Differential response of human cardiac fibroblasts to angiotensin I and angiotensin II

The vasoactive peptide angiotensin II (Ang II) has been implicated as a mediator of myocardial fibrosis. We carried out a comparative investigation of the effects of Ang II and its precursor Ang I on collagen metabolism and proliferation in cultured human cardiac fibroblasts. Cardiac fibroblasts responded to both Ang I and Ang II with concentration-dependent increases in collagen synthesis but no proliferation. The stimulatory effect of Ang II was abolished by the AT(1) receptor antagonist losartan but not the AT(2) receptor antagonist PD123319. The response to Ang I was not affected by either antagonist, nor by the angiotensin-converting enzyme (ACE) inhibitor captopril. In conclusion, Both Ang I and Ang II stimulate collagen synthesis of human cardiac fibroblasts, the effect of Ang II occurring via the AT(1) receptor whilst Ang I appears to exert a direct effect through non-Ang II-dependent mechanisms. These results suggest distinct roles for angiotensin peptides in the development of cardiac fibrosis.     

Effects of angiotensin II on pressor responses to norepinephrine in humans

In previous studies in the conscious rabbit and in isolated artery preparations, low doses of angiotensin II synergistically amplified the pressor effects of the sympathetic neurotransmitter, norepinephrine (NE). To determine whether these observations could be replicated in humans, 9 normal adult male volunteers (mean age: 34) each were given 3 i.v. doses of NE (25, 50 and 100 micrograms.kg-1.min-1) during consecutive 10 min infusion periods. On a second study day, the procedure was repeated during infusion of angiotensin II in a subpressor dose (1.25 ng.kg-1.min-1). The angiotensin II didn't alter the BP responses to NE, but it attenuated the heart rate (HR) decreases associated with the NE infusions by 80% (P less than 0.05), 42% (P less than 0.05) and 42% (P less than 0.1). The two study days were then repeated following 2 weeks of oral treatment with the angiotensin converting enzyme inhibitor captopril (which, despite significantly decreasing baseline BP, also tended to decrease HR). In the presence of captopril, the pressor responses to the NE challenges were reduced by 50% (P less than 0.05), 33% (P less than 0.05) and 13% (P less than 0.1) compared with the pre-captopril responses. Thus, angiotensin II in subpressor doses appears to enhance NE pressor effects by attenuating the compensatory HR responses, whereas inhibition of endogenous angiotensin II mechanisms weakens the BP-raising actions of NE. These findings in humans are consistent with earlier observations that the renin-angiotensin system can directly amplify sympathetic pressor effects in two separate ways: by modifying baroreceptor sensitivity and by enhancing the actions of norepinephrine on vascular smooth muscle.     

Individual behavioral and autonomic response to emotional stress in humans

Healthy subjects (n = 53) performed a sound version of the proof-reading test under normal conditions and in the state of emotional stress. Stress resistance was evaluated by the overall number of errors. The propensity to active or passive response to stress was evaluated by the number of "false alarms" and signal omissions. The reaction pattern to emotional stress in stress-resistant subjects, irrespective of their behavioral features, consisted in an increase in sympathetic effects on the cardiac rhythm and a decrease in the reaction time to significant signals. In subjects with low stress resistance, no statistically significant changes in the level of sympathetic tone and reaction time were revealed in the state of stress. Subjects with active behavioral response to stress, irrespective of their level of stress resistance, were characterized by aggressiveness, boldness and independence. Subjects with passive response to stress were inclined to conformism, dependence, and passivity.     

Atg5 deficiency-mediated mitophagy aggravates cardiac inflammation and injury in response to angiotensin II

