[Medication and comedication in COVID-19 patients]

This paper discusses the possible effects of comedication on COVID-19 and the current treatment options for this infection. It is very doubtful that comedication has a disadvantageous effect on the course of the disease. NSAIDs should be avoided in any patient with a possible severe disease, because of potential side effects. Inhibitors of the renin-angiotensin aldosterone system should be continued when there is a solid indication, and stopped in case of hemodynamic problems. There is no preference for either ACE inhibitors or angiotensin II receptor inhibitors. Currently, chloroquine and remdesivir are possible treatment options. There is no sound evidence for either treatment. Chloroquine has side effects (nausea, QT prolongation) and there are several drug interactions. The treatment should be reconsidered in the event of side effects and when inferior medication for comorbidity must be prescribed because of possible interactions. Lopinavir/ritonavir is not effective. Supportive care is at present the mainstay of the treatment.

Abstract 017: Effect of Sildenafil on Nitric Oxide-Mediated Vasodilation in the Human Placenta: an Ex-Vivo Placental Perfusion Study

Preeclampsia (PE) is a serious pregnancy complication characterized by suboptimal placentation, leading to increased vascular resistance and generalized endothelial dysfunction. A promising treatment is sildenafil, a phosphodiesterase-5 (PDE5) inhibitor that enhances nitric oxide (NO) mediated vasodilation. Although there are currently sildenafil trials ongoing in pregnant women, the effects of sildenafil on the placenta are still unknown. Placentas of healthy (n=17), early-onset (Eo)PE (n=6) and late-onset (Lo)PE (n=5) pregnancies were dually perfused, pre-constricted with serotonin, and subsequently exposed to the NO donor SNP in the absence or presence of 1 μmol/L sildenafil. Two healthy placentas were perfused with sildenafil on the maternal side to study placental transfer. Placental protein expression of PDE5, PDE1A, eNOS and iNOS was assessed using Western blot. Mean baseline pressure ±SEM was significantly lower (p<0.05) in EoPE (22.3±2.8 mmHg) and LoPE (22.8±1.7 mmHg) vs. healthy placentas (33.1±2.2 mmHg). There was no effect of sildenafil on baseline pressure or serotonin-induced pre-constriction. Sildenafil tended to enhance vasodilatory response to 10 -6 M SNP in healthy (mean pressure decrease 4.3±0.8 vs. 8.1±1.9 mmHg, p=0.1) and LoPE placentas (3.0±1.0 vs. 7.3±3.2 mmHg), while no improvement was seen in EoPE placentas (6.0±2.0 vs. 5.0±1.0 mmHg). When sildenafil was added at the maternal side, average fetal-maternal concentration ratio was 0.22 after 3 hours of perfusion, as compared to 0.86 for antipyrine, a freely diffusing molecule. Placental levels of PDE1A tended to be higher in PE (p=0.08), while no differences in expression of PDE5, eNOS and iNOS were observed between PE and healthy placentas. Our study reveals that PE placentas have a significantly lower baseline pressure compared to healthy placentas, possibly due to lower resistance in the feto-placental vasculature as a compensation mechanism for the increased resistance in the spiral arteries. Although sildenafil tended to enhance vasodilation in healthy and LoPE placentas, it did not have those beneficial effects in EoPE. Possibly PDE1A-selective inhibitors should be applied in PE, or PDE is not the appropriate target for restoring disturbed vasodilation.

Abstract P246: Salt-sensitivity of Angiogenesis Inhibition-induced Blood Pressure (BP) Rise: Role of Interstitial Sodium Accumulation?

Objective: Angiogenesis inhibition with the VEGF-inhibitor sunitinib, an established anti-cancer therapy, induces hypertension and proteinuria. Exposed to osmotic stress, the mononuclear-phagocyte-system (MPS) cells produces VEGF-C and exert homeostatic regulatory activity by promoting lymphatic Na+ drainage; interference with this process resulted in salt-sensitive hypertension. Therefore, we hypothesized that sunitinib, via blockade of the VEGF pathway, leads to Na+ accumulation in the skin and salt-sensitive hypertension.

Design and Methods: In male WKY rats, mean arterial pressure (MAP) was monitored telemetrically during oral treatment with sunitinib (7 mg/kg.day, n=7-8) or vehicle (n=7-8) after a normal salt diet (NSD: 0.5-1.0% NaCl and tap water) or a high salt diet (HSD: 8% NaCl and saline water) for 2 weeks. After 8 days of sunitinib or vehicle administration, 24-h urine was collected. After sacrificing, blood was collected for biochemical measurements, skin for Na+ concentration ([Na+]) using dry-ashing, and ears for staining of MPS cells (CD68).

Results: MAP during NSD was 101±0.9 mmHg. HSD increased MAP by 27±3 mmHg (P<0.05 vs. NSD). Sunitinib increased MAP by 15±1 mmHg during NSD (P<0.05 vs. NSD alone) and by 23±4 mmHg during HSD (P<0.05 vs. HSD alone). Although body weight, plasma [Na+] and plasma [cystatin-C] did not change in response to HSD and/or sunitinib, skin [Na+] increased from 90±1 (NSD) to 100±4 (HSD), and 108±4 mmol/L (HSD+sunitinib), respectively (P<0.01 for linear trend). Skin [Na+] correlated with MAP (r=0.57, P<0.01). Compared to NSD, proteinuria increased during HSD, rising further (P<0.05) with sunitinib. CD68 positive area increased during HSD from 0.29% to 0.43% (P<0.05), and increased even further with sunitinib (0.63%, P<0.05).

Conclusions: Angiogenesis inhibition-induced hypertension is salt-sensitive. The parallel increases in BP and skin [Na+], in the face of unaltered plasma [Na+] and bodyweight, support the existence of a Na+-buffering compartment in the skin that may contribute to the salt-dependent volume and BP homeostasis during VEGF inhibition.

Abstract 528: Dose- And Salt-dependency Of Angiogenesis Inhibition-induced Blood Pressure Rise And Renal Toxicity

Angiogenesis inhibition with the VEGF inhibitor sunitinib is an established anti-cancer therapy, inducing hypertension and nephrotoxicity. We explored the dose- and salt-dependency of these side effects. In male WKY rats, mean arterial pressure (MAP) was monitored telemetrically during oral treatment with a high (27.5 mg/kg.day, n=14), an intermediate (14 mg/kg.day, n=6) and low dose (7 mg/kg.day, n=6) of sunitinib or vehicle (n=8) after normal salt diet for 2 weeks. The low dose-model was also combined with a high salt diet (8% NaCl and saline water). Eight days after administration rats were sacrificed and blood and 24h urine samples collected for biochemical measurements.

With the high dose of sunitinib, MAP increased from 94.7±0.9 mmHg to 125.8±1.5 mmHg (Δ31.1±0.9 mmHg, p<0.001). The intermediate and low doses induced MAP rises of 24.3±2.7 mmHg (p<0.001) and 13.4±3.3 mmHg (p<0.001), respectively. The low dose of sunitinib with high salt, induced a MAP rise of 43.5±2.2 mmHg (p<0.001 compared to normal salt). With the high dose, circulating ET-1 increased from 0.6±0.1 pg/ml to 1.6±0.2 pg/ml (p<0.01) and serum cystatine-C from 4.5±0.1 mg/L to 6.6±0.3 mg/L (p<0.001). Comparable increases in circulating ET-1 were seen with the intermediate and low doses, whereas serum cystatine-C did increase with the intermediate dose (to 6.3±0.1 mg/L, p0.05). Serum cystatine-C levels with low and high salt were identical. With the high dose of sunitinib, proteinuria increased from 7.5±1.3 to 33.3±4.8 mg/day (p<0.05). The rise in proteinuria was attenuated with the intermediate (16.2±2.1 mg/day, p<0.01) and low dose (19.9±3.3 mg/day, p<0.01), but increased to 40.4±30.1 mg/day (p>0.05) with high salt.

Angiogenesis inhibition-induced hypertension and nephrotoxicity are dose-dependent with a lower threshold for the rise in BP than for renal toxicity. The BP rise observed with the low dose of sunitinib observed in normotensive rats is comparable to the sunitinib-induced BP rise observed in patients and clearly is salt-sensitive. Since cystatine-C levels during normal and high salt diet were comparable, the BP rise during high salt seems independent of renal dysfunction.

Abstract 184: Deterioration of Kidney Function by the (Pro)renin Receptor Blocker Handle Region Peptide in Aliskiren-treated Diabetic Transgenic (mRen2)27 Rats

Objective Renal function in patients with diabetes mellitus (DM) might be influenced by the level of prorenin due to its binding to the (pro)renin receptor ((P)RR) and the subsequently occurring angiotensin production and/or the direct agonistic effects of prorenin mediated via this receptor. Indeed, in DM elevated prorenin levels are correlated with the development of microvascular complications such as nephropathy.

Design and Methods In this study we evaluated renal function in diabetic TGR(mREN2)27 rats (a high prorenin hypertensive model), treated with vehicle, the renin inhibitor aliskiren, or aliskiren plus the putative (P)RR antagonist HRP for 3 weeks. 24-hour urine was collected, and blood and kidney were evaluated for renin-angiotensin system components and pathology.

Results Increased diuresis and proteinuria due to DM were prevented by aliskiren, but not aliskiren+HRP. Aliskiren+HRP additionally decreased creatinine clearance, and increased the plasma levels of the profibrotic marker plasminogen-activator inhibitor-1. The increased natriuresis and renal collagen-1 expression in this model were unaffected by aliskiren±HRP. Aliskiren increased rat renin expression in the renal cortex. This was associated with a decline in (P)RR and AT 1 receptor mRNA expression, and these changes were unaffected by HRP. Glomerular volume and interlobar arterial lumen diameter modestly increased in the aliskiren+HRP group, and were unaffected by aliskiren alone.

