Atrial natriuretic-like peptide and its prohormone within metasequoia.

Metasequoia glyptostroboides was one of the dominant conifers in North America, Asia, and Europe for more than 100 million years since the late Cretaceous Albian Age, but Quaternary glaciations drove the Metasequoia population to apparent extinction. A small pocket of Metasequoia, however, was found in central China in the 1940s representing the only surviving population of this "living fossil" species. Atrial natriuretic peptide, a 28-amino-acid peptide hormone that causes sodium and water excretion in animals, has been found to be part of the first peptide hormonal system in lower plants. The existence of this hormonal system has never been examined within trees of any genus. High-performance gel permeation chromatography of the leaves and stems (i.e., branches) of Metasequoia followed by atrial natriuretic peptide radioimmunoassay revealed an ANP-like peptide and its prohormone (i.e., approximately 13,000 mol wt) were present in both leaves and stems of this conifer. The elution profile of ANP-like peptide in stems of Metasequoia had a shoulder to the left of where pure synthetic ANP elutes suggesting the possibility of a slightly larger peptide eluting within this shoulder secondary to alternate processing of the ANP-like prohormone and similar to what occurs with the kidney of animals. The elution profile of ANP-like peptide in the leaves of Metasequoia revealed two peaks; one where ANP elutes and a second peak suggesting a smaller peptide that has been metabolically processed. The presence of the ANP-like prohormone strongly suggests that ANP-like gene expression is occurring in both leaves and stems of Metasequoia since this prohormone is the gene product of this hormonal system. The presence of the ANP-like hormonal system in trees implies that this hormonal system may have been present early in land plant evolution to allow trees to reach heights of greater than 30 feet where a water flow-enhancing substance is absolutely necessary for water flow to occur to these heights.     

Atrial natriuretic peptide prohormone gene expression: hormones and diseases that upregulate its expression

Atrial natriuretic peptides consist of a family of peptide hormones that are synthesized by three separate genes and then stored as three different prohormones (i.e., 126-amino acid [a.a.]) atrial natriuretic peptide (ANP), 108-a.a. brain natriuretic peptide (BNP), and 126-aa. C-natriuretic peptide (CNP) prohormones. The gene encoding for the synthesis of the atrial natriuretic peptide prohormone (proANP) consists of three exons and two introns. Exon 1 encodes the signal peptide and the first 16 aa. of the ANP prohormone. These 16 a.a. form the N-terminus of a peptide hormone named long-acting natriuretic hormone (LANH). A valine-to-methionine substitution in LANH results in a 2-fold increased incidence of strokes in humans. Exon 2 of the proANP gene encodes for three peptide hormones, i.e., vessel dilator, kaliuretic hormone, and ANP. Each of the proANP gene products have vasodilatory, diuretic, natriuretic, and/or kaliuretic properties. Stretch, glucocorticoids, thyroid hormone(s), mineralocorticoids, and calcium enhance proANP gene expression. Enhanced proANP gene expression is found in congestive heart failure, hypertension, and cirrhosis with ascites. The proANP gene is present with invertebrates and plants as well as in humans and other vertebrates.     

Atrial natriuretic peptide concentrations in pre-eclampsia.

The concentration of plasma immunoreactive atrial natriuretic peptide is positively associated with right atrial and pulmonary capillary wedge pressure, suggesting that blood volume and hence atrial pressure govern its release. Expansion of plasma volume is a central physiological adjustment in normal pregnancy. Conversely, pregnancies complicated by pre-eclampsia are associated with a reduction in plasma volume and central venous pressure. A study was therefore undertaken to test the hypothesis that plasma atrial natriuretic peptide concentrations are low in pre-eclampsia owing to deficient secretion. Concentrations of the peptide were measured by a specific radioimmunoassay. The mean plasma immunoreactive atrial natriuretic peptide concentration in healthy pregnant women (n = 22; third trimester) was higher (56 (1 SD 29) ng/l) than in 25 young, non-pregnant controls (37 (19) ng/l). Concentrations in patients suffering from mild pre-eclampsia (n = 9) were higher (127 (60) ng/l) than in normal pregnant women, and in patients with severe pre-eclampsia (n = 6) concentrations were higher still (392 (225) ng/l). Despite failure of plasma volume expansion and low central venous and pulmonary capillary wedge pressures in pre-eclampsia this condition is associated with greatly increased plasma concentrations of plasma immunoreactive atrial natriuretic peptide, which increase still further with the severity of the disease. These findings are clear evidence that atrial pressure may not be the principal determinant of the release of the natriuretic peptide in pre-eclampsia.     

