Natriuretic effect of digoxin-like immunoreactive substance on dog kidney

We previously reported that digoxin-like immunoreactive substance (DLIS) was found only in the blood of those dialysis patients who were hypertensive and had high systemic vascular resistance. In order to determine whether the DLIS was a marker for the natriuretic hormone, renal infusion studies were carried out in anesthetized dogs. When ultrafiltrates from patients with high blood DLIS levels were infused into the renal artery of one kidney there was a significant increase in the fractional excretion of sodium (FE Na) from its baseline value. Further, the FE Na of these kidneys were significantly higher than the FE Na noted for the contralateral kidneys which were simultaneously infused with ultrafiltrates obtained from dialysis patients lacking DLIS activity in their blood. We conclude that the DLIS is or represents a marker for natriuretic hormone. Since the natriuresis noted was independent of renal plasma flow and glomerular filtration rate and since the fractional excretion of potassium was not influenced by the infusion, we believe that DLIS is different from atrial natriuretic factor.     

Effect of atrial natriuretic peptide on arterial pressure and renal function in cirrhotic rats with ascites

Glomerular filtration rate, urine volume, sodium excretion and mean arterial pressure were measured in 10 rats with Cl4C induced cirrhosis presenting sodium retention and ascites, and in 10 control rats before and during the iv administration of the 28 aminoacid rat alpha-Atrial Natriuretic Peptide (alpha-ANP) (a bolus of 1 microgram followed by a constant infusion of 33 ng/min). alpha-ANP induced a similar increase in glomerular filtration rate and filtered sodium load in both groups of rats. In contrast, the increase in urine volume and sodium excretion produced by alpha-ANP was significantly lower in cirrhotic rats (from 13.8 +/- 1.9 to 37.9 +/- 9.1 microliters/min., and from 0.5 +/- 0.1 to 3.3 +/- 1.0 microEq/min) than in control animals (from 14.6 +/- 1.3 to 102.5 +/- 17.7 microliters/min., p less than 0.005; and from 1.0 +/- 0.3 to 14.1 +/- 3.2 microEq/min., p less than 0.001). The results indicate that in rats with experimental cirrhosis and ascites there are blunted diuretic and natriuretic responses to alpha-ANP, probably as a consequence of the exaggerated tubular sodium reabsorption present in these animals.     

Potentiation of the natriuretic effect of clonidine following indomethacin in the rat.

Previous studies have demonstrated a diuretic effect of clonidine at low intrarenal infusion rates with a natriuretic effect being observed at high infusion rates (greater than or equal to 3 micrograms.kg-1.min-1). The natriuresis at high infusion rates may have been secondary to increased renal prostaglandin production. We therefore evaluated the effects of indomethacin (a cyclooxygenase inhibitor) on the response to clonidine in the anesthetized rat. Intrarenal infusions of saline (vehicle) or clonidine (0.1, 0.3, 1, and 3 micrograms.kg-1.min-1) were examined both in the presence and absence of pretreatment with indomethacin (5 mg/kg, i.p.). Clonidine produced a dose-related increase in urine volume and free water clearance at 0.3, 1, and 3 micrograms.kg-1.min-1 as compared with the vehicle group. Sodium excretion and osmolar excretion were increased only at the highest infusion rate investigated. Following indomethacin pretreatment, clonidine produced a greater increase in urine volume at each infusion rate investigated. The indomethacin pretreatment also resulted in a potentiation of the natriuretic effect of clonidine at all infusion rates. Interestingly, this was associated with an increase in osmolar clearance but not free water clearance. These effects of indomethacin were reversed by infusion of prostaglandin E2. An infusion of prostaglandin E2 attenuated the indomethacin-induced increase in both urine flow rate and sodium excretion, indicating that the effects of indomethacin were mediated by prostaglandin inhibition. These results suggest that endogenous prostaglandin production attenuates the renal effects of clonidine, and as well, that in the presence of alpha 2-adrenoceptor stimulation, prostaglandin E2 mediates an antidiuretic and antinatriuretic effect.     

