Rat Atrial Natriuretic Peptide Research Articles

Radioimmunoassay for Rat B-Type Natriuretic Peptide (BNP-45)

Rat BNP-45 is the main circulating form of BNP in rat plasma. To understand the role of BNP in physiological and pathophysiological conditions, a specific radioimmunoassay (RIA) for the quantitative determination of the peptide in plasma and tissues is necessary. An assay using rBNP-45 as the standard in conjunction with antisera directed against this peptide has not been described in the literature, though some investigators have reported values ranging from 0.73-2.0 pmol/L using either BNP-26 or BNP-32 as the standard peptide. Unfortunately, these forms of BNP do not exist in rat plasma. In our studies, we have developed a specific RIA for rBNP-45 using rBNP-45 as the standard peptide and Tyro-rBNP-45 as the radioligand. We have used two specific antisera for assay purposes; one against rBNP-45, and the second to a peptide composed of the first 20 amino acids of rBNP-45 (rBNP[1-20]). The recovery of various amounts of rBNP-45 added to control plasma was 50-80% depending on the method of extraction and purification. The interassay and intraassay coefficients of variation were 12% and 6% respectively. Values obtained were similar for blood sampled by either cardiac puncture, decapitation, or aortic puncture. The method was used to measure rBNP-45 in the plasma of normal (WKY) and Spontaneously Hypertensive (SHR) rats. The values obtained were 5.46 +/- 0.43 and 19.6 +/- 2.36 pmol/L respectively. The rat atrial natriuretic peptide (ANP[99-126]) values in the same extracts were 23.2 +/- 0.45 and 51.6 +/- 3.16 pmol/L.

Localization and characteristics of atrial natriuretic peptide receptors in prenatal and postnatal rat brain

We studied the expression of atrial natriuretic peptide (ANP) receptor subtypes during development in the rat forebrain, using quantitative autoradiography. Highest ANP binding was observed in the cortical neuroepithelium at embryonic day 17. Lower ANP binding was found in cingulate and frontal cortices at postnatal day 10, but none was detectable at 8 weeks of age. In the neuroepithelium of the embryonic rat, binding was displaced with a potency of rat ANP-(1–28) (rANP) > porcine type-C natriuretic peptide (pCNP−22) = rat ANP fragment C-ANP -(4–23) (rC-ANP-(4–23)) = rat brain natriuretic peptide (rBNP−32), different from that of any of the well-characterized (ANP A, ANP B, and ANP C) natriuretic peptide receptors. The present results support the hypothesis of a role for ANP during brain maturation and indicate that the ANP receptors highly expressed in the embryonic neuroepithelium may belong to a new ANP recptor subtype not nyet

Regulation of atrial natriuretic peptide receptors in vascular smooth muscle cells: role of cGMP

We tested the hypothesis that intracellular guanosine 3',5'-cyclic monophosphate (cGMP) regulates atrial natriuretic peptide (ANP) receptors. The effect of chronic exposure to ANP, sodium nitroprusside (SNP), and 8-bromo-cGMP (8-BrcGMP) on ANP receptors and cGMP formation was determined in guinea pig thoracic aorta smooth muscle cells (TASM) and in coronary artery smooth muscle cells (CASM). TASM express both the ANP-activated guanylyl cyclase (B-receptor) and the clearance receptor (C-receptor) and respond to ANP with increased cGMP. CASM exhibit only the ANP C-receptor. In TASM, 24-h treatment with 1 microM atriopeptin (AP) III [rat ANP-(103-126)] caused a sixfold increase in basal cGMP levels, which were unaltered in CASM. In AP III-treated TASM, maximal binding of 125I-labeled AP III (Bmax) was reduced 40% while affinity [dissociation constant (KD)] was unaltered. In CASM, Bmax and KD were not affected. In treated TASM, washed free of AP III, acute dose-response curves of cGMP to AP III were not different from that in untreated cells. In both TASM and CASM, basal cGMP levels were elevated and Bmax was decreased by 6-h treatment with SNP. SNP did not alter the acute response of cGMP to AP III. In both cell types, 8-BrcGMP for 6 h caused reduction in Bmax. These findings support the conclusion that elevated cGMP was necessary for ANP-induced downregulation of receptors. The unaltered responsiveness of cGMP to AP III suggests the B-receptor was not altered and the reduced Bmax was due to decreased C-receptor.

