Evidence for Angiotensin II as a Naturally Existing Suppressor for the Guanylyl Cyclase A Receptor and Cyclic GMP Generation

The natriuretic peptide system (NPS) and renin-angiotensin-aldosterone system (RAAS) function oppositely at multiple levels. While it has long been suspected that angiotensin II (ANGII) may directly suppress NPS activity, no clear evidence to date supports this notion. This study was designed to systematically investigate ANGII-NPS interaction in humans, in vivo, and in vitro. Circulating atrial, b-type, and c-type natriuretic peptides (ANP, BNP, CNP), cyclic guanosine monophosphate (cGMP), and ANGII were simultaneously investigated in 128 human subjects. Prompted hypothesis was validated in vivo to determine the influence of ANGII on ANP actions. The underlying mechanisms were further explored via in vitro approaches. In humans, ANGII demonstrated an inverse relationship with ANP, BNP, and cGMP. In regression models predicting cGMP, adding ANGII levels and the interaction term between ANGII and natriuretic peptides increased the predictive accuracy of the base models constructed with either ANP or BNP, but not CNP. Importantly, stratified correlation analysis further revealed a positive association between cGMP and ANP or BNP only in subjects with low, but not high, ANGII levels. In rats, co-infusion of ANGII even at a physiological dose attenuated cGMP generation mediated by ANP infusion. In vitro, we found the suppressive effect of ANGII on ANP-stimulated cGMP requires the presence of ANGII type-1 (AT1) receptor and mechanistically involves protein kinase C (PKC), as this suppression can be substantially rescued by either valsartan (AT1 blocker) or Go6983 (PKC inhibitor). Using surface plasmon resonance (SPR), we showed ANGII has low binding affinity to the guanylyl cyclase A (GC-A) receptor compared to ANP or BNP. Our study reveals ANGII is a natural suppressor for the cGMP-generating action of GC-A via AT1/PKC dependent manner and highlights the importance of dual-targeting RAAS and NPS in maximizing beneficial properties of natriuretic peptides in cardiovascular protection.

EVIDENCE FOR ANGIOTENSIN II AS A NATURALLY EXISTING SUPPRESSOR FOR THE NATRIURETIC PEPTIDE SYSTEM

Background

Natriuretic peptide system (NPS) and renin angiotensin aldosterone system (RAAS) function oppositely at multiple levels. While it has long been suspected that angiotensin II (ANGII) may directly suppress NPS activity, no clear evidence to date support this notion.

Objectives

This study was designed to systematically investigate ANGII-NPS interaction in humans, in vivo, and in vitro for translational insights.

Methods

Circulating atrial, b-type, and c-type natriuretic peptides (ANP, BNP, CNP), cyclic guanosine monophosphate (cGMP), and ANGII were simultaneously investigated in 128 human subjects. Prompted hypothesis was validated in rat model to determine influence of ANGII on ANP actions. Multiple engineered HEK293 cells and surface plasmon resonance (SPR) technology were leveraged for mechanistic exploration.

Results

In humans, ANGII showed inverse relationship with ANP, BNP, and cGMP. In regression models predicting cGMP, adding ANGII levels and interaction term between ANGII and natriuretic peptide increased predicting accuracy of base models constructed with either ANP or BNP, but not CNP. Importantly, stratified correlation analysis further revealed positive association between cGMP with ANP or BNP only in subjects with low, but not high, ANGII levels. In rats, co-infusion of ANGII even at physiological dose attenuated blood pressure reduction and cGMP generation triggered by ANP infusion. In vitro, we showed that the suppression effect of ANGII on ANP-stimulated cGMP requires the presence of ANGII type-1 (AT1) receptor and mechanistically involves protein kinase C (PKC), which can be substantially rescued by either valsartan (AT1 blocker) or Go6983 (PKC inhibitor). Using SPR, we showed ANGII has low affinity for particulate guanylyl cyclase A (GC-A) receptor binding compared to ANP or BNP.

Conclusions

Our study reveals ANGII as a natural suppressor for cGMP-generating action of GC-A via AT1/PKC dependent manner and highlights importance of dual-targeting RAAS and NPS in maximizing beneficial properties of natriuretic peptides in cardiovascular disease.

