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Biomedical subjects

R Kato

Publications and source records attributed to R Kato.

At least 595 records · Page 33Linked to original sources
PubMed1983

Interactions between the active metabolite of tryptophan pyrolysate mutagen, N-hydroxy-Trp-P-2, and lipids: the role of lipid peroxides in the conversion of N-hydroxy-Trp-P-2 to non-reactive forms.

The interactions between lipids and the mutagenic active metabolite of 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) and 3-hydroxyamino-1-methyl-5H-pyrido[4,3-b]indole (N-hydroxy-Trp-P-2), were studied. Oleic acid showed an inhibitory effect on the formation of this active metabolite mainly by inhibition of hepatic microsomal oxidation systems. On the other hand, microsomal lipids from rat liver and commercial pig liver lecithin diminished the amount of N-hydroxy-Trp-P-2 without inhibiting the metabolism of Trp-P-2. The direct reaction of these lipids with N-hydroxy-Trp-P-2 was disclosed by experiments using N-hydroxy-Trp-P-2 and lipids without microsomes. Furthermore, the participation of lipid peroxides in this reaction was suggested by a linear relationship between the concentrations of the conjugated diene of lipids and the disappearance of N-hydroxy-Trp-P-2. When [3H]N-hydroxy-Trp-P-2 was incubated in the presence of pig liver lecithin, the polar products which were not formed in the incubation without lipids were newly detected by thin-layer chromatography (TLC) analysis.

Animals↗
PubMed1983

Metabolic activation of Trp-P-2, a tryptophan-pyrolysis mutagen, by isolated rat hepatocytes.

Metabolic activation of a tryptophan-pyrolysis product, 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), by isolated rat hepatocytes was studied. The substrate (Trp-P-2) disappearance by hepatocytes from untreated rats was slow, but enhanced by 3-methylcholanthrene (MC) pretreatment of rats. The covalent binding of Trp-P-2 to cellular macromolecules was detected in hepatocytes from untreated rats. The amount of covalent binding of Trp-P-2 to protein and RNA was greater than that to DNA. The covalent binding to Trp-P-2 to DNA, RNA and protein in hepatocytes from untreated rats was about 5-10 times less than that in hepatocytes from MC-pretreated rats. 7,8-Benzoflavone strongly inhibited the substrate disappearance and the binding of Trp-P-2 to DNA in hepatocytes from MC-pretreated rats. These results indicate that Trp-P-2 is metabolically activated by the P-448 type of cytochrome P-450 which is induced by MC. Diethylmaleate enhanced by about 50% the binding of Trp-P-2 to DNA in hepatocytes from MC-pretreated rats. On the other hand, cysteine inhibited the binding of Trp-P-2 to DNA with a concomitant reduction in the accumulation of the active metabolite, N-hydroxy-Trp-P-2 (N-OH-Trp-P-2). Sulfhydryl compounds seemed to play important roles in the detoxification of Trp-P-2.

Animals↗
PubMed1983

Protection against alloxan-induced diabetes in mice by stimulation of alpha 2-adrenergic receptors.

A single intravenous injection of alloxan in mice induced hyperglycemia in a dose dependent fashion. This diabetogenic action of alloxan was prevented by a single intraperitoneal injection of the alpha 2-adrenergic agonists, i.e. oxymetazoline, clonidine or epinephrine 40 min prior to the injection of alloxan. The alpha 1-adrenergic agonists, i.e. methoxamine and phenylephrine, and a beta-adrenergic agonist, isoproterenol, failed to prevent the diabetogenic action of alloxan. The inhibitory effect of clonidine on alloxan-induced diabetes was antagonized by yohimbine or phentolamine, but not by prazosin. Although alpha 2-adrenergic agonists caused a transient hyperglycemia at the time of alloxan administration (40 min after the administration of alpha 2-adrenergic agonists), the plasma glucose level at the time of alloxan injection did not correlate with the anti-diabetogenic effect of alpha 2-adrenergic agents. These results clearly demonstrate that the alpha 2-adrenergic mechanism which inhibits insulin release from pancreatic B cells prevented the diabetogenic action of alloxan in mice.

