Search PubMed⌕ Search

Biomedical subjects

K Hashizume

Publications and source records attributed to K Hashizume.

At least 415 records · Page 23Linked to original sources
PubMed1983

[Effect of thyroid hormones on the beta-adrenergic receptor internalization in isolated rat hepatocytes].

The effect of the thyroid hormone(T4) on the internalization of beta-adrenergic receptors in isolated hepatocytes was examined. Uptake of [3H]-dihydroalprenolol(DHA) by the cells, which were prepared from untreated-rats, was increased by the time-dependent manner in vitro. The amount of incorporated-[3H]-DHA was decreased by further incubation in the presence of 10(-5) M of d, 1-isoproterenol. However, about 30% of incorporated-[3H]-DHA remained in the cells by this treatment. The amount of this [3H]-DHA remaining in the cells was lowered by pretreatment of the cells with methylamine, monodansylcadaverine, d, 1-isoproterenol or d, 1-propranolol. Then the amount of this [3H]-DHA was recognized as an internalized-receptor-hormone(or -DHA) complex. The total uptake(internalized- + membrane bound-) of [3H]-DHA by the cells was not significantly different between the thyroidectomized (TX + Saline) and T4-treated-thyroidectomized(TX + T4) rats. However, the rate of disappearance of incorporated-[3H]-DHA was greater in the TX + T4 animals compared to that in the TX + Saline animals. In the cells obtained from the TX + T4 animals, internalized-[3H]-DHA was significantly higher than that of the TX + Saline animals. The number of membrane associated beta adrenergic receptors was significantly lower in the TX + T4 group. These results suggest that the thyroid hormone induces an acceleration of internalization of beta adrenergic receptors in hepatocytes.

Alprenolol↗
PubMed1983

Guanosine 5'-triphosphate modulation of S-adenosyl-L-methionine-mediated methylation of phosphatidylethanolamine in rat liver plasma membrane.

Effect of guanosine 5'-triphosphate(GTP) on the S-adenosyl-L-methionine-mediated methylation of phosphatidylethanolamine was examined using rat liver plasma membranes. Methyltransferase I, which catalyzes methylation of phosphatidylethanolamine to phosphatidyl-N-mono-methylethanolamine was inhibited by GTP, whereas methyltransferase II, which transfers methyl groups from S-adenosyl-L-methionine to produce phosphatidyl-N,N-dimethylethanolamine or phosphatidyl-choline was stimulated by GTP. d,l-isoproterenol stimulated methyl-transferase II activity slightly. This stimulation was greatly augmented by GTP. d,l-isoproterenol inhibited methyltransferase I and this inhibition was enhanced by GTP. The results indicate that GTP has a regulatory role in the methylation of phospholipids in the plasma membrane through inactivation of methyltransferase I and activation of methyltransferase II by binding to these enzymes.

Animals↗
PubMed1983

Evidence for the existence of protein inhibitors for S-adenosyl-L-methionine-mediated methylation of phosphatidylethanolamine in rat liver cytosol.

The effect of rat liver cytosol on phosphatidylcholine biosynthesis via the N-methylation of phosphatidylethanolamine has been studied. The purified rat liver plasma membrane was used as an enzyme source. The rat liver 105,000 x g supernatant(cytosol) contained two different inhibitors for S-adenosyl-L-methionine-mediated methylation of phosphatidylethanolamine to phosphatidyl-N-mono-methylethanolamine. The inhibitors were inactivated by pretreatment with trypsin or heating at 96 degrees C, but were not inactivated by RNase. The inhibitors did not inhibit the synthesis of phosphatidylcholine from phosphatidyl-N-mono-methylethanolamine. The results indicate that two different protein inhibitors for methylation are present in rat liver cytosol fraction and that the inhibition by these proteins may have a role for the regulation of phosphatidylcholine synthesis in the plasma membrane.

Animals↗
PubMed1983

Thyrotropin secretion in patients with hyperparathyroidism or hypoparathyroidism: effect of serum calcium on thyrotropin release.

