Insulin/glucose induces natriuretic peptide clearance receptor in human adipocytes: a metabolic link with the cardiac natriuretic pathway.

Cardiac natriuretic peptides (NP) are involved in cardiorenal regulation and in lipolysis. The NP activity is largely dependent on the ratio between the signaling receptor NPRA and the clearance receptor NPRC. Lipolysis increases when NPRC is reduced by starving or very-low-calorie diet. On the contrary, insulin is an antilipolytic hormone that increases sodium retention, suggesting a possible functional link with NP. We examined the insulin-mediated regulation of NP receptors in differentiated human adipocytes and tested the association of NP receptor expression in visceral adipose tissue (VAT) with metabolic profiles of patients undergoing renal surgery. Differentiated human adipocytes from VAT and Simpson-Golabi-Behmel Syndrome (SGBS) adipocyte cell line were treated with insulin in the presence of high-glucose or low-glucose media to study NP receptors and insulin/glucose-regulated pathways. Fasting blood samples and VAT samples were taken from patients on the day of renal surgery. We observed a potent insulin-mediated and glucose-dependent upregulation of NPRC, through the phosphatidylinositol 3-kinase pathway, associated with lower lipolysis in differentiated adipocytes. No effect was observed on NPRA. Low-glucose medium, used to simulate in vivo starving conditions, hampered the insulin effect on NPRC through modulation of insulin/glucose-regulated pathways, allowing atrial natriuretic peptide to induce lipolysis and thermogenic genes. An expression ratio in favor of NPRC in adipose tissue was associated with higher fasting insulinemia, HOMA-IR, and atherogenic lipid levels. Insulin/glucose-dependent NPRC induction in adipocytes might be a key factor linking hyperinsulinemia, metabolic syndrome, and higher blood pressure by reducing NP effects on adipocytes.

Screening for frailty in elderly emergency department patients by using the Identification of Seniors At Risk (ISAR).

OBJECTIVES: Frail older adults are at an increased risk for adverse outcomes after an Emergency Department (ED) visit. Comprehensive geriatric assessment (CGA) has been proposed to screen for frailty in the ED, but it is difficult to carry out. We tested whether a CGA-based approach using the Identification of Seniors At Risk (ISAR) screening tool was associated with the brief deficit accumulation index (DAI) of frailty. DESIGN: Prospective observational study. SETTING: Two urban EDs in Italy. PARTICIPANTS: A cohort of 200 elderly (≥65 years) ED patients. MEASUREMENTS: Identifiers, triage, clinical and social data along with the administration of ISAR. CGA was performed using: Charlson Index, Short Portable Mental Status Questionnaire and Katz's ADL. Follow-up data at 30 and 180 days included: mortality, ED revisit, hospital admission, and functional decline. Frailty was defined according to a brief DAI. Logistic regression evaluated the consistency of the frailty definition; ROC curves evaluated ISAR ability in identifying frailty. RESULTS: Frailty was present in 117 (58.5%) subjects and predicted ED revisit and frequent ED return, hospitalization and 6-month mortality. ISAR had an AUC of 0.92 (95%CI 0.88-0.96, p<0.0001) in identifying frail elders in the ED and using a cut-off of 2 showed 94% sensitivity and 63% specificity. CONCLUSION: ISAR is a useful screening tool for frailty and identifies elderly patients at risk of adverse outcomes after an ED visit. ISAR can also be used to select high-risk patients more likely to benefit from a geriatric approach or intervention, independently of admission or discharge.

Carotid artery atherosclerosis in hypertensive patients with a functional LDL receptor-related protein 6 gene variant.

