Evaluation of atrial natriuretic peptide and brain natriuretic peptide in atrial granules of rats with experimental congestive heart failure.

The natriuretic peptides are believed to play an important role in the pathophysiology of congestive heart failure (CHF). We utilized a quantitative cytomorphometric method, using double immunocytochemical labeling, to assess the characteristics of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in atrial granules in an experimental model of rats with CHF induced by aortocaval fistula. Rats with CHF were further divided into decompensated (sodium-retaining) and compensated (sodium-excreting) subgroups and compared with a sham-operated control group. A total of 947 granules in myocytes in the right atrium were analyzed, using electron microscopy and a computerized analysis system. Decompensated CHF was associated with alterations in the modal nature of granule content packing, as depicted by moving bin analysis, and in the granule density of both peptides. In control rats, the mean density of gold particles attached to both peptides was 347.0 +/- 103.6 and 306.3 +/- 89.9 gold particles/microm2 for ANP and BNP, respectively. Similar mean density was revealed in the compensated rats (390.6 +/- 81.0 and 351.3 +/- 62.1 gold particles/microm2 for ANP and BNP, respectively). However, in rats with decompensated CHF, a significant decrease in the mean density of gold particles was observed (141.6 +/- 67.3 and 158.0 +/- 71.2 gold particles/microm2 for ANP and BNP, respectively; p<0.05 compared with compensated rats, for both ANP and BNP). The ANP:BNP ratio did not differ between groups. These findings indicate that the development of decompensated CHF in rats with aortocaval fistula is associated with a marked decrease in the density of both peptides in atrial granules, as well as in alterations in the quantal nature of granule formation. The data further suggest that both peptides, ANP and BNP, may be regulated in the atrium by a common secretory mechanism in CHF.     

Rosiglitazone treatment restores renal responsiveness to atrial natriuretic peptide in rats with congestive heart failure

The thiazolidinedione (TZD) class of Peroxisome proliferator‐activated receptor gamma agonists has restricted clinical use for diabetes mellitus due to fluid retention and potential cardiovascular risks. These side effects are attributed in part to direct salt‐retaining effect of TZDs at the renal collecting duct. A recent study from our group revealed that prolonged rosiglitazone (RGZ) treatment caused no Na+/H₂O retention or up‐regulation of Na⁺ transport‐linked channels/transporters in experimental congestive heart failure (CHF) induced by surgical aorto‐caval fistula (ACF). The present study examines the effects of RGZ on renal and cardiac responses to atrial natriuretic peptide (ANP), Acetylcholine (Ach) and S‐Nitroso‐N‐acetylpenicillamine (SNAP‐NO donor). Furthermore, we assessed the impact of RGZ on gene expression related to the ANP signalling pathway in animals with ACF. Rats subjected to ACF (or sham) were treated with either RGZ (30 mg/kg/day) or vehicle for 4 weeks. Cardiac chambers pressures and volumes were assessed invasively via Miller catheter. Kidney excretory and renal hemodynamic in response to ANP, Ach and SNAP were examined. Renal clearance along with cyclic guanosine monophosphate (cGMP), gene expression of renal CHF‐related genes and ANP signalling in the kidney were determined. RGZ‐treated CHF rats exhibited significant improvement in the natriuretic responses to ANP infusion. This ‘sensitization’ to ANP was not associated with increases in neither urinary cGMP nor in vitro cGMP production. However, RGZ caused down‐regulation of several genes in the renal cortex (Ace, Nos3 and Npr1) and up‐regulation of ACE2, Agtrla, Mme and Cftr along down‐regulation of Avpr2, Npr1,2, Nos3 and Pde3 in the medulla. In conclusion, CHF+RGZ rats exhibited significant enhancement in the natriuretic responses to ANP infusion, which are known to be blunted in CHF. This ‘sensitization’ to ANP is independent of cGMP signalling, yet may involve post‐cGMP signalling target genes such as ACE2, CFTR and V2 receptor. The possibility that TZD treatment in uncomplicated CHF may be less detrimental than thought before deserves additional investigations.     

