Low dose of eicosapentaenoic acid inhibits the exaggerated growth of vascular smooth muscle cells from spontaneously hypertensive rats through suppression of transforming growth factor-beta

OBJECTIVE

To evaluate effects of eicosapentaenoic acid (EPA), an n-3 polyunsaturated fatty acid, on the exaggerated growth of vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR).

DESIGN

Cultured VSMC were prepared by an explant method from thoracic aortas in 8-week-old male Wistar-Kyoto (WKY)/Izumo rats and SHR/Izumo. Effects of EPA on basal DNA synthesis, expression of growth factors and cyclin-dependent kinase 2 (cdk2) activity were examined in VSMC from WKY rats and SHR.

METHODS

The cell cycles were synchronized with serum deprivation, then DNA synthesis in VSMC was measured by [3H]-thymidine incorporation. Fatty acid composition of the phospholipid fraction in VSMC was measured by gas chromatography. Expression of platelet-derived growth factor (PDGF) A-chain, transforming growth factor (TGF)-beta1 and basic fibroblast growth factor (bFGF) mRNAs was evaluated by reverse-transcription and polymerase chain reaction analysis. Cdk2 activity was determined by autoradiography after polyacrylamide gel electrophoresis of VSMC extracts that had been immunoprecipitated with anti-cdk2 antibody and protein A sepharose, and then incubated with 32P-ATP and histone H1.

RESULTS

High concentrations (40 and 80 micromol/I) of EPA significantly inhibited basal DNA synthesis in VSMC from both rat strains. Low dose (20 micromol/l) of EPA significantly inhibited basal DNA synthesis in VSMC from SHR, whereas the same dose of EPA stimulated DNA synthesis in VSMC from WKY rats. In analysis of fatty acid composition, low dose of EPA was considerably incorporated in VSMC. Low dose of EPA significantly inhibited angiotensin II- and phorbol ester milisterol-stimulated DNA synthesis in VSMC from both rat strains, whereas EPA did not affect PDGF-AA-stimulated DNA synthesis in VSMC from either rat strain. Low dose of other polyunsaturated fatty acids such as docosahexaenoic acid, arachidonic acid and linoleic acid did not significantly affect basal DNA synthesis in VSMC from either strain. Low dose of EPA significantly inhibited expression of TGF-beta1 mRNA in VSMC from SHR, whereas EPA did not affect expression of PDGF A-chain and bFGF mRNAs in VSMC from SHR. Cdk2 activity in VSMC from SHR was higher than that from WKY rats. Low dose of EPA inhibited cdk2 activity in VSMC from SHR, whereas it stimulated the activity in VSMC from WKY rats.

CONCLUSION

Low dose of EPA exerted specific inhibition of the exaggerated growth of VSMC from SHR through the suppression of TGF-beta.

Eicosapentaenoic acid inhibits vasopressin-activated Ca2+ influx and cell proliferation in rat aortic smooth muscle cell lines

The purpose of this study was to clarify how eicosapentaenoic acid (EPA), an omega-3 polyunsaturated fatty acid, modulates the vascular action of vasopressin in rat aortic smooth muscle cell lines. The effects of EPA on Ca2+ mobilization and DNA synthesis elicited by vasopressin were investigated and compared to those of Ca2+ channel blocking agents, by means of Ca2+ measurements and the incorporation of [3H]thymidine. Patch-clamp techniques were also employed. Vasopressin (100 nM) elicited an initial peak of intracellular Ca2+ ([Ca2+]i), followed by a sustained phase due to Ca2+ entry. Nifedipine or nicardipine (1 microM), a potent L-type Ca2+ channel blocker, partly inhibited the sustained phase, but La3+ completely abolished it. EPA (10 microM) also inhibited it even in the presence of nicardipine. Under voltage-clamp conditions with CsCl-internal solution, depolarizing pulses positive to -30 mV from a holding potential of -40 mV elicited a slow inward current. The inward current was blocked by La3+, nicardipine, and nifedipine (1 microM), suggesting that the inward current mainly consisted of the voltage-dependent L-type Ca2+ channel (ICa.L). EPA (1-30 microM) also inhibited ICa.L in a concentration-dependent manner. The inhibitory effect of EPA was observed at concentrations higher than 1 microM, and its half-maximal inhibitory concentration (IC50) was 7.6 microM. Vasopressin induced a long-lasting inward current at a holding potential of -40 mV. The vasopressin-induced current was considered as a non-selective cation current (Icat) with a reversal potential of approximately +0 mV. Both nifedipine and nicardipine (10 microM) failed to inhibit it significantly, but La3+ completely abolished Icat. EPA also inhibited vasopressin-induced Icat in a concentration-dependent manner; its IC50 value was 5.9 microM. Vasopressin (100 nM) stimulated [3H]thymidine incorporation. Exclusion of extracellular Ca2+ with EGTA or La3+ markedly inhibited it. EPA (3-30 microM) also inhibited the incorporation induced by vasopressin, while nifedipine and nicardipine (1 microM) only partly inhibited it. These results suggested that EPA, unlike nifedipine and nicardipine, inhibited vasopressin-induced Ca2+-entry and proliferation in rat vascular smooth muscle cells, where the inhibitory effects of EPA on Icat as well as ICa.L might be involved. Thus, EPA would exert hypotensive and antiatherosclerotic effects.

