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Biomedical subjects

R Takayanagi

Publications and source records attributed to R Takayanagi.

At least 145 records · Page 8Linked to original sources
PubMed1985

Biochemical studies of rat atrial natriuretic factor.

The natriuretic substances were purified from rat atrium (ANF, atrial natriuretic factor) and were shown to be identical with the inhibitor of norepinephrine-induced contraction of smooth muscle. Their four native forms were isolated. Amino acid sequence analyses showed they are peptides with 35, 31, 30 and 25 amino acid residues respectively and contain a ring structure consisting of 17 amino acid residues and a disulfide bridge. The presence of a high molecular weight prohormone was shown. cDNA coding for the precursor was cloned and used to deduce the amino acid sequence of the preprohormone. Genomic DNA for ANF was cloned and the presence of two introns were found. Several ANF peptides were synthesized. Structure-function studies showed that the ring structure is essential for the activity. Antibodies produced against the synthetic 25 amino acid residue ANF were used to develop radioimmunoassay. The presence of ANF in rat plasma was demonstrated as evidence that ANF is a circulating hormone. ANF was also found in the hypothalamus of rats. The quantitative determination of the synthetic ability of ANF has been determined by the application of ANF cDNA for the quantification of ANF messenger RNA. Immunohistochemical methods localized ANF in cardiac atriocytes, gonadotrophs in anterior pituitary and adrenal medulla (chromaffin cells). A strong immuno-reactivity was found in dark cells of the collecting ducts of the kidney. ANF increases cyclic GMP in target cells suggesting that cyclic GMP may be the intracellular mediator of ANF action.

Adrenal Cortex↗
PubMed1984

Atrial natriuretic factor: purification of active peptides, cloning of cDNA and determination of structures of active peptides and precursors.

Four peptides possessing both natriuretic and smooth muscle relaxant activities were purified from rat heart atrium and their amino acid sequences were determined. All contained a common sequence which contains a macro-ring structure formed by 17 amino acid residues and a disulphide bridge. The major atrial peptide in the atrium was identified as that containing 31 amino acid residues. The cDNA of the atrial peptide precursor was cloned and its nucleotide sequence determined. The amino acid sequence of the precursor deduced from the nucleotide sequence contained 152 residues and a potential signal peptide sequence characteristic of secretory polypeptides.

Amino Acid Sequence↗
PubMed1982

Superoxide-forming NADPH oxidase preparation of pig polymorphonuclear leucocyte.

A phagocytic vesicle fraction with high NADPH-dependent superoxide-forming activity was obtained in large quantity from pig blood polymorphonuclear leucocytes, phagocytosing oil droplets in the presence of cyanide. The activity of the homogenate of the phagocytosing cells was 40 times that of the resting cells, and 70% of the activity in the homogenate was recovered in the phagocytic vesicle fraction. Essentially all of the superoxide-forming activity was extracted by repeated extraction with a mixture containing deoxycholate and Tween 20. The extract had a superoxide-forming activity of 1 mumol/min per mg of protein with NADPH, and one-fifth of this with NADH, Km values being similar to those of the vesicle fraction (40 microM for NADPH and 400 microM for NADH). A stoichiometric relationship of 1:2 for NADPH oxidation and superoxide formation was obtained, in agreement with the reaction NADPH +2O2 leads to NADP+ + 2O2 -. + H+. The activity of the extract was enhanced 2-fold by the addition of FAD, suggesting that the flavin is a component of the enzyme system. The Km value for FAD was 0.077 microM. The activities in both vesicle fraction and extract were labile even on refrigeration, but could be kept for several months at -70 degrees C.

Animals↗
PubMed1980

NADH- and NADPH-dependent lipid peroxidation in bovine heart submitochondrial particles. Dependence on the rate of electron flow in the respiratory chain and an antioxidant role of ubiquinol.

