Localization of brain and atrial natriuretic peptide in human and porcine heart.

We have compared the localization of brain and atrial natriuretic peptide-like immunoreactivity in human and porcine hearts, using immunohistochemical techniques at both the light and ultrastructural level and specific antisera to amino-(cardiodilatin) and carboxy-terminal regions of the atrial natriuretic precursor molecule and to brain natriuretic peptide. Atrial myocardial cells in human fetal, normal adult and failing explanted hearts, displayed immunoreactivity for both brain and atrial natriuretic peptide-like sequences. At the subcellular level, brain natriuretic peptide-, cardiodilatin- and alpha-atrial natriuretic peptide-like immunoreactivity were co-localized to secretory granules in atrial myocardial cells. Immunoreactivity was also detected in the left (64%) and right ventricular free walls (23%) of 22 failing explanted hearts, but not in donor cardiac tissues. A gradient of natriuretic peptide immunostaining was observed across ventricular free walls and immunoreactivity for both natriuretic peptide sequences co-localized to secretory granules in a subpopulation of myocardial cells, concentrated in subendocardial regions of the ventricular walls. Brain and atrial natriuretic peptide-like immunoreactivity were also demonstrated in porcine atrial myocardium and cells of the ventricular conduction system. The parallel distribution of cardiac brain and atrial natriuretic peptide-like immunoreactivity suggests a dual regulation and co-storage of the natriuretic peptides in human and porcine hearts.     

Localisation of atrial natriuretic peptide immunoreactivity in the ventricular myocardium and conduction system of the human fetal and adult heart.

Atrial natriuretic peptide immunoreactivity was found in ventricular and atrial tissues with specific antisera raised to the amino and carboxy terminal regions of the precursor molecule. In 13 developing human hearts (7-24 weeks' gestation) the immunoreactivity was concentrated in the atrial myocardium and ventricular conduction system but it was also detected in the early fetal ventricular myocardium. Immunoreactivity in five normal adults was largely confined to the atrial myocardium although it was also found in the ventricular conduction tissues of hearts removed from 10 patients who were undergoing cardiac transplantation. The ventricular conduction system is an extra-atrial site for the synthesis of atrial natriuretic peptide. In the failing heart this synthesis may be further supplemented by expression of the gene in the ventricular myocardium. It is possible that ventricular production of the peptide contributes to the raised circulating concentrations of atrial natriuretic peptide immunoreactivity found in severe congestive heart disease, particularly in patients with dilated cardiomyopathy.     

Relationship between left atrial appendage function and plasma concentration of atrial natriuretic peptide.

BACKGROUND: It has been reported that the most intensely granuled cardiocytes secreting atrial natriuretic peptide (ANP) are located in the atrial appendages. AIMS: To evaluate the mechanisms of ANP release in congestive heart failure. METHODS AND RESULTS: The relationship between ANP and left atrial appendage (LAA) function was evaluated in 36 patients who underwent both transoesophageal echocardiography and cardiac catheterization. ANP level correlated positively with mean pulmonary capillary wedge pressure (mPCWP; r=0.75, P<0.0001), whereas it showed no significant correlation with the mean right atrial pressure. mPCWP correlated positively with the maximal LAA area (LAAa; r=0.79, P<0.0001) and negatively with the LAA ejection fraction during atrial contraction (LAA-EF; r=-0.61, P<0.0001) and peak late diastolic LAA emptying flow velocity (LAAF; r=-0.69, P<0.0001). ANP level correlated negatively with the LAA-EF (r=-0.56, P<0.001) and with LAAF (r=-0.61, P<0.0001). ANP level correlated more closely with the LAAa (r=0.79, P<0.0001) than with maximal LA volume (r=0.34, P<0.05). Multiple stepwise regression analysis selected LAAa as the only factor independently related to the plasma concentration of ANP (ANP=-22.4+28.6 LAAa, r=0.79, P<0.0001). CONCLUSIONS: We conclude that the factor most predictive for ANP in patients with left-sided cardiac dysfunction is distension of the LAA wall rather than elevation in the LA pressure or distension of the body of LA. This is consistent with the known distribution of ANP-secreting cardiocytes.     

