The effect of angiotensin II and ADH on the secretion of atrial natriuretic factor

Studies in intact animals have suggested that angiotensin II (AII) and antidiuretic hormone (ADH) increase the plasma concentration of atrial natriuretic factor (ANF). The purpose of these studies was to examine the effects of AII and ADH on ANF secretion in a rat heart-lung preparation under conditions where aortic pressure could be regulated and other indirect effects of these hormones eliminated. ANF secretion was estimated as the total amount of ANF present in a perfusion reservoir at the end of each 30-min period. A pump was used to deliver a fluorocarbon perfusate to the right atrium at rates of either 2 or 5 ml/min. In a time control series where venous return was maintained at 2 ml/min for three 30-min periods ANF secretion was 672 +/- 114, 794 +/- 91, and 793 +/- 125 pg/min (n = 6, P greater than 0.05). When venous return was increased from 2 to 5 ml/min ANF secretion increased from 669 +/- 81 to 1089 +/- 127 pg/min (P less than 0.01). The addition of AII to the perfusate in concentrations of 50, 100, or 200 pg/ml (n = 6 in each group) had no significant effect on basal ANF secretion or the ANF response to increasing venous return. Similarly, the addition of ADH to the perfusate in concentrations of 5, 25, or 100 pg/ml had no significant effect on ANF release from the heart. These results suggest that the ability of AII and ADH to increase plasma ANF concentration in vivo may be due to the effects of these hormones on right or left atrial pressure.     

Atrial natriuretic factor inhibits the CRH-stimulated secretion of ACTH and cortisol in man.

Corticotrophic secretion of ACTH is stimulated by corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP), and suppressed by glucocorticoids. In vitro and preclinical studies suggest that atrial natriuretic factor (ANF) may be a peptidergic inhibitor of pituitary-adrenocortical activity. The aim of this study was to elucidate a possible role of ANF as a modulator of ACTH release in humans. A bolus injection of 100 micrograms human CRH (hCRH) during a 30 min intravenous infusion of 5 micrograms/min human alpha atrial natriuretic factor (h alpha ANF) was administered at 19:00 to six healthy male volunteers. In comparison to saline, a blunted CRH-stimulated secretion of ACTH (mean maximum plasma level +/- SD 45 min after hCRH: saline 46.2 +/- 14.2 pg/ml, h alpha ANF 34.6 +/- 13.8 pg/ml, p-value = 0.007) and a delayed rise (10 min) in cortisol were detected. The maximum plasma cortisol levels remained nearly unchanged between saline and h alpha ANF administration (mean maximum plasma level +/- SD 60 min after hCRH: saline 182 +/- 26 ng/ml, h alpha ANF 166 +/- 54 ng/ml). No effects of h alpha ANF on basal cortisol levels were observed; in contrast, basal ACTH plasma levels were slightly reduced. Basal blood pressure and heart rate remained unaffected. In the control experiment, infusion of 3 IU AVP in the same experimental paradigm increased basal and stimulated ACTH and cortisol levels significantly in comparison to saline. These observations suggest that intravenously administered haANF inhibits the CRH-stimulated release of ACTH in man.     

Water immersion increases the concentration of the immunoreactive N-terminal fragment of proatrial natriuretic factor in human plasma

Atrial natriuretic factor (ANF) N-terminal (ANF 1-98) and C-terminal (ANF 99-126) fragments were determined by radioimmunoassay in human plasma. Mean basal plasma ANF N-terminal concentrations in 9 healthy subjects were 461 +/- 58 fmol/ml, significantly (p less than 0.0001) higher than ANF C-terminal concentrations (4.8 +/- 0.5 fmol/ml). Central volume stimulation by one hour head-out water immersion (WI) induced a significant (p less than 0.01) increase of the C-terminal peptide levels to 11.6 +/- 2.3 fmol/ml, paralleled by a significant (p less than 0.001) increase of the N-terminal fragment levels to 749 +/- 96 fmol/ml. Increases of plasma concentrations of both fragments upon WI correlated significantly (r = 0.71; p less than 0.05). These data suggest cosecretion of the N-terminal fragment with the C-terminal fragment of pro ANF 1-126 following a physiological stimulus of ANF release in man.     

