(1/383) The subtype 2 of angiotensin II receptors and pressure-natriuresis in adult rat kidneys.
The present work examined the effects of the subtype 2 of angiotensin II (AT2) receptors on the pressure-natriuresis using a new peptide agonist, and the possible involvement of cyclic guanosine 3', 5' monophosphate (cyclic GMP) in these effects. In adult anaesthetized rats (Inactin, 100 mg kg(-1), i.p.) deprived of endogenous angiotensin II by angiotensin converting enzyme inhibition (quinapril, 10 mg kg(-1), i.v.), T2-(Ang II 4-8)2 (TA), a highly specific AT2 receptor agonist (5, 10 and 30 microg kg(-1) min(-1), i.v.) or its solvent was infused in four groups. Renal functions were studied at renal perfusion pressures (RPP) of 90, 110 and 130 mmHg and urinary cyclic GMP excretion when RPP was at 130 mmHg. The effects of TA (10 microg kg(-1) min(-1)) were reassessed in animals pretreated with PD 123319 (PD, 50 microg kg(-1) min(-1), i.v.), an AT2 receptor antagonist and the action of the same dose of PD alone was also determined. Increases in RPP from 90 to 130 mmHg did not change renal blood flow (RBF) but induced 8 and 15 fold increases in urinary flow and sodium excretion respectively. The 5 microg kg(-1) min(-1) dose of TA was devoid of action. The 10 and 30 microg kg(-1) min(-1) doses did not alter total RBF and glomerular filtration rate, but blunted pressure-diuresis and natriuresis relationships. These effects were abolished by PD. TA decreased urinary cyclic GMP excretion. After pretreatment with PD, this decrease was reversed to an increase which was also observed in animals receiving PD alone. In conclusion, renal AT2 receptors oppose the sodium and water excretion induced by acute increases in blood pressure and this action cannot be directly explained by changes in cyclic GMP. (+info)
(2/383) Cardiac growth factors in human hypertrophy. Relations with myocardial contractility and wall stress.
The aim of the present study was to investigate whether and which cardiac growth factors are involved in human hypertrophy, whether growth factor synthesis is influenced by overload type and/or by the adequacy of the hypertrophy, and the relationships between cardiac growth factor formation and ventricular function. Cardiac growth factor formation was assessed by measuring aorta-coronary sinus concentration gradient in patients with isolated aortic stenosis (n=26) or regurgitation (n=15) and controls (n=12). Gene expression and cellular localization was investigated in ventricular biopsies using reverse transcriptase-polymerase chain reaction and in situ hybridization. Cardiac hypertrophy with end-systolic wall stress <90 kdyne/cm2 was associated with a selective increased formation of insulin-like growth factor (IGF)-I in aortic regurgitation and of IGF-I and endothelin (ET)-1 in aortic stenosis. mRNA levels for IGF-I and preproET-1 were elevated and mainly expressed in cardiomyocytes. At stepwise analysis, IGF-I formation was correlated to the mean velocity of circumferential fiber shortening (r=0.86, P<0.001) and ET-1 formation to relative wall thickness (r=0.82, P<0. 001). When end-systolic wall stress was >90 kdyne/cm2, IGF-I and ET-1 synthesis by cardiomyocytes was no longer detectable, and only angiotensin (Ang) II was generated, regardless of the type of overload. The mRNA level for angiotensinogen was high, and the mRNA was exclusively expressed in the interstitial cells. Ang II formation was positively correlated to end-systolic stress (r=0.89, P<0.001) and end-diastolic stress (r=0.84, P<0.001). Multivariate stepwise analysis selected end-systolic stress as the most predictive variable and left ventricular end-diastolic pressure as the independent variable for Ang II formation (r=0.93, P<0.001). In conclusion, the present results indicate that the course of human left ventricular hypertrophy is characterized by the participation of different cardiac growth factors that are selectively related both to the type of hemodynamic overload and to ventricular function. (+info)
(3/383) Angiotensin regulates the selectivity of the Na+-K+ pump for intracellular Na+.
