The vasodilator potency of atrial natriuretic peptide in man

Angiotensin receptor-neprilysin inhibitors: Comprehensive review and implications in hypertension treatment

Angiotensin receptor-neprilysin inhibitors (ARNIs) are a new class of cardiovascular agents characterized by their dual action on the major regulators of the cardiovascular system, including the renin-angiotensin system (RAS) and the natriuretic peptide (NP) system. The apparent clinical benefit of one ARNI, sacubitril/valsartan, as shown in clinical trials, has positioned the drug class as a first-line therapy in patients with heart failure, particularly with reduced ejection fraction. Accumulating evidence also suggests that sacubitril/valsartan is superior to conventional RAS blockers in lowering blood pressure in patients with hypertension. To decide whether to apply an ARNI to treat hypertension clinically, it is important to understand the potential properties of the drug in modulating multiple factors inside and outside the cardiovascular system beyond its effect on reducing peripheral blood pressure. In this context, ARNIs are distinct from preexisting antihypertensive medications in terms of the multiple actions of NPs in various organs and the pharmacological potential of neprilysin inhibitors to modulate multiple cardiac and noncardiac peptides. In particular, analysis of the clinical trials of sacubitril/valsartan implies that ARNIs can provide additional clinical benefits independent of their original purpose, including alleviation of glycemic control and renal impairment in patients with heart failure. Understanding the potential mechanisms of action of ARNIs will help interpret the relevance of their additional benefits beyond lowering blood pressure in hypertension. This review summarizes the comprehensive clinical evidence and relevance of ARNIs by specifically focusing on the potential properties of this new drug class in treating patients with hypertension.

Effects of a low salt diet on isolated systolic hypertension: A community-based population study

Evidence has shown that long-term sodium reduction can not only reduce blood pressure, but also provide cardiovascular benefits. To date, there is little evidence related to the effects of salt reduction on isolated systolic hypertension (ISH).A total of 126 hypertensive patients were divided into an ISH group (n = 51) and a non-ISH (NISH) group (n = 75). The members of each group were then randomly assigned to low sodium salt (LSSalt) or normal salt (NSalt) diets for 6 months. Their blood pressure was measured every 2 months. Serum plasma renin-angiotensin activity, blood biochemical assays and urinary measurements were determined at the baseline and at the end of the 6 months.At the end of the study, the mean systolic blood pressure (SBP) of the ISH LSSalt group had significantly decreased by 10.18 mm Hg (95% confidence interval (CI): 3.13 to 17.2, P = .006) compared with that of the ISH NSalt group, while the mean SBP only decreased by 5.10 mm Hg (95% CI: -2.02 to 12.2, P = .158) in the NISH LSSalt group compared with that of the NISH NSalt group. The mean diastolic blood pressure (DBP) had no significant differences in the ISH and NISH groups. No obvious renin angiotensin system activation was found after LSSalt intervention. Regarding the urinary excretion of electrolytes and blood biochemical assays, the LSSalt treatment had the same effects on the ISH group as on the NISH group.The present study showed that the SBP of ISH patients was significantly decreased with the LSSalt intervention, while neither the SBP of the NISH patients nor the DBP of either group were similarly decreased, which indicated that ISH patients were more sensitive to salt restriction.

Effects of Sacubitril/Valsartan (LCZ696) on Natriuresis, Diuresis, Blood Pressures, and NT-proBNP in Salt-Sensitive Hypertension

Salt-sensitive hypertension (SSH) is characterized by impaired sodium excretion and subnormal vasodilatory response to salt loading. Sacubitril/valsartan (LCZ696) was hypothesized to increase natriuresis and diuresis and result in superior blood pressure control compared with valsartan in Asian patients with SSH. In this randomized, double-blind, crossover study, 72 patients with SSH received sacubitril/valsartan 400 mg and valsartan 320 mg once daily for 4 weeks each. SSH was diagnosed if the mean arterial pressure increased by ≥10% when patients switched from low (50 mmol/d) to high (320 mmol/d) sodium diet. The primary outcome was cumulative 6- and 24-hour sodium excretion after first dose administration. Compared with valsartan, sacubitril/valsartan was associated with a significant increase in natriuresis (adjusted treatment difference: 24.5 mmol/6 hours, 50.3 mmol/24 hours, both P <0.001) and diuresis (adjusted treatment difference: 291.2 mL/6 hours, P <0.001; 356.4 mL/24 hours, P =0.002) on day 1, but not on day 28, and greater reductions in office and ambulatory blood pressure on day 28. Despite morning dosing of both drugs, ambulatory blood pressure reductions were more pronounced at nighttime than at daytime or the 24-hour average. Compared with valsartan, sacubitril/valsartan significantly reduced N-terminal pro B-type natriuretic peptide levels on day 28 (adjusted treatment difference: −20%; P =0.001). Sacubitril/valsartan and valsartan were safe and well tolerated with no significant changes in body weight or serum sodium and potassium levels with either treatments. In conclusion, sacubitril/valsartan compared with valsartan was associated with short-term increases in natriuresis and diuresis, superior office and ambulatory blood pressure control, and significantly reduced N-terminal pro B-type natriuretic peptide levels in Asian patients with SSH.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT01681576.

Vascular Effects of Natriuretic Peptides in Healthy Men

Background: Most effects of atrial (ANP) and B-type natriuretic peptide (BNP) result from stimulation of the guanylyl-cyclase type A receptor. Chronic elevation causes hyporesponsiveness to ANP, whereas BNP effects tend to be preserved, implying an additional pathway of action. We, therefore, investigated the hemodynamic effects of co-infusion of ANP, BNP, and, as a positive control acting on type B receptor, C-type natriuretic peptide (CNP). Furthermore, vascular responses to short and prolonged infusions were compared to investigate rapid hyporesponsiveness of guanylyl-cyclase type A receptor.

Methods: In 11 healthy volunteers, arterial response to continuous intra-arterial infusion of ANP (60 pmol/100 mL forearm tissue volume [FAV]/min) was assessed by venous occlusion plethysmography. Then, co-infusion of a similar dose of ANP, BNP, or CNP was administered in randomized order. Each infusion phase was followed by a washout period. Then, ANP was restarted, followed by co-infusion of one of the natriuretic peptides not yet infused. After a further washout period, ANP was restarted, followed by co-infusion of the natriuretic peptide not yet co-infused. In 6 subjects, infusion time was adjusted to plasma half-lives (5 times), and in the other 5 subjects, infusion time was 5 minutes.

Results: ANP alone caused the expected vasodilation from 2.7 ± 0.3 mL/min/100 mL FAV to 6.0 ± 0.9 mL/min/100 mL FAV ( P < .004). This response remained unchanged in the group that received short-term infusions (6.2 ± 0.8 mL/min/100 mL FAV to 6.6 ± 1.1 mL/min/100mL FAV) but was reduced over time in the group receiving longer-term infusions (6.5 ± 1.2 mL/min/100 mL FAV to 4.5 ± 0.7 mL/min/100mL FAV, P < .05; difference between groups P < .05). Co-infusions of ANP, BNP, and CNP caused minor additional vasodilation (mean 0.8 ± 0.2 mL/min/100ml FAV, P < .01), which did not differ between the different co-infused natriuretic peptides.

Conclusion: Our data provide evidence for rapid desensitization of the guanylyl-cyclase type A receptor in humans, but do not support the presence of a BNP-specific receptor.

Atrial natriuretic peptide and regulation of vascular function in hypertension and heart failure: implications for novel therapeutic strategies

Atrial natriuretic peptide (ANP) plays a pivotal role in modulation of vascular function and it is also involved in the pathophysiology of several cardiovascular diseases. We provide an updated overview of the current appraisal of ANP vascular effects in both animal models and humans. We describe the physiological implications of ANP vasomodulatory properties as well as the involvement of ANP, through its control of vascular function, in hypertension and heart failure. The principal molecular mechanisms underlying regulation of vascular tone, that is natriuretic peptide receptor type A/cyclic guanylate monophosphate, natriuretic peptide receptor type C, nitric oxide system, are discussed. We review the literature on therapeutic implications of ANP in hypertension and heart failure, examining the potential use of ANP analogues, neutral endopeptidase (NEP) inhibitors, ACE/NEP inhibitors, angiotensin receptor blocker (ARB)/NEP inhibitors, the new dual endothelin-converting enzyme (ECE)/NEP inhibitors and ANP-based gene therapy. The data discussed support the role of ANP in different pathological conditions through its vasomodulatory properties. They also indicate that ANP may represent an optimal therapeutic agent in cardiovascular diseases.

The brachial artery remodels to maintain local shear stress despite the presence of cardiovascular risk factors

OBJECTIVE

Under physiological conditions, arteries remodel in response to changes in blood flow to maintain local shear stress. Risk factors and developing atherosclerosis may be associated with maladaptive remodeling that produces relatively large arteries with low levels of shear stress. Recent studies have shown that the brachial artery and other peripheral arteries are enlarged in patients with risk factors and cardiovascular disease, and we tested the hypothesis that this finding represents maladaptive remodeling.

METHODS AND RESULTS

We measured brachial artery diameter and flow by ultrasound and calculated shear stress in a diverse cohort of 1583 subjects (age 53+/-17 years, 62% male, and 51% with coronary artery disease and/or peripheral arterial disease). In a stepwise linear regression model, age (P<0.001), gender (P<0.001), body mass index (P<0.001), hypertension (P=0.005), and hypercholesterolemia (P=0.02) were associated with larger brachial diameter. Older age was associated with lower shear stress (P<0.01), consistent with maladaptive remodeling. However, body mass index, hypertension, hypercholesterolemia, and prevalent atherosclerosis were associated with proportionate changes in blood flow and no difference in shear stress compared to reference groups, suggesting adaptive remodeling.

