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Query: UMLS:C0004135 (ATM)
 13,001 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Immortalized rat proximal tubule cell (IRPTC) lines should be useful for investigation of proximal tubule (PT) regulation and function but previously have been unavailable. We now report the establishment and characterization of an immortalized transformed, temperature-sensitive IRPTC cell line containing renin-angiotensin system (RAS) components. Primary PT cells prepared from male Wistar rats (4-5 wk old) after collagenase digestion, sieving, and Percoll gradient were cultured on collagen-coated T-75 flasks in Dulbecco's modified Eagle's medium containing 5% fetal calf serum. Subconfluent PT cells were transfected with the temperature-sensitive SV40 mutant viruses (tsA SV40) by direct exposure. After 7-8 wk, several clones were obtained, from which one has been characterized and designated as line 3-2. This cell line appears stable up to 45 passages. Clonal cells transformed with this virus exhibit a transformed phenotype at a permissive temperature of 34 degrees C and grow in multiple layers. When the cells are subsequently placed at a nonpermissive temperature of 41 degrees C, they return to morphology similar to that of untransformed cells of the same lineage. At either 34 degrees C or 41 degrees C, this cell line expresses a variety of PT markers including alkaline phosphatase, cytokeratin, carbonic anhydrase, and glucose transporter isoform 2 (GLUT2), while not expressing factor VIII. Uniquely, these cells also appear to express PT proteins gp330 and CHIP28, markers which are usually lost in cultured cells. Furthermore, the cell line expresses protein and mRNA components of RAS, including angiotensinogen, angiotensin converting enzyme, and renin. The IRPTC cell line expresses few angiotensin II (ANG II) receptors at 34 degrees C, the permissive temperature. However, at the nonpermissive temperature, 41 degrees C, IRPTC expresses ANG II receptor (dissociation constant of 0.7 nM; maximum binding capacity of 265 fmol/mg protein). ANG II (10(-8) M) induced a transient rise in cytoplasmic Ca2+ concentration, which was nearly abolished with losartan but not PD-123319, suggesting this finding is AT1 receptor mediated. This cell line should provide an excellent model of PT and should make it possible to study the cell and molecular biology of the RAS, as well as other regulatory systems of the PT.
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PMID:Temperature-sensitive SV40 immortalized rat proximal tubule cell line has functional renin-angiotensin system. 790 Aug 43

The objective of this study was to evaluate the mechanisms of the renin secretion response to the angiotensin II (AII) receptor type 1 (AT1) antagonist losartan (DuP 753) in anesthetized rabbits. All receptor blockade with losartan (4 mg/kg bolus and 2 mg/kg/hr i.v.) decreased blood pressure (BP) and increased plasma renin activity (PRA) and heart rate (HR) significantly, whereas the beta-1 adrenoceptor antagonist atenolol (0.02 mg/kg/min i.v.) caused significant reductions in these parameters. Atenolol blocked HR and PRA responses but not the effect of losartan on BP. Cyclooxygenase inhibition with indomethacin (5 mg/kg bolus and 40 micrograms/kg/min i.v.) did not result in significant effects, and the coadministration of indomethacin and losartan resulted in a greater PRA effect than with losartan alone. These results preclude the involvement of prostaglandins, such as PGE2 and PGI2, in the renin response to losartan. The PRA response to atenolol alone suggests that renin release in anesthetized rabbits is under tonic control by beta adrenergic receptors. Furthermore, the discrepancy in the PRA responses to equipotent hypotensive doses of hydralazine and losartan indicates that beta adrenoceptor activation in the kidney, probably the result of blockade of AII-mediated inhibition of renin secretion, contributes to the renin-releasing effect of the AT1 receptor antagonist losartan.
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PMID:Beta adrenoceptor blockade in rabbit inhibits the renin-releasing effect of AT1 receptor antagonist losartan. 790 89