The influence of changes in the serum calcium concentration on TSH secretion was evaluated in patients with primary hyperparathyroidism and idiopathic hypoparathyroidism and in normal subjects. Serum calcium concentrations were 12.7 +/- 0.8, 9.0 +/- 0.4, and 5.7 +/- 0.5 mg/100 ml in hyperparathyroid, normal, and hypoparathyroid subjects, respectively, and were significantly different from each other. Serum T3 and T4 concentrations were comparable among the three groups. The basal serum TSH concentration was highest in hypoparathyroid, lowest in hyperparathyroid, and intermediate in normal subjects. However, all values were within normal limits and were not significantly different from each other. TRH-stimulated TSH secretion was significantly greater in hypoparathyroid patients and significantly less in hyperparathyroid patients than in normal subjects, respectively. The TSH response to TRH was normalized when the serum calcium concentration was normalized by parathyroidectomy in a hyperparathyroid patient or by 1 alpha-hydroxyvitamin D3 administration in a hypoparathyroid patient. To further clarify the mechanism responsible for the modified TSH response to TRH in the hypercalcemic state, rats were made chronically hypercalcemic by the administration of 1 alpha-hydroxyvitamin D3 (0.2 micrograms/100 g BW, ip, for 10 days) and 3% calcium chloride in drinking water. The pituitary TSH content of hypercalcemic rats was significantly greater than that of control rats. The results suggest that decreased TSH secretion produced by chronic hypercalcemia is due to diminished TSH release, rather than to decreased pituitary TSH reserve.

Adolescent↗
PubMed1982

Monoamine oxidase inhibitory modulators in rat heart cytosol: evidence for induction by thyroid hormone.

Inhibitory modulators of monoamine oxidase (MAO) were found in rat heart 105,000 X g supernatant. The modulators inhibited MAO activity present in the outer mitochondrial membrane. The inhibition was noncompetitive when using membrane-associated MAO as enzyme source. The modulators did not, however, inhibit the enzyme activity in the soluble fraction prepared from outer mitochondrial membranes. MAO inhibitory modulator concentration in rat heart cytosol was increased by the administration of T4 to rats. Three different inhibitory molecules were identified by gel filtration studies. These results suggest that thyroid hormone regulates membrane-associated MAO activity via the production of MAO inhibitory modulators, that the modulators probably bind to specific sites on the outer mitochondrial membrane, and that this binding of modulators to the membranes may result in a structural change in the mitochondrial membrane and a decrease in MAO enzyme activity.

Animals↗
PubMed1981

[Viscoelastic property of human brain -for the analysis of impact injury (author's transl)].

1. Viscoelasticity of the human brain was investigated in order to understand the physical properties of the brain and to apply it to the analysis of the head injury mechanisms. 2. Static shear modulus (G) of the human white matter was 2.4 X 10(3) dyne/cm2. 3. Complex Young's modulus (E*(omega) = E' + iE") of the white matter, the gray matter, and the brain stem was measured in the range of 3-36 degrees C and 3-35 Hz using the dynamic viscoelastometer. Storage Young's modulus (E') of both white and gray matters of human brain was in the figures of 10(5) dyne/cm2 and loss Young's modulus (E") of those showed 10(4)-15(5) dyne/cm2. 4. The viscoelasticity of human brain is illustrated in Fig. 4 on the assumption of the equivalence of time and temperature. In case of head injury with impact duration of 5 msec it is proper to use the following value : E' = 4 X 10(5) dyne/cm2, E" = 2 X 10(5) dyne/cm2 in the white matter and E' = 3 X 10(5) dyne/cm 2, in the gray matter. 5. The visoelasticity of gelatin and bean curds were also examined to know whether or not simulation of the brain was possible. The viscoelasticity of 5-15% gelatin with an addition of 5% formalin was decreased 1-2 figures compared with that of the brain. The viscoelasticity of bean curds was about the same as that of the brain.

Adult↗
PubMed1980

Release of thyrotropin receptor from thyroid plasma membranes: effect of hydrocortisone, propranolol, and adenosine 3',5'-monophosphate.

