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D J Nunez

Publications and source records attributed to D J Nunez.

At least 19 recordsLinked to original sources
PubMed2001

Right ventricular hypertrophy secondary to pulmonary hypertension is linked to rat chromosome 17: evaluation of cardiac ryanodine Ryr2 receptor as a candidate.

BACKGROUND: Fischer 344 (F344) rats are relatively resistant to hypoxia-induced right ventricular (RV) hypertrophy compared with the Wistar-Kyoto (WKY) strain. These 2 strains were used to examine the genetic basis for the differential response. METHODS AND RESULTS: Male F(2) offspring from an F344xWKY intercross were exposed to hypoxia (10% O(2)) for 3 weeks, and pulmonary artery pressure and cardiac chamber weights were measured. Genomic DNA was screened by use of polymorphic microsatellite markers across the whole genome (excluding the sex chromosomes). A quantitative trait locus (QTL) for RV weight was identified on rat chromosome 17 (lod score 6.5) that accounted for 22% of the total variance of RV weight in the F(2) population and was independent of pulmonary artery pressure. The peak was centered over marker D17Rat41, close to Chrm3, with a 1-lod support interval of 5 cM. Comparison of homologous regions in mice and humans suggested that Ryr2, the cardiac isoform of the ryanodine receptor, colocalizes with our QTL. A panel of somatic cell hybrids and fluorescence in situ hybridization mapped Ryr2 close to the gene Chrm3 within our QTL. [(3)H]Ryanodine binding to cardiac membranes from the parental strains showed a 21% reduction in B(max) in the WKY compared with the F344 strain, with no difference in K:(d). CONCLUSIONS: These data provide the first demonstration of a QTL linked to the RV response to hypoxia-induced pulmonary hypertension. The Ryr2 receptor gene lies within this QTL and merits further investigation as a candidate for this differential RV response.

Animals↗
PubMed2000

Echocardiographic characterization of cardiomyopathy in Friedreich's ataxia with tissue Doppler echocardiographically derived myocardial velocity gradients.

BACKGROUND: Conventional and tissue Doppler echocardiographically derived myocardial velocity gradients (MVGs) were used to characterize the myocardium in patients with Friedreich's ataxia (FRDA), and the relationship between MVGs and the mutation in the FRDA gene, a GAA triplet repeat expansion, was investigated. METHODS AND RESULTS: We studied 29 patients with FRDA (10 men, mean age 31+/-9 years) who were homozygous for the GAA expansion in the FRDA gene and were without cardiac symptoms. A comparison was made with a group of 30 age-matched control subjects. In patients with FRDA, interventricular septal thickness (1.17+/-0.26 versus 0.85+/-0.13 cm, P:<0.005), posterior left ventricular wall thickness (1.00+/-0.24 versus 0.88+/-0.15 cm, P:<0.01), and left atrial diameter (3.3+/-0.5 versus 2.9+/-0.3 cm, P:=0.01) were increased compared with control subjects. MVGs were reduced in FRDA during systole (3.1+/-1.2 versus 4.5+/-0.5 s(-1), P:<0.0001) and in early diastole (4.9+/-2.7 versus 8.8+/-1.8 s(-1), P:<0.0001) but increased in late diastole (2.0+/-1. 3 versus 1.1+/-0.9 s(-1), P:<0.01). The strongest relationship was seen between age-corrected early diastolic MVGs and the GAA expansion in the smaller allele of the FRDA gene (r=-0.68, P:<0. 0001). CONCLUSIONS: MVGs offer a means of further characterizing the myocardial abnormalities in patients with FRDA. Early diastolic MVGs appear to relate most closely to the genetic abnormality and the consequential reduction in frataxin protein.

Adaptor Proteins, Signal Transducing↗
PubMed1999

Marked variation in the cardiomyopathy associated with Friedreich's ataxia.

