Genes encoding atrial and brain natriuretic peptides as candidates for sensitivity to brain ischemia in stroke-prone hypertensive rats

B-type natriuretic peptide over N-terminal pro-brain natriuretic peptide to predict incident atrial fibrillation after cryptogenic stroke

BACKGROUND AND PURPOSE

B-type natriuretic peptide (BNP) and N-terminal pro-brain natriuretic peptide (NT-proBNP) are well-known surrogates of atrial fibrillation (AF) detection but studies usually present data on either BNP or NT-proBNP. The aim was to determine and directly compare the validity of the two biomarkers as a tool to predict AF and guide prolonged cardiac monitoring in cryptogenic stroke patients.

METHODS

Non-lacunar acute ischaemic stroke (<72 h) patients over 55 years of age with cryptogenic stroke after standard evaluation were included in the Crypto-AF study and blood was collected. BNP and NT-proBNP levels were determined by automated immunoassays. AF was assessed by 28 days' monitoring. Highest (optimizing specificity) and lowest (optimizing sensitivity) quartiles were used as biomarker cut-offs to build predictive models adjusted by sex and age. The integrated discrimination improvement index (IDI) and DeLong test were used to compare the performance of the two biomarkers.

RESULTS

From 320 patients evaluated, 218 were included in the analysis. AF was detected in 50 patients (22.9%). NT-proBNP (P < 0.001) and BNP (P < 0.001) levels were higher in subjects with AF and their levels correlated (r = 0.495, P < 0.001). BNP showed an increased area under the curve (0.720 vs. 0.669; P = 0.0218) and a better predictive capacity (IDI = 3.63%, 95% confidence interval 1.36%-5.91%) compared to NT-proBNP. BNP performed better than NT-proBNP in a specific model (IDI = 3.7%, 95% confidence interval 0.87%-6.5%), whilst both biomarkers performed similarly in the case of a sensitive model.

CONCLUSIONS

Both BNP and NT-proBNP were increased in cryptogenic stroke patients with AF detection. Interestingly, BNP outperforms NT-proBNP, especially in terms of specificity.

Molecular Implications of Natriuretic Peptides in the Protection from Hypertension and Target Organ Damage Development

The pathogenesis of hypertension, as a multifactorial trait, is complex. High blood pressure levels, in turn, concur with the development of cardiovascular damage. Abnormalities of several neurohormonal mechanisms controlling blood pressure homeostasis and cardiovascular remodeling can contribute to these pathological conditions. The natriuretic peptide (NP) family (including ANP (atrial natriuretic peptide), BNP (brain natriuretic peptide), and CNP (C-type natriuretic peptide)), the NP receptors (NPRA, NPRB, and NPRC), and the related protease convertases (furin, corin, and PCSK6) constitute the NP system and represent relevant protective mechanisms toward the development of hypertension and associated conditions, such as atherosclerosis, stroke, myocardial infarction, heart failure, and renal injury. Initially, several experimental studies performed in different animal models demonstrated a key role of the NP system in the development of hypertension. Importantly, these studies provided relevant insights for a better comprehension of the pathogenesis of hypertension and related cardiovascular phenotypes in humans. Thus, investigation of the role of NPs in hypertension offers an excellent example in translational medicine. In this review article, we will summarize the most compelling evidence regarding the molecular mechanisms underlying the physiological and pathological impact of NPs on blood pressure regulation and on hypertension development. We will also discuss the protective effect of NPs toward the increased susceptibility to hypertensive target organ damage.

Plasma B-type natriuretic peptide level in patients with acute cerebral infarction according to infarction subtype and infarction volume

BACKGROUND

Plasma B-type natriuretic peptide (BNP) is used as a diagnostic marker of cardiovascular diseases. BNP is secreted mainly from the myocardium and has been detected by immunoreactivity in brain and cerebral arteries. The aim of our study was to investigate plasma BNP in patients with acute cerebral infarction according to infarction subtype and infarction volume.

METHODS

We studied 141 patients with acute cerebral infarction, classified as large artery atherosclerosis (LAA), cardioembolism (CE), or small vessel disease (SA) according to the Trial of Org 10172 in Acute Stroke Treatment classification. Plasma BNP level was measured in patients and 61 healthy controls. We analyzed various clinical and laboratory variables of patients according to plasma BNP level.

