Yuichiro Ishiyama

Hemodynamic effects of a novel hypotensive peptide, human adrenomedullin, in rats

The hemodynamic effects of human adrenomedullin were investigated in anesthetized Wistar rats. Intravenous administration of adrenomedullin (1.0 nmol/kg) caused a rapid and marked reduction in mean blood pressure associated with a decrease in total peripheral resistance. This reduction in mean blood pressure was closely correlated with the decrease in total peripheral resistance. These findings indicate that human adrenomedullin is a potent vasodilator and may have some role in the regulation of blood pressure.

Upregulation of Angiotensin-Converting Enzyme 2 After Myocardial Infarction by Blockade of Angiotensin II Receptors

Abstract—We investigated in Lewis normotensive rats the effect of coronary artery ligation on the expression of cardiac angiotensin-converting enzymes (ACE and ACE 2) and angiotensin II type-1 receptors (AT1a-R) 28 days after myocardial infarction. Losartan, olmesartan, or the vehicle (isotonic saline) was administered via osmotic minipumps for 28 days after coronary artery ligation or sham operation. Coronary artery ligation caused left ventricular dysfunction and cardiac hypertrophy. These changes were associated with increased plasma concentrations of angiotensin I, angiotensin II, angiotensin-(1–7), and serum aldosterone, and reduced AT1a-R mRNA. Cardiac ACE and ACE 2 mRNAs did not change. Both angiotensin II antagonists attenuated cardiac hypertrophy; olmesartan improved ventricular contractility. Blockade of the AT1a-R was accompanied by a further increase in plasma concentrations of the angiotensins and reduced serum aldosterone levels. Both losartan and olmesartan completely reversed the reduction in cardiac AT1a-R mRNA observed after coronary artery ligation while augmenting ACE 2 mRNA by approximately 3-fold. Coadministration of PD123319 did not abate the increase in ACE 2 mRNA induced by losartan. ACE 2 mRNA correlated significantly with angiotensin II, angiotensin-(1–7), and angiotensin I levels. These results provide evidence for an effect of angiotensin II blockade on cardiac ACE 2 mRNA that may be due to direct blockade of AT1a receptors or a modulatory effect of increased angiotensin-(1–7).

Identification and hypotensive activity of proadrenomedullin N‐terminal 20 peptide (PAMP)

Proadrenomedullin N‐terminal 20 peptide (PAMP) is a candidate for a novel biologically active peptide processed from an adrenomedullin precursor. Using a radioimmunoassay for human PAMP, major and minor immunoreactive PAMPs were purified from porcine adrenal medulla and complete amino acid sequences were determined. The major immunoreactive peptide was PAMP itself with an amidated carboxy terminus. The minor one was determined to be PAMP[5–20]. An intravenous bolus injection of human PAMP in anesthetized rats caused a rapid and strong hypotensive effect in a dose dependent manner. The present data indicate that PAMP is an endogenous biologically active peptide which is processed from adrenomedullin precursor.

Cardiac Angiotensin-(1-7) in Ischemic Cardiomyopathy

Background—Accumulating evidence suggests that angiotensin-(1-7) (Ang-[1-7]) may play an important role in counteracting the pressor, proliferative, and profibrotic actions of angiotensin II in the heart. Thus, we evaluated whether Ang-(1-7) is expressed in the myocardium of normal rats and those in which myocardial infarction was produced 4 weeks beforehand. Methods and Results—The left coronary artery in 10-week-old Lewis rats was either ligated (n=5) or exposed but not occluded in age-matched controls (sham; n=5). Left ventricular end-diastolic pressures were significantly elevated 4 weeks after myocardial infarction (25±1 versus 5±1 mm Hg for sham; P <0.001), whereas left ventricular systolic pressures were significantly reduced (ligated 86±4 versus sham 110±5 mm Hg; P <0.01). Hemodynamic effects of coronary artery ligation were accompanied by significant cardiac hypertrophy (heart weight to body weight: ligated 4.3±0.1 versus sham 2.9±0.1 mg/g; P <0.001). In both ligated and sham rats, Ang-(1-7) immunoreactivity was limited to cardiac myocytes and absent in interstitial cells and coronary vessels. Ang-(1-7) immunoreactivity was significantly augmented in ventricular tissue surrounding the infarct area in the heart of rats with myocardial infarction. Conclusions—Development of heart failure subsequent to coronary artery ligation leads to increased expression of Ang-(1-7),which was restricted to myocytes.

Effect of chronically infused adrenomedullin in two-kidney, one-clip hypertensive rats.

The hypotensive effect of chronically infused adrenomedullin, a potent vasodilator peptide, was examined in conscious two-kidney, one-clip (2K-1C) hypertensive and sham-operated rats. They were infused with 1.0 microgram/h of synthetic human adrenomedullin for 14 days by means of osmotic minipumps. Control groups were infused on the same schedule with 0.9% saline. Systolic blood pressure was measured before and during the infusion. Plasma renin activity, aldosterone and human adrenomedullin concentrations were determined at day 14 of the infusion. A significant reduction of systolic blood pressure was observed in the adrenomedullin-infused 2K-1C rats at day 4, and systolic blood pressure remained significantly lower throughout the experiment compared to that of the control 2K-1C. A similar hypotensive effect was seen in the adrenomedullin-infused sham-operated rats. Both the plasma renin activity and aldosterone concentrations of the adrenomedullin-infused 2K-1C and sham groups were significantly reduced compared to those of the respective control, whereas, the plasma human adrenomedullin concentration in the adrenomedullin-infused groups was found to be within the physiological range. These findings demonstrated that chronically infused adrenomedullin had a hypotensive effect accompanied by significant reductions of plasma renin activity and plasma aldosterone concentration in 2K-1C hypertensive and sham-operated rats.

