Atrial Natriuretic Factor Concentrations Research Articles

Non-Invasive Ultrasound Modulation of Solitary Tract Nucleus Exerts a Sustainable Antihypertensive Effect in Spontaneously Hypertensive Rats.

We applied the method of non-invasive ultrasound (US) neuromodulation to regulate blood pressure (BP) by stimulating the solitary tract nucleus (NTS) of spontaneously hypertensive rats (SHRs). The rats were exposed to US stimulation for 20 mins every day for two months. Morphology and function of the hypertensive target organs (heart and kidney) were then examined by echocardiography and immunohistochemical staining. C-fos immunofluorescence assays were used to evaluate neuronal activity in the US stimulated areas and to explore related neural pathways. Moreover, the effects of US stimulation on biochemical indicators angiotensinII (ANGII), aldosterone (Aldo), endothelin-1 (ET-1), atrial natriuretic factor (ANF), cortisol (Cor) in SHRs were detected. In addition, HE, TUNEL, and Nissl staining were performed to evaluate the safety of long-term transcranial US stimulation. After two months of US stimulation, systolic blood pressure (SBP) decreased from 170 ± 1.1 mmHg to 158 ± 1.8 mmHg, p < 0.01. What's more, US stimulation effectively inhibited the pathological process of target organs from both morphological and functional levels. With US stimulation, neuronal activities were also significantly enhanced in the NTS, ventrolateral periaqueductal gray (vlPAG), and the caudal ventrolateral medulla (CVLM) region. And US stimulation did not cause brain tissue damage. Meanwhile, the plasma levels of ANF, ANGII, Aldo, and Cor content were inhibited. US stimulation of the NTS could significantly lower BP in SHRs. Non-invasive transcranial US stimulation acting on the NTS might be a potential therapeutic intervention due to its efficacy and safety.

Central Transient Receptor Potential Vanilloid 4 Contributes to Systemic Water Homeostasis through Urinary Excretion.

Intracerebroventricular (icv) injection of transient receptor potential vanilloid 4 (TRPV4) agonists 4α-phorbol-12, 13-didecanoate (4α-PDD) and GSK101690A increased urinary excretion under the physiological condition. TRPV4 antagonists ruthenium red and HC-067047 significantly blocked increased urinary volume after intragastric administration of water and 4α-PDD-induced diuresis. Administration of the TRPV4 agonists did not significantly change the plasma concentration of vasopressin or atrial natriuretic factor. Pretreatment with indomethacin inhibited the diuresis induced by 4α-PDD. Moreover, icv injection of prostaglandin (PG) F2α produced diuretic effects. These findings indicate that central TRPV4 regulates urine excretion, which contributes to systemic water homeostasis in vivo. The underlying mechanisms are suggested to involve PG synthesis, but not release of vasopressin or atrial natriuretic factor.

Humoral and Renal Response to Acute Volume Loading in Patients with Essential Hypertension

The effect of acute volume expansion (2 liters of saline solution in 2 h) on plasma concentrations of atrial natriuretic factor (ANF), plasma aldosterone concentration (PAC), plasma renin activity (PRA) and their relationship to the renal excretion of urine, sodium and potassium were studied in 6 control subjects and 7 patients with essential hypertension (EH) WHO stage I. Saline infusion provoked comparable rise in plasma ANF in both groups (from 2.98 +/- 0.45 to 12.36 +/- 1.74 pmol/l in the control subjects and from 3.80 +/- 0.72 to 15.78 +/- 2.06 pmol/l in EH patients), significant drop in PRA (from 0.915 +/- 0.419 to 0.256 +/- 0.127 nmol/l/h in controls and from 1.711 +/- 0.324 to 0.714 +/- 0.128 nmol/l/h in EH) and in PAC (from 0.30 +/- 0.07 to 0.14 +/- 0.03 nmol/l in control subjects and from 0.53 +/- 0.13 to 0.24 +/- 0.07 nmol/l in EH). The increase of plasma ANF concentrations after volume expansion might be involved in the suppression of PRA and PAC found after this stimulus. Similar increase in plasma ANF after saline infusion in both groups was associated with significantly greater urine and sodium excretion in EH than in controls. From these results it may be suggested that the acute volume expansion during saline infusion evokes a comparable release of ANF into circulation in both EH patients and controls. In EH patients, however, the similar rise in ANF is accompanied by a more pronounced diuretic and natriuretic response. This exaggerated natriuresis after acute volume and sodium loading cannot be explained solely by a rise in ANF.(ABSTRACT TRUNCATED AT 250 WORDS)

