Acute effects of physiological increments of alpha-atrial natriuretic peptide in man

Regulation of renin release by local and systemic factors

The renin-angiotensin system (RAS) is critically involved in the regulation of the salt and volume status of the body and blood pressure. The activity of the RAS is controlled by the protease renin, which is released from the renal juxtaglomerular epithelioid cells into the circulation. Renin release is regulated in negative feedback-loops by blood pressure, salt intake, and angiotensin II. Moreover, sympathetic nerves and renal autacoids such as prostaglandins and nitric oxide stimulate renin secretion. Despite numerous studies there remained substantial gaps in the understanding of the control of renin release at the organ or cellular level. Some of these gaps have been closed in the last years by means of gene-targeted mice and advanced imaging and electrophysiological methods. In our review, we discuss these recent advances together with the relevant previous literature on the regulation of renin release.

Effect of posture-induced blood volume expansion on systemic and regional hemodynamics in patients with cirrhosis

BACKGROUND/AIMS

This study aimed to investigate the effects of posture-induced blood volume expansion on systemic and regional hemodynamics in patients with cirrhosis.

METHODS

The mean arterial pressure, cardiac index, peripheral vascular resistance index, and flow volume index of the superior mesenteric artery (SMA) and femoral artery (FA) were measured in 10 patients with cirrhosis and portal hypertension and 10 controls after they had been standing for 2 h. Plasma atrial natriuretic peptide, plasma renin activity, and plasma glucagon levels were also determined. These measurements were repeated after 30 min and 60 min when the patients were recumbent.

RESULTS

In the upright posture, systemic hemodynamics, FA blood flow index, plasma atrial natriuretic peptide level, and plasma renin activity level were similar in patients and controls. However, SMA blood flow index and plasma glucagon level were significantly higher in patients than in controls. On the assumption of the supine position, cardiac index and plasma atrial natriuretic peptide level significantly increased in the two groups, but the changes were greater in patients than in controls. Mean arterial pressure remained unchanged. The reduction in peripheral vascular resistance index was therefore greater in patients in controls. SMA and FA blood flow index increased significantly in the two groups, but the changes were greater in patients than in controls. Furthermore, SMA blood flow fraction (SMA blood flow index/cardiac index) was steady in controls, whereas it increased significantly in patients. In contrast, FA blood flow fraction (FA blood flow index/cardiac index) remained unchanged in the two groups. In patients, the change in peripheral vascular resistance index was correlated inversely with that of SMA blood flow index, but not with that of FA blood flow index. Plasma renin activity level dropped significantly, but the decline was similar in the two groups. Plasma glucagon level was not modified in either group.

CONCLUSIONS

In patients with cirrhosis, splanchnic vasodilation appears to be present, even in the upright position, and further abnormal vasodilation occurs on recumbency-induced blood volume expansion. This abnormal shear-stress phenomenon observed in the splanchnic circulation seems to be mediated by a local vasodilator rather than a general vasodilator.

The atrial natriuretic peptide receptor antagonist HS 142-1 improves cardiovascular filling and mean arterial pressure in a hyperdynamic ovine model of sepsis

OBJECTIVE

To test whether systemic vascular resistance and mean arterial pressure increase during the administration of the atrial natriuretic peptide antagonist, HS 142-1, in ovine experimental hyperdynamic sepsis.

DESIGN

Prospective trial.

SETTING

Research laboratory at a large university medical center.

SUBJECTS

Chronically instrumented Merino breed ewes (n = 14).

INTERVENTIONS

Continuous infusion of Pseudomonas aeruginosa (2.5 x 10(6) colony-forming units/min) for the experimental period of 48 hrs. One group (HS 142-1) received a continuous infusion of HS 142-1 (3 mg/kg/hr) from 40 to 48 hrs; the remaining sheep ("control") were given the vehicle sodium chloride 0.9%.

MEASUREMENTS AND MAIN RESULTS

All sheep developed a hyperdynamic cardiovascular response by 40 hrs that was characterized by low values of systemic vascular resistance index (p < .05) and mean arterial pressure (p < .05), and an increased cardiac index (p < .05). HS 142-1 increased cardiac filling pressures (p < .05) without apparent effects on fluid balance, and was associated with a significantly (p < .05) higher mean arterial pressure than was found in the control group at 44 and 48 hrs. HS 142-1 did not change systemic vascular resistance index. At 44 and 48 hrs, cardiac index values were found to have significantly (p < .05) increased in the animals receiving HS 142-1, when these data were compared with cardiac output values at 40 hrs.

