Asymmetrical dimethylarginine, an endogenous nitric oxide synthase inhibitor, in experimental hypertension.

NG,NG-dimethyl-L-arginine (ADMA) is an endogenously synthesized nitric oxide (NO) synthase inhibitor which has potent pressor/vasoconstrictor effects. Dimethylargininase metabolizes ADMA to L-citrulline and plays a key role in determining the in vivo levels of ADMA. To investigate the role of ADMA in the pathogenesis of hypertension, we measured 24-hour urinary excretion of ADMA (UADMA) and nitrate/nitrite (NOx) in Dahl salt-sensitive hypertensive rats and spontaneously hypertensive rats (SHR). In Dahl salt-resistant rats, high-salt diet (8% NaCl) did not increase blood pressure and increased urinary NOx (P < .01) without changes in UADMA compared with low-salt diet (0.3% NaCl). In contrast, in Dahl salt-sensitive rats, high-salt diet increased blood pressure (P < .01), did not change urinary NOx excretion, and increased UADMA (P < .01). There was a significant (r = .65, P < .01) correlation between UADMA and the level of blood pressure in Dahl salt-sensitive rats. Plasma levels of NOx and ADMA and renal dimethylargininase content were comparable among them. These results may suggest that in Dahl salt-resistant rats, blood pressure is kept constant during high-salt intake, possibly due to the compensatory increased production of NO, and that in Dahl salt-sensitive rats, high-salt intake increases the production of ADMA, attenuates the compensatory increases in NO, and increases blood pressure. These results also suggest that the systemic production of ADMA is not dependent on renal dimethylargininase. SHR had significantly greater urinary NOx excretion (P < .05) and smaller UADMA than Wistar-Kyoto rats (P < .05), and UADMA was inversely correlated with their mean arterial pressure (r =.64, P < .05). In conclusion. ADMA, independently of the renal dimethylargininase content, may play a role in the pathogenesis in Dahl salt-sensitive hypertensive rats but not in SHR.

Multiplicity in type V adenylylcyclase: type V-a and type V-b.

Type V mammalian adenylylcyclase cDNA was originally isolated from two animal species, the dog and rat. The amino acid sequences from the two species are highly homologous, but completely different in the putative N-terminal, cytoplasmic region. Northern blot analysis using oligonucleotide probes unique to either of the two clones has revealed that the two forms of type V adenylylcyclase mRNA, canine form (= type V-a) and rat form (= type V-b), are co-expressed as splicing variants in both species. Genomic Southern blot analysis has suggested that the two forms are the products of a single gene. When overexpressed, however, deletion of the N-terminal domain did not alter any biochemical properties. Thus multiple splicing variants with unique N-terminal amino acid sequences of type V adenylylcyclase can be generated from a single gene, however, biochemical properties of these variants may not be different.

Alterations in beta-adrenergic receptor density and cyclic-AMP level in the myocardium of rats chronically treated with alcohol.

An impaired function of the myocardial beta-adrenergic receptor system has been reported in patients with end-stage heart failure and this impairment has been postulated to be a factor in further deterioration of cardiac contractile function. As ventricular dysfunction is often associated with prolonged alcohol abuse, we investigated whether or not chronic administration of ethanol could induce alterations in the beta-adrenergic receptor adenylate-cyclase system in rats. Male Wistar rats of 8 weeks of age received 33% ethanol in drinking water for 3 months. As compared with control rats drinking water, the ethanol-treated rats showed weight loss and an increase in the heart/body weight ratio. Chronic ethanol increased myocardial contents of norepinephrine and epinephrine, possibly resulting from sympathoadrenal activation. The beta-adrenergic receptor density (Bmax) of the myocardial membrane was significantly decreased in the ethanol-treated rats (27.7 +/- 9.9 vs 39.0 +/- 6.0 fmol/mg protein, p < 0.01), while the affinity (Kd) did not differ between the two groups. The myocardial content of cyclic-AMP was also reduced in the ethanol rats (865 +/- 59 vs 1055 +/- 83 pmol/g w.w., p < 0.01). These observations indicate that chronic ethanol administration depresses the function of the beta-adrenergic receptor adenylate-cyclase system. The decreased beta-adrenergic receptor density was partly attributed to down-regulation due to increased sympathetic stimulation. This impaired function may contribute to the cardiac contractile dysfunction observed in chronic alcoholics.

Regulation of adenylyl cyclase by protein kinase A.

The changing relationship between stimuli and responses after prolonged receptor stimulation is a general feature of hormonal signaling systems, termed desensitization. This phenomenon has been best exemplified in the covalent modification of the G protein-linked catecholamine receptors. However, other components within this signaling pathway can be involved in desensitization. Here we present evidence that desensitization occurs at the level of the effector enzyme itself through phosphorylation. Type V adenylyl cyclase (AC) is the major isoform expressed in the heart. Using purified enzymes, we demonstrate that protein kinase A (PKA) directly phosphorylates and thereby inhibits type V AC catalytic activity. This inhibition was negated in the presence of PKA inhibitor. Analysis of enzyme kinetics revealed that this inhibition was due to a decrease in the catalytic rate, not to a decrease in the affinity for the substrate ATP. Our results indicate that AC catalytic activity can be regulated through PKA-mediated phosphorylation, suggesting another mechanism of desensitization for receptor pathways which signal via increases in intracellular cAMP.

