Endocrinol. Japon. 1988, 35(4), 523-529

Atrial Natriuretic Peptide in Kidney of Renal Disease Patients and Healthy Persons

FUMIAKI MARUMO, HISATO SAKAMOTO#, NAOKI UMETANI# AND MICHIHITO OKUBO#

Second Department of Internal Medicine, Tokyo Medical and Dental University, Yushima, Tokyo, and #Department of Medicine,Kitasato University School of Medicine, Sagamihara,Kanagawa Japan

Abstract

Regulation of renal excretion of atrial natriuretic peptide (ANP) was studied in kidney disease patients and healthy kidney donors. The measured ANP concentration in the patient's plasma did not correlate with their creatinine clearance (Ccr), while the fractional excretion of ANP (FEANP) significantly correlated with Ccr. FEANP in healthy persons is less than 1%. In the healthy donors of kidneys for transplantation, approximately 80% of the plasma ANP from the renal artery appeared in the renal vein. From these results, this high recovery of ANP in the veins does not appear to be adequately explained by its degradation in the renal arterioles and nephrons. The FEANP from kidney disease patients significantly correlated with FENa, FEK and FEp, but not with FEca and FEMg. The manner of ANP handling in the nephron may possibly differ from that of Ca or Mg.

Although atrial natriuretic peptide (Marumo et al., 1986). (ANP) is known to cause natriuresis and The plasma ANP entering from the diuresis, it has not been established whether renal artery into the kidney may be 1) ANP is reabsorbed or degradated in the consumed by the receptors and/or degraded human kidney. Some human polypeptide by peptidase in the vasculature and tubules, hormones are excreted into the urine, like 2) reabsorbed from the nephron after being vasopressine, for example, while others filteredby the glomeruli,or 3)excreted into including insulin are not. Because ANP is the urine. Thus, we tried to determine a small peptide (28 amino acids) it is whether ANP was consumed or degraded probably excreted into the urine. It has in the kidney, was reabsorbed from the not been reported before that ANP is ex- tubules, or was excreted into the urine. creted into urine, except for our observation

Received September 1, 1987 Reprints request to: FUMIAKI MARUMO, Patients and Methods Second Department of Internal Medicine, Tokyo Medical and Dental University, Yushima, Tokyo, 36 men and 20 women with kidney disease, 113 Japan 45 with chronic glomerulonephritis, 7 with Endocrinol. Japon. 524 MARUMO et al. August 1988 cystic kidney disease and 4 with nephrosclerosis reagents. 0.1ml samples were mixed with 0.1ml who visited the Renal Division, Department of of rabbit anti-ANP serum [produced with a- Medicine, Kitasato University Hospital as out hANP (1-28)-thyroglobulin as immunogen] and patients, with ages ranging frofn 16 to 76 years 0.1ml of the assay buffer. After allowing each old, averaging 27.8•}11.8 (mean•}SD) years, mixture to stand for 20hrs at 4•Ž. 0.05ml of were studied. [125I]α.hANP(specific activity of 74TBq/mmol, Patients with congestive heart failure, un- 120pg/ml) was added followed by incubation for controlled hypertension, diabetes or edema were an additional 24 hrs at 4•Ž. Bound and free excluded. Pregnant women and diuretic recipients ligands were separated by the addition of 0.5ml were also excluded. Blood and urine samples of an assay buffer containing 10ƒÊ1 of goat anti- were taken and creatinine clearance (Ccr) values rabbit ƒÁ-globulin, 1ƒÊl of normal rabbit serum were measured by a conventional method in the and 5% polyethylene glycol (mean Mr, 7500). out-patient clinic. Their mean Ccr was 50.8•} The amount of ANP in the samples was read 32.0ml/min, ranging from 4.6 to 123.3. from a standard curve plotted using the values

