Event-related brain potentials and case information in syntactic ambiguities

In an ERP study, German sentences were investigated that contain a case-ambiguous NP that may be assigned accusative or dative case. Sentences were disambiguated by the verb in final position of the sentence. As our data show, sentences ending in a verb that assigns dative case to the ambiguous NP elicit a clear garden-path effect. The garden-path effect was indicated by a broad centro-posterior negative shift that occurred between 300 and 900 msec after the dative-assigning verb was presented. No enhanced P600 following the misanalysis was observed. Noun phrases whose case ambiguity was resolved in favor of accusative case and unambiguously dative-marked NPs did not trigger significant ERP differences. We will discuss the implications of our results for parsing and its neuropsychological correlates. The results of this study support a parser design according to which the so-called structural case (nominative or accusative) is assigned without any delay in the absence of morpho-lexical counterevidence. It is argued that the enhancement of a negative ERP component with a "classical" N400 topography reflects the difficulty of reanalysis due to reaccessing morpho-lexical information that lies outside the domain of the parsing module. Consequently, ERP responses to garden-path effects are not confined to a late positivity but vary depending on the level of processing involved in reanalysis. The fact that garden-path effects may also elicit an N400 can be linked to the nonhomogeneous linguistic properties of the constructions from which they arise.

Local renin-angiotensin system in the pineal gland

Besides the classical endocrine renin-angiotensin system (RAS), a local RAS has been described also in the brain. We attempted to clarify the existence of a local RAS in the pineal gland. Through the use of a ribonuclease protection assay, it proved possible to detect the mRNA for angiotensinogen (AOGEN), for the angiotensin receptor type 1A (AT1a) and 1B (AT1b) and for the angiotensin-converting enzyme (ACE) in pineal glands from rats. Renin mRNA, however, could not be found by this method. By in situ hybridization and immunocytochemistry, AOGEN mRNA was co-localized with the astrocyte marker glial fibrillary acidic protein. AT1b mRNA expression exceeded the expression of AT1a mRNA and was co-localized with the pinealocyte-specific tryptophan hydroxylase. Thus, in the mammalian pineal gland there is a local formation of the components of the RAS. The presence of angiotensin II receptors further substantiates a role for angiotensins and the pineal RAS in the physiology of this gland.

Ambient and biochemical effect monitoring of workers exposed to ethylene oxide

OBJECTIVES

Ethylene oxide is an alkylating agent known to be a directly acting mutagen and carcinogen. This study describes the relationship between workplace ambient air concentrations of ethylene oxide and the concentration of N-2-hydroxyethylvaline in the globin of exposed workers.

METHODS

During the sterilization of medical equipment, 12 workers were occupationally exposed to ethylene oxide. Personal and stationary ambient air measurements were carried out to monitor the external exposure. The determination of the protein adducts was based on the N-alkyl-Edman method, introducing a new commercially available dipeptide standard for calibration purposes.

RESULTS

Ethylene oxide concentrations ranging from 0.2 to 8.5 ppm were found in the workplace air. The adduct concentrations ranged from 5,219 to 32,738 pmol N-2-hydroxyethylvaline/g globin in the case of regularly exposed workers (n = 9) and from 518 to 3,321 pmol N-2-hydroxyethylvaline/g globin for three persons with occasional contact with ethylene oxide.

CONCLUSIONS

The Deutsche Forschungsgemeinschaft established in 1993 a relationship between the ethylene oxide concentration in ambient air and the amount of N-2-hydroxyethylvaline in human globin. By extrapolation, constant exposure to 1 ppm ethylene oxide should yield approximately 4,000 pmol N-2-hydroxyethylvaline/g globin. The ambient air concentrations of ethylene oxide and the amount of N-2-hydroxyethylvaline determined within the present study confirm this extrapolation in practice. In addition, the determination of adducts based on the use of commercially available dipeptide standards for calibration purposes turned out to be an advantageous alternative to the commonly used protein standards.

Prednicarbate versus conventional topical glucocorticoids: pharmacodynamic characterization in vitro

PURPOSE

Pharmacodynamic characterization of topical glucocorticoids as prednicarbate (PC), its metabolites prednisolone 17-ethylcarbonate (PEC) and prednisolone (PD), betamethasone 17-valerate (BMV), betamethasone (BM) and desoximetasone (DM) by evaluating their effects on epidermal and dermal cells. Synopsis of pharmacokinetic and pharmacodynamic studies, possibly explaining the improved benefit-risk ratio of prednicarbate.