Atrial natriuretic peptide induces natriuretic peptide receptor-cGMP-dependent protein kinase interaction

Circulating natriuretic peptides such as atrial natriuretic peptide (ANP) counterbalance the effects of hypertension and inhibit cardiac hypertrophy by activating cGMP-dependent protein kinase (PKG). Natriuretic peptide binding to type I receptors (NPRA and NPRB) activates their intrinsic guanylyl cyclase activity, resulting in a rapid increase in cytosolic cGMP that subsequently activates PKG. Phosphorylation of the receptor by an unknown serine/threonine kinase is required before ligand binding can activate the cyclase. While searching for downstream PKG partners using a yeast two-hybrid screen of a human heart cDNA library, we unexpectedly found an upstream association with NPRA. PKG is a serine/threonine kinase capable of phosphorylating NPRA in vitro; however, regulation of NPRA by PKG has not been previously reported. Here we show that PKG is recruited to the plasma membrane following ANP treatment, an effect that can be blocked by pharmacological inhibition of PKG activation. Furthermore, PKG participates in a ligand-dependent gain-of-function loop that significantly increases the intrinsic cyclase activity of the receptor. PKG translocation is ANP-dependent but not nitric oxide-dependent. Our results suggest that anchoring of PKG to NPRA is a key event after ligand binding that determines distal effects. As such, the NPRA-PKG association may represent a novel mechanism for compartmentation of cGMP-mediated signaling and regulation of receptor sensitivity.     

Atrial natriuretic peptide in hypoxia

A growing number of mammalian genes whose expression is inducible by hypoxia have been identified. Among them, atrial natriuretic peptide (ANP) synthesis and secretion is increased during hypoxic exposure and plays an important role in the normal adaptation to hypoxia and in the pathogenesis of cardiopulmonary diseases, including chronic hypoxia-induced pulmonary hypertension and vascular remodeling, and right ventricular hypertrophy and right heart failure. This review discusses the roles of ANP and its receptors in hypoxia-induced pulmonary hypertension. We and other investigators have demonstrated that ANP gene expression is enhanced by exposure to hypoxia and that the ANP so generated protects against the development of hypoxic pulmonary hypertension. Results also show that hypoxia directly stimulates ANP gene expression and ANP release in cardiac myocytes in vitro. Several cis-responsive elements of the ANP promoter are involved in the response to changes in oxygen tension. Further, the ANP clearance receptor NPR-C, but not the biological active NPR-A and NPR-B receptors, is downregulated in hypoxia adapted lung. Hypoxia-sensitive tyrosine kinase receptor-associated growth factors, including fibroblast growth factor (FGF) and platelet derived growth factor (PDGF)-BB, but not hypoxia per se, inhibit NPR-C gene expression in pulmonary arterial smooth muscle cells in vitro. The reductions in NPR-C in the hypoxic lung retard the clearance of ANP and allow more ANP to bind to biological active NPR-A and NPR-B in the pulmonary circulation, relaxing preconstricted pulmonary vessels, reducing pulmonary arterial pressure, and attenuating the development of hypoxia-induced pulmonary hypertension and vascular remodeling.     

Atrial natriuretic factor prohormone peptides are present in a variety of tissues.

