Natriuretic peptide receptors regulate endothelin synthesis and release from parathyroid cells.

Cloned rat parathyroid cells (PTr cell line) that produce parathyroid hormone-related peptide plus endothelin 1 and primary cultures of human parathyroid cells were tested for growth and differentiation responses to atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). High- and low-affinity binding sites for ANP were found on PTr cells; BNP appeared to bind to the same receptors with similar affinities. Either ANP or BNP stimulated production of cGMP and caused a 30% decrease in Na(+)-K(+)-Cl- cotransport. Each peptide increased synthesis and secretion of endothelin 1 by PTr cells in a dose-dependent fashion, but cell growth was not affected. Human parathyroid cells (normal and pathological) also responded to ANP or BNP with an increase in cGMP production. The finding of receptors for natriuretic hormones on parathyroid cells with consequent effects on release of endothelin 1 might be of relevance in understanding the clinical association between hyperparathyroidism and hypertension.     

C-type natriuretic peptide (CNP) effects in anterior pituitary cell lines: evidence for homologous desensitisation of CNP-stimulated cGMP accumulation in alpha T3-1 gonadotroph-derived cells

C-type natriuretic peptide (CNP), the third member of the natriuretic peptide family, has been found at its highest tissue concentrations in the anterior pituitary, where it is localised in gonadotrophs. Its specific guanylyl cyclase-containing receptor, GC-B, is also expressed on several anterior pituitary cell types, and CNP potently stimulates cGMP accumulation in rat pituitary cell cultures and pituitary cell lines. The mouse gonadotroph-derived alpha T3-1 cell line has been shown to express CNP as well as GC-B (but not GC-A) receptors, suggesting that CNP may well be an autocrine regulator of gonadotrophs. Comparing effects of three natriuretic peptides (atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP) and CNP) on cGMP accumulation in four pituitary cell lines (alpha T3-1, TtT-GF, AtT-20 and GH(3)) we find that CNP is most potent and effective in alpha T3-1 cells. In these cells, CNP-stimulated cGMP accumulation was found to desensitise during a 30 min exposure to CNP. Pretreatment with CNP for up to 6 h also caused a significant reduction in the ability of CNP to subsequently stimulate cGMP accumulation. This effect was receptor specific, because pretreatment with sodium nitroprusside (an activator of nitric oxide-sensitive guanylyl cyclase), or with ANP or BNP, did not cause desensitisation of CNP-stimulated cGMP accumulation. Protein kinase C activation with phorbol esters also inhibited CNP-stimulated cGMP accumulation and such inhibition was also seen in cells desensitised by pretreatment with CNP. Thus it appears that the endogenous GC-B receptors of alpha T3-1 cells are subject to both homologous and heterologous desensitisation, that the mechanisms underlying these forms of desensitisation are distinct, and that cGMP elevation alone is insufficient to desensitise GC-B receptors.     

Receptor selectivity of natriuretic peptide family, atrial natriuretic peptide, brain natriuretic peptide, and C-type natriuretic peptide.

To elucidate the ligand-receptor relationship of the natriuretic peptide system, which comprises at least three endogenous ligands, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP), and three receptors, the ANP-A receptor or guanylate cyclase-A (GC-A), the ANP-B receptor or guanylate cyclase-B (GC-B), and the clearance receptor (C-receptor), we characterized the receptor preparations from human, bovine, and rat tissues and cultured cells with the aid of the binding assay, Northern blot technique, and the cGMP production method. Using these receptor preparations, we examined the binding affinities of ANP, BNP, and CNP for the C-receptor and their potencies for cGMP production via the ANP-A receptor (GC-A) and the ANP-B receptor (GC-B). These analyses revealed the presence of a marked species difference in the receptor selectivity of the natriuretic peptide family, especially among BNPs. Therefore, we investigated the receptor selectivity of the natriuretic peptide family using the homologous assay system with endogenous ligands and receptors of the same species. The rank order of binding affinity for the C-receptor was ANP greater than CNP greater than BNP in both humans and rats. The rank order of potency for cGMP production via the ANP-A receptor (GC-A) was ANP greater than or equal to BNP much greater than CNP, but that via the ANP-B receptor (GC-B) was CNP greater than ANP greater than or equal to BNP. These findings on the receptor selectivity of the natriuretic peptide family provide a new insight into the understanding of the physiological and clinical implications of the natriuretic peptide system.     

