Autoradiographic visualization of the natriuretic peptide receptor-B in rat tissues

Physiological and Pathophysiological Effects of C-Type Natriuretic Peptide on the Heart

Simple Summary

C-type natriuretic peptide (CNP) is the third member of the natriuretic peptide family. Unlike atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), CNP was not previously regarded as an important cardiac modulator. However, recent studies have revealed the physiological and pathophysiological importance of CNP in the heart; in concert with its cognate natriuretic peptide receptor-B (NPR-B), CNP has come to be regarded as the major heart-protective natriuretic peptide in the failed heart. In this review, I introduce the history of research on CNP in the cardiac field.

Abstract

C-type natriuretic peptide (CNP) is the third member of the natriuretic peptide family. Unlike other members, i.e., atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), which are cardiac hormones secreted from the atrium and ventricle of the heart, respectively, CNP is regarded as an autocrine/paracrine regulator with broad expression in the body. Because of its low expression levels compared to ANP and BNP, early studies failed to show its existence and role in the heart. However, recent studies have revealed the physiological and pathophysiological importance of CNP in the heart; in concert with the distribution of its specific natriuretic peptide receptor-B (NPR-B), CNP has come to be regarded as the major heart-protective natriuretic peptide in the failed heart. NPR-B generates intracellular cyclic guanosine 3′,5′-monophosphate (cGMP) upon CNP binding, followed by various molecular effects including the activation of cGMP-dependent protein kinases, which generates diverse cytoprotective actions in cardiomyocytes, as well as in cardiac fibroblasts. CNP exerts negative inotropic and positive lusitropic responses in both normal and failing heart models. Furthermore, osteocrin, the intrinsic and specific ligand for the clearance receptor for natriuretic peptides, can augment the effects of CNP and may supply a novel therapeutic strategy for cardiac protection.

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.

Expression of guanylyl cyclase-B (GC-B/NPR2) receptors in normal human fetal pituitaries and human pituitary adenomas implicates a role for C-type natriuretic peptide

C-type natriuretic peptide (CNP/Nppc) is expressed at high levels in the anterior pituitary of rats and mice and activates guanylyl cyclase B receptors (GC-B/Npr2) to regulate hormone secretion. Mutations in NPR2/Npr2 can cause achondroplasia, GH deficiency, and female infertility, yet the normal expression profile within the anterior pituitary remains to be established in humans. The current study examined the expression profile and transcriptional regulation of NPR2 and GC-B protein in normal human fetal pituitaries, normal adult pituitaries, and human pituitary adenomas using RT-PCR and immunohistochemistry. Transcriptional regulation of human NPR2 promoter constructs was characterized in anterior pituitary cell lines of gonadotroph, somatolactotroph, and corticotroph origin. NPR2 was detected in all human fetal and adult pituitary samples regardless of age or sex, as well as in all adenoma samples examined regardless of tumor origin. GC-B immunoreactivity was variable in normal pituitary, gonadotrophinomas, and somatotrophinomas. Maximal transcriptional regulation of the NPR2 promoter mapped to a region within -214 bp upstream of the start site in all anterior pituitary cell lines examined. Electrophoretic mobility shift assays revealed that this region contains Sp1/Sp3 response elements. These data are the first to show NPR2 expression in normal human fetal and adult pituitaries and adenomatous pituitary tissue and suggest a role for these receptors in both pituitary development and oncogenesis, introducing a new target to manipulate these processes in pituitary adenomas.