1. Regional haemodynamic responses to the homologous peptides, pituitary adenylate cyclase-activating peptide (1-27) (PACAP27) and vasoactive intestinal polypeptide (VIP) were assessed by giving 20 min infusions (1.5-15 nmol kg-1 h-1) in conscious, chronically-instrumented, Long Evans rats. 2. PACAP27 caused dose-dependent depressor and tachycardic effects associated with renal, mesenteric and hindquarters vasodilatations, although only in the latter vascular bed was there a sustained increase in flow. 3. VIP caused dose-dependent depressor and tachycardic effects that were not significantly different from those caused by equimolar doses of PACAP27. However, the hindquarters vasodilator effects of VIP (at 7.5 and 15 nmol kg-1 h-1) were greater than those of PACAP27 (at the same doses), and accompanied by reductions in renal and mesenteric flows and conductances. 4. In the presence of the nitric oxide (NO) synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME; 11 mumol kg-1 h-1), there was significant inhibition of the hindquarters vasodilator effects of PACAP27 and VIP (at 7.5 and 15 nmol kg-1 h-1). Under these circumstances the renal and mesenteric vasoconstrictor effects of VIP were abolished. 5. The beta 2-adrenoceptor antagonist, ICI 118551 (670 nmol kg-1 bolus, 335 nmol kg-1 h-1 infusion), reduced the matched hindquarters vasodilator responses to PACAP27 (15 nmol kg-1 h-1) and VIP (7.5 nmol kg-1 h-1), and also abolished the renal vasoconstrictor effects of VIP. 6. The AT1-receptor antagonist, losartan potassium (20 mumol kg-1), had no significant effect on the haemodynamic response to PACAP27 (15 nmol kg-1 h-1), but augmented the hypotensive action of VIP (7.5 nmol kg-1 h-1). This influence of losartan was associated with conversion of the renal and mesenteric vasoconstrictor effect of VIP to vasodilatation. 7. Our findings show that similar changes in mean systemic arterial blood pressure in response to PACAP27 and VIP conceal substantial differences in their regional haemodynamic actions. Although the hindquarters vasodilator effects of both peptides involve NO- and Beta2-adrenoceptor-mediated mechanisms,it appears that activation of the renin-angiotensin system contributes significantly to the haemodynamic effects of VIP, but not to those of PACAP27.
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PMID:Regional haemodynamic responses to pituitary adenylate cyclase-activating polypeptide and vasoactive intestinal polypeptide in conscious rats. 791 21

The rabbit proximal tubule (PT) has been widely utilized to study the direct effects of angiotensin II (ANG II) on PT function. The purpose of the present study was to characterize the binding properties of PT ANG II receptors, using nonpeptide antagonists, and to clone a rabbit PT ANG II receptor. In rat and rabbit kidney cortical brush-border and basolateral membranes, specific binding of 125I-ANG II was inhibited by the AT1 ANG II-receptor antagonist DuP 753, but not by the AT2 antagonist PD 123319. Using a rabbit kidney cortex cDNA library, we isolated cDNA encoding an ANG II receptor, with an open-reading frame sharing a high degree of sequence homology to previously cloned AT1 ANG II receptors. In transfected COS-1 cells, this rabbit ANG II receptor had properties of the AT1 class. Northern analysis revealed high levels of mRNA expression for this receptor in rabbit kidney cortex and adrenal gland. Within the kidney, message was detected in primary cultures of rabbit PT cells, as well as in freshly isolated rabbit PT segments. Message was also present in cells of the mouse PT line, MCT, and in rat glomerular mesangial cells. Utilizing polymerase chain reaction (PCR) with primers derived from the 1st and 4th transmembrane domains of the rat AT1A ANG II receptor, a 279-bp DNA fragment was amplified from reverse-transcribed RNA from rabbit PT cells. This DNA encoded an amino acid sequence identical to that encoded by the rabbit kidney cDNA clone in the corresponding region and differed by a single base substitution. Southern analysis of rabbit genomic DNA restriction digests with the rabbit ANG II receptor probe revealed hybridization to a single band in each lane. These results indicate that an AT1 ANG II receptor is present in the PT and that a single gene codes for the AT1 receptor in rabbit. The clone isolated in the present study should provide a useful tool with which to study the regulation of the PT renin-angiotensin system.
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PMID:Cloning of a rabbit kidney cortex AT1 angiotensin II receptor that is present in proximal tubule epithelium. 791 79

In the present study we used radiotelemetry technology to investigate: 1) the time course for development of hypertension in 2-kidney, 1-clip (2K1C) rats and 2) the effect of chronic caffeine consumption on blood pressure in 2K1C rats. Rats received water or caffeine (0.1%) in drinking water and were instrumented with radiotelemetry devices to permit continuous monitoring of blood pressure. A clip was placed on the left renal artery of rats in both the water (WATER/CLIP) and caffeine (CAFFEINE/CLIP) groups. The clip was applied briefly to, then removed from, the renal artery of caffeine- and water-treated rats randomized to the sham-operated (SHAM) group. Mean arterial blood pressure (MABP) increased by approximately 35 mm Hg within 2 hr of clipping. MABP in the WATER/CLIP and CAFFEINE/CLIP groups differed significantly from the SHAM group, but not from each other, for the first 10 days after clipping. Thereafter, MABP was greater in the CAFFEINE/CLIP rats as compared to WATER/CLIP rats. At 4.5 weeks after clipping, MABP values differed significantly in the CAFFEINE/CLIP, WATER/CLIP and SHAM rats (140 +/- 4, 122 +/- 4 and 103 +/- 2 mm Hg, respectively). Involvement of the renin-angiotensin system was assessed by treatment with the AT1 receptor antagonist, losartan, and the converting enzyme inhibitor, captopril. Results from this study indicate: 1) hypertension develops rapidly after clipping in rats monitored with telemetry; 2) the renin-angiotensin system is involved in maintaining hypertension in 2K1C rats even beyond 4 weeks after clipping; and 3) caffeine augments the increase of blood pressure in 2K1C rats, apparently through the involvement of the renin-angiotensin system.
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PMID:Telemetric blood pressure monitoring in benign 2-kidney, 1-clip renovascular hypertension: effect of chronic caffeine ingestion. 793 54