Plasma levels of adrenomedullin and atrial natriuretic peptide in patients with congestive heart failure of various etiologies

OBJECTIVE: The aim of this study was to evaluate the plasma levels of the adrenomedullin (ADM) and atrial natriuretic peptide (ANP) in adult and pediatric patients with congestive heart failure (CHF) of various etiologies and to investigate their relations with haemodynamic variables e.g. echocardiographic left ventricular ejection fraction (LVEF) and fractional shortening (FS). SUBJECTS AND METHODS: The study was made in 38 adult and 21 pediatric patients with CHF of various etiologies and compared with 15 adult and 10 pediatric normal healthy controls. Patients with CHF were classified according to the New York Heart Association (NYHA) functional classification into grades II to IV in adult patients and into grade IV in all pediatric patients. ADM and ANP plasma levels were determined prior to the treatment with enzyme immunoassay. RESULTS: A statistically significant difference in the plasma levels of ADM and ANP were found between pediatrics and adult patients and corresponding healthy controls. Their levels were progressively increased with severity of NYHA class in adult patients. We found a significant positive correlation between plasma levels of each of ADM and ANP and pulse rate, systolic and diastolic blood pressure; and a significant negative correlation between their plasma levels and echocardiographic LVEF and FS. A significant positive correlation between plasma levels of ADM and ANP in both pediatrics and adult patients were also found. CONCLUSION: Plasma levels of ADM and ANP increased in adult and pediatric patients with CHF irrespective of the cause. They were positively correlated with each other and negatively correlated with LVEF and FS. These findings might have important clinical implications in that a noninvasive blood test may be used to identify high-risk subjects for HF for more invasive procedures.     

Attenuated diuretic and natriuretic effects of atrial natriuretic peptide in rats with heart failure

Plasma levels of atrial natriuretic peptide (ANP) and renal responses to ANP were examined in rats with chronic cardiac failure produced by coronary artery ligation and in sham-operated controls. Plasma ANP levels were elevated in the rats with severe cardiac failure as compared with the controls (P less than 0.001). ANP injections at the doses of 1, 5, 25 and 50 micrograms/kg increased water and sodium excretion significantly at all but the lowest dose in the controls; only the two largest doses caused clear diuresis and natriuresis in the heart failure group. The diuretic and natriuretic effects of ANP were significantly weaker at the doses of 5 and 25 micrograms/kg in the rats with heart failure as compared with the controls. We conclude, that natriuretic and diuretic effects of ANP are attenuated in this chronic heart failure mode.     

Cardiac secretion of atrial natriuretic factor with exercise in chronic congestive heart failure patients.

We have previously reported a fivefold increase of plasma atrial natriuretic factor (ANF) in patients with congestive heart failure (CHF) compared with normal subjects. However, given the marked increase of ANF under basal conditions, the extent to which ANF secretion can further increase under physiological stress is not been clarified in CHF. We therefore evaluated ANF secretion during ergometric exercise in 11 patients with CHF, with peripheral venous ANF samples obtained at rest and peak exercise. In seven patients, simultaneous peripheral venous and right ventricular ANF samples were obtained to estimate myocardial ANF secretion. Hemodynamic characteristics of exercise included a significant increase of heart rate, mean arterial pressure, and cardiac output (all P < 0.01); reduction of systemic vascular resistance (P < 0.001); and increase of right atrial and pulmonary wedge pressures (P < 0.001). ANF was abnormally elevated at baseline (108 +/- 58 fmol/ml) yet increased further to 183 +/- 86 fmol/ml with exercise (P < 0.003). A step-up of right ventricular ANF, particularly during exercise, was consistent with active myocardial secretion, despite elevated baseline ANF levels.     

Pathophysiology of congestive heart failure: role of atrial natriuretic factor and therapeutic implications.

Endogenous atrial natriuretic factor (ANF) serves a functional role to maintain sodium homeostasis and inhibit activation of the renin-angiotensin-aldosterone system in acute congestive heart failure despite arterial hypotension. However, as heart failure progresses, maximal synthesis and release of ANF from both the atrial and ventricular myocardium may occur resulting in relative ANF deficiency. This relative deficiency of ANF results in a progressive inability to excrete sodium and antagonize the renin-angiotensin-aldosterone system. Consequently, agents that increase circulating ANF and (or) enhance its local action have potential therapeutic efficacy. Recent studies suggest that inhibitors of neutral endopeptidase 24.11, which block ANF degradation, potentiate the natriuretic action of endogenous ANF independent of systemic or renal hemodynamics. This action does not parallel increases in plasma ANF and is associated with marked increases in urinary ANF and cyclic guanosine monophosphate consistent with enhanced local action of the peptide. In addition, agents that selectively bind to biologically inactive ANF clearance receptors increase endogenous plasma ANF and promote increases in renal sodium excretion. These studies suggest a therapeutic role for neutral endopeptidase inhibition and clearance receptor blockade, while advancing our understanding of the pathophysiology of ANF in congestive heart failure.     

Circadian rhythm of blood pressure in congestive heart failure and effects of ACE inhibitors.

