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Biomedical subjects

L Fan

Publications and source records attributed to L Fan.

At least 145 records · Page 8Linked to original sources
PubMed1994

Colocalization of human papillomavirus type 11 E1[symbol: see text]E4 and L1 proteins in human foreskin implants grown in athymic mice.

The most abundant viral mRNA species in tissues infected with HPV 11 consists of two exons, joining a short segment of open reading frame (ORF) E1 to ORF E4, potentially encoding an protein of 10 kDa. E4 gene products have previously been identified by immunohistochemistry in human tissues infected with HPV 1 and HPV 16, and in HPV 11-infected raft cultures. The E1[symbol: see text]E4 mRNA is produced in abundance in HPV 11-infected human foreskin implants grown in athymic mice. In contrast, the L1 mRNA is present at low levels and appears late in the course of infection. To characterize the relationship of these proteins, polyclonal rabbit antisera were produced against bacterially expressed HPV 11 trpE/E1[symbol: see text]E4 and trpE/L1 fusion proteins and tested in an immunohistochemical assay of paraffin-embedded sections of HPV 11-infected human foreskin tissue fixed with 10% buffered formalin phosphate or zinc formalin. In sections fixed with either fixative, the anti-L1 serum stained nuclei of cells in the upper spinous and granular layers. In contrast, the anti-E1[symbol: see text]E4 serum stained the cell membrane and, to a lesser degree, the cytoplasm of cells in the upper spinous and granular layers of tissue fixed with zinc formalin, but not 10% buffered formalin phosphate. In sections treated with both the E1[symbol: see text]E4 and L1 antisera, cell membrane staining occurred in the same cells that exhibited nuclear staining. The HPV 11 E1[symbol: see text]E4 protein appears to be a cell membrane-associated protein. Expression of the HPV 11 E1[symbol: see text]E4 and L1 proteins may be influenced by similar factors in differentiating cells.

Animals↗
PubMed1994

Inhibition of plasmid reporter gene expression in CHO cells by DNA adducts of 2-amino-3-methylimidazo[4,5-f]quinoline and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine.

2-Amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) are two members of a family of carcinogenic heterocyclic amines (HAs) found in cooked meats that form DNA adducts after activation to N-acetoxy derivatives. The ability of IQ- and PhIP-DNA adducts to inhibit gene expression was investigated using a human growth hormone (hGH) reporter gene in a pUC12-based mammalian expression vector under the control of either the herpes simplex virus-1 thymidine kinase promoter or the human immunodeficiency virus-1 long terminal repeat. The plasmids were treated in vitro with 0, 5, 10, or 40 microM N-hydroxy-IQ or N-hydroxy-PhIP in the presence of a 10-fold molar excess of acetic anhydride to generate the N-acetoxy derivatives in situ. The adduct levels in the plasmids were quantitated by the 32P-postlabeling method. The adducted (and control) plasmids were each transfected into repair-deficient or -proficient Chinese hamster ovary cells, and expression of hGH was measured by immunoassay of growth hormone secreted into the cell medium. The results showed that IQ- and PhIP-DNA adducts inhibited gene expression in both plasmids and that the degree of inhibition of hGH production was proportional to the levels of IQ- and PhIP-DNA adducts. The degree of inhibition, however, was independent of the promoter, despite the differences in the strengths of the two promoters to drive hGH production. Repair capacity influenced the extent of inhibition of gene expression by HA adducts since, in general, fewer adducts were needed to inhibit reporter gene expression in repair-deficient cells than in repair-proficient cells. In both cell lines, DNA adducts of PhIP appeared to be more potent in inhibiting hGH expression than adducts of IQ. Whether alteration of gene expression by HA adducts plays a role in the carcinogenicity of these compounds deserves further study.

Animals↗
PubMed1994

HLA-DPB1 polymorphism in the Thais of Southeast Asia.

In this study we examined DPB1 allele frequencies in five ethnic Thai populations resident in different regions of Thailand and neighboring countries. In contrast to other Asian and Pacific populations such as the Japanese, Chinese, Korean, and Papua New Guineans, where DPB1*0501 has consistently been shown to be the most frequent allele, NE Thais and Thai-Khmers demonstrate a prevalence of DPB1*1301. Comparison of DPB1 allele frequencies in the Thais of SE Asia, with known frequencies in the Chinese and Japanese populations of E Asia, would appear to confirm previous calculations of genetic divergence between these Oriental populations.