One man and six women who were healthy obtained from assay of the a-hANP standard. donors of kidneys for transplantation, with an The immunological cross-reactivity of the anti- average age of 44.7•}4.8 years, ranging from 32 serum with ƒ¿-rat ANP (1-28), decomposed ƒ¿- to 68, were also studied. Renal artery, vein hANP (7-28), ƒ¿-hANP (5-27) and ƒÀ-hANP was

plasma and urine samples were collected from 100%, while with ƒ¿-rat ANP (5-25) (atriopeptin these living donors at the time of operation I) and bovine-thyroglobulin,it was less than under general anesthesia. 0.01% in the molar ratio of these substances. The measurement of the ANP concentration RIA with antiserum recognized the carboxyl- was performed by subjecting a small volume of terminal end segment of hANP, a-hANP (25- a sample (0.1ml) to our highly sensitive and 27). The minimal quantity of hANP detected in specific RIA (Marumo et al., 1986). The assay this assay was 0.3pg/tube with 99% confidence, buffer was 0.1M phosphate buffer, pH 7.4 and and the ID50 of [125I] a-hANP binding was 3.6 contained 0.15M NaC1, 0.01M K2 EDTA, 0.02 pg/tube. M glycine, 0.01M s-aminocaproic acid, 0.001M Linear regression analyses were carried out sodium azide, and 11 mg/ml inactivated human by the least squares method. serum albumin. It was used to dissolve all

n=56 n=53 r=-0.142 r=-0.530 p=ns p<0.01 y=1.97-0.155x

Fig. 1. Correlation between plasma ANP concentration, fractional excretion of ANP , and crea- tinine clearance. The figure on the left side indicates the correlation between plasma ANP concen- tration and Ccr, and the figure on the right side indicates the correlation between FEANP and Ccr . Vol.35, No.4 ANP IN RENAL DISEASE AND. HEALTHY PERSONS 525

both Ccr (n=53, r=-0.523, p<0.01) and Results FEANP (n=50, r=0.43, p<0.01). As shown in Fig. 4, fractional excretion phosphate As shown in Fig. 1, there was no cor- (FEe) significantly correlated with Ccr (n= relation between the plasma ANP concen- 53, r=-0.717, p<0.01). However, there tration and Ccr (n=56, r=-0.142), while were no correlations, between fractional the fractional excretion of ANP (FEANP) excretion of calcium (FEca) and magnesium showed a significant correlation with Ccr (FEMg), and Ccr (n=46, r=0.03 and n=29, (n=53, r=-0.530, p<0.01). r=-0.17,respectively).Neither,FEca nor Fractional excretion of sodium (FENa) FEMg correlated with FEANP (n=46, r= significantly correlated with Ccr (n=53, 0.008 and n=29, r=0.043, respectively). r=-0.575,P<0.01)and also correlated As shown in Table 1, plasma ANP con- with FEANP (n=53, r=0.382, p<0.01), as centrations in the renal artery and vein shown in Fig. 2. Fractional excretion of were 60.8•}6.22 and 47.7•}6.18pg/ml, re- potassium (FEK) significantly correlated with spectively. The plasma ANP concentration Ccr (n=53, r=-0.620, p<0.01) and also decreased to 78.2•}4.36% after passage correlated with FEANP(n=53, r=0.367, p< into the kidney. FEANP was 0.49•}0.20%

0.01), as evident from Fig. 3. Fractional (n=7). excretion of chloride (FEc1) correlated with

n=53 n=53 r=-0.575 r=0382 p<0.01 p<0.01 y=3.31-0.024x y=1.31+0.70x

Fig. 2. Correlation. between FEANP and FENa. The figure on the left side indicates the correlation between FENa and Ccr, and the figure on the right side indicates the correlation between FEANP and FENa. Endocrinol. Japon. 526 MARUMO et al. August 1988

n=53 n=53 r=-0.620 r==0,367 p<0.01 p<0.01 y=31.2-0.23X y=12.3+4.83x

Fig. 3. Correlation between FEANP and FEK. The figure on the left side indicates the correlation between FEK and Ccr, and the figure on the right side indicates the correlation between FEANP and FeK.

n=53 n=53 r=-0.717 r=0.515 p<0.01 p<0.01 y=47.4-0.392x y=13.5+12.2x

Fig. 4. Correlation between FEANP and FEp. The figure on the left side indicates the correlation between FEp and Ccr, and the figure on the right side indicates the correlation between FEANP and FEp. Vol.35, No.4 ANP IN RENAL DISEASE AND HEALTHY PERSONS 527

Table 1. Plasma ANP levels in the renal artery and vein and ANP levels in the urine from living persons donating a kidney for transplantation.