Renal effects of dopamine and ANP in high volume expanded rats

Both dopamine (DA) and atrial natriuretic peptide (ANP) have been postulated to exert similar effects on the kidney, participating in the regulation of body fluid and sodium homeostasis. In the present study, experiments were performed in anesthetized and isotonic sodium chloride volume expanded rats. After acute volume expansion at 15 % of body weight during 30 min, glomerular filtration rate, urine output, sodium excretion, fractional sodium excretion, proximal and distal sodium excretion and blood pressure were measured. In additional groups we administered ANP or haloperidol or the combination of both to volume expanded animals. Blockade of DA receptors with haloperidol, attenuated diuretic and natriuretic responses to volume load. Proximal sodium excretion was not modified by haloperidol in all experimental groups of rats. Reduction in distal tubular excretion was induced by haloperidol in saline infusion expanded rat but not in ANP treated expanded animals. In conclusion, when exaggerated volume expansion is provoked, both DA and ANP exert renal tubular events, but ANP have a major central role in the regulation of renal sodium handling.     

A role for the angiotensin IV/AT4 system in mediating natriuresis in the rat

Angiotensin II (AngII) or Angiotensin IV (AngIV) was infused into the renal artery of anesthetized rats while renal cortical blood flow was measured via laser Doppler flowmetry. The infusion of AngII produced a significant elevation in mean arterial pressure (MAP) with an accompanying decrease in cortical blood flow, glomerular filtration rate (GFR), urine volume, and urine sodium excretion. The infusion of AngIV induced significant increases in renal cortical blood flow and urine sodium excretion, without altering MAP, GFR, and urine volume. Pretreatment infusion with a specific AT1 receptor antagonist, DuP 753, blocked or attenuated the subsequent AngII effects, while pretreatment infusion with the specific AT4 receptor antagonist, Divalinal-AngIV, blocked the AngIV effects. These results support distinct and opposite roles for AngII and AngIV, i.e. AngII acts as an anti-natriuretic agent, while AngIV acts as a natriuretic agent.     

Effects of rat bile infusion on renal function in rats.

The influence of rat bile infusion on renal function in rats and the possible role of bile-induced hemolysis in these effects were examined. The hemolytic action of rat bile and some bile salts were determined in vitro. After the i.v. infusion of rat bile (70 mg freeze-dried powder/2.55 ml) into pentobarbitone-anesthetized rats, the urine, sodium and potassium excretion rates were reduced more than half, which was due to the decrease of glomerular filtration rate and increase of tubular water and sodium reabsorption. A fall in blood pressure, a rise in hematocrit, and hemolysis were also found. Infusion of hemolysed (30 microliters RBC) solution produced by distilled water and then made isotonic caused a short-duration increase in renal excretion and glomerular filtration rate, and the blood pressure was unchanged. Infusion of a rat bile-hemolysed solution after removal of bile acids with cholestyramine increased renal excretions at first with reduction thereafter. Infusion of the rat bile-hemolysed solution treated with barium sulfate produced a renal response very similar to rat bile alone. It is proposed that two factors are involved in the renal response after bile infusion, namely bile acid-induced hemolysis producing diuresis with natriuresis, and bile acid-induced antidiuresis and antinatriuresis, possibly due to a direct renal effect.     

Cerebral salt wasting in subarachnoid hemorrhage rats: model, mechanism, and tool

Cerebral salt wasting (CSW) frequently occurs concomitantly with aneurysmal subarachnoid hemorrhage (SAH). CSW induces excessive natriuresis and osmotic diuresis, and reduces total blood volume. As a result, the risk of symptomatic cerebral vasospasm may be elevated. Therefore, it is important to determine the mechanism of CSW. The purpose of this study was to evaluate whether the rat SAH model exhibits CSW and to investigate the relationship between CSW and natriuretic peptides. A SAH model was produced in 24 rats by perforating a cerebral artery with a nylon thread up through the common carotid artery. To evaluate CSW, urine was cumulatively collected from SAH onset to 12 hours and sodium (Na) excretion was analyzed. Body weight and hematocrit were analyzed before and after SAH onset. Concentrations of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in plasma were also analyzed. Urine volume and total Na excretion of SAH rats were significantly higher than those of sham rats (p<0.05). Body weight of SAH rats significantly decreased and hematocrit significantly increased (p < 0.05). ANP concentration was significantly decreased in SAH rats (p<0.05). However, BNP concentrations did not change. This study demonstrated for the first time that a rat SAH model exhibited CSW. It was suggested that the cause of CSW was neither ANP nor BNP. In addition, this rat SAH model will be useful for study of CSW after SAH.     

