Koh-ichi Murakawa

Plasma Immunoreactive Endothelin in Essential Hypertension

PURPOSE Endothelin plays a role in the regulation of vascular tonus. Therefore, it has been hypothesized that increased production or release of endothelin or both may contribute to the pathogenesis of hypertension. To assess any changes in the plasma endothelin concentration in essential hypertension, plasma immunoreactive endothelin concentrations were measured in patients with essential hypertension. PATIENTS AND METHODS We measured plasma immunoreactive endothelin concentrations in 42 subjects with essential hypertension, 12 subjects with borderline hypertension, and 25 normotensive control subjects. RESULTS The concentrations were higher in hypertensive patients than in borderline hypertensive patients and normotensive subjects (both p less than 0.05), although values in normotensives and hypertensives overlapped. Reverse-phase high-performance liquid chromatography (HPLC) and radioimmuno-assay showed two components of plasma endothelin, one corresponding to synthetic endothelin-1 (1-21) and the other corresponding to synthetic big endothelin (human, 1-38). The HPLC profile of plasma endothelin of hypertensive patients was the same as that of normotensive subjects. Hypertensives with reduced glomerular filtration rates or increased serum creatinine levels had higher plasma endothelin concentrations than hypertensive patients as a whole (p less than 0.05). Mean blood pressure and serum creatinine levels were correlated to plasma endothelin in the hypertensives. Correlation was negative between glomerular filtration rate and the endothelin level in the hypertensives. CONCLUSION Plasma endothelin was elevated in many hypertensive patients with severe hypertension or renal involvement. Its major components were endothelin-1 and big endothelin.

Brain natriuretic peptide as a cardiac hormone in essential hypertension

PURPOSE A natriuretic peptide, brain natriuretic peptide (BNP), has been isolated from porcine hearts. We performed this study to determine if BNP is secreted from the heart and to identify changes, if any, in the plasma BNP concentration in essential hypertension. PATIENTS AND METHODS We measured the immunoreactive (ir) BNP concentration at intracardiac sites including the coronary sinus of five patients with heart disease during cardiac catheterization. We examined plasma ir-BNP in 48 hypertensive patients, 15 borderline hypertensive patients, and 25 normotensive subjects. RESULTS Plasma ir-BNP in the coronary sinus was greater than at other cardiac sites. The concentration was significantly higher in hypertensive subjects than in borderline hypertensive or normotensive subjects. Hypertensive patients with left ventricular hypertrophy (LVH) established by echocardiography had higher plasma ir-BNP levels than those without LVH. In the hypertensive group, plasma ir-BNP was closely correlated with the LV mass index. In these patients, BNP levels were correlated with mean arterial pressure and inversely correlated with the LV ejection fraction, although these correlations were weak. Reverse-phase high-pressure liquid chromatography showed that the major component of circulating ir-BNP in the hypertensive and normotensive subjects corresponded to authentic human BNP-32. CONCLUSIONS Human BNP-32 was secreted through the coronary sinus from the heart and may act as a cardiac hormone. Plasma BNP was increased in many of the hypertensive subjects with LVH. The increase in BNP seemed to be related to LVH or the cardiac overload associated with LVH.

Serial changes in atrial and brain natriuretic peptides in patients with acute myocardial infarction treated with early coronary angioplasty

To examine the role of brain natriuretic peptide (BNP) in acute myocardial infarction (AMI), we measured the plasma concentration of immunoreactive (ir) BNP together with that of atrial natriuretic peptide (ANP) over the 4-week course of AMI in 16 patients treated with early coronary angioplasty. Both the plasma ir-ANP and ir-BNP levels were increased on the first day of the infarction compared with the values in normal subjects. During the clinical course of the infarction, the plasma ir-ANP concentration soon decreased, while the plasma ir-BNP level remained elevated at 2 weeks after the infarction, also exhibiting a high level at 4 weeks. Plasma ir-BNP levels on day 1 or days 14 and 28 were inversely correlated with left ventricular ejection fraction obtained by left ventriculography at the acute or chronic phase, respectively. Plasma ir-BNP concentrations on days 14 and 28 were positively correlated with the maximal myosin light chain I level, an indicator of infarct size. These observations suggest that the plasma ir-BNP level increased to compensate for the ventricular dysfunction associated with the size of the infarct in AMI. BNP may act as a cardiac hormone in AMI, differing somewhat from ANP in its synthetic, secretory, or clearance behavior.

