JPH04321699A - New diuretic peptide - Google Patents

Abstract

PURPOSE:To provide a new diuretic peptide for diuretic agents, hypotensive agents, vasodepressors etc., obtainable from the shark's auricle, ventricle or brain, having such structure that amino acids are not bound toward the C-terminal from the cysteine on the C-terminal side of the basic skeleton. CONSTITUTION:The auricle, ventricle and brain are taken out from sharks and boiled in distilled water for 5min and then cooled; acetic acid is then added to the system followed by homogenization with a mixer to effect extraction, and the extract liquor is centrifugalized to collect the supernatant. This supernatant is then brought to dryness under reduced pressure and the resulting residue is dissolved in 1M acetic acid followed by addition of acetone and then centrifugation. The resultant sedimented residue is dissolved in 1M acetic acid again followed by gel filtration to collect a fraction with chicken rectum preparation relaxative activity, which is, in turn, put to cation exchange high-performance liquid chromatography and reversed-phase high-performance liquid chromatography, successively, to effect purification, thus obtaining the objective diuretic peptide of e.g. formula I (X is H, the entire sequence of formulae, etc.) having such structure that amino acids are not bound toward the C-terminal from the cysteine on the C-terminal side of the basic skeleton made up of 17 amino acids.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD The present invention relates to a novel diuretic peptide, and more particularly to a diuretic peptide obtained from shark heart or brain. The present invention also relates to a method for producing this peptide and a pharmaceutical composition containing this peptide as an active ingredient, particularly antihypertensive agents, diuretics, and vasodilators.

0002

BACKGROUND OF THE INVENTION It is known that the heart or brain secretes hormones that play an important role in regulating body fluid balance. All of the diuretic peptides discovered so far as such hormones are 1 formed by disulfide bonds (S-S bonds) between cysteines.
The cyclic structure (basic skeleton) consisting of seven amino acids is highly conserved, and differences can be seen in amino acid substitutions within the basic skeleton or in the number and type of amino acids extending from the N-terminus or C-terminus. Currently, diuretic peptides are classified into four types, ie, type A, type B, type C, and type V, based on their origin and amino acid sequence homology, and each type has different biological activities.

The structure of type A atrial natriuretic peptide (hereinafter referred to as ANP) has been determined in humans, rats, pigs, eels, etc., and the structure of type B brain natriuretic peptide (abbreviated as ANP) has been determined in humans, rats, pigs, eels, etc.
The structure of BNP (hereinafter abbreviated as BNP) has been determined in pigs, humans, rats, eels, etc. A second type of BNP recently discovered in pig brains is C-type natriuretic peptide (hereinafter referred to as
It is called CNP (abbreviated as CNP) and is characterized by the fact that the peptide chain does not extend to the C-terminal side of the basic skeleton. Furthermore, in eel, the structure of V-type ventricular natriuretic peptide (VNP), which has a long peptide extending on the C-terminal side, was determined.

[0004] All of these peptides have water and natriuretic effects, antihypertensive effects, and smooth muscle relaxing effects, but the strength of each effect differs depending on the type of peptide. Type C diuretic peptides have weaker water and natriuretic effects than type A peptides, but tend to have similar smooth muscle relaxing and hypotensive effects. Therefore, type C is expected to be particularly useful as an antihypertensive agent or a vasodilator.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is to develop a diuretic peptide that enhances the pharmacological activity spectrum of type C, in which smooth muscle relaxing and antihypertensive effects are more dominant than water and natriuresis than type A. and to provide a drug containing the peptide.

[0006]

[Means for Solving the Problem] Since sharks live in seawater where the difference in sodium concentration between the body and the outside world is small, it is assumed that the main diuretic peptides of sharks have a C-type pharmacological activity spectrum. As a result of conducting research based on these speculations, the present inventors succeeded in isolating a peptide with a strong rectal muscle relaxing effect from the heart and brain of sharks, and determined the structure of this peptide. They also discovered that this peptide has natriuretic, antihypertensive, and smooth muscle relaxing effects, and completed the present invention. below,
This peptide was converted into shark CNP (C-type natri
uretic peptide).

That is, the present invention provides a diuretic peptide obtained from the ventricle, atrium, or brain of sharks, which has no amino acid bonded in the C-terminal direction from cysteine on the C-terminal side of the diuretic peptide basic skeleton consisting of 17 amino acids.・Peptides with natriuretic, antihypertensive, and smooth muscle relaxing effects.