Conclusions HRP, when given on top of aliskiren in DM TGR(mREN2)27 rats worsens kidney damage and counteracts the beneficial effects of aliskiren. (P)RR blockade is therefore contraindicated in DM.

Superoxide does not mediate the acute vasoconstrictor effects of angiotensin II: a study in human and porcine arteries

OBJECTIVE

To investigate whether superoxide mediates angiotensin (Ang) II-induced vasoconstriction.

METHODS

Human coronary arteries (HCAs), porcine femoral arteries (PFA) and porcine coronary arteries (PCAs) were mounted in organ baths and concentration-response curves to Ang II, the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine (SNAP) and the NAD(P)H oxidase substrate NADH were constructed in the absence and presence of superoxide inhibiting and activating drugs. Extracellular superoxide was measured using cytochrome c reduction.

RESULTS

Ang II constricted both HCAs and PFAs. In HCAs, the NAD(P)H inhibitors diphenyleneiodonium (DPI) and apocynin, and the xanthine oxidase (XO) inhibitor allopurinol, but not the superoxide dismutase (SOD) mimetic tempol or the SOD inhibitor diethyldithiocarbamate (DETCA), reduced this constriction. Catalase potentiated Ang II in HCAs, indicating a vasodilator role for H2O2. DPI, tempol and SOD did not affect Ang II in PFAs. DPI, apocynin and allopurinol relaxed preconstricted HCAs. Although the relaxant effects of the NO donor SNAP in PCAs was reduced by DETCA, indicating that superoxide-induced constrictions depend on NO inactivation, the apocynin-induced relaxations were NO independent. Moreover, NADH relaxed all vessels, and this effect was blocked by KCl but not DPI or NO removal. Xanthine plus XO also relaxed HCAs and PCAs. Incubation of human or porcine arteries with Ang II or NADH did not result in detectable increases of extracellular superoxide within 1 h.

CONCLUSIONS

Acute vasoconstriction by Ang II is not mediated via superoxide generated through NAD(P)H oxidase and/or XO activation. Such activation, if occurring, rather results in the generation of the vasodilator H2O2.

Intrarenal angiotensin II: interstitial and cellular levels and site of production

BACKGROUND

Both local production and angiotensin II subtype 1 (AT1) receptor-mediated uptake from the circulation contribute to the high levels of angiotensin (Ang) II in the kidney. It is largely unknown where Ang II is produced in the kidney and how much of it originates from the circulation.

METHODS

The concentrations of endogenous and 125I-labeled Ang I and II were measured in renal tissue and in blood from pigs receiving systemic infusions of 125I-Ang I. Pigs were either untreated or treated with the angiotensin converting enzyme (ACE) inhibitor captopril or the AT1 receptor antagonist eprosartan.

RESULTS

125I-Ang I was undetectable in renal tissue but the steady-state concentrations of 125I-Ang II in cortical and medullary tissue were four and two times the concentration in arterial blood plasma, respectively. The tissue concentrations of endogenous Ang II were 100 and 60 times higher than in arterial plasma. Eprosartan reduced 125I-Ang II accumulation by 90%, but did not lower tissue Ang II. Captopril did not alter either 125I-Ang II accumulation or tissue Ang II.

CONCLUSIONS

The bulk of Ang II in the kidney is cell-associated. The high tissue/blood concentration ratio of endogenous Ang II may depend on the same mechanism as demonstrated for 125I-Ang II, that is, AT1 receptor-mediated binding to cells and endocytosis. If so, the results indicate that most renal AT1 receptors are exposed to locally generated Ang II rather than Ang II from the circulation. We propose the existence of a low-Ang II vascular system-related interstitial compartment that is separate from tubular fluid, where, according to micropuncture studies, Ang II levels might be high.

AT(2) receptor-mediated vasodilation in the heart: effect of myocardial infarction

To investigate the functional consequences of postinfarct cardiac angiotensin (ANG) type 2 (AT(2)) receptor upregulation, rats underwent coronary artery ligation or sham operation and were infused with ANG II 3-4 wk later, when scar formation is complete. ANG II increased mean arterial pressure (MAP) more modestly in infarcted animals than in sham animals. The AT(1) receptor antagonist irbesartan, but not the AT(2) receptor antagonist PD123319, decreased MAP and antagonized the ANG II-mediated systemic hemodynamic effects. Myocardial (MVC) but not renal vascular conductance (RVC) was diminished in infarcted versus sham rats. ANG II did not affect MVC and reduced RVC in all rats. MVC was unaffected by irbesartan and PD123319 in all animals. However, with PD123319, ANG II reduced MVC in sham but not infarcted animals, and, with irbesartan, ANG II increased MVC in infarcted but not sham animals. Irbesartan increased RVC and antagonized the ANG II-mediated renal effects in all animals. RVC, at baseline or with ANG II, was not affected by PD123319 in infarcted and sham animals. In conclusion, coronary but not renal AT(2) receptor stimulation results in vasodilation, and this effect is enhanced in infarcted rats.

Angiotensin II type 2 receptors and cardiac hypertrophy in women with hypertrophic cardiomyopathy

The development of left ventricular hypertrophy in subjects with hypertrophic cardiomyopathy (HCM) is variable, suggesting a role for modifying factors such as angiotensin II. Angiotensin II mediates both trophic and antitrophic effects, via angiotensin II type 1 (AT(1)-R) and angiotensin II type 2 (AT(2)-R) receptors, respectively. Here we investigated the effect of the AT(2)-R gene A/C(3123) polymorphism, located in the 3' untranslated region of exon 3, on left ventricular mass index (LVMI) in 103 genetically independent subjects with HCM (age, 12 to 81 years). LVMI and interventricular septum thickness were determined by 2D echocardiography. Extent of hypertrophy was quantified by a point score (Wigle score). Plasma prorenin, renin, and ACE were determined by immunoradiometric or fluorometric assays, and genotyping was performed by polymerase chain reaction. In men, no associations between AT(2)-R genotype and any of the measured parameters were observed, whereas in women, LVMI decreased with the number of C alleles (211+/-19, 201+/-18, and 152+/-10 g/m(2) in women with the AA, AC, and CC genotype, respectively; P=0.015). Similar C allele-related decreases in women were observed for interventricular septum thickness (P=0.13), Wigle score (P=0.05), plasma renin (P=0.03), and plasma prorenin (P=0.26). Multiple regression analysis revealed that the AT(2)-R C allele-related effect on LVMI (beta=-30.7+/-11.1, P=0.010) occurred independently of plasma renin, the AT(1)-R gene A/C(1166) polymorphism, or the ACE gene I/D polymorphism. In conclusion, AT(2)-Rs modulate cardiac hypertrophy in women with HCM, independently of the circulating renin-angiotensin system. These data support the contention that AT(2)-Rs mediate antitrophic effects in humans.

Negative inotropic effect of bradykinin in porcine isolated atrial trabeculae: role of nitric oxide

OBJECTIVES

To investigate whether bradykinin affects cardiac contractility independently of its effects on coronary flow and noradrenaline release, and whether such inotropic effects, if present, are mediated via nitric oxide (NO).

METHODS

Right atrial trabeculae were obtained from 35 pigs, suspended in organ baths and attached to isometric transducers. Resting tension was set at approximately 750 mg and tissues were paced at 1.5 Hz. Tissue viability was checked by constructing a concentration response curve (CRC) to noradrenaline. Next, CRCs were constructed to bradykinin, either under baseline conditions or after pre-stimulation with the positive inotropic agent forskolin (1 or 10 micromol/l), in the absence or presence of the bradykinin type 2 (B2) receptor antagonist D-Arg [Hyp3-Thi5, d-Tic7, Oic8]-bradykinin (Hoe 140) (1 micromol/l), the NO synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) (100 micromol/l) and/or the NO scavenger hydroxocobalamin (200 micromol/l).

RESULTS

Bradykinin exerted a negative inotropic effect, both with and without forskolin pre-stimulation, reducing contractility by maximally 22 +/- 3.6% (mean +/- SEM) and 23 +/- 3.6%, respectively (pEC50 8.37 +/- 0.23 and 8.62 +/- 0.22, respectively). L-NAME reduced this effect in pre-stimulated, but not in unstimulated, trabeculae. Hoe 140 and hydroxocobalamin fully blocked the inotropic effect of bradykinin.

CONCLUSIONS

Bradykinin induces a modest negative inotropic effect in porcine atrial trabeculae that is mediated via B2 receptors and NO. The inconsistent results obtained with L-NAME suggest that it depends on NO synthesized de novo and/or NO from storage sites.

Bradykinin potentiation by angiotensin-(1-7) and ACE inhibitors correlates with ACE C- and N-domain blockade

ACE inhibitors block B(2) receptor desensitization, thereby potentiating bradykinin beyond blocking its hydrolysis. Angiotensin (Ang)-(1-7) also acts as an ACE inhibitor and, in addition, may stimulate bradykinin release via angiotensin II type 2 receptors. In this study we compared the bradykinin-potentiating effects of Ang-(1-7), quinaprilat, and captopril. Porcine coronary arteries, obtained from 32 pigs, were mounted in organ baths, preconstricted with prostaglandin F(2alpha), and exposed to quinaprilat, captopril, Ang-(1-7), and/or bradykinin. Bradykinin induced complete relaxation (pEC(50)=8.11+/-0.07, mean+/-SEM), whereas quinaprilat, captopril, and Ang-(1-7) alone were without effect. Quinaprilat shifted the bradykinin curve to the left in a biphasic manner: a 5-fold shift at concentrations that specifically block the C-domain (0.1 to 1 nmol/L) and a 10-fold shift at concentrations that block both domains. Captopril and Ang-(1-7) monophasically shifted the bradykinin curve to the left, by a factor of 10 and 5, respectively. A 5-fold shift was also observed when Ang-(1-7) was combined with 0.1 nmol/L quinaprilat. Repeated exposure of porcine coronary arteries to 0.1 micromol/L bradykinin induced B(2) receptor desensitization. The addition of 10 micromol/L quinaprilat or Ang-(1-7) to the bath, at a time when bradykinin alone was no longer able to induce relaxation, fully restored the relaxant effects of bradykinin. Angiotensin II type 1 or 2 receptor blockade did not affect any of the observed effects of Ang-(1-7). In conclusion, Ang-(1-7), like quinaprilat and captopril, potentiates bradykinin by acting as an ACE inhibitor. Bradykinin potentiation is maximal when both the ACE C- and N-terminal domains are inhibited. The inhibitory effects of Ang-(1-7) are limited to the ACE C-domain, raising the possibility that Ang-(1-7) synergistically increases the blood pressure-lowering effects of N-domain-specific ACE inhibitors.

