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Biomedical subjects

T Inagami

Publications and source records attributed to T Inagami.

At least 235 records · Page 13Linked to original sources
PubMed1991

Cyclosporine promotes glomerular endothelin binding in vivo.

It has previously been shown that administration of cyclosporine causes a prompt (within 15 min after infusion) increase in circulating level of endothelin 1 and a pattern of glomerular hypoperfusion and hypofiltration which can be ameliorated with antiendothelin antibody. We now show that 60 min after cyclosporine, serum endothelin 1 level falls to less than 2.55 +/- 0.31 pg/mL (N = 6), a value comparable to that found in normal animals (less than 2 pg/mL). The study presented here also examines whether sustained cyclosporine-induced glomerular dysfunction is associated with altered endothelin receptor characteristics. Saturation and competitive inhibition binding studies in isolated glomerular membranes showed two binding sites. Of these, the density of the low-affinity site was affected by cyclosporine treatment (851 +/- 117 versus 425 +/- 61 fmol/mg of protein; P less than 0.05; N = 6) without a change in equilibrium dissociation constant, KD. The high-affinity site was not affected. The receptor characteristics of another vasoconstrictor, angiotensin II, were not affected by cyclosporine. In addition, there was no difference in endothelin binding sites in hepatic tissue between cyclosporine and control rats. These results raise the intriguing possibility that cyclosporine-induced glomerular dysfunction involves upregulation of endothelin binding sites and that altered endothelin receptors appear specific to the kidney.

Animals↗
PubMed1991

A role for atrial natriuretic peptide in endothelin-induced natriuresis.

Systemic administration of low-dose endothelin increases urinary sodium excretion rate despite mild to moderate reductions in renal plasma flow and glomerular filtration rates. The role of atrial natriuretic peptide in endothelin-induced natriuresis was investigated. Administration of 2.50 pmol/min of endothelin to euvolemic rats resulted in increases in plasma atrial natriuretic peptide levels from 127 +/- 18 to 169 +/- 23 pg/mL. However, a lower dose of endothelin (0.63 pmol/min) or saline did not increase plasma levels of atrial natriuretic peptide. Mean arterial pressure was unchanged at the lower dose of endothelin and increased only slightly in rats receiving 2.5 pmol/min. To assess functional significance, renal responses to endothelin (2.5 pmol/min) in the absence and presence of a specific anti-rat atrial natriuretic peptide antibody were compared. Equivalent reductions in renal blood flow were observed. Urinary sodium excretion rates increased significantly in non-ANP-antibody-treated rats by 33 +/- 7 and 82 +/- 20% at 10 and 30 min, respectively. Atrial natriuretic peptide antibody blunted markedly endothelin-induced natriuresis: urinary sodium excretion rates changed insignificantly by 18 +/- 10 and 30 +/- 14%, respectively. Thus, endothelin infusion results in increases in plasma atrial natriuretic peptide levels, which may contribute to endothelin-induced natriuresis, providing evidence for potentially significant interactions between these peptide hormones in the regulation of sodium balance and renal vascular tone.

Animals↗
PubMed1991

Exaggerated response to electrical nerve stimulation of angiotensin II release in isolated perfused hind legs of spontaneously hypertensive rats.

Previously we reported that a large amount of immunoreactive angiotensin II (Ang II) was released from isolated perfused rat hind legs at steady rates for several hours. In view of a recent intriguing hypothesis that the vascular renin-angiotensin system plays an important role in the maintenance of high blood pressure in certain forms of experimental hypertensive models, the release of immunoreactive Ang II from isolated hind legs of spontaneously hypertensive rats (SHR) was examined in comparison with normotensive rats of Wistar-Kyoto strain (WKY) by using a Sep-Pak C18 cartridge directly connected to the perfusion system. We also examined effect of electrically-induced nerve stimulation on the release of immunoreactive Ang II in the two strains. High performance liquid chromatography demonstrated the presence of Ang II in the perfusate. The spontaneous release of immunoreactive Ang II was as high as about 300 to 500 pg/30 min, tended to be higher in SHR rats (435.0 +/- 68.2 pg/30 min) than in WKY rats (342.1 +/- 65.1 pg/30 min), and stable up to 3 hours of perfusion for both strains. Periarterial nerve stimulation elicited a significant increment in the release of immunoreactive Ang II in either SHR (p less than 0.02) or WKY rats (p less than 0.05); however, the amount of released immunoreactive Ang II evoked by nerve stimulation was significantly greater in SHR than in WKY rats (781.3 +/- 89.6 vs 498.8 +/- 54.6 pg/30 min, p less than 0.05). These results further provide evidence for local generation and release of Ang II in peripheral vascular tissues, and are consistent with the hypothesis that the vascular renin-angiotensin system is one of important factors responsible for the maintenance of blood pressure.