Treatment of rabbits with angiotensin-converting enzyme (ACE) inhibitors increases the apparent affinity of the Na+-K+ pump for Na+. To explore the mechanism, we voltage clamped myocytes from control rabbits and rabbits treated with captopril with patch pipettes containing 10 mM Na+. When pipette solutions were K+ free, pump current (Ip) for myocytes from captopril-treated rabbits was nearly identical to that for myocytes from controls. However, treatment caused a significant increase in Ip measured with pipettes containing K+. A similar difference was observed when myocytes from rabbits treated with the ANG II receptor antagonist losartan and myocytes from controls were compared. Treatment-induced differences in Ip were eliminated by in vitro exposure to ANG II or phorbol 12-myristate 13-acetate or inclusion of the protein kinase C fragment composed of amino acids 530-558 in pipette solutions. Treatment with captopril had no effect on the voltage dependence of Ip. We conclude that ANG II regulates the pump's selectivity for intracellular Na+ at sites near the cytoplasmic surface. Protein kinase C is implicated in the messenger cascade. (+info)
(4/383) Central lead administration inhibits water intake and sodium appetite in rats.
We have demonstrated that acute third ventricle injections of lead acetate (PbAc) exert a powerful antidipsogenic effect and induce a significant increase in renal sodium excretion. In the present study we confirm the antidipsogenic effect of lead and demonstrate that central administration of this metal, in minute amounts, significantly reduces salt intake both during dehydration and after central angiotensinergic stimulation. Adult male Wistar rats had the third ventricle cannulated seven days before the experiments. During this period they had free access to distilled water and hypertonic saline solution (1.5%). After a 24-h period of fluid deprivation, experimental animals received third ventricle injections of PbAc (0.3, N = 8 and 3.0 nmol/rat, N = 14) while controls received sodium acetate (NaAc; 3.0 nmol/rat, N = 10). Rats treated with PbAc at the highest dose showed a significant reduction (P<0.05) both in water and hypertonic saline intake when compared to controls. When the effect of lead administration on angiotensin II-induced water and salt intake was studied, normohydrated animals received third ventricle injections of angiotensin II (9.6 nmol/rat) after pretreatment with 3.0 nmol/rat of PbAc (experimental group, N = 10) or NaAc (controls, N = 8). The group pretreated with PbAc presented a significant reduction (P<0.05) in both water and salt intake compared to controls. Thus, this study confirms the antidipsogenic effect of central lead injections and demonstrates that the presence of lead in the brain exerts a significant inhibition of sodium appetite. (+info)
(5/383) Self-protection by cardiac myocytes against hypoxia and hyperoxia.
Cardiac muscle must maintain a continuous balance between its energy supply and work performed. An important mechanism involved in achievement of this balance is cross talk via chemical signals between cardiac myocytes and the cardiac muscle vascular system. This has been demonstrated by incubating isolated cardiac myocytes in different concentrations of oxygen and then assaying the conditioned media for vasoactive substances on isolated aortic rings and small-resistance arteries. With increasing oxygen concentrations above 6%, cardiac myocytes produce increasing amounts of angiotensin I, which is converted to angiotensin II by the blood vessel. The angiotensin II stimulates vascular endothelial cells to secrete endothelin and increase vascular tone. Below 6% oxygen, cardiac myocytes secrete adenosine, which acts directly on vascular smooth muscle to block the effect of alpha-adrenergic agonists and reduce vascular tone. In an intact heart, the net effect of these 2 regulatory systems would be the maintenance of oxygen concentration within a narrow range at the cardiac myocytes. By acting as oxygen sensors, cardiac myocytes modulate vascular tone according to the needs of the myocytes and reduce potential problems of hypoxia and extensive formation of reactive oxygen species. (+info)
(6/383) Regulated expression of human angiotensinogen gene by hepatocyte nuclear factor 4 and chicken ovalbumin upstream promoter-transcription factor.
We previously identified various upstream and downstream regulatory elements and factors important for hepatic expression of the human angiotensinogen (ANG) gene, the precursor of vasoactive octapeptide angiotensin II. In the present study, to further investigate the molecular mechanism of human ANG transcriptional regulation, we generated transgenic mice carrying the fusion gene composed of the 1. 3-kilobase promoter of the human ANG gene, its downstream enhancer, and the chloramphenicol acetyltransferase reporter gene. Because expression of the chloramphenicol acetyltransferase gene was observed strongly in the liver and weakly in the kidney, we suspected that hepatocyte nuclear factor (HNF) 4 with a tissue expression pattern similar to that of the reporter gene would regulate ANG transcription. In vitro assays indicated that HNF4 bound to the promoter elements and strongly activated the ANG transcription, but that chicken ovalbumin upstream promoter transcription factor (COUP-TF), a transcriptional repressor, dramatically repressed human ANG transcription through the promoter elements and the downstream enhancer core elements. Furthermore, COUP-TF dramatically decreased the human ANG transcription in the mouse liver by the Helios Gene Gun system in vivo. These results suggest that an interplay between HNF4 and COUP-TF could be important in hepatic human ANG transcription. (+info)
(7/383) Evaluation of the angiotensin challenge methodology for assessing the pharmacodynamic profile of antihypertensive drugs acting on the renin-angiotensin system.