Prorenin accumulation and activation in human endothelial cells: importance of mannose 6-phosphate receptors

ACE inhibitors improve endothelial dysfunction, possibly by blocking endothelial angiotensin production. Prorenin, through its binding and activation by endothelial mannose 6-phosphate (M6P) receptors, may contribute to this production. Here, we investigated this possibility as well as prorenin activation kinetics, the nature of the prorenin-activating enzyme, and M6P receptor-independent prorenin binding. Human umbilical vein endothelial cells (HUVECs) were incubated with wild-type prorenin, K/A-2 prorenin (in which Lys42 is mutated to Ala, thereby preventing cleavage by known proteases), M6P-free prorenin, and nonglycosylated prorenin, with or without M6P, protease inhibitors, or angiotensinogen. HUVECs bound only M6P-containing prorenin (K(d) 0.9+/-0.1 nmol/L, maximum number of binding sites [B(max)] 1010+/-50 receptors/cell). At 37 degrees C, because of M6P receptor recycling, the amount of prorenin internalized via M6P receptors was >25 times B(max). Inside the cells, wild-type and K/A-2 prorenin were proteolytically activated to renin. Renin was subsequently degraded. Protease inhibitors interfered with the latter but not with prorenin activation, thereby indicating that the activating enzyme is different from any of the known prorenin-activating enzymes. Incubation with angiotensinogen did not lead to endothelial angiotensin generation, inasmuch as HUVECs were unable to internalize angiotensinogen. Most likely, therefore, in the absence of angiotensinogen synthesis or endocytosis, M6P receptor-mediated prorenin internalization by endothelial cells represents prorenin clearance.

Angiotensin converting enzyme is the main contributor to angiotensin I-II conversion in the interstitium of the isolated perfused rat heart

OBJECTIVES

Recent studies in homogenized hearts suggest that chymase rather than angiotensin converting enzyme (ACE) is responsible for cardiac angiotensin I to angiotensin II conversion. We investigated in intact rat hearts whether (i) enzymes other than ACE contribute to angiotensin I to angiotensin II conversion and (ii) the localization (endothelial/extra-endothelial) of converting enzymes.

DESIGN AND METHODS

We used a modified version of the rat Langendorff heart, allowing separate collection of coronary effluent and interstitial fluid. Hearts were perfused with angiotensin I (arterial concentration 5-10 pmol/ml) under control conditions, in the presence of captopril (1 micromol/l) or after endothelium removal with 0.2% triton X-100. Endothelium removal was verified as the absence of a coronary vasodilator response to 10 nmol bradykinin. Angiotensin I and angiotensin II were measured in coronary effluent and interstitial fluid with sensitive radioimmunoassays.

RESULTS

In control hearts, 45% of arterial angiotensin I was metabolized during coronary passage, partly through conversion to angiotensin II. At steady-state, the angiotensin I concentration in interstitial fluid was three to four-fold lower than in coronary effluent, while the angiotensin II concentrations in both fluids were similar. Captopril and endothelium removal did not affect coronary angiotensin I extraction, but increased the interstitial fluid levels of angiotensin I two- and three-fold, respectively, thereby demonstrating that metabolism (by ACE) as well as the physical presence of the endothelium normally prevent arterial angiotensin I from reaching similar levels in coronary effluent and interstitial fluid. Captopril, but not endothelium removal, greatly reduced the angiotensin II levels in coronary effluent and interstitial fluid. With the ACE inhibitor, the angiotensin II/I ratios in coronary effluent and interstitial fluid were 83 and 93% lower, while after endothelium removal, the ratios were 33 and 71% lower.

CONCLUSIONS

In the intact rat heart, ACE is the main contributor to angiotensin I to angiotensin II conversion, both in the coronary vascular bed and the interstitium. Cardiac ACE is not limited to the coronary vascular endothelium.

Subcellular localization of angiotensin II in kidney and adrenal

OBJECTIVES

To investigate whether tissue angiotensin II generation occurs intra- or extracellularly, we studied the subcellular localization of angiotensin II in kidney and adrenal, two organs with high endogenous angiotensin II concentrations.

DESIGN AND METHODS

Tissues were obtained, following a 1 h infusion of 125I-angiotensin I or 125I-angiotensin II to simultaneously determine the localization of plasma-derived angiotensin II, from five control pigs and four pigs that had been pretreated with the AT1 receptor antagonist eprosartan. Subcellular organelles, prepared by differential centrifugation from homogenized tissue, were characterized using organelle-specific markers.

RESULTS

125I-angiotensin II and angiotensin II were present in all organelles, with identical distribution profiles. In mitochondria-enriched fractions the relative specific activities [RSAs = (concentration per mg protein in fraction)/(concentration per mg protein in homogenate)] of the two peptides were similar to those in homogenate, whereas in cytosol-enriched fractions their RSAs were five- to 10-fold lower (P< 0.05 versus homogenate). In microsome- as well as in lysosome-enriched fractions the RSAs of 125I-angiotensin II and angiotensin II were two- to four-fold higher than in homogenate (P < 0.05), and their RSAs were also higher in renal nuclei-enriched fractions (P< 0.05). Eprosartan increased plasma angiotensin II to a larger degree than tissue angiotensin II and greatly reduced tissue 125I-angiotensin II. This led to similar decreases in the tissue/plasma concentration ratios of 125I-angiotensin II and angiotensin II. The subcellular distribution of both angiotensin II peptides was not affected by eprosartan.

CONCLUSIONS

Local angiotensin II synthesis in adrenal and kidney occurs predominantly extracellularly, and is followed by rapid AT1 receptor-mediated endocytosis, thereby leading to high intracellular angiotensin II levels.

Cardiomyocytes bind and activate native human prorenin : role of soluble mannose 6-phosphate receptors

Cardiomyocytes bind, internalize, and activate recombinant human prorenin through mannose 6-phosphate/insulin-like growth factor II (M6P/IGFII) receptors. To investigate whether this also applies to native human prorenin, neonatal rat myocytes were incubated for 4 hours at 37 degrees C with various prorenin-containing human body fluids. Uptake and activation by M6P/IGFII receptors were observed for plasma prorenin from subjects with renal artery stenosis and/or hypertension and for follicular fluid prorenin. The total amount of cellular renin and prorenin (expressed as percentage of the levels of renin and prorenin in the medium) after 4 hours of incubation was 4 to 10 times lower than after incubation with recombinant human prorenin. Although plasma contains alkaline phosphatases capable of inactivating the M6P label as well as soluble M6P/IGFII receptors that block prorenin binding in a competitive manner and proteins (eg, insulin, IGFII) that increase the number of cell-surface M6P/IGFII receptors, these factors were not responsible for the modest uptake of native human prorenin. Uptake did not occur during incubation of myocytes with plasma prorenin from anephric subjects or with amniotic fluid prorenin, and this was not due to the presence of excessively high levels of M6P/IGFII receptors and/or phosphatase activity in these fluids. In conclusion, myocytes are capable of binding, internalizing, and activating native human prorenin of renal and ovarian origin through M6P/IGFII receptors. Differences in prorenin glycosylation and/or phosphorylation as well as the concentration of soluble M6P/IGFII receptors and growth factors affecting cell-surface M6P/IGFII receptor density determine the amount of prorenin entering the heart and thus cardiac angiotensin II production.

Renin-angiotensin system gene polymorphisms: potential mechanisms for their association with cardiovascular diseases

Since the first description of the angiotensin-converting enzyme insertion/deletion polymorphism more than a decade ago, many hundreds of investigations have reported associations between this polymorphism and cardiovascular diseases. Subsequently, similar studies were performed in relationship with several other renin-angiotensin system gene polymorphisms, most notably the angiotensinogen M235T polymorphism and the angiotensin AT(1) receptor A1166C polymorphism. Surprisingly however, especially in view of the many contradictory results that have been obtained, very little attention has been paid to the mechanism(s) that may link these genetic variants and respective diseases. Here, we review the limited evidence that is currently available on the functional consequences (including compensatory mechanisms) of the above three renin-angiotensin system gene polymorphisms, in order to provide an explanation for the reported associations (or lack thereof) between these polymorphisms and cardiovascular diseases.

Angiotensin-converting enzyme inhibition and angiotensin II type 1 receptor blockade prevent cardiac remodeling in pigs after myocardial infarction: role of tissue angiotensin II

BACKGROUND

The mechanisms behind the beneficial effects of renin-angiotensin system blockade after myocardial infarction (MI) are not fully elucidated but may include interference with tissue angiotensin II (Ang II).

