Elevated 12-Lipoxygenase Activity in the Spontaneously Hypertensive Rat

We have previously demonstrated that administration of inhibitors of the lipoxygenase (LO) pathway of arachidonic acid metabolism lowers blood pressure in hypertensive rats. In addition, we have shown that LO inhibition attenuates pressor agonist-induced vascular reactivity in vitro and calcium mobilization in cultured vascular smooth muscle cells (VSMC). To further elucidate the relationship between elevated LO activity and hypertension, 4, 8, and 12 week old hypertensive SHR were compared with age-matched Wistar-Kyoto (WKY) rats for plasma 12(S)-hydroxyeicosatetraenoic acid (12-HETE) concentration. 12-HETE levels were significantly elevated in the SHR compared to the WKY (SHR elevated by 154%, 159%, and 272% compared to WKY at 4, 8, and 12 weeks, respectively, P < .01 for all ages). There were no differences in plasma potassium levels between SHR and WKY at any of the ages tested. Plasma aldosterone levels and plasma renin activity were in the normal range at the three ages. At 12 weeks of age, both serum (4.72 ± 0.23 v 2.18 ± 0.33 μg/mL, P < .01), and aortic smooth muscle 12-HETE levels (0.94 ± 0.09 v 0.66 ± 0.08 μg/mg protein, P < .05) were elevated in SHR compared with WKY. The 12 week old SHR were given a bolus of the LO inhibitor 5,8,11-eicosatriynoic acid (ETI, 7 mg/kg, intravenously) and blood pressure measured after 20 min. ETI reduced mean systolic blood pressure from 175.8 ± 4.2 to 141.6 ± 5.9 mm Hg (P < .05). To investigate these effects of HETEs, cultured vascular smooth muscle cells were pretreated for 1 min with 12(S)HETE and then challenged with angiotensin II (AngII). The addition of 12(S)HETE increased AngII-induced intracellular calcium levels in normal cultured rat vascular smooth muscle cells by 78% compared to vehicle (P < .05). Thus, LO products, which are high in SHR, may contribute to vascular tone through alterations in the intracellular calcium signal by potentiating calcium responses to pressors such as Ang II.     

Effect of Insulin on Norepinephrine Overflow at Peripheral Sympathetic Nerve Endings in Young Spontaneously Hypertensive Rats

To determine how the effect of insulin is related to the development of salt-induced hypertension, and whether a hyporesponse to insulin exists in the peripheral sympathetic nerves of a hypertensive model rat, we measured norepinephrine overflow from the periarterial nerve of isolated mesenteric arteries exposed to insulin in spontaneously hypertensive rats (SHR) as well as Wistar-Kyoto rats (WKY) fed diets that were high and low in salt. Salt loading (diet containing 8% salt for 4 weeks) accelerated the development of hypertension in young, spontaneously hypertensive rats (SHR) (157 ± 5 mm Hg υ 198 ± 4 mm Hg, P < .01) but did not affect the blood pressure of Wistar-Kyoto rats (WKY) (102 ± 7 mm Hg υ 104 ± 6 mm Hg, P = NS). Basal norepinephrine overflow did not differ in the SHR and WKY rats, but the overflow of norepinephrine after periarterial electrical stimulation (8 Hz 1 min.) was significantly greater in SHR (0.806 ± 0.079 ng/g) than in WKY (0.723 ± 0.022 ng/g P < .01). Although insulin reduced the norepinephrine overflow by periarterial nerve stimulation in both WKY and SHR, the decrease with insulin was significantly greater in the SHR than in WKY (−18.4% ± 4.0% υ −32.0% ± 4.6%, P < .05). The inhibitory effect of insulin on norepinephrine overflow was reduced by salt loading in SHR (−8.8% ± 4.0%, P < .05), but not in WKY (−32.5% ± 4.7%, P = NS). Cocaine and ouabain completely blocked the effect of insulin in all four groups. In contrast to insulin, direct stimulation of Na⁺-K⁺ ATPase with a high-potassium buffer (12 mmol/L) reduced NE overflow to the same extent among the four groups. These findings show that SHR have a blunted response to the suppression by insulin of norepinephrine overflow. Salt loading reduced the insulin response at peripheral sympathetic nerves of young SHR, but did not affect that of age-matched WKY. Thus, hyporeactivity to insulin may play a role in the development of salt-induced hypertension in young SHR, possibly through a reduced suppression of norepinephrine overflow from sympathetic nerve endings. Am J Hypertens 1996;9:1119–1125     

