Effects of atrial natriuretic peptide on the coronary arterial vasculature in humans

Angiotensin receptor-neprilysin inhibitor improves coronary collateral perfusion

Background

We investigated the pleiotropic effects of an angiotensin receptor-neprilysin inhibitor (ARNi) on collateral-dependent myocardial perfusion in a rat model of coronary arteriogenesis, and performed comprehensive analyses to uncover the underlying molecular mechanisms.

Methods

A rat model of coronary arteriogenesis was established by implanting an inflatable occluder on the left anterior descending coronary artery followed by a 7-day repetitive occlusion procedure (ROP). Coronary collateral perfusion was measured by using a myocardial particle infusion technique. The putative ARNi-induced pro-arteriogenic effects were further investigated and compared with an angiotensin-converting enzyme inhibitor (ACEi). Expression of the membrane receptors and key enzymes in the natriuretic peptide system (NPS), renin-angiotensin-aldosterone system (RAAS) and kallikrein-kinin system (KKS) were analyzed by quantitative polymerase chain reaction (qPCR) and immunoblot assay, respectively. Protein levels of pro-arteriogenic cytokines were measured by enzyme-linked immunosorbent assay, and mitochondrial DNA copy number was assessed by qPCR due to their roles in arteriogenesis. Furthermore, murine heart endothelial cells (MHEC5-T) were treated with a neprilysin inhibitor (NEPi) alone, or in combination with bradykinin receptor antagonists. MHEC5-T proliferation was analyzed by colorimetric assay.

Results

The in vivo study showed that ARNis markedly improved coronary collateral perfusion, regulated the gene expression of KKS, and increased the concentrations of relevant pro-arteriogenic cytokines. The in vitro study demonstrated that NEPis significantly promoted MHEC5-T proliferation, which was diminished by bradykinin receptor antagonists.

Conclusion

ARNis improve coronary collateral perfusion and exert pro-arteriogenic effects via the bradykinin receptor signaling pathway.

Low-dose carperitide (α-human A-type natriuretic peptide) alleviates hemoglobin concentration decrease during prolonged oral surgery: a randomized controlled study

PURPOSE

Surgical injury stimulates the renin-angiotensin-aldosterone system (RAAS) and causes antidiuresis, leading to postoperative oliguria. Carperitide (α-human A-type natriuretic peptide) is a cardiac peptide hormone secreted from the atrium. This peptide hormone enhances diuresis by suppressing the RAAS. In our experience, carperitide alleviates decreased hemoglobin (Hb) concentration during elective surgery. In the current study, we investigated the relationship between low-dose carperitide (0.01 µg/kg/min) and Hb concentration during oral surgery.

METHODS

Patients (ASA-PS: I-II, 40-80 years old) undergoing oral maxillofacial surgery (duration of operation >8 h) were enrolled in this study. Patients were divided into two groups: the carperitide group received carperitide at 0.01 µg/kg/min and the control group received normal saline. Body fluid water [including total body water (TBW), extracellular water (ECW), and intracellular water (ICW)], urine volume, and chemical parameters such as Hb concentration, PaO₂, and serum electrolytes were evaluated every 2 h.

RESULTS

In the carperitide group (n = 15), Hb decreased from 12.6 ± 1.1 to 10.8 ± 1.5 g/dl, while it decreased from 12.6 ± 1.4 to 9.5 ± 1.3 g/dl in the control group (n = 15) (p < 0.05). Urine volume (2557.3 ± 983.5 mL) in the carperitide group was significantly more than it was in the control group (1108.8 ± 586.4 mL; p < 0.001). There were no significant differences in clinical characteristics, body fluid water, PaO₂, and serum electrolytes between the two groups. In addition, there were no perioperative clinical respiratory and hemodynamic complications in the groups.

CONCLUSION

The Hb concentration in the group administered low-dose carperitide at 0.01 µg/kg/min remained higher than that in the control group during surgery. Administration of low-dose carperitide may therefore reduce the risk of blood transfusion during surgery.

Effects of intravenous atrial natriuretic peptide and nitroglycerin on coronary vasodilation and flow velocity determined using 3 T magnetic resonance imaging in patients with nonischemic heart failure

Although atrial natriuretic peptide (ANP) is widely used in patients with congestive heart failure (CHF), little is known about its effect on epicardial coronary arteries. Magnetic resonance imaging (MRI) enables precise measurement of coronary vasodilation and flow velocity. In this study, we examined the changes in epicardial coronary artery size and flow velocity in response to intravenous infusion of ANP or nitroglycerin (NTG) by using 3 T MRI in patients with CHF. The study cohort contained a total of 14 subjects: 8 patients with CHF and 6 healthy volunteers as controls, randomly divided into two groups: the ANP group (0.03 μg/kg/min) and the NTG group (0.3 μg/kg/min). Cross-sectional MR angiography and phase-contrast flow velocity of the right coronary artery in the same in-plane slice were obtained at the baseline, during drug infusion, and at two subsequent time points after stopping drug infusion. A significant increase was observed in the coronary cross-sectional area at 15 min after drug infusion in both groups compared with that at baseline; however, a late peak was observed at 15 min after stopping infusion in the ANP group. No significant differences were detected in the flow velocity in both groups. Furthermore, although NTG increased the heart rate, this change was not found in the ANP group. Coronary vasodilation and flow velocity can be measured simultaneously using 3 T MRI. Using this method, we showed that the effects of ANP on the coronary artery vasodilation and flow velocity were not inferior to those of NTG, with no significant alteration in heart rate.

Low-dose atrial natriuretic peptide for chronic kidney disease in coronary surgery

PURPOSE

Chronic kidney disease (CKD) is an independent risk factor for cardiovascular disease. We investigated the effectiveness of human atrial natriuretic peptide (hANP) infusion in CKD patients undergoing coronary artery bypass grafting (CABG).

PATIENTS AND METHODS

We analyzed 134 consecutive cases in which CABG had been performed in our hospital from 2002 to 2005. They were divided into four groups: Group A (n = 19) was CKD + placebo, Group B (n = 30) was non-CKD + placebo, Group C (n = 22) was CKD + hANP, and Group D (n = 63) was non-CKD + hANP). The serum creatinine (mg/dl) and estimated glomerular filtration rate (ml/min/1.73 m²) were measured as evaluation values.

RESULTS

The value of sCr changed preoperatively and at 1 year postoperatively from 1.09 ± 0.09, 51.3 ± 4.4 to 1.26 ± 0.42, 49.4 ± 14.4 in Group A, from 0.77 ± 0.14, 75.5 ± 12.1 to 0.91 ± 0.40, 72.3 ± 19.5 in Group B, from 0.99 ± 0.12, 54.8 ± 3.0 to 0.93 ± 0.16, 64.2 ± 12.3 in Group C and from 0.77 ± 0.13, 77.7 ± 13.4 to 0.83 ± 0.17, 75.9 ± 16.2 in Group D, respectively. There was a significant difference between Group A and Group C regarding the change of creatinine (p =0.0022).

CONCLUSION

Our study has confirmed that an infusion of hANP during CABG in patients with CKD not only improves perioperative renal function, but also prevents the progression of CKD.