Angiotensin II↗
PubMed1991

Juxtaglomerular cells as a source of intrarenal angiotensin II production.

While the contribution of angiotensin (Ang) II to the regulation of various renal functions is recognized, evidence exists that the kidney also is a major site for the production of Ang II. Since circulating renin in plasma accounts for only a small portion of intrarenally produced Ang II, we investigated juxtaglomerular (JG) cells as a source of Ang I and II. Light and electronmicroscopic immunohistochemical methods revealed highly concentrated Ang I and II in JG cells. This finding was supported by the demonstration of colocalization of renin, Ang I, and Ang II in cultured JG cells and in dense granular fractions of rat kidney separated by gradient centrifugation of rat kidney homogenate. Perfusion of rat kidney with Krebs-Ringer buffer containing bovine serum albumin showed that Ang I and Ang II are released in the perfusate in quantities which may account for a greater part of the intrarenal generation of Ang II observed in vivo. These results support the hypothesis that Ang II is intrarenally synthesized inside the JG cells, thereby contributing to the regulation of certain renal functions.

Angiotensin I↗
PubMed1990

ANP-like immunoreactivity in neuronal perikarya and processes associated with vessels of the pia and cerebral parenchyma in dog.

The existence of neocortical neurons displaying processes which penetrate the glia limitans (GL) and closely approach pial as well as intracerebral microvessels was determined in the dog from immunohistochemical localization of atrial natriuretic peptide (ANP). Scattered ANP-positive pyramidal somata located in cortical layers II and III displayed spinous dendritic arbors and delicate, beaded axon collaterals. Dendritic branches, as well as axon collaterals, traversed the GL near blood vessels entering the parenchyma, or encircled microvessels deep to the GL. These findings suggest that single ANP-like immunoreactive cortical neurons may monitor and control local cerebrovascular flow or permeability of the blood-brain barrier.

Animals↗
PubMed1990

Effect of delapril hydrochloride on angiotensin II release from isolated rat hind legs.

The effect of the newly developed angiotensin-converting enzyme (ACE) inhibitor, delapril hydrochrolide (CV-3317), on the release of immunoreactive angiotensin II (irAng II) from isolated rat hind legs was compared with that of captopril. Both ACE inhibitors, added to the perfusion medium (2 X 10(-9) - 10(-6) M), suppressed irAng II release in a dose-dependent manner, but the inhibition was greater with delapril than with captopril. The results provide further support for the concept that vascular tissues produce Ang II and release it in a regulated fashion. The results also suggest a possible link between the antihypertensive mechanism of ACE inhibitors, including delapril, and the suppression of vascular Ang II release.

Angiotensin II↗
PubMed1990

Native form of endothelin receptor in human placental membranes.

Little is known about the native form of endothelin receptor. To clarify its functional and structural properties, we solubilized the receptor from human placenta in an active form using mild detergents CHAPS and digitonin and showed that it is able to bind 125I-endothelin-1 in a specific manner, with a pH optimum between 6 and 8 in contrast to a reported pH optimum of 4. The molecular weight of the receptor was estimated as 340,000 by gel filtration of the solubilized membrane in the presence of 0.2% (w/v) digitonin. When the solubilized membranes were labeled with 125I-endothelin-1 prior to gel filtration, the radioactive ligand also migrated in the position corresponding to a 340 kDa protein. These results indicated that the native form of endothelin receptor in human placenta is a 340 kDa protein.

Chromatography, Gel↗
PubMed1990

Blockade of the pre- and postjunctional effects of angiotensin in vivo with a non-peptide angiotensin receptor antagonist.

