Biomedical subjects

P Corvol

Publications and source records attributed to P Corvol.

At least 55 records · Page 3Linked to original sources

PubMed1999

Ontogeny of angiotensin II type 2 receptor mRNA expression in fetal and neonatal rat brain.

Recent studies have provided evidence for a specific role of the angiotensin II type 2 receptor (AT2) in in vitro neuron differentiation, and in AT2 knock-out mice that display central neurological anomalies. The role of AT2 in brain development is currently unknown. By using radiolabeled cRNA probes for in situ hybridization histochemistry, we determined the ontogenic development of AT2 mRNA in fetal and neonatal rat brain, from 11 days of gestation (E11) to 28 days postnatal (P28). Brain AT2 mRNA is first detected in the lateral hypothalamic neuroepithelium at E13. AT2 mRNA is detected beginning at E15 in the subthalamic and hypoglossus nuclei; at E17 in the pedunculopontine nucleus, cerebellum, motor facial nucleus, and the inferior olivary complex; at E19 in the thalamus, bed nucleus of the supraoptic decussation, interstitial nucleus of Cajal, nuclei of the lateral lemniscus, locus coeruleus, and supragenual nucleus; and at E21 in the lateral septal and medial amygdaloid nuclei, medial geniculate body, and the superior colliculus. The substantia nigra and many telencephalic and medullary nuclei express AT2 mRNA only after birth. Certain structures express AT2 mRNA strongly but transiently during embryonic life, such as the differentiating lateral hypothalamic area at E13, the superior olivary complex at E19 and E21, and the red nucleus at E15 and E17. In conclusion, during brain development, expression of AT2 mRNA appears early at E13, is strongly but transiently expressed in certain structures, and is high and persists until brain maturity in nuclei involved in motor functions and sensory integration. Our results support a dual role of AT2 during brain development in early maturation and differentiation, but also in modulation of established functions during perinatal and adult life.

Aging↗

PubMed1999

RXP 407, a phosphinic peptide, is a potent inhibitor of angiotensin I converting enzyme able to differentiate between its two active sites.

The human somatic angiotensin converting enzyme (ACE) contains two homologous domains, each bearing a zinc-dependent active site. All of the synthetic inhibitors of this enzyme used in clinical applications interact with these two active sites to a similar extent. Recently, several lines of evidence have suggested that the N-terminal active site of ACE might be involved in specific hydrolysis of some important physiological substrates, like Acetyl-Seryl-Aspartyl-Lysyl-Proline, a negative regulator of hematopoietic stem cell differentiation and proliferation. These findings have stimulated studies aimed at identifying new ACE inhibitors able to block only one of the two active sites of this enzyme. By screening phosphinic peptide libraries, we discovered a phosphinic peptide Ac-Asp-(L)Phepsi(PO2-CH2)(L)Ala-Ala-NH2, called RXP 407, which is able to differentiate the two ACE active sites, with a dissociation constant three orders of magnitude lower for the N-domain of the enzyme. The usefulness of a combinatorial chemistry approach to develop new lead structures is underscored by the unusual chemical structure of RXP 407, as compared with classical ACE inhibitors. As a highly potent and selective inhibitor of the N-terminal active site of wild ACE (Ki = 12 nM), RXP 407, which is metabolically stable in vivo, may lead to a new generation of ACE inhibitors able to block in vivo only a subset of the different functions regulated by ACE.

Amino Acid Sequence↗

PubMed1999

N-domain selectivity of angiotensin I-converting enzyme as assessed by structure-function studies of its highly selective substrate, N-acetyl-seryl-aspartyl-lysyl-proline.