OBJECTIVE: To document the cardiac phenotype associated with Friedreich's ataxia, a recessively inherited disorder characterised by spinocerebellar degeneration. SETTING: Individuals with Friedreich's ataxia who accepted the invitation to participate in the study. HYPOTHESIS: The cardiomyopathy associated with Friedreich's ataxia may offer a human model for the study of factors modulating cardiac hypertrophy. METHODS: 55 patients (mean (SD) age 30 (9) years) with a clinical diagnosis of Friedreich's ataxia were studied by clinical examination, electrocardiography, cross sectional and Doppler echocardiography, and analysis of the GAA repeat in the first intron of the frataxin gene. RESULTS: A wide variety of cardiac morphology was documented. Subjects with normal frataxin alleles had no evidence of cardiomyopathy. In homozygous subjects, a relation was found between the thickness of the interventricular septum (r = 0.53, p < 0.005), left ventricular mass (r = 0.48, p < 0.01), and the number of GAA repeats on the smaller allele of the frataxin gene. No relation was shown between the presence of electrocardiographic abnormalities (mainly repolarisation changes) and either the pattern of ventricular hypertrophy (if present) and degree of neurological disability or the length of time since diagnosis. No tendency to ventricular thinning or dilatation with age was found. Although ventricular systolic function appeared impaired in some cases, Doppler studies of ventricular filling were within the normal range for age. CONCLUSIONS: The cardiomyopathy associated with Friedreich's ataxia shows a variable phenotype which is not concordant with the presence of ECG abnormalities or the neurological features of the condition. As the genetic basis for Friedreich's ataxia has been established, further studies will help to clarify the molecular mechanisms of the cardiac hypertrophy.

Adolescent↗
PubMed1999

Genetic determination of cardiac mass in normotensive rats: results from an F344xWKY cross.

Genetic determinants affect adult cardiac mass and the predisposition to develop cardiac hypertrophy. The aim of this study was to identify quantitative trait loci (QTL) that control heart and left ventricular (LV) weight by use of normotensive inbred rat strains that differ in their adult cardiac mass phenotype. We studied 126 male F2 rats derived from a cross of normotensive Wistar-Kyoto and Fischer 344 rats. At 12 weeks of age, total heart weight and LV weight were measured. Genomic DNA from these animals was screened by use of polymorphic microsatellite markers across the whole genome (excluding the sex chromosomes). In this cross, the genetic contribution to total heart weight variation was 56%, and the genetic contribution for LV weight was 55%. Using the Mapmaker/QTL computer package, we identified a significant QTL on chromosome 3 with a log10 likelihood (LOD) score of 4.8, which accounted for 16.5% of the total variance of LV weight. This QTL was centered close to the marker D3Rat29. The QTL was also found to be significantly linked with total heart weight (LOD=4.4). These data provide the first demonstration of a QTL on chromosome 3 that plays a role in determining the difference in LV mass between normotensive Fischer 344 and Wistar- Kyoto inbred rat strains. The prostaglandin synthase 1 gene is located within the QTL.

Animals↗
PubMed1998

Human beta-myosin heavy chain mRNA prevalence is inversely related to the degree of methylation of regulatory elements.

OBJECTIVE: Methylation of cytosine in CG dinucleotides within regulatory elements is believed to silence gene expression. These dinucleotides occur in certain important regulatory elements in the promoter region of the human beta-myosin heavy chain (beta-MHC) gene. We therefore investigated whether methylation of these elements correlates with beta-MHC gene transcription in human 'expressing' (right atrial) and 'non-expressing' (peripheral blood leucocytes) cells. METHODS: We employed 2 techniques to assess promoter methylation: (i) analysis of the susceptibility to digestion of a particular CCGG restriction site in the promoter region when genomic DNA is cleaved with the restriction endonucleases MspI (methylation-insensitive) and HpaII (methylation-sensitive), and (ii) the bisulphite-PCR method to examine in detail the methylation patterns of 3 important regulatory elements that contain CG dinucleotides. beta-MHC mRNA expression in right atrium and leucocytes was assessed using reverse-transcription-PCR with specific primers that do not detect alpha-MHC cDNA. RESULTS: The digestion pattern observed with MspI or HpaII indicated that the CCGG site was almost completely methylated in leucocytes, but relatively unmethylated in atrial myocardium from the same patients. When methylation was examined with the bisulphite-PCR method we found a reciprocal relationship between the level of beta-MHC mRNA expression in leucocytes and atrial myocardium and the degree of methylation of CG dinucleotides in the 5' regulatory elements of the gene. CONCLUSIONS: Tissue-specific methylation of the human beta-MHC gene promoter may play a role in determining the pattern of expression of this gene. Furthermore, alteration of the level of methylation may underlie the changes in transcription of this gene that occur, for example, when atrial or ventricular myocardium hypertrophies.

