Discovery of atrial natriuretic factor in the brain: its characterization and cardiovascular implication

The exocrine pancreas is an extracardiac source of atrial natriuretic peptide

Previous studies have shown that atrial natriuretic peptide (ANP) regulates exocrine pancreatic function in health and disease. As extracardiac sources of ANP have been identified and ANP-like immunoreactivity has been reported in the exocrine pancreas, in the present work we sought to establish whether ANP was produced in the rat exocrine pancreas and if conditions like fasting/feeding or acute pancreatitis were reflected on ANP expression. By using RT-PCR, immunoblotting, and immunofluorescence microscopy assays, it was found that both mRNA and protein ANP were present in the acinar cells of the exocrine pancreas. The amount of ANP in the pancreas was lower in than the atrium but similar to other tissues like the kidney and liver. Immunogold labeling electron microscopy studies revealed that ANP was localized in zymogen granules and the endoplasmic reticulum suggesting local synthesis and package into granules. ANP protein expression was significantly increased not only in fasting but also in acute pancreatitis, the latter probably related to impaired secretion. Natriuretic peptide receptor type C which mediates ANP biological effects in the exocrine pancreas was also present in acinar cells and its expression did not change with either fasting or acute pancreatitis. Present findings show that the exocrine pancreas is a relatively important extracardiac source of ANP and further support previous studies strongly suggesting the active role of the peptide in pancreatic physiology and pathophysiology.

Immunohistochemical localization of atrial natriuretic factor and autoradiographic distribution of atrial natriuretic factor-binding sites in the brain of the cave salamander Hydromantes genei (Amphibia, Plethodontidae)

The distribution of atrial natriuretic factor (ANF)-like immunoreactivity in the central nervous system of the cave salamander Hydromantes genei (Amphibia, Plethodontidae) was investigated by using antisera raised against rat and human ANF(1-28). Concurrently, the location of ANF-binding sites was determined by autoradiography, using radioiodinated human ANF(1-28) as a tracer. In several regions of the brain, including the olfactory bulb, the preoptic area, the ventral thalamus, the tectum of the mesencephalon, and the choroid plexuses inside the ventricles, a good correlation was observed between the distribution of ANF-immunoreactive elements and the location of ANF-binding sites. Mismatching was found in the habenular nucleus, the commissura habenularis, the fasciculum retroflexus, and the interpeduncular nucleus, which contained high levels of binding sites but were devoid of ANF-immunoreactive structures. In contrast, a few other regions, such as the pineal gland and the subcommissural organ, showed a high concentration of ANF-like immunoreactivity but did not contain ANF-binding sites. This study provides the first localization of ANF-like immunoreactivity and ANF-binding sites in the brain of an urodele amphibian. The results show that the ANF peptidergic system in the cave salamander has an organization more simple than the organizations described for the brain of frog or other vertebrates. This feature is probably related to the expression of highly pedomorphic characters in plethodontids. The anatomical distribution of ANF-immunoreactive elements and ANF-binding sites suggests that ANF-related peptides may act as hypophysiotropic hormones as well as neurotransmitters and/or neuromodulators in the salamander brain.

Increased central AT(1)-receptor activation, not systemic vasopressin, sustains hypertension in ANP knockout mice

We tested the hypothesis that hypertension in atrial natriuretic peptide (ANP) knockout mice is caused in part by disinhibition of angiotensin II-mediated vasopressin release. Inactin-anesthetized F(2) homozygous ANP gene-disrupted mice (-/-) and wild-type (+/+) littermates were surgically prepared for carotid arterial blood pressure measurement (ABP) and background intravenous injection of physiological saline or vasopressin V(1)-receptor antagonist (Manning compound, 10 ng/g body wt) and subsequent intracerebroventricular (left lateral ventricle) injection of saline (5 microl) or ANP (0.5 microg) or angiotensin II AT(1)-receptor antagonist losartan (10 microg). Only (-/-) showed significant decrease in ABP after intracerebroventricular ANP or losartan. Both showed significant hypotension after intravenous V(1) antagonist, but there was no difference between their responses. We conclude that 1) vasopressin contributes equally to ABP maintenance in ANP-disrupted mice and wild-type controls; 2) permanently elevated ABP in ANP knockouts is associated with increased central nervous angiotensin II AT(1)-receptor activation; 3) disinhibition of central nervous angiotensin II AT(1) receptors in ANP-deficient animals does not lead to a significant increase in the importance of vasopressin as a mechanism for blood pressure maintenance.