Alleles↗
PubMed1994

Extracting instantaneous mean frequency information from Doppler signals using the Wigner distribution function.

The Wigner distribution function (WDF) does not require the analysed signals to be stationary within the time segment used for analysis, and instantaneous frequency (IF) information can be obtained from it. Because of the influence of the cross-power of the signal components, however, the interpretation of the IF results is physically clear only for monocomponent signals with infinite data lengths. The IF results for multicomponent signals also suffer from spike problems and are quite unstable even when the signal-to-noise ratio is high. It is suggested that a "pseudo-instantaneous mean frequency," which uses the positive part of the WDF to follow the power distribution changes among frequency components, is used as a simple and rapid way to track frequency changes of Doppler signals. Simulation results show that the pseudo-instantaneous mean frequency does not have the same spike problems and gives stable and relatively accurate information about frequency changes when the sampling frequency is properly chosen.

Ultrasonography, Doppler↗
PubMed1994

A real-time and fine resolution analyser used to estimate the instantaneous energy distribution of Doppler signals.

Doppler ultrasound signal analysers in current use require that the signal be stationary within the time interval of processing, and yield average results for that interval. A real-time instantaneous frequency analyser based on the Wigner distribution function (WDF) has been developed, which provides a means of analysing time-varying signals or signals with short stationary time periods, and also produces results with very high instantaneous temporal resolution without causing significant deterioration of frequency resolution. In addition to the real-time processing, the most recent 2.4 s of Doppler signal is stored in the analyser so that the operator can perform further fine analysis and obtain results with very high resolutions in both the time and frequency domains. The pseudo-instantaneous mean frequency (PIMF) and the Pseudo-Instantaneous Power Distribution (PIPD) are calculated and displayed every 4.0 ms in the real-time processing mode, and with a resolution of between 80 microseconds and 2 ms in the fine resolution analysis mode. The analyser utilises an algorithm developed so that the WDF can be calculated efficiently using the conventional Fast Fourier Transform (FFT) method, and the PIPDs are calculated from data that contribute equally.

Signal Processing, Computer-Assisted↗
PubMed1994

Changes in host muscles induced by excretory/secretory products of larval Trichinella spiralis and Trichinella pseudospiralis.

Excretory/secretory (ES) products obtained by in vitro culture of infective-stage larvae of Trichinella spiralis and T. pseudospiralis were injected intramuscularly at various intervals into mice. Mini-osmotic pumps containing T. spiralis ES products were also implanted subcutaneously and intraperitoneally into rats. The introduction of ES materials into muscles elicited extensive lesions which included dissolution of myofibres, mobilization of mononuclear and polymorphonuclear leucocytes, angiogenesis, hypertrophy of myonuclei, myotube formation, mitosis, muscle bundles becoming rounded and separated from each other, disappearance of Z, I and A bands of sarcomeres, increase in endoplasmic reticulum and Golgi complexes, decrease in glycogen and relocation of mitochondria. These are considered as degenerative/regenerative changes of muscles to injury. Immunodominant epitopes of specific 45-53 kDa glycoproteins in ES antigens of T. spiralis could not be detected in hypertrophic nuclei of injected muscles by using polyclonal and monoclonal antibodies and immunocytochemical methods. ES products of T. spiralis failed to stimulate unsensitized lymphocytes in the lymphocyte transformation test. Infective-stage larvae of T. spiralis released from muscles were found capable of forming nurse cells after injection subcutaneously into rats. It is postulated that the invasion of muscles by trichinellids elicits two independent events, i.e. a general degenerative/regenerative response of muscles and a specific change in genomic expression of myonuclei. The two events are probably mediated by different effector molecules.

Animals↗
PubMed1994

Quadrature-to-directional format conversion of Doppler signals using digital methods.

Four possible quadrature-to-directional format conversion methods using digital techniques are described. These are the phasing-filter technique, the extended Weaver receiver technique, the Hilbert transform in the frequency domain, and the complex FFT. All methods are implemented to give separated time domain outputs as well as frequency domain outputs. The theoretical descriptions are verified by practical implementations. Each of the methods has been implemented in real-time using a commercially available digital signal processing board.

Algorithms↗
PubMed1994

Differences in the power structures of Fourier transform and autoregressive spectral estimates of narrow-band Doppler signals.

