Biomedical subjects

Y M Yu

Publications and source records attributed to Y M Yu.

At least 55 records · Page 3Linked to original sources

PubMed1994

Estradiol inhibits growth hormone receptor gene expression in rabbit liver.

We studied the ontogeny of GH receptor mRNA levels and the effect of exogenous estradiol administration on GH receptor mRNA levels in rabbit liver. A solution hybridization-RNase protection assay revealed a predominant 370-base long protected band corresponding to the mRNA encoding the transmembrane GH receptor, and a 241-base long protected band, representing about 9.0%, with the predicted size for the truncated form of the GH receptor. To study the developmental profile of GH receptor expression, we studied 12 female rabbits, at ages 1, 3, 5 and 7 months. Maximal GH receptor mRNA levels were observed in 3-month-old animals and decreased in 7-month-old animals. To investigate the effect of estradiol, 8-week-old immature female rabbits were randomly divided into five groups, and received subcutaneous pellets containing either placebo or estradiol at doses of 0.1, 0.5, 1.5 and 5.0 mg for 3 weeks. Exogenous administration of estradiol, at doses that resulted in physiological circulating levels, induced a reduction in GH receptor expression, measured both by GH binding (36 and 46%), and GH receptor mRNA levels (38 and 87%), in animals receiving pellets containing 1.5 and 5.0 mg of estradiol, respectively. We conclude that estradiol decreases GH receptor expression in rabbit liver. The results of our study suggest that there is an inverse relationship between circulating estrogen concentrations and liver GH receptor expression.

Aging↗

PubMed1994

Enhanced amino acid uptake in both skeletal muscle and liver by burn plasma in rats.

The study was designed to test amino acid uptake in skeletal muscle after burn injury (up to 72 h). Also examined were the effects of plasma from burned rats over varying periods postburn (1-72 h), when plasma was added in vitro to incubated muscles and liver slices. Major burn injury (40 per cent total body surface area (TBSA)) was produced in male Sprague-Dawley rats weighing 60-80 g. Both soleus muscles were dissected intact at 1, 3, 6, 12, 24, 48 and 72 h postburn. Amino acid transport was measured by determining intracellular uptake of [3H] alpha-aminoisobutyric acid (AIB) during a 2 h incubation. In the second series of experiments, whole plasma from burned rats was added in vitro to incubated muscles and liver slices from healthy animals, and amino acid uptake was determined. AIB uptake in burned rat muscle was reduced by 24 per cent by 24 h postburn and 16 per cent by 48 h postburn. There was an increased effect from burn plasma on normal incubated muscles and liver slices, 72 per cent on muscles and 30 per cent on livers. Present results suggest an intrinsic decrease in amino acid uptake by muscle from burned rats. A factor or factors existed in plasma which increased both muscle and liver amino acid uptake postburn.

Amino Acids↗

PubMed1994

Methionine and cysteine kinetics at different intakes of cystine in healthy adult men.

We investigated plasma methionine and cysteine kinetics in eight healthy adult men receiving for 6 d each of five L-amino acid diets supplying 13 mg methionine.kg-1.d-1 without cystine or 6.5 mg methionine.kg-1.d-1 plus 0, 5.2, 10.5, or 20.9 mg cystine.kg-1.d-1. On the morning of day 7, primed, constant intravenous infusions of L-[2H3-methyl, 1-13C]methionine and L-[3,3-2H]cysteine were given for 8 h (for the first 3 h subjects remained in a fasted state and for the next 5 h received small, equal meals at hourly intervals to achieve a fed state). Methionine and cysteine fluxes and rate of methionine oxidation were estimated from plasma methionine and cysteine labeling and 13C in expired air. Methionine oxidation declined (P < 0.05) with lowered methionine intake. Cysteine flux was similar across diets and dietary cystine did not affect tracer methionine oxidation. If there is a sparing effect of dietary cystine on the methionine requirement in adults, it probably takes place during the "first-pass" removal of these amino acids within the splanchnic region.

Adult↗

PubMed1994

A general model for analysis of the tricarboxylic acid cycle with use of [13C]glutamate isotopomer measurements.