Attenuated ANF Response to Exercise in Athletes with Exercise-Induced Hypoxemia

Some highly trained endurance athletes develop an exercise-induced hypoxemia (EIH) at least partially due to a hemodynamic factor with a potential stress failure on pulmonary capillaries. Atrial natriuretic factor (ANF) is a pulmonary vasodilatator and its release during exercise could be reduced with endurance training. We hypothesized that athletes exhibiting EIH, who have a greater training volume than non-EIH athletes, have a reduced ANF release during exercise explaining the pathophysiology of EIH. Ten highly trained EIH-athletes (HT-EIH), ten without EIH (HT-nEIH), and nine untrained (UT) males performed incremental exercise to exhaustion. No between group differences occurred in resting ANF plasma levels. In contrast to HT-nEIH and UT (p < 0.05), HT-EIH showed a smaller increase in ANF concentration between rest and maximal exercise (HT-EIH: 8.12 +/- 0.69 vs. 14.1 +/- 1.86 pmol x l (-1); HT-nEIH: 10.46 +/- 1 vs. 18.7 +/- 1.8 pmol x l (-1); UT: 6.23 +/- 0.95 vs. 20.38 +/- 2.79 pmol x l (-1)). During the recovery, ANF levels decreased significantly in HT-nEIH and UT groups (p < 0.05). Electrolyte values increased in all groups during exercise but were higher in both trained groups. In conclusion, this study suggested that ANF response to exercise may be important for exercise-induced hypoxemia.

Effects of the order of running and cycling of similar intensity and duration on pulmonary diffusing capacity in triathletes.

To study the pathophysiological mechanisms involved in the decrease of post-triathlon diffusing capacity (DLco), blood rheologic properties (blood viscosity: eta(b); changes in plasma volume: deltaPV) and atrial natriuretic factor (ANF) were assessed in ten triathletes during cycle-run (CR) and run-cycle (RC) trials at a metabolic intensity of 75% of maximal oxygen consumption ( VO(2max)). The DLco was measured before and 10 min after trials. ANF and deltaPV were measured at rest, after the cycle and run of CR and RC trials, and at the end of and 10 min after exercise. RC led to a greater deltaDLco decrease, a lower ANF concentration and a lower deltaPV than did CR, whereas for both CR and RC eta(b) was increased throughout exercise and 10 min after. In addition, after CR the deltaDLco decrease was inversely correlated ( r=-0.764; P<0.01) with deltaPV. The association of decreased plasma volume, increased eta(b), and lower ANF concentrations after RC suggested that lower blood pulmonary volume may have caused the greater decrease in Dlco as compared with CR. The inverse correlation between deltaPV and deltaDLco reinforces the hypothesis that fluid shifts limit the post-exercise DLco decrease after the CR succession in triathletes. Lastly, cycling in the crouched position might increase intra-thoracic pressure, decrease thorax volume due to the forearm position on the handlebars, and weaken peripheral muscular pump efficacy, all of which would limit venous return to the heart, and thus result in low pulmonary blood volume. Compared with cycling, running appeared to induce the opposite effects.

Discoordinate re-expression of cardiac fetal genes in N(omega)-nitro-L-arginine methyl ester (L-NAME) hypertension.