Cyclic Guanosine Monophosphate and Risk of Incident Heart Failure and Other Cardiovascular Events: the ARIC Study

Background

Cyclic guanosine monophosphate (cGMP) is a second messenger regulated through natriuretic peptide and nitric oxide pathways. Stimulation of cGMP signaling is a potential therapeutic strategy for heart failure with preserved ejection fraction (HFpEF) and atherosclerotic cardiovascular disease (ASCVD). We hypothesized that plasma cGMP levels would be associated with lower risk for incident HFpEF, any HF, ASCVD, and coronary heart disease (CHD).

Methods and Results

We conducted a case–cohort analysis nested in the ARIC (Atherosclerosis Risk in Communities) study. Plasma cGMP was measured in 875 participants at visit 4 (1996–1998), with oversampling of incident HFpEF cases. We used Cox proportional hazard models to assess associations of cGMP with incident HFpEF, HF, ASCVD (CHD+stroke), and CHD. The mean (SD) age was 62.4 (5.6) years and median (interquartile interval) cGMP was 3.4 pmol/mL (2.4–4.6). During a median follow‐up of 9.9 years, there were 283 incident cases of HFpEF, 329 any HF, 151 ASCVD, and 125 CHD. In models adjusted for CVD risk factors, the hazard ratios (95% CI) associated with the highest cGMP tertile compared with lowest for HFpEF, HF, ASCVD, and CHD were 1.88 (1.17–3.02), 2.18 (1.18–4.06), 2.84 (1.44–5.60), and 2.43 (1.19–5.00), respectively. In models further adjusted for N‐terminal‐proB‐type natriuretic peptide, associations were attenuated for HFpEF and HF but remained statistically significant for ASCVD (2.56 [1.26–5.20]) and CHD (2.25 [1.07–4.71]).

Conclusions

Contrary to our hypothesis, higher cGMP levels were associated with incident CVD in a community‐based cohort. The associations of cGMP with HF or HFpEF may be explained by N‐terminal‐proB‐type natriuretic peptide, but not for ASCVD and CHD.

Urinary cGMP predicts major adverse renal events in patients with mild renal impairment and/or diabetes mellitus before exposure to contrast medium

BACKGROUND

The use of iodine-based contrast agents entails the risk of contrast induced nephropathy (CIN). Radiocontrast agents elicit the third most common cause of nephropathy among hospitalized patients, accounting for 11-12% of cases. CIN is connected with clinically significant consequences, including increased morbidity, prolonged hospitalization, increased risk of complications, potential need for dialysis, and increased mortality rate. The number of in-hospital examinations using iodine-based contrast media has been significantly increasing over the last decade. In order to protect patients from possible complications of such examinations, new biomarkers are needed that are able to predict a risk of contrast-induced nephropathy. Urinary and plasma cyclic guanosine monophosphate (cGMP) concentrations are influenced by renal function. Urinary cGMP is primarily of renal cellular origin. Therefore, we assessed if urinary cGMP concentration may predict major adverse renal events (MARE) after contrast media exposure during coronary angiography.

METHODS

Urine samples were prospectively collected from non-randomized consecutive patients with either diabetes or preexisting impaired kidney function receiving intra-arterial contrast medium (CM) for emergent or elective coronary angiography at the Charité Campus Mitte, University Hospital Berlin. Urinary cGMP concentration in spot urine was analyzed 24 hours after CM exposure. Patients were followed up over 90 days for occurrence of death, initiation of dialysis, doubling of plasma creatinine concentration or MARE.

RESULTS

In total, 289 consecutive patients were included into the study. Urine cGMP/creatinine ratio 24 hours before CM exposure expressed as mean±SD was predictive for the need of dialysis (no dialysis: 89.77±92.85 μM/mM, n = 277; need for dialysis: 140.3±82.90 μM/mM, n = 12, p = 0.008), death (no death during follow-up: 90.60±92.50 μM/mM, n = 280; death during follow-up: 169.88±81.52 μM/mM, n = 9; p = 0.002), and the composite endpoint MARE (no MARE: 86.02±93.17 μM/mM, n = 271; MARE: 146.64±74.68 μM/mM, n = 18, p<0.001) during the follow-up of 90 days after contrast media application. cGMP/creatinine ratio stayed significantly increased at values exceeding 120 μM/mM in patients who developed MARE, required dialysis or died.