Endothelin-1 released by vascular smooth muscle cells enhances vascular responsiveness of rat mesenteric arterial bed exposed to high perfusion flow

Vasodilation of resistance vessels ensues in response to increased perfusion flow to maintain tissue perfusion. The flow-induced vasodilation is mainly dependent on nitric oxide (NO), which also regulates vascular responsiveness to vasoconstrictors. Besides NO, however, high flow increases endothelin-1 (ET-1) production from endothelial cells. It is likely, therefore, that the interaction between NO and ET-1 may play a critical role in the control of arterial vascular tone under high perfusion flow.In this study, the vascular responsiveness (VR) to high flow rate and the role of ET-1 released by vascular smooth muscle cells (VSMC) were evaluated in isolated and in vitro-perfused mesenteric arteries (MA). MA were perfused at constant (3.5 mL/min; CPF) and increased flow rate (4.5, 5.5, 6.5 mL/min; IPF). VR was evaluated by infusing norepinephrine (NE; 5 μmol/L) and potassium chloride (KCl; 80 mmol/L). Mesenteric vascular resistance (MVR), ET-1, and cGMP release were measured under different flow rates. The role of endothelium-derived ET-1 was evaluated by perfusing MA with phosphoramidon (endothelin converting enzyme inhibitor), whereas the role of other endothelium-derived vasoactive substances was excluded by measuring VR in MA without endothelium. Finally, ETA and ETB receptor antagonists were perfused in disendothelized MA. In the IPF group of intact MA, MVR dropped (P < .05) and both ET-1 and cGMP increased in the perfusate (P < .05). VR was enhanced by high flow after NE (101 ± 9 v 56 ± 12 mm Hg in CPF, P < .005) and KCl (119 ± 12 v 51 ± 10 mm Hg in CPF, P < .005) and it was unaffected by either phosphoramidon or endothelium removal. On the contrary, BQ-610 abolished the flow-dependent increase in VR. No further additive effect was achieved with BQ-788. In conclusion, in MA, high flow reduces MVR and concurrently enhances VR, likely through VSMC-derived ET-1.     

Quinapril Inhibits c-Myc Expression and Normalizes Smooth Muscle Cell Proliferation in Spontaneously Hypertensive Rats

A number of data suggest that angiotensin II-dependent activation of the protooncogene c-myc participates in the proliferative response of smooth muscle cells (SMC) of rats with spontaneous hypertension (SHR). We therefore investigated the effects of chronic treatment with the angiotensin converting enzyme (ACE) inhibitor quinapril on the oncoprotein c-Myc and the proliferating cell nuclear antigen cyclin A in SMC of small intramyocardial arteries from the left ventricle of SHR. The expression of c-Myc and cyclin A was assessed by immunocytochemical analysis. The number of smooth muscle cells was assessed by morphometrical analysis. As compared to normotensive Wistar-Kyoto (WKY) rats, untreated SHR exhibited an increased percentages of cells expressing c-Myc (33% ± 4% v 19% ± 2%, mean ± SEM, P < .005) and cyclin A (25 ± 2 v 11% ± 1%, P < .001). In quinapril-treated SHR compared with untreated SHR, we found decreased expression of c-Myc (22% ± 2%, P < .005) and cyclin A (13% ± 1%, P < .001). No significant differences were found between WKY rats and quinapril-treated SHR in the above parameters. Cyclin A was directly correlated with the number of SMCs in each group of rats. These results suggest that an enhanced expression of c-Myc may be involved in the increased proliferation seen in SMCs from small arteries of SHR. Quinapril administration normalizes proliferation in the SMCs of SHR, possibly by inhibiting the expression of the oncoprotein c-Myc and its effects on the cell cycle.     

Comparison of K+ channel properties in freshly isolated myocytes from thoracic aorta of WKY and SHR

