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T Inagami

Publications and source records attributed to T Inagami.

At least 91 records · Page 5Linked to original sources
PubMed1991

Role of vascular wall renin: intracellular and extracellular mechanism.

Inhibitors of angiotensin-converting enzyme, renin and angiotensin II receptor lower the blood pressure of spontaneously hypertensive rats (SHRs) used as a model of essential hypertension. Since their plasma renin levels were normal or subnormal, renin in the vascular tissue was considered to play a key role in the maintenance of the hypertension. To clarify the source and localization of vascular renin in SHRs, the effects on blood pressure of antirenin antibodies, the converting enzyme inhibitors delapril and enalapril, and the angiotensin II receptor antagonist DuP 753 were examined in intact and bilaterally nephrectomized SHRs and their normotensive controls. The efficient hypotensive action of the renin antibody indicated that renin of the renal origin is a dominant factor. The gradual but complete disappearance of the antihypertensive action of these inhibitors of the renin-angiotensin system upon bilateral nephrectomy indicated the importance of membrane-associated renin of the renal origin and angiotensin-converting enzyme in the maintenance of the spontaneous hypertension.

Animals↗
PubMed1991

Isolation of preferentially expressed genes in the kidneys of hypertensive rats.

By differential hybridization, three complementary DNAs designated as S3, S2, and SA were isolated, and the corresponding messenger RNAs (mRNAs) were differentially expressed between the kidneys of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. S3 is identical to cytochrome P450 IV A2. SA encoded a protein of 546 amino acid residues, and its carboxyl terminal region had a slight homology to luciferase. No homologous sequence has been reported in S2 sequences. S3 mRNA was about four times more abundantly expressed in the kidneys of 28-day-old SHR than in those of age-matched WKY rats, but there was no difference at age 16 weeks. A low NaCl diet positively modulated the expression of the S3 gene. S2 mRNA was almost undetectable in the kidneys of 28-day-old WKY rats but was clearly detected in those of age-matched SHR. The expression level of S2 mRNA in the livers of 16-week-old SHR was about five times higher than that of age-matched WKY rats. The expression of S2 mRNA in the livers was modulated by dietary NaCl and captopril. SA mRNA was more than 10 times more abundantly expressed in the kidneys of SHR than in those of WKY rats from age 4 weeks. With the administration of captopril, the expressions of SA mRNA in the livers of SHR were positively modulated. Because these three genes are not only differentially expressed between SHR and WKY rats but also related to sodium metabolism or blood pressure control, the identification of these genes may provide important probes to examine the mechanisms of hypertension.

Amino Acid Sequence↗
PubMed1991

Significance of vascular renin for local generation of angiotensins.

The effects of specific renin inhibitors, angiotensin converting enzyme inhibitors, indomethacin, and prostaglandin I2 analogue on the release of angiotensins from isolated and Krebs-Ringer-perfused rabbit mesenteric arteries were examined. Three different renin inhibitors suppressed release of angiotensins in dose-dependent manners. At the highest concentration (10(-7) M), the inhibitors EMD 52,620, EMD 54,388, and EMD 52,742 induced 46%, 52%, and 48% decreases, respectively, in the basal rate of immunoreactive angiotensin II release. These results provide clear evidence that released angiotensins are produced by the specific action of vascular renin and that the renin inhibitors suppress the vascular renin-angiotensin system as well as the circulating renin-angiotensin system and appear to provide a useful mode for the treatment of hypertension. Nonsulfhydryl angiotensin converting enzyme inhibitors cilazapril and delapril were more effective than captopril, and ramipril was equipotent to captopril, suggesting that the effectiveness of angiotensin converting enzyme inhibitors on the vascular renin-angiotensin system cannot be explained only by its inhibitory effect on angiotensin converting enzyme. Indomethacin, which was reported to suppress angiotensin II release from rat hind limbs, elicited a dose-dependent increase of angiotensin release from rabbit mesenteric arteries. These results suggest that a difference exists in the regulatory mechanisms in the release of angiotensins from diverse vascular beds.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1991

Distinct localization of renin and angiotensins in separate subcellular fractions of the rat adrenal cortex.

The subcellular localization of renin and immunoreactive angiotensins I and II was studied in rat adrenal cortical tissues. The identity of the immunoreactive angiotensins was confirmed as angiotensin I and angiotensin II by radioimmunoassay and high-performance liquid chromatography, respectively, with reference to standard compounds. By differential centrifugation of tissue homogenate in 0.25 M sucrose/30 mM Tris-HCl/l mM EDTA, pH 7.4, specific immunoreactive renin was found to be localized principally (60%) in the mitochondrial fraction (P2), whereas about 40% of both angiotensins I and II was contained in the soluble fraction; only 18-20% of both peptides was contained in the P2 fraction. On Percoll density gradient centrifugation of P2, renin was fractionated mostly in a denser band whereas angiotensins I and II were contained in a lighter density area closely corresponding to mitochondrial and lysosomal marker enzymes. These results suggest that renin and angiotensins in the cells of the rat adrenal gland reside in different subcellular compartments and argue against intracellular formation of angiotensins by renin in renin granules.

Adrenal Cortex↗
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↗