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Biomedical subjects

R Ma

Publications and source records attributed to R Ma.

At least 109 records · Page 6Linked to original sources
PubMed1995

Comparative study of body composition by dual-energy x-ray absorptiometry.

UNLABELLED: Dual-energy x-ray absorptiometry (DEXA) is a readily available technique that has recently been applied to measurement of body composition. In order to validate this technique, results from DEXA were compared with fat-free mass (FFM) and fat mass (FM) measured by total body levels of potassium (TBK), nitrogen (TBN), water (TBW) and carbon (TBC). METHODS: A healthy population of 127 white women and 38 black women with a body mass index of 18-30 were recruited. RESULTS: Compared with each of the other methods, DEXA overestimated FM and underestimated FFM. The slopes of the FM by DEXA versus the FM from each of the four methods were approximately the same, with a s.e.e. ranging from 2.4 to 3.0 units. The slopes of DEXA in comparison to FFM, however, ranged from 0.61 to 0.74 and were significantly less than unity, with a s.e.e. of 1.6 to 2.4 units. CONCLUSION: These findings suggest that at high values of FFM, DEXA is measuring something different from the FFM measured by TBW, TBN and TBK. The program for separating bone and soft tissue and for separating soft tissue into fat and lean at higher values in the DEXA method may need to be adjusted.

Absorptiometry, Photon↗
PubMed1994

Black swallowtail (Papilio polyxenes) alleles encode cytochrome P450s that selectively metabolize linear furanocoumarins.

Cytochrome P450 monooxygenases are involved in metabolism of hostplant allelochemicals by larval Lepidoptera. Biochemical purification of the P450 polypeptide induced in Papilio polyxenes (black swallowtail) larvae in response to xanthotoxin, a linear furanocoumarin, has allowed us to clone cDNAs encoding two allelic variants of the CYP6B1 locus. Expression of these alleles in lepidopteran cell lines using baculovirus expression vectors has demonstrated that both P450 isoforms metabolize substantial amounts of linear furanocoumarins, such as xanthotoxin and bergapten, but not angular furanocoumarins, such as angelicin and sphondin. These linear furanocoumarins are ubiquitous constituents of the hostplants of P. polyxenes. The efficiency of linear furanocoumarin metabolism is strongly affected by the nature of the substituents on the benzene ring; methoxy-derivatives are metabolized more efficiently than are derivatives with smaller (hydroxy-) or larger (8-O isopentenyl) groups. Metabolism of either bergapten or xanthotoxin is inhibited in the presence of the other. In addition, metabolism of linear furanocoumarins is inhibited by the presence of nonmetabolizable angular furanocoumarins, indicating that the active site of CYP6B1 binds angular furanocoumarins. The reactivities described here indicate that P. polyxenes larvae express at least two selective furanocoumarin-metabolic P450s: CYP6B1, which metabolizes a discrete set of linear furanocoumarins, and another P450, as yet unidentified, which metabolizes angular furanocoumarins more efficiently than does CYP6B1.

Alleles↗
PubMed1994

Potent anti-tumor activity and low toxicity of tubeimoside 1 isolated from Bolbostemma paniculatum.

Bolbostemma paniculatum (Maxim.) Franquet (Cucurbitaceae) is a traditional Chinese medicinal plant (1), from which tubeimoside 1 was isolated. The antitumor activity and toxicity of tubeimoside 1 was investigated in vivo and in vitro. The results showed that tubeimoside 1 exerts potent anti-tumor activity with low toxicity. The compound inhibited DNA synthesis and induced phenotypic reverse transformation of tumor cells.

Animals↗
PubMed1994

[Clinical study on repeated infantile respiratory tract infection treated by kanggan zhibao oral liquor].

The clinical observation of repeated infantile respiratory tract infection treated by Kanggan Zhibao (KGZB) oral liquor and controlled with levomisole was studied. The results showed that the total effective rate of KGZB was 93.2%, which was significantly more effective than that of the control group (P < 0.05). In relieving symptoms and signs, KGZB was also superior to the control group (P < 0.05). Both the KGZB and the levomisole could enhance and modulate the immunity function of T-lymphocyte and they could increase RBC-C3b receptor rosette formation rate, so that it had no significant difference in comparing with the healthy group (P > 0.05). It suggested that the therapeutic mechanism was related to this.

Adolescent↗
PubMed1994

[Intracellular recordings and electrophysiological properties of neurons of pancreatic ganglia in vitro].