[0008] This peptide has conventional ANP, BNP,
Like CNP and VNP, they exhibit antihypertensive, diuretic, and smooth muscle relaxing effects, and are similar in that they have a diuretic peptide basic skeleton.In particular, they do not have a peptide chain on the C-terminal side of the basic skeleton. , has high homology with rat, frog, and chicken CNP, eel BNP, and medaka brain ANP. However, the fourth amino acid in the N-terminal direction from cysteine on the N-terminal side of the basic skeleton is proline, and it is a C-type diuretic peptide with five or more long peptide chains extending in the N-terminal direction. different from others.

The present invention further provides a peptide having an amino acid sequence represented by the following general formula (1) and a salt thereof.

X-Gly-Pro-Ser-Arg-Gly-Cys
-Phe-Gly-Val-Lys-Leu-Asp-
Arg-Ile-Gly-Ala-MetSer-Gl
y-Leu-Gly-Cys-OH

...(1) (wherein, the X group is hydrogen or H-Arg-Pro-A
rg-Ser-Asp-Asp-Ser-Leu-Gl
n-Thr-Leu-Ser-Arg-Leu-Leu
-Glu-Asp-Glu-Tyr-Gly-His-
Tyr-Leu-Pro-Ser-Asp-Glu-L
eu-Asn-Asn-Glu-Ala-Glu-Gl
u-Met-Ser-Pro-Ala-Ala-Ser
-Leu-Pro-Glu-Leu-Asn-Ala-
Asp-Gln-Ser-Asp-Leu-Glu-L
eu-Pro-Trp-Glu-Arg-Glu-Se
r-Arg-Glu-Ile-Gly-Gly-Arg
-Pro-Phe-Arg-Gln-Glu-Ala-
Val-Leu-Ala-Arg-Leu-Leu-L
ys-Asp-Leu-Ser-Asn-Asn-Pr
o-Leu-Arg-Phe-Arg-Gly-Arg
-Ser-Lys-Lys- or in this sequence, amino acid residues are sequentially 1 from the N-terminus.
It is represented by a partial sequence in which each individual is removed, and the N-terminal hydrogen of the X group may be replaced with Tyr- or a functional group capable of binding to a radioisotope label or avidin. Cystine residues in the peptide may be cross-linked to each other by disulfide bonds. ) 17 from cysteine to cysteine in the underlined part in the above general formula (1)
A peptide chain consisting of these amino acids corresponds to the basic skeleton here. Furthermore, in the following explanation, the X group in formula (1) may be expressed as, for example, X(15), and the number in parentheses indicates the number of amino acid residues in the X group. For example, X(1) represents H-Lys-, and X(16) represents the next peptide chain.

H-Lys-Asp-Leu-Ser-A
sn-Asn-Pro-Leu-Arg-Phe-Ar
When the N-terminal hydrogen of the g-Gly-Arg-Ser-Lys-Lys-X group is substituted with Tyr- or a functional group capable of binding to a radioisotope label or avidin, the peptide of the present invention can be labeled. This can be used to elucidate and analyze the metabolic dynamics of the peptide of the present invention by measuring the blood or tissue concentration of the peptide of the present invention, or by measuring the half-life and site of action. The amino acid abbreviations used in this specification and drawings have the following meanings.

[0012] Three-letter notation Gly: glycine, Leu: leucine, Ile: isoleucine, Ser: serine, Thr: threonine, Asp: aspartic acid, Asn: asparagine, Lys: lysine,
Arg: Arginine, Cys: Cystine, Phe: Phenylalanine, Met: Methionine, Trp
: tryptophan, Tyr: tyrosine Glu: glutamic acid, His: histidine, Ala: alanine, Gln: glutamine, Val: valine Pro: proline The main body of shark CNP obtained from shark atrium or ventricle is represented by the general formula (1) where X is 16), X (17)
, and X(93), and the main body of shark CNP obtained from the brain is a peptide in general formula (1) where X is hydrogen and X(93).

[0013] If the peptide of the present invention contains an amino acid sequence other than the X group in its structure in general formula (1), the peptide can be used at any position of the peptide chain consisting of 93 amino acid residues of the X group. It may be cut by. That is, it includes peptides in which the X group is hydrogen or X(1) to X(93). These peptides are useful because they exhibit diuretic, hypotensive, and smooth muscle relaxing effects as described below.