Atrial natriuretic factor in liver cirrhosis--the influence of volume expansion

Plasma levels of atrial natriuretic factor (ANP) were examined in 12 patients with liver cirrhosis (6 with ascites) and 6 controls before and after the administration of the infusion of 2000 ml of saline solution per 70 kg of body weight during 2 hours. Basal concentration of ANF tended to be slightly, but nonsignificantly higher in patients with ascitic liver cirrhosis (5.5 +/- 1.3 fmol/ml) than in controls (3.0 +/- 1.0 fmol/ml) and in patients with non-ascitic liver cirrhosis (4.6 +/- 1.3 fmol/ml). Saline administration led to the comparable increase of plasma ANF in ascitic (14.2 +/- 4.0 fmol/ml) and non-ascitic cirrhotics (15.7 +/- 3.7 fmol/ml) and in controls (12.4 +/- 4.3 fmol/ml). The increase of plasma ANF was accompanied by the suppression of plasma renin activity (PRA) and plasma aldosterone (PA) in all groups; in ascitic patients, however, PRA and PA remained above the normal range. While in controls and non-ascitic cirrhotics saline administration led to the increase of urine flow rate /from 0.74 +/- 0.13 to 2.04 +/- 0.44 ml/min, P less than 0.01, in controls; from 0.83 +/- 0.05 to 1.28 +/- 0.07 ml/min, P less than 0.01, in non-ascitic cirrhotics) and urinary sodium excretion (from 110.7 +/- 21.3 to 364.8 +/- 74.4 umol/min, P less than 0.01, in controls; from 125.0 +/- 16.7 to 218.7 +/- 24.3 umol/min, P less than 0.01 in non-ascitic cirrhotics), in patients with ascitic liver cirrhosis neither urine flow rate (from 0.66 +/- 0.1 to 0.72 +/- 0.15 ml/min, n.s.), nor urinary sodium excretion (from 16.7 +/- 9.9 to 54.2 +/- 40.3 umol/min, n.s.) changed significantly.(ABSTRACT TRUNCATED AT 250 WORDS)     

Presence of the atrial natriuretic factor (ANF) in human ascitic fluid

Presence of atrial natriuretic factor (ANF)-like material was demonstrated by radioimmunoassay in ascitic fluid of 14 patients with cirrhosis of the liver. Immunoreactive ANF concentrations (M +/- SEM) were 2.4 +/- 0.5 fmol/ml in ascites, significantly lower (p less than 0.001) than the corresponding plasma concentrations of 15.5 +/- 2.6 fmol/ml. High performance gel permeation chromatography and reverse phase high performance chromatography of the ascitic ANF immunoreactivity showed correspondence to the alpha human ANF (99-126). ANF levels in ascites were significantly (p less than 0.01) correlated to levels in plasma (r = 0.66).     

Plasma immunoreactive atrial natriuretic factor (IR-ANF) increases markedly after alpha 2-adrenergic stimulation with clonidine in normally-hydrated rats

Clonidine, an alpha 2-adrenergic agonist, induced a marked, dose-related increase of plasma IR-ANF in normally-hydrated rats. Maximal ANF release was observed at 10 min after injection of 50 micrograms clonidine, rising from 40.5 +/- 4.6 pg/ml (X +/- SEM) to 1064.4 +/- 22.4 pg/ml. This effect on plasma IR-ANF was partially blocked by pretreatment with 0.8 mg naloxone, whereas synthetic Arg8-vasopressin (AVP) did not inhibit clonidine's action. These findings indicate that increased ANF release may be involved in the mechanism of clonidine-induced diuresis. The clonidine's effect on ANF release may be mediated via activation of opioid receptors besides stimulation of alpha 2-adrenergic receptors.     