METHODS AND RESULTS

Forty-nine pigs underwent coronary artery ligation or sham operation and were studied up to 6 weeks. To determine coronary angiotensin I (Ang I) to Ang II conversion and to distinguish plasma-derived Ang II from locally synthesized Ang II, (125)I-labeled and endogenous Ang I and II were measured in plasma and in infarcted and noninfarcted left ventricle (LV) during (125)I-Ang I infusion. Ang II type 1 (AT(1)) receptor-mediated uptake of circulating (125)I-Ang II was increased at 1 and 3 weeks in noninfarcted LV, and this uptake was the main cause of the transient elevation in Ang II levels in the noninfarcted LV at 1 week. Ang II levels and AT(1) receptor-mediated uptake of circulating Ang II were reduced in the infarct area at all time points. Coronary Ang I to Ang II conversion was unaffected by MI. Captopril and the AT(1) receptor antagonist eprosartan attenuated postinfarct remodeling, although both drugs increased cardiac Ang II production. Captopril blocked coronary conversion by >80% and normalized Ang II uptake in the noninfarcted LV. Eprosartan did not affect coronary conversion and blocked cardiac Ang II uptake by >90%.

CONCLUSIONS

Both circulating and locally generated Ang II contribute to remodeling after MI. The rise in tissue Ang II production during angiotensin-converting enzyme inhibition and AT(1) receptor blockade suggests that the antihypertrophic effects of these drugs result not only from diminished AT(1) receptor stimulation but also from increased stimulation of growth-inhibitory Ang II type 2 receptors.

L-NAME-resistant bradykinin-induced relaxation in porcine coronary arteries is NO-dependent: effect of ACE inhibition

1. NO synthase (NOS)inhibitors partially block bradykinin (BK)-mediated vasorelaxation. Here we investigated whether this is due to incomplete NOS inhibition and/or NO release from storage sites. We also studied the mechanism behind ACE inhibitor-mediated BK potentiation. 2. Porcine coronary arteries (PCAs) were mounted in organ baths, preconstricted, and exposed to BK or the ACE-resistant BK analogue Hyp(3)-Tyr(Me)(8)-BK (HT-BK) with or without the NOS inhibitor L-NAME (100 microM), the NO scavenger hydroxocobalamin (200 microM), the Ca(2+)-dependent K(+)-channel blockers charybdotoxin+apamin (both 100 nM), or the ACE inhibitor quinaprilat (10 microM). 3. BK and HT-BK dose-dependently relaxed preconstricted vessels (pEC(50) 8.0+/-0.1 and 8.5+/-0.2, respectively). pEC(50)'s were approximately 10 fold higher with quinaprilat, and approximately 10 fold lower with L-NAME or charybdotoxin+apamin. Complete blockade was obtained with hydroxocobalamin or L-NAME+ charybdotoxin+apamin. 4. Repeated exposure to 100 nM BK or HT-BK, to deplete NO storage sites, produced progressively smaller vasorelaxant responses. With L-NAME, the decrease in response occurred much more rapidly. L-Arginine (10 mM) reversed the effect of L-NAME. 5. Adding quinaprilat to the bath following repeated exposure (with or without L-NAME), at the time BK and HT-BK no longer induced relaxation, fully restored vasorelaxation, while quinaprilat alone had no effect. Quinaprilat also relaxed vessels that, due to pretreatment with hydroxocobalamin or L-NAME+charybdotoxin+apamin, previously had not responded to BK. 6. In conclusion, L-NAME-resistant BK-induced relaxation in PCAs depends on NO from storage sites, and is mediated via stimulation of guanylyl cyclase and/or Ca(2+)-dependent K(+)-channels. ACE inhibitors potentiate BK independent of their effect on BK metabolism.

Angiotensin II and the heart : on the intracrine renin-angiotensin system

-The active end product of the renin-angiotensin system, angiotensin II (Ang II), through the activation of specific Ang II receptors, regulates cardiac contractility, cell coupling, and impulse propagation and is involved in cardiac remodeling, growth, and apoptosis. We review these subjects, as well as the second messengers that are involved, and the synthesis of Ang II in the heart under normal and pathological conditions. Finally, we discuss the possibility that there is an intracrine renin-angiotensin system in the heart that plays a role in the control of cell communication and inward Ca(2+) current.

Pharmacokinetics of intravenous ATP in cancer patients

OBJECTIVE

To characterise the pharmacokinetics of adenosine 5'-triphosphate (ATP) in patients with lung cancer after i.v. administration of different ATP dosages.

METHODS

Twenty-eight patients received a total of 176 i.v. ATP courses of 30 h. Fifty-two infusions were given as low-dose infusions of 25-40 microg kg(-1) min(-1), 47 as middle-dose infusions of 45-60 microg kg(-1) min(-1) and 77 as high-dose infusions of 65-75 microg kg(-1) min(-1) ATP. Kinetic data of ATP concentrations in erythrocytes were available from 124 ATP courses. Results are expressed as mean +/- SEM.

RESULTS

Most ATP courses in cancer patients were without side effects (64%), and side effects occurring in the remaining courses were mild and transient, resolving within minutes after decreasing the infusion rate. Baseline ATP concentration in erythrocytes was 1,554 +/- 51 micromol l(-1). ATP plateau levels at 24 h were significantly increased by 53 +/- 3, 56 +/- 3 and 69 +/- 2% after low-dose, middle-dose and high-dose ATP infusions, respectively. At the same time, significant increases in plasma uric acid concentrations were observed: 0.06 +/- 0.01, 0.11 +/- 0.01 and 0.16 +/- 0.01 mmol l(-1), respectively. The mean half-time for disappearance of ATP from erythrocytes, measured in five patients, was 5.9 +/- 0.5 h.

CONCLUSIONS

During constant i.v. infusion of ATP in lung cancer patients, ATP is taken up by erythrocytes and reaches dose-dependent plateau levels 50-70% above basal concentrations at approximately 24 h.

Functional importance of angiotensin-converting enzyme-dependent in situ angiotensin II generation in the human forearm

To assess the importance for vasoconstriction of in situ angiotensin (Ang) II generation, as opposed to Ang II delivery via the circulation, we determined forearm vasoconstriction in response to Ang I (0.1 to 10 ng. kg(-1). min(-1)) and Ang II (0.1 to 5 ng. kg(-1). min(-1)) in 14 normotensive male volunteers (age 18 to 67 years). Changes in forearm blood flow (FBF) were registered with venous occlusion plethysmography. Arterial and venous blood samples were collected under steady-state conditions to quantify forearm fractional Ang I-to-II conversion. Ang I and II exerted the same maximal effect (mean+/-SEM 71+/-4% and 75+/-4% decrease in FBF, respectively), with similar potencies (mean EC(50) [range] 5.6 [0.30 to 12.0] nmol/L for Ang I and 3.6 [0.37 to 7.1] nmol/L for Ang II). Forearm fractional Ang I-to-II conversion was 36% (range 18% to 57%). The angiotensin-converting enzyme (ACE) inhibitor enalaprilat (80 ng. kg(-1). min(-1)) inhibited the contractile effects of Ang I and reduced fractional conversion to 1% (0.1% to 8%), thereby excluding a role for Ang I-to-II converting enzymes other than ACE (eg, chymase). The Ang II type 1 receptor antagonist losartan (3 mg. kg(-1). min(-1)) inhibited the vasoconstrictor effects of Ang II. In conclusion, the similar potencies of Ang I and II in the forearm, combined with the fact that only one third of arterially delivered Ang I is converted to Ang II, suggest that in situ-generated Ang II is more important for vasoconstriction than circulating Ang II. Local Ang II generation in the forearm depends on ACE exclusively and results in vasoconstriction via Ang II type 1 receptors.

The angiotensin-converting enzyme gene polymorphism and responses to angiotensins and bradykinin in the human forearm

The deletion (D) allele of the angiotensin-converting enzyme (ACE) is associated with high ACE levels. Subjects homozygous for the D allele should therefore exhibit enhanced angiotensin I-induced vasoconstrictor responses and diminished bradykinin-induced vasodilator responses as compared with subjects homozygous for the insertion (I) allele. In eight II and eight DD normotensive male subjects, angiotensin I, bradykinin, and angiotensin II were infused in the forearm. Changes in forearm blood flow were registered with venous occlusion plethysmography. Blood was sampled to quantify angiotensin I to II conversion. Plasma ACE levels were 60% higher, and DD subjects showed an enhanced response to angiotensin I infusion (p < 0.05). No differences in angiotensin I to II conversion, angiotensin H vasoconstriction, and bradykinin vasorelaxation were found. The ACE-inhibitor enalaprilate inhibited angiotensin I-induced vasoconstriction, but did not significantly affect bradykinin-induced vasodilation. The AT1-receptor antagonist losartan (3,000 ng/kg/min) inhibited angiotensin II-induced vasoconstriction. In conclusion, subjects with the DD genotype display an enhanced vasoconstrictor response to angiotensin I, which cannot be explained on the basis of a similarly enhanced angiotensin I to II conversion rate or a difference in vascular reactivity. Possibly therefore, differences in angiotensin I to II conversion occur within the vascular wall only, at a site that does not readily equilibrate with blood plasma.

Cardiac interstitial fluid levels of angiotensin I and II in the pig

OBJECTIVE

To study whether cardiac interstitial fluid levels of angiotensin I and II (Ang I and II) can be monitored in vivo, using the microdialysis technique, and to assess the contribution of plasma-derived angiotensins to the interstitial fluid levels of these peptides.

DESIGN AND METHODS

Microdialysis probes were placed in the left ventricular (LV) myocardium of eight anaesthetized pigs, three of which were untreated and five treated with the angiotensin II type 1 (AT1) receptor antagonist L-158,809 (10 mg intracoronary). All pigs were given a 1 h intracoronary infusion of 125I-Ang II. Aortic and coronary venous blood samples were taken under steady-state conditions, and interstitial dialysate was collected during the entire infusion period. Immediately after stopping the infusion, LV tissue pieces were obtained at various time points.

