Effects of different angiotensins during acute,double blockade of the renin system in conscious dogs

Evidence of biological activity of fragments of ANG II is accumulating. Fragments considered being inactive degradation products might mediate actions previously attributed to ANG II. The study aimed to determine whether angiotensin fragments exert biological activity when administered in amounts equimolar to physiological doses of ANG II. Cardiovascular, endocrine, and renal effects of ANG II, ANG III, ANG IV, and ANG-(1-7) (6 pmol.kg-1.min-1) were investigated in conscious dogs during acute inhibition of angiotensin I-converting enzyme (enalaprilate) and aldosterone (canrenoate). Furthermore, ANG III was investigated by step-up infusion (30 and 150 pmol.kg-1.min-1). Arterial plasma concentrations [ANG immunoreactivity (IR)] were determined by an ANG II antibody cross-reacting with ANG III and ANG IV. Metabolic clearance rates were higher for ANG III and ANG IV (391 +/- 19 and 274 +/- 13 ml.kg-1.min-1, respectively) than for ANG II (107 +/- 13 ml.kg-1.min-1). ANG II increased ANG IR by 60 +/- 7 pmol/ml, blood pressure by 30%, increased plasma aldosterone markedly (to 345 +/- 72 pg/ml), and plasma vasopressin transiently, while reducing glomerular filtration rate (40 +/- 2 to 33 +/- 2 ml/min), sodium excretion (50 +/- 7 to 16 +/- 4 micromol/min), and urine flow. Equimolar amounts of ANG III induced similar antinatriuresis (57 +/- 8 to 19 +/- 3 micromol/min) and aldosterone secretion (to 268 +/- 71 pg/ml) at much lower ANG IR increments ( approximately 1/7) without affecting blood pressure, vasopressin, or glomerular filtration rate. The effects of ANG III exhibited complex dose-response relations. ANG IV and ANG-(1-7) were ineffective. It is concluded that 1) plasma clearances of ANG III and ANG IV are higher than those of ANG II; 2) ANG III is more potent than ANG II in eliciting immediate sodium and potassium retention, as well as aldosterone secretion, particularly at low concentrations; and 3) the complexity of the ANG III dose-response relationships provides indirect evidence that several effector mechanisms are involved.     

Determinants of the natriuresis after acute, slow sodium loading in conscious dogs

The relative importance of systemic volume, concentration, and pressure signals in sodium homeostasis was investigated by intravenous infusion of isotonic (IsoLoad) or hypertonic (HyperLoad) saline at a rate (1 micromol Na(+) x kg(-1) x s(-1)), similar to the rate of postprandial sodium absorption. IsoLoad decreased plasma vasopressin (-35%) and plasma ANG II (-77%) and increased renal sodium excretion (95-fold), arterial blood pressure (DeltaBP; +6 mmHg), and heart rate (HR; +36%). HyperLoad caused similar changes in plasma ANG II and sodium excretion, but augmented vasopressin (12-fold) and doubled DeltaBP (+12 mm Hg) without changing HR. IsoLoad during vasopressin clamping (constant vasopressin infusion) caused comparable natriuresis at augmented DeltaBP (+14 mm Hg), but constant HR. Thus vasopressin abolished the Bainbridge reflex. IsoLoad during normotensive angiotensin clamping (enalaprilate plus constant angiotensin infusion) caused marginal natriuresis (9% of unclamped response) despite augmented DeltaBP (+14 mm Hg). Cessation of angiotensin infusion during IsoLoad immediately decreased BP (-13 mm Hg) and increased glomerular filtration rate by 20% and sodium excretion by 45-fold. The results suggest that fading of ANG II is the cause of acute "volume-expansion" natriuresis, that physiological ANG II deviations override the effects of modest systemic blood pressure changes, and that endocrine rather than hemodynamic mechanisms are the pivot of normal sodium homeostasis.     