There is considerable interest in the application of autoregressive (AR) spectral analysis to ultrasonic Doppler signals. Sonograms produced using this technique are, however, very different from those produced using classic Fourier transform methods. Simulations have shown that the heights of the peaks in the AR spectra of narrow-band signals are not necessarily proportional to signal power, and should be used with caution in the context of Doppler signal processing.

Algorithms↗
PubMed1994

Renal perfusion pressure and renin secretion in bilaterally renal denervated sheep.

To further investigate the influence of renal nerves on renin secretion, the renin secretion responses to step reductions of renal perfusion pressure (RPP) were studied in conscious sheep with innervated kidneys (n = 5) and with bilaterally denervated kidneys (n = 5). The average basal level of RPP in sheep with denervated kidneys (82 +/- 4 mmHg; 1 mmHg = 133.3 Pa) was similar to that in sheep with innervated kidneys (83 +/- 3 mmHg). RPP was reduced in four sequential 15-min steps, to a final level of 54 +/- 2 mmHg in sheep with innervated kidneys and to 57 +/- 1 mmHg in denervated sheep. The renin secretion rate was increased as RPP was reduced in sheep with innervated kidneys. Baseline peripheral plasma renin activity was reduced and there was almost no response of renin secretion rate to reduction of RPP in sheep with denervated kidneys. Also, baseline renal blood flow, urine flow rate, sodium excretion rate, and potassium excretion rate were higher in sheep with denervated kidneys than those with innervated kidneys. Baseline plasma angiotensin II was similar in both groups of sheep. As RPP was decreased, plasma angiotensin II was increased in sheep with innervated kidneys, but was not RPP or renal denervation. In conclusion, hormonal factors, such as angiotensin II and atrial natriuretic factor, do not account for the dramatic suppression of renin secretion in response to the reduction of RPP in sheep with bilateral renal denervation. Renal nerves are a necessary component in the control of renin secretion during reduction of RPP and may contribute to the regulation of baseline plasma renin activity and sodium excretion rate in conscious ewes.

Angiotensin II↗
PubMed1994

Influences of renal nerves and pregnancy on renin secretion in sheep.

To investigate the role of the renal nerves in the control of renin secretion during pregnancy, we prepared sheep with one denervated kidney, bilateral renal vein catheters, and an inflatable aortic occluder. The renin secretory responses to step reductions of renal perfusion pressure (RPP) of the innervated and denervated kidneys were compared in eight nonpregnant and nine pregnant (115-130 days gestation) sheep in a normal conscious state. Nonpregnant sheep had average basal levels of mean arterial pressure (MAP) of 91 +/- 3 mmHg, plasma renin activities (PRA) of 2.3 +/- 0.4 ng ANG I.ml-1.3 h-1, and plasma angiotensin (ANG) concentrations of 8.4 +/- 1.1 pg/ml. Pregnant sheep had reduced levels (P < 0.01) of MAP (76 +/- 3 mmHg) but elevated levels of PRA (3.8 +/- 0.4 ng ANG I.ml-1.h 3-1; P < 0.5) and ANG II (12.0 +/- 1.6 pg/ml; P = 0.08). Four successively reduced levels of RPP were observed for 15 min each in both groups of sheep. In both groups, RPP was reduced to a final level of 51 +/- 2 mmHg. The renal venous-arterial difference of PRA (v-aPRA) from the innervated kidneys was increased as RPP was reduced. However, there was little response of v-aPRA to RPP in denervated kidneys. In nonpregnant sheep, the relationship between RPP and renin secretion rate was characterized by an initially slow phase, over which small reductions of RPP resulted in small increases in renin secretion. As RPP fell, this relationship became progressively steeper in nonpregnant ewes.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗
PubMed1994

Altered gene structure and tissue expression of islet amyloid polypeptide in the chicken.

