Does the natriuretic peptide system exist throughout the animal and plant kingdom?

The Natriuretic Peptide System: A Single Entity, Pleiotropic Effects

In the modern scientific landscape, natriuretic peptides are a complex and interesting network of molecules playing pleiotropic effects on many organs and tissues, ensuring the maintenance of homeostasis mainly in the cardiovascular system and regulating the water-salt balance. The characterization of their receptors, the understanding of the molecular mechanisms through which they exert their action, and the discovery of new peptides in the last period have made it possible to increasingly feature the physiological and pathophysiological role of the members of this family, also allowing to hypothesize the possible settings for using these molecules for therapeutic purposes. This literature review traces the history of the discovery and characterization of the key players among the natriuretic peptides, the scientific trials performed to ascertain their physiological role, and the applications of this knowledge in the clinical field, leaving a glimpse of new and exciting possibilities for their use in the treatment of diseases.

Citrus Canker Pathogen, Its Mechanism of Infection, Eradication, and Impacts

Citrus canker is a ravaging bacterial disease threatening citrus crops. Its major types are Asiatic Canker, Cancrosis B, and Cancrosis C, caused by Xanthomonas citri pv. citri (Xcc), Xanthomonas citri pv. aurantifolii pathotype-B (XauB), and pathotype-C (XauC), respectively. The bacterium enters its host through stomata and wounds, from which it invades the intercellular spaces in the apoplast. It produces erumpent corky necrotic lesions often surrounded by a chlorotic halo on the leaves, young stems, and fruits, which causes dark spots, defoliation, reduced photosynthetic rate, rupture of leaf epidermis, dieback, and premature fruit drop in severe cases. Its main pathogenicity determinant gene is pthA, whose variants are present in all citrus canker-causing pathogens. Countries where citrus canker is not endemic adopt different methods to prevent the introduction of the pathogen into the region, eradicate the pathogen, and minimize its dissemination, whereas endemic regions require an integrated management program to control the disease. The main aim of the present manuscript is to shed light on the pathogen profile, its mechanism of infection, and fruitful strategies for disease management. Although an adequate method to completely eradicate citrus canker has not been introduced so far, many new methods are under research to abate the disease.

Modified Natriuretic Peptides and their Potential Role in Cancer Treatment

The natriuretic peptide family (NPs) is a group of natural endocrine hormones, containing a 17-amino acid ring structure connected by disulfide bonds of two cysteines. In this review, the members of the natriuretic peptide family and their corresponding receptors as well as the anti-cancer effects are introduced. Four cardiac hormones of NPs (ANP, VD, KP and LANP) can effectively inhibit the growth of human small cell lung cancer, breast cancer and other tumors and significantly reduce tumor volume in vivo. The in vitro experiments also show that cardiac hormones, CNP and urodilatin can effectively inhibit the growth of most tumor cells. We then further summarized the anti-cancer mechanism of natriuretic peptides. Finally, we introduce several methods that modify natriuretic peptides, leading to enhance their stability and prolong the biological effects of these peptides, which might be helpful for the clinical application in the future. Peptide therapy is a very promising field for cancer treatments since they can induce the death of cancer cells without dramatically affecting normal cells. The synthesis of a useful and stable natriuretic peptide can enhance the effect of cancer treatments and significantly reduce drug resistance and toxicity.

ScPNP-A, a plant natriuretic peptide from Stellera chamaejasme, confers multiple stress tolerances in Arabidopsis

As a class of peptide hormone, plant natriuretic peptides (PNPs) play an important role in maintaining water and salt balance in plants, as well as in the physiological processes of biotic stress and pathogen resistance. However, in plants, except for some PNPs, such as the Arabidopsis thaliana PNP-A (AtPNP-A), of which the function has not yet been thoroughly revealed, few PNPs in other plants have been reported. In this study, a PNP-A (ScPNP-A) has been identified and characterized in Stellera chamaejasme for the first time. ScPNP-A is a double-psi beta-barrel (DPBB) fold containing protein and is localized in the extracellular (secreted) space. In S. chamaejasme, the expression of ScPNP-A was significantly up-regulated by salt, drought and cold stress. Changes at the physiological and biochemical levels and the expression of resistance-related genes indicated that overexpression of ScPNP-A can significantly improve salt, drought and freezing tolerance in Arabidopsis. ScPNP-A could stimulate the opening, not the closing of stomata, and its expression was not enhanced by external application of ABA. Furthermore, overexpression of ScPNP-A resulted in the elevated expression of genes in the ABA biosynthesis and reception pathway. These suggested that there may be some cross-talk between ScPNP-A and the ABA-dependent signaling pathways to regulate water related stress, however further experimentation is required to understand this relationship. In addition, overexpression of ScPNP-A can enhance the resistance to pathogens by enhancing SAR in Arabidopsis. These results indicate that ScPNP-A could function as a positive regulator in plant response to biotic stress and abiotic stress.