Hypertension produced by chronic inhibition of nitric oxide (NO) synthase by N(omega)-nitro-L-arginine methyl ester (L-NAME) was used to determine the effect of severe pressure overload with or without left ventricular (LV) hypertrophy on the transcriptional activation of the cardiac fetal genes encoding for the natriuretic peptides (NP) atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP), and for beta-myosin heavy chain (MHC) in both atrial and ventricular muscle. A previously reported association of LV hypertrophy with the activation of cardiac renin and angiotensin-converting enzyme (ACE) in this hypertension model was also investigated. Male Sprague-Dawley rats received L-NAME (75 mg/kg/day) or were left untreated for 4 (n=12) or 8 (n=12) weeks. L-NAME-treated rats became severely hypertensive in both treatment groups but only five out of 12 8-week treatment animals showed a significantly increased LV weight to body weight (BW) ratio (LVW/BW). LV ANF mRNA, but not LV BNP mRNA, correlated significantly with LVW/BW only in animals showing LV hypertrophy. No changes were observed in atrial gene expression or plasma concentration of ANF or BNP. A significant correlation was found between LVW/BW and LV renin mRNA and LV ACE activity in rats with LV hypertrophy. LV beta-MHC mRNA levels were significantly increased in the LV of rats with or without LV hypertrophy at both 4 and 8 weeks of treatment. It is concluded that pressure overload per se does not promote NP or cardiac renin-angiotensin system gene expression while increased beta-MHC expression is a marker of LV pressure overload even in the absence of LV hypertrophy. It is apparent that L-NAME causes a disruption in the coordinated transcriptional activation of cardiac fetal genes expected of hypertrophic stimuli acting on the LV.

Distinct gene-sex interactions regulate adult rat cardiomyocyte width and length independently.

Wistar-Kyoto (WKY) and WKY-derived hyperactive (WKHA) rats are two genetically-related inbred strains of rats that are both normotensive yet exhibit differences in left ventricular mass (LVM). We had shown previously that cardiomyocytes from male WKHA are wider than that of male WKY, and that there was genetic linkage between LVM and a locus on chromosome 5 (RNO5) in the male progeny of a F2 WKHA/WKY cross. We show here that cardiomyocyte width is linked to the same RNO5 locus in male reciprocal congenic rats derived from WKHA and WKY. Contrary to males, we found no genetic linkage between LVM and the RNO5 locus in female rats. However, ventricular hypertrophy in females might be of a different nature, because cardiomyocytes from female WKHA were shorter than their WKY counterparts (with no difference in width). The RNO5 locus contains that of the natriuretic peptide precursor A (Nppa) gene. In male congenic rats, changes in cardiomyocyte width always correlated with reciprocal changes in the LV concentration of atrial natriuretic factor (ANF, i.e., the peptide product of Nppa). Taken together with other functional data, the small size of the RNO5 locus (approximately 63 cR) increased the likelihood that both cardiomyocyte width and LV ANF concentration could be linked to only one gene (possibly Nppa) in male rats. Moreover, our results support the notion that genes and sex interact to regulate cardiomyocyte width and length independently from one another.

Atrial natriuretic factor in amniotic fluid and in maternal venous blood of pregnancies with fetal cardiac malformations and chromosomal abnormalities

Objective: We evaluated the levels of atrial natriuretic factor (ANF) in amniotic fluid and in maternal venous blood in pregnancies with fetal cardiac malformations and chromosomal abnormalities.Method: Between the 16th and 18th week of pregnancy, 151 women were divided into three groups. Group A included patients at lowest risk, carrying a fetus with a normally developing heart andnormal karyotype (control group). Group B included women with a fetus suffering from cardiac malformations, with or without associated chromosomal abnormalities. Group C included women carrying a fetusaffected with chromosomal abnormalities without congenital cardiopathies. ANF was evaluated by radioimmunoassay.Results: In maternal venous blood, the mean levels of ANF were 42.1, 53.1 and38.7 pg/ml in groups A, B and C, respectively. In amniotic fluid, the mean levels of ANF were 34.2, 101.8 and 35.8 pg/ml in groups A, B and C, respectively. In group A (control group) there was no statisticaldifference in ANF levels across the gestational age range of 16-18 weeks, either in amniotic fluid or in maternal venous blood. A significant difference of ANF content in maternal venous blood was revealedin comparing group A with group B (p < 0.01), and group C with group B (p < 0.01). A statistically significant difference in ANF levels was also found in amniotic fluid between groupA and group B (p < 0.01), and between group C and group B (p < 0.01). No statistically significant differences were found between group C and group A in comparing ANF levels in maternalvenous blood and amniotic fluid.Conclusion: ANF levels in amniotic fluid and in maternal venous blood are increased early in the case of fetuses with cardiac malformations, with or without associatedkaryotype alteration. Chromosomally abnormal fetuses without heart malformations have normal ANF levels. These results could be useful for elucidating fetal pathophysiology mechanisms.