Enhanced resistance to blast (Magnaporthe grisea) in transgenic Japonica rice by constitutive expression of rice chitinase

Rice blast is the most devastating plant disease in Japan. Our goal is to create new rice varieties which show enhanced resistance against blast, regardless of the race of blast. By an Agrobacterium-mediated transformation method, we reintroduced a rice class-I chitinase gene, Cht-2 or Cht-3, under the control of the enhanced CaMV 35S promoter and a hygromycin phosphotransferase gene, as a selection marker into the Japonica rice varieties Nipponbare and Koshihikari, which have retained the best popularity over a long period in Japan. In regenerated plants (R(0)), the Cht-2 product was found to accumulate intracellularly whereas the Cht-3 product was found to be targeted extracellularly. The transgenic rice plants which constitutively expressed either chitinase gene showed significantly higher resistance against the rice blast pathogen Magnaporthe grisea races 007.0 and 333. Both high-level expression of the chitinase and blast-resistance were stably inherited by the next generation in several lines.

Production of angiotensin II by homogeneous cultures of vascular smooth muscle cells from spontaneously hypertensive rats

Production of angiotensin II (Ang II) in spontaneously hypertensive rats (SHR)-derived vascular smooth muscle cells (VSMC) has now been investigated. A nonpeptide antagonist (CV-11974) of Ang II type 1 receptors inhibited basal DNA synthesis in VSMC from SHR, but it had no effect on cells from Wistar-Kyoto (WKY) rats. Ang II-like immunoreactivity, determined by radioimmunoassay after HPLC, was readily detected in conditioned medium and extracts of SHR-derived VSMC, whereas it was virtually undetectable in VSMC from WKY rats. Isoproterenol increased the amount of Ang II-like immunoreactivity in conditioned medium and extracts of SHR-derived VSMC, whereas the angiotensin-converting enzyme inhibitor delapril significantly reduced the amount of Ang II-like immunoreactivity in conditioned medium and extracts of these cells. Reverse transcription-polymerase chain reaction analysis revealed that the abundance of mRNAs encoding angiotensinogen, cathepsin D, and angiotensin-converting enzyme was greater in VSMC from SHR than in cells from WKY rats. The abundance of cathepsin D protein by Western blotting was greater in VSMC from SHR than in cells from WKY rats. Ang I-generating and acid protease activities were detected in VSMC from SHR, but not in cells from WKY rats. These results suggest that SHR-derived VSMC generate Ang II with increases in angiotensinogen, cathepsin D, and angiotensin-converting enzyme, which contribute to the basal growth. Production of Ang II by homogeneous cultures of VSMC is considered as a new mechanism of hypertensive vascular disease.

A study on the daily physical activity of junior high school students in Japan

The purpose of this study was to estimate daily energy expenditure (EE) and daily activity factor (DAF: EE/basal metabolism - 1) of junior high school students in Japan using heart rate (HR) monitoring method. Daily activity recording and 24 hour HR monitoring were measured in all the subjects. The relational formulas between HR and oxygen consumption were obtained from bicycle ergometer test. Subjects were 112 junior high school students (68 male and 44 female) from the 1st to the 3rd year. The averages of EE (kcal/kg) of the 1st, 2nd, and 3rd year students were 54.3, 46.7, and 44.5 (kcal/kg) for males and 50.1, 44.4, and 40.5 (kcal/kg) for females respectively. In the same way DAF were 0.80, 0.61, and 0.59 for males and 0.77, 0.65, and 0.51 for females. It was shown that EE (kcal/kg) and DAF have a tendency to decrease as school year increases in both male and female students.

