Search PubMed⌕ Search

Biomedical subjects

D Chen

Publications and source records attributed to D Chen.

At least 721 records · Page 40Linked to original sources
PubMed1994

Pituitary adenylate cyclase-activating peptide in the adrenal gland of mammals: distribution, characterization and responses to drugs.

The occurrence, cellular distribution and nature of the 27-amino acid form of pituitary adenylate cyclase-activating peptide (PACAP-27) in the adrenal glands of mammals was investigated by means of immunohistochemistry, radioimmunoassay and chromatography. The concentrations (pmol/g wet weight) of PACAP-27-like immunoreactivity (LI) varied considerably between the species examined: mouse (n = 8), 12.1 +/- 2.0; hamster (n = 4), 9.1 +/- 1.5; rat (n = 13), 2.0 +/- 0.3; cow (n = 3), 0.8 +/- 0.1, and pig (n = 5), 0.7 +/- 0.1. Upon HPLC, the immunoreactivity in extracts of rat, mouse and hamster adrenals coeluted with synthetic PACAP-27 while the immunoreactivity in extracts of cow and pig adrenals eluted as less hydrophobic material. Immunohistochemistry revealed the presence of PACAP-27-LI in the noradrenaline-storing chromaffin cells of the adrenal medulla. No nerve fibers exhibiting PACAP-27-LI could be detected. The effects of drug administration in vivo on the stores of PACAP-27-LI in the rat adrenal were studied and compared with the effects on the adrenal stores of neuropeptide Y (NPY)-LI. Splanchnic activation following insulin-induced hypoglycemia elicited a 41% depletion of NPY-LI 2 h after insulin injection, while the concentrations of PACAP-27-LI remained unchanged. Two days after reserpine administration the stores of PACAP-27-LI and NPY-LI were depleted by 62 and 41%, respectively. Two days later, the concentrations of NPY-LI were increased to 216% of controls, while the concentrations of PACAP-27-LI were similar to that of controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗
PubMed1994

ECL cells: biology and pathobiology.

During recent years, the so-called ECL cells of the acid-producing part of the stomach have attracted much attention, mainly due to the fact that mice and rats were found to develop gastric carcinoids (ECL cell tumors) following life-long treatment with blockers of acid secretion. These observations touched off concern about the safety of the long-term clinical use of such drugs. The ECL cells are the predominant endocrine cell population in the oxyntic mucosa. They produce histamine, chromogranin A/pancreastatin and an as yet unidentified peptide hormone. They respond to gastrin by the release of secretory products; more long-term responses include adaptation to the gastrin stimulus, hypertrophy and hyperplasia. Intravenous infusion of maximally effective doses of gastrin promptly reduced the number of cytoplasmic vesicles in the ECL cells and their content of histamine and pancreastatin. Despite the ongoing infusion of gastrin, the number of vesicles and the content of histamine and pancreastatin were back to normal 4-6 h after the start of the infusion. The histidine decarboxylase (HDC) activity and HDC mRNA level increased progressively until plateaus were reached after 6-8 h of gastrin infusion. The size of the ECL cells started to increase about 4 days after the start of a subcutaneous gastrin infusion (resulting in half-maximally effective serum gastrin concentrations). The ECL cell size reached maximum after about 2 weeks and then remained at this level.The number of cytoplasmic vesicles was increased; this effect seemed to reach a maximum after 1-2 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Phenylalanine-780 near the C-terminus of the mouse glucocorticoid receptor is important for ligand binding affinity and specificity.

Site-directed mutagenesis was employed to make two single amino acid substitutions for highly conserved amino acid residues near the C-terminus of the 783-amino acid mouse glucocorticoid receptor. Substitution of leucine for histidine-781 caused little or no change in the concentration of dexamethasone required for half-maximal activation of a chloramphenicol acetyltransferase reporter gene expressed from a mouse mammary tumor virus promoter. However, when phenylalanine-780 was changed to alanine, the half-maximal concentrations of various agonists were increased as follows, compared with the wild-type glucocorticoid receptor: triamcinolone acetonide by 7-fold, dexamethasone by 25-fold, and hydrocortisone and deoxycorticosterone by more than 150-fold. Binding of labeled steroids by the mutant receptor in vitro and in vivo was also decreased. In contrast, this mutation caused a small decrease in the concentration of RU486 required for antagonist or partial agonist activity. Thus, the phenyl group of phenylalanine-780 of the mouse glucocorticoid receptor is an important determinant of ligand binding affinity and specificity.

