Cloning and sequence analysis of cDNA encoding a precursor for human atrial natriuretic polypeptide

George E. Brown memorial lecture. Role of atrial peptides in body fluid homeostasis

Extracts of mammalian atria, but not ventricles, induce marked diuresis, natriuresis, and reduction in blood pressure when infused systemically in rats and dogs. These extracts also inhibit aldosterone biosynthesis and renal renin release. Natriuretic peptides, 21 amino acids and longer, have been isolated from atria of rodents and man, and share a nearly homologous amino acid sequence at the carboxyterminus. Natriuretic activity resides in a 17-amino acid ring formed by a disulfide bridge, and the C-terminal Phe-Arg appears necessary for full biological potency. The deoxyribonucleic acid-encoding atrial natriuretic peptides have been cloned and the gene structure elucidated. Reduction of the diuretic and natriuretic responses to an acute volume load by right atrial appendectomy first suggested a role for atrial peptides in the physiological response to plasma volume expansion. Subsequently, release of peptides with natriuretic and spasmolytic properties from isolated heart preparations in response to right atrial distension was demonstrated by bioassay and radioimmunoassay. The presence of these peptides in normal rat and human plasma in concentrations of 20-100 pM, and the findings of increased levels in response to acute and chronic plasma volume expansion, rapid atrial tachyarrhythmias, systemic hypertension, congestive heart failure, and renal insufficiency imply that they play an important role in body fluid homeostasis. The mechanisms by which atrial peptides increase renal salt and water excretion are as yet unclear. Renal vascular effects have been consistently demonstrated, and limited evidence for direct actions on tubule ion transport has also been reported recently. In vitro, these peptides cause precontracted vascular and nonvascular smooth muscle to relax, mediated by a direct action on smooth muscle cells. Specific receptors for these peptides have been characterized in crude membranes prepared from whole kidney homogenates and adrenal glomerulosa cells, in intact glomeruli and cultured glomerular mesangial cells, and in intact bovine aortic smooth muscle and endothelial cells. Natriuretic peptides stimulate cyclic guanosine monophosphate accumulation in target tissues, and augment particulate guanylate cyclase activity in membrane fractions, suggesting that cyclic guanosine monophosphate is the second messenger mediating their cellular action.

Atrial natriuretic factor receptors in rat kidney, adrenal gland, and brain: autoradiographic localization and fluid balance dependent changes

Mammalian atria contain natriuretic peptides designated atrial natriuretic factors (ANF). Using in vitro autoradiography with 125I-labeled ANF, we have localized high-affinity (Kd = 150 pM) ANF binding sites to the glomeruli of the kidney, zona glomerulosa of the adrenal gland, and choroid plexus of the brain. The numbers of sites in both kidney and adrenal are increased in rats deprived of water; increases are detectable within 72 hr of water deprivation in the kidney and within 24 hr in the adrenal gland. Receptor numbers decline in rats given 2.0% NaCl as drinking water and in diabetic rats. The discrete localizations and dynamic alterations of these receptors suggest that ANF regulates fluid balance through diverse but coordinated effects on receptors in numerous organs including the kidney, adrenal, and brain.

Atrial natriuretic factor determinations and chronic sodium homeostasis

To examine the physiological role of atrial natriuretic factor (ANF) in the maintenance of sodium homeostasis under various conditions, we performed experiments in rats across a wide range of sodium intake, in rats with chronic renal insufficiency at extremes of sodium intake, and in rats given desoxycorticosterone acetate. After three weeks of a very low sodium diet, regular diet, or regular diet plus 1% saline as drinking water, no difference in plasma values of immunoreactive atrial natriuretic factor (IR-ANF) were identified, while rats at the lowest level of sodium intake had elevated atrial values. Normal rats, and rats with 5/6 nephrectomy has plasma values of IR-ANF which were no different irrespective of their sodium intake, nor were atrial values in these rats different. Although mineralocorticoid "escape" could be documented by changes in urine sodium excretion, neither plasma nor atrial IR-ANF values showed differences either at 24 or 72 hr after "escape". The data are consistent with previous observations that ANF serves the purpose of affecting rapid adjustments to large alterations in circulating fluid volume. Chronic high sodium intake, adaptation to renal insufficiency, and adjustment to the effect of mineralocorticoid do not appear to be associated with increased circulating plasma concentrations of IR-ANF.

Structure and analysis of the bovine atrial natriuretic peptide precursor gene

The isolation and sequence analysis of the gene encoding the bovine atrial natriuretic peptide (ANP) precursor is described. The bovine-ANP coding sequences are located on three exons which are interrupted by two intervening sequences. Comparison of the bovine, human, rat and mouse ANP gene sequences reveals a common organization of introns and exons and a high degree of sequence homology in the 5'-flanking and coding regions. Examination of the pre-proANP amino acid sequence derived from the bovine gene with those from rat, mouse and human, indicates a high degree of sequence homology in both the amino-terminal and biologically-active carboxy-terminal ANP region. The latter region in the bovine sequence resembles its human counterpart except for a carboxy-terminal Arg-Arg dipeptide.

Increased release of atrial natriuretic polypeptides in rats with DOCA-salt hypertension

This study compared atrial and plasma concentrations of immunoreactive alpha-rat atrial natriuretic polypeptide (i alpha-rANP) in rats given tap water (control), a 1% saline solution (salt), deoxycorticosterone acetate (DOCA) and DOCA plus 1% saline solution (DOCA-salt) after 1 and 8 weeks of treatment. DOCA (100 mg/kg) was given by implanting a piece of silicon rubber impregnated with DOCA subcutaneously. Atrial i alpha-rANP increased, while plasma i alpha-rANP decreased with time in all groups. Atrial concentration of i alpha-rANP was significantly lower in the DOCA-salt group than in the other groups at 1 week, and was reduced in the DOCA and DOCA-salt groups as compared to the control group at 8 weeks. On the other hand, plasma concentration of i alpha-rANP was significantly higher in the DOCA and the DOCA-salt groups than in the control group at 1 week; the DOCA and DOCA-salt group values were also higher than the control and salt group values at 8 weeks. Atrial concentration of i alpha-rANP was inversely correlated with systolic blood pressure in the all rats at 1 week (r = 0.48, p less than 0.001) and at 8 weeks (r = 0.33, p less than 0.05). Plasma concentration of i alpha-rANP was positively correlated with systolic blood pressure at 8 weeks (r = 0.37, p less than 0.05). In addition, there was a significant positive correlation between plasma/atrial ratio of i alpha-rANP concentration and systolic blood pressure at either stage (r = 0.41, p less than 0.01 at 1 week; r = 0.40, p less than 0.01 at 8 weeks). Thus, it seems likely that the release of ANPs is increased in response to expansion of extracellular fluid volume or elevation of blood pressure, modifying the development of hypertension in DOCA-salt rats.