ObjectiveHypertension induces end-organ damage through inflammation, and autophagy plays a crucial role in the regulation of cellular homeostasis. In the present study, we aimed to define the role of autophagy in the development of inflammation and cardiac injury induced by angiotensin II (Ang II).Methods and ResultsAutophagy protein 5 (Atg5) haplodeficiency (Atg5^+/−) and age-matched wild-type (WT) C57BL/6 J mice were infused with Ang II (1500 ng/kg/min) or saline for 7 days. Heart sections were stained with hematoxylin and eosin (H&E), Masson's trichrome, and immunohistochemical stains. Cytokine and LC3 levels were measured using real-time PCR or western blot analysis. After Ang II infusion, the WT mice exhibited marked macrophage accumulation, cytokine expression, and reactive oxygen species (ROS) production compared with saline-infused controls. However, these effects induced by Ang II infusion were aggravated in Atg5^+/− mice. These effects were associated with Atg5-mediated impaired autophagy, accompanied by increased production of ROS and activation of nuclear factor-κB (NF-κB) in macrophages. Finally, increased cardiac inflammation in Atg5 haplodeficient mice was associated with increased cardiac fibrosis.ConclusionAtg5 deficiency-mediated autophagy increases ROS production and NF-κB activity in macrophages, thereby contributing to cardiac inflammation and injury. Thus, improving autophagy may be a novel therapeutic strategy to ameliorate hypertension-induced inflammation and organ damage.     

Impact of waist circumference on cardiac phenotype in hypertensives according to gender

Our aim was to assess the differential effect of waist circumference on left-ventricular (LV) structural and functional alterations, in hypertensive males and females. One thousand seven hundred and eighty nine consecutive, nondiabetic, essential hypertensives (aged 55.8 +/- 13.5 years, 966 females), included in the 3H Study, an ongoing registry of hypertension-related-target-organ damage, were classified to obese and nonobese groups according to Adult Treatment Panel III criteria. All participants underwent complete echocardiographic study including LV diastolic function evaluation by means of conventional and tissue Doppler imaging (TDI) methods, averaging early and late diastolic mitral annular peak velocities (Em, Am, Em/Am) from four separate sites of measurement. Hypertensive obese women compared with nonobese exhibited significantly greater LV mass index and prevalence of LV hypertrophy (by 5.5 g/m(2), P = 0.003, and 8.8%, P = 0.005, respectively), while such differences were not present among men. Obese women compared to nonobese ones were accompanied by lower transmitral E/A (by 0.08, P < 0.001), TDI-derived Em/Am (by 0.12, P < 0.001), and higher E/Em ratio (by 0.8, P = 0.016). In contrast, hypertensive obese men compared to nonobese ones exhibited lower E and Em (by 0.04 m/s and 0.6 cm/s, both P < 0.05). A significant interaction between sex and abdominal obesity was observed only regarding TDI-derived Am and Em/Am. Furthermore, waist circumference was a predictor of E/A (beta = -0.097, P = 0.002) and Em/Am (beta = -0.116, P = 0.001), independently of body size, in females but not in males. The adverse effect of abdominal obesity on LV alterations is more pronounced among female hypertensives, suggesting that routine measurement of waist circumference provides additional information on cardiac phenotype especially in women.     

Aldosterone response to angiotensin II during hypoxemia

Exercise in humans causes increases in plasma renin activity (PRA) and plasma aldosterone concentrations (PAC) except when performed at high altitude or while the subjects breathe hypoxic gas. Under those conditions, PRA increases with exercise but PAC does not. We speculated that the PAC suppression during hypoxemic exercise was due to hypoxemia-induced release of a circulating inhibitor of angiotensin II-mediated aldosterone secretion. To test this hypothesis, we measured the PAC response to graded infusions of angiotensin II during hypoxemia and normoxemia. Eight normal volunteers were given increasing doses of angiotensin II (first 2 ng X kg-1 X min-1 and then 4, 8, and finally 12 ng X kg-1 X min-1, each for 20-min periods) on 2 separate days, once while breathing room air and the other day while breathing hypoxic gas adjusted to maintain the subjects' hemoglobin saturation at 90%. The PAC response to different doses of angiotensin II did not significantly differ during hypoxemia from normoxemia. We conclude that our model of hypoxemia does not cause release of an inhibitor of angiotensin II-mediated aldosterone release.     