METHODS

Isolated foreskin keratinocytes were used to investigate the influence on epidermal inflammatory processes, dermal fibroblasts of the same origin to study antiproliferative activities of glucocorticoids. Interleukins were measured by ELISA-assay, the influence on II-1 alpha-production also on mRNA-level by RNAse protection assay. Proliferation was assessed by 3H thymidine incorporation and biodegradation by HPLC/UV-absorption. Cell viability was controlled by MTT assay.

RESULTS

In keratinocytes, inflammation was induced by TNF alpha, resulting in an increased II-1 alpha synthesis. This cytokine was particularly suppressed by PC and BMV, whereas PEC, PD, DM and BM were less potent (p < or = 0.05). Since, however, the double ester PC is rapidly degraded in keratinocytes, a RNAse-protection assay of II-1 alpha mRNA was performed allowing short incubation times and thus minimizing biodegradation effects. In agreement with the previous experiment, the antiinflammatory potency of native PC was confirmed. In fibroblasts, II-1 alpha and II-6 synthesis indicate proliferation and inflammation respectively. Whereas PC inhibited II-1 alpha and II-6 production in fibroblasts to a minor extent only, it was strongly reduced by the conventional glucocorticoids and PEC (p < or = 0.05). The minor unwanted effect of PC on fibroblasts was also reflected by its low influence on cell proliferation as assayed by 3H thymidine incorporation. More pronounced antiproliferative features were observed with BM, PEC and especially BMV.

CONCLUSIONS

Correlating antiphlogistic effects in keratinocytes (suppression of II-1 alpha) with antiproliferative effects in fibroblasts (suppression of II-1 alpha and II-6), the improved benefit-risk ratio of PC compared to conventional glucocorticoids does not result only from distinct drug metabolism in the skin but also from a specific influence on the cytokine network.

Renovascular hypertension with low-to-normal plasma renin: clinical and angiographic features

1. Low-to-normal renin renovascular hypertension (RVH) and the accuracy of renal vein renin ratios were investigated in 129 consecutive patients referred for suspected RVH. Forty-nine had essential hypertension, 24 unilateral renoparenchymal hypertension and 56 renal artery obstruction. Of the latter, 86% were diagnosed retrospectively as RVH, based on fall in blood pressure with correction of renal ischaemia. We measured baseline, captopril-stimulated and renal vein plasma renin activity (PRA) levels, as well as several other parameters. 2. PRA was low-to-normal in 37% of the RVH patients [low-to-normal renin (LNR-) RVH group] and elevated in the remaining 63% [high-renin (HR-) RVH group]. In the LNR-RVH group, low-to-normal renin levels, by immunoreactive active renin and plasma renin concentration measurements, and a blunted response of PRA to captopril, were seen. As compared with HR-RVH, LNR-RVH patients had a longer duration of hypertension (P < 0.05), higher serum K+ (P = 0.04) and lower diastolic blood pressure (P = 0.02). However, they did not differ for the other variables, including the fall in blood pressure after correction of renal ischaemia. Although the number of bilateral stenoses was similar in the two groups, no patient in the LNR-RVH group had total renal artery occlusion compared with 53% in the HR-RVH group (P = 0.00015). The accuracy of renal vein renin indices were high enough to justify their use only in the patients with total occlusion of a renal artery. 3. Thus LNR-RVH is common in patients with longstanding hypertension without a totally occluded renal artery. Since the sensitivity of renin measurements is low, cure of hypertension would be precluded for more than one third of RVH patients, if these tests were a prerequisite for identifying RVH.