BACKGROUND AND AIMS: Rare (611C) and common (1062V) variants of the Low-Density Lipoprotein Receptor-Related Protein 6 (LRP6) display reduced activation of Wnt/ß-catenin signaling. The rare gene variant was associated with hypertension, metabolic abnormalities, and early coronary artery disease. We investigated whether the common 1062V LRP6 variant was related to carotid artery atherosclerosis (CAA) in hypertensive patients. METHODS AND RESULTS: Retrospective study of 334 hypertensive patients (<65 years old) who underwent carotid artery ultrasonography. Hypertension, type 2 diabetes, dyslipidemia, glomerular filtration rate, and smoking habit were evaluated. CAA was defined by the presence of atherosclerotic plaques (focal intima-media thickness ≥ 1.3 mm). Logistic regression models were used to estimate the independent effect of 1062V allele. The relationship between LRP6 genotypes and LRP6 gene expression in carotid plaques was also investigated. No difference was observed between genotypes in clinical variables except for a slightly higher fasting glucose in 1062V carriers. The 1062V LRP6 variant was an independent risk factor for CAA in both unadjusted (OR 2.08, 95%CI 1.27-3.41, p=0.003) and adjusted models (OR 1.92, 95%CI 1.09-3.39, p=0.02). LRP6 was expressed in carotid atherosclerotic plaques at significantly lower levels (p=0.015) in 1062V carriers. CONCLUSION: Beside the role of established risk factors, 1062V variant of LRP6 and CAA are strongly associated in hypertensive patients, making LRP6 a novel relevant candidate gene for atherosclerosis in the presence of hypertension.

Angiotensinogen promoter variants influence gene expression in human kidney and visceral adipose tissue.

Human angiotensinogen (AGT) gene promoter polymorphisms (G-217A; A-20C; G-6A) influence AGT transcription in vitro and have been implicated in the genetics of essential hypertension. We analysed the association among AGT promoter variants and AGT mRNA levels in human kidney and visceral adipose tissue (VAT) in vivo. Samples of kidney and VAT were obtained from 35 consecutive patients undergoing renal surgery. The AGT gene promoter of each patient was sequenced to identify variants. AGT gene expression was studied by real-time PCR TaqMan assay. Clinical data obtained before surgery were also considered in the statistical analysis. Two new polymorphisms at -175 and at -163 were identified. Although AGT expression was significantly higher in VAT than in the kidney, when both variants were present together AGT expression in VAT was about fivefold lower (P=0.033) than in the wild haplotype. This lower AGT expression in VAT suggests that the proximity and linkage of -175A and -163A variants might destabilize the binding of specific transcription factors to an acute-phase responsive element 3. Among the known AGT promoter variants, only -20C SNP has an important effect on tissue-specific differential AGT expression in the human tissues studied, inducing a 3.8-fold increase in AGT mRNA localized only in the kidney medulla (P=0.038). The other known polymorphisms (G-6A; G-217A) were not associated with different levels of AGT expression. Our results support the hypothesis that some human AGT promoter variants influence transcriptional activity in a tissue-specific way in humans.

Angiotensin II stimulates and atrial natriuretic peptide inhibits human visceral adipocyte growth.

OBJECTIVE: Cardiovascular peptides such as angiotensin II (Ang II) and atrial natriuretic peptide (ANP) have metabolic effects on adipose cells. These peptides might also regulate adipocyte proliferation and visceral adipose tissue (VAT) expansion. Well-differentiated and stabilized primary cultures of human visceral mature adipocytes (MA) and in vitro-differentiated preadipocytes (DPA) were used as a model to study regulation of VAT expansion. METHODS: Adipocyte differentiation was evaluated by Oil Red O staining and antiperilipin antibodies. MA and DPA from intra- and retro-peritoneal depots were treated with increasing Ang II (with or without valsartan, a highly selective, competitive, 'surmountable' AT1 antagonist devoid of peroxisome proliferator-activated receptor gamma agonistic activity) or ANP concentrations. Cell counts and bromodeoxyuridine incorporation were used to evaluate proliferation. Apoptosis was evaluated by Hoechst 33342 staining. 8-Bromo cyclic guanosine monophosphate (8Br-cGMP) was used to investigate ANP effects, and real-time PCR to evaluate Ang II and ANP receptors' expression. RESULTS: Cell proliferation was progressively stimulated by increasing Ang II concentrations (starting at 10-11 M) and inhibited by ANP (already at 10-13 M) in both MA and DPA. Co-incubation with increasing Ang II concentrations and valsartan indicated that Ang II effects were AT1-mediated. Indeed, AT2 receptors were not expressed. Valsartan alone slightly inhibited basal proliferation indicating an autocrine/paracrine growth factor-like effect of endogenous, adipocyte-derived Ang II. 8Br-cGMP experiments indicated that the effects of ANP were mediated by the guanylyl cyclase type A receptor. CONCLUSION: A cell-culture model to study VAT growth showed stimulation by Ang II and inhibition by ANP at physiological concentrations. Because similar effects are likely to occur in vivo, Ang II and ANP might be important modulators of VAT expansion and associated metabolic and cardiovascular consequences.