Functional Alterations of the Nppa Promoter Are Linked to Cardiac Ventricular Hypertrophy in WKY/WKHA Rat Crosses

Cardiac left ventricular hypertrophy (LVH) is commonly associated with hypertension, but its variance is determined for more than 50% by blood pressure-independent genetic factors. Because it constitutes one of the most important risk factors for cardiovascular mortality, we have performed a genome-wide scan of the F2 progeny of crosses between inbred WKY and WKHA rats to detect quantitative trait loci (QTL) linked to cardiac mass. In addition to left ventricular mass (LVM), we also measured left ventricle (LV) concentration of atrial natriuretic factor (ANF), because we have previously established that there was a genetic link between these 2 traits in the same animal cross. We found 2 contiguous QTL on chromosome 5 that were linked to either LVM (logarithm of odds [LOD]=3.5) or log(n) (LV ANF) (LOD=12). The 1-LOD support intervals of both QTL shared a region overlapping the locus of natriuretic peptide precursor A (NPPA:) (ie, the ANF-coding gene). We found by sequencing 2 single nucleotide polymorphisms (SNPs) within the first 650 bp of the NPPA: minimal promoters of the genes from both strains. One of these SNPs increased the transcriptional activity of the NPPA: minimal promoter in transfected neonatal cardiomyocytes in keeping with the higher LV concentration of ANF observed in WKY versus WKHA rats. Taken together with the previous reports showing that ANF may protect cardiomyocytes against hypertrophy, our genetic data single out NPPA: as a strong candidate gene for the determination of LVM.

Genetic Screening of F2 WKY/WKHA Crosses Reveals That the Traits of High Ventricular Mass and Low Ventricular ANF Concentration Are Linked to a Locus on Chromosome 5 That Overlaps with the Locus of the Natriuretic Peptide Precusor A (Nppa) Gene.

55 The cardiac ventricular mass of WKHA inbred rats is higher than that of WKY rats, yet both strains exhibit normal and identical values of blood pressure (as verified by telemetry). We have shown previously in the F2 male progeny of WKY/WKHA crosses that low ventricular concentration of atrial natriuretic factor (ANF) co-segregated significantly with high cardiac ventricular mass (Circ. Res. 84:1453-1458, 1999). To extend these findings, we have performed a scan of the whole genome of 158 rats originating from the male F2 progeny of the WKY/WKHA cross. By linkage analysis, we have identified on chromosome 5 one QTL that was linked to left ventricular ANF concentration (QTL ANF ) with a LOD score of 17, and one QTL that was was linked to left ventricular mass (QTL LVM ) with a LOD score of 3.5. The 2-LOD confidence interval for the location of QTL ANF ranged from positions 94 to 104 cM, which overlaps partly with the 2-LOD confidence interval for the location of QTL LVM between positions 80 to 103 cM. The locus of the natriuretic peptide precursor A ( Nppa ) gene (at about 100 cM) is located within an interval covered by both QTL’s. Sequencing of a 600 bp fragment of the promoter regions of the Nppa genes from WKY and WKHA revealed that there were single nucleotide polymorphisms within two different regions of the promoters. These mutations lie within regions known to contain response elements to transcription factors, but the results of ongoing experiments are needed to determine whether they can affect the ability of the respective promoters to drive the expression of reporter genes in transfected cardiomyocytes. Altogether, these data suggest that the Nppa gene may be considered as a candidate gene to explain, at least in part, the variance of left ventricular ANF concentration and/or left ventricular mass in WKY and WKHA rats. They also define the region that will be studied in congenic lines to obtain a better spatial resolution of the QTL’s, and in particular to determine whether QTL ANF and QTL LVM are identical or adjacent.

Genetic Screening of F2 WKY/WKHA Crosses Reveals That the Traits of High Ventricular Mass and Low Ventricular ANF Concentration Are Linked to a Locus on Chromosome 5 That Overlaps with the Locus of the Natriuretic Peptide Precusor A ( Nppa ) Gene.