Differential brain atrial natriuretic peptide expression co-segregates with occurrence of early stroke in the stroke-prone phenotype of the spontaneously hypertensive rat

OBJECTIVE

To determine how the downregulation of atrial natriuretic peptide (ANP) gene expression, previously demonstrated to occur only in the brain of the stroke-prone spontaneously hypertensive rat (SHRsp), in contrast to the stroke-resistant SHR (SHRsr), co-segregates with stroke occurrence in SHRsp/SHRsr F2 descendants in order to study the 'protective' role towards stroke previously demonstrated in SHRsp for the quantitative trait locus STR2 that also carries the ANP gene.

DESIGN AND METHODS

Eight male SHRsp, eight male SHRsr and 16 male SHRsp/SHRsr F2-intercross animals (progeny of brother/sister mated F1 hybrids from an original cross between F0 SHRsp and SHRsr) were selected for this study. All rats were exposed to a stroke-permissive Japanese-style diet starting at the age of 6 weeks. Half of the F2 animals had early strokes; the remainder had late strokes. Blood pressure was measured before sacrifice. Analysis of brain ANP expression using an RNase protection assay was performed in all animals.

RESULTS

Downregulation of brain ANP in the stroke-prone phenotype was found to co-segregate with the occurrence of early strokes in the F2 rats independently of blood pressure levels.

CONCLUSIONS

The observed lower expression of ANP in the brains of stroke-prone rats appears to be the result of an inhibitory effect by another gene or genes. It seems unlikely that this specific trait represents a primary protective mechanism.

Altered structure, regulation, and function of the gene encoding the atrial natriuretic peptide in the stroke-prone spontaneously hypertensive rat

Through the genotype/phenotype cosegregation analysis of an F(2) intercross, from the crossbreeding of stroke-prone spontaneously hypertensive rats (SHRSP) and stroke-resistant spontaneously hypertensive rats (SHR), we previously identified a quantitative trait locus for stroke on rat chromosome 5 (STR2) that colocalized with the genes encoding atrial and brain natriuretic peptides (ANP and BNP) and conferred a stroke-delaying effect. To further characterize ANP and BNP as candidates for stroke, we performed additional studies. Comparative sequence analysis revealed point mutations in both the coding and regulatory regions of ANP, whereas no interstrain differences were found for BNP. In in vitro studies in COS-7 and AtT-20 cells that were performed to test the relevance of a G-->A substitution at position 1125, a Gly-->Ser transposition in the SHRSP pro-ANP peptide resulted in different posttranslational processing of the SHRSP ANP gene product that was also associated with higher cGMP production (P<0.05). Furthermore, an analysis of a 5' end mutation affecting a PEA2 regulatory binding site in the 5' untranslated regulatory sequence of SHRSP ANP demonstrated a significantly lower ANP promoter activation in endothelial cells (P<0.05 versus the SHR ANP). In addition, the expression of ANP was significantly reduced in the brain, but not in the atria, of SHRSP compared with SHR (P<0.0001). No differences were detected with regard to BNP expression. The present results reveal substantial differences in ANP, but not BNP, structure and product among SHR and SHRSP, which supports a role of ANP in the pathogenesis of stroke in the SHRSP animal model.

