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Biomedical subjects

C Y Cheung

Publications and source records attributed to C Y Cheung.

At least 37 records · Page 2Linked to original sources
PubMed2001

Erythropoietin responses to progressive blood loss over 10 days in the ovine fetus.

Long-term loss of fetal blood can occur with fetomaternal hemorrhage, vasoprevia, or placental previa. Our objective was to determine the effects of progressive fetal blood loss over 10 days on fetal plasma erythropoietin (EPO) concentration and its relationship to arterial PO(2), hematocrit, and the volume of blood loss. Late-gestation fetal sheep (n = 8) were hemorrhaged daily at a rate of 1 ml/min over 10 days. The extent of hemorrhage differed in each fetus and ranged from 30 to 80 ml/day, with the cumulative volume removed ranging from 78 to 236 ml/kg estimated fetal weight. Four fetuses served as time controls. EPO concentration measurements were by radioimmunoassay. Statistical analyses included regression, correlation, and analysis of variance. We found that EPO and arterial PO(2) were unchanged until the cumulative hemorrhage volume exceeded 20-40 ml/kg. Once this threshold was exceeded, plasma EPO concentration increased progressively throughout the study and averaged 14.3 +/- 3.2 times basal values on day 10. EPO concentration, arterial PO(2), and hematocrit changes were related curvilinearly to cumulative hemorrhage volume (P < 0.01), whereas the relationship between plasma EPO and arterial PO(2) was log linear (P < 0.001). We conclude that 1) fetal plasma EPO concentration and arterial PO(2) are insensitive to a slow, mild-to-moderate blood loss over several days; 2) unlike the rapid return of EPO to normal within 48 h after acute hemorrhage, fetal EPO concentration undergoes a progressive increase with moderate-to-severe blood loss over several days; 3) the long-term hemorrhage-induced changes in EPO are best correlated with arterial PO(2); and 4) the fetal EPO response to hemorrhage does not appear to be limited by the fetus's ability to produce EPO.

Animals↗
PubMed2000

Association of human herpesvirus 7 with cytomegalovirus disease in renal transplant recipients.

BACKGROUND: Recent studies have linked human herpesviruses 6 (HHV-6) and 7 (HHV-7) with posttransplant cytomegalovirus (CMV) disease. METHODS: Thirty-seven renal transplant recipients were monitored weekly for CMV, HHV-6, and HHV-7 DNA and serological responses for 12 weeks after transplantation. Plasma CMV load and the occurrence of CMV disease was related to HHV-6 and -7 detection. RESULTS: CMV disease was identified in 12 patients. In a logistic regression analysis, factors significantly associated with CMV disease were the detection of HHV-7 DNA in peripheral blood leucocytes and donorrecipient CMV serostatus. Patients with detectable HHV-7 DNA had significantly higher peak plasma CMV loads (P=0.01). CONCLUSIONS: An association was found between HHV-7, but not HHV-6, DNA detection and CMV disease, suggesting a possible role of HHV-7 in its pathogenesis.

Cytomegalovirus↗
PubMed2000

Effect of esophageal ligation on amniotic fluid volume and urinary flow rate in fetal sheep.

