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Biomedical subjects

L Chen

Publications and source records attributed to L Chen.

At least 1,189 records · Page 66Linked to original sources
PubMed1994

Luciferase activity as a marker of tumor burden and as an indicator of tumor response to antineoplastic therapy in vivo.

The gene encoding firefly luciferase has been used as a reporter gene for the study of gene function. The luciferase catalyzes its substrate and subsequently produces luminescence. In addition, it is not present in mammalian cells. We have therefore explored its use in monitoring the growth of tumors in vivo. The luciferase gene was transfected into two murine tumor lines, i.e. c162 melanoma and M109 lung carcinoma, and the luciferase activity associated with the cells was determined by a rapid chemiluminescent reaction. Luciferase activity was well-correlated with the number of tumor cells in vitro. Luciferase activity also correlated with the tumor burden in vivo, as well as with the effect of an adoptive T cell transfer therapy in the syngeneic C3H/HeN mice experimental tumor model. This assay offers the advantage of being quantitative, rapid, and reliable for the detection of tumor burden and for the evaluation of the effect of antineoplastic therapy.

Animals↗
PubMed1994

An investigation on the accuracy of three-dimensional space reconstruction using the direct linear transformation technique.

An investigation on the three-dimensional calibration errors associated with the direct linear transformation (DLT) technique was carried out using a two video camera system. Thirty different configurations in five groupings of different numbers of control points were tested. The results showed that the accuracy improved as the number of control points increased from 8 to 24. Further, it was demonstrated that the best accuracy was achieved when the control points were evenly distributed throughout the control region. For the system under investigation, an accuracy of 1-2 mm in the x and y directions, 4-6 mm in the z direction and 6-7 mm for the resultant was obtained in a control space of 2.10 x 1.35 x 1.00 m. Additionally, the accuracy for points outside the control space and the systematic error associated with the control object were studied. Tests were done on a 32-point rectangular calibration frame, and the results indicated that the calibration errors could be reduced by 20-40% when an appropriate quadratic function was used to modify the standard DLT method.

Calibration↗
PubMed1994

The dose-response relationship for hypoxic pulmonary vasoconstriction.

In 12 pentobarbital anesthetized dogs the lungs were independently ventilated with a double piston ventilator. The right lung was ventilated throughout with 100% oxygen. Blood was drawn from the right atrium and pumped through a bubble oxygenator to a cannula in the ligated left main pulmonary artery. The pressures in the left main pulmonary artery and the left atrium were recorded during constant flow while the oxygen tension in the left lung alveolar gas and the perfusate were varied either to match each other (Protocol 1) or differ (Protocol 2) over the range from "zero" to "100%" oxygen. From the combined data a three dimensional response surface for hypoxic pulmonary vasoconstriction was derived. The maximum increase of pulmonary vascular resistance (r%PVRmax) was defined at a stimulus oxygen tension (PSO2) of 10 mmHg amounting to a 3.15 +/- (0.18)-fold increase of the vascular resistance on "100%" oxygen. The stimulus oxygen tension was shown to be PSO2 = PVO2(0.41) x PAO2(0.59) and the dose-response sigmoid for hypoxic pulmonary vasoconstriction in canine lungs was derived as r%PVRmax = 100 (PSO2(-2.616))/(6.683 x 10(-5) + PSO2(-2.616)) These results appear to reconcile observations from a number of laboratories and to be of quite general application.

Animals↗
PubMed1994

PCPA reduces both monoaminergic afferents and nonmonoaminergic synapses in the cerebral cortex.

In order to examine the possible trophic, nontransmitter role of monoaminergic fibers in the adult CNS, synaptic structures were examined in different laminae of the somatosensory cortex of the rat following a p-chlorophenylalanine (PCPA)-induced decrease of monoamine. Synaptic densities were reduced in a dose-dependent fashion by 30-50% in the target area of monoamine fibers following four injections of PCPA made over a 1-week period. Although serotonin- and tyrosine hydroxylase-immunopositive profiles were frequently observed in all laminae of the cerebral cortex, only a few such profiles had the morphology of synapses. Therefore, virtually all of the reduction in synaptic structures following PCPA treatment involved nonmonoaminergic fibers.

Animals↗
PubMed1994

An experimental study of contralateral C7 root transfer with vascularized nerve grafting to treat brachial plexus root avulsion.