CONCLUSIONS

Urinary cGMP/creatinine ratio ≥ 120 μM/mM before CM exposure is a promising biomarker for the need of dialysis and all-cause mortality 90 days after CM exposure in patients with preexisting renal impairment or diabetes.

Serum adrenomedullin and urinary thromboxane B2 help early categorizing of acute kidney injury in decompensated cirrhotic patients: A prospective cohort study

AIMS

Increases in the systemic vasodilator adrenomedullin and the renal vasoconstrictors thromboxane A₂ in cirrhotic patients are pathogenic factors for the development of functional acute kidney injury (AKI), including pre-renal azotemia (PRA) and hepatorenal syndrome (HRS), which is associated with high mortality. This study aims to find biomarkers that can diagnose HRS at an early stage, to enable treatment as soon as possible.

METHODS

Acute decompensated cirrhotic patients who had been admitted to hospital were enrolled in this prospective cohort study. Blood and urinary samples were collected immediately after admission. In addition to initially categorizing AKI cases into PRA, acute tubular necrosis (ATN), and HRS groups, their final diagnosis was adjudicated by a nephrologist and a hepatologist who checked the corrected and misclassification rates for significant biomarkers.

RESULTS

The cut-off values for serum adrenomedullin and urinary thromboxane B₂ (TXB₂ ), when used as predictors for functional AKI (adrenomedullin >283 pg/mL, urinary TXB₂ >978 [pg/mg urinary creatinine]), for HRS (adrenomedullin >428, urinary TXB₂  >1604), and for good terlipressin plus albumin treatment responders (adrenomedullin >490, urinary TXB₂  >1863), were observed. Patients with HRS who could be treated, due to high mortality, had significantly higher serum adrenomedullin and urinary TXB₂ levels compared to HRS patients receiving standard treatment. In addition to predicting 60-day mortality, a combination of these two markers further increased diagnostic accuracy for HRS among functional AKI.

CONCLUSIONS

Prompt diagnosis of HRS by differentiating it from PRA and ATN can be achieved by using serum adrenomedullin and urinary TXB₂ in acute decompensated cirrhotic patients. In combination with severe clinical courses, these two markers are useful to select HRS patients who cannot be treated.

Alternative hematological and vascular adaptive responses to high-altitude hypoxia in East African highlanders

Elevation of hemoglobin concentration, a common adaptive response to high-altitude hypoxia, occurs among Oromo but is dampened among Amhara highlanders of East Africa. We hypothesized that Amhara highlanders offset their smaller hemoglobin response with a vascular response. We tested this by comparing Amhara and Oromo highlanders at 3,700 and 4,000 m to their lowland counterparts at 1,200 and 1,700 m. To evaluate vascular responses, we assessed urinary levels of nitrate (NO₃^-) as a readout of production of the vasodilator nitric oxide and its downstream signal transducer cyclic guanosine monophosphate (cGMP), along with diastolic blood pressure as an indicator of vasomotor tone. To evaluate hematological responses, we measured hemoglobin and percent oxygen saturation of hemoglobin. Amhara highlanders, but not Oromo, had higher NO₃^- and cGMP compared with their lowland counterparts. NO₃^- directly correlated with cGMP (Amhara R² = 0.25, P < 0.0001; Oromo R² = 0.30, P < 0.0001). Consistent with higher levels of NO₃^- and cGMP, diastolic blood pressure was lower in Amhara highlanders. Both highland samples had apparent left shift in oxyhemoglobin saturation characteristics and maintained total oxyhemoglobin content similar to their lowland counterparts. However, deoxyhemoglobin levels were significantly higher, much more so among Oromo than Amhara. In conclusion, the Amhara balance minimally elevated hemoglobin with vasodilatory response to environmental hypoxia, whereas Oromo rely mainly on elevated hemoglobin response. These results point to different combinations of adaptive responses in genetically similar East African highlanders.

Serum biomarkers in uncontrolled no heart-beating donors may identify kidneys that will never work after transplantation

BACKGROUND/AIMS

Kidneys from uncontrolled non heart-beating donors achieve a good level of renal function after transplantation. However, a number of them will never function in the recipient. Our aim was to determine if serum biomarkers associated with platelet activity, inflammation and the nitric oxide system in uncontrolled non heart-beating donors may help to predict no renal function recovery after renal transplantation.