Atrial natriuretic polypeptide-like immunoreactivity in the rat pituitary: light and electron microscopic studies

Immunoreactive atrial natriuretic polypeptide (ANP) was investigated in the pituitary of rats by light and electron microscopy using the indirect immunofluorescence and peroxidase-antiperoxidase techniques. ANP-like immunoreactivity was present in 30-35% of anterior pituitary cells. These cells have two types of secretory granules being characteristic of rat gonadotrophin-storing granules, and were usually adjacent to the capillary endothelium. The results of this study suggest the co-occurrence of ANP and gonadotrophins in the anterior pituitary cells.

Acute volume expansion as a physiological stimulus for the release of atrial natriuretic peptides in the rat

The concentration of immunoreactive atrial natriuretic peptide(s) (ANP) was measured in normovolemic conscious rats and 15 min after 10% and 20% blood volume expansion. A 20% blood volume expansion caused a 2-fold increase in plasma ANP. While plasma ANP increased linearly, atrial levels of ANP remained unaltered. The increase in plasma ANP parallelled increases of central blood volume and central venous pressure. It is concluded that acute blood volume expansion is a major physiological stimulus for the release of atrial natriuretic peptides into the circulation.

Lack of direct action of alpha-human atrial natriuretic polypeptide on the in vitro perfused segments of Henle's loop isolated from rabbit kidney

We examined direct effects of alpha-human atrial natriuretic polypeptide (alpha-hANP) on water and NaCl transport across the segments of Henle's loop by the in vitro microperfusion technique. In the medullary and the cortical thick ascending limb, 10(-6) M alpha-hANP did not affect the transmural voltage (Vt) and the lumen to bath 36Cl flux whether it was added to the perfusate or to the bath. In the thin ascending limb, 10(-6) M alpha-hANP did not affect the lumen to bath 36Cl flux. The peptide may not affect permselectivity of the thin ascending limb, since it did not influence the diffusion potential generated in the presence of a NaCl gradient. In the descending limb, 10(-6) M alpha-hANP did not affect osmotic water permeability, whether it was added to the perfusate or to the bathing fluid. From these observations, we conclude that alpha-hANP does not show direct effects on water and NaCl transport in the segments of Henle's loop at least under our experimental conditions. Therefore, natriuresis by alpha-hANP may be caused either by an action on nephron segments other than Henle's loop or by an action on renal vasculatures.

A comparison of synthetic rat and human atrial natriuretic factor in conscious dogs

The renal and hypotensive responses to intravenous infusions of 10, 50, 100, and 200 pmol/kg/min of synthetic rat atrial natriuretic factor (Arg101-Arg-Ser-Ser-Cys-Phe-Gly-Gly-Arg-Ile110-Asp-Arg-Ile-G ly-Ala-Gln-Ser-Gly -Leu-Gly120-Cys-Asn-Ser-Phe-Arg-Tyr; disulfide bond between cysteines) were compared with those produced by synthetic human atrial natriuretic factor (Met110) in five conscious dogs. Increasing doses of rat or human atrial natriuretic factor lowered mean arterial pressure in a dose-related manner. At 200 pmol/kg/min, the maximally effective dose for both peptides, mean arterial pressure was reduced from 116 +/- 4 to 96 +/- 5 mm Hg and from 117 +/- 5 to 100 +/- 3 mm Hg (p less than 0.01), respectively. Neither peptide affected heart rate. Fractional sodium excretion increased from 0.69 +/- 0.22 to 3.95 +/- 1.23% and from 0.69 +/- 0.16 to 4.62 +/- 0.72% during infusions of 200 pmol/kg/min of rat and human atrial natriuretic factor, respectively. Urine volume and fractional chloride excretion rose during infusions of rat or human atrial natriuretic factor in a manner that resembled the elevation in sodium excretion. The stimulation of fractional potassium excretion by both rat and human peptides was more variable and not as clearly dose-dependent. Glomerular filtration rate was enhanced by both rat and human atrial natriuretic factor, while neither peptide significantly changed renal plasma flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of immunoreactive atrial natriuretic peptides in the central nervous system of the rat

The distribution of immunoreactive (ir) atrial natriuretic peptides (ANPs) in 47 microdissected brain and spinal cord regions of the rat was determined by radioimmunoassay. The highest concentrations of ir-ANPs exist in the paraventricular nucleus and median preoptic nucleus (580.9 and 558.0 fmol/mg protein, respectively). High concentrations of ir-ANP (greater than 300 fmol/mg protein) are present in the interpeduncular nucleus, preoptic and hypothalamic periventricular nuclei, median eminence and organum vasculosum of the lamina terminalis. Moderate concentrations of ir-ANPs (between 100 and 300 fmol/mg protein) are found in 16 brain regions such as the bed nucleus of the stria terminalis, nucleus of the diagonal band, most of the hypothalamic nuclei, central gray, locus coeruleus and parabrachial nuclei. Low levels of ir-ANPs (less than 100 fmol/mg protein) exist in 22 brain regions including cortical areas, amygdala, caudate nucleus, nucleus accumbens, hippocampus, supraoptic nucleus, subfornical organ, medial mammillary nucleus, substantia nigra, dorsal raphe nucleus, cerebellum, nucleus of the solitary tract and others. Cervical spinal cord and neurointermediate lobe of pituitary gland contain low levels of ir-ANPs.

