Lysophosphatidic acid induces tyrosine phosphorylation and activation of MAP-kinase and focal adhesion kinase in cultured Swiss 3T3 cells

Lysophosphatidic acid (LPA) added to serum-starved Swiss 3T3 cells induced, in a time- and concentration-dependent manner, tyrosine phosphorylation of multiple proteins, including proteins of 43, 64, 88 kDa and a group of proteins between 110 and 130 kDa. Among them, two proteins, p43 and p120, were identified as mitogen-activated protein kinase (MAP-kinase) and focal adhesion kinase (FAK), respectively, by immunoprecipitation and immunoblot analysis. Tyrosine phosphorylation of p64 peaked at 1 min and declined rapidly, whereas that of MAP-kinase and FAK peaked at 5 and 10 min after the addition of LPA, respectively. The activity of MAP-kinase determined as phosphorylation of myelin basic protein increased transiently about 3-fold at 5 min, and correlated with tyrosine phosphorylation. These results indicate that tyrosine phosphorylation of these proteins is a part of the signal transduction by LPA and may be involved in its mitogenic responses.

ADP-ribosylation of the rhoA gene product by botulinum C3 exoenzyme causes Swiss 3T3 cells to accumulate in the G1 phase of the cell cycle

Using botulinum C3 exoenzyme, which specifically ADP-ribosylates the rho gene products (rho proteins), we examined the role of these proteins in cell cycle progression in Swiss 3T3 cells. Incubation of cell lysates with C3 exoenzyme revealed a single [32P]ADP-ribosylated protein with an M(r) of 23K. This protein was identified as rhoA protein by isoelectric focusing and peptide mapping. When C3 exoenzyme was added to the culture, it ADP-ribosylated the substrate protein in the cells and reduced their growth rate and saturation density. The reduction was dependent on the amount of C3 exoenzyme and on the extent of ADP-ribosylation of the rho protein in the cells. Flow cytometric analysis of logarithmically growing cells showed that the enzyme treatment concentration-dependently accumulated the cells in the G1 phase of the cell cycle. When G1-enriched cells were treated with C3 exoenzyme and cell cycle progression initiated by the addition of serum was monitored, inhibition of G1-S transition was clearly observed. These results suggest that the rhoA gene product plays a critical role in G1-S progression in cultured Swiss 3T3 cells and that the ADP-ribosylation abolishes this activity and causes the cells to accumulate in G1 phase.

Inhibition of PMA-induced, LFA-1-dependent lymphocyte aggregation by ADP ribosylation of the small molecular weight GTP binding protein, rho

Botulinum C3 exoenzyme specifically ADP-ribosylates a group of ras-related small molecular weight GTP-binding proteins, rho, and inhibits their biological activity. Using this enzyme, we examined the function of rho in PMA-induced activation of lymphocyte function-associated antigen-1 (LFA-1) in a B lymphoblastoid cell line, JY. Northern blot analysis revealed that among the three rho genes, rhoA mRNA was predominantly expressed in JY cells. Consistently, only one [32P]ADP-ribosylated band was found when the lysate of the cells was subjected to ADP ribosylation by C3 exoenzyme. When the cells were cultured with C3 exoenzyme, this substrate was ADP-ribosylated in situ in a time- and concentration-dependent manner. Concomitant with this ADP ribosylation, PMA-induced LFA-1/intercellular adhesion molecule (ICAM)-1-dependent aggregation of JY cells was inhibited. This inhibition was blocked by prior treatment of the enzyme with an anti-C3 monoclonal antibody, and overcome by stimulation with higher concentrations of PMA. The C3 exoenzyme-induced inhibition was not affected by shaking of the cell suspension, while inhibition of aggregation by cytochalasin B was abolished by this procedure, suggesting that the inhibitory effect of the C3 exoenzyme treatment was not due to decrease in cell motility. The C3 exoenzyme treatment affected neither protein phosphorylation in JY cells before and after PMA stimulation, nor affected surface expression of LFA-1 and ICAM-1. These results suggest that rhoA protein works downstream of protein kinase C activation linking PMA stimulation to LFA-1 activation and aggregation in JY cells.