A generalized steady-state model was developed for determining tricarboxylic acid cycle fractional fluxes from 13C nuclear magnetic resonance (NMR) data. The model relates the measured mole fractions of [13C]glutamate isotopomers to the fractional fluxes and predicted mole fractions of isotopomers of oxaloacetate (OAA) and acetyl-CoA. This model includes cycling between OAA and fumarate. Fractional fluxes are determined by fitting the model equations to NMR parameters by use of nonlinear least squares. Although only fractional fluxes can be determined from 13C-NMR data, when they are combined with mass spectroscopic measurements, absolute values can be derived. A specific metabolic system represented by published 13C-NMR data from extracts of hearts perfused with [13C]acetate, [13C]pyruvate (PYR), and [13C]acetate plus [13C]PYR was used to test the model. The intensities of predicted 13C-NMR splitting patterns were compared with observed values, and there was excellent agreement between observed and predicted signal intensities. With this model, important physiological parameters, including the OAA-derived fraction of inflow to PYR, PYR-derived fraction of inflow to acetyl-CoA, citrate-derived fraction of inflow to OAA, and PYR-derived fraction of inflow to OAA, can be determined.

Animals↗

PubMed1994

Dexamethasone increases growth hormone receptor messenger ribonucleic acid levels in liver and growth plate.

Glucocorticoid inhibits linear growth and renders target tissues, particularly liver and growth plate, insensitive to GH. We hypothesized that glucocorticoid-induced GH insensitivity is due to decreased gene expression of the GH receptor at the messenger RNA (mRNA) level. To test this hypothesis, we treated 4.5-wk-old male rabbits (n = 6-9 per group) with ip dexamethasone or vehicle and measured GH receptor mRNA levels (by RNase protection assay) and serum GH-binding protein levels (by radioimmunoprecipitation assay). Contrary to our hypothesis, dexamethasone administered in growth-suppressing doses did not decrease GH receptor mRNA levels in liver or growth plate. Instead a tissue-specific stimulation of GH receptor mRNA levels was observed. The dose-response relationship of this effect was biphasic, since the lower growth-suppressing dose of dexamethasone (0.1 mg/kg.day) caused the greater increase in GH receptor mRNA levels, whereas the higher growth-suppressing dose (4 mg/kg.day) had less effect. The dexamethasone-induced increase in GH receptor mRNA was observed in growth plate and liver, target tissues important for linear growth, but not in kidney. Serum GH-binding protein levels also showed a stimulatory response to dexamethasone treatment, with a biphasic dose-response relationship. These data suggest that glucocorticoid-induced GH insensitivity cannot be explained by decreased GH receptor mRNA levels. To the contrary, dexamethasone causes a tissue-specific stimulation in GH receptor mRNA levels with a biphasic dose-response relationship.

Animals↗

PubMed1994

Phenylalanine and tyrosine kinetics in critically ill children with sepsis.

To better understand the impact of severe illness on the amino acid economy and nutritional needs of pediatric patients, we studied plasma phenylalanine and tyrosine kinetics in eleven critically ill patients (six full-term newborns and five young infants). Within 48 h of the diagnosis of sepsis they were given primed constant i.v. infusions of L-[1-13C]phenylalanine and L-[3,3,2H2]tyrosine for 4 h. Routine nutritional support continued during this period by parenteral administration of dextrose, lipid emulsion, and an amino acid mixture low in tyrosine. Phenylalanine and tyrosine fluxes and rate of phenylalanine hydroxylation did not differ significantly between the two age groups, and so the data were combined for evaluation. For the entire group, values (mumol.kg-1.h-1; mean +/- SD) for phenylalanine and tyrosine fluxes and rate of phenylalanine hydroxylation were 132 +/- 24, 66 +/- 16, and 29 +/- 12, respectively. Plasma phenylalanine to tyrosine concentration ratio was 1.67 +/- 0.6. From a comparison of the rate of phenylalanine hydroxylation with measured phenylalanine intakes, it was concluded that their routine, clinical nutritional support was inadequate to achieve body phenylalanine balance. In comparison with published data, the relative rate of phenylalanine hydroxylation appears to be high. We speculate that tyrosine is a conditionally indispensable amino acid under these conditions; it would be desirable to establish the intake levels and ratio of phenylalanine to tyrosine that effectively support aromatic amino acid balance in these critically ill patients.