Characterization and distribution of receptors for the atrial natriuretic peptides in mammalian brain

Both rat 125I-labeled atrial natriuretic polypeptide [125I-ANP or atrial natriuretic factor fragment ANF-(99-126)] and human 125I-ANP [125I-alpha-ANP or human ANF-(99-126)] bind with high specificity and affinity (Kd = 20-80 pM) to an apparent single class of sites in guinea pig brain. The ligand selectivity pattern demonstrates that ANF-(101-126) greater than ANF-(99-126) greater than ANF-(103-125) greater than ANF-(103-123) on 125I-alpha-ANP binding sites. [International nomenclature starting at the end of the signal peptide of the recently sequenced prepropeptide is used; thus, ANF-(101-126) corresponds to the earlier designation ANF-(8-33), ANF-(103-123) to rat atriopeptin I, and ANF-(103-125) to rat atriopeptin II.] Similar results have been reported in peripheral tissues, which indicate that central and peripheral ANP binding sites have fairly similar structural requirements. In vitro receptor autoradiography shows that in the guinea pig brain, 125I-ANP binding sites are highly concentrated in the external plexiform layer of the olfactory bulb, subfornical organ, various thalamic nuclei, medial geniculate nucleus, and cerebellum. Lower densities are found in the central nucleus of the amygdala, dentate gyrus, hippocampus, and area postrema. Most remaining regions contain much lower densities of sites. In rat brain, 125I-ANP binding sites are differentially distributed, with high densities in the subfornical organ, area postrema, and linings of ventricles but low densities in the thalamus and cerebellum. In monkey brain, 125I-ANP binding sites are concentrated in the cerebellum. The presence of high densities of 125I-ANP binding sites in various brain regions strongly suggests the existence of a family of brain-heart peptides, in analogy to the well-known brain-gut peptides. Moreover, the extensive distribution of 125I-ANP binding sites in mammalian brain suggests that the possible roles of ANP/ANF-like peptides in brain are not restricted to the central regulation of cardiovascular parameters.

Human cardiac plasma concentrations of atrial natriuretic peptide quantified by radioreceptor assay

The presence of high affinity receptors for atrial natriuretic peptide in bovine adrenal cortex has enabled the development of a sensitive, specific and rapid radioreceptor assay for this peptide in human plasma. In 18 normal subjects, venous plasma atrial natriuretic peptide concentration ranged from 6 to 65 pM. This plasma concentration was two-fold higher in right atrium as compared to venous blood in 12 patients investigated by cardiac catheterisation, confirming that the right atrium is the site of release of atrial natriuretic peptide into circulation. There was a further step up in plasma atrial natriuretic peptide concentration between pulmonary arterial and aortic plasma. This finding indicates that released hormone in man may undergo further activation in the lungs, or that there may be direct release from the left atrium.

The inhibition of progesterone secretion and the regulation of cyclic nucleotides by atrial natriuretic factor in gonadotropin responsive murine Leydig tumor cells

We have found that atrial natriuretic factor (ANF) has a profound effect on testicular cells in altering intracellular cyclic nucleotide levels as well as progesterone secretion. Using clonal cultured Leydig tumor cells we found that 1 X 10(-8)M ANF caused a two thousand-fold elevation in the accumulation of cellular cGMP and inhibited cAMP in treated cells by more than 90% as compared to the controls. ANF (1 X 10(-8)M) also significantly inhibited gonadotropin-stimulated accumulation of cAMP in response to bovine luteinizing hormone (bLH) or human chorionic gonadotropin (hCG). Gonadotropin-stimulated progesterone secretion was inhibited by ANF (1 X 10(-10) - 1 X 10(-9)M) in these cultured Leydig tumor cells. Approximately 50% inhibition of progesterone secretion was observed at the peptide concentration of 1 X 10(-9) M.

Concomitant increase in plasma atrial natriuretic peptide and cyclic GMP during volume loading

To investigate the effects of fluid expansion on endogenous atrial natriuretic peptide (ANP) and cyclic 3',5'-guanosine monophosphate (cGMP), four male volunteers were studied before, during and after intravasal volume loading. Volume expansion was performed by intravenous infusion of 2,000 ml isotonic saline solution within 30 min. Mean plasma ANP levels increased 2.5-fold from 31.2 pg/ml to 81.7 pg/ml 40 min after the start of infusion. Plasma cGMP levels paralleled the rise in ANP, showing a mean cGMP increment from 2.7 pmol/ml to a maximum of 8.2 pmol/ml. Both ANP and cGMP levels were back to basal levels 120 min after termination of the infusion. Stimulation of endogenous ANP release by volume loading suggests that ANP is involved in the regulation of fluid homeostasis in man. The parallel rise in plasma cGMP levels supports the idea that cGMP is a mediator for the effects of ANP.

Distribution of atrial natriuretic factor-like immunoreactive neurons in the rat brain

Using antisera generated in rabbits against rat atriopeptin III [alpha-rANP(5-28)] and human alpha-atrial natriuretic polypeptide we mapped the distribution of atrial natriuretic factor-like immunoreactivity throughout the rat central nervous system. Cell bodies were observed in the telencephalon (nucleus interstitialis striae terminalis and between the amygdala centralis and medialis), throughout the diencephalon in all nuclei of the "anteroventral third ventricle", the base of the hypothalamus, the subzona incerta area, the medial forebrain bundle and the medial habenula, in the mesencephalon (mamillary body, substantia nigra lateralis, dorsal and ventral parabrachial nuclei) and very sparse in the medulla oblongata along the fourth ventricle towards the vestibular nuclei, the nucleus tractus solitarii and nervi trigemini. Fibers were present wherever cell bodies were located. The highest relative densities were observed in the anteroventral third ventricle area and the medial habenula. Sparse fibers were also seen in the spinal cord (dorsal and ventral horn and around the central canal) and in the posterior pituitary. The predominance of the atrial natriuretic factor-like perikarya and fibers in the anteroventral third ventricle area suggests an involvement of this peptide in central blood pressure control.