Role of metabotropic glutamate receptors in the hypersusceptibility to pentylenetetrazole-induced seizure during diazepam withdrawal

To clarify the contribution of metabotropic glutamate (mGlu) receptors in brain to benzodiazepine withdrawal signs, we now examine the effects in mice of selective ligands for three subgroups of mGlu receptor on the hypersusceptibility to pentylenetetrazole-induced seizure during diazepam withdrawal. The seizure threshold for pentylenetetrazole was significantly decreased by the discontinuation of chronic diazepam treatment. The decrease in the seizure threshold for pentylenetetrazole during diazepam withdrawal was significantly suppressed by intracerebroventricular (i.c.v.) pretreatment with the group 1 mGlu receptor antagonist, (S)-4-carboxyphenylglycine ((S)-4CPG: 56 and 100 nmol). These doses of (S)-4CPG did not alter the seizure threshold in chronically vehicle-treated (control) mice. Pretreatment i.c.v. with a presynaptic mGlu receptor agonist (the group 2 mGlu receptor agonist (2S,1'S,2'S)-2-(carboxycyclopropyl)-glycine (L-CCG-I: 3.0 and 5.6 nmol) and the group 3 mGlu receptor agonist, L-amino-4-phosphonobutyric acid (L-AP4: 3.0 and 5.6 nmol)) failed to suppress the decrease in seizure threshold in diazepam-withdrawn mice, but increased the seizure threshold in control mice. Pretreatment i.c.v. with the group 1 mGlu receptor antagonist/group 2 mGlu receptor agonist, (S)-4-carboxy-3-hydroxyphenylglycine ((S)-4C3HPG: 56 and 100 nmol), significantly increased the seizure threshold in control mice and suppressed the decrease in seizure threshold in diazepam-withdrawn mice. These findings suggest that enhancement of group 1 mGlu receptor function and a decline in both group 2 and group 3 mGlu receptor functions may play an important role in the hypersusceptibility to pentylenetetrazole-induced seizure during diazepam withdrawal.

Structure of the type B human natriuretic peptide receptor gene and association of a novel microsatellite polymorphism with essential hypertension

The natriuretic peptide (NP) system may play a crucial role in development of essential hypertension (EH). C-type NP dilates arteries and lowers blood pressure and inhibits proliferation of vascular smooth muscle cells via the type B NP receptor (NPR-B). However, the association of the human NPR-B gene with EH has not been studied, because little is known about the genomic organization of this gene. We designed oligonucleotide primers based on the cDNA sequence of the human NPR-B gene, and long-range polymerase chain reaction (PCR) was performed. The amplified fragments were sequenced directly, and the exon/intron organization of the human NPR-B gene was determined. The gene, which spans approximately 16.5 kbp, is composed of 22 exons, and the intron-exon junctions follow the GT-AG rule. Seven hundred fifty base pairs of the 5'-flanking region were sequenced using a thermal asymmetric interlaced-PCR (TAIL-PCR) method. This region contains 10 potential Sp1 binding sites and lacks a TATA box. Rapid amplification of cDNA ends (RACE) revealed the transcriptional start site at -14 bp. A CA/GT microsatellite repeat was identified with a hybridization-based method and was converted to a sequence-tagged site (STS). The GT microsatellite repeat was localized to intron 2 approximately 150 bp downstream of the exon-intron junction. Two alleles, (GT)10 and (GT)11, were detected in both EH patients and age-matched normotensive (NT) controls. Multiple logistic linear regression analysis indicated that the NPR-B genotype is associated significantly with EH (odds ratio 1.55; 95% confidence interval, 1.02 to 2.35). The (GT)11 frequency was 0.316 (65/206) for the EH group and 0.218 (44/202) for the NT group and differed significantly between the EH and NT groups (chi2=4.97, P=0.026). The structural organization of the human NPR-B gene was determined, and a novel GT repeat polymorphism, which associated with EH, was identified. These results suggest that one cause of EH is a mutation in this gene or a closely related gene or region.

Nitric oxide synthase gene polymorphism and its influence on cardiovascular disease

Several lines of evidence indicate a significant association between variations of the endothelial constitutive nitric oxide synthase gene and the incidence of cardiovascular disease, and discrepant findings may be attributable to racial differences. The detection of functional allelic polymorphisms may be needed to confirm this association, because direct evidence to support a causative role for the endothelial constitutive nitric oxide synthase gene is not yet available. There are no available data to confirm that neural and inducible nitric oxide synthases are associated with cardiovascular diseases.