Purification and characterization of PAMP-12 (PAMP(9-20)) in porcine adrenal medulla as a major endogenous biologically active peptide

Proadrenomedullin N‐terminal 20 peptide (PAMP‐20) is a potent hypotensive peptide processed from the adrenomedullin (AM) precursor. We developed a specific radioimmunoassay which recognizes the C‐terminal region of PAMP‐20. Using this radioimmunoassay, the distribution of immunoreactive (ir‐) PAMP was determined in porcine tissues. High concentrations of ir‐PAMP were observed in the adrenal medulla and in the atrium, and these values were comparable to the corresponding concentrations of ir‐AM. The concentration of ir‐PAMP was almost the same as that of ir‐AM in the kidney, while ir‐PAMP was significantly lower than ir‐AM in the ventricle, lung, and aorta. Reversed‐phase high performance liquid chromatography in each porcine tissue sample revealed that two major peaks of ir‐PAMP existed: one emerged at a position identical to that of authentic porcine PAMP‐20; the other unknown peak was eluted earlier. The unknown peptide was purified to homogeneity from porcine adrenal medulla, and its complete amino acid sequence was determined. This peptide was found to be PAMP[9–20] with a C‐terminal amide structure, and was named PAMP‐12. Intravenous injections of PAMP‐12 in anesthetized rats showed a significant hypotensive effect in a dose‐dependent fashion, and the effect was comparable to that of PAMP‐20. These data indicate that PAMP‐12, a major component of ir‐PAMP, is processed from the AM precursor, as is PAMP‐20, and may participate in cardiovascular control.

HAEMODYNAMIC RESPONSES TO RAT ADRENOMEDULLIN IN ANAESTHETIZED SPONTANEOUSLY HYPERTENSIVE RATS

1. The haemodynamic effects of rat adrenomedullin (AM), a novel hypotensive peptide, were examined in anaesthetized 16–18 week old spontaneously hypertensive rats (SHR) and Wistar‐Kyoto rats (WKY).

Plasma adrenomedullin in patients with primary aldosteronism.

Adrenomedullin (AM) is a novel hypotensive peptide originally isolated from the pheochromocytoma tissue of humans. To examine the pathophysiological role of AM in primary aldosteronism (PA), the plasma concentration of AM in patients with PA was measured with a specific radioimmunoassay and compared to that in age- and sex-matched healthy normotensive subjects. In addition, the concentrations of AM as well as catecholamines in the plasma from both the adrenal vein and the inferior vena cava (IVC) were measured to determine whether or not the circulating AM in these PA patients is supplied from the adrenal medulla, which contains a much higher concentration of AM than any other human tissue does. The plasma concentration of AM in the PA patients (4.57 +/- 0.32 fmol/mL, n = 6) was significantly (P < .01) higher than that in the healthy subjects (3.06 +/- 0.20 fmol/mL, n = 12). A significant positive correlation (r = 0.62, P < .01) was observed between the mean blood pressure and the plasma AM level. The AM concentration in plasma from the adrenal vein was almost the same level as that from the IVC although the concentrations of both epinephrine and norepinephrine in the adrenal vein were much higher than those in the IVC. Therefore, it seems unlikely that the plasma AM in the PA patients is mainly supplied from the adrenal medulla. Judging from the potent hypotensive activity of AM, the present findings suggest that AM participates in defense mechanisms acting against the elevation of blood pressure in the patients with PA.

Increased plasma proadrenomedullin N-terminal 20 peptide in patients with essential hypertension

The novel hypotensive peptide, proadrenomedullin N-terminal 20 peptide (PAMP), is processed from the adrenomedullin precursor. Recently, we identified PAMP-12 [PAMP(9-20)] from the porcine adrenal medulla as a major endogenous and biologically active peptide. Using a new, sensitive radioimmunoassay which recognizes the C-terminal region of PAMP-20 [PAMP(1-20)], we investigated the role of PAMP in patients with essential hypertension who had normal renal function, and whether PAMP-12 is present in humans. The mean PAMP plasma concentration, like that of adrenomedullin, was significantly higher in hypertensive [1·51 fmol/mL, standard error of the mean (SEM) 0·09 fmol/mL] than normotensive participants (1·08 fmol/mL, SEM 0·05). The increase in plasma PAMP concentration in patients with organ damage accompanied by hypertension was significantly higher than that in patients without organ damage. The PAMP concentration had a significant positive correlation with mean blood pressure and adrenomedullin concentration. The immunoreactive PAMP in human tissue and plasma was characterized by reverse-phase high-performance liquid chromatography. PAMP-12, as well as PAMP-20, was abundant in the phaeochromocytoma tissue. These findings suggest that PAMP plays some pathophysiological role against the development of essential hypertension.

Identification of amidicin: a novel peptide with C-terminal amide structure isolated from porcine cardiac atrium

Using a novel method employing a V8 protease digestion coupled with ethyl acetate extraction, we have purified a peptide with C-terminal amide structure from porcine cardiac atrium. The peptide was determined to be Ala-Val-Leu-Gly-Leu-CONH2. According to the sequence, we have raised an antibody and established the radioimmunoassay. Using this radioimmunoassay, we have isolated a novel 14 amino acid peptide where C-terminus was amidated. This peptide was termed amidicin. Amidicin is widely distributed in porcine tissue and is especially abundant in pituitary gland, cardiac ventricle, and spleen.