The physiological functions of angiotensin I-converting enzyme (ACE) are not limited to its cardiovascular role. ACE constantly degrades N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP), a natural circulating regulator of the hematopoietic stem cell proliferation, and thereby may be involved in hematopoietic stem cell regulation. AcSDKP is hydrolyzed 50-fold faster by the N-domain active site compared to the C-domain active site. The aim of the present study was to investigate which aminoacid residues from AcSDKP are required to ensure N-domain specificity. Several peptides were designed by progressively increasing the length of the peptidic chain from a tripeptide to a pentapeptide. Kinetic studies of the wild-type ACE and of the two ACE mutants containing a single active domain (N- or C-domain) were performed using Bz (benzoyl) Asp-Lys-Pro, benzoyl-glycyl (Bz-Gly)-Asp-Lys-Pro, and Bz-Gly-Ser-Asp-Lys-Pro (with its intermediate product Bz-Gly-Ser-Asp) as substrates. The unexpected importance of an aspartic acid in the P1 position was discovered, as well as the interaction of the P2 and P3 positions in the substrate to increase or decrease N-domain specificity. Substrates longer than five residues may involve interdependence between subsites. Finally, the discovery of highly specific and novel N-domain substrates cannot be predicted from single subsite mapping, but may require other approaches such as combinatorial peptide libraries.

Binding Sites↗

PubMed1999

Expression of the chicken angiotensin II receptor: atypical pattern compared to its mammalian homologues.

We have recently cloned and characterized pharmacologically a chicken angiotensin II receptor (cAT). To evaluate its putative role in developmental processes, we investigated its spatio-temporal distribution in the chicken embryo up to E14. The cAT mRNA is expressed in a developmental manner in the mesonephros and allantois, as well as in the heart, branchial arches or limbs. These results, the first to report the embryonic distribution of an angiotensin receptor in a non-mammalian species, show that its expression pattern does not correspond to either one of the two angiotensin receptor types in mammalian species.

Allantois↗

PubMed1999

Hydrolysis by somatic angiotensin-I converting enzyme of basic dipeptides from a cholecystokinin/gastrin and a LH-RH peptide extended at the C-terminus with gly-Arg/Lys-arg, but not from diarginyl insulin.

Endoproteolytic cleavage of protein prohormones often generates intermediates extended at the C-terminus by Arg-Arg or Lys-Arg, the removal of which by a carboxypeptidase (CPE) is normally an important step in the maturation of many peptide hormones. Recent studies in mice that lack CP activity indicate the existence of alternative tissue or plasma enzymes capable of removing C-terminal basic residues from prohormone intermediates. Using inhibitors of angiotensin I-converting enzyme (ACE) and CP, we show that both these enzymes in mouse serum can remove the basic amino acids from the C-terminus of CCK5-GRR and LH-RH-GKR, but only CP is responsible for converting diarginyl insulin to insulin. ACE activity removes C-terminal dipeptides to generate the Gly-extended peptides, whereas CP hydrolysis gives rise to CCK5-GR and LH-RH-GK, both of which are susceptible to the dipeptidyl carboxypeptidase activity of ACE. Somatic ACE has two similar protein domains (the N-domain and the C-domain), each with an active site that can display different substrate specificities. CCK5-GRR is a high-affinity substrate for both the N-domain and C-domain active sites of human sACE (Km of 9.4 microm and 9.0 microm, respectively) with the N-domain showing greater efficiency (kcat : Km ratio of 2.6 in favour of the N-domain). We conclude that somatic forms of ACE should be considered as alternatives to CPs for the removal of basic residues from some Arg/Lys-extended peptides.

Animals↗

PubMed1999

Aminopeptidase A activity and angiotensin III effects on [Ca2+]i along the rat nephron.