RESULTS

Compared to controls, the patients had higher plasma BNP (11.9 ± 11.7 pg/mL versus 124.6 ± 228.8 pg/mL, p <0.01). The highest quartile BNP group was associated with advanced age, female gender, current non-smoker, atrial fibrillation, heart failure, CE group, increased white blood cell counts, increased high sensitivity C-reactive protein, increased left atrium size, decreased left ventricular ejection fraction, increased initial National Institute of Health Stroke Scale, and increased infarction volume. According to multiple regression analysis, CE group, female gender, and infarction volume were independently associated with plasma BNP. Plasma BNP level showed statistically significant differences among LAA (n = 71), CE (n = 50), and SA (n = 20) groups (p <0.001), and the expression decreased in order of CE (253.8 ± 337.1 pg/mL), LAA (61.6 ± 78.8 pg/mL), and SA (25.3 ± 24.8 pg/mL). Increased plasma BNP correlated with increased infarction volume (r = 0.42, p <0.001).

CONCLUSIONS

Plasma BNP may be helpful for prediction of etiologic classification of acute cerebral infarction and infarction volume.

Plasma NT-proBNP and white matter hyperintensities in type 2 diabetic patients

Abstract

Elevated plasma N-terminal (NT)-proBNP from the heart as well as white matter hyperintensities (WMH) in the brain predict cardiovascular (CV) mortality in the general population. The cause of poor prognosis associated with elevated P-NT-proBNP is not known but WMH precede strokes in high risk populations. We assessed the association between P-NT-proBNP and WMH or brain atrophy measured with magnetic resonance imaging (MRI) in type 2 diabetic patients, and age-matched controls.

Methods and results

We measured P-NT-proBNP(ng/l) in 20 diabetic patients without prior stroke but with(n = 10) or without(n = 10) asymptomatic coronary artery disease(CAD) in order to include patients with a wide-ranging CV risk profile. All patients and 26 controls had a 3D MRI and brain volumes(ml) with WMH and brain parenchymal fraction(BPF), an indicator of brain atrophy, were determined.

P-NT-proBNP was associated with WMH in linear regression analysis adjusted for CV risk factors(r = 0.94, p = 0.001) and with BPF in univariate analysis(r = 0.57, p = 0.009). Patients divided into groups of increased P-NT-proBNP levels were paralleled with increased WMH volumes(geometric mean[SD];(2.86[5.11] ml and 0.76[2.49] ml compared to patients with low P-NT-proBNP 0.20[2.28] ml, p = 0.003)) and also when adjusted for age, sex and presence of CAD(p = 0.017). The association was strengthened by CV risk factors and we did not find a common heart or brain specific driver of both P-NT-proBNP and WMH. Patients and particular patients with CAD had higher WMH, however no longer after adjustment for age and sex.

Conclusion

P-NT-proBNP was associated with WMH in type 2 diabetic patients, suggesting a linkage between heart and brain disease.

Placental ischemia impairs middle cerebral artery myogenic responses in the pregnant rat

One potential mechanism contributing to the increased risk for encephalopathies in women with preeclampsia is altered cerebral vascular autoregulation resulting from impaired myogenic tone. Whether placental ischemia, a commonly proposed initiator of preeclampsia, alters cerebral vascular function is unknown. This study tested the hypothesis that placental ischemia in pregnant rats (caused by reduced uterine perfusion pressure [RUPP]) leads to impaired myogenic responses in middle cerebral arteries. Mean arterial pressure was increased by RUPP (135±3 mm Hg) compared with normal pregnant rats (103±2 mm Hg) and nonpregnant controls (116±1 mm Hg). Middle cerebral arteries from rats euthanized on gestation day 19 were assessed in a pressure arteriograph under active (+Ca(2+)) and passive (0 Ca(2+)) conditions, whereas luminal pressure was varied between 25 and 150 mm Hg. The slope of the relationship between tone and pressure in the middle cerebral artery was 0.08±0.01 in control rats and was similar in normal pregnant rats (0.05±0.01). In the RUPP model of placental ischemia, this relationship was markedly reduced (slope=0.01±0.00; P<0.05). Endothelial dependent and independent dilation was not different between groups, nor was there evidence of vascular remodeling assessed by the wall:lumen ratio and calculated wall stress. The impaired myogenic response was associated with brain edema measured by percentage of water content (RUPP P<0.05 versus control and normal pregnant rats). This study demonstrates that placental ischemia in pregnant rats leads to impaired myogenic tone in the middle cerebral arteries and that the RUPP model is a potentially important tool to examine mechanisms leading to encephalopathy during preeclamptic pregnancies.