The effect of atrial natriuretic peptide on acid-base balance in rats with chronic renal failure

We explored the effects of 12-hour infusion of atrial natriuretic peptide (alpha-rANP:rat, 1-28) on arterial acid-base balance, using 5/6 nephrectomized rats with chronic renal failure. Before the infusion, nephrectomized rats had a higher mean arterial blood pressure, greater urine volume, and lower creatinine clearance than the normal controls, but they did not show a significant difference in arterial hydrogen ion concentration (pH), plasma bicarbonate concentration (HCO3-), partial pressure of carbon dioxide (PCO2), plasma base excess (BE), or plasma ANP concentration. alpha-rANP infusion produced a continuous blood pressure reduction in both nephrectomized and control rats. Urine volume and urinary sodium and potassium excretion tended to increase at 2-hour infusion, but not at 12-hour infusion. In the controls alpha-rANP significantly increased pH from 7.47 to 7.50, and decreased PCO2 by 14%. In contrast, in nephrectomized rats alpha-rANP significantly decreased pH from 7.48 to 7.44, HCO3- by 13%, and BE from -0.07 to -3.22 meq/l. Rats with chronic renal failure had greater reduction in HCO3- than the controls (p less than 0.05). There was no difference in plasma ANP level between the two groups. Thus, it is indicated that the long-term infusion of alpha-rANP reduces pH in rats with chronic renal failure, thereby adversely affecting the acid-base balance.     

Prostaglandin E2 induced changes in renal blood flow, renal interstitial hydrostatic pressure and sodium excretion in the rat

Prostaglandin E2, when infused into the renal artery of the dog, is a vasodilator and increases both renal interstitial hydrostatic pressure and sodium excretion. Similar studies in the rat, however, have been inconclusive. The present study examined the effect of prostaglandin E2 infusion into the renal interstitium, by means of a chronically implanted matrix, on renal blood flow, renal interstitial hydrostatic pressure and sodium excretion in the rat. Prostaglandin E2 was continuously infused directly into the kidney interstitium to mimic endogenous prostaglandin E2 production by renal cells. The maximum change in each of these parameters occurred when 10(-5) M PGE2 was infused. Renal blood flow increased from 4.70 +/- 0.91 to 5.45 +/- 0.35 ml/min (p less than 0.05) while renal interstitial hydrostatic pressure decreased from 3.9 +/- 0.4 to 2.6 +/- 0.5 mmHg (p less than 0.05) and fractional excretion of sodium decreased from 1.02 +/- 0.20 to 0.61 +/- 0.12% (p less than 0.05). Thus, the present study demonstrates that renal interstitial infusion of prostaglandin E2 increases total renal blood flow but decreases both renal interstitial hydrostatic pressure and urinary sodium excretion in the rat.     

Renal responses to atrial natriuretic factor during converting enzyme inhibition

The effect of converting enzyme inhibitor (CEI) on the renal response to atrial natriuretic factor (ANF) was determined in the rat. In the absence of CEI, ANF produced rapid and significant increases in sodium, potassium, calcium, and urine excretions while blood pressure declined transiently. In the presence of CEI, ANF enhanced the excretion of sodium and potassium but not of calcium and urine. The activity of CEI was documented by observing that, in the presence of CEI, the elevation of blood pressure produced by angiotensin I was significantly attenuated. The potentiating effect of CEI on the natriuretic response to ANF supports the hypothesis that converting enzyme may be involved in the metabolism of ANF.     