The elderly in the emergency department: a critical review of problems and solutions.

The elderly are an ever increasing population in overcrowded emergency departments (EDs) in many countries. They have multiple health problems and consume more time and resources than younger patients. They are more frequently admitted and experience adverse outcomes after they are discharged from the ED. These frail patients could require specific skills, instruments and organisational models of emergency care in order to look after their complex needs. As such, several approaches have been tried and tested to improve emergency care for them. This article analyses the epidemiological load and problems faced when confronted with elder ED patients. We critically review organisational models, clinical approaches and methodologies in order to reduce ED physicians' difficulties and to improve quality of care and outcomes for elder patients. Triage, clinical assessment and discharge are identified as critical moments during an emergency care process, and interesting and useful instruments are proposed as possible solutions.

Expression of potassium channel isoforms mRNA in normal human adrenals and aldosterone-secreting adenomas.

Increased aldosterone secretion has been found in a mouse lacking the KCNE1 gene which codes for a regulatory protein of the KCNQ1 gene product, forming the channel for the outward rectifying delayed K+ current. Abnormalities in proteins regulating the K+ fluxes across membranes may be responsible for aldosterone-secreting adenomas (aldosteronomas) also because K+ channels are involved in cell growth. Normal and adenomatous adrenal samples and NCI-H295 cell line were used to: a) evaluate KCNE1 and KCNQ1 gene expression, b) sequence the full length cDNAs of KCNE1 and both KCNQ1 isoforms. These differently spliced KCNE1 and KCNQ1 mRNAs were expressed in adrenal tissue. In contrast, KCNQ1 isoform 2 mRNA was not expressed in kidney control tissues and NCl-H295 cell line. NCI-H295 cell line also had a significantly lower expression of KCNQ1 isoform 1 mRNA than normal adrenals and aldosteronomas. We did not find any somatic mutations in the coding sequences of both genes. This different expression pattern of KCNQ1 isoforms in NCI-H295 cell line with the lack of the mRNA for the dominant-negative KCNQ1 isoform 2 supports the involvement of voltage-gated K+ channel in cell proliferation.

Cardiovascular effects of sildenafil in hypertensive men with erectile dysfunction and different alleles of the type 5 cGMP-specific phosphodiesterase (PDE5).

Erectile dysfunction (ED) is frequent in patients with essential hypertension (EH); a likely common pathogenetic pathway could be a reduced ability of arteriolar vascular smooth muscle (VSM) to relax. Increasing intracellular levels of cGMP reduce the contractile status of VSM; on the contrary, type 5 cGMP-specific phosphodiesterase (PDE5, codified by PDE5A gene) regulates cGMP levels through its clearance. The PDE5A gene represents a good candidate for the intermediate phenotype EH/ED: genetic variants of the PDE5A may predispose to EH and ED and could affect the local and systemic response to sildenafil administration. Thus, a functionally relevant portion of PDE5 5'-flanking promoter region was analyzed by PCR and direct sequencing in patients with EH and idiopathic ED. The sequences obtained showed a T/G polymorphism at position -1142, near an AP1 regulatory element, that was not apparently associated with the intermediate phenotype. We also studied the relationship between this polymorphism and the effects of oral sildenafil on blood pressure (BP) and heart rate (HR) in men with ED. Sildenafil caused a significant decrease of BP, but had no effects on HR; statistical analysis showed no differences in BP and HR variations among PDE5A genotypes. In conclusion, our data showed no correlations of a novel polymorphism of the PDE5A promoter gene with the intermediate phenotype EH/ED and the BP and HR response to sildenafil administration. Further studies are necessary to define the role of this polymorphism and to study the genetic predisposition for EH with ED.