CONCLUSION

HS 142-1 increases cardiac filling pressures and maintains mean arterial pressure in hyperdynamic sepsis without reversal of sepsis-induced vasodilation.

Reduced plasma cyclic GMP but normal renal responses to atrial natriuretic factor in pre-hypertension

The amount of, and response of the kidneys to, endogenous natriuretic factor(s) could be important in the pathogenesis of essential hypertension. Searching for possible disturbance(s) related to atrial natriuretic factor (ANF) and its second messenger, cyclic guanosine monophosphate (c-GMP), we assessed plasma immunoreactive (ir) ANF and c-GMP, effective renal plasma flow (ERPF), glomerular filtration rate (GFR), urinary c-GMP, absolute and fractional (FE) excretions of sodium (Na) and chloride (Cl) before and during infusions of low ANF doses or vehicle (V) in 7 normotensive sons of essential hypertensive parents (SEH) compared with 7 sons of normotensive parents (SN). Each subject was infused at 2-week intervals in a single-blind randomized sequence with 4 different solutions: V only or ANF 0.004, 0.008 and 0.016 microgram/kg/min, infused over 90 min. Plasma irANF was lower in SEH than in SN (p < 0.001) during vehicle infusion. Basal plasma c-GMP levels were, on all 4 different study days lower (p < 0.05 to < 0.01) in SEH in SN. Response of plasma c-GMP to infused ANF was also slightly decreased in SEH (p < 0.05 to < 0.01). BP, ERPF and GFR did not differ between SEH and SN and were unchanged during the 4 infusions. Urinary c-GMP excretion, FENa and FECl increased dose-dependently during ANF (p < 0.05 to < 0.0001) but not V infusions. These findings indicate that at the stage of pre-hypertension a disturbance in the ANF-c-GMP regulatory pathway may occur, which is expressed primarily at the circulatory rather than the renal excretory level.

Blunted natriuretic response to low-dose brain natriuretic peptide infusion in nonazotemic cirrhotic patients with ascites and avid sodium retention

Patients with cirrhosis and ascites have high plasma levels of atrial (ANP) and brain (BNP) natriuretic peptides, two cardiac hormones released by the atria and ventricles, respectively. We evaluated renal hemodynamics, sodium excretion, and intrarenal sodium handling (lithium clearance method) in seven cirrhotic patients with ascites and avid sodium retention before, during, and after the infusion of synthetic human BNP, at the dose of 4 pmol/kg.min for 1 hour, which has been shown to increase renal plasma flow, glomerular filtration rate (GFR), and sodium excretion in healthy subjects without affecting systemic hemodynamics. Plasma BNP levels were 7.31 +/- 0.85 pmol/L in baseline conditions, and increased to 33.60 +/- 2.96 pmol/L at the end of the infusion (P < .01 vs. baseline). Urinary excretion of guanosine 3',5'-cyclic monophosphate (cGMP) also significantly increased during the infusion, indicating stimulation of natriuretic peptide receptors by BNP. BNP administration did not modify renal plasma flow, GFR, sodium excretion or tubular sodium reabsorption to any appreciable extent. Arterial pressure heart rate, plasma norepinephrine, and plasma renin activity (PRA) where also unchanged, whereas plasma aldosterone concentration showed a significant, 35% reduction at the end of the postinfusion period, ruling out the possibility that BNP-induced vasodilation might be responsible for failure of the peptide to induce a natriuretic response. Overactivity of antinatriuretic factors is probably the main determinant of the blunted natriuretic effect of BNP in these patients.