Critical symbiont signals drive both local and systemic changes in diel and developmental host gene expression

The colonization of an animal's tissues by its microbial partners creates networks of communication across the host's body. We used the natural binary light-organ symbiosis between the squid Euprymna scolopes and its luminous bacterial partner, Vibrio fischeri, to define the impact of colonization on transcriptomic networks in the host. A night-active predator, E. scolopes coordinates the bioluminescence of its symbiont with visual cues from the environment to camouflage against moon and starlight. Like mammals, this symbiosis has a complex developmental program and a strong day/night rhythm. We determined how symbiont colonization impacted gene expression in the light organ itself, as well as in two anatomically remote organs: the eye and gill. While the overall transcriptional signature of light organ and gill were more alike, the impact of symbiosis was most pronounced and similar in light organ and eye, both in juvenile and adult animals. Furthermore, the presence of a symbiosis drove daily rhythms of transcription within all three organs. Finally, a single mutation in V. fischeri-specifically, deletion of the lux operon, which abrogates symbiont luminescence-reduced the symbiosis-dependent transcriptome of the light organ by two-thirds. In addition, while the gills responded similarly to light-organ colonization by either the wild-type or mutant, luminescence was required for all of the colonization-associated transcriptional responses in the juvenile eye. This study defines not only the impact of symbiont colonization on the coordination of animal transcriptomes, but also provides insight into how such changes might impact the behavior and ecology of the host.

Natriuretic Peptides and Normal Body Fluid Regulation

Natriuretic peptides are structurally related, functionally diverse hormones. Circulating atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are delivered predominantly by the heart. Two C-type natriuretic peptides (CNPs) are paracrine messengers, notably in bone, brain, and vessels. Natriuretic peptides act by binding to the extracellular domains of three receptors, NPR-A, NPR-B, and NPR-C of which the first two are guanylate cyclases. NPR-C is coupled to inhibitory proteins. Atrial wall stress is the major regulator of ANP secretion; however, atrial pressure changes plasma ANP only modestly and transiently, and the relation between plasma ANP and atrial wall tension (or extracellular volume or sodium intake) is weak. Absence and overexpression of ANP-related genes are associated with modest blood pressure changes. ANP augments vascular permeability and reduces vascular contractility, renin and aldosterone secretion, sympathetic nerve activity, and renal tubular sodium transport. Within the physiological range of plasma ANP, the responses to step-up changes are unimpressive; in man, the systemic physiological effects include diminution of renin secretion, aldosterone secretion, and cardiac preload. For BNP, the available evidence does not show that cardiac release to the blood is related to sodium homeostasis or body fluid control. CNPs are not circulating hormones, but primarily paracrine messengers important to ossification, nervous system development, and endothelial function. Normally, natriuretic peptides are not powerful natriuretic/diuretic hormones; common conclusions are not consistently supported by hard data. ANP may provide fine-tuning of reno-cardiovascular relationships, but seems, together with BNP, primarily involved in the regulation of cardiac performance and remodeling. © 2017 American Physiological Society. Compr Physiol 8:1211-1249, 2018.

The Kinome of Pacific Oyster Crassostrea gigas, Its Expression during Development and in Response to Environmental Factors

Oysters play an important role in estuarine and coastal marine habitats, where the majority of humans live. In these ecosystems, environmental degradation is substantial, and oysters must cope with highly dynamic and stressful environmental constraints during their lives in the intertidal zone. The availability of the genome sequence of the Pacific oyster Crassostrea gigas represents a unique opportunity for a comprehensive assessment of the signal transduction pathways that the species has developed to deal with this unique habitat. We performed an in silico analysis to identify, annotate and classify protein kinases in C. gigas, according to their kinase domain taxonomy classification, and compared with kinome already described in other animal species. The C. gigas kinome consists of 371 protein kinases, making it closely related to the sea urchin kinome, which has 353 protein kinases. The absence of gene redundancy in some groups of the C. gigas kinome may simplify functional studies of protein kinases. Through data mining of transcriptomes in C. gigas, we identified part of the kinome which may be central during development and may play a role in response to various environmental factors. Overall, this work contributes to a better understanding of key sensing pathways that may be central for adaptation to a highly dynamic marine environment.

Hypoxic conditions stimulate the release of B-type natriuretic peptide from human retinal pigment epithelium cell culture

PURPOSE

A-type peptide, a natriuretic peptide belonging to the natriuretic peptide family, has been shown to be increased in the vitreous of patients suffering from diabetic retinopathy and that human retina has a well-developed natriuretic peptide system. The stimulus to which the synthesis of natriuretic peptides responded in these patients has, however, remained unknown. As the natriuretic peptides have recently been shown to respond to hypoxic conditions, the genes of both A-type and B-type have a hypoxia-response element (HRE) in their promoter sequence, we therefore hypothesized that hypoxia in the human retinal pigment epithelium will increase the secretion of NT-proBNP, the most common natriuretic peptide monitored in clinical medicine.

METHODS

We used cultured human retinal pigment epithelium cell line (ARPE-19) which was exposed either to normoxia or to hypoxia for 2 hr, 4 hr, 6 hr and 24 hr. NT-proBNP was measured with enzyme immunoassay, VEGF with ELISA and HIF-1α with Western blotting.

RESULTS

Hypoxia induced VEGF 165 release in culture medium and HIF-1α expression in cultured ARPE-19 cells. Time-dependent NT-proBNP release was detected when the ARPE-19 cells were cultured under normoxia. When hypoxia was induced, a statistically significant increase in NT-proBNP release was demonstrated in the culture medium.

CONCLUSIONS

Hypoxic conditions increase the release of a natriuretic peptide from retinal pigment epithelium (RPE) cells. The secretion of VEGF was also enhanced. The responses were associated with the up-regulation of the HIF-1α transcription factor. These results explain the previous findings from patients with diabetes, which also suggest that hypoxia is a ubiquitous stimulus for the secretion of natriuretic peptides in human body.