Malondialdehyde formations by bovine heart submitochondrial particles supported by NADH or NADPH in the presence of ADP and FeCl3 was studied. The NADH-dependent reaction was maximal at very low rate of electron input from NADH to the respiratory chain and it decreased when the rate became high. The reaction was stimulated by rotenone and inhibited by antimycin A when the input was fast, whereas it was not affected by the inhibitors when the input was slow. The input rate of the electrons from NADPH was also so low that the reaction supported by NADPH was not affected by the inhibitors. Most of the endogenous ubiquinone in the particles treated with antimycin A was reduced by NADH even in the presence of ADP-Fe3+ chelate, but uniquinone was not reduced by NADPH when ADP-Fe3+ was present. Succinate strongly inhibited both NADH- and NADPH-dependent lipid peroxidation. The inhibition was abolished when uniquinone was removed from the particles, and it appeared again when uniquinone was reincorporated into the particles. Reduced uniquinone-2 also inhibited the peroxidation, but duroquinol, which reduces cytochrome b without reducing endogenous uniquinone, did not. Thus the malondialdehyde formation appeared to be inversely related to the extent of the reduction of endogenous uniquinone. These observations suggest that both NADH- and NADPH-dependent liquid-peroxidation reactions are closely related to the respiratory chain and that the peroxidation is controlled by the concentration of reduced ubiquinone.

Animals↗
PubMed1980

Lipid peroxidation and the reduction of ADP-Fe3+ chelate by NADH-ubiquinone reductase preparation from bovine heart mitochondria.

The NADH-ubiquinone reductase preparation (Complex I) of bovine hart mitochondria catalysed in the presence of reduced coenzymes and ADP-Fe3+ the lipid peroxidation of liposomes prepared from mitochondrial lipids. The apparent Km values for the coenzymes and the optimal pH of the reactions agreed well with those of the lipid peroxidation of the submitochondrial particles treated with rotenone. On assay of the reduction of ADP-Fe3+ chelate by the reduction of cytochrome c in the presence of superoxide dismutase and antimycin A or by the oxidation of reduced coenzymes, the reactions were not affected by rotenone but were inhibited by thiol-group inhibitors. The properties of the ADP-Fe3+ reductase activity were highly consistent with those of the lipid-peroxidation reaction. These observations suggest that electrons from reduced coenzymes are transferred to ADP-Fe3+ chelate from a component between a mercurial-sensitive site and the rotenone-sensitive one of the NADH dehydrogenase and that the reduction of ADP-Fe3+ chelate by the NADH dehydrogenase is an essential step in the lipid peroxidation.

Adenosine Diphosphate↗
PubMed1980

Interdigestive migrating contraction in short bowel dogs.

Extraluminal force transducers were chronically implanted onto the serosal surface of the gastrointestinal tract in dogs and the interdigestive migrating contractions (IMC) were studied in conscious dogs. When the IMC occurring periodically in the stomach reaches the distal ileum, the next IMC develops in the stomach. We therefore studied the effect of isolation or resection of the lower third of the small bowel on the periodic occurrence of IMC in the stomach. Transducers were sutured onto the antrum, the upper jejunum, the mid intestine and the terminal ileum. After control records on gastrointestinal motility were made for these dogs, the abdominal cavity was again opened to prepare a Thiry loop in the lower third of the small bowel. (isolation group) Next, the loop was removed (resection group) and gastrointestinal motility was recorded. In these groups, we 1) measured the time from the feeding to the initiation of the first IMC. 2) measured the time from the termination of one IMC to the termination of the next IMC. 3) measured the migrating time of the IMC. 4) and measured the duration of the IMC in the stomach. As a result, it was found that the time interval between the termination of one IMC in the stomach and the termination of the next was almost constant throughout all experiments. The migrating time of the IMC from the stomach to the terminal ileum in isolation and resection groups was slightly shortened. These findings indicate that the existence of the lower gut has no significant influence upon the regular periodic occurrence of the IMC in the stomach and the migrating time.

Animals↗
PubMed1978

Characteristic motor activity of the gastrointestinal tract in fasted conscious dogs measured by implanted force transducers.

Gastrointestinal contractile actiivity from the gastric body to the terminal ileum in conscious dogs was continuously recorded for several weeks by means of chronically implanted strain-gage force transducers. It was found that the 24-hr changes in the gastrointestinal contractile activity consisted of the two different major patterns, the digestive and interdigestive patterns. In the interdigestive state, a cyclic, recurring, caudad-moving band of strong contractions starting in the stomach and the duodenum and traversing the entire length of the small intestine was observed. When one band of strong contractions reached the distal ileum, another developed in the stomach and the duodenum again and propagated in a caudad direction. Such recycling episodes interrupted by long-lasting quiescence repeatedly occurred until the next meal. These characteristic contractile activities observed in our dogs are identical with the interdigestive myoelectric complex of the stomach and the small bowel recently reported by Code and Marlett (5). Four sequential phases (I-IV) of the migrating myoelectric complex, defined in terms of action potential activity, seem to correspond to the resting (quiescence), preceding irregular contractions, strong contractions, and subsiding contractions observed in the present study, respectively. Function and control mechanism of the interdigestive contractile activity were discussed.

