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Biomedical subjects

D Zhao

Publications and source records attributed to D Zhao.

At least 199 records · Page 11Linked to original sources
PubMed1992

Molecular cloning of a complementary deoxyribonucleic acid encoding the thyrotropin-releasing hormone receptor and regulation of its messenger ribonucleic acid in rat GH cells.

Rat pituitary GH cells have been used extensively to study the biochemical actions of TRH on lactotropic cells. To investigate the structure and regulation of the rat TRH receptor (rTRHR), we have cloned its cDNA from GH4C1 cells. Using the polymerase chain reaction with degenerate primers and pools of cloned cDNAs from a GH4C1 cDNA library, a fragment sharing high similarity to the mouse thyrotrope TRHR (mTRHR) was identified. Conventional library screening with this fragment was used to isolate a single cDNA. mRNA synthesized in vitro from this cDNA was injected into Xenopus oocytes, and a characteristic conductance response to TRH was detected by voltage clamp recording. DNA sequence analysis revealed a molecule of 412 amino acid residues, with 96% similarity to the mTRHR. However, in contrast to the mTRHR, the rTRHR had an additional 19 amino acid residues at its carboxy-terminus. A mRNA of about 4 kilobases was identified in GH3 cells. Regulation of the rTRHR mRNA concentration was studied in GH3 cells. Steady state rTRHR mRNA levels were decreased to 30% of the control level by incubation with TRH for 48 h and increased 4-fold by incubation with dexamethasone for 12 h. Southern blot analysis of genomic DNA from GH3 cells gave a simple banding pattern consistent with a single copy gene. We conclude that the rTRHR shares high primary sequence similarity to the mTRHR, but the rTRHR has an extension of 19 amino acids at its carboxy-terminus, which is lacking in the mTRHR.

Amino Acid Sequence↗
PubMed1992

Interim report of Sino-Monica-Beijing for the years 1985-1989.

Interim results of Sino-Monica-Beijing for the 5 year period 1985-1989 are reported. The cardiovascular disease (CVD) risk factors increased between the surveys carried out in 1984-1985 and 1988-1989, especially blood cholesterol and body mass index.

Adult↗
PubMed1992

[Further studies of collagen biosynthesis by hepatocytes].

Electron microscopic observation was carried out on 32 biopsies from liver and biliary system diseases. It was found that proliferative collagen in the liver was located not only in the portal space and Disse space, but also in the hepatocytes. Most of the collagen seen in hepatocytes were in the form of collagen fibrils, oriented irregularly, intermingled with the organelles and without a delimiting membrane. Therefore, the authors suggest that these collagen fibrils were produced by the hepatocytes themselves.

Biopsy↗
PubMed1991

Effects of hippocampal kindling on paired-pulse response in CA1 in vitro.

Kindled rats were given high-frequency stimulations delivered to hippocampal CA1 on one side to induce afterdischarges (ADs). Control rats received the same number of pulses of a similar intensity at 0.17 Hz (low-frequency stimulations (LFSs)). On 1-2 days or on 21-23 days after fifteen ADs/LFSs (delivered hourly, 5 times a day over 3 days), hippocampal slices were prepared and incubated in vitro, with the experimenter blind to the previous history of stimulation of the rat. Extracellular responses following single or paired-pulse stimulation of the Schaffer collaterals (stratum radiatum) were recorded at the CA1 cell layer in vitro, and analyzed as population excitatory postsynaptic potentials (EPSPs) and population spikes. At 1.5, 2 or 4 times the response threshold, and on either day 1 or day 23 after the last AD/LFS, the paired-pulse response at interpulse intervals of 30-200 ms was significantly larger for the kindled group of slices than for the control group (ANOVA, typically P less than 0.0001), for either the population spike or the population EPSP. Stimulus thresholds for the evoked response did not differ between kindled and control group of slices. The population EPSP and spike in response to a single pulse were enhanced (as compared to the control group) on day 1 but not on day 23 after kindling. The facilitation of paired-pulse response may be interpreted as caused by a decrease in postsynaptic (and possibly presynaptic) inhibition in the hippocampal CA1 region, which persisted to at least 3 weeks after hippocampal kindling.

Animals↗
PubMed1991

Purification and composition of Ca2+/Mg2+ ATPase from rat heart plasma membrane.