BACKGROUND: This study examined the specific effects of angiotensin III (Ang III) along the nephron. METHODS: We examined the distribution of aminopeptidase A (APA) activity by using a specific APA inhibitor and by immunostaining with an antirat kidney APA antibody, the Ang III-induced variations of [Ca2+]i by using fura-2 and the characterization of the receptor subtype involved in the response to Ang III in cortical thick ascending limb (CTAL). RESULTS: APA activity was found all along the nephron but was higher in the cortex than in the medulla. This was confirmed by immunostaining. Increases in [Ca2+]i elicited by 10(-7) mol/liter Ang III were observed all along the nephron. The characterization of the receptor subtype involved in the [Ca2+]i response to Ang III in CTAL indicated that EC50 values for Ang III and Ang II were similar (13.5 and 10.3 nmol/liter, respectively), and Ang III-induced responses were totally abolished by AT1 receptor but not by AT2 receptor antagonists. There was a cross-desensitization of [Ca2+]i responses to 10(-7) mol/liter Ang III and Ang II, and the [Ca2+]i responses to 10(-7) mol/liter Ang II and Ang III were not additive. CONCLUSION: These results show that in CTAL, the [Ca2+]i responses to Ang II and Ang III occur through the same AT1a receptor because this subtype is predominant in this segment. Taken together, these data suggest that APA could be a key enzyme to generate Ang III from Ang II in the kidney.

Aminopeptidases↗

PubMed1999

Mapping of a first locus for autosomal dominant myxomatous mitral-valve prolapse to chromosome 16p11.2-p12.1.

Myxomatous mitral-valve prolapse (MMVP), also called Barlow disease, is a common cardiac abnormality and affects up to 5% of the population. It is characterized by an excess of tissue that leads to billowing of the mitral leaflets, sometimes complicated by prolapse. Typical histological findings include myxomatous degeneration and degradation of collagen and elastin. Previous reports have proposed an autosomal dominant inheritance of the trait, with age- and sex-dependent expression. By systematic echocardiographic screening of the first-degree relatives of 17 patients who underwent mitral-valve repair, we have identified four pedigrees showing such an inheritance. Genomewide linkage analysis of the most informative pedigree (24 individuals, three generations) showed a significant linkage for markers mapping to chromosome 16p, with a two-point maximum LOD score for D16S3068 (Zmax=3.30 at straight theta=0). Linkage to D16S3068 was confirmed in a second family (Zmax=2.02 at straight theta=0) but was excluded for the two remaining families, thus demonstrating the genetic heterogeneity of the disease. Multipoint linkage analysis performed, with nine additional markers, on the two families with linkage gave maximum multipoint LOD scores of 5.45 and 5.68 for D16S3133, according to a conservative and a stringent model, respectively. Haplotype analysis defined a 5-cM minimal MMVP-1 locus between D16S3068 (16p11.2) and D16S420 (16p12. 1) and a 34-cM maximal interval between D16S404 and D16S3068 when recombination events were taken into account only in affected individuals. The identification of this locus represents a first step toward a new molecular classification of mitral-valve prolapse.

Chromosome Mapping↗

PubMed1999

Polymorphisms of the gamma subunit of the epithelial Na+ channel in essential hypertension.

OBJECTIVE: The gamma subunit of the epithelial Na channel (gammaENaC) has been implicated in Liddle's syndrome. The objective of this study was to examine its status in essential hypertension. DESIGN AND METHODS: The search for molecular variants was performed using the SSCP technique after determination of the intron-exon boundaries of the transcribed sequence. We found an additional 205 bp intron splitting the published exon 10 in two. The last exon of gammaENaC was tested with samples from a series of 245 normotensive patients and 453 hypertensive subjects (383 Caucasians, 70 Afro-Caribbeans), all probands of hypertensive families in the HYPERGENE data set. The search was extended to the other 11 transcribed exons in a subset of 65 patients with low-renin profile. RESULTS: Four neutral polymorphisms were detected, three in the third exon of the gene (T387C, T474C, C549T) and one in the last exon (C1990G). These four variants were found with similar frequencies in hypertensive and normotensive Caucasian subjects as well as in patients with low-renin profile. Hypertensive Caucasians and hypertensive subjects of African ancestry also had similar frequencies. Lastly, we found two rare mutations, one the insertion of a proline residue at position 594 of the mature protein (594insP), the other an Arg-to-His substitution at position 631 (R631H). Compared to wild-type (1.00 +/- 0.42, n = 26), expression of the 594insP (1.10 +/- 0.43, n = 26) and R631H (0.97 +/- 0.43, n = 26) variants in Xenopus oocytes produced no significant increase in Na+ current. CONCLUSIONS: Screening of the entire coding sequence of gammaENaC does not suggest that this subunit is frequently involved in essential hypertension.

