Synergistic effect of angiotensin-(1-7) on bradykinin arteriolar dilation in vivo

The interaction between angiotensin [Ang-(1-7)] and bradykinin (BK) was determined in the mesentery of anesthetized Wistar rats using intravital microscopy. Topical application of BK and Ang-(1-7) induced vasodilation that was abolished by the BK B2 receptor antagonist HOE-140 and the Ang-(1-7) antagonist A-779, respectively. BK (1 pmol)-induced vasodilation, but not SNP and ACh responses, was potentiated by Ang-(1-7) 10 pmol and 100 pmols. The effect of 100 pmol of Ang-(1-7) on BK-induced vasodilation was abolished by A-779, indomethacin, and L-nitroarginine methyl esther, whereas losartan was without effect. Enalaprilat treatment enhanced the BK- and Ang-(1-7)-induced vasodilation and the potentiating effect of Ang-(1-7) on BK vasodilation. The potentiation of BK-induced vasodilation by Ang-(1-7) is a receptor-mediated phenomenon dependent on cyclooxygenase-related products and NO release.

Potentiation of the hypotensive effect of bradykinin by angiotensin-(1-7)-related peptides

In this study, we evaluated the bradykinin potentiating activity and ACE inhibitory activity of several Ang-(1-7)-related peptides: Ang-(2-7), Ang-(3-7), Ang-(4-7), Ang-(1-6), Ang-(1-5) and the selective antagonist of Ang-(1-7): D-[Ala7]Ang-(1-7) (A-779). In vivo experiments were performed in freely moving Wistar rats. ACE activity was evaluated by a fluorometric assay in rat plasma using Hip-His-Leu as a substrate. Intravenous injections of Ang-(1-7) (2.2 nmol) transformed the effect of a single dose of bradykinin (1 nmol) into the effect produced by a double dose. A similar bradykinin potentiating activity was demonstrated for Ang-(2-7) and Ang-(3-7). On the other hand, Ang-(1-5), Ang-(1-6), Ang-(4-7) and A-779 did not change the hypotensive effect of bradykinin in doses ranging from 8 up to 25 nmols. The hypotensive effect of bradykinin was increased by intravenous infusion (0.3 ng/min) of Ang-(1-7) > Ang-(2-7) > Ang-(3-7). Conversely, Ang-(1-5), Ang-(1-6), Ang-(4-7) or A-779 did not change the hypotensive effect of bradykinin. ACE inhibition with Ang-(1-7) related peptides occurred in the order: Ang-(2-7) > or = Ang-(3-7) > Ang-(1-7) [>>] Ang-(1-5) > Ang-(4-7) > or = Ang-(1-6) > or = A-779. A-779 in concentrations up to 10(-5) M did not change the ACE inhibitory activity of Ang-(1-7). These results suggest that Ang-(1-7), Ang-(2-7) and Ang-(3-7) can modulate bradykinin actions in vivo. More important, our data pointed out that alternative mechanisms besides interaction with ACE are required to explain the bradykinin potentiating activity of Ang-(1-7).

Interaction of bradykinin and angiotensin-(1-7) in the central modulation of the baroreflex control of the heart rate

OBJECTIVE

Previous studies have shown that angiotensin-(1-7) potentiates the vascular actions of bradykinin. In the present study, we evaluated the interaction of bradykinin and angiotensin-(1-7) in the central modulation of baroreflex control of the heart rate.

MATERIALS AND METHODS

Blood pressure and reflex bradycardia, elicited by intravenous injection of phenylephrine, were evaluated in conscious male Wistar rats before and at the end of 1 h of an intracerebroventricular infusion of angiotensin-(1-7) at 0.5 or 1.0 microg/h combined with bradykinin at 2.5 microg/h; or angiotensin-(1-7) at 2.0 microg/h combined with bradykinin at 4.0 microg/h; or angiotensin-(1-7) alone at 2.0 or 4.0 microg/h; or bradykinin alone at 4.0 or 8.0 microg/h; or saline at 8 microl/h. In addition, baroreflex bradycardia was evaluated before and at the end of 1 and 2 h of intracerebroventricular infusion of angiotensin-(1-7) at 4 microg/h for 2 h; or saline at 8 microl/h in the first hour followed by HOE 140 at 90 ng/h in the second hour; or angiotensin-(1-7) at 4 microg/h in the first hour followed by angiotensin-(1-7) at 4 microg combined with HOE 140 at 90 ng/h in the second hour; or HOE 140 at 90 ng/h in the first hour followed by HOE 140 at 90th ng/h combined with angiotensin-(1-7) at 4 microg/h in the second hour; or saline at 8 microl/h for 2 h.

RESULTS

The intracerebroventricular infusion of angiotensin-(1-7) or bradykinin alone required a dose of 4.0 and 8.0 microg/h, respectively, to facilitate baroreflex control of the heart. However, a simultaneous infusion of these peptides at subeffective rates was able to produce a significant increase in baroreflex sensitivity. In addition, the facilitation of the baroreflex control of the heart rate induced by angiotensin-(1-7) at 4.0 microg/h was inhibited by HOE 140.