Role of the natriuretic peptide system in lipogenesis/lipolysis.

AIM: There is recent evidence that the natriuretic peptide (NP) system promotes adipose tissue lipolysis in primates. This effect is mediated by the interaction of NP with its active receptors through guanylyl cyclase activation and cGMP production. This review will briefly focus on the new aspects of NP pathophysiology in man. DATA SYNTHESIS: NP receptors have been described in rodent adipocytes, and the expression of their mRNA is found in human adipose tissue together with high level of ANP binding sites. In isolated fat cells, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were able to stimulate lipolysis as much as isoproterenol, a non-selective beta-adrenergic receptor agonist, whereas C-type natriuretic peptide (CNP) had the lowest lipolytic effect. The potent lipolytic effect of NP has also been confirmed in samples of abdominal adipose tissue from healthy subjects. The potency order of the lipolytic effect (ANP > BNP > CNP) and ANP-induced cGMP production supported the presence of type A natriuretic peptide receptor in human fat cells. The effect of NP on lipid metabolism is confirmed by the fact that intravenous ANP infusion is followed by plasma NEFA and glycerol concentration increase (reflecting lipid mobilisation). CONCLUSIONS: The NP system seems to play an important role in lipid metabolism, possibly affecting the pathophysiology of obesity and obesity-related disorders, such hypertension. Further studies, however, are needed to completely establish the mechanisms involved in NP-induced lipolysis and the real relevance of this new pathway specific of primates.

Absence of somatic mutations in natriuretic peptide receptor type A gene in human aldosterone-secreting adenomas.

Somatic mutations of genes codifying for key regulatory proteins are the cause of different types of hormone-secreting adenomas. Natriuretic peptides (NP) are the strongest inhibitors of aldosterone secretion but aldosterone-secreting adenomas (aldosteronomas) are resistant to this inhibition and have reduced binding sites for NPs. The objective of this study was to sequence the entire coding region of the NP receptor type A (NPRA, codified by the Npr1 gene) to find loss-of-function somatic mutations. Total RNA was extracted from eight aldosteronomas and cDNA was synthesized. NPRA mRNA expression was evaluated by Northern blot analysis and compared with beta-actin mRNA as the housekeeping gene. Twelve primer couples were designed on the basis of the Npr1 gene organization to amplify, by PCR, all 22 coding exons of the gene. The two strands of amplified DNAs were purified and directly sequenced by automated capillary sequencer. NPRA mRNA expression did not differ among aldosteronomas. Npr1 open reading frame sequences obtained from eight aldosteronomas did not contain any mutation. The coding sequences of all 22 exons were identical in all samples and identical to published sequences. In the 3'-untranslated region (3'-UTR) a new length difference 3C/4C polymorphism was found at position 15 129 (three adenomas were 3C/4C and two were 3C/3C). Such a 3C/4C polymorphism was present in genomic DNA from 80 control subjects (25, 4C/4C; 40, 3C/4C; 15, 3C/3C). Mutations in the coding exons of the Npr1 gene do not appear to be a common cause of aldosteronomas. Moreover, the exons of Npr1 encoding for the translated portion of mRNA do not appear to be prone to polymorphisms. The polymorphism identified in the 3'-UTR might affect mRNA stability resulting in lower receptor synthesis, but it is not likely to confer a predisposition to the development of aldosteronomas.