Selective on-line enrichment and separation of peptides having aromatic amino acids at their C-termini by column-switching high-performance liquid chromatography using an anhydrochymotrypsin-immobilized precolumn

A column switching high-performance liquid chromatographic system in which peptides retained on an anhydrochymotrypsin (AHC)-immobilized diol-silica precolumn were selectively transferred to and separated on a reversed-phase analytical column was developed. An investigation of the affinity characteristics of 40 peptides to the AHC precolumn showed that among eleven peptides having Tyr or Phe at their C-termini and more than five amino acid residues, ten were retained almost quantitatively on the precolumn, and two peptides having Trp at their C-termini were less retained. Two peptides having C-terminal PheNH 2 were also retained, but the peptide having C-terminal D-PheNH 2 was not retained. Among eighteen peptides having no aromatic amino acids at their C-termini, two were retained, one slightly and the other moderately. Calibration graphs for rat atrial natriuretic peptide constructed at various sample sizes were nearly identical, indicating that the peptide could be enriched by this system. The AHC precolumn showed no loss of analytical performance over 1 year, during which about 450 samples were analysed.

C-type natriuretic peptide receptors and signaling in rectal gland of Squalus acanthias.

Recent evidence suggests that the newly described natriuretic peptide, C-type natriuretic peptide (CNP), may be the circulating form of natriuretic peptide in the shark. In the shark CNP has a major site of action in the rectal gland, which augments chloride secretion in response to stimulation by volume loading or CNP infusion. We therefore examined the shark rectal gland for natriuretic peptide receptors and determined the presence of guanylate cyclase-linked receptors and non-guanylate cyclase-linked receptors for CNP in this tissue. CNP binds with uniform high affinity (dissociation constant of 78 +/- 11 pM) to receptors of high density (receptor density of 61 +/- 0.7 fmol/mg protein) in plasma membranes prepared from the rectal gland. By use of rat atrial natriuretic peptide (rANP) as a competing ligand, two classes of receptors become apparent in this population, both of which have similar affinity for CNP, but different affinities for rANP. The low-molecular-weight natriuretic peptide receptor-specific peptide, des-[Gln116,Ser117,Gly118, Leu119,Gly120]rANP-(102-121), binds to 50% of the receptors in the rectal gland, but fails to bind to the remaining 50% even at micromolar concentrations. Porcine brain natriuretic peptide (pBNP) binds with uniformly diminished affinity to all receptors, whereas the unrelated peptide, porcine vasoactive intestinal peptide, does not bind these receptors. The importance of the integrity of the ring structure of CNP is underlined by the significant loss of affinity when the peptide ring is opened.(ABSTRACT TRUNCATED AT 250 WORDS)

C-type natriuretic peptides are potent dilators of shark vascular smooth muscle.

Previous studies of the effects of C-type natriuretic peptides (CNP) in intact mammals have demonstrated limited hypotensive responses, in contrast to other natriuretic peptides. Our previous studies, on isolated vascular smooth muscle (VSM) from various fish species, utilizing either mammalian or non-homologous fish atrial natriuretic peptides (ANP), have demonstrated vasodilation with a relatively high sensitivity (EC50 approximately 5 nM). The recent sequencing of a C-type natriuretic peptide from the heart of the dogfish shark, Squalus acanthias, has enabled us to compare the efficacy of this peptide on aortic VSM from that species with two other CNPs (from killifish and pig), as well as rat ANP. The EC50 of dilation for sCNP, as well as kCNP and pCNP, was 0.5 nM, over 15 times lower than the EC50 of the response to rANP. These data suggest that CNP is released from the dogfish shark heart and is a circulating hormone with potent vasodilatory effects, in sharp contrast to the apparent role of CNP predominantly as a brain neuropeptide in mammals.