Expression of guanylyl cyclase (GC)-A and GC-B during brain development: evidence for a role of GC-B in perinatal neurogenesis

Atrial (ANP) and C-type (CNP) natriuretic peptide generate physiological effects via selective activation of two closely related membrane receptors with guanylyl cyclase (GC) activity, known as GC-A and GC-B. As yet, however, the discrete roles for ANP/GC-A vs. CNP/GC-B signaling in many mammalian tissues are still poorly understood. We here used receptor affinity labeling and GC assays to characterize comparatively GC-A/GC-B expression and functional activity during rat brain development. The study revealed that GC-B predominates in the developing and GC-A in the adult brain, with regional differences each between cerebral cortex, cerebellum, and brain stem. Whereas GC-A levels nearly continuously increase between embryonal d 18 and adult, GC-B expression in brain is highest and widely distributed around postnatal d 1. The striking perinatal GC-B peak coincides with elevated expression of nestin, a marker protein for neural stem/progenitor cells. Immunohistochemical investigations revealed a cell body-restricted subcellular localization of GC-B and perinatal abundance of GC-B-expressing cells in regions high in nestin-expressing cells. However, and supported by examination of nestin-GFP transgenic mice, GC-B and nestin are not coexpressed in the same cells. Rather, GC-B(+) cells are distinguished by expression of NeuN, an early marker of differentiating neurons. These findings suggest that GC-B(+) cells represent neuronal fate-specific progeny of nestin(+) progenitors and raise the attention to specific and pronounced activities of CNP/GC-B signaling during perinatal brain maturation. The absence of this activity may cause the neurological disorders observed in GC-B-deficient mice.

C-type natriuretic peptide in growth: a new paradigm

C-type natriuretic peptide (CNP), acting through its receptor, natriuretic peptide receptor-B (NPR-B), plays a critical role in linear growth. Knockout mice for CNP and NPR-B are dwarfed, and transgenic mice overexpressing CNP are overgrown. CNP has a direct regulatory effect on growth plate chondrocytes, acting primarily to promote terminal differentiation and hypertrophy. In humans, homozygous NPR-B mutations are the cause of acromesomelic dysplasia, Maroteaux type (AMDM), a severe form of disproportionate dwarfism. A patient with AMDM and the NPR-B knockout mouse both have low insulin-like growth factor I (IGF-I) levels, suggesting an interaction between these regulatory systems. Heterozygous carriers of NPR-B mutations also have reduced stature, but no other abnormalities. Hence, heterozygous NPR-B mutations are another cause of "idiopathic" short stature. The CNP-NPR-B system has only recently been found to be an important regulator of human growth, and abnormalities in this system have clinical implications. Considerable work is needed to further understand this new paradigm of human growth regulation.

Atrial natriuretic peptide-like immunoreactivity in neurons and astrocytes of human cerebellum and inferior olivary complex

Atrial natriuretic peptide (ANP) has previously been localized in areas of mammalian brain associated with olfaction, cardiovascular function, and fluid/electrolyte homeostasis. Despite the presence of several types of natriuretic peptide receptors in mammalian cerebellum, neither intrinsic nor extrinsic sources of the natriuretic peptides have been described. In this report we describe the immunohistochemical localization of both intrinsic and extrinsic sources for ANP in human cerebellum. ANP-like immunoreactivity (ANP-LIR) was observed in climbing fibers in the cerebellar molecular layer that probably originated from isolated immunopositive neurons of the inferior olivary complex. Intrinsic sources of ANP-LIR included small subpopulations of protoplasmic and fibrous astrocytes and Bergmann glia, as well as Golgi and Lugaro neurons of the granule cell layer. These results suggest that, in addition to its presumptive roles in local vasoregulation, ANP may serve as a modulator of the activity of Purkinje neurons.

Natriuretic peptide signalling: molecular and cellular pathways to growth regulation

The natriuretic peptides (NPs) constitute a family of polypeptide hormones that regulate mammalian blood volume and blood pressure. The ability of the NPs to modulate cardiac hypertrophy and cell proliferation as well is now beginning to be recognized. The NPs interact with three membrane-bound receptors, all of which contain a well-characterized extracellular ligand-binding domain. The R1 subclass of NP receptors (NPR-A and NPR-B) contains a C-terminal guanylyl cyclase domain and is responsible for most of the NPs downstream actions through their ability to generate cGMP. The R2 subclass lacks an obvious catalytic domain and functions primarily as a clearance receptor. This review focuses on the signal transduction pathways initiated by ligand binding and other factors that help to determine signalling specificities, including allosteric factors modulating cGMP generation, receptor desensitization, the activation and function of cGMP-dependent protein kinase (PKG), and identification of potential nuclear or cytoplasmic targets such as the mitogen-activated protein kinase signalling (MAPK) cascade. The inhibition of cardiac growth and hypertrophy may be an important but underappreciated action of the NP signalling system.