Cardiomyopathy, Hypertrophic↗
PubMed1997

Downregulation of natriuretic peptide C-receptor protein in the hypertrophied ventricle of the aortovenocaval fistula rat.

OBJECTIVES: This study examined the expression of the C-type receptor for the natriuretic peptide family (NPR-C) in the ventricles of normal and aortovenocaval (AV)-fistula rats, the latter a model of cardiac volume overload producing hypertrophy of both ventricles. METHODS: Western blotting with a rabbit anti-NPR-C antibody was used to quantify NPR-C levels in ventricular membranes. NPR-C expression was localised anatomically and measured in frozen sections of cardiac tissue by histochemistry and in vitro autoradiography. RESULTS: Western blot analysis revealed a single band (approximately 120 kDa) in ventricular membranes which was reduced to approximately 60 kDa after treatment with beta-mercaptoethanol. NPR-C immunoreactivity and [125I]rat ANP1-28 binding (displaceable by the NPR-C-specific ligand C-ANP 4-23) were localised to the endocardium. NPR-C protein levels, as measured by all three techniques, were reduced significantly in the hypertrophied ventricles of AV-fistula rats compared to sham-operated animals. CONCLUSIONS: Volume-induced cardiac hypertrophy in the AV-fistula rat is associated with downregulation of endocardial NPR-C. This may be one mechanism by which the endocardium regulates the myocardial response to changes in haemodynamic load.

Animals↗
PubMed1996

Hypertensive cardiac hypertrophy--is genetic variance the missing link?

1. Hypertensive cardiac hypertrophy is a major independent predictor of adverse cardiovascular events. In man the cardiac response to increased afterload is very variable, even when ambulatory blood pressure monitoring is used. Analysis of breeding experiments using normotensive and hypertensive rat strains, human twin studies and other data indicate that genetic factors play a significant role in regulating cardiac mass; in other words, a large component of total variability is accounted for by genetic variance. 2. The observation that some patients with only mild-to-moderate hypertension exhibit gross left ventricular hypertrophy (LVH) similar to the inherited hypertrophic cardiomyopathies such as familial hypertrophic cardiomyopathy (FHC) and Friedreich's ataxia (FA) has prompted us to investigate the hypothesis that genetic factors associated with excessive myocardial hypertrophy, viz. mutations in FHC and FA genes alter the hypertrophic response of the heart to pressure overload. Here we review briefly three lines of study: (i) association analysis to test whether the allele frequencies differ in hypertensive patients with or without left ventricular hypertrophy; (ii) characterization of the cardiac manifestations of FA to understand the mechanism by which the heart is affected in a disease associated with pathology in a subgroup of neurons, and (iii) creation of transgenic models to facilitate the investigation of the interaction between hypertrophic stimuli and underlying genetic predisposition. 3. Information on the nature of the cardiac-mass-modifying genes involved may be useful not only for selecting high risk patients in strategies aimed at preventing the development of LVH, but also in opening new avenues of research on the reprogramming of cardiac myocytes to encourage them to hypertrophy in situations where cardiac muscle has been damaged or is hypoplastic.

Animals↗
PubMed1996

Angiotensin II receptor expression and inhibition in the chronically hypoxic rat lung.