Utilizing two sensitive and specific radioimmunoassays which immunologically recognize 1) the 98 amino acid (a.a.) N-terminus and 2) the 28 a.a. C-terminus (i.e., a.a. 99-126) of the 126 a.a. atrial natriuretic (ANF) prohormone, various tissues including aorta, kidney, small intestine, colon, liver, spleen, lung, and testis were investigated to determine if the ANF prohormone was present in any of these tissues in addition to its previously demonstrated presence in heart and brain. Aorta with 62.3 +/- 3 ng of the N-terminus/g of tissue and 51.6 +/- 1.8 ng of the C-terminus of the ANF prohormone/g of tissue had the highest concentration of the ANF prohormone of the previously undescribed ANF prohormone-containing tissues. The next highest concentration of the ANF prohormone was in the intestine, followed by lung and spleen. Pancreas, liver and kidney had similar levels of immunologically recognized ANF prohormone (approximately 1/50 of the aorta), while the testis and cerebrum had low levels. These results suggest that a much larger variety of tissues synthesize and/or store the ANF prohormone than is presently thought.     

Atrial and brain natriuretic peptide in adrenal steroidogenesis.

We elucidated the role of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in human and bovine adrenocortical steroidogenesis. The urinary volume, sodium excretion and cyclic GMP (cGMP) excretion and plasma cGMP were markedly increased by the synthetic alpha-human ANP (alpha-hANP) infusion in healthy volunteers. Plasma arginine vasopressin (AVP) and aldosterone levels were significantly suppressed. Both ANP and BNP inhibited aldosterone, 19-OH-androstenedione, cortisol and DHEA secretion dose-dependently and increased the accumulation of intracellular cGMP in cultured human and bovine adrenal cells. alpha-hANP significantly suppressed P450scc-mRNA in cultured bovine adrenal cells stimulated by ACTH. Autoradiography and affinity labeling of [125I]hANP, and Scatchard plot demonstrated a specific ANP receptor in bovine and human adrenal glands. Purified ANP receptor from bovine adrenal glands identified two distinct types of ANP receptors, one is biologically active, the other is silent. A specific BNP receptor was also identified on the human and bovine adrenocortical cell membranes. The binding sites were displaced by unlabelled ANP as well as BNP. BNP showed an effect possibly via a receptor which may be shared with ANP. The mean basal plasma alpha-hANP level was 25 +/- 5 pg/ml in young men. We confirmed the presence of ANP and BNP in bovine and porcine adrenal medulla. Plasma or medullary ANP or BNP may directly modulate the adrenocortical steroidogenesis. We demonstrated that the lack of inhibitory effect of alpha-hANP on cultured aldosterone-producing adenoma (APA) cells was due to the decrease of ANP-specific receptor, which caused the loss of suppression of aldosterone and an increase in intracellular cGMP.     

Atrial natriuretic peptide hormonal system in plants.

To determine if atrial natriuretic peptides are present in plants as well as animals, where they are important for water and sodium metabolism, the leaves and stems of the Florida Beauty (Dracena godseffiana) were examined. The N-terminus consisting of amino acids (a.a.) 1-98 (i.e., pro ANF 1-98), the mid portion of the N-terminus (a.a. 31-67; pro ANF 31-67), and C-terminus (a.a. 99-126; ANF) of the 126 a.a. atrial natriuretic factor (ANF) prohormone were all present in the leaves and stems of this plant. The concentrations of pro ANF 1-98, pro ANF 31-67 and ANF-like peptides of 120 +/- 20, 123 +/- 21, and 129 +/- 20 ng/g of plant tissue in leaves and 109 +/- 20, 96 +/- 21, and 124 +/- 18 ng/g of tissue, respectively, in the stems were lower (P less than 0.05) than their concentrations in rat (Rattus norvegicus) heart atria of 196 +/- 40, 192 +/- 28, and 189 +/- 15 ng/g of tissue respectively, but higher (P less than 0.001) than their respective concentrations of 4.3 +/- 1.4, 4.1 +/- 1.2, and 3.9 +/- 1 ng/g of rat heart ventricular tissue. We conclude that the atrial natriuretic peptide-like hormonal system is present in the plant kingdom as well as in the animal kingdom.     