Amino Acid Sequence↗
PubMed1994

Binding and aggregation of human gamma-globulin by cis-diamminedichloroplatinum(II) through disulfide bond.

The incubation of gamma-globulin with cis-diamminedichloroplatinum (II) (cis-DDP) resulted in gradual formation of insoluble aggregates. Since the precipitates, composed of polymerized gamma-globulin and cis-DDP, were completely solubilized with urea, the reaction mixture containing precipitate was examined in terms of the binding of cis-DDP and the effect on disulfide (S-S) bonds in the gamma-globulin. When gamma-globulin was incubated with 30 molar excess cis-DDP at pH 7.4 and 37 degrees C, cis-DDP gradually bound to as much as 12 mol per mol of gamma-globulin in 14 d. Concurrently, about four disulfide bonds were cleaved without reaching a certain plateau. An sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of the aggregated gamma-globulin induced by cis-DDP was significantly different from that of the heat-denaturated aggregate form or the reduced form by sulfitolysis. The aquated complexes of cis-DDP also produced an insoluble precipitate and affected the S-S bond to a greater extent than the parent drug.

Cisplatin↗
PubMed1994

Endogenous gastrin and cholecystokinin do not promote growth of rat liver.

BACKGROUND: The purpose of the study was to evaluate the trophic effects of endogenous hypergastrinemia and hypercholecystokininemia on intact and regenerating rat liver. We also examined the effects on the liver of portacaval shunting (PCS) alone or together with hypergastrinemia or hyperCCKemia. PCS is known to enhance the trophic effects of gastrin on the so-called enterochromaffin-like cells of the stomach and of CCK on the pancreas. METHODS: Hypergastrinemia was induced by treatment with omeprazole (400 mumol/kg/day) or extirpation of the acid-producing part of the stomach (fundectomy). HyperCCKemia was induced by pancreaticobiliary diversion (PBD). After 4 weeks half of the rats were killed; the rest underwent partial hepatectomy and were killed 60 h later. PCS rats were killed 4 weeks after start of omeprazole treatment or after PBD. The concentrations of circulating gastrin and CCK were measured by radioimmunoassay. The liver weight and DNA content were analyzed. RESULTS: Endogenous hypergastrinemia and hyperCCKemia failed to stimulate growth of either intact or regenerating liver. There were no differences in liver weight and DNA content between rats subjected to PCS and to combinations of PCS and omeprazole treatment, on the one hand, and PCS and PBD, on the other. CONCLUSION: Gastrin and CCK are unlikely to be physiologically important in the regulation of liver growth and regeneration in the rat.

Animals↗
PubMed1994

[Increased blood pressure during hypoglycemia in patients with IDDM].

34 patients with IDDM (17 normotensive and 17 hypertensive) were studied over a 24 hour period by monitoring blood glucose level at 1 h frequencies during waking hours, ambulatory blood pressure using the accutracker and urinary free catecholamine by HPLC. Hypoglycemia appeared to lead to elevated blood pressure in 4 patients (23.5%) both normotensive and hypertensive. The average blood glucose levels were 2.4 +/- 0.72mmol/L and 3.3 +/- 0.62mmol/L, and the average blood pressure increase was 2.53 +/- 1.43/1.60 +/- 1.65 kPa and 4.66 +/- 2.60/1.73 +/- 1.55 kPa for normotensive and hypertensive groups, respectively. Significant difference appeared (P < 0.05) between the two groups (normotensive and hypertensive). This shows that hypertensive patients with IDDM are more liable to have high blood pressure. This study suggested that stable blood glucose level is necessary for stable blood pressure for patients with IDDM.

Adult↗
PubMed1994

[Interruption of perinatal transmission of HBV by Chinese recombinant hepatitis B vaccine].

Sixty-two infants who were born from HBsAg and HBeAg both positive mothers were vaccinated with 20 micrograms/dose recombinant hepatitis B vaccine, which was made in Beijing Institute of Biologic Products (Vaccinia virus recombinant hepatitis B vaccine) and Changchun Institute of Biologic Products (Chinese hamster ovary cells recombinant hepatitis B vaccine), at 0, 1, 6 months. All the babies were followed up for 9 or 12 months. The results showed that the protective rates of Beijing vaccine and Changchun vaccine were 79.2% and 80.2%, respectively, the positive rates of anti-HBs were 78.8% and 79.3%, respectively. Local or systematic reactions were not found in all the babies 3 days after injection. These results suggested that the Chinese recombinant hepatitis B vaccine was safe and effective. It was better than the plasma vaccine with the same dose.