Antihypertrophic actions of the natriuretic peptides in adult rat cardiomyocytes: importance of cyclic GMP

Atrial natriuretic peptide (ANP) prevents hypertrophy of neonatal cardiomyocytes. However, whether this effect is retained in the adult phenotype or if other members of the natriuretic peptide family exhibit similar antihypertrophic properties, has not been elucidated. OBJECTIVE: Our objective was to examine whether the natriuretic peptides protect against adult cardiomyocyte hypertrophy in vitro. METHODS: Adult rat cardiomyocytes were incubated with angiotensin II (Ang II)+/-ANP, B-type (BNP) or C-type (CNP) natriuretic peptides for determination of [3H]phenylalanine incorporation, c-fos mRNA expression and cyclic GMP. The effects of 8-bromo-cyclic GMP (cyclic GMP analogue), HS-142-1 (particulate guanylyl cyclase inhibitor) and KT5823 (cyclic GMP-dependent protein kinase inhibitor) were also investigated. RESULTS: Ang II-stimulated increases in markers of hypertrophy, [3H]phenylalanine incorporation (to 136+/-3% of control, n=9) and c-fos mRNA expression (4.3+/-1.4-fold, n=5), were completely prevented by each of ANP, BNP or CNP. This protective action was accompanied by increased cardiomyocyte cyclic GMP. Inhibitory actions on [3H]phenylalanine incorporation were mimicked by 8-bromo-cyclic GMP, and were abolished by HS-142-1. KT5823 blocked the response to BNP and CNP, but not to ANP. CONCLUSION: ANP prevents hypertrophy of adult rat cardiomyocytes. This protective action is shared by BNP and CNP and involves activation of particulate guanylyl cyclase receptors. Antihypertrophic effects of BNP and CNP are mediated through cyclic GMP-dependent protein kinase, but ANP can activate additional pathways independent of cyclic GMP to prevent adult cardiomyocte hypertrophy. These novel findings are of interest particularly since BNP appears to exert antifibrotic rather than antihypertrophic actions in vivo, while CNP is thought to act at least in part via the endothelium.     

Atrial natriuretic peptide effects in AtT-20 pituitary tumour cells.

Whether atrial natriuretic peptide (ANP)-evoked inhibition of corticotrophin-releasing factor (CRF)-stimulated ACTH secretion was also manifest in ACTH secreting AtT-20 pituitary tumour cells was investigated. ANP stimulated increases in cGMP accumulation at concentrations of the peptide above 10(-8) M which indicates the presence of the ANP receptors on these cells. CRF stimulated a concentration-dependent increase in ACTH secretion from AtT-20 cells which was unaffected by ANP, 8-bromo-cGMP, or sodium nitroprusside (SNP). Calcium stimulated a concentration-dependent increase in ACTH secretion from electrically permeabilised cells which was unaffected by co-incubation with cGMP but potentiated by cAMP. These results reveal the presence of ANP receptors on AtT-20 cells but suggest that an incomplete expression of the stimulus-secretion coupling mechanisms for ANP, at some point after cGMP production, prevents the effects of natriuretic peptides upon ACTH secretion being manifest in these cells.     