Nitric oxide synthase and renin-angiotensin system gene expression in salt-sensitive and salt-resistant Sabra rats

The molecular mechanisms of salt sensitivity and the contribution of the kidney to salt-induced hypertension in Sabra rats are imperfectly defined. We investigated the expression of the nitric oxide (NO) system (endothelial, inducible, and neural NO synthases) and renin-angiotensin system (renin, angiotensinogen, and angiotensin II type 1A receptor) gene components in the kidneys of SBN/y (salt-resistant) and SBH/y (salt-sensitive) Sabra rat substrains, with and without deoxycorticosterone acetate (DOCA)-salt treatment. We also looked for immunocytochemical evidence of angiotensin II, the effector peptide of the renin-angiotensin system. Inducible and neural NO synthase gene expression values were lower in SBH/y than in SBN/y before and after DOCA-salt treatment. The gene expression level of endothelial NO synthase was not different in SBH/y and SBN/y, either with or without DOCA salt. Renin gene expression was significantly higher in kidneys of SBN/y than in kidneys of SBH/y rats, whereas angiotensinogen gene expression was significantly lower in SBN/y. After DOCA-salt treatment, renin gene expression was strongly suppressed in both strains but more so in SBH/y. Angiotensinogen gene expression, on the other hand, was increased by DOCA salt in SBN/y rats so that the two strains were no longer different. Angiotensin II immunoreactivity was significantly higher in SBN/y than in SBH/y; however, after DOCA salt, immunoreactivity in both strains was no longer detectable. Angiotensin II type 1A receptor gene expression was not different between the two strains, either before or after DOCA-salt administration. We conclude that DOCA salt induced a decrease in the activity of the renin-angiotensin system but did not change NO synthase gene expression in SBH/y and SBN/y. Inducible and neural NO synthase gene expression values were less in SBH/y than in SBN/y, independent of DOCA-salt administration. Thus, the NO system could explain, at least in part, the salt resistance of SBN/y.

Effects of angiotensin II and IV on geniculate activity in nontransgenic and transgenic rats

Microiontophoretic ejection of angiotensin II and angiotensin IV in the vicinity of geniculate neurons was used to study the effects of these peptides on the discharge rate and the discharge pattern of extracellularly recorded activity. The main aim of the experiments was to study the effects of angiotensins in different strains of rats anesthetized with urethane (normotensive Wistar, normotensive Sprague-Dawley and hypertensive, transgenic (TGR(mREN2)27) rats). Both angiotensins mostly increased the spontaneous activity of angiotensin-sensitive geniculate neurons in all strains. Angiotensin II reduced the number of bursts in most neurons, whereas angiotensin IV significantly enhanced it. Inhibitory effects of angiotensins on spontaneous as well as on light-evoked activity could be effectively blocked by GABA(A) or GABA(B) receptor antagonists. Therefore, it can be supposed that angiotensin-containing afferent fibers innervate both projection and local circuit neurons of the dorsal lateral geniculate nucleus. In addition, angiotensin II suppressed excitation induced by glutamate receptor agonists in most neurons tested. Angiotensin-induced effects could be blocked by specific receptor antagonists. There were no significant differences in the effects of angiotensins in the various strains of rats, except for the latencies of the neuronal responses to the iontophoretic ejection of angiotensins.

Less efficacy with alternating regimen as adjuvant chemotherapy in stage II node-positive breast cancer: results at 8 years (Pronacam 85)

A randomized trial to compare adjuvant treatment with an alternating regimen with conventional chemotherapy was performed. A total of 589 node-positive patients were included and stratified according to number of positive nodes (N1-3 and N > 4) and menopausal status. Premenopausal N1-3 patients were randomized to cyclophosphamide, methotrexate and fluorouracil (CMF) or CMF/4'-epirubicin, cyclophosphamide (EC), post-menopausal N1-3 patients to fluorouracil, 4 epirubicin, cyclophosphamide (FEC) or CMF/EC and pre- and post-menopausal patients with N > or = 4 to fluorouracil, 4' epirubicin, cyclophosphamide, methotrexate, prednisone (FECMP) or CMF/EC. In premenopausal patients, CMF was superior to CMF/EC in terms of disease-free survival (DFS) (65% vs 45%, P = 0.0149) and survival (72.3% vs 50.2%, P = 0.0220) whereas, for N > or = 4 patients, differences between FECMP and CMF/EC did not achieve statistical significance (DFS 35% vs 26.2%; survival 50% vs 38.1%, P = NS). For post-menopausal patients, FEC was superior to CMF/EC in DFS (58.6% vs 36.8%, P = 0.0215) and survival (66.2% vs 46%, P = 0.0155). In post-menopausal patients with N > 4, differences favouring CMF/EC were significant in DFS (40.4% vs 22%, P = 0.0371) but not in survival (47.4% vs 32.2%, P = 0.1185). Alternating regimens did not offer better results in premenopausal and post-menopausal N1-3 patients. Results regarding post-menopausal N > 4 women require further confirmation.