B-type natriuretic peptide (BNP), not ANP, is the principal cardiac natriuretic peptide in vertebrates as revealed by comparative studies

The natriuretic peptide (NP) family consists of at least seven members; cardiac ANP, BNP and VNP and brain CNPs (CNP1-4). Phylogenetic and comparative genomic analyses showed that CNP4 is the ancestral molecule of the family, from which CNP3 and CNP1/2 were duplicated in this order, and that the three cardiac NPs were generated from CNP3 by tandem duplication. Seven members existed at the divergence of ray-finned fishes and lobe-finned fishes (tetrapods), but some of the NP genes have disappeared during the course of evolution. In ray-finned fishes, all three cardiac NPs exist in chondrostei and some migratory teleost species, but VNP is generally absent and ANP is absent in a group of teleosts (Beloniformes). In tetrapods, ANP and BNP are present in mammals and amphibians, but ANP is usually absent in reptiles and birds. Thus, BNP is a ubiquitous cardiac NP in bony fishes and tetrapods though elasmobranchs and cyclostomes have only CNP3/4 as a cardiac NP. Functional studies indicate that cardiac NPs are essential Na(+)-extruding hormones throughout vertebrates; they play critical roles in seawater (SW) adaptation in teleosts, while they are important volume-depleting hormones in mammals as water and Na(+) are regulated in parallel in terrestrial animals. In mammals, cardiac NPs become prominent in pathological conditions such as heart failure where they are used in diagnosis and treatment. Although the functional role of BNP has not yet been fully elucidated compared with ANP in non-mammalian vertebrates, it appears that BNP plays pivotal roles in the cardiovascular and body fluid regulation as shown in mammals. ANP has previously been recognized as the principal cardiac NP in mammals and teleosts, but comparative studies have revealed that BNP is the only cardiac NP that exists in all tetrapods and teleosts. This is an excellent example showing that comparative studies have created new insights into the molecular and functional evolution of a hormone family.

Central role of guanylyl cyclase in natriuretic peptide signaling in hypertension and metabolic syndrome

Studied for nearly 30 years for its ability to control many parameters, such as vascular smooth muscle cell relaxation, heart fibrosis, and kidney function, the natriuretic peptide (NP) system is now considered to be a key element in several other major metabolic pathways. After stimulation by NPs, natriuretic peptide receptors (NPR) convert GTP to the second messenger cGMP. In addition to its vasodilatory effects and natriuretic and diuretic functions, cGMP has been positively associated with fat cell function, apoptosis, and NPR expression/activity modulation. The NP system is also closely linked to metabolic syndrome (MetS) progression and obesity control. A new era is now on its way targeting the NP system to not only treat high blood pressure, but to also assist in the fight against the obesity pandemic. Here, we summarize recent data on the role of NPs in hypertension and MetS.

The response of non-traditional natriuretic peptide production sites to salt and water manipulations in the rainbow trout

Natriuretic peptides (NPs) and their receptors (NPRs) comprise an evolutionarily conserved signaling system with profound physiological effects on vertebrate renal and cardiovascular systems. Some NPs (ANP, BNP and VNP)are primarily of cardiac origin whereas CNP is common in the brain. In mammals, non-traditional sites of NPs synthesis, BNP in brain and CNP in atrium, appear to have complementary actions. In the present study, trout were chronically adapted to freshwater (FW) (a volume-loading, salt-depleting environment), saltwater (SW) (a volume-depleting, salt-loading environment),FW and fed a high-salt diet (FW–HSD) (a volume- and salt-loading regime)or acutely volume depleted or expanded by hemorrhage or infusion with dialyzed plasma to perturb volume homeostasis. The responses of brain and atrial BNP and CNP mRNA, pro-peptide, NPR-A and NPR-B were evaluated using quantitative PCR and western analysis. Brain pro-BNP and NPR-A was increased in FW–HSD trout and decreased in SW trout. Brain pro-CNP was largely unaffected whereas NPR-B mRNA was increased in FW–HSD trout. Atrial CNP,although produced at lower levels than other cardiac NPs, was markedly elevated in chronically (FW–HSD) and acutely volume expanded trout(dialyzed-plasma infusion) whereas decreased in hemorrhaged trout. These findings indicate that non-traditional NP synthesis sites in the trout probably complement the broad hypovolemic and hypotensive actions of traditional (cardiac) NP synthesis sites in response to volume expansion but not to plasma osmolarity. This supports the hypothesis that the piscine and mammalian NP systems are fundamentally similar and appear to protect the heart from volume overload.