Atrial natriuretic hormone, the renin-aldosterone axis, and blood pressure-electrolyte homeostasis

The renin-angiotensin-aldosterone axis exerts major control over sodium and potassium balance and arterial blood pressure. These three functions are continuously regulated by changes in angiotensin II and aldosterone levels in response to wide variations in dietary intake of sodium and potassium. In addition, changes in intrarenal physical factors cause changes in the supply of distal tubular sodium that, in turn, work to determine sodium and potassium excretion and to modulate the release of renal renin. However, certain aspects of sodium homeostasis cannot be fully explained either by the activity of the renin system or by intrarenal physical factors, and this has led investigators to search for other natriuretic hormonal mechanisms. Recently, it has become clear that atrial tissue contains a group of peptides, at least one of which is probably secreted as a regulatory hormone. In animals, these atrial peptides produce immediate, marked natriuresis associated with a rise in glomerular filtration rate (but no alteration of total renal flow) and a simultaneous decrease in arterial blood pressure. Atrial peptides also inhibit renal renin secretion and adrenal cortical secretion of aldosterone, and they oppose the vasoconstrictive action of angiotensin II. One of these atrial peptides may therefore be the long-sought natriuretic hormone, though in a different form and shape than was envisioned. The fact that atrial peptide works to oppose the renin system at four points suggests that this new hormone could have a major complementary role in long-term regulation of blood pressure and electrolyte homeostasis. In this construction the renin system primarily defends sodium balance and blood pressure, with the atrial hormone having an increasing counter-influence in situations involving high blood pressure or sodium surfeit. We can soon expect to learn more about this atrial hormone, including which peptide is the active circulating hormone, what induces or inhibits its release, and what part it plays in cardiovascular diseases.

Structure of dog and rabbit precursors of atrial natriuretic polypeptides deduced from nucleotide sequence of cloned cDNA

The structure of precursors of dog and rabbit atrial natriuretic polypeptides was determined by nucleotide sequence analysis of cloned cDNA of mRNA encoding the peptides. The dog and rabbit precursors are 149 and 153 residues long having 23- and 25-residue putative signal peptides at their N-termini respectively. The 28-residue peptide with identical sequence to that of human, which has potent natriuretic activity, is located at the C-terminus of the dog precursor. The 28-residue peptide of identical sequence to that of mouse/rat is located at C-terminus of rabbit precursor followed by additional Arg-Arg sequence which is also found in rat/mouse precursors and is apparently removed during processing.

Molecular forms of immunoactive atrial natriuretic peptide released from cultured rat atrial myocytes

Primary cultures of atrial myocytes were prepared from newborn rats and maintained for 8 days in complete serum-free medium. The culture content of immunoactive atrial natriuretic peptide (ANP) increased from 10 to 25 ng/culture during this time. The cells released immunoactive ANP at a rate of 2 to 3% of culture content per hour in a linear fashion for at least 6 hours. When analyzed by gel filtration the major immunoactive material released by and contained within the cells displayed a molecular weight of approximately 15,000 daltons. The medium and cellular ANP-related peptides were further shown to be indistinguishable by reversed-phase HPLC. When the 15,000 dalton material was incubated with rat serum it was converted to ANP-related material possessing a molecular weight of approximately 3,000 daltons. These results suggest that under basal conditions, atrial myocytes release a large molecular weight form of ANP that is converted in the circulation to a low molecular weight form of ANP, which has been previously identified in plasma.

Biochemical and immunological evidence for a cardiodilatin-like substance in the snail neurocardiac axis

Cardiac hormones, which have been isolated recently from mammalian atria, are potent regulatory peptides of blood pressure and blood volume. By using biochemical and immunological methods to determine cardiac hormones of the cardiodilatin family, this type of peptide hormone was detected in a neurosecretory system projecting from the subesophageal ganglion to the heart of the snail. The cardiodilatin-like molecule was characterized by its biological effects on mammalian vascular smooth muscle, by radioimmunoassay combined with high-performance liquid chromatography, and by immunocytochemistry. In mammals cardiodilatin-like peptides appear to serve purely endocrine functions. In contrast, in the snail they are present in a neuroendocrine system, the function of which remains to be established.

Effect of atrial peptides on aldosterone production

This study examines the effects of the synthetic atrial peptides (atriopeptin I, II, and III) on aldosterone and corticosterone production by rat adrenal cell suspensions. Furthermore, we studied the effect of atriopeptin II infusion on the plasma aldosterone response to angiotensin II in the rat in vivo. Atriopeptin I, II, and III decreased aldosterone release from zona glomerulosa cells in a dose-dependent fashion. 10 pM atriopeptin II inhibited basal aldosterone release significantly (P less than 0.01), and 10 nM atriopeptin II or III lowered it by 79%. Atriopeptin II decreased the sensitivity of the glomerulosa cells to adrenocorticotropic hormone (ACTH) and angiotensin II. Atriopeptin II had no effect on basal or ACTH-stimulated corticosterone release by fasciculata-medullary cells. In vivo infusions of angiotensin II with or without simultaneous infusions of atriopeptin II showed that atriopeptin II significantly inhibited the aldosterone response to angiotensin II. This inhibition by atriopeptin II was independent of any effect on plasma renin activity, serum potassium, or ACTH. These data raise the possibility that the atrial natriuretic peptides may affect sodium excretion by the kidney, not only directly, but also indirectly through the inhibition of aldosterone production.