Bunazosin hydrochloride inhibits exaggerated growth of vascular smooth muscle cells from spontaneously hypertensive rats by suppressing the response to growth factors

Selective alpha1-adrenoreceptor blockers were recently reported to have an in vivo antiproliferative effect on hypertensive cardiovascular organs. Cultured vascular smooth-muscle cells (VSMCs) from spontaneously hypertensive rats (SHRs) show exaggerated growth compared with cells from Wistar-Kyoto (WKY) rats. We investigated the effects of an alpha1-adrenoreceptor blocker, bunazosin hydrochloride (HCl), on the growth of VSMCs from SHRs. In the absence of serum, bunazosin HCl significantly inhibited basal DNA synthesis by VSMCs from SHRs, but not by cells from WKY rats. In the presence of serum, bunazosin HCl significantly inhibited DNA synthesis by VSMCs from both rat strains. Angiotensin (Ang) II, platelet-derived growth factor (PDGF)-AA, and epidermal growth factor (EGF) dose-dependently increased DNA synthesis by VSMCs from SHRs, but not by VSMCs from WKY rats. Bunazosin HCl significantly suppressed the response of DNA synthesis to PDGF-AA and EGF, but not to Ang II, in VSMCs from SHRs. Expression of basic fibroblast growth factor (bFGF), transforming growth factor-beta1 (TGFbeta1), and PDGF messenger RNA (mRNA) was markedly greater in VSMCs from SHRs than in cells from WKY rats. Bunazosin HCl significantly inhibited the expression of bFGF and TGFbeta1 mRNA in VSMCs from SHRs, but not in cells from WKY rats. These findings suggest that the inhibition of growth factor hyperresponsiveness and inhibition of the expression of growth factors in VSMCs from SHRs are associated with the antiproliferative effect of bunazosin.

A T1083C polymorphism in the human adenosine A2a receptor gene is not associated with essential hypertension

The adenosine A2a receptor (A2aAR) gene is thought to be involved in essential hypertension because adenosine elicits vasodilation and decreases arterial blood pressure via this receptor, and because disruption of the A2aAR gene increases blood pressure in mice. Therefore, using a restriction fragment length polymorphism (RFLP) of the A2aAR gene, we performed an association study in patients with essential hypertension. One hundred forty-two patients with essential hypertension and 142 age-matched subjects with normal blood pressure were studied. Polymerase chain reaction (PCR) was applied to amplify the T1083C polymorphic site in the A2aAR gene, and restriction analysis of the PCR product was employed to score the T and C alleles. Overall distributions of allele frequencies in the two groups were not significantly different. Thus, the alleles detected by this RFLP polymorphism in the A2aAR gene are not associated with essential hypertension.

Effects of oral and transdermal hormone replacement therapy on lipoprotein(A) and lipids: a randomized controlled trial

OBJECTIVE

Our purpose was to compare the effect of oral and transdermal hormone replacement therapy on lipoprotein(a) and other plasma lipids in healthy postmenopausal women.

DESIGN

A total of 120 postmenopausal women were enrolled in a prospective randomized controlled study, and allocated either to transdermal 17 beta-estradiol (50 micrograms/day) or to oral conjugated estrogen (0.625 mg/day). Forty-one age-matched women were used as the reference group. Plasma lipids and lipoproteins were determined every 3 months and differences were sought by statistical analysis.

RESULTS

Plasma lipoprotein(a) dropped after 3 months of treatment either with transdermal estradiol (p < 0.01) or oral estrogen (p < 0.01). Lipoprotein(a) was reduced by 12% and 22%, respectively. No further decreases were seen later on. Plasma total and low-density lipoprotein (LDL) cholesterol concentrations were decreased significantly with both treatments after 3 months of therapy. No difference was seen in the lowering effect on lipoprotein(a), LDL and total cholesterol concentrations between regimens. Plasma high-density lipoprotein (HDL) cholesterol and triglyceride concentrations increased throughout the study only in patients treated with oral estrogen.

CONCLUSIONS

These data demonstrate that hormone replacement therapy reduces the concentration of lipoprotein(a) when given both orally and transdermally. The lowering effect is achieved quickly because the maximal effect is observed after 3 months of therapy.

Hypoxia and endothelin-1 induce VEGF production in human vascular smooth muscle cells

Vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) is a secreted mitogen for vascular endothelial cells, and it promotes vascular permeability and neovascularization in vivo. We investigated the mechanisms by which low oxygen tension modulates the expression of VEGF in human aortic vascular smooth muscle cells (h-SMC) in vitro. Moreover, we measured VEGF levels in the cultured medium with or without endothelin-1 (ET-1) using a newly developed, highly sensitive, enzyme-linked immunosorbent assay. Hypoxia resulted in a substantial induction of VEGF transcripts at 3 and 24 hr. VEGF levels were significantly higher when h-SMC were cultured in medium containing ET-1 than when cultured in medium without ET-1. In conclusion, hypoxia and ET-1 constitute potent stimuli for VEGF production in h-SMC.