Volume expansion during NOS substrate donation with L-arginine: regulatory offsetting of renal response?

The responses to infusion of nitric oxide synthase substrate (L-arginine 3 mg.kg(-1).min(-1)) and to slow volume expansion (saline 35 ml/kg for 90 min) alone and in combination were investigated in separate experiments. L-Arginine left blood pressure and plasma ANG II unaffected but decreased heart rate (6 +/- 2 beats/min) and urine osmolality, increased glomerular filtration rate (GFR) transiently, and caused sustained increases in sodium excretion (fourfold) and urine flow (0.2 +/- 0.0 to 0.7 +/- 0.1 ml/min). Volume expansion increased arterial blood pressure (102 +/- 3 to 114 +/- 3 mmHg), elevated GFR persistently by 24%, and enhanced sodium excretion to a peak of 251 +/- 31 micromol/min, together with marked increases in urine flow, osmolar and free water clearances, whereas plasma ANG II decreased (8.1 +/- 1.7 to 1.6 +/- 0.3 pg/ml). Combined volume expansion and L-arginine infusion tended to increase arterial blood pressure and increased GFR by 31%, whereas peak sodium excretion was enhanced to 335 +/- 23 micromol/min at plasma ANG II levels of 3.0 +/- 1.1 pg/ml; urine flow and osmolar clearance were increased at constant free water clearance. In conclusion, L-arginine 1) increases sodium excretion, 2) decreases basal urine osmolality, 3) exaggerates the natriuretic response to volume expansion by an average of 50% without persistent changes in GFR, and 4) abolishes the increase in free water clearance normally occurring during volume expansion. Thus L-arginine is a natriuretic substance compatible with a role of nitric oxide in sodium homeostasis, possibly by offsetting/shifting the renal response to sodium excess.     

Diuretic and natriuretic actions of extract prepared from rat erythrocytes

Freeze-dried preparation of rat erythrocytes was extracted into distilled water and after heat treatment the extract was chromatographed on Sephadex G-25 column. The effluent fractions were pooled, freeze-dried, dissolved in Ringer's solution and bioassayed for diuretic and natriuretic responses in anaesthetized non-diuretic rats. The active fractions potently enhanced urine output (about 9-fold control) and urinary sodium excretion (about 7-fold control). The responses started to develop after a lag period of approximately 10-20 min, peaked between 60-80 min post-injection and then diminished. The augmentation of sodium excretion persisted longer than the increased diuresis. The biological activity of the extract was retained after dialysis in a tube with nominal molecular weight cut-off below 1,000.     

Antisera to atrial natriuretic factor reduces urinary sodium excretion and increases plasma renin activity in rats

Although the presence of atrial natriuretic factor in the blood has been demonstrated by radioimmunoassay, its biological activity and physiological significance has not been elucidated. Using specific antiserum against atrial natriuretic factor, we investigated the effect of passive immunization in rats. A significant reduction of urine output and urinary sodium excretion lasted for about 30 min after intravenous administration of antiserum. The effects were more pronounced in rats pretreated with deoxycorticosterone acetate and saline. Plasma renin activity was increased after the administration of antiserum. No significant effects on the urinary sodium excretion was observed following injection of normal rabbit serum. The results of this study provide evidence indicating that endogenous atrial natriuretic factor plays an important role in the regulation of urinary water and sodium excretion and plasma renin activity.     

Changes in urinary water and electrolyte excretion in sodium-loaded sheep in response to intravenous infusion of arginine vasopressin.