Immunocytochemical localization, binding, and effects of atrial natriuretic peptide in rat adipocytes

The metabolic effects of atrial natriuretic peptide (ANP) have not been widely investigated. Since adipocyte cells represent a model system extensively used to examine the metabolic actions of many peptide hormones, we sought to establish whether ANP could bind to adipocyte membranes, alter cyclic nucleotide metabolism, and affect spontaneous or hormone-stimulated lipolysis. Using in vitro autoradiographic techniques, radiolabelled ANP was found to bind specifically to mammary gland fat cells. Additionally, endogenous ANP-like immunoreactivity could be localized in the plasma membrane compartment and cytoplasmic matrix of fat cells, but not in fat vacuoles. [125I]ANP bound to single high affinity sites (Kd = 0.72 nM) in fat cell membranes. The binding was rapid (equilibrium within 1 min at 25 degrees C) and specific. The atrial peptide was capable of stimulating a time- and concentration-dependent increase in cGMP accumulation in isolated adipocytes, but had no effect on spontaneous or stimulated [-)-isoproterenol, ACTH, forskolin) cAMP formation. ANP did not alter the increase in glycerol production stimulated by l-epinephrine in isolated fat cells. While i.v. infusion of ANP stimulated a marked increase in circulating levels of cGMP, the atrial peptide did not alter plasma triglyceride levels. These data demonstrate the presence of specific ANP binding sites on adipocyte membranes and internalization of ANP-associated immunoreactivity. These receptors are biochemically functional given the ability of ANP to augment cGMP formation. The peptide, however, does not exert an action on adipocyte lipolysis. Adipocytes, therefore, represent an ANP target tissue in which the physiological action of the peptide is yet to be defined.     

Atrial natriuretic peptide, oxytocin, and vasopressin increase guanosine 3',5'-monophosphate in LLC-PK1 kidney epithelial cells

The effect of atrial natriuretic peptide (ANP), arginine vasopressin (AVP), and oxytocin (OT) on cAMP and cGMP accumulation was investigated in LLC-PK1 kidney epithelial cells. The addition of ANP, AVP, and OT to intact cells produced a time- and concentration-dependent increase in cGMP accumulation. ANP produced a 1.7-fold increase in cGMP at 10 pM and a maximal 28-fold increase in cGMP at 1 microM. ANP had no effect on basal or AVP-induced stimulation of cAMP accumulation. OT was 10-fold more potent than AVP at increasing cGMP levels, producing a 2.1-fold increase in cGMP at 0.1 nM, whereas AVP was 100-fold more potent at increasing cAMP levels. At a concentration of 1 microM, AVP and OT produced a maximal 12 to 14-fold increase in cGMP, while OT and AVP produced 50- and 90-fold increase in cAMP, respectively. The selective OT agonist [Thr4, Gly7]oxytocin was very effective at increasing cGMP, but not at increasing cAMP levels. The V2-vasopressin agonist [deamino-Pen1,Val4, D-Arg8]vasopressin did not increase cGMP levels, but produced a 20-fold increase in cAMP levels. The addition of ANP together with either AVP or OT produced an additive increase in cGMP content. Simultaneous addition of AVP and OT did not lead to a greater increase in cAMP or cGMP levels. These results suggest that the AVP- and OT-induced increase in cGMP is mediated by OT receptors, whereas the increase in cAMP is probably mediated by vasopressin receptors. ANP increased the activity of particulate guanylate cyclase by 6-fold, while AVP and OT has no effect on particulate guanylate cyclase activity. The relatively selective inhibitor of soluble guanylate cyclase, methylene blue, had no effect on the ANP-induced increase in cGMP content in intact cells, but produced a 50% inhibition of the increase in cGMP by AVP and OT. Methylene blue did not alter the stimulation of cAMP by AVP or OT. These results demonstrate that ANP, AVP, and OT increase cGMP in LLC-PK1 kidney epithelial cells. The increase in cGMP by ANP is mediated by particulate guanylate cyclase, whereas AVP and OT probably increase cGMP by interacting with OT receptors coupled to soluble guanylate cyclase.     

Expression of receptors for atrial natriuretic peptide on the murine bone marrow-derived stromal cells.