Opioid peptides attenuate blood pressure increase in acute respiratory failure

Plasma opioid peptides, norepinephrine, atrial natriuretic factor (ANF) and blood pressure (BP) were assessed in 24 chronic obstructive pulmonary disease patients with acute respiratory failure. Hypoxemic-hypercapnic patients had high BP, beta-endorphin, Met-enkephalin and dynorphin B, whereas hypoxemic-normocapnic and hypoxemic-hypocapnic patients showed normal BP, high beta-endorphin, and normal Met-enkephalin and dynorphin B. Norepinephrine and ANF were high in all patients, particularly in hypoxemic-hypercapnic patients. Infusion with the opioid antagonist naloxone hydrochloride significantly increased systolic blood pressure (SBP) in hypoxemic-hypercapnic (182.0 +/- 3.2 versus 205.1 +/- 3.0 mmHg; P < 0.01), hypoxemic-normocapnic (149.3 +/- 1.8 versus 169.1 +/- 2.2 mmHg; P < 0.01) and hypoxemic-hypocapnic (147.3 +/- 1.3 versus 166.8 +/- 2.2 mmHg; P < 0.01) patients, norepinephrine in hypoxemic-hypercapnic patients (3583.2 +/- 371.8 versus 5371.3 +/- 260.0 fmol/ml; P < 0.01), and reduced ANF in hypoxemic-normocapnic (18.3 +/- 0.8 versus 11.9 +/- 1.0 fmol/ml; P < 0.05) and hypoxemic-hypocapnic (18.1 +/- 1.2 versus 12.1 +/- 2.1 fmol/ml; P < 0.05) patients. These results indicate that the endogenous opioid system attenuates SBP responses in acute respiratory failure by affecting norepinephrine or ANF release.     

Alterations in atrial and plasma atrial natriuretic factor (ANF) content during development of hypoxia-induced pulmonary hypertension in the rat

Distension of the atrial wall has been proposed as a signal for the increased release of atrial natriuretic factor (ANF) from atrial myocytes in response to perceived volume overload. To determine whether pressure changes resulting from hypertension in the pulmonary circulation may stimulate release of ANF, rats were exposed to chronic hypobaric hypoxia for 3 or 21 days and the ANF concentration in the atria and plasma were determined by specific radioimmunoassay. Exposure to chronic hypoxia resulted in significant increases in hematocrit at both 3 (p less than 0.025) and 21 days (p less than 0.005) and in the development of right ventricular hypertrophy (RVH) expressed as the ratio of the weight of the right ventricle to the weight of the left ventricle and septum (RV/LV+S) at both 3 (RV/LV+S = 0.278 +/- 0.005) and 21 days (RV/LV+S = 0.536 +/- 0.021). After 21 days, left atrial (LA) ANF content was significantly increased in hypoxic rats compared to controls (508 +/- 70 ng/mg tissue vs 302 +/- 37 ng/mg), while right atrial (RA) ANF content was significantly reduced (440 +/- 45 vs 601 +/- 58 ng/mg). At this time, plasma ANF concentration was significantly elevated compared to controls (238 +/- 107 pg/ml vs 101 +/- 10 pg/ml). These results suggest that the development of pulmonary hypertension following chronic hypobaric exposure induces altered atrial ANF content and increased plasma ANF concentration as a result of altered distension of the atrial wall.     

NH2-terminal fragment of rat pro-atrial natriuretic factor in the circulation: identification, radioimmunoassay and half-life

A radioimmunoassay was developed to measure the NH2-terminal counterpart of rat pro-atrial natriuretic factor (pro-ANF) in plasma. Synthetic rat ANF (Asp 11-Ala 37) coupled to bovine serum albumin was used to immunize New Zealand rabbits. The antiserum demonstrated good immunoreactivity towards rat ANF (Asn 1-Arg 98), (Asn 1-Tyr 126), (Asp 11-Ala 37) and even human ANF (Asn 1-Ser 30). The standard curve had an ED80 of 9.5 +/- 2.5 and ED50 of 44.0 +/- 10.5 fmol/tube. Immunoreactive ANF NH2-terminal peptide was measured directly in rat plasma without prior extraction. In fact, extraction of ANF NH2-terminal from plasma by C18 silica gel chromatography revealed inconsistent recovery and a lack of parallelism. Morphine (0.75 mg/100 g), chosen to elicit increased ANF (Ser 99-Tyr 126) secretion, elevated its plasma concentration from 54.1 +/- 3.2 to 190.8 +/- 55.8 fmol/ml after 20 min. At the same time, the immunoreactive NH2-terminal fragment rose from 378 +/- 16 to 1181 +/- 201 fmol/ml. The identity of this immunoreactive material was verified following affinity chromatography and reverse-phase high-performance liquid chromatography (HPLC) of plasma from morphine-treated rats. Molecular sieving and amino acid sequencing demonstrated that it appears to be consistent with or identical to rat ANF (Asn 1-Arg 98). The disappearance rate of ANF (Asn 1-Arg 98) was studied by injecting radioactive material into anesthetized rats. The exponential decay was analyzed by a two-compartment model in which the fast and slow components had a half-life of 2.5 +/- 0.3 and 54.8 +/- 3.9 min, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cardiac secretion of atrial natriuretic factor with exercise in chronic congestive heart failure patients.