Adrenergic alpha-Agonists↗
PubMed1983

Inhibition of dibutyryl cyclic AMP-induced insulin release by alpha-2 adrenergic stimulation.

Effects of alpha adrenergic agonists and antagonists on dibutyryl cAMP (Bt2cAMP)-induced insulin release were investigated with isolated rat pancreatic islets. Bt2cAMP (4 mM) produced 2-fold stimulation of insulin release in all the concentrations of glucose examined (3.3-16.7 mM). Clonidine but not phenylephrine inhibited the Bt2cAMP-stimulated insulin release in a concentration-dependent manner with approximate EC50 of nanomolar range. Yohimbine but not prazosin antagonized the inhibitory effect of clonidine on the Bt2-cAMP-induced insulin release. These results suggest that alpha-2 adrenergic mechanisms are involved in a step distal to cAMP generation.

Adrenergic alpha-Agonists↗
PubMed1983

Comparative evaluation of depressed automaticity in sick sinus syndrome by Holter monitoring and overdrive suppression test.

To ascertain whether the long cardiac pauses on the Holter ECGs of patients with the sick sinus syndrome were related to the spontaneously occurring overdrive suppression, the heart rates for the 12 seconds preceding the cardiac pauses longer than 5 seconds were compared with that averaged for 24 hours. Even in six out of seven patients with bradycardia-tachycardia syndrome the former rate was not significantly greater than the latter, indicating that episodes of such long cardiac pauses may not result from spontaneously occurring overdrive suppression. This observation was also consistent with the result that no statistically significant correlation was obtained between the maximum pauses measured from Holter ECGs of sick sinus syndrome and those obtained by the overdrive suppression test. In conclusion, many episodes of long life-threatening cardiac pauses observed in sick sinus syndrome may be attributed to accidental depression of the sinus nodal and subsidiary pacemaker activity rather than to spontaneously occurring overdrive suppression; therefore, Holter monitoring may be useful as an additional tool for diagnosis of sick sinus syndrome.

Adolescent↗
PubMed1983

Experimental studies on sick sinus syndrome: relationship of extent of right atrial lesions to subsidiary pacemaker shift and its function.

An area where the sinus node was located in 36 dogs was defined as the "SN-area." Five to 7 days after cauterization of the SN-area, a subsidiary pacemaker remained in the SN-area in seven (group S) and shifted to outside the SN-area in 14 dogs (group E). The SN-area in group S had escaped complete destruction, but that in group E was destroyed completely. Heart rate in group S and group E was 154.0 +/- 27.1 and 107.6 +/- 16.8 beats/min (p less than 0.001), respectively. Maximum duration of asystole after overdrive (maxDAO) in group S and group E was 656.7 +/- 260.2 and 2470.2 +/- 2271.6 msec (p less than 0.01), respectively. Propranolol (0.2 mg/kg intravenously) decreased heart rate in group S and group E to 88.3 +/- 7.9 and 71.7 +/- 8.7% (p less than 0.001), and prolonged maxDAO to 140.1 +/- 28.1 and 492.7 +/- 591.4% (p less than 0.025), respectively. It is concluded that the rate and stability of subsidiary pacemakers after cauterization of the sinus node have a close relationship with their location in the right atrium, which is dependent on the extent of lesions in the SN-area. Sympathetic tone played a significant role in maintaining these functions in group E.

Animals↗
PubMed1983

Sex difference of cytochrome P-450 in the rat: purification, characterization, and quantitation of constitutive forms of cytochrome P-450 from liver microsomes of male and female rats.