CONCLUSIONS

These findings suggest that enlargement of the brachial artery in the setting of obesity, hypertension, hypercholesterolemia, and atherosclerosis reflects adaptive remodeling. The results provide further support for the concept that arterial remodeling is an important homeostatic response that is maintained despite the presence of risk factors and developing atherosclerosis.

Hemodynamic and humoral effects of atrial natriuretic peptide on pulmonary circulation after cardiac surgery

PURPOSE

Human atrial natriuretic peptide (h-ANP) elicits biological effects such as natriuresis, diuresis, and vasodilation, and plays a role in regulating pulmonary circulation. We conducted this clinical study to define its role and elucidate its mechanisms.

METHODS

Twelve consecutive adult patients scheduled to undergo cardiac surgery with cardiopulmonary bypass (CPB) were prospectively selected for this study. After the completion of surgery, h-ANP was infused from the right atrium through a Swan-Ganz (S-G) catheter. Blood samples for measurement of ANP and cyclic guanosine monophosphate (cGMP), the second messenger of ANP, were drawn from the pulmonary artery (PA) through the S-G catheter and from the left atrium (LA) through the left atrial pressure line, before and after the infusion of h-ANP. Hemodynamic values were measured at the same time.

RESULTS

After the h-ANP infusion, the plasma levels of ANP were significantly lower in the LA than in the PA, whereas the plasma levels of cGMP were significantly higher in the LA than in the PA. The infusion of h-ANP decreased the mean PA pressure significantly, and the systolic PA pressure remarkably.

CONCLUSION

The infusion of h-ANP after cardiac surgery stimulates the secretion of cGMP from the pulmonary vascular bed and dilates the PA, thereby decreasing the PA pressure.

Atrial natriuretic peptide prevents diabetes-induced endothelial dysfunction

Atrial natriuretic peptide (ANP) exerts beneficial effects on the cardiovascular system in part by exerting antioxidant activity. Given that oxidant stress is a key cause of endothelial dysfunction in diabetes, we investigated whether ANP improves endothelial function in rats with diabetes. Rats were injected with streptozotocin (55 mg/kg iv) to induce type 1 diabetes or the citrate vehicle as controls (n=12). After 4 weeks the diabetic rats were treated with ANP (10 pmol/kg/min sc, n=12) or the antioxidant tempol (1.5 mmol/kg/day sc, n=11), both by osmotic minipump, ramipril (1 mg/kg per day in the drinking water) or remained untreated (n=11). After a further 4 weeks, anaesthetised rats were killed by exsanguination and the thoracic aortae collected for examination of vascular activity and measurement of superoxide generation. Diabetic rats showed elevated plasma glucose concentration (45+/-3 mM) compared to controls (10+/-1 mM) and this was not affected by ANP (43+/-3 mM), ramipril (41+/-2 mM) or tempol (43+/-2 mM). Endothelium-dependent relaxation ex vivo in response to acetylcholine was impaired in diabetic rats (Rmax=66+/-4%) compared to control rats (Rmax=94+/-1%) but treatment with ANP (Rmax=80+/-4%), ramipril (Rmax=88+/-2%) or tempol (Rmax=81+/-5%) significantly improved those responses. Relaxant responses to the endothelium-independent vasodilator sodium nitroprusside were enhanced by treatment of diabetic rats with ANP or ramipril and their combination; but not by tempol. Superoxide generation was significantly elevated in aorta from untreated diabetic rats (649+/-146% of control). In diabetic rats, superoxide generation was significantly attenuated by ANP (to 229+/-78%) or tempol (to 186+/-64%). This study demonstrates that ANP improves vascular oxidant stress in concert with endothelial function, independent of any effect on plasma glucose levels. These studies may lead to new therapies, based on natriuretic peptide and/or antioxidant approaches, for ameliorating the vascular complications of diabetes.

Systemic and renal effects of atrial natriuretic peptide in patients with heart failure treated with angiotensin-converting enzyme inhibitor or in acute saline solution loading

BACKGROUND

Our purpose was to study the effects of atrial natriuretic peptide (ANP) on cardiorenal functions when it is used to manage patients with heart failure who are receiving an angiotensin-converting enzyme inhibitor (ACEi) or in acute saline solution loading.

METHODS

Seventeen patients with mild to moderate heart failure were entered into protocol 1 or 2. Protocol 1 was ANP (30 ng/kg/min) infused before and after treatment with ACEi (n = 9). Protocol 2 was acute saline loading with or without coadministration of ANP (n = 8). In both protocols cardiorenal hemodynamics and urinary sodium excretion were assessed before and after each intervention.

RESULTS

Protocol 1: Although ANP infusion significantly increased urinary sodium excretion to a similar extent before and after ACEi treatment, the infusion increased the glomerular filtration rate (75 +/- 16 --> 82 +/- 15 mL/min, P <.05) and renal blood flow (390 +/- 123 --> 438 +/- 140 mL/min, P <.05) only before ACEi treatment. Protocol 2: Acute saline solution loading decreased plasma renin activity (P <.05) but did not affect ANP level. Coadministration of ANP with saline solution load enhanced the increase of urinary sodium excretion (75% +/- 34% increase) compared with the acute saline solution load alone (49% +/- 33% increase) (P <.05) but had no affect on renal hemodynamics.

CONCLUSIONS

When ANP is used in patients with mild to moderate heart failure who are on combined ACEi treatment or in acute saline solution loading, the vasodilatory effect of ANP is blunted while the natriuretic effect of ANP is preserved. The renin-angiotensin system seems to modulate the vasodilatory effect of ANP.

Long-term oestrogen therapy is associated with improved endothelium-dependent vasodilation in the forearm resistance circulation of biological males

1. The aim of the present study was to determine the effects of long-term oestrogen on resistance vessel reactivity in biological males. 2. Recent studies have demonstrated that long-term oestrogen therapy favourably alters the lipid profile and improves vasodilator function in the conduit arteries of biological males. Whether a similar benefit is exerted on the resistance circulation is not known. Therefore, we examined the effects of long-term oestrogen therapy on skeletal muscle resistance vessel function in biological males and the potential mechanisms by which it may exert its effects. 3. Forearm blood flow (FBF) and resistance were compared in 15 male-to-female transsexuals being prescribed oestrogen, with 14 age-matched healthy males, at rest and in response to the endothelium-dependent nitric oxide (NO) vasodilator acetylcholine (ACh), the endothelium-independent but NO-mediated vasodilator sodium nitroprusside (SNP), the endothelium-independent and non-NO-mediated vasodilator verapamil (VER) and the endothelium-independent vasoconstrictor phenylephrine (PE). 4. Basal blood flows were similar in the two groups. However, the male-to-female transsexuals had a significant upward and leftward shift in FBF responses to ACh compared with males, with a 52% increase in FBF responses at the highest dose of ACh used. Forearm blood flow in transsexuals rose from a mean (+/- SEM) baseline level of 3.02 +/- 0.25 to a maximum of 19.5 +/- 2.59 mL/min per 100 mL forearm tissue (compared with 3.24 +/- 0.41 and 9.43 +/- 1.97 mL/min per 100 mL forearm tissue, respectively, in males) with the highest dose of ACh (+2.73 micrograms/min per 100 mL; P < 0.0005). Forearm vascular resistance was also significantly reduced in transsexuals compared with males (P < 0.05). Vasodilator responses to SNP, VER and PE were similar in both groups. 5. There were no differences observed in total cholesterol and low-density lipoprotein-cholesterol levels. However, male-to-female transsexuals had 20% higher high-density lipoprotein-cholesterol levels compared with males (1.57 +/- 0.11 vs 1.26 +/- 0.08 mmol/L, respectively; P < 0.05) and 47% higher triglyceride levels (P < 0.005). Serum testosterone levels (an index of oestrogen therapy) was a predictor of responses to endothelium-dependent vasodilation (rs = -0.50; P < 0.01). 6. Long-term oestrogen therapy enhances endothelium-dependent vasodilation in the skeletal muscle microcirculation of biological males. The effects appear to be selective because endothelium-independent vasodilation and vasoconstriction are not altered.

Effects of physiological or pathological pressure load in vivo on myocardial expression of ET-1 and receptors

Endothelin (ET)-1 has potent positive inotropic and chronotropic activity in the heart and induces cardiac hypertrophy. The production of ET-1 in the heart is reported to be increased under some conditions. In normal circulation, the pressure load to the left ventricle (LV) is much greater than that to the right ventricle (RV). In this study, we investigated the gene expression of the myocardial ET-1 system (ET-1, ET(A) receptor, and ET(B) receptor) in the RV and LV of normal rats and also investigated these genes in hypertrophied RV due to pathological pulmonary hypertension (PH). Normal rats showed no differences between the RV and LV in the gene expression of either ET-1, ET(A) receptor, or ET(B) receptor in either the adult stage (11 wk old) or the neonatal stage (1 and 8 days old). On the other hand, the expression of both atrial natriuretic peptide (ANP) mRNA and B-type natriuretic peptide (BNP) mRNA was significantly greater in the LV than in the RV in adult rats. Gene expression of ET-1, ET(A) receptor, and ET(B) receptor in the RV was markedly higher in rats with monocrotaline-induced (pathological) PH than that in control rats. The expression of ANP mRNA and BNP mRNA in the RV was also markedly higher in the rats with PH. In conclusion, the data suggest that gene expression of the ET-1 system in the myocardium is not affected by physiological pressure load in either the adult stage or neonatal stage; however, it is enhanced by pathological pressure overload such as that in PH.