We have previously reported a fivefold increase of plasma atrial natriuretic factor (ANF) in patients with congestive heart failure (CHF) compared with normal subjects. However, given the marked increase of ANF under basal conditions, the extent to which ANF secretion can further increase under physiological stress is not been clarified in CHF. We therefore evaluated ANF secretion during ergometric exercise in 11 patients with CHF, with peripheral venous ANF samples obtained at rest and peak exercise. In seven patients, simultaneous peripheral venous and right ventricular ANF samples were obtained to estimate myocardial ANF secretion. Hemodynamic characteristics of exercise included a significant increase of heart rate, mean arterial pressure, and cardiac output (all P < 0.01); reduction of systemic vascular resistance (P < 0.001); and increase of right atrial and pulmonary wedge pressures (P < 0.001). ANF was abnormally elevated at baseline (108 +/- 58 fmol/ml) yet increased further to 183 +/- 86 fmol/ml with exercise (P < 0.003). A step-up of right ventricular ANF, particularly during exercise, was consistent with active myocardial secretion, despite elevated baseline ANF levels.     

Atrial natriuretic factor and renal sodium excretion during ventilation with PEEP in hypervolemic dogs.

Controlled mandatory ventilation with positive end-expiratory pressure (PEEP) reduces renal sodium excretion. To examine whether atrial natriuretic factor (ANF) is involved in the renal response to alterations in end-expiratory pressure in hypervolemic dogs, experiments were performed on anesthetized dogs with increased blood volume. Changing from PEEP to zero end-expiratory pressure (ZEEP) increased sodium excretion by 145 +/- 61 from 310 +/- 61 mumol/min and increased plasma immunoreactive (ir) ANF by 104 +/- 27 from 136 +/- 21 pg/ml. Changing from ZEEP to PEEP reduced sodium excretion by 136 +/- 36 mumol/min and reduced plasma irANF by 98 +/- 22 pg/ml. To examine a possible causal relationship, ANF (6 ng.min-1.kg body wt-1) was infused intravenously during PEEP to raise plasma irANF to the same level as during ZEEP. Sodium excretion increased by 80 +/- 36 from 290 +/- 78 mumol/min as plasma irANF increased by 96 +/- 28 from 148 +/- 28 pg/ml. We conclude that alterations in end-expiratory pressure lead to great changes in plasma irANF and sodium excretion in dogs with increased blood volume. Comparison of the effects of altering end-expiratory pressure and infusing ANF indicates that a substantial part of the changes in sodium excretion during variations in end-expiratory pressure can be attributed to changes in plasma irANF.     

Radioreceptor assay for atrial natriuretic factor

Interest in accurate measurement of atrial natriuretic factor (ANF) in biological fluids and various tissues has been stimulated by recent data indicating the possible role of ANF in the homeostasis of salt and water. The presence of high-affinity binding sites for ANF in rat glomeruli has allowed us to develop a rapid, sensitive, and simple radioreceptor assay (RRA). A saturable high-affinity binding site on the membranes of rat glomeruli has been characterized by a dissociation constant of 33 pM and binding capacity of 396 fmol/mg protein. Rat plasma extracts or atrial homogenates or standards were incubated with radioiodinated ANF and a preparation of rat glomerular membranes. The receptor-bound and free radioactivity were separated by filtration on Whatman GF/C paper after 1 h incubation at room temperature. The sensitivity of the RRA was 2.08 fmol. The effective concentration of standard ANF that displaced 50% of labeled receptor-bound ANF (EC50) was 43.3 +/- 2.6 fmol/ml (n = 7). Both intra- and interassay coefficients of variation were smaller than 11%. This RRA assay has been compared with radioimmunoassay (RIA). High correlations for 19 plasma extracts and 34 atrial homogenates (r = 0.973 and r = 0.954, respectively) tested by RRA and RIA were obtained. This good correlation between the two methods suggests that the immunoreactive material found in rat plasma and atrial homogenates also displays biological activity.     