Recent reports indicate that some imidazole-5-acetic acid derivatives are competitive antagonists of angiotensin II receptors. However, to our knowledge, there is no published information regarding: 1) what constant infusion rate of these non-peptide angiotensin receptor blockers is necessary to effectively antagonize angiotensin receptors in vivo, 2) whether imidazole-5-acetic acid derivatives antagonize both prejunctional and postjunctional angiotensin receptors, and 3) whether effective levels of these compounds exert non-specific actions and/or partial agonist activity. To address these issues, either vehicle, 2-butyl-4-chloro-1-(2-nitrobenzyl) imidazole-5-acetic acid (CV-2961; 30 and 100 micrograms/min) or a standard angiotensin receptor blocker, 1Sar8Ile-angiotensin II (100 ng/min), was infused intravenously into captopril-treated rats that were prepared for in situ perfusion of their mesenteric vascular beds. Infusion of CV-2961 for two and one-half hours did not alter arterial blood pressure, mesenteric perfusion pressure, plasma aldosterone level, or mesenteric vascular responses to sympathetic nerve stimulation or exogenous norepinephrine. The higher dose of CV-2961 (100 micrograms/min) completely blocked angiotensin II-induced enhancement of vascular responses to sympathetic nerve stimulation and shifted the angiotensin dose-response curve 10-fold to the right with respect to angiotensin II-induced increases in mesenteric perfusion pressure. The effects of the lower dose of CV-2961 (30 micrograms/min) on these actions of angiotensin II were not statistically significant. 1Sar8Ile-angiotensin II abolished both the prejunctional and postjunctional effects of angiotensin II. We conclude that in intact rats CV-2961, infused at 100 micrograms/min, antagonizes both prejunctional and postjunctional angiotensin II receptors, yet has a somewhat greater effect on the prejunctional actions of angiotensin II. CV-2961 is devoid of partial agonist activity, and no non-specific actions of CV-2961 are evident. Imidazole-5-acetic acid derivatives may find considerable utility as pharmacological probes and as therapeutic agents.

Aldosterone↗
PubMed1990

Molecular cloning of a complementary DNA to rat cyclophilin-like protein mRNA.

Using the technique of differential plaque filter hybridization, a rat cDNA was isolated whose corresponding gene expression in the kidney was positively modulated up to threefold by sodium depletion. This mRNA was more abundantly expressed in the kidneys of 17-week-old spontaneously hypertensive rats than those of age-matched Wistar-Kyoto rats. The putative protein encoded by this cDNA is a homologue of cyclophilin, a cytosolic binding protein for cyclosporin A. This cyclophilin-like protein mRNA was expressed in all the tissues examined, including the adrenal, atrium, brain, kidney, liver, lung, spleen, and ventricle. Sodium depletion in rats increased the expression level of this mRNA not only in the kidney but also in the liver. The administration of cyclosporin A in rats increased the expression level of this mRNA in the kidneys and livers. By virtue of its possible involvement in sodium homeostasis and its homology to cyclophilin, this molecule might have significant implications in the mechanism of cyclosporine-induced renal insufficiency and hypertension.

Amino Acid Sequence↗
PubMed1990

Role of endothelin in cyclosporine-induced glomerular dysfunction.

Since recent studies indicate that cyclosporine (CsA) disrupts endothelial integrity and that injured endothelial cells release excess endothelin, we examined endothelin's role in acute cyclosporine nephrotoxicity. Following CsA (20 mg/kg i.v.), rabbit anti-porcine endothelin (aE) serum was continuously infused into a first order branch of the main renal artery in Munich-Wistar rats whereupon the hemodynamics of glomeruli not infused with aE as well as those infused with aE within the same kidney were simultaneously assessed by micropuncture techniques. In CsA treated kidneys, in glomeruli not infused with aE, single nephron GFR (SNGFR) and glomerular plasma flow rate (QA) fell profoundly (on average by 42 and 48%, respectively) below the baseline values in association with lower glomerular capillary pressure and elevated afferent arteriolar resistance. By contrast, in glomeruli infused with aE within the same CsA treated kidneys, this vasoconstrictive pattern was markedly attenuated: SNGFR was, on average, only 19% lower than baseline and values for QA as well as other parameters determining glomerular filtration were at or near the levels observed before administration of CsA. In another group of rats (N = 6) an identical dose of CsA was given to measure the circulating level of endothelin. In these CsA treated rats, endothelin level (measured by radioimmunoassay) was elevated at 41.7 +/- 14.7 pg/ml, contrasting the value of less than 2 pg/ml uniformly observed in identically instrumented normal rats not given CsA (N = 5). Thus, cyclosporine is a potential inducer for endothelin release and endothelin appears to have a pivotal role in pathophysiology of cyclosporine-induced acute renal vasoconstriction and glomerular dysfunction.

