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Biomedical subjects

M L Cheng

Publications and source records attributed to M L Cheng.

33 records · Page 2Linked to original sources
PubMed1987

Pregnancy-associated esterase in sera of baboons.

Baboon serum samples were resolved by starch gel electrophoresis and polyacrylamide gradient gel electrophoresis and stained with naphthol substrates for esterase activity. An esterase that hydrolyzed alpha-naphthyl butyrate in preference to alpha-naphthyl acetate was found in very high activities in some individuals but not others. It migrated just cathodal of the albumin band in starch gels. In polyacrylamide gradient gels, it co-migrated with albumin and had an apparent molecular weight of approximately 65,000 daltons. Electrophoretic analysis by gel electrophoresis of random serum samples from male and female baboons indicated that this esterase was present only in the sera of pregnant baboons. Further investigation of serial samples collected from carefully monitored baboons confirmed that the amount of activity of this esterase was correlated with stage of pregnancy. Therefore, it was named pregnancy esterase (PE). PE was detectable by gel electrophoresis and chromogenic staining techniques as early as day 30 of pregnancy; its activity gradually increased with progressive pregnancy and reached maximum activity near full term (182 days). Soon after parturition, the activity of PE decreased rapidly and was not detected in maternal sera by day 14 postpartum. No evidence of PE was detected in sera of pregnant humans.

Animals↗
PubMed1986

A novel system for storage of sera frozen in small aliquots.

A novel sample storage system involves the storage of frozen sera and other fluids within small heat-sealed segments of Tygon tubing. Each series of attached segments comprises one sample divided into small aliquots and protected by a cellulose acetate butyrate tube situated in a specially constructed rack in a low-temperature freezer. This storage system offers several benefits including elimination of repeated freezing and thawing, protection against contamination of bulk samples, simplicity in keeping inventory records, ease of retrieving samples, and elimination of the need to return samples to storage. It is efficient, economical and applicable to a variety of liquid specimens, and greatly increases the length of potential storage life.

Animals↗
PubMed1985

A versatile technique for drying polyacrylamide slab gels.

Slab gels of different thickness, and of various homogeneous or gradient concentrations of acrylamide, can be dried rapidly and consistently using a newly developed drying procedure. After drying, stained gels retain excellent resolution of electrophoretic patterns, and unstained gels are suitable for use in autoradiography and fluorography.

Animals↗
PubMed1985

Biological and biophysical properties of the tumor-localizing component of hematoporphyrin derivative.

Reverse-phase chromatography, aqueous gel exclusion, and nonaqueous gel exclusion were assessed as procedures for preparative fractionation of the tumor-localizing product hematoporphyrin derivative. Porphyrin accumulation, fluorescence, and photodynamic cytotoxicity were monitored using the murine Sarcoma 180 tumor. Aqueous gel exclusion chromatography can provide a hematoporphyrin derivative fraction enriched in the tumor-localizing component. A further enrichment occurs when this procedure is carried out at 55 degrees C, but nonlocalizing porphyrins could not be eliminated. While providing a better separation, reverse-phase chromatography cannot provide a tumor-localizing fraction free from contaminating protoporphyrin. However, this and other contaminants can be eliminated from the tumor-localizing fraction via nonaqueous gel exclusion chromatography. This latter separation provides two tumor-localizing products: a fast-eluting fraction enriched in the major photosensitizing component(s); and a more complex slowly eluting fraction enriched in fluorescence localizers.

Animals↗
PubMed1982

Role of a modified ovitrap in the control of Aedes aegypti in Houston, Texas, USA.

A modified ovitrap from which larvae could not escape was employed for one year for the control of Aedes aegypti at Blossom Heights, Houston, Texas. At the end of this period, the Breteau index in the ovitrap area had declined by 36%, in contrast to a sharp increase of nearly 500% in the non-ovitrap area. The premises index in the ovitrap area remained unchanged, while the index in the non-ovitrap area increased by 440%. The problems associated with this control campaign and the use of these "autocidal" ovitraps are discussed.Annual fluctuations in the egg populations of A. aegypti and A. triseriatus were studied by weekly collections of eggs from the ovitrap paddles. The weekly fluctuations of egg numbers, the percentage of ovitraps with eggs of Aedes mosquitos, as well as the ovitrap premises index (i.e., percentage of premises with at least one ovitrap positive) all exhibited a similar fluctuation pattern, with a distinct peak extending from June to October.

Aedes↗
PubMed1979

The genetics of hexokinase in a mosquito, Culex pipiens.