Xanthomonas axonopodis pv. citri uses a plant natriuretic peptide-like protein to modify host homeostasis

Plant natriuretic peptides (PNPs) are a class of extracellular, systemically mobile molecules that elicit a number of plant responses important in homeostasis and growth. The bacterial citrus pathogen, Xanthomonas axonopodis pv. citri, also contains a gene encoding a PNP-like protein, XacPNP, that shares significant sequence similarity and identical domain organization with plant PNPs but has no homologues in other bacteria. We have expressed and purified XacPNP and demonstrated that the bacterial protein alters physiological responses including stomatal opening in plants. Although XacPNP is not expressed under standard nutrient rich culture conditions, it is strongly induced under conditions that mimic the nutrient poor intercellular apoplastic environment of leaves, as well as in infected tissue, suggesting that XacPNP transcription can respond to the host environment. To characterize the role of XacPNP during bacterial infection, we constructed a XacPNP deletion mutant. The lesions caused by this mutant were more necrotic than those observed with the wild-type, and bacterial cell death occurred earlier in the mutant. Moreover, when we expressed XacPNP in Xanthomonas axonopodis pv. vesicatoria, the transgenic bacteria caused less necrotic lesions in the host than the wild-type. In conclusion, we present evidence that a plant-like bacterial PNP can enable a plant pathogen to modify host responses to create conditions favorable to its own survival.

Natriuretic peptides in hormonal regulation of hypoxia responses

The possibility that natriuretic peptides' effects are important in hypoxia responses of vertebrates is reviewed. Both the transcription and release of natriuretic peptides are affected by oxygen tension. Furthermore, many of the effects observed in hypoxia, such as diuresis and a reduction of plasma volume, are also caused by treatment of the animal with natriuretic peptides. Also, several clinical observations about changes in natriuretic peptide levels in, e.g., sleep apnea and cyanotic congenital heart disease, are consistent with the idea that hypoxia is involved in the etiology of conditions, in which natriuretic peptide levels increase. Virtually all published information on the relationship between oxygen and natriuretic peptides is based on human studies. Because hypoxic conditions are more common in aquatic than terrestrial environments, future studies about the possible role of natriuretic peptides in hypoxia, as well as the role of hypoxia in the evolution of natriuretic peptides, including the different subtypes, should increasingly involve also aquatic organisms.

Comparative physiology of the piscine natriuretic peptide system

The natriuretic peptide (NP) family is a seemingly ubiquitous sodium and volume reducing endocrine system of predominantly cardiac origin. Members of the NP system include ANP, BNP, CNP, VNP, their guanylate cyclase (GC)-linked receptors (NPR-A and NPR-B), and clearance receptor (NPR-C). Through the activation of their membrane-bound GC receptors, these small peptides modulate cellular functions that affect both salt and water balance. The elucidation of piscine NP sequences, structure, and functions has steadily advanced over the past 15 years spearheaded by research from Dr. Yoshio Takei's laboratory. The development of these homologous NPs has led to extensive research into both the evolutionary and physiological significance of NPs in fishes. One outcome has been the development of two seemingly disparate hypotheses of NP function; a role in salt excretion, the osmoregulatory hypothesis, versus a role in protecting the heart, the cardioprotective hypotheses. In the osmoregulatory hypothesis NPs are released in response to elevated ambient salinity and inhibit drinking and intestinal uptake of salt, thereby effectively reducing plasma sodium levels. In contrast, the cardioprotective theory depicts NPs acting to prevent debilitating cardiodilation from an excess of either venous or arterial pressure through vasodilation and a reduction of blood volume. These seemingly distinct hypotheses may be elements of a more general regulatory system and certainly require further investigation. Undoubtedly their resolution will not only give us a better perspective of the evolutionary basis of the NP system but will provide us with a greater appreciation of salt and water homeostasis in vertebrates.

Co-expression and promoter content analyses assign a role in biotic and abiotic stress responses to plant natriuretic peptides

BACKGROUND

Plant natriuretic peptides (PNPs) are a class of systemically mobile molecules distantly related to expansins. While several physiological responses to PNPs have been reported, their biological role has remained elusive. Here we use a combination of expression correlation analysis, meta-analysis of gene expression profiles in response to specific stimuli and in selected mutants, and promoter content analysis to infer the biological role of the Arabidopsis thaliana PNP, AtPNP-A.

RESULTS

A gene ontology analysis of AtPNP-A and the 25 most expression correlated genes revealed a significant over representation of genes annotated as part of the systemic acquired resistance (SAR) pathway. Transcription of these genes is strongly induced in response to salicylic acid (SA) and its functional synthetic analogue benzothiadiazole S-methylester (BTH), a number of biotic and abiotic stresses including many SA-mediated SAR-inducing conditions, as well as in the constitutive SAR expressing mutants cpr5 and mpk4 which have elevated SA levels. Furthermore, the expression of AtPNP-A was determined to be significantly correlated with the SAR annotated transcription factor, WRKY 70, and the promoters of AtPNP-A and the correlated genes contain an enrichment in the core WRKY binding W-box cis-elements. In constitutively expressing WRKY 70 lines the expression of AtPNP-A and the correlated genes, including the SAR marker genes, PR-2 and PR-5, were determined to be strongly induced.

CONCLUSION

The co-expression analyses, both in wild type and mutants, provides compelling evidence that suggests AtPNP-A may function as a component of plant defence responses and SAR in particular. The presented evidence also suggests that the expression of AtPNP-A is controlled by WRKY transcription factors and WRKY 70 in particular. AtPNP-A shares many characteristics with PR proteins in that its transcription is strongly induced in response to pathogen challenges, it contains an N-terminal signalling peptide and is secreted into the extracellular space and along with PR-1, PR-2 and PR-5 proteins it has been isolated from the Arabidopsis apoplast. Based on these findings we suggest that AtPNP-A could be classified as a newly identified PR protein.