Animals↗

PubMed1999

Dissection of silencer elements in first intron controlling the human renin gene.

OBJECTIVE: A silencer within the renin first intron (intron A) was identified using Calu-6 cells, a pulmonary carcinoma cell line which produced renin. In the present study, a dissection of the first intron was performed to determine precisely the cis-regulatory elements involved in the silencer transcriptional effects. MATERIALS AND METHODS: Intron A was completely sequenced to characterize potential binding sites for known transcription factors. Partial portions of intron A were subcloned upstream the 892 bp of the renin promoter and transfected in different models of renin-producing cells: primary culture of human chorionic cells, human Calu-6 cells and mouse As4.1 cells. RESULTS: There is significant DNA homology (67%) between the 3' and 5' ends of the human and rat renin first intron. Several transcription factor binding sites identified in human first intron, but not in rat intron, do not contribute to the reported silencer activity. Transfections of renin/ luciferase constructs containing partial portions of first intron inserted upstream of the 892 bp in both renin-producing cells do not allow the precise characterization of cis-elements involved in the silencer effect. CONCLUSIONS: The silencer located renin intron A is cell specific. The integrity of the human first intron seems necessary for its repressor activity on renin proximal promoter in renin-producing cells.

Animals↗

PubMed1999

PC18, a specific aminopeptidase N inhibitor, induces vasopressin release by increasing the half-life of brain angiotensin III.

Angiotensin III (AngIII), which is metabolized in vivo by aminopeptidase N (APN), was previously shown to be one of the main effector peptides of the brain renin-angiotensin system (RAS) in the control of vasopressin release. Recently, a potent APN inhibitor, PC18 (2-amino-4-methylsulfonyl butane thiol, methionine thiol), has been developed. In this study, we first checked the in vitro selectivity of PC18 towards APN, aminopeptidase A (APA) and aminopeptidase B (APB), three zinc metalloproteases with significant identity between their amino acid sequences. The Ki values of this compound on APN were found to be in the nanomolar range (Ki = 8.0 +/- 1.7 nM) but it was 2,150 and 125 times less active on APA and APB, respectively. Secondly, we evaluated in vivo the effect of brain APN inhibition with PC18 on the inactivation of brain AngIII and on vasopressin secretion in mice. For this purpose, mice received [3H]AngII intracerebroventricularly in the presence or absence of the APN inhibitor PC18 (30 microg). At different times after the injection, [3H]AngIII levels were evaluated from hypothalamus homogenates after separation by cation-exchange chromatography. PC18 induced an accumulation of [3H]AngIII, increasing its half-life 3.9 times as compared with control values. In addition, the effect of PC18 on vasopressin release was studied in mice. PC18 (10-100 microgram) was injected intracerebroventricularly, and plasma vasopressin levels were estimated by radioimmunoassay. PC18 increased vasopressin levels in a dose-dependent manner. The maximal increase in vasopressin release (+220%) is observed for a dose of PC18 of 100 microgram and was inhibited 75% by the coadministration of the AngII receptor antagonist (Sar1-Ala8)-AngII (0.5 microgram). These results indicate that in vivo, in the mouse brain, APN inhibition by PC18 increases the half-life of endogenous AngIII, resulting in an enhanced vasopressin release.

Aminopeptidases↗

PubMed1999

Seven lessons from two candidate genes in human essential hypertension: angiotensinogen and epithelial sodium channel.