OBJECTIVE: Although the fetus normally swallows large volumes of amniotic fluid each day, it is unclear whether amniotic fluid volume increases after fetal esophageal obstruction or whether fetal urine production changes. Our objective was to determine the effects of fetal esophageal ligation on amniotic fluid volume and urinary flow rate over time. STUDY DESIGN: Seven late-gestation fetal sheep underwent esophageal ligation, and 7 served as time control animals. The urachus was ligated to eliminate urine flow to the allantoic cavity. On days 1, 3, 5, 7, and 9 after surgery, we measured the composition of amniotic fluid, fetal urine, and fetal and maternal blood, as well as amniotic fluid volume and fetal urinary flow rate. A 3-factor analysis of variance was used for statistical analysis. RESULTS: Amniotic fluid volume did not change with time in the control group, averaging 876 +/- 142 mL (mean +/- SEM), and it decreased in the esophageal ligation group (P =.020), averaging 309 +/- 75 mL on day 9. Fetal urinary flow rate was lower (P =.0063) in the esophageal ligation group (431 +/- 27 mL/d) than in the control group (631 +/- 54 mL/d). There were no differences in fetal or maternal blood compositions between the two groups. Amniotic fluid sodium and chloride increased in the ligated animals. CONCLUSION: Polyhydramnios did not occur after esophageal ligation, even though the fetuses excreted approximately 4000 mL of urine over the 9-day study period. This suggests that intramembranous absorption is substantially increased. With only small changes in amniotic solute concentrations, intramembranous solute absorption must occur simultaneously with water, suggesting a near-zero reflection coefficient for solutes. We speculate that fetal urine, lung secretions, or both contain a factor that increases intramembranous permeability.

Amniotic Fluid↗
PubMed1999

A bioseparation apparatus with high-pressure fluid injection and fluid sampling.

A novel apparatus in which fluids may be injected and sampled at high pressure is described. Bioseparation applications of the apparatus were demonstrated in three model systems: (1) lambdaDNA was eluted under pressure from an anion exchange column into a low-salt (0.25 M) buffer, thereby eliminating conventional time-consuming desalting procedures required for downstream analysis of the DNA; (2) RNA was separated under pressure from a RNA/DNA mixture, thereby enabling rapid differential preparation of nucleic acids; and (3) an antibody was purified from a protein mixture by affinity capture at one pressure and dissociation from the antigen binding partner at a second pressure, thereby enabling the immunoreactivities of both antibody and antigen to be preserved during the separation process.

Animals↗
PubMed1999

Characterization of SYBR Gold nucleic acid gel stain: a dye optimized for use with 300-nm ultraviolet transilluminators.

The highest sensitivity nucleic acid gel stains developed to date are optimally excited using short-wavelength ultraviolet or visible light. This is a disadvantage for laboratories equipped only with 306- or 312-nm UV transilluminators. We have developed a new unsymmetrical cyanine dye that overcomes this problem. This new dye, SYBR Gold nucleic acid gel stain, has two fluorescence excitation maxima when bound to DNA, one centered at approximately 300 nm and one at approximately 495 nm. We found that when used with 300-nm transillumination and Polaroid black-and-white photography, SYBR Gold stain is more sensitive than ethidium bromide, SYBR Green I stain, and SYBR Green II stain for detecting double-stranded DNA, single-stranded DNA, and RNA. SYBR Gold stain's superior sensitivity is due to the high fluorescence quantum yield of the dye-nucleic acid complexes ( approximately 0.7), the dye's large fluorescence enhancement upon binding to nucleic acids ( approximately 1000-fold), and its capacity to more fully penetrate gels than do the SYBR Green gel stains. We found that SYBR Gold stain is as sensitive as silver staining for detecting DNA-with a single-step staining procedure. Finally, we found that staining nucleic acids with SYBR Gold stain does not interfere with subsequent molecular biology protocols.

Animals↗
PubMed1999

The effect of streptozotocin-diabetes on beta-endorphin level and proopiomelanocortin gene expression in the rat pituitary.

Streptozotocin-induced diabetes for 4 weeks resulted in a decrease in proopiomelanocortin (POMC) mRNA in both the anterior lobe (AL) and the neuro-intermediate lobe (NIL) of the rat pituitary. The beta-endorphin levels decreased in the NIL but not in the AL. It is concluded that the synthesis of POMC in the pituitary is inhibited in diabetic rats and that there is a decrease in beta-endorphin release from the anterior pituitary.

Animals↗
PubMed1999

Correction of hemorrhage-induced anemia with intra-amniotic iron in the ovine fetus.