Female↗
PubMed1994

[The prognostic characteristics of hypertensive left ventricular hypertrophy in a rural population].

One hundred and twenty-six rural hypertensive patients with ECG left ventricular hypertrophy (HT-LVH) were followed up for 10 years to investigate the prognostic characteristics in a population with low prevalence of hypertension (2.93%) and low plasma cholesterol (4.59 +/- 1.00mmol/L). A cohort of age, sex, region and occupation matched hypertensives without LVH (HT, n = 163) and normotensives (NT, n = 275) served as controls. The major cause of death in rural hypertensives with ECG LVH in this study was stroke (56.8%). After stratification of BP, no significant difference of stroke risk was found between patients with LVH and hypertensives without LVH, while cardiovascular risk in the patients with LVH plus ST segment depression persisted. LVH per se seems not to be an independent factor for stroke. The high stroke rate in patients with LVH may be ascribed to the coexisting higher level of BP. After adjustment of coexisting hypertension, ECG LVH based on voltage only was not an independent risk factor of stroke and cardiovascular events, while LVH plus ST segment depression was closely related to cardiovascular events. In this low level, plasma cholesterol did not affect the mortality rate of stroke.

Adult↗
PubMed1994

Programming for recognition and programming for response. Separate developmental subroutines in the murine thymus.

Pre-T cells become programmed with the capacity to make functional responses to activating stimuli in a process that occurs prior to, and independently of, T-cell receptor gene rearrangement and T-cell receptor-dependent positive selection. In spite of this early programming, as differentiation proceeds further the cells enter a stage in which they appear to be unable to make any functional responses. This 'eclipse' phase begins when the cells undergo successful T-cell receptor beta-chain rearrangement and ends, with the return of their functional competence, only when they successfully traverse positive selection. These results suggest that pre-T cells are subject to two distinct subroutines of differentiation, which cannot operate at the same time: one which confers function and one which confers and selects recognition specificity. To provide a possible molecular basis for the relationship between these two processes, we consider specific alterations in response-associated transcription factors that may cause the changes in responsiveness observed during programming for recognition. The interplay of the two differentiation subroutines is proposed to be a consequence of the use of common transcription factors in different combinatorial contexts for functional responses, assembly of T-cell receptor complexes, and selection.

Aging↗
PubMed1994

Enhancement of expression of human granulocyte-macrophage colony stimulating factor by argU gene product in Escherichia coli.

Human granulocyte-macrophage colony stimulating factor (hGM-CSF) was cloned into expression vector pIN III-ompA1 and expressed in Escherichia coli JA221. When supplementation with a minor tRNA(AGA/AGG)Arg encoded by the E. coli argU gene, the expression level of hGM-CSF was raised about 3-4-fold, although there is only one rare AGG codon in hGM-CSF cDNA gene.

Base Sequence↗
PubMed1994

[Effects and mechanism of total saponins of Panax Notoginseng on anti-inflammation and analgesia].

In this study the effects of total saponins of Panax notoginseng (TSPN) and electroacupuncture (EA) were compared. Liquid paraffin was intraperitoneally injected (0.1 ml/mouse) to establish the animal model with inflammation. The mice were randomly divided into 4 groups with different treatments for 7 days: EA group, TSPN group (100 mg.kg intraperitoneal administration), Naloxone (Nx) plus TSPN group and EA plus TSPN group. The pain threshold was measured by a detector (EQ-9E) and the nitroblue tetrazolium test (NBT) for polymorphonuclear neutrophil (PMN) bacteriocidal activity and the alpha-naphthyl acetate esterase (ANAE) histochemical staining for detection of the focal pattern lymphocyte subpopulation and the toluidine blue histochemical staining for detection of degranulation rate peritoneal mast cells were performed. The results showed that in TSPN, EA and EA plus TSPN group the pain threshold was elevated significantly, the enumeration of NBT positive PMN and the ANAE-F lymphocyte subpopulation was enhanced. All the above effects could be partially inhibited by naloxone. Between TSPN group and Nx group the degranulation rate of peritoneal mast cells had no significant difference. Since the TSPN and EA have similar effects e.g. anti-inflammatory, analgesic and immunomodulatory action, it suggested that the TSPN might be somewhat agonist of the opioid like peptide receptor without addiction side reactions.

Acupuncture Analgesia↗
PubMed1994

Effect of neuromuscular blockade on facial nerve monitoring.