A rho gene product in human blood platelets. II. Effects of the ADP-ribosylation by botulinum C3 ADP-ribosyltransferase on platelet aggregation

In the accompanying paper (Nemoto, Y., Namba, T., Teru-uchi, T., Ushikubi, F., Morii, N., and Narumiya, S. (1992) J. Biol. Chem. 267, 20916-20920), we have identified rhoA protein as the sole substrate protein for botulinum C3 ADP-ribosyltransferase (C3 exoenzyme) in human blood platelets. Here we examined the role of rhoA protein in platelet functions. C3 exoenzyme added to washed platelets dose- and time-dependently ADP-ribosylated rhoA protein in situ in the cells. Concomitant with this modification, inhibition of thrombin-induced platelet aggregation was observed. This inhibition was not reversed by washing the treated platelets, but was not found when C3 exoenzyme was pretreated with mouse monoclonal anti-C3 exoenzyme antibody. C3 exoenzyme treatment did not affect thrombin-induced inositol 1,4,5-trisphosphate production. Secretion of preloaded [14C]serotonin was delayed by the enzyme treatment, but the extent of the secretion was not influenced. In addition, the enzyme treatment did not change the expression of the glycoprotein IIb-IIIa complex on the platelet surface. The enzyme treatment also suppressed platelet aggregation induced by phorbol myristate acetate. These results suggest that rhoA protein plays a role mainly in the aggregation process downstream from receptor-phospholipase C coupling. This, together with the previous finding that rhoA protein modulates stress fiber formation in cultured fibroblasts (Paterson, H. F., Self, A. J., Garrett, M. D., Just, I., Aktories, K., and Hall, A. (1990) J. Cell Biol. 111, 1001-1007), suggests that rhoA protein regulates the assembly of actin filaments and the avidity of the platelet integrin (glycoprotein IIb-IIIa) in the aggregation process.

A rho gene product in human blood platelets. I. Identification of the platelet substrate for botulinum C3 ADP-ribosyltransferase as rhoA protein

A substrate protein for botulinum C3 ADP-ribosyltransferase (C3 exoenzyme) in human platelets was purified to apparent homogeneity from the cytosol by ammonium sulfate fractionation and successive chromatography on columns of DEAE-Sepharose, hydroxylapatite, phenyl-Sepharose, and TSK phenyl-5PW. The purified protein yielded an amino acid sequence identical to that of rhoA protein. When platelet cytosol and membranes were incubated with C3 exoenzyme and [32P]NAD and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and isoelectric focusing, they gave only one [32P]ADP-ribosylated band on each electrophoresis that showed an M(r) of 22,000 and a pI of 6.0. The radioactive bands from the two fractions co-migrated with each other and with the [32P]ADP-ribosylated purified protein. When these radioactive products were partially digested with either alpha-chymotrypsin or trypsin and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the same digestion pattern was found in the three samples. These results suggest that the ADP-ribosylation substrate for C3 exoenzyme in the platelet cytosol and membrane is rhoA protein and that it is the sole substrate detectable in human platelets.

[ras oncogene-related small molecular weight GTP-binding protein, rho gene product and botulinum C3 ADP-ribosyltransferase]

The ras oncogene products (ras p21s) are 21-KDa proteins with activities of GTP binding and hydrolysis. A number of proteins homologous to ras p21 have been discovered and collectively named small molecular weight GTP-binding proteins. These proteins undergo post-translational modification with isoprenoid residues attached to cysteine in their carboxyl terminal. With this modification, they attach to cellular membranes. The biochemical activities of these proteins, i.e., GTP hydrolysis and binding, are regulated by various regulatory factors such as GDP-GTP exchange proteins and GTPase-activating proteins, but little is known about the cellular functions and physiological pathways through which they regulate these functions. Botulinum C3 ADP-ribosyltransferase, a 23-KDa exoenzyme secreted from certain strains of types C and D Clostridium botulinum, specifically ADP-ribosylates the rho family of these GTP-binding proteins. This ADP-ribosylation occurs at a specific asparagine residue in their putative effector domain, and presumably interferes with their interaction with a putative effector molecule downstream in signal transduction. C3 exoenzyme, when incubated with or microinjected into cultured cells, ADP-ribosylates a rho gene product in the cells, and causes profound cell rounding with loss of adhesion plaques and collapse of stress fiber. Microinjection of an activated mutant of rho A protein, on the contrary, induced extensive adhesion and actin assembly in cultured cells. These results suggest that the rho family of proteins are involved in morphogenesis and motility of cells via assembly and disassembly of cytoskeletal systems, and botulinum ADP-ribosyltransferase is a useful tool for clarifying the molecular mechanism of these processes.