[0014] As a method for producing the diuretic peptide of the present invention, there is a method for recovering the peptide from cells that produce the peptide. Producer cells include isolated atrium, ventricular, or brain tissue cells, cells grown from these by cell culture, or cells made to produce the desired peptide by genetic modification. There is also a method of recovering from cell culture supernatant. In order to isolate and purify the diuretic peptide of the present invention from these cells or culture supernatant, peptide isolation and purification methods such as extraction, gel filtration chromatography, ion exchange chromatography, high performance liquid chromatography, electrophoresis, and recrystallization can be used. It can be carried out in combination with treatments commonly used for this purpose, and a method including reversed-phase high performance liquid chromatography is particularly preferred.

Alternatively, shark C isolated and purified in this way
Based on the information on the amino acid sequence revealed by analysis of NP, it can be chemically synthesized from amino acids. As the synthesis method, conventional peptide synthesis methods such as solid phase amino acid synthesis method and liquid phase amino acid synthesis method can be used. A specific example of a method for isolating and purifying shark CNP is shown below. first,
The heart or brain is removed from many sharks. This may be used as it is, but it is also possible to use cultured cells or culture supernatant obtained by proliferating cardiac tissue cells or brain cells by cell culture.

An example using ventricular tissue as the starting material is shown below. The extracted heart is divided into atria and ventricles, and only the ventricular tissue is boiled in distilled water, cooled, and extracted by adding acetic acid and homogenizing it. The obtained extract was centrifuged to obtain a supernatant,
After drying under reduced pressure, dissolve in acetic acid, add acetone, and centrifuge. The precipitate is dissolved in acetic acid and subjected to gel filtration and desalting. Chick rectal specimen relaxant active fractions were submitted to cation exchange chromatography, yielding peaks 1, 2 and 3. Next, the chick rectal specimen is purified by reverse-phase high performance liquid chromatography using the relaxant activity as a marker.

The amino acid sequence of the purified shark CNP and the shark CNP fragment that has been limitedly degraded with peptidase is determined using an automatic amino acid sequencer. The amino acid sequence of shark CNP (1-115) using peak 1 as a starting material is as shown by SEQ ID NO: 1 in the sequence listing below. This is a peptide in which the X group in general formula (1) consists of 93 amino acid residues, ie, X(93). Furthermore, the obtained peptide was subjected to amino acid analysis to obtain the following amino acid composition.

Asp 12.1 (13), Thr 1.
1(1), Ser 10.7(12), Glu 16.
5(15), Pro 7.7(8), Gly 11.1
(10), Ala 6.9 (7), CM-Cys 1.
5(2), Val 1.6(2), Met 1.6
(2), Ile 1.9 (2), Leu 15.
5 (17), Tyr 1.4 (2), Phe 3.
0(3), Trp-(1), His 0.4(
1), Lys 3.6 (4), Arg 11.3
(13) However, the numbers in parentheses are theoretical molar ratios. The molecular weight was 12,883.

Shark CNP (7
Shark CNP (7-115) and shark CNP (78-115) had the amino acid sequences shown by SEQ ID NO: 2 and 3 in the sequence listing below, respectively, and were peptides contained within the structure of shark CNP (1-115). This peptide has the general formula (1) where X is X(17) and X(16). In addition, shark CNP (94-115) obtained from shark brain has the amino acid sequence shown in SEQ ID NO: 4 in the sequence listing below, and shark CNP (1-115), shark CNP (77-115)
and a peptide contained within the structure of shark CNP (78-115). This peptide has the general formula (1) where X is hydrogen and consists of 22 amino acids.

[0020]

[Function] The shark CNP of the present invention has water and natriuretic effects, antihypertensive effects, smooth muscle relaxing effects, and chick rectal specimen relaxing effects. Therefore, it can be used as a therapeutic agent such as a diuretic, an antihypertensive agent, and a vasodilator. For example, it is useful as a diuretic for congestive heart failure where excessive water retention is observed, and in the treatment of hypertension, where vasodilatory effects play an important role. In addition to being used for treatment, it can also serve as a clue for analyzing the fluid balance regulation function of living organisms and elucidating the pathological conditions of patients with circulatory system diseases.