55 The cardiac ventricular mass of WKHA inbred rats is higher than that of WKY rats, yet both strains exhibit normal and identical values of blood pressure (as verified by telemetry). We have shown previously in the F2 male progeny of WKY/WKHA crosses that low ventricular concentration of atrial natriuretic factor (ANF) co-segregated significantly with high cardiac ventricular mass (Circ. Res. 84:1453-1458, 1999). To extend these findings, we have performed a scan of the whole genome of 158 rats originating from the male F2 progeny of the WKY/WKHA cross. By linkage analysis, we have identified on chromosome 5 one QTL that was linked to left ventricular ANF concentration (QTL ANF ) with a LOD score of 17, and one QTL that was was linked to left ventricular mass (QTL LVM ) with a LOD score of 3.5. The 2-LOD confidence interval for the location of QTL ANF ranged from positions 94 to 104 cM, which overlaps partly with the 2-LOD confidence interval for the location of QTL LVM between positions 80 to 103 cM. The locus of the natriuretic peptide precursor A ( Nppa ) gene (at about 100 cM) is located within an interval covered by both QTL’s. Sequencing of a 600 bp fragment of the promoter regions of the Nppa genes from WKY and WKHA revealed that there were single nucleotide polymorphisms within two different regions of the promoters. These mutations lie within regions known to contain response elements to transcription factors, but the results of ongoing experiments are needed to determine whether they can affect the ability of the respective promoters to drive the expression of reporter genes in transfected cardiomyocytes. Altogether, these data suggest that the Nppa gene may be considered as a candidate gene to explain, at least in part, the variance of left ventricular ANF concentration and/or left ventricular mass in WKY and WKHA rats. They also define the region that will be studied in congenic lines to obtain a better spatial resolution of the QTL’s, and in particular to determine whether QTL ANF and QTL LVM are identical or adjacent.

Central natriuretic peptides regulation of peripheral atrial natriuretic factor release

Atrial natriuretic factor (ANF) and C-type natriuretic peptide (CNP) receptors have been described in encephalic areas and nuclei related to the regulation of cardiovascular as well as sodium and water homeostasis. Stimulation of the anterior ventral third ventricular region of the brain modifies plasma ANF concentration, suggesting the participation of the central nervous system in the regulation of circulating ANF. The aim of this work was to study the effect of centrally applied ANF or CNP on plasma ANF. Normal and blood volume expanded rats (0.8 ml isotonic saline/100 g body weight) were intra cerebralventricularly injected with 1, 10 or 100 ng/μl/min ANF. Blood volume expanded animals were also centrally injected with the same doses of CNP. Blood samples were collected at 5 and 15 min. after intracerebralventricular administration of either ANF or CNP. Centrally applied ANF did not affect circulating ANF in normal blood volume rats. In blood volume expanded animals both ANF (1, 10 or 100 ng/μl/min) and CNP (1 ng/μl/min) decreased plasma ANF concentration after 15 min. Moreover, CNP (10 and 100 ng/μl/min) lowered circulating ANF levels not only at 15 min but also at 5 min. Neither ANF nor CNP elicited any change in mean arterial pressure and heart rate in normal and blood volume expanded rats. These results suggest the existence of a central regulation exerted by natriuretic peptides on circulating ANF levels. Furthermore, this is the first study reporting an effect on plasma ANF induced by centrally applied CNP.

Water Immersion Increases Urinary Excretion of Aquaporin-2 in Healthy Humans

Many previous studies have shown that aquaporin-2 (AQP2), the vasopressin-regulated water channel, is excreted in the urine and that the excretion increases in response to vasopressin. Moreover, recently a close correlation between AQP2 excretion in urine and kidney AQP2 expression has been demonstrated, showing that urinary excretion of AQP2 is a reliable indicator for AQP-2 function. As head-out water immersion causes an expansion in the central vascular volume equal to that induced by 2 liters of saline, without modifying plasma composition, we used immersion in water to evaluate if the response to acute expansion of the central vascular volume could involve vasporessin (AVP) and AQP2. In healthy subjects, concentrations of plasma atrial natriuretic factor (ANF) and AVP, and urinary AQP2 were measured during a 2-hour immersion period. In all subjects, immersion caused a prompt and marked increase in immunoreactive ANF (23.0 ± 2.12 pg/ml at second hour vs. 2.17 ± 0.42 pg/ml at baseline) and in urinary excretion of AQP2 (23.9 ± 2.69 pmol/mg creatinine at second hour vs. 4.42 ± 0.14 pmol/mg creatinine at baseline), while a significant decrease was found in plasma AVP. Recovery was associated with a prompt return to pre-study levels. These findings demonstrate that heat-out water immersion stimulates urinary excretion of AQP2 in absence of an increase in plasma AVP.