The Ca2+/Mg2+ ATPase, which is activated by millimolar concentrations of Ca2+ or Mg2+, was solubilized from rat heart plasma membrane by employing lysophosphatidylcholine, CHAPS, NaI, EDTA and Tris-HCl at pH 7.4. The enzyme was purified by sucrose density gradient, Affi-Gel Blue column and Sepharose 6B column chromatography. The purified enzyme was seen as a single peptide band in the sodium dodecyl sulfate polyacrylamide gel electrophoresis with a molecular weight of about 90,000. The apparent molecular weight of the holoenzyme as determined under non-dissociating conditions by gel filtration on Sepharose 6B column was about 180,000 indicating two subunits. The enzyme was insensitive to ouabain, verapamil, vanadate, oligomycin, N,N-dicyclohexylcarbodiimide and NaN3, but was markedly inhibited by 20 microM gramicidin S and 50 microM trifluoperazine. Analysis of the purified Ca2+/Mg2+ ATPase revealed the presence of 17 amino acids where leucine, glutamic acid and aspartic acid were the major components and histidine, cysteine and methionine were the minor components. The purified enzyme was associated with 19.7 mumol phospholipid/mg protein which was 60 times higher than the phospholipid content in plasma membrane. The cholesterol content in the purified enzyme preparation was 0.75 mumol/mg protein and this represented an 8-fold enrichment over plasma membrane. The glycoprotein nature of the enzyme was evident from the positive periodic acid-Schiff staining of the purified Ca2+/Mg2+ ATPase in the sodium dodecyl sulfate polyacrylamide gel. The polysaccharide content of the enzyme was enriched 8-fold over plasma membrane; neuraminidase treatment decreased the polysaccharide content. Concanavalin A prevented the ATP-dependent inactivation of the purified Ca2+/Mg2+ ATPase and was found to bind to the purified enzyme with a KD of 576 nM and Bmax of 4.52 nmol/mg protein. The results indicate that Ca2+/Mg2+ ATPase is a glycoprotein and contains a large amount of lipids.

Amino Acids↗
PubMed1991

Characterization of the purified rat heart plasma membrane Ca2+/Mg2+ ATPase.

The purified Ca2+/Mg2+ ATPase from rat heart plasma membrane was activated by Ca2+ and Mg2+ with Ka values of 1.47 mM and 2.51 mM, respectively; other divalent cations also activated the enzyme but to a lesser extent. Divalent cations like Cu2+, Zn2+, Ni2+, Cd2+ were potent inhibitors of the enzyme activity in the presence of Ca2+ or Mg2+ whereas Na+, K+ or HCO3- did not affect the Ca2+/Mg2+ ATPase activity; the pH optima was 8.5. The enzyme hydrolyzed ATP with a Km of 0.34 mM for Ca2+ ATPase and 0.48 mM for Mg2+ ATPase; various nucleoside triphosphate such as ITP, CTP, GTP, and UTP were also hydrolyzed. Phospholipase A and C as well as neuraminidase decreased the Ca2+/Mg2+ ATPase activity whereas phospholipase D was ineffective. The purified Ca2+/Mg2+ ATPase was found to bind ATP-r-35S with two affinities; the KD values were 50.9 +/- 0.8 and 1160 +/- 198 nM and the Bmax values were 8.71 +/- 0.16 and 145 +/- 9.7 nmol/mg protein for high and low affinity sites, respectively. Treatment of the enzyme preparation with phospholipases and neuraminidase did not affect the ATP-r-35S binding. Ca2+ was also found to bind with Ca2+/Mg2+ ATPase with a KD of 0.384 mM and a Bmax of 1.85 mumol/mg protein; Ni2+, Mn2+, Zn2+ at 1 mM concentrations inhibited the Ca2+ binding but Mg2+ and verapamil were without effect. Phospholipase A and neuraminidase decreased the Ca2+ binding by 20-30%; this indicated that Ca2+ binding with the purified enzyme may be partly due to the phospholipids and sialic acid residues associated with the enzyme. These results show that the purified Ca2+/Mg2+ ATPase is a Ca2+ binding glycoprotein having two binding sites for ATP. Furthermore, this study suggests that phospholipids associated with purified Ca2+/Mg2+ ATPase are required for maximal activity.

Adenosine Triphosphate↗
PubMed1991

Comparison of amide proton exchange in reduced and oxidized Rhodobacter capsulatus cytochrome c2: a 1H-15N NMR study.

The hydrogen-deuterium exchange rates of the reduced and oxidized forms of Rhodobacter capsulatus cytochrome c2 were studied by 1H-15N homonuclear multiple quantum correlation spectroscopy. Minimal differences were observed for the N- and C-terminal helices on changing redox state suggesting that although these helices are structurally important they do not affect the relative stability of the two redox states and hence may not be important in determining the redox potential differences observed amongst the class I c-type cytochromes. However, significant differences were observed for other regions of the protein. For example, all slow exchanging protons of the helix spanning Phe82 to Asp87 are similarly affected on reduction indicating that the unfolding equilibrium of this helix is altered between the two redox states. Other regions are not as simple to interpret; however, the difference in NH exchange rates between the redox states for a number of residues including His17, Leu37, Arg43, Ala45, Gly46, Ile57, Val58, Leu60, Gly61 and Leu100 suggest that interactions affecting the causes of these differences may be important factors in determining redox potential.

Amides↗
PubMed1991

Prostaglandin protects against bile salt induced increases in proton permeation of duodenal brush border membrane.