The effects of atrial natriuretic peptide on food-reinforced conditioning in rats. Interactions with neurotransmitters

The effects of two doses of rat atrial natriuretic peptide (TANP-1–28), 200 and 500 ng, on 6-day acquisition and extinction of food-reinforced conditional learning (conditional stimulus: light) were studied in rats following administration into the lateral cerebroventricle. With the higher dose, there was a tendency for facilitated acquisition and significantly delayed extinction of the positively reinforced learning task. In order to clarify whether the effect of the peptide is obtained through the involvement of neurotransmitters, the experimental animals were pretreated with different receptor blockers in selected doses that did not influence the behavioral test. Haloperidol, atropine, phenoxybenzamine, and propranolol blocked the action of ANP on extinction of the food-reinforced conditioning, whereas naloxone, bicuculline, and methysergide were ineffective. The results suggest that ANP might be considered a modulating agent in a positively reinforced conditional learning task, and that its action might involve dopaminergic, cholinergic, and α- and β-adrenergic mechanisms.

Immunohistochemical localisation of natriuretic peptides in the brains and hearts of the spiny dogfish Squalus acanthias and the Atlantic hagfish Myxine glutinosa.

The avidin-biotin peroxidase technique was used to determine the distribution of natriuretic peptides in the hearts and brains of the dogfish Squalus acanthias and the Atlantic hagfish Myxine glutinosa. Three antisera were used: one raised against porcine brain natriuretic peptide which cross-reacts with atrial natriuretic and C-type natriuretic peptides (termed natriuretic peptide-like immunoreactivity); the second raised against porcine brain natriuretic peptide which cross-reacts with C-type natriuretic peptide, but not with atrial natriuretic peptide (termed porcine brain natriuretic peptide-like immunoreactivity); and the third raised against rat atrial natriuretic peptide (termed rat atrial natriuretic peptide-like immunoreactivity). Only natriuretic peptide-like immunoreactivity was observed in the heart of S. acanthias which was most likely due to the antiserum cross-reacting with C-type natriuretic peptide. No immunoreactivity was found in the M. glutinosa heart. In the brain of S. acanthias, natriuretic peptide-like immunoreactive fibres were located in many areas of the telencephalon, diencephalon, mesencephalon, rhombencephalon, and spinal cord. Extensive immunoreactivity was observed in the hypothalamo-hypophyseal tract and the neurointermediate lobe of the hypophysis. Natriuretic peptide-like immunoreactive perikarya were found in ventromedial regions of the telencephalon and in the nucleus preopticus. Most perikarya had short, thick processes which extended toward the ventricle. Another group of perikarya was observed in the rhombencephalon. Porcine brain natriuretic peptide-like immunoreactive fibres were observed in the telencephalon, diencephalon, mesencephalon, and rhombencephalon, but perikarya were only present in the preoptic area. In the M. glutinosa brain, natriuretic peptide-like immunoreactive fibres were present in all regions. Immunoreactive perikarya were observed in the pallium, primordium hippocampi, pars ventralis thalami, pars dorsalis thalami, nucleus diffusus hypothalami, nucleus profundus, nucleus tuberculi posterioris, and nucleus ventralis tegmenti. Porcine brain natriuretic peptide-like immunoreactive perikarya and fibres had a similar, but less abundant distribution than natriuretic peptide-like immunoreactive structures. Although the chemical structures of natriuretic peptides in the brains of dogfish and hagfish are unknown, these observations show that a component of the natriuretic peptide complement is similar to porcine brain natriuretic peptide or porcine C-type natriuretic peptide. The presence of natriuretic peptides in the brain suggest they could be important neuromodulators and/or neurotransmitters. Furthermore, there appears to be divergence in the structural forms of natriuretic peptides in the hearts and brains of dogfish and hagfish.