Angiotensin II attenuates the natriuresis of water immersion in humans

The hypothesis was tested that suppression of generation of ANG II is one of the mechanisms of the water immersion (WI)-induced natriuresis in humans. In one protocol, eight healthy young males were subjected to 3 h of 1) WI (WI + placebo), 2) WI combined with ANG II infusion of 0.5 ng. kg(-1). min(-1) (WI + ANG II-low), and 3) a seated time control (Con). In another almost identical protocol, 7-10 healthy young males were investigated to delineate the tubular site(s) of action of ANG II by the lithium clearance method (C(Li)) and were on an additional fourth study day subjected to infusion of ANG II at a rate of 1.5 ng. kg(-1). min(-1) (WI + ANG II-high). During WI + placebo, plasma concentration of ANG II decreased from 16 +/- 2 to 8 +/- 1 pg/ml (P < 0.05) and renal sodium excretion increased from 104 +/- 15 to 294 +/- 27 micromol/min (P < 0.05). During WI + ANG II-low, plasma ANG II was not suppressed by WI, and the natriuresis was blunted by 52 +/- 13% (P < 0.05). During WI + ANG II-low and WI + ANG II-high, an increase in C(Li) was prevented that was otherwise observed during WI, and fractional distal reabsorption of sodium was facilitated. In conclusion, maintaining plasma concentration of ANG II unchanged at the level of control attenuates the natriuresis of WI considerably in humans. Therefore, suppression of generation of ANG II is an important mechanism of the natriuresis of WI in humans. Furthermore, infusion of ANG II during WI prevents an otherwise induced increase in C(Li) and facilitates the fractional distal reabsorption of sodium, probably via an effect on aldosterone release.     

Hormonal regulation of renal sodium and water excretion during normotensive sodium loading in conscious dogs

Saline was infused intravenously for 90 min to normal, sodium-replete conscious dogs at three different rates (6, 20, and 30 micromol x kg(-1) x min(-1)) as hypertonic solutions (HyperLoad-6, HyperLoad-20, and HyperLoad-30, respectively) or as isotonic solutions (IsoLoad-6, IsoLoad-20, and IsoLoad-30, respectively). Mean arterial blood pressure did not change with any infusion of 6 or 20 micromol x kg(-1) x min(-1). During HyperLoad-6, plasma vasopressin increased by 30%, although the increase in plasma osmolality (1.0 mosmol/kg) was insignificant. During HyperLoad-20, plasma ANG II decreased from 14+/-2 to 7+/-2 pg/ml and sodium excretion increased markedly (2.3+/-0.8 to 19+/-8 micromol/min), whereas glomerular filtration rate (GFR) remained constant. IsoLoad-20 decreased plasma ANG II similarly (13+/-3 to 7+/-1 pg/ml) concomitant with an increase in GFR and a smaller increase in sodium excretion (1.9+/-1.0 to 11+/-6 micromol/min). HyperLoad-30 and IsoLoad-30 increased mean arterial blood pressure by 6-7 mm Hg and decreased plasma ANG II to approximately 6 pg/ml, whereas sodium excretion increased to approximately 60 micromol/min. The data demonstrate that, during slow sodium loading, the rate of excretion of sodium may increase 10-fold without changes in mean arterial blood pressure and GFR and suggest that the increase may be mediated by a decrease in plasma ANG II. Furthermore, the vasopressin system may respond to changes in plasma osmolality undetectable by conventional osmometry.     

Effect of angiotensin II blockade on a new congenic model of hypertension derived from transgenic Ren-2 rats

The generation of the Lew.Tg(mRen2) congenic hypertensive rat strain, developed through a backcross of the hypertensive (mRen2)27 transgenic rat with normotensive Lewis rats, provides a new model by which primary hypertension can be studied without the genetic variability found in the original strain. The purpose of this study was to characterize the Lew.Tg(mRen2) rats by dually investigating the effects of type 1 angiotensin II (ANG II) receptor (AT(1)) blockade and angiotensin-converting enzyme (ACE) activity inhibition on the ANG-(1-7)/ACE2 axis of the renin-angiotensin system in this new hypertensive model. The control of blood pressure elicited by 12-day administration of either lisinopril (mean difference change = 92 +/- 2, P < 0.05) or losartan (mean difference change = 69 +/- 2, P < 0.05) was associated with 54% and 33% increases in cardiac ACE2 mRNA and 54% and 43% increases in cardiac ACE mRNA, respectively. Lisinopril induced a 3.1-fold (P < 0.05) increase in renal cortical expression of ACE2, whereas losartan increased ACE2 mRNA 3.5-fold (P < 0.05). Both treatment regimens increased renal ACE mRNA 2.6-fold (P < 0.05). The two therapies augmented ACE2 protein activity, as well as increased cardiac and renal AT(1) receptor mRNAs. ACE inhibition reduced plasma ANG II levels (81%, P < 0.05) and increased plasma ANG-(1-7) (265%, P < 0.05), whereas losartan had no effect on the peptides. In contrast with what had been shown in normotensive rats, ACE inhibition decreased renal ANG II excretion and transiently decreased ANG-(1-7) excretion, whereas losartan treatment was associated with a consistent decrease in ANG-(1-7) urinary excretion rates. In response to the treatments, the expression of both renal cortical renin and angiotensinogen mRNAs was significantly augmented. The paradoxical effects of blockade of ANG II synthesis and activity on urinary excretion rates of the peptides and plasma angiotensins levels suggest that, in Lew.Tg(mRen2) congenic rats, a failure of compensatory ACE2 and ANG-(1-7)-dependent vasodepressor mechanisms may contribute both to the development and progression of hypertension driven by increased formation of endogenous ANG II.     