In 33 patients with heart failure (NYHA II-III), the 24-h blood pressure rhythm was examined before and after the titration period of two ACE inhibitors. Blood pressure was measured by the oscillometric method using the blood pressure monitor 90202 from SpaceLabs, Inc. The measurements were taken from 06:00 to 22:00 h every 20 min and from 22:00 to 06:00 h every hour. Patients were randomized to therapy with either captopril (group 1, n = 17) or enalapril (group 2, n = 16). The average daily dosage of captopril was 41 +/- 3 mg given in three divided doses (08:00, 12:00, and 17:00 h). The mean dose of enalapril was 8 +/- 1 mg once daily (08:00 h). Serum electrolytes, serum creatinine, and plasma renin activity were measured before and during therapy with both ACE inhibitors. Twenty-four-hour blood pressure measurements were taken before and on the fifth day of treatment with ACE inhibitors. Both groups were not different with respect to the degree of heart failure, the concomitant medication, and the 24-h profiles of blood pressure and heart rate before initiation of ACE inhibition. The 24-h blood pressure values on day 5 were consistently below the pretreatment values (p less than 0.005) in both groups. Both groups did not differ significantly during ACE inhibition in their 24-h blood pressure and heart rate profiles. In both groups, the mesor of the systolic and diastolic blood pressure decreased significantly by the same degree (by 4.7/5.1 mmg Hg in group 1 and 6.4/4.1 mm Hg in group 2). The systolic/diastolic blood pressure amplitude decreased slightly in both groups. Before treatment, serum sodium, potassium, and creatinine were within the normal range. The increase in potassium (0.5 +/- 0.1 mmol/L) reached statistical significance (p less than 0.01) only in the captopril group, whereas it was not significant in the enalapril group (0.1 +/- 0.1 mmol/L). Serum creatinine was not significantly altered by both ACE inhibitors. No relationship could be found between the changes in serum potassium or creatinine and the mean of the 24-h blood pressure values during ACE inhibition. Captopril and enalapril showed comparable blood pressure profiles and similar effects on renal function at the end of the titration on day 5. It can therefore be concluded that the effects on blood pressure rhythm and renal function are similar with a single daily dose of enalapril compared to captopril given three times daily.     

Effect of human atrial natriuretic peptide on blood pressure after sodium depletion in essential hypertension.

Human atrial natriuretic peptide was infused over four hours in three patients with essential hypertension. When the patients had a sodium intake of 200 mmol (mEq) daily an infusion of 0.5 micrograms atrial natriuretic peptide/min caused no significant change in blood pressure, whereas an infusion of 1.0 micrograms/min caused a gradual decrease in blood pressure and an increase in heart rate. After two to three hours of infusion with the higher dose two patients showed a sudden decrease in heart rate, with symptomatic hypotension. When the same patients had an intake of 50 mmol sodium daily their blood pressure was more sensitive to infusion of atrial natriuretic peptide; one patient again developed symptomatic hypotension, this time during an infusion of 0.5 micrograms/min. During all infusions distinct natriuresis occurred irrespective of whether blood pressure was affected. Prolonged, relatively low dose infusions of atrial natriuretic peptide can cause unwanted symptomatic hypotension. The effect on blood pressure is enhanced after sodium depletion, and blood pressure should be monitored carefully during longer infusions of atrial natriuretic peptide in patients with essential hypertension.     

Morphometric analysis of atrial natriuretic peptide-containing granules in atriocytes of rats with experimental congestive heart failure

The morphometric characteristics of atrial natriuretic peptide-containing granules were studied in atrial myoendocrine cells of rats with aorto-caval fistula, an experimental model of congestive heart failure. A total of 6680 granules of control and aorto-caval rats were analyzed by a computerized image analysis system that evaluated the number and sectioned surface area of granules and their subcellular location. Compared with control animals, rats with congestive heart failure displayed a slight increase in the number of peripheral granules, adjacent to the sarcolemma, but not centrally located in the Golgi areas. The mean sectioned surface area of granules in rats with congestive heart failure was about 50% of that in controls, both in the right and left atria. Rats with aortocaval fistula had a higher percent of small granules and lower percent of large granules compared with controls. The data demonstrate different morphometric characteristics in atrial natriuretic peptide-containing granules in atriocytes in rats with experimental congestive heart failure; this may reflect the enhanced synthesis and release of atrial natriuretic peptide in heart failure.     