Atrial natriuretic factor increases cyclic GMP and inhibits cyclic AMP in rat renal papillary collecting tubule cells in culture

The present study was undertaken to determine whether human atrial natriuretic factor (hANF) produces guanosine-3', 5'-monophosphate (cGMP) and alters arginine vasopressin (AVP)- and forskolin (F)- induced adenosine-3', 5'-monophosphate (cAMP) production in the cultured rat renal papillary collecting tubule cells. hANF increased cellular cGMP levels in a dose dependent manner. AVP and F, however, did not affect cGMP production. hANF significantly inhibited AVP- and F-stimulated cAMP levels, but hANF by itself did not affect cellular cAMP production. Since F activates adenylate cyclase at a step of catalytic unit and the cellular action of AVP to activate adenylate cyclase is mediated through receptor-catalytic units, the present results indicate that hANF may directly inhibit the AVP- and F-stimulated adenylate cyclase in renal papillary collecting tubules.

Atrial natriuretic peptide in plasma of volume-overloaded children with chronic renal failure

The effect of volume changes on the plasma concentration of atrial natriuretic peptide (ANP) in children with chronic renal failure was investigated by the use of a specific and sensitive radioimmunoassay. Predialysis plasma ANP was significantly higher in children with end-stage renal disease than in healthy children and children with advanced renal failure without evidence of volume expansion. During haemodialysis plasma ANP decreased significantly and plasma renin activity rose slightly, whereas plasma arginine vasopressin and aldosterone did not change. Plasma ANP correlated positively with volume status (body weight gain during the interval between two haemodialysis sessions). An expanded extracellular fluid volume thus seems to be a major stimulus for the rise in ANP in children with end-stage renal disease. The findings suggest that ANP may be important in volume homoeostasis.

Neuromedin B-32 and B-30: two "big" neuromedin B identified in porcine brain and spinal cord

In mammalian spinal cord, we have previously discovered "neuromedin B", whose structure is closely related to amphibian bombesin. By utilizing a specific radioimmunoassay for neuromedin B, we have isolated two novel "big" neuromedin B, designated neuromedin B-32 and B-30, from pig brain and spinal cord, both of which were identified as N-terminally extended forms of neuromedin B. The amino acid sequence of neuromedin B-32 was determined to be: Ala-Pro-Leu-Ser-Trp-Asp-Leu-Pro-Glu-Pro- Arg-Ser-Arg-Ala-Gly-Lys-Ile-Arg-Val-His-Pro-Arg-Gly-Asn-Leu-Trp-Ala- Thr-Gly-His-Phe-Met-NH2, while neuromedin B-30 was found to be an N-terminal two amino acids deleted form of neuromedin B-32. Isolation of a family comprising neuromedin B, B-30 and B-32 is indicative of their biosynthetic relationship.

Solubilization and molecular weight estimation of atrial natriuretic factor receptor from bovine adrenal cortex

Receptors for atrial natriuretic factor (ANF) have been solubilized with 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate from bovine adrenal cortex and characterized. The detergent extract retained specific high-affinity binding sites for 125I-ANF. Scatchard analysis of the equilibrium binding data revealed a single class of binding site with a K-d of 1.8 nM and a maximum binding capacity of 2.5 pmol/mg of protein. The size of the 125I-ANF X receptor complexes was estimated to be 140,000 daltons by gel filtration on TSK gel G3000SW. Affinity labeling followed by electrophoresis under nonreducing conditions and autoradiography also revealed a single band of a similar size (Mr = 130,000); this band, however, migrated as a Mr = 70,000 species under reducing electrophoretic conditions. These results indicate that the ANF receptor, having a Mr of 130,000 - 140,000, is composed of disulfide-linked subunits and the ANF-binding site is located on the 70-kDa component.

Plasma atrial natriuretic peptide in cardiac disease and during infusion in healthy volunteers

Plasma concentrations of immunoreactive atrial natriuretic peptide (ANP) were low or undetectable in 8 healthy subjects and 9 control patients without cardiac disease, and raised in 17 patients with congestive heart failure (CHF). Highest concentrations were measured in patients with severe CHF. High plasma ANP levels were also found in 2 patients with paroxysmal supraventricular tachycardia and associated transient polyuria. Infusion of synthetic human alpha-ANP, 110-125 micrograms over 30 min, to 3 healthy males resulted in a 2.3-fold increase in natriuresis and diuresis but had no effect on kaliuresis. Plasma levels of renin activity, aldosterone, and antidiuretic hormone did not change significantly. ANP infusion gave plasma ANP levels of the same magnitude as those found in severe CHF; levels returned to baseline within 15 min of stopping the infusion. Thus ANP appears to be a circulating hormone in man, at least in severe CHF and supraventricular tachycardia.

Comparison of hydrolysis of atriopeptin II stand-in substrate by atrial dipeptidyl carboxyhydrolase and angiotension I-converting enzyme

We recently found and partially purified a new membrane-bound metallo dipeptidyl dipeptidase from bovine atrial tissue homogenates (Harris, R.B. & Wilson, I.B. (1984) Arch. Biochem. Biophys. 233, 667-675). We suggested that this enzyme was capable of cleaving the dipeptide, phenylalanyl-arginine from the C-terminus of atriopeptin II to give atriopeptin I. The atriopeptins are two atrial natriuretic peptides and the existence of the atrial peptide system has implicated the mammalian heart as an endocrine organ. The tetrapeptide benzoyl-glycyl-seryl-phenylalanyl-arginine was synthesized because it contains the C-terminal tripeptide sequence of atriopeptin II and should be useful to test the roles of the atrial enzyme and angiotensin I-converting enzyme in processing the atrial peptides. We found that for the atrial enzyme, Vmax was 13-fold higher and Km 7-fold-lower for this stand-in substrate than for benzoyl-glycyl-histidyl-leucine, a standard substrate used to measure converting enzyme activity. The ratio of Vmax/Km as a measure of substrate specificity indicates that the stand-in substrate is 86-fold better than benzoyl-glycyl-histidyl-leucine. In contrast, the stand-in substrate is a 20-fold poorer substrate for the converting enzyme than benzoyl-glycyl-histidyl-leucine. With the stand-in substrate, the converting enzyme showed pronounced substrate inhibition. An effective Vmax and Km were calculated using only concentrations of S below the optimum substrate concentration. These results confirm that the atrial enzyme is distinct from the converting enzyme. They also suggest that the conversion of atriopeptin II to atriopeptin I is a physiological process that is mediated by this enzyme.