Purification of GTPase-activating protein specific for the rho gene products

A GTPase-activating protein specific for the rho gene products (rho-GAP) was purified from the cytosol of bovine adrenal gland. Purification procedures consisted of ammonium sulfate fractionation, chromatographies on columns of phenyl-Sepharose and CM-Sepharose, gel filtration on a TSK-gel G3000SW, and Mono S fast protein liquid chromatography. By these procedures the activity was purified about 36,000-fold with a recovery of 0.6%. The final preparation showed a major protein band at Mr 28,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and stimulated GTP hydrolysis by the purified rho A protein in a time- and dose-dependent manner. No stimulation was found for ras p21. The ADP-ribosylation on the rho protein by botulinum C3 exoenzyme did not affect its interaction with the purified rho-GAP.

Immunochemical identification of the ADP-ribosyltransferase in botulinum C1 neurotoxin as C3 exoenzyme-like molecule

Botulinum C1 neurotoxin and C3 exoenzyme were purified to apparent homogeneity from the culture filtrate of Clostridium botulinum type C strain 003-9. Both preparations catalyzed ADP-ribosylation of the same substrate, the Mr 22,000 rho gene product (Gb). When the light and heavy chains of C1 toxin were separated, ADP-ribosyltransferase activity in the toxin was quantitatively recovered in the light chain fraction. Anti-C1 toxin antiserum precipitated the ADP-ribosyltransferase activity and the neurotoxicity of C1 toxin in parallel, whereas it had no effect on C3 exoenzyme. On the other hand, anti-C3 exoenzyme antiserum precipitated the ADP-ribosyltransferase activities of both C3 exoenzyme and C1 toxin. This antibody, however, did not precipitate the neurotoxicity of C1 toxin. The ADP-ribosyltransferase in C1 toxin was quantitatively adsorbed onto the anti-C3 antibody column and separated from the majority of C1 toxin protein. The enzyme was then eluted with acidic urea and Western blotting analysis of this eluate revealed the appearance of a protein band positively stained with anti-C3 antibody at a position similar to that of C3 exoenzyme. Quantitative determination by enzyme-linked immunosorbent assay showed that the C3-like immunoreactivity is present in the C1 toxin molecules at the molecular ratio of 1 to 1,000. These results suggest that the ADP-ribosyltransferase activity in C1 toxin is expressed by a C3-like molecule which is present in a small amount in the toxin preparation and appears to bind to the toxin component(s). The above results also indicate that the ADP-ribosyltransferase in C1 toxin is not related to its neurotoxin action.

ADP-ribosylation of the rho/rac proteins induces growth inhibition, neurite outgrowth and acetylcholine esterase in cultured PC-12 cells

Botulinum ADP-ribosyltransferase C3 (C3 exoenzyme) was purified to homogeneity and added to cultured rat pheochromocytoma PC-12 cells. Incubation with this exoenzyme caused inhibition of cell growth and induced neurites as well as acetylcholine esterase in these cells. These changes were dependent on the amount of the enzyme added to the culture, which correlated with the in situ ADP-ribosylation of the rho/rac proteins in the cells. Preincubation with a specific anti-C3 exoenzyme monoclonal antibody inhibited both the ADP-ribosyltransferase activity and the neurite-inducing activity of the enzyme preparation. These results suggest that C3 exoenzyme affected the cellular function of the rho/rac proteins by ADP-ribosylation to induce these changes in the cells.

Chronic blockade of endogenous atrial natriuretic polypeptide (ANP) by monoclonal antibody against ANP accelerates the development of hypertension in spontaneously hypertensive and deoxycorticosterone acetate-salt-hypertensive rats