Acute effects of physiological increments of brain natriuretic peptide in humans

To investigate the effects of physiological increases in plasma brain natriuretic peptide concentration in humans, we studied six healthy volunteers who received incremental infusions (0.25 pmol/kg per minute in the first hour and 0.50 pmol/kg per minute in the second) of synthetic human brain natriuretic peptide-32 in a placebo-controlled, crossover study. Peptide plasma levels were 1.69 +/- 0.39 pmol/L at baseline and rose 1.5- and 3-fold with the lower and higher doses, respectively. These values were within the normal range and also comparable to those reported in patients with mild essential hypertension. The urinary excretion rate of cGMP also increased during brain natriuretic peptide infusion, indicating stimulation of natriuretic peptide receptors. Peptide administration induced a significant 1.7-fold increase in urinary sodium excretion without affecting renal plasma flow (para-aminohippurate clearance), glomerular filtration rate (creatinine clearance), and urine flow rate. Fractional proximal sodium reabsorption (lithium clearance method) was unchanged, and fractional distal sodium reabsorption significantly decreased. Brain natriuretic peptide caused no changes in arterial pressure, heart rate, hematocrit, and serum proteins, but it exerted an inhibitory effect on the renin-aldosterone axis, as indicated by the significant 50% or more decrease of plasma renin activity and urinary excretion rate of aldosterone. These results suggest that brain natriuretic peptide may be involved in the overall regulation of body fluid and cardiovascular homeostasis in humans, mainly through its natriuretic and endocrine effects.

Hyperdynamic circulation of advanced cirrhosis: a re-appraisal based on posture-induced changes in hemodynamics

Little is known about the effect of posture on the circulatory abnormalities of advanced cirrhosis. We evaluated the systemic hemodynamics, measured by Doppler-echocardiography, atrial natriuretic factor, plasma renin activity and plasma norepinephrine, in 10 patients with cirrhosis and ascites and 10 healthy controls, after 2 h of standing and during lying down for a further 2 h. Standing hemodynamic patterns of controls and patients with cirrhosis did not differ significantly. The latter, however, showed higher plasma renin activity, norepinephrine and atrial natriuretic factor. The assumption of the supine position led to greater increases in cardiac index and atrial natriuretic factor, and reduction in systemic vascular resistance in patients with cirrhosis. Norepinephrine and plasma renin activity declined in both groups to a similar extent, while heart rate only slowed in controls. Thus, after 2 h in the supine position, patients with cirrhosis showed hyperdynamic circulation with increased cardiac index and heart rate and reduced systemic vascular resistance. Norepinephrine, plasma renin activity and atrial natriuretic factor were also elevated. The hyperdynamic circulation in advanced cirrhosis appears during or is enhanced by lying down. This finding suggests that this syndrome is, at least in part, attributable to excessive blood volume translocation towards the central area. However, the persistent activation of renin-angiotensin and sympathoadrenergic systems suggests that a concomitant reduced vascular sensitivity to vasoconstrictors concurs in its development.

Hemodynamic and renal effects of ascites apheresis, concentration and reinfusion in advanced cirrhosis

BACKGROUND/AIMS

We studied the effects of ascites apheresis, concentration and reinfusion, a new form of treatment for tense or refractory ascites, on systemic hemodynamics and renal function.

METHODS

Twelve patients with advanced cirrhosis (two belonging to Child-Pugh's class B and the remainder to class C) were monitored. They were evaluated under baseline conditions, just after the treatment, and 24 and 48 h after baseline assessment. In addition to systemic hemodynamics--as evaluated by Doppler echocardiography--and renal function, indirect markers of effective volemia, such as atrial natriuretic factor, plasma renin activity and aldosterone concentration, and plasma norepinephrine were also measured.

RESULTS

The technique led to significant changes in systemic hemodynamics, such as an increase in stroke volume and cardiac output. However, due to a striking reduction in peripheral vascular resistance, mean arterial pressure also declined. The hemodynamic changes were associated with a parallel increase in atrial natriuretic factor. Despite the reduction in arterial pressure, plasma renin activity also significantly declined, while plasma norepinephrine did not undergo significant changes. Although an improvement in glomerular filtration rate and renal sodium excretion occurred, neither change reached statistical significance. All the hemodynamic, renal and neuro-humoral changes described above subsided almost entirely after 48 h, when no significant changes with respect to baseline values were any longer detectable with the exception of a slight reduction in mean arterial pressure.

CONCLUSIONS

In advanced cirrhosis ascites apheresis, concentration and reinfusion enhance central volemia, but an exaggerated peripheral vasodilation largely wastes the potential favourable effect on arterial volemia. As a result, no significant improvement in renal perfusion and sodium excretion can ensue.