Renal vascular tachyphylaxis to angiotensin II: Specificity of the response for angiotensin

Hypotheses concerning angiotensin's role in states characterized by severe and sustained renal vasoconstriction, must account for the poorly sustained renal response to this agent in healthy animals and man. To assess the specificity of renal vascular tachyphylaxis to angiotensin II (AII), renal blood flow was measured with an electromagnetic flowmeter in eight anesthetized dogs. Bolus injections of AII and norepinephrine into the renal artery were adjusted to produce at least a 50% reduction in renal blood flow, and were followed by a continuous infusion of AII sufficient to reduce renal blood flow acutely by 60 ± 10%. The response to the continuous infusion was poorly sustained, blood flow returning to near baseline within 10 minutes: At this time the response to bolus administration of AII was lost, but the response to norepinephrine was sustained. At 30 minutes the response to norepinephrine was also reduced, and there was no response in three of the eight dogs. After stopping the AII infusion, renal vascular responsiveness to norepinephrine returned almost immediately, but 30–60 minutes were required before responsiveness to AII was restored. We conclude that there is true, specific renal vascular tachyphylaxis to AII--which may well reflect receptor modulation or occupation--and that with time an additional, non-specific vasodilator mechanism can come into play.     

Effect of age on contractile response to angiotensin II in rat aorta

The effects of aging on contractile response to angiotensin II and tachyphylaxis to it were investigated using aortic strips from rats aged 1.5, 4 and 22 months. Whether the endothelium was present or not, the contractile response to angiotensin II was greater and tachyphylaxis to it was less in 1.5-month-old rats than in 4- and 22-month-old rats. The differences between 4- and 22-month-old rats were not significant. Removal of the endothelium enhanced angiotensin II-induced maximal contraction and depressed the tachyphylaxis, these endothelial effects being greater in 4- rather than in 1.5-month-old rats. When the contractile force of angiotensin II was adjusted to a similar level for 1.5- and 4-month-old rats, the endothelial effect on the tachyphylaxis was greater in the 4-month-old rats, but no significant difference was noted in the endothelial effect on the contractile force. These results suggest that during growth, the contractile response of rat aorta to angiotensin II decreases while the endothelial effect on it increases.     

Role of thromboxane receptors in the dipsogenic response to central angiotensin II

Central angiotensin II (ANG II) regulates thirst. Because thromboxane A2-prostaglandin H2 (TP) receptors are expressed in the brain and mediate some of the effects of ANG II in the vasculature, we investigated the hypothesis that TP receptors mediate the drinking response to intracerebroventricular (icv) injections of ANG II. Pretreatment with the specific TP-receptor antagonist ifetroban (Ifet) decreased water intake with 50 ng/kg icv ANG II (ANG II + Veh, 7.2 +/- 0.7 ml vs. ANG II + Ifet, 2.8 +/- 0.8 ml; n = 5 rats; P < 0.001) but had no effect on water intake induced by hypertonic saline (NaCl + Veh, 8.4 +/- 1.1 ml vs. NaCl + Ifet, 8.9 +/- 1.8 ml; n = 5 rats; P = not significant). Administration of 0.6 microg/kg icv of the TP-receptor agonist U-46,619 did not induce drinking when given alone but did increase the dipsogenic response to a near-threshold dose of 15 ng/kg icv ANG II (ANG II + Veh, 1.1 +/- 0.7 vs. ANG II + U-46,619, 4.5 +/- 0.9 ml; n = 5 rats; P < 0.01). We conclude that central TP receptors contribute to the dipsogenic response to ANG II.     

Role of ionic currents in the physiological response to angiotensin II.

Studies using conventional and patch-clamp microelectrode techniques demonstrate that in a number of cell types angiotensin II (AII) causes reversible changes in transmembrane ionic currents, and that these effects can be mimicked by various membrane-associated and cytosolic messengers. AII modulates the current amplitude of ion channels, as well as their activation threshold and their open/closed time probability. Stimulatory and inhibitory effects on ion channel activity are a fundamental feature of the development of AII actions on target organs.     

Cardiovascular autonomic function correlates with the response to aerobic training in healthy sedentary subjects