To explain the pathophysiological significance of endogenous atrial natriuretic polypeptide (ANP) in the development of hypertension, we examined the effect of chronic, repetitive administrations of MAb raised against alpha-rat ANP in two rat models of hypertension, spontaneously hypertensive rats of the stroke prone substrain (SHR-SP), and deoxycorticosterone acetate (DOCA)-salt rats. Weekly intravenous administrations of MAb with high affinity for alpha-rat ANP, named KY-ANP-II (MAb[KY-ANP-II]), started at the age of 6 wk, significantly augmented the rise in blood pressure of SHR-SP, compared with control SHR-SP treated with another MAb with quite low affinity for alpha-rat ANP, named KY-ANP-I (MAb[KY-ANP-I]), throughout the observation period. The administrations of MAb[KY-ANP-II] had no significant effect on blood pressure of age-matched normotensive Wistar Kyoto rats, compared with those receiving MAb[KY-ANP-I]. Weekly administrations of MAb[KY-ANP-II] also significantly aggravated hypertension in DOCA-salt rats. Blood pressure of DOCA-salt rats treated with MAb[KY-ANP-II] was significantly higher than that of DOCA-salt rats treated with MAb[KY-ANP-I] throughout 8 wk of DOCA and 1% saline administration. The administration of MAb[KY-ANP-II] also significantly attenuated exaggerated diuresis and natriuresis in DOCA-salt rats compared with those treated with MAb[KY-ANP-I]. Elevated plasma cGMP levels of both SHR-SP and DOCA-salt rats were significantly reduced by the administration of MAb[KY-ANP-II]. These results suggest the compensatory role of augmented secretion of ANP in these hypertensive rats and support the concept that augmented secretion of ANP could represent an antihypertensive deterrent mechanism.

Expression of atrial natriuretic factor gene in hearts from neonates of spontaneously hypertensive rats and stroke-prone spontaneously hypertensive rats

In order to further elucidate the expression of the atrial natriuretic factor (ANF) gene in spontaneously hypertensive rats (SHR) and the substrain, stroke-prone SHR (SHRSP), ANF messenger (m)RNA levels in the atrium and in the ventricle were measured in neonates of SHR and SHRSP and were compared with those in control Wistar-Kyoto rats (WKY). The levels of ANF mRNA in ventricles of the three strains reached approximately 7% of those in atria; however, no significant difference was observed in atrial and ventricular ANF mRNA levels among the three strains. These results demonstrate that the expression of the ANF gene in hearts from neonates of WKY, SHR and SHRSP is similar among the three strains.

Exaggerated secretion of atrial natriuretic polypeptide during dynamic exercise in patients with essential hypertension

The plasma concentration of atrial natriuretic polypeptide (ANP) was measured in nine patients with essential hypertension during two grades of exercise tests performed in the supine position on a bicycle ergometer. The plasma ANP concentration significantly increased from 97.0 +/- 19.2 pg/ml to 107.6 +/- 23.7 pg/ml (p less than 0.05) during low-grade exercise (50% of the maximal heart rate) and from 96.2 +/- 16.5 pg to 192.8 +/- 30.7 pg/ml (p less than 0.01) during high-grade exercise (75% of the maximal heart rate). During high-grade exercise plasma epinephrine and norepinephrine concentrations showed significant increases. The plasma ANP concentration was significantly correlated with systolic blood pressure (r = 0.51; p less than 0.05). Patients with essential hypertension showed greater absolute increases in the plasma ANP concentration and systolic blood pressure during exercise compared to normotensive subjects. These results suggest that exercise stimulates secretion of ANP in response to its intensity in patients with essential hypertension and that a greater rise in atrial pressure, resulting from a greater elevation of systolic blood pressure, may be involved in the exaggerated secretion of ANP in patients with essential hypertension.

Purification and properties of the cytosolic substrate for botulinum ADP-ribosyltransferase. Identification as an Mr 22,000 guanine nucleotide-binding protein

The substrate for ADP-ribosyltransferase from Clostridium botulinum was purified from the cytosol of bovine adrenal gland. Purification procedures consisted of ammonium sulfate fractionation, chromatographies on columns of DEAE-Sepharose and phenyl-Sepharose, gel filtration on a TSK-gel G3000SW column, and Mono Q fast protein liquid chromatography. On DEAE-Sepharose chromatography, the substrate activity was eluted in two separate peaks, and electrophoretic analyses revealed that the substrates in the two peaks are of similar molecular weight but different isoelectric points. The major peak of the substrate was further purified. It was purified about 1,800-fold with a recovery of 2.2% by the above procedures. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the final preparation showed a single protein band at Mr 22,000. The purified protein served as a substrate for botulinum ADP-ribosyltransferase and was maximally ADP-ribosylated to the extent of about 0.7 mol of ADP-ribose/mol of protein. A guanosine 5'-(3-O-thio)triphosphate (GTP gamma S) binding activity was co-purified with the ADP-ribosylation substrate, and the purified protein maximally bound about 0.5 mol of GTP gamma S/mol. GTP gamma S binding was effectively competed by GTP and GDP but not by GMP, ATP, and ADP. Thus, the ADP-ribosylation substrate is a GTP-binding protein. This protein, designated Gb (b for botulinum), is widely distributed in various tissues. It was rich in brain, pituitary, and adrenal glands, and poor in heart, smooth, and skeletal muscles.