Atrial natriuretic peptide (ANP) receptors were identified on both murine bone marrow-derived stromal cell lines A-3 and ALC and primary cultured cells using [125I]ANP binding assays and Northern blot analyses. The binding of [125I] ANP to the stromal cells was rapid, saturable, and of high affinity. The dissociation constants between ANP and its receptors on these cells showed no difference among cell types, while maximal binding capacity values were different among cell types. Competitive inhibition of [125I]ANP binding with C-atrial natriuretic factor, specific for ANP clearance receptor (ANPR-C), revealed that most of [125I]ANP-binding sites corresponded to ANPR-C. Northern blotting data corroborated that bone marrow-derived stromal cells expressed ANPR-C. However, in ALC cells, ANP biological receptors (either ANPR-A or ANPR-B), the mol wt of which is approximately 130K, were detected, and cGMP was accumulated after stimulation with ANP. On the other hand, in another stromal cell clone, A-3 cells, the expression of biological receptor was not detected in the affinity cross-linking and competitive inhibition experiments using [125I]ANP. However, A-3 cells accumulated cGMP by responding to ANPR-B-specific ligand, C-type natriuretic peptide. These results suggest that ALC cells equally express ANPR-A and ANPR-B, while A-3 cells express ANPR-B dominantly. Although the physiological roles of these receptors in the bone marrow is still not resolved, ANP is expected to play a role in the regulation of stromal cell functions in bone marrow.     

Role of the natriuretic peptide system in lipogenesis/lipolysis

AIM: There is recent evidence that the natriuretic peptide (NP) system promotes adipose tissue lipolysis in primates. This effect is mediated by the interaction of NP with its active receptors through guanylyl cyclase activation and cGMP production. This review will briefly focus on the new aspects of NP pathophysiology in man. DATA SYNTHESIS: NP receptors have been described in rodent adipocytes, and the expression of their mRNA is found in human adipose tissue together with high level of ANP binding sites. In isolated fat cells, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were able to stimulate lipolysis as much as isoproterenol, a non-selective beta-adrenergic receptor agonist, whereas C-type natriuretic peptide (CNP) had the lowest lipolytic effect. The potent lipolytic effect of NP has also been confirmed in samples of abdominal adipose tissue from healthy subjects. The potency order of the lipolytic effect (ANP > BNP > CNP) and ANP-induced cGMP production supported the presence of type A natriuretic peptide receptor in human fat cells. The effect of NP on lipid metabolism is confirmed by the fact that intravenous ANP infusion is followed by plasma NEFA and glycerol concentration increase (reflecting lipid mobilisation). CONCLUSIONS: The NP system seems to play an important role in lipid metabolism, possibly affecting the pathophysiology of obesity and obesity-related disorders, such hypertension. Further studies, however, are needed to completely establish the mechanisms involved in NP-induced lipolysis and the real relevance of this new pathway specific of primates.     

Augmentation of the cardiac natriuretic peptides by beta-receptor antagonism: evidence from a population-based study

Objectives. The present retrospective analysis of data derived from a population-based study examined the relationship between intake of beta-receptor antagonists and plasma concentrations of the cardiac natriuretic peptides and their second messenger.

Background. Beta-receptor antagonists are widely used for treatment of cardiovascular disease. In addition to direct effects on heart rate and cardiac contractility, recent evidence suggests that beta-receptor antagonists may also modulate the cross talk between the sympathetic nervous system and the cardiac natriuretic peptide system.

Methods. Plasma concentrations of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and their second messenger cyclic guanosine monophosphate (cGMP) were assessed in addition to anthropometric, hemodynamic and echocardiographic parameters in a population-based sample (n = 672), of which 80 subjects used beta-receptor antagonists.