Plasma and urine samples from each donor were obtained at the time of kidney transplantation.

show high ANP concentrations in their plasma. Usually, furosemide is used for Discussion patients with hypertension, edema, or other volume-overloaded conditions. Thus, it is It has been suggested that ANP is not suitable to include these patients as released from the atrium in response to subjects of the study. However, Hasegawa various hemodynamic conditions associated et al. (1986) mentioned that some of their with atrial distension or stretch and induces subjected patients received furosmide, and diuresis, natriuresis and vasorelaxation (De Rascher et al.(1985) did not mention Lean et al., 1985). In the kidney, receptors whether furosemide was given or not given for ANP were found in the glomeruli and at to their patients. In our present study, all other sites in the nephrons (De Lean et al., the types of patients mentioned above were 1985); Koseki et al., 1986). It may be excluded, as well as all patients receiving commonly accepted that ANP is filtered by diuretics. the glomeruli, due to its relatively small It is a well known fact that the half molecular weight. However, the physio- life of ANP in the plasma is very short logical effects of ANP have been discussed, (Nakao et al., 1986). Thus, hardly any but not unanimously agreed upon (Sonnerberg ANP may remain in the plasma even if et al., 1982; Huang et al., 1985; Kondo et ANP excretion from the kidney decreases al., 1986. Torikai, 1986; Nonoguchi et al., due to a loss of kidney mass. Further- 1987; Ando et al., 1987). There is no more, FEANp increases with a decrease in report indicating whether ANP is reabsorbed renal function. These findings support our or, except for our report (Marumo et al., results that the plasma ANP concentration 1986), whether it is excreted into the urine. in kidney disease patients does not signifi- It has been observed that plasma ANP cantly increase even after renal function is concentrations are higher in non-dialyzed impaired. Furthermore, our assay recognizes patients with chronic renal failure than in the carboxyl end terminal segment of ANP healthy persons (Rescher et al., 1985; which is a biologically active site. It is Hasegawa et al., 1986). It is a well known possible that Rascher et al.(1985) or fact that patients having hypertension or Hasegawa et al.(1986) measured biologically edema and patients who have had congestive non-active fragments of ANP because their heart failure, in addition to pregnant women, assay may not be able to distinguish active Endocrinol. Japon. 528 MARUMO et al. August 1988 from non-active fragments. available to compare the manner of re- Plasma ANP concentrations in renal absorption between ANP and Na, K or P. vessels have previously been measured (Sato In end stage renal disease, Ca absorption et al., 1986; Richards et al., 1986). In the from intestine decreases and Mg metabolism present study, simultaneous sampling of the is not disturbed by severe renal dysfunction. plasma from both the renal artery and Thus, neither FEca nor FEMg may correlate vein was seen as necessary because the half with FEANp. life of ANP in the plasma is short. In conclusion, approximately 20% of ANP binding sites were noted in the plasma ANP from the renal artery which vasculature of kidney (Bianchi et al., 1985) passed into kidney was not recovered. Most and in the aorta (Koseki et al., 1986). of it disappeared in the kidney possibly Murthy et al. (1986) suggested that degra- because of consumption by the receptors dation of ANP may occur either after and/or degradation by peptidase in the internalization in the vascular cells or by a vasculature and renal tubules, and the rest membrane bound enzyme in the vasculature. was excreted into the urine. Thus, some of the plasma ANP which entered the kidney from the renal artery may be degraded in the vasculature. Gener- Acknowledgements ally, the glomerular filtration rate is 20% of the renal blood flow, however, the plasma This work was supported in part by the ANP content filtered by the glomeruli may Grant in Aid for Scientific Research from the be less than 20% of that in the renal Ministry of Education, Science and Culture (No . artery because ANP is degraded in the 62570403) and a grant from the Life Science vasculature in the kidney. In the present Laboratories. study, 80% of plasma ANP in the renal artery appeared in the renal vein. 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