[0021] When administered as a therapeutic agent, it can be administered parenterally such as intravenous injection, intramuscular injection, subcutaneous injection, orally, or locally administered such as eye drops. It is also possible to administer the drug through mucous membranes other than the gastrointestinal tract, such as rectally, sublingually, or intranasally, and in this case, it can be administered in the form of suppositories, sublingual tablets, nasal sprays, and the like. In the case of the present invention, intravenous injection is preferred. The dosage is
It is 0.01 nmol to 100 nmol/kg, and in the case of intravenous injection, the dose is usually dissolved in 1 to 10 ml of physiological saline and used depending on body weight and expected effect.

When the peptide of the present invention is used as a drug, it can be formulated into various forms such as emulsions, wettable powders, tablets, aqueous solutions, powders, granules, capsules, and pills containing the peptide and additives. Can be used. Pharmaceutically acceptable excipients, disintegrants, lubricants, binders, dispersants, plasticizers, fillers, carriers, and the like can be used as additives for the above formulation. Excipients include lactose and glucose, disintegrants include starch and agar powder, lubricants include talc and liquid paraffin, and binders include simple syrup and ethanol.
Examples of dispersants include methyl cellulose and ethyl cellulose, and examples of plasticizers include glycerin and starch.

In addition to shark CNP (1-115), peptides in which the amino acid residues of the X group are deleted one by one from the N-terminus, such as shark CNP (77-115), shark CNP
(78-115) and shark CNP (94-115) also have water/natriuretic, antihypertensive, and smooth muscle relaxing effects.

[0024]

【Example】

[0025]

[Example 1] Isolation and Purification of Shark CNP Only the atrium (7 g), only the ventricle (42 g), and the brain (53 g) were extracted from a shark. Ventricle was used as the material, and after boiling for 5 minutes in 7 times the volume of distilled water and cooling, acetic acid was added to make 1M, and extraction was performed by homogenizing with a Polytron mixer. The obtained extract was heated at 25,000×
The mixture was centrifuged at 16,000 x g for 30 minutes, and cooled acetone was added dropwise to the supernatant to give a concentration of 67%, followed by centrifugation at 16,000 x g for 30 minutes to obtain a supernatant. The supernatant was dried under reduced pressure, the resulting residue was dissolved in 1M acetic acid, acetone was added to make the solution 99%, and the mixture was centrifuged at 16,000 xg for 30 minutes to obtain a precipitate. This precipitate was redissolved in 1M acetic acid, and Sephadex G25
(Pharmacia, 5 x 82 cm, eluent: 1M acetic acid,
Gel filtration and desalting were performed at a flow rate of 85 ml/h, fraction size: 7 ml).

Chick rectal specimen fractions with relaxant activity were collected and subjected to cation exchange high performance liquid chromatography (
(manufactured by JASCO Corporation, IEC-CM, 7.5 x 75 mm, flow rate 1 ml/min, fraction size 4 ml). Ammonium acetate (p) containing 10% acetonitrile
Elution was performed with a linear concentration gradient from 10mM to 1M of H6.8) (80 minutes). Chick rectal specimen fractions with relaxant activity (peak 1, peak 2, peak 3) were obtained (Figure 1)
.

[0027] Reverse phase high performance liquid chromatography (manufactured by Tosoh, ODS-120T, 4.6 × 25
0 mm, flow rate 1 ml/min) from 10% to 60% of acetonitrile containing 0.1% trifluoroacetic acid.
% linear concentration gradient (40 minutes). The active fraction was again subjected to reverse-phase high-performance liquid chromatography (
(same as above) and eluted with a linear concentration gradient from 30% to 50% of acetonitrile containing 0.1% trifluoroacetic acid (40 minutes). Peak 1 made from shark ventricle
8.3 nmol of pure shark CNP (1-1
15) was obtained. Also, from peak 2, shark CNP (77-
115) and shark CNP (78-115) were obtained. Shark CNPs similar to those of the ventricle were also obtained when shark atrium was used as the material. In addition, when shark brain is used as a material, shark CNP (
1-115), shark CNP (94-115) was obtained.