Atrial natriuretic peptide binds to ANP-R 1 receptors in neuroblastoma cells or is degraded extracellularly at the Ser-Phe bond

ANP-R 1 receptors for atrial natriuretic peptide (ANP) showed the following rank order of affinity in intact human neuroblastoma cells NB-OK-1: human ANP-(99–126)≈ human ANP-(102–126) ≈ rat ANP-(99–126) (K 1 17–32 pM) > human ANP-(103–126) > porcine brain natriuretic peptide (BNP). Analogues truncated at the C-terminal extremity or devoid of a disulphide bridge, such as rat ANP-(103–123), rat C-ANP-(102–121), rat ANP-(111–126), rat ANP-(99–109) and rat [desCys 105,Cys 121]ANP-(104–126) and chicken C-type natriuretic peptide, were not recognized. The occupancy of these high affinity ANP-R 1 receptors led to marked cyclic GMP accumulation in the presence of 3-isobutyl 1- methylxanthine. An ectoenzymic activity, partiy shed in the incubation medium, provoked the stepwise release of Phe-Arg-[ 125I]Tyr, Arg-[ 125I]Tyr and [ 125I]Tyr from rat [ 125I]ANPW-(99–126), at an optimal pH of 7.0. Its inhibition by 1,10-phenanthroline, EDTA and bacitracin but not by thiorphan suggests the contribution of at least one neutral metalloendopeptidase, distinct from EC 3.4.24.11, for which ANP showed high affinity.

Degradation and inactivation of rat atrial natriuretic peptide 1–28 by neutral endopeptidase-24.11 in rat pulmonary membranes

Atrial natriuretic peptide (ANP), a 28-residue peptide with cardiovascular and renal effects, is rapidly cleared from the circulation. Beside renal clearance, an extra-renal metabolism by the enzyme neutral endopeptidase-24.11 (NEP-24.11) has been proposed, since specific NEP-24.11-inhibitors increase endogenous plasma-ANP. NEP-24.11 is present in rat lung but its significance for ANP hydrolysis within the lung is unclear. The aim of this study was to investigate a possible degradation of rat ANP in a membrane preparation from rat lung. Hydrolysis products of ANP were separated by HPLC and further characterized by a pulmonary artery bioassay, by radio-immunoassay with different antisera, by peptide sequencing and by masspectrometry. Rat pulmonary membranes degraded ANP to one main metabolite lacking biological activity and with poor cross-reactivity to an antiserum recognising the central ring-structure of the peptide. Formation of the hydrolysis product was prevented by the NEP-24.11-inhibitor phosphoramidon (1 μM). Peptide sequencing of the metabolite revealed a cleavage between Cys 7 and Phe 8, which was confirmed by mass-spectrometry. The metabolite had an HPLC elution time identical to that of the product formed by purified porcine NEP-24.11. These findings suggest that ANP is metabolized and inactivated by endopeptidase-24.11 in rat lungs, the first organ exposed to ANP released from the heart.

Structure-activity studies on the effects of atrial natriuretic peptide, brain natriuretic peptide and their analogs on fear-motivated learning behavior in rats

Our previous studies have demonstrated that rat atrial natriuretic peptide (rANP 1–28) and porcine brain natriuretic peptide (pBNP 1–32) administered into the lateral brain facilitate the consolidation of a passive avoidance response and delay the extinction of an active avoidance response in fear-motivated learning in rats. To study the structure-activity relationships in the same learning processes, the effects of several fragments related to ANP and BNP were investigated following their intracerebroventricular administration to rats. The following peptides were studied: rANP 1–28, rANP 5–28, rANP 5–27, rANP 7–23 (ring), rANP 17–23, hANP 10–28, hANP 15–28, hANP 20–28, hANP 1–28, pBNP 1–32 and pBNP 7–32. The peptides were used in equimolar concentration. Two of the peptides studied, ANP 20–28 and ANP 17–23, were ineffective on the extinction of active avoidance behavior and on the consolidation of passive avoidance learning. They exhibited similar actions. The results showed that small fragments of ANP and BNP can carry the biological activity of ANP and BNP on the central nervous system (CNS). It is likely that the biological active center for ANP lies between amino acids 15 and 23 and it is suspected that the ring structure is not absolutely important for the CNS activity.