Atrial natriuretic peptide and circadian blood pressure regulation: clues from a chronobiological approach

A critical review of the data available in the literature today permits a better understanding of the multiple actions of atrial natriuretic peptide (ANP) on the cardiovascular system. Moreover, the results of chronobiological studies suggest a role for this peptide in the determination of the circadian rhythm of blood pressure (BP). ANP can affect BP by several mechanisms, including modification of renal function and vascular tone, counteraction of the renin-angiotensin-aldosterone system, and action on brain regulatory sites. A series of interrelated events may follow from very small changes in the plasma levels of ANP. The endpoints are blood volume and BP reduction, but they are rapidly offset (mainly by reactive sympathetic activation) as soon as blood volume or pressure is threatened. The circadian rhythms of BP and ANP are antiphasic under normal conditions and in essential hypertension. The loss in the nocturnal decrease of BP is accompanied by a comparable loss in the nocturnal surge of ANP in hypertensive renal failure and hypotensive heart failure. In the latter condition, BP and ANP variabilities correlate significantly both before and after therapy-induced functional recovery, independently of the mean BP levels. Autonomic function modulates the secretion of ANP, which seems more apt to determine only transient changes in BP levels, as suggested by the short half-life of the peptide and the buffering role of its clearance receptors. There is now sufficient evidence that ANP contributes to short-term control over BP and electrolyte balance, in contrast and in opposition to the renin-angiotensin-aldosterone system, which is involved primarily in long-term BP control. By interfering with other well-established neurohormonal factors, ANP appears to be an additional modulator of the circadian rhythm of BP.

Extra-natriuretic effects of atrial peptide in humans

To evaluate extra-natriuretic effects of atrial natriuretic peptide (ANP), plasma ANP (pANP) levels were assessed in seven healthy men on low-sodium diet (80 mEq NaCl/day), in basal conditions and during stepwise infusion of human ANP (2, 4, 8 and 16 ng/min/kg). To determine the individual physiological (PHY) pANP level, we measured pANP in the same subjects after a high-salt diet (400 mEq NaCl/day), that is, in a physiological stimulation of ANP. We then compared the effects of the PHY levels of ANP to the effects of pharmacological (PHA) pANP levels. Neither PHY nor PHA pANP levels modified creatinine clearance or blood pressure. The progressive rise in pANP levels was associated with increases in urinary excretion of Na+, K+ and urea. ANP alone respectively accounted for 41%, 30% and 92% of the increase in natriuresis, kaliuresis and urea excretion that occurred after changing salt intake from 80 to 400 mEq/day. Pharmacological ANP levels raised CH2O and reduced UOsm. Interestingly, PHA levels were associated with significant decrease in serum K+ (from 4.5 +/- .1 to 4.0 +/- .1 mEq/liter) and plasma urea (from 31.9 +/- 5 to 24.2 +/- 4 mg/dl). The mean cumulative urinary potassium and urea losses corresponded to the theoretical body losses of potassium and urea; moreover, the individual cumulative urinary losses of potassium and urea significantly correlated with the corresponding decrement in their plasma levels. In conclusion, ANP has both physiological and pharmacological significance in the control of potassium and urea metabolism by decreasing plasma levels of K+ and urea through effects on the renal excretory function.

Suppression of plasma endothelin-1 level by alpha-human atrial natriuretic peptide and angiotensin converting enzyme inhibition in normal men

The effect of synthetic alpha-human atrial natriuretic peptide (alpha-hANP) on plasma endothelin-1 (ET-1) level was examined in 6 healthy subjects. Intravenous infusion of alpha-ANP (0.1 micrograms/kg/min) resulted in significant falls in plasma renin activity and aldosterone, but without effect on ET-1 level. An angiotensin converting enzyme inhibitor, captopril, increased plasma renin activity and decreased aldosterone, respectively. However, plasma ET-1 levels were not modified by captopril. In cases with alpha-hANP infusion after captopril (25 mg, p.o.,), the renin-angiotensin-aldosterone system was further inhibited compared with the first group, and ET-1 at 60 min was significantly suppressed from the baseline. These data suggest that alpha-hANP when combined with captopril brings about the suppression of plasma ET-1 concentrations in men.