A prospective study of brain natriuretic peptide levels in three subgroups: Stroke with hypertension, stroke without hypertension, and hypertension alone

Aim:

To study brain natriuretic peptide (BNP) levels in three subgroups: patients having stroke with hypertension (HT), those having stroke without HT, and those with HT alone. We also tried to identify whether BNP levels predict the length of stay in hospital and mortality.

Materials and Methods:

The groups were formed by patients who had been admitted to the emergency department in the first 4–12 h after the onset of symptoms. There were 30 stroke patients with a history of HT (group I), 30 stroke patients without a history of HT (group II), and 20 HT patients without stroke (group III). Patients with congestive heart failure, chronic cor pulmonale, severe valvular heart disease, chronic renal failure, liver insufficiency, diabetes mellitus, atrial fibrillation, and those with a history of stroke were excluded from the study since these diseases can affect the plasma BNP levels.

Results:

The demographic characteristics, except the age distribution, were similar among the groups. The mean BNP levels in the three groups were 168.8 ± 223.9 pg/ml, 85.0 ± 75.1 pg/ml, and 84.8 ± 178.3 pg/ml, respectively. The differences between the groups were statistically significant.

Conclusion:

The mean BNP levels were affected by HT and/or stroke. The simultaneous presence of HT and stroke results in a more significant increase BNP than the presence of either stroke or HT alone. When diseases that can affect the plasma BNP levels are excluded, the BNP levels in stroke patients without a history of HT are similar to the levels seen in patients with only HT.

Factors Affecting the B-Type Natriuretic Peptide Levels in Stroke Patients

Introduction: This study aims to evaluate the relationship between increased B-type natriuretic peptide (BNP) levels in stroke patients and clinical parameters such as age, sex, medical history, blood pressure, Glasgow Coma Score (GCS) and National Institutes of Health Stroke Scale (NIHSS). Materials and Methods: This is a prospective study of 123 stroke patients at the Emergency Department. The patients were divided into 3 groups according to the NIHSS scores. The analysis of the mean difference between continuous variables and plasma BNP levels was assessed using the Mann-Whitney and Kruskal-Wallis. Spearman correlation analysis was performed for BNP and other clinical parameters. Results: The BNP levels of patients who had a medical history of hyperlipidaemia, chronic obstructive pulmonary disease, diabetes mellitus and coronary artery disease were significantly higher than in patients without these diseases. Patients who had atrial fibrillation (AF) in their electrocardiography had significantly higher BNP levels than patients with sinus rhythm. A positive correlation was found between plasma BNP levels with age, blood urea nitrogen (BUN) and NIHSS and a negative correlation was found between plasma BNP levels and GCS. There was a significant difference between the BNP levels of NIHSS groups. Conclusion: We consider that plasma BNP levels could help us in interpreting the general clinical severity, functional capacity and clinical progress of stroke patients at the time of admission in the Emergency Department. In evaluating the high BNP levels in stroke patients, we must keep in mind that age, AF, BUN and medical history can affect the BNP levels. Key words: Emergency Department, Progress, Relationship

Brain natriuretic peptide improves long-term functional recovery after acute CNS injury in mice