Altered function of smooth muscle cell K⁺ channels have been reported in hypertension, but the contribution of various K⁺ channel types to these changes has not been completely determined. The purpose of this study was to compare the contribution of K⁺ channel types to whole cell K⁺ currents recorded from isolated thoracic aorta myocytes of 13 to 15 week old Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Cells were isolated by collagenase and elastase digestion, and K⁺ currents recorded using whole cell voltage clamp methods at room temperature. Cells were superfused with a solution containing (in mmol/L) 140 NaCl, 5 KCl, 2 CaCl₂, 1 MgCl₂, 10 HEPES, and 10 glucose. Pipettes were filled with a solution containing (in mmol/L) 120 KCl, 5 NaCl, 5 MgATP, 20 HEPES, and 10 BAPTA. The K⁺ currents (I_K) recorded from a holding potential (HP) of −80 mV were smaller in the SHR compared to those in WKY (for example, at 20 mV: WKY = 6.1 ± 0.6 pA/pF and SHR = 3.7 ± 0.2 pA/pF). Values of cell capacitance were not different between the two groups (WKY = 25.2 ± 3.2 pF and SHR = 26.6 ± 1.9 pF). A component of I_K inhibited by voltage (K_v) over the range from −80 to −20 mV was smaller in SHR. The voltage dependence of K_v availability and activation were not significantly different between the two groups. I_K recorded from a HP = −20 mV (K_Ca) was not different between the two groups. Difference currents calculated from I_K measured at HP of −80 and −20 mV (that is, K_v) were smaller in SHR as was the fraction of I_K inhibited by 4-aminopyridine. These results suggest that under conditions of low intracellular [Ca²⁺] there are no differences in K_Ca currents, but the K_v currents are smaller in SHR. Inhibition of K_v by 4-aminopyridine (0.1 to 10 mmol/L) caused larger increases in basal tone in WKY aorta. These results suggest that K_v channels contribute to resting K⁺ conductance in both WKY and SHR aorta, but with a relatively larger contribution in the WKY.     

Intracellular Mg++ concentrations in smooth and striated muscle cells in spontaneously hypertensive rats

Decreased intracellular Mg⁺⁺ concentrations seem to be involved in the pathogenesis of primary hypertension. Of special interest is the smooth muscle cell with its electrolyte metabolism in primary hypertension, but also heart muscle cells and their Mg⁺⁺ concentrations are of growing interest. Therefore, in aortic smooth muscle cells and striated heart muscle cells (left ventricle) from 20 spontaneously hypertensive rats (SHR) of the Münster strain and 20 normotensive Wistar-Kyoto rats (WKY), the intracellular Mg⁺⁺ content was measured. The electron probe x-ray microanalysis technique was used to determine intracellular Mg⁺⁺ concentrations under nearly in vivo conditions in aortic cryosections 3 μm thick and striated heart muscle cells 4 μm thick (Camscan CS 24 apparatus). Vascular smooth muscle Mg⁺⁺ content was 36.4 ± 3.1 mmol/kg dry weight in SHR versus 48.6 ± 3.7 mmol/kg dry weight in WKY (P < .001). In striated heart muscle cell Mg⁺⁺ concentrations, there was no significant difference in SHR and WKY (79.9 ± 5.6 versus 80.3 ± 5.9 mmol/ kg dry weight). In conclusion, the present study revealed that genetic hypertension in the spontaneously hypertensive rat is accompanied by significantly decreased intracellular Mg⁺⁺ concentrations in vascular smooth muscle cells. In striated heart muscle cells, Mg⁺⁺ content was not significantly different in SHR and WKY. Mg⁺⁺ handling is different in vascular smooth muscle and striated heart muscle cells in WKY and SHR (P < .01).     

Hyperinsulinemia in glucose-tolerant women with preeclampsia A controlled study

Essential hypertension is associated with insulin resistance and hyperinsulinemia. To assess whether hyperinsulinemia is also present in hypertensive disease induced by pregnancy, we studied the plasma glucose and insulin responses to 50 g of oral glucose in 10 women with definite, severe preeclampsia but normal glucose tolerance, and compared them with the responses observed in a well-matched control group of healthy pregnant women. Fasting plasma glucose concentrations were similar in healthy and preeclamptic pregnant mothers (4.1 ± mmol/L v 4.5 ± mmol/L, respectively, P =NS). Similar plasma glucose levels were also observed after glucose ingestion (5.5.0 ± 0.3 mmol/L v 6.2 ± 0.3 mmol/L in healthy and preeclamptic women, respectively P = NS). In contrast, fasting plasma insulin concentrations in the preeclamptic women were significantly higher than in normal pregnant mothers (175 ± 29 pmol/L v 101 ± 11 pmol/L, P < .05). Postload plasma insulin concentrations were nearly fourfold higher in the preeclamptic group as compared with the control group (1162 ± 70 pmol/L v 366 ± 39 pmol/L, P < .01).We conclude that preeclampsia is associated with marked hyperinsulinemia both in the fasting state and after oral glucose ingestion, suggesting that insulin resistance may play a role in pregnancy-induced hypertension.     