Angiotensinogen messenger RNA stabilization by angiotensin II

OBJECTIVE

To further characterize the molecular mechanism whereby angiotensin II stabilizes the angiotensinogen messenger (m)RNA through binding studies of the previously isolated polysomal stabilizing protein to partial and mutagenized sequences of the 3' untranslated region of the gene and to explore its importance to rodent genetic hypertension.

DESIGN

Analysis of angiotensinogen mRNA mutants for half-life and binding to a polysomal protein with a molecular weight of 12000.

METHODS

Protein/RNA interactions were determined in band shift assays employing radiolabelled 3' untranslated region of angiotensinogen mRNA. Measurement of the mRNA half-life used a cell-free incubation system and 3' untranslated region DNA sequences were polymerase chain reaction (PCR) cloned and sequenced. Sequences of normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rat (SHR) strains were compared. Point mutations were introduced by site directed mutagenesis.

RESULTS

The angiotensinogen 3' untranslated region exhibited specific binding to the polysomal 12000 molecular weight protein which, in an in vitro incubation system, increased 10-fold the half-life of full-length angiotensinogen mRNA; no effect was observed with 3' deleted angiotensinogen mRNA indicating a regulatory function of protein at the 3' untranslated region. Sequence analysis of PCR amplified DNA fragments identified a (G-->C) point mutation in the La Jolla colony SHR. Following introduction of this point mutation into wild-type 3' untranslated regions, protein binding significantly increased (wild-type binding constant, 19 mumol/l; mutant binding constant 3.5 mumol/l), indicating that this point mutation affects 3' untranslated region secondary structure, binding of the RNA stabilizing protein and, consequently, the half-life of angiotensinogen mRNA. Deletion of a U-rich region (position 1609-1613, UCCUU) expressed twice in the 3' untranslated region almost completely abolished protein binding suggesting this sequence as one part of the putative binding motif in the 3' untranslated region.

CONCLUSIONS

Angiotensin II regulates hepatic angiotensinogen synthesis and secretion by inhibiting degradation of angiotensinogen mRNA by the action of a polysomal protein. Mutations in the 3' untranslated region mRNA coding sequence alter binding and half-life and may significantly affect the half-life of angiotensinogen mRNA thereby altering the secretion rate of angiotensinogen.

Reduction of cardiac hypertrophy in TGR(mREN2)27 by angiotensin II receptor blockade

TGR(mREN2)27 is a transgenic rat harboring the murine Ren-2 gene and exhibit fulminant hypertension and marked heart hypertrophy. In order to study the role of angiotensin II in the increase of cardiac mass, these animals were treated with antihypertensive and non-antihypertensive doses of the angiotensin II receptor AT1 antagonist Telmisartan for 9 weeks. All doses led to significant reductions of heart hypertrophy detected by the evaluation of the diameter of cardiac muscle bundles. We conclude from this study that cardiac hypertrophy in TGR(mREN2)27 is characterized by an increased volume of cardiomyocytes and an unchanged amount of fibrous tissue and that angiotensin II plays an important role in the mechanisms leading to this phenotype.

Behaviour of the transgenic (mREN2)27 rat

The first model of genetically engineered hypertension, the transgenic rat TGR (mREN2)27, provides a unique opportunity to study the behavioural effects of an altered brain renin-angiotensin system. The TGR (mREN2)27 rats, characterised by fulminant hypertension, show differences in both the peripheral and central angiotensin systems. The behaviour of male transgenic TGR (mREN2)27 and male Sprague-Dawley rats were determined by 4 behavioural tests. While on the elevated X-maze the TGR (mREN2)27 rat showed a greater 'anxiogenic' profile (fewer open arm entries) than the control Sprague-Dawley rats, this 'anxiogenic' profile increased further during a second exposure to the elevated X-maze 24 h later. In comparison the behaviour of the male Sprague-Dawley rats was not different between the two exposures to the elevated X-maze. Locomotor activity did not differ between either the TGR (mREN2)27 or Sprague-Dawley rats when placed in a 1 m2 open-field for 10 min. A short period of fluid-deprivation (3 h) reversed the 'anxiogenic' profile of the TGR (mREN2)27 on the elevated X-maze. Administration of captopril (20 mg . kg-1 body weight) in the drinking water of the TGR (mREN2)27 rats and Sprague-Dawley rats reversed the anxiogenic profile of the TGR (mREN2)27 rat on the elevated X-maze but did not alter the behaviour of the Sprague-Dawley rats.