Results. Compared to subjects without medication, subjects receiving beta-receptor antagonists were characterized by substantially elevated ANP, BNP and cGMP plasma concentrations (plus 32%, 89% and 18%, respectively, p < 0.01 each). Analysis of subgroups revealed that this effect was highly consistent and present even in the absence of hypertension, left atrial enlargement, left ventricular hypertrophy or left ventricular dysfunction. The most prominent increase was observed in a subgroup with increased left ventricular mass index. By multivariate analysis, a statistically significant and independent association between beta-receptor antagonism and ANP, BNP and cGMP concentrations was confirmed. Such an association could not be demonstrated for other antihypertensive agents such as angiotensin-converting enzyme inhibitors or diuretics.

Conclusions. Beta-receptor antagonists appear to augment plasma ANP, BNP and cGMP concentrations. The current observation suggests an important contribution of the cardiac natriuretic peptide system to the therapeutic mechanism of beta-receptor antagonists.     

Adenosine 3',5'-cyclic monophosphate enhances dopamine accumulation in rat hypothalamic cell culture containing dopaminergic neurons

The regulation of dopamine accumulation in cultured rat hypothalamic cells by adenosine 3',5'-cyclic monophosphate (cAMP) was investigated in cultures of newborn rat hypothalamic cells. Both dibutyryl cAMP, (Bu)2-cAMP, and forskolin enhanced [3H]dopamine accumulation in a dose-dependent manner. cAMP also enhanced [3H]dopamine accumulation, but to a lesser degree. Neither n-butyrate nor adenosine alone enhanced [3H]dopamine accumulation. (Bu)2-cAMP had no effect on basal efflux of [3H]radioactivity. The effect of (Bu)2-cAMP appeared on day 5 of culture, reached a maximum on day 6, and then rapidly decreased. These results suggest that dopamine uptake by cultured rat hypothalamic cells is regulated by intracellular cAMP.     

Cyclic GMP production by ANP, BNP, and NO during worsening and improvement of chronic heart failure

Cyclic GMP (cGMP) serves as an intracellular second messenger of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and nitric oxide (NO) and its peripheral blood concentration is an index of its biological activity. It has been reported that the plasma concentration of cGMP is correlated with the concentrations of ANP and BNP and is related to the prognosis of chronic heart failure patients, but the relation with NO has not been studied. Therefore, we investigated the roles of ANP, BNP, and NO in relation to cGMP in the blood during worsening and improvement of chronic heart failure. The subjects were 25 patients who were hospitalized in our hospital for acute worsening of chronic heart failure. Plasma concentrations of NO, norepinephrine (NE), ANP, BNP, and cGMP were measured on acute worsening (admission) and improvement (discharge) of heart failure. The cGMP concentration on worsening showed a positive correlation with the NO concentration (r = (0.57, P < 0.01), but no correlations with ANP or BNP were observed. The cGMP concentration on improvement showed no correlation with the NO concentration, but a positive correlation with ANP (r = 0.69, P < 0.001) and BNP (r = 0.67, P < 0.001). No correlation was observed between the NO and NE concentrations. We also studied serious cases of NYHA IV and mild cases of NYHA II to III. The cGMP concentration in the serious group showed a positive correlation with the NO concentration but no correlations with ANP or BNP concentrations on worsening. However, in the mild group, the cGMP concentration during worsening showed positive correlations with both the NO and BNP concentrations. On improvement, the cGMP concentration showed no correlation with the NO concentration but positive correlations with both the ANP and BNP concentrations in both the severe and mild groups. The results suggest the possibility that cGMP is produced mainly by NO during worsening, and by ANP and BNP rather than NO during improvement of chronic heart failure.     