Chronic activation of plasma renin is log-linearly related to dietary sodium and eliminates natriuresis in response to a pulse change in total body sodium

Responses to acute sodium loading depend on the load and on the level of chronic sodium intake. To test the hypothesis that an acute step increase in total body sodium (TBS) elicits a natriuretic response, which is dependent on the chronic level of TBS, we measured the effects of a bolus of NaCl during different low-sodium diets spanning a 25-fold change in sodium intake on elements of the renin-angiotensin-aldosterone system (RAAS) and on natriuresis. To custom-made, low-sodium chow (0.003%), NaCl was added to provide four levels of intake, 0.03-0.75 mmol.kg(-1).day(-1) for 7 days. Acute NaCl administration increased PV (+6.3-8.9%) and plasma sodium concentration (~2%) and decreased plasma protein concentration (-6.4-8.1%). Plasma ANG II and aldosterone concentrations decreased transiently. Potassium excretion increased substantially. Sodium excretion, arterial blood pressure, glomerular filtration rate, urine flow, plasma potassium, and plasma renin activity did not change. The results indicate that sodium excretion is controlled by neurohumoral mechanisms that are quite resistant to acute changes in plasma volume and colloid osmotic pressure and are not down-regulated within 2 h. With previous data, we demonstrate that RAAS variables are log-linearly related to sodium intake over a >250-fold range in sodium intake, defining dietary sodium function lines that are simple measures of the sodium sensitivity of the RAAS. The dietary function line for plasma ANG II concentration increases from theoretical zero at a daily sodium intake of 17 mmol Na/kg (intercept) with a slope of 16 pM increase per decade of decrease in dietary sodium intake.     

Acute effects of angiotensin II on renal haemodynamics and excretion in conscious dogs

The effects of a 60-min intravenous infusion of angiotensin II (A II; 4 or 20 ng A II/min/kg body weight) on renal blood flow (RBF; electromagnetic flow transducer, control value 19-25 ml/min/kg), glomerular filtration rate (GFR; control value 4.2-5.0 ml/min/kg), mean arterial blood pressure, sodium excretion, water excretion, and plasma A II and plasma aldosterone concentrations were examined in 6 chronically instrumented female conscious beagle dogs kept on three different dietary sodium intakes (SI): SI 0.5 or SI 2.5 mmol Na/kg/day or SI 4.5 mmol Na/kg/day plus an oral saline load prior to the experiment SI 4.5(+) dogs. Four nanograms A II decreased RBF and GFR in SI 4.5(+) dogs without changing the filtration fraction (FF%); in SI 0.5 dogs the RBF decreased, and the FF% increased. Twenty nanograms A II decreased RBF and increased FF% in all dietary protocols, less in SI 4.5(+) dogs. The mean arterial blood pressure increased in all dietary protocols by 10-15 mm Hg (4 ng A II) and 32-37 mm Hg (20 ng A II). Sodium and water excretions decreased by 32 and 46%, respectively, in SI 4.5(+) dogs at both doses of A II. The plasma aldosterone concentration increased in all but one protocol: 4 ng A II, SI 4.5(+) dogs. It is concluded that when A II plasma concentrations are most likely borderline to pathophysiological conditions (up to an average of 370 pg/ml), the GFR is less decreased than the RBF. This phenomenon also can be observed at lower plasma A II concentrations (average 200 pg/ml), when the renin-angiotensin system had been previously moderately activated.     

Volume expansion during NOS substrate donation with L-arginine: regulatory offsetting of renal response?