Massive spontaneous perirenal hematoma and accelerated hypertension in a patient with polyarteritis nodosa.

A 43-year-old Albanian man is presented who underwent nephrectomy for a huge right spontaneous perirenal hematoma. The diagnosis of polyarteritis nodosa as the etiology of the hematoma has been made only by histological examination, because of the quick and unforeseeable onset of this complication and the nonspecificity of symptoms. We hypothesize a relationship between reactivation of polyarteritis nodosa and treatment with rifampicin and isoniazid.

Aldosterone synthase alleles and cardiovascular phenotype in young adults.

The C(-344)T promoter polymorphism of the human aldosterone synthase (CYP11B2) gene has been associated with hypertension and cardiac hypertrophy, but there were contrasting data. We analysed the genotype/phenotype associations between this polymorphism and cardiovascular variables in a young adult population, where interactions among genes, gene-environment, and acquired ageing-related organ damage are reduced. Anthropometric measurements, blood pressure, heart rate, left ventricular variables (by echocardiography), and carotid artery wall intimal-media thickness (by high-resolution sonography and digitalized morphometry) were taken in 420 white Caucasian students (mean age 23.5 years, s.d. 2.5 years). CYP11B2 alleles were detected by genomic polymerase chain reaction followed by digestion. Taking into account the three possible models of inheritance, we found no differences in the considered variables, except for an independent effect of the C(-344) allele on SBP in males (TT 125.6 (1.6), TC 128.4 (1.2) and CC 130.5 (2.2), mmHg, media (ES), P=0.03), and on interventricular septum thickness in diastole in females (CC 6.98 (0.12) vs TT 6.87 (0.09) and TC 6.87 (0.07), mmHg, P<0.01), in the codominant model. In conclusion, the CYP11B2 C(-344)T polymorphism appears to have a slight role in the cardiovascular phenotype of young healthy adults, even if these genotype/phenotype relationships might change with ageing.

Cardiovascular phenotype of young adults and angiotensinogen alleles.

OBJECTIVES AND DESIGN: Angiotensinogen (AGT) gene variants influence angiotensinogen plasma levels in children and young adults. The angiotensinogen promoter (-6)A variant facilitates gene transcription in human tissues and it has been associated with high blood pressure in older adults. A young adult population can be used as a model to study genotype/phenotype associations between AGT (-6) variants and cardiovascular variables. METHODS AND RESULTS: Anthropometric measurements, blood pressure and heart rate were taken in 422 white Caucasian students (mean age 23.5 years, SD 2.5 years). Family history for hypertension, physical activity and smoking history were evaluated. Left ventricular variables were measured by echocardiography. Carotid artery wall intimal-media thickness (IMT) was measured by high resolution sonography and digitalized morphometry. The AGT G(-6)A alleles were evaluated by mutagenically separated polymerase chain reaction controlled by direct sequencing. No significant associations were found between angiotensinogen genotype and blood pressure, cardiac variables [except for deceleration time in females which increased with the number of (-6)A alleles] and IMT. Allele frequencies were similar between the first and third tertile of blood pressure and left ventricular mass, and were also similar between negative or positive family history for hypertension (the last group having significantly higher systolic blood pressure in males, P = 0.04 and diastolic blood pressure in females, P < 0.01). Moreover, no relevant interaction on the cardiovascular variables was found between AGT genotype and body mass index. CONCLUSIONS: The angiotensinogen G(-6)A variants do not affect cardiovascular parameters in young adults, but an effect of this polymorphism on cardiovascular phenotype (and hypertension) in older adults cannot be excluded. Additional factors, associated with ageing, should be present to unleash the supposed unfavourable potential of the (-6)A angiotensinogen variant.

Prediction and consistency of blood pressure salt-sensitivity as assessed by a rapid volume expansion and contraction protocol. Salt-Sensitivity Study Group of the Italian Society of Hypertension.