Differential effect of low-dose thiazides on the renin angiotensin system in genetically hypertensive and normotensive rats

Fifty years since thiazide diuretics were introduced, they are established as first-line antihypertensive therapy. Because the thiazide dosing profile lessened, the blood pressure lowering mechanism may lie outside their diuretic properties. We evaluated this mechanism in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) by examining the effects of low-dose hydrochlorothiazide (HCTZ) administration on renin-angiotensin system components. The 7-day, 1.5 mg/kg per day HCTZ did not change systolic pressure (SBP) in WKY, but decreased SBP by 41 ± 2 mm Hg (P < .0001) in SHR, independent of increased water intake, urine output, or alterations in electrolyte excretion. HCTZ significantly increased the plasma concentrations of angiotensin I (Ang I) and angiotensin II (Ang II) in both WKY and SHR while reducing angiotensin-converting enzyme (ACE) activity and the Ang II/Ang I ratio (17.1 ± 2.9 before vs. 10.3 ± 2.9 after, P < .05) only in SHR. HCTZ increased cardiac ACE2 mRNA and activity, and neprilysin mRNA in WKY. Conversely in SHR, ACE2 activity was decreased and aside from a 75% increase in AT₁ mRNA in the HCTZ-treated SHR, the other variables remained unaltered. Measures of cardiac mas receptor mRNA showed no changes in response to treatment in both strains, although it was significantly lower in untreated SHR. These data, which document for the first time the effect of low-dose thiazide on the activity of the ACE2/Ang-(1-7)/mas receptor axis, suggest that the opposing arm of the system does not substantially contribute to the antihypertensive effect of thiazides.     

Alterations in Membrane Fatty Acid Unsaturation and Chain Length in Hypertension as Observed by 1H NMR Spectroscopy

Alterations in fatty acids of membrane phospholipids in essential hypertension may account for altered membrane ion transport, elasticity, and contractility properties of hypertensive tissues. To investigate the abnormalities in membrane fatty acids in essential hypertension, the degree of fatty acid unsaturation ([–CHCH–]/[–CH₃]), the average carbon chain length, ratio of glycerol to fatty acyl chains, ratio of phosphatidylcholine to fatty acyl chains, and the ratio of free and acylated cholesterol to fatty acyl chains in fatty acid fractions of membrane phospholipids of aorta, kidney, and heart were determined in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats by ¹H nuclear magnetic resonance (NMR) spectroscopy. The degrees of fatty acid unsaturation in the aorta and the kidney membranes were significantly lower in SHR than in WKY rats (aorta, 0.53 ± 0.01 v 0.63 ± 0.01, n = 5, P = .01; kidney, 0.70 ± 0.01 v 0.84 ± 0.03, n = 10, P = .01). No significant difference could be detected in fatty acid unsaturation in heart membranes between these two strains. For aorta, kidney, and heart membranes, the average carbon chain lengths of fatty acid fractions of membrane phospholipids were significantly shorter for SHR than for WKY rats (aorta, 15.1 ± 0.2 v 18.3 ± 0.7, n = 5, P = .02; kidney, 14.5 ± 0.2 v 16.4 ± 0.4, n = 10, P = .01; heart, 17.3 ± 0.5 v 18.8 ± 0.6, n = 10, P = .05). The lower unsaturated fatty acid content in membrane phospholipids of the aorta and the kidney, with concomitant reduction in average chain length, may arise from increased oxidation of fatty acid double bonds in hypertensive tissues and may account, in part, for the increased aortic stiffness and abnormal kidney function associated with essential hypertension. Whether the lower unsaturated fatty acid content and decreased carbon chain length of phospholipid membranes in the aorta and the kidney are a cause or a consequence of the high blood pressure, however, remains unknown.     