Specific binding of atrial natriuretic factor to renal glomeruli during day or night antiorthostatic suspension in the rat

We observed a significant increase in plasma atrial natriuretic factor (ANF) in antiorthostatic hypokinetic suspension (AOH) rats after 2 h of suspension when the experiment was made during day. Plasma ANF was investigated in relation to renal glomerular ANF receptors during AOH at night. The aim of this study was 1) to compare the day and night ANF responses to AOH 2) to determine whether the renal glomerular ANF receptors are involved. The rats were divided into 2 groups: i) 24 population cage (PC), and ii) 24 were attached by the tail (Morey's model) and remained in the horizontal position (attached horizontal-AH). Six AH were suspended (30 degrees) for 2 hours (AOH) and sacrificed with the controls: PC and AH (12.00h). The same experiment was made during the night (24.00h). A significant increase in plasma ANF was found in both AOH and AH after 2 h of suspension during day and night (19 +/- 2.3 pg/ml vs 9 +/- 0.95 and 18 +/- 3 pg/ml vs 10.2 +/- 1.8 respectively). PC rats had a significantly higher ANF level (38 +/- 5 pg/ml) than AH or AOH. The glomerular ANF receptor population was slightly lower in AOH than in AH (429 +/- 12 fmol/mg protein vs 507 +/- 5) during day. During night, a significantly lower number of ANF receptors was observed in AOH animals as compared to AH (168 +/- 2 fmol/mg protein vs 455 +/- 3). A decrease in glomerular receptors was also noted in PC during night. Day-time head-down tilt, bed rest or head-out water induced a natriuretic and diuretic response, whereas the normal recumbency at night does not lead to such effects. We conclude that the natriuretic and diuretic response not observed during night was associated with elevated plasma ANF levels and decreased ANF receptor density.     

Effects of synthetic atrial natriuretic factor (ANF) on renin-aldosterone axis in the conscious newborn calf

The effects of synthetic atrial natriuretic factor (ANF) on the renin-aldosterone axis were studied in fifteen 4-7 day-old male milk-fed calves divided into 3 groups of 5 animals each. Synthetic ANF intravenous (i.v.) administration (1.6 micrograms/kg body wt over 30 min) induced a transient significant fall in plasma renin activity (from 2.5 +/- 0.3 to 1.7 +/- 0.3 ng angiotensin l/ml/h; P less than 0.05) but failed to reduce basal plasma aldosterone levels in the first group of animals. Administration (i.v.) of angiotensin II (AII) (0.8 micrograms/kg body wt for 75 min) was accompanied by a progressive fall in plasma renin activity (from 2.2 +/- 0.3 to 0.8 +/- 0.1 ng angiotensin l/ml/h; P less than 0.01) and by an increase in plasma aldosterone levels (from 55 +/- 3 to 86 +/- 5 pg/ml; P less than 0.01) both in the second and the third groups; addition of ANF to AII infusion (AII: 0.5 mu/kg body wt for 45 min; AII: 0.3 micrograms/kg body wt and ANF 1.6 micrograms/kg body wt during 30 min) in the third group did not modify plasma renin activity or AII-stimulated plasma aldosterone levels when compared to the AII-treated group. These findings show that in the newborn calf ANF is able to reduce plasma renin activity but fails to affect basal and AII-stimulated plasma aldosterone levels, suggesting that the zona glomerulosa of the newborn adrenal cortex is insensitive to a diuretic, natriuretic and hypotensive dose of the atrial peptide.     

Determinants of atrial natriuretic factor secretion in dogs expanded with isotonic saline or colloid solutions.