Transcriptional regulatory elements in the rat bradykinin B2 receptor gene

In an attempt to elucidate the mechanisms underlying the regulation of bradykinin B2 receptor gene expression, the molecular structure of the rat gene including the 5'-flanking region was characterized (J. Biol. Chem. 269: 26920-26925, 1994). In this study we show that the gene spans about 32 kb, including a long first intron of 25 kb. The promoter region drives reporter gene expression in NG108-15 neuroglioma cells, and its expression is upregulated by cAMP, bradykinin, phorbol esters and by coexpression of an activated ras oncogene but not by dexamethasone.

Physiological characterization of the hypertensive transgenic rat TGR(mREN2)27

Transgenic techniques represent powerful tools for the study of gene-related mechanisms of diseases such as hypertension, which results from a complex interaction between genetic and environmental factors. The renin-angiotensin system, a biochemical cascade in which renin functions as the key enzyme in the formation of the effector peptide angiotensin II, plays a major role in the regulation of blood pressure. The renin gene, therefore, represents an important candidate gene for hypertension. Because rats are more suited than mice for a number of experimental settings often employed in cardiovascular research, we modified the transgenic technique to generate the transgenic rat strain TGR(mREN2)27 harboring the murine Ren-2 gene. These transgenic rats develop fulminant hypertension at an early age despite low levels of renin in plasma and kidney. In addition, high expression of the transgene in a number of extrarenal tissues is associated with increased local formation of angiotensin II. Thus the TGR(mREN2)27 rat represents a model of hypertension with a defined genetic background. Studies on the transgenic rat may not only provide new insights into pathophysiological mechanisms of hypertension in this animal model but also offer the unique possibility to investigate the function and regulation of renin-angiotensin systems in extrarenal tissues. The aim of this review is to compile the knowledge that has been accumulated to date on this transgenic rat and to discuss possible mechanisms responsible for its hypertensive phenotype.

Molecular cloning and functional characterization of a mouse bradykinin B1 receptor gene

The gene encoding a putative mouse bradykinin B1 receptor was cloned from a genomic library by low stringency screening. Analysis of two isolated clones revealed a region which contains an open reading frame uninterrupted by introns and encodes a 334 amino acid protein, which exhibits seven potential transmembrane domains and is 68% identical to the human and rabbit bradykinin B1 receptors. Lipopolysaccharide-treatment induces B1 receptor transcripts in the heart, liver, and lung. Stable expression of the coding region in COS-7 cells resulted in high levels of binding sites for the specific B1 ligand des-ARG10 kallidin (Kd = 1.3 nM; Bmax = 51 fmol/mg protein). The rank order of affinity of the receptor for the agonists and antagonists was: des-Arg9BKdes-Arg9Leu8BKdes- Arg10kallidin >> Hoe-140=bradykinin. Functional coupling of the cloned receptor was demonstrated by the dose-dependent effects of des-Arg(9)BK on the extracellular acidification rate in stably transfected COS-7 cells. This effect was not produced by bradykinin and could be blocked by the B1 antagonist des-Arg9Leu8BK.