One of each constitutive form of cytochrome P-450 from liver microsomes of adult male and female rats was purified essentially following the same method to an apparent homogeneity as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The molecular weights estimated by the electrophoresis were 52,000 and 50,000 for forms of cytochrome P-450, P-450-male, and P-450-female, purified from male and female rats, respectively. In addition, the purified preparations of P-450-male and P-450-female showed properties different from each other with respect to spectral characteristics and catalytic activities. In Ouchterlony double diffusion plates, partially purified rabbit immunoglobulin G (IgG) raised against P-450-male and P-450-female showed very weak or no cross-reactivity with P-450-female and P-450-male, respectively. From these results, P-450-male was confirmed to be a form distinct from P-450-female. The anti-P-450-male and anti-P-450-female antibodies, which had been further purified by immunoadsorption, did not form any apparent precipitation bands with liver microsomes from untreated female and male rats, respectively. Supporting this, radial immunodiffusion analysis for P-450-male and P-450-female with an agarose gel impregnated with the rabbit antibodies showed that P-450-male and P-450-female appear in liver microsomes rather specifically depending on the sex hormones. Based on these results, sex differences in drug metabolism in the rat were confirmed as explicable, at least in part, by the presence of distinct forms of cytochrome P-450 in microsomes of male and female rats.

Animals↗
PubMed1983

Inhibition of 12-O-tetradecanoylphorbol-13-acetate-induced tumor promotion and ornithine decarboxylase activity by quercetin: possible involvement of lipoxygenase inhibition.

Quercetin (30 mumol/mouse) markedly suppressed the effect of 12-O-tetradecanoylphorbol-13-acetate (TPA, 20 nmol/mouse) on skin tumor formation in the CD-1 mice initiated by 7,12-dimethylbenz[a]anthracene (200 nmol/mouse). TPA (20 nmol/mouse)-induced epidermal ornithine decarboxylase (ODC) activity was also inhibited by quercetin (10-30 mumol/mouse), but it failed to inhibit the stimulation of epidermal DNA synthesis by TPA. In addition, quercetin potently inhibited lipoxygenase from 105 000 g supernatant of epidermal homogenate of mice. The 50% inhibition of lipoxygenase was observed by quercetin at 1.3 microM. These results suggest that the inhibition of lipoxygenase by quercetin is one of the major actions of the above agent to inhibit tumor promotion and TPA-induced ODC activity.

Animals↗
PubMed1983

Syntheses of hydroxyamino, nitroso and nitro derivatives of Trp-P-2 and Glu-P-1, amino acid pyrolysate mutagens, and their direct mutagenicities towards Salmonella typhimurium TA98 and TA98NR.

Hydroxyamino, nitroso and nitro derivatives of 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) and 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1), mutagens-carcinogens produced on pyrolysis of amino acids, were synthesized from Trp-P-2 and Glu-P-1. 3-Hydroxyamino-1-methyl-5H-pyrido[4,3-b]indole (N-OH-Trp-P-2) and 2-hydroxyamino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (N-OH-Glu-P-1) were obtained with good yields by controlled catalytic reduction of 3-nitro-1-methyl-5H-pyrido[4,3-b]indole and 2-nitro-6-methyldipyrido[1,2-a:3',2'-d]imidazole. Subsequent oxidation of N-OH-Trp-P-2 and N-OH-Glu-P-1 with gamma-manganese dioxide yielded 3-nitroso-1-methyl-5H-pyrido[4,3-b]indole and 2-nitroso-6-methyldipyrido[1,2-a:3',2'-d]imidazole. All six synthesized compounds were mutagenic to Salmonella typhimurium TA98 without mammalian activation systems. The mutagenic activities of hydroxyamino and nitroso derivatives were identical for both S. typhimurium TA98 and TA98NR, the nitroreductase deficient strain. However, nitro derivatives were essentially mutagenic only towards S. typhimurium TA98.

Carbolines↗
PubMed1983

Activation and detoxication of N-hydroxy-Trp-P-2 by glutathione and glutathione transferases.