Soluble TSH receptors were released into the medium when bovine thyroid plasma membranes were incubated in 0.01 M Tris-HCl, pH 7.5, at 0 or 20 C. This is a conventional hypotonic medium used in binding assays. The characteristics of binding of bovine [125I]TSH to the released TSH receptor were almost the same as those of binding to TSH receptors solubilized by lithium 3,5-diiodosalicylate or to the original plasma membrane. Released TSH receptor had two binding sites with Ka values of 0.7 x 10(10) and 0.1 x 10(8) M-1. T3, T4, KI, methimazole, and propylthiouracil had no effect on spontaneous TSH receptor release or on bovine [125I]TSH binding to solubilized TSH receptor. Hydrocortisone (10(-5)--10(-3) M) and d,l-propranolol (10(-3) M) inhibited receptor release. cAMP increased the release of TSH receptor. Hydrocortisone, d,l-propranolol, and cAMP had no effect on bovine [125I]TSH binding to solubilized or released TSH receptor. d,l-Propranolol and hydrocortisone may act as membrane-stabilizing agents. cAMP stimulation of release suggests that the release mechanism could depend upon a protein kinase-phosphoprotein system. Although these studies were conducted with membranes in an unphysiological medium, receptor release may occur normally and could be a source of circulating antigen related to production of antireceptor antibody in autoimmune thyroid diseases. Release of receptors during incubation in vitro may affect the results of studies of hormone-receptor interaction.

Animals↗
PubMed1980

[Cyclic-AMP dependent protein kinase activity in the soluble thyrotropin receptor complex (author's transl)].

The relationship between the thyrotropin (TSH) receptor and adenosine 3':5'-monophosphate (cyclic-AMP) dependent protein kinase activity in bovine thyroid plasma membrane fraction was investigated. After solubilization of thyroid plasma membranes, the molecular sizes of TSH binding protein and protein kinase activities were compared using the sucrose density gradient technique. Cyclic-AMP dependent protein kinase activity was present in a soluble thyrotropin receptor fraction. The Km of this enzyme was 2.2 x 10(-6) M for casein substrate in the absence or presence of 10(-5) M cyclic-AMP. A [3H]-cyclic-AMP binding protein was also found in this fraction. The Ka for cyclic-AMP binding was 0.11 x 10(6) M-1, with 3 nmoles per mg protein of total binding capacity. After fractionation using a continuous sucrose density gradient, one of the several [125I]-bovine TSH binding peaks corresponded to a [3H]-cyclic-AMP binding peak. After fractionation on a sucrose density gradient containing 0.4 M NaCl at pH 6.5, a major peak of protein kinase activity was stimulated by adding 10(-5) M cyclic-AMP. A peak of [3H]-cyclic-AMP binding activity corresponded to the same peak. Protein kinase activity in the receptor fraction was stimulated by adding 6 mg/ml bovine TSH. The soluble TSH receptor fraction also had an adenylate cyclase activity stimulated by TSH. These results suggest that some TSH receptors in thyroid plasma membranes have associated adenylate cyclase activity and cyclic-AMP dependent protein kinase activity. The receptor, cyclase, and kinase activities may exist in a functional primary receptor unit which is a component of thyroid plasma membranes.

Adenylyl Cyclases↗
PubMed1980

Inhibition of peptidoglycan transpeptidase by beta-lactam antibiotics: structure-activity relationships.

The inhibitory activities of representative beta-lactam compounds, such as penicillins G and N, cephalosporins C and G, clavulanic acid, nocardicin A and thienamycin against Escherichia coli KN-126 and Bacillus megaterium KM peptidoglycan transpeptidases were studied. Their modes of action against E. coli are discussed on the basis of the results and the published binding data for penicillin binding proteins. The effects of modifications at position 3 and 7 of the cephalosporin and those at alpha-carbon of the benzyl side-chain of cephalosporin G and penicillin G were studied. The introduction of an amino group at this position in cephalosporin G together with the removal of an acetoxy group from the acetoxymethyl group at position 3 reduced the inhibitory activity against E. coli transpeptidase considerably. The activity was restored by the replacement of the methyl group at position 3 of cephalexin with chlorine. The restoration was accompanied by about 15-fold increase in the lytic activity of cephachlor against E. coli.

Acyltransferases↗