CONCLUSIONS

These results suggest that centrally, bradykinin and angiotensin-(1-7) can interact in order to modulate baroreflex control of the heart rate. In addition, our data indicate that the central modulatory effect of angiotensin-(1-7) on the baroreflex is mediated, at least in part, by the release of kinins.

Varicella-zoster virus glycoprotein gE: endocytosis and trafficking of the Fc receptor

Varicella-zoster virus (VZV) encodes a functional cell membrane Fc receptor called glycoprotein gE. VZV gE resembles other mammalian cell membrane receptors, such as the mammalian Fc receptor. In further analyses by transient transfection, the cellular trafficking of VZV gE was compared to other cell surface receptors. VZV gE was shown to undergo endocytosis from the cell membrane when visualized by laser scanning confocal microscopy. The endocytosis and trafficking pathway of VZV gE followed closely the pathway defined for the human transferrin receptor. Receptor-mediated endocytosis of VZV gE was dependent on a YAGL motif in its cytoplasmic tail. In addition, VZV gE underwent receptor-mediated endocytosis when it bound the Fc portion of immunoglobulin. Thus, this detailed study of VZV gE cellular trafficking has revealed potential roles for gE during viral infection.

Antigenic variation of varicella zoster virus Fc receptor gE: loss of a major B cell epitope in the ectodomain

Varicella zoster virus (VZV) is considered to possess a genetically stable genome; only one serotype is recognized around the world. The 125-kbp genome contains approximately 70 open reading frames. One that has received particular attention is open reading frame 68, which codes for glycoprotein gE, the predominant 623-residue viral envelope product that harbors both B and T cell epitopes. This report describes the initial characterization of a community-acquired VZV isolate that was a distinguishable second serotype (i.e., it had lost a major B cell epitope defined on the gE ectodomain by a murine monoclonal antibody called mAb 3B3). The mAb 3B3 epitope was found not only on the prototype sequenced Dumas strain from Holland and all previously tested North American isolates but also on the varicella vaccine Oka strain originally attenuated in Japan. Sequencing of the mutated gE ectodomain demonstrated that codon 150 exhibited a single base change that led to an amino acid change (aspartic acid to asparagine). Observation of the monolayers infected with the mutant VZV strain also led to the surprising discovery that the topography of egress was altered. Wild-type VZV emerges along distinctive viral highways, whereas the mutant strain virions were nearly uniformly distributed over the cell surface in a pattern more closely resembling egress of herpes simplex virus 1. The mutant VZV strain was designated VZV-MSP because it was isolated in Minnesota.

Effect of selective angiotensin antagonists on the antidiuresis produced by angiotensin-(1-7) in water-loaded rats

In the present study we evaluated the nature of angiotensin receptors involved in the antidiuretic effect of angiotensin-(1-7) (Ang-(1-7)) in water-loaded rats. Water diuresis was induced in male Wistar rats weighing 280 to 320 g by water load (5 ml/100 g body weight by gavage). Immediately after water load the rats were treated subcutaneously with (doses are per 100 g body weight): 1) vehicle (0.05 ml 0.9% NaCl); 2) graded doses of 20, 40 or 80 pmol Ang-(1-7); 3) 200 nmol Losartan; 4) 200 nmol Losartan combined with 40 pmol Ang-(1-7); 5) 1.1 or 4.4 nmol A-779; 6) 1.1 nmol A-779 combined with graded doses of 20, 40 or 80 pmol Ang-(1-7); 7) 4.4 nmol A-779 combined with graded doses of 20, 40 or 80 pmol Ang-(1-7); 8) 95 nmol CGP 42112A, or 9) 95 nmol CGP 42112A combined with 40 pmol Ang-(1-7). The antidiuretic effect of Ang-(1-7) was associated with an increase in urinary Na+ concentration, an increase in urinary osmolality and a reduction in creatinine clearance (CCr: 0.65 +/- 0.04 ml/min vs 1.45 +/- 0.18 ml/min in vehicle-treated rats, P < 0.05). A-779 and Losartan completely blocked the effect of Ang-(1-7) on water diuresis (2.93 +/- 0.34 ml/60 min and 3.39 +/- 0.58 ml/60 min, respectively). CGP 42112A, at the dose used, did not modify the antidiuretic effect of Ang-(1-7). The blockade produced by Losartan was associated with an increase in CCr and with an increase in sodium and water excretion as compared with Ang-(1-7)-treated rats. When Ang-(1-7) was combined with A-779 there was an increase in CCr and natriuresis and a reduction in urine osmolality compared with rats treated with Ang-(1-7) alone. The observation that both A-779, which does not bind to AT1 receptors, and Losartan blocked the effect of Ang-(1-7) suggests that the kidney effects of Ang-(1-7) are mediated by a non-AT1 angiotensin receptor that is recognized by Losartan.