We have shown that acute (24-hr) unilateral ureteral obstruction (UUO) induces the genes encoding for renin, in juxtaglomerular apparatuses and in tubules, for angiotensin converting enzyme in vascular endothelial cells, and for angiotensinogen in perivascular fat. These molecular changes occur in temporal association to marked reductions in renal blood flow (RBF) and glomerular filtration rate (GFR), suggesting that angiotensin II (Ang II) is at least partly responsible for the renal vasoconstriction. We tested the hypothesis that down-regulation of the Ang II type-1 receptor (AT1-R) gene occurs in UUO in response to Ang II, by examining the effects of an ACE inhibitor [lisinopril (Li), 5 mg/kg/day] and of the specific nonpeptidic AT1-R blocker, losartan (Lo) (10 mg/kg/day). UUO or sham operated (which included manipulation but not obstruction of the ureter) rats (S) were studied. Northern blot analysis of the steady state concentration of AT1-R mRNA corrected for GAPDH mRNA showed a marked decrease in receptor expression (-77%, N = 4, P < 0.01) in the obstructed kidney (UUO) compared to S; sham diminished gene expression modestly compared to the contralateral kidneys (C) of UUO. In situ hybridization for AT1-R mRNA also showed diminished expression in UUO compared to C kidneys (N = 4). Treatment of UUO rats (N = 4) with Lo increased AT1-R mRNA five times above the levels in UUO rats receiving vehicle; the increase induced by Li was 50% that of Lo; S (N = 4) and C (N = 4) did not change. Losartan, but not vehicle treatment increased RBF (sixfold) and GFR (fivefold) in the UUO kidneys.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Regulation of the renal angiotensin II receptor gene in acute unilateral ureteral obstruction. 793 8

There is increasing evidence that an activated intrarenal renin-angiotensin system (RAS) alters renal hemodynamics and fluid balance and that such events may lead to the development of hypertension. To examine the role of the glomerular RAS in the development of hypertension in the spontaneously hypertensive (SHR) rat, we studied angiotensin (ANG) II receptors in isolated glomeruli from young (4- to 5-wk-old) and adult (10- to 12-wk-old) SHR and from age-matched, normotensive Wistar-Kyoto (WKY) rats. Glomerular ANG II receptor density in young SHR is 3-fold higher than in age-matched WKY rats (2033 +/- 154 versus 742 +/- 151 receptors/microns2; p < 0.05) and 1.5-fold higher than in adult SHR and WKY rats (1128 +/- 85 and 1198 +/- 181 receptors/microns2, respectively; p < 0.05). Additional studies demonstrated that the differences in receptor density are not related to disparity in receptor occupancy and that they are also independent of systemic ANG levels. Suppression of RAS by ANG converting enzyme inhibitors resulted in a 3-fold increase in receptor density in young SHR rats and a 4.5-fold increase in young WKY rats; receptor density remained greater in young SHR rats (5915 +/- 318 versus 3358 +/- 234 receptors/microns2, p < 0.05). Furthermore, competitive binding experiments using the nonpeptide ANG II antagonists losartan (AT1) and PD 123319 (AT2) indicate that the greater ANG II receptor density in the young SHR rats represents an increase in the number of a single population of AT1 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Glomerular losartan (DuP 753)-sensitive angiotensin II receptor density is increased in young spontaneously hypertensive rats. 793 16