Immunocytochemical localization of atrial natriuretic factor and autoradiographic distribution of atrial natriuretic factor binding sites in the brain of the African lungfish, Protopterus annectens

The localization of atrial natriuretic factor (ANF)-immunoreactive elements was investigated in the brain of the African lungfish, Protopterus annectens, by using antisera raised against rat and human ANF(1-28). Concurrently, the distribution of ANF binding sites was studied by autoradiography using radioiodinated human ANF(1-28) as a tracer. In general, there was a good correlation between the distribution of ANF-immunoreactive structures and the location of ANF binding sites in several areas of the brain, particularly in the ventral part of the medial subpallium, the rostral preoptic region, the preoptic periventricular nucleus, the caudal hypothalamus, the neural lobe of the pituitary, and the mesencephalic tectum. In contrast, mismatching was observed in the pallium (which contained a high density of binding sites and a low concentration of ANF immunoreactive elements) as well as in the lateral subpallium and the medial region of the ventral thalamus, in which a low concentration of binding sites but a high density of ANF-immunoreactive fibers were detected. The present data provide the first localization of ANF-related peptides in the brain of dipnoans and the first anatomical distribution of ANF binding sites in the brain of fish. The results show that the ANF peptidergic systems of P. annectens exhibit similarities with those previously described in the frog Rana ridibunda, supporting the existence of relationships between dipnoans and amphibians. The location of ANF-like immunoreactivity and the distribution of ANF binding sites suggest that ANF-related peptides may act as hypothalamic neurohormones as well as neurotransmitters and/or neuromodulators in the lungfish brain.

Water and sodium disorders following surgical excision of pituitary region tumours

A prospective observational study of the pathophysiology of sodium and water disorders in patients with pituitary region tumours after surgical excision was carried out in 20 patients. Serial pre-operative and post-operative fluid and sodium balance, plasma and urine elctrolyte biochemistry and their derived parameters, and circulating hormones associated with fluid balance, atrial natriureic peptide (ANP) and antidiuretic hormone (ADH) were documented to correlate with the patients' clinical conditions. Ten out of these twenty cases developed diabetes insipidus (DI) requiring ADH replacement therapy, although in the majority (6 cases), this way only a transient event. Of the nine patients who developed hyponatraemia, six had symptoms such as impaired consciousness and convulsions. Four patients developed alternating hypoatraemia and hypernatraemia, which constituted a difficult group, where appropriate sodium and fluid management, and ADH replacement therapy were based upon twice daily plasma and urine biochemistry and their derived parameters. Whilst DI in this group of patients was the result of a low circulating ADH level, hyponatraemia was not associated with an exaggerated ADH activity (6.0 +/- 2.3 vs 7.4 +/- 2.3 pmol/ml, mean +/- SEM). Rather, hyponatraemia was strongly associated with an elevated circulating ANP concentration (82.4 +/- 10.5 vs 30.0 +/- 3.1 pmol/ml, mean +/- SEM, p < 0.001), resulting in salt wasting and hypovolaemia.

Distribution of natriuretic peptide precursor mRNAs in the rat brain

Atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) represent members of a recently discovered neuropeptide family involved in central regulation of endocrine and autonomic functions. The present study employed an in situ hybridization approach to provide the first detailed comparative mapping of ANP, BNP, and CNP mRNAs in brain. Results indicate that ANP mRNA is highly expressed in anterior olfactory nuclei, limbic cortices, dorsal endopiriform nucleus, hippocampal subfield CA1, cortical amygdaloid nuclei, medial habenula, anteroventral periventricular and arcuate nuclei, periventricular stratum, zona incerta, mammillary nuclei, inferior olive, nucleus ambiguus, and pontine paragigantocellular nuclei. CNP mRNA is expressed at highest levels in olfactory nuclei, limbic cortices, dorsal endopiriform nucleus, hippocampal subfields CA1-3, anteroventral periventricular and arcuate nuclei, and numerous brainstem regions (including the pontine, lateral reticular, solitary tract, prepositus hypoglossal, and spinal trigeminal nuclei). Positive labeling for BNP mRNA was not observed in brain. The presence of both ANP and CNP mRNA in the same regions of distinct nuclei (e.g., the anteroventral periventricular and arcuate nuclei) suggests the potential for coexpression. Overall, the present data are consistent with a prominent role for both ANP and CNP in neuroendocrine regulation and central cardiovascular integration. The extensive localization of ANP and/or CNP mRNA in olfactory nuclei, limbic cortex, hippocampus, amygdala and diencephalic limbic relays further indicate a putative role for ANP and CNP as neuromodulators of olfactory/limbic information processing.