Heterogeneity in relaxation of different sized porcine coronary arteries to nitrovasodilators: role of PKG and MYPT1

The present study was to determine the role of the type I isoform of cGMP-dependent protein kinase (PKG I) and its downstream effector myosin phosphatase target subunit 1 (MYPT1) in the responses of different sized coronary arteries to nitrovasodilators. Relaxations of isolated porcine coronary arteries were determined by isometric tension recording technique. Protein levels of PKG I and its effectors were analyzed by Western blotting. The activities of PKG I and MYPT1 were studied by analyzing phosphorylation of vasodilator-stimulated phosphoprotein (VASP) and MYPT1, respectively. Nitroglycerin, DETA NONOate, and 8-Br-cGMP caused greater relaxations in large than in small coronary arteries. Relaxations were attenuated to a greater extent by Rp-8-Br-PET-cGMPS (a PKG inhibitor) in large vs. small arteries. The expressions of PKG I and MYPT1 in large arteries were more abundant than in small arteries. DETA NONOate stimulated phosphorylation of VASP at Ser239 and inhibited phosphorylation of MYPT1 at Thr853 to a greater extent in large than in small arteries. A suppressed phosphorylation of MYPT1 at Thr853 was caused by 8-Br-cGMP in large but not small arteries, which was inhibited by Rp-8-Br-PET-cGMPS. These results suggest that the greater responsiveness of large coronary arteries to nitrovasodilators result in part from greater activities of PKG I and MYPT1. Dysfunction in nitric oxide signaling is implicated in the vulnerability of large coronary arteries to certain disorders such as atherosclerosis and spasm. Augmentation of PKG I-MYPT1 signaling may be of therapeutic benefit for combating these events.

Atrial natriuretic peptide augments coronary collateral blood flow: a study during coronary angioplasty

BACKGROUND AND HYPOTHESIS

In vitro studies have shown that atrial natriuretic peptide (ANP) causes relaxation of preconstricted blood vessel strips and inhibits the contraction of isolated vessels in response to norepinephrine and angiotensin II. The present study examined the effects of exogenous ANP on the coronary collateral blood flow during angioplasty.

METHODS

We studied 15 patients undergoing elective balloon angioplasty during the second and third balloon inflations. A Doppler flow guidewire was advanced distal to the lesion and used for the estimation of coronary blood flow velocity. After the second balloon inflation, 25 ng/kg/min of ANP were administered intracoronarily for 8 min. Electrocardiogram, pressure, and flow velocity were recorded immediately before each balloon deflation. Fourteen other patients served as controls and received normal saline infusion.

RESULTS

Velocity time integral increased from 65 +/- 40 to 79 +/- 46 mm (p < 0.05) during the third balloon inflation, whereas ST deviation decreased from 1.3 +/- 0.9 to 0.7 +/- 1.0 mV (p < 0.05). These variables did not change in the control group during the two tested balloon inflations.

CONCLUSION

Exogenous ANP augments coronary collateral blood flow and ameliorates myocardial ischemia during angioplasty.

Coronary endothelial dysfunction and impaired microcirculation response to atrial natriuretic peptide in hyperinsulinemia

Endothelial dysfunction occurs in hyperinsulinemia (HI). Coronary microcirculation responses to vasoactive agents are examined in 57 patients with angiographically normal coronary arteries. Patients were divided into 2 groups, 37 with normoinsulinemia (NI) and 20 with HI based on results of a 75-g oral glucose tolerance test. Epicardial artery vasoactivity in response to acetylcholine chloride is measured to assess endothelial function. Coronary microcirculation function is evaluated by intracoronary administration of 50 microg of adenosine triphosphate, 1 mg of isosorbide dinitrate, and 0.05 mg/kg of atrial natriuretic peptide. Epicardial artery vasoconstriction in response to 100 microg of acetylcholine is mildly reduced in HI (P = .04). Coronary flow reserve in response to adenosine triphosphate in NI is similar to that in HI. In NI, the resting mean (SD) peak velocity in response to isosorbide dinitrate (40.7 [10.9] cm/s) vs atrial natriuretic peptide (39.6 [10.9] cm/s) is similar. In contrast, the resting mean (SD) peak velocity in response to atrial natriuretic peptide (31.3 [9.3] cm/s) vs isosorbide dinitrate (43.5 [10.0] cm/s) in HI is statistically significantly blunted (P < .001). Atrial natriuretic peptide may have a pathologic effect on coronary microcirculation even in mild endothelial dysfunction among patients with HI.

Atrial Natriuretic Peptide Protects Against Ischemia-Reperfusion Injury in Rabbit Hearts In Vivo

The aim of this study is to investigate whether atrial natriuretic peptide can mimic preconditioning to protect ischemia or reperfusion injury in rabbit hearts. New Zealand white rabbits were randomized into 3 groups: (1) Controls. Hearts received a 60 minute-occlusion of the left anterior descending artery, followed by a 180 minute-reperfusion. (2) Preconditioning. Two 5-minute periods of ischemia separated by a 10-minute reperfusion, followed by a 60-minute ischemia and a 180-minute reperfusion. (3) Atrial natriuretic peptide treatment. Bolus injection of exogenous atrial natriuretic peptide (2.5 µg/kg) given intravenously at 15 minutes prior to 60 minute-ischemia followed by a 180-minute reperfusion. Myocardial necrotic area and area at risk of necrosis were determined by triphenyltetrazolium chloride staining. Ratio of necrotic area to area at risk was 49.95% ± 1.15%, 7.95% ± 0.33%, and 8.36% ± 0.61% in the controls, preconditioning group, and atrial natriuretic peptide group, respectively. Both preconditioning and atrial natriuretic peptide significantly reduced the size of infarct caused by ischemia (preconditioning vs controls, P < .05; atrial natriuretic peptide vs controls, P < .05). Atrial natriuretic peptide can mimic ischemic preconditioning to protect rabbit hearts from prolonged ischemia and reperfusion injury. It may be involved in the cardioprotective mechanisms of preconditioning.

Efficacy of continuous low-dose hANP administration in patients undergoing emergent coronary artery bypass grafting for acute coronary syndrome

BACKGROUND

Low-dose continuous human atrial natriuretic peptide (hANP) administration during cardiac surgery has been reported on previously. In the present study, the efficacy of the therapy during emergent coronary artery bypass grafting (CABG) for acute coronary syndrome (ACS) is investigated.

METHODS AND RESULTS

One hundred and twenty-four patients patients undergoing emergent CABG for ACS were divided into 2 groups; a group receiving administration of hANP (hANP group) and a group not receiving hANP infusion (non-hANP group). The postoperative peak levels of creatine kinase-MB were significantly lower in the hANP group as compared with those in the non-hANP group. The incidence of postoperative arrhythmias was also significantly lower in the hANP group as compared with that in the non-hANP group. The postoperative brain natriuretic peptide was significantly lower in the hANP group as compared with that in the non-hANP group until 1 year after the operation. The free-rate of cardiac events after the operation was also significantly higher in the hANP group as compared with that in the non-hANP group.

CONCLUSIONS

It is therefore considered that hANP might not only be effective for overcoming some major shortcomings of cardiopulmonary bypass, but also might be effective to attenuate ischemia-reperfusion injury, protect the myocardium, have an anti-arrhythmic effect, and suppress left ventricular remodeling.

Efficacy of continuous low-dose human atrial natriuretic peptide given from the beginning of cardiopulmonary bypass for thoracic aortic surgery

PURPOSE

Cardiac surgery performed under cardiopulmonary bypass (CPB) causes abnormalities of the renin-angiotensin-aldosterone system, resulting in decreased urine output and an accumulation of water in the third space. We studied the efficacy of continuous low-dose human atrial natriuretic peptide (hANP) in patients undergoing thoracic aortic surgery.