Diuresis and natriuresis produced by long term administration of a selective Angiotensin-(1-7) antagonist in normotensive and hypertensive rats

In this study we evaluated the renal effects of chronic administration of the selective Angiotensin-(1-7)[Ang-(1-7)] antagonist, A-779, in normotensive and spontaneously hypertensive rats (SHR). Male adult SHR and Wistar rats were housed in metabolic cages with tap water and standard chow, for three-five days before starting infusion (Alzet osmotic mini-pumps) of A-779 (Wistar: 1 microg/h, n = 9; 2.5 microg/h, n = 6; SHR:2.5 microg/h, n = 6) or vehicle (0.9% NaCl - 1 microl/h, n = 7 and n = 10 for SHR and Wistar rats, respectively). Urine volume, water and food intake and urinary Na+ were measured daily. On the last day of infusions mean arterial pressure (MAP) was recorded and urine and blood samples were collected to determine renal function parameters. Chronic infusion of A-779 produced a sustained increase in diuresis in normotensive rats [seventh day values: 0.75+/-0.08 ml/h (1 microg/h) and 0.94+/-0.13 ml/h (2.5 microg/h) vs. 0.42 + 0.03 ml/h for the control group, P<0.05] associated to a dose-dependent increase in the creatinine clearance. In SHR, diuresis increased significantly after chronic infusion of A-779 (fifth day values: 0.44 + 0.06 ml/h vs. 0.25+/-0.04 ml/h for the control group, P<0.05), without changes in creatinine clearance. Infusion of A-779 in normotensive rats produced a decrease in water reabsorption. A-779 infusion also produced a dose-dependent increase in urinary Na+ excretion (1.49 + 0.14 mEq, 1 microg/h vs. 2.37+/-0.22 mEq, 2.5 microg/h, P<0.05), in Wistar rats, without modifying the fractional excretion of Na+. In SHR, urinary Na+ excretion was also increased by A-779 (2.21+/-0.46 mEq vs. 0.94+/-0.22 mEq for the control group, P<0.05). No significant changes in blood pressure were observed. These findings suggest that endogenous Ang-(l-7) participates in the control of hydroelectrolyte balance by modulating water excretion, acting at tubular and glomerular sites.

A comparative analysis of preprocessing techniques of cardiac event series for the study of heart rhythm variability using simulated signals

In the present study, using noise-free stimulated signals, we performed a comparative examination of several preprocessing techniques that are used to transform the cardiac event series in a regularly sampled time series, appropriate for spectral analysis of heart rhythm variability (HRV). First, a group of noise-free simulated point event series, which represents a time series of heartbeats, was generated by an integral pulse frequency modulation models. In order to evaluate the performance of the preprocessing methods, the differences between the spectra of the preprocessed simulated signals and the true spectrum (spectrum of the model input modulating signals) were surveyed by visual analysis and by contrasting merit indices. It is desired that estimated spectra match the true spectrum as close as possible, showing a minimum of harmonic components and other artifacts. The merit indices proposed to quantify these mismatches were the leakage rate, defined as a measure of leakage components (located outside some narrow windows centered at frequencies of model input modulating signals) with respect to the whole spectral components, and the numbers of leakage components with amplitudes greater than 1%, 5% and 10% of the total spectral components. Our data, obtained from a noise-free simulation, indicate that the utilization of heart rate values instead of heart period values in the derivation of signals representative of heart rhythm results in more accurate spectra. Furthermore, our data support the efficiency of the widely used preprocessing technique based on the convolution of inverse interval function values with a rectangular window, and suggest the preprocessing technique based on a cubic polynomial interpolation of inverse interval function values and succeeding spectral analysis as another efficient and fast method for the analysis of HRV signals.

Potentiation of the hypotensive effect of bradykinin by short-term infusion of angiotensin-(1-7) in normotensive and hypertensive rats

In this study we evaluated the effect of angiotensin-(1-7) on the hypotensive action of bradykinin (BK) in normotensive rats, renal hypertensive rats (RHR), and spontaneously hypertensive rats (SHR). In addition, we evaluated the effect of angiotensin-converting enzyme (ACE) inhibition with enalaprilat treatment (10 mg/kg I.V.) on the BK-potentiating activity of Ang-(1-7). Renal hypertension was produced by aorta coarctation between the origin of renal arteries. Ang-(1-7) (0.3 pmol/min) or saline (0.9% NaCl, 5 microL/min) was infused intravenously in conscious male Wistar rats, adult SHR, or RHR. Intravenous bolus injections of BK (0.1 to 1.6 nmol in RHR and SHR; 0.625 to 5 nmol in Wistar rats) were made before and within 30 and 60 minutes of Ang-(1-7) infusion. Ang-(1-7) infusion did not change mean arterial pressure (MAP) of Wistar rats (MAP=97+/-3 mm Hg), RHR (MAP=173+/-3 mm Hg), or SHR (MAP=177+/-5 mm Hg). In Wistar rats, Ang-(1-7) increased the BK hypotensive effect by 24+/-6% within 60 minutes of infusion. No significant changes were observed at 30 minutes of infusion. In additional groups of rats, Ang-(1-7) (5 pmol/min, n=5) was infused alone or combined with its selective antagonist D-Ala7-Ang-(1-7) (A-779) (5 pmol/min, n=6). The bradykinin-potentiating activity of Ang-(1-7) was completely abolished by A-779. In SHR and RHR, Ang-(1-7) significantly increased the hypotensive effect of BK by 59+/-8% and 57+/-9.8%, respectively, within 60 minutes of infusion. No significant changes were observed with saline infusion. In Wistar rats, enalaprilat treatment increased the BK-potentiating activity of Ang-(1-7) transforming the effect of 0.3 pmol/min into that observed with a rate 16-fold higher (5 pmol/min). On the other hand, in SHR enalaprilat did not change the Ang-(1-7) effect, while it abolished the BK potentiation in RHR. Our data show that the BK-potentiating activity of Ang-(1-7) is preserved and even augmented in hypertensive rats. The finding that the BK-potentiating activity of Ang-(1-7) could be demonstrated at a very low infusion rate suggests that this angiotensin can act as an endogenous modulator of the vascular actions of kinins. ACE inhibition can influence differently the BK-potentiating activity of Ang-(1-7) in normotensive and hypertensive rats.