Localisation of atrial natriuretic peptide immunoreactivity in the ventricular myocardium and conduction system of the human fetal and adult heart

Atrial natriuretic peptide immunoreactivity was found in ventricular and atrial tissues with specific antisera raised to the amino and carboxy terminal regions of the precursor molecule. In 13 developing human hearts (7-24 weeks' gestation) the immunoreactivity was concentrated in the atrial myocardium and ventricular conduction system but it was also detected in the early fetal ventricular myocardium. Immunoreactivity in five normal adults was largely confined to the atrial myocardium although it was also found in the ventricular conduction tissues of hearts removed from 10 patients who were undergoing cardiac transplantation. The ventricular conduction system is an extra-atrial site for the synthesis of atrial natriuretic peptide. In the failing heart this synthesis may be further supplemented by expression of the gene in the ventricular myocardium. It is possible that ventricular production of the peptide contributes to the raised circulating concentrations of atrial natriuretic peptide immunoreactivity found in severe congestive heart disease, particularly in patients with dilated cardiomyopathy.     

Regulation of receptors for atrial natriuretic peptide in the rat and human

Summary Atrial natriuretic factor or peptide (ANP) is a peptide recently isolated from mammalian atria with potent natriuretic, vasorelaxant, and aldosterone-inhibitory properties. ANP may glay an important role in the regulation of blood pressure and body salt and fluid balance. The presence of binding sites for ANP in the vasculature and adrenal glomerulosa of rats and in platelets in humans has been demonstrated. These sites are involved in the mediation of the vasorelaxant effect of ANP and its inhibitory action on aldosterone seeretion. The role of binding sites on platelets is unknown, but the availability of platelets makes them a useful model for investigating the regulation of receptors for atrial natriuretic factor in humans. The effect of sodium depletion and loading and mineralocorticoids on the density of rat vascular and adrenal sites for ANP was examined, as well as changes that occur after development of renovascular and DOCA-salt hypertension in rats. Sodium loading in the presence of reduced renal mass (unilateral nephrectomy) or mineralocorticoid administration produced renin suppression and resulted in down-regulation of vascular ANP receptors. In one-kidney, one-clip Goldblatt hypertensive rats and in DOCA-salt hypertensive rats, two models of volume-expanded, non-renin-dependent experimental hypertension, the density of ANP binding sites in the mesenteric arterioles was significantly decreased. The sensitivity to ANP of precontracted aorta from renovascular and mineralocortieoid hypertensive rats was significantly reduced. No consistent changes occured in the density of ANP binding sites in the adrenal glomerulosa. Thus, in normotensive or hypertensive animals with volume expansion, a condition which produces increases in circulating ANP, ANP receptors in blood vessels were down-regulated. In cultured rat vascular smooth muscle cells, exposure to 10 nM ANP for 24 hours resulted in down-regulation of ANP binding sites. In humans, binding sites for ANP in platelets had the same molecular requirements as vascular ANP sites in the rat. Sodium loading of normal human volunteers resulted in increased concentration of ANP in plasma and decreased density of ANP binding sites in platelets. In patients with severe congestive heart failure, and elevated concentration of ANP in plasma, the density of ANP sites on platelets was significantly decreased. ANP binding sites in human platelets are regulated similarly to ANP vascular receptors in the rat and may therefore serve as a model for the study of vascular ANP receptors in humans. Increased plasma ANP down-regulates ANP receptors in the rat and human beings. Decreased vascular relaxation secondary to reduced responsiveness to ANP due to down-regulated ANP receptors may play a role in elevation of blood pressure in some models of experimental hypertension. Decreased density of ANP receptors may contribute to the sodium retention of severe congestive heart failure in humans.     