Omega-3 polyunsaturated fatty acids--modulation of voltage-dependent L-type Ca2+ current in guinea-pig tracheal smooth muscle cells

Omega-3 polyunsaturated fatty acids have been reported to be associated with favorable changes in the respiratory system. To determine one of the mechanisms for this effect, membrane currents were recorded in guinea-pig tracheal myocytes by using the whole-cell voltage clamp technique. Without EGTA in the patch pipette containing the Cs-internal solution, command voltage pulses positive to +0 mV from a holding potential of -60 mV elicited a voltage-dependent L-type Ca2+ current (I(Ca x L)) and a subsequent outward current. Upon repolarization, slowly decaying inward tail currents were recorded. The outward currents and the inward tail current were enhanced by methyl-1,4,-dihydro-2,6-dimethyl-3-nitro-4-(2-trigluromethylphenyl )-pyridine-5-carboxylate, and blocked by Cd2+ or nifedipine. Inclusion of EGTA (5 mM) in the patch pipette also abolished these currents, indicating that they were Ca2+-dependent. When [Cl-]o or [Cl-]i was changed, the reversal potential of these currents shifted, thus behaving like a Cl(-)-sensitive ion channel. 4,4'-Diisothiocyanatostilbene-2,2'-disulphonic acid. a Cl- channel blocker, inhibited the currents. The omega-3 polyunsaturated fatty acids eicosapentaenoic acid (3-30 microM) and docosahexaenoic acid (30 microM) suppressed I(Ca x L) and then inhibited I(Ca x Cl) in a reversible manner. Similar inhibitory effects of eicosapentaenoic acid on I(Ca x L) were observed with 5 mM EGTA in the patch pipette. Neurokinin A (1 microM) and caffeine (10 mM) also transiently activated I(Cl x Ca), probably due to Ca2+ release from Ca2+ storage sites. Pretreatment of the cells with eicosapentaenoic acid markedly suppressed the activation of I(Cl x Ca) by neurokinin A or caffeine. These results suggest that omega-3 polyunsaturated fatty acids inhibit voltage-dependent L-type Ca2+ currents and also Ca2+-activated Cl- currents in tracheal smooth muscle cells from the guinea-pig, which may play a role in modulation of tracheal smooth muscle tone.

Field studies on imposex and organotin accumulation in the rock shell, Thais clavigera, from the Seto Inland Sea and the Sanriku region, Japan

Field studies on imposex and organotin (butyltin and phenyltin) contamination in the Japanese molluscs (the rock shell, Thais clavigera, and the Pacific oyster, Crassostrea gigas) were conducted along the coast of both the Seto Inland Sea and the Sanriku region, Japan, during February-March 1996. The percentage occurrence of imposex in the rock shell, Thais clavigera, was still 100% at all sites surveyed (22 and seven sites in the Seto Inland Sea and the Sanriku regions, respectively). Observed values of the Relative Penis Length (RPL) index (%), defined as the ratio of mean penis length in females to that in males, exceeded 50 at many sites. Sterile individuals whose oviducts were blocked by vas deferens formation were also extensively observed. Tissue concentrations of organotin compounds in the rock shell and the Pacific oyster were higher than those from other areas of Japan. The degree of imposex (RPL index) was correlated with the sum of TBT and TPT concentrations in tissue of the rock shell. Less recovery from imposex in the rock shell and less amelioration of TBT pollution were observed, suggesting that organotin use in antifouling paints has still continued for vessels larger than 25 m in length and that it has influenced imposex symptoms in the rock shell.

Production of eicosanoids and angiotensin II in resistance vessels in spontaneously hypertensive rats

