Shojiro Naomi

Endothelin-1 Inhibits Endothelin-Converting Enzyme-1 Expression in Cultured Rat Pulmonary Endothelial Cells

BACKGROUND The lung expresses large amounts of endothelin-converting enzyme-1 (ECE-1), which catalyzes a step in the biosynthesis of potent vasoactive endothelin-1 (ET-1) from the inactive intermediate big ET-1. Because there has been no report concerning a possible relationship between ET-1 and ECE-1, we investigated the effects of ET-1 on ECE-1 expression in cultured rat pulmonary endothelial cells. METHODS AND RESULTS ECE-1 messenger RNA (mRNA) and protein expression in cultured endothelial cells were assayed by Northern and Western blotting, respectively. Incubation with ET-1 for 6 hours caused a significant decrease in ECE-1 mRNA expression. The action of ET-1 on ECE-1 mRNA expression was antagonized by pretreatment with BQ788, a specific ETB receptor antagonist, but not by pretreatment with BQ123, a specific ETA receptor antagonist. The expression of ECE-1 protein was also inhibited at 6 hours after incubation with ET-1. The effects of ET-1 on ECE-1 mRNA and protein expression were shown to be mimicked by ionomycin, a calcium ionophore, but not by 12-O-tetradecanoylphorbol 13-acetate, a protein kinase C activator. CONCLUSIONS The present results demonstrate that ET-1 suppressed ECE-1 protein levels by inhibiting ECE-1 mRNA expression through the ETB receptor, suggesting the existence of a feedback action of ET-1 on ECE-1 in pulmonary endothelial cells.

The effect of low and high NaCl diets on oral glucose tolerance

SummaryThe effects of low and high NaCl diets on plasma glucose and insulin responses to glucose ingestion were investigated in 15 patients with essential hypertension. Oral glucose (75 g) tolerance tests were carried out while patients were taking diets with low (2 g/day) and high (20 g/day) NaCl content. Fasting plasma glucose and insulin levels were both significantly lower during ingestion of the high NaCl diet (p<0.05). After glucose ingestion, the incremental areas under the two hour plasma glucose and insulin curves were significantly smaller during ingestion of the high NaCl diet (glucosep<0.005 and insulinp<0.025). These findings that low NaCl diets increase the glycemic response to glucose loads suggest that use of NaCl restriction for the treatment of essential hypertension may not always be desirable.

Endothelin Converting Enzyme-1 Gene Expression in the Kidney of Spontaneously Hypertensive Rats

Abnormal renal handling of water and sodium is implicated in the pathogenesis of hypertension in spontaneously hypertensive rats (SHR). Alteration of renal endothelin-1 synthesis is also reported in SHR. Endothelin-1, a potent vasoconstrictor and regulator of sodium reabsorption in the nephron, has a pathophysiological potential in the development of hypertension. Because synthesis of bioactive endothelin-1 requires endothelin converting enzyme-1 (ECE-1), we investigated whether renal ECE-1 gene expression is altered in the kidney of SHR. Kidneys from both 4- and 12-week-old SHR and age-matched Wistar-Kyoto rats (WKY) were studied. ECE-1 mRNA in microdissected nephron segments was assessed by reverse transcription-competitive polymerase chain reaction, and ECE-1 protein level by Western blot. In 4-week-old SHR, ECE-1 mRNA was significantly increased in the proximal straight tubule, medullary thick ascending limb, cortical thick ascending limb, and inner medullary collecting duct. ECE-1 protein level was increased in both the outer and inner medulla. In 12-week-old SHR, ECE-1 gene expression was significantly increased in the proximal straight tubule, medullary thick ascending limb, and also in the glomeruli. Glomerular preproendothelin-1 mRNA expression was not different between the two strains at both 4 and 12 weeks. We conclude that high ECE-1 gene expression in the nephron, via increase of endothelin-1 synthesis, may promote sodium retention that contributes to the development and/or maintenance of hypertension in SHR.

Increase of human atrial natriuretic polypeptide in response to cardiac pacing

6 weeks, but in a few, as in the subject of this report, the only identifiable precipitant is major surgery.8 In the 8 days between coronary artery bypass surgery and the onset of symptoms, there was no sign of viral illness in this patient, nor was there a history of viral infection in the weeks preceding his surgery. There was a pericardial reaction after operation manifest as a transient rub, and probably contributing to supraventricular arrhythmias. Such a reaction is common, and more likely to be due to trauma than to occult viral illness. There was no pleurisy, arthralgia, coryza, headache, or rash. The incidence of Guillain-Barre syndrome after coronary artery bypass grafting is low, and it is unlikely that bypass surgery or cardiopulmonary bypass represent a special stress or trigger to this process. However, one should be alert to unexplained weakness occurring after any major operative procedure, including cardiac surgery.