Peroxynitrite versusnitric oxide in early diabetes

BackgroundPeroxynitrite is a toxic compound formed during the inactivation of nitric oxide (NO) by the superoxide anion. The physiologic significance of this pathway of NO metabolism has never been documented in vivo. Because peroxynitrite provides a pathway for the inactivation of NO we postulated that peroxynitrite's correlation with physiologic parameters would be the opposite of those associated with NO, which is a vasodilator and suppresses sudomotor function. We assessed the significance of peroxynitrite by comparing its associations with blood pressure (BP) and sudomotor responses with those of NO.MethodsThirty-seven patients with type 1 diabetes enrolled in a longitudinal study of oxidative stress. Nitric oxide was assessed from nitrite and nitrate (collectively NOx) and peroxynitrite was assessed from the nitrotyrosine (nTy) content of protein.ResultsnTy was 13.3 ± 2.0 μmol/L in the control subjects and 26.8 ± 4.4 μmol/L, 26.1 ± 4.3 μmol/L, and 32.7 ± 4.3 μmol/L in the diabetic patients (P < .01) at the time of the first, second, and third evaluations, respectively. Patients with increased nitrotyrosine/tyrosine (nTy/Ty) had higher mean BP than those with low nTy/Ty (81.1 ± l.9 mm Hg v 75.5 ± 1.7 at the third evaluation, P < .025). The ratio of nTy/NOx correlated with BP at the first (P < .05), second (P < .05), and third (P < .01) evaluations. Patients with high nTy/Ty had increased sudomotor responses (5.85 ± 0.75 μL of total sweat) at the third evaluation compared to those with low nTy/Ty (3.32 ± 0.43 μL, P < .005) and normal controls (3.90 ± 0.41 μL, P < .05). The associations of nTy with BP and sudomotor responses were the opposite of those with NOx.ConclusionsThe conversion of NO oxide to peroxynitrite is physiologically significant in humans.     

Type 1A dopamine receptor expression in the heart is not altered in spontaneously hypertensive rats

We have recently demonstrated that type 1A dopamine (D_1A) receptor is expressed in the rat heart, but its function still remains unknown. In the present study, we investigated possible changes in the expression level and the distribution of the cardiac D_1A receptor in the development of left ventricular hypertrophy in spontaneously hypertensive rats/Izumo strain (SHR/Izm) at the ages of 4, 8, and 20 weeks. We examined D_1A receptor protein distribution by immunohistochemistry and gene expression by competitive polymerase chain reaction (competitive PCR). In SHR/Izm, compared with the age-matched Wistar Kyoto rats/ Izmo strain (WKY/Izm), blood pressure and heart/body weight ratio were significantly increased at 8 and 20 weeks. By immunohistochemistry, the D_1A receptor was localized in cardiomyocytes and vascular smooth muscle cells of coronary arteries, but not in interstitial fibrotic tissue. D_1A receptor distribution was not changed either by the strain or the age. Competitive PCR analysis showed that the D_1A receptor mRNA level was significantly higher at 4 weeks than at 8 and 20 weeks in both strains of rats and that there was no significant difference in D_1A receptor mRNA between SHR/Izm and WKY/Izm at any age ( 43.2 ± 10.4 attomol × 10⁻³/L v 43.1 ± 11.2 attomol × 10⁻³/L at 4 weeks, P = not significant, 3.9 ± 0.9 attomol × 10⁻³/L v 4.0 ± 1.3 attomol × 10⁻³/L at 8 weeks, P = not significant, 3.0 ± 1.2 attomol × 10⁻³/L v 1.9 ± 1.6 attomol × 10⁻³/L at 20 weeks, P = not significant). These results do not support the hypothesis that changes in D_1A receptor expression are associated with the development of left ventricular hypertrophy in SHR.     

Is Insulin Resistance in the Spontaneously Hypertensive Rat Related to Changes in Protein Kinase C in Skeletal Muscle?

The mechanism of insulin resistance in the spontaneously hypertensive rat (SHR) has not been clearly identified, but protein kinase C (PKC) has been implicated as a mechanism of insulin resistance in obesity and diabetes mellitus and in a diet-induced (fructose-fed) model of insulin resistance and hypertension. This study compared PKC enzyme activity (cytosol and particulate fractions) and expression of the muscle-specific isoform, PKC-θ (Western blotting), in red (soleus) and white (tensor fascia latae) hindlimb muscles from SHR (n = 12) and WKY (n = 12) rats. SHRs were hypertensive and insulin resistant, as shown by higher insulin (188 ± 34 v 169 ± 22 pmol/L), triglycerides (1.65 ± 0.07 v 1.38 ± 0.06 mmol/L), and nonesterified fatty acids (0.99 ± 0.05 v 0.78 ± 0.04 mmol/L) concentrations. PKC activity was significantly greater in the membrane fraction, compared with the cytosol, but there were no significant differences either in PKC activity or subcellular distribution, or expression of PKC-θ, between the two strains. Thus, insulin resistance in the SHR (in contrast to the fructose-fed dietary model of insulin resistance and hypertension) is not related to changes in PKC signaling or expression of PKC-θ in skeletal muscle.     