Atrial natriuretic peptide in the eel, Anguilla anguilla L.: its cardiac distribution, receptors and actions on isolated branchial cells.

The presence of atrial natriuretic peptide (ANP) and the nature of its binding sites were studied in fresh-water (FW)- and seawater (SW)-adapted eels using a heterologous analogue, that of the rat (rANP). Rat ANP-like immunoreactivity was demonstrated in the cardiac atria and ventricles of both FW and SW eels, and electron-dense ANP-like granules were observed. The atria and ventricles of FW eels contained significantly more granules than those of SW animals and, in both types, the atria were more granular than the ventricles. Specific binding sites for rANP were demonstrated by displacement and uptake experiments using labelled rANP in dispersed eel branchial cell preparations, enriched in chloride cells. The concentration of rANP required to produce a 50% inhibition of binding in FW cells was significantly lower than that in SW cells. Scatchard analyses revealed the presence of two classes of binding site in SW eel branchial cells but only a single class of receptor in FW cells. The affinity of the FW receptor was not significantly different from that of the SW high affinity site. Rat ANP stimulated the production of cyclic GMP (cGMP) in a dose-dependent manner, and both basal and stimulated levels of cGMP were significantly greater in SW branchial cells. These studies suggest that ANP is involved in the adaptation of the euryhaline eel to differing environmental salinities; the levels of the peptide in the heart alter with changing salinity, and the nature of the receptors in the sodium chloride-transporting epithelium of the gill changes in response to the need either to eliminate or to absorb sodium chloride.

The role of the C-terminal region of rat brain natriuretic peptide in receptor selectivity

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) have different C-terminal tail structures compared with the rather conservative ring structures which consist of 17 amino acid residues. To examine the different effects of the tail structures of ANP and BNP on their interaction with receptors, we synthesized several peptide analogs and measured their biological actions in three different assay systems. Deletion of the C-terminal tail from rat BNP did not effect the vasorelaxation activity against rat aorta, but it promoted cGMP production in cultured rat aortic smooth muscle cells (RASMC). Deletion of the C-terminal tail from rat ANP diminished both vasorelaxant and cGMP producing activities. In a binding competition assay with RASMC and [ 125I]rat ANP-(1–28), the competition activities of both ANP and BNP were greatly reduced by C-terminal deletion. In addition, we obtained agonists with novel receptor selectivity.

Selective downregulation of rat renal clearance receptors for atrial natriuretic peptide by chronic high-salt intake: study on isolated membranes using 125I-labelled c-atrial natriuretic peptide-(4-23).

1. 125I-labelled c-atrial natriuretic peptide-(4-23) was used as radioligand for the direct quantification of atrial natriuretic peptide clearance receptors, and 125I-labelled rat atrial natriuretic peptide-(1-28) was used for the determination of total and biologically active atrial natriuretic peptide receptors, in renal glomerular and papillary membrane preparations of chronically salt-loaded and control rats. 2. The membrane preparation technique included acid-washing (pH 5), and receptor binding was assessed by saturation studies at 4 degrees C for 3 h. Chronic salt loading revealed a 35% decrease in clearance receptor number in the glomerular membrane and a 42% decrease in the papillary membranes. The absolute decrease in clearance receptor number was almost identical with the observed reduction in absolute number of total atrial natriuretic peptide receptors. Biologically active receptors were not affected by chronic salt loading. 3. Selective downregulation of clearance receptors for atrial natriuretic peptide may reflect an important role for the rat renal atrial natriuretic peptide system in long-term fluid and electrolyte regulation.

Cardiovascular and renal effects of eel and rat atrial natriuretic peptide in rainbow trout, Salmo gairdneri.