Role of inhibition of atrial natriuretic factor release in the down-regulation of salt excretion

We investigated the role of atrial natriuretic factor (ANF) in the down-regulation of sodium excretion (UNaV). Seven subjects were sequentially studied while ingesting a normal-salt diet (220 mmol NaCl/day, NSD), a very low-salt diet (20 mmol NaCl/day, VLSD) for six days, and again at NSD for nine days. After one day of VLSD, a negative salt balance of 85 mmol was achieved and plasma ANF decreased from 19.1 (SE 2.5) to 7.2 (SE 2.1) pg/ml, whereas plasma renin activity (PRA) and plasma aldosterone (ALD) increased after the third and second day, respectively. During restoration of volemia (NSD), ANF increased after the third day; in contrast, PRA and ALD decreased earlier. Seven other subjects kept at low-salt diet (50 mmol NaCl/day) were studied during ANF infusion (at 2, 4, 8 ng/min/kg body wt). Increases of ANF from 10.3 (SE 0.9) pg/ml (basal condition) to levels of 24.0 (SE 1.9) pg/ml (infusion study), occurring physiologically in the same subjects after NSD, evoked increases in UNa V that accounted for 62% of UNa V rise necessary to balance the NSD, whereas PRA or ALD did not change. Plasma ANF, unlike PRA or ALD, was directly correlated with UNa V.

IN CONCLUSION

(a) ANF changes earlier than PRA and plasma aldosterone during VLSD; (b) PRA and ALD respond more promptly than ANF in the recovery from hypovolemia; (c) during ingestion of a low-salt diet, changes in plasma ANF by infusion account for more than half the increase in UNa V following the shift from low- to normal-salt diet independently of alterations in PRA and ALD.

The hemodynamic status of preascitic cirrhosis: an evaluation under steady-state conditions and after postural change

To assess the hemodynamic status of patients with compensated cirrhosis, mean arterial pressure, cardiac index and peripheral vascular resistance and markers of central (plasma concentrations of atrial natriuretic factor) and arterial volemia (plasma norepinephrine concentration, plasma renin activity) were studied in 10 patients and 10 healthy control subjects under steady-state conditions (after 2 hr of standing) and after assumption of the supine position (30, 60, and 120 min). After standing, neither hemodynamics nor markers of effective volemia differed significantly between controls and patients. By evaluating the areas under the curve during the 2 hr of supine posture, the increase in cardiac output and plasma natriuretic factor and the decrease in peripheral vascular resistance were greater in patients (2.59 +/- 0.43 [S.E.M.] L/min/hr; 32.8 +/- 7.2 pg/ml/hr -1,103 +/- 248.4 dyn.sec/cm5/hr, respectively) than in controls (0.53 +/- 0.24 L/min/hr, p = 0.005; 17.4 +/- 4.7 pg/ml/hr, p = 0.005; -265.5 +/- 206.2 dyn.sec/cm5/hr, p = 0.02). The declines in heart rate, plasma norepinephrine concentration and plasma renin activity did not differ significantly. Mean arterial pressure did not significantly change. Our results suggest that during periods of upright posture, cirrhotic patients in the preascitic stage, who are known to have expanded blood volume, compensate for dilatation of the splanchnic vascular bed through total hypervolemia. The latter becomes excessive during recumbency, leading to supernormal increases in venous return, central volemia and cardiac index. The decline in peripheral vascular resistance appears to be a compensatory mechanism to maintain steady arterial blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Refractory ascites: modulation of atrial natriuretic factor unresponsiveness by mannitol

