidation, suggesting the involvement of phospholipid metabolites in AN-II-mediated macrophage lipid peroxidation. Extracellular calcium ions, which active phospholipases, were also essential for AN-II-mediated macrophage lipid peroxidation since calcium channel blockers substantially inhibited cellular lipid peroxidation. Finally, the nature of the oxidant and oxygenase involved in AN-II-mediated cellular lipid peroxidation was studied using oxygenase inhibitors. Angiotensin II-mediated macrophage lipid peroxidation was found to involve the action of cellular NADPH oxidase as well as 15-lypoxygenase. We conclude that AN-II stimulates macrophage-mediated mediated oxidation of LDL secondary to cellular lipid peroxidation, and this may have a role in the accelerated atherosclerosis found in hypertensive patients.

Hormonal regulation of adipose differentiation

Adipose differentiation is a multistep process with the following sequence: adipoblasts --> preadipocytes --> adipocytes. Adipogenic agents are only involved in the terminal differentiation of preadipocytes to adipocytes by means of circulating hormones (growth hormone, glucocorticoids, or triiodothyronine) and locally produced hormones (prostacyclin). Fatty acids also behave as hormones and act as transcriptional regulators of lipid-related genes. Once differentiated, adipocytes become secretory cells able to synthetize and release an impressive number of peptide and nonpeptide compounds, suggesting a potential link between excess of adipose tissue mass and various physiopathphysiologic consequences.