METHODS

We divided 40 patients undergoing thoracic aortic surgery into two groups: the hANP group, which received 0.02 microg/kg per minute of hANP and the non-hANP group, which did not. The hemodynamics, urine output, intensive care unit (ICU) and hospital stay, bleeding volume, homologous blood transfusion volume, furosemide dose, corrected KCl volume, and postoperative respiratory, hepatic, and renal function were compared in the two groups.

RESULTS

The urine output during CPB and from CPB weaning to return to ICU was significantly better in the hANP group. The bleeding volume, homologous blood transfusion volume, furosemide dose, and corrected KCl volume were all significantly less in the hANP group.

CONCLUSIONS

These findings support the consensus that hANP exerts its diuretic effects to their full potential when administered continuously at low doses during thoracic aortic surgery. We found it to be effective for postoperative hemostasis and for preventing ischemic reperfusion injury.

In vivo dilatation of the postnatal ductus arteriosus by atrial natriuretic peptide in the rat

BACKGROUND

Alpha-human atrial natriuretic peptide (hANP) reportedly increases in premature infants with patent ductus arteriosus (PDA).

OBJECTIVES

To clarify a possible hANP effect to reopen the postnatal ductus, we studied in vivo reopening of the postnatal DA by a recombinant hANP, carperitide, in rats.

METHODS

Near-term rat pups were incubated at 33 degrees C following caesarean section. The inner diameter of the ductus was measured with a microscope and a micrometer following rapid whole-body freezing. The DA constricted quickly after birth, and the inner diameter was 0.80 and 0.08 mm at 0 min (fetal state) and 60 min after birth. hANP concentration in the pup blood and the ductus-dilating effect of hANP were studied by subcutaneous injection of hANP at 60 min after birth, and by measurement 7, 15, 30 and 60 min later.

RESULTS

The peak hANP concentration was 790 pg/ml at 7 min with 1 mg/kg, which is similar to the level seen in preterm infants with symptomatic PDA. hANP dilated the postnatal ductus dose dependently and maximally at 7 min after injection. hANP dilated the postnatal constricted ductus completely to 0.79 mm in diameter with a large dose (10 mg/kg) and to 0.55 mm with 1 mg/kg.

CONCLUSIONS

hANP reopens the constricted postnatal DA dose dependently in rats. The increased hANP, accompanying premature PDA, may delay closure of the DA.

Atrial natriuretic peptide and related peptides

In recent years, biomarkers have been recognized as important tools for diagnosis, risk stratification, and therapeutic decision-making in cardiovascular diseases. Currently, the clinical potential of several natriuretic peptides is under scientific investigation. The well-known counter-regulatory hormones are atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), C-type natriuretic peptide (CNP), dendroaspis natriuretic peptide (DNP) and urodilatin, which play an important role in the homeostasis of body fluid volume. ANP and BNP have already been demonstrated to have diagnostic usefulness in a great number of studies, which have progressed from bench to bedside. This article summarizes existing data on ANP and related peptides in cardiovascular and other disorders, and outlines the potential clinical usefulness of these markers.

Clin Chem Lab Med 2007;45:1259–67.

A review of the natriuretic hormone system's diagnostic and therapeutic potential in critically ill children

OBJECTIVE

To review the natriuretic hormone system and discuss its diagnostic, prognostic, and therapeutic potential in critically ill children.

DATA SOURCE

A thorough literature search of MEDLINE was performed using search terms including heart defects, congenital; cardiopulmonary bypass, atrial natriuretic factor; natriuretic peptide, brain; carperitide; nesiritide. Preclinical and clinical investigations and review articles were identified that describe the current understanding of the natriuretic hormone system and its role in the regulation of vascular tone and fluid balance in healthy adults and children and in those with underlying cardiac, pulmonary, and renal disease.

RESULTS

A predictable activation of the natriuretic hormone system occurs in children with congenital heart disease and congestive heart failure. Further study is needed to confirm preliminary reports that measurement of natriuretic hormone levels in critically ill children provides diagnostic and prognostic information, as has been demonstrated in adult cardiac populations. Natriuretic hormone infusions provide favorable hemodynamic changes and symptomatic relief when used in adults with decompensated congestive heart failure, and uncontrolled case series suggest that similar benefits may exist in children. The biological activity of the natriuretic hormone system may be decreased following pediatric cardiopulmonary bypass, and additional studies are needed to determine whether natriuretic hormone infusions provide clinical benefit in the postoperative period. Preliminary reports suggest that natriuretic hormone infusions cause physiologic improvements in adults with acute lung injury and asthma but not in those with acute renal failure.

CONCLUSIONS

Although important perturbations of the natriuretic hormone system occur in critically ill infants and children, further investigation is needed before the measurement of natriuretic peptides and the use of natriuretic hormone infusions are incorporated into routine practice.

Efficacy of Low-Dose Continuous Infusion of .ALPHA.-Human Atrial Natriuretic Peptide (hANP) During Cardiac Surgery Possibility of Postoperative Left Ventricular Remodeling Effect

BACKGROUND

The aim of the present study was to evaluate the efficacy of alpha-human atrial natriuretic peptide (hANP) in cardiac surgery under cardiopulmonary bypass (CPB).

METHODS AND RESULTS

A prospective randomized study was conducted with 150 patients who underwent scheduled coronary artery bypass grafting to compare a group of patients receiving 0.02 microg x kg(-1) x min(-1) of hANP from the initiation of CPB with a group not receiving hANP. Hemodynamics, levels of atrial and brain natriuretic peptides (BNP), angiotensin-II and aldosterone, renin activity, and left ventricular (LV) function were examined. The hANP group showed significantly lower renin activity and lower levels of angiotensin-II and aldosterone during the early postoperative period, compared with the non-hANP group. The incidence of postoperative ventricular arrhythmia and the postoperative peak level of creatine kinase-MB were significantly lower in the hANP group. BNP at 1 month after surgery and measures of LV function were also significantly lower in the hANP group.

CONCLUSIONS

Low-dose continuous infusion of hANP during cardiac surgery not only had a compensatory effect for the imperfections of CPB during the early postoperative period but also an inhibitory effect on postoperative LV remodeling and a reduction in ischemia/reperfusion injury. hANP should be part of the postoperative care for cardiac surgery.

Acute myocardial hypoxia increases BNP gene expression

It is well established that cardiac failure increases cardiac B-type natriuretic peptide (BNP) expression due to myocardial stretching. However, patients with ischemic heart disease also display increased plasma BNP and proBNP concentrations despite preserved cardiac function. In this study, we examined whether acute myocardial hypoxia increases cardiac BNP expression. Surgical reduction of the blood flow to an area of the anterior ventricular wall in pigs reduced the myocardial oxygen tension from 46 +/- 4 to 13 +/- 5 mmHg. The tissue contents of VEGF and BNP mRNA increased 1.8-fold and 3.5-fold, respectively (n=10, P<0.005) in hypoxic compared with normoxic ventricular myocardium after 2.2 +/- 0.2 h; the magnitude of the increase in BNP mRNA expression was positively correlated with that of VEGF in hypoxic myocardium (r=0.66, P<0.05). In support of a hypoxia-induced increase of BNP gene transcription, the content of a premature BNP mRNA was increased in hypoxic myocardium (4.8-fold, P<0.005) and in freshly harvested ventricular myocytes when kept in culture flasks and oxygen-deprived for 3 h (2.2-fold, P=0.002). ProBNP peptide accumulated in the medium of freshly harvested ventricular myocyte cultures but was undetectable in ventricular myocardium, indicating rapid release of the newly synthesized proBNP peptide. Accordingly, the plasma proBNP concentration increased after 2 h of myocardial hypoxia (P=0.028). Cumulatively, the data suggest that acute hypoxia stimulates cardiac BNP expression.