BACKGROUND: This multicenter trial in essential hypertensive patients (n=94) is aimed i) to evaluate the distribution of blood pressure salt-sensitivity by a rapid volume expansion/contraction protocol over three days; ii) to investigate the within-patient reproducibility and to identify predictors of the response to the test; iii) to compare this response with the response to dietary NaCl restriction. METHODS: The study design included: 1) screening for salt-sensitivity by the rapid test; 2) a controlled trial of dietary salt restriction; 3) repetition of the rapid test in a subgroup of patients. RESULTS: The mean BP response to the rapid test fitted a Gaussian curve. In multivariate regression analysis, controlling for the effect of potential confounders, the blood pressure increment during the intravenous saline infusion was the best independent predictor of the response to the test (r=0.713) with minor contributions by the 24-h urinary sodium excretion before the test and by baseline fasting serum insulin. These three variables together explained 61% of the overall variability of the response. The Spearman rank correlation coefficient between the BP response to the rapid test and the response to the dietary protocol was 0.21, p=0.05. Upon repetition of the rapid test, the correlation coefficient between the responses observed on the two occasions was 0.60 (n=19, p<0.01); there were no patients misclassified across the extreme tertiles of the distribution of salt-sensitivity. CONCLUSION: We conclude that the rapid test reproducibly identified patients in the upper and lower parts of the distribution of salt sensitivity. The analysis of possible predictors of the response to the test suggested that the evaluation of the blood pressure response to saline infusion, upon careful standardization of dietary NaCl intake, may represent an alternative to the completion of the whole test for the screening of the salt-sensitivity.

A novel promoter variant of the natriuretic peptide clearance receptor gene is associated with lower atrial natriuretic peptide and higher blood pressure in obese hypertensives.

OBJECTIVE AND DESIGN: The clearance receptor for natriuretic peptides (NPRC), a candidate gene for essential hypertension, is highly expressed in adipose tissue, where is nutritionally regulated. The objectives of the present study were to sequence the human 5'-flanking regulatory region of NPRC, to identify allelic variants and their frequencies, and to study the genotype/phenotype correlation in hypertensive patients. METHODS AND RESULTS: Using polymerase chain reaction (PCR) and direct automated sequencing, a biallelic (A/C) polymorphism was detected at position -55 in a conserved promoter element named P1. The novel C(-55) variant makes the promoter sequence identical to the mouse gene and introduces a second Hgal site in the amplified DNA, allowing the genotyping of a large number of subjects. In a random sample of 232 white Caucasians the C(-55) allele was more commonly found (81.7% of all alleles) with 155 CC (66.8%), 69 AC (29.7%) and only eight AA (3.5%) genotypes. Atrial natriuretic peptide (ANP) levels were determined in 84 patients with essential hypertension. In the presence of obesity (body mass index (BMI) > or = 30 kg/m2) the homozygous CC hypertensives (n = 21) had significantly lower plasma ANP (33.6 +/- 11.1 pg/ml) compared with the AC patients (n = 11; 46.8 +/- 15.9 pg/ml; P = 0.01), whereas systolic blood pressure (SBP) and mean blood pressure (MBP) had the opposite association (SBP 163.9 +/- 18.7 versus 150.9 +/- 12.9 and MBP 123.3 +/- 12 versus 114.5 +/- 5.9 mmHg; P< 0.05). The difference in ANP levels were also present when overweight patients (BMI > or = 27 kg/m2) were considered. CONCLUSION: A common 'ancestral' C(-55) variant of the NPRC P1 promoter is associated with lower ANP levels and higher SBP and MBP in obese hypertensives. The C(-55) variant, in the presence of increased adiposity, might reduce plasma ANP through increased NPRC-mediated ANP clearance, contributing to higher blood pressure.

Natriuretic peptides receptors in human aldosterone-secreting adenomas.