The responses to infusion of nitric oxide synthase substrate (L-arginine 3 mg.kg(-1).min(-1)) and to slow volume expansion (saline 35 ml/kg for 90 min) alone and in combination were investigated in separate experiments. L-Arginine left blood pressure and plasma ANG II unaffected but decreased heart rate (6 +/- 2 beats/min) and urine osmolality, increased glomerular filtration rate (GFR) transiently, and caused sustained increases in sodium excretion (fourfold) and urine flow (0.2 +/- 0.0 to 0.7 +/- 0.1 ml/min). Volume expansion increased arterial blood pressure (102 +/- 3 to 114 +/- 3 mmHg), elevated GFR persistently by 24%, and enhanced sodium excretion to a peak of 251 +/- 31 micromol/min, together with marked increases in urine flow, osmolar and free water clearances, whereas plasma ANG II decreased (8.1 +/- 1.7 to 1.6 +/- 0.3 pg/ml). Combined volume expansion and L-arginine infusion tended to increase arterial blood pressure and increased GFR by 31%, whereas peak sodium excretion was enhanced to 335 +/- 23 micromol/min at plasma ANG II levels of 3.0 +/- 1.1 pg/ml; urine flow and osmolar clearance were increased at constant free water clearance. In conclusion, L-arginine 1) increases sodium excretion, 2) decreases basal urine osmolality, 3) exaggerates the natriuretic response to volume expansion by an average of 50% without persistent changes in GFR, and 4) abolishes the increase in free water clearance normally occurring during volume expansion. Thus L-arginine is a natriuretic substance compatible with a role of nitric oxide in sodium homeostasis, possibly by offsetting/shifting the renal response to sodium excess.     

Angiotensin receptors contribute to blood pressure homeostasis in salt-depleted SHR

This study evaluated the contribution of angiotensin peptides acting at various receptor subtypes to the arterial pressure and heart rate of adult 9-wk-old male conscious salt-depleted spontaneously hypertensive rats (SHR). Plasma ANG II and ANG I in salt-depleted SHR were elevated sevenfold compared with peptide levels measured in sodium-replete SHR, whereas plasma ANG-(1-7) was twofold greater in salt-depleted SHR compared with salt-replete SHR. Losartan (32.5 micromol/kg), PD-123319 (0.12 micromol. kg(-1). min(-1)), [d-Ala(7)]ANG-(1-7) (10 and 100 pmol/min), and a polyclonal ANG II antibody (0.08 mg/min) were infused intravenously alone or in combination. Combined blockade of AT(2) and AT((1-7)) receptors significantly increased the blood pressure of losartan-treated SHR (+15 +/- 1 mmHg; P < 0.01); this change did not differ from the blood pressure elevation produced by the sole blockade of AT((1-7)) receptors (15 +/- 4 mmHg). On the other hand, sole blockade of AT(2) receptors in losartan-treated SHR increased mean arterial pressure by 8 +/- 1 mmHg (P < 0.05 vs. 5% dextrose in water as vehicle), and this increase was less than the pressor response produced by blockade of AT((1-7)) receptors alone or combined blockade of AT((1-7)) and AT(2) receptors. The ANG II antibody increased blood pressure to the greatest extent in salt-depleted SHR pretreated with only losartan (+11 +/- 2 mmHg) and to the least extent in salt-depleted SHR previously treated with the combination of losartan, PD-123319, and [d-Ala(7)]ANG-(1-7) (+7 +/- 1 mmHg; P < 0.01). Losartan significantly increased heart rate, whereas other combinations of receptor antagonists or the ANG II antibody did not alter heart rate. Our results demonstrate that ANG II and ANG-(1-7) act through non-AT(1) receptors to oppose the vasoconstrictor actions of ANG II in salt-depleted SHR. Combined blockade of AT(2) and AT((1-7)) receptors and ANG II neutralization by the ANG II antibody reversed as much as 67% of the blood pressure-lowering effect of losartan.     

Role of plasma ANG II in the excretion of acute sodium load in a bird with salt glands (Anas platyrhynchos)

This study was designed to further examine the role of plasma ANG II in the excretion of sodium in the Pekin duck, a bird with salt glands. Renal and extrarenal (salt gland) excretion of an intravenously administered isotonic saline load was monitored over a 4-h period in a group of eight birds under two conditions: the control condition, in which isotonic saline infusion decreased endogenous plasma ANG II from 102.6 to 16.5 pg/ml, and the experimental condition, in which ANG II suppression was prevented by intravenous infusion of a 3.5 ng. kg(-1). min(-1) dose of synthetic ANG II. ANG II infusion significantly decreased the total sodium excretion (by 15%), primarily via an inhibition of salt gland output. The results suggest that ANG II suppression facilitates the excretion of an administered sodium load in birds with salt glands.     