Effects of natriuretic peptides (ANP, BNP, CNP) on catecholamine synthesis and TH mRNA levels in PC12 cells

Atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) are present in adrenal chromaffin cells, and are co-secreted with catecholamines suggesting that these natriuretic peptides (NPs) may modulate functions of chromaffin cells in an autocrine and/or paracrine manner. Therefore, we investigated the effects of NPs on tyrosine hydroxylase (TH: a rate-limiting enzyme in biosynthesis of catecholamine) mRNA in rat pheochromocytoma PC12 cells. It was also determined whether the cyclic GMP/cGMP-dependent protein kinase (cGMP/PKG) pathway was involved in theses effects. Finally, we examined the effects of NPs on intracellular catecholamine content to confirm increase of catecholamine synthesis following TH mRNA induction. NPs (0.1 microM) induced significant increases of the TH mRNA (ANP= BNP> CNP). Also, the effects of NPs on TH mRNA were mimicked by 8-bromo cyclic GMP (1mM), and were blocked by KT5823 (1 microM) (inhibitor PKG) or LY83583 (1 microM) (guanylate cyclase inhibitor). Moreover, NPs were shown to induce significant increases of intracellular catecholamine contents (ANP= BNP> CNP). These findings suggest that NPs induced increases of TH mRNA through cGMP/PKG dependent mechanisms, which, in turn, resulted in stimulation of catecholamine synthesis in PC12 cells.

Guanylyl cyclase-B represents the predominant natriuretic peptide receptor expressed at exceptionally high levels in the pineal gland

The generation and function(s) of the signalling molecule cyclic GMP (cGMP) in brain are still poorly understood. One mechanism to raise intracellular cGMP levels is binding of C-type natriuretic peptide (CNP) to a membrane guanylyl cyclase (GC), termed GC-B. Here, we demonstrate an exceptionally strong expression of GC-B in the pineal gland. Crosslinking experiments performed with 125I-Tyr(0)-CNP and membranes from various rat tissues identified the receptor as a 130-kDa protein, expressed at highest levels in pineal membranes. Receptor autoradiography on brain sections confirmed a striking density of CNP binding sites in pineal tissue, whereas binding sites for the related atrial natriuretic peptide (ANP) predominate in other regions of the brain. Incubations of freshly dissected whole pineal glands in either the absence or presence of natriuretic peptides followed by immunohistochemical analyses of cGMP revealed strong accumulations of cGMP in response to CNP but not to ANP in the majority of pinealocytes. Stimulation of soluble GC (sGC) activity by use of sodium nitroprusside (SNP) resulted in a very similar pattern of cGMP immunostaining, indicating a co-expression at high levels of particulate and soluble forms of GC. These findings point to a major role of cGMP signalling in pinealocytes and suggest an important regulatory function for CNP.

Characterisation of the effects of natriuretic peptides upon ACTH secretion from the mouse pituitary

The involvement of natriuretic peptides in the regulation of ACTH secretion in mice hemi-pituitary preparations was investigated. Atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) all inhibited CRF (10(-9) M)-evoked ACTH secretion over a concentration range of 10(-12)-10(-10) M and also stimulated cyclic GMP accumulation over a concentration range of 10 (-8)-10(-5) M. CNP was the most effective both in the inhibition of ACTH secretion and in the stimulation of cyclic GMP accumulation. Coincubation of hemi-pituitaries with 8bromo-cyclic GMP (10(-4) M) completely inhibited CRF (10(-9) M)-evoked ACTH secretion. Northern blot analysis revealed that all three major isoforms of the natriuretic peptide receptors are expressed in the mouse pituitary. These results demonstrate that natriuretic peptides do inhibit CRF-stimulated ACTH secretion from mouse pituitary preparations. A role for cGMP in mediating this effect on hormone secretion is indicated but the discrepancy between the efficacies of natriuretic peptides in inhibiting the secretory response and stimulating cyclic GMP accumulation suggest a more complicated stimulus-secretion coupling pathway is in operation.