Biology of the natriuretic peptides

The biology of the natriuretic peptide (NP) system is complex, yet highly phylogenetically preserved. It regulates salt and water handling, promotes vasodilatation, and exerts favorable effects on the heart in the context of processes such as heart failure. Prior assumptions about the production of B-type NP (BNP) and its amino-terminal precursor fragment (NT-proBNP) have recently been refuted. It is now recognized that rather than a 1:1 secretion of these 2 NPs, a mixture of cleaved and uncleaved NPs is released by the cardiomyocyte. It is also recognized that BNP is rapidly modified into a mixture of various fragments. Commercial assays for the detection of BNP and NT-proBNP measure a mixture of cleaved and uncleaved NPs as well as varying amounts of degraded BNP. BNP and NT-proBNP are cleared differentially: BNP is actively removed from the bloodstream and also has passive clearance mechanisms, including renal clearance; NT-proBNP is cleared more passively by organs with high rates of blood flow, including the kidney.

Endocrine disrupting pesticides: implications for risk assessment

Endocrine disrupting (ED) chemicals are compounds that alter the normal functioning of the endocrine system, potentially causing disease or deformity in organisms and their offspring. Pesticides are used widely to kill unwanted organisms in crops, public areas, homes and gardens and medicinally to kill parasites. Many are proven or suspected to be EDs. Ancient physiological similarities between different vertebrate groups suggest that disorders observed in wildlife may indicate risks to humans. This makes accurate risk assessment and effective legislation difficult. In this paper, the hazardous properties of pesticides which are known to have ED properties are reviewed in order to assess the implications for risk assessment. As well as data on sources of exposure in the United Kingdom (UK) an assessment of the evidence on the health effects of ED pesticides is also included. In total, 127 have been identified from the literature and their effects and modes of action are listed in this paper. Using the UK as a case study, the types and quantities of pesticides used, and their methods of application are assessed, along with their potential pathways to humans. In the UK reliable data are available only for agricultural use, so non-agricultural routes of pesticide exposure have been poorly quantified. The exposure of people resident in or visiting rural areas could also have been grossly under-estimated. Material links between ED pesticide use and specific illnesses or deformities are complicated by the multifactorial nature of disease, which can be affected by factors such as diet. Despite these difficulties, a large body of evidence has accumulated linking specific conditions to ED pesticides in wildlife and humans. A more precautionary approach to the use of ED pesticides, especially for non-essential purposes is proposed.

C-type natriuretic peptide and heart failure

C-type natriuretic peptide (CNP) is a peptide produced by the vascular endothelium with vasodilative properties. It shares structural and physiological properties with the atrial and brain natriuretic peptides (ANP and BNP), whose central role in the pathophysiology of heart failure (CHF) is firmly established. The role of CNP, first isolated from porcine brain, has not been yet completely determined. The transcription of the gene, that in man is located on chromosome 2, is regulated by factors such as tumor necrosis factor and interleukin-1. Two mature forms of the peptide exist: CNP-53, that predominates in tissues and CNP-22, found mainly in plasma. As recently found, CNP is produced directly in the myocardium and an increase in plasma levels of this peptide and of its precursor was observed in CHF. The aim of this review was to examine the current literature relating to cardiovascular functions of CNP and in particular to its role in CHF. In fact, CNP may represent an important new local autocrine and endocrine mediator in CHF although further evaluations are required to define its full pathophysiological role in this disease.

Hormonal control of salt and water balance in vertebrates

The endocrine system mediates many of the physiological responses to the homeostatic and acclimation demands of salt and water transport. Many of the hormones involved in the control of salt and water transport are common to all vertebrates, although their precise function and target tissues have changed during evolution. Arginine vasopressin (vasotocin), angiotensin II, natriuretic peptides, vasoactive intestinal peptide, urotensin II, insulin and non-genomic actions of corticosteroids are involved in acute (minutes and hours) alterations in ion and water transport. This rapid alteration in transport is primarily the result changes in behavior, blood flow to osmoregulatory organs, and membrane insertion or activation (e.g., phosphorylation) of existing transport proteins, ion and water channels, contransporters and pumps. Corticosteroids (through genomic actions), prolactin, growth hormone, and insulin-like growth factor I primarily control long-term (several hours to days) changes in transport capacity that are the result of synthesis of new transport proteins, cell proliferation, and differentiation. In addition to the important task of establishing broad evolutionary patterns in hormones involved in ion regulation, comparative endocrinology can determine species and population level differences in signaling pathways that may be critical for adaptation to extreme or rapidly changing environments.

Synergistic activation of salmon cardiac function by endothelin and beta-adrenergic stimulation

The aim was to find out the effects of endothelin-1 (ET-1) in salmon (Salmo salar) cardiac contractile and endocrine function and its possible interaction with beta-adrenergic regulation. We found that ET-1 has a positive inotropic effect in salmon heart. ET-1 (30 nM) increased the contraction amplitude 17+/-4.7% compared with the basal level. beta-Adrenergic activation (isoprenaline, 100 nM) increased contraction amplitude 30+/-13.1%, but it did not affect the contractile response to ET-1. ET-1 (10 nM) stimulated the secretion of salmon cardiac natriuretic peptide (sCP) from isolated salmon ventricle (3.3+/-0.14-fold compared with control) but did not have any effect on ventricular sCP mRNA. Isoprenaline alone (0.1-1,000 nM) did not stimulate sCP release, but ET-1 (10 nM) together with isoprenaline (0.1 nM) caused a significantly greater increase of sCP release than ET-1 alone (5.4+/-0.07 vs. 3.3+/-0.14 times increase compared with control). The effects on the contractile and secretory function could be inhibited by a selective ETA-receptor antagonist BQ-610 (1 microM), whereas ETB-receptor blockage (by 100 nM BQ-788) enhanced the secretory response. Thus ET-1 is a phylogenetically conserved regulator of cardiac function, which has synergistic action with beta-adrenergic stimulation. The modulatory effects of ET-1 may therefore be especially important in situations with high beta-adrenergic tone.