Normal Responses of Atrial Natriuretic Factor and Renal Tubular Function to Sodium Loading in Hypertension-Prone Humans

Background: In order to explore the hypothesis of an atrial natriuretic factor (ANF) deficiency in prehypertension, we compared the response to sodium loading on ANF and renal function in subjects with positive and negative histories of hypertension. Methods: Twenty-two offspring of hypertensive parents (OH) and 20 offspring of normotensive parents (ON) were studied after 4 days of low (50 mmol/day) or high (300 mmol/day) dietary sodium intake. The diets were allocated randomly. Blood pressure (BP), renal function, plasma concentration of ANF, cyclic guanosine monophosphate (cGMP), renin, angiotensin I and II, aldosterone, endothelin and catecholamines were determined during a clearance period of 90 min on both diets. Neurohormones were measured by radioimmunoassays. Renal function was determined by simultaneous measurements of 51Cr-ethylenediaminetetraacetate (a marker of glomerular filtration rate), lithium and sodium clearances. Results: Supine systolic and diastolic BPs were significantly elevated in OH, with both low and high dietary sodium intake. There was no difference in ANF and cGMP concentrations on the low sodium diet. Increasing sodium intake caused a similar increase in ANF in OH and ON but cGMP did not change significantly. As expected the activity of the renin-angiotensin-aldosterone system was decreased by enhancing sodium intake but with both low and high sodium intake plasma renin concentration was significantly higher in OH than in ON. Activation of the sympathetic nervous system with low sodium intake was indicated by a moderate increase in plasma concentrations of epinephrine and norepinephrine in both groups. The renal effects were characterized by significant increases in GFR, lithium and sodium clearances with increasing sodium intake. There were no differences between OH and ON. Estimated values of fractional proximal and distal tubular sodium reabsorption decreased significantly and in a similar way in both OH and ON. Conclusion: These results indicate that the renal and neuroendocrine responses to dietary sodium loading are similar in both OH and ON. The only difference was a higher BP and an elevated plasma renin concentration on both dietary regimens in OH compared with ON. In particular, in OH and ON an identical increase in plasma ANF concentration in response to sodium loading was found. Thus, this study cannot support the hypothesis of a dysregulation of ANF in hypertension-prone humans.

Comparison of the short-term effects of candoxatril, an orally active neutral endopeptidase inhibitor, and frusemide in the treatment of patients with chronic heart failure

Background Candoxatril is a novel neutral endopeptidase inhibitor that increases plasma concentrations of atrial natriuretic factor and thereby produces natriuresis, diuresis, and vasorelaxation. This profile of action offers theoretical advantages over standard diuretic therapy in the treatment of patients with heart failure. The aims of the study were to compare the effects of candoxatril with those of frusemide in the treatment of patients with mild heart failure. Methods Male patients with mild heart failure were randomly assigned to 9 days of therapy with 20 mg frusemide twice a day, 200 mg candoxatril twice a day, or 400 mg candoxatril twice a day (n = 10 per group) after a 14-day placebo washout phase. Systemic hemodynamic measurements, exercise tolerance, and urinary and plasma hormone concentrations were assessed during the placebo run-in and at the beginning and end of the double-blind therapy. Results Frusemide and candoxatril caused similar diuresis and natriuresis. Candoxatril caused a slight decrease in systolic blood pressure and a dose-dependent increase in plasma and urinary concentrations of atrial natriuretic factor without elevating plasma renin activity. Frusemide reduced plasma concentrations of atrial natriuretic factor and increased plasma renin activity. Treadmill exercise capacity decreased 30 ± 26 seconds after use of frusemide, compared with increases of 12 ± 35 seconds after use of 200 mg candoxatril twice a day and 35 ± 31 seconds after use of 400 mg candoxatril twice a day ( P = .13; frusemide versus 400 mg candoxatril twice a day). Conclusions In the treatment of patients with mild heart failure, candoxatril has diuretic effects equivalent to those of 20 mg frusemide twice a day without the associated and potentially detrimental activation of the renin-angiotensin-aldosterone system. The trend for improved exercise capacity with candoxatril warrants further investigation. (Am Heart J 1999;138:1149-57.)

Pulmonary natriuretic peptide system during rat development.