There is emerging evidence to suggest that brain natriuretic peptide (BNP) is elevated after acute brain injury, and that it may play an adaptive role in recovery through augmentation of cerebral blood flow (CBF). Through a series of experiments, we tested the hypothesis that the administration of BNP after different acute mechanisms of central nervous system (CNS) injury could improve functional recovery by improving CBF. C57 wild-type mice were exposed to either pneumatic-induced closed traumatic brain injury (TBI) or collagenase-induced intracerebral hemorrhage (ICH). After injury, either nesiritide (hBNP) (8 microg/kg) or normal saline were administered via tail vein injection at 30 min and 4 h. The mice then underwent functional neurological testing via rotorod latency over the following 5 days and neurocognitive testing via Morris water maze testing on days 24-28. Cerebral blood flow (CBF) was assessed by laser Doppler from 25 to 90 min after injury. After ICH, mRNA polymerase chain reaction (PCR) and histochemical staining were performed during the acute injury phase (<24 h) to determine the effects on inflammation. Following TBI and ICH, administration of hBNP was associated with improved functional performance as assessed by rotorod and Morris water maze latencies (p < 0.01). CBF was increased (p < 0.05), and inflammatory markers (TNF-alpha and IL-6; p < 0.05), activated microglial (F4/80; p < 0.05), and neuronal degeneration (Fluoro-Jade B; p < 0.05) were reduced in mice receiving hBNP. hBNP improves neurological function in murine models of TBI and ICH, and was associated with enhanced CBF and downregulation of neuroinflammatory responses. hBNP may represent a novel therapeutic strategy after acute CNS injury.

Elevated plasma brain natriuretic peptide levels independent of heart disease in acute ischemic stroke: correlation with stroke severity

We tested the hypothesis that plasma brain natriuretic peptide (BNP) levels are elevated in patients with acute cerebrovascular diseases (CVD) independent of heart disease, and reflect CVD severity. After careful evaluations for heart disease, the study included 79 consecutive patients with CVD without any evidence of heart disease admitted within 48 h after onset (71+/-10 years), and 26 control subjects without CVD (CT, 67+/-12 years). Ischemic stroke subtypes were defined by the TOAST classification. Large-artery atherosclerosis (LAA, n=27), small-artery occlusion (SAO, n=27), and intracerebral hemorrhage (ICH, n=25) were included. The plasma BNP levels were measured at admission and 1 month later. Stroke severity and brain infarct volume were evaluated. There were no significant differences in the clinical profiles including echocardiographic parameters among the groups. The plasma BNP level (pg/mL) upon admission was higher in LAA (70.6+/-53.9) than in SAO (38.2+/-28.4) and CT (28.5+/-19.9) (both p<0.05). The level in ICH (47.3+/-28.6) was not significantly different from that in CT. The BNP level in ischemic stroke was positively correlated with the NIH Stroke Scale (NIHSS) (rho=0.42, p<0.05) and infarct volume (r=0.34, p<0.05). Brain infarct volume and NIHSS were independent contributors to the plasma BNP level in ischemic stroke. One month later, the BNP level was significantly decreased and was similar in all CVD groups. The plasma BNP level transiently increased in patients with LAA independently of heart disease, and reflected infarct volume and the severity of acute ischemic stroke.

Do in vivo experimental models reflect human cerebral small vessel disease? A systematic review

Cerebral small vessel disease (SVD) is a major cause of stroke and dementia. Pathologically, three lesions are seen: small vessel arteriopathy, lacunar infarction, and diffuse white matter injury (leukoaraiosis). Appropriate experimental models would aid in understanding these pathologic states and also in preclinical testing of therapies. The objective was to perform a systematic review of animal models of SVD and determine whether these resemble four key clinicopathologic features: (1) small, discrete infarcts; (2) small vessel arteriopathy; (3) diffuse white matter damage; (4) cognitive impairment. Fifteen different models were included, under four categories: (1) embolic injuries (injected blood clot, photochemical, detergent-evoked); (2) hypoperfusion/ischaemic injury (bilateral common carotid occlusion/stenosis, striatal endothelin-1 injection, striatal mitotoxin 3-NPA); (3) hypertension-based injuries (surgical narrowing of the aorta, or genetic mutations, usually in the renin-angiotensin system); (4) blood vessel damage (injected proteases, endothelium-targeting viral infection, or genetic mutations affecting vessel walls). Chronic hypertensive models resembled most key features of SVD, and shared the major risk factors of hypertension and age with human SVD. The most-used model was the stroke-prone spontaneously hypertensive rat (SHR-SP). No model described all features of the human disease. The optimal choice of model depends on the aspect of pathophysiology being studied.