Role of angiotensin-(1-7) in the modulation of the baroreflex in renovascular hypertensive rats

In this study, we evaluated the effect produced by lateral ventricle (intracerebroventricular, I.C.V.) infusion of the selective angiotensin (Ang)-(1-7) antagonist, D-Ala7-Ang-(1-7) (A-779), in the modulation of the baroreflex control of heart rate in two-kidney, one clip renovascular hypertensive rats (2K1C) treated with the angiotensin-converting enzyme (ACE) inhibitor enalapril. Twenty days after the surgery to produce renovascular hypertension, I.C.V. cannulas were implanted in the rats with blood pressure (BP) greater than 145 mm Hg (n=33) and in sham-operated rats (n=32). Five days later, the rats were treated with enalapril (10 mg x kg(-1) x d(-1); 6 days, in the drinking water) or vehicle (tap water). On the sixth day of treatment, direct continuous BP recording and measurement of reflex changes in heart rate elicited by phenylephrine were made in conscious rats before and at 1 hour of I.C.V. infusion of saline (8 microL/h) or A-779 (4 microg/h). To evaluate the degree of ACE blockade produced by enalapril treatment, the pressor effect of Ang I (50 ng, I.V., and 100 ng, I.C.V.) and plasma ACE activity was determined. As expected, enalapril treatment in 2K1C produced a significant fall in BP, significant attenuation in the pressor response of Ang I (I.V.), and a reduction in plasma ACE activity. In addition, enalapril treatment increased the baroreflex sensitivity (0.76+/-0.04 versus 0.43+/-0.04 ms/mm Hg in 2K1C untreated rats). I.C.V. infusion of A-779 reverted the improvement in baroreflex sensitivity produced by enalapril treatment in 2K1C (from 0.80+/-0.07 to 0.42+/-0.08 ms/mm Hg) and also attenuated the baroreflex sensitivity in untreated 2K1C (0.36+/-0.05 versus 0.48+/-0.06 ms/mm Hg) and untreated sham-operated rats (1.21+/-0.05 versus 0.78+/-0.17 ms/mm Hg). These results suggest that central endogenous Ang-(1-7) is involved at least in part in the improvement of baroreflex sensitivity observed in 2K1C after peripheral chronic ACE inhibition.

Effect of angiotensin-(1-7) on reperfusion arrhythmias in isolated rat hearts

There is increasing evidence that angiotensin-(1-7)(Ang-(1-7)) is an endogenous biologically active component of the renin-angiotensin system(RAS). In the present study, we investigated the effects of Ang-(1-7) on reperfusion arrhythmias in isolated rat hearts. Isolated rat hearts were perfused with two different media, i.e., Krebs-Ringer (2.52 mM CaCl2) and low-Ca2+ Krebs-Ringer (1.12 mM CaCl2). In hearts perfused with Krebs-Ringer, Ang-(1-7) produced a concentration-dependent (27-210 nM) reduction in coronary flow (25% reduction at highest concentration), while only slight and variable changes in contraction force and heart rate were observed. Under the same conditions, angiotensin II (Ang II; 27 and 70 nM) produced a significant reduction in coronary flow (39% and 48%, respectively) associated with a significant increase in force. A decrease in heart rate was also observed. In low-Ca2+ Krebs-Ringer solution, perfusion with Ang-(1-7) or Ang II at 27 nM concentration produced similar changes in coronary flow, contraction force and heart rate. In isolated hearts perfused with normal Krebs-Ringer, Ang-(1-7) produced a significant enhancement of reperfusion arrhythmias revealed by an increase in the incidence and duration of ventricular tachycardia and ventricular fibrillation (more than 30-min duration). The facilitation of reperfusion arrhythmias by Ang-(1-7) was associated with an increase in the magnitude of the decreased force usually observed during the postischemic period. The effects of Ang-(1-7) were abolished in isolated rat hearts perfused with low-Ca2+ Krebs-Ringer. The effect of Ang II (27 nM) was similar but less pronounced than that of Ang-(1-7) at the same concentration. These results indicate that the heart is a site of action for Ang-(1-7) and suggest that this heptapeptide may be involved in the mediation of the cardiac effects of the RAS.