Angiotensin II (ANG II) is a potent vasoconstrictor in isolated human placental cotyledons and may contribute to the regulation of fetoplacental perfusion. We have used quantitative in vitro receptor autoradiography to examine antagonist ((Sar1,Ile8)-[125I]ANG II) and agonist ligand ([125I]ANG II) binding sites in normal-term, preeclamptic and fetal (intrauterine) growth retarded pregnancies. A similar distribution of binding sites was demonstrated using both ligands, localized to blood vessels in placental villi. Binding density was inversely related to vessel size, being significantly greater on microvessels in distal regions of the villous tree than on proximal vessels in main stem villi. Binding sites exhibited the characteristics of the AT1 class of ANG II receptor, ligand binding being sensitive to dithiothreitol, completely inhibited by nonpeptide AT1 antagonists (Losartan, EXP3174 and SKF108566) and not inhibited by the AT2 antagonist (PD123319). Guanine nucleotides also inhibited [125I]ANG II binding and abolished the high affinity component of agonist inhibition of (Ser1,Ile8)-[125I]ANG II binding, indicating G protein coupling. The capacity and affinity of the binding sites were significantly lower in placentae from pregnancies complicated by preeclampsia and intrauterine growth retardation compared to that in normal-term controls. These differences were apparently not due to prior receptor occupancy by endogenous ligand, but may reflect activation of the placental renin-angiotensin system and receptor down-regulation. Locally generated ANG II, acting via AT1 receptors, may contribute to the regulation of fetoplacental blood flow and influence placental perfusion in preeclamptic and growth retarded pregnancies.
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PMID:Angiotensin II (AT1) vascular binding sites in human placentae from normal-term, preeclamptic and growth retarded pregnancies. 796 63

We examined the renal effects of a specific adenosine A1-receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 10 micrograms.kg-1.min-1 iv). Since adenosine is a potent inhibitor of renin release, additional experiments were performed with an angiotensin AT1-receptor antagonist (losartan, 10 mg/kg i.v.). DP CPX alone induced a significant (P < 0.05) decrease in afferent arteriolar resistance (RA, 1.83 +/- 0.18 to 1.43 +/- 0.06 dyn.s.cm-5 x 10(10); P < 0.05). This led to a rise in the transcapillary hydraulic pressure difference (delta P, 35 +/- 1 to 43 +/- 2 mmHg; P < 0.05). Surprisingly, the glomerular capillary ultrafiltration coefficient (Kf) fell (0.101 +/- 0.017 to 0.064 +/- 0.009 nl.s-1.mmHg-1, P < 0.05). Additionally, DPCPX infusion resulted in dramatic increases in both urine flow and sodium excretion. With losartan pretreatment, DPCPX did not cause significant changes in RA and delta P. Also, DPCPX increased Kf (0.057 +/- 0.005 to 0.075 +/- 0.008 nl.s-1.mmHg-1, P < 0.05). Furthermore, the large DPCPX-induced increases in urine flow and sodium excretion were largely suppressed by pretreatment with losartan. These data indicate that endogenous adenosine plays a significant role in maintaining afferent arteriolar tone and that the renin-angiotensin system may mediate some of the wide ranging renal effects of adenosine.
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PMID:Effects of selective A1 receptor blockade on glomerular hemodynamics: involvement of renin-angiotensin system. 797 81

1. The in vivo inhibition of angiotensin II (AII) receptor binding in the rat brain, kidney and adrenal was investigated after intravenous administration of the AT1-selective AII receptor antagonist losartan. 2. Male Sprague-Dawley rats were administered intravenously either vehicle, or losartan at doses of 1, 3 or 10 mg/kg. Plasma samples were collected and tissues removed at 1, 2, 8 or 24 h after administration of the antagonist. The effects of losartan on AII receptor binding were assessed by quantitative in vitro autoradiography. 3. Losartan significantly increased plasma renin activity (PRA) by six-fold and nine-fold at doses of 1 and 10 mg/kg, respectively (P < 0.05). Plasma losartan concentrations rose from 0.83 micrograms/mL at 1 mg/kg to 46.5 micrograms/mL at 10 mg/kg 1 h after administration of the drug. Plasma renin activity returned to control, whilst losartan was undetectable 24 h after injection of the antagonist. 4. In the brain, losartan produced a dose-dependent inhibition of AII receptor binding to the brain structures which express exclusively, or predominantly, AT1 receptors both outside and within the blood brain barrier. By contrast, losartan did not affect binding to the nuclei which contain exclusively, or predominantly, AT2 receptors. 5. In the kidney, losartan blocked AII receptor binding to all anatomical sites in a dose-dependent manner. The inhibition peaked at 1 h and persisted beyond 24 h despite the fact that PRA had returned to control, and losartan was not detectable in the circulation. In the adrenal gland, where AT1 and AT2 receptors occur in both the cortex and medulla, losartan caused partial inhibition at both regions. 6. These results indicate that losartan, administered intravenously at these doses, and/or its active metabolites, partially penetrate the blood brain barrier to selectively inhibit central AT1 receptors, and exert selective and prolonged blockade at AT1 receptors in peripheral target tissues.
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PMID:Blockade by intravenous losartan of AT1 angiotensin II receptors in rat brain, kidney and adrenals demonstrated by in vitro autoradiography. 798 88


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