OBJECTIVE: This study tested the hypothesis that intra-amniotic iron treatment would enhance fetal red blood cell production after an acute, severe fetal hemorrhage of 40% of estimated blood volume over 2 hours. STUDY DESIGN: Three groups of late-gestation ovine fetuses were studied for 10 days: (1) control fetuses (n = 8), (2) fetuses hemorrhaged on day 3 (n = 11), and (3) similarly hemorrhaged fetuses supplemented with a single bolus of 60 mg of iron injected intra-amniotically immediately after the hemorrhage (n = 7). Statistical analysis was by 3-factor analysis of variance. RESULTS: At 24 hours after hemorrhage, red blood cell mass increased 5% in the control group and was reduced equally in both hemorrhage groups by 32% below day 3 prehemorrhage values. At 7 days after hemorrhage, red blood cell mass increased 27.8% +/- 2.6% (SE) above day 3 baseline values in the control fetuses. In the nonsupplemented hemorrhaged fetuses, red blood cell mass was not different from prehemorrhage values after 7 days (+3.7% +/- 4.1%), whereas red blood cell mass increased by 29.9% +/- 6.1% above prehemorrhage values in the iron-supplemented hemorrhage group (P <.001). CONCLUSION: Intra-amniotic iron supplementation resulted in full restoration of red blood cell mass within 7 days after a large loss of blood in fetal sheep, whereas restoration failed without iron supplementation. Intra-amniotic iron treatment may be of therapeutic value in restoring red blood cell mass in human fetuses with certain types of anemia such as that resulting from fetal or fetomaternal hemorrhage.

Amnion↗
PubMed1998

RNA quantitation by fluorescence-based solution assay: RiboGreen reagent characterization.

We describe the development of a sensitive fluorescence-based solution assay for RNA using a new dye, RiboGreen RNA quantitation reagent. RiboGreen reagent exhibits >1000-fold fluorescence enhancement and high quantum yield (0.65) upon binding nucleic acids, with excitation and emission maxima near those of fluorescein. Unbound dye is essentially nonfluorescent and has a large extinction coefficient (67,000 cm-1 M-1). The RiboGreen assay allows detection of as little as 1.0 ng/ml RNA in a standard fluorometer, filter fluorometer, or fluorescence microplate reader-surpassing the sensitivity achieved with ethidium bromide by 200-fold. The linear quantitation range for RiboGreen reagent extends over three orders of magnitude in RNA concentration. Using 750 nM RiboGreen reagent, we quantitated 20 ng/ml to 1.0 microg/ml RNA. By diluting the reagent to 75 nM, we could quantitate 1.0 to 50 ng/ml RNA. Both assay ranges exhibited linear fluorescence increases versus RNA concentration (r2 = 0.999). Assay linearity was maintained in the presence of salts, protein, urea, ethanol, chloroform, agarose, and some detergents. Several different RNA types yielded similar signal intensities and detection sensitivities. The assay is easy to use, rapid, and readily adaptable for automation.

Artifacts↗
PubMed1998

Early diagnosis of primary human herpesvirus 6 infection in childhood: serology, polymerase chain reaction, and virus load.

Qualitative and quantitative polymerase chain reaction (PCR) for human herpesvirus 6 (HHV-6) DNA in whole blood and plasma was correlated with serology and clinical assessment in 143 children hospitalized for undifferentiated febrile illness to evaluate options for diagnosis of primary HHV-6 infection on the acute blood specimen. PCR and serology for HHV-7 were done in parallel to define serologic cross-reactions. Using HHV-6 seroconversion as the reference standard, detection of HHV-6 DNA in whole blood in the absence of antibody in the plasma was the most reliable evidence of primary HHV-6 infection. Detection of HHV-6 DNA in plasma and a high virus load in whole blood (>3.3 log10 copies/5 microL) had a sensitivity of 90% and 100%, respectively, in diagnosing primary HHV-6 infection. However, both were occasionally found in patients with other infections, possibly associated with HHV-6 reactivation. Maternal antibody may confound interpretation of serology in patients under 3 months of age.