Decreased expression of natriuretic peptide A receptors and decreased cGMP production in the choroid plexus of spontaneously hypertensive rats

Atrial natriuretic peptide receptor (ANP) subtypes and their signal transduction response were characterized in choroid plexus of spontaneously hypertensive (SHR) and normotensive (WKY) rats. We found two ANP receptor subtypes, guanylate cyclase coupled and uncoupled, in both rat strains. Binding of ANP was lower in SHR choroid plexus when compared to WKY. The lower ANP binding in SHR was the result of a decrease of binding to the guanylate cyclase-coupled receptor subtype A, a decrease that correlated well with the decreased ANP-induced cGMP formation in SHR. Forskolin stimulated cGMP production to the same extent in both strains. In WKY rats, ANP increased basal and forskolin-stimulated cAMP production; conversely, in SHR, ANP did not affect the basal level of cAMP and inhibited the forskolin-stimulated cAMP production. These results demonstrate differences in ANP receptor subtype expression, and ANP signal transduction in choroid plexus of hypertensive and normotensive rats, which is of possible significance to the central mechanisms of blood pressure control.

Receptors for natriuretic peptides in adrenal chromaffin cells

Atrial, brain, and C-type natriuretic peptides of the atrial natriuretic peptide family are present in adrenal chromaffin cells, and are secreted with catecholamines by exocytosis. These peptides modulate the physiological functions of the cells such as synthesis and secretion of catecholamines in an autocrine manner interacting with natriuretic peptide receptors.

Localization of natriuretic peptide-activated guanylate cyclase mRNAs in the rat brain

Physiological actions of atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP) are elaborated by membrane-bound natriuretic peptide receptors (NPRs). These receptors possess intracellular guanylate cyclase domains that mobilize cyclic guanosine monophosphate upon binding of peptide. Two distinct NPR subtypes have been described in brain: the NPR-A selectively binds ANP, whereas NPR-B exhibits high affinity for CNP. To define further the potential domains of ANP and CNP action in brain, the present study used in situ hybridization histochemistry to map NPR-A and NPR-B mRNA-expressing cell populations. Significant levels of neuronal NPR-A mRNA expression were observed only in the mitral cell layer of the olfactory bulb, medial habenula, subfornical organ, and area postrema. Expression of NPR-A mRNA was observed in forebrain white matter tracts, suggesting synthesis in glial cells. In contrast, NPR-B mRNA was widely expressed throughout the neuraxis. In the telencephalon, signal was abundant throughout limbic cortex and neocortex, olfactory bulb, hippocampus, and amygdala. Intense NPR-B mRNA hybridization was observed in preoptic-hypothalamic neuroendocrine circuits and in motor nuclei of cranial nerves. Intermediate expression of NPR-B mRNA was observed in brainstem nuclei controlling autonomic function. Labeling for NPR-B but not NPR-A mRNA was observed in pituicytes in the neural lobe of the pituitary and in scattered cells of the anterior pituitary. These results suggest that CNP is the primary biologically active natriuretic peptide in brain. In contrast with NPR-B, NPR-A appears to be expressed largely in restricted cell populations containing high levels of ANP and in circumventricular organs. These data implicate the NPR-A in autoregulation of ANP neurons and central registration of cardiac ANP release.