Bovine atrial natriuretic peptide in heart failure

The present study describes the concentration and molecular form of atrial natriuretic peptide (ANP) in Holstein dairy cattle with mild (bacterial endocarditis; BEC) or severe (dilated cardiomyopathy; DCM) heart failure. Significant increases in plasma concentration of ANP were observed in cattle with DCM (73.3 +/- 16.02 pmol/l, n = 4, P less than 0.01) and BEC (20.6 +/- 3.45 pmol/l, n = 7, P less than 0.05), when compared with those in control cattle (14.5 +/- 1.84 pmol/l, n = 12). The concentration of ANP in cattle with DCM was significantly (P less than 0.01) higher compared with that in cattle with BEC. Plasma concentration of ANP correlated significantly with right atrial pressure (r = 0.95, P less than 0.01) and left ventricular end-diastolic pressure (r = 0.84, P less than 0.01). Gel-permeation chromatography of ANP in plasma and the right atrium from control and cattle with BEC revealed a single peak corresponding to the elution position of authentic human ANP(99-126) in plasma, and two peaks corresponding to those of authentic human ANP(99-126) and pro-ANP in the atrial extract. In cattle with DCM, however, peaks corresponding to the elution positions of authentic human beta-ANP and/or pro-ANP were detected in addition to the peak corresponding to ANP(99-126). The content of ANP in the right atrium of cattle with DCM was significantly (P less than 0.05) increased compared with that in control cattle and those with BEC. The present study therefore suggests that the synthesis and secretion of ANP might be stimulated by atrial distention induced by increased atrial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Secretion of atrial natriuretic peptide from the heart in man.

Plasma concentrations of atrial natriuretic peptide were measured in eight patients undergoing elective cardiac catheterisation and angiography. All patients had normal resting pressures in the cardiac chambers and no clinical evidence of heart failure. Plasma atrial natriuretic peptide rose significantly from the superior vena cava into the right atrium and right ventricle. The increase into the right atrium was variable, with no increase in three subjects, but there was a consistent increase in all subjects from the superior vena cava to to the right ventricle. These findings in the right atrium are probably caused by inadequate mixing and streaming of blood from the coronary sinus containing high concentrations of atrial natriuretic peptide. There was no increase in the concentration of natriuretic peptide from the pulmonary artery to the left ventricle, but the concentrations in the left ventricle were significantly higher than in the superior vena cava. These findings demonstrate that the heart secretes atrial natriuretic peptides in the absence of cardiac failure. Studies based on sampling of the right atrium will not accurately measure cardiac secretion of atrial natriuretic peptide and will therefore be likely to obscure the mechanisms responsible for regulating its secretion. The right ventricle and pulmonary artery are the best sampling sites to measure atrial natriuretic peptide release from the right atrium.     

Plasma atrial natriuretic peptide in carcinoid heart disease

Plasma atrial natriuretic peptide (ANP) concentration was determined and cardiac ultrasound studies were performed in 50 patients with malignant mid-gut carcinoid tumors. The extent of carcinoid-related heart disease varied among the patients. The patients with the most severe right-sided heart disease, who often had signs of right ventricular failure, had significantly (p less than 0.001) higher plasma ANP concentrations than either patients with less or no abnormal ultrasound findings or age- and sex-matched healthy control subjects. ANP levels were serially determined for 0.5 to 4 years (median 2.1) in 12 patients. The levels increased above the reference range in patients with clinical findings of right ventricular failure. In patients without cardiac decompensation the levels remained within the reference range. In 3 patients who had successful tricuspid and pulmonary valve replacements, signs and symptoms of right ventricular failure disappeared and plasma ANP levels declined and normalized. Five patients with progressive right ventricular failure and increasing plasma ANP levels during follow-up eventually died from cardiac decompensation. This study demonstrates the predictive value of serial determinations of plasma ANP in carcinoid heart disease. Such measurements can be an additional guide in the clinical management of these patients.     