The C-type natriuretic peptide receptor is the predominant natriuretic peptide receptor mRNA expressed in rat hypothalamus

The natriuretic peptide receptors (NPR) are membrane-bound guanylate cyclases with extracellular binding domains specific for particular members of the natriuretic peptide family. NPR-A binds atrial natriuretic peptide (ANP) with high affinity, whereas the NPR-B appears to be specific for C-type natriuretic peptide (CNP). Previous data indicating extensive overlap between localization of ANP and CNP in hypothalamic neuroendocrine circuits suggest the importance of determining whether specificity of natriuretic peptide action may be conferred via receptor type present on target cells. To address this issue, we used in situ hybridization histochemistry to localize NPR-A and NPR-B mRNA in the hypothalamus. NPR-A mRNA was not found in substantial abundance in any hypothalamic nucleus; however, detectable NPR-A signal was observed in other brain regions, including the subfornical organ and medial habenula. In contrast, NPR-B mRNA was expressed throughout the hypothalamus, including neurons of the magnocellular and parvocellular paraventricular, the arcuate, and the supraoptic nuclei. Expression was also seen in other nuclei essential to neuroendocrine control, including the median preoptic, anteroventral periventricular, tuberomammilary, ventromedial and suprachiasmatic nuclei. NPR-B mRNA was also observed in the neural lobe of the pituitary gland, suggesting expression by pituicytes. The results suggest that NPR-B is the primary natriuretic peptide receptor in hypothalamus, and by inference indicate that CNP is the primary active natriuretic peptide in neuroendocrine regulation.

Atrial natriuretic peptide and its potential role in pharmacotherapy

Atrial natriuretic peptide (ANP) is a 28 amino-acid polypeptide secreted into the blood by atrial myocytes after atrial pressure and distension. Although its role in humans is not clear, it can produce a variety of physiologic effects including vasodilatation, natriuresis, and suppression of the renin-angiotensin-aldosterone axis. These actions are potentially useful in a variety of pathologic states such as hypertension and congestive heart failure, and diverse methods to augment the effects of ANP in these states have been devised. The results are exciting and, despite some problems, may lead to the pharmacologic use of enhancement of ANP actions in several clinical disorders.

[Atrial natriuretic factor: retrospective and perspectives]

Since the hypotensive and natriuretic properties of crude cardiac extracts were first demonstrated in 1981 in the rat, the effector molecule has been isolated, purified and synthesized. The hormonal factor is produced by atrial myocytes in mammals and stored as a prohormone. Secretion mainly results from a volemic stress inducing an atrial stretch. Secretion includes a maturation step. A peptide of 28 amino-acids (ANP) is then released into the bloodstream. ANP has a half-life of a few minutes. ANP binds to specific receptors expressed at the target cell surface. B-receptors mediate the biological actions of ANP by an increase in cGMP while C-receptors are involved in clearance of the peptide. The kidney as well as the cardiovascular and endocrine systems are the main target sites for ANP. The renal effects of ANP are expressed by an enhanced diuresis and natriuresis which may result from an increased glomerular filtration rate and/or a reduced tubular reabsorption of salt and water. Renal hemodynamics may also be modified due to a renal specific vasodilator effect of ANP. The reduction of systemic blood pressure may result from changes in cardiac output and/or in peripheral vascular resistance. Several neurohumoral interactions of ANP also contribute to sustain the cardiovascular and renal effects described above. In view of these properties, ANP is of particular interest in order to understand the homeostasis of salt and water under physiological as well as or physiopathological conditions. In this regard, therapeutic prospects are intensively investigated. Finally, evolutionary perspectives are actually considered from studies in lower vertebrates.