METHODS

Serum levels of interleukin (IL)-6, IL-10, intercellular cell adhesion molecule-1 (ICAM-1), cyclic guanosine monophosphate (cGMP), nitrite + nitrate and platelet factor-4 (PF4) were measured using enzyme-linked immunosorbent assay (ELISA) kits in 88 uncontrolled non heart-beating donors divided according to the renal functionality achieved in the recipients into functional (n = 76) and non functional (n = 12).

RESULTS

Kidneys from donors with higher IL-6 levels (>900 pg/ml) were functional after transplantation. Serum cGMP levels below 372.3 fmol/l were also associated with kidneys that recovered the renal function. However, serum levels of PF4 showed the best correlation with recovery of renal functional in the recipients since they were significantly lower in the donors whose kidneys functioned after transplantation.

CONCLUSIONS

Serum PF4 levels in uncontrolled non heart-beating donors may be a good predictor for kidneys that never will reach functional recovery. Some serum cGMP, IL-6 and IL-10 levels may simply help identify kidneys that will function after transplantation.

M-atrial natriuretic peptide and nitroglycerin in a canine model of experimental acute hypertensive heart failure: differential actions of 2 cGMP activating therapeutics

Background

Systemic hypertension is a common characteristic in acute heart failure (HF). This increasingly recognized phenotype is commonly associated with renal dysfunction and there is an unmet need for renal enhancing therapies. In a canine model of HF and acute vasoconstrictive hypertension we characterized and compared the cardiorenal actions of M‐atrial natriuretic peptide (M‐ANP), a novel particulate guanylyl cyclase (pGC) activator, and nitroglycerin, a soluble guanylyl cyclase (sGC) activator.

Methods and Results

HF was induced by rapid RV pacing (180 beats per minute) for 10 days. On day 11, hypertension was induced by continuous angiotensin II infusion. We characterized the cardiorenal and humoral actions prior to, during, and following intravenous M‐ANP (n=7), nitroglycerin (n=7), and vehicle (n=7) infusion. Mean arterial pressure (MAP) was reduced by M‐ANP (139±4 to 118±3 mm Hg, P<0.05) and nitroglycerin (137±3 to 116±4 mm Hg, P<0.05); similar findings were recorded for pulmonary wedge pressure (PCWP) with M‐ANP (12±2 to 6±2 mm Hg, P<0.05) and nitroglycerin (12±1 to 6±1 mm Hg, P<0.05). M‐ANP enhanced renal function with significant increases (P<0.05) in glomerular filtration rate (38±4 to 53±5 mL/min), renal blood flow (132±18 to 236±23 mL/min), and natriuresis (11±4 to 689±37 mEq/min) and also inhibited aldosterone activation (32±3 to 23±2 ng/dL, P<0.05), whereas nitroglycerin had no significant (P>0.05) effects on these renal parameters or aldosterone activation.

Conclusions

Our results advance the differential cardiorenal actions of pGC (M‐ANP) and sGC (nitroglycerin) mediated cGMP activation. These distinct renal and aldosterone modulating actions make M‐ANP an attractive therapeutic for HF with concomitant hypertension, where renal protection is a key therapeutic goal.

Cyclic GMP transporters

The biokinetics of guanosine 3',5'-cyclic monophosphate (cGMP) is characterized by three distinct processes: synthesis by guanylate cyclases (GCs), conversion of cGMP to GMP by cyclic nucleotide phosphodiesterases (PDEs) and the excretion of unchanged cGMP by transport proteins in the cell membrane. Efflux is observed in virtually all cell types including cells which originate from brain. Studies of intact cells, in which metabolic inhibitors and probenecid reduced extrusion of cGMP and wherein cGMP was extruded against concentration gradients, indicated the existence of ATP requiring organic anion transport system(s). Functional studies of inside-out vesicles have revealed cGMP transport systems wherein translocation is coupled to hydrolysis of ATP. The extrusion of cGMP is inhibited by a number of unrelated compounds and this indicates that cGMP is substrate for multispecific transporters. Recent transfection studies suggest that members of the MRP (multidrug resistance protein) family; MRP4, MRP5 and MRP8 translocate cGMP across the cell membrane. Many of the MRPs have been detected in brain. In addition tertiary active transport by the organic anion transporter family has also been identified. At least one member (OAT1) shows relative high affinity for cGMP and is also expressed in brain. The biological significance of cGMP transporters has to be clarified. Their role in cGMP biokinetics, being responsible for one of the cellular elimination pathways, is well established. However, there is growing evidence that extracellular cGMP has effects on cell physiology and pathophysiology by an auto- or paracrine mechanism.