Altered thyroidal status and the in vivo synthesis of atrial natriuretic peptide in the rat heart

The effect of altered thyroidal status on levels of immunoreactive (ir)- atrial natriuretic peptide (ANP) in serum and the four cardiac chambers, and of tissue ANP mRNA, was determined in groups of rats given vehicle, thyroxine (T4), propylthiouracil (PTU) or T4 plus PTU for 3 weeks. Serum levels of ir-ANP were approximately 3-fold higher in T4-treated animals compared with control; levels in PTU or PTU/T4 groups were not different from control. Right ventricular ANP mRNA was below detection; in other chamber, levels rose with T4, alone or plus PTU, and fell after PTU compared with control. Atrial ir-ANP levels were unchanged by T4, but increased (left atrium, LA) or decreased (right atrium, RA) after PTU alone. After PTU/T4, some indices (e.g. tissue weight) remained at control levels, others (e.g. ANP mRNA levels) were equivalent to levels in the T4-alone group, and others (e.g. LA ir-ANP) were equivalent to those seen with PTU alone. We conclude that the role of thyroid hormones on ANP synthesis may be similar between chambers but their effects on release appear to differ widely. The extent to which this represents secondary rather than direct effects, or possible T3-versus T4-specific events, awaits elucidation.     

Endothelin stimulates basal and stretch-induced atrial natriuretic peptide secretion from the perfused rat heart

To examine the role of intracellular signals in the regulation of atrial natriuretic peptide (ANP) release, the effects of endothelin (ET), a putative endogenous agonist for voltage-dependent Ca2+ channels on basal and atrial stretch-stimulated ANP release as well as on hemodynamic parameters (perfusion pressure, heart rate, contractile force) in isolated perfused rat hearts were studied. Infusion of ET (0.9 x 10(-9)-2.3 x 10(-9) M) alone for 30 min caused a dose-dependent sustained increase in the perfusate immunoreactive ANP (IR-ANP) concentration and coronary vasoconstriction. An initial inotropic response with a later decrease in the contractile force in response to ET was observed, while heart rate remained unchanged. A phorbol ester, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), known to stimulate protein kinase-C activity, at a dose of 4.6 x 10(-8) M caused a gradual, slowly progressive increase in perfusate IR-ANP levels and a more rapid increase in perfusion pressure. ET, when infused in combination with TPA, enhanced IR-ANP secretion induced by the phorbol ester. When hearts from spontaneously hypertensive rats (SHR) were examined, the vasoconstrictor response to infusion of ET was greater than that in the normotensive Wistar-Kyoto (WKY) rats. Infusion of eguipressor doses of ET increased the release of IR-ANP in WKY rats, but had no effect on perfusate IR-ANP levels in SHR. To examine effects of ET on stretch-stimulated ANP release, the modified perfused rat heart preparation that enabled the stepwise distension of the right atrium was used. The increase in right atrial pressure (2.65 +/- 0.13 mm Hg) was accompanied by an increase in the perfusate IR-ANP concentration (from 8.3 +/- 1.1 to 13.9 +/- 2.0 ng/5 min; P less than 0.05; n = 15). The increase in right atrial pressure during the ET infusions resulted in a significantly greater increase in the perfusate IR-ANP concentration than vehicle alone. The calculated ANP increase corresponding to the 2-mm Hg increase in the right atrial pressure was 1.52-fold in the control group and 1.74-fold when 1.9 x 10(-9) M ET was infused (P less than 0.05). This study shows that ET stimulates both basal and atrial stretch-stimulated ANP secretion from the isolated perfused heart and suggests that ET is involved in the regulation of stretch-induced ANP release. The results further confirm the potent vasoconstrictor and cardiac effects of ET.     

Secretion of atrial natriuretic peptide from the heart in man

Plasma concentrations of atrial natriuretic peptide were measured in eight patients undergoing elective cardiac catheterisation and angiography. All patients had normal resting pressures in the cardiac chambers and no clinical evidence of heart failure. Plasma atrial natriuretic peptide rose significantly from the superior vena cava into the right atrium and right ventricle. The increase into the right atrium was variable, with no increase in three subjects, but there was a consistent increase in all subjects from the superior vena cava to to the right ventricle. These findings in the right atrium are probably caused by inadequate mixing and streaming of blood from the coronary sinus containing high concentrations of atrial natriuretic peptide. There was no increase in the concentration of natriuretic peptide from the pulmonary artery to the left ventricle, but the concentrations in the left ventricle were significantly higher than in the superior vena cava. These findings demonstrate that the heart secretes atrial natriuretic peptides in the absence of cardiac failure. Studies based on sampling of the right atrium will not accurately measure cardiac secretion of atrial natriuretic peptide and will therefore be likely to obscure the mechanisms responsible for regulating its secretion. The right ventricle and pulmonary artery are the best sampling sites to measure atrial natriuretic peptide release from the right atrium.     