Maturational changes in the rat lung natriuretic peptide system were studied postnatally in 1-, 4-, and 22-day-old rats. Lung atrial natriuretic factor (ANF) content increased significantly from day 1 to day 4 (712+/-188 vs. 1905+/-520 pg/mg protein; p<0.01) but decreased to 532+/-41 pg/mg protein, on day 22. These changes paralleled ANF messenger RNA (mRNA) detected by reverse transcribed polymerase chain reaction (RT-PCR). Rat pulmonary development also was associated with quantitative and qualitative alterations in ANF receptors. Competitive-binding radioreceptor assays of lung membranes with 125I-ANF and increasing concentrations of unlabeled ANF revealed that the natriuretic peptide receptor-binding sites (Bmax) progressively increased with age from 112 +/-21 fmol/mg protein at day 1 to 211+/-16 (p<0.02) and 326+/-62 fmol/mg protein (p<0.04) in 4- and 22-day-old rats, respectively. Autoradiographic studies of 125I-tyr(0)CNP binding to lung sections revealed that the levels of the natriuretic peptide receptor B (NPR-B) were undetectable. On the other hand, binding of 125I-ANF increased with age, and the higher binding at 4 days was mainly due to increased density of the clearance receptor-C (NPR-C), and at 22 days due to increased natriuretic peptide receptor-A (NPR-A). The increase in natriuretic peptide binding was confirmed at the level of synthesis, where RT-PCR revealed that NPR-A mRNA significantly increased (p<0.01) in 22-day-old rats. In conclusion, these studies demonstrate that the rat pulmonary natriuretic peptide system is altered during development. The altered synthesis of lung natriuretic peptides and their receptors may play a role in the postnatal adaptation of pulmonary circulation.

Coadministration of albumin and furosemide in patients with the nephrotic syndrome

In patients with nephrotic syndrome, the natriuretic effect of furosemide (FU) is diminished. The effect of coadministration of FU and human albumin (HA) has remained controversial. In a double-blind, placebo-controlled study, nine nephrotic patients (six males, 48 +/- 4 years) on standardized sodium chloride intake, in random order on three separate days, received by intravenous administration for 60 minutes either (a) 60 mg FU plus a sham infusion, (b) 60 mg FU plus 200 ml of a 20% solution of HA, or (c) sham infusion plus 200 ml of a 20% solution of HA. Urinary volume, sodium, albumin and FU excretion, renal hemodynamics, and plasma atrial natriuretic factor concentration were assessed. Administration of FU alone significantly (P < 0.01) increased mean cumulative urinary sodium (259 +/- 30 mmol) and volume excretion (2684 +/- 167 ml) in the first eight hours as compared with the HA infusion alone (118 +/- 12 mmol, 1827 +/- 141 ml). The coadministration of FU and HA caused an even more marked increase (P < 0.01 vs. HA alone) of urinary sodium (312 +/- 28 mmol) and volume excretion (3230 +/- 201 ml); the difference to FU administration alone was significant (P < 0.05). Plasma atrial natriuretic factor, serum albumin concentration, and urinary albumin excretion increased significantly on both HA infusion days, whereas urinary excretion of FU remained unchanged with HA coadministration. Glomerular filtration rate (CIn) was not significantly affected by any of the infusion protocols, but effective renal plasma flow (CPAH) increased significantly on both HA infusion days. Coadministration of HA potentiates the action of FU in patients with the nephrotic syndrome, but only modestly. This effect is mediated by changes in renal hemodynamics.

Potential paracrine role of the pericardium in the regulation of cardiac function.