Antibodies, Viral↗
PubMed1998

Ovine vascular endothelial growth factor: nucleotide sequence and expression in fetal tissues.

To examine the role of vascular endothelial growth factor (VEGF) in mediating angiogenesis and vascular permeability during fetal development, we determined the gene expression of VEGF in ovine fetal tissues. Further, we cloned and sequenced the ovine VEGF cDNA encoding VEGF164 from sheep placenta. VEGF protein was localized in epithelial cells of the placenta and fetal kidney, and in hepatocytes of the fetal liver. By Northern analysis, a major VEGF mRNA species of 3.7 kb was identified in all tissues examined, with abundance highest in the lung and lowest in the liver. The most prominent molecular form expressed in ovine fetal tissues appeared to be VEGF164 with low levels of expression of VEGF120 and VEGF188. Cloning and sequence analysis of the most abundant form of ovine VEGF cDNA in the placenta confirmed the prediction of a 164-amino acid peptide, with a putative N-terminal signal sequence of 26 amino acids. Comparison of the VEGF cDNA sequence among different species revealed that VEGF is highly conserved suggesting an important role in development.

Amino Acid Sequence↗
PubMed1998

High-pressure-mediated dissociation of immune complexes demonstrated in model systems.

The use of pressure to disrupt immune complexes was demonstrated in two model systems: prostate-specific antigen (PSA) and anti-PSA antibody; and epiglycanin, a mucin glycoprotein, and an antibody specific to that protein. Dissociation of the anti-PSA antibody from the immobilized PSA antigen was observed when pressures of 415 MPa and 550 MPa (1 MPa approximately 144 psi) were applied at room temperature (approximately 21 degrees C). Application of pressures ranging from 140 MPa to 550 MPa resulted in dissociation of antibody from epiglycanin. In both cases, the rebinding of dissociated antibody to immobilized antigen indicated that the effect of high pressure on the binding of the immune complexes was reversible. These findings suggest that application of high hydrostatic pressure has the potential to be used to significantly improve the sensitivity and specificity of clinical assays.

Antibodies↗
PubMed1997

Human herpesvirus-6 and human herpesvirus-7 infections in bone marrow transplant recipients.

Human cytomegalovirus (HCMV), human herpesvirus-6 (HHV-6), and human herpesvirus-7 (HHV-7) DNA in peripheral blood leukocytes (PBL) of 61 bone marrow transplant recipients was monitored weekly during the first 12 weeks post-transplantation by a nested polymerase chain reaction (PCR). Thirty-seven (61%), 17 (28%), and 32 (53%) of patients had one or more PBL specimens positive for HCMV, HHV-6 or HHV-7 DNA, respectively. HHV-7 DNA in PBL during the early post-transplant period was associated with a longer time to neutrophil engraftment (mean 28.8 days vs 19.8 days; P = 0.01). In two patients who failed to engraft, HHV-6 DNA and HHV-7 DNA was detected in plasma and PBL, respectively, early in their post-transplant period. Patients with HCMV disease were more likely to have concurrent HHV-7 DNA in PBL prior to onset of disease than were patients with asymptomatic HCMV infection, suggesting that HHV-7 may be a cofactor in the progression from HCMV infection to HCMV disease. In the 17 patients (179 specimens) in whom viral DNA in plasma was studied (in addition to PBL), a positive result was found only in 3. In each, viral DNA in plasma appeared to correlate with clinically significant disease. HHV-7 DNA in plasma was associated with encephalitis in an allograft recipient.

Acyclovir↗
PubMed1997

Effect of three hours of hypoxia on atrial natriuretic factor gene expression in the ovine fetal heart.