Prolonged blood pressure elevation after endothelin administration in bilaterally nephrectomized rats

The hemodynamic effect of a novel potent vasoconstrictive peptide (endothelin) on systemic blood pressure was studied in bilaterally nephrectomized and sham-operated rats under conscious and almost unrestrained condition. Following bolus IV administration of porcine endothelin, plasma endothelin concentration was measured by radioimmunoassay. After a transient decline, blood pressure was gradually elevated by endothelin administration. At 20, 30, and 40 minutes after injection, blood pressure was significantly elevated in bilaterally nephrectomized rats compared with sham-operated rats. Arterial plasma endothelin concentrations increased and rapidly decreased after injection in both rat groups. Bilateral nephrectomy significantly delayed the disappearance of endothelin from the plasma. These results suggest that the kidney plays a role in the plasma clearance of IV bolus endothelin administration and that the prolonged plasma half-life of endothelin is in part associated with the prolonged blood pressure elevation after endothelin administration in bilaterally nephrectomized rats.

Circulating atrial natriuretic peptides in hyperthyroidism and hypothyroidism

Plasma concentrations of atrial natriuretic peptides were measured in 32 normal control subjects, 25 patients with hyperthyroidism, and 18 patients with hypothyroidism. Atrial natriuretic peptide values were measured before and after successful therapy with methimazole or 1-thyroxine. Plasma atrial natriuretic peptide concentration was increased in patients with hyperthyroidism (48.0 +/- 19.5 pg/ml) but was decreased in patients with severe hypothyroidism (16.3 +/- 5.7 pg/ml) compared with values in normal control subjects (31.2 +/- 9.5 pg/ml). There was no significant difference between values in normal control subjects and mildly hypothyroid patients (35.0 +/- 12.2 pg/ml). The plasma atrial natriuretic peptide concentration was correlated with the serum thyroxine level and heart rate. The elevated atrial natriuretic peptide concentration in hyperthyroidism decreased, whereas the reduced atrial natriuretic peptide concentration in severe hypothyroidism increased, compared with the initial value after successful therapy. These results suggest that plasma atrial natriuretic peptide concentration is frequently increased in hyperthyroidism and is frequently decreased in severe hypothyroidism, and that thyroid hormone is one of the regulatory factors for circulating atrial natriuretic peptides.

Stimulation of endothelin-1 release by low density and very low density lipoproteins in cultured human endothelial cells

To examine the effects of lipoproteins on the secretion of endothelin-1 from endothelial cells, we measured immunoreactive (ir) endothelin-1 release from cultured human umbilical vein endothelial cells in the presence or absence of various concentrations of native low density lipoprotein (LDL), oxidized LDL, and very low density lipoprotein (VLDL). Cultured endothelial cells secreted ir-endothelin-1 into serum-free medium in a time-dependent manner, and the secretion was clearly stimulated following a 15-24-h incubation with 10 micrograms/ml oxidized LDL. The secretion of ir-endothelin-1 increased in a dose-dependent manner after a 24-h incubation with oxidized LDL, while only a high dose of native LDL and VLDL significantly increased ir-endothelin-1 secretion. The release of ir-endothelin-1 stimulated by 20 micrograms/ml oxidized LDL was reproduced by the same concentration of acetylated LDL but not native LDL. These observations indicate that the release of ir-endothelin-1 from endothelial cells is stimulated by lipoproteins, in particular by oxidized LDL, probably through the endothelial scavenger receptor. This increase in ir-endothelin-1 release induced by oxidized LDL may contribute to the development of atherosclerotic vascular lesions.

Production of endothelin by cultured porcine endothelial cells: modulation by adrenaline.

Cultured porcine endothelial cells derived from aortas spontaneously released immunoreactive endothelin into the medium in a time-dependent manner. This release was completely inhibited by cycloheximide and is, therefore, directly related to de novo protein synthesis. The endothlin-induced release was further stimulated by adrenaline. Adrenaline-induced stimulation was completely inhibited by the alpha-adrenergic blocker phentolamine and was not inhibited by the beta-adrenergic blocker propranolol. Cycloheximide completely prevented the adrenaline-stimulated as well as the basal release. These results suggest that cultured endothelial cells release endothelin slowly but continuously and that this release can be stimulated by adrenaline via alpha-adrenergic receptors. We speculate that the endothelium generates vasoconstrictor signals through endothelin production, thus contributing to the regulation of vascular tone.