1. Angiotensin II (AngII) and eicosanoids may be important in vascular remodelling and the pressor response via autocrine and paracrine mechanisms. We evaluated the influences of ageing and beta-adrenoceptor stimulation on the production of vascular AngII and eicosanoids in male spontaneously hypertensive rats (SHR), aged 5, 17 and 30 weeks, and age-matched Wistar-Kyoto (WKY) rats. 2. All rats were weighed and their systolic blood pressure (SBP) was measured by the tail-cuff method. Mesenteric arteries were isolated and perfused with Krebs'-Henseleit solution. The outflows of prostaglandin E2 (PGE2), 6-keto-PGF1 alpha, thromboxane B2 (TxB2) and AngII were measured by specific radioimmunoassays. 3. The SBP was higher in SHR than in WKY rats in the 17- and 30-week-old groups and increased with age. Basal levels of PGE2 were significantly lower in SHR than in WKY rats. The ratios of 6-keto-PGF1 alpha to TxB2 and PGE2 to TxB2 were significantly lower in 17-week-old SHR compared with age-matched WKY rats. Basal AngII release did not differ between SHR and WKY rats and decreased with age. Isoproterenol stimulated the release of AngII; the magnitude of the increment was greater in WKY rats than in age-matched SHR. These results show that there is an imbalance in the production of vasodilator and vasoconstrictor eicosanoids in the resistance vessels of SHR at ages at which hypertension developed. 4. This imbalance may contribute to the increased vasoconstrictor response and vascular remodelling in SHR. Our findings suggest that vascular AngII plays a role in the ageing process and that beta-adrenoceptor-stimulated release of vascular AngII is impaired in SHR.

Organization of the human natriuretic peptide receptor A gene

We have determined the structural organization of the human natriuretic peptide receptor A (hNPRA) gene without screening the genomic library. Based on the information for the cDNA of hNPRA, we amplified some fragments of the long polymerase chain reaction (PCR) products covering all genomic sequences of the gene and directly sequenced the products after extraction and purification. The hNPRA gene spans approximately 16 kb and contains 22 exons and 21 introns. All of the exon-intron junction sequences coincide with the GT/AG consensus sequence. The sequence encoding the transmembrane domain, one part of the hNPRA topological structure, exists in exon 7. The results of this first study, determination of the hNPRA gene structure, will facilitate further genetic analysis of the hNPRA gene and its related diseases.

Influence of cellular incorporation of n-3 eicosapentaenoic acid on intracellular Ca2+ concentration and membrane potential in vascular smooth muscle cells

Long-term treatment with n-3 eicosapentaenoic acid (EPA) has been shown to exert hypotensive effects and have beneficial effects on atherosclerosis. To elucidate one of the underlying mechanisms of these effects, intracellular calcium concentration [Ca2+]i, and resting membrane potential were measured in rat vascular smooth muscle cells (A7r5 cell) treated with EPA, using Ca2+-sensitive dye fura-2 AM and the patch clamp technique. The alterations in fatty acid compositions of phospholipids and cell migration after treatment with EPA (30 microM) for 6 h-7 days were also examined. After treating cells with EPA, the EPA and DPA (docosapentaenoic acid) content of the phospholipid fraction (mol.%) increased in a time-dependent manner. Alternatively, arachidonic acid (AA) decreased, and then the ratio of EPA and AA (EPA/AA) increased significantly. The resting [Ca2+]i decreased from 170 +/- 46 nM (n = 16) in control cells to 123 +/- 29 nM (n = 16) in cells treated with EPA (30 microM) for 7 days. Vasopressin (100 nM), endothelin-1 (100 nM) and platelet-derived growth factor (PDGF 5 ng/ml) evoked an initial peak of [Ca2+]i, followed by a smaller sustained rise of [Ca2+]i in the presence of extracellular Ca2+. In EPA-treated cells, both the peak and the sustained rise of [Ca2+]i induced by these agonists decreased in comparison to the control cells. EPA treatment also decreased the transient [Ca2+]i rise evoked by these agonists in the absence of extracellular Ca2+. Under the current clamp condition, resting membrane potential was significantly higher in EPA-treated cells (-49.8 +/- 10.4 mV, n = 41) than in control cells (-44.6 +/- 7.4 mV, n = 41, P < 0.05), and the input resistance of the cell was lower in EPA-treated cells, while cell size and capacitance were not statistically different. In addition, long-term treatment with EPA for 7 days significantly inhibited PDGF-induced cell migration. These results suggest that cellular incorporation of n-3 eicosapentaenoic acid attenuates intracellular mechanisms related to changes of [Ca2+]i and affects membrane potential, thereby inhibiting migration of vascular smooth muscle cells. These actions of EPA may contribute to its vasorelaxant and antiatherosclerotic effects.