Molecular forms of immunoactive atrial natriuretic peptide in the rat hypothalamus and atrium

Acid extracts of rat hypothalamus and atrium were prepared by a procedure previously shown to minimize proteolytic degradation of peptides. The majority of the immunoactive material in the atrial extracts had a molecular weight of approximately 9,000 to 15,000 daltons, while that in the hypothalamic extracts had a molecular weight of about 1,500 to 1,800 daltons. The major molecular weight forms of atrial natriuretic peptide from each extract were further distinguishable when analyzed by RP-HPLC. These results suggest that small peptides such as atriopeptins I, II, and III, may not be authentic post-translational processing products in the atrium, and that the hypothalamus and atrium may differentially cleave pro-atrial natriuretic peptide to form tissue-specific products.

[The heart as an endocrine organ: the discovery of a new hormone]

Ever since the early work of Henry and Gauer (1956) it has been clear that a link exists between the atria of mammals and diuresis. In 1981, De Bold et al. described that atrial extracts, injected intravenously into rats, caused diuresis. The hormone responsible for this diuresis has quickly been identified. The peptide hormone, atrial natriuretic factor (ANF), which is also known as atrial natriuretic peptide(s) (ANP), cardionatrin, cardiodilatin, atrin or auriculin, has been sequenced and synthetically produced. Its genomic DNA has been cloned. ANF raises cyclic GMP in target cells and activates particulate guanylate cyclase but not soluble guanylate cyclase. So far, no other hormone has conclusively been shown to activate particulate guanylate cyclase. ANF is formed and secreted in the atria but not in the ventricles of mammals, including man. The action of ANF involves natriuresis, vasorelaxation and inhibition of aldosterone secretion. ANF or ANF derivatives may represent a therapeutically useful new class of agents.

Alpha-human atrial natriuretic polypeptide is released from the heart and circulates in the body

In order to clarify whether or not atrial natriuretic polypeptides are hormones in man, we have measured plasma alpha-human atrial natriuretic polypeptide (alpha-hANP)-like immunoreactivity (alpha-hANP-LI) with or without extraction procedure. alpha-hANP-LI was detected in plasma extracts from all 5 normal subjects and 7 patients with heart diseases. The alpha-hANP-LI concentration in normal peripheral plasma was 37.7 +/- 7.0 pg/ml (mean +/- SE). Plasma concentrations of alpha-hANP-LI in the coronary sinus obtained by cardiac catheterization were 3 to 10 times higher than those in the peripheral vein, inferior vena cava, right atrium, pulmonary artery and aorta. High performance gel permeation chromatography coupled with a radioimmunoassay (RIA) for alpha-hANP revealed that alpha-hANP-LI in normal peripheral plasma eluted at the position corresponding to that of authentic alpha-hANP without detectable amounts of high molecular weight forms. alpha-hANP-LI extracted from plasma taken from the coronary sinus of two patients also showed a single peak of alpha-hANP-LI co-eluting with alpha-hANP. In contrast, not only alpha-hANP but gamma-hANP and beta-hANP, high molecular weight forms, were present in the human atrial tissue. These results indicate that alpha-hANP is the predominant form of alpha-hANP-LI in human plasma and that this form generated in the atrial cardiocytes is preferentially released from these cells and circulates in the body.

Cardiodilatin-immunoreactive neurons in the hypothalamus of Tupaia

Using various region specific antibodies raised against partial sequences of synthetic cardiodilatin (CDD) we detected immunoreactive neurons with their perikarya in the nucleus periventricularis of Tupaia belangeri. The fibers could be traced laterally directed towards the amygdaloid complex and some varicosities were also observed in the lateral parts of the nucleus periventricularis. It is postulated that brain CDD represents a new neuropeptide and that these CDD-IR neurons are involved in specific functions related to the modulation of the cardiovascular centers.

Molecular forms of atrial natriuretic polypeptides in mammalian tissues and plasma

A highly sensitive radioimmunoassay detecting for all the atrial natriuretic polypeptides isolated so far from human and rat (hANPs and rANPs) has been established by using an antiserum raised against alpha-hANP, since the antiserum recognizes the subsequence flanked by two cysteine residues (positions 7 and 23) in alpha-hANP and crossreacts with human as well as rat ANPs. By using the radioimmunoassay combined with gel chromatography or high performance liquid chromatography, it was revealed that ANP immunoreactivity in human atria is composed of alpha-(28 residues), beta-(56 residues: alpha-hANP dimer) and gamma-hANP(126 residues) in various ratios. In rat, porcine and bovine atrial tissues, however, gamma-rANP(126 residues) was found to be a major component. In contrast with atrial ANP, plasma ANP was found to be predominantly alpha-form in rat.

Highly conserved sequences in the 3' untranslated region of mRNAs coding for homologous proteins in distantly related species

Comparison of the nucleotide sequence of mRNAs coding for several vertebrate actins revealed a high degree of sequence homology in the 3' untranslated region (3' UTR) between those mRNAs coding for homologous (isotypic) actins in different organisms but not between mRNAs coding for very similar isoforms differing in their function or tissue specificity. A similar pattern of sequence conservation in the 3' UTR is also found in several other genes. Furthermore, while there is a great variation in the size of the 3' UTR of mRNAs coding for different proteins, mRNA coding for isotypic proteins in distantly related organisms often have 3' UTR of similar size. The data suggest that the 3' UTR may play an important role in the regulation of expression of at least some genes at the transcriptional or posttranscriptional level.