Natriuretic peptides in the pathophysiology of congestive heart failure

A hallmark of congestive heart failure (CHF) is the activation of the cardiac endocrine system, in particular atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). The natriuretic peptides are a group of structurally similar but genetically distinct peptides that have diverse actions in cardiovascular, renal, and endocrine homeostasis. ANP and BNP are of myocardial cell origin and C-type natriuretic peptide (CNP) is of endothelial origin. ANP and BNP bind to the natriuretic peptide-A receptor (NPR-A), which, via 3',5'-cyclic guanosine monophosphate (cGMP), mediates natriuresis, vasodilatation, renin inhibition, antimitogenesis, and lusitropic properties. CNP lacks natriuretic actions but possesses vasodilating and growth inhibiting actions via the guanylyl cyclase-linked natriuretic peptide-B receptor. All three peptides are cleared by the natriuretic peptide-C receptor and degraded by the ectoenzyme neutral endopeptidase 24.11, both of which are widely expressed in kidney, lung, and vascular wall. Recently, a fourth member of the natriuretic peptide, Dendroaspis natriuretic peptide (DNP) has been reported to be present in human plasma and atrial myocardium and is elevated in plasma of human CHF.     

Atrial and brain natriuretic peptides inhibit the endothelin-1 secretory response to angiotensin II in porcine aorta.

We have recently shown that the porcine aorta releases immunoreactive endothelin-1 in a time-dependent way. Here, we examined the inhibition by atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) of endothelin-1 secretion after stimulation with angiotensin II (Ang II) by using porcine aorta. Ang II dose-dependently stimulated immunoreactive endothelin-1 secretion. Porcine ANP-(1-28) and porcine BNP-26 both inhibited such secretion in a dose-dependent way. The addition of a cyclic guanosine 5'-monophosphate (cGMP) analogue, 8-bromo-cGMP, reduced the immunoreactive endothelin-1 secretion after stimulation with Ang II. In cultured porcine endothelial cells the inhibition by porcine ANP-(1-28) and porcine BNP-26 of immunoreactive endothelin-1 secretion after stimulation with Ang II was paralleled by an increase in the cellular cGMP level. Rat ANP-(5-25) was weaker than porcine ANP-(1-28) in inhibiting immunoreactive endothelin-1 secretion and increasing cGMP in cultured cells. There was negative correlation between the percent decrease in immunoreactive endothelin-1 and the percent increase in cGMP. Neither porcine ANP-(1-28) nor BNP-26 affected the number or sensitivity of Ang II binding sites in cultured porcine endothelial cells. These results suggest that ANP and BNP inhibit endothelin-1 secretion after stimulation with Ang II, probably through a cGMP-dependent process.     

Current biochemistry, molecular biology, and clinical relevance of natriuretic peptides

The mammalian natriuretic peptide family consists of atrial (ANP), brain [B-type; BNP] and C-type natriuretic peptide (CNP) and three receptors, natriuretic receptors-A (NPR-A), -B (NPR-B) and -C (NPR-C). Both ANP and BNP are abundantly expressed in the heart and are secreted mainly from the atria and ventricles, respectively. By contrast, CNP is mainly expressed in the central nervous system, bone and vasculature. Plasma concentrations of both ANP and BNP are elevated in patients with cardiovascular disease, though the magnitude of the increase in BNP is usually greater than the increase in ANP. This makes BNP is a clinically useful diagnostic marker for several pathophysiological conditions, including heart failure, ventricular remodeling and pulmonary hypertension, among others. Recent studies have shown that in addition to BNP-32, proBNP-108 also circulates in human plasma and that levels of both forms are increased in heart failure. Furthermore, proBNP-108 is O-glycosylated and circulates at higher levels in patients with severe heart failure. In this review we discuss recent progress in our understanding of the biochemistry, molecular biology and clinical relevance of the natriuretic peptide system.     