Individual responses to aerobic training vary from almost none to a 40% increase in aerobic fitness in sedentary subjects. The reasons for these differences in the training response are not well known. We hypothesized that baseline cardiovascular autonomic function may influence the training response. The study population included sedentary male subjects (n = 39, 35 +/- 9 yr). The training period was 8 wk, including 6 sessions/wk at an intensity of 70-80% of the maximum heart rate for 30-60 min/session. Cardiovascular autonomic function was assessed by measuring the power spectral indexes of heart rate variability from 24-h R-R interval recordings before the training period. Mean peak O2 uptake increased by 11 +/- 5% during the training period (range 2-19%). The training response correlated with age (r = -0.39, P = 0.007) and with the values of the high-frequency (HF) spectral component of R-R intervals (HF power) analyzed over the 24-h recording (r = 0.46, P = 0.002) or separately during the daytime hours (r = 0.35, P = 0.028) and most strongly during the nighttime hours (r = 0.52, P = 0.001). After adjustment for age, HF power was still associated with the training response (e.g., P = 0.001 analyzed during nighttime hours). These data show that cardiovascular autonomic function is an important determinant of the response to aerobic training among sedentary men. High vagal activity at baseline is associated with the improvement in aerobic power caused by aerobic exercise training in healthy sedentary subjects.     

Conversion of brain angiotensin II to angiotensin III is critical for pressor response in rats

The present investigation measured the relative pressor potencies of intracerebroventricularly infused ANG II, ANG III, and the metabolically resistant analogs d-Asp(1)ANG II and d-Arg(1)ANG III in alert freely moving rats. The stability of these analogs was further facilitated by pretreatment with the specific aminopeptidase A inhibitor EC33 or the aminopeptidase N inhibitor PC18. The results indicate that the maximum elevations in mean arterial pressure (MAP) were very similar for each of these compounds across the dose range 1, 10, and 100 pmol/min during a 5-min infusion period. However, d-Asp(1)ANG II revealed significantly extended durations of pressor effects before return to base level MAP. Pretreatment intracerebroventricular infusion with EC33 blocked the pressor activity induced by the subsequent infusion of d-Asp(1)ANG II, whereas EC33 had no effect on the pressor response to subsequent infusion of d-Arg(1)ANG III. In contrast, pretreatment infusion with PC18 extended the duration of the d-Asp(1)ANG II pressor effect by about two to three times and the duration of d-Arg(1)ANG III's effect by approximately 10 to 15 times. Pretreatment with the specific AT(1) receptor antagonist losartan blocked the pressor responses induced by the subsequent infusion of both analogs indicating that they act via the AT(1) receptor subtype. These results suggest that the brain AT(1) receptor may be designed to preferentially respond to ANG III, and ANG III's importance as a centrally active ligand has been underestimated.     

Influence of sarmesin on the cardiac and vascular actions of angiotensin II

Summary The angiotensin II (ANG II) receptor blocker properties of sarmesin and its influence on the homotropic cooperativity of ANG II receptors were studied in two experimental models: isolated rabbit aorta and isolated rabbit atria. The results show that: (i) sarmesin is a specific competitive antagonist of ANG II receptors, with high affinity (pA₂=8.93 in the isolated aorta and 8.66 in the isolated atria); and (ii) the slope of the concentration-response curves to ANG II and the Hill coefficient increased in the presence of sarmesin, the latter suggesting an enhancement of the positive homotropic cooperativity of ANG II receptors. These results may be explained overall by the reciprocal negative modulation of receptor affinity between sarmesin and ANG II, due, possibly, to opposite effects on the binding of G-proteins to ANG II receptors.     

Vectorcardiography analysis of the repolarization response to pharmacologically induced autonomic nervous system modulation in healthy subjects

Autonomic nervous system activity is essential for regulation of ventricular repolarization (VR) and plays an important role in several arrhythmogenic conditions. This study in 31 healthy adult subjects (16 men, 15 women) evaluated the VR response to pharmacologically modulated autonomic nervous system activity applying vectorcardiography (VCG) analysis. During continuous VCG recording, 0.01-0.1 μg·kg(-1)·min(-1) isoprenaline (Iso) was infused at an increasing flow rate until three targeted heart rates (HR) were reached. After Iso washout, one intravenous bolus of 0.04 mg/kg atropine was given followed by an intravenous bolus of 0.2 mg/kg propranolol. A 5-min steady-state VCG recording was analyzed for each of the seven phases (including baseline 1 and 2). Furthermore, during the first 4 min following atropine, six periods of 10-s VCG were selected for subanalysis to evaluate the time course of change. The analysis included QRS, QT, and T-peak to T-end intervals, measures of the QRS and T vectors and their relation, as well as T-loop morphology parameters. By increasing HR, Iso infusion decreased HR dependent parameters reflecting total heterogeneity of VR (T area) and action potential morphology (ventricular gradient). In contrast, Iso prolonged QT HR corrected according to Bazett and increased the T-peak to T-end-to-QT ratio to levels observed in arrhythmogenic conditions. HR acceleration after atropine was accompanied by a transient paradoxical QT prolongation and delayed HR adaptation of T area and ventricular gradient. In addition to the expected HR adaptation, the VR response to β-adrenoceptor stimulation with Iso and to muscarinic receptor blockade with atropine thus included alterations previously observed in congenital and acquired long QT syndromes, demonstrating substantial overlap between physiological and pathophysiological electrophysiology.     