Atrial natriuretic peptide: direct effects on human red blood cell dynamics.

The ability to deform is an important feature of red blood cells (RBCs) for performing their function of oxygen delivery. Little is known about the hormonal regulation of RBC deformability. Here we report that human atrial natriuretic peptide (ANP) acts directly on human RBCs leading to the elevation of local bending fluctuations of the cell membrane. These changes are accompanied by an increase in the filterability of RBCs. These ANP effects were mimicked by cyclic GMP analogues, suggesting modulation of local membrane bending fluctuations and RBC filterability via a cyclic GMP-dependent pathway. The effect of ANP on the mechanical properties of RBCs suggests that ANP may increase the passage red blood cells through capillaries resulting in an improved oxygen delivery to the tissues.     

Atrial natriuretic peptide in infants and children

Atrial natriuretic peptide (ANP) was measured in the plasma of 192 normal infants and children aged 1 day to 18 years. Plasma ANP was high during postnatal adaptation, particularly in premature infants. In 96 infants and children aged 4 months to 18 years, plasma ANP was similar to values obtained in 7 healthy adult volunteers (23.9 +/- 11.9 vs. 25.7 +/- 4.6 fmol/ml). There was no significant relationship between ANP and age. ANP is elevated about twofold in full-term neonates being 3-4 days of age, and returned to normal thereafter. It is concluded that ANP is raised during the postnatal adaptation. This hormone is possibly involved in the postnatal volume contraction and may antagonize vasoconstrictor hormones that are elevated during the postnatal period.     

Atrial natriuretic peptide in the sheep

To study atrial natriuretic peptide (ANP) physiology in the chronically catheterized pregnant sheep model we developed a heterologous radioimmunoassay for ovine ANP using an antiserum raised against 1-28 human ANP. This antiserum (Tor I) is specific for the aminoterminus of the human ANP molecule and shows little cross reaction with any carboxyterminus ANP fragments. Ovine ANP immunoreactivity was characterized using this antiserum and a commercially available carboxyterminus ANP antiserum obtained from Peninsula Laboratories. Each antiserum detected 2 peaks of immunoreactivity in ovine atrial extracts chromatographed on a Biogel P-10 column. The minor peak migrated at a position close to 125I-human ANP whereas the major peak represented a larger molecular weight species of ANP. Examination of gel filtration eluates of ovine plasma extracts showed one immunoreactive ANP peak using the Tor I assay system and 2 peaks with the Peninsula Laboratories assay. Plasma immunoreactive ANP levels were determined in 9 sheep using both radioimmunoassay systems. Mean (+/- SEM) levels were similar using the Peninsula Laboratories and the Tor I assay systems (57 +/- 8 pg/ml versus 43 +/- 4 pg/ml, P greater than 0.05). Using the Tor I antiserum, fetal plasma immunoreactive ANP levels were found to be significantly higher than maternal levels (188 +/- 17 versus 48 +/- 8 pg/ml, P less than 0.01) whereas pregnant and nonpregnant adult sheep had similar plasma immunoreactive ANP levels (48 +/- 8 versus 43 +/- 4 pg/ml, P greater than 0.05). Disappearance curves of synthetic human ANP from the plasma of maternal and fetal sheep were assessed using both immunoassay systems and found to be similar.     

Atrial natriuretic peptide, B-type natriuretic peptide, and serum collagen markers after acute myocardial infarction.