In mammals, islet amyloid polypeptide (IAPP) is a putative pancreatic peptide hormone that is coproduced and cosecreted with insulin in the beta-cells. However IAPP is also structurally and functionally similar to calcitonin gene-related peptide (CGRP), a 37-amino acid peptide that is expressed predominantly in neurones, and it has been suggested that these peptides arose from a common ancestral gene. In the present study we have characterized an avian IAPP cDNA and gene and have analyzed their expression in various tissues. The cloned chicken IAPP cDNA encodes a 135-amino acid (aa) precursor in which the mature 37-residue IAPP is 80% identical to human IAPP. However, the N-terminal propeptide of chicken proIAPP (55 aa) is considerably longer than that found in the mammalian proIAPPs (9-12 aa) and is comparable in length to that of chicken proCGRP (52 aa). Most of this additional peptide material was found to be encoded in an exon of the cloned chicken IAPP gene that is homologous to exon 3 in the CGRP gene. This exon is absent in the human IAPP gene and thus the exon-intron organization of the chicken IAPP gene more closely resembles that of mammalian CGRP genes. Northern blot analyses demonstrated that chicken IAPP mRNA is expressed predominantly in intestine and brain but at a much lower level in pancreas. The pancreas and intestine contained a single 0.7 kilobase (kb) IAPP transcript while two transcripts, 0.7 kb and 0.9 kb, were detected in brain. Densitometric analysis indicated that IAPP transcripts were 11 times more abundant in brain and intestine than pancreas.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1994

Effect of dynorphin microinjection in the paraventricular nucleus on the hemodynamic response to hemorrhage in the rat.

We studied the effect of dynorphin A-(1-13), dynorphin A-(1-17), des-tyr dynorphin A-(2-17) (inactive at opioid receptor) or normal saline (NS) microinjected into the paraventricular nucleus (PVN) (n = 9/treatment) on mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), stroke volume (SV), and left ventricular stroke work (LVSW) during fixed-volume hemorrhage in conscious rats. Microinjection of dynorphin A-(1-13) (6 nmol) into PVN at 15 min following the termination of fixed volume hemorrhage (8 ml/300 g) significantly decreased MAP from 50 min to 2 hr postinjection (P < 0.05 compared to animals receiving NS), while dynorphin A-(1-17) (6 nmol) significantly decreased MAP from 30 min up to 2 hr postinjection (P < 0.05). Microinjection of des-tyr dynorphin A-(2-17) (6 nmol) into the PVN did not significantly affect MAP following hemorrhage. Recovery of MAP in the dynorphin A-(1-13) and dynorphin A-(1-17) groups following hemorrhage was found to be significantly attenuated compared to the NS group (P < 0.05 and P < 0.01, respectively). Dynorphin A-(1-13) increased heart rate at 20 min and decreased stroke volume at 60 min after microinjection directly into the PVN following hemorrhage when compared with the NS group (P < 0.05). Both dynorphin A-(1-13) and dynorphin A-(1-17) significantly decreased LVSW after PVN injection following hemorrhage compared to NS group (both P < 0.05). No significant effects were observed on CO following microinjection of active or inactive opioid peptides into the PVN following hemorrhage.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Characterization of DNA polymerase-alpha/primase complex from developing embryonic chicken brains.

DNA polymerase-alpha and primase activities present in a complex, have been isolated, partially purified, and characterized from embryonic chicken brain. DNA polymerase-alpha activity, characterized by its sensitivity to N-ethyl-maleimide, high sedimentation coefficient (11.3 S), and acidic isoelectric point (5-5.5) was found in all embryonic ages. Primase activity, the enzyme responsible for the initiation of DNA synthesis, co-sedimented with DNA polymerase-alpha activity on a continuous glycerol velocity gradient. A complex containing both DNA polymerase-alpha and primase activities was isolated by DE-23 cellulose column chromatography of cell-free extracts of different embryonic ages of chicken brain. In addition to the primase complexed with DNA polymerase-alpha, a free primase activity was isolated by DE-23 cellulose column chromatography of an ammonium sulfate (0-45%; w/v) precipitated fraction of embryonic chicken brain cell-free extract. DNA polymerase-alpha activity from developing chicken brains in the embryonic stage was purified by immuno-affinity column chromatography. Of all the single-stranded DNA templates tested, primase activity was found to be maximally active with poly dC. Primase activity was not inhibited by a high concentration of alpha-amanitin. The results obtained may provide insight into further understanding of regulation of chromosomal DNA replication in developing tissues.

Animals↗
PubMed1993

Cardiovascular effects of microinjection of dynorphin fragments into the nucleus of the solitary tract (NTS) are mediated by non-opioid mechanisms.