Physiological antagonism of endothelin-1 in human conductance and resistance coronary artery

The ability of four endogenous vasodilators, nitric oxide (NO; 0.01 - 30 microM), atrial (ANP), brain (BNP) and C-type (CNP) natriuretic peptide (0.1 - 300 nM), to reverse endothelin-1 (ET-1; 10 nM) constrictions in human resistance and conductance coronary arteries (CA) in vitro was investigated. ET-1 (0.1 - 300 nM) constricted resistance CA more potently than conductance CA (P<0.05; EC(50) values 2.98 nM (95% CI: 1.49 - 5.95 nM and 8.58 (4.72 - 15.6 nM) respectively)). The NO-donor diethylamine NONOate fully reversed the ET-1 constriction in conductance CA (E(MAX) 127+/-9.16%), however only partial reversal was observed in resistance CA (E(MAX) 78.8+/-8.13; P<0.05). The soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (100 microM) reduced the maximum response to diethylamine NONOate to 76.9+/-14.4% in conductance CA (P<0.05), but had no effect on resistance CA (E(MAX) 77.2+/-18.4%). There was no difference between responses to ANP in conductance and resistance CA (EC(50) values 4.25 nM (0.84 - 21.4 nM) and 18.4 nM (2.92 - 116 nM), E(MAX) 53.1+/-14.7% and 48.6+/-11.8% respectively). BNP was a more potent vasodilator of conductance than resistance CA. In conductance CA the mean EC(50) value was 2.4 nM (0.74 - 7.75 nM), E(MAX) 54.5+/-14.9%. Concentration-response curves to BNP were incomplete in resistance CA. Concentration-response curves to CNP were incomplete in both conductance and resistance CA. The greater potency of ET-1 in resistance vessels may exacerbate the effects of increased circulating levels of the peptide in disease. Only NO could fully reverse ET-1 mediated constrictions in conductance CA, and none of the dilators tested could completely counteract constrictions in resistance CA.

Usefulness of carperitide for the treatment of refractory heart failure due to severe acute myocardial infarction

Carperitide (synthetic atrial natriuretic peptide) is a newly developed drug for the treatment of heart failure. Although this drug has been used for various types of heart failure, it remains unknown whether it has additive effects on hemodynamic parameters or renal excretory function during intensive treatment for acute refractory heart failure. We have examined the cardiorenal and hormonal effects of carperitide (0.05-0.10 microg / min / kg) in 9 patients (mean age: 67+/-8 years) with severe heart failure complicated with acute myocardial infarction, in which a range of intensive treatments have already been started. Hemodynamic parameters were determined before and 4, 24 and 48 hours after initiation of carperitide. Pulmonary capillary wedge pressure (mean+/-SD) had decreased dramatically from 21+/-6 to 11+/-5 mmHg (p<0.01) 4 hours after the treatment without significant renal effects. Heart rate and systemic blood pressure were not significantly changed. These beneficial effects were maintained for at least 24 hours. Plasma aldosterone levels fell significantly in response to the drug (from 148+/-68 to 56+/-29 pg / ml; p<0.05). However, mean hourly urine output remained unchanged after carperitide. In conclusion, intravenous infusion of carperitide promptly and persistently reduces left ventricular filling pressure without diuresis, hypotension, reflex tachycardia, or neurohormonal activation in patients with refractory heart failure due to severe acute myocardial infarction.

Two possible mechanisms underlying nitrate tolerance in monkey coronary arteries

1. Previous studies using isolated arteries have demonstrated cross-tolerance between nitric oxide (NO) donors such as nitroglycerin (NTG) and sodium nitroprusside (SNP). However, it remains unclear whether the vasorelaxing effect of atrial natriuretic peptide (ANP), an activator of particulate guanylate cyclase, is affected by treatment with NO donors. To investigate the cross-tolerance and interactions between NTG and ANP in coronary vasorelaxant responses, we used two models of monkey coronary arterial strips (Macaca fuscata). 2. In one model, which was induced by a 1 h treatment with 4.4 x 10(-4) mol/L NTG followed by washout of the agent for 1 h, the vasorelaxing effects of subsequent NTG were markedly attenuated, whereas those of ANP and NO were not affected. These findings suggest that the development of NTG tolerance is associated with a biotransformation process from NTG to NO. In the other model, which did not include washout after exposure to 3 x 10(-6) mol/L NTG, the vasorelaxant responses to 10(-8) mol/L ANP (31.1+/-5.4 vs 5.1+/-2.1%, respectively; P < 0.001), 10(-6) mol/L NO (61.5+/-2.4 vs 29.5+/-8.5%, respectively; P < 0.001) and 10(-8) mol/L SNP (49.4+/-6.4 vs 8.0+/-2.0%, respectively; P < 0.001) were significantly attenuated. The concentration- response curve for 8-bromo-cGMP (8-Br-cGMP) was shifted to the right, whereas responses to papaverine and forskolin were unchanged. These findings suggest that an intracellular process that occurs after the synthesis of cGMP is responsible for this interaction. 3. As a mechanism of NTG tolerance, two possible processes may be impaired: (i) biotransformation from NTG to NO; and (ii) an intracellular process that occurs after the synthesis of cGMP.

Alpha-human atrial natriuretic peptide, carperitide, reduces infarct size but not arrhythmias after coronary occlusion/reperfusion in dogs

Carperitide, a recombinant form of alpha-hANP, possesses potent diuretic, natriuretic, and vasodilatory activity, and inhibits the renin-aldosterone system and sympathetic nervous activity. However, its beneficial effects on ischemic myocardium have not been studied fully. We examined carperitide's effects on infarct size, hemodynamics, and arrhythmia frequency in anesthetized dogs (n = 20) subjected to a 90-min coronary artery occlusion/6-h reperfusion protocol. Intravenous infusion of carperitide (0.2 microg/kg/min) commenced 15 min after occlusion and continued during occlusion/reperfusion. Ventricular fibrillation developed in two of 10 control versus three of 10 treated dogs (p = NS). Hemodynamics, collateral blood flow to the ischemic wall measured 10 min after occlusion, and extent of area at risk were comparable for the two groups. Infarct size/area at risk was smaller in treated than in control dogs (4.5 +/- 2.1% vs. 27.8 +/- 7.8%, respectively; p < 0.05). During occlusion, carperitide tended to increase collateral blood flow (+39%) and significantly decreased left ventricular systolic pressure (-13%) and end-diastolic pressure (-40%) compared with baseline. In control dogs, collateral blood flow tended to decrease (-8.3%), whereas most hemodynamic parameters did not change significantly with respect to baseline. The number of arrhythmias recorded during occlusion/reperfusion was similar in the two groups. Intravenous administration of carperitide limited infarct size, but did not reduce incidence of ventricular arrhythmias after 90-min coronary occlusion/6-h reperfusion in anesthetized dogs. Although the beneficial effects of carperitide may be attributable to concomitant changes in hemodynamics and collateral blood flow, the precise mechanisms require further investigation.

Low-dose continuous infusion of human atrial natriuretic peptide during and after cardiac surgery

BACKGROUND

We evaluated the effects of human atrial natriuretic peptide (hANP) during cardiopulmonary bypass (CPB).

METHODS

Forty patients undergoing coronary artery bypass grafting were investigated. A group of patients given hANP for 24 hours from the start of CPB (hANP group) was compared with a non-hANP group. Parameters examined were hemodynamics, urine volume, dosage of furosemide, respiratory index, pleural effusion, ANP, cyclic guanosine monophosphate, renin activity (renin), angiotensin-II, aldosterone, and glomerular filtration rate.