Production of immunoreactive atrial natriuretic polypeptide in neuroendocrine tumors

BACKGROUND

Peptide hormone synthesis in neuroendocrine tumors is a well-recognized phenomenon. However, production in neuroendocrine tumors of atrial natriuretic polypeptide (ANP), a newly discovered peptide hormone from the heart, has not been studied extensively.

METHODS

The presence of immunoreactive human ANP (IR-hANP) in neuroendocrine tumors was determined using a specific human ANP radioimmunoassay. Neuroendocrine tumors examined included 9 small cell carcinomas of the uterus, 28 small cell carcinomas of the lung, 20 carcinoid tumors, 54 pancreatic endocrine tumors, 17 neuroblastic tumors, 14 pheochromocytomas, and 14 medullary carcinomas of the thyroid. Twenty atrial tissues also were examined as the control. Molecular size of IR-hANP in the extracts of atrial and tumor tissues was determined by gel chromatography.

RESULTS

IR-hANP was detected in the extracts of small cell carcinoma of the uterus, small cell carcinoma of the lung, and carcinoid tumor, with concentrations ranging from 3.1 to 210 ng/g wet weight tissue. No IR-hANP was detected in the extracts of pancreatic endocrine tumor, neuroblastic tumor, pheochromocytoma, and medullary carcinoma of the thyroid. The frequency of production of IR-hANP in neuroendocrine tumors was highest in small cell carcinoma of the uterus (44%), followed by small cell carcinoma of the lung (18%) and carcinoid tumor (15%). IR-hANP present in the extracts of small cell carcinomas of the uterus had molecular size heterogeneity, with three fragments in addition to alpha-, beta- and gamma-human ANP.

CONCLUSIONS

These results indicate that IR-hANP is produced by neuroendocrine tumors and that the molecular size of IR-hANP in tumor tissues is different from that in atrial tissues.

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 alpha- and beta-adrenergic mechanisms.

Effects of atrial natriuretic factor on norepinephrine release in the rat hypothalamus

The effects of atrial natriuretic factor on the mechanisms involved in norepinephrine release were studied 'in vitro' in slices of Wistar rat hypothalamus. Atrial natriuretic factor (10, 50 and 100 nM) decreased spontaneous [3H]norepinephrine secretion in a concentration dependent way. In addition, the peptide (10 nM) also reduced acetylcholine induced output of norepinephrine. The atrial factor (10 nM) was unable to alter the amine secretion when the incubation medium was deprived of calcium or when a calcium channel blocker such as diltiazem (100 microM) was added. In conclusion, atrial natriuretic factor reduced both spontaneous and acetylcholine evoked [3H]norepinephrine release in the rat hypothalamus. These findings suggest that the atrial natriuretic factor may alter catecholamine secretion by modifying the calcium available for the exocytotic process of catecholamine output.

Atrial natriuretic peptide modulates baroreceptor reflex in spontaneously hypertensive rat

Our previous studies have suggested that atrial natriuretic peptide in the caudal nucleus tractus solitarii is involved in the centrally mediated regulation of blood pressure in the salt-sensitive spontaneously hypertensive rat (SHR). The current study tested the hypothesis that endogenous atrial natriuretic peptide in the caudal nucleus tractus solitarii participates in baroreceptor reflex control of heart rate in this hypertensive model. Salt-sensitive SHR and control Wistar-Kyoto (WKY) rats maintained on basal (1%) salt intake were studied. Arterial baroreceptor reflex-mediated changes in heart rate were recorded in conscious unrestrained rats during phenylephrine (5-40 micrograms.kg-1.min-1 infusion; 30 minutes later, atrial natriuretic peptide (50 ng), monoclonal antibody to atrial natriuretic peptide (0.55 micrograms), purified mouse immunoglobulin G (0.55 micrograms), or artificial cerebrospinal fluid vehicle (50 nl) was microinjected into the caudal nucleus tractus solitarii. Phenylephrine infusion was then repeated and mean arterial pressure and heart rate were monitored as before. The slope of the heart rate/mean arterial pressure relation was significantly less (p less than 0.05) in the salt-sensitive SHR than in the WKY control, indicating that baroreceptor reflex control of heart rate was blunted in this hypertensive model. Microinjection of atrial natriuretic peptide into the caudal nucleus tractus solitarii further blunted (p less than 0.05) baroreceptor reflex control of heart rate in salt-sensitive SHR but not in WKY rats. In contrast, microinjection of the monoclonal antibody enhanced the sensitivity of baroreceptor reflex control of heart rate in salt-sensitive SHR but not in WKY rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic peptide kinetic studies in patients with cardiac dysfunction