Permanent inhibition of angiotensinogen synthesis by antisense RNA expression

The renin-angiotensin system plays a pivotal role in blood pressure regulation. Recent molecular biological findings led to the new concept that in addition to the classic endocrine system, local tissue systems may also play an important role in cardiovascular diseases such as hypertension. In particular, the brain renin-angiotensin system was shown to influence the central control of blood pressure and is thought to contribute to the hypertensive phenotype of genetically hypertensive rat models. To identify the physiological role of these local systems, we established an antisense strategy to downregulate the expression of the precursor hormone angiotensinogen (AOGEN) in cell culture, which can also be used to establish transgenic rat lines. Plasmids encoding an RNA sequence complementary to the rat AOGEN mRNA under control of different viral and tissue-specific promoters were constructed and transfected into an AOGEN-expressing cell line. A competitive reverse transcription-polymerase chain reaction method was established for the quantification of AOGEN mRNA. Depending on the level of antisense RNA, the expression of the AOGEN gene was reduced down to 22% of control levels. Furthermore, the secretion of AOGEN protein was totally abolished. These results clearly demonstrate that the antisense constructs used are functional in reducing the AOGEN gene expression in vivo and can be used for the production of transgenic rats.

Phase I trial of 9-cis retinoic acid in adults with solid tumors

Retinoids have been shown to be potent inhibitors of epithelial carcinogenesis. Recent evidence has demonstrated that retinoid actions are mediated through nuclear receptors, which are proteins encoded by the retinoic acid receptor and retinoid X receptor gene families. These receptors are activated by binding to specific retinoids; of the known naturally occurring retinoids, 9-cis retinoic acid is unique in its ability to bind to both receptor families. Because of its unique receptor-binding characteristics, 9-cis retinoic acid may have biological activity not possible with other retinoids. For this reason, we conducted a Phase I trial of 9-cis retinoic acid in adult patients with solid tumors. Twenty-two patients were treated twice daily with p.o. 9-cis retinoic acid at doses ranging from 20 mg/m2/day to 150 mg/m2/day. The patients had non-small cell lung cancer (n = 8), breast cancer (n = 5), colorectal cancer (n = 3), head and neck cancer (n = 2), nonmelanoma skin cancer (n = 2), or ovarian cancer (n = 2). The dose-limiting (WHO grade III) toxic effects, which occurred at the 150-mg/m2/day dose level, were headaches and diarrhea. Less severe (grades I and II) toxic effects included cheilitis, dry skin, conjunctivitis, fatigue, hypertriglyceridemia, alkaline phosphatase elevation, myalgia/arthralgia, and hypercalcemia. Of the 15 patients evaluable for tumor response, no objective responses were observed. Pharmacokinetic analysis revealed a reduction in peak 9-cis retinoic acid plasma levels with chronic administration. Based on this study, the recommended Phase II dose of 9-cis retinoic acid in adult patients with solid tumors is 100 mg/m2/day administered in a divided dose twice daily.

Analysis of N-alkylated amino acids in human hemoglobin: evidence for elevated N-methylvaline levels in smokers

To investigate the contribution of cigarette smoking to the levels of N-methylvaline and N-hydroxyethylvaline in hemoglobin we analyzed samples from 32 smokers and 37 nonsmokers. The average background levels of the nonsmoking individuals were determined to be 1175 +/- 176 pmol N-methylvaline/g globin, ranging from 722 to 1516 pmol/g globin, and 46 +/- 12 pmol N-hydroxyethylvaline/g globin, ranging from 19 to 64 pmol/g globin. A significant correlation (P < 0.001) was found between both amino acids and the amount of cigarettes smoked per day, with an increase of 42 pmol N-methylvaline/g globin/cigarette per day and 11 pmol N-hydroxyethylvaline/g globin/cigarette per day. No influence of age, sex, and occupational exposure was observed. Furthermore, the levels of N-hydroxyethylvaline and N-methylvaline correlated for smokers but not for nonsmokers, indicating cigarette smoking as a common source for both adducts. To our knowledge, this is the first time N-methylvaline levels are reported to differ significantly between smokers and nonsmokers in the general population. Especially the analysis of N-methylvaline following low-level exposures to methylating agents should therefore take into consideration the influence of individual smoking habits. Additionally, the results of our study confirm the reliability of N-hydroxyethylvaline as an indicator of individual cigarette consumption. We successfully applied a new calibration technique to the analysis of N-hydroxyethylvaline, introducing a commercially available and well-defined dipeptide standard. The observed levels of N-hydroxyethylvaline in the samples are in line with those reported in the literature and verify the applicability of our calibration method.