Plasma concentrations of brain natriuretic peptide in patients with acute ischemic stroke

BACKGROUND

Acute blood pressure (BP) elevation and cardiac abnormalities are known to follow ischemic stroke. Brain natriuretic peptide (BNP), which is produced in response to such cardiovascular alterations, is expected to play a hemodynamic role. We measured plasma BNP concentrations in patients with cerebral infarction (CI) to determine the implications of BNP in acute ischemic stroke.

METHODS

Eighty-eight patients with CI, 59 with essential hypertension, 44 with spontaneous intracerebral hemorrhage, 22 with asymptomatic atrial fibrillation (Af), and 20 age- and sex-matched healthy volunteers were recruited in the study. CI patients were divided into 2 subgroups either having Af (27 patients) or not (61 patients). BNP levels were repeatedly measured in 58 patients with CI. BNP levels were compared between ischemic subgroups categorized by size of infarction. Correlation was investigated between BNP levels and hemodynamic parameters.

RESULTS

BNP levels in CI patients were significantly higher, but they decreased in the subacute period. BNP levels in CI patients without Af were correlated with mean arterial blood pressure (MAP) on admission or the degree of reduction in MAP at day 1, while in CI patients with Af BNP levels showed negative correlation with MAP on admission. Follow-up serum sodium levels in CI patients with Af were negatively correlated with BNP levels on admission.

CONCLUSIONS

This study suggests the hemodynamic implications of BNP in acute ischemic patients.

Cosegregation analysis of natriuretic peptide genes and blood pressure in the spontaneously hypertensive rat

1. The natriuretic peptide precursor A (Nppa) and B (Nppb) genes are candidate genes for hypertension and cardiac hypertrophy in the spontaneously hypertensive rat (SHR). The purpose of the present study was to determine the role of the Nppa and Nppb genes in the development of hypertension in the SHR. 2. A cohort (n = 162) of F2 segregating intercross animals was established between strains of hypertensive SHR and normotensive Wistar-Kyoto rats. Blood pressure and heart weight were measured in each rat at 12-16 weeks of age. Rats were genotyped using 11 informative microsatellite markers, distributed in the vicinity of the Nppa marker on rat chromosome 5 including an Nppb marker. The phenotype values were compared with genotype using the computer package mapmaker 3.0 (Whitehead Institute, Boston, MA, USA) to determine whether there was a link between the genetic variants of the natriuretic peptide family and blood pressure or cardiac hypertrophy. 3. A strong correlation was observed between the Nppa marker and blood pressure. A quantitative trait locus (QTL) for blood pressure on chromosome 5 was identified between the Nppa locus and the D5Mgh15 marker, less than 2 cM from the Nppa locus. The linkage score for the blood pressure QTL on chromosome 5 was 3.8 and the QTL accounted for 43% of the total variance of systolic blood pressure, 54% of diastolic blood pressure and 59% of mean blood pressure. No association was found between the Nppb gene and blood pressure. This is the first report of linkage between the Nppa marker and blood pressure in the rat. There was no correlation between the Nppa or Nppb genes or other markers in this region and either heart weight or left ventricular weight in F2 rats. 4. These findings suggest the existence of a blood pressure-dependent Nppa marker variant or a gene close to Nppa predisposing to spontaneous hypertension in the rat. It provides a strong foundation for further detailed genetic studies in congenic strains, which may help to narrow down the location of this gene and lead to positional cloning.