A direct protective action of prostaglandin on luminal cell membranes was investigated by preincubating rabbit duodenal brush border membrane vesicles with prostaglandin E2 (PGE2) before incubation with bile salts. Membrane perturbation was assessed by measuring the net proton permeability (Pnet). Bile salts (deoxycholate, glycodeoxycholate, and taurodeoxycholate; 0.1-1.0 mmol/l) resulted in concentration dependent increases in Pnet: from (mean (SE] 5.42 (0.17) (n = 20) to 8.44 (0.24) x 10(-4) (n = 13) cm/s with 0.5 mmol/l deoxycholate. PGE2, 10(-8)-10(-6) mol/l, when added alone had no effect on Pnet: 5.41 (0.21) x 10(-4) (n = 14) cm/s with 10(-6) M PGE2. When duodenal brush border membranes were preincubated with PGE2, 10(-7)-10(-6) mol/l, however, the bile salt induced increase in Pnet was significantly reduced: 7.22 (0.18) x 10(-4) (n = 13) cm/s with 10(-7) mol/l PGE2 and 0.5 mmol/l deoxycholate. These findings indicate that PGE2 exerts a direct protective action on duodenal luminal membranes.

Animals↗
PubMed1991

[Comparison of Spatholobus suberectus Dum, Euonymus alatus (Thunb.) Sieb. and Eupolyphaga sinensis Walker on regulation of plasma lipid].

The Spatholobus suberectus (SS) of hexue type, the Euonymus alatus (EA) of huoxue type and the Eupolyphaga sinensis (ES) of poxue type were selected and their influence on plasma lipid in the experimental hyperlipidemia quails was observed. The ES could raise plasma HDL-C/TC ratio and increase LCAT activity. The SS could raise plasma HDL2-C/HDL3-C ratio. The effect of EA on plasma HDL-C/TC, HDL2-C/HDL3-C and LCAT levels was between SS and ES. All the three huoxue huayu Chinese drugs could lower plasma HDL3-C level and slow down the progress of atherosclerosis to a certain degree. The above-mentioned results show that certain orders exist between the action range of huoxue huayu drugs and their effect on regulating plasma lipid.

Animals↗
PubMed1990

[Ultrastructural study of moniliformin-induced lesions on the myocardium of rats and mice].

Effects of moniliformin on the ultrastructure of the myocardium of mice and rats were studied. Mice were given moniliformin orally at the dosage of 29.46 mg/kg. One hour later lesions of the mitochondria of the myocardial cells were found which became more severe 2-3 hours later. Ultrastructural lesions were also observed in the myofibrils and sarcolemma. Rats were given moniliformin orally at the dosage of 6 mg/kg once daily for 56 days. Lesions of the mitochondria and myofibrils were relatively mild. Myocardiac specimens taken 21 days after toxin administration, lesions of the sarcolemma became more obvious. Various amounts of collagen were produced by the myocardiac cells. These moniliformin-induced lesions were similar to the ultrastructural changes in the myocardium of patients with Keshan disease. Our findings indicate that there may be a close and important relationship between moniliformin intoxication and Keshan disease.

Animals↗
PubMed1990

A real-time adaptive ultrasonic imaging system.

The performance of an experimental, adaptive, phased array imaging system in improving the quality of abdominal organ images in healthy volunteers was assessed. Trials were conducted under usual clinical imaging conditions and when phase aberrators of known shape and magnitude were introduced into the imaging system. The system, which uses local target brightness as a quality factor, was able to improve clinical image quality when aberrators introduced externally were present and had a negligible effect on image quality when they were not. On several of the volunteers, the phase aberrations were measured directly across the abdomen. The implications of these results for the future clinical application of adaptive imaging systems and the future system modifications are reported.

Adult↗
PubMed1989

Changes of proenkephalin and prodynorphin mRNAs and related peptides in rat brain during the development of deep prepyriform cortex kindling.

The effects of deep prepyriform cortex (DPC) kindling on the amount of proenkephalin and prodynorphin mRNAs, Met5-enkephalin (ME) and dynorphin (DYN) in rat brain were examined. Animals received electrical stimulation of the DPC until two consecutive stage 2 seizures (S2) or stage 5 seizures (S5) were attained. The proenkephalin mRNA and ME contents in the entorhinal cortex were increased 24 h after S2 and also 5 min and 24 h post S5. In the hippocampus, the proenkephalin mRNA level was reduced 24 h after S2 but increased 5 min and 24 h after S5. Elevated hippocampal ME concentration was observed 24 h after S2 and S5. Similarly, the ME level in the frontal cortex was increased 24 h after S2 and S5 but the proenkephalin mRNA content was only elevated at S5. In the striatum, the proenkephalin mRNA level was slightly increased 24 h after S2 and S5, but no change in ME content was found. The amount of prodynorphin mRNA in the hippocampus was attenuated only at 24 h after S5, whereas DYN concentration was reduced 5 min after S5. No change in striatal DYN concentration was observed despite a slight elevation of prodynorphin mRNA 24 h post S2 and S5. Six weeks after the last seizure, no difference in ME and DYN was found between kindled and control animals. These findings indicate that the enkephalin-containing perforant pathway in the entorhinal cortex-hippocampal region is particularly sensitive to electrical stimulations applied to the DPC. Its role and importance in the development of kindling are discussed.

Animals↗