Gamma-atrial natriuretic polypeptide (gamma ANP)-derived peptides in human plasma: cosecretion of N-terminal gamma ANP fragment and alpha ANP

Using RIAs for the N- and C-terminal fragments of the human atrial natriuretic polypeptide (ANP) precursor gamma ANP, that is gamma ANP-(1-25), and alpha ANP [gamma ANP-(99-126)], we studied the secretion of gamma ANP-derived peptides from the heart in normal subjects and patients with heart disease, chronic renal failure, and cirrhosis. We detected gamma ANP-(1-25)-like immunoreactivity (-LI) in plasma from normal subjects (n = 17) in considerable amounts [mean, 510 +/- 62 (+/- SE) pg/mL (174 +/- 21 pmol/L)]; the mean plasma alpha ANP-LI level at the same time in these subjects was 32.8 +/- 4.4 pg/mL (10.7 +/- 1.4 pmol/L). Gel permeation chromatographic analysis of plasma samples from normal subjects and patients with heart disease and chronic renal failure revealed two major components; one was alpha ANP, and the other was the 10K N-terminal gamma ANP fragment (N-peptide) resulting from the removal of alpha ANP (3K) from gamma ANP (13K). In addition, gamma ANP (13K), which possessed both gamma ANP-(1-25)-LI and alpha ANP-LI, and beta ANP, an antiparallel dimer of alpha ANP, were detected in some patients as minor components. A significant positive correlation between plasma levels of the N-terminal gamma ANP fragment and alpha ANP (P less than 0.01) and almost equal step-ups in the coronary sinus plasma levels of the N-terminal gamma ANP fragment and alpha ANP suggest that they are cosecreted in equimolar amounts. The high molar ratio of plasma gamma ANP-(1-25)-LI to alpha ANP-LI (17.4 +/- 1.4) in normal subjects and the significantly higher ratio in patients with chronic renal failure (36.9 +/- 7.1; P less than 0.01) suggest the slower clearance of the N-terminal gamma ANP fragment than alpha ANP and a role for the kidney in its degradation. Since the molar ratio of plasma gamma ANP-(1-25)-LI to alpha ANP-LI in patients with cirrhosis (20.7 +/- 2.7) was similar to that in normal subjects, it is unlikely that the N-terminal gamma ANP fragment is metabolized by the liver. In patients with heart disease, plasma gamma ANP-(1-25)-LI and alpha ANP-LI levels were higher in those with cardiac decompensation and were positively correlated with right atrial pressure, pulmonary arterial pressure, and pulmonary capillary wedge pressure, indicating cosecretion of the N-terminal gamma ANP fragment and alpha ANP in response to atrial stretch.(ABSTRACT TRUNCATED AT 400 WORDS)

A monoclonal antibody to alpha-human atrial natriuretic polypeptide

A monoclonal antibody to alpha-human atrial natriuretic polypeptide (alpha-hANP), KY-ANP-I, has been produced by fusion of a nonproducing mouse myeloma cell line, X63-Ag8.653, with spleen cells from BALB/c mice immunized with synthetic alpha-hANP conjugated to bovine thyroglobulin using the carbodiimide coupling procedure. Hybridomas were screened for antibody production by radioimmunoassay using culture media and 125I-alpha-hANP. They were cloned by the limiting dilution technique, expanded in culture, and injected intraperitoneally into BALB/c mice. The obtained antibody belonged to the immunoglobulin G1 subclass. Analysis by a Scatchard plot revealed a high affinity for alpha-hANP, with an association constant of 3.1 x 10(10) M-1. With this monoclonal antibody, a specific radioimmunoassay for alpha-hANP has been established. The antibody in mouse ascites was available for radioimmunoassay at a final dilution of 1:10(6). Values of IC10 and IC50 in this radioimmunoassay were 3 and 30 fmol/tube, respectively. The radioimmunoassay showed a cross-reactivity of 0.9% with alpha-rat ANP. alpha-hANP-(8-22) and alpha-ANP-(1-6) exhibited less cross-reactivity than alpha-rat ANP on a molar basis. There was no cross-reaction with alpha-ANP-(17-28). Thus, the recognized epitope must be located in the N-terminal half of the ring structure of alpha-hANP including Met12 residue. This radioimmunoassay could detect gamma-hANP and beta-hANP as well as alpha-hANP. The monoclonal antibody was also useful for immunohistochemical studies. ANP-positive cells were finely stained in the human atrium using the avidin-biotin-peroxidase complex technique.(ABSTRACT TRUNCATED AT 250 WORDS)