OBJECTIVES: The current study investigated the effects of 3 hours of hypoxia on atrial natriuretic factor gene expression and peptide content in each of the four cardiac chambers of the near-term ovine fetus. STUDY DESIGN: Twenty-three chronically catheterized ovine fetuses at 125 to 129 days' gestation (term 145 days) were used for this study. Fetal hypoxia was induced for 3 hours in 12 fetuses by infusion of nitrogen into the maternal trachea. The remaining fetuses were used as controls. Fetal arterial PO2 and plasma atrial natriuretic factor concentrations were measured during hypoxia. At the end of the hypoxic period atrial natriuretic factor peptide contents and messenger ribonucleic acid levels in each cardiac chamber were determined by radioimmunoassay and Northern blot analysis, respectively. RESULTS: With infusion of nitrogen into the maternal trachea, fetal arterial PO2 was reduced within 30 minutes by an average of 8.0 +/- 0.3 (SEM) mm Hg (p < 0.0001) and remained reduced at this level throughout the entire hypoxic period. Plasma atrial natriuretic factor concentrations increased by 1152 +/- 212 pg/ml (p < 0.003) and the increase was sustained for the duration of hypoxia. Atrial natriuretic factor peptide and messenger ribonucleic acid levels were much higher in the atria than in the ventricles. Hypoxia did not result in alterations of atrial natriuretic factor peptide content or messenger ribonucleic acid abundance in each cardiac chamber. CONCLUSIONS: In the near-term ovine fetus, 3 hours of hypoxia resulted in greatly elevated plasma atrial natriuretic factor concentrations; this response was sustained for the duration of hypoxia. However, the increase was not associated with a detectable change in atrial natriuretic factor peptide content or an induction of atrial natriuretic factor gene expression in the atria and ventricles.

Animals↗
PubMed1996

Activation of tyrosine hydroxylase by pituitary adenylate cyclase-activating polypeptide (PACAP-27) in bovine adrenal chromaffin cells.

The effect of pituitary adenylate cyclase-activating polypeptide (PACAP-27) on tyrosine hydroxylase activity has been studied in intact, cultured, bovine adrenal chromaffin cells. Tyrosine hydroxylase activity was determined in situ by measuring the production of 14CO2 following the hydroxylation and rapid decarboxylation of [14C]tyr offered to the cells. PACAP-27 increased tyrosine hydroxylase activity 3-fold over 10 min. With an EC50 of 10-20 nM. PACAP-38 was approximately 2-fold less potent. Removing extracellular Ca2+ reduced basal tyrosine hydroxylase activity and the activation produced by both PACAP-27 and forskolin by about 20%. In the absence of extracellular Ca2+, chelation of intracellular Ca2+ by treating cells with BAPTA-AM (50 microM) caused a consistent 40-50% reduction in basal tyrosine hydroxylase activity and in the responses to forskolin and PACAP-27. The tyrosine hydroxylase activation produced by PACAP-27 was unaffected by the protein kinase C inhibitor Ro 3l-8220 (3 microM), but was reduced by 85% by the protein kinase A inhibitor H89 (10 microM). PACAP-27 increased cellular cyclic AMP levels 3-fold at 100 nM. The results suggest that PACAP-27 activates tyrosine hydroxylase in bovine chromaffin cells through cyclic AMP formation and protein kinase A activation, and that both extracellular and intracellular Ca2+ modulate the effect of the adenylate cyclase/cyclic AMP/protein kinase A signalling pathway on tyrosine hydroxylase activity.

Animals↗
PubMed1995

Vascular endothelial growth factor gene expression in ovine placenta and fetal membranes.