Bacterial Infections↗

PubMed1993

Changes in the expression of insulin-like growth factor II/mannose-6-phosphate receptor during endochondral bone development.

Endochondral bone development can be induced by subcutaneous implantation of demineralized bone matrix (DBM) in rats. We used this in vivo model to study the relationship between endochondral bone formation and expression of IGF-II/M-6-P receptor, a multifunctional protein which binds not only IGF-II, but also lysosomal enzyme bearing mannose-6-phosphate motif. We found that IGF-II/M-6-P receptor was present in implants from day 1 to day 21; the highest levels were expressed on day 11 during bone differentiation. IGF-II/M-6-P receptor mRNA content was highest on day 9. We conclude from these data that IGF-II/M-6-P receptor expression is developmentally regulated during endochondral bone formation. This regulation occurs in part at the level of IGF-II/M-6-P receptor mRNA. The relatively high level of IGF-II/M-6-P receptor during ossification suggests that this receptor might play a role in bone formation and remodeling.

Animals↗

PubMed1993

Plasma arginine and citrulline kinetics in adults given adequate and arginine-free diets.

The fluxes of arginine and citrulline through plasma and the rate of conversion of labeled citrulline to arginine were estimated in two pilot studies (with a total of six adult subjects) and in a dietary study with five healthy young men. These latter subjects received an L-amino acid-based diet that was arginine-rich or arginine-free each for 6 days prior to conduct, on day 7, of an 8-hr (first 3 hr, fast; final 5 hr, fed) primed continuous intravenous infusion protocol using L-[guanidino-13C]arginine, L-[5,5-2H2]citrulline, and L-[5,5,5-2H3]leucine, as tracers. A pilot study indicated that citrulline flux was about 20% higher (P < 0.05) when determined with [ureido-13C]citrulline compared with [2H2]citrulline, indicating recycling of the latter tracer. Mean citrulline fluxes were about 8-11 mumol.kg-1.hr-1 for the various metabolic/diet groups and did not differ significantly between fast and fed states or arginine-rich and arginine-free periods. Arginine fluxes (mean +/- SD) were 60.2 +/- 5.4 and 73.3 +/- 13.9 mumol.kg-1.hr-1 for fast and fed states during the arginine-rich period, respectively, and were significantly lowered (P < 0.05), by 20-40%, during the arginine-free period, especially for the fed state, where this was due largely to reduced entry of dietary arginine into plasma. The conversion of plasma citrulline to arginine approximated 5.5 mumol.kg-1.hr-1 for the various groups and also was unaffected by arginine intake. Thus, endogenous arginine synthesis is not markedly responsive to acute alterations in arginine intake in healthy adults. We propose that arginine homeostasis is achieved largely via modulating arginine intake and/or the net rate of arginine degradation.

Adult↗

PubMed1993

Chondrogenesis in chick limb bud mesodermal cells: reciprocal modulation by activin and inhibin.

Activin and inhibin are members of the transforming growth factor-beta superfamily sharing a common beta-subunit, but with opposite biological activities on the release of follicle-stimulating hormone from pituitary. Recent studies have demonstrated that activin is the long sought after mesoderm induction factor in amphibians. To determine if activin and inhibin affect the proliferation and differentiation of chick limb bud mesodermal cells during cartilage formation of the limb, recombinant human activin A and inhibin A were tested on stage 24 chick limb bud mesodermal cells. The results showed that activin A has an inhibitory effect on chondrogenic differentiation, as indicated by Alcian blue staining and decreased [35S]sulfate incorporation into proteoglycans. In addition, the expression of type II collagen mRNA, a specific phenotypic marker of cartilage, was greatly inhibited when cultures were exposed to activin A for 5 days at a dose of 10 ng/ml. In contrast, inhibin A stimulated cartilage formation, as indicated by increased expression of type II collagen mRNA and synthesis of proteoglycans. These results imply that activin A and inhibin A can modulate chondrogenesis during differentiation of limb bud cells in culture.

Activins↗

PubMed1993

A kinetic study of L-2H3-methyl-1-13C-methionine in patients with severe burn injury.