Intrarenal transfer of an intracellular fluorescent fusion of angiotensin II selectively in proximal tubules increases blood pressure in rats and mice

The present study tested the hypothesis that intrarenal adenoviral transfer of an intracellular cyan fluorescent fusion of angiotensin II (ECFP/ANG II) selectively in proximal tubules of the kidney increases blood pressure by activating AT(1) (AT(1a)) receptors. Intrarenal transfer of ECFP/ANG II was induced in the superficial cortex of rat and mouse kidneys, and the sodium and glucose cotransporter 2 (sglt2) promoter was used to drive ECFP/ANG II expression selectively in proximal tubules. Intrarenal transfer of ECFP/ANG II induced a time-dependent, proximal tubule-selective expression of ECFP/ANG II in the cortex, which peaked at 2 wk and was sustained for 4 wk. ECFP/ANG II expression was low in the glomeruli and the entire medulla and was absent in the contralateral kidney or extrarenal tissues. At its peak of expression in proximal tubules at day 14, ANG II was increased by twofold in the kidney (P < 0.01) and more than threefold in proximal tubules (P < 0.01), but remained unchanged in plasma or urine. Systolic blood pressure was increased in ECFP/ANG II-transferred rats by 28 ± 6 mmHg (P < 0.01), whereas fractional sodium excretion was decreased by 20% (P < 0.01) and fractional lithium excretion was reduced by 24% (P < 0.01). These effects were blocked by losartan and prevented in AT(1a) knockout mice. Transfer of a scrambled ECFP/ANG IIc had no effects on blood pressure, kidney, and proximal tubule ANG II, or sodium excretion. These results provide evidence that proximal tubule-selective transfer of an intracellular ANG II fusion protein increases blood pressure by activating AT(1a) receptors and increasing sodium reabsorption in proximal tubules.     

Enzymatic processing of angiotensin peptides by human glomerular endothelial cells

The intraglomerular renin-angiotensin system (RAS) is linked to the pathogenesis of progressive glomerular diseases. Glomerular podocytes and mesangial cells play distinct roles in the metabolism of angiotensin (ANG) peptides. However, our understanding of the RAS enzymatic capacity of glomerular endothelial cells (GEnCs) remains incomplete. We explored the mechanisms of endogenous cleavage of ANG substrates in cultured human GEnCs (hGEnCs) using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and isotope-labeled peptide quantification. Overall, hGEnCs metabolized ANG II at a significantly slower rate compared with podocytes, whereas the ANG I processing rate was comparable between glomerular cell types. ANG II was the most abundant fragment of ANG I, with lesser amount of ANG-(1-7) detected. Formation of ANG II from ANG I was largely abolished by an ANG-converting enzyme (ACE) inhibitor, whereas ANG-(1-7) formation was decreased by a prolylendopeptidase (PEP) inhibitor, but not by a neprilysin inhibitor. Cleavage of ANG II resulted in partial conversion to ANG-(1-7), a process that was attenuated by an ACE2 inhibitor, as well as by an inhibitor of PEP and prolylcarboxypeptidase. Further fragmentation of ANG-(1-7) to ANG-(1-5) was mediated by ACE. In addition, evidence of aminopeptidase N activity (APN) was demonstrated by detecting amelioration of conversion of ANG III to ANG IV by an APN inhibitor. While we failed to find expression or activity of aminopeptidase A, a modest activity attributable to aspartyl aminopeptidase was detected. Messenger RNA and gene expression of the implicated enzymes were confirmed. These results indicate that hGEnCs possess prominent ACE activity, but modest ANG II-metabolizing activity compared with that of podocytes. PEP, ACE2, prolylcarboxypeptidase, APN, and aspartyl aminopeptidase are also enzymes contained in hGEnCs that participate in membrane-bound ANG peptide cleavage. Injury to specific cell types within the glomeruli may alter the intrarenal RAS balance.     