Angiotensin II receptor blockade in TGR(mREN2)27: effects of renin-angiotensin-system gene expression and cardiovascular functions

OBJECTIVE

To study the effect of angiotensin II receptor AT1 blockade on blood pressure, gene expression and pathomorphology of transgenic rats harbouring the mouse Ren-2 gene [TGR(mREN2)27], that develop fulminant hypertension while exhibiting suppressed components of the circulating renin-angiotensin system.

DESIGN

TGR(mREN2)27 were treated orally with the newly developed AT1-specific angiotensin receptor antagonist Telmisartan, 4'-[(1,4'-dimethyl-2'-propyl[2,6'-bi-1H-benzimidazol]-1'-yl) methyl]-[1,1'-biphenyl]-2-carboxylic acid, in three doses (0.1, 1 and 3 mg/kg body weight) for 9 weeks.

METHODS

The concentrations of the renin-angiotensin system components were analysed in plasma and tissues by radioimmunoassay. Messenger RNA levels for the angiotensinogen and renin genes were quantified by RNAase protection assay in several tissues. Heart hypertrophy and kidney morphology and function were monitored at the end of the treatment.

RESULTS

In contrast to 0.1 mg/kg, 1 and 3 mg/kg Telmisartan normalized tail blood pressure measured once a week. Plasma renin and angiotensin II concentration increases were dose-dependent. The renin-angiotensin system genes in various cardiovascular organs were differentially regulated by angiotensin II receptor blockade. Treatment with Telmisartan stimulated angiotensinogen gene expression in the liver, kidney and heart, whereas it remained unchanged in the hypothalamus, thymus and adrenal gland. In the kidney, the expression of the endogenous, but not of the mouse Ren-2 gene, was increased in parallel to the renin concentration. Telmisartan reduced the severe glomerulosclerosis and proteinuria as well as cardiac hypertrophy observed in untreated TGR(mREN2)27 even with the lowest dose of 0.1 mg/kg, at which the blood pressure of the rats still exceeded 225 mmHg and the plasma renin-angiotensin system parameters were unchanged.

CONCLUSION

From these experiments using a specific antagonist we can conclude that high blood pressure in TGR(mREN2)27 is angiotensin II-dependent. Furthermore, the expression of the renin-angiotensin system genes seems to be regulated not only by blood pressure and the plasma renin-angiotensin system but also by other, tissue-specific mechanisms. Pathomorphological changes in the kidney and in the heart do not seem to be caused by the systemic hypertension exclusively, but are also influenced by angiotensin II directly.

Chronic dexamethasone treatment suppresses hypertension development in the transgenic rat TGR(mREN2)27

INTRODUCTION

The transgenic rat TGR(mREN2)27 is a monogenetic rat model in hypertension research. Integration of mouse Ren-2 gene into the rat genome led to fulminant hypertension despite suppressed plasma and kidney renin concentrations. Renin is highly expressed in extrarenal tissues, especially throughout the adrenal cortex.

AIMS AND METHODS

Because plasma and urinary corticosteroid concentrations are elevated during the development of hypertension in these rats, we investigated the effect of dexamethasone on blood pressure, adrenal renin and steroid metabolism.

RESULTS

A daily injection of 100 micrograms/kg dexamethasone for 8 weeks was capable of suppressing the development of hypertension in the transgenic rats. The same regimen did not alter blood pressure in Sprague-Dawley control rats. Plasma concentrations of adrenocorticotrophic hormone (ACTH)-dependent steroids (corticosterone and 18-hydroxydeoxycorticosterone) decreased markedly in both strains treated with dexamethasone, but more pronouncedly in transgenic rats. Surprisingly, plasma aldosterone concentrations increased exclusively in the transgenic rats, and not in control rats, treated with dexamethasone. The decrease in corticosterone and 18-hydroxydeoxycorticosterone production was accompanied by a decrease in the abundance of the messenger RNA (mRNA) encoding the rate-limiting enzyme in steroidogenesis (P450scc cholesterol side-chain cleavage) and a decrease in the mRNA encoding P450c11 beta (11 beta-hydroxylase). The increase in aldosterone was accompanied by a massive increase in the abundance of the mRNA encoding zona glomerulosa-specific P450c11AS (aldosterone synthase), which was not increased in control rats.

CONCLUSION

We conclude that ACTH-dependent steroids other than the mineralocorticoid aldosterone are responsible for the development of hypertension in the transgenic rat.