[0028]

[Example 2] Amino acid sequence analysis of shark CNP Each isolated and purified shark CNP was treated with S-carboxyl methylate, and amino acids were determined using a gas phase automated amino acid sequencer (Model 470A/120A, manufactured by Applied Biosystems). The sequence was analyzed. Shark CNP (
1-115), fragments degraded using a peptidase that limitedly degrades only certain amino acid sequences were also subjected to an automatic amino acid sequencer. The enzymatic decomposition treatment was as follows: (1) Using lysyl endopeptidase, 0.1 M sodium bicarbonate (pH 8) containing 4 M urea was used.
．． 3) Treat at 30° C. for 4 hours (LE). (2) Using endoproteinase Asp-N, 1M urea and 20
50mM phosphate buffer containing mM methylamine hydrochloride (
pH 8.0) for 4 hours at 37°C (DN-A)
. (3) Using endoproteinase Glu-C, 1
0.1 M ammonium bicarbonate (pH 7) containing M urea
．． 8) at 37°C for 3 hours (V8). After each of these enzymatic degradation treatments was performed, it was subjected to reverse phase high performance liquid chromatography (under the same conditions as in Example 1), and 0.1%
2% to 50% of acetonitrile containing trifluoroacetic acid
% linear concentration gradient (75 minutes). The peaks where ultraviolet absorption was observed were provided to an automatic amino acid sequencer. The amino acid sequence obtained in this way is shown in FIG.

[0029]

Example 3 Synthesis of shark CNP A peptide having the same amino acid sequence as shark CNP (94-115) obtained in Example 1 was chemically synthesized. Amino acid coupling was performed by the Fmoc method using a fully automatic peptide synthesizer manufactured by Applied Biosystems. The synthesized product was subjected to reverse phase high performance liquid chromatography (Waters PrepLC System).
500). Furthermore, the reverse phase high performance liquid chromatography (Tosoh, ODS
-120T) and this synthetic peptide was purified by natural shark CNP (94-
115) was confirmed to be at the same elution position.

[0030]

[Example 4] The peptide synthesized in Example 3 was dissolved in physiological saline, and a 10-4M solution was prepared as an injection. Using this injection, antihypertensive action, diuretic action, relaxing activity in chick rectal specimens, and smooth muscle relaxing activity were investigated.

Test method [Diuretic effect] and [hypertensive effect] Urine is collected from a cannula inserted into the bladder of an SD rat. At the same time, blood pressure is measured using a cannula inserted into the femoral artery. de
The method of Bold et al. (Life Sci. 28:89
-94, 1981). [Vascular smooth muscle relaxing activity] Method discovered by Currie et al. (Science 221:585-592, 198
4) Measure the relaxing activity of the rat aorta specimen. [Chick rectal specimen relaxing activity] Method discovered by Currie et al. (Science 221:585-592,
The relaxant activity of chick rectal specimens is measured according to (1984). As a result, diuretic effect (Figure 3), antihypertensive effect (Figure 4), chick rectal specimen relaxing activity (Figure 5), and smooth muscle relaxing activity were confirmed.

[0032]

[Example 5] Peptide shark CNP obtained in Example 1
(77-115) and a peptide having the same amino acid sequence as shark CNP (78-115) were chemically synthesized by the method described in Example 3.

[0033]

[Example 6] Regarding the peptide synthesized in Example 5, the same study as in Example 4 was conducted. The results showed that 1 nM administration showed 100% relaxing activity in chick rectal specimens, showing an effect comparable to that of shark CNP (94-115).

[0034]

[Example 7] Shark CNP (1-11
5), the same study as in Example 4 was conducted. It showed relaxing activity in chick rectal specimens.

[0035]

[Effects of the Invention] As detailed above, according to the present invention, a novel peptide can be provided. This peptide exhibits antihypertensive, diuretic, and smooth muscle relaxing effects;
It is useful as a therapeutic agent such as an antihypertensive agent, a diuretic agent, or a vasodilator.Since it is a C-type diuretic peptide with particularly strong smooth muscle relaxing and antihypertensive effects, it is expected to be used as a vasodilator or antihypertensive agent. . In addition to its use as a therapeutic agent, it is also expected to play an important role in regulating body fluid balance and elucidating the causes of hypertension.