Immunohistochemical modifications of vasoactive neuropeptides and excitatory amino acids in the nervous tissue of the Mongolian gerbil after transient cerebral ischemia

Modifications in the tissue concentration of vasoactive peptides (Endothelin, Calcitonin Gene Related Peptide, Atrial Natriuretic Peptide) and excitatory amino acids (glutamate, aspartate) were found in the nervous tissue of Mongolian gerbils after transient cerebral ischemia which was induced by unilateral occlusion of the common carotid artery for 30 min 4 h. In fact, immunostaining for these peptides was more intense in the ischemic tissue: the greatest increases of tissue immunoreactivity were observed for Endothelin; smaller differences were found for Calcitonin Gene Related Peptide and Atrial Natriuretic Peptide. Immunostaining for Neuropeptide Y, another vasoactive neuropeptide, was virtually unchanged. Infarct areas, when present, contained numerous Endothelin-immunoreactive cell bodies. On the contrary, the same areas were completely void of glutamate- or aspartate-immunostained neurons, normally present in the correspondent regions of the control tissue. The present results suggest that severe cerebral ischemia is paralleled by an unbalance of local vasoactive factors. The predominance of vasoconstrictor action of Endothelin might play a major role in the irreversible damage, together with the excitotoxic effect of the extracellular accumulation of excitatory amino acids, probably due to a leakage from neuronal cell somata, as suggested by the disappearance of glutamate- or aspartate-immunostained neurons.

Cyclosporine A and control of vascular tone in the human forearm: influence of post-transplant hypertension

OBJECTIVE

The use of cyclosporine A after organ transplantation is associated with a high incidence of hypertension, but the underlying mechanisms for this process are not clear. We investigated the effects of blockade of basal release of endothelial nitric oxide and the effects of endothelium-independent and -dependent vasodilators and vasoconstrictors in patients treated with cyclosporine A after heart transplantation.

DESIGN

We measured blood pressure and forearm blood flow responses to brachial artery infusions of NG-monomethyl-L-arginine (L-NMMA), sodium nitroprusside, acetylcholine, norepinephrine and vasodilating and vasoconstricting doses of endothelin-1 in eight patients early (< 3 months) and in 11 patients late (> 18 months) after transplantation.

RESULTS

Diastolic blood pressure was higher late after transplantation, but calculated forearm vascular resistance was lower (P < 0.01). Thus, increased forearm vascular resistance does not contribute to the increase in blood pressure. The vasoconstrictor response to L-NMMA was similar in both groups but a reduced endothelium-dependent vasodilator response to acetylcholine was seen late after transplantation. However, impaired smooth muscle responsiveness to nitric oxide may have contributed to this finding, since the response to sodium nitroprusside tended to be reduced. Vasoconstrictor responses to norepinephrine and endothelin-1 were comparable but no vasodilation was seen with low doses of endothelin-1 late compared with early after transplantation (P < 0.05).

CONCLUSIONS

The findings in the forearm circulation question the concept of generalized increases in vasoconstrictor responses or a disturbance of tonic, basal release nitric oxide in the pathogenesis of cyclosporine-A-induced hypertension. Although the forearm vasodilator responses to the stimulation of endothelial nitric oxide production and release by acetylcholine, and to low doses of endothelin-1, were impaired, these findings could be explained by the increase in blood pressure rather than cyclosporine A itself.

Hemodynamic effect of amrinone depends on pretreatment vascular resistance in patients with evolving congestive heart failure: correlation between vascular resistance and neurohormonal activity

We investigated the hemodynamic effects of amrinone and assessed its effects on neurohormonal factors in 15 patients with evolving congestive heart failure with various origins. We serially determined the pulmonary and systemic vascular-resistance indices after amrinone infusion and examined the relation between changes in hemodynamic parameters and changes in concentrations of norepinephrine, atrial natriuretic peptide, angiotensin II, and endothelin-1 in the pulmonary capillary wedge region (PCWR) and in the peripheral veins. Amrinone significantly reduced pulmonary vascular-resistance index (PVRI; Wood x m2) in patients with high PVRI (> or =15) before the infusion, significantly reduced systemic vascular-resistance index (SVRI; Wood x m2) in patients with high SVRI (> or =50) before the infusion, and had little effect on vascular resistances in patients with low PVRI (<15) and low SVRI (<50). The reduction in PVRI was correlated with the reduction in the endothelin-1 level (r = 0.75) in the PCWR, and the reduction in SVRI with norepinephrine level (r = 0.70) in the peripheral veins. The angiotensin II level did not change throughout the study. These findings suggest that amrinone had selective hemodynamic effects on pulmonary and systemic circulations with neurohormonal effects, according to PVRI and SVRI before infusion.

Plasma atrial natriuretic peptide is elevated in patients with hypertrophic cardiomyopathy

STUDY OBJECTIVES

To determine if plasma levels of atrial natriuretic peptide are elevated in patients with hypertrophic cardiomyopathy and to determine the relationship of atrial natriuretic peptide to symptoms and echocardiographic indices of left ventricular structure and diastolic function in these patients.

DESIGN

A prospective study in which atrial natriuretic peptide was measured in peripheral venous plasma in 14 patients (age 44 +/- 14 years) with hypertrophic cardiomyopathy and 17 healthy controls. Echocardiography was performed in all cases and 30 controls to examine indices of left heart structure and function. All patients underwent clinical evaluation.

RESULTS

The concentration of atrial natriuretic peptide was significantly higher in patients with hypertrophic cardiomyopathy than controls, (17.86 +/- 8.72 vs. 6.22 +/- 3.26 pmol/l, P = 0.0001). Diastolic dysfunction was observed in 11 of 14 patients with hypertrophic cardiomyopathy. No correlation was demonstrated between atrial natriuretic peptide levels and the degree of diastolic dysfunction, septal or free wall thickness, left atrial size, degree of mitral regurgitation or New York Heart Association functional class.

CONCLUSIONS

Plasma levels of atrial natriuretic peptide are elevated in patients with hypertrophic cardiomyopathy but do not correlate with symptoms or echocardiographically-derived indices of left ventricular structure or diastolic function.

Influence of angiotensin converting enzyme inhibition on relation of atrial natriuretic peptide concentration to atrial pressure in heart failure

OBJECTIVE

To examine the relation between haemodynamics and atrial natriuretic peptide concentration during short term angiotensin converting enzyme inhibition.

DESIGN

Patients were randomly allocated to receive placebo or one of three doses of the angiotensin converting enzyme inhibitor ramipril.

SETTING

Cardiac units of two tertiary referral hospitals.

SUBJECTS

38 Patients with stable congestive heart failure caused by ischaemic heart disease.

METHODS

Data were collected over a 24 hour period and assessed with the aim of distinguishing between the haemodynamic effects on plasma concentrations of atrial natriuretic peptide and the direct effects of the study drug, vasopressin concentrations, and angiotensin converting enzyme activity.

RESULTS

Pulmonary capillary wedge pressure was the main predictor of the plasma concentration of atrial natriuretic peptide. A higher plasma concentration of this peptide with a given pulmonary capillary wedge pressure was found after 24 hours of treatment with 2.5 mg and 5 mg of ramipril. Plasma concentration of the active metabolite, change in arginine vasopressin concentration or degree of angiotensin converting enzyme inhibition did not significantly predict change in plasma concentration of atrial natriuretic peptide or in the ratio of atrial natriuretic peptide concentration to pulmonary capillary wedge pressure.

CONCLUSIONS

A gradual increase in plasma concentration of atrial natriuretic peptide with a given pulmonary capillary wedge pressure, occurs during short term high degree inhibition of angiotensin converting enzyme. The causative mechanisms are yet to be identified. Such a change in the relation between central haemodynamics and atrial natriuretic peptide concentration may contribute to the beneficial effects of angiotensin converting enzyme inhibition in patients with congestive heart failure due to ischaemic heart disease.

Diminished vascular response to inhibition of endothelium-derived nitric oxide and enhanced vasoconstriction to exogenously administered endothelin-1 in clinically healthy smokers

BACKGROUND

Smoking is a major risk factor for the development of atherosclerosis. Because endothelial dysfunction may be a marker for future atherosclerosis, we investigated the effects of smoking on endothelium-dependent control of vascular tone.

METHODS AND RESULTS

The effects of brachial arterial infusions of NG-monomethyl-L-arginine (L-NMMA), a nitric oxide synthesis inhibitor; sodium nitroprusside; endothelin-1; and norepinephrine on forearm blood flow (strain-gauge plethysmography) were compared in 29 long-term smokers and 16 nonsmokers. The acute effects of smoking on systemic hemodynamics, plasma catecholamines, and forearm vascular responses to these compounds were investigated in smokers only. Smokers did not differ from nonsmokers (n = 16) regarding the vascular effects of sodium nitroprusside (n = 13) or vasoconstriction due to norepinephrine and endothelin-1 (n = 16). Low-dose endothelin-1-induced vasodilation, believed to reflect endothelial prostacyclin or nitric oxide release, was absent in smokers (n = 16), and their increase of forearm vascular resistance (FVR) after L-NMMA (n = 13) was impaired (35.6 +/- 27.9% versus 118.8 +/- 43.2%, P < .001). Short-term smoking (n = 11) increased blood pressure, heart rate, and plasma epinephrine concentrations (P < .05 or less); enhanced endothelin-1-induced vasoconstriction (delta FVR, 457 +/- 192% versus 254 +/- 143%, P < .01); and decreased norepinephrine-induced vasoconstriction (P < .05), but had no effect on the other interventions.

CONCLUSIONS

Long-term smoking is associated with a diminished nitric oxide-dependent component of basal vascular tone and an impaired endothelium-dependent vasodilator response to low-dose endothelin-1 and short-term smoking enhances endothelin-1-induced vasoconstriction. Impaired endothelial control of vascular tone might reflect impairment of normal antiatherosclerotic endothelial functions in smokers, but the relevance of smoking-induced enhancement of endothelin-1 vasoconstriction remains to be determined.