Abnormal regulation of transforming growth factor-beta receptors on vascular smooth muscle cells from spontaneously hypertensive rats by angiotensin II

The effects of angiotensin II (Ang II) on the expression and characteristics of transforming growth factor-beta (TGF-beta) receptors on vascular smooth muscle cells (VSMC) from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) were investigated. TGF-beta-induced stimulation of DNA synthesis by VSMC from WKY rats was abolished with Ang II, whereas basal and TGF-beta-stimulated DNA synthesis by VSMC from SHR was increased with Ang II. Ang II stimulated DNA synthesis by VSMC from WKY rats in the presence but not in the absence of neutralizing antibody to TGF-beta1. Antibody to TGF-beta1 enhanced the stimulatory effect of Ang II on DNA synthesis by VSMC from SHR. Ang II increased the specific binding of TGF-beta to VSMC from WKY rats by increasing both the expression of the lower-affinity of TGF-beta receptors as well as the total number of TGF-beta binding sites. In contrast, VSMC from SHR showed a higher affinity and number of TGF-beta receptors in the absence of Ang II than did cells from WKY rats, and these parameters were not affected by Ang II. Ang II increased the expression of TGF-beta type I receptor mRNA in VSMC from WKY rats but had no effect of TGF-beta receptor type I or II mRNA in VSMC from SHR, which predominantly express the type II receptor. These results indicate that an increase in the expression of the TGF-beta type I receptor by Ang II may facilitate the ability of endogenous TGF-beta to counteract the stimulatory effect of Ang II on growth in VSMC from WKY rats, whereas endogenous TGF-beta induced by Ang II cannot counteract the growth-promoting action of Ang II in VSMC from SHR. The abnormal regulation of TGF-beta receptors by Ang II may be associated with the exaggerated growth of VSMC from SHR.

Association of a variable number of tandem repeats in the endothelial constitutive nitric oxide synthase gene with essential hypertension in Japanese

An impaired synthesis of nitric oxide (NO) by the vascular endothelium has been implicated in the pathogenesis of essential hypertension (EH). The possible association between a variable number of tandem repeats (VNTR) polymorphism in intron 4 of the endothelial constitutive NO synthase (ecNOS) gene and EH in Japanese subjects was investigated. A total of 123 individuals with EH and 120 normotensive control subjects were studied. The VNTR region of the ecNOS gene was amplified by the polymerase chain reaction to determine the number of repeats, and the allele frequencies were compared between the hypertensive and normotensive groups. Two alleles, containing four and five repeats, were identified. The overall distributions of allele frequencies differed significantly between the two groups, with the four-repeat allele more frequent in the EH group than in the normotensive group (P = .00027, odds ratio = 4.0). The four-repeat allele of the ecNOS gene was thus associated with EH and may be a genetic marker of this disease in Japanese subjects.

Adrenal renin-angiotensin-aldosterone system in streptozotocin-diabetic rats

Previous studies have indicated that the local renin-angiotensin system (RAS) plays an important role in the regulation of aldosterone release. We focused this study on examining the dissociating changes in circulating RAS and adrenal RAS, and we produced a low plasma renin status in streptozotocin (STZ)-induced diabetic rats. Four and six weeks after treatment with STZ, the rats showed hyperglycemia, hyporeninemia, decrease in plasma angiotensin II (AII), and a slight, but non-significant increase in plasma aldosterone in the rats. The adrenal renin activity and aldosterone concentration were significantly increased in the group of rats six weeks after induction of diabetes compared to those in control rats. The group of rats four weeks after induction of diabetes showed an increase in adrenal aldosterone concentration and a slight, but non-significant increase in adrenal renin activity. Plasma ACTH, serum sodium, and potassium were unchanged in both treatment groups compared to the control. The present results indicate that hyperactivity or residual activity of adrenal RAS under hyporeninemia is associated with severe diabetes mellitus.

Sequences of exon 6 and the adjacent intron boundaries of the rat platelet-derived growth factor A-chain gene: implications for alternative splicing

Platelet-derived growth factor (PDGF) is a potent stimulator of vascular smooth muscle cell growth. Two isoforms of PDGF A-chain mRNA that either include (long form) or exclude (short form) exon 6 are produced as a result of alternative splicing in mouse, rabbit, and human. The short form of PDGF A-chain is expressed in both resting and activated cells, while the long form is present predominantly in activated cells. Reverse transcription-polymerase chain reaction analysis with primers encompassing exon 6 revealed the presence of both long- and short-form PDGF A-chain transcripts in rat vascular smooth muscle cells. The nucleotide sequences of exon 6 and its intron boundaries were determined from rat vascular smooth muscle cell cDNA and rat leukocyte genomic DNA. Translation of the long form of PDGF A-chain mRNA was shown to terminate in the 70-base pair exon 6. Conserved sequences that may contribute to the regulation of alternative RNA splicing were identified in intron 5.