Exhaled nitric oxide: a marker of pulmonary hemodynamics in heart failure

OBJECTIVES

We sought to test the hypothesis that patients with decompensated heart failure (HF) lose a compensatory process whereby nitric oxide (NO) maintains pulmonary vascular tone.

BACKGROUND

Exhaled nitric oxide (eNO) partially reflects vascular endothelial NO release. Levels of eNO are elevated in patients with compensated HF and correlate inversely with pulmonary artery pressures (PAP), reflecting pulmonary vasodilatory activity.

METHODS

We measured the mean mixed expired NO content of a vital-capacity breath using chemiluminescence in patients with compensated HF (n = 30), decompensated HF (n = 7) and in normal control subjects (n = 90). Pulmonary artery pressures were also measured in patients with HF. The eNO and PAP were determined sequentially during therapy with intravenous vasodilators in patients with decompensated HF (n = 7) and in an additional group of patients with HF (n = 13) before and during administration of milrinone.

RESULTS

The eNO was higher in patients with HF than in control subjects (9.9 +/- 1.1 ppb vs. 6.2 +/- 0.4 ppb, p = 0.002) and inversely correlated with PAP (r = -0.81, p < 0.00001). In marked contrast, patients with decompensated HF exhibited even higher levels of eNO (20.4 +/- 6.2 ppb) and PAP, but there was a loss of the inverse relationship between these two variables. During therapy (7.3 +/- 6 days) with sodium nitroprusside and diuresis, hemodynamics improved, eNO concentrations fell (11.2 +/- 1.2 ppb vs. before treatment, p < 0.05), and the relationship between eNO and PAP was restored. After milrinone, eNO rose proportionally with decreased PAP (p < 0.05).

CONCLUSIONS

Elevated eNO may reflect a compensatory circulatory mechanism in HF that is lost in patients with clinically decompensated HF. The eNO may be an easily obtainable and quantifiable measure of the response to therapy in advanced HF.

Head-to-head comparison of N-terminal pro-brain natriuretic peptide, brain natriuretic peptide and N-terminal pro-atrial natriuretic peptide in diagnosing left ventricular dysfunction

Brain natriuretic peptide (BNP), NT-proBNP and NT-pro-atrial natriuretic peptide (NT-proANP) were measured in blood samples from 57 patients using immunoassays and immunoradiometric assays to evaluate the usefulness as diagnostic markers for the detection of heart failure. For the detection of impaired left ventricular ejection fraction (LVEF), receiver operating characteristic curves showed that BNP had the best diagnostic performance with an area under curve (AUC) of 0.75+/-0.06. However, NT-proBNP (AUC: 0.67+/-0.07) and NT-proANP (AUC: 0.69+/-0.08) showed no significant difference to BNP. In a further analysis for the detection of resting LVEF <40%, BNP again was the best marker with an AUC of 0.83+/-0.06. NT-proBNP showed only a slightly smaller AUC (0.79+/-0.07). The AUC for NT-proANP was significantly smaller (0.65+/-0.08) compared to BNP. Additionally, BNP and NT-proBNP correlated negatively with the resting LVEF (BNP: -0.472, p<0.001; NT-proBNP: -0.306, p=0.026), whereas NT-proANP showed no significant correlation. In summary, BNP was the best marker to detect patients with impaired LVEF compared to NT-proBNP and NT-proANP. However, NT-proBNP showed no significant differences to BNP and it is therefore a new promising alternative marker for the detection of left ventricular dysfunction.