Atrial natriuretic peptide (ANP) and B-type or brain natriuretic peptide (BNP) inhibit aldosterone secretion in humans both in vitro and in vivo. Unresponsiveness of aldosterone-secreting adenomas (aldosteronomas) to ANP in vitro and in vivo, might be due to reduced expression of the biologically-active natriuretic peptide receptor type A (NPr-A) and/or increased expression of the clearance receptor for natriuretic peptides (NPr-C). Therefore, we have analyzed NPr gene expression and ANP binding sites in human adrenals and aldosteronomas. Using reverse transcription and polymerase chain reaction, we cloned and characterized cDNAs for NPr-A, NPr-C, and the receptor (NPr-B) for the C-type natriuretic peptide (CNP). Total RNA from three normal human adrenals (obtained at surgery from patients with renal cancer) and five aldosteronomas were used for Northern analysis. NPr-A mRNA (approximately 4 kb) and NPr-B mRNA (approximately 4 kb) were expressed without significant differences in adrenals and in aldosteronomas except in an aldosteronomas that contained only very low amounts of NPr mRNAs. The gene expression of NPr-C was barely detectable both in adrenals and in aldosteronomas. ANP binding sites were analyzed by autoradiography with 125I-labeled ligand in other six aldosteronomas. Only one of the adenomas analyzed showed ANP binding sites with density of granules similar to nonadenomatous glomerulosa, whereas the others had significantly reduced densities. In summary, aldosteronomas express the genes encoding for NPr but mainly NPr-A, similarly to control adrenals. On the contrary, the binding sites for ANP are greatly reduced in most aldosteronomas. A somatic mutation or a post-transcriptional defect that reduces ANP binding sites might be present in some aldosteronomas.

Low calorie diet enhances renal, hemodynamic, and humoral effects of exogenous atrial natriuretic peptide in obese hypertensives.

The expression of the natriuretic peptide clearance receptor is abundant in human and rat adipose tissue, where it is specifically inhibited by fasting. In obese hypertensives, plasma atrial natriuretic peptide (ANP) levels were found to be lower than in obese normotensives. Therefore, the increased adipose mass might influence ANP levels and/or its biological activity. The aim of the present study was to evaluate whether the humoral, hemodynamic, and renal effects of exogenous ANP in obese hypertensives might be enhanced by a very low calorie diet. Eight obese hypertensives received a bolus injection of ANP (0.6 mg/kg) after 2 weeks of a normal calorie/normal sodium diet, and blood pressure (BP), heart rate, ANP, cGMP, plasma renin activity, and aldosterone were evaluated for 2 hours before and after the injection. Diuresis and natriuresis were measured every 30 minutes. The patients then started a low calorie/normal sodium diet (510 kcal/150 mmol/d) for 4 days, and then the ANP injection protocol was repeated. The low calorie diet induced a slight weight loss (from 90.6+/-1.1 to 87. 7+/-1.2 kg; P<0.01), which was accompanied by increase of cGMP excretion (from 146.0+/-10.1 to 154.5+/-9.5 nmol/24 h; P<0.05) together with a reduction of BP (P<0.01 versus basal levels). ANP injection after diet was followed by an increase of ANP levels similar to that observed before diet, but plasma cGMP, diuresis, and natriuresis increased significantly only after diet. Similarly, the decrease of BP after ANP administration was significantly higher after diet (change in mean arterial pressure, -6.4+/-0.7 versus -4. 0+/-0.6 mm Hg; P<0.05) as well as that of aldosterone (P<0.01). These data show that a low calorie diet enhances the humoral, renal, and hemodynamic effects of ANP in obese hypertensives and confirm the importance of caloric intake in modulating the biological activity of ANP, suggesting that the natriuretic peptide system can play a role in the acute changes of natriuresis and diuresis associated with caloric restriction.

The natriuretic peptide system in obesity-related hypertension: new pathophysiological aspects.