Experimental rat models of simulated brachial plexus injuries were devised to compare the effect of contralateral C7 root transfer with phrenic neurotization. The effect of vascularized nerve grafting (VNG) was also compared with the use of conventional nerve grafts (CNG) in the treatment of root avulsion of the brachial plexus. 160 rats were randomly divided into four groups of 40 each; contralateral C7 root transfer with a vascularized ulnar nerve graft (C7-VNG), contralateral C7 root transfer with conventional ulnar nerve grafting (C7-CNG), ipsilateral phrenic nerve transfer with a vascularized ulnar nerve graft (P-VNG) and ipsilateral phrenic nerve transfer with conventional ulnar nerve grafting (P-CNG). Electrophysiological and histological examinations and functional evaluation were performed at different post-operative intervals. C7 root transfer was found to be superior to phrenic nerve transfer and VNG superior to CNG. Severance of the C7 nerve root was not found to affect limb function on the healthy side.

Animals↗
PubMed1994

Localization and specificity of cytochromes and other electron transfer proteins from sulfate-reducing bacteria.

Recently data have accumulated concerning the electron transfer chains of sulfate-reducing bacteria in general and of the genus Desulfovibrio in particular. Because of the ever growing number of newly discovered individual redox proteins, it has become essential to try to assign them to physiologically relevant chains. This work presents some new data concerning the localization of these proteins within the bacterial cell and the specificity of electron transfer between the three types of hydrogenases which have been found so far in Desulfovibrio, namely the iron-only, the iron-nickel and the iron-nickel-selenium enzymes. The iron-only hydrogenase reduces cytochromes which have bis-histidinyl heme ligation or histidinyl-methionyl heme ligation. In contrast, the iron-nickel and iron-nickel-selenium hydrogenases cannot reduce cytochromes having a His-Met heme ligation, but are very active toward the cytochromes having a bis-histidinyl ligand. This observation has been used to demonstrate that the tetraheme cytochrome c3 can exchange electrons with the monoheme cytochrome c553. No clear specificity has been established for the reaction of hydrogenases toward the hexadecaheme cytochromes from either D vulgaris or D gigas.

Amino Acid Sequence↗
PubMed1994

Cochlear frequency-place map in adult chickens: intracellular biocytin labeling.

A cochlear frequency-place map was developed for adult chickens by labeling cochlear ganglion neurons with biocytin and correlating the location of each labeled fiber along the basilar papilla with the characteristic frequency of the unit's tuning curve. Labeled fibers showed little or no branching within the sensory epithelium and most fibers appeared to terminate on a single hair cell along the neural side of the basilar papilla. The CFs of the labeled neurons ranged from 353 Hz to 3145 Hz and the location of the labeled neurons ranged from 30.1% to 74.4% of the total distance from the apex of the papilla. CFs increased in an orderly manner from the apex towards the base of the papilla. The cochlear frequency map for adult chickens was similar to that estimated from previous cochlear lesion studies carried out on 30 day old chicks, although the predicted frequencies in the adults were slightly higher in some regions of the basilar papilla than in 30 day old animals. However, previous maps developed in young animals (< or = 21 days) using lesion or labeling data predict significantly lower frequencies for a given location than in adult animals particularly in the basal half of the cochlea.

Acoustic Stimulation↗
PubMed1994

Attenuation of coronary flow reserve and myocardial function after temporary subtotal coronary artery occlusion and increased myocardial oxygen demand in dogs.

OBJECTIVES: We examined whether subtotal coronary artery occlusion and reperfusion alter coronary flow reserve and regional myocardial function. BACKGROUND: Total coronary artery occlusion followed by reperfusion results in decreased coronary flow reserve and regional myocardial dysfunction. METHODS: Thirteen anesthetized dogs were subjected to subtotal occlusion of the left anterior descending coronary artery for 1 h, followed by reperfusion for 1 h. During subtotal left anterior descending occlusion, heart rate was increased by atrial pacing. After reperfusion, coronary flow reserve, indicated by reactive hyperemia, as well as coronary flow responses to acetylcholine and nitroglycerin, regional myocardial function and myocardial leukocyte accumulation were measured. RESULTS: After reperfusion, coronary flow reserve was decreased in the ischemic left anterior descending but not the nonischemic circumflex coronary artery region. Myocardial function was also depressed in the left anterior descending coronary region and did not improve on reperfusion. Histologic study showed no leukocyte infiltration in the ischemic left anterior descending coronary region. Myeloperoxidase, an index of myocardial leukocyte accumulation, was similar in the left anterior descending and circumflex coronary regions. Sensitivity of epicardial left anterior descending coronary artery rings to the thromboxane A2 analog U46,619 was enhanced, and relaxation of these rings in response to endothelium-dependent relaxants was decreased. CONCLUSIONS: Coronary flow reserve is reduced and regional myocardial function depressed after subtotal coronary artery occlusion and increased heart rate. A decreased synthesis or increased breakdown of endothelium-derived relaxing factor may be related to a decrease in coronary flow reserve. However, the reduction in coronary flow reserve appears to be unrelated to leukocyte accumulation in the reperfused region.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1994

A sustained elevation in retinoic acid receptor-beta 2 mRNA and protein occurs during retinoic acid-induced fetal dysmorphogenesis.