RESULTS

L-158,809 did not affect the levels of endogenous Ang I and II or the levels of plasma 125I-Ang II. Aortic Ang I and II levels (22 and 16 fmol/ml; geometric mean of eight pigs) were comparable to coronary venous Ang I and II levels, whereas the coronary venous 125I-Ang II levels (6650 c.p.m./ml) were approximately 30 times higher than those in the aorta. Tissue Ang I and II levels were 5 and 17 fmol/g, respectively. In untreated animals, the 125I-Ang II levels per g LV tissue were similar to the levels per ml coronary venous plasma, and the ex vivo half-life of tissue 1251-Ang II was > 30 min. In treated animals, tissue 125I-Ang II was < 5% of coronary venous 125I-Ang II and became undetectable within 15 min. 125I-Ang II, Ang I and Ang II levels in the interstitial fluid were close to or below the detection limit (200 c.p.m., 60 fmol and 20 fmol per ml, respectively) in all animals.

CONCLUSIONS

Plasma and myocardial interstitial fluid angiotensin levels are of the same order of magnitude. Plasma Ang II does not contribute to the interstitial fluid level of Ang II, most likely because of its rapid metabolism in the vascular wall. Binding to AT1 receptors protects Ang II against metabolism.

No vasoactive role of the angiotensin II type 2 receptor in normotensive Wistar rats

OBJECTIVE

To investigate the vasoactive consequences of angiotensin II type 2 receptor stimulation in vivo.

DESIGN AND METHODS

Three consecutive 10 min intravenous infusions of angiotensin (Ang) II (100, 300 and 1000 ng/kg per min) were given to 20 pentobarbitone-anaesthetized normotensive Wistar rats (weight 330+/-6 g, mean +/- SEM). The rats had been pretreated with saline (n = 8), the angiotensin II type 1 receptor antagonist, irbesartan (100 microg/kg per min for 30 min, n = 6), or the angiotensin II type 2 receptor antagonist, PD123319 (20 microg/kg per min for 30 min followed by continuous infusion throughout the entire experiment, n = 6). Regional haemodynamic effects of Ang II were studied using the radioactive microsphere method.

RESULTS

Ang II increased mean arterial blood pressure (MAP) and heart rate by, maximally, 44+/-9 and 26+/-6%, respectively (P < 0.05 compared with baseline), and decreased cardiac output and systemic vascular conductance (cardiac output/MAP) by, maximally, 24+/-8 and 47+/-4%, respectively (P < 0.05 compared with baseline). The Ang II-induced decrease in systemic vascular conductance was caused by decreases in vascular conductances (regional flow/MAP) of the gastrointestinal tract (52+/-4%), kidney (63+/-3%), skeletal muscle (39+/-8%), skin (63+/-4%), mesentery + pancreas (32+/-11%), adrenal (27+/-11%) and spleen (57+/-6%) (all P < 0.05 compared with baseline). Irbesartan increased baseline vascular conductances in adrenal, brain and kidney, and inhibited all haemodynamic responses induced by Ang II. PD123319 affected neither baseline values nor the Ang II-induced haemodynamic responses.

CONCLUSIONS

Ang II-induced systemic and regional haemodynamic effects in normotensive Wistar rats are mediated exclusively via angiotensin II type 1 receptors. No evidence for angiotensin II type 2 receptor-mediated vasoactive responses was obtained.

Angiotensin I to angiotensin II conversion in the human forearm and leg. Effect of the angiotensin converting enzyme gene insertion/deletion polymorphism

OBJECTIVE

The angiotensin-converting enzyme (ACE) gene I/D polymorphism accounts for part of the variation in ACE concentration; subjects with one or two D alleles have approximately 25 and 50% higher ACE levels, respectively, than subjects with two I alleles. Data from studies on the pressor effects of angiotensin (Ang) I in DD compared with II subjects are inconsistent, because enhanced conversion in DD subjects may have been masked by a decreased responsiveness to Ang II. Here we quantify ACE genotype-related Ang I to Ang II conversion in the human forearm and leg using non-pressor 125I-Ang I infusions.

DESIGN AND METHODS

Infusions were given to 12 women and 17 men (age 24-67 years) who were undergoing renal vein sampling followed by renal angiography for diagnostic purposes. 125I-Ang I was infused for 20 min into the right antecubital vein, and blood samples for the measurement of 125I-labelled and endogenous Ang I and Ang II were taken from the aorta, the left antecubital vein and a femoral vein under steady-state conditions. Genotype frequencies were determined by polymerase chain reaction.

RESULTS

Fractional conversion (i.e. the percentage of arterially delivered 125I-Ang I that is converted to 125I-Ang II) in the forearm (38+/-4, 30+/-3 and 31+/-6% in 8 II, 16 ID and 5 DD subjects, respectively; mean +/- SEM) and leg (52+/-4, 48+/-3 and 42+/-5%) was similar in all three groups. In addition, no genotype-related differences in plasma Ang II/I ratio (a measure of ACE activity) were observed at the three sampling sites.

CONCLUSIONS

Regional Ang I to Ang II conversion does not parallel the previously described D allele-related differences in ACE concentration, suggesting that effects other than enhanced conversion may underlie the reported associations between the D allele and various cardiovascular diseases.

Is there a local renin-angiotensin system in the heart?

The existence of a local renin-angiotensin system in the heart is still a controversial issue. This review discusses the evidence, obtained from studies in cardiac cells, in isolated perfused hearts and in intact animals and humans, both under normal and pathological conditions, for local production of prorenin, renin, angiotensinogen, angiotensin-converting enzyme, angiotensin I and angiotensin II at cardiac tissue sites. In addition, the role of alternative angiotensin-generating enzymes (cathepsin, chymase) and the possibility of (pro)renin uptake from the circulation is evaluated.

Vasoconstriction by in situ formed angiotensin II: role of ACE and chymase

OBJECTIVE

To assess the importance, for vasoconstriction, of in situ angiotensin (Ang) II generation, as opposed to ang II delivery to AT receptors via the organ bath fluid.

METHODS

Ang I and II concentration-response curves in human and porcine coronary arteries (HCAs, PCAs) were constructed in relation to estimates of the clearances of Ang I and II (ClAngI, ClAngII) from the organ bath and the release of newly formed Ang II (RAngII) into the bath fluid. HCAs were from 25 heart valve donors (age 5-54 years), and PCAs from 14 pigs (age 3 months).

RESULTS

Ang I- and II-evoked constrictions were inhibited by the AT1 receptor antagonist, irbesartan, and were not influenced by the AT2 receptor antagonist, PD123319. In HCAs Ang II was only three times more potent than Ang I, wheres, in the experiments with Ang I, comparison of ClAngI with ClAngII and RAngII indicated that most of the arterially produced Ang II did not reach the bath fluid. Also in PCAs Ang I and II showed similar potency. In HCAs both the ACE inhibitor, captopril, and the chymase inhibitor, chymostatin, inhibited Ang I-evoked vasoconstriction, while only chymostatin had a significant effect on ClAngI. In PCAs Ang I-evoked vasoconstriction was almost completely ACE-dependent.

CONCLUSIONS

This study points towards the functional importance of in situ ACE- and chymase-dependent Ang II generation, as opposed to Ang II delivery via the circulation. It also indicates that functionally relevant changes in local Ang I-II conversion are not necessarily reflected by detectable changes in circulating Ang II.

Cultured neonatal rat cardiac myocytes and fibroblasts do not synthesize renin or angiotensinogen: evidence for stretch-induced cardiomyocyte hypertrophy independent of angiotensin II

OBJECTIVE

The hypertrophic response of cardiomyocytes exposed to mechanical stretch is assumed to depend on the release of angiotensin (Ang) II from these cells. Here we studied the synthesis of renin-angiotensin system (RAS) components by cardiac cells under basal conditions and after stretch.

METHODS

Myocytes and fibroblasts were isolated by enzymatic dissociation from hearts of 1-3-day-old Wistar rat strain pups, grown for 1 day in serum-supplemented medium and then cultured in a chemically defined, serum-free medium. Medium and cell lysate were collected 5 days later or after exposure of the cells to cyclic stretch for 24 h. Prorenin, renin and angiotensinogen were measured by enzyme-kinetic assay; Ang I and Ang II were measured by radioimmunoassay after SepPak extraction and HPLC separation.

RESULTS

Prorenin, but none of the other RAS components, could be detected in the medium of both cell types. However, its levels were low and the Ang I-generating activity corresponding with these low prorenin levels could not be inhibited by the specific rat renin inhibitor CH-732, suggesting that it was most likely due to bovine and/or horse prorenin sequestered from the serum-containing medium to which the cells had been exposed prior to the serum-free period. When incubated with Ang I, both myocytes and fibroblasts generated Ang II in a captopril-inhibitable manner. Myocyte and fibroblast cell lysates did not contain prorenin, renin, angiotensinogen, Ang I or Ang II in detectable quantities. Stretch increased myocyte protein synthesis by 20%, but was not accompanied by Ang II release into the medium.

CONCLUSION

Cardiac myocytes and fibroblasts do not synthesize renin, prorenin or angiotensinogen in concentrations that are detectable or, it not detectable, high enough to result in Ang II concentrations of physiological relevance. These cells do synthesize ACE, thereby allowing the synthesis of Ang II at cardiac tissue sites when renin and angiotensinogen are provided via the circulation. Ang II is not a prerequisite to observe a hypertrophic response of cardiomyocytes following stretch.

Uptake and proteolytic activation of prorenin by cultured human endothelial cells

OBJECTIVE

To investigate the mechanisms of vascular uptake of prorenin and renin and to explore the possibility of vascular activation of prorenin.

DESIGN AND METHODS

Human umbilical vein endothelial cells (HUVECs) cultured in a chemically defined medium were incubated with recombinant human prorenin or renin in the presence or absence of putative inhibitors of renin internalization. Cell surface-bound and internalized prorenin or renin were separated by the acid-wash method and were quantified by enzyme-kinetic assays. The activation of prorenin was also monitored by a direct immunoradiometric assay (IRMA) with use of a monoclonal antibody directed against the -p24-Arg to -1p-Arg C-terminal propeptide sequence of prorenin.