Existence of atrial natriuretic polypeptide in kidney

Using a specific radioimmunoassay (RIA) for alpha-atrial natriuretic polypeptide (alpha-ANP), we have demonstrated the presence of alpha-rat ANP-like immunoreactivity (alpha-rANP-LI) in the rat kidney which is considered to be a target organ for atrial natriuretic polypeptides released from the heart. Most of alpha-rANP-LI was localized in the cortex. High performance gel permeation chromatography coupled with the RIA revealed that renal alpha-rANP-LI was eluted at the position of a low molecular weight form corresponding to alpha-rANP without detectable amounts of high molecular weight forms. This is in contrast to the observation that gamma-rANP, a high molecular weight form of 13k daltons, is the dominant form of alpha-rANP-LI in the rat atrium. In water-deprived rats, the concentration and content of alpha-rANP-LI in the kidney showed a significant decrease compared with control rats. In addition, the alpha-rANP-LI concentration and content in this organ revealed a substantial decrease after perfusion with physiological saline. These results indicate the existence of atrial natriuretic polypeptide (ANP) in the kidney and suggest that part of renal ANP may originate from the heart.

Effects of changes in water-sodium balance on levels of atrial natriuretic factor messenger RNA and peptide in rats

Responses of atrial mRNA, atrial peptide and plasma peptide of atrial natriuretic factor (ANF) to treatments to alter fluid volume were studied in rats using RNA dot hybridization assay and radioimmunoassay. Specific changes in the level of ANF mRNA relative to total atrial RNA were observed in atria from sodium restricted rats and water deprived then sodium loaded rats, demonstrating an association of change in water-sodium balance with the expression of ANF gene. The levels of mRNA and the immunoreactive ANF in plasma decreased to 30% and 15% of controls, respectively, on water-deprivation and then increased again to control levels after administering 1.8% NaCl solution, whereas atrial immunoreactive ANF increased to about twice the control on water-deprivation and decreased again after supplying NaCl solution, in parallel with the level of the hematocrit. These findings suggest that atrial ANF content is dependent more on ANF release than on biosynthesis.

Molecular studies of the atrial natriuretic factor gene

The molecular biology of human atrial natriuretic factor was studied. A cloned rat cDNA probe was used to analyze tissue for the synthesis of atrial natriuretic factor, and the human gene was identified and sequenced. Nucleotide sequence comparison of human and rodent atrial natriuretic factor genes suggests regions that are critical for regulated expression of this cardiac hormone.

Conversion of atriopeptin II to atriopeptin I by atrial dipeptidyl carboxy hydrolase

We are examining the substrate specificity of atrial dipeptidyl carboxyhydrolase, a membrane-bound metallo enzyme that we isolated from bovine atrial tissue homogenates. This enzyme readily removes the dipeptide, Phe-Arg, from Bz-Gly-Ser-Phe-Arg, a stand-in substrate for atriopeptin II, one of several atrial natriuretic factors. We now report that the atrial enzyme cleaves the C-terminal dipeptide, Phe-Arg, from atriopeptin II to form atriopeptin I. The km (pH 7.5) is 25 microM and the ratio of relative Vmax/km as a measure of substrate specificity indicates that atriopeptin II is a 240-fold better substrate than Bz-Gly-His-Leu. Only Phe-Arg was detected as a hydrolysis product, indicating that sequential cleavage of Asn-Ser from atriopeptin II does not occur, and that atriopeptin I is not a substrate. Bz-Gly-Asn-Ser was as good a substrate for the atrial enzyme as Bz-Gly-His-Leu, but Bz-Cys(bzl)-Asn-Ser was not hydrolyzed. This result suggests that the presence of an intact disulfide bond or an S-alkylated residue in the P1 position of a substrate (as in atriopeptin I) prevents hydrolysis by the atrial enzyme. Comparative studies were made with the angiotensin I converting enzyme. Atriopeptin II was not a substrate. The stand-in substrates for atriopeptin I, Bz-Cys(bzl)-Asn-Ser and Bz-Gly-Asn-Ser were barely hydrolyzed, which by itself suggests that atriopeptin I is not a substrate of the angiotensin converting enzyme. Our results strongly suggest that atriopeptin II is converted to atriopeptin I and that hydrolysis is mediated by the atrial enzyme. The angiotensin I converting enzyme plays no role in processing these peptides. We suggest that the atrial enzyme be named atrial peptide convertase.

Effect of atrial natriuretic factor on blood pressure, renin, and aldosterone in Goldblatt hypertension

We previously provided evidence that atrial natriuretic factor (ANF) antagonizes angiotensin II-induced vascular contractility and angiotensin II-stimulated aldosterone production by isolated adrenal cells. To examine the importance of these effects in vivo, synthetic ANF (auriculin A) was administered intravenously (2 micrograms/kg bolus followed by 0.3 microgram/kg/min constant infusion) to conscious, unrestrained two-kidney, one-clip and one-kidney, one-clip rats on normal sodium intake and their sham-operated controls. The one-kidney, one-clip rats also were studied on a sodium-deficient diet. Mean blood pressure, plasma renin activity, and plasma aldosterone levels were measured before and after 60-minute infusion. In saralasin-responsive two-kidney, one-clip rats (n = 10), ANF administration reduced blood pressure (from 187 +/- 11 [SE] to 153 +/- 11 mm Hg; p less than 0.001) and plasma aldosterone levels (from 182 +/- 61 to 125 +/- 60 ng/dl; p less than 0.05), while plasma renin activity increased (from 59 +/- 16 to 82 +/- 20 ng/ml/hr; p less than 0.05). Lesser changes in blood pressure occurred in saralasin-nonresponsive two-kidney, one-clip rats (149 +/- 10 to 143 +/- 8 mm Hg; n = 5), sodium-replete one-kidney, one-clip rats (183 +/- 9 to 170 +/- 11 mm Hg; n = 9), two-kidney sham-operated rats (122 +/- 3 to 115 +/- 4 mm Hg; n = 8), and one-kidney sham-operated rats (117 +/- 3 to 112 +/- 3 mm Hg; n = 7). Control plasma renin and aldosterone levels were not elevated in these latter groups and did not change significantly with ANF administration. In sodium-depleted one-kidney, one-clip rats, which became saralasin responsive, ANF administration significantly reduced blood pressure (from 184 +/- 11 to 156 +/- 12 mm Hg; n = 8), plasma aldosterone levels (from 286 +/- 41 to 179 +/- 36 ng/dl), and plasma renin activity (from 69 +/- 19 to 44 +/- 13 ng/ml/hr).(ABSTRACT TRUNCATED AT 250 WORDS)