[0036]

[Sequence list]

Sequence number: 1 Sequence length: 115 Sequence type: Amino acids Topology: Both types Sequence type: Peptide Originating organism name: Scyliorhinus ca
nicula, Triakis scyllia) Tissue name: Ventricular, atrium, brain Sequence number: 2 Sequence length: 39 Sequence type: Amino acids Topology: Both forms Sequence type: Peptide Originating organism name: Scyliorhinus ca
nicula, Triakis scyllia) Tissue name: Ventricular, atrium, brain Sequence number: 3 Sequence length: 38 Sequence type: Amino acids Topology: Both forms Sequence type: Peptide Originating organism name: Scyliorhinus ca
nicula, Triakis scyllia) Tissue name: Ventricular, atrium, brain Sequence number: 4 Sequence length: 22 Sequence type: Amino acids Topology: Both forms Sequence type: Peptide Originating organism name: Scyliorhinus ca
nicula, Triakis scyllia) Tissue name: brain, ventricle, atrium

[Brief explanation of the drawing]

[Figure 1] Ultraviolet absorbance of each fraction of cation exchange high performance chromatography using shark ventricular tissue as the starting material (
280 nm) and chick rectal specimen relaxant activity compared with human A
Value converted to NP (hANP) activity (black bar)
FIG.

FIG. 2 is a diagram showing the analysis results of the amino acid sequence of shark CNP (1-115).

Figure 3: Various concentrations of shark CNP (d
The natriuretic effect of human ANP (fCNP)
hANP).

Figure 4: Various concentrations of shark CNP (
The antihypertensive effect of human ANP (hANP)
This is a comparison diagram.

FIG. 5 is a diagram comparing the relaxant activity of various concentrations of shark CNP (dfCNP) in chick rectal specimens to that of human ANP (hANP).

Claims (9)

[Claims] Claim 1: A diuretic peptide obtained from the atrium, ventricle or brain of sharks, with no amino acids bonded from the C-terminal cysteine to the C-terminal of the basic skeleton of a diuretic peptide consisting of 17 amino acids, with water and natriuretic properties; A peptide that has antihypertensive and smooth muscle relaxing effects. 2. A peptide represented by the following general formula and a salt thereof. X-Gly-Pro-Ser-Arg-Gly-Cys
-Phe-Gly-Val-Lys-Leu-Asp-
Arg-Ile-Gly-Ala-MetSer-Gl
y-Leu-Gly-Cys-OH (wherein, the X group is hydrogen or H-Arg-Pro-A
rg-Ser-Asp-Asp-Ser-Leu-Gl
n-Thr-Leu-Ser-Arg-Leu-Leu
-Glu-Asp-Glu-Tyr-Gly-His-
Tyr-Leu-Pro-Ser-Asp-Glu-L
eu-Asn-Asn-Glu-Ala-Glu-Gl
u-Met-Ser-Pro-Ala-Ala-Ser
-Leu-Pro-Glu-Leu-Asn-Ala-
Asp-Gln-Ser-Asp-Leu-Glu-L
eu-Pro-Trp-Glu-Arg-Glu-Se
r-Arg-Glu-Ile-Gly-Gly-Arg
-Pro-Phe-Arg-Gln-Glu-Ala-
Val-Leu-Ala-Arg-Leu-Leu-L
ys-Asp-Leu-Ser-Asn-Asn-Pr
o-Leu-Arg-Phe-Arg-Gly-Arg
-Ser-Lys-Lys- or in this sequence, amino acid residues are sequentially 1 from the N-terminus.
The N-terminal hydrogen of the X group may be replaced with Tyr- or a functional group capable of binding to a radioisotope label or avidin. Cystine residues in the peptide may be cross-linked to each other by disulfide bonds. ) 3. The peptide and its salt according to claim 2, which has the amino acid sequence of any one of SEQ ID NOS: 1 to 4. 4. The method for producing the peptide according to claim 1 or 2, which comprises recovering the peptide from cells that produce the peptide according to claim 1 or 2. 5. The method according to claim 4, wherein the recovery is performed by a method including high performance liquid chromatography. 6. A pharmaceutical composition comprising the peptide according to claim 1 or 2 or a salt thereof as an active ingredient and a pharmaceutically acceptable additive. 7. An antihypertensive agent comprising the peptide according to claim 1 or 2 or a salt thereof as an active ingredient. 8. A diuretic comprising the peptide according to claim 1 or 2 or a salt thereof as an active ingredient. 9. A vasodilator comprising the peptide according to claim 1 or 2 or a salt thereof as an active ingredient.