The candidate gene approach to understanding the genetics of human essential hypertension is discussed by analyzing the contribution of 2 genes, angiotensinogen (AGT) and epithelial amiloride-sensitive sodium channel (ENaC). From a large series of studies conducted in humans and animals, it appears that the AGT gene plays a significant but modest role in human blood pressure variance. Mutations of the beta- and gamma-ENaC subunits are responsible for Liddle's syndrome, but the implication of the 3 ENaC subunits in essential hypertension is still questionable. Several lessons can be learned from these studies and applied to other candidate genes in essential hypertension: (1) Many linkage or association studies have a limited statistical power; (2) The genetic findings may vary greatly according to the populations studied; (3) There is a need for better phenotyping of the hypertensive population; (4) The causal relationship between molecular variants and hypertension is and will be difficult to establish firmly; (5) The contribution of genetic studied in rodents to the molecular genetics of human hypertension must be re-examined; (6) Most molecular variants lead to a low attributable risk in the population or a low individual effect at the individual level; and (7) It is too early to propose dietary recommendations and specific drug treatment according to patients' genotypes.

Angiotensin II↗

PubMed1999

Genetic, biochemical, and clinical studies of patients with A328V or R213C mutations in 11betaHSD2 causing apparent mineralocorticoid excess.

Apparent mineralocorticoid excess is a recessively inherited hypertensive syndrome caused by mutations in the 11beta-hydroxysteroid dehydrogenase type 2 gene, which encodes the enzyme normally responsible for converting cortisol to inactive cortisone. Failure to convert cortisol to cortisone in mineralocorticoid-sensitive tissues permits cortisol to bind to and activate mineralocorticoid receptors, causing hypervolemic hypertension. Typically, these patients have increased ratios of cortisol to cortisone and of 5alpha- to 5beta-cortisol metabolites in serum and urine. We have studied 3 patients in 2 families with severe, apparent mineralocorticoid excess and other family members in terms of their genetic, biochemical, and clinical parameters, as well as normal controls. Two brothers were homozygous for an A328V mutation and the third patient was homozygous for an R213C mutation in the 11beta-hydroxysteroid dehydrogenase type 2 gene; both mutations caused a marked reduction in the activity of the encoded enzymes in transfection assays. The steroid profiles of the 7 heterozygotes and 2 other family members studied were completely normal. The results of a novel assay used to distinguish 5alpha- and 5beta-tetrahydrometabolites suggest that 5beta-reductase activity is reduced or inhibited in apparent mineralocorticoid excess. In 1 patient undergoing renal dialysis for chronic renal insufficiency, direct control of salt and water balance completely corrected the hypertension, emphasizing the importance of mineralocorticoid action in this syndrome.

11-beta-Hydroxysteroid Dehydrogenases↗

PubMed1999

Cellular distribution of endothelin-converting enzyme-1 in human tissues.

Endothelin-converting enzyme-1 (ECE-1) is the key enzyme of endothelin biosynthesis, catalyzing the final processing step. As shown by the targeted disruption of the ECE-1 gene, mature endothelins must be produced at specific sites for normal embryonic development. Therefore, it is important to know the exact pattern of ECE-1 gene expression. In this study we investigated the cellular distribution of ECE-1 in a variety of human tissues by in situ hybridization and immunohistochemistry. Widespread expression of the ECE-1 gene was noted, with a similar distribution pattern for mRNA and protein in normal human tissues, suggesting a major biological role for ECE-1. ECE-1 levels were particularly high in the cardiovascular, reproductive, and endocrine systems. There was strong and consistent labeling for ECE-1 in the vascular endothelial cells of all organs examined and in various nonvascular cells, especially some glandular cells. A large amount of ECE-1 protein and mRNA was detected in the Leydig cells of the testis and in the granulosa and theca cells of the ovary. In the adrenal gland, ECE-1 was detected in the cortex and medulla, with the strongest labeling in the zona glomerulosa. Therefore, ECE-1 may be involved in other systems, such as the regulation of hormone secretion, rather than exclusively generating ET-1 from its precursor. These results point out the potential side effects of ECE-1 inhibitors that are currently under development for treatment of cardiovascular diseases. (J Histochem Cytochem 47:447-461, 1999)

Adolescent↗

PubMed1999

Identification of endocrine cell populations expressing the AT1B subtype of angiotensin II receptors in the anterior pituitary.