We have previously shown that oral treatment of pregnant mice with all-trans retinoic acid (RA) at doses which cause 100% fetal dysmorphogenesis results in a rapid elevation in the mRNA of one specific isoform of the RA receptor-beta, RAR-beta 2, in susceptible embryonic regions. To further investigate the involvement of RAR-beta 2 mRNA in teratogenesis, we have examined its expression in mouse embryos exposed to marginal/nonteratogenic and teratogenic dosing regimens of both 13-cis RA and all-trans RA. We have found that the mere elevation in embryonic RAR-beta 2 mRNA levels and free retinoid levels is not sufficient to result in dysmorphogenesis. Rather, retinoid-induced dysmorphogenesis of embryos appears to occur only when RAR-beta 2 mRNA and unbound retinoid levels remain elevated for at least 6-9 h following retinoid treatment resulting in a significant and prolonged elevation in RAR-beta protein levels.

Animals↗
PubMed1994

Association between protein intake and 1-y weight and height gains in Bangladeshi children aged 3-11 y.

We examined 1-y weight and height gains among 238 rural Bangladeshi children aged 3-11 y old to address the hypothesis that dietary protein composition is associated with growth velocity. Energy-adjusted total protein and energy-adjusted protein from sources other than cereal (animal, pulses, and vegetables) were associated with higher weight gains, after adjustment for age, sex, land ownership, diarrhea, acute respiratory infections, other fevers, nutritional status at the beginning of the study, and average body mass index of the mother [daily intake of energy-adjusted noncereal protein (beta +/- SE): 14.2 +/- 6.4 g.y-1.g-1, P = 0.03; total protein: 13.1 +/- 6.3 g.y-1.g-1, P = 0.04; and protein as percent of energy intake: 39.5 +/- 20.2 g.y-1.% of energy from protein-1, P = 0.05]. These findings are compatible with the hypotheses that protein intake may be a limiting factor for weight gain in this population, or that higher protein intake from animal sources (mostly fish) and legumes (lentils and peas) may be accompanied by higher intakes of limiting micronutrients.

Anthropometry↗
PubMed1994

Development of a human lymphoblastoid cell line constitutively expressing human CYP1A1 cDNA: substrate specificity with model substrates and promutagens.

AHH-1 TK+/- cell derivatives were developed that stably express human CYP1A1 cDNA, and an AHH-1 TK+/- derivative expressing higher levels of CYP1A2 cDNA in extrachromosomal vectors which confer resistance to 1-histidinol. The CYP1A1-expressing cell lines, designated h1A1 and h1A1v2, differ by containing one and two CYP1A1 cDNA expression units per vector. The CYP1A2-expressing cell line, designated h1A2v2, also has two CYP1A2 cDNA expression units per vector. Microsomes prepared from CYP1A1 cDNA expressing cells exhibit high, constitutive levels of 7-ethoxyresorufin deethylase (EROD), 7-ethoxycoumarin deethylase (ECD), 7-ethoxy-4-trifluoromethylcoumarin deethylase (EFCD), benzo[a]-pyrene hydroxylase (BPH) activities and spectrally quantifiable cytochrome P450. Kinetic comparisons between cDNA-expressed CYP1A1 and CYP1A2 indicate that CYP1A1 is more active than CYP1A2 for EROD, ECD, EFCD and BPH. CYP1A2 was more active than CYP1A1 for acetanilide hydroxylation and activation of aflatoxin B1 (AFB1). The mutagenicity of selected promutagens were examined in h1A1 cells and control cells. Relative to control cells, the h1A1 cell line exhibits increased sensitivity to the mutagenicity of benzo[a]pyrene, cyclopenta[c,d]pyrene, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and AFB1.

B-Lymphocytes↗
PubMed1994

Sequential effects of follicle-stimulating hormone and luteinizing hormone on mouse cumulus expansion in vitro.

LH and FSH play critical roles in the development and function of the cumulus oophorus of the mammalian follicle, but the significance of cumulus LH receptors and the nature of the functional interaction between LH and FSH in relation to the process of cumulus expansion are not well understood. Controversy may arise from contradictory results of cumulus LH receptor assays, possibly as a consequence of relative sensitivities of the assays utilized, limited availability of tissue of specific developmental stages, or limitations on the access of radiolabeled ligands to cumulus LH receptors in the intact follicle. It has also been difficult to understand the basis for the apparent difference in gonadotropin requirements for cumulus expansion in vitro and in vivo; FSH seems to be required for expansion in vitro and LH initiates expansion in vivo. In this study, we show that expansion of mouse cumulus-oocyte complexes (COCs) in vitro occurs to a degree comparable to that seen in vivo when COCs are challenged with highly purified FSH (hpFSH) and highly purified LH (hpLH) together or when treatment with hpFSH precedes treatment with LH. Saturation radioreceptor assays revealed that FSH up-regulates cumulus cell LH receptors in the absence of LH and that LH may stimulate expansion upon binding to these acutely formed receptors. A model of cumulus expansion describing effects of both FSH and LH in vivo is proposed.