Potent depressor action of leumorphin, a kappa-opioid agonist, in conscious rats

To investigate the role of leumorphin, a kappa-opioid agonist derived from proenkephalin B (neoendorphin/dynorphin precursor) in the central cardiovascular control, the effects of intracerebroventricular (ICV) administration of leumorphin on basal blood pressure and angiotensin II (AII)-stimulated pressor response were examined in conscious unrestrained rats. The ICV injection of 0.06 and 0.6 nmol of leumorphin caused a significant decrease in basal blood pressure (delta mean arterial pressure (MAP): -6.5 +/- 2.7 and -7.2 +/- 1.7 mm Hg, respectively). The ICV injection of AII (0.1 nmol) elicited a pressor response (delta MAP: 21.4 +/- 1.1 mm Hg). This pressor response was significantly reduced by the simultaneous administration of leumorphin, and furthermore, the blood pressure was lowered below the basal level. These depressor actions of leumorphin were partially antagonized by the preadministration of naloxone, an opiate antagonist. These results together with our previous works on the potent inhibitory actions of leumorphin on drinking and vasopressin secretion suggest the possible involvement of leumorphin in the central regulation of blood pressure and body fluid homeostasis.

Atrial natriuretic polypeptide in bovine adrenal medulla

Two radioimmunoassays for alpha-human atrial natriuretic polypeptide (alpha-hANP) with different specificities were used to study the tissue level and the nature of alpha-hANP-like immunoreactivity in the bovine adrenal gland. A considerable amount of alpha-hANP-like immunoreactivity was detected in the adrenal medulla (90.8 +/- 21.1 and 90.0 +/- 23.1 ng/g with the two radioimmunoassays), while no detectable amount (less than 1.0 ng/g) was present in the cortex. Gel permeation chromatographic analysis showed that ANP in the medulla is composed of two components of alpha-hANP-like immunoreactivity with high and low molecular weights in the approximate ratio of 2:1, eluting at the elution positions of gamma-hANP and alpha-hANP, respectively. Reverse-phase high performance liquid chromatographic analysis revealed that alpha-hANP-like immunoreactivity with a low molecular weight in the medulla consists of two major components, which comigrate with synthetic alpha-hANP(5-28) and alpha-hANP. When cultured bovine adrenal chromaffin cells were incubated in the presence of nicotine (10(-5) M), alpha-hANP-like immunoreactivity was released into the medium concomitantly with catecholamines from chromaffin cells. These findings indicate that a discrete ANP system is present in the adrenal medulla and that ANP is cosecreted with catecholamines from chromaffin cells, suggesting the possible involvement of ANP in the adrenomedullary function.

Effects of intravenously administered beta-human atrial natriuretic polypeptide in humans

beta-Human atrial natriuretic polypeptide (beta-hANP) is an antiparallel dimer of alpha-human ANP (alpha-hANP) that was isolated from human atria. Using synthetic beta-hANP and a radioimmunoassay for alpha-hANP that also detects beta-hANP, we have previously demonstrated that beta-hANP is converted into alpha-hANP in human plasma in vitro. In the present study, we compared the effects of intravenous administration of beta-hANP (100 micrograms) to five normal human volunteers with those of an equimolar administration of alpha-hANP (50 micrograms) to the same subjects, and we also investigated the possible mechanisms of actions of beta-hANP. Although the administration of alpha-hANP caused a significant decrease in blood pressure with a reactional increase of heart rate, beta-hANP elicited minimal change of blood pressure. In contrast, beta-hANP exerted more potent and longer lasting diuretic and natriuretic activities than did alpha-hANP. Net changes in urine volume and sodium excretion induced by beta-hANP (579 +/- 65 ml, 56.0 +/- 9.9 mEq) were significantly greater than those elicited by alpha-hANP (396 +/- 50 ml, 34.7 +/- 4.9 mEq; p less than 0.05, respectively). The administration of beta-hANP revealed a longer retention of the ANP-like immunoreactivity level in plasma, compared with that of alpha-hANP. High performance gel permeation chromatography coupled with the radioimmunoassay revealed that beta-hANP (Mr = 6000) was also converted into alpha-hANP (Mr = 3000) in human plasma in vivo. The demonstrated conversion of beta-hANP into alpha-hANP could be relevant to the observed effects of beta-hANP in humans.