Omega-3 polyunsaturated fatty acids inhibit migration of human vascular smooth muscle cells in vitro

Arterial smooth muscle cell migration from the media to the intima is a crucial process in the pathogenesis of atherosclerosis. Platelet-derived growth factor (PDGF) has been proposed to play a key role in the development of advanced atherosclerotic lesions by stimulating the migration and proliferation of vascular smooth muscle cells. Polyunsaturated fatty acids (PUFA) of the omega-3 series, extracted from fish oil has been shown to have beneficial effects on atherosclerosis. In this study, we evaluated the effects of omega-3 PUFA on the migration of human aortic smooth muscle cell (hASMC) in vitro. The migration assay was performed according to the Capsoni's method using transwell culture plates. PDGF, fibrinogen or 10% FCS significantly stimulated hASMC migration, however, omega-3 PUFA significantly inhibited PDGF-induced migration of hASMC. These results suggest that the inhibitory effect of omega-3 PUFA on cell migration may be an important aspect by which omega-3 PUFA exerts its antiatherosclerotic influence.

VEGF gene transfer reduces intimal thickening via increased production of nitric oxide in carotid arteries

Thickening of the arterial intima and smooth muscle cell (SMC) proliferation remain major problems after vascular surgery and other types of vascular manipulations. We studied the effect of endothelial cell (EC)-specific vascular endothelial growth factor (VEGF) gene transfer on the thickening of the intima using a silicone collar inserted around carotid arteries that acted both as the agent that caused intimal SMC growth and as a reservoir for the transfected gene. The model preserved EC integrity and permitted direct extravascular gene transfer without any intravascular manipulation. Compared to beta-galactosidase (lacZ)-transfected control arteries, plasmid/liposome-mediated VEGF gene transfer significantly reduced intimal thickening 1 week after the gene transfer. Administration to the experimental animals of the nitric oxide (NO) synthase inhibitor L-NAME abolished the difference in intimal thickening between VEGF and lacZ-transfected arteries. Furthermore, VEGF caused NO release from cultured human umbilical vein EC. It is concluded that extravascular VEGF gene transfer attenuates intimal growth and could be useful for the prevention of intimal thickening during vascular surgery. Our results further suggest that VEGF may reduce SMC proliferation via a mechanism that involves VEGF-induced NO production from the endothelium.

Antisense oligodeoxynucleotide complementary to platelet-derived growth factor A-chain messenger RNA inhibits the arterial proliferation in spontaneously hypertensive rats without altering their blood pressures

OBJECTIVE

To evaluate the effects of the antisense oligodeoxynucleotide (ODN) to platelet-derived growth factor (PDGF) A-chain messenger RNA (mRNA) on the growth of cardiovascular organs in hypertension.

DESIGN

15-Mer antisense ODN complementary to the initiation codon region of rat PDGF-A chain mRNA and non-sense ODN of identical proportion but with a random order of bases relative to that of antisense ODN were synthesized with a DNA synthesizer.

METHODS

We examined the effects of the antisense ODN on the growth of vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats, and on the expression of PDGF A-chain mRNA by reverse transcription and polymerase chain reaction and PDGF A-chain protein by Western blot analysis in vitro. We evaluated the distribution of 32P-labeled antisense ODN and examined the effects of the antisense ODN on the growth of cardiovascular organs in vivo.

RESULTS

The antisense ODN reduced the basal DNA synthesis of VSMC from SHR significantly, but did not do so in cells from Wistar-Kyoto rats. Mutations in the antisense ODN sequence reduced the ODN-induced inhibition of DNA synthesis. Addition of serum or transforming growth factor-beta 1 increased the DNA synthesis in the SHR-derived VSMC that was inhibited by the antisense ODN. The antisense ODN inhibited the production of PDGF A-chain protein, but not of the PDGF A-chain mRNA. The injection of 32P-antisense ODN in vivo led to a greater accumulation of radioactivity in the aorta than in other organs. Infusion of antisense ODN for 28 days did not alter the systolic blood pressure appreciably in rats of either strain. However, in SHR, it reduced markedly the elevated DNA content, [3H]-thymidine uptake, and incorporation of [3H]-thymidine into aortic DNA, and suppressed the production of aortic PDGF A-chain protein. These results indicated that the PDGF A-chain is involved in the exaggerated growth of VSMC from SHR by which inhibition of the translation of PDGF A-chain mRNA to the protein with antisense ODN occurs in vitro, and that antisense ODN to PDGF A-chain suppresses the exaggerated arterial proliferation in SHR without altering the high blood pressure in vivo.

CONCLUSION

These results imply that inhibition of the final responsible growth factor PDGF A-chain by antisense ODN can suppress the arterial proliferation in hypertension without altering the blood pressure, suggesting that the arterial proliferation in hypertension is independent of the high blood pressure in part, and that antisense therapy could be feasible for treating hypertension.