Effect of hypoxia on plasma immunoreactive endothelin-1 concentration in anesthetized rats

The present study was designed to examine the possible influence of hypoxia on plasma immunoreactive (ir) endothelin-1 concentrations in anesthetized rats. Plasma ir-endothelin-1 concentration, blood pressure, heart rate, and arterial gas levels were measured 1 and 2 hours after exposure to normoxic (20% O2), mildly hypoxic (16% O2), and severely hypoxic (12% O2) gas. Mean blood pressure and heart rate were significantly decreased and the plasma ir-endothelin-1 concentration was significantly increased in severely hypoxic rats after both 1 and 2 hours. In mildly hypoxic rats, the plasma ir-endothelin-1 concentration was also increased, but this value was not statistically significant. The plasma ir-endothelin-1 concentration was inversely correlated with arterial blood PO2 in the three study groups (normoxic, mildly hypoxic, and severely hypoxic rats) after 1 hour (n = 18, r = -.74, P less than .01), and after 2 hours (n = 18, r = .71, P less than .01). Our results indicate that severe hypoxia increased the plasma ir-endothelin-1 level in anesthetized rats. The observed increase in plasma ir-endothelin-1 level may represent a compensatory mechanism against the blood pressure reduction associated with severe hypoxia.

Increased plasma immunoreactive endothelin-1 concentration in hypercholesterolemic rats

This study examined the influence of hypercholesterolemia on the concentration of plasma immunoreactive (ir) endothelin-1 in rats. Plasma ir-endothelin-1, total cholesterol, triglycerides, and lipoprotein fraction concentrations were measured in three groups of rats; ie, fed a standard diet, a high cholesterol diet, or a high cholesterol diet supplemented with the antihypercholesterolemic drug clinofibrate for 4 and 8 weeks. In the rats fed cholesterol for 8 weeks, morphological changes in thoracic and abdominal aortas were examined. Plasma total cholesterol, low density lipoprotein (LDL), very low density lipoprotein (VLDL) and ir-endothelin-1 concentrations increased significantly in the cholesterol-fed rats after both 4 and 8 weeks. In the clinofibrate-treated rats, these lipid parameters and plasma ir-endothelin-1 levels after 4 and 8 weeks were significantly lower than in the cholesterol-fed rats. The plasma ir-endothelin-1 concentration was correlated with plasma total cholesterol, LDL, and VLDL concentrations in the three study groups after 4 and 8 weeks. Morphologically, neither foam cells formation nor intimal thickening was observed in rats fed the high cholesterol diet for 8 weeks. These observations indicate that hypercholesterolemia without atherosclerosis elevates the plasma ir-endothelin-1 level in rats. The observed increase in plasma ir-endothelin-1 associated with hypercholesterolemia may play a role in the initiation or development of atherosclerotic vascular lesions.

Improvement of erythrocyte deformability by cholesterol-lowering therapy with pravastatin in hypercholesterolemic patients

Erythrocyte deformation is an important regulatory factor of the microcirculation. The present study was designed to examine whether erythrocyte deformability is altered in hypercholesterolemic patients and, if so, whether cholesterol-lowering therapy affects this parameter in these patients. The erythrocyte deformability of 37 hypercholesterolemic patients was evaluated before and after 1 year of therapy with pravastatin, an inhibitor of hepatic hydroxymethyl glutaryl coenzyme A reductase, under various shear stresses (4.7, 9.5, 23.6, 47.3, 118.1, and 236.2 dyne/cm2) using laser diffractometry. At study entry, erythrocyte deformability under 4.7 and 9.5 dyne/cm2 shear stress, which is actually observed in human vessels, was reduced compared with that in 20 age-matched normocholesterolemic subjects and was inversely correlated with serum cholesterol and low-density lipoprotein (LDL) cholesterol. Pravastatin therapy for 1 year, which reduced serum cholesterol from 288 +/- 28 to 223 +/- 20 mg/dL, significantly improved erythrocyte deformability by approximately 20%. There was a significant relation between the improvement of erythrocyte deformability and the reduction of serum cholesterol or LDL cholesterol. The results suggest that erythrocyte deformability is reduced in hypercholesterolemic patients, and that long-term cholesterol-lowering therapy can improve reduced erythrocyte deformability, which may contribute to the improvement of organ perfusion.