RESULTS

Central venous pressure, systemic vascular resistance index, and pulmonary vascular resistance index were significantly lower in the hANP group than in the non-hANP group. The hANP group showed significantly higher levels of ANP, cyclic guanosine monophosphate, glomerular filtration rate, and respiratory index, and significantly lower levels of renin, angiotensin-II, aldosterone, and pleural effusion, as compared with the non-hANP group. The dosage of furosemide was significantly lower and the urine volume was significantly larger in the hANP group.

CONCLUSIONS

hANP can satisfactorily compensate for the shortcomings of CPB by decreasing the peripheral vascular resistance, suppressing the renin-angiotensin-aldosterone system, and exerting a strong diuretic effect.

Vasorelaxing effects of atrial and brain natriuretic peptides on coronary circulation in heart failure

Natriuretic peptide (NP) receptor has been postulated to be downregulated under a high concentration of atrial NP (ANP) in congestive heart failure (CHF), but limited information is available on how the vascular functional responsiveness to NPs is altered in coronary circulation during CHF. We assessed the relaxant effects of ANP, brain NP (BNP), and other vasodilators in isolated coronary arteries obtained from dogs with and without severe CHF induced by rapid right ventricular pacing. In CHF dogs, plasma ANP and cGMP concentrations were elevated compared with control dogs. In CHF arteries the relaxant effects of ANP and BNP (10(-8) and 10(-7) mol/l) were suppressed compared with control arteries. Nitroglycerin, nitric oxide, 8-bromo-cGMP, and beraprost sodium produced similar concentration-response curves in both arteries. The addition of 10(-7) mol/l ANP increased the level of tissue cGMP in control arteries, but not in CHF arteries. We conclude that there was a specific reduction in the relaxant effects of ANP and BNP in isolated coronary arteries in severe CHF dogs, which suggests the possibility of the downregulation of NP receptors coupled to guanylate cyclase.

Atrial natriuretic peptide attenuates pacing-induced myocardial ischemia during general anesthesia in patients with coronary artery disease

Atrial natriuretic peptide (ANP) exerts a dilatory effect on coronary arteries in humans. We investigated the effects of ANP on pacing-induced myocardial ischemia during enflurane anesthesia in patients with coronary artery disease (CAD). In 20 patients with CAD, myocardial ischemia was induced by atrial pacing before and after an i.v. infusion of ANP (50 mg x kg(-1) min(-1), n = 10) or placebo (n = 10). We studied the effects of ANP or placebo on pacing-induced changes in central hemodynamics, myocardial blood flow and regional myocardial indices of lactate uptake (RMLU), and oxygen consumption (RMVO2) and extraction (RMO2E). ST-segment depression was less pronounced during pacing with ANP compared with control pacing (-0.09 +/- 0.01 vs -0.24 +/- 0.02 mV; P < 0.001). RMLU decreased to -11.1 micromol/min during control pacing compared with -0.7 micromol/min during pacing with ANP (P < 0.01). ANP did not affect pacing-induced changes in RMVO2, RMO2E, or the rate pressure product. Placebo did not affect pacing-induced changes in ST-segment depression or RMLU. In conclusion, ANP attenuates ischemic ST-segment depression and lactate release during pacing-induced myocardial ischemia in patients with CAD. The antiischemic effect of ANP was not accompanied by any improvement in the regional myocardial oxygen supply/demand relationship.

IMPLICATIONS

We evaluated the effects of i.v. atrial natriuretic peptide (50 ng x kg(-1) x min(-1)) on pacing-induced myocardial ischemia during general anesthesia in patients with coronary artery disease. In contrast to placebo, atrial natriuretic peptide attenuated ST-segment depression and myocardial lactate production and improved left ventricular function during pacing-induced ischemia.

Serum N-terminal pro-atrial natriuretic factor 1-98 before and during thyroxine replacement therapy in severe hypothyroidism

Decreased plasma concentrations of atrial natriuretic factor (ANF) and of its N-terminal prohormones have been demonstrated in severely hypothyroid patients compared with control subjects, and shown to normalize with thyroxine (T4) replacement therapy. Whether this depends on thyroid hormone deficiency exclusively or is secondary to hemodynamic changes that result from it remains a matter of debate. In a recent investigation dose-related increases in both ANF and N-terminal prohormones of ANF by T4 replacement therapy in incremental doses increased at 4-week intervals were demonstrated. It was suggested that thyroid hormones may enhance synthesis rather than release of atrial peptide hormones. The aim of the present study was to confirm this assumption in hypothyroid patients with normal cardiac performance. Serum N-terminal amino acids 1-98 (ie, pro-ANF 1-98) of pro-ANF was determined in 11 severely hypothyroid patients without pericardial effusion and with normal cardiac left ventricular function. Mean pro-ANF 1-98 concentration before T4 replacement therapy remained unchanged after 10 days on T4 (p = .12). After 2 months of therapy, mean pro-ANF 1-98 was significantly increased compared with pretreatment values (p < .003). A significant correlation to the increase in free T4 (r = 0.48, p < .01) but not to the decrease in thyrotropin (TSH) (r = -0.32, p = .09) was found. The present results indicate that thyroid hormones directly increase pro-ANF 1-98 independently of cardiac hemodynamics in the hypothyroid state.

Myocardial circulatory and metabolic effects of atrial natriuretic peptide after coronary artery bypass grafting

The purpose of this study was to examine the effects of incremental infusion rates of human atrial natriuretic peptide (ANP), 25, 50, 100 ng.kg-1. min-1, on myocardial blood flow and metabolism (n = 10), and to compare the effects of ANP on these variables with those of equipotent infusion rates of sodium nitroprusside (SNP) (n = 9) 1-3 h after coronary artery bypass grafting (CABG). ANP induced a dose-dependent decrease in mean arterial blood pressure and systemic vascular resistance. There were no changes in cardiac index, heart rate, or cardiac filling pressures. ANP caused no changes in myocardial blood flow or its distribution, and caused no changes in myocardial oxygen extraction. Regional myocardial lactate uptake (RMLU) and extraction (RMLE) increased significantly (P < 0.05) at 50 ng.kg-1.min-1 (10.2 +/- 3.8 mumol/min and 8.2% +/- 3.0%, respectively) as compared to control (-1.1 +/- 3.0 mumol/min and -1.3% +/- 3.3%, respectively). RMLE and RMLU were significantly (P < 0.05) higher with ANP (5.7% +/- 2.5% and 6.8 +/- 3.7 mumol/min, respectively) compared to SNP (-1.5% +/- 2.1% and -0.1 +/- 3.7 mumol/min, respectively). We conclude that ANP has no dilatory effects on coronary vascular resistance vessels and thus lacks the potential to maldistribute flow, and that ANP improves myocardial lactate metabolism after CABG.