Renal actions of angiotensin-(1-7)

The heptapeptide angiotensin-(1-7) is considered to be a biologically active endproduct of the renin-angiotensin system. This angiotensin, which is devoid of the most known actions of angiotensin II such as induction of drinking behavior and vasoconstriction, has several selective effects in the brain and periphery. In the present article we briefly review recent evidence for a physiological role of angiotensin-(1-7) in the control of hydroelectrolyte balance.

Cardiovascular effects produced by microinjection of angiotensins and angiotensin antagonists into the ventrolateral medulla of freely moving rats

In this study we determined the cardiovascular effects produced by microinjection of angiotensin peptides [Angiotensin-(1-7) and Angiotensin II] and angiotensin antagonists (losartan, L-158,809, CGP 42112A. Sar1-Thr8-Ang II, A-779) into the rostral ventrolateral medulla of freely moving rats. Microinjection of angiotensins (12.5-50 pmol) produced pressor responses associated to variable changes in heart rate, usually tachycardia. Unexpectedly, microinjection of both AT1 and AT2 ligands produced pressor effects at doses that did not change blood pressure in anesthetized rats. Conversely, microinjection of Sar1-Thr8-Ang II and the selective Ang-(1-7) antagonist, A-779, produced a small but significant decrease in MAP an HR. These findings suggest that angiotensins can influence the tonic activity of vasomotor neurons at the RVLM. As previously observed in anesthetized rats, our results further suggest a role for endogenous Ang-(1-7) at the RVLM. The pressor activity of the ligands for AT1 and AT2 angiotensin receptor subtypes at the RVLM, remains to be clarified.

An investigation of rat mammary healthy and R3230AC tumor tissues and cells by means of solid-state 13C NMR

The first results are shown of a low temperature 13C solid-state, cross-polarization magic angle spinning (CPMAS) NMR study of R3230AC rat mammary carcinoma transplanted into female Fischer rats. Intact, healthy mammary tissues and tumor tissues, quickly frozen at -78 degrees C after excision, were examined, as were normal epithelial cells and tumor cells extracted from these tissues. The experiments were performed at -100 degrees C and -40 degrees C. The solid-state 13C NMR spectrum of the healthy tissue is dominated by the triacylglycerols present in the adipose tissue. The solid-state spectra of the other compounds differ significantly from the spectrum of the healthy tissue, and are dominated by the phospholipids and the large molecular weight proteins, for a major part present in the membranes. The spectra of the tumor tissues and the tumor cells were very similar, in accordance with the fact that the tumor tissues consisted of 80-90% tumor cells. The spectrum of the normal cells shows the same general features as those of the tumor tissue and tumor cells, but also exhibits some significant differences. The main difference at -100 degrees C is that, in the tumor samples, the relative intensity of the resonance line arising at 30 ppm, which is due to methylene chains, is reduced. At -40 degrees C this intensity is further reduced in the tumor samples, whereas the spectrum of the normal cells remains unaltered. It is tentatively concluded that the spectral differences between the normal and the malignant cells are due to changes in mobilities occurring in the cells after tumorigenesis, and that compared with normal epithelial cells the tumor cells contain an increased amount of mobile methylene chains. These differences virtually disappear if the samples are preserved at temperatures equal to or above 4 degrees C, emphasizing the importance of sample preservation at low temperatures, and hence of the solid-state NMR approach to investigate structures and dynamics in cells before and after tumor formation.

Pressor action of angiotensin I at the ventrolateral medulla: effect of selective angiotensin blockade

In this study we explored the possibility that angiotensin-(1-7) (Ang-(1-7)) is involved in the control of blood pressure at the rostral ventrolateral medulla (RVLM) by determining the effect of angiotensin antagonists (DuP 753 and A-779) and the effect of the angiotensin converting enzyme inhibitor, ramiprilat on the pressor action produced by angiotensin I (Ang I). The pressor effect produced by bilateral microinjection of Ang I into the RVLM of anesthetized rats was not significantly altered by DuP 753 or by the ACE inhibitor ramiprilat. Conversely, the Ang-(1-7) antagonist, A-779, reduced significantly the pressor effect produced by Ang I. These data suggest that in our experimental condition Ang I was preferentially converted to Ang-(1-7) at RVLM, or that Ang I and/or one of its fragments acts through a receptor blocked by A-779.