Through increments in blood volume and atrial pressure are thought to be the primary stimuli for ANF secretion, plasma levels of this peptide do not always behave as a simple function of volume status. To outline the relationship between the latter and cardiac ANF release, we used five different volume-expansion protocols in anesthetized dogs. A stepwise expansion of plasma volume (PV) was achieved by two consecutive infusions: 0.9% saline followed or preceded by 4 or 25% bovine serum albumin (BSA), 4 or 25% dextran (Dx), or homologous plasma. Saline expansion led to a two- to four-fold increase in arterial plasma ANF level in all five protocols. Both 4 and 25% BSA caused no or very modest increase in plasma ANF, while all other colloid expanders caused the expected ANF release. In all protocols, plasma ANF closely correlated with central venous pressure (CVP). BSA expansion was the only protocol with no correlation between PV and ANF release. Changes in serum Ca2+ could not explain this finding. During BSA expansion, the lack of atrial response was related to the absence of increment (or even fall) in CVP despite the expanded PV. Similarly, urinary Na+ excretion was correlated both with CVP and ANF level but not with PV in BSA expansion. When the dogs were depleted of histamine before BSA infusion, the atrial secretory response was restored, suggesting that this colloid was associated with augmented capillary leakiness and vascular fluid efflux. These results show that the expansion of PV leads neither to ANF release nor to Na+ excretion if it is not accompanied by an expanded central blood volume with elevated atrial pressure.     

Release of atrial natriuretic polypeptide by graded right atrial distension in anesthetized dogs

In order to verify the contribution of right atrial pressure to atrial natriuretic polypeptides (ANP) release, we measured plasma levels of immunoreactive (ir)-ANP when graded rise of right atrial pressure was executed in anesthetized dogs. Increasing right atrial pressure (RAP) from 2.7 +/- 0.6 to 9.0 +/- 0.7 mmHg, plasma levels of ir-ANP in aorta tended to increase by 33% but not significantly (p greater than 0.05). However, when RAP was increased from 9.0 +/- 0.7 to 17.0 +/- 1.1 mmHg, ir-ANP levels in aorta were significantly (p less than 0.05) increased by 132% of control within 5 min from the start of RAP elevation. The RAP elevation produced a sustained increase in plasma levels of ir-ANP. There was a positive correlation between right atrial pressure and plasma levels of ir-ANP. The plasma levels of ir-ANP were similar between aorta and pulmonary artery. These results demonstrate that increasing atrial pressure is closely correlated with ANP release and ANP is not greatly metabolized by pulmonary circulation.     

Norepinephrine-induced atriopeptin release in conscious dogs is mediated by alterations in atrial pressure

This study was designed to determine whether the increase in atriopeptin secretion induced by an intravenous infusion of norepinephrine is mediated directly by adrenergic receptor stimulation or indirectly by the associated increase in atrial pressure. Norepinephrine was infused at 0.5 microgram.kg-1.min-1 for 30 min into both sham-operated (intact) and cardiac-denervated conscious dogs. The infusion increased mean arterial pressure in all dogs. On the other hand, left atrial pressure increased from 5.0 +/- 0.7 to 9.6 +/- 1.6 mmHg (p less than 0.01) in intact dogs, but decreased from 5.5 +/- 1.0 to 2.0 +/- 0.7 (p less than 0.01) in cardiac-denervated dogs. Right atrial pressure changes followed similar trends, but were not significant in the intact group. Plasma atriopeptin increased from 73 +/- 12 to 110 +/- 18 pg/ml (p less than 0.01) as left atrial pressure increased in intact dogs and decreased from 79 +/- 15 to 54 +/- 10 pg/ml (p less than 0.01) as left atrial pressure decreased in cardiac-denervated dogs. The changes in plasma atriopeptin correlated closely with the changes in left atrial pressure (r = 0.941, p less than 0.001) and to a lesser extent with the changes in right atrial pressure (r = 0.413, p less than 0.05). These results suggest that the change in plasma atriopeptin induced by infusion of norepinephrine into conscious dogs is mediated by the concomitant change in atrial pressures.     

Atrial natriuretic factor release during acute infusion of isoproterenol in the conscious rat.