Haemoconcentration via diuresis in short-term hypoxia: a possible role for cardiac natriuretic peptide in rainbow trout

Rainbow trout, exposed to acute hypoxia (decrease of oxygen level from full to 30% air saturation for 1 h, stable 30% air saturation for 2 h), showed more than twofold increase in urine flow rate. Hypoxic diuresis was associated with a sustained increase in dorsal aortic cardiac peptide (sCP) level, and the diuresis could be completely inhibited by a bolus injection of sCP antiserum. These results suggest that hypoxic haemoconcentration, which is partially achieved via increased urine flow rate in vertebrates, is caused by cardiac peptides. The results further suggest that cardiac peptide receptors in hypoxic fish gills modulate the postbranchial systemic level of sCP.

The presence of ANP in rat peritoneal mast cells

Atrial natriuretic peptide (ANP) is an important component of the natriuretic peptide system. A great role in many regulatory systems is played by mast cells. Meanwhile involvement of these cells in ANP activity is poorly studied. In this work, we have shown the presence of ANP in rat peritoneal mast cells. Pure fraction of mast cells was obtained by separation of rat peritoneal cells on a Percoll density gradient. By Western blotting, two ANP-immunoreactive proteins of molecular masses of 2.5 kDa and 16.9 kDa were detected in lysates from these mast cells. Electron microscope immunogold labeling has revealed the presence of ANP-immunoreactive material in storage, secreting and released granules of mast cells. Our findings indicate the rat peritoneal mast cells to contain both ANP prohormone and ANP. These both peptides are located in mast cell secretory granules and released by mechanism of degranulation. It is discussed that many mast cell functions might be due to production of natriuretic peptides by these cells.

Molecular evolution of the natriuretic peptide system as revealed by comparative genomics

The natriuretic peptide (NP) family is a group of peptides involved in cardiovascular and body fluid regulation in vertebrates. While only C-type NP (CNP) has been found in elasmobranchs, atrial NP (ANP), B-type NP (BNP) and CNP have been found in mammals, and ventricular NP (VNP) instead of BNP in teleosts. Thus, it was once hypothesized that CNP is the ancestral NP, from which ANP and BNP/VNP were generated. However, the discovery of hfNP in the hagfish, and CNP in the lamprey suggested that the ancestral NP had characteristics common to these two peptides. Genomic studies in ray-finned fish revealed multiplication processes of NP genes: The ancestral gene was duplicated into four CNP genes before the divergence of elasmobranchs, and ANP, BNP and VNP genes were generated from one of the four CNP genes by tandem duplications. From up to seven NP genes thus generated, tetrapods are supposed to have lost some of them. Concerning NP receptors, teleosts also have more subtypes (three guanylyl cyclase-coupled receptors and two clearance receptors) than mammals. It is of interest to examine how the complicated NP system in teleosts compared with tetrapods, is involved in the adaptation to a wide variety of osmotic environments.

Atrial natriuretic peptide induces an acrosome reaction in giant panda spermatozoa and enhances their penetration of salt-stored porcine oocytes

Atrial natriuretic peptide (ANP) is a vasodilator peptide primarily produced in the heart. Locally synthesized ANP has been found in reproductive tissues of various mammals and humans, and plays an important role in rat oocyte maturation and human sperm function. The objective of the present study was to determine the effects of ANP on the function (acrosome reaction and zona penetration) of giant panda spermatozoa. In fresh and frozen-thawed spermatozoa that had been preincubated for 2.5h, treatment with ANP (for 60 min) significantly increased the proportion of acrosome-reacted spermatozoa; maximal response (an acrosome reaction in 18.3 and 21.8% of fresh and frozen-thawed spermatozoa, respectively) was detected at 1 nM ANP. Treatment with C-ANP-(4-23), an analogue of ANP and specific binder to natriuretic peptide receptors-C (NPRC), had no significant effect on the acrosome reaction. However, the cyclic guanosine 5'-monophosphate (cGMP)-dependent protein kinase (PKG) inhibitor KT5823 completely abolished the effect of ANP on acrosome reaction. The effects of ANP, caffeine and heparin on frozen-thawed sperm function were studied by insemination of porcine salt-stored oocytes in a modified Tris-buffered medium (mTBM). The presence of ANP, caffeine or heparin in the insemination medium resulted in a higher proportion (P < 0.05) of oocytes with spermatozoa in the zona and perivitelline space (PVS), and a higher average number of spermatozoa/oocyte (P < 0.05) in the zona and PVS. However, in the absence of ANP, caffeine and heparin, there were no oocytes with a spermatozoon in the PVS. There were no differences among ANP, caffeine or heparin treatments for the proportion of oocytes penetrated or average number of spermatozoa/oocyte in the zona and PVS. In conclusion, we inferred that ANP induced the acrosome reaction of preincubated giant panda spermatozoa by a PKG pathway. Furthermore, ANP enhanced the penetrability of porcine salt-stored oocytes by frozen-thawed giant panda spermatozoa.