Three studies were performed: (1) a controlled investigation of alpha-human atrial natriuretic peptide (alpha-hANP) total body production and metabolic clearance rates using a bolus infusion technique (controls, patients 1 to 6); (2) a study of alpha-hANP kinetics in cardiac dysfunction patients using a constant infusion method (patients 7 to 14); and (3) a right heart catheterization study to determine the amount of alpha-hANP released into the circulation at the level of the right heart, estimated by the step-up in alpha-hANP concentration between the superior and inferior vena cava and the pulmonary artery, in the patients with left ventricular dysfunction. Baseline venous plasma alpha-hANP was 27.3 +/- 16.5 pg/ml in the controls (mean +/- SD; N = 6), 141.6 +/- 138.0 pg/ml in patients 1 to 6 (P less than 0.05 compared to controls), and 167.5 +/- 145.7 pg/ml in patients 7 to 14. Total body alpha-hANP production rate was markedly elevated in patients 1 to 6 compared to controls (0.45 +/- 0.36 vs. 0.11 +/- 0.06 micrograms/min, P less than 0.05) and was similar to that determined by the continuous infusion technique in patients 7 to 14 (0.62 +/- 0.44 micrograms/min, P = 0.49 compared to patients 1 to 6). alpha-hANP release into the right heart (0.17 +/- 0.11 micrograms/min), however, was significantly lower than total body production rate in the cardiac dysfunction patients, indicating that total body alpha-hANP secretion occurs from sites in addition to drainage into the right heart via the coronary sinus and anterior cardiac veins. Right atrial pressure correlated with the alpha-hANP released into the right heart.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitation of hypothalamic atrial natriuretic peptide messenger RNA in hypertensive rats

Previous studies from our laboratory have shown that spontaneously hypertensive rats have increased atrial natriuretic peptide stores and reduced norepinephrine release from nerve terminals in the anterior hypothalamus. We have postulated that atrial natriuretic peptide inhibits norepinephrine release in anterior hypothalamus, reducing excitation of sympathoinhibitory neurons, increasing sympathetic outflow, and elevating blood pressure in this model. The current study tested the hypothesis that atrial natriuretic peptide messenger RNA (mRNA) transcript levels are increased in anterior hypothalamus of spontaneously hypertensive rats compared with normotensive Wistar-Kyoto rats. Atrial natriuretic peptide mRNA in hypothalamic regions was measured by the quantitative polymerase chain reaction technique using a p-SELECT mutant atrial natriuretic peptide RNA as an internal standard. Atrial natriuretic peptide mRNA from hypothalamic regions of spontaneously hypertensive and Wistar-Kyoto rats and the internal standard were coamplified in a single reaction in which the same primers were used. Since the polymerase chain reaction product of the internal standard contained a new EcoRI restriction site, it could be distinguished from the atrial natriuretic peptide mRNA product by EcoRI digestion after the polymerase chain reaction. We found regional inhomogeneity of atrial natriuretic peptide mRNA in the hypothalamus of spontaneously hypertensive and Wistar-Kyoto rats, but we found no significant differences in atrial natriuretic peptide mRNA levels in anterior, posterior, or ventral hypothalamic areas between spontaneously hypertensive rats and Wistar-Kyoto rats fed normal (1%) or high (8%) salt diets. These data do not support the hypothesis that increased atrial natriuretic peptide stores in anterior hypothalamus of spontaneously hypertensive rats are related to increased gene transcription.