Animals↗
PubMed1990

Effects of chronic converting enzyme inhibition on the vascular renin-angiotensin system.

1. The effects of chronic oral administration of inhibitors of angiotensin converting enzyme (ACE) on the vascular renin-angiotensin system were studied. 2. Male Sprague-Dawley rats were treated orally with five ACE inhibitors, captopril, enalapril, ramipril, cilazapril and CS-622 (10 mg/kg per day), for periods of 1-2 weeks. Their mesenteric arteries were then isolated and perfused in vitro with Krebs'-Ringer solution, and the angiotensin II (AII) released into the perfusate was measured under unstimulated and isoproterenol-stimulated conditions. The vascular renin activity was also determined after treatments with ACE inhibitors. 3. Treatment with captopril for 1 week suppressed the isoproterenol-stimulated increase in AII release, but had little effect on the baseline release. Oral treatment with captopril for 2 weeks or with other ACE inhibitors for 1 week markedly inhibited both the unstimulated and stimulated release of AII from the mesenteric vasculature. 4. Both the vascular renin activity and the plasma renin activity increased on captopril treatment, but their changes with time were different. 5. These results indicate that virtually complete inhibition of the vascular renin-angiotensin system can be achieved after prolonged treatment with ACE inhibitors, and suggest that the chronic antihypertensive action of ACE inhibitors is not solely due to inhibition of the plasma renin-angiotensin system.

Administration, Oral↗
PubMed1990

Identification of individual renocortical cells that secrete renin.

Successful application of the reverse hemolytic plaque assay was developed to identify individual renocortical cells that secrete renin directly. The plaque assay was validated by a number of established criteria. Using this technique, we demonstrate an increase in renin secretion with beta-adrenergic stimulation and an inhibition of renin secretion with extracellular calcium in groups of renin-secreting cells. Transmission electron microscopy of the cell in the center of a hemolytic plaque demonstrated a modified vascular smooth muscle cell with densely packed secretory granules. Electron microscopy immunocytochemistry demonstrated the presence of renin in the secretory granules, confirming the identity of the cell as a renal juxtaglomerular cell. The technology developed here has allowed the precise identification and study of the individual renin-secreting juxtaglomerular cell.

Animals↗
PubMed1990

Angiotensin II regulates renin gene expression.

We investigated the effect of angiotensin II (ANG II) and enalapril on accumulation of renin messenger RNA (mRNA) and on renal renin distribution (immunohistochemical analysis). Adult Wistar-Kyoto rats received enalapril (0.2 mg/ml) in distilled drinking water for 8 or 12 days. On day 5 of enalapril treatment, an osmotic minipump was implanted in the peritoneum that caused sustained release of ANG II (200 ng.kg-1.min-1) or vehicle (bovine serum albumin) for 3 or 7 days. Control rats received water for 8 or 12 days and osmotic minipump implantation (containing vehicle solution) on the 5th day. Renin mRNA was identified by hybridization with a 32P-labeled full-length complementary DNA and was detected by autoradiography. Enalapril treatment increased renal renin mRNA specific activity (renin mRNA/total RNA). Subsequent infusion of angiotensin II for 3 or 7 days decreased renal renin mRNA specific activity. In addition, renin immunostaining increased along the afferent arteriole after enalapril treatment; however, enalapril-induced spread of renin immunostaining was not inhibited by ANG II. Thus ANG II attenuates the accumulation of renin mRNA stimulated by enalapril treatment without alteration of renal renin distribution. The lack of effect of ANG II on renal renin distribution may be due to the length of turnover time for stored protein. These findings suggest the shortloop negative feedback of ANG II on renin reflects inhibition of renin synthesis by ANG II. Therefore, we propose that ANG II exerts a direct inhibitory effect on renin by regulation of renin gene expression in renal vasculature.