1. Angiotensin II (AII) binding density and the effect of chronic AII receptor blockade were examined in the rat model of hypoxia-induced pulmonary hypertension. 2. [125I]-[Sar1,Ile2]AII binding capacity was increased in lung membranes from rats exposed to hypoxia (10% fractional inspired O2) for 7 days compared to normal rats (Bmax 108 +/- 12 vs 77 +/- 3 fmol mg-1 protein; P < 0.05), with no significant change in dissociation constant. Competition with specific AII receptor subtype antagonists demonstrated that AT1 is the predominant subtype in both normal and hypoxic lung. 3. Rats treated intravenously with the AT1 antagonist, GR138950C, 1 mg kg-1 day-1 rather than saline alone during 7 days of exposure to hypoxia developed less pulmonary hypertension (pulmonary arterial pressure: 21.3 +/- 1.7 vs 28.3 +/- 1.1 mmHg; P < 0.05), right ventricular hypertrophy (right/left ventricle weight ratio: 0.35 +/- 0.01 vs 0.45 +/- 0.01; P < 0.05) and pulmonary artery remodelling (abundance of thick-walled pulmonary vessels: 9.6 +/- 1.4% vs 20.1 +/- 0.9%; P < 0.05). 4. The reduction in cardiac hypertrophy and pulmonary remodelling with the AT1 antagonist was greater than that achieved by a dose of sodium nitroprusside (SNP) that produced a comparable attenuation of the rise in pulmonary arterial pressure during hypoxia. 5. The data suggest that AII, via the AT1 receptor, has a role in the early pathogenesis of hypoxia-induced pulmonary hypertension in the rat.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1996

Adrenomedullin activity in chronically hypoxic rat lungs.

Adrenomedullin (AM) is a novel vasodilator with structural similarities to calcitonin gene-related peptide (CGRP). This study investigated AM activity in the rat lung during hypoxia-induced pulmonary hypertension. Both rat AM (0.2-10 nmol) and alpha-CGRP (0.2-2 nmol) produced dose-related reductions in pulmonary artery pressure in the isolated perfused lung ventilated with 2% O2. Pretreatment with alpha-CGRP, which demonstrated tachyphylaxis, or its antagonist, CGRP-(8-37), reduced the hypotensive response to AM, suggesting that part of the response to AM is mediated by CGRP receptors. 125I-labeled AM and 125I-labeled CGRP binding was significantly increased in lung membranes from 7-day hypoxic animals (AM from 1.94 +/- 0.3 to 3.36 +/- 0.4 and CGRP from 0.06 +/- 0.01 to 0.12 +/- 0.02 pmol/mg protein), with no change in dissociation constant. Moreover, the hypotensive response to both peptides was increased in the lungs of 7-day hypoxic rats. There was no significant change in lung immunoreactive AM concentrations (hypoxic 5.04 +/- 0.48 vs. control 6.28 +/- 0.76 pmol/g wet wt of tissue) or steady-state AM mRNA levels in 7-day hypoxic rats. Nonetheless, AM may be useful for the acute pharmacological manipulation of pulmonary artery pressure in hypoxia-induced pulmonary hypertension.

Adrenomedullin↗
PubMed1995

Messenger RNAs encoding the natriuretic peptides and their receptors are expressed in the eye.

The rates of secretion and removal of aqueous humour are major determinants of intraocular pressure (IOP). The natriuretic peptides, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) are vasodilators with variable effects on electrolyte and water transport at sites such as the nephron. There is some evidence that they may also affect fluid balance in the eye. As a first step in understanding the function of these peptides in the eye, we have used the technique of cDNA amplification with the polymerase chain reaction to demonstrate the presence of mRNA transcripts encoding the three natriuretic peptide receptors (NPR-A, NPR-B and NPR-C) in the retina, choroid and ciliary process of the rat and rabbit eye. In addition we have observed a differential distribution of ANP, BNP and CNP mRNAs in ocular tissues suggesting that at least part of the natriuretic peptide immunoreactivity detected in the eye arises from local synthesis of peptide. Thus, the eye appears to be able to synthesize all the components of the natriuretic peptide system necessary to modulate IOP independently of changes in the plasma concentrations of these peptides.

Animals↗
PubMed1995

Selective increase in endothelin-1 and endothelin A receptor subtype in the hypertrophied myocardium of the aorto-venacaval fistula rat.