The role of natriuretic peptides in cardioprotection

Atrial natriuretic peptide (ANP) and brain (B-type) natriuretic peptide (BNP) are circulating hormones of cardiac origin that play an important role in the regulation of intravascular blood volume and vascular tone. The plasma concentrations of ANP and BNP are elevated in heart failure, and they are considered to compensate for heart failure because of their diuretic, natriuretic, and vasodilating actions and inhibitory effects on renin and aldosterone secretion. Evidence is also accumulating from recent work that ANP and BNP exert their cardioprotective functions not only as circulating hormones but also as local autocrine and/or paracrine factors. In studies using cultured neonatal myocytes and fibroblasts, exogenous administration of both ANP and ANP antagonists demonstrated that ANP has antihypertrophic and antifibrotic functions. Corroborating these in vitro results, mice lacking natriuretic receptor-A (NPR-A), the receptor for ANP and BNP, develop cardiac hypertrophy and fibrosis independent of their blood pressure. Recent studies also suggest that the intracardiac natriuretic peptides/cGMP system plays a counter-regulatory role against the intracardiac renin-angiotensin-aldosterone system and TGF-beta mediated pathway. In a clinical setting, human recombinant ANP and BNP may be used for a therapy of heart failure; however, further evaluation is required in the future.     

Calcium-calmodulin kinase II is the common factor in calcium-dependent cardiac expression and secretion of A- and B-type natriuretic peptides

Peptides derived from the precursor of A- and B-type natriuretic peptides (ANP and BNP) are powerful clinical markers of cardiac hypertrophy and dysfunction. It is known that many stimuli affecting the intracellular calcium concentration also induce ANP and BNP secretion. It was our intention to study the mechanisms by which calcium regulates the secretion of ANP and BNP. The effects of pacing and calcium-calmodulin kinase II activity on natriuretic peptide secretion were studied in isolated perfused rat atria and cultured rat neonatal cardiomyocytes. In isolated rat atrium pacing induced an increase in diastolic, systolic, and averaged intracellular free calcium concentration and a frequency-dependent increase in the secretion of both ANP and BNP. The molar ratio of the secreted natriuretic peptides (ANP to BNP) remained nearly constant ( approximately 1000) at all the pacing frequencies tested (1, 3, 6, and 8 Hz). Calmodulin kinase II inhibitor KN-93 (3 mum) did not affect intracellular free calcium concentration but showed a frequency-dependent inhibitory effect on ANP and BNP secretion without a change in ANP to BNP ratio. In the neonatal cardiomyocytes, KN-93 (3 mum) suppressed the secretion and gene expression of both ANP and BNP. Overexpression of constitutively active (T286D) or nuclear (delta(B)) calcium-calmodulin kinase II induced an increase in ANP and BNP gene expression. The results indicate that the calcium-dependent secretion and gene expression of A- and B-type natriuretic peptides are similarly regulated by calmodulin kinase II-dependent mechanisms. This is a plausible mechanism contributing to exercise-induced natriuretic peptide secretion and the augmented secretion in heart dysfunction due to impaired calcium handling.     

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

BACKGROUND: Screening for patients with asymptomatic left ventricular dysfunction is of considerable importance because they may benefit from early treatment with angiotensin converting enzyme inhibitors. It has been suggested that atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and cyclic guanosine 3',5'-monophosphate (cGMP) might be useful markers for screening. OBJECTIVE: To compare directly the power of the three immunoreactive forms of ANP (CT-ANP, beta-ANP, NT-ANP) and BNP and cGMP to detect asymptomatic left ventricular dysfunction. METHODS AND RESULTS: Radionuclide ventriculography was used to study left ventricular ejection fraction in 37 patients with asymptomatic left ventricular dysfunction, 32 patients with mild to moderate congestive heart failure, and 38 controls. CT-ANP, NT-ANP, beta-ANP, BNP, and cGMP were measured at rest and 3 minutes after exercise. Plasma BNP was the most sensitive marker for patients with asymptomatic left ventricular dysfunction but it reached only a sensitivity of 58% and a specificity of 76% at rest and a sensitivity of 65% and a specificity of 84% after exercise. Combined measurements of all natriuretic peptides and cGMP did not improve the power to detect asymptomatic left ventricular function above that of a single BNP measurement. CONCLUSIONS: Although natriuretic peptides and cGMP measured at rest and three minutes after ergometry may be useful for monitoring left ventricular dysfunction they are unlikely to be suitable for more general routine screening for completely asymptomatic left ventricular dysfunction.