RESULTS

Prorenin and renin were internalized at 37 degrees C in a dose-dependent manner; with 1000 microU prorenin/ml medium, the quantity of cell-associated prorenin after 3 h of incubation was 9.3 +/- 1.0 microU/4 x 10(5) cells, and with 75,000 microU/ml medium it was 670 +/- 75 microU/4 x 10(5) cells (mean +/- SD; n = 5). Results for renin were similar. Prorenin that had been treated with endoglycosidase H to remove N-linked oligosaccharides was not internalized. Addition of mannose 6-phosphate (M-6-P) to the medium caused a dose-dependent inhibition of renin and prorenin internalization. Fifty per cent inhibition was observed at 70 micromol/M-6-P, whereas mannose 1-phosphate, glucose 6-phosphate and alpha-methylmannoside at this concentration had no effect Ammonium chloride (50 mmol/l) and monensin (10 micromol/l) also inhibited internalization. Prorenin was activated by HUVECs, and cell-activated prorenin was only found in the internalized fraction, whereas the surface-bound prorenin remained inactive. Thus, it appears that the activation of prorenin took place at the time of its internalization or thereafter. The results of the prorenin IRMA indicated that activation was associated with proteolytic cleavage of the propeptide.

CONCLUSIONS

Our findings provide evidence for M-6-P receptor-dependent endocytosis of (pro)renin and proteolytic prorenin activation by vascular endothelial cells.

Angiotensinogen (M235T) and angiotensin-converting enzyme (I/D) polymorphisms in association with plasma renin and prorenin levels

OBJECTIVE

The angiotensinogen T235 allele is associated with elevated plasma angiotensinogen levels whereas the angiotensin-converting enzyme (ACE) deletion (D) allele is associated with elevated ACE activity. It remains unclear, however, whether these genetically mediated elevations of angiotensinogen and ACE levels are functionally relevant Given that the renin-angiotensin system is subject to renin feedback regulation, we specifically investigated the associations between the angiotensinogen T235 allele and the ACE D allele with plasma renin and prorenin levels.

DESIGN AND METHODS

Plasma levels of renin, prorenin, angiotensinogen, ACE and aldosterone, as well as angiotensinogen and ACE genotypes were determined in 228 men and 168 women (age 52-65 years), who had participated in a population survey in southern Germany. Subjects taking antihypertensive drugs or oestrogen replacement therapy were excluded.

RESULTS

We corroborated previous findings demonstrating associations between the T235M polymorphism and plasma angiotensinogen levels (P < 0.05) and between the ACE I/D polymorphism and plasma ACE (P < 0.01). After adjustment for sex, age and blood pressure, the T235 allele of the angiotensinogen gene was also related to lower plasma prorenin (P < 0.03) and renin (P < 0.01) levels, but not to plasma ACE and aldosterone. By contrast, the ACE I/D polymorphism was not related to components of the system other than plasma ACE.

CONCLUSIONS

The angiotensinogen T235 allele is associated with decreased renin levels. This finding may point to a mechanism that counteracts the genetic elevation of angiotensinogen plasma levels and, thus, the plasmatic angiotensin II-generating pathway in subjects carrying the angiotensinogen T235 allele. These results may help to explain discrepant findings regarding associations between this allele and cardiovascular disorders. Furthermore, the presumed feedback downregulation of renin levels supports the importance of angiotensinogen as a determinant of angiotensin II generation. Finally, no evidence was found suggesting that the ACE D allele affects components of the circulating renin-angiotensin system other than plasma ACE.

Angiotensin I-to-II conversion in the human renal vascular bed

OBJECTIVE

During previous studies in humans and pigs, using infusions of 125I-angiotensin into the right antecubital vein or the left cardiac ventricle, we were unable to demonstrate conversion of arterial angiotensin I in the renal vascular bed. The arterial 125I-angiotensin I levels in these studies may have been too low to result in detectable renal venous 125I-angiotensin II levels, especially in view of the extensive degradation of angiotensins in the kidney. To overcome this problem, we now infused 125I-angiotensin I directly into the renal artery.

DESIGN AND METHODS

Five subjects (three women, two men) with essential hypertension (n = 4) or unilateral renal artery stenosis (n = 1), not treated with an ACE inhibitor, were given a 10-min infusion of 125I-angiotensin I (3.6+/-0.4 x 10(6) cpm/min, mean +/- SEM) into the left (n = 4) or right (n = 1) renal artery. Blood samples for the measurement of endogenous and radiolabelled angiotensin I and II were taken under steady-state conditions from the aorta and the renal vein of the 125I-angiotensin I-perfused kidney.

RESULTS

At steady-state, the levels of 125I-angiotensin I in renal venous blood were 5-6 fold lower, and those of 125I-angiotensin II were 4-5 fold higher than in renal arterial blood. On the basis of these levels, angiotensin I extraction in the renal vascular bed was calculated to be 80+/-3%, of which 9+/-1% was due to angiotensin I-to-II conversion. The renal venous levels of endogenous angiotensin I were 50% higher than its arterial levels, whereas the levels of endogenous angiotensin II were 50% lower in renal venous blood than in arterial blood. Taking into consideration the regional metabolism of arterially delivered angiotensins, and the generation of angiotensin I in circulating blood by plasma renin activity, it could be calculated that renal venous angiotensin I is largely derived from renal tissue sites, and that renal venous angiotensin II has no other sources than arterially delivered angiotensin I and II and angiotensin I generated by plasma renin activity in the renal vascular bed.

CONCLUSIONS

Less than 10% of arterially delivered angiotensin I is converted to angiotensin II in the renal vascular bed. Conversion of angiotensin I generated at renal tissue sites does not contribute to the level of angiotensin II in the renal vein, although it is the main source of angiotensin II in renal tissue. Thus, the intrarenal formation of angiotensin II is highly compartmentalised.

AT1 receptor A/C1166 polymorphism contributes to cardiac hypertrophy in subjects with hypertrophic cardiomyopathy

The development of left ventricular hypertrophy (LVH) in subjects with hypertrophic cardiomyopathy (HCM) is variable, suggesting a role for modifying factors such as angiotensin II. We investigated whether the angiotensin II type 1 receptor (AT1-R) A/C1166 polymorphism, the angiotensin-converting enzyme (ACE) insertion/deletion (I/D) polymorphism, and/or plasma renin influence LVH in HCM. Left ventricular mass index (LVMI) and interventricular septal thickness were determined by 2-dimensional echocardiography in 104 genetically independent subjects with HCM. Extent of hypertrophy was quantified by a point score (Wigle score). Plasma prorenin, renin, and ACE were measured by immunoradiometric or fluorometric assays, and ACE and AT1-R genotyping were performed by polymerase chain reactions. The ACE D allele did not affect any of the measured parameters except plasma ACE (P<0.04). LVMI was higher (P<0.05) in patients carrying the AT1-R C allele (190+/-8.3 g/m2) than in AA homozygotes (168+/-7.2 g/m2), and similar patterns were observed for interventricular septal thickness (23.0+/-0.7 versus 21. 6+/-0.7 mm) and Wigle score (7.0+/-0.3 versus 6.3+/-0.3). Plasma renin was higher (P=0.05) in carriers of the C allele than in AA homozygotes. Multivariate regression analysis, however, revealed no independent role for renin in the prediction of LVMI. Plasma prorenin and ACE were not affected by the AT1-R A/C1166 polymorphism, nor did the ACE and AT1-R polymorphisms interact with regard to any of the measured parameters. We conclude that the AT1-R C1166 allele modulates the phenotypic expression of hypertrophy in HCM, independently of plasma renin and the ACE I/D polymorphism.

Differential effects of antihypertensive drugs on neurohormonal activation: insights from a population-based sample

OBJECTIVES

The clinical course of hypertension or heart failure may be modified by the extent of concurrent neurohormonal activation. Factors that regulate neurohormones in patients with these conditions are complex. In the present study, we examined the relative contribution of antihypertensive therapy to the variability of neurohormonal levels in a well defined population based sample.

DESIGN AND SETTING

Cross-sectional study of a mixed urban and rural population.

SUBJECTS

Middle-aged individuals (n = 646) were analysed in order to elucidate determinants of neurohormone levels by uni- and multivariate comparisons. The assessment included anthropometric, echocardiographic and, if appropriate, genotype information.

RESULTS

The intake of antihypertensive drugs was related to significant alterations of neurohormone levels that, in part, exceeded the contribution of all other variables studied. Multivariate analyses revealed that renin levels were independently related to the intake of beta blockers (n = 80; -8.4 mU L-1; P = 0.001), angiotensin-converting enzyme (ACE)-inhibitors (n = 39; +15.9 mU L-1; P = 0.0001), diuretics (n = 62; +14.3 mU L-1; P = 0.0001), and calcium channel blockers (n = 45; +5.9 mU L-1; P = 0.05). Aldosterone levels were related to ACE-inhibition (-156.5 pmol L-1; P = 0.04) and diuretic treatment (+422.4 pmol L-1; P = 0.0001) in an opposite fashion whereas beta blockers and calcium channel blockers had no significant independent effects. The levels of the atrial natriuretic peptide were significantly related to the use of beta blockers (+3.9 pmol L-1; P = 0.002) and calcium channel blockers (+3.1 pmol L-1; P = 0.05). Finally, serum angiotensinogen levels and ACE activity were not found to be significantly affected by antihypertensive medication but were rather related to gender or genotype.

CONCLUSIONS

The data emphasize that antihypertensive treatment with different classes of drugs may modulate serum levels of neurohormones substantially resulting in distinct patterns of activation. These drug-related effects may require consideration when neurohormonal activation is of functional relevance or when neurohormones serve as prognostic predictors in patients with cardiovascular disorders.

Angiotensin production by the heart: a quantitative study in pigs with the use of radiolabeled angiotensin infusions

BACKGROUND

Beneficial effects of ACE inhibitors on the heart may be mediated by decreased cardiac angiotensin II (Ang II) production.