Natriuresis induced by mild hypernatremia in humans

The hypothesis that increases in plasma sodium induce natriuresis independently of changes in body fluid volume was tested in six slightly dehydrated seated subjects on controlled sodium intake (150 mmol/day). NaCl (3.85 mmol/kg) was infused intravenously over 90 min as isotonic (Iso) or as hypertonic saline (Hyper, 855 mmol/l). After Hyper, plasma sodium increased by 3% (142.0 +/- 0.6 to 146.2 +/- 0.5 mmol/l). During Iso a small decrease occurred (142.3 +/- 0.6 to 140.3 +/- 0.7 mmol/l). Iso increased estimates of plasma volume significantly more than Hyper. However, renal sodium excretion increased significantly more with Hyper (291 +/- 25 vs. 199 +/- 24 micromol/min). This excess was not mediated by arterial pressure, which actually decreased slightly. Creatinine clearance did not change measurably. Plasma renin activity, ANG II, and aldosterone decreased very similarly in Iso and Hyper. Plasma atrial natriuretic peptide remained unchanged, whereas plasma vasopressin increased with Hyper (1.4 +/- 0.4 to 3.1 +/- 0.5 pg/ml) and decreased (1.3 +/- 0.4 to 0.6 +/- 0.1 pg/ml) after Iso. In conclusion, the natriuretic response to Hyper was 50% larger than to Iso, indicating that renal sodium excretion may be determined partly by plasma sodium concentration. The mechanism is uncertain but appears independent of changes in blood pressure, glomerular filtration rate, the renin system, and atrial natriuretic peptide.     

Localized accumulation of angiotensin II and production of angiotensin-(1-7) in rat luteal cells and effects on steroidogenesis

These studies aim to investigate subcellular distribution of angiotensin II (ANG II) in rat luteal cells, identify other bioactive angiotensin peptides, and investigate a role for angiotensin peptides in luteal steroidogenesis. Confocal microscopy showed ANG II distributed within the cytoplasm and nuclei of luteal cells. HPLC analysis showed peaks that eluted with the same retention times as ANG-(1-7), ANG II, and ANG III. Their relative concentrations were ANG II >or= ANG-(1-7) > ANG III, and accumulation was modulated by quinapril, an inhibitor of angiotensin-converting enzyme (ACE), Z-proprolinal (ZPP), an inhibitor of prolyl endopeptidase (PEP), and parachloromercurylsulfonic acid (PCMS), an inhibitor of sulfhydryl protease. Phenylmethylsulfonyl fluoride (PMSF), a serine protease inhibitor, did not affect peptide accumulation. Quinapril, ZPP, PCMS, and PMSF, as well as losartan and PD-123319, the angiotensin receptor type 1 (AT1) and type 2 (AT2) receptor antagonists, were used in progesterone production studies. ZPP significantly reduced luteinizing hormone (LH)-dependent progesterone production (P < 0.05). Quinapril plus ZPP had a greater inhibitory effect on LH-stimulated progesterone than either inhibitor alone, but this was not reversed by exogenous ANG II or ANG-(1-7). Both PCMS and PMSF acutely blocked LH-stimulated progesterone, and PCMS blocked LH-sensitive cAMP accumulation. Losartan inhibited progesterone production in permeabilized but not intact luteal cells and was reversed by ANG II. PD-123319 had no significant effect on luteal progesterone production in either intact or permeabilized cells. These data suggest that steroidogenesis may be modulated by angiotensin peptides that act in part through intracellular AT1 receptors.     

Biological activities of angiotensin II-(1-6)-hexapeptide and angiotensin II-(1-7)-heptapeptide in man

Biological activities of angiotensin II-(1-6)-hexapeptide [ANG-(1-6)] and angiotensin II-(1-7)-heptapeptide [ANG-(1-7)] were studied in 5 normal men and 3 patients with Bartter's syndrome. The angiotensins were infused iv in each subject from 0900 h to 0915 h at a rate of 21 nmol(16.8 micrograms)/kg X min and 18 nmol(16.2 micrograms)/kg X min for ANG-(1-6) and ANG-(1-7), respectively. In the normal men a significant rise in blood pressure was observed by the infusions of both peptides. Average increments of blood pressure for ANG-(1-6) were 17/14, 23/18, 22/15 and 17/14 mmHg at 2, 5, 10 and 15 min, respectively, and those for ANG-(1-7) were 19/15, 20/17, 13/13 and 15/13 mmHg at 2, 5, 10 and 15 min, respectively. The duration of pressor actions after the cessation of the infusions (T) was 10 min for ANG-(1-6) and 20 (for systolic) and 30 (for diastolic) min for ANG-(1-7). T for ANG-(1-6) was shorter than and T for ANG-(1-7) was similar to T for Ile5-angiotensin II (Ile5-ANG II) reported previously in 7 normal men 5 of whom were the same as examined in the present study. On the other hand, both peptides did not cause a rise in blood pressure in the 3 patients with Bartter's syndrome. Both angiotensins did not cause an increase in plasma aldosterone but did cause a significant decrease in plasma renin activity both in the normal men and in the patients. From these results and our previous observations of inactivity of angiotensin II-(5-8)-tetrapeptide, a pressor action of angiotensin II-(4-8)-pentapeptide, and pressor, renin-suppressing and steroidogenic actions of angiotensin II-(3-8)-hexapeptide in normal men, it is thought that ANG-(1-6) and ANG-(1-7) are bound to angiotensin II (ANG II) receptor in the peripheral arterioles and show pressor actions (less than 0.024% and less than 0.028% of Ile5-ANG II, respectively) and suppress renin mainly via short loop feedback and that the shortest biologically active ANG II molecules for pressor, renin-suppressing and steroidogenic actions are Tyr-Ile-His, Val-Tyr-Ile-His and Val-Tyr-Ile-His-Pro-Phe, respectively, in man. It is also evident that ANG-(1-6) is more rapidly metabolized than ANG-(1-7) or Ile5-ANG II in man.     

