Rat brain natriuretic peptide is localized in atrial granules and released into the circulation

Comparison of N-terminal pro-atrial natriuretic peptide and three cardiac biomarkers for discriminatory ability of clinical stage in dogs with myxomatous mitral valve disease

Plasma N-terminal pro-atrial natriuretic peptide (NT-proANP) concentration increases with progression of myxomatous mitral valve disease (MMVD) in dogs. This multicentre, prospective study compared plasma NT-proANP, N-terminal pro-brain natriuretic peptide (NT-proBNP), ANP, and cardiac troponin I (cTnI) concentrations in dogs with MMVD for their characteristics and discriminatory ability to detect cardiac dilatation and congestive heart failure (CHF). Thirty-six healthy dogs and 69 dogs with MMVD were included. Clinical variables were obtained via physical examination, thoracic radiography, and echocardiography. The discriminatory ability of each cardiac biomarker (CB) to determine the presence or absence of cardiac dilatation (event 1) and CHF (event 2) was evaluated using the receiver operating characteristic curves. Plasma NT-proANP, NT-proBNP, and ANP concentrations showed a significant association with the left atrium/aorta ratio (P<0.01). The area under the curve of plasma NT-proANP and NT-proBNP concentrations were 0.72 and 0.75, respectively in event1 and 0.72 and 0.76, respectively in event2. Plasma NT-proANP and NT-proBNP concentrations showed sensitivity 80.0 and 80.0%; specificity 67.6 and 64.7% in event1 (cutoff value; 8,497.81 pg/ml and 1,453.00 pmol/l, respectively) and sensitivity 85.7 and 81.0%; specificity 60.4 and 64.6% in event2 (cutoff value; 8,684.33 pg/ml and 1,772.00 pmol/l, respectively). In dogs with MMVD, plasma NT-proANP, NT-proBNP, and ANP concentrations increase with left atrial enlargement. Particularly, plasma NT-proANP and NT-proBNP concentrations appeared to be equally useful in the discriminatory ability to detect cardiac dilatation and CHF.

Localization profiles of natriuretic peptides in hearts of pre-hibernating and hibernating Anatolian ground squirrels (Spermophilus xanthoprymnus)

The Anatolian ground squirrel (Spermophilus xanthoprymnus) is a typical example of true mammalian hibernators. In order to adapt to extreme external and internal environments during hibernation, they lower their body temperatures, heart rates and oxygen consumption; however, pathological events such as ischemia and ventricular fibrillation do not occur in their cardiovascular systems. During the hibernation, maintenance of cardiac function is very important for survival of ground squirrels. Natriuretic peptides (NPs) are key factors in the regulation of cardiovascular hemostasis. Since NPs' role on the protection of heart during hibernation are less clear, the aim of this study was to investigate dynamic changes in NPs content in the cardiac chambers and to reveal the possible role of NPs on establishing cardiac function in ground squirrel during hibernation using immunohistochemistry. The immunohistochemical results indicate that cardiac NP expressions in atrial and ventricular cardiomyocytes were different from each other and were sex-independent. ANP and BNP were expressed in a chamber-dependent manner in female and male squirrel hearts. Furthermore, cardiac NPs expression levels in hibernation period were lower than those at the pre-hibernation period. During prehibernation period, ANP, BNP and CNP were expressed in the white and beige adipocytes of epicardial adipose tissue (EAT); while during hibernation period, the brown adipocytes of EAT were positive for BNP and CNP. These data suggest that the hibernation-dependent reduction in levels of NPs, particularly ANP, in cardiac chambers and EAT may be associated with low heart rate and oxygen consumption during hibernation. However, further studies are needed to better delineate the roles of NPs during the hibernation.

Usefulness of the brain natriuretic peptide to atrial natriuretic peptide ratio in determining the severity of mitral regurgitation

BACKGROUND

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) levels were characterized in subjects with mitral regurgitation (MR).

METHODS

Sixty-two cases of moderate or severe chronic MR were studied. The blood levels of neurohormonal factors were stratified by the known MR prognostic factors of New York Heart Association (NYHA) functional class, left ventricular end-diastolic diameters, left ventricular end-systolic diameter (LVDs), ejection fraction (EF), left atrial diameter and presence of atrial fibrillation (AF).

RESULTS

ANP levels were higher in NYHA class II and lower in classes I and III/IV (P=0.0206). BNP levels were higher in NYHA class II than class I (P=0.0355). The BNP/ANP ratio was significantly higher in NYHA classes II and III/IV than in class I (P=0.0007). To differentiate between NYHA classes I/II and III/IV, a cut-off BNP/ANP ratio of 2.97 produced a sensitivity of 78% and specificity of 87%. Compared with subjects in sinus rhythm, patients with AF had an enlarged left atrium and lower ANP levels. The BNP/ANP ratio correlated significantly with left atrial diameter, LVDs and EF (r=0.429, P=0.0017; r=0.351, P=0.0117; and r=-0.349, P=0.0122; respectively), and was significantly higher among all the known operative indications for MR tested (LVDs 45 mm or more, EF 60% or less, NYHA class II or greater and AF; P=0.0073, P=0.003, P=0.0102 and P=0.0149, respectively).

CONCLUSIONS

In chronic MR, levels of ANP and BNP, and the BNP/ANP ratio are potential indicators of disease severity.