The roles of non-enzymatic and enzymatic glutathione (GSH) conjugation in the activation and detoxication of 3-hydroxy-amino-1-methyl-5H-pyrido[4,3-b]indole (N-OH-Trp-P-2) were studied in vitro. N-OH-Trp-P-2 is an active metabolite of 3-amino-1-methyl-5H-pyrido[4,3-d]indole (Trp-P-2), a mutagenic and carcinogenic heterocyclic amine. 3-Nitroso-1-methyl-5H-pyrido[4,3-b]indole (NO-Trp-P-2) reacted rapidly and non-enzymatically with GSH to form N-OH-Trp-P-2 and a small amount of two GSH conjugates (CN-1 and CN-2). On the other hand, non-enzymatic reaction of GSH with N-OH-Trp-P-2 was very slow, but the GSH conjugation with N-OH-Trp-P-2 was catalyzed by rat liver GSH transferase and a rat liver cytosol fraction to form three conjugates (CH-1, CH-2 and CH-3). The enzymatic conjugation was effectively inhibited by organic tin compounds which are known as powerful GSH transferase inhibitors. The conjugates were unstable enough to yield Trp-P-2 (from CN-1, CN-2 and CH-2) or N-OH-Trp-P-2 (from CH-3) on incubation at 37 degrees C for 30-60 min. Only CH-1 was stable under similar conditions. The mutagenicities of the GSH conjugates and the effects of GSH and GSH transferase were studied by using Salmonella typhimurium TA98 as the tester strain. The GSH conjugates except for CH-3 were completely detoxicated products, but CH-3 was found to be a more potent mutagen than N-OH-Trp-P-2. The mutagenicity of CH-3 seemed to be due to the direct action of the conjugate, and not to N-OH-Trp-P-2 formed from it.

Animals↗
PubMed1983

Specificity of hepatic cytochrome P-450 isoenzymes from PCB-treated rats and participation of cytochrome b5 in the activation of aflatoxin B1.

Employing six forms of cytochrome P-450s fractionated from the hepatic microsomes of PCB-treated rats, the activation of aflatoxin B1 (AFB1) was examined in the reconstituted cytochrome P-450 system. AFB1 was specifically activated into DNA-binding form by cytochrome P-450 I-a, which is one of P-450 type cytochromes and possesses an absorption peak at 450.0 nm in its carbon monoxide difference spectrum. This activation was enhanced by cytochrome b5 and the maximal enhancement (1.6-fold of the control) was observed with the molar ratio of 0.25 cytochrome b5:1.0 cytochrome P-450.

Aflatoxin B1↗
PubMed1983

N-hydroxylation of carcinogenic and mutagenic aromatic amines.

N-Hydroxylation and mutagenic activation of heterocyclic aromatic amines from protein pyrolysis products were studied in rat liver microsomes and nuclei, rat hepatocytes and various species of purified cytochrome P-450. These mutagenic amines include Trp-P-2 (3-amino-1-methyl-5H-pyrido[4,3-b]indole), Trp-P-1 (3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole), Glu-P-1 (2-amino-6-methyldipyrido-[1,2-a:3',2'-d]imidazole), Glu-P-2 (2-amino-dipyrido[1,2-a:3',2'-d]imidazole) and IQ (2-amino-3-methyl-3H-imidazo-[4,5-f]quinoline). The number of revertants of Salmonella typhimurium TA 98 was always correlated to the amount of each of the N-hydroxylated metabolites in various experimental conditions. The N-hydroxylated amines covalently bound to DNA directly or after being acylated with amino acids by amino-acyl-tRNA synthetase. Various species of cytochrome P-450 preparations showed markedly different activity in N-hydroxylation and mutagenic activation of Trp-P-2, Glu-P-1 and IQ. A high spin form of cytochrome P-450, isolated from the liver of PCB-treated rats, showed very high activity in N-hydroxylation of Trp-P-2, Glu-P-1 and 2-aminofluorene, although its activity was very low in benzo(a)pyrene hydroxylation. The present results indicate that different species of cytochrome P-450 are involved in the N-hydroxylation and mutagenic activation of aromatic amines.

Amines↗
PubMed1983

Mechanism of morphine in increasing plasma cyclic GMP level in male mice.