To explore the consequences of severe burn injury on methionine metabolism we carried out tracer studies, using [1-13C, 2H3-methyl] methionine, given by continuous intravenous infusion, in 12 adult patients. Each was studied in the "fasted" and in the fed state while receiving parenteral nutrition. Compared with findings obtained in our previous studies in healthy adults using a similar protocol, the rates of transmethylation (Tm), homocysteine remethylation (Rm), and methionine oxidation (C) were all substantially increased in burn patients. From the relationships between these systems, it appears that there is a relative increase in the recycling of methionine carbon via Rm during the fasted state. This implies active methyl group transfer and utilization in burn patients. Parenteral feeding increased methylmethionine flux (Qm) and the rates of Tm, Rm, and C. However, the Tm/Qm ratio did not change with feeding in the patients, whereas it increased in healthy young adults. This may not necessarily reflect the consequences of burn injury, but may be due to differences in the route of methionine intake or its level relative to requirement, compared with the conditions of study in healthy adults. Further studies on methionine-cysteine interrelationships, using an isotopic approach, in burned patients are needed to evaluate these possibilities.

Adult↗

PubMed1993

High-level cryIVD and cytA gene expression in Bacillus thuringiensis does not require the 20-kilodalton protein, and the coexpressed gene products are synergistic in their toxicity to mosquitoes.

Interactions among the 20-kDa protein gene and the cytA and cryIVD genes located in a 9.4-kb HindIII fragment were studied. A series of plasmids containing a combination of these different genes was constructed by using the Escherichia coli/Bacillus thuringiensis shuttle vector pHT3101. The plasmids were then used to transform an acrystalliferous strain, cryB, derived from B. thuringiensis subsp. kurstaki. The results from sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analyses suggest that although the 20-kDa protein is required for the efficient CytA protein production in E. coli, it is not required in B. thuringiensis. With or without the truncated 20-kDa protein gene, the CtyA and/or CryIVD proteins are produced and form parasporal inclusions in B. thuringiensis cells. However, more-efficient expression is obtained when a second protein, probably acting as a chaperonin, is present. In addition, the time course studies show that the CytA and CryIVD proteins are coordinately produced. Both the crude B. thuringiensis culture and purified inclusions from each recombinant B. thuringiensis strain are toxic to Culex quinquefasciatus larvae. The parasporal inclusions formed in B. thuringiensis cells are mosquitocidal, with CytA synergizing CryIVD toxicity.

Animals↗

PubMed1993

Dietary arginine uptake by the splanchnic region in adult humans.

To determine the uptake of dietary arginine and leucine by the splanchnic region, two experiments were carried out, each involving four healthy young adult men who received a diet supplying 1 g protein.kg-1.day-1 for 7 and 10 days before conducting a primed constant tracer infusion protocol. In study 1, subjects received for 8 h (3-h fast; 5-h fed state, achieved by a constant intragastric infusion of the diet formula) L-[5,5-2H2; guanidino-15N2]arginine ([M4]Arg), L-[guanidino-13C]arginine ([13C]Arg), and L-[5,5,5-2H3]leucine ([2H3]Leu) simultaneously by an intragastric infusion on day 7 and a repeat of this protocol on day 10 except with tracer administration given by vein. Plasma arginine fluxes were essentially the same for the two arginine tracers but differed significantly with route of administration. In study 2 the subjects received on day 7 a constant intravenous infusion of [13C]Arg and [2H3]Leu and a simultaneous intragastric infusion of [M4]Arg and [1-13C]leucine. On day 10 the routes of administration of these tracer pairs were reversed. During the fed state in study 1, splanchnic uptake of dietary arginine was 31 +/- 10 and 34 +/- 8%, based on the [13C]Arg and [M4]Arg tracers, respectively, and it was significantly higher (P < 0.01) than for leucine, which was 10 +/- 6%. In study 2, splanchnic uptake of dietary arginine, estimated from a series of tracer-protocol combinations for the fed state, was approximately 38% compared with a lower (P < 0.01) value of approximately 15% for leucine.

Adult↗

PubMed1993

[Effect of Rhodobryum roseum on hemorheology following acute coronary occlusion in dogs].