Experimental data suggest that atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) act locally as antifibrotic factors in heart. We investigated the interrelationships of natriuretic peptides and collagen markers in 93 patients receiving thrombolytic treatment for their first acute myocardial infarction (AMI). Collagen formation following AMI, evaluated as serum levels of amino terminal propeptide of type III procollagen, correlated with NH(2)-terminal proANP (r = 0.45, P < 0.001), BNP (r = 0.55, P < 0.001) and NH(2)-terminal proBNP (r = 0.50, P < 0.01) on day 4 after thrombolysis. Levels of intact amino terminal propeptide of type I procollagen decreased by 34% (P < 0.001), and levels of carboxy terminal cross-linked telopeptide of type I collagen (ICTP) increased by 65% (P < 0.001). ICTP levels correlated with NH(2)-terminal proBNP (r = 0.25, P < 0.05) and BNP (r = 0.28, P < 0.05) on day 4. Our results suggest that ANP and BNP may act as regulators of collagen scar formation and left ventricular remodeling after AMI in humans. Furthermore, degradation of type I collagen is increased after AMI and may be regulated by BNP.     

Atrial natriuretic peptide and vasopressin in human plasma

Using a specific radioimmunoassay for atrial natriuretic peptide (ANP), plasma immunoreactive ANP was measured in 17 normal subjects and 83 patients with various diseases. Plasma ANP concentration in normal subjects was 14.1 +/- 1.7 pg/ml (mean +/- S.E.). Relatively high plasma ANP concentrations were detected in patients with diabetes mellitus, hyperthyroidism, atrial fibrillation and liver cirrhosis. Plasma ANP concentrations in the patients correlated positively with mean arterial blood pressure and plasma AVP concentrations. Plasma ANP concentrations in the patients also had positive correlations with left atrial dimension and left ventricular diastolic dimension determined by echocardiography. Another positive correlation was observed in the patients between plasma AVP concentrations and mean arterial blood pressure. These results suggest that ANP is a volume regulatory hormone but also that ANP may be involved in the blood pressure regulating system.     

Atrial natriuretic peptide in the heart and pancreas

We used antisera to pure atrial natriuretic peptide to localise this peptide by immunocytochemistry in rat and human tissue. We showed that both rat and human atrial cardiocytes gave a positive reaction while ventricular cardiocytes were consistently negative. Peripheral islet cells in rat but not in human pancreas also showed positive staining for ANP. We showed by double labelling techniques that the ANP was present in the glucagon containing cells.     

Atrial natriuretic peptide in acute mountain sickness

To test the hypothesis that elevated atrial natriuretic peptide (ANP) may be involved in altered fluid homeostasis at high altitude, we examined 25 mountaineers at an altitude of 550 m and 6, 18, and 42 h after arrival at an altitude of 4,559 m, which was climbed in 24 h starting from 3,220 m. In 14 subjects, symptoms of acute mountain sickness (AMS) were absent or mild (group A), whereas 11 subjects had severe AMS (group B). Fluid intake was similar in both groups. In group B, urine flow decreased from 61 +/- 8 (base line) to 36 +/- 3 (SE) ml/h (maximal decrease) (P less than 0.05) and sodium excretion from 7.9 +/- 0.9 to 4.6 +/- 0.7) mmol.l-1.h-1 (P less than 0.05); ANP increased from 31 +/- 4 to 87 +/- 26 pmol/l (P less than 0.001), plasma aldosterone from 191 +/- 27 to 283 +/- 55 pmol/l (P less than 0.01 compared with group A), and antidiuretic hormone (ADH) from 1.0 +/- 0.1 to 2.9 +/- 1.2 pmol/l (P = 0.08 compared with group A). These variables did not change significantly in group A, with the exception of a decrease in plasma aldosterone from 189 +/- 19 to 111 +/- 17 pmol/l (P less than 0.01). There were no measurable effects of elevated ANP on natriuresis, cortisol, or blood pressure. The reduced diuresis in AMS may be explained by increased plasma aldosterone and ADH overriding the expected renal action of ANP. The significance of elevated ANP in AMS remains to be established.(ABSTRACT TRUNCATED AT 250 WORDS)