Morphine given systemically or centrally increases the plasma concentration of cyclic GMP in male, ddY strain mice. Normorphine also increased the plasma cyclic GMP level, whereas the same dose of ketocyclazocine and SKF 10,047 had no effect. The effect of morphine on plasma cyclic GMP was mimicked by opioid peptides such as (D-Ala2, Met)-enkephalinamide, FK 33,824 or beta-endorphin. The effect of morphine and opioid peptides on plasma cyclic GMP was antagonized by naloxone, indicating the involvement of the opiate receptor. The increase in plasma cyclic GMP elicited by morphine was abolished by vagotomy and pretreatment with hexamethonium and atropine and was partly inhibited by pretreatment with phentolamine. Adrenalectomy and pretreatment with propranolol, which inhibited the increase in plasma cyclic AMP level elicited by morphine (Muraki et al., 1979), did not alter the cyclic GMP response to morphine. The development of tolerance to the cyclic GMP increase was observed in morphine-tolerant/dependent mice. These results suggest that morphine increases the plasma cyclic GMP level by activating the preganglionic parasympathetic tone via the stimulation of the opiate receptors, thereby increasing the generation of cyclic GMP through the muscarinic receptors on the effector cells.

Adrenalectomy↗
PubMed1983

A high-spin form of cytochrome P-450 highly purified from polychlorinated biphenyl-treated rats. Catalytic characterization and immunochemical quantitation in liver microsomes.

A high-spin form of cytochrome P-450 (termed PCB P-448-H) was purified from liver microsomes of polychlorinated biphenyl (PCB)-treated rats to homogeneity as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This high-spin form of cytochrome P-450 was distinguishable from a low-spin form of cytochrome P-450 (PCB P-448-L) purified from microsomes of PCB-treated rats by the criteria of molecular weights, peptide mapping, and immunochemical properties. In addition, PCB P-448-H catalyzed the hydroxylation of acetanilide (position 4) and biphenyl (positions 2 and 4), and N-hydroxylation of the promutagens 3-amino-1-methyl-5H-pyrido(4,3-b)indole (Trp-P-2), 2-amino-6-methyl-dipyrido(1,2-alpha:3',2'-d)imidazole (Glu-P-1), 2-aminofluorene, and 4-aminobiphenyl at much faster rates than did PCB P-448-L. These promutagens and aflatoxin B1 were efficiently metabolized to mutagens by this high-spin form of hemoprotein. Rabbit immunoglobulin G (IgG) raised against PCB P-448-H inhibited the microsomal O-depropylation activity of p-propoxyaniline. Radial immunodiffusion assay with the IgG showed that PCB P-448-H was one of the major forms of cytochrome P-450 in liver microsomes of PCB-treated rats. On the basis of these results, we propose that this high-spin form of cytochrome P-450 is a key enzyme activating a variety of environmental promutagens in the 9000 x g supernatant fraction of PCB-treated rats, which has been widely used as an activation system in routine mutation tests.

Animals↗
PubMed1983

Microsomal activation of 2-amino-3-methylimidazo[4,5-f]quinoline, a pyrolysate of sardine and beef extracts, to a mutagenic intermediate.

The mechanism involved in the metabolic activation of 2-amino-3-methylimidazo[4,5-f]quinoline, which is a pyrolysate isolated from broiled foods, to a mutagenic intermediate was studied in vitro. In a system containing hepatic microsomes and reduced nicotinamide adenine dinucleotide phosphate, 2-amino-3-methylimidazo[4,5-f]quinoline was converted to a product which was directly mutagenic to Salmonella typhimurium. The structure of the mutagenic metabolite was determined as the 2-N-hydroxy derivative on the basis of the chemical properties and the mass spectral evidence of the azoxy adduct with o-nitrosotoluene. The activation reaction was mediated by microsomal enzymes and was inhibited by carbon monoxide, 7,8-benzoflavone, and other chemicals which were known to inhibit the cytochrome P-450-dependent reaction. With the use of four forms of purified cytochrome P-450, the N-hydroxylation of 2-amino-3-methylimidazo[4,5-f]quinoline and the induction of the reverse mutation of the bacteria were clearly demonstrated to be catalyzed mainly by a high-spin form of cytochrome P-450, P-448 II-a.

Animals↗