Dehydration-induced alterations in rat brain vasopressin and atrial natriuretic factor immunoreactivity

Potent natriuretic and spasmolytic peptides present in cardiac extracts recently have been identified. These atrial natriuretic factors (ANF) exert vascular and renal actions quite contrary to those of vasopressin (AVP). The ability of ANF to inhibit AVP secretion suggested a role for the peptides in the control of AVP release. The present studies report the measurement of ANF-like immunoreactivity within brain regions associated with the hypothalamo-neurohypophyseal tract and demonstrate significant water deprivation-induced reductions in ANF content of several structures (neural lobe, organum vasculosum lamina terminalis, suprachiasmatic and supraoptic nuclei) but not in others (median eminence, paraventricular nucleus, cortex and pituitary). The data suggest the production of ANF-like peptides within the brain and, further, the involvement of central ANF in extracellular fluid volume regulation.     

Frog lymph heart synthesizes and stores immunoreactive atrial natriuretic peptide.

The presence of immunoreactive atrial natriuretic peptide (irANP) and ANP gene expression in the frog lymph heart was examined by a radioimmunoassay (RIA) combined with HPLC and by Northern blot hybridization of total RNA. Serial dilution curve of the lymph heart extract was paralleled with the RIA standard curve. The lymph heart contained 153.32 +/- 35.80 pg of irANP/mg of wet tissue. The major form of irANP in the frog lymph heart was high molecular weight on reverse-phase and gel permeation high performance liquid chromatography as in the frog atria and ventricles. The frog lymph heart, as well as frog atria and ventricles, was shown to express mRNA coding for ANP. Dense core secretory granules similar to those observed in the mammalian atria were also found in the frog lymph heart. The presence of irANP and the expression of ANP gene in the frog lymph heart suggest that the lymph heart may participate in the regulation of homeostasis of lymph circulation and blood volume change through the synthesis and release of ANP.     

Circulating forms of human atrial natriuretic peptide in patients with congestive heart failure

To elucidate the circulating forms of human atrial natriuretic peptide (hANP) in patients with congestive heart failure (CHF), plasma samples obtained from 36 patients with CHF were analyzed and compared with those from normal subjects. Plasma concentrations of hANP-like immunoreactivity (LI) from normal subjects and patients with mild CHF (class I), as classified by the New York Heart Association (NYHA) functional criteria, did not differ (15 +/- 1 vs. 16 +/- 1 pmol/L, mean +/- SE), whereas plasma levels of hANP-LI in patients with moderate and severe CHF significantly (P less than 0.01) increased in relation to the severity of CHF (class II, 44 +/- 4 pmol/L; class III, 116 +/- 24 pmol/L; class IV, 141 +/- 21 pmol/L). Reverse-phase HPLC and gel permeation chromatography coupled with RIA for hANP revealed that the circulating forms of hANP-LI consisted of alpha-hANP, beta-hANP, and gamma-hANP in CHF, whereas alpha-hANP predominated in normal plasma. The percentage of beta-hANP in total hANP-LI as calculated from the chromatograms by gel filtration was greater in severe CHF (NYHA class III and IV) than those in mild CHF (NYHA class I and II), and apparently exceeded those of other forms. Successful medical treatment for CHF resulted in a marked reduction of total plasma hANP-LI levels with a concomitant disappearance or reduction of beta-hANP in 14 patients examined. These data suggest that beta-hANP and gamma-hANP are secreted from the failing human heart, possibly resulting from the augmented synthesis and/or the altered processing of hANP precursor in cardiocytes, and that circulating beta-hANP may serve as a potential marker for the severity of CHF in man.