Angiotensin II (Ang II) participates in the regulation of anterior pituitary hormone secretion by acting either directly on the anterior pituitary or indirectly on the hypothalamus. When applied directly on pituitary cells, Ang II increases both ACTH and PRL secretion and has also been reported to affect GH secretion. Three distinct subtypes of Ang II receptors (AT1A, AT1B, and AT2) have been identified; they are unequally distributed and differently regulated in various tissues. We have previously demonstrated that only AT1A receptors are present in the hypothalamus while anterior pituitary cells express predominantly the AT1B subtype. Using in situ hybridization in combination with immunohistochemistry, the aim of the present study was to identify the phenotype of the endocrine cell expressing AT1B receptor messenger RNA (mRNA) in the anterior pituitary of adult male Sprague-Dawley rats. Expression of AT1B receptor mRNA was present in 33.9 +/- 1.0% of anterior pituitary cells. AT1B mRNA is predominantly expressed by lactotropes (78.2 +/- 2.1% of AT1B mRNA-expressing cells) and to a lower degree by corticotropes (18.3 +/- 2.1%) and is not detectable in somatotropes, mammosomatotropes, gonadotropes, or thyrotropes. These results indicate that in adult male rats, Ang II, which has been shown to be synthesized in gonadotropes, can directly stimulate PRL and ACTH release from lactotropes and corticotropes through activation of AT1B receptors. As only 53.8 +/- 2.7% of lactotropes and 23.6 +/- 2.8% of corticotropes expressed AT1B mRNA, our findings suggest a functional heterogeneity of both cell types regarding their sensitivity to Ang II.

Adrenocorticotropic Hormone↗

PubMed1999

Effects of mineralocorticoid receptor gene disruption on the components of the renin-angiotensin system in 8-day-old mice.

Targeted disruption of mineralocorticoid receptor (MR) gene results in pseudohypoaldosteronism type I with failure to thrive, severe dehydration, hyperkalemia, hyponatremia, and high plasma levels of renin, angiotensin II, and aldosterone. In this study, mRNA expression of the different components of the renin-angiotensin system (RAS) were evaluated in liver, lung, heart, kidney and adrenal gland to assess their response to a state of extreme sodium depletion. Angiotensinogen, renin, angiotensin-I converting enzyme, and angiotensin II receptor (AT1 and AT2) mRNA expressions were determined by Northern blot and RT-PCR analysis. Furthermore, in situ hybridization and immunohistochemistry allowed us to identify the cell types involved in the variation of the RAS component expression. In the heterozygous mice (MR+/-), compared with wild-type mice (MR+/+), there was no significant variation of any mRNA of the RAS components. In MR knockout mice (MR-/-), compared with wild-type mice, there were significant increases in the expression level of several RAS components. In the liver, angiotensinogen and AT1 receptor mRNA expressions were moderately stimulated. In the kidney, renin mRNA was increased up to 10-fold and in situ hybridization showed a marked recruitment of renin-producing cells; however, the levels of angiotensin-I converting enzyme mRNA and AT1 mRNA were not changed. Interestingly, in adrenal gland, renin expression was also strongly up-regulated in a thickened zona glomerulosa, whereas AT1 mRNA expression remained unchanged. Altogether, these results demonstrate that in the MR knockout mice model, RAS component expressions are differentially altered, renin being the most stimulated component. Angiotensinogen and AT1 in the liver are also increased, but the other elements of the RAS are not affected.

Adrenal Glands↗

PubMed1999

Two di-leucine-based motifs account for the different subcellular localizations of the human endothelin-converting enzyme (ECE-1) isoforms.