Animals↗
PubMed1994

Histomorphology of neochondrogenesis after antihelical fold creation: a comparison of three otoplasty techniques in the rabbit.

The purpose of this article is twofold: (1) to investigate the histomorphology of cartilaginous proliferation using three different otoplasty techniques and (2) to determine whether recurrence is related either to the method of otoplasty or the duration of suture fixation. Eighteen 6-week-old New Zealand white rabbits were divided into three equal groups. In each animal, a skin pocket was developed on the posterior surface of both ears; the perichondrium of the left ear was stripped off, whereas the perichondrium of the right ear was left undisturbed. Otoplasties were performed by inserting permanent mattress sutures with (Converse-Wood-Smith) or without (Mustardé) cartilaginous incisions or by scoring of the anterior cartilaginous surface of the antihelix (Stenstrom). In each group, sutures were cut at 1, 2, 4, and 6 weeks and the animals killed 1 week later. Histomorphometric analysis was performed. Perichondrial stripping stimulated cartilaginous proliferation in all groups. The antihelical fold maintained its shape best in group 3, in which the anterior perichondrium was rasped; a fibrocartilaginous cap formed over the rasped convex surface of the antihelical fold, reinforcing and stabilizing the newly created fold. Groups 1 and 2, in contrast, demonstrated significantly less anterior cartilaginous proliferation than did group 3, and cap formation was not observed. No significant differences were apparent between groups 1 and 2 in either the quantity or quality of cartilaginous proliferation in any of the time periods. Cutting the sutures at 1 week resulted in loss of shape or "flattening" of the fold in all groups; however, increased cartilaginous proliferation between 2 and 6 weeks stabilized the fold, minimizing deformability.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

The distally based radial forearm fasciosubcutaneous flap with preservation of the radial artery: an anatomic and clinical approach.

The axial-pattern reverse radial forearm fasciocutaneous flap has become one of the primary flaps for reconstruction of soft-tissue defects of the hand. The two main disadvantages of this flap are (1) sacrifice of a major artery that may possibly jeopardize hand viability and (2) morbidity and appearance of the donor site. In an effort to overcome these drawbacks, an anatomic study of a distally based radial forearm fasciosubcutaneous flap with preservation of the radial artery was conducted. Seventeen fresh cadaver forearms were dissected to investigate the contribution of the distal radial artery and its superficial and deep branches to the fasciosubcutaneous plexus of the forearm. The blood supply to the radial forearm fasciosubcutaneous tissue was found to emanate from 6 to 10 septocutaneous perforators of the distal radial artery in the vicinity of the anatomic snuff box that "fan out" at the level of the deep fascia to form a rich plexus supplying the forearm fascia, subcutaneous tissue, and skin. There appeared to be a definite directional component, with the arterioles running longitudinally along the intermuscular septum. The deep fascia and subcutaneous tissue were found to have their own venous system accompanying the small perforating arterioles. Encouraged by these findings, we proceeded to utilize this fasciosubcutaneous flap for coverage of the thumb-index web space (three patients), the dorsum of the hand (two patients), and both the palmar and dorsal aspects of the hand (one patient). Five flaps had almost complete survival. The largest flap in our series suffered significant loss. Minor skin-graft loss occurred in a few cases, and we now delay skin grafting for several days. The distally based radial forearm fasciosubcutaneous flap with preservation of the radial artery can be a very useful and reliable alternative for repairing soft-tissue defects of the hand, obviating the need for the classic fasciocutaneous flap or even a free flap. This flap not only preserves the radial artery, which is essential in cases where only the radial artery is functioning, such as following severe hand injuries, but also provides a more acceptable donor site.

Adolescent↗
PubMed1994

Lower face reconstruction using a neurosensory osteocutaneous radial forearm flap and Webster modification lip repair.

An innervated bipaddled osteocutaneous radial forearm free flap was combined with a Webster modification lip repair to successfully reconstruct in one stage the lower face following a devastating shotgun injury with loss of the anterior mandible, floor of the mouth, full-thickness chin, and subtotal lower lip. In addition to a pleasing aesthetic appearance with restoration of facial contour, the patient had a sensate flap with intelligible speech and no problems with drooling or mastication. This approach to a most complex reconstructive problem is technically feasible with a satisfactory aesthetic and functional outcome.

Adult↗