Neurochemical modulation of cardiovascular control in the nucleus tractus solitarius

The central control of cardiovascular function has been keenly studied for a number of decades. Of particular interest are the homeostatic control mechanisms, such as the baroreceptor heart-rate reflex, the chemoreceptor reflex, the Bezold-Jarisch reflex and the Breuer-Hering reflex. These neurally-mediated reflexes share a common termination point for their respective centrally-projecting sensory afferents, namely the nucleus tractus solitarius (NTS). Thus, the NTS clearly plays a critical role in the integration of peripherally initiated sensory information regarding the status of blood pressure, heart rate and respiratory function. Many endogenous neurochemicals, from simple amino acids through biogenic amines to complex peptides have the ability to modulate blood pressure and heart rate at the level of the NTS. This review will attempt to collate the current knowledge regarding the roles of neuromodulators in the NTS, the receptor types involved in mediating observed responses and the degree of importance of such neurochemicals in the tonic regulation of the cardiovascular system. The neural pathway that controls the baroreceptor heart-rate reflex will be the main focus of attention, including discussion of the identity of the neurotransmitter(s) thought to act at baroafferent terminals within the NTS. In addition, this review will provide a timely update on the use of recently developed molecular biological techniques that have been employed in the study of the NTS, complementing more classical research.

Neuropeptides in the adrenal gland: distribution, localization of receptors, and effects on steroid hormone synthesis

In this review we defined and classified the neuropeptides (NPs) related to the adrenal gland, according to Palkovits (Frontiers Neuroendocrinol 10:1 1988). The concentration (RIA) and distribution (immunohistochemistry) of NPs, as well as the localization of the receptors (radioligand studies) were summarized. Direct effects of NPs on aldosterone and corticosterone synthesis obtained by in vivo, in situ perfusion, and in vitro experimental approaches were reviewed. Data (from different rat strains and genders) for 35 NPs are presented.

Identification of renal natriuretic peptide receptor subpopulations by use of the non-peptide antagonist, HS-142-1

1. The renal actions of natriuretic peptides are dictated by the distribution of guanylyl cyclase-linked (NPRA and NPRB) and non-guanylyl cyclase-linked (NPRC) receptors. Natriuretic peptide receptors have previously been distinguished on the basis of their differential affinity for peptide fragments and analogues; however, most of the available ligands are not fully selective. We have used the specific guanylyl cyclase-linked receptor antagonist, HS-142-1, to investigate the differential distribution of natriuretic peptide receptor subtypes in the human, bovine and rat kidney. 2. Specific, high affinity 3-([125I]-iodotyrosyl)-rat-ANP-(1-28)([125I]-rANP1-28) binding sites were identified in all three species, localized to glomeruli, inner medulla, intrarenal arteries and regions in the outer medulla corresponding to vasa recta bundles. Binding sites were also identified in the smooth muscle lining of the hilar region in the bovine and rat kidney. 3. In the rat, [125I]-rANP1-28 binding was inhibited by unlabelled peptide sequences with a rank order of potency (rANP1-28 > pCNP1-22 > C-ANP4-23). The glomeruli exhibited a heterogeneous population of binding sites, C-ANP4-23 and pCNP1-22 producing a significantly better fit to a two component inhibition curve compared to the single component curve for rANP1-28. 4. Competitive inhibition experiments with the receptor selective ligands, C-ANP4-23 and HS-142-1, suggested that, like the rat, human and bovine glomeruli possessed a heterogeneous population of binding sites, whilst those in the inner medulla and intrarenal arteries of all three species represented a homogeneous population. Rat glomeruli exhibited a high proportion (>80%) of the NPRc receptor subtype whereas in human and bovine glomeruli this receptor represented less than 20% of the total population, the majority of binding sites being HS-142-1-sensitive.5. C-ANP4-23 exhibited a significantly higher inhibitory potency for binding sites in rat glomeruli compared to those in human and bovine kidney whilst HS-142-1 was significantly more potent in the rat and bovine kidney compared to man. No evidence was found to suggest the presence of a renal NPRBreceptor subtype.6. The relative density, affinity and proportion of natriuretic receptor subtypes in the kidney exhibit significant species differences. HS-142-1 may be a valuable tool in further elucidating the localization and function of these receptors, but heterogeneity between species should be considered when selecting experimental models.