Morphological changes in cavernous tissue in spontaneously hypertensive rats

Erectile dysfunction has an increased prevalence in hypertensive patients and is associated with cardiovascular diseases. For many years the discussion has been polarized on whether in hypertensive patients, it is the arterial hypertension or the antihypertensive therapy that is the cause of male erectile dysfunction. The aim of our study was to determine the morphologic changes in cavernous tissue (CT) in an animal model of arterial hypertension. Male spontaneously hypertensive rats (SHR) (n = 15) and normotensive Wistar-Kyoto (WKY) rats (n = 15) were studied for 8 months. Animals were allowed to drink tap water and fed a standard rat chow ad libitum. Systolic blood pressure (SBP) was measured monthly by the tail/cuff method. At the end of the experiment all the animals were sacrificed for microscopic studies. Cavernous tissue was processed by hematoxylin and eosin, Masson’s trichrome, and monoclonal anti-α smooth muscle actin. Cavernous smooth muscle (CSM) and vascular smooth muscle (VSM) proliferation and CT fibrosis were evaluated by a semiquantitative score. SHR showed a higher proliferative score in CSM (2.7 ± 0.28 v 1.1 ± 0.07; P < .001), as well as in VSM (2.7 ± 0.25 v 1 ± 0.05; P < .001), and higher CT fibrosis score (2.8 ± 0.28 v 0.1 ± 0.07; P < .001), when compared to WKY rats. Furthermore, SHR showed a positive correlation between SBP and CSM proliferative score (r² = 0.9277), SBP and VSM proliferative score (r² = 0.8828), and SBP and CT fibrosis score (r² = 0.7775). In addition, an increase in the surrounding connective tissue at the perineurium and endoneurium of the amielinic nerves in CT was observed in the SHR group. According to these results we conclude that SHR present morphologic changes in vessels as well as in cavernous spaces of the erectile tissue that have a high positive correlation with high blood pressure. Moreover, the increase in extracellular matrix expansion seems to affect not only the interstitium but also the neural structures of the penis.     

Vasorelaxant effects of cicletanine and its (+)- and (−)-enantiomers in isolated human pulmonary arteries

The purpose of the study was to investigate, in isolated human pulmonary artery, the ability of cicletanine and its (−) and (+)-enantiomers to attenuate the endothelin-1 (Et-1) induced vasoconstriction, and to potentiate vasorelaxation (relative to plateau of the effect of Et-1) by sodium nitroprusside (SNP) and human atrial natriuretic peptide (ANP). In pulmonary artery rings, Et-1 induced a concentration-dependent vasoconstriction with median effective concentration (EC₅₀ = 26 ± 2.8 nmol/L. Pretreatment of the vessels with 100 μmol/L (±)-cicletanine reduced the effect of Et-1 (EC₅₀ = 36 ± 3.5 nmol/L; P < .01). (−)-enantiomer displayed greater capacity to antagonize the vasoconstrictor action of Et-1 (EC₅₀ = 47 ± 4.2 nmol/L) v (+)-enantiomer (EC₅₀ = 29.9 ± 6.5 nmol/L; P < .01). In arterial rings, precontracted with 10 nmol/L Et-1, ANP caused vasorelaxation (EC₅₀ = 9.7 ± 1.9 nmol/L). The relaxant effect of ANP was potentiated by 100 μmol/L of (−)-(EC₅₀ = 4.2 ± 0.6 nmol/L; P < .01), but not (+)-cicletanine (EC₅₀ = 7.6 ± 0.7 nmol/L). Sodium nitroprusside relaxed pulmonary artery rings precontracted with 10 nmol/L Et-1 (EC₅₀ = 41 ± 11 nmol/L). The effect of SNP was potentiated by 10 μmol/L (±)-cicletanine (EC₅₀ = 9.0 ± 0.7 nmol/L; P < .05). The potentiating effect of 10 μmol/L (+)-cicletanine was weaker (EC₅₀ = 7.9 ± 1.8 nmol/L) than that of (−)-enantiomer (EC₅₀ = 3.3 ± 0.54 nmol/L; P < .05). The relaxant effect of SNP was not further potentiated by 100 μmol/L (±)-cicletanine. The present results demonstrate that, cicletanine antagonizes Et-1 induced vasoconstriction in an isolated human pulmonary artery and potentiates vasorelaxation by two guanylate cyclase activators, ANP and SNP. (−)-Cicletanine displays greater vasorelaxant activity v (+)-enantiomer.     