The nucleus of the solitary tract (NTS) is important for the regulation of cardiovascular homeostasis. In the present study we investigated the effect of dynorphin A-(1-13), dynorphin A-(1-17) and dynorphin A-(2-17) microinjected into the NTS on mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), stroke volume (SV) and left ventricular stroke work (LVSW) following hemorrhage in conscious rats. Following fixed-volume hemorrhage (8 ml/300 g), microinjection of dynorphin A-(2-17) (6 nmol), which is inactive at opioid receptors, into the NTS significantly attenuated the recovery of CO, SV and LVSW following hemorrhage when compared to those animals receiving a microinjection of normal saline (NS) vehicle into the NTS (P < 0.01). NTS microinjection of dynorphin A-(2-17) also increased HR following hemorrhage when compared with the NS group (P < 0.05). No significant effects were observed on CO, SV and LVSW following NTS microinjection of the kappa-opioid agonists, dynorphin A-(1-13) and dynorphin A-(1-17), although dynorphin A-(1-13) microinjection increased HR following hemorrhage when compared with control animals (P < 0.05). Microinjection of all three peptide fragments had no significant effect on MAP when compared with MAP of the control group following hemorrhage. The results of this study suggest that dynorphin A-(2-17) in the NTS can attenuate the compensatory cardiovascular responses to hemorrhage, perhaps via a non-opioid mechanism.

Analysis of Variance↗
PubMed1993

Cloning and analysis of the gene encoding hummingbird proinsulin.

Because hummingbirds exhibit the highest mass-specific metabolic rates seen among vertebrates and rely on sugars as their main energy source, we have investigated the structure of hummingbird insulin (Selaphorus rufus) to determine whether it possesses structural adaptations that increase its receptor binding affinity (potency). We report here the nucleotide sequence of hummingbird proinsulin determined from hummingbird genomic DNA. The predicted amino acid sequence of the A-chain of hummingbird insulin is identical to that of chickens and the B-chain differs by only one amino acid at a noncritical position, B2 (Val in hummingbird and Ala in chicken). These findings suggest that alterations in secretory and metabolic dynamics of insulin are of greater importance than changes in binding affinity in the adaptation to states of high carbohydrate flux in these very energetic organisms.

Amino Acid Sequence↗
PubMed1993

Suggested approaches for research protocols involving the potential for life-threatening reactions.

These guidelines are intended to reduce the potential for serious or life-threatening reactions when clinical research is conducted. The following issues were addressed: identifying the risks involved in the research, providing adequate safeguards in the protocol design and during withholding of medication, anticipating risks, minimizing the chances for human error, providing resuscitative equipment sufficient to deal with the most serious anticipated life-threatening reactions, planning for medical support in case of a life-threatening emergency, and optimizing the use of medical personnel and expertise to handle emergency situations. The guidelines also discuss important general issues about protocol design and implementation and the human subject consent form, which should facilitate the approval of protocols by the governing institutional review board. The guidelines are not meant to be inflexible or applicable to all research situations. However, it is our hope that they will allow for clinical research to be conducted in a manner that affords the research subjects a high degree of protection from unnecessary and possibly fatal injuries.

Bronchi↗
PubMed1993

Effect of dynorphin microinjection in the anterior hypothalamus (AV3V) region on the hemodynamic response to hemorrhage in the rat.

The region surrounding the anteroventral part of the third ventricle (AV3V) is important for the regulation of cardiovascular homeostasis. In the present study we investigated the effect of the kappa-opioid receptor agonists dynorphin A-(1-17) and dynorphin A-(1-13) microinjected into the AV3V region on mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), stroke volume (SV), and left ventricular stroke work (LVSW) during fixed-volume hemorrhage in conscious rats. During fixed-volume hemorrhage (8 ml/300 g), dynorphin A-(1-17) (6 nmol), microinjected into the AV3V, significantly decreased MAP up to 30 min postinjection (P < 0.05). Recovery of MAP, SV, and LVSW in the dynorphin A-(1-17) group following hemorrhage was found to be significantly attenuated compared to that in animals receiving microinjection of normal saline (NS) vehicle into the AV3V (P < 0.05). Hypothalamic microinjection of dynorphin A-(1-13) (6 nmol) also attenuated the recovery of SV following hemorrhage compared with the NS group (P < 0.05). No significant effects were observed on HR or CO following microinjection of dynorphin into the AV3V region. The results of this study suggest that activation of the kappa-opiate receptor system in the AV3V region of the hypothalamus can attenuate the compensatory cardiovascular responses to hemorrhage.

Animals↗