Novel salmon cardiac peptide hormone is released from the ventricle by regulated secretory pathway

We used the secretion of the novel salmon cardiac peptide (sCP) as a model to examine the mechanisms of ventricular hormone release. Mechanical load increased dose dependently the secretion of immunoreactive sCP from isolated perfused salmon ventricle, with 3. 3-fold increase when a load of 13 cmH(2)O was applied. Endothelin-1 (5 nmol/l) was also able to rapidly increase the secretion of sCP. The released peptide corresponded to the biologically active sCP-29, whereas the large ventricular storage consisted of pro-sCP-sized material. With the use of immunoelectron microscopy, a large number of granules containing immunoreactive sCP could be detected in salmon ventricle. As judged by RNA blot analysis, there was very active basal expression of the sCP gene in the ventricle, which was not increased by mechanical load of up to 2-h duration. Our results show that the ventricle actively expresses the gene of sCP, stores the prohormone in secretory granules, and releases the peptide in response to mechanical load and endothelin-1. Thus the salmon ventricle uses the regulated pathway to produce and release a hormone structurally related to the mammalian natriuretic peptides.

Altered regulation of natriuretic peptides in the rat heart by prenatal exposure to morphine

1. Both endogenous and exogenous opioids modulate blood pressure and cardiac function by stimulating cardiac synthesis of atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP). Since morphine crosses the placental barrier, it could alter the ANF-BNP system in the fetal heart. The aim of this study was to characterize cardiac natriuretic peptides in normal rat development and in rats prenatally exposed to morphine. 2. Female rats received either saline or morphine (10 or 20 mg kg-1 day-1) via osmotic minipumps during gestation. The effects of this treatment were investigated in offspring at 1, 4 and 22 days of age. 3. During maturation, atrial ANF and ANF mRNA increased by 3-fold from birth to 3 weeks of age, but BNP and BNP mRNA tended to decrease. In the ventricles, both ANF and BNP content decreased at 3 weeks after birth, from 25.11 +/- 3.6 to 0.81 +/- 0.1 ng (mg protein)-1 (P < 0.001), and from 3.36 +/- 0.33 to 0.19 +/- 0.01 ng (mg protein)-1 (P < 0.001), respectively. However, whereas ventricular ANF mRNA decreased, BNP mRNA levels did not change during maturation. Prenatal exposure to morphine significantly increased ANF content in the left atria of 22-day-old rats, and in the right atria of 1-, 4- and 22-day-old rats compared with age-matched saline controls. In contrast, prenatal exposure to 20 mg kg-1 day-1 morphine significantly inhibited BNP and BNP mRNA in the ventricles at all ages studied. 4. These observations suggest that alterations in mRNA synthesis or stability and/or post-translational processing of ANF and BNP occur in the heart during maturation, and that prenatal exposure to morphine alters cardiac production, and possibly release, of both peptides.

A hormone-encoding gene identifies a pathway for cardiac but not skeletal muscle gene transcription

In contrast to skeletal muscle, the mechanisms responsible for activation and maintenance of tissue-specific transcription in cardiac muscle remain poorly understood. A family of hormone-encoding genes is expressed in a highly specific manner in cardiac but not skeletal myocytes. This includes the A- and B-type natriuretic peptide (ANP and BNP) genes, which encode peptide hormones with crucial roles in the regulation of blood volume and pressure. Since these genes are markers of cardiac cells, we have used them to probe the mechanisms for cardiac muscle-specific transcription. Cloning and functional analysis of the rat BNP upstream sequences revealed unexpected structural resemblance to erythroid but not to muscle-specific promoters and enhancers, including a requirement for regulatory elements containing GATA motifs. A cDNA clone corresponding to a member of the GATA family of transcription factors was isolated from a cardiomyocyte cDNA library. Transcription of this GATA gene is restricted mostly to the heart and is undetectable in skeletal muscle. Within the heart, GATA transcripts are localized in ANP- and BNP-expressing myocytes, and forced expression of the GATA protein in heterologous cells markedly activates transcription from the natural cardiac muscle-specific ANP and BNP promoters. This GATA-dependent pathway defines the first mechanism for cardiac muscle-specific transcription. Moreover, the present findings reveal striking similarities between the mechanisms controlling gene expression in hematopoietic and cardiac cells and may have important implications for studies of cardiogenesis.

A hormone-encoding gene identifies a pathway for cardiac but not skeletal muscle gene transcription

In contrast to skeletal muscle, the mechanisms responsible for activation and maintenance of tissue-specific transcription in cardiac muscle remain poorly understood. A family of hormone-encoding genes is expressed in a highly specific manner in cardiac but not skeletal myocytes. This includes the A- and B-type natriuretic peptide (ANP and BNP) genes, which encode peptide hormones with crucial roles in the regulation of blood volume and pressure. Since these genes are markers of cardiac cells, we have used them to probe the mechanisms for cardiac muscle-specific transcription. Cloning and functional analysis of the rat BNP upstream sequences revealed unexpected structural resemblance to erythroid but not to muscle-specific promoters and enhancers, including a requirement for regulatory elements containing GATA motifs. A cDNA clone corresponding to a member of the GATA family of transcription factors was isolated from a cardiomyocyte cDNA library. Transcription of this GATA gene is restricted mostly to the heart and is undetectable in skeletal muscle. Within the heart, GATA transcripts are localized in ANP- and BNP-expressing myocytes, and forced expression of the GATA protein in heterologous cells markedly activates transcription from the natural cardiac muscle-specific ANP and BNP promoters. This GATA-dependent pathway defines the first mechanism for cardiac muscle-specific transcription. Moreover, the present findings reveal striking similarities between the mechanisms controlling gene expression in hematopoietic and cardiac cells and may have important implications for studies of cardiogenesis.