Cardiorenal and neurohumoral effects of endogenous atrial natriuretic peptide in dogs with severe congestive heart failure using a specific antagonist for guanylate cyclase-coupled receptors

BACKGROUND

To elucidate the extent of the compensatory role of endogenous atrial natriuretic peptide (ANP) in severe congestive heart failure (CHF), we examined the changes in hemodynamics and neuroendocrine and renal functions after incremental administration of an ANP antagonist, HS-142-1 (HS), in dogs with CHF.

METHODS AND RESULTS

We assessed the effects of HS on the suppression of plasma and urinary cGMP levels as a marker of endogenous ANP activity in dogs without CHF. Bolus injections of 0.3 and 1.0 mg/kg HS reduced plasma cGMP levels to 77% and 60% and urinary cGMP excretion to 78% and 61% of the relevant control levels, respectively. Then the study was performed in dogs with CHF induced by chronic rapid ventricular pacing, and the plasma ANP level was sixfold higher than that in the controls. Hemodynamic, hormonal, and renal variables were determined both before and after subsequent incremental administration (0.3, 1.0, and 3.0 mg/kg every 30 minutes) of HS. HS lowered the plasma and urinary cGMP levels dose dependently to 32% and 37% of the control levels, respectively. Mean arterial, pulmonary capillary wedge, and right atrial pressures and cardiac output did not change significantly. However, plasma renin activity, aldosterone level, and norepinephrine level increased rapidly to 226%, 179%, and 252% of the control values, respectively. Urine flow rate and urinary sodium excretion were significantly inhibited, with no concomitant change in glomerular filtration rate or renal plasma flow.

CONCLUSIONS

These findings suggest that endogenous ANP contributes to the suppression of the activation of the renin-aldosterone system and sympathetic nervous activity and body fluid retention but that the vasodilative action of this peptide is attenuated in advanced CHF.

Acute effects of nitric oxide on left ventricular relaxation and diastolic distensibility in humans. Assessment by bicoronary sodium nitroprusside infusion

BACKGROUND

In isolated mammalian cardiomyocytes, papillary muscle preparations, and ejecting hearts, nitric oxide (NO) or other cyclic GMP-elevating interventions increase diastolic cell length and reduce peak contractile performance by hastening onset of myocardial relaxation. In the present study, the effect of NO on left ventricular (LV) relaxation and diastolic distensibility was investigated in humans.

METHODS AND RESULTS

The NO donor substance sodium nitroprusside was infused during cardiac catheterization in the global coronary bed of the LV of patients (n = 13) investigated for chest pain who were without evidence of obstructive coronary artery or other cardiac disease. Sodium nitroprusside was infused intracoronarily at a dosage (< or = 4 micrograms/min) that was previously shown to be devoid of systemic effects when infused into the brachial artery to investigate the reactivity of the forearm vascular bed. The effect of this global intracoronary infusion of the NO donor sodium nitroprusside was assessed by sequential LV angiograms and tip-micromanometer pressure recordings. During global intracoronary nitroprusside infusion, there was a decrease in heart rate from 78 +/- 11 to 76 +/- 12 beats per minute (P < .05), in LV peak systolic pressure from 161 +/- 18 to 146 +/- 18 mm Hg (P < .001), and in time to onset of LV relaxation (interval from Q wave on the ECG to LV dP/dtmin) from 432 +/- 36 to 419 +/- 36 milliseconds (P < .01). In 7 patients in whom adequate sequential LV angiograms could be obtained, LV end-diastolic volume increased from 158 +/- 34 to 165 +/- 40 mL (P < .05), whereas LV end-diastolic pressure fell from 18 +/- 5 to 12 +/- 3 mm Hg (P < .02), and in 5 of these 7 patients, a downward shift of the diastolic LV pressure-volume relation was observed. In 5 patients, a right atrial infusion of sodium nitroprusside was performed either before (n = 2) or after the global intracoronary infusion. The decrease in LV peak systolic pressure observed during right atrial infusion was significantly smaller (P < .01) than during global intracoronary infusion.

CONCLUSIONS

The present study reveals reduced LV pressure development, an LV relaxation-hastening effect, and improved LV diastolic distensibility during global intracoronary infusion of the NO donor substance sodium nitroprusside. These effects appeared to be unrelated to systemic vasodilation or to pericardial constraint and could be explained by a direct myocardial effect of NO, probably through activation of guanylyl cyclase to increase cyclic GMP or through modification of other cellular proteins.

Short-term effects of eating on vasoactive hormones and haemodynamics in patients with heart failure

OBJECTIVES

To investigate if eating can influence the measurements of vasoactive hormones or their relationship to important haemodynamic variables.

DESIGN

Haemodynamic variables and plasma concentrations of atrial natriuretic peptide (ANP), arginine vasopressin and angiotensin enzyme (ACE) activity were measured. During the 24-h study period the patients ate ordinary hospital meals and thus were studied both in the absorptive and post-absorptive phases.

SETTING

Two university hospitals in Sweden participated in the study.

SUBJECTS

Ten patients with heart failure, due to ischaemic heart disease.

INTERVENTION

Eating.

MAIN OUTCOME MEASURES

Change in haemodynamic variables and plasma concentrations of vasoactive hormones related to eating.

RESULTS

After a meal (absorptive phase) pulmonary capillary wedge pressure and plasma concentrations of ANP were significantly lower compared to the postabsorptive phase, 13 +/- 1.7 vs. 16 +/- 1.9 mmHg and 57 +/- 9.5 vs. 72 +/- 12.2 pmol l-1, respectively. The relationship between ANP and its main predictor, pulmonary capillary wedge pressure, was not altered during the study period. Plasma concentration of arginine vasopressin, ACE activity and mean right atrial pressure decreased with time and the cardiac index increased with time over the study period.

CONCLUSIONS

A meal may significantly influence plasma concentrations of ANP. Studies on vasodilator treatment and its interactions with ANP should take account of these basal fluctuations. The present data confirm previous reports on haemodynamic improvement during the first 24 h of supine cardiac catheterization in patients with heart failure, and add new information about decreasing concentrations of arginine vasopressin and ACE.

The effect of low and high sodium diets on plasma atrial natriuretic factor, the renin-aldosterone system and blood pressure in subjects with essential hypertension

OBJECTIVE

Increasing dietary sodium intake increases blood pressure in some subjects with essential hypertension. Atrial natriuretic factor (ANF) has a potential role in modifying these changes. The purpose of this study was to observe the blood pressure and plasma ANF responses to low and high sodium diets in subjects with essential hypertension to see if the plasma ANF and blood pressure responses were related.

DESIGN

An in-patient study of subjects taking their normal diet (day 1), a 12 mmol sodium diet for 6 days and a 250 mmol diet for 6 days.

PATIENTS

Seven men with essential hypertension.

MEASUREMENTS

Continuous 24 hour urine collections were analysed for sodium excretion. Blood pressure was recorded at 0900, 1205 and 1700 h on days 1, 7 and 13. Blood was taken at 0900 h (fasting supine overnight) and at 1200 h (after 2 hours erect posture) on the above days for plasma ANF, plasma renin activity (PRA) and serum aldosterone.

RESULTS

Urinary sodium excretion was (mean +/- SEM) 11 +/- 1 mmol on day 5 of the low sodium diet, and 294 +/- 17 mmol during the fifth day of the high sodium diet. Plasma ANF (supine and erect) was significantly lower (2.8 +/- 0.6, 1.6 +/- 0.2 pmol/l) on the low sodium diet when compared to the high sodium diet (8.6 +/- 2.4, 5.0 +/- 1.6 pmol/l (P < 0.05)). Supine and erect PRA and serum aldosterone were significantly higher on the low compared to the high sodium diet. Blood pressure responses were heterogeneous rather than bimodal. Mean arterial blood pressure was 107 +/- 3 mmHg on the low sodium diet and 111 +/- 4 mmHg on the high sodium diet (P < 0.05). Changes of blood pressure did not correlate with the changes of plasma ANF.

CONCLUSIONS

Failure of plasma atrial natriuretic factor to rise with increasing dietary sodium did not therefore determine the blood pressure response to the change in dietary sodium. No link was established between plasma atrial natriuretic factor response and sodium sensitivity.

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.

Electrophysiological effects of atrial natriuretic peptide on the cardiac conduction system in man

We assessed the effect of atrial natriuretic peptide (ANP) on electrophysiological parameters in man. Electrophysiological parameters were measured before, at 15, and at 30 minutes after the commencement of ANP or placebo infusions (six patients in each group). ANP levels were normal prior to infusion and rose with ANP to 159 +/- 43 pmol/L, but were stable during placebo infusion. No change in heart rate or blood pressure occurred in either group. ANP infusion resulted in significant falls in intraatrial conduction time (60 +/- 15 to 49 +/- 15 msec), PR interval (170 +/- 21 to 155 +/- 16 msec), right atrial effective refractory period (232 +/- 33 to 218 +/- 33 msec), and ventriculoatrial refractory period (452 +/- 148 to 393 +/- 183 msec) while no change was seen with placebo. We conclude that ANP infusion appears to affect atrial refractoriness and velocity of conduction and atrioventricular nodal refractoriness. However, the mechanism of action and clinical significance of this observation remain to be determined.