Impact of α- Versus β-Blockers on Hypertensive Target Organ Damage: Results of a Double-Blind,Randomized, Controlled Clinical Trial

In hypertensive disease, the extent of target organ damage determines the prognosis. We conducted a 6-month, double-blind randomized study to compare the effects of an α₁-adrenoreceptor blocker (bunazosin) with those of a β₁-adrenoreceptor blocker (metoprolol) on early hypertensive target organ damage at a similar level of blood pressure reduction. The study consisted of 43 patients (29 men and 14 women) of varying ages (mean age 52 ± 9 years) with essential hypertension World Health Organization stage I–II. Both the α- and the β-blocker lowered blood pressure to a similar extent measured by 24-h blood pressure monitoring. The left ventricular mass was comparably reduced in both cohorts (α-blocker 284 ± 80 v 259 ± 67 g, P < .05, β-blocker 282 ± 74 v 254 ± 70 g, P < .05). Treatment with the α-blocker led to reduced total peripheral resistance (22.9 ± 8.0 v 19.9 ± 5.3 U, P < .05), whereas therapy with the β-blocker resulted in an elevated total peripheral resistance (25.5 ± 8.4 v 28.5 ± 9.3 U, P < .10; P < .05 for the difference in both groups). Renal plasma flow remained constant in the α-blocker treated group but decreased in the β-blocker treated group (508 ± 141 v 477 ± 134 mL/min/1.73 m², P < .05). Glomerular filtration rate as measured by inulin clearance tended to increase after treatment with the α-blocker (112 ± 20 v 115 ± 18 mL/min/1.73 m², P < .10) in accordance with a decrease of serum creatinine (1.00 ± 0.14 v 0.93 ± 0.12 mg/dL, P < .001). Plasma cholesterol and LDL cholesterol was lowered after treatment with the α-blocker (238 ± 48 v 312 ± 37 mg/dL; P < .001, and 153 ± 32 v 130 ± 25 mg/dL; P < .05) while remaining unchanged in group treated with the β-blocker. Left ventricular hypertrophy was similarily reduced with α- and with β-blockade at a comparable reduction of 24-h blood pressure. α-Blockers effected a more favorable renal and systemic hemodynamic profile than β-blockers, but only long-term prospective studies will answer the question whether these hemodynamic effects result into a better cardiovascular prognosis.     

Effect of Dietary Sodium on Insulin Sensitivity in Older,Obese, Sedentary Hypertensives

Increased dietary sodium intake has been associated with an increase in blood pressure as well as a decrease in insulin-mediated glucose disposal in young healthy adults. The purpose of this study was to determine whether dietary sodium intake is associated with changes in oral glucose tolerance, insulin sensitivity, and blood pressure in older, sedentary, overweight hypertensives. Eight older (70.0 ± 1.4 years, mean ± SEM), overweight (40.2 ± 3.1% body fat), mildly hypertensive (151 ± 8/82 ± 2 mm Hg) patients with a fasting plasma glucose < 7.8 mmol/L were studied after 2 weeks on low (3 g/day) and 2 weeks on high (10 g/day) sodium diets. To examine carbohydrate metabolism we performed a 2 h oral glucose tolerance test and a two-dose (240 and 600 pmol/m ²/min) hyperinsulinemic-euglycemic clamp at the end of each sodium diet. High sodium intake was associated with a significantly greater urinary sodium excretion (364 ± 45 mmol/day v 112 ± 21 mmol/day; P < .0001). The increase in dietary sodium from low to high did not result in significant differences in fasting plasma glucose (6.0 ± 0.2 v 5.8 ± 0.1 mmol/L, P = .20) or insulin (72.5 ± 7.8 v 69.9 ± 12.4 pmol/L, P = 0.71) levels or in the glucose (374.0 ± 50.8 v 493.2 ± 45.0 mmol/min/L, P = .12) and insulin (43,783 ± 10,278 v 44,110 ± 12,392 pmol/min/L, P = .96) areas determined during the oral glucose tolerance test. Similarly, there was no effect of dietary sodium on insulin-mediated glucose disposal at low (5.87 ± 1.02 v 5.60 ± 0.94 mg/kg LBM/min, P = .36) or high (12.15 ± 1.49 v 11.91 ± 1.49 mg/kg _LBM/min, P = .64) insulin infusion rates. Our findings suggest that, in insulin resistant hypertensives, increased dietary sodium does not affect either glucose or insulin responses during an oral glucose tolerance test or glucose disposal during a hyperinsulinemic euglycemic clamp.     