Presence of C-type natriuretic peptide in human kidney and urine

The current study was undertaken to investigate the presence of CNP immunoreactivity in both human kidney and urine. Immunohistochemical staining with an indirect immunoperoxidase method utilizing an antibody which is 100% cross-reactive to both CNP-53 and CNP-22 was performed on five human kidney specimens (three biopsies of normal cadaveric donor kidneys and two of normal autopsy specimens). CNP immunoreactivity was positive in proximal, distal and medullary collecting duct tubular cells in a cytoplasmic and granular staining pattern. CNP immunoreactivity was also determined in the urine of five healthy volunteers utilizing a sensitive and specific double-antibody radioimmunoassay with a mean concentration of 10.8 +/- 1.0 pg/ml. With the utilization of high pressure liquid chromatography, this immunoreactivity proved to be consistent with both the low molecular weight form, CNP-22, as well as the high molecular weight form, CNP-53. Urinary excretion of CNP was also measured in normal subjects (N = 5) and in patients with congestive heart failure (CHF, N = 6). CHF patients excreted over three times more CNP than normals (27.2 +/- 2.8 vs. 8.7 +/- 0.81 pg/min, P < 0.004) despite no difference between the two groups in plasma CNP concentrations (6.97 +/- 0.28 vs. 8.08 +/- 1.52 pg/ml, P = NS). This study demonstrates for the first time the presence of CNP immunoreactivity in human kidney and suggests that renal tubular cells may be an additional non-vascular site of synthesis for this cardiorenal acting peptide. This study also demonstrates an increase in urinary CNP excretion in congestive heart failure.

C-type natriuretic peptide stimulates secretion of growth hormone from rat-pituitary-derived GH3 cells via a cyclic-GMP-mediated pathway

Although C-type natriuretic peptide (CNP) has been shown to exist at the highest concentration in the anterior pituitary in rat tissues, its physiological role(s) there is (are) not clear. In this study, we report a novel function of CNP examined with anterior pituitary-derived cell lines, GH3 and AtT20/D16v-F2. Both CNP and atrial natriuretic peptide (ANP) increased cellular cGMP levels in both cell lines in dose-dependent manners. CNP, but not ANP, stimulated growth hormone (GH) release from GH3 cells. In contrast, neither ANP nor CNP had any significant effect on the corticotropin release from AtT20/D16v-F2 cells. An activator for cGMP-dependent protein kinase (cGK), dibutyryl cGMP, mimicked the stimulation of GH release from GH3 cells by CNP. Constitutive GH release from GH3 cells was greatly diminished in the presence of inhibitors for cAMP-dependent protein kinase, while stimulative GH release by CNP was not affected. However, inhibitors which can block cGK almost completely diminished the stimulative effect of CNP. An inhibitor for protein kinase C did not show any effect on either constitutive or CNP-stimulative GH release. Our observations indicate that the stimulation of GH release from GH3 cells by CNP is mediated mainly by the cGK signal-transduction pathway, not by cAMP-dependent protein kinase or protein kinase C, through a CNP-specific receptor (possibly ANP-B receptor). Thus, CNP may act as a local modulator in the anterior pituitary.

Immunoreactive C-type natriuretic peptide in human adrenal glands and adrenal tumors

C-type natriuretic peptide (CNP) in human adrenal glands and adrenal tumors was measured with a specific radioimmunoassay for CNP. Tissue immunoreactive (IR-) CNP concentrations were 0.54 +/- 0.40 pmol/g wet tissue (gwt) (mean +/- SD) in 14 pheochromocytomas, 0.69 +/- 0.19 pmol/gwt in six adrenocortical tumors, and 0.49 +/- 0.22 pmol/gwt in seven normal adrenal glands (cortex and medulla mixed). These concentrations were comparable to those found in tissues from human brains. Sephadex G-50 superfine column chromatography and reverse-phase high performance liquid chromatography revealed that IR-CNP in normal adrenal glands and pheochromocytoma consisted of at least two components: a component in low molecular weight form chromatographically identical to CNP-22 and the other, a high molecular weight form very similar to human CNP-53. This study has shown that IR-CNP is present in human adrenal glands and adrenal tumors with similar molecular forms and comparable concentrations to those in the human brain.