Plasma atrial natriuretic factor levels, impaired myocardial contractility and pain intensity in uncomplicated acute myocardial infarction

To investigate the relationship between plasma atrial natriuretic factor (ANF) levels, impaired myocardial contractility and pain intensity in acute myocardial infarction (AMI) we introduced a procedure estimating the pain component not influenced by the individual emotional reaction to stress, i.e., the original pain sensation. We deduced this pain component during AMI by correcting the personal report of AMI pain, quantified on a VAS, with the emotional reaction of each patient estimated by using a custom-built instrument which applies electrical stimuli of different intensities. Twenty-five patients with uncomplicated AMI were studied. According to plasma ANF levels and AMI pain values reported on the VAS, patients were categorized into 2 groups: pain and no-pain. Plasma ANF levels were significantly lower in pain (35.9 +/- 2.5 pg/ml) than in no-pain patients (70.8 +/- 3.3 pg/ml), whereas the ejection fraction (EF) was significantly higher in pain (49.6 +/- 1.7%) than in no-pain patients (29.3 +/- 1.9%). Within each group, a negative correlation was found between ANF and EF; the corresponding regression lines did not differ significantly in their slopes or intercepts, suggesting that AMI pain does not affect ANF release. The significant negative correlation between original pain sensation and EF found in pain patients indicates that this pain component may be useful to gauge the severity of impaired myocardial contractility during AMI. Moreover, the much higher plasma ANF levels observed in no-pain patients suggest that ANF may be involved in preventing AMI pain.

Control of coronary blood flow by autacoids

Coronary flow and thus myocardial perfusion is regulated by myogenic, metabolic, humoral and neuro-hormonal factors which closely interact with local autacoids released from the endothelial lining of the coronary bed. In a number of disease states an impaired synthesis and release of autacoids decisively limit the overall capacity of coronary regulation and adaptation of myocardial perfusion to increased metabolic demands. The important factors for these control mechanisms are analyzed and reviewed in this article.

Effects of brain (B-type) natriuretic peptide on coronary artery diameter and coronary hemodynamic variables in humans: comparison with effects on systemic hemodynamic variables

OBJECTIVES

This study attempted to clarify the effects of human brain (B-type) natriuretic peptide on coronary artery diameter and coronary vascular resistance in humans.

BACKGROUND

Brain natriuretic peptide induces vasodilation in systemic circulation by activating particulate guanylate cyclase of the vascular smooth muscle.

METHODS

In 13 patients with normal coronary arteries and left ventricular function, brain natriuretic peptide was infused at 0.5 microgram/kg body weight per min for 4 min into the left main coronary artery (six patients, Group A) or into the pulmonary artery (seven patients, Group B). Systemic hemodynamic variables and coronary sinus blood flow were measured before and after the infusion. The lumen diameter of the left coronary artery was quantitatively measured.

RESULTS

In both groups, brain natriuretic peptide significantly increased heart rate and decreased mean arterial pressure. Rate-pressure product remained unchanged in both groups. Brain natriuretic peptide decreased systemic vascular resistance index significantly in both groups (both p < 0.01 vs. baseline), and there was no difference in the effect between the groups. Brain natriuretic peptide decreased coronary vascular resistance in Group A (p < 0.01 vs. baseline) but did not affect coronary vascular resistance in Group B (p < 0.01 vs. Group A). The lumen diameters of the proximal and distal segments of the left coronary artery were increased significantly after brain natriuretic peptide in both groups. After infusion of brain natriuretic peptide, mean plasma level of brain natriuretic peptide in the coronary sinus increased from 36 to 130,411 pg/ml in Group A and from 64 to 12,329 pg/ml in Group B.

CONCLUSIONS

Brain natriuretic peptide shows a vasodilator effect on the coronary artery system in humans. However, the effect does not appear uniformly but is seen preferentially in the epicardial coronary artery. The sensitivity of the coronary resistance vessels to brain natriuretic peptide is low compared with that of the resistance vessels of the systemic circulation.

Suppression of hyperventilation-induced attacks with infusion of B-type (brain) natriuretic peptide in patients with variant angina

B-type (brain) natriuretic peptide (BNP) forms a peptide family with A-type (atrial) natriuretic peptide (ANP), which is involved in the regulation of blood pressure and fluid volume. We have demonstrated that BNP is a novel cardiac hormone secreted predominantly from the ventricle and that plasma levels of BNP markedly increase in proportion to the severity of congestive heart failure. Spasm of a major coronary artery (coronary spasm) is the cause of variant angina and can be induced by hyperventilation. We examined whether BNP infusion suppresses coronary spasm in patients with variant angina. The effect of BNP infusion on anginal attacks induced by hyperventilation was studied in 11 patients with variant angina in whom the attacks were reproducibly induced by hyperventilation. This study was performed in the early morning on 3 consecutive days. Fourteen minutes after infusion of BNP was begun (day 2, 0.05 micrograms/kg/min) or saline (days 1 and 3), hyperventilation was started and continued for 6 minutes. Anginal attacks were induced in all 11 patients by hyperventilation on days 1 and 3, respectively. Anginal attacks were not induced in any patient on day 2 (BNP infusion). Fourteen minutes after BNP infusion was begun, plasma BNP levels increased from 23.7 +/- 6.7 pg/ml to peak levels of 2591 +/- 255 pg/ml (p < 0.01) and plasma ANP levels increased from 28.9 +/- 7.5 pg/ml to peak levels of 69.2 +/- 13.2 pg/ml. Five minutes after BNP infusion was finished, plasma levels of cyclic guanosine monophosphate (cGMP) increased from 20.3 +/- 7.4 pg/ml to peak levels of 63.5 +/- 13.7 pg/ml (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression of hyperventilation-induced attacks with infusion of atrial natriuretic peptide in patients with variant angina pectoris

Atrial natriuretic peptide (ANP) is reported to dilate a major coronary artery in both experimental animals and humans. Spasm of a major coronary artery is the cause of variant angina pectoris and can be induced by hyperventilation. The effect of the ANP infusion on anginal attack induced by hyperventilation was studied in patients with variant angina pectoris. The study was performed in the early morning on 3 consecutive days in 11 patients with variant angina pectoris in whom the attacks were reproducibly induced by hyperventilation. On days 1 and 3 (saline solution infusion), and day 2 (ANP infusion), hyperventilation was started 14 minutes after beginning infusion of ANP (0.1 microgram/kg/min) or saline solution for 6 minutes. The attacks were induced in all 11 patients by hyperventilation on days 1 and 3. However, the attacks were not induced in any patient on day 2 of the ANP infusion. The plasma ANP level increased from 33 +/- 7 pg/ml to the peak level of 2,973 +/- 479 pg/ml (p < 0.01) at the end of the ANP infusion, and the plasma level of cyclic guanosine monophosphate (cGMP) increased from 5 +/- 1 pmol/ml to the peak level of 58 +/- 6 pmol/ml (p < 0.01) 5 minutes after the ANP infusion. The plasma levels of ANP and cGMP did not change after hyperventilation on days 1 and 3. It is concluded that the ANP infusion suppresses the attacks induced by hyperventilation in patients with variant angina pectoris, and cGMP is related to the mechanisms of suppression of the attacks.

Effects of alpha-human atrial natriuretic peptide in guinea-pig isolated heart

The aim of the present investigation has been to ascertain whether or not atrial natriuretic peptides (ANP) can exert a direct effect on myocardial contractility. Alpha-human ANP (alpha-hANP) concentrations ranging from 1 pM to 50 nM have been used to perfuse guinea-pig isolated hearts in a non-recirculating Langendorff apparatus. A dual concentration-related effect has been induced by alpha-hANP on myocardial function. A maximal increase of +LV dP/dtmax (+56%; P < 0.001) has been observed when guinea-pig hearts were perfused with 100 pM alpha-hANP, whereas a 25% decrease (P < 0.01) occurred with 50 nM alpha-hANP. Similar effects have also been induced by alpha-hANP on the coronary flow rate (CFR). A significant CFR increase (maximal at 10 pM alpha-hANP) was induced by picomolar concentrations of alpha-hANP, whereas a progressive decrease, which was maximal (-28%; P < 0.01) at 50 nM alpha-hANP, was observed with nanomolar concentrations of the peptide. No effects have been observed on heart rate. These results suggest that ANP has direct effects on both vascular and myocardial muscle cells. Coronary vasoconstriction induced by nanomolar concentrations of ANP can contribute to the cardiodepression, whereas ANP in picomolar concentrations can induce a coronary vasodilation which is not coupled with the enhanced myocardial contractility. The latter is the likely expression of a direct effect of the peptide on myocardial function.