We have previously shown that unresponsiveness to atrial natriuretic factor is a marker of the severity of ascites. The tubular mechanisms are unknown, but it seems that increased reabsorption of sodium proximal to the main site of action of atrial natriuretic factor (i.e., the inner medullary collecting duct) plays an important role. We attempted to decrease the proximal reabsorption of sodium with mannitol in patients unresponsive to atrial natriuretic factor. The results of mannitol in such a group of patients has previously been conflicting. We studied 10 patients with massive, resistant ascites who were off diuretics and on a 20-mmol/day sodium diet for 7 days. Atrial natriuretic factor unresponsiveness was confirmed by failure of a 2-hr atrial natriuretic factor infusion to induce a natriuresis. The next day all patients received an infusion of 40 gm of mannitol and subsequently a combined infusion of mannitol and atrial natriuretic factor. Proximal reabsorption of sodium and water were evaluated by lithium clearance, and glomerular filtration rate and renal blood flow were evaluated by inulin clearance and p-aminohippurate clearances, respectively. Six patients responded to mannitol alone with an increased diuresis (from 39 +/- 7 to 148 +/- 35 ml/hr) and natriuresis (from 0.27 +/- 0.05 mmol/hr to 1.65 +/- 0.53 mmol/hr; p less than 0.05) (responders), whereas four did not (nonresponders). The combination of atrial natriuretic factor and mannitol induced a further significant increase in sodium excretion (3.28 +/- 0.68 mmol/hr) but not in urine excretion, compared with mannitol alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic factor: its (patho)physiological significance in humans

The first human studies using relatively high-doses of ANF revealed similar effects as observed in the preceding animal reports, including effects on systemic vasculature (blood pressure fall, decrease in intravascular volume), renal vasculature (rise in GFR, fall in renal blood flow), renal electrolyte excretion (rises in many electrolytes), and changes in release of a number of different hormones. Whether all these changes are the result of direct ANF effects or secondary to a (single) primary event of the hormone remains to be determined. Certainly, it has been proven that more physiological doses of ANF fail to induce short-term changes in many of these parameters leaving only a rise in hematocrit, natriuresis and an inhibition of the RAAS as important detectable ANF effects in humans. This leads us to hypothesize that ANF is a "natriuretic" hormone with physiological significance. The primary function in humans is to regulate sodium homeostasis in response to changes in intravascular volume (cardiac atrial stretch). Induction of excess renal sodium excretion and extracellular volume shift appear to be the effector mechanisms. The exact mechanism of the natriuresis in humans still needs to be resolved. It appears however, that possibly a small rise in GFR, a reduction in proximal and distal tubular sodium reabsorption, as well as an ensuing medullary washout, are of importance. The pathophysiological role of ANF in human disease is unclear. One may find elevated plasma irANF levels and/or decreased responses to exogenous ANF in some disease states. Whether these findings are secondary to the disease state rather than the cause of the disease remains to be resolved. Therapeutic applications for ANF, or drugs that intervene in its production or receptor-binding, seem to be multiple. Most important could be the antihypertensive effect, although areas such as congestive heart failure, renal failure, liver cirrhosis and the nephrotic syndrome cannot be excluded. Although the data that have been gathered to date allowed us to draw some careful conclusions as to the (patho)physiological role of ANF, the exact place of ANF in sodium homeostatic control must still be better defined. To achieve this, we will need more carefully designed low-dose ANF infusion, as well as ANF-breakdown inhibitor studies. Even more promising, however, is the potential area of studies open to us when ANF-receptor (ant)agonists become available for human use.

Abnormal tubular handling of sodium and water induced by atrial natriuretic peptide in essential hypertension

Atrial natriuretic peptide (ANP) was given as an intravenous bolus injection (2.0 micrograms kg-1) to 12 essential hypertensive patients (EH) and 13 normotensive control subjects (C) in order to study the effect of ANP on renal glomerular and tubular function using the lithium clearance technique. Urinary sodium excretion (EH, + 370% vs. C, + 120%; P less than 0.001) and urine volume (EH, + 137% vs. C, + 62%; P less than 0.01) increased significantly more in EH than in controls after ANP injection. Glomerular filtration rate, renal plasma flow, and plasma concentrations of angiotensin II, aldosterone and arginine vasopressin remained almost unchanged after ANP injection, whereas the filtration fraction increased to the same extent in both groups. Both proximal (EH, - 15% vs. C, - 5%; P less than 0.01) and distal fractional reabsorption (EH, - 12% vs. C, - 5%; P less than 0.01) of sodium decreased more markedly after ANP in EH than in controls. The increase in plasma cGMP and urinary excretion of cGMP was the same in the two groups. Mean blood pressure decreased and heart rate increased to the same extent in both groups. It is concluded that the increase in urinary sodium excretion and urine volume induced by ANP bolus injection is exaggerated in EH due to a more pronounced reduction in the reabsorption of sodium and water in both the proximal and the distal tubule.