Comparative study of atrial peptides ANF (1-98) and ANF (99-126) as diagnostic markers of atrial distension in patients with cardiac disease

To evaluate the possible role of atrial natriuretic peptides ANF (1-98) and ANF (99-126) as diagnostic parameters of atrial distension, measurements of peptide levels were performed in 47 patients with chronic ischemic and/or left sided valvular heart disease. Plasma samples were drawn from the pulmonary artery (PA) and superior vena cava (SVC) during diagnostic right heart catheterization. Forty of the patients also underwent left heart haemodynamic measurements, and in 28 patients two dimensional echocardiography with determination of left atrial diameter was performed. Enhanced plasma concentrations of both peptides were observed with increasing severity of heart failure assessed by the NYHA classification. Mean plasma levels of both peptides were closely correlated to mean pulmonary artery pressure (ANF (1-98): n = 47, r = 0.69 (SVC)/r = 0.72 (PA), p < 0.0001; ANF (99-126): n = 46, r = 0.75 (SVC)/r = 0.68 (PA), p < 0.0001) and mean pulmonary capillary wedge pressure (ANF (1-98): n = 47, r = 0.69 (SVC)/r = 0.72 (PA), p < 0.0001; ANF (99-126): n = 46, r = 0.70 (SVC)/r = 0.64 (PA), p < 0.0001). Positive correlations were also obtained between peptide levels and mean right atrial pressure and left ventricular end-diastolic pressure. When patients with high right atrial pressures (n = 2) were excluded from analysis, a significant correlation was found between peptide levels and echocardiography assessed left atrial diameter. The present study demonstrates the close correlation between concentrations of both atrial peptides and cardiopulmonary haemodynamics in patients with chronic heart disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Possibility of downregulation of atrial natriuretic peptide receptor coupled to guanylate cyclase in peripheral vascular beds of patients with chronic severe heart failure

BACKGROUND

High levels of endogenous atrial natriuretic peptide (ANP) are thought to compensate the condition of patients with heart failure by reducing preload and afterload. However, recent reports have indicated that a high plasma ANP level is a prognostic predictor in patients with heart failure. Therefore, the role of endogenous ANP has not been clearly established in patients with heart failure.

METHODS AND RESULTS

The plasma ANP and cGMP levels were determined in the femoral artery and the femoral vein of 97 patients with chronic congestive heart failure (CHF). The plasma ANP level decreased significantly, whereas the plasma cGMP levels increased significantly from the femoral artery to the femoral vein. Among patients with mild CHF (n = 52), the plasma cGMP level correlated with the ANP level, and the calculated ANP extraction level also correlated with the calculated cGMP production in the peripheral circulation (r = 0.70, p < 0.001). In contrast, these correlations were not found in patients with severe CHF (n = 45). Among these patients, the plasma cGMP levels seemed to reach a plateau despite high levels of plasma ANP, and the molar ratio of cGMP production to ANP extraction in the peripheral circulation was significantly lower than in patients with mild CHF (36.7 +/- 9.5 versus 183 +/- 17, p < 0.001). In patients with acute severe CHF (n = 9) and those with mild CHF, patients who were administered exogenous ANP, plasma cGMP levels increased in proportion to those of plasma ANP without saturation.

CONCLUSIONS

These results indicate that downregulation of ANP receptors coupled to guanylate cyclase may occur in the peripheral vascular beds of patients with chronic severe CHF.

Treatment of intraoperative hypertension with enflurane, nicardipine, or human atrial natriuretic peptide: haemodynamic and renal effects

The purpose of this study was to assess the effects of the calcium entry blocker nicardipine and alpha human atrial natriuretic peptide (hANP) on antihypertensive and diuretic activity in hypertensive surgical patients. The site of the diuretic actions of these drugs along the nephron were also investigated by measuring the excretion rate of inorganic phosphate (PO4). Hypertension during gastrectomy was treated by increasing the concentration of enflurane, by nicardipine infusion (0.5-2.0 micrograms.kg-1 x min-1), or by hANP infusion (0.05-0.2 microgram.kg-1 x min-1) under general anaesthesia. Enflurane, nicardipine and hANP all decreased arterial pressure to the same extent. Urine flow, Na and PO4 excretion increased following the administration of nicardipine or hANP. Fractional distal reabsorption of sodium was suppressed from 89.7 +/- 2.8% to 82.1 +/- 5.0% by the hANP, but not by the nicardipine infusion. Creatinine clearance was increased by hANP infusion, but did not change in the nicardipine group. It is concluded that nicardipine and hANP can be used safely for the treatment of hypertension during surgery. Both drugs induced phosphaturic diuresis, but the site of action of the two drugs on the nephron may be different. Phosphate reabsorption is considered to occur largely in the renal proximal tubule, so that its appearance in the urine in increased quantities without the change of renal circulation in the nicardipine group suggests a proximal tubular action of this drug. However, the site of action of hANP in the kidney was not determined because GFR increased and distal sodium reabsorption was suppressed due to the drug infusion.

Maintenance of forearm vasodilator action of atrial natriuretic factor in congestive heart failure secondary to ischemic or idiopathic dilated cardiomyopathy

Infusions of atrial natriuretic factor (ANF) are frequently associated with attenuated natriuretic and diuretic responses in patients with congestive heart failure. However, ANF infusions result in systemic vasodilation, suggesting that end organ responsiveness to ANF may not be uniformly decreased. To determine if the vasodilator effects of ANF were altered in heart failure, strain-gauge plethysmography was utilized to measure forearm blood flow responses to the intraarterial infusion of ANF using a dose range that was low enough to avoid systemic effects. In 9 control subjects, ANF infusions of 0.5, 1.0, 2.0 and 4.0 micrograms/min/100 ml forearm volume significantly increased forearm blood flow from 3.21 +/- 1.71 to 5.69 +/- 3.14, 6.20 +/- 2.57, 6.64 +/- 2.53 and 6.97 +/- 2.49 ml/min/100 ml forearm volume, respectively (all p less than 0.01). In 7 patients with heart failure, ANF infusion significantly increased forearm blood flow from 2.19 +/- 0.98 to 3.18 +/- 1.70, 3.76 +/- 2.0 and 4.42 +/- 2.80 ml/min/100 ml forearm volume for the 0.5, 1.0 and 2.0 micrograms doses, respectively (all p less than 0.05). By analysis of variance, the forearm blood flow responses pooled over all doses were not significantly different between the 2 groups. At the 2.0 micrograms dose, the peak increase in forearm blood flow in normal subjects represented a 107% increase over baseline compared with a 102% increase in patients with heart failure. In summary, these data demonstrate that intraarterial administration of ANF in patients with heart failure resulted in dose-related increases in forearm blood flow. The responses were not significantly different from normal subjects expressed both as an absolute response and as a percent increase.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Reversal of endothelin-1-induced vasoconstriction by nifedipine in human resistance vessels in vivo in healthy subjects

The influence of blockade of voltage-operated calcium channels by nifedipine on endothelin-1-induced vasoconstriction was investigated in 10 healthy volunteers. Brachial artery infusions of nifedipine (0.25, 0.5, 1 and 3 micrograms/min/100 ml forearm tissue) resulted in dose-dependent increases (mean +/- SD) in forearm blood flow (103 +/- 63% to 833 +/- 426%). Intraarterial infusions of endothelin-1 (50 ng/min/100 ml) resulted in transient increases in forearm blood flow (2.6 +/- 0.9 vs 3.9 +/- 2.0 ml/min/100 ml, p less than 0.01) in the first minute of infusion and subsequent decreases (to 1.0 +/- .5 ml/min/100 ml, p less than 0.01) in the third minute of infusion. Endothelin-1-induced vasoconstriction was reversed by the lowest dose of nifedipine, whereas the higher dosages of nifedipine further increased forearm blood flow to 12.5 +/- 6.4 ml/min/100 ml. The percent increase of forearm blood flow during co-infusion of endothelin-1 and the highest dosage of nifedipine was significantly greater compared with nifedipine alone (1,204 +/- 531% vs 833 +/- 426%, p less than 0.05). The results demonstrate a dual action of luminally applied endothelin-1 in human resistance vessels in vivo (e.g., transient initial vasodilation followed by pronounced vasoconstriction) and suggest that blockade of voltage-operated calcium channels can effectively counteract the vasoconstrictor effects of endothelin-1.

Transient myocardial ischemia stimulates atrial natriuretic factor release

Atrial natriuretic factor release during transient myocardial ischemia was investigated in 29 patients with coronary artery disease and symptoms of angina (Canadian Cardiovascular Association classes II-III). Eleven patients (group I) underwent single-vessel percutaneous transluminal coronary angioplasty. Repeat determinations of mean pulmonary artery wedge pressure and blood sampling from pulmonary artery for atrial natriuretic factor measurements were performed at baseline, and at 2, 5, and 15 minutes after percutaneous transluminal coronary angioplasty was begun. Baseline atrial natriuretic factor levels (34.6 +/- 4.5 pg/ml) rose to 56.3 +/- 7.3 pg/ml (p = 0.02) and decreased at 5 minutes (43.7 +/- 5.7 pg/ml, not significant) and 15 minutes (35.3 +/- 4.4 pg/ml, not significant). Changes in atrial natriuretic factor concentrations were significantly correlated with those in mean pulmonary artery wedge pressure (2 minutes: r = 0.69, p = 0.02; 5 minutes: r = 0.90, p less than 0.001). In group II (n = 10) the increase in atrial natriuretic factor after dye load occurred later (baseline: 25.8 +/- 2.1; 60 minutes: 40.6 +/- 2.6 pg/ml; p = 0.005) than that observed in group I after percutaneous transluminal coronary angioplasty. In group III, atrial natriuretic factor during angina rose as early (baseline 11.3 +/- 1.3; 5 minutes: 20 +/- 2.3 pg/ml; p = 0.006) as after percutaneous transluminal coronary angioplasty. Results indicate that transient myocardial ischemia stimulates atrial natriuretic factor release, probably through changes in cardiac function.