Hyponatraemia in neurosurgical patients: diagnosis using derived parameters of sodium and water homeostasis

Seventeen unselected, consecutive patients with intracranial disease and accompanying hyponatraemia were studied. All would previously have been diagnosed as having the syndrome of inappropriate antidiuretic hormone (ADH) secretion on the basis of spot plasma/urinary electrolyte testing with the application to them of existing standard laboratory criteria. Timed urinary collections and matching plasma samples were available in all but three cases for the derivation of creatinine, osmotic and free-water clearances, tubular reabsorbed water, and fractional water and sodium excretions. In a number of patients the plasma renin, aldosterone and ADH levels were also assayed. On the basis of the overall findings, 13 patients were diagnosed as in fact having a salt-wasting state whilst in only four patients was the diagnosis of inappropriate ADH secretion (SIADH) substantiated. It is suggested that obtaining simple derived parameters of sodium and water homeostasis can add significantly in differentiating between these quite opposite syndromes.

Origin and characterization of atrial natriuretic peptide in the rat parotid gland

The heart atria represent the major site of synthesis for atrial natriuretic peptide (ANP) which exerts potent natriuretic, diuretic and vasoactive functions. Recently, ANP-immunoreactivity has been detected in extracardial organs involved in water and electrolyte homeostasis, such as the intestine and certain exocrine glands. The present study investigates ANP in the parotid gland. It was found by immunohistochemical techniques that the peptide is localized in ductal cells of the gland. An analysis of the immunoreactive material by high-pressure liquid chromatography and radioimmunoassay revealed the prohormone of ANP (ANP 1-126) and the biologically active fragment (ANP 99-126). Furthermore, Northern blot hybridization disclosed the presence of mRNA coding for ANP. It is suggested that ANP is synthesized and released from the parotid gland and functions in the control of saliva production.

Blockade of endogenous anterior hypothalamic atrial natriuretic peptide with monoclonal antibody lowers blood pressure in spontaneously hypertensive rats

We have previously shown that the atrial natriuretic peptide (ANP) content of the anterior hypothalamic region of NaCl-sensitive spontaneously hypertensive rats (SHR-S) is higher than that of Wistar-Kyoto (WKY) rats. ANP has been shown to inhibit neuronal norepinephrine release and to reduce the excitability of hypothalamic neurons. This study tested the hypothesis that blockade of endogenous ANP in the anterior hypothalamus by local microinjection of a monoclonal antibody to ANP (MAb KY-ANP-II) lowers blood pressure in SHR-S. Purified MAb KY-ANP-II (0.055 and 0.55 micrograms) or control mouse IgG in 200 nl saline was microinjected into the anterior hypothalamic area (AHA) of conscious SHR-S and control WKY rats. As a further control, Mab KY-ANP-II (0.55 microgram) was microinjected into the posterior hypothalamic area (PHA) of SHR-S. Anterior hypothalamic microinjection of MAb KY-ANP-II caused significant dose-related decreases in mean arterial pressure (MAP) and heart rate (HR) in SHR-S but not in WKY rats. Control injections of equal volumes of IgG had no effect on MAP or HR. Microinjection of Mab KY-ANP-II into PHA produced no significant alteration in MAP or HR in SHR-S. These data provide the first demonstration that endogenous ANP in a region of brain known to influence cardiovascular function mediates BP and HR control in the rat. These findings suggest that the increased endogenous ANP in the anterior hypothalamus of SHR-S may be involved in the central regulation of BP in the model.

Atrial natriuretic peptide in peripheral organs other than the heart

The heart atria represent the major site of synthesis of atrial natriuretic peptide (ANP) in mammals including man, and its function as a regulator of water and salt homeostasis has been repeatedly suggested. However, more recently ANP has been located in organs not intimately related to cardiovascular physiology, e.g. the adrenals, lungs, and gut, as well as tissues belonging to the lymphatic, reproductive or endocrine systems. Thus, ANP might serve many more physiological roles than originally thought, but the functional significance of ANP in these non-cardiac tissues is presently poorly understood.