METHODS AND RESULTS

To determine whether cardiac Ang I and Ang II are produced in situ or derived from the circulation, we infused 125I-labeled Ang I or II into pigs (25 to 30 kg) and measured 125I-Ang I and II as well as endogenous Ang I and II in cardiac tissue and blood plasma. In untreated pigs, the tissue Ang II concentration (per gram wet weight) in different parts of the heart was 5 times the concentration (per milliliter) in plasma, and the tissue Ang I concentration was 75% of the plasma Ang I concentration. Tissue 125I-Ang II during 125I-Ang II infusion was 75% of 125I-Ang II in arterial plasma, whereas tissue 125I-Ang I during 125I-Ang I infusion was <4% of 125I-Ang I in arterial plasma. After treatment with the ACE inhibitor captopril (25 mg twice daily), Ang II fell in plasma but not in tissue, and Ang I and renin rose both in plasma and tissue, whereas angiotensinogen did not change in plasma and fell in tissue. Tissue 125I-Ang II derived by conversion from arterially delivered 125I-Ang I fell from 23% to <2% of 125I-Ang I in arterial plasma.

CONCLUSIONS

Most of the cardiac Ang II appears to be produced at tissue sites by conversion of in situ-synthesized rather than blood-derived Ang I. Our study also indicates that under certain experimental conditions, the heart can maintain its Ang II production, whereas the production of circulating Ang II is effectively suppressed.

Beta adrenergic blockers lower renin in patients treated with ACE inhibitors and diuretics

OBJECTIVE

To examine the effect of concomitant intake of beta blockers with angiotensin converting enzyme (ACE) inhibitors, diuretics, or both on plasma renin concentrations in a population based sample (MONICA survey, Augsburg, Germany).

SUBJECT AND METHODS

728 individuals were studied, of whom 171 were treated using monotherapy (ACE inhibitor (n = 21), diuretic (n = 10), or beta blocker (n = 72)), or combination treatment (ACE inhibitor + diuretic (n = 32), ACE inhibitor + beta blocker (n = 7), diuretic + beta blocker (n = 22), ACE inhibitor + diuretic + beta blocker (n = 7)). The remaining 557 individuals were untreated. Indications for treatment were hypertension (75%), coronary artery disease with (12%) or without (3%) hypertension, or unknown (10%).

RESULTS

Mean (SEM) renin concentrations in individuals treated with an ACE inhibitor (41 (8) mU/l), a diuretic (41 (10) mU/l), or the combination of an ACE inhibitor and a diuretic (54 (10) mU/l) were raised compared with untreated individuals (17 (1) mU/l; p < 0.05 each). Monotherapy with a beta blocker, however, decreased mean renin concentrations (12 (1) mU/l; p < 0.01 v untreated). Renin concentrations in individuals taking a beta blocker with either an ACE inhibitor (21 (8) mU/l), or a diuretic (22 (4) mU/l), or with both an ACE inhibitor and a diuretic (21 (7) mU/L), were significantly lower compared with renin concentrations in groups not receiving beta blocker treatment (p < 0.05 each).

CONCLUSION

These data suggest that the upregulation of renin by treatment with ACE inhibitors, diuretics, or both can be largely prevented by concomitant beta blocker treatment.

Determinants of interindividual variation of renin and prorenin concentrations: evidence for a sexual dimorphism of (pro)renin levels in humans

BACKGROUND

Plasma renin concentrations are an important factor in cardiovascular risk profiling.

OBJECTIVE

To investigate the effects of sex, medication, and anthropometric factors that may contribute to the interindividual variation in the plasma concentrations of renin and its precursor prorenin.

DESIGN AND METHODS

Prorenin and renin levels in 327 men and 383 women, aged 52-69 years, who participated in a 1994 reexamination of a previous population survey in Bavaria, were measured by immunoradiometric assay.

RESULTS

Prorenin and renin levels in men were significantly higher than those in women, those in women without estrogen replacement therapy were significantly higher than those in women with estrogen replacement therapy, and those in diabetics were significantly higher than those in nondiabetics. Prorenin level was correlated negatively to blood pressure and positively to age and the use of diuretics; it was normal in subjects using angiotensin converting enzyme inhibitors and beta-adrenergic antagonists (beta-blockers). Renin level was correlated negatively to atrial natriuretic peptide level and the use of beta-blockers, and it was elevated above normal levels in subjects using angiotensin converting enzyme inhibitors and diuretics as well as in subjects who had previously suffered myocardial infarction. After exclusion of data for women being administered estrogen replacement therapy, multivariate analysis revealed that sex (P<0.001), age (P<0.02), blood pressure (P<0.002), diabetes (P<0.05), and the use of angiotensin converting enzyme inhibitors (P<0.002), beta-blockers (P<0.001), and diuretics (P<0.05) were independent determinants of plasma prorenin. Plasma renin was independently related to atrial natriuretic peptide level (P<0.01) and the use of angiotensin converting enzyme inhibitors (P<0.001), beta-blockers (P<0.001), and diuretics (P<0.05).

CONCLUSIONS

These data demonstrate that there is a sexual dimorphism of prorenin levels in humans, suggesting that sex hormones affect the regulation of the renin gene. Data confirm previous reports of elevated prorenin levels in diabetics and older subjects, as well as of lower than normal prorenin levels in subjects with hypertension in smaller populations. Our findings may help to clarify the potential (patho)physiologic functions of prorenin and to identify the factors that influence the constitutive secretion and intracellular processing of this prohormone.

Localization and production of angiotensin II in the isolated perfused rat heart

We used a modification of the isolated perfused rat heart, in which coronary effluent and interstitial transudate were separately collected, to investigate the localization and production of angiotensin II (Ang II) in the heart. During combined renin (0.7 to 1.5 pmol Ang I/mL per minute) and angiotensinogen (6 to 12 pmol/mL) perfusion (4 to 8 mL/min) for 60 minutes (n=3), the steady-state levels of Ang II in interstitial transudate in two consecutive 10-minute periods were 4.3+/-1.5 and 3.6+/-1.5 fmol/mL compared with 1.1+/-0.4 and 1.1+/-0.6 fmol/mL in coronary effluent (mean+/-half range). During perfusion with Ang II (n=5), steady-state Ang II in interstitial transudate was 32+/-19% of arterial Ang II compared with 65+/-16% in coronary effluent (mean+/-SD, P<.02). During perfusion with Ang I (n=5), Ang II in interstitial transudate was 5.1+/-0.6% of arterial Ang I compared with 2.2+/-0.3% in coronary effluent (P<.05). The tissue concentration of Ang II in the combined renin/angiotensinogen perfusions (per gram) was as high as the concentration in interstitial transudate (per milliliter). Addition of losartan (10(-6) mol/L) to the renin/angiotensinogen perfusion (n=3) had no significant effect on the tissue level of Ang II, whereas losartan in the perfusions with Ang I (n=5) or Ang II (n=5) decreased tissue Ang II to undetectably low levels. The results indicate that the heart is capable of producing Ang II and that this can lead to higher levels in tissue than in blood plasma. Cardiac Ang II does not appear to be restricted to the extracellular fluid. This is in part due to AT1-receptor-mediated cellular uptake of extracellular Ang II, but our results also raise the possibility of intracellular Ang II production.

Bradykinin-induced release of nitric oxide by the isolated perfused rat heart: importance of preformed pools of nitric oxide-containing factors

OBJECTIVE

To study whether the vasorelaxant effect of bradykinin in the coronary vascular bed depends on the release of NO from preformed pools and/or de-novo synthesis of NO resulting from bradykinin-induced stimulation of NO synthase.

DESIGN AND METHODS

Rat hearts were perfused according to Langendorff's method. Coronary flow was measured continuously. We constructed concentration-response curves for bradykinin and L-arginine under control conditions, after downregulation of NO synthase by exposing the heart to high concentrations (10 mmol/l) of NO and during chronic inhibition of NO synthase, obtained by perfusing the heart for 30 min with 0.1 mmol/l N(omega)-nitro-L-arginine methyl ester. The effect of acute inhibition of NO synthase was studied by infusing single submaximal doses of bradykinin and of L-arginine in the absence and presence of 0.1 mmol/l N(omega)-nitro-L-arginine methyl ester.

RESULTS

Coronary flow [baseline 9 +/- 2 ml/min (mean +/- SD)] increased to maximally 23 +/- 6 ml/min with bradykinin and to 16 +/- 4 ml/min with L-arginine. Maximal coronary flow, established as the maximal effect in response to NO, was 22 +/- 4 ml/min. Chronic inhibition of NO synthase reduced coronary flow to 4 +/- 1 ml/min. Coronary flow did not change after downregulation of NO synthase by NO. Neither downregulation nor acute inhibition of NO synthase affected the response to bradykinin, whereas chronic inhibition of NO synthase blocked the bradykinin-induced increase in coronary flow by > 90%. Administration of L-arginine no longer increased coronary flow under all tested conditions.

CONCLUSIONS

Preformed pools of NO-containing factors exist within the isolated perfused heart and bradykinin exerts its vasorelaxant effects at least in part by the mobilization of these preformed pools. These data may reconcile previous discrepancies about the (lack of) effect of NO synthase inhibitors on bradykinin-induced coronary vasodilatation.