Role of the renin-angiotensin system during alterations of sodium intake in conscious mice

The present studies were performed to quantify circulating components of the renin-angiotensin-aldosterone axis and to determine the functional importance of this system during alterations in sodium intake in conscious mice. Increasing sodium intake from approximately 200 to 1,000 microeq/day significantly decreased plasma renin concentration from 472 +/- 96 to 304 +/- 83 ng ANG I. ml(-1). h(-1) (n = 5) but did not alter plasma renin activity from the low-sodium level of 7.7 +/- 1.1 ng ANG I. ml(-1). h(-1). Despite the elevated plasma renin concentration, plasma ANG II in mice on low-sodium level averaged 14 +/- 3 pg/ml and was significantly suppressed to 6 +/- 1 pg/ml by high-sodium intake (n = 7). Consistent with the modulation of ANG II, plasma aldosterone significantly decreased from 41 +/- 8 to 8 +/- 3 ng/dl when sodium intake was elevated (n = 6). In a final set of experiments, the continuous infusion of ANG II (20 ng. kg(-1). min(-1)) led to a mild salt-sensitive increase in mean arterial pressure from 108 +/- 2 to 131 +/- 2 mmHg as sodium intake was varied from low to high (n = 7). In vehicle-infused mice, mean arterial pressure was unaltered from 109 +/- 2 mmHg when sodium intake was increased (n = 6). These studies indicate that the physiological suppression of circulating ANG II may be required to maintain a constancy of arterial pressure during alterations in sodium intake in normal mice.     

Central ventilatory and cardiovascular actions of angiotensin peptides in trout

In the brains of teleosts, angiotensin II (ANG II), one of the main effector peptides of the renin-angiotensin system, is implicated in various physiological functions notably body fluid and electrolyte homeostasis and cardiovascular regulation, but nothing is known regarding the potential action of ANG II and other angiotensin derivatives on ventilation. Consequently, the goal of the present study was to determine possible ventilatory and cardiovascular effects of intracerebroventricular injection of picomole doses (5-100 pmol) of trout [Asn(1)]-ANG II, [Asp(1)]-ANG II, ANG III, ANG IV, and ANG 1-7 into the third ventricle of unanesthetized trout. The central actions of these peptides were also compared with their ventilatory and cardiovascular actions when injected peripherally. Finally, we examined the presence of [Asn(1)]-ANG II, [Asp(1)]-ANG II, ANG III, and ANG IV in the brain and plasma using radioimmunoassay coupled with high-performance liquid chromatography. After intracerebroventricular injection, [Asn(1)]-ANG II and [Asp(1)]-ANG II two ANG IIs, elevated the total ventilation through a selective stimulatory action on the ventilation amplitude. However, the hyperventilatory effect of [Asn(1)]-ANG II was threefold higher than the effect of [Asp(1)]-ANG II at the 50-pmol dose. ANG III, ANG IV, and ANG 1-7 were without effect. In addition, ANG IIs and ANG III increased dorsal aortic blood pressure (P(DA)) and heart rate (HR). After intra-arterial injections, none of the ANG II peptides affected the ventilation but [Asn(1)]-ANG II, [Asp(1)]-ANG II, and ANG III elevated P(DA) (50 pmol: +80%, +58% and +48%, respectively) without significant decrease in HR. In brain tissue, comparable amounts of [Asn(1)]-ANG II and [Asp(1)]-ANG II were detected (ca. 40 fmol/mg brain tissue), but ANG III was not detected, and the amount of ANG IV was about eightfold lower than the content of the ANG IIs. In plasma, ANG IIs were also the major angiotensins (ca. 110 fmol/ml plasma), while significant but lower amounts of ANG III and ANG IV were present in plasma. In conclusion, our study suggests that the two ANG II isoforms produced within the brain may act as a neurotransmitter and/or neuromodulator to regulate the cardioventilatory functions in trout. In the periphery, two ANG IIs and their COOH-terminal peptides may act as a circulating hormone preferentially involved in cardiovascular regulations.     