Differential activation of adenylyl cyclase by protein kinase C isoenzymes.

Cyclic AMP production within cells is altered upon protein kinase C (PKC) activation; however, whether PKC directly modulates adenylyl cyclase (AC) catalytic activity has been controversial. Molecular studies have elucidated the existence of multiple PKC isoenzymes although the functional role of this diversity is not clear. Using purified PKC and AC isoenzymes, we demonstrate that PKC zeta directly phosphorylates type VAC, leading to an approximate 20-fold increase in its catalytic activity, a significantly larger enhancement than that achieved with forskolin (approximately 5-fold), the most potent activator of AC. When forskolin and PKC phosphorylation are combined, type V AC catalytic activity is increased 100-fold over basal levels. The two PKC isoenzymes (alpha and zeta) are additive in their capacity to activate AC, although PKC alpha is less potent than PKC zeta. Our data indicate that PKC can directly and potently regulate AC activity in an isoenzyme-specific manner, suggesting that direct cross-talk plays a major role in coordinating the activity of these two principal signal transduction pathways.

[Hypertrophic cardiomyopathy manifesting different modes of illness: report of three cases].

Three cases of hypertrophic cardiomyopathy (HCM) which presented with different modes of appearance of left ventricular hypertrophy are reported. Case 1: A 24-year-old man had three relatives with HCM. At 13 years of age, he showed no electrocardiographic or echocardiographic abnormalities characteristic of HCM. During the ensuing 11 years, he developed asymmetric septal hypertrophy (ASH) and systolic anterior motion of the mitral valve (SAM), with right bundle branch block and T-wave inversion. Cardiac catheterization confirmed the diagnosis of hypertrophic obstructive cardiomyopathy by demonstrating an intraventricular pressure gradient of 25 mmHg. These observations indicate that this case developed abnormal hypertrophy during adolescence on the basis of genetic predisposition of an autosomal dominant trait. Case 2: A 51-year-old woman had three proven and three possibly affected relatives. At 35 years of age, she had a normal electrocardiogram, although the echocardiogram was not available. Now, 16 years later, she had developed ASH with abnormal Q-waves and was diagnosed as having non-obstructive HCM. These suggest that ASH can be manifested as late as during middle-age, even in those with genetic predisposition. Case 3: A 47-year-old woman was diagnosed as having hypertension and her blood pressure was 190/100 mmHg at 40 years of age, though she had no abnormal electrocardiographic findings and heart murmurs. Now, at 47 years of age, she had developed T-wave inversion, ASH, SAM, and an intraventricular pressure gradient of 50 mmHg. Thus, her ASH appeared during middle-age, and was probably provoked by hypertension, though a complete family survey could not be conducted. These three patients' findings indicate that there may be various modes of appearance of left ventricular hypertrophy in HCM. In the majority of patients with genetic predisposition, abnormal hypertrophy may develop during adolescence as in Case 1. In others, it may develop in middle-age, as it did in Case 2. The disease spectrum of HCM may additionally include those who develop abnormal hypertrophy during middle-age, following provocation by hypertension, as in Case 3.

[Hypertrophic cardiomyopathy with left ventricular dilatation].

There is increasing interest in the notion that some patients with hypertrophic cardiomyopathy (HCM) progress to morphological and functional manifestations similar to those of dilated cardiomyopathy (DCM). From 165 consecutive patients with HCM, 20 patients with left ventricular dilatation (left ventricular end-diastolic diameter greater than or equal to 50 mm) were selected and designated as dilated HCM. The diagnosis of HCM was established in these patients either by detection of the classical form of HCM in family members, with 2-dimensional echocardiographic evidence of asymmetric septal hypertrophy (ASH; septal thickness greater than or equal to 15 mm and a ratio of septal to posterior wall thickness greater than or equal to 1.3); or by demonstrating myocardial fiber disarray in autopsy or biopsy samples. The clinical manifestations of these patients with dilated HCM were then compared with those of other forms of HCM without left ventricular dilatation; 1) 40 patients with hypertrophic obstructive cardiomyopathy (HOCM) who had resting intraventricular pressure gradients of 20 mmHg or more, 2) 80 patients with non-obstructive HCM, each of whom had ASH of the entire ventricular septum (typical ASH), and 3) 25 non-obstructive patients whose hypertrophy was localized to the apical region of the ventricular septum (apical ASH). Patients having apical hypertrophy with a spade-like configuration on the left ventriculogram were excluded from the study. Compared with HOCM and typical ASH groups, the patients with dilated HCM had family histories of significantly more frequent HCM and less frequent hypertension. The patients with dilated HCM also had significantly less fractional shortening (FS), decreased interventricular septal thickness, greater left ventricular end-diastolic pressure (LVEDP), and left ventricular dilatation. During the follow-up period (average: 3.5 years), seven patients (35%) with dilated HCM died; five from congestive heart failure (CHF), one suddenly, and one three days following mitral valve replacement. The other five patients had CHF at the time of their follow-up examination. The patients with apical ASH had clinical features similar to those of dilated HCM; a higher familial frequency, less marked septal hypertrophy, and higher LVEDP. They tended to develop left ventricular dilatation, associated with reduced fractional shortening, although left ventricular diameter at end-diastole did not exceed 50 mm. These findings suggested that dilated HCM is not a rare condition. It is observed in 12% of consecutive patients with HCM.(ABSTRACT TRUNCATED AT 400 WORDS)