AIMS: The performance of the experimental paradigm of angiotensin challenges with continuous non-invasive blood pressure measurement was evaluated. Angiotensin dose-response relationships were characterized, along with the influence of clinical covariates. The stability of angiotensin-induced peaks and the variability of the angiotensin doses were assessed. Finally, the predictive value of studies based on angiotensin challenges to determine drug doses effective in therapeutics was evaluated. METHODS: The data were gathered from 13 clinical studies on nine angiotensin II receptor antagonists, one ACE inhibitor and one dual ACE-NEP inhibitor, using Finapres for measuring the response to exogenous angiotensin challenges. Modelling of angiotensin dose-response curves and determination of the inter and intrasubject variability were performed by nonlinear regression (NONMEM). The different sources of variations in angiotensin I and II doses and angiotensin-induced peaks were evaluated by analyses of variance. The dose of ACE inhibitors and angiotensin II receptor antagonists inhibiting blood pressure increase by at least 75%, as measured by this method, was chosen for comparison with the labelled starting dose. RESULTS: Angiotensin challenges exhibited a clear dose-response relationship which can be characterized both by an Emax or a log linear model. The log linear model gave an average systolic/diastolic response of 24+/-6/20+/-5 mmHg for a unit dose of 1 microgram of angiotensin II equivalents, and an increase of 6/6 mmHg for each doubling of the dose. The angiotensin ED50 calculated values were 0.67 microgram for systolic and 0.84 microgram for diastolic blood pressure. The angiotensin doses for eliciting a given response and the angiotensin induced peaks were fairly constant between period and subject, but vary significantly between studies. Based on an inhibition of blood pressure by 75%, the agreement was good between the doses of ACE inhibitors and angiotensin receptor antagonists predicted from studies using the methodology of angiotensin challenges and the doses shown to be clinically efficacious, in spite of high intersubject and intrasubject variabilities. CONCLUSIONS: This experimental method represents a valid surrogate for the therapeutic target and a useful tool for the pharmacokinetic and pharmacodynamic profiling of drugs acting on the renin-angiotensin system. (+info)
(8/383) Angiotensin I-converting enzyme antisense gene therapy causes permanent antihypertensive effects in the SHR.
The renin-angiotensin system plays a critical role in the control of blood pressure (BP), and its hyperactivity is associated with the development and maintenance of hypertension. Although traditional pharmacological therapies targeted toward the inhibition of the renin-angiotensin system are effective in the control of this disease, they pose significant limitations. We used an antisense gene delivery strategy to circumvent these limitations and established that a single intracardiac administration of angiotensin type 1 receptor antisense (AT(1)R-AS) causes permanent prevention of hypertension in the spontaneously hypertensive rat (SHR), an animal model of primary human hypertension. Our objectives in this study were 2-fold: to determine (1) whether the targeting of angiotensin I-converting enzyme (ACE) mRNA by a similar antisense strategy would prevent the SHR from developing hypertension and (2) whether the antihypertensive phenotype is transmitted to the offspring from the antisense-treated parents. Administration of a retroviral vector containing ACE antisense (LNSV-ACE-AS) caused a modest yet significant attenuation of high BP ( approximately 15+/-2 mm Hg) exclusively in the SHR. This was associated with a complete prevention of cardiac and renovascular pathophysiological alterations that are characteristic of hypertension. Like their parents, the F(1) generation offspring of the LNSV-ACE-AS-treated SHR expressed lower BP, decreased cardiac hypertrophy, and normalization of renal arterial excitation-coupling compared with offspring derived from the LNSV-ACE-tS (truncated sense)-treated SHR. In addition, the endothelial dysfunction commonly observed in the SHR renal arterioles was significantly prevented in both parents and offspring of the LNSV-ACE-AS-treated SHR. Polymerase chain reaction followed by Southern analysis revealed that the ACE-AS was integrated into the SHR genome and transmitted to the offspring. These observations suggest that transmission of ACE-AS by retroviral vector may be responsible for the transference of normotensive phenotypes in the SHR offspring. (+info)