Renal sodium handling and sodium transport inhibitor in salt-sensitive essential hypertension.

To investigate the mechanism whereby blood pressure rises with NaCl loading in salt-sensitive essential hypertension, salt-sensitivity index was determined along with sodium and lithium clearances, plasma Na+, K+-ATPase inhibitor and intra-erythrocyte sodium and potassium concentrations. Salt-sensitivity index was defined as the percentage of change in mean blood pressure when NaCl intake was changed from low (34 mmol/day) to high (342 mmol/day). Salt-sensitivity index was inversely correlated with fractional excretion of lithium both on the low and high NaCl diets (r = −0.721, P < 0.01 and r = −0.591, P < 0.02, respectively; n = 16), but not with fractional excretion of sodium. The change of plasma Na+, K+-ATPase inhibition with NaCl loading had a direct correlation with salt-sensitivity index (r = 0.704, P < 0.01; n = 16). Either intra-erythrocyte sodium and potassium concentrations or the ratio of these two values did not change significantly with an increase of dietary NaCl intake. These results suggest that an enhancement of proximal tubular sodium reabsorption stimulates secretion of plasma Na+, K+-ATPase inhibitor which may be involved in a rise in blood pressure with sodium loading. They also suggest that lithium clearance is a determinant which can predict salt sensitivity without actual NaCl loading.

Is salt sensitivity in essential hypertension affected by ageing

To investigate the question of whether the salt sensitivity of blood pressure in human essential hypertension is affected by ageing, the salt-sensitivity index was determined in 54 hospitalized patients with essential hypertension, aged 26–67 years (mean ± s.d. 46.9 ± 9.5 years) as well as plasma inhibition of Na+, K+-ATPase (sodium-pump inhibitor), erythrocyte sodium and potassium concentrations and fractional excretion of lithium. The salt-sensitivity index was calculated as the percentage change in mean blood pressure when the dietary sodium content was increased from 34 mmol/day (low sodium) to 340 mmol/day (high sodium) for 8 days each. Despite wide range of ages, age showed no correlation with the salt-sensitivity index, the sodium-pump inhibitor, the erythrocyte Na+: K+ ratio or fractional excretion of lithium. Furthermore, the distribution of the salt-sensitivity index did not differ between older (45 years old) and younger (<45 years old) age groups. In contrast, the distribution of this index was correlated positively with the change in sodium pump inhibition induced by a sodium load (r = 0.415, P> 0.05) and negatively with the fractional excretion of lithium (r = −0.725, P> 0.01). The erythrocyte Na+: K+ ratio tended to be higher in patients with a salt-sensitivity index of 10% than in those with an index of <5%. These results indicate that the salt-sensitivity index is less affected by ageing than by (genetically determined?) sodium reabsorption at proximal tubules; an increase in sodium tubular reabsorption will lead to a rise in blood pressure through stimulation of sodium-pump inhibitor secretion and a consequent increase in intracellular sodium.

A sensitive radioimmunoassay of α human atrial natriuretic polypeptide using monoclonal antibody recognizing human form ring structure

A monoclonal antibody (C351) against alpha human atrial natriuretic polypeptide (alpha hANP) recognizing human form ring structure was established and applied to a radioimmunoassay of plasma alpha hANP. The minimum detectable amount in terms of 10% radioligand displacement relative to zero dose were 0.28 fmol/tube, corresponding to 0.7 fmol/ml in plasma after extraction using Sep-Pak C18 cartridges. When the mean plasma levels at recumbent position in fasted morning were compared in 10 young (less than 30 years) and 10 elderly (greater than or equal to 50 years) healthy subjects taking normal sodium diet, it was slightly higher in the latter (3.2 +/- 0.4 vs 4.7 +/- 0.5 fmol/ml, mean +/- SE, p less than 0.05). After i.v. infusion of hypertonic saline (2.5% NaCl) at a rate of 0.24 ml/kg/min for 20 min in 6 normal subjects (26 to 35 years), it was increased from 4.1 +/- 0.4 to 5.9 +/- 0.7 fmol/ml (p less than 0.01). In 6 patients with essential hypertension (34 to 57 years), it was elevated with high salt intake, i.e. 3.3 +/- 0.3, 3.9 +/- 1.03 and 7.6 +/- 1.5 fmol/ml under 34, 170 and 340 mEq NaCl/day for 7 days, respectively. From these results, the radioimmunoassay of plasma IR-alpha hANP using MAb C351 seems to be quite suitable to detect rather small changes at low plasma concentrations and to investigate a physiological importance of alpha hANP in man.