Both coronary and endocardial endothelium regulate cardiac contractile function via paracrine pathways. We investigated whether pericardial fluid (PF) and pericardial mesothelial cells (PMC) could exert a similar paracrine action. Both PF and PMC were extracted from sheep pericardial space. Endothelin-1, prostaglandins and atrial natriuretic factor were measured in PF in vivo. In the other hand, PMC were grown on T-75 flasks and microcarrier beads to investigate endothelin-1, nitric oxide and prostaglandin pathways in vitro. In addition, effects of PF and PMC effluent were tested on adult rat cardiac myocyte contraction in vitro. In vitro, cultured PMC expressed endothelin-1 mRNA but not the endothelial nitric oxide synthase III, and released endothelin-1 and prostaglandins. Both PF and cultured PMC superfusate induced a potent, rapidly reversible decrease in the shortening of isolated rat cardiac myocytes. This effect was not associated with changes in intracellular calcium. In vivo, prostaglandins, atrial natriuretic factor and endothelin were present in PF. A greater concentration of atrial natriuretic factor was present in PF than in serum, suggesting molecular diffusion from the myocardium to PF. Preliminary results show that the instillation of vasoactive agents into the pericardial space of dogs rapidly alter coronary and systemic vascular tone, consistent with a molecular diffusion of these substances from PF into the myocardium and circulation. In addition to its mechanical role, the pericardium may contribute to the integration and the regulation of cardiovascular function via a paracrine mechanism.

Adrenomedullin suppresses atrial natriuretic factor (ANF) secretion from isolated atrium

Atrial natriuretic factor (ANF) secretion was studied using isolated perfused right atria prepared from rats. Adrenomedullin (ADM), a recently identified 52-amino acid peptide whose biological activity has a striking resemblance to that of ANF, was added to the perfusate at a concentration of 1μg/ml. The concentration of ANF secreted into the perfusate was measured by radioimmunoassay, under basal conditions (atrial wall unstressed), and during atrial distention (intraluminal pressure raised to 4 and to 6 cm water). It was found that basal secretion of ANF was not altered by ADM. However, when intraluminal pressure was raised, there was a significantly smaller increase in ANF secretion in the ADM-infused atria than in the control atria. It is concluded that ADM significantly reduces stretch-induced secretion of ANF, while having only minimal effects on basal secretion. Such an inhibitory mechanism would ensure the necessary negative feedback mechanism to counter the previously-reported stimulatory actions of ANF on ADM secretion. Moreover, these results support the hypothesis that ADM could be responsible for the reduction in stretch-induced ANF release observed during pregnancy.

Plasma atrial natriuretic factor levels in the inferior petrosal sinus blood of patients with Cushing's disease before and after corticotropin-releasing hormone administration.

Atrial natriuretic factor (ANF) was suggested to be involved as neurohormone in the modulation of hypothalamus-pituitary-adrenal axis in humans. However, this role is still controversial and widely discussed. In order to evaluate whether ANF is secreted in the hypothalamus-pituitary system in humans, plasma ANF concentrations were assayed in samples collected in the inferior petrosal sinus (IPS) blood of patients subjected to IPS sampling for diagnostic purposes or neurosurgical indications. In this retrospective study were included 22 patients: 10 with Cushing's disease (CD) and 12 patients with GH or PRL-secreting pituitary adenoma, used as control group. In the patients with CD, plasma ANF concentration was also assayed after CRH test (hCRH 100 micrograms as i.v. bolus with blood samples after 5, 10 and 15 min). Both in patients with CD and in patients with GH- or PRL-secreting pituitary adenoma, no significant difference was found in plasma ANF levels between IPS ipsilateral (13.0 +/- 1.5 and 12.2 +/- 1.2 pmol/l) or controlateral (13.0 +/- 1.6 and 12.2 +/- 1.4 pmol/l) to the adenoma and peripheral blood (14.2 +/- 2.0 and 13.7 +/- 1.5 pmol/l, respectively). Similarly, no difference was found between the IPS ipsilateral and controlateral to the adenoma in both groups of patients. In patients with CD, CRH administration induced a significant increase of ACTH levels (periphery: 34.9 +/- 6.2 vs 11.5 +/- 2.3 pmol/l, p < 0.05) but it did not induce any significant change of plasma ANF levels (14.0 +/- 2.0 vs 13.4 +/- 1.4 pmol/l in the ipsilateral IPS and 13.4 +/- 1.6 vs 13.4 +/- 1.5 pmol/l in the ipsilateral IPS and 13.4 +/- 1.6 vs 13.4 +/- 1.5 pmol/l in the contralateral IPS). In conclusion, the lack of ANF concentration gradient between IPS and peripheral blood, the lack of any difference in ANF concentrations between patients with CD and acromegalics or hyperprolactinemics and the absence of ANF response to CRH administration do not support the hypothesis of a role for ANF as neurohormone involved in the hypothalamus-pituitary control and particularly in the hypothalamus-pituitary-adrenal axis modulation in humans.