Prevention of angiotensin II-induced cardiac remodeling by angiotensin-(1-7)

Cardiac remodeling, which typically results from chronic hypertension or following an acute myocardial infarction, is a major risk factor for the development of heart failure and, ultimately, death. The renin-angiotensin system (RAS) has previously been established to play an important role in the progression of cardiac remodeling, and inhibition of a hyperactive RAS provides protection from cardiac remodeling and subsequent heart failure. Our previous studies have demonstrated that overexpression of angiotensin-converting enzyme 2 (ACE2) prevents cardiac remodeling and hypertrophy during chronic infusion of angiotensin II (ANG II). This, coupled with the knowledge that ACE2 is a key enzyme in the formation of ANG-(1-7), led us to hypothesize that chronic infusion of ANG-(1-7) would prevent cardiac remodeling induced by chronic infusion of ANG II. Infusion of ANG II into adult Sprague-Dawley rats resulted in significantly increased blood pressure, myocyte hypertrophy, and midmyocardial interstitial fibrosis. Coinfusion of ANG-(1-7) resulted in significant attenuations of myocyte hypertrophy and interstitial fibrosis, without significant effects on blood pressure. In a subgroup of animals also administered [d-Ala(7)]-ANG-(1-7) (A779), an antagonist to the reported receptor for ANG-(1-7), there was a tendency to attenuate the antiremodeling effects of ANG-(1-7). Chronic infusion of ANG II, with or without coinfusion of ANG-(1-7), had no effect on ANG II type 1 or type 2 receptor binding in cardiac tissue. Together, these findings indicate an antiremodeling role for ANG-(1-7) in cardiac tissue, which is not mediated through modulation of blood pressure or altered cardiac angiotensin receptor populations and may be at least partially mediated through an ANG-(1-7) receptor.     

ANG-(1-7) reduces ANG II-induced insulin resistance by enhancing Akt phosphorylation via a Mas receptor-dependent mechanism in rat skeletal muscle

The nonapeptide angiotensin II (ANG II) induces vasoconstriction via the ANG II type I receptor, while its splice product ANG-(1-7) elicits an antihypertensive effect via the Mas receptor. Although a critical role of ANG II in the etiology of skeletal muscle insulin resistance is well documented, the role of the ANG-(1-7)/Mas receptor axis in this context is poorly understood. Therefore, we determined whether ANG-(1-7) is effective in ameliorating the negative effects of ANG II on insulin-stimulated insulin signaling and glucose transport activity in isolated soleus muscle from normotensive lean Zucker rats. ANG II alone (500 nM for 2 h) decreased insulin-stimulated glucose transport activity by 45% (P < 0.05). In the presence of 500-1000 nM ANG-(1-7), insulin-stimulated glucose transport activity in muscle exposed to ANG II improved by ∼30% (P < 0.05). Moreover, ANG-(1-7) treatment increased Akt Ser⁴⁷³ phosphorylation (47%, P < 0.05) without an effect on glycogen synthase kinase-3β Ser⁹ phosphorylation. The dependence of ANG-(1-7) action on the Mas receptor was assessed using A779 peptide, a selective Mas receptor antagonist. The positive effects of ANG-(1-7) on insulin-stimulated glucose transport activity and Akt Ser⁴⁷³ phosphorylation in soleus muscle were completely prevented in presence of 1000 nM A779. In conclusion, the present study demonstrates that ANG-(1-7), via a Mas receptor-dependent mechanism, can ameliorate the inhibitory effect of ANG II on glucose transport activity in mammalian skeletal muscle, associated with enhanced Akt phosphorylation. These results provide further evidence supporting the targeting of the renin-angiotensin system for interventions designed to reduce insulin resistance in skeletal muscle tissue.