Changes in the baroreflex control of heart rate produced by central infusion of selective angiotensin antagonists in hypertensive rats

We have recently shown that an angiotensin-(1-7) [Ang-(I-7)] analogue, D-Ala7-Ang-(1-7) (A-779), is a selective Ang-(1-7) antagonist with no significant action on angiotensin type 1 or type 2 receptors. The availability of selective angiotensin antagonists prompted us to evaluate the role of Ang-(1-7) and Ang II on central modulation of the baroreflex control of heart rate in normotensive Wistar rats and spontaneously hypertensive rats (SHR). Blood pressure recording and reflex changes in heart rate elicited by intravenous bolus injections of phenylephrine were made before and within 1 and 3 hours of intracerebroventricular (ICV, lateral ventricle) infusion of saline (8 microL/h), A-779 (4 microg/h), DuP 753 (100 microg/h), or CGP 42112A (50 mu g/h) in conscious rats. The slope of the relationship between changes in pulse interval versus changes in mean arterial pressure was used as an index of the baroreflex control of heart rate. ICV infusion of saline or any of the antagonists did not significantly change basal levels of mean arterial pressure and heart rate in SHR (170 +/- 6 mm Hg nd 360 +/- 9 beats per minute, respectively; n = 29) or Wistar rats (108 +/- 2 mm Hg and 377 +/- 6 beats per minute, respectively; n=29). Three hours of ICV infusion of A-779 markedly decreased baroreflex sensitivity in Wistar rats (from a basal slope of 1.09 +/- O.3). In contrast, A-779 did not significantly alter the depressed baroreflex sensitivity of SHR (0.61 +/- O.l). ICV infusion of DuP 753 produced a significant increase (60 percent) in baroreflex control of heart rate in both Wistar rats and SHR. Saline or CGP 42112A infusions did not significantly alter baroreflex control of heart rate. These results suggest that endogenous Ang II and Ang-(1-7) are differentially affecting central baroreflex modulation, acting probably through distinct receptor subtypes. Although the central Ang II inhibitory effect is mediated by the type 1 receptor subtype, the facilitatory effect of Ang-(1-7) might be mediated by a different, unidentified receptor.

Global negative regulation of Streptomyces coelicolor antibiotic synthesis mediated by an absA-encoded putative signal transduction system

Streptomycete antibiotic synthesis is coupled to morphological differentiation such that antibiotics are produced as a colony sporulates. Streptomyces coelicolor produces several structurally and genetically distinct antibiotics. The S. coelicolor absA locus was defined by four UV-induced mutations that globally blocked antibiotic biosynthesis without blocking morphological differentiation. We show that the absA locus encodes a putative eubacterial two-component sensor kinase-response regulator system. All four mutations lie within a single open reading frame, designated absA1, which is predicted to encode a sensor histidine kinase. A second gene downstream of absA1, absA2, is predicted to encode the cognate response regulator. In marked contrast to the antibiotic-deficient phenotype of the previously described absA mutants, the phenotype caused by disruption mutations in the absA locus is precocious hyperproduction of the antibiotics actinorhodin and undecylprodigiosin. Precocious hyperproduction of these antibiotics is correlated with premature expression of XylE activity in a transcriptional fusion to an actinorhodin biosynthetic gene. We propose that the absA locus encodes a signal transduction mechanism that negatively regulates synthesis of the multiple antibiotics produced by S. coelicolor.

Effect of acute volume expansion associated with salt load on the profile of plasma angiotensins in rats

We measured the changes produced in renin and the peptide components of the circulating renin-angiotensin system by acute volume expansion alone or associated with salt load in rats. With both maneuvers, there was a decrease of plasma renin activity (PRA) and plasma angiotensin (Ang) concentrations, but the changes were more pronounced in the salt-load group. In contrasting to Ang I and Ang II, plasma Ang-(1-7) concentration decreased significantly only within 60 min of 5.0% NaCl infusion (19.5 +/- 2.9 vs 30.5 +/- 1.9 pg/ml in the control group). As expected, plasma vasopressin increased markedly in the animals submitted to acute salt load (144.0 +/- 42.0 vs 5.0 +/- 0.2 pg/ml in the control group). The dissociation between the changes in plasma Ang-(1-7) and that of other plasma angiotensins is consistent with our previous studies using chronic salt load, and suggests that during acute volume expansion associated with salt load Ang I is preferentially converted to Ang-(1-7). In contrast to vasopressin, however, plasma Ang-(1-7) concentration increased only after chronic salt load, suggesting that this angiotensin may be more involved with long-term mechanisms of control of hydromineral balance.

Cardiovascular effects produced by bradykinin microinjection into the nucleus tractus solitarii of anesthetized rats