ATPase activity and transport by a cGMP transporter in human erythrocyte ghosts and proteoliposome-reconstituted membrane extracts

We previously described the [(3)H]cGMP-binding characteristics of a CHAPS-solubilized protein that we proposed to be a cGMP transporter. We now report the ATPase activity of the membrane-bound, solubilized and reconstituted form of a cGMP transporter. The membrane-bound protein of unsealed ghosts had a linear ATPase activity over a 120 min incubation period with optimal activity of about 400 pmol/mg/min. The apparent K(m) and V(max) for ATP were about 0.5 mM and 300 pmol/mg/min, respectively. When solubilized with CHAPS the specific activity of the protein was reduced to about 70 pmol/mg/min. Reconstitution of the CHAPS preparation into phospholipid bilayer using rapid detergent removal by Extracti-gel column resulted in proteoliposomes which had ATPase activity similar to that found in the erythrocyte membranes. The proteoliposomes displayed a linear ATP-dependent uptake of [(3)H]cGMP with an apparent K(m) value of 1. 0 microM. This low K(m)-uptake of [(3)H]cGMP in proteoliposomes was not affected by 10 microM of AMP, cAMP and GMP, but was completely abolished in the presence of the non-hydrolyzable ATP analogue, ATP-gamma-S. Some ATPase activation was also observed in the presence of 2 microM cAMP, but it is unclear whether this activity was coupled to the cGMP transporter. Our results show that the membrane protein responsible for cGMP transport has an ATPase activity and transports the cyclic nucleotide in the presence of ATP.

Increased urinary excretion of uroguanylin in patients with congestive heart failure

Uroguanylin is a small-molecular-weight peptide that activates membrane-bound receptor-guanylate cyclases in the intestine, kidney, and other epithelia. Uroguanylin has been shown to participate in the regulation of salt and water homeostasis in mammals via cGMP-mediated processes, bearing a distinct similarity to the action of the atriopeptins, which play a defined role in natriuresis and act as prognostic indicators of severe congestive heart failure (CHF). The objectives of this study were to measure the urinary levels of uroguanylin and the circulating plasma levels of atrial natriuretic peptide (ANP) in healthy individuals (n = 53) and patients with CHF (n = 16). Urinary excretion of uroguanylin was assessed by a cGMP accumulation bioassay employing human T84 intestinal cells. In individuals without CHF, the concentration of uroguanylin bioactivity was 1.31 +/- 0.27 nmol cGMP/ml urine and 1.73 +/- 0.25 micromol cGMP/24-h urine collection. The urinary bioactivity of uroguanylin in males (1.74 +/- 0.55 nmol cGMP/ml urine; n = 27) tended to be higher than the excretion levels in females (0.94 +/- 0.16 nmol cGMP/ml urine; n = 26) over a 24-h period but did not achieve statistical significance. Both male and female groups showed 24-h temporal diurnal variations with the highest uroguanylin levels observed between the hours of 8:00 AM and 2:00 PM. The circulating level of ANP was 12.1 +/- 1.6 pg/ml plasma and did not significantly vary with respect to male/female population or diurnal variation. In patients with CHF, the concentration of plasma ANP and urinary uroguanylin bioactivity increased substantially (7.5-fold and 70-fold, respectively, both P </= 0.001) compared with healthy levels. Uroguanylin was purified from the urine of CHF patients and shown to be the bioactive, COOH-terminal, 16 amino acid portion of the human prouroguanylin protein. The increased urinary uroguanylin excretion observed during CHF may be an adaptive response to this cardiovascular pathophysiology.

Inverse relationship of urinary cyclic GMP to blood pressure reactivity in the CARDIA study: vasodilatory regulation of sympathetic vasoconstriction. Coronary Artery Risk Development in Young Adults

OBJECTIVE

To determine whether urinary cyclic GMP (cGMP), which mediates the actions of the vasodilators nitric oxide and atrial natriuretic factor, is inversely related to blood pressure (BP) reactivity. In previous work, we found that urinary cGMP was inversely related to diastolic BP, but cGMP levels were higher among individuals presumed to have increased adrenergic activity, increased reactivity, and increased risk of hypertension (blacks, individuals with a family history of hypertension).

METHOD

We measured 24-hour urinary cGMP levels in a substudy of 529 individuals in the Coronary Artery Risk Development in Young Adults (CARDIA) study; the sample was 23 to 35 years of age and approximately balanced for race (black/white) and gender. BP reactivity to stressors (video game, star-tracing, cold pressor) was tested 3 years earlier. Baseline BP was included as a covariate in all analyses.

RESULTS

Diastolic BP reactivity to cold pressor was inversely related to cGMP excretion (p < .05); the relationship was strongest among black women with a family history of hypertension (partial r = -.33, p < .01). Systolic BP reactivity to star-tracing was also inversely related to cGMP (p < .01); the relationship for both star-tracing and video game stressors was strongest among black men (partial r values = -.25 and -.24, respectively; p values < .01).