Molecular regulation of the brain natriuretic peptide gene

After brain natriuretic peptide (BNP) was isolated in 1988, rapid progress was made in cloning its cDNA and gene, facilitating studies of tissue-specific expression and molecular regulation of gene expression. This review focuses on the molecular determinants of regulation of the rat and human BNP genes, including signaling pathways that impact on changes in gene expression and cis regulatory elements responsive to these signaling pathways. For both rat and human genes, elements in the proximal promoter (-124 to -80), including GATA, MCAT, and AP-1-like, have been shown to contribute to basal and inducible regulation. More distal elements in the human BNP gene respond to calcium signals (an NF-AT site at -927), thyroid hormone (a thyroid-responsive element at -1000), and mechanical stretch (shear stress-responsive elements at -652 and -162). Understanding how BNP is regulated by signaling molecules that are activated in the hypertrophied and ischemic heart should be useful in understanding the underlying pathology. This may lead to therapeutic strategies that prevent hypertrophy while allowing for the beneficial effects of BNP production.

C-type natriuretic peptide in vascular physiology and disease

Natriuretic peptides play a critical role in coordination of fluid/electrolyte balance and vascular tone. The renal effects of circulating atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are distinct from the paracrine effects of vascular C-type natriuretic peptide (CNP). CNP is widely expressed throughout the vasculature and is found in particularly high concentrations in the endothelium. Recent studies demonstrate that CNP is a novel endothelium-derived hyperpolarising factor (EDHF) that complements the actions of other endothelial vasorelaxant mediators such as nitric oxide (NO) and prostacyclin. Since several cardiovascular disorders are associated with dysfunction of natriuretic peptide activity, selective modulation of the natriuretic peptide pathways represents an important therapeutic target; whilst this has been exploited to some degree in terms of ANP/BNP, the therapeutic potential of CNP has yet to be tapped. This review focuses on recent findings on the actions and mechanism of locally produced endothelial-derived CNP in the cardiovascular system and highlights many potential avenues for therapeutic intervention, via modulation of CNP-signalling, in cardiovascular disease.

Atrial natriuretic peptide negatively regulates follicle-stimulating hormone-induced porcine oocyte maturation and cumulus expansion via cGMP-dependent protein kinase pathway

This study examined the effect of atrial natriuretic peptide (ANP) on porcine cumulus-enclosed oocyte (CEO) maturation and cumulus expansion. ANP negatively regulated follicle-stimulating hormone (FSH)-stimulated germinal vesicle breakdown (GVBD; 90.1, 81.2 and 68.2% for FSH, FSH+10nM ANP and FSH+1 microM ANP, respectively), first polar body emission (PB1; 86.1, 75.3 and 53.3% for FSH, FSH+1 nM ANP and FSH+1 microM ANP, respectively) and cumulus expansion (CEI; 3.47, 3.16 and 2.43 for FSH, FSH+1 nM ANP and FSH+1 microM ANP, respectively) in a dose-dependent manner when CEOs were cultured in the maturation medium containing porcine follicular fluid (pFF). This negative effect showed a time-dependent manner after preincubation with 100 nM ANP for 5h (78.4% PB1), 10h (81.7% GVBD and 74.1% PB1), 20 h (78.5% GVBD and 68.9% PB1), and 44 h (75.3% GVBD and 60.5% PB1), respectively. ANP also significantly inhibited FSH-induced porcine oocyte GVBD (47.6% versus 83.8%) and PB1 emission (22.4% versus 45.2%) when CEOs were cultured in pFF-free maturation medium. cGMP analog 8-Br-cGMP (10 microM to 1mM) mimicked the effects of ANP on GVBD, PB1, and CEI. The negative effect of ANP was completely reversed by KT5823 (a specific inhibitor of cGMP-dependent protein kinase), while C-ANP-(4-23) (an analogue of ANP and specific binder for natriuretic peptide receptors-C) was ineffective in oocyte maturation. Neither ANP nor C-ANP-(4-23) had an effect on spontaneous porcine oocyte maturation and cumulus expansion. These results suggested that ANP negatively regulates FSH-activated porcine oocyte meiotic resumption, meiotic maturation and cumulus expansion. The function of ANP on porcine oocyte maturation is via the cGMP dependent protein kinase (PKG) pathway.

The Multifunctional Fish Gill: Dominant Site of Gas Exchange, Osmoregulation, Acid-Base Regulation, and Excretion of Nitrogenous Waste

The fish gill is a multipurpose organ that, in addition to providing for aquatic gas exchange, plays dominant roles in osmotic and ionic regulation, acid-base regulation, and excretion of nitrogenous wastes. Thus, despite the fact that all fish groups have functional kidneys, the gill epithelium is the site of many processes that are mediated by renal epithelia in terrestrial vertebrates. Indeed, many of the pathways that mediate these processes in mammalian renal epithelial are expressed in the gill, and many of the extrinsic and intrinsic modulators of these processes are also found in fish endocrine tissues and the gill itself. The basic patterns of gill physiology were outlined over a half century ago, but modern immunological and molecular techniques are bringing new insights into this complicated system. Nevertheless, substantial questions about the evolution of these mechanisms and control remain.