In this study, we characterized the cardiovascular effects produced by microinjection of doses in the femtomole range of bradykinin (BK) into the nucleus tractus solitarii of male Wistar rats (230-280 g, n = 120) anesthetized with urethane (1.2 g/kg, i.p.). Microinjections of BK (1, 10, 100 fmol, and 1 and 10 pmol, in 50 nl) or vehicle (NaCl, 0.9%) were made by using a triple-barreled glass micropipette into the medial nTS (0.4 mm anterior, 0.3 mm lateral to the obex and 0.3 mm deep from the dorsal surface). Microinjection of BK produced a shallow dose-dependent decrease in mean arterial pressure and heart rate reaching -18 +/- 6 mmHg and -21 +/- 5 beats/min, with the dose of 10 pmol. The peripheral mechanism of these effects, tested in animals treated with methylatropine (2 mg/kg, i.v.), or propranolol (2 mg/kg, i.v.) or prazosin (30 micrograms/kg, i.v.), was shown to be mainly dependent on an increase in vagal efferent activity for bradycardia and a decrease in sympathetic activity for hypotension. In order to investigate the receptor subtype involved in these effects, BK was microinjected into the nTS before and after the injection of the B1 receptor antagonist, Des-Arg9-Leu8-BK (DALBK) (11.5 pmol) or before and after the B2 receptor antagonist, HOE-140 (7.7 pmol). The cardiovascular effects of BK were significantly attenuated by the microinjection of HOE-140 and DALBK into the nTS. The effect of BK microinjected into the nTS on the baroreflex modulation was also investigated. While BK produced a significant facilitation of the baroreflex, HOE-140 and DALBK produced a significant attenuation of the baroreceptor control of heart rate. Taken together, the data presented in this study indicate the nTS as a site, in the central nervous system, for the modulatory effect of BK on the central cardiovascular control.

Evidence for a physiological role of angiotensin-(1-7) in the control of hydroelectrolyte balance

In this study we evaluated the possibility that angiotensin-(1-7) [Ang-(1-7)] acts as an endogenous osmoregulatory peptide by determining the effect of acute administration of its selective antagonist [D-Ala7]Ang-(1-7) (A-779) on renal function parameters in rats. In addition, we investigated the physiological mechanisms involved in the antidiuretic effect of Ang-(1-7). The antidiuretic effect of Ang-(1-7) (40 pmol/0.05 mL per 100 g BW) in water-loaded rats was completely blocked by A-779 (vehicle-treated, 3.34 +/- 0.43 mL/h; Ang-(1-7), 1.48 +/- 0.23; A-779, 2.72 +/- 0.35; Ang-(1-7) plus A-779, 3.26 +/- 0.49). In contrast, the antidiuretic effect of Ang-(1-7) was not significantly changed by a vasopressin V2 receptor antagonist in a dose that completely blocked the antidiuresis produced by an equipotent dose of vasopressin. In addition, Ang-(1-7) administration did not significantly change vasopressin plasma levels in water-loaded rats. The antidiuretic effect of Ang-(1-7) in water-loaded rats was associated with a reduction of creatinine clearance (0.68 +/- 0.04 versus 1.38 +/- 0.32 mL/min in vehicle-treated rats, P <.05) and an increase in urine osmolality (266.8 +/- 32.7 versus 182.8 +/- 14 mOsm/kg in vehicle-treated rats, P <.05). An effect of Ang-(1-7) in tubular water transport was demonstrated in vitro by a fourfold increase in the hydraulic conductivity of inner medullary collecting ducts in the presence of 1 nmol/L Ang-(1-7). Subcutaneous administration of A-779 (2.3 to 9.2 nmol/100 g) produced a significant increase in urine volume (4.6 nmol/100 g, 0.45 +/- 0.12 mL/h; vehicle-treated rats, 0.16 +/- 0.03 mL/h; P <.05) comparable to that of acute administration of a vasopressin V2 receptor antagonist. The diuretic effect of A-779 was associated with an increase in creatinine clearance and decrease in urine osmolality. In contrast, no significant effects on urine volume were observed after systemic administration of angiotensin subtype 1 or 2 receptor antagonists (DuP 753 and CGP 42112A, respectively). These findings suggest that endogenous Ang-(1-7), acting on specific receptors, participates in the control of hydroelectrolyte balance by influencing especially water excretion.

Angiotensin-(1-7) potentiates the hypotensive effect of bradykinin in conscious rats

Treatment with angiotensin-converting enzyme inhibitors increases the angiotensin-(1-7) [Ang-(1-7)] and bradykinin concentrations in plasma and tissue. In this study we evaluated the interaction between these peptides by determining the effect of Ang-(1-7) on the hypotensive action of bradykinin in conscious rats. Administration of Ang-(1-7) (5 nmol) did not change mean arterial pressure or heart rate. However, the hypotensive effect of bradykinin, produced by an intravenous or intra-arterial route, was potentiated by Ang-(1-7) in a dose-dependent manner. The Ang-(1-7) doses necessary to transform the effect of a single dose of bradykinin into that produced by a double dose (potentiating unit) were 2 nmol i.v. and 5 nmol IA. The Ang-(1-7) dose used did not change either the pressor effect of Ang II or the hypotensive effect of sodium nitroprusside. The bradykinin-potentiating Ang-(1-7) activity was significantly attenuated by pretreatment with indomethacin (5 mg/kg IM, n = 4). In an additional group the bradykinin-potentiating activity of Ang-(1-7) was evaluated 30 minutes after treatment with the angiotensin-converting enzyme inhibitor enalaprilat (10 mg/kg i.v., n = 9). Under this condition the bradykinin-potentiating activity of Ang-(1-7) was substantially increased, resulting in a potentiating unit of approximately 0.2 nmol IV. Pretreatment with indomethacin (5 mg/kg IM, n = 7) also attenuated the bradykinin-potentiating activity of Ang-(1-7) in enalaprilat-treated rats. These results show that Ang-(1-7) is a bradykinin-potentiating peptide in vivo. Furthermore, the data obtained with indomethacin suggest that prostaglandins participate in the mechanism of the bradykinin potentiation by Ang-(1-7). More importantly, these data suggest that the interaction between Ang-(1-7) and bradykinin can contribute to the pharmacological effects of angiotensin-converting enzyme inhibitors.