Evaluation of the atrial natriuretic peptide gene in stroke

The atrial natriuretic peptide (ANP) gene was, though inconclusive, implied to be etiologically related to stroke in rats and recently in humans. The present study tested the candidacy of ANP for stroke susceptibility by a combination of molecular genetic approaches. First, we undertook an association study using a reported ANP variant, G664A, in two case-control panels independently collected, which involved 970 Japanese subjects. Second, we compared the rat ANP gene sequences and neighboring marker alleles among stroke-prone SHR (SHRSP), normal SHR and WKY of an original inbred colony and we also compared brain ANP expression between SHRSP and normal SHR. In humans, we found no significant association between the 664A variant and stroke in the studied population. In rats, 21 polymorphic sites were identified by direct sequencing of 2170-bp ANP fragments, from which two distinct alleles, SHRSP- and WKY-types, were inferred. From a genealogical point of view, our data indicated that an SHRSP-type allele could not play a determinant role in stroke-proneness. Overall results did not support the disease relevance of ANP, disagreeing with previous reports. Thus, considerable caution should be taken when one attempts to transfer findings in the animal model to humans.

Alterations of the nitric oxide pathway in cerebral arteries from spontaneously hypertensive rats

Hypertension-associated alterations of the nitric oxide (NO) pathway were analyzed in middle cerebral arteries (MCA) from normotensive (WKY) and hypertensive (SHR) rats. The vasoconstrictor response to prostaglandin F2alpha (PGF(2 alpha), 30 and 100 microM) was smaller in MCA from SHR than from WKY. Endothelium-dependent relaxations to bradykinin (1 nM-10 microM) or acetylcholine (10 microM) were similar in MCA from both strains, whereas the endothelium-independent response to sodium nitroprusside (1 nM-0.1 mM) was smaller in MCA from SHR. L-arginine (L-Arg, 10 microM) similarly inhibited the vasoconstrictor responses in both strains; however, the inhibitory effect of 100 microM of L-Arg was greater in MCA from SHR. N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM), but not aminoguanidine (100 microM) or 7-nitroindazole (10 microM), increased basal tone, potentiated the PGF(2 alpha)-induced vasoconstrictor responses and reduced the bradykinin-elicited relaxation in a similar way in MCA from WKY and SHR. N(omega)-nitro-L-arginine methyl ester also antagonized the inhibitory effect of 10 microM of L-Arg. Incubation for 5 h with lipopolysaccharide (10 microg/ml) similarly reduced the response to PGF(2 alpha) in MCA from WKY and SHR; this reduction was antagonized by dexamethasone (1 microM). Cerebral arteries expressed endothelial (eNOS) and neuronal (nNOS) NO synthase similarly in both strains, but inducible NOS (iNOS) expression was more evident in SHR. Lipopolysaccharide increased iNOS expression in both strains to a similar level. The basal constitutive NOS (cNOS) and iNOS activities were similar in arteries from WKY and SHR. Lipopolysaccharide increased iNOS activity only in arteries from SHR. These results indicate that hypertension did not impair endothelial NO production by NOS activation but induced an up-regulation of basal iNOS expression.

Two closely linked interactive blood pressure QTL on rat chromosome 5 defined using congenic Dahl rats

Previously we reported the construction of a congenic strain, S.LEW, spanning a large region of rat chromosome 5. The Lewis (LEW) strain was the donor, and the Dahl salt-sensitive (S) strain was the recipient. The congenic strain included a blood pressure quantitative trait locus (QTL). In the present work, a series of nine congenic substrains were constructed from S.LEW which defined two closely linked blood pressure QTL in the region previously thought to contain only one. LEW low-blood-pressure alleles at both QTL were required for a major effect on blood pressure. Neither LEW allele alone had a significant effect on blood pressure. The two QTL were localized to regions 6.3 and 4.6 cM, and these were 1.0 cM apart.

Stroke genomics: approaches to identify, validate, and understand ischemic stroke gene expression

Sequencing of the human genome is nearing completion and biologists, molecular biologists, and bioinformatics specialists have teamed up to develop global genomic technologies to help decipher the complex nature of pathophysiologic gene function. This review will focus on differential gene expression in ischemic stroke. It will discuss inheritance in the broader stroke population, how experimental models of spontaneous stroke might be applied to humans to identify chromosomal loci of increased risk and ischemic sensitivity, and also how the gene expression induced by stroke is related to the poststroke processes of brain injury, repair, and recovery. In addition, we discuss and summarise the literature of experimental stroke genomics and compare several approaches of differential gene expression analyzes. These include a comparison of representational difference analysis we have provided using an experimental stroke model that is representative of stroke evolution observed most often in man, and a summary of available data on stroke differential gene expression. Issues regarding validation of potential genes as stroke targets, the verification of message translation to protein products, the relevance of the expression of neuroprotective and neurodestructive genes and their specific timings, and the emerging problems of handling novel genes that may be discovered during differential gene expression analyses will also be addressed.