Direct facial nerve stimulation and monitoring during cerebellopontine angle (CPA) tumor surgery are critical for identification and preservation of function. Electrically evoked facial nerve monitoring was compared with ulnar train-of-four monitoring under progressive neuromuscular blockade. Using a rabbit model, the facial nerve function of six controls was compared to that of six specimens with acute or chronic injuries. Eight of 18 patients who had undergone CPA tumor resection during one year were also studied. Regression analysis correlated between ulnar nerve monitoring and facial electromyographic (EMG) peak voltage in all groups. Facial EMG was measurable, even with 75 percent receptor blockade. The results of this study support the hypothesis that high degrees of neuromuscular blockade do not preclude satisfactory EMG monitoring of the facial nerve during CPA tumor surgery. This study did demonstrate that chronically injured facial nerves may show greater sensitivity to the effects of neuromuscular blockade. Lower levels or avoidance of neuromuscular blockade should be employed under these circumstances.

Animals↗
PubMed1994

Early onset posttraumatic cystic myelopathy complicating spinal cord injury.

Three cases of posttraumatic cystic myelopathy occurring early in the postinjury period are reported. A patient with C5 tetraplegia developed bilateral upper extremity paresthesias and right upper extremity weakness 2 and a half months postinjury necessitating immediate syringo-subdural shunting. A patient with C6 tetraplegia complained of left upper extremity paresthesias 2 months postinjury. A syringoperitoneal shunt was placed 19 months postinjury due to new onset intermittent weakness of the right upper extremity. A patient with C4 tetraplegia developed right upper extremity paresthesias, sensory loss, and weakness 56 days postinjury; it was treated conservatively. Two years postinjury he required surgery because of progression of symptoms. A review of the literature reveals that posttraumatic cystic myelopathy has been found to be an incidental pathologic finding at autopsy within 2 months postinjury. However, sensory and motor loss have not been clinically described as an early complication of spinal cord injury. We conclude that posttraumatic cystic myelopathy should be considered in the differential diagnosis of motor or sensory loss occurring early in the postinjury period.

Adult↗
PubMed1993

Activation of the leu-500 promoter: a topological domain generated by divergent transcription in a plasmid.

The Salmonella typhimurium leu-500 promoter is active only in topA strains. In an earlier study (Chen, D., Bowater, R., Dorman, C., & Lilley, D. M. J. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 8784-8788), we showed that the activity of this promoter on a circular plasmid is a function of the transcription and translation of an adjacent tetA gene, and we suggested that the effect arises because of increased local negative superhelix density due to transcription (Liu, L. F., & Wang, J. C. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 7024-7027) initiated at the tetA promoter. In this study we show that translation of the 5' (N-terminal) section of tetA is required for activity of the leu-500 promoter, consistent with a requirement for membrane association of TetA. We have also shown the importance of a second transcription unit, the ampicillin resistance gene bla, in the activation of the leu-500 promoter. Thus the activity of the leu-500 promoter was reduced by partial deletion or premature termination of bla and was increased when the transcription of bla was boosted by the insertion of the stronger tac promoter. However, even in the latter situation the role of the tetA gene is dominant, and deletion of the tetA gene reduced activity of the leu-500 promoter to very low levels. These results suggest the existence of a topological domain defined by the divergent bla and tetA transcription units. Membrane insertion at tetA is essential to provide an anchorage point.(ABSTRACT TRUNCATED AT 250 WORDS)

Antiporters↗
PubMed1993

Biodistribution of calcitonin encapsulated in liposomes in mice with particular reference to the central nervous system.

The biodistribution of [125I]porcine calcitonin (pCT) encapsulated in reverse-phase evaporation vesicles (REVs) in mice upon the intravenous administration was examined. It was found that sulfatide significantly improved the stability of REVs in vivo, and altered the relative distribution of [125I]pCT encapsulated in liposomes in mice. These sulfatide-containing REVs were able to target [125I]pCT into the liver and central nervous system (CNS) reasonably well, with the maximal effect of about 40% and 2% of the injected doses occurring at 30 min and 90 min, respectively, after injection. Neither free [125I]pCT, nor sulfatide-free liposome-encapsulated [125I]pCT, nor a mixture of free [125I]pCT and empty sulfatide liposomes was effective. [125I]pCT was widely distributed in the CNS, with predominance in hypothalamus, brainstem, striatum and spinal cord. The results indicate that pCT encapsulated in sulfatide-containing liposomes is able to pass through the blood-brain barrier (BBB), and calcitonin, thus encapsulated, may be applicable to studies on its functions in the CNS.

Animals↗