Modulation of cardiac Na channels by angiotensin II

The modulation of Na channels by the vasoactive peptide angiotensin II (AT II) has been studied in isolated ventricular cells of guinea pigs using the patch clamp technique. In cell-attached patches the maximal probability of the channel being open was increased in a concentration range between 0.05 and 1 microM, but decreased at higher concentrations. A maximal increased of 2.5 +/- 0.86 was found at 1 microM AT II. The increase in the probability of the channel being open was due to a decrease in the number of nulls. In all affected cells (n = 17) we observed a delayed inactivation after application of AT II at concentrations between 0.05 and 10 microM. At -30 mV, the time constant of inactivation increased from 1.1 +/- 0.1 ms (controls) to 5.6 +/- 1.6 ms (10 microM AT II). This effect was due to an increased number of openings per sweeps. No significant effect on the mean open time and the first latency were observed. However, due to pronounced bursting, the averaged closed time was significantly increased from 0.8 +/- 0.1 ms to 1.3 +/- 0.1 ms in the presence of 1 microM AT II at -30 mV. An effect of AT II on cardiac Na channels via protein kinase C is discussed.     

Effects of angiotensin II on autonomic components of nasopharyngeal stimulation in male conscious rabbits.

Angiotensin II (ANG II) is known to activate central sympathetic neurons. In this study we determined the effects of ANG II on the autonomic components of the cardiovascular responses to stimulation of nasopharyngeal receptors with cigarette smoke. Experiments were carried out in conscious New Zealand White rabbits instrumented to record arterial pressure and heart rate. Rabbits were exposed to 50 ml of cigarette smoke before and after subcutaneous osmotic minipump delivery of ANG II at a dose of 50 ng.kg(-1).min(-1) for 1 wk in one group and intracerebroventricular (icv) infusion at a dose of 100 pmol/min for 1 h in a second group. The responses were compared before and after heart rate was controlled by pacing. Autonomic components were evaluated by intravenous administration of atropine methyl bromide (0.2 mg/kg) and prazosin (0.5 mg/kg). ANG II given either systemically or icv significantly blunted the pressor response to smoke (P < 0.05) when the bradycardic response was prevented. This blunted response was not due to an absolute increase in baseline blood pressure after ANG II infusion (71.64 +/- 11.6 vs. 92.1 +/- 19.8 mmHg; P < 0.05) because normalization of blood pressure with sodium nitroprusside to pre-ANG II levels also resulted in a significantly blunted pressor response to smoke. The effect of smoke was alpha(1)-adrenergic receptor-mediated because it was essentially abolished by prazosin in both the pre- and the post-ANG II states (P < 0.05). These results suggest that elevations in central ANG II reduce the sympathetic response to smoke in conscious rabbits. This effect may be due to an augmentation of baseline sympathetic outflow and a reduction in reflex sensitivity similar to the effect of ANG II on baroreflex function.     

The steroidogenic response to angiotensin II in the Australian lungfish,Neoceratodus forsteri

Corticosterone, aldosterone and cortisol were found to be present in lungfish plasma. Plasma levels of these hormones were measured in lungfish following separate single intramuscular injections of three forms of angiotensin II; [Asp¹, Ile⁵], [Asp¹, Val⁵] and [Asn¹, Val⁵]. Aldosterone levels were significantly elevated in response to [Asp¹, Ile⁵] AII and [Asn¹, Val⁵] AII injection. [Asp¹, Val⁵] AII increased plasma corticosterone levels. The difference between these data and the negative results previously reported by Blair-West et al. (1977) are discussed.Abbreviations AII angiotensin II - bw body weight - DOC deoxycorticosterone - RAS renin-angiotensin system - RIA radioimmuno assay