Coronary vasodilatation and improved myocardial lactate metabolism after angiotensin converting enzyme inhibition with cilazapril in patients with congestive heart failure

The effects of angiotensin converting enzyme inhibition on systemic and coronary hemodynamics and on myocardial lactate metabolism were investigated before and 2 and 6 hours after cilazapril at rest and during supine submaximal exercise in 10 patients with New York Heart Association class II or III chronic congestive heart failure. Angiotensin converting enzyme inhibition, indicated by a significant increase in plasma renin activity, resulted in significant reductions in blood pressure and systemic vascular resistance. Myocardial oxygen demand decreased (resting double product 10.9 +/- 3.7 vs 12.2 +/- 3.8 mm Hg beats/min 10(-3); p less than 0.05), but coronary sinus blood flow remained unchanged and calculated coronary resistance decreased (0.45 vs 0.5 units, rest 6 hours; p less than 0.05) suggesting coronary vasodilatation. Changes in coronary vascular resistance were directly related to changes in systemic vascular resistance (r = 0.75, p less than 0.5). Myocardial lactate extraction increased at rest (47 +/- 60 vs 134 +/- 132 mumol/min; p less than 0.5) and during exercise (27 +/- 54 vs 491 +/- 317 mumol/min; p less than 0.05) both in patients with coronary artery disease (n = 5) and idiopathic dilated cardiomyopathy (n = 5). Resting lactate production was converted to lactate extraction in two patients with coronary artery disease. Neither plasma catecholamine nor atrial natriuretic peptide concentrations changed significantly. The results suggest coronary vasodilation and improved aerobic myocardial metabolism by angiotensin converting enzyme inhibition in patients with congestive heart failure.

Failure of atrial natriuretic factor to increase with saline load in patients with dilated cardiomyopathy and mild heart failure

To investigate whether the response of atrial natriuretic factor (ANF) to volume expansion is impaired in the early stages of dilated cardiomyopathy, the effects of saline load (SL; 0.25 ml/kg.min for 120 min) were assessed in 12 patients with dilated cardiomyopathy and asymptomatic to mildly symptomatic heart failure (HF) and in nine normal subjects (N). SL increased plasma ANF levels in N (from 14.3 +/- 2 to 19.5 +/- 3 and 26 +/- 4 pg/ml, at 60 and 120 min, respectively, P less than 0.001), but not in HF (from 42.9 +/- 9 to 45.9 +/- 9 and 43.9 +/- 8 pg/ml). Left ventricular end-diastolic volume (LVEDV) and stroke volume were increased (P less than 0.001) by SL in N but not in HF. Urinary sodium excretion (UNaV) increased in N more than in HF during SL, whereas forearm vascular resistance (FVR) did not change in N and increased in HF (P less than 0.001). In five HF patients SL was performed during ANF infusion (50 ng/kg, 5 ng/kg.min) that increased ANF levels from 37.1 +/- 10 to 146 +/- 22 pg/ml. In this group, SL raised both LVEDV (P less than 0.01) and ANF (P less than 0.05), whereas FVR did not rise. In addition, the UNaV increase and renin and aldosterone suppressions by SL were more marked than those observed in HF under control conditions. Thus, in patients with dilated cardiomyopathy and mild cardiac dysfunction, plasma ANF levels are not increased by volume expansion as observed in N. The lack of ANF response is related to the impaired cardiac adaptations. The absence of an adequate increase of ANF levels may contribute to the abnormal responses of HF patients to saline load.

Plasma levels of atrial natriuretic peptide at rest and during exercise in heart failure--influence of cardiac rhythm and haemodynamics

The relationship between plasma levels of immunoreactive atrial natriuretic peptide (ir-ANP), arginine vasopressin (AVP), cardiac rhythm and different haemodynamic variables were studied at rest and during exercise in 16 patients with heart failure undergoing heart catheterization for clinically indicated reasons. Even though there was no significant relationship between pulmonary capillary wedge pressure (PCW) and ir-ANP at rest (r = 0.39; P = 0.14) changes in these variables with exercise correlated well (r = 0.71; P = 0.002). Change in right atrial mean pressure, heart rate, mean arterial blood pressure or cardiac index did not significantly influence change in plasma levels of ir-ANP. The correlation between PCW and AVP at rest (r = 0.92; P less than 0.001) disappeared during exercise. Calculated ir-ANP/PCW ratios decreased slightly during exercise, but were not influenced by initial atrial pressures or atrial fibrillation. These observations provide evidence for a similar responsiveness of ANP in patients with sinus rhythm and atrial fibrillation. The ability of rapid change in ANP plasma levels during exercise was preserved and proportional to changes in PCW over a wide pressure range in the studied patient group. This finding indicates that left atrium distension rather than right atrium distension is the major determinant for the release of ANP in patients with congestive heart failure. The observed rapid responsiveness of ANP to change in left atrial pressure may allow the hormone to modulate haemodynamic response during short periods of exercise.

Endothelin-1-induced vasoconstriction in humans. Reversal by calcium channel blockade but not by nitrovasodilators or endothelium-derived relaxing factor

The vascular effects of endothelin-1 (ET) in humans were investigated by brachial artery infusions of ET into 25 healthy volunteers. Forearm blood flow increased from a mean +/- SD value of 2.3 +/- 1.5 to 2.5 +/- 1.5 ml/min/100 ml forearm tissue (n = 25, p less than 0.05) in response to low dose (0.5 ng/min/100 ml forearm tissue) ET infusion and decreased to 1.78 +/- 1.3 and 1.1 +/- 0.9 ml/min/100 ml forearm tissue (p less than 0.001) during higher dosages (25 and 50 ng/min/100 ml forearm tissue). Sodium nitroprusside (0.6 micrograms/min/100 ml forearm tissue, n = 6), acetylcholine (16 micrograms/min/100 ml forearm tissue, n = 7), nifedipine (6 micrograms/min/100 ml forearm tissue, n = 6), and verapamil (80 micrograms/min/100 ml forearm tissue, n = 6) were infused alone and in combination with ET to evaluate the interactions between ET-induced vasoconstriction and stimulation of vascular muscle cyclic GMP levels by sodium nitroprusside, release of endothelium-derived relaxing factor by acetylcholine, and blockade of voltage-operated calcium channels by nifedipine and verapamil. Neither the vasodilator nor the vasoconstrictor response to ET was influenced by sodium nitroprusside or acetylcholine. In contrast, both calcium antagonists converted ET-induced vasoconstriction (e.g., delta forearm vascular resistance to ET 50 ng/min/100 ml forearm tissue, 151 +/- 100% and 164 +/- 92% in verapamil and nifedipine groups, respectively) to vasodilation (-35 +/- 12% and -21 +/- 16%, p less than 0.05). Our results demonstrate both ET-induced vasodilation (at low dosages) and vasoconstriction (at high dosages) in resistance vessels of normal humans. Blockade of voltage-operated calcium channels prevented ET-induced vasoconstriction and unmasked the vasodilator effect of high ET dosages. In human resistance vessels, blockade of voltage-operated Ca2+ channels but not cyclic GMP-dependent vasodilation may be an effective tool to inhibit ET-induced vasoconstriction.

Renal and hormonal effects and tolerance of an ANP analogue in healthy man

The effect of an analogue of atrial natriuretic peptide (P-ANP) on glomerular filtration rate (GFR), renal plasma flow (RPF), urinary flow rate, urinary sodium excretion, tubular function estimated by the lithium clearance technique, and plasma levels of sodium and water homeostatic hormones, has been studied in 40 healthy males. Placebo or P-ANP 0.3, 1.5, or 3.0 micrograms.kg-1 bwt were given as an intravenous bolus injection to different groups. P-ANP did not cause any immediate change in GFR or RPF, but significant dose-dependent increases in filtration fraction, urinary flow rate and urinary excretion rate of sodium were detected during the first 30 min after administration. Proximal absolute and fractional tubular reabsorption and distal absolute tubular reabsorption of sodium did not change after injection of P-ANP, while the distal fractional reabsorption of sodium was reduced in a dose dependent manner during the first 30 min. Plasma angiotensin II and aldosterone were significantly increased 30 and 150 min after dosage, whereas plasma atrial natriuretic peptide, plasma arginine vasopressin, and urinary excretion of prostaglandin E2 were unchanged. Cyclic guanosine monophosphate both in plasma and urine were increased in a dose-dependent manner. P-ANP cause a significant reduction in diastolic blood pressure and an increase in pulse rate. Two subjects had vasovagal syncope 30-60 min after injection of P-ANP. It is concluded that P-ANP has natriuretic, diuretic and hypotensive properties in healthy man.

Mechanisms involved in the response to prolonged infusion of atrial natriuretic factor in patients with chronic heart failure

We examined the mechanisms involved in the cardiovascular and renal response to prolonged infusion of atrial natriuretic factor (ANF) in patients with chronic heart failure. ANF infusion was titrated to produce a 30% decrease in pulmonary capillary wedge pressure or a 20% increase in cardiac output, and this dose (average, 75 +/- 4 ng/kg/min) was then administered for 20 hours. The short-term response to ANF included significant reductions in central filling pressures, increases in cardiac output, modest increases in diuresis and glomerular filtration rates, significant reduction in plasma aldosterone levels, and a 3.6-fold increase in plasma cyclic GMP levels. During prolonged infusion, plasma cGMP levels and cardiac output gradually returned to baseline. Similarly, the initially increased diuretic effects were completely abolished during prolonged ANF infusion, although plasma alpha-hANF levels remained consistently elevated above baseline values (control, 198 +/- 38; titration, 2,760 +/- 596; 20 hours, 3,499 +/- 659 pg/ml). Four hours after beginning the ANF infusion, marked increases in hematocrit levels were noted (42.5 +/- 1.0% versus 45.3 +/- 1.4%, control and infusion, respectively, p less than 0.05); during this time, no change in total plasma protein concentration occurred, indicating extravascular shift of fluid and plasma proteins. No evidence was noted for activation of vasoconstrictor hormones during prolonged ANF infusion, although mean arterial pressure was significantly reduced throughout the infusion period. Plasma pro-ANF (31-67) levels, determined as a marker for endogenous ANF secretion, were significantly suppressed as were the reductions of central filling pressures. After ANF discontinuation, heart rate and pulmonary capillary wedge pressure increased significantly above baseline values without evidence for sympathetic stimulation. We conclude that 1) prolonged infusion of ANF causes only transient increases in plasma cGMP levels but a sustained reduction of the cardiac release of ANF and that 2) the beneficial hemodynamic effects of ANF, that is, unloading of the ventricles, may be associated with or, in part, may be secondary to a shift of plasma constituents into the extravascular space. The latter may limit the therapeutic potential of ANF for long-term treatment.