Vascular receptor binding activities and cyclic GMP responses by synthetic human and rat atrial natriuretic peptides (ANP) and receptor down-regulation by ANP

Biological activities of a variety of synthetic human (h) and rat (r) atrial natriuretic peptide (ANP) and related peptides as assessed by receptor binding and cyclic GMP response, and regulation of vascular ANP receptors were studied in rat aortic vascular smooth muscle cells (VSMC) in culture. alpha-hANP1-28 and alpha-hANP7-28 equally inhibited the binding of 125I-labeled-alpha-hANP to its vascular receptors, whereas Met(O)12-alpha-hANP1-28 was less potent and reduced and carboxymethylated (RCM)-alpha-hANP1-28 was ineffective. rANP5-27 and rANP5-28 were equipotent in receptor binding, whereas rANP5-25 had somewhat less potent effect and rANP8-28 fragment was ineffective. alpha-hANP1-28, alpha-hANP7-28, rANP5-27 and rANP5-28 similarly stimulated intracellular cyclic GMP formation, whereas rANP5-25 showed less stimulatory effect, and RCM-alpha-hANP1-28, Met12-sulfoxide and rANP fragment were ineffective. Pretreatment with unlabeled alpha-hANP (3.2 X 10(-9) and 3.2 X 10(-8)M) for 24 hrs resulted in a substantial reduction (55 and 75%) of total receptor number without changing the affinity of ANP receptors. These results suggest that the common ring structure formed by the disulfide bond in the molecule is critical for receptor binding and subsequent biological actions, and that a hydrophobic amino acid located at the position of 12, and (24-26) residues at the C-terminal side, but not (1-6) at the N-terminal side, of the disulfide bridge may play a part in modulating receptor binding and/or biological functions. The present study also indicates "down-regulation" of vascular ANP receptors by homologous ligand.

Alignment of rat cardionatrin sequences with the preprocardionatrin sequence from complementary DNA

Mammalian atria contain peptides that promote the excretion of salt and water from the kidney. When rat atrial tissue is extracted under conditions known to inhibit proteolysis, four natriuretic peptides, cardionatrins I to IV, are consistently isolated. These peptides derive from a common precursor, preprocardionatrin, of 152 amino acids, whose sequence was determined by DNA sequencing of a complementary DNA clone. Amino acid sequencing located the start points of cardionatrins I, III, and IV in the overall sequence. Cardionatrin IV most closely resembles procardionatrin because it begins immediately after the signal sequence at residue 25. Cardionatrin III begins at residue 73, and cardionatrin I, sequenced previously, begins at residue 123. Compositional analysis indicated that each of these cardionatrins extends up to tyrosine at position 150 but lacks the terminal two arginine residues.

Differential structure-activity relationships of atrial peptides as natriuretics and renal vasodilators in the dog

Natriuretic-diuretic and vasodilator activities of synthetic atriopeptin (AP)-related peptides were examined in the anesthetized dog. We have selected, the naturally occurring, APIII as the reference compound for comparison with various related peptides. APIII is a 24 amino acid peptide with the sequence ser-ser-cys-phe-gly-gly-arg-ile-asp-arg-ile-gly-ala-gln-ser-gly-leu-gly- cys-asn-ser-phe-arg-tyr-OH. APII, another peptide isolated from atrial extracts, lacks the C-terminal arg- of APIII. N-terminal amino acid extensions on APIII or APII, exhibited enhanced natriuretic-diuretic effectiveness. Furthermore, the maximum response obtained by ser-leu-arg-arg-APIII and arg-arg-APIII were significantly higher and the dose-response curve was not parallel to that obtained with APIII. In contrast, there were no significant qualitative or quantitative differences between the renal blood flow responses produced by the N-terminal extended peptides and APII or APIII. These results suggest a heterogeneity of AP receptors in vascular and renal tubular tissues.

Atrial natriuretic factor

Mammalian atria contain different peptides with potent diuretic, natriuretic, smooth muscle relaxing and blood pressure lowering properties. A preprohormone of these peptides is synthetized and stored in specific granules in atrial myocytes. Different peptides have been isolated, analyzed and in vitro synthetized. Their biological activity indicates a potential role in the regulation of volume and sodium homeostasis as well as in blood pressure regulation.

Comparative vascular pharmacology of the atriopeptins

The atriopeptins are potent relaxants of norepinephrine-constricted aortic strips or are dilators of renal blood vessels in isolated perfused rat kidneys that are constricted by norepinephrine. This vasorelaxant property of the atriopeptins requires the presence of phenylalanine arginine (i.e., atriopeptin II, III, or ser-leu-arg-arg atriopeptin III) residues in the carboxy terminus which are considerably more effective than atriopeptin I (the 21 amino acid peptide which lacks the phe-arg C-terminus) or the core peptide (residues 3-19). However, these artificially in vitro precontracted preparations do not accurately predict the vascular effectiveness of the atriopeptins in intact rats. Intravenous administration of the atriopeptins (including atriopeptin I) to anesthetized rats produces concentration-dependent hypotension, a selective decrease in renal resistance in low doses (determined with microspheres), and pronounced diuresis. At higher doses, atriopeptins increase blood flow in other vascular beds. On the other hand, in the anesthetized dog, injection (intraarterially) of the phe-arg-containing peptides produces a concentration-dependent increase in both renal blood flow and sodium excretion, whereas atriopeptin I is inactive. Although there is a species difference in responsiveness to atriopeptin I, these data demonstrate a direct correlation between the renal vasodilation and diuresis produced by this novel family of atrial peptides.