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Biomedical subjects

T Oka

Publications and source records attributed to T Oka.

At least 1,351 records · Page 75Linked to original sources
PubMed1979

Induction by lithium ion of multiplication of mouse mammary epithelium in culture.

Lithium ion at concentrations between 2 and 20 mM simulated the stimulatory effects of insulin on the uptake of alpha-aminoisobutyric acid, synthesis of RNA and DNA, and cell multiplication in mouse mammary gland explants cultured in a chemically defined synthetic medium. Other monovalent cations were virtually ineffective. In most instances the stimulatory effect of lithium ion was somewhat smaller than and additive to that of insulin. However, lithium ion was incapable of substituting for the action of insulin in augmenting milk protein synthesis in mammary explants cultured with other lactogenic hormones, prolactin, and glucocorticoid. The observed similarities of the responses of mammary cells to lithium and insulin suggest that possible importance of cation(s) in the regulation of mammary cell proliferation, which may be a common basis for the action of the two agents. On the other hand, the observed inability of lithium to mimic the lactogenic effect of insulin indicates a specific function of the hormone in the functional differentiation of mammary cells.

Animals↗
PubMed1979

Calcium requirements for electrically-induced release of an endogenous opiate receptor ligand from the guinea-pig ileum.

Calcium requirements for electrically-induced release of an endogenous opiate receptor ligand in the myenteric plexus-longitudinal muscle strip of the guinea-pig ileum were studied. The naloxone-reversible depression of the electrically evoked contraction caused by stimulation at 10 Hz in normal Krebs solution was markedly reduced by decreasing the calcium concentration in the solution. The depression was greatly diminished by increasing the magnesium concentration in the solution. These results show that the electrically-induced release of an opiate-like material requires calcium ions.

Animals↗
PubMed1978

Indication and appreciation of operative procedures for mandibular ankylosis.

Mandibular ankylosis may be of various etiology. A number of operative procdures have been presented and criticized, but the most appropriate procedure for ankylosis is not universally accepted. During the past decade, 17 cases of mandibular ankylosis have been treated surgically in the Nagoya University Hospital. The etiology includes both temporomandibular ankylosis and extraarticular origin. Three different surgical procedures were used: (1) High operation, in which skin incision is made in the preauricular region. This method is applied for moderate arthrogenic cases. (2) Low operation, in which skin incision is made in the submandibular region. This is applied for severe arthrogic cases and extraarticular ossification cases. (3) Tubed pedicle skin grafting is applied for buccal contracture cases caused by noma etc. A long-term follow-up to 10 years has disclosed many interesting findings and made it possible to evaluate each operative procedure.

Adult↗
PubMed1978

Peptide bond synthesis catalyzed by alpha-chymotrypsin.

alpha-Chymotrypsin [EC 3.4.21.1] catalyzed the syntheses of peptide bonds with various N-acylated amino acids or peptides having aromatic or hydrophobic amino acid residues at the C-terminal position as carboxyl components, and amino acid derivatives, peptides or their derivatives as amine components. A neutral pH was most efficient and quite high concentrations of alpha-chymotrypsin and starting materials were required for synthesis. Four amine components, hydrophobic or bulky amino acid residues were useful at the N-terminal position. Stereospecificity was also observed at the N-terminal position of amine components. Peptide synthesis was not usually seen when the products were soluble in the reaction mixture. This could be partly overcome by increasing the concentration of either the carboxyl or the amine component to more than ten times that of the other.

Amines↗
PubMed1978

Effect of beta-lactam antibiotics on in vitro peptidoglycan cross-linking by a particulate fraction from Escherichia coli K-12 and Bacillus megaterium KM.

The binding constants of several beta-lactam antibiotics towards penicillin-binding components in Escherichia coli K-12 (Spratt, Eur. J. Biochem. 72:341-352, 1977) and the antibiotic concentrations required to inhibit the peptidoglycan transpeptidase of E. coli 50% were compared. Penicillin-binding component 1B may have been the transpeptidase working in vitro. The structure-activity relationships of beta-lactam antibiotics and the mechanisms of action in E. coli and Bacillus megaterium are discussed.

Bacillus megaterium↗
PubMed1977

alpha-Chymotrypsin as the catalyst for peptide synthesis.

alpha-Chymotrypsin (EC 3.4.21.1)-catalysed syntheses of peptides were performed with various N-acylated amino acid or peptide esters as donors, and amino acid derivatives, peptides or their derivatives as acceptors. Under optimal conditions the synthesis was almost quantitative. As acceptor nucleophiles, free amino acids or the ester derivatives were inadequate, but amino acid amides or hydrazides, di- or tri-peptides, or the amides, hydrazides and esters of the peptides were useful. The nucleophile specificity for synthesis was markedly similar to the leaving-group specificity in hydrolysis; hydrophobic or bulky amino acid residues were most effecient at both P1' and P2' positions [notation of Schechter & Berger (1967) Biochem. Biophys. Res. Commun. 27, 157-162], but L-proline as well as D-amino acid residues were the worst choices. The synthesis was further dependent on the solubility of the products synthesized; a higher yield of products was expected with lower solubility. As donor esters, good substrates were all useful. Accordingly, fragment condensation was possible by using N-acylated peptide esters and various peptides. The present study suggested that alpha-chymotrypsin may become a useful tool for peptide synthesis.

Amino Acids↗
PubMed1977

Effect of neurohumoral modulators on the morphine-induced hyperthermia in non-tolerant rats.

Wistar rats from one supplier have been shown to exhibit the atypical body temperature responses to morphine. In contrast to commonly used rats, in which morphine induced dose-dependent changes in body temperature, the initial administration of morphine (5, 10, 20, and 40 mg/kg, s.c.) to rats of this particular strain produced a consistent and prominent hyperthermia. This hyperthermia is mediated via an action on the typical morphine receptors since it was completely prevented by a specific narcotic antagonist, naloxone. Effects of neurohumoral modulators on the hyperthermia have been investigated in these rats. Pretreatment of animals with p-chlorophenylalanine, alpha-methyltyrosine, phenoxybenzamine or propranolol did not alter the hyperthermia. In contrast, the s.c. administration of 1 mg/kg of either tertiary or quaternary anticholinergic drug such as scopolamine, atrophine, methscopolamine and methylatropine significantly inhibited the hyperthermia. These results suggest that morphine causes hyperthermia in some strains of rats by a cholinergic mechanism and the involvement of an adrenergic or serotonergic mechanism in this case appears unlikely.

Animals↗