ACE-inhibitors in coronary artery disease?

Angiotensin converting enzyme (ACE)-inhibitors are established in the treatment of arterial hypertension and heart failure. In recent years ACE-inhibitors have also been used in the treatment of patients with coronary artery disease (CAD), since from experimental data an antiischemic action of these agents is suggested. Antiischemic effects of ACE-inhibitors may be exerted through a reduction of myocardial oxygen demand, by a reduction of angiotensin-mediated coronary vasoconstriction, by an interaction with bradykinin and the prostaglandin system, by a modulation of endothelial control of vascular tone, and by an interaction with the sympathetic nervous system. However, clinical findings on potential beneficial effects of ACE-inhibitors in patients with CAD are inconsistent and controversial. While in hypertensive patients with CAD ACE-inhibitors generally seem to attenuate myocardial ischemia at rest and during exercise, a significant fraction of about 30% of normotensive patients with CAD does not benefit or even deteriorates. Lowering of coronary perfusion pressure and alteration of transmural blood flow distribution may be responsible for this. In patients with left ventricular dysfunction (SOLVD) or congestive heart failure (CONSENSUS, SOLVD) ACE-inhibitors have been proven to prevent progressive deterioration in left ventricular function and to reduce mortality. In patients with asymptomatic left ventricular dysfunction after myocardial infarction (SAVE), long-term administration of captropril was associated with an improvement in survival and reduced morbidity and mortality due to major cardiovascular events. Therefore, from a prognostic viewpoint patients with CAD and left ventricular dysfunction or congestive heart failure should be treated with ACE-inhibitors, although the clinical use of ACE-inhibitors in patients with ongoing angina pectoris may be limited by an aggravation of angina, presumably due to critically lowering coronary perfusion pressure. Finally, ACE-inhibitors failed to prevent restenosis after successful PTCA. In conclusion, from a prognostic viewpoint patients with CAD and congestive heart failure or left ventricular dysfunction should be treated with ACE-inhibitors. In hypertensive patients ACE-inhibitors generally seem to attenuate myocardial ischemia. In normotensive patients with CAD and angina pectoris but without left ventricular dysfunction ACE-inhibitors cannot generally be recommended at present, unless the patients, which may have benefit from ACE-inhibitor treatment can be better defined.

Atrial natriuretic factor: its (patho)physiological significance in humans

The first human studies using relatively high-doses of ANF revealed similar effects as observed in the preceding animal reports, including effects on systemic vasculature (blood pressure fall, decrease in intravascular volume), renal vasculature (rise in GFR, fall in renal blood flow), renal electrolyte excretion (rises in many electrolytes), and changes in release of a number of different hormones. Whether all these changes are the result of direct ANF effects or secondary to a (single) primary event of the hormone remains to be determined. Certainly, it has been proven that more physiological doses of ANF fail to induce short-term changes in many of these parameters leaving only a rise in hematocrit, natriuresis and an inhibition of the RAAS as important detectable ANF effects in humans. This leads us to hypothesize that ANF is a "natriuretic" hormone with physiological significance. The primary function in humans is to regulate sodium homeostasis in response to changes in intravascular volume (cardiac atrial stretch). Induction of excess renal sodium excretion and extracellular volume shift appear to be the effector mechanisms. The exact mechanism of the natriuresis in humans still needs to be resolved. It appears however, that possibly a small rise in GFR, a reduction in proximal and distal tubular sodium reabsorption, as well as an ensuing medullary washout, are of importance. The pathophysiological role of ANF in human disease is unclear. One may find elevated plasma irANF levels and/or decreased responses to exogenous ANF in some disease states. Whether these findings are secondary to the disease state rather than the cause of the disease remains to be resolved. Therapeutic applications for ANF, or drugs that intervene in its production or receptor-binding, seem to be multiple. Most important could be the antihypertensive effect, although areas such as congestive heart failure, renal failure, liver cirrhosis and the nephrotic syndrome cannot be excluded. Although the data that have been gathered to date allowed us to draw some careful conclusions as to the (patho)physiological role of ANF, the exact place of ANF in sodium homeostatic control must still be better defined. To achieve this, we will need more carefully designed low-dose ANF infusion, as well as ANF-breakdown inhibitor studies. Even more promising, however, is the potential area of studies open to us when ANF-receptor (ant)agonists become available for human use.

Differential regional expression of three natriuretic peptide receptor genes within primate tissues

The natriuretic peptide receptors are three homologous cell surface proteins, each with a single transmembrane domain. The atrial natriuretic peptide receptor type A (ANPRA) and the homologous receptor type B (ANPRB) are both membrane guanylyl cyclases that synthesize cyclic GMP as an intracellular second messenger. The third receptor in this family, the atrial natriuretic peptide receptor type C (ANPRC), is not coupled to cyclic GMP production. We report on the distribution of the ANPRA, ANPRB, and ANPRC mRNAs in rhesus monkey tissues assayed by in situ hybridization. ANPRA mRNA is most abundantly expressed in the kidney glomerulus, adrenal zona glomerulosa, pituitary, cerebellum, and endocardial endothelial cells of the right and left atrium and right ventricle. In contrast, abundant ANPRB expression appears to be confined to the adrenal medulla, pituitary, and cerebellum. ANPRC mRNA appeared to be expressed very differently than ANPRA and ANPRB. In the heart, ANPRC mRNA is expressed most prominently in endocardial endothelial cells of all four chambers but is also found throughout the myocardium only in the right atrium. These data identify major sites of natriuretic peptide receptor mRNA expression and suggest that there may be prominent cell type-specific differential distribution of these receptors in central and peripheral targets for the natriuretic peptides.

Differential regional expression of three natriuretic peptide receptor genes within primate tissues

The natriuretic peptide receptors are three homologous cell surface proteins, each with a single transmembrane domain. The atrial natriuretic peptide receptor type A (ANPRA) and the homologous receptor type B (ANPRB) are both membrane guanylyl cyclases that synthesize cyclic GMP as an intracellular second messenger. The third receptor in this family, the atrial natriuretic peptide receptor type C (ANPRC), is not coupled to cyclic GMP production. We report on the distribution of the ANPRA, ANPRB, and ANPRC mRNAs in rhesus monkey tissues assayed by in situ hybridization. ANPRA mRNA is most abundantly expressed in the kidney glomerulus, adrenal zona glomerulosa, pituitary, cerebellum, and endocardial endothelial cells of the right and left atrium and right ventricle. In contrast, abundant ANPRB expression appears to be confined to the adrenal medulla, pituitary, and cerebellum. ANPRC mRNA appeared to be expressed very differently than ANPRA and ANPRB. In the heart, ANPRC mRNA is expressed most prominently in endocardial endothelial cells of all four chambers but is also found throughout the myocardium only in the right atrium. These data identify major sites of natriuretic peptide receptor mRNA expression and suggest that there may be prominent cell type-specific differential distribution of these receptors in central and peripheral targets for the natriuretic peptides.