Atrial natriuretic factor as a vasodilator agent in hypertensive patients

To investigate the role of Atrial Natriuretic Factor (ANF) in modulating arteriolar tone in hypertension, a synthetic 25 AA human ANF-analogue (anaritide) was infused intraarterially in the forearm vascular bed of five patients with mild hypertension. A dose-dependent increase in blood flow (plethysmographic technique) was seen at rates covering a thousand-fold range (0.008, 0.08, 0.8, 8.0 micrograms/dl tissue/min x 15 minutes each). At the lowest infusion rate, the forearm blood flow increment was associated with changes in local venous ANF concentrations comparable with those reported during biological stimuli in hypertensive man and consistent with an ANF physiologic role in forearm arterioles of hypertensive patients. However, at local venous concentrations greater than 1000 pg/ml, ANF did not relax forearm vessels by more than about one-fourth of the total forearm vasodilator capacity (as assessed through a maximally active ischemic stimulus). These data confirm the low potency of ANF as an endogenous vasodilator, although vasodilator potency is not a necessary requirement for physiologic systems involved in the regulation of muscular vascular tone. Systemic arterial pressure, heart rate, and contralateral flow did not change during the study in spite of the markedly increased peripheral ANF levels recirculating from the local forearm administration. This behavior indicates that arteriolar vasodilation is apparently not the main mechanism of action of ANF on systemic hemodynamics in hypertensive patients.

Attenuated forearm vasodilative response to intra-arterial atrial natriuretic peptide in patients with heart failure

It has been shown that renal responses to atrial natriuretic peptide (ANP) are markedly attenuated in patients with heart failure. This study aimed to determine if vasodilative response to ANP is altered in patients with heart failure. In patients with heart failure (n = 7) and age-matched normal subjects (n = 7), forearm blood flow was measured using a strain-gauge plethysmograph during intra-arterial infusion of alpha-human ANP (50, 100, 200, and 400 ng/min) or nitroglycerin (100, 200, 400, and 600 ng/min). Forearm vasodilatation evoked with intra-arterial alpha-human ANP in patients with heart failure was considerably less (p less than 0.01) than that in normal subjects. In contrast, nitroglycerin produced comparable forearm vasodilatation in the two groups. Plasma ANP and cyclic guanosine monophosphate (GMP) levels at rest were higher in patients with heart failure than in normal subjects (p less than 0.05 for both), but the increases in plasma ANP and cyclic GMP in the venous effluents during intra-arterial ANP infusion did not differ between the two groups. These results indicate that the direct vasodilative effect of ANP on forearm vessels was attenuated in patients with heart failure as compared with that in normal subjects. The mechanisms responsible for this alteration are not clear but might involve mechanisms other than down-regulation of the ANP receptors because the increases in venous plasma cyclic GMP caused by intra-arterial ANP were comparable between patients with heart failure and normal subjects.

Different effects of alpha-human atrial natriuretic peptide and nitroglycerin on cardiac dimensions in humans

This study aimed to examine whether alpha-human atrial natriuretic peptide (alpha-hANP) alters cardiac dimensions in humans. Left atrial (LA) and left ventricular diastolic (LV) diameters were measured by echocardiography at control and with lower body negative pressure (LBNP) at -10 and -20 mmHg during intravenous (IV) infusion of saline or alpha-hANP at a dose of 0.03-0.04 microgram/kg per minute (n = 8). Studies were also done during IV infusion of saline or nitroglycerin (NG) at a dose of 10-15 micrograms/kg per minute in another group of subjects (n = 6). LBNP decreased central venous pressure (CVP) and the LA and LV diameter. alpha-hANP lowered CVP at rest and with LBNP at -10 and -20 mmHg compared with corresponding values during saline infusion; NG produced comparable decreases in CVP, which suggests that decreases in venous return caused by the two drugs were similar. However, NG decreased, but alpha-hANP did not alter the LA and LV diameter at rest or with LBNP. In another group of subjects (n = 4), we observed that alpha-hANP caused comparable decreases in CVP and pulmonary capillary wedge pressure. These data suggest that ANP may dilate the cardiac chambers in humans.

Sympathoinhibitory effects of atrial natriuretic factor in normal humans

In rats, atrial natriuretic factor (ANF) reduces sympathetic nerve activity (SNA) reflexively by sensitizing cardiac mechanoreceptors with inhibitory vagal afferents. We performed three series of experiments in 26 normal young men to document whether ANF inhibits SNA in humans and if so, to determine potential mechanisms for this phenomenon. First, we recorded muscle SNA before and during brief infusions of ANF, vehicle (saline solution), and sodium nitroprusside, titrated to achieve reductions similar to those produced by ANF in diastolic pressure and central venous pressure, and we also assessed the effect of ANF on sympathetic nerve responses to a cold pressor test (CPT). Second, we determined the effect of ANF on Doppler-derived measurements of cardiac output and responses to hypotensive (-40 mm Hg) lower-body negative pressure (LBNP) and its sudden cessation. Third, we applied nonhypotensive (-15 mm Hg) LBNP to selectively unload cardiopulmonary baroreceptors, and we released LBNP to stimulate these inhibitory afferents during sequential infusions of nitroglycerin, vehicle (saline solution), and ANF. Our key findings were that 1) reductions in arterial and central venous pressures during ANF infusion were not accompanied by anticipated reflex increases in muscle SNA; 2) ANF blunted the increase in SNA with CPT; 3) ANF increased stroke volume and cardiac output; and 4) sympathoneural responses to both the application and the sudden cessation of nonhypotensive LBNP were attenuated, not augmented, by ANF. Changes in plasma norepinephrine concentrations reflected these sympathetic nerve responses to ANF. These results do not support the concept that ANF inhibits sympathetic outflow reflexively in humans by increasing discharge from cardiac mechanoreceptors with inhibitory vagal afferents but are consistent with either a central or a ganglionic sympathoinhibitory action of ANF. ANF could facilitate hypotension and natriuresis in humans by attenuating the reflex sympathetic response to baroreceptor deactivation.

Indirect evidence for release of endothelium-derived relaxing factor in human forearm circulation in vivo. Blunted response in essential hypertension

In isolated blood vessels, acetylcholine releases endothelium-derived relaxing factor (EDRF). In vivo, the vasodilator action of acetylcholine may be mediated by EDRF, but prostacyclin or prejunctional inhibition of adrenergic neurotransmission may also be involved. Therefore, we investigated whether acetylcholine releases EDRF in humans in vivo and, if so, whether the response altered in essential hypertension. Acetylcholine was infused into the brachial artery, and forearm blood flow measured by venous occlusion plethysmography. In control subjects, acetylcholine (0.02-16 micrograms/min/100 ml tissue) increased flow from 2.4 +/- 5.0 to 20.6 +/- 5.2 ml/min/100 ml tissue (n = 14; p less than 0.05) and decreased forearm vascular resistance from 42.0 +/- 4.1 to 6.0 +/- 1.4 units (p less than 0.03), a response comparable to that of sodium nitroprusside (0.6 micrograms/min ml tissue). Acetylsalicylic acid (500 mg i.v.) given to block vascular prostacyclin production did not alter the response (n = 14). alpha-Adrenoceptor blockade by phentolamine (12 micrograms/min/100 ml tissue) did not prevent the increase in flow evoked by acetylcholine. In hypertensive patients, the decrease in forearm vascular resistance induced by acetylcholine but not evoked by sodium nitroprusside was reduced as compared with controls (14.5 +/- 3.1 and 6.1 +/- 1.6 units, respectively; n = 8; p less than 0.05). Thus, the vascular effects of acetylcholine in the human forearm circulation are independent of prostaglandins and adrenergic neurotransmission and therefore are most likely to be mediated by EDRF; the acetylcholine-induced release of EDRF is blunted in patients with essential hypertension.

Interactive effect of body posture on exercise-induced atrial natriuretic peptide release

The purpose of this investigation was to test the hypothesis that supine exercise elicits a greater atrial natriuretic peptide (ANP) response than upright exercise because of higher atrial filling pressure attained in the supine posture. Plasma ANP concentration ([ANP]) was measured during continuous graded supine and upright exercise in eight healthy men at rest after 4 min of cycling exercise at 31, 51, and 79% of posture-specific peak oxygen uptake (VO2 peak), after 2 min of cycling at posture-specific VO2 peak, and 5 and 15 min postexercise. [ANP] was significantly increased (P less than 0.05) above rest by 64, 140, and 228% during supine cycling at 51 and 79% and VO2 peak, respectively. During upright cycling, [ANP] was significantly increased (P less than 0.05) at 79% (60%) and VO2 peak (125%). After 15 min of postexercise rest, [ANP] remained elevated (P less than 0.05) only in the supine subjects. [ANP] was 63, 79, and 75% higher (P less than 0.05) in the supine than in the upright position during cycling at 51 and 79% and VO2 peak. Systolic, diastolic, and mean blood pressures were not significantly (P greater than 0.05) different between positions in all measurement periods. Heart rates were lower (P less than 0.05) in the supine position compared with the upright position. In conclusion, these results suggest that supine exercise elicits greater ANP release independent of blood pressure and heart rate but presumably caused by greater venous return, central blood volume, and concomitant atrial filling pressure and stretch.