Metabolism of angiotensin I in isolated rat hearts. Effect of angiotensin converting enzyme inhibitors

In this study, the formation of biologically active angiotensins from angiotensin I (Ang I) in isolated rat hearts was evaluated. The role of angiotensin converting enzyme (ACE) in Ang I metabolism was also investigated. HPLC analysis of heart perfusate showed that 125I-Ang I was metabolized extensively (single passage) in the rat coronary circulation in vitro leading to the formation of the biologically active angiotensins: angiotensin II (Ang II), Ang-(2-8), Ang-(3-8) and Ang-(1-7). Ang II was the major product identified in HPLC fractions, corresponding to 7.8 +/- 0.89% of the total radioactivity recovered. A similar profile was observed when single-passage metabolism of non-isotopic Ang I was evaluated by HPLC, followed by radioimmunoassay of the eluate fractions. When 125I-Ang I was perfused in the presence of ACE inhibitors (enalaprilat, ramiprilat) in concentrations up to 130 microM, the formation of Ang II was only partially inhibited (approximately 50%). A similar tendency was observed for Ang-(2-8), Ang-(3-8) and Ang-(2-7). The formation of Ang-(1-7) and its related fragments Ang-(3-7) and Ang-(4-7) was not changed significantly by ACE inhibitors, although a slight increase in formation of these fragments was observed. No significant changes were observed for the carboxyl-terminal fragments of Ang I: Ang-(2-10), Ang-(3-10), and Ang-(4-10). The fractional metabolism of Ang I was not modified by ACE inhibition. These findings suggest that biologically active angiotensins can be formed from Ang I in the rat coronary circulation. These locally generated peptides may contribute to the actions of the renin-angiotensin system in the heart.

Evidence that angiotensin-(1-7) plays a role in the central control of blood pressure at the ventro-lateral medulla acting through specific receptors

In this study we determined which angiotensin receptors may mediate the cardiovascular effects elicited by angiotensin-(1-7) [Ang-(1-7)] in the rostral ventrolateral medulla (RVLM) and caudal pressor area (CPA) of the ventrolateral medulla (VLM) of anesthetized rats. Furthermore the role of endogenous angiotensins in these areas was also investigated. The pressor effect produced by unilateral microinjection of Ang-(1-7) into the RVLM or CPA was not modified by either the AT1 receptor antagonist, DuP 753 or by the AT2 receptor antagonist, CGP 42112A, but was completely blocked by the Ang-(1-7) selective antagonist, A-779. In contrast, the pressor effect produced by microinjection of angiotensin II (Ang II) was completely blocked by DuP 753 but was not changed by CGP 42112A or A-779. Bilateral microinjection of A-779 into the RVLM or CPA produced a significant fall in mean arterial pressure and heart rate. Microinjection of DuP 753 produced a pressor effect comparable to bilateral injection of vehicle. These results indicate that, although Ang II acts in the VLM through an AT1 receptor subtype, the cardiovascular effects produced by microinjection of Ang-(1-7) into the RVLM and CPA are mediated by a specific angiotensin receptor (AT5?). Furthermore, our data provide evidence that endogenous Ang-(1-7) participates at the VLM in the neural control of arterial blood pressure.

Central and peripheral actions of angiotensin-(1-7)

1. In this article we review the physiological actions of the heptapeptide angiotensin-(1-7) [Ang-(1-7)] at the periphery and on central pathways involved in the control of arterial pressure. Peripherally Ang-(1-7) has been shown to present a potent antidiuretic effect on water-loaded rats. Microinjection of pmol amounts of Ang-(1-7) into the dorsomedial or ventrolateral medulla (VLM) of anesthetized rats produces cardiovascular effects comparable to Ang II. In addition, in vitro experiments have shown that Ang-(1-7) has a potent vasopressin and prostaglandin releasing activity and excites neuronal activity in the hypothalamus and medulla. 2. Evidence for the existence of a new angiotensin receptor subtype that mediates the central cardiovascular actions of this active peptide of the renin-angiotensin system (RAS) is also provided. Neither the AT1 receptor antagonist DUP 753 or the AT2 receptor antagonist CGP 42112A blocked the pressor response produced by microinjection of Ang-(1-7) into the rostral VLM. However, the effect of Ang-(1-7) on VLM was completely abolished by the non-specific angiotensin receptor antagonist, Sar1-Thr8-Ang II. 3. The data presented here reinforce the hypothesis of the existence of complex site-specific interactions between multiple angiotensins and multiple receptors in the mediation of important central and peripheral effects of the RAS.