A recombinant plant natriuretic peptide causes rapid and spatially differentiated K+, Na+ and H+ flux changes in Arabidopsis thaliana roots

Plant natriuretic peptides (PNPs) belong to a novel class of systemically mobile molecules that are structurally similar to the N-terminal domain of expansins and affect physiological processes such as protoplast volume regulation at nano-molar concentrations. Here we demonstrate that AtPNP-A, a recombinant Arabidopsis thaliana PNP causes rapid H(+) influx in the elongation zone of A. thaliana roots but not in the mature zone. AtPNP-A also induces significant K(+) and Na(+) efflux and this effect is seen in the mature root zone only. These observations suggest that responses to AtPNP-A are developmental stage and tissue specific and point to a complex role in plant growth and homeostasis.

Expression of natriuretic peptides, nitric oxide synthase, and guanylate cyclase activity in frog mesonephros during the annual cycle

Natriuretic peptides (NPs), a family of structurally related hormones and nitric oxide (NO), generated by nitric oxide synthase (NOS), are believed to be involved in the regulation of fluid balance and sodium homeostasis. Differential expression and regulation of these factors depend on both physiological and pathological conditions. Both NPs and NO act in target organs through the activation of guanylate cyclase (GC) and the generation of guanosine 3',5'-cyclic monophosphate (cGMP), which is considered a common messenger for the action of these factors. The present study was designed to investigate--by histochemical methods--the expression of some NPs (proANP and ANP) and isoforms of NOS (neuronal NOS, nNOS, and inducible NOS, iNOS) in the mesonephros of Rana esculenta in different periods of the year including hibernation, to evaluate possible seasonal changes in their expression. We also studied the enzyme activity of NOS-related nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) and of GC. The experiments were performed on pieces of kidney of R. esculenta collected in their natural environment during active and hibernating life. The study was carried out using immunohistochemical techniques to demonstrate proANP, ANP, and some NOS isoforms. Antigen capture by enzyme linked immunosorbent assay (ELISA) was also performed to determine the presence of NPs in the frog kidney extract. Enzyme histochemistry was used to demonstrate the NOS-related NADPHd activity at light microscopy; GC activity was visualized at the electron microscope, using cerium as capture agent. The application of the immunohistochemical techniques demonstrated that frog mesonephros tubules express different patterns of distribution and/or expression of ANP and NOS during the annual cycle. Comparing the results obtained on active and hibernating frogs has provided interesting data; the NOS/NADPHd and GC activities showed some variations as well. Furthermore, the presence of NPs in the frog kidney extract was evidenced by dose-dependent response in the ELISA. The data suggest that both ANP and NO are intra-renal paracrine and/or autocrine factors which may modulate the adaptations of frog renal functions to seasonal changes through the action of the cGMP generated from GC activity.

Natriuretic peptides--a class of heterologous molecules in plants

Immunological and physiological evidence suggests the presence of biologically active natriuretic peptide hormones (NPs) in plants. Evidence includes specific binding of rat atrial NP, [rANP (99-126)] to plant membranes and the promotion of cyclic guanosine-3',5'-monophosphate (cGMP) mediated stomatal responses. Furthermore, anti-ANP affinity purifies biologically active plant immunoreactants (irPNPs) and a biologically active Arabidopsis thaliana irPNP (AtPNP-A) has been identified. AtPNP-A belongs to a novel class of molecules that share some similarity with the cell wall loosening expansins but do not contain the carbohydrate-binding wall anchor, thus suggesting that irPNPs and ANP are heterologues. We hypothesise that irPNP-like molecules have evolved from primitive glucanase-like molecules that have been recruited to become systemically mobile modulators of homeostasis acting via the plasma membrane. Such a function is compatible with localisation in the conductive tissue and the physiological and cellular modes of action of irPNPs reported to-date.

Cardiac role of frog ANF: negative inotropism and binding sites in Rana esculenta

To elucidate the role of atrial natriuretic peptides (NPs) in the amphibian heart, the myotropic effects and the cardiac distribution of frog atrial natriuretic factor (fANF) have been studied in Rana esculenta. Spontaneously, beating in vitro isolated working heart preparations were treated with increased concentrations (10(-11)-10(-8) M) of fANF-(1-24). The peptide at 10(-9) and 10(-8) M significantly reduced heart rate (HR) and, on the electrically paced preparations, decreased cardiac output (CO), stroke volume (SV) and work. Such negative inotropism was abolished by pretreatment with the pertussis toxin or by blocking the particulate guanylate cyclase (GC) with anantin while it was independent both from the functional impairment of the endocardium-endothelium by Triton X-100 and the inhibition of the soluble guanylate cyclase by 1 H-(1,2,4,) oxadiazolo-(4,3-a) quinoxalin-1-one (ODQ). By autoradiography, two classes of high and low affinity NPs binding sites were detected in the ventricular endocardium and myocardium and in the bulbus arteriosus. The analysis of displacement binding data using the radioligand [125I]-rat atrial natriuretic peptide [125I-rANP-(1-28)], its cold counterpart and the fANF-(1-24) showed that in the ventricular myocardium, the low affinity NPs sites bound both the heterologous and the homologous ligands at a concentration close to that responsible for the negative inotropism and chronotropism.