The association between obesity and hypertension is well known but the pathophysiology of weight-related changes on blood pressure is still a matter of debate. Although obesity-related hypertension is considered to be sodium-sensitive, little attention has been given to a possible pathophysiological role of Atrial Natriuretic Peptides (ANP) and their receptors (NPr) system. Since the early phase of weight loss induced by very-low-calorie diet or fasting is followed by a significant increase in diuresis and natriuresis together with an increase in circulating ANP, we focused our attention on the possible role of adipose tissue in mediating these changes. We first demonstrated that human and rat adipose tissue contain high levels of mRNA specific for both type A (NPr-A), which is biologically active, and type C (NPr-C) which is biologically inactive, receptors. We then demonstrated in the rat that fasting exerts a tissue-specific and gene-specific suppression of NPr-C gene expression in adipose tissue that appears to be accompanied by an increased biological activity of ANP. These experimental observations were confirmed in man studying gene expression of NPr-A and NPr-C in adipose tissue obtained through subcutaneous peri-umbilical needle aspiration in obese and non-obese hypertensive patients. We found that NPr-A: NPr-C mRNA ratio was significantly lower in obese hypertensive patients as compared with non-obese hypertensives. These findings suggest that overxpression of the clearance receptor in the obese may trap more molecules of circulating ANP so reducing their biological activity at renal level. More recent results were obtained in obese hypertensive patients in whom the intravenous bolus injection of ANP (0.6 mg/kg body weight) was performed before and after four days of very-low-calorie diet which induced a weight loss accompanied by a significant reduction of BP and an increase in the urinary excretion of cGMP. The infusion of ANP after low-calorie diet was followed by an increase of ANP levels similar to that observed before diet, but plasma cGMP, diuresis and natriuresis significantly increased only after caloric restriction and the effects of ANP infusion on BP were more pronounced. Taken together our studies suggest that the abundance of NPr-C in adipose tissue may play a significant role in explaining at least part of the sodium retention characteristic of obesity associated hypertension.

Cardiovascular phenotype of a mouse strain with disruption of bradykinin B2-receptor gene.

BACKGROUND: To evaluate the role of kinins in the regulation of cardiovascular function, we studied the phenotype of a mouse strain with disruption of the bradykinin B2-receptor gene (Bk 2r-/-). METHODS AND RESULTS: Under basal conditions, tail-cuff blood pressure was higher in Bk2r-/- than in wild-type Bk2r+/+ and heterozygous Bk2r+/- mice (124+/-1 versus 109+/-1 and 111+/-2 mm Hg, respectively; P<.01 for both comparisons), a difference that was confirmed by measurements of intra-arterial blood pressure in unanesthetized mice. Heart weight was greater in Bk2r-/- than in Bk2r+/+ and Bk2r+/- mice (505+/-10 versus 449+/-12 and 477+/-10 mg/100 g body wt, P<.05). Chronic blockade of B2-receptors by Icatibant (50 nmol/100 g body wt twice a day S.C.) or inhibition of nitric oxide synthase by nitro-L-arginine-methyl ester (0.14 mmol/100 g body wt orally) increased the blood pressure of Bk2r+/+ to the levels of Bk2r-/- mice. Compared with the wild-type strain, both Bk2r-/- and Bk2r+/- mice showed exaggerated vasopressor responses to angiotensin II. In addition, chronic administration of an angiotensin AT1-receptor antagonist reduced the basal blood pressure of Bk2r-/- by 21+/-3 mmHg (P<.05) to the levels of Bk2r+/+. No difference was detected between strains as far as plasma renin activity and the expression of renin and AT1-receptor genes are concerned. Chronic salt loading (0.84 mmol/g chow for 15 days) increased the blood pressure of Bk2r-/- and Bk2r+/- by 34+/-3 and 14+/-6 mm Hg, respectively, whereas it was ineffective in Bk2r+/+. CONCLUSIONS: Our results suggest that a normally functioning B2-receptor is essential for the maintenance of cardiovascular homeostasis in mice. Dysfunction of the kallikrein-kinin system could contribute to increase blood pressure levels by leaving the activity of vasoconstrictor agents unbalanced.