Characterization of binding sites in rat for A, B and C-type natriuretic peptides

Binding studies, affinity cross-linking and guanylate cyclase assays allowed a comparison of receptors with which the rat forms of atrial/A-type natriuretic peptide (rANP), brain/B-type natriuretic peptide (rBNP) and C-type natriuretic peptide (rCNP) interact in rat kidney cortex and lung. This work represents the first study in which the rat form of BNP (= rBNP-45/iso-rANP(1-45)) has been used as a radiolabelled tracer to further characterize its receptors in these tissues. In addition, these studies stress the use of the same species of natriuretic peptide and assay system, an important experimental des ign given that BNPs show species-specific differences in structure. rBNP-45 bound with lower affinity to rANP (99-126) receptors, namely guanylate cyclase-linked receptor(s) and C-receptor. No receptor which interacted with only rBNP-45 was detectable in lung and kidney cortex. Since rBNP-45 interacted preferentially with the C-receptor and was less potent than rANP(99-126) in stimulating glomerular guanylate cyclase, rBNP-45 may signal through another second messenger in addition to cyclic GMP. Work with truncated analogues of this hormone pinpointed regions of this peptide which may contribute to receptor binding affinity and guanylate cyclase activation. CNP-22 bound to only a subset of ANP receptors and was least effective in stimulating glomerular guanylate cyclase, suggesting a differential mode of action from ANP.

Cell-type-specific function of the C-type natriuretic peptide gene promoter in rat anterior pituitary-derived cultured cell lines

The promoter function of the human C-type natriuretic peptide (CNP) gene in various cultured cells was examined by transient transfection assays. The CNP promoter functioned very effectively in GH3 cells, which originated from the growth hormone-producing tumor of the rat anterior pituitary and somatomammotroph phenotype, but functioned much less effectively in GH1 cells, another type of rat pituitary-derived cell with a somatotroph phenotype, and rat primary cardiocytes. The CNP promoter did not function at all in other cells, including AtT20 cells of murine pituitary corticotroph origin. Functional analyses of the deleted promoters with various 5' deletion breakpoints revealed the existence of at least two negative and one positive regulatory regions. Within the positive regulatory region (positions -54 to -19), which conferred 90% of the promoter activity in GH3 cells, two equipotent GC-rich cis elements (positions -49 to -45 and -40 to -35) were identified. Both sites shared half of the promoter activity and binding properties to the nuclear protein in GH3 cells. Rat anterior pituitary tissue contained the binding protein of the identified cis element, which was identical or similar to that of GH3 cells. With Southwestern (DNA-protein) analysis, a 70-kDa specific binding protein distinct from known factors such as SP-1, AP-2, and Pit-1 was identified in the nuclear extract of GH3 cells.

Cell-type-specific function of the C-type natriuretic peptide gene promoter in rat anterior pituitary-derived cultured cell lines

The promoter function of the human C-type natriuretic peptide (CNP) gene in various cultured cells was examined by transient transfection assays. The CNP promoter functioned very effectively in GH3 cells, which originated from the growth hormone-producing tumor of the rat anterior pituitary and somatomammotroph phenotype, but functioned much less effectively in GH1 cells, another type of rat pituitary-derived cell with a somatotroph phenotype, and rat primary cardiocytes. The CNP promoter did not function at all in other cells, including AtT20 cells of murine pituitary corticotroph origin. Functional analyses of the deleted promoters with various 5' deletion breakpoints revealed the existence of at least two negative and one positive regulatory regions. Within the positive regulatory region (positions -54 to -19), which conferred 90% of the promoter activity in GH3 cells, two equipotent GC-rich cis elements (positions -49 to -45 and -40 to -35) were identified. Both sites shared half of the promoter activity and binding properties to the nuclear protein in GH3 cells. Rat anterior pituitary tissue contained the binding protein of the identified cis element, which was identical or similar to that of GH3 cells. With Southwestern (DNA-protein) analysis, a 70-kDa specific binding protein distinct from known factors such as SP-1, AP-2, and Pit-1 was identified in the nuclear extract of GH3 cells.