Mature sheep receiving supplements of sodium chloride into the rumen were given intravenous infusions of arginine vasopressin at rates varying from 4-6-23 pmol/min (2-10 mU/min). Infusion of the hormone led to an increase in urine flow and to increases in the amounts of sodium and chloride excreted, the effect on flow was, however, the greater so that the osmolality of the urine fell during the infusions. In sheep given intravenous infusions of a hypertonic sodium chloride solution addition of vasopressin to the infusate led to the formation of a larger volume of urine containing a higher proportion of the infused salt load compared to when the salt solution alone was given. As before the effect on flow was the greater and hence the osmolality of the urine was lower when the hormone was given. In other experiments intravenous infusion of a hypertonic sodium chloride solution at rates providing 2-8 mmol NaCl/min led to increases in urine flow and increases in sodium and chloride excretion, the size of these increases being proportional to infusion rate. Plasma vasopressin levels markedly increased during these infusions, the levels seen being similar to those seen in sheep given vasopressin in amounts which increased both urine flow and electrolyte excretion. This suggests that during hypertonic salt loading vasopressin probably contributes directly to the increases in urine flow and the increases in electrolyte excretion which are seen. Further evidence in support of this was obtained in experiments in which a greater natriuretic response was seen in sheep given a hypertonic sodium chloride solution into the carotid artery as opposed to the given a hypertonic sodium chloride solution into the carotid artery as opposed to the jugular vein and where it was shown that plasma vasopressin levels were indeed higher when the solution was given into the artery.     

Effect of sodium intake on the excretion of urinary natriuretic factor in essential hypertensives

A simplified method for the determination of natriuretic factor in the urine as measured by digoxin-like substance was studied. Digoxin-like substance in the urine was estimated by RIA using anti-digoxin antibody after being extracted by reversed phase cartridge column but without gel filtration. The values found by radioimmunoassay (RIA) yielded a significant correlation with those of the inhibitory effect of Na-K-ATPase activity which was measured by biochemical assay as described by Hamlyn et al. Using this RIA method, the effect of salt intake on natriuretic factor in urine was studied in patients with essential hypertension. The natriuretic factor on a high sodium diet (NaCl 20 g/day for three days) increased approximately 1.5 times, as compared to those on a low sodium diet (NaCl 3 g/day) (p less than 0.05). The Natriuretic factor showed a positive correlation with urinary Na excretion (P less than 0.050) when the patients were placed on ad. lib. sodium diet. From these results, it is suggested that secretion of natriuretic factor in the urine might be regulated in part by salt intake.     

Renal effects of administered atrial natriuretic peptide in the conscious, aging rat

Studies were performed in conscious, chronically catheterized male Sprague-Dawley rats to investigate the effect of administered atrial natriuretic peptide (ANP) on blood pressure, renal hemodynamics and urinary electrolyte excretion. Studies were performed on young adult (3-4 month old) rats and on aging rats (18-24 months of age). Low dose ANP (80 ng/kg/min for 60 min) had no effects on renal hemodynamics in either young or old rats and produced only a slight blood pressure reduction in young animals. No effect on urinary electrolyte excretion was evident in young rats whereas in the old animals, low dose ANP produced large rises in the rate of sodium excretion, fractional excretion of sodium and urine flow rate. A four fold higher dose of ANP evoked a moderate natriuretic and a marked antihypertensive response in young rats. Time control studies indicated that time alone had no influence on urinary sodium excretion rate, the fractional excretion of sodium or urine flow rate. These studies indicate a much enhanced sensitivity to the natriuretic effects of administered ANP by the kidneys of old rats.     

Interaction among atrial natriuretic factor (ANF), vasopressin, and renal nerves in terms of renal responses in rats.

The relationship between the renal nerves and vasopressin in terms of the natriuretic and diuretic responses to atrial natriuretic factor (ANF--0.25 microgram/kg/min for 15 min), was investigated in unilaterally denervated anesthetized rats before and after the administration of a vasopressin V2 specific antagonist (AVPX)--(40 micrograms/kg bolus followed by 0.4 microgram/kg/min infusion). Administration of the AVPX or ANF did not alter the arterial pressure. Acute renal denervation or AVPX administration independently produced significant increases in sodium and water excretion. ANF infusion by itself produced a greater increase in urine flow and sodium excretion from the denervated kidney compared to the intact kidney before the administration of AVPX. However, after the administration of AVPX renal responses to ANF from the intact kidneys were enhanced such that they were not significantly different from the denervated kidneys. These results suggest that the full physiological response to ANF may be masked by tonic renal nerve activity or antidiuretic actions of vasopressin. Furthermore, since combined renal denervation and AVPX administration does not produce any greater potentiation of the renal responses to ANF than either of these manipulations alone, it is suggested that they may act via a common mechanism, possibly altering activity in the renal nerves.     