The genetics of hexokinase (HK) variants in a mosquito, Culex pipiens L., was studied using starch gel electrophoresis. Three isozymic forms of HK, all migrating anodally, were present in all three body regions, but in differing proportions. No obvious differences in specificity for three hexose sugars was detected among the three isozymic bands. However, qualitative differences in staining intensity indicate the following order of substrate affinity: glucose greater than fructose greater than mannose. The inheritance of the HK variants is controlled by a pair of co-dominant alleles at a single genetic locus.

Alleles↗
PubMedDate not supplied

The various effects of fractionated oxidized low density lipoproteins on the growth of smooth muscle cells in culture.

The effects of fractionated oxidized low density lipoproteins (oxidized LDL) on the growth of vascular smooth muscle cells (VSMC) and their relationship to the formation of lysophosphatidylcholine (lyso-PC) as well as the activation of protein kinase C (PKC) were studied. VSMC were isolated from porcine aorta by explant culture. LDL was isolated from porcine blood by sequential ultracentrifugation and oxidized LDL was obtained by incubating LDL with 5 microM CuSO(4) at 37 degrees C for various lengths of time. Our results showed that LDL oxidized for 12 h and eluted from fast protein liquid chromatography at 43 min inhibited the growth of VSMC, and that LDL oxidized for longer than 48 h and eluted at 48 min stimulated the growth of VSMC. The formation of lyso-PC in the oxidized LDL correlated well with its stimulatory effect, suggesting that lyso-PC is responsible for the mitogenic effect of oxidized LDL. This stimulatory effect of oxidized LDL was inhibited by staurosporine, a PKC inhibitor. Treatment with oxidized LDL increased the activity of membrane PKC, but it decreased that of cytosolic PKC, suggesting the translocation of PKC from cytosol to the membrane in the presence of oxidized LDL. These results suggested that the oxidized LDL-stimulated VSMC growth was mediated by the formation of lyso-PC and the activation of PKC.

Animals↗
PubMedDate not supplied

Desflurane potentiates atracurium in humans: a comparative study with isoflurane.

STUDY OBJECTIVE: (1) To evaluate the neuromuscular effects of desflurane and its interactions with atracurium and (2) to compare desflurane and isoflurane in these effects. DESIGN: Sequential entry of informed and consenting patients randomly assigned to receive desflurane (n = 25) or isoflurane (n = 25). SETTING: Operating suite of a county-university medical center. PATIENTS: Fifty adults, ASA physical status I, undergoing elective orthopedic surgery. INTERVENTIONS: Following establishment of steady desflurane or isoflurane anesthesia, at 1.25 minimum alveolar concentration (MAC) exhaled for 15 minutes, a randomly predetermined dose of atracurium (0.05, 0.1, or 0.15 mg/kg) was injected intravenously (IV). At the end of surgery, neostigmine 0.04 mg/kg IV was given to reverse the residual block. The neuromuscular effects of desflurane or isoflurane alone, and the dose-response relationship, time course, and reversibility of the neuromuscular effects of atracurium with either anesthetic, were examined in detail and compared using electromyographic quantification of the response of the first dorsal interosseous muscle to train-of-four (TOF) stimulation of the ulnar nerve. MEASUREMENTS AND MAIN RESULTS: TOF fade and depression of the first response (T1) of the TOF were measured in response to desflurane or isoflurane, atracurium, and neostigmine. Desflurane caused more TOF fade than isoflurane prior to atracurium administration. The TOF ratios were 0.91 +/- 0.02 and 0.98 +/- 0.01, respectively (p < 0.05). For other measured neuromuscular parameters, atracurium-induced depression tended to be greater in the presence of desflurane than in the presence of isoflurane, but none of the measured differences reached the statistical significance level of p < 0.05. The ED50, ED95, and 25-75% recovery index of atracurium were 0.038 mg/kg (95% confidence level; range 0.030 to 0.047 mg/kg), 0.11 mg/kg (0.095 to 0.14 mg/kg), and 31 +/- 4 minutes (means +/- SEM) with desflurane anesthesia, versus 0.043 mg/kg (0.035 to 0.052 mg/kg), 0.13 mg/kg (0.11 to 0.16 mg/kg), and 23 +/- 4 minutes with isoflurane anesthesia (p = 0.1-0.2). Continuation of either anesthetic at 1.25 MAC prevented complete recovery of neuromuscular functions spontaneously or following neostigmine 0.04 mg/kg. CONCLUSION: In ASA physical status I adults, 9% desflurane has neuromuscular effects equal to or slightly in excess of those of 1.6% isoflurane.

Adolescent↗