OBJECTIVE: The purpose of this study was to explore the gene expression of vascular endothelial growth factor (VEGF) in placental cotyledon, chorion, and amnion of the ovine fetus. STUDY DESIGN: Time-dated pregnant sheep with singleton or twin fetuses at a gestational age ranging from 100 to 140 days were used for the study. Placental cotyledonary, chorionic, and amniotic tissues were collected and processed for messenger ribonucleic acid analysis by Northern blotting and reverse transcription-polymerase chain reaction. RESULTS: By use of a phosphorus 32-labeled human VEGF complementary deoxyribonucleic acid probe, a prominent VEGF messenger ribonucleic acid transcript of 3.7 kb was detected in the cotyledon, chorion, and amnion. A minor band of 1.7 kb was also found but only in the cotyledon and chorion. The abundance of messenger ribonucleic acid encoding VEGF was highest (p < 0.001) in the cotyledon and lowest in the amnion. In these tissues polymerase chain reaction-amplified products corresponding to VEGF121, VEGF165, VEGF189, and VEGF206 were identified by ethidium bromide. In addition, a polymerase chain reaction fragment corresponding to VEGF145 was observed. These fragments produced specific hybridization signals with the human VEGF radioactive probe where the intensity of the signal was strongest for VEGF165 and weakest for VEGF189. CONCLUSIONS: VEGF gene expression was detected in the cotyledon, chorion, and amnion of the near-term ovine fetus. These findings suggest that vascular endothelial growth factor may play a role in the induction of angiogenesis and promotion of permeability in the microvessels that perfuse the placental and fetal membranes.

Animals↗
PubMed1995

Regulation of atrial natriuretic factor secretion and expression in the ovine fetus.

The cardiac hormone atrial natriuretic factor (ANF) is present in the fetal circulation at high concentrations and exceeds that in the maternal circulation. Administration of exogenous ANF into the near-term ovine fetus lowers arterial pressure and reduces blood volume. The fetal kidney responds to ANF with a diuresis and natriuresis. The physiological stimuli which modulate ANF secretion in the fetus include vascular volume expansion, hyperosmolality and hypoxia, with hypoxia being the most potent stimulus. In addition, endothelin administration into the fetus increases plasma ANF concentrations. The fetal atria appears to be the primary site of ANF synthesis, although the ventricles also produce ANF. The expression of ANF peptide and its messenger RNA in the fetal atria and ventricles demonstrate a developmental pattern. Thus, the secretion of ANF may be mediated by factors such as endothelin and may be augmented by stimuli such as hypoxia which acts through induction of cardiac ANF gene expression.

Animals↗
PubMed1994

Regulation of atrial natriuretic factor release by endothelin in ovine fetuses.

Endothelin is a potent vasoconstrictor synthesized by vascular endothelial cells. In the adult, endothelin has been shown to stimulate the release of atrial natriuretic factor (ANF) through a direct action on atrial cardiocytes. The present study was designed to investigate, in the fetus, whether endothelin would similarly release ANF into the circulation. In addition, the effects of endothelin on fetal cardiovascular and urinary functions were explored. Chronically catheterized ovine fetuses between 126 and 139 days gestation (term 147 days) were used for the study. After a 30-min control period, the fetuses were infused intravenously with vehicle (n = 6) or endothelin-1 (n = 9) at 25 ng.min-1.kg-1 for 30 min, and this was followed by a 60-min recovery period. In response to endothelin infusion, plasma ANF levels were significantly elevated. Endothelin infusion acutely increased fetal arterial pressure without affecting venous pressure. Fetal heart rate decreased, and blood volume was reduced. Fetal urine flow rate and urinary excretion of electrolytes did not change during the endothelin infusion but were elevated during the recovery period. The fetus developed hypoxia and acidemia. Thus our study demonstrates that endothelin is effective in stimulating ANF release in the fetus, and this effect appears to be unrelated to the venous pressure changes. In addition, the results suggest that endothelin is a potent vasoconstrictor of the fetal systemic and umbilical vascular beds. The decrease in blood volume and increase in urinary excretion of fluid and electrolytes in response to endothelin are consistent with the known actions of ANF, which is elevated during endothelin infusion.

Animals↗