Rapid changes of atrial natriuretic peptide concentration during percutaneous transluminal coronary angioplasty

In 34 patients undergoing routine coronary angioplasty, concentrations of atrial natriuretic peptide (ANP), plasma renin (PR), and plasma aldosterone (PA) were estimated before, during, and after vessel occlusion and were correlated with hemodynamic changes. For the group as a whole, averaged right atrial pressure rose significantly (p less than 0.001) from 4.4 +/- 1.8 mm Hg at baseline to 6.7 +/- 3.0 mm Hg during vessel occlusion, and average right atrial ANP concentrations increased significantly (p less than 0.005) from 50.1 +/- 18.8 pg/ml to 59.7 +/- 21.4 pg/ml during balloon inflation. Data analysis of subgroups did not show any differences in right atrial pressure elevations between patients with left anterior descending artery (LAD) or right coronary artery (RCA) disease; ANP elevation was significant only in patients with LAD occlusion (p less than 0.001). In individual patients no statistically significant correlations were found to be present between changes in right atrial pressures and changes in atrial ANP concentrations. During vessel occlusion, PR dropped from 0.86 +/- 1.11 ng/ml/hr to 0.65 +/- 0.85 ng/ml/hr (p less than 0.001) in all patients, and PA decreased from 63.0 +/- 50.9 ng/ml to 52.2 +/- 43.4 ng/ml (p less than 0.01). Our data support the concept that, although an increase in right atrial pressure leads to ANP release in the majority of patients, atrial pressure and stretch are not the only regulatory factors of ANP release in humans.

Effects of inhibition of nitric oxide formation on basal vasomotion and endothelium-dependent responses of the coronary arteries in awake dogs

The role of nitric oxide in basal vasomotor tone and stimulated endothelium-dependent dilations in the coronary arteries in chronically instrumented awake dogs was studied by examining the consequences of inhibiting endogenous nitric oxide formation with the specific inhibitor of nitric oxide formation, NG-monomethyl-L-arginine (L-NMMA). In four awake dogs, coronary dimension crystals were chronically implanted on the circumflex artery for the measurement of epicardial coronary diameter, and Doppler flow probes were implanted for quantitation of phasic coronary blood flow (vasomotion of distal regulatory resistance vessels). Basal epicardial coronary diameter, acetylcholine-stimulated endothelium-dependent dilation, and flow-induced endothelium-dependent dilation of the epicardial arteries and phasic blood flow were recorded before, and after 5, 15, 50, and 120 mg/kg of L-NMMA. L-NMMA induced a dose-related increase in basal epicardial coronary vasomotor tone. There was an accompanying increase in aortic pressure and a decrease in heart rate. At doses greater than or equal to 50 mg/kg, rest phasic coronary blood flow was also decreased. Left ventricular end-diastolic pressure and contractility were not significantly changed. In contrast, the flow-induced or acetylcholine-stimulated endothelium-dependent responses were attenuated only after infusion of the highest does of L-NMMA (120 mg/kg). The changes in the basal vasomotor tone and acetylcholine-stimulated endothelium-dependent responses returned towards the control states in the presence of L-arginine (660 mg/kg). These data support the view that nitric oxide plays a significant role in modulating basal vasomotion and endothelial-dependent dilation stimulated by acetylcholine or increase in blood flow in epicardial coronary arteries and also influence the regulation of coronary blood flow during physiologic conditions.

Diproteverine (BRL 40015): a new type of calcium antagonist with potential antianginal properties

The calcium channel-blocking activity and associated cardiovascular effects of diproteverine, a novel compound derived from papaverine, were investigated. Electrophysiological measurements in sheep Purkinje fibres showed diproteverine to reduce the amplitude of the slow action potential (IC30 = 2 microM) and to shorten the duration of the fast action potential at 50% repolarisation (IC30 = 2.5 microM). Higher concentrations (4-5 times) were required to block block the sodium channel, as assessed by a reduction in Vmax of the fast action potential. Papaverine was found to possess marginal membrane channel-blocking activity and to be much more potent than diproteverine as a cAMP-phosphodiesterase inhibitor. The most significant haemodynamic property of diproteverine, seen in anaesthetised dogs and conscious dogs pretreated with atropine, was to cause a reduction in heart rate. This appeared to be a particular feature of diproteverine as the other calcium antagonists studied produced either a smaller decrease in heart rate or tachycardia as a reflex response to hypotension. In a chronic myocardial infarct model in dogs, diproteverine caused a redistribution of the available coronary blood flow, to the benefit of an ischaemic area of the myocardium. Diproteverine resembled diltiazem in its effects on coronary blood flow, with both these agents being preferable to nifedipine and verapamil, which caused coronary steal in this model. The combination of the reduction in heart rate, to lower cardiac oxygen demand, with the beneficial action on coronary blood flow should result in diproteverine being particularly beneficial for the treatment of angina pectoris.

Coronary hemodynamic effects of atrial natriuretic peptide in humans

Studies of the effects of atrial natriuretic peptide on the coronary circulation have yielded conflicting results in animals and have not been fully investigated in human subjects. To further characterize the direct coronary hemodynamic actions of atrial natriuretic peptide in humans and to assess the safety of its administration in patients with coronary artery disease, incremental doses of synthetic atrial natriuretic peptide and nitroglycerin were infused into the left coronary artery in 14 patients, 11 of whom had coronary artery disease. Both agents caused dose-related increases in total coronary sinus blood flow. The largest dose of atrial natriuretic peptide given to all patients (100 micrograms) increased mean coronary sinus blood flow from 127 +/- 7 to 149 +/- 9 ml/min (p less than 0.05) and decreased coronary vascular resistance from 0.93 +/- 0.07 to 0.81 +/- 0.05 mm Hg/ml per min (p less than 0.05); mean arterial blood pressure and heart rate were not affected by this dose of atrial natriuretic peptide. The greatest changes in coronary sinus blood flow (+25%) and coronary vascular resistance (-18%) after atrial natriuretic peptide administration occurred in the patients with coronary artery disease and no other associated cardiovascular disease. The maximal effects of atrial natriuretic peptide were similar to those of nitroglycerin, and no untoward effects were observed. Thus, atrial natriuretic peptide is a direct coronary vasodilator in humans. Its maximal dose effects are similar to those of nitroglycerin and were well tolerated in this small group of patients. The physiologic importance and therapeutic potential of atrial natriuretic peptide in patients with coronary artery disease merit further investigation.

Renal, hormonal, and hemodynamic effects of low-dose infusion of atrial natriuretic factor in acute myocardial infarction

The effects of low-dose infusion of atrial natriuretic factor (ANF; 3 pmol/kg/min; i.e., 10 ng/kg/min) were investigated in a single-blind, random-order, placebo-controlled study of 12 patients with uncomplicated acute myocardial infarction (MI). Compared with the placebo, ANF induced an increase in urine volume (p less than 0.05), sodium excretion (p less than 0.05), and chloride excretion (p less than 0.05). Urinary potassium and creatinine clearance were unchanged. The maximal response of urinary sodium excretion rate after ANF infusion was positively correlated with the basal sodium excretion rate (r = 0.579; p less than 0.05) and inversely correlated with basal plasma renin activity (r = -0.623; p less than 0.05). Furthermore, the plasma aldosterone concentration (PAC) after infusion of ANF was significantly decreased compared with the basal level. The maximal change in PAC was closely correlated with the basal PAC (r = -0.857; p less than 0.01). However, no significant effect on hemodynamic variables was detected with infusion of ANF. Although additional studies are needed to assess the clinical efficacy of ANF infusion in acute MI, our observations suggest that low-dose infusion of the peptide is potentially valuable, as either sole or adjunctive therapy, for the management of water-sodium retention in acute MI.