The renal and in vitro vascular effects of atrial natriuretic peptides have been examined in several species of fish. However, comparatively few investigations have described the effects of these peptides on the cardiovascular system in vivo. In the present experiments the dorsal aorta and urinary bladder were cannulated and the effects of atrial natriuretic peptides from rat and eel were monitored in conscious trout during bolus injection or continuous atrial natriuretic peptide infusion. The results show that the initial pressor effect of atrial natriuretic peptides is independent of environmental salinity adaptation (fresh or seawater) and the chemical form of atrial natriuretic peptide injected, but it is affected by the rate of atrial natriuretic peptide administration. This pressor response, and the accompanying diuresis, are mediated through alpha-adrenergic activation. Continuous infusion of either rat or eel atrial natriuretic peptide produces a steady fall in mean arterial blood pressure, which is temporally preceded by an increase in heart rate and a decrease in pulse pressure. Diuresis induced by atrial natriuretic peptides is only partially sustained during continuous infusion. Propranolol partially blocks the increase induced in heart rate by atrial natriuretic peptides, but does not affect either pulse pressure or mean arterial pressure. Propranolol significantly increases urine flow in saline-infused animals but has no apparent effect on animals subjected to infusions of atrial natriuretic peptides. These results indicate that there are multiple foci for the action of atrial natriuretic peptides in trout and that in many instances the effects of atrial natriuretic peptides are mediated through secondary effector systems.

Immunohistochemical localisation of natriuretic peptides in the heart and brain of the gulf toadfish Opsanus beta.

The distribution of natriuretic peptide immunoreactivity was determined in the heart and brain of the gulf toadfish Opsanus beta using the avidin-biotin peroxidase technique. Four antisera were used: the first raised against porcine brain natriuretic peptide which cross-reacts with atrial natriuretic and C-type natriuretic peptides (termed natriuretic peptide-like immunoreactivity); the second raised against porcine brain natriuretic peptide which cross-reacts with C-type natriuretic peptide but not with atrial natriuretic peptide (termed porcine brain natriuretic peptide-like immunoreactivity); the third raised against rat atrial natriuretic peptide; and the fourth raised against eel atrial natriuretic peptide. Natriuretic peptide- and porcine brain natriuretic peptide-like immunoreactivity was observed in all cardiac muscle cells of the atrium. In the ventricle, natriuretic peptide-like immunoreactivity was found in all cardiac muscle cells, however, porcine brain natriuretic peptide-like immunoreactivity was confined to muscle cells adjacent to the epicardium. There was no discernible difference in the distribution of natriuretic peptide-like immunoreactivity and porcine brain natriuretic peptide-like immunoreactivity in the brain. Immunoreactive perikarya were observed only in the preoptic region of the diencephalon, and many immunoreactive fibres were found in the telencephalon, preoptic area, and rostral hypothalamus, lateral to the thalamic region. There was no immunoreactivity in any region of the hypophysis. A pair of distinct immunoreactive fibre tracts ran caudally from the preoptic area to the thalamic region, from which fibres extended to the posterior commissure, area praetectalis, dorsolateral regions of the midbrain tegmentum, and tectum.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of eel atrial natriuretic peptide on NaCl and water transport across the intestine of the seawater eel.

Eel atrial natriuretic peptide inhibited the serosa-negative transepithelial potential difference and short-circuit current, accompanied by a decrease in NaCl and water absorption across the seawater eel intestine. Similar effects were obtained after treatment with N-terminally truncated eel atrial natriuretic peptide (5-27), indicating that N-terminal amino acids are not essential for the action of eel atrial natriuretic peptide. Although mammalian atrial natriuretic peptides also inhibited the short-circuit current, a 100-fold higher concentration was required to obtain the same effect as with eel atrial natriuretic peptide, indicating that eel atrial natriuretic peptide is 100 times as potent in eel intestine as the mammalian atrial natriuretic peptides. Similarly, in mammalian atrial natriuretic peptide, the four N-terminal amino acids had no significant effects. However, when the C-terminal tyrosine was removed, the potency of rat atrial natriuretic peptide was lowered. Compared with the effects of acetylcholine, serotonin and histamine, eel atrial natriuretic peptide was the most potent inhibitor, with 100% inhibition at 10(-7) M; 50% inhibition was obtained at 10(-2) M in acetylcholine, and 30% inhibition in serotonin (10(-5) M) and histamine (10(-3) M). These inhibitory effects of eel atrial natriuretic peptide were not diminished even in the presence of tetrodotoxin, and were mimicked by 8-bromoguanosine 3',5'-cyclic monophosphate. Based on these results, structure-activity relationships of eel atrial natriuretic peptide and a possible mechanism of action of eel atrial natriuretic peptide are discussed.