Aldosterone↗
PubMed1990

Re-evaluation of the plasma renin-angiotensin system in anephric patients.

In view of recent observations that a number of extrarenal tissues have the potential to produce angiotensin II and release it in a regulated fashion, we made measurements of immunoreactive angiotensin I (irAng I) and angiotensin II (irAng II), along with active and inactive renin, and angiotensinogen in plasma of seven anephric patients and of 16 normal healthy volunteers to gain insight into possible sources of plasma Ang II. High performance liquid chromatography clearly demonstrated that the predominant component of irAng II in anephric plasma is the biologically active octapeptide Ang II. Plasma renin activity (PRA), and active and inactive renin all were detected in all of the anephrics but their levels were decreased to 33% for PRA, 12% for active renin, and 18% for inactive renin when compared with those in healthy subjects. While plasma angiotensinogen was significantly but only slightly increased in anephric patients (+28% over the mean value for normal subjects), irAng I and irAng II both were present in quantities almost comparable with those in normals. These results suggest that local angiotensin production contributes, in part at least, to the circulating plasma Ang II. Vascular tissue seems to be the best candidate responsible for such a mechanism, on the basis of recent demonstrations of unequivocal, regulated release of Ang II from diverse vascular beds.

Adult↗
PubMed1990

Intracellular formation and release of angiotensins from juxtaglomerular cells.

Evidence accumulates that intrarenal angiotensin II (Ang II) plays important roles in the regulation of renal functions. To determine the mechanism and site of the intrarenal formation of Ang II, we employed histochemical, cell biological and ex vivo perfusion methods. Immunohistochemical studies have revealed the co-existence of renin and Ang II in juxtaglomerular (JG) cells, and electron microscopic studies and subcellular organelle fractionation have demonstrated the localization of renin and angiotensin in renin granules. Cloned and cultured renin-containing cells derived from rat kidney were also found to contain renin, ACE, and Ang I and Ang II. The subcellular fractionation of renin granules from rat kidney homogenate demonstrated the presence of Ang I and Ang II in the renin granule fractions. The findings suggest the formation of both angiotensins in JG cells. To study the release of Ang I and Ang II, we determined the release of these peptides from isolated rat kidney perfused with Krebs-Ringer buffer at a constant pressure. Release of both peptides was stable for as long as two hours in the absence of angiotensinogen in the perfusion medium. There was a positive correlation between renin secretion rate and Ang I secretion rate, and also between Ang I secretion rate and Ang II secretion rate. Since the perfusate does not contain angiotensinogen, these results lead to the hypothesis that Ang II is formed in JG cells in the kidney and is directly secreted with renin into plasma or the interstitial fluid, and that Ang II formed in the kidney cells may participate in various renal functions along with Ang II produced in the plasma.

Angiotensin I↗
PubMed1989

Direct evidence for local generation and release of angiotensin II in human vascular tissue.

A direct measurement of both angiotensins I and II immunoreactive substances was made in the perfusate from isolated human umbilical vein perfused with Krebs-Ringer solution which was free of any component of the renin-angiotensin system. The identity of the immunoreactive peptides was confirmed as angiotensin I and angiotensin II by high-performance liquid chromatography in reference to standard compounds. The rate of release of angiotensins was 41.9 +/- 7.4 and 63.4 +/- 12.0 pg for angiotensins I and II, respectively, during the first perfusion period of 30 min, and it remained stable at least for 3 hours. Angiotensin-converting enzyme inhibitor captopril, added to the perfusion medium (10(-9) to 5 x 10(-6) M), suppressed immunoreactive angiotensin II release in a dose-dependent fashion; the maximal percent inhibition of angiotensin II release evoked by captopril (5 x 10(-6) M) was approximately 56%. These results taken together with the previous observations of presence of essential components of the renin-angiotensin system in vascular tissue provide direct evidence for local generation and subsequent release of angiotensin II in vascular beds of human beings.

Angiotensin I↗