Pathophysiologic levels of atrial natriuretic factor do not alter reflex sympathetic control: direct evidence from microneurographic studies in humans

To determine if circulating levels of atrial natriuretic factor comparable with those seen in pathophysiologic states alter autonomic control of the circulation, direct recordings of hemodynamic variables and efferent sympathetic nerve activity to muscle (microneurography) were obtained during two separate protocols in a total of 21 normal men (age 25 +/- 1 years). In protocol 1, the responses of 10 men were compared during incremental mechanical unloading of cardiopulmonary baroreceptors with lower body negative pressure versus responses to comparable unloading during infusion of alpha-human atrial natriuretic factor. Lower body negative pressure decreased pulmonary artery diastolic and right atrial pressures, did not alter arterial pressure or heart rate and increased muscle sympathetic nerve activity from 205.2 +/- 36.3 to 438.7 +/- 100.2 units/min (p less than 0.01). Intravenous infusion of atrial natriuretic factor (25 ng/kg per min) increased plasma levels of the hormone from 24 +/- 4 to 322 +/- 34 pg/ml (p less than 0.01, n = 6), produced similar decreases in pulmonary artery diastolic and right atrial pressures, did not alter arterial pressure, increased heart rate and increased sympathetic nerve activity from 233.1 +/- 35.6 to 387.2 +/- 64.9 units/min (p less than 0.05). Thus, during similar hemodynamic perturbations produced by lower body negative pressure or infusion of atrial natriuretic factor at the dose used in this study, these subjects exhibited comparable sympathoexcitatory responses, with a 109 +/- 23% increase in sympathetic activity during lower body negative pressure and a 76 +/- 19% increase during atrial natriuretic factor infusion (p = NS). In protocol 2, the responses of 11 additional men were examined during lower body negative pressure performed before and again during infusion of atrial natriuretic factor (12.5 ng/kg per min). During baseline (prehormone) trials, lower body negative pressure (-14.5 +/- 1.6 mm Hg) decreased central venous pressure, did not change arterial pressure or heart rate and increased sympathetic nerve activity from 215 +/- 47.7 to 372.3 +/- 64.3 units/min (p less than 0.001). Infusion of atrial natriuretic factor increased plasma levels of the hormone from 39 +/- 8 to 313 +/- 18 pg/ml (p less than 0.01, n = 7); central venous pressure was held constant during hormone infusion by intravenous infusion of saline solution.(ABSTRACT TRUNCATED AT 400 WORDS)

Vasodilatory action of endogenous atrial natriuretic factor in a rat model of chronic heart failure as determined by monoclonal ANF antibody

Elucidation of the role of (elevated) endogenous atrial natriuretic factor (ANF) in chronic heart failure has been hampered by a lack of specific inhibitors. We used a newly developed monoclonal antibody that has been shown to specifically block both exogenously and endogenously released ANF in vivo. For assessment of the vasodilatory action of ANF in chronic heart failure, either this antibody against ANF or ascites (control serum) was injected in rats with myocardial infarction and failure and in sham animals. Ascites did not alter central hemodynamics in either the sham or infarcted group. Antibody significantly increased right atrial pressure, left ventricular end-diastolic pressure, and systemic vascular resistance (SVR) in the infarction group but did not affect these variables in the sham group. Because renal blood flow, as measured by radioactive microspheres, decreased significantly in all four groups, probably due to nonspecific renal vasoconstrictor effects of the ascites, a separate group of infarcted animals was treated with purified ANF antibody (devoid of nonspecific effects) or mouse IgG as a control injection. In these animals, right atrial pressure increased from 1.1 +/- 0.7 to 2.6 +/- 0.7 mm Hg (p less than 0.001). Although SVR, renal blood flow velocity (measured by Doppler probe), and renal vascular resistance did not change in the infarcted animals after administration of purified ANF antibody, a significant correlation was found between baseline plasma ANF values and the change in SVR exerted by purified ANF antibody (r = 0.758, p less than 0.02, n = 9); that is, SVR increased in rats with high baseline plasma ANF (greater than 350 pg/ml), but decreased in animals with plasma ANF less than 200 pg/ml. These results suggest that moderately elevated endogenous plasma ANF levels in chronic heart failure do affect central hemodynamics, primarily by reducing venous pressure (e.g., by decreasing intravascular volume or by venous dilation). Arterial vasodilation, however, appears to emerge when plasma ANF is greatly increased.

Concentrations of plasma atrial natriuretic factor during and after reversion of ventricular tachycardia

Plasma concentrations of immunoreactive atrial natriuretic factor were considerably increased (mean 745 (376) pg/ml) in 15 patients during spontaneous ventricular tachycardia. There was no significant relation, however, between concentrations of plasma atrial natriuretic factor and systolic arterial blood pressure during tachycardia. Samples taken 30 minutes and 24 hours after reversion of ventricular tachycardia to sinus rhythm showed that, although plasma concentrations of atrial natriuretic factor had fallen significantly, they were still raised after 24 hours. Raised concentrations of atrial natriuretic factor during ventricular tachycardia did not seem to contribute significantly to the hypotension that is often associated with the arrhythmia.

Atrial natriuretic peptide level and intracardiac pressure in cardiac transplant recipients

Blood pressures and plasma atrial natriuretic peptide (ANP) concentrations have been measured in venous and intracardiac sites in 11 patients (10 men and 1 woman) given cardiac transplants. The mean plasma ANP level was 214.4 pg.ml-1 in the superior vena cava and 281 pg.ml-1 in the right atrium. This significantly higher level was maintained in the right ventricle (269) and in the pulmonary artery (295). The level in controls was 25 pg.ml-1. Intra cardiac and mean arterial pressures were in normal range in all patients, and there was no correlation between plasma ANP level and intracardiac pressure. The data suggest that in cardiac transplant patients right atrial pressure does not have a primary role in releasing ANP. The transplanted heart is denervated and remains so for many months after operation, thus suggesting that innervation is not obligatory for ANP secretion. Further studies are required to determine the relative contribution of donor and recipient atrial tissues to ANP secretion.

Atrial natriuretic factor and arterial baroreceptor reflexes in unanesthetized rats

The modulation exerted by atrial natriuretic factor (ANF) on the cardiac and vascular influences of arterial baroreceptors was investigated in two groups of unanesthetized, chronically instrumented normotensive rats. In group 1, the reflex control of heart rate was assessed by graded baroreceptor stimulations and deactivations obtained by intravenous boluses of phenylephrine and nitroprusside. Under either circumstance, baroreceptor reflex sensitivity was expressed as the linear regression slope relating the chronotropic responses to the drug-induced mean arterial pressure changes. In group 2, right common carotid occlusion was performed in rats with their aortic and left carotid sinus baroreceptors denervated to assess the baroreceptor control of blood pressure; the reflex response was quantitated as the peak blood pressure rise observed during the maneuver. The reflex studies were performed before and during atriopeptin III infusion (0.15-0.20 micrograms/kg/min for 60 minutes). ANF augmented the bradycardic response to phenylephrine by 102.5 +/- 29% (p less than 0.01), reduced the tachycardic response to nitroprusside by 67.7 +/- 6.4% (p less than 0.01), and failed to modify the pressor response to carotid occlusion (-6.8 +/- 2.1%, p = NS). In a separate group of rats infused with low dose nitroprusside, no change in the baroreceptor-heart rate reflex was observed. ANF infusion (0.20 micrograms/kg/min) performed in further separate groups of conscious rats raised plasma ANF to 480 +/- 58 fmol/ml. Values in control vehicle-infused rats were 50 +/- 8 fmol/ml. Vascular reactivity (pressor response to intravenous phenylephrine boluses in anesthetized, sinoaortic-denervated rats) was only minimally reduced by ANF.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic and renal effects of atrial natriuretic peptide in congestive heart failure

The hemodynamic and renal effects of anaritide (human atrial natriuretic peptide 102-126), a synthetic analog of atrial natriuretic peptide, were evaluated in 35 patients with chronic New York Heart Association class II to IV heart failure. There were 32 men and 3 women, aged 33 to 75 (mean +/- standard error of the mean 56 +/- 2) years. In the first phase of the study, right-sided heart catheterization was performed, and anaritide was administered as 1-hour infusions. The rate of the infusion varied among patients from 0.03 to 0.3 micrograms/kg/min. In response to anaritide, there were decreases in mean systemic arterial (94 +/- 2 to 87 +/- 2 mm Hg), right atrial (10 +/- 1 to 8 +/- 1 mm Hg), mean pulmonary arterial (33 +/- 2 to 28 +/- 2 mm Hg) and pulmonary artery wedge (22 +/- 2 to 15 +/- 2 mm Hg) pressures (all p less than 0.05). Cardiac index increased (2.39 +/- 0.15 to 2.62 +/- 0.15 liters/min/m2, p less than 0.05) and heart rate was unchanged. Systemic vascular resistance decreased significantly, but pulmonary vascular resistance was unchanged. There were increases in urine volume (1.6 +/- 0.2 to 2.3 +/- 0.4 ml/min), sodium excretion (47 +/- 13 to 74 +/- 20 muEq/min) and fractional excretion of sodium (0.41 +/- 0.11 to 0.59 +/- 0.14%, all p less than 0.05), while potassium excretion and creatinine clearance did not change. In the second phase of the study, patients received 2-hour infusions of anaritide (0.03 to 0.6 micrograms/kg/min) and placebo with noninvasive monitoring.(ABSTRACT TRUNCATED AT 250 WORDS)