Atrial natriuretic peptide receptor subtypes in rat neuronal and astrocyte glial cultures.

We have compared the levels and subtypes of atrial natriuretic peptide (ANP) receptors in astrocyte glial and neuronal cultures prepared from the hypothalamus and brain stem of 1-day-old rats. Astrocyte glial cultures contain approximately twice the number of ANP receptors, as measured by 125I-ANP specific binding, compared with neuronal cultures. Rat ANP-(99-126), rat brain natriuretic peptide (BNP32), C-type natriuretic peptide (CNP-22), atriopeptin I, and [des-Gln18,Ser19,Gly20,Leu21, Gly22]atrial natriuretic factor-(4-23)-NH2[C-ANF-(4-23)] all competed strongly for 125I-ANP binding in both culture types, with inhibitory constant values ranging from 0.47 to 8.07 nM. The presence of ANP-C receptors (clearance type) in both cell types is indicated from the strong competition of 125I-ANP specific binding by C-ANF-(4-23). The potency profiles for stimulation of guanosine 3',5'-cyclic monophosphate levels by these peptides were ANP = BNP much greater than CNP-22 greater than atriopeptin I in astrocyte glia and CNP-22 much greater than BNP32 greater than ANP greater than atriopeptin I in neuronal cultures. These results indicate that both types of culture contain guanylate cyclase-coupled ANP receptors, with astrocytes containing predominantly the ANP-A subtype and neurons predominantly the ANP-B subtype.

Effect of atrial natriuretic peptide on DOPA potentiation in mice

The effect of rat atrial natriuretic peptide (ANP 1–28) on the pargyline-DOPA potentiation test was studied following its administration into the lateral brain ventricle in mice. Thirty minutes after pargyline pretreatment, three doses of ANP (200, 500, or 1,000 ng/mouse) were administered simultaneously with DOPA and animals were then observed for 2 h. ANP in doses of 500 and 1,000 ng markedly enhanced the effect of DOPA. The maximum intensity of the effect was registered 30–45 min following administration of the peptide. The data suggest that ANP might be regarded as a dopaminergic-modulating agent in the CNS.

Localization of cGMP after infusion of ANP or nitroprusside in the maturing rat.

To determine the ontogeny of intrarenal distribution of guanosine 3',5'-cyclic monophosphate (cGMP) formation in response to atrial natriuretic peptide (ANP) or sodium nitroprusside (SNP), adult and neonatal Sprague-Dawley rats were anesthetized and infused for 60 s with rat ANP (5-2,500 micrograms/kg) or SNP (0.1-10.0 mg/kg). cGMP was identified by the immunoperoxidase technique using a specific antibody. In adult rats, infusion of ANP localized cGMP primarily to the glomerular podocytes, whereas stimulation by SNP increased cGMP in the mesangium only (P less than 0.01). In neonatal rats, although overall renal cGMP immunostaining was greater than in adults, specific localization to podocytes (ANP) or mesangium (SNP) resulted only with higher doses of agonists. Although basal generation of cGMP by isolated glomeruli was greater in neonatal rats, the threshold for stimulation by ANP was lower in glomeruli from adult rats. We conclude that in vivo ANP stimulates glomerular particulate guanylate cyclase primarily in the podocytes, whereas SNP stimulates soluble guanylate cyclase localized to the mesangial cells. There is a maturational increase in the sensitivity for activation of glomerular particulate and soluble guanylate cyclase.