Increased Atrial Natriuretic Factor Receptor Density in Cultured Vascular Smooth Muscle Cells of the Spontaneously Hypertensive Rat: Revised

To explore the role of the atrial natriuretic factor (ANF) system in the pathophysiology of hypertension we examined the binding kinetics of synthetic ANF to cultured vascular smooth muscle cells (VSMCs) derived from the spontaneously hypertensive rat (SHR) and two normotensive controls-the Wistar Kyoto (WKY) and American Wistar (W). The number of maximal binding sites (Bmax) per cell (mean ± SEM; × 10³) were: SHR = 278.0 ± 33.0, WKY = 28.3 ± 7.1 and W = 26.6 ± 4.2. The differences between the SHR and normotensive strains were significant at p<0.001. The equilibrium dissociation constant (Kd; × 10^?9M) was higher in SHR VSMCs (0.94 ± 0.14) than in WKY (0.22 ± 0.09; p <0.01) and W (0.39 ± 0.14; p <0.02) cells. The plasma levels of the imnunoreactive ANF were higher in SHR than the normotensive controls. We suggest that the relatively greater ANF receptor density in cultured VSMCs of the SHR represents a response to the invitro environment which is relatively more deficient in ANF for VSMCs of the SHR as compared with the normotensive rats. Thus, the capacity of the SHR VSMC to regulate ANF receptor density appears to be independent of the blood pressure level.     

Modulation of human t cell responses by nitric oxide and its derivative,s-nitrosoglutathione

Objective. To examine the effects of nitric oxide (NO) and its more stable derivative, S-nitrosoglutathione (SNO-GSH), on the response of activated T lymphocytes. Methods. The effects of NO and SNO-GSH on DNA synthesis, interleukin-2 (IL-2) production, IL-2 receptor expression, and cGMP accumulation were determined in phytohemagglutinin–activated peripheral blood mononuclear cells (PBMC) and spleen T cells. Results. Nitric oxide (half-life [T_1/2] < 15 seconds) did not inhibit T cell proliferation. However, the derivative SNO-GSH (25 μM) (T_1/2 >2 hours) inhibited DNA synthesis by a mean ± SD of 65 ± 19.6% (P < 0.001) in PBMC and 75 ± 15% (P < 0.001) in spleen cells. Macrophage depletion of PBMC did not abrogate the inhibition. SNO-GSH had no effect on IL-2 production or IL-2 receptor expression. NO (25 μM) increased the cGMP content of PBMC (0.65 ± 0.15 pmoles/10⁶ cells; P < 0.04), as did SNO-GSH (25 μM) in both PBMC (3.8 ± 1; P < 0.001) and spleen T cells (5.2 ± 1.2; P < 0.001). Methylene blue and hemoglobin, which are NO inhibitors, inhibited SNO-GSH–induced cGMP accumulation (P < 0.001). Conclusion. SNO-GSH inhibits T cell DNA synthesis independently of IL-2 production and in association with cGMP accumulation via a NO-dependent mechanism. We suggest that NO and its S-nitrosothiol derivatives may act as endogenous inhibitors of T cell–mediated inflammation.     

Nitric oxide/cGMP signalling mediates the cardioprotective action of adrenomedullin in reperfused myocardium

We demonstrated previously that adrenomedullin (AM), when given during early reperfusion, limited infarct size in rat heart. The present study was undertaken to provide direct evidence of the NO-dependency of AM’s cardioprotective action by assessing NO biosynthesis and involvement of the soluble guanylyl cyclase (sGC) pathway. Perfused hearts from male CD-1 mice were subjected to 30-min left coronary occlusion and 60-min reperfusion. Infarct size was determined by tetrazolium staining. AM 10 nM was administered from 20 min after coronary occlusion until 10 min after reperfusion. Coronary effluent was analysed for NO₂ ⁻ and NO₃ ⁻, and myocardial samples were analysed for NO₂ ⁻, NO₃ ⁻, nitroso-adducts and cGMP concentration. To examine the role of NO/sGC signalling in the infarct-limiting action of AM, further hearts received the sGC inhibitor ODQ 2 μM. AM treatment stimulated NO synthesis, indicated by increased NO₂ ⁻ efflux in coronary effluent throughout reperfusion (summarised as area under curve, AM 29.2 ± 3.9 vs. control 14.4 ± 2.8 μmol min² mL⁻¹, P < 0.05). AM limited infarct size (35.4 ± 2.7 vs. 12.2 ± 2.3%, P < 0.01), associated with a 2.45-fold increase (P < 0.05) in myocardial cGMP concentration at 10 min after reperfusion. ODQ abolished the infarct size-limiting effect of AM (28.9 ± 4.3%). These data provide the first evidence that AM increases NO bioavailability in intact murine myocardium and confirm that the NO/sGC/cGMP pathway is central to the cytoprotective action of AM against ischaemia–reperfusion injury.