Postmortem stability of the rat atrial natriuretic peptide in blood and atrial tissue

The postmortem stability of the rat Atrial Natriuretic Peptide (ANP) has been studied as a necessary and previous step to be applied in the forensic field as a postmortem marker. This peptide--whose extreme sensitivity to slight changes in blood volume is well known--could have great importance in thanatochemistry to establish a correct diagnosis when macroscopical observations and classical parameters are not conclusive or cannot be employed. The results show high stability in atrial tissue, where values are similar from 0 hours (108.99 pm/mg) to 8 hours (109.41 pm/mg) and decrease uniformly until 15 pm/mg) at 32 hours, time of our last determination. Blood ANP showed similar stability from 0 h (105.43 pg/ml) to 8 h (106.62 pg/ml).     

Diurnal circadian rhythms of renal function and electrolyte excretion in heart failure

Diurnal cycles of glomerular filtration rate (GFR), effective renal plasma flow (ERPF), and of excretion rates of sodium, potassium, magnesium, chloride and phosphate were measured in a 22 year old man with moderately severe heart failure under standardized conditions. Cycles of GFR, ERPF and excretion of potassium, chloride, and phosphate were indistinguishable from those of normals. The phases of the sodium and probably the magnesium excretory cycles were reversed from normal. The significance of some of the observations is discussed.     

Atrial natriuretic factor as a marker in congestive heart failure

Cardiac overload is associated with an overexpression of the atrial natriuretic-factor (ANF) gene in experimental models and in man. Sites of ANF gene overexpression are the atria but also the ventricular myocardium. This recruitment phenomenon of the ventricle to synthesise and secrete ANF is directly dependent on the increase in stress-stretch relationship in each cardiocyte. Therefore, the levels of plasma ANF and its second messenger, cyclic glycophosphate mutase in plasma and urine appear as markers of congestive heart failure in animal models and in man. Particularly, plasma ANF has been recognized recently as independent prognostic factor in congestive heart failure.     

Involvement of atrial natriuretic peptide in blood pressure reduction induced by estradiol in spontaneously hypertensive rats

The aim of the present study was to determine the involvement of atrial natriuretic peptide (ANP) in blood pressure (BP) alterations induced by estradiol treatment. Spontaneously hypertensive rats (SHR) and Wistar rats (WR) were ovariectomized and, after 3 weeks, were injected daily for 4 days with estradiol benzoate (E2; 5 microg/100 g/day) or a vehicle. One day after the last injection, the animals were decapitated, blood was collected, and both right and left atrial appendages were quickly removed for determination of ANP by radioimmunoassay (RIA), or used for ANP mRNA determination. Estradiol treatment induced a significant reduction of blood pressure in SHR, but not in WR. This reduction was correlated with the increase of plasma ANP levels that were significantly increased in E2-treated, compared with vehicle-treated, SHR. E2-treated SHR showed significant increases in ANP concentration in the right and left atria compared to the vehicle-treated animals. These observations were confirmed by ANP mRNA. In summary, the present study shows that short-term estradiol treatment reduces the blood pressure of ovariectomized SHR, but not of WR. This reduction was highly correlated with increased plasma estradiol and ANP levels. These results suggest that ANP is involved in mediating the effect of estradiol on blood pressure reduction.     

Mice show circadian rhythms of blood pressure during each wake-sleep state

A daily rhythm of blood pressure (BP), with maximum values in the activity period, carries important prognostic information. The extent to which this rhythm depends on behavioral factors remains debated. Mice are the species of choice for functional genomics. In mice, episodes of wakefulness and sleep are not restricted to particular daily periods, allowing BP in each wake-sleep state to be measured at each time of day. The aim of this study was to investigate whether a circadian rhythm of BP is manifest in each wake-sleep state in mice. Mice with B6 genetic background (n?=?26) were implanted with a telemetric BP transducer and electrodes to discriminate wake-sleep states and recorded while housed under a 12:12?h light-dark period. For each mouse, 8 values of BP were obtained in each wake-sleep state (wakefulness, non-rapid-eye-movement sleep, and rapid-eye-movement sleep) by averaging over successive 3-h time bins. Analysis of variance evidenced a significant time effect in each wake-sleep state as well as a significant wake-sleep state?×?time interaction effect. In an additional group of mice (n?=?3) recorded in constant darkness, the Lomb-Scargle periodogram also revealed a significant circadian rhythm of BP in each wake-sleep state. These findings demonstrate that during each wake-sleep state, mice show daily and circadian rhythms of BP in conditions of entrainment to the light-dark cycle and in free-running conditions of constant darkness, respectively.     