Etiology and pathophysiology of stroke as a complex trait

Stroke (brain attack) is currently the third leading cause of death in Western societies. Recent advances in molecular genetics have finally demonstrated what has long been suggested by the clinical observation, that is, stroke is not only the complication of major pathologic conditions such as atherosclerosis, hypertension, or cardiac diseases, but rather it represents a complex trait itself. Thus, the pathogenesis of stroke is often the result of the combined effects of genes exerting a direct contributory role and of their interactions with several environmental determinants. A genetic dissection of stroke has been attempted in suitable animal models and in humans. With this approach, the genetic defects underlying monogenic disorders associated with stroke were identified. Moreover, important findings have recently highlighted the contribution of genes encoding cardiovascular hormones, such as the atrial natriuretic peptide, for the pathogenesis of multifactorial, polygenic forms of stroke. A more thorough understanding of the fine mechanisms, dependent from mutations within stroke susceptibility genes and underlying the disease pathogenesis, may help to introduce new specific tools to achieve better prevention and treatment of stroke.

Genetic analysis of inherited hypertension in the rat

Blood pressure is a quantitative trait that has a strong genetic component in humans and rats. Several selectively bred strains of rats with divergent blood pressures serve as an animal model for genetic dissection of the causes of inherited hypertension. The goal is to identify the genetic loci controlling blood pressure, i.e., the so-called quantitative trait loci (QTL). The theoretical basis for such genetic dissection and recent progress in understanding genetic hypertension are reviewed. The usual paradigm is to produce segregating populations derived from a hypertensive and normotensive strain and to seek linkage of blood pressure to genetic markers using recently developed statistical techniques for QTL analysis. This has yielded candidate QTL regions on almost every rat chromosome, and also some interactions between QTL have been defined. These statistically defined QTL regions are much too large to practice positional cloning to identify the genes involved. Most investigators are, therefore, fine mapping the QTL using congenic strains to substitute small segments of chromosome from one strain into another. Although impressive progress has been made, this process is slow due to the extensive breeding that is required. At this point, no blood pressure QTL have met stringent criteria for identification, but this should be an attainable goal given the recently developed genomic resources for the rat. Similar experiments are ongoing to look for genes that influence cardiac hypertrophy, stroke, and renal failure and that are independent of the genes for hypertension.

Differential brain atrial natriuretic peptide expression co-segregates with occurrence of early stroke in the stroke-prone phenotype of the spontaneously hypertensive rat

OBJECTIVE

To determine how the downregulation of atrial natriuretic peptide (ANP) gene expression, previously demonstrated to occur only in the brain of the stroke-prone spontaneously hypertensive rat (SHRsp), in contrast to the stroke-resistant SHR (SHRsr), co-segregates with stroke occurrence in SHRsp/SHRsr F2 descendants in order to study the 'protective' role towards stroke previously demonstrated in SHRsp for the quantitative trait locus STR2 that also carries the ANP gene.

DESIGN AND METHODS

Eight male SHRsp, eight male SHRsr and 16 male SHRsp/SHRsr F2-intercross animals (progeny of brother/sister mated F1 hybrids from an original cross between F0 SHRsp and SHRsr) were selected for this study. All rats were exposed to a stroke-permissive Japanese-style diet starting at the age of 6 weeks. Half of the F2 animals had early strokes; the remainder had late strokes. Blood pressure was measured before sacrifice. Analysis of brain ANP expression using an RNase protection assay was performed in all animals.

RESULTS

Downregulation of brain ANP in the stroke-prone phenotype was found to co-segregate with the occurrence of early strokes in the F2 rats independently of blood pressure levels.

CONCLUSIONS

The observed lower expression of ANP in the brains of stroke-prone rats appears to be the result of an inhibitory effect by another gene or genes. It seems unlikely that this specific trait represents a primary protective mechanism.