CONCLUSIONS

The results indicate that vasodilatory activity may impact the BP response to stress through modulation of adrenergic activation, particularly among blacks.

Relationship of diastolic blood pressure with cyclic GMP excretion among young adults (the CARDIA Study): influence of a family history of hypertension. Coronary Artery Risk Development in Young Adults

BACKGROUND

Guanosine 3':5'-cyclic monophosphate (cGMP) is the second messenger of nitric oxide and atrial natriuretic factor, and mediates local vasodilatation. These vasodilatory factors are important in blood pressure regulation and possibly in the etiology of hypertension. Urinary cGMP levels among normotensive young adults have not previously been studied.

SUBJECTS

A subset of normotensive participants from the CARDIA study (n = 563), aged 23-35 years, was studied. The sample was approximately balanced for sex and race (black/white).

METHODS

Twenty-four-hour urinary cGMP levels were measured using an enzyme immunoassay; levels were adjusted for creatinine excretion. The blood pressure, smoking status, and risk factors for hypertension [including a family history of hypertension (FHH), the body mass index, education, alcohol intake, and sodium excretion] were also measured.

RESULTS

Women excreted more cGMP than did men, and blacks excreted more cGMP than did whites (both P < 0.0001). Excretion of cGMP was also greater among smokers (P < 0.001) and those with an FHH (P = 0.05), and was related directly and independently to sodium excretion (P < 0.02). The diastolic blood pressure (DBP) was related inversely to the excretion of cGMP among individuals without an FHH (r = -0.36, P < 0.001), but not among individuals with an FHH. In multiple regression analysis, the excretion of cGMP remained related significantly to the DBP and accounted for more variance in DBP than did any other variable among those without an FHH (delta R2 = 0.08, P < 0.001).

CONCLUSIONS

Urinary cGMP excretion is related inversely and independently to the DBP among those without an FHH but not among those with an FHH, suggesting that cGMP-related vasodilatation is impaired in those with an FHH. Sex differences in urinary excretion of cGMP are consistent with results from studies showing that estrogen increases the endothelial production of nitric oxide.

Natriuretic peptides and cyclic guanosine 3',5'-monophosphate in asymptomatic and symptomatic left ventricular dysfunction

BACKGROUND

Screening for patients with asymptomatic left ventricular dysfunction is of considerable importance because they may benefit from early treatment with angiotensin converting enzyme inhibitors. It has been suggested that atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and cyclic guanosine 3',5'-monophosphate (cGMP) might be useful markers for screening.

OBJECTIVE

To compare directly the power of the three immunoreactive forms of ANP (CT-ANP, beta-ANP, NT-ANP) and BNP and cGMP to detect asymptomatic left ventricular dysfunction.

METHODS AND RESULTS

Radionuclide ventriculography was used to study left ventricular ejection fraction in 37 patients with asymptomatic left ventricular dysfunction, 32 patients with mild to moderate congestive heart failure, and 38 controls. CT-ANP, NT-ANP, beta-ANP, BNP, and cGMP were measured at rest and 3 minutes after exercise. Plasma BNP was the most sensitive marker for patients with asymptomatic left ventricular dysfunction but it reached only a sensitivity of 58% and a specificity of 76% at rest and a sensitivity of 65% and a specificity of 84% after exercise. Combined measurements of all natriuretic peptides and cGMP did not improve the power to detect asymptomatic left ventricular function above that of a single BNP measurement.

CONCLUSIONS

Although natriuretic peptides and cGMP measured at rest and three minutes after ergometry may be useful for monitoring left ventricular dysfunction they are unlikely to be suitable for more general routine screening for completely asymptomatic left ventricular dysfunction.