Radioimmunoassay of atrial natriuretic peptide in human plasma: application to studies of volume and blood pressure homeostasis

Sensitive radioimmunoassay for determination of immunoreactive atrial natriuretic peptide (ANP) in human plasma was developed and employed for the study of plasma ANP concentrations in healthy controls under basal conditions (2.4 +/- 0.1 pmol/l) and during volume expansion by saline infusion (9.6 +/- 2.0 pmol/l and 14.2 +/- 1.8 pmol/l, respectively). Plasma renin activity and plasma aldosterone concentration exhibited opposite changes during saline infusion. In pathological states associated with extracellular fluid volume (ECFV) expansion, ANP concentration were significantly higher than in the controls (liver cirrhosis 8.6 +/- 0.9; congestive heart failure 33.1 +/- 4.8; chronic renal failure before haemodialysis 72.2 +/- 6.4 pmol/l). Further volume expansion in liver cirrhosis by saline infusion led to the further increase in ANP (13.3 +/- 1.3 and 16.1 +/- 1.5 pmol/l, respectively) and ECFV reduction by ultrafiltration during haemodialysis in chronic renal failure diminished but did not normalize plasma ANP (22.5 +/- 2.9 pmol/l). In patients with arterial hypertension the concentration of ANP exceeded the normal range by 62.5% and reached 8.0 +/- 0.5 pmol/l on the average. Our results support the suggestion that ANP is an important regulatory humoral mechanism participating in the regulation of sodium, volume and blood pressure homeostasis.     

Immunoreactive atrial natriuretic peptide in the fish heart and blood plasma examined by electron microscopy,immunohistochemistry and radioimmunoassay

Summary The immunoreactivity of atrial natriuretic peptide and ultrastructure of cardiocytes were examined in 5 species each of freshwater and seawater teleosts, as well as in 2 species each of elasmobranchs and cyclostomes. Immunoreactivity was strong in the atria of Cyprinus carpio, Anguilla japonica and Conger myriaster, rather weak in atria of Channa maculata, Lepomis macrochirus, Salmo gairdneri, Oplegnathus fasciatus and Eptatretus burgeri, very weak in atria of Pagrus major, Trachurus japonicus and Triakis scyllia, and not detectable in atria of Hexagrammos otakii, Narke japonica and Lampetra japonica. The immunoreactivity of the atrial cardiocytes was generally stronger in freshwater than seawater fish. Ventricular immunoreactivity was detected only in 7 species, always being weaker than that observed in the atrium. Ultrastructurally, however, secretory granules were found in atria and ventricles of all species examined, being more frequent in the former than the latter. By radioimmunoassay, immunoreactive ANP was detected in the extracts of blood plasma and both atrial and ventricular tissues of all species examined. There were no statistically significant differences in the values between freshwater and seawater species.     

Irradiation-induced changes in circadian DDT-susceptibility and metabolic rhythms in the housefly.

The diel pattern of susceptibility to DDT of houseflies, reared under LD 14 : 10, was shown to be affected by 10 Krads of gamma radiation administered at the pupal stage. An additional peak in susceptibility of the flies to DDT corresponded to the time of irradiation of the pupae. Irradiated flies had higher general LD50 values than untreated flies. Flies reared in darkness demonstrated no discernable group rhythm apart from an altered susceptibility at the pupal irradiation time. Respiration rates of irradiated flies were slightly lower than the control flies and did not change at the time of irradiation. Groups of flies reared in darkness have no significant respiration rhythm.     

Effects of atrial natriuretic peptide infusion and its metabolism in patients with chronic renal failure.

Synthetic alpha-human atrial natriuretic peptide (hANP) was infused continuously at a rate of 80 ng/kg/min for 20 min into normal volunteers and patients with chronic renal failure (CRF) receiving hemodialysis. Blood pressure (BP) decreased significantly both in normals and in patients with CRF. The magnitude and the duration of the decrease, however, were greater in patients with CRF. The plasma aldosterone concentration (PAC) decreased significantly in normals and only minimally in patients with CRF. The half time (T1/2) of plasma hANP in patients with CRF (M +/- SE: 4.5 +/- 0.5 min) was longer than that in normals (1.8 +/- 0.2 min). Moreover, the metabolic clearance rate in patients with CRF (64 +/- 7 ml/kg/min) was less than in normals (150 +/- 20 ml/kg/min). Thus, the T1/2 in plasma of hANP in patients with CRF was noticeably longer than in a normal control group. These findings suggest that hANP suppresses PAC regardless of electrocyte imbalances and/or volume change induced by kidney dysfunction and that the kidney may be important in degrading hANP.