Mannose 6-phosphate receptor-mediated internalization and activation of prorenin by cardiac cells

The binding and internalization of recombinant human renin and prorenin (2500 microU/mL) and the activation of prorenin were studied in neonatal rat cardiac myocytes and fibroblasts cultured in a chemically defined medium. Surface-bound and internalized enzymes were distinguished by the addition of mannose 6-phosphate to the medium, by incubating the cells both at 37 degrees C and 4 degrees C, and by the acid-wash method. Mannose 6-phosphate inhibited the binding of renin and prorenin to the myocyte cell surface in a dose-dependent manner. At 37 degrees C, after incubation at 4 degrees C for 2 hours, 60% to 70% of cell surface-bound renin or prorenin was internalized within 5 minutes. Intracellular prorenin was activated, but extracellular prorenin was not. The half-time of activation at 37 degrees C was 25 minutes. Ammonium chloride and monensin, which interfere with the normal trafficking and recycling of internalized receptors and ligands, inhibited the activation of prorenin. Results obtained with cardiac fibroblasts were comparable to those in the myocytes. This study is the first to show experimental evidence for the internalization and activation of prorenin in extrarenal cells by a mannose 6-phosphate receptor-dependent process. Our findings may have physiological significance in light of recent experimental data indicating that angiotensin I and II are produced at cardiac and other extrarenal tissue sites by the action of renal renin and that intracellular angiotensin II can elicit important physiological responses.

Human renin binding protein: complete genomic sequence and association of an intronic T/C polymorphism with the prorenin level in males

The role of renin binding protein (RnBP) in human (patho)physiology, despite its biochemical characterization, is as yet unclear. RnBP has been shown to bind and inactivate renin, a key player of the blood pressure regulating renin-angiotensin system. This renders the RnBP gene a promising candidate gene in human hypertension. Herein, a molecular genetic approach was employed to investigate if RnBP might affect renin, prorenin and/or blood pressure levels. Sequencing of the human Xq28 chromosomal region provided the precise chromosomal location and full genomic sequence of the RnBP gene. All 11 exons, adjacent intronic splice sites and the promoter region were sequenced in 20 patients with essential hypertension of early onset and possible X-linked inheritance and in four normotensive individuals. The only variant found was a single base exchange polymorphism 61 base pairs upstream of the intron 6/exon 7 boundary (T61C). Several cardiovascular parameters, the renin, and prorenin levels and the T61C allele status were determined in 505 Caucasian individuals. Male individuals without medication who were hemizygous for the C allele were characterized by lower prorenin levels (196 +/- 15 versus 256 +/- 12 mU/l, P = 0.05) and a significantly higher renin/prorenin ratio (10.7 +/- 1.5 versus 7.7 +/- 0.3%, P = 0.002), whereas no variations in circulating renin, blood pressure, heart rate and left ventricular mass index were associated with the C allele. No significant association was observed in women. The data do not exclude a role of RnBP in essential hypertension. The complete genomic structure of the RnBP gene, including the identified repetitive sequence elements, provides an essential tool for further studies of the RnBP gene in hypertensive patients with a different genetic background.

Eighth European Meeting on Hypertension

The Eighth European Meeting on Hypertension, held in Milan, Italy, was attended by approximately 4000 people. The programme consisted of 120 presentations, 337 poster sessions, 6 invited lectures/debates (endothelin antagonists; cardiac renin-angiotensin system; cancer and hypertension; adducin; angiotensin converting enzyme (ACE) gene polymorphism; pulse pressure) and 2 plenary sessions on 'sleep apnea and hypertension' and 'treatment of hypertension in the elderly'.

Angiotensin II-mediated growth and antigrowth effects in cultured neonatal rat cardiac myocytes and fibroblasts

Angiotensin II (Ang II) stimulates cardiovascular growth and remodeling via AT1 receptors. Recent experiments have shown that Ang II may also exert antiproliferative effects via AT2 receptors. We studied the effects of Ang II on protein and DNA content and synthesis rate in unstimulated and endothelin-1 (ET-1)-stimulated neonatal rat cardiomyocytes and fibroblasts, isolated from 1-3-day-old Wistar strain pups. Total protein and total DNA, as well as [3H]leucine and [3H]thymidine incorporation were measured following incubation with either vehicle, Ang II, ET-1 or Ang II+ET-1, both in the presence or absence of the AT1 receptor blocker losartan or the AT2 receptor blocker PD123319. In myocytes, ET-1 increased total protein (+38% relative to control) as well as [3H]leucine (+66%) and [3H]thymidine (+77%) incorporation. Ang II did not affect any of these parameters, nor did it influence the ET-1-induced responses. However, in the presence of PD123319 Ang II stimulated [3H]leucine (+24%) and [3H]thymidine (+30%) incorporation. In fibroblasts, ET-1 and Ang II did not significantly affect total DNA and [3H]thymidine incorporation. Ang II tended to increase total protein in these cells, an effect which was significant only in the presence of PD123319 (+17%). Ang II stimulated [3H]leucine incorporation (+24%) in fibroblasts. This effect was absent with losartan and enhanced in the presence of PD123319. These data demonstrate that AT1 receptor-mediated proliferative effects of Ang II in neonatal cardiac cells may become apparent only when its AT2 receptor-mediated antigrowth effects are blocked. The net growth effect of Ang II therefore depends on the cellular AT1/AT2 receptor ratio. Ang II does not appear to interfere with ET-1-induced effects.

Prorenin, renin, angiotensinogen, and angiotensin-converting enzyme in normal and failing human hearts. Evidence for renin binding

BACKGROUND

A local renin-angiotensin system in the heart is often invoked to explain the beneficial effects of ACE inhibitors in heart failure. The heart, however, produces little or no renin under normal conditions.

METHODS AND RESULTS

We compared the cardiac tissue levels of renin-angiotensin system components in 10 potential heart donors who died of noncardiac disorders and 10 subjects with dilated cardiomyopathy (DCM) who underwent cardiac transplantation. Cardiac levels of renin and prorenin in DCM patients were higher than in the donors. The cardiac and plasma levels of renin in DCM were positively correlated, and extrapolation of the regression line to normal plasma levels yielded a tissue level close to that measured in the donor hearts. The cardiac tissue-to-plasma concentration (T/P) ratios for renin and prorenin were threefold the ratio for albumin, which indicates that the tissue levels were too high to be accounted for by admixture with blood and diffusion into the interstitial fluid. Cell membranes from porcine cardiac tissue bound porcine renin with high affinity. The T/P ratio for ACE, which is membrane bound, was fivefold the ratio for albumin. Cardiac angiotensinogen was lower in DCM patients than in the donors, and its T/P ratio was half that for albumin, which is compatible with substrate consumption by cardiac renin.

CONCLUSIONS

These data in patients with heart failure support the concept of local angiotensin production in the heart by renin that is taken up from the circulation. Membrane binding may be part of the uptake process.

Renin-angiotensin system components in the interstitial fluid of the isolated perfused rat heart. Local production of angiotensin I

We used a modification of the isolated perfused rat heart, in which coronary effluent and interstitial transudate were separately collected, to investigate the uptake and clearance of exogenous renin, angiotensinogen, and angiotensin I (Ang I) as well as the cardiac production of Ang I. The levels of these compounds in interstitial transudate were considered to be representative of the levels in the cardiac interstitial fluid. During perfusion with renin or angiotensinogen, the steady-state levels (mean +/- SD) in interstitial transudate were 64 +/- 34% (P < .05 for difference from the arterial level, n = 8) and 108 +/- 42% (n = 6) of the arterial level, respectively; the levels in coronary effluent were not significantly different from those in interstitial transudate. Ang I was not detectable in interstitial transudate during perfusion with Tyrode's buffer or angiotensinogen. It was very low in interstitial transudate during perfusion with renin and rose to much higher levels during combined renin and angiotensinogen perfusion. The total production rate of Ang I present in interstitial fluid could be largely explained by the renin-angiotensinogen reaction in the fluid phase of the interstitial compartment. In contrast, the total production rate of Ang I present in coronary effluent and the net ejection rate of Ang I via coronary effluent were, respectively, 4.6 +/- 2.2 and 2.8 +/- 1.3 (P < .01 and P < .05 for difference from 1.0, n = 6) times higher than could be explained by Ang I formation in the fluid phase of the intravascular compartment. Ang I from the interstitial fluid contributed little to the Ang I in the intravascular fluid and vice versa. These data reveal two tissue sites of Ang I production, ie, the interstitial fluid and a site closer to the blood compartment, possibly vascular surface-bound renin. There was no evidence that the release of locally produced Ang I into coronary effluent and interstitial transudate occurred independently of blood-derived renin or angiotensinogen.

Effects of estrogen replacement therapy on the renin-angiotensin system in postmenopausal women

BACKGROUND

Oral estrogen replacement therapy (ERT) is known to stimulate the synthesis of angiotensinogen. The effects of such therapy on renin, ACE, and aldosterone are less clear. This seems noteworthy, however, since further activation of the system could be disadvantageous to postmenopausal women who replace estrogen in the context of heart failure, coronary artery disease, or hypertension.

METHODS AND RESULTS

Estrogen status and components of the renin-angiotensin system were examined in a population-based sample of postmenopausal women and age-matched men. Renin was quantified immunoradiometrically, ie, independent of substrate abundance; aldosterone, angiotensinogen, and ACE activity were determined by standard methods. Renin levels were lower in women with ERT (n = 107; 12.0 +/- 0.7 mU/L) compared with women without ERT (n = 223; 16.6 +/- 0.9 mU/L; P = .001) or men (n = 342, 20.5 +/- 1.5 mU/L, P < .0001). In contrast, angiotensinogen was higher in women with ERT (1.36 +/- 0.08 mg/L) compared with women without ERT (1.03 +/- 0.02 mg/L; P < .0001) or compared with men (0.97 +/- 0.01 mg/L; P < .0001). Renin suppression was seen with either oral or transdermal estrogen replacement (-30% and -31%, respectively; both P < .001). In contrast, the increase of angiotensinogen was limited to women taking oral estrogens (+58%, P < .001). Multivariate analysis revealed that these estrogen effects were independent of age, body mass index, blood pressure, and/or antihypertensive medication. Finally, only marginal differences between groups were observed for serum ACE activity and aldosterone.

CONCLUSIONS

Aside from a well-documented induction of angiotensinogen, ERT is related to a substantial suppression of renin, a phenomenon that might have received little attention because of widely used indirect measurements of the hormone.