Action Potentials↗
PubMed1978

Interdigestive motor activity of Heidenhain pouches in relation to main stomach in conscious dogs.

A great number of studies using Heidenhain pouches have been reported, but most of them have been concerned with secretory activity. Studies on the motor activity of the pouch are few, and our knowledge about it is rather limited. In the present study, therefore, long-term changes in contractile activity of the Heidenhain pouches were recorded simultaneously with those of the main stomach in conscious dogs by means of chronically implanted force transducers. It was found that during the interdigestive state Heidenhain pouches contracted precisely in association with the main stomach. During this time a series of strong contractions arose simultaneously in the Heidenhain pouch and the main stomach, lasted for 24.2 +/- 1.90 min, and then ceased abruptly. Such strong contractions were followed by a long period of motor quiescence lasting for 86.9 +/- 6.06 min. These characteristic recurring episodes in the Heidenhain pouch and the main stomach lasted during the interdigestive state but were inhibited by the ingestion of food or intravenous administration of pentagastrin. These findings indicate that the interdigestive motor activity of the stomach is strongly controlled by a humoral factor(s) rather than the parasympathetic nervous system; however, we also propose a possible role for the sympathetic nervous system for coordinated occurrence of the interdigestive contractions between the Heidenhain pouch and the main stomach.

Animals↗
PubMed1977

Diurnal changes in gastric motor activity in conscious dogs.

Twenty-four-hour changes in gastric motor activity were recorded in 4 healthy adult dogs in the conscious state by means of extraluminal force transducers. Three major different gastric motor activity patterns were recognized during 24 hr: digestive, intermediate, and interdigestive. The digestive pattern was characterized by steady low-amplitude contractions in the gastric antrum, with no significant motor activity in the gastric body. The interdigestive pattern consisted of series of high-amplitude contractions of 14-23 min duration in both the gastric body and antrum with intervening and long-lasting (68-109 min) motor quiescence. The intermediate pattern is considered to be the pattern midway when the digestive pattern is changing to the interdigestive pattern. These changes in gastric motor activity are precisely controlled day after day if the animals are fed at regular time intervals and are healthy. The digestive pattern may represent principally a mixing function of ingested food and the interdigestive pattern a cleaning function in preparation for the next meal

Animals↗
PubMed1977

Effect of synthetic motilin on gastric motor activity in conscious dogs.

The effect of intravenous infusion of synthetic motilin on gastric motor activity was investigated by means of chronically implanted force transducers in 4 conscious dogs. Since the gastric motor pattern consisted of two major subpatterns, digestive and interdigestive motor activity, motilin was tested for its motor stimulating activity in both states. It was found that motilin had no influence upon gastric motor activity in the digestive state. However, during the interdigestive state, intravenous infusion of motilin in doses of 0.3-2.7 microgram/kg/hr induced motor activity similar to the naturally occurring interdigestive contractions in a dose-related fashion. Since motilin is released by duodenal alkalinization in the dog, it may be postulated that motilin is a substance to control the interdigestive contractions in the dog, although other reports describe motilin release by duodenal acidification and inhibition of gastric emptying in man. Endogenous stimuli leading to motilin release may be different among species. The present study clearly indicates that motilin induces a contractile pattern similar to that seen during the interdigestive state in conscious dogs.

Animals↗
PubMed1977

An extraluminal force transducer for recording contractile activity of the gastrointestinal smooth muscle in the conscious dogs: its construction and implantation.

An extraluminal strain-gauge force transducer has been developed for recording contractile activity of the gastrointestinal smooth muscle. The details of its construction and implantation were described. The transducer unit allows for continuous long-term recordings (more the 5 months) from conscious experimental animals. It could be constructed in any laboratory and easily implanted in animals if it is done in aseptic technique. Since it is sutured onto the outside of the gut, it does not interfere passage of the contents. The only disadvantages are that it only measures muscle contractions and it is hard to determine movements of intraluminal contents especially in the digestive state.

Animals↗