Effects of atrial natriuretic factor on urinary concentration of catecholamines and renin secretion in dogs

This study evaluated the effects of synthetic atrial natriuretic factor (ANF) on renal hemodynamics, urinary excretion of electrolytes, norepinephrine (NE), and dopamine (DA); and renal production of renin in anesthetized dogs. Following a bolus (1 micrograms/kg body weight) and infusion (0.1 microgram/kg/min) for 30 min, there was significant increase in urine flow (220 +/- 41%), glomerular filtration rate (72 +/- 14%), and urinary sodium excretion (170 +/- 34%). There was a decrease in renin secretory rate and the concentration ratio of urine NE to DA following ANF was decreased (p less than 0.05). These data suggest that ANF decreases renal production of NE and renin.     

Effects of tilting and volume loading on plasma levels and urinary excretion of relaxin, NT-pro-ANP, and NT-pro-BNP in male volunteers.

The polypeptide relaxin (RLX) has been suggested to play a role in cardiorenal integration and to be related to the natriuretic peptide system. We hence examined the effects of variations in thoracic blood volume and intravenous volume loading on plasma and urinary RLX levels and associated changes in natriuretic peptide levels in healthy men. Two groups of eight subjects were randomly tilted into a 15 degrees feet-down or a 15 degrees head-down position. Ten volunteers were crossover subjected to an infusion of 15 ml/kg of 0.9% NaCl (over 60 min) or control during an observation period of 10 h. Blood and urine were sampled at timed intervals. RLX, NH(2)-terminal prohormones of atrial natriuretic peptide (NT-pro-ANP), and NH(2)-terminal prohormones of brain natriuretic peptide (NT-pro-BNP) were determined by enzyme, radio-, and electrochemoluminescence immunoassays, respectively. NT-pro-ANP levels (in percentage of baseline levels) were higher (P < 0.05) during the head-down (124 +/- 13%) than during the feet-down position (82 +/- 6%). NT-pro-BNP and RLX were not affected by tilting. Volume loading induced a short-lasting increase in plasma NT-pro-ANP, a delayed increase in plasma NT-pro-BNP, had no effect on plasma RLX, and induced a parallel increase in urine flow, renal excretion of sodium, RLX, and NT-pro-BNP. It is concluded that variations in thoracic blood volume in healthy men are not associated with variations in plasma RLX. Increased urinary RLX and NT-pro-BNP excretion during volume loading suggest renal production and a possible role of kidney-derived RLX and brain natriuretic peptide in sodium homeostasis in men.     

Four-hour atrial natriuretic peptide infusion in conscious rats: effects on urinary volume, sodium, and cyclic GMP

Atrial natriuretic peptide (ANP) is released from the cardiac atria in response to acute volume loads; when infused acutely ANP causes diuresis and natriuresis. Cyclic GMP (cGMP) appears to be the second messenger for ANP in the kidney. The role that ANP plays in the long-term regulation of salt and water balance is unclear, however, since resistance to ANP's natriuretic and diuretic activity develops during prolonged administration. The purpose of the present study is to examine the relationship between the rate of cGMP excretion in response to ANP and the development of resistance to ANP's diuretic and natriuretic activity. Following a 30-min baseline period of infusion of Ringer's solution conscious rats received ANP at 15 micrograms/kg/hr (n = 6) or Ringer's alone (n = 5) for 240 min. ANP-infused rats had a significant diuresis and natriuresis during the first hour of infusion; urinary cGMP excretion also increased compared to baseline. By 120 min after initiating the infusion in ANP-rats urinary volume and sodium excretion had declined to values not significantly different from those of baseline or control. In contrast, urinary cGMP excretion remained elevated for the duration of the ANP infusion, whether compared to baseline values or the control group. Resistance to the diuretic and natriuretic activity of ANP is not a result of mechanisms that involve cGMP generation.