The effect of beta-adrenergic stimulation on atrial natriuretic factor (ANF) release was studied in conscious rats. 20-min infusion of 85 or 850 ng kg-1 min-1 isoproterenol (ISO) resulted in positive inotropic and chronotropic responses and no elevation of atrial pressures. A slight increase in plasma ANF, together with a drop in blood pressure, were observed only in the group infused with the higher dose. During the infusion of 850 ng kg-1 min-1 ISO, there was no relationship between plasma ANF and any of the haemodynamic parameters, with the exception of mean arterial pressure (r = 0.72, P less than 0.05, n = 9). Larger doses (greater than 3 micrograms kg-1 min-1) were toxic. We conclude that beta-adrenergic stimulation is not an important stimulus for ANF release when diastolic resting tension is low.     

Effect of atrial natriuretic factor on plasma vasopressin in conscious rats

An intravenous (IV) bolus injection (10 μg) of synthetic rat atrial natriuretic factor [ANF (Arg 101-Tyr 126)] into normal conscious Sprague-Dawley rats produced a significant decrease of plasma arginine vasopressin (AVP) while 1-, 2-, and 5-μg doses exerted no such effect. Mean arterial blood pressure (MAP) was lowered about 15 mmHg by an IV 10 μg bolus injection of ANF. When plasma AVP rose significantly in rats exposed to such osmotic stimuli as 600 mM NaCl and 900 mM mannitol intraperitoneally (IP), subsequent IV injection of ANF (10 μg) markedly depressed this parameter. Lower doses of ANF were ineffective against 600 mM NaCl IP. The significant elevation of plasma AVP levels by hypertonic sucrose 900 mM IP was not modified by ANF (10 μg). Blood pressure remained unchanged after IP administration of various osmotic stimuli, except mannitol, and in all these experiments an IV bolus of ANF exerted a lowering effect on MAP. Seventy-two hr water deprivation (mixed osmotic and volume stimulus) resulted in elevated plasma AVP levels which were unaffected by an IV bolus injection of ANF at doses of 0.06–10 μg. Immunoreactive ANF (IR-ANF) rose in plasma to 39.3±13 ng/ml 1 min after an IV bolus injection of 10 μg ANF, dropping to 1.01±0.2 ng/ml after 5 min and to 0.32±0.01 ng/ml after 10 min (when ANF and AVP interactions were studied), but still remained approximately six times higher than in control rats. These results suggest that, in the conscious rat, only pharmacological levels of ANF observed after an IV bolus infusion may influence both resting and osmotically-stimulated AVP levels.     

A sensitive radioimmunoassay of alpha human atrial natriuretic polypeptide using monoclonal antibody recognizing human form ring structure

A monoclonal antibody (C351) against alpha human atrial natriuretic polypeptide (alpha hANP) recognizing human form ring structure was established and applied to a radioimmunoassay of plasma alpha hANP. The minimum detectable amount in terms of 10% radioligand displacement relative to zero dose were 0.28 fmol/tube, corresponding to 0.7 fmol/ml in plasma after extraction using Sep-Pak C18 cartridges. When the mean plasma levels at recumbent position in fasted morning were compared in 10 young (less than 30 years) and 10 elderly (greater than or equal to 50 years) healthy subjects taking normal sodium diet, it was slightly higher in the latter (3.2 +/- 0.4 vs 4.7 +/- 0.5 fmol/ml, mean +/- SE, p less than 0.05). After i.v. infusion of hypertonic saline (2.5% NaCl) at a rate of 0.24 ml/kg/min for 20 min in 6 normal subjects (26 to 35 years), it was increased from 4.1 +/- 0.4 to 5.9 +/- 0.7 fmol/ml (p less than 0.01). In 6 patients with essential hypertension (34 to 57 years), it was elevated with high salt intake, i.e. 3.3 +/- 0.3, 3.9 +/- 1.03 and 7.6 +/- 1.5 fmol/ml under 34, 170 and 340 mEq NaCl/day for 7 days, respectively. From these results, the radioimmunoassay of plasma IR-alpha hANP using MAb C351 seems to be quite suitable to detect rather small changes at low plasma concentrations and to investigate a physiological importance of alpha hANP in man.