Enhanced urinary excretion of albumin and beta 2 microglobulin in essential hypertension induced by atrial natriuretic peptide

Atrial natriuretic peptide (ANP) was given as an intravenous bolus injection (2.0 micrograms kg-1) to 12 essential hypertensive patients (EH) and 10 normotensive control subjects (C) in order to study the effect of ANP on urinary excretion of albumin and beta 2-microglobulin, and on glomerular filtration rate (GFR), renal plasma flow (RPF), and filtration fraction (FF). After the ANP injection, urinary excretion of albumin increased significantly (p less than 0.01) in EH from 7.3 micrograms min to 125 micrograms min (medians) and in C from 2.9 micrograms min-1 to 8.1 micrograms min-1 (p less than 0.05). Urinary excretion of beta 2-microglobulin increased in EH from 70 ng min-1 to 1022 ng min-1 (p less than 0.01) and in C from 118 ng min-1 to 170 ng min-1 (p less than 0.01). The increase in urinary excretion of both albumin (p less than 0.01) and B2-microglobulin (p less than 0.01) was significantly more pronounced in EH than in C. GFR and RPF were almost unchanged in both groups. FF rose to the same degree in the two groups. The increase in fractional excretion of sodium and in urine volume after ANP was enhanced in EH. It is concluded that ANP in pharmacological doses increased urinary excretion of albumin and beta 2-microglobulin to a considerably larger extent in essential hypertensive patients than in normotensive control subjects.

Adsorption of atrial natriuretic peptide to different materials: a factor influencing results of in vitro experiments?

Studies on atrial natriuretic peptide (ANP) in ex vivo situations, include a risk of adsorption to surrounding materials. In order to investigate this potential source of error, known concentrations of ANP in Krebs solution were prepared in test tubes of different materials. The solutions were analyzed for ANP-concentration by radioimmunoassay (RIA), using a standard-curve of ANP in phosphate buffer supplemented with 0.1% human serum albumin (HSA) and 0.1% Triton X100. A considerable adsorption was seen to the different materials tested, also to siliconized glass and polypropylene. With 1 ml ANP-solution in concentrations from 1 x 10(-9) to 1 x 10(-5)M an adsorption varying between 10 and 31% was seen to a 15 cm2 polystyrene-surface, corresponding to a conventional test tube. With 1 ml of ANP 120 pM in Krebs solution serially dispensed into six empty polystyrene test tubes, 73% of the initial peptide amount was lost due to adsorption. The adsorption could be prevented or partly reversed by adding HSA or Triton X100 to the solutions. These findings indicate that adsorption entails a risk of disturbing the results of in vitro experiments in studies on ANP.

Mannitol stimulates atrial natriuretic peptide release in humans

The purpose of this study was to determine if mannitol stimulates atrial natriuretic peptide (ANP) release in humans and to examine potential mechanisms for this effect. Twenty patients requiring cardiac catheterization were randomized to receive either mannitol (15-g bolus followed by 15% infusion mixed in 75 mmol/L saline at 100 mL/h for 1 hour) or an equal volume of 75 mmol/L saline, intravenously (IV). All measurements were made at three time points: at baseline, at 10 minutes (after the bolus but before radiocontrast administration), and at 60 minutes (after completion of the study). Baseline plasma ANP (PANP) measurements (mean +/- SE) were similar in both groups (saline, 73 +/- 38 pg/mL; mannitol, 62 +/- 11 pg/mL). PANP increased significantly over time for the set of all patients (analysis of variance [ANOVA], P less than 0.05); however, at 10 minutes PANP increased significantly only in the group receiving mannitol (saline, 76 +/- 43 pg/mL; mannitol, 100 +/- 29 pg/mL) (P less than 0.04). Serum osmolality (SOSM), over time for the set of all patients (ANOVA, P less than 0.04). At 10 minutes there were significant increases only in the group receiving mannitol, and after radiocontrast, there were significant increases in both groups for all parameters. Regression analysis demonstrated a significant correlation between the change in PANP and the change in SOSM (P less than 0.04, r = 0.33). In conclusion, intravascular infusion of mannitol or radiocontrast increased PANP levels. The mechanism may be multifactorial, with a potential role for an increase in SOSM and/or PADH.