Synthesis of atrial natriuretic polypeptide in human failing hearts. Evidence for altered processing of atrial natriuretic polypeptide precursor and augmented synthesis of beta-human ANP

To elucidate the synthesis of atrial natriuretic polypeptide (ANP) in the failing heart, 20 human right auricles obtained at cardiovascular surgery were studied. The concentration of alpha-human ANP-like immunoreactivity (alpha-hANP-LI) in human right auricles ranged from 13.8 to 593.5 micrograms/g, and the tissue alpha-hANP-LI concentration in severe congestive heart failure (CHF) (New York Heart Association [NYHA] functional class III and class IV) (235.4 +/- 57.2 micrograms/g) was much higher than that in mild CHF (NYHA class I and class II) (52.5 +/- 15.6 micrograms/g). Atrial alpha-hANP-LI levels were significantly correlated with plasma concentrations of alpha-hANP-LI in these patients (r = 0.84, P less than 0.01). High performance gel permeation chromatography and reverse phase high performance liquid chromatography coupled with radioimmunoassay for ANP revealed that the alpha-hANP-LI in the human auricle consisted of three major components of ANP, gamma-human ANP (gamma-hANP), beta-human ANP (beta-hANP) and alpha-human ANP (alpha-hANP). Comparing percentages of gamma-hANP, beta-hANP, and alpha-hANP in alpha-hANP-LI in severe CHF with those in mild CHF, the predominant component of alpha-hANP-LI was gamma-hANP in mild CHF, whereas beta-hANP and/or alpha-hANP were prevailing in severe CHF and, especially, beta-hANP was markedly increased in human failing hearts. These results demonstrate that the total ANP concentration in the atrium of the human heart is increased in severe CHF and that the increase of ANP in the human failing heart is mainly due to the increase of small molecular weight forms of ANP, beta-hANP, and alpha-hANP, especially beta-hANP, and indicate that the processing of ANP precursor, or gamma-hANP, in the human failing heart differs from that in the normal heart, suggesting that the failing heart augments synthesis and secretion of ANP as one of its own compensatory responses.

Augmented expression of atrial natriuretic polypeptide gene in ventricles of spontaneously hypertensive rats (SHR) and SHR-stroke prone

Tissue levels of atrial natriuretic polypeptide (ANP) and ANP messenger RNA (mRNA) in the atrium and ventricle were measured simultaneously in spontaneously hypertensive rats (SHR) and its substrain, SHR-stroke prone (SHRSP), and these levels were compared with those in control Wistar-Kyoto rats (WKY). At 27 weeks of age with established hypertension and ventricular hypertrophy, ANPmRNA levels in ventricles from SHR and SHRSP were markedly increased, and total contents of ventricular ANPmRNA in SHR and SHRSP were approximately 50% and 250%, respectively, of the corresponding atrial contents. However, levels and total contents of atrial ANPmRNA in SHR and SHRSP were similar to those of WKY, and the total content of ventricular ANPmRNA in WKY was only 6% of the content of atrial ANPmRNA. ANP concentrations in ventricles of SHR and SHRSP were increased in association with the augmentation of ANPmRNA levels. During the prehypertensive stage at 6 weeks of age, slight increases in levels and total contents of ANPmRNA and ANP in the ventricle were observed only in SHRSP. These results demonstrate that the expression of the ANP gene is markedly augmented in ventricles of SHR and SHRSP, especially of SHRSP, at the stage of established hypertension and ventricular hypertrophy, and they also suggest that these genetically hypertensive rats are one of the best animal models to investigate the biosynthesis, storage, and secretion of ventricular ANP.