Export of guanosine 3',5'-cyclic monophosphate (cGMP) from human erythrocytes characterized by inside-out membrane vesicles

The present study was undertaken to characterize the export of cGMP from human erythrocytes at 37 degrees C. Inside-out membrane vesicles were exposed to cGMP and [3H]-cGMP in the presence and absence of 2 mmol l-1 ATP. In the absence of ATP, an equilibrium was reached within 15 min for the lowest tested concentration (0.65 mumol l-1), and the amount of cGMP in the vesicles was linearly correlated to the cGMP concentrations in the incubate. These observations suggest that the ATP-independent process represents passive diffusion or non-saturated binding to membrane components. In the presence of ATP, cGMP accumulated linearly during the test period (up to 120 min) and the transport into the inside-out vesicles was dependent on both low- and high-Km transport. The kinetic parameters for the low-Km process were determined after 5 and 120 min, the Km values being 4.6 (SD 1.9) and 4.7 (SD 1.1) mumol l-1 (n = 3), respectively. The corresponding Vmax values were 400 (SD 50) and 440 (SD 70) fmol mg-1 min-1. The high-Km process was characterized by Km = 170 (SD 50) mumol-1 and Vmax = 1610 (SD 280) fmol mg-1 min-1 (n = 5). The present data demonstrate an ATP-requiring saturable transport system for cGMP in human erythrocytes.

Effect of probenecid, verapamil and progesterone on the concentration-dependent and temperature-sensitive human erythrocyte uptake and export of guanosine 3',5' cyclic monophosphate (cGMP)

Elevated extracellular cGMP levels have been observed in various clinical conditions, and the analyte has been proposed as a diagnostic marker of cardiovascular as well as malignant diseases. However, the use of extracellular cGMP as a pathophysiological marker requires detailed knowledge about the cellular biokinetics of cGMP (synthesis, metabolic conversion and export). In the present study the transport of cGMP in human erythrocytes has been further characterized. The uptake of cGMP was dependent on a concentration gradient and was temperature-sensitive, compatible with passive diffusion. The cGMP export was temperature-sensitive, saturable (Km = 3.4 +/- 1.0 mu mol l-1), inhibited by probenecid and verapamil and stimulated by progesterone. The results show that human erythrocytes possess a cGMP transport system similar to that found in other cells and that extracellular levels of cGMP are dependent on intracellular levels, membrane transport and influenced by physiological factors and pharmacological agents.

Urinary cGMP levels during pregnancy with and without uterine contractions

OBJECTIVE

The purpose of this study was to investigate the nitric oxide-cGMP (NO-cGMP) system by urinary cGMP level determinations in pregnant women with and without uterine contractions.

DESIGN AND SUBJECTS

cGMP expressed in nmol/mmol of creatinine was performed by radio immuno-assay (Amersham UK) in urine samples obtained from 94 pregnant women with non-complicated pregnancies. Population A without contractions (n = 62) was divided into three groups according to the gestational age (group I, < or = 15 weeks; group II, 16-33 weeks; group III, > 33 weeks). The group III from A population was compared to B population (of the same gestational age) presenting uterine contractions (n = 32).

RESULTS

In A population, no significant urinary cGMP level differences were observed whatever the gestational age. Nevertheless, the comparison between patients with or without uterine contractions (A III and B populations) showed a significant difference by a variance analysis (P < 0.05). Lower levels of cGMP were seen when uterine contractions occurred.

CONCLUSION

Urinary cGMP levels are significantly decreased in pregnant women with uterine contractions, without any difference from early to late pregnancy. These results, completed by more precise investigations, could suggest that the NO-cGMP system might be implicated in uterine quiescence.

Neopterin derivatives together with cyclic guanosine monophosphate induce c-fos gene expression

We have previously shown that neopterin enhances hydrogen peroxide and chloramine T activity in a luminol-dependent chemiluminescence assay and strengthens toxicity of these agents against bacteria at slightly alkaline pH (pH 7.5), while 7,8-dihydroneopterin was shown to be a scavenger independent of the pH value. Besides various oxidants, phenolic antioxidants were shown to specifically induce expression of the c-fos and c-jun mRNAs. Using an inducible cfosCAT reporter transactivation system we studied the function of the pteridine derivatives on c-fos transactivation. For the first time, we demonstrate that neopterin and 7,8-dihydroneopterin, particularly together with cyclic guanosine monophosphate, induce c-fos gene expression. In humans, interferon-gamma induces the release of neopterin and 7,8-dihydroneopterin and also the synthesis of nitric oxide radical which in turn stimulate the formation of cGMP. Thus, in certain situations all three substances, namely neopterin, 7,8-dihydroneopterin and cGMP, may be present locally and even in the circulation at the same time. Based on our findings this constellation would significantly enhance the risk of c-fos gene expression and therefore promote tumour growth and development.