OBJECTIVE: At present little is known about the factors that regulate the expression of the endothelins and their receptors in cardiac tissue in vivo. The aim of this study was to investigate changes in expression of the endothelins (ET-1, ET-2, and ET-3) and their receptors (ETAR and ETBR) in the hypertrophied heart of the aortovenocaval (AV) fistula rat. METHODS: Reverse transcription-polymerase chain reaction (RT-PCR) was used to quantify cardiac mRNA expression of the endothelins and their receptors during the development of cardiac hypertrophy, while radioligand binding was employed to quantify the amount of [125I]-ET-1 binding to cardiac membranes. Tissue and plasma concentrations of ET-1 were measured by radioimmunoassay. RESULTS: In control sham operated animals, ET-1 mRNA was approximately fivefold greater in atria than in ventricles (P < 0.05), but there were no atrioventricular differences in ET-2 or ET-3 mRNA. In the AV fistula rats there was a prompt three- to fourfold increase in ET-1 mRNA in atria and a progressive five- to sevenfold rise in ventricles during cardiac hypertrophy. There were no changes in ET-2 or ET-3 transcript prevalences, except for a late rise (35 d) in ET-2 mRNA levels in left ventricle. Consistent with ET-1 mRNA measurements, immunoreactive endothelin levels were increased by 7 d in atria, but not in ventricles. In control rat hearts, ETAR mRNA levels were similar in atria and ventricles, but the prevalence of ETBR was approximately sevenfold greater in the former. ETAR mRNA prevalence increased with hypertrophy in all chambers, while ETBR transcript levels were raised only in the right ventricle. There was no significant difference in [125I]-ET-1 binding between atrial samples from 35 d control and 35 d AV fistula rats, suggesting rapid turnover of endothelin receptors balanced by increased transcription from the ETAR gene. CONCLUSIONS: During cardiac hypertrophy in AV fistula rats there is increased activity of the endothelin system mediated principally by ET-1 and the ETAR subtype.

Animals↗
PubMed1993

Differential regulation of natriuretic peptide receptor messenger RNAs during the development of cardiac hypertrophy in the rat.

The heart expresses the three natriuretic peptide receptors (NPR), namely NPR-A, NPR-B, and NPR-C. We have examined the temporal relationship between the expression of mRNA transcripts for atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) and their receptors in the heart during the development of cardiac hypertrophy in the aortovenocaval fistula rat. Messenger RNAs were measured by cDNA amplification. Progressive cardiac hypertrophy was accompanied by increased ANP mRNA prevalence throughout the heart and increased BNP mRNA in the left atrium. The most striking observation was the gradual disappearance of NPR-C transcripts (the putative "clearance" receptor) in all chambers; this was in marked contrast to the increase in mRNA levels for NPR-A and NPR-B (the guanylyl cyclase-linked receptors). Our observations have important therapeutic implications if the transcript changes are mirrored at the receptor protein level because (a) the apparent down-regulation of NPR-C may enhance the local action of natriuretic peptides on the heart, and (b) the loss of NPR-C, particularly if it is widespread, may reduce the rate of elimination of the natriuretic peptides, restricting the therapeutic potential of specific NPR-C ligands designed to reduce peptide clearance.

Animals↗
PubMed1992

Spectroscopic characterization of heme A reconstituted myoglobin.

The focus of this study was to examine the functional role of the unusual peripheral substitution of heme A. The effects of heme A stereochemistry on the reconstitution of the porphyrin have been examined in the heme A-apo-myoglobin complex using optical absorption and resonance Raman and electron paramagnetic resonance spectroscopies. The addition of one equivalent of heme A to apo-Mb produces a complex which displays spectroscopic signals consistent with a distribution of high- and low-spin heme chromophores. These results indicate that the incorporation of heme A into apo-Mb significantly perturbs the protein refolding.

Animals↗
PubMed1992

c-fos may code for a common transcription factor within the hypothalamic neural circuits involved in osmoregulation.

Conscious rats were given an intraperitoneal (i.p.) injection of isotonic or hypertonic saline, and killed 10-240 min later. In the hypothalamus of hypertonic saline-injected rats, c-fos-mRNA positive cells were mainly restricted to the supraoptic and paraventricular nuclei and to structures associated with the lamina terminalis of the third ventricle, including in particular the subfornical organ, the organum vasculosum of the lamina terminalis (OVLT) and the median preoptic nucleus. These structures comprise the proposed anterior hypothalamic 'osmoreceptor complex' for regulation of vasopressin release. The time course of the appearance and disappearance of c-fos mRNA signals was similar in all regions. Thus c-fos protein (Fos) may be a common transcription factor in the hypothalamic neural circuits involved in osmoregulation.

Animals↗