The work was carried out to investigate electrophysiological properties of neurons of cat intrapancreatic ganglia in vitro by means of intracellular recordings. The mean value of resting membrane potential was -58.5 +/- 8.7 mV (chi +/- s chi, n = 35) with a range from -45 to 72 mV. The mean values of membrane input resistance (Rm), time constant (tau) and capacity (Cm) were 68.6 +/- 5.1M omega, 3.4 +/- 0.2 ms and 50.8 +/- 3.9pF (n = 28), respectively. When depolarizing electrotonic potentials induced by intracellular injection of depolarizing current pulses (0.05-0.5nA, 5ms) reached the threshold potential level, all of the neurons could fire action potentials. The threshold, amplitude, overshoot and duration of spikes were 19.2 +/- 0.5mV, 81.0 +/- 1.7mV, 22.6 +/- 0.9mV and 2.9 +/- 0.1ms (n = 35), respectively. The spike was followed by a prolonged after spike hyperpolarization with amplitude of 20.5 +/- 0.8mV (n = 35). In most of neurons, fast excitatory postsynaptic potentials (f-EPSP) or orthodromic action potentials were recorded during stimulation of nerve trunks attached to the intrapancreatic ganglia. The mean values of amplitude, duration of the f-EPSP and conduction velocity of the nerves were 8.9 +/- 0.7mV, 25.8 +/- 1.9ms and 0.48 +/- 0.04m/s (n = 24), respectively. The ongoing synaptic activity was observed in all of cells. Moreover, f-Epsp, was induced by acetylcholine mediated through nicotinic receptors.

Action Potentials↗
PubMed1993

Calibration for measuring total body nitrogen with a newly upgraded prompt gamma neutron activation facility.

A description is given of the calibration and performance of the upgraded facility at Brookhaven National Laboratory (BNL) for measuring total body nitrogen using the technique of prompt gamma neutron activation analysis. With the improved calibration, total body nitrogen can be more accurately measured not only in normal subjects but also in obese and wasted patients. Body hydrogen is used as an internal standard. We examined the effect of a heavy-water premoderator on the uniformity of composite sensitivity, nitrogen and hydrogen measurement statistics, and dose to the subject. The calibration technique corrects the ratio of nitrogen-to-hydrogen counts measured from the subject for body size. Additionally, a correction for subcutaneous adipose tissue on the nitrogen-to-hydrogen count ratio is introduced. The newly upgraded BNL facility provides precision in counting statistics using a Remcal anthropomorphic phantom filled with a tissue-equivalent solution of 2.1% for a body dose of 0.35 mSv using a 2.5 cm D2O premoderator. The measurements were made at five 20 cm sections, counting for 200 s per section.

Calibration↗
PubMed1993

Body composition and aging: a study by in vivo neutron activation analysis.

Human body composition can be organized into five levels; atomic, molecular, cellular, tissue-system and whole body. Six elements (carbon, nitrogen, calcium, potassium, sodium and chlorine) can be directly measured in vivo at the atomic level using three neutron-activation systems at Brookhaven National Laboratory. When combined with an estimate of total body water, the six elements can be used to quantify the major chemical components at molecular level. In the present report, we first describe the neutron-activation approach to evaluating chemical compartments in vivo. Then, we present an example of how in vivo estimates of human chemical composition can be used to study the validity of two-compartment indirect methods of quantifying total body fat in the elderly. Our studies and the work of other investigators at Brookhaven National Laboratory suggest that neutron activation analysis provides an important opportunity to study the relation between aging and changes in elemental and chemical composition of humans in vivo.

Aging↗
PubMed1993

Genealogy and regional distribution of lipoprotein lipase deficiency in French-Canadians of Quebec.

Lipoprotein lipase (LPL) deficiency, an autosomal recessive disorder causing chylomicronemia, has a high prevalence in the French-Canadian population of Quebec. The molecular basis of LPL deficiency has been defined, and two major mutations have been shown to have an uneven geographic distribution. Two mutations, one at residue 188 (M-188) and the other at residue 207 (M-207), are described here; they account for 95% of the mutant alleles. The carrier rate of M-188 was highest in western Quebec (1/326) but that of M-207 was much higher in the eastern part of the province (1/85). Genealogical reconstruction has revealed that both mutations were introduced to the French-Canadian population by migrants from France in the seventeenth century. M-188 is likely to have a Scottish ancestor, whereas M-207 appears to be of French origin.

France↗
PubMed1992

Geographic distribution and genealogy of mutation 207 of the lipoprotein lipase gene in the French Canadian population of Québec.

Mutations in the lipoprotein lipase (LPL) gene, leading to partial or total inactivation of the enzyme, result in a hereditary clinical syndrome called familial LPL deficiency. The French Canadian population, which is primarily and historically located in the province of Québec, has the highest worldwide frequency of LPL-deficient patients. We have analyzed the prevalence, spatial distribution, and genealogy in the Québec population of a LPL gene mutation, M-207 (P207L in conventional notation), which changes the amino acid proline to leucine in position 207 of the LPL protein and inactivates the enzyme. Our results show that M-207 is the most prevalent LPL gene mutation among French Canadians and accounts for the largest proportion of LPL-deficient patients in this population. Genealogical reconstruction of French Canadian LPL-deficient patients point to 16 founders of M-207, all of whom migrated to Québec in the early seventeenth century from the north-western part of France, especially from the region of Perche. Most of the carriers of M-207 are, at present, found in Charlevoix, Saguenay-Lac-St-Jean regions of eastern Québec. On the basis of the number of homozygote M-207 LPL-deficient patients so far identified, we estimate that there are at least 31,000 carriers of this mutation in the province of Québec. This constitutes a large pool of individuals at risk for atherosclerosis and other lipid-related diseases, since LPL deficiency is considered to be a significant contributing factor in the etiology and development of these diseases.

Alleles↗