Endothelin-converting enzyme (ECE-1) is a type II integral membrane protein which plays a key role in the biosynthetic pathway of the vasoconstricting endothelins. Three ECE-1 isoforms, differing by their N-terminal cytoplasmic tails, are generated from a single gene. When expressed in CHO cells, they display comparable enzymatic activity but whereas ECE-1a is strongly expressed at the cell surface, ECE-1b is exclusively intracellular and ECE-1c presents an intermediate distribution. In the present study these different localizations were further described at the ultrastructural level, by electron microscope immunocytochemistry. To characterize the motifs responsible for the intracellular localization of ECE-1b we constructed chimeric proteins and point mutants. Two di-leucine-based motifs, contained in the N-terminal part of ECE-1b, were thus identified. One of these motifs (LV), displayed by both ECE-1b and ECE-1c, accounts for the reduced surface expression of ECE-1c as compared to ECE-1a. Mutation of both motifs (LL and LV) induces a very strong appearance of ECE-1b at the cell surface indicating that their presence in the N-terminal extremity of ECE-1b is critical for its exclusively intracellular localization.

Amino Acid Motifs↗

PubMed1999

In vivo assessment of captopril selectivity of angiotensin I-converting enzyme inhibition: differential inhibition of acetyl-ser-asp-lys-pro and angiotensin I hydrolysis.

Angiotensin I-converting enzyme (ACE) is a zinc metallopeptidase that plays a major role in blood pressure regulation. The demonstration that the hemoregulatory peptide acetyl-Ser-Asp-Lys-Pro (AcSDKP) is a natural and specific substrate of the N-active site of ACE suggests that this enzyme may have a new physiological role such as the modulation of hematopoietic stem cells. In vitro studies have shown that ACE inhibitors displayed various potencies in inhibiting the degradation of different natural or synthetic substrates of ACE, among which captopril inhibits AcSDKP hydrolysis more potently than angiotensin I hydrolysis. To look for this selectivity in vivo, we investigated the pharmacodynamic effect of increasing doses of captopril (0.01-10 mg/kg) during the 90 min after i.v. administration to spontaneously hypertensive rats. Plasma and urinary AcSDKP levels were measured. The renin-angiotensin system was evaluated by measurements of ACE activity in plasma samples, using the synthetic substrate Hip-His-Leu, by determinations of plasma renin concentrations and measurements of arterial blood pressure. The results showed that captopril (0.01-0.3 mg/kg) selectively inhibited AcSDKP hydrolysis, with limited effects on the renin-angiotensin system. AcSDKP levels in plasma and urine rose to a plateau 4 times the basal level for doses more than 0.3 mg/kg. All of the parameters reflecting the renin-angiotensin system were significantly affected at doses of 1 and 10 mg/kg. The present study therefore confirms that captopril can be used to protect hematopoietic stem cells during antitumor chemotherapy while having only a limited effect on cardiovascular homeostasis.

Angiotensin I↗

PubMed1999

Several interesting phenotypes of the AT1 receptor produced by site-directed mutagenesis.

The angiotensin II (AngII) AT1 receptor is a seven-transmembrane domain receptor coupled to a Gq/11 protein and phospholipase C, but also to other G proteins and to several tyrosine kinase pathways. These signaling pathways transduce inside the cells the classical actions of AngII (vasoconstriction, aldosterone secretion, etc.), but also the mitogenic action of this vasoactive peptide. In the past 5 yr, site-directed mutagenesis has elucidated the molecular determinants of the AngII and nonpeptidic analogue-binding sites together with those of G protein interaction. In addition, these studies have demonstrated that modifications of the specific interactions between transmembrane domains are responsible for the activation of the receptor. Therefore, several mutations of these domains are able to block the receptor in active or inactive states. Finally, these mutagenesis studies identify two interesting phenotypes of the AT1 receptor. (1) A carboxy-terminal truncation of the AT1 receptor produces a mutant that is unable to be internalized and desensitized and therefore is functionally hyper-reactive. (2) A replacement of the distal part of the third intracellular loop of the AT1 receptor by the homologous segment of the beta2-adrenergic receptor produces a mutant coupled to both Gq and Gs proteins, which is unable to transduce the mitogenic action of AngII.

Animals↗