Following acute occlusion of the left anterior descending coronary artery, the significant and constant hemorheologic changes were observed in venous blood from ischemic area. 30 min after occlusion, the high shear rate (r = 230s-1), middle shear rate (r = 23s-1) and low shear rate (r = 5.75s-1), viscosity of whole blood (eta b) increased significantly, and this change occurred in viscosity of plasma (eta p) and in red cell electrophoretic time (RCET) also. These increases continued thereafter. In another group of dogs, 30 min after coronary occlusion, rapid dripping was performed with Rhodobryum roseum (Huixincao) injection from right femoral vein. After 10 min, eta b at all shear rate reduced significantly, and this reduction was observed in eta p and in RCET also. These findings suggested that the hyperviscosity syndrome developed in acute myocardial ischemic could be blocked by Hui Xin Cao.

Animals↗

PubMed1993

[The synthesis and bioactivities of cholinergic tropane alkaloids].

Ten analogs of baogongteng A, the natural cholinergic tropane alkaloid isolated from Erycibe obtusifolia Benth, were designed and synthesized. The tropane skeleton was kept unchanged, while the substituting groups on N and C3 were modified. In myotic experiments in rabbits 3-paramethyl benzoyloxy-6-acetoxy nortropane(4), 3-propionyloxy-6-acetoxy nortropane(5), and 3-isobutyryloxy-6-acetoxy nortropane(6) showed cholinergic activities.

Animals↗

PubMed1993

[Quantitative analysis of 200 human tongue pictures].

Photoelectricity integration was applied to detect and analyse the colorimetric tongue pictures in 200 human beings. The results showed that among various tongue pictures there were evident differences in colorimetric features. This method could also assess the thickness of tongue coating, thus obtaining the colorimetric features including color of tongue proper, color of coating as well as thickness index in common tongue pictures. Therefore it might provide scientific basis for objective and quantitative assessment of tongue pictures in TCM.

Adult↗

PubMed1992

Natural bovine osteogenin and recombinant human bone morphogenetic protein-2B are equipotent in the maintenance of proteoglycans in bovine articular cartilage explant cultures.

Osteogenin and related bone morphogenetic proteins are members of the transforming growth factor-beta superfamily, and were isolated by their ability to induce cartilage and bone formation in vivo. The influence of osteogenin, purified from bovine bone, and of recombinant human bone morphogenetic protein-2B (BMP-2B) has been examined in bovine articular cartilage explants. Both differentiation factors stimulated in a dose-dependent manner the synthesis of proteoglycans and decreased their rate of degradation. At a dose of 30 ng/ml, proteoglycan synthesis was increased to levels observed with either 20 ng/ml insulin-like growth factor I, 10 ng/ml transforming growth factor-beta, or 20% fetal bovine serum. This increase of biosynthetic rates above basal medium levels was observed in young, adolescent, and adult tissues. Analysis of the size of the newly synthesized proteoglycans, the glycosaminoglycan chain size, and the glycosaminoglycan type of explants treated with osteogenin or BMP-2B were very comparable to each other, and to proteoglycans isolated from cartilage treated with either insulin-like growth factor I or fetal bovine serum. These results demonstrate that osteogenin and BMP-2B alone are capable of stimulating and maintaining the chondrocyte phenotype in vitro.

Aging↗

PubMed1992

Uptake of alpha-aminoisobutyric acid and cycloleucine on skeletal muscles in burned rats.

The uptake of alpha-aminoisobutyric acid (AIB) and aminocyclopentane-carboxylic acid (cycloleucine) was studied in soleus muscles isolated from small rats (body weight 50-60 g) during the first 6 h after a major thermal injury, the so-called 'ebb phase' or 'hypometabolic phase'. Soleus muscles were dissected intact from rats at 0.5, 1, 3 and 6 h after extensive deep burn injury (30 per cent TBSA) and then incubated for 2 h in Krebs-Henseleit bicarbonate buffer (pH 7.4), 5.5 mM glucose, bovine serum albumin and radiolabelled AIB or cycloleucine. The results were expressed as the distribution ratio of AIB or cycloleucine between intracellular and extracellular fluid. The AIB uptake in vitro was found to be significantly increased (30 per cent) in the initial half hour postburn only, and then slowly reduced during the subsequent hours to near the value found in non-burn animals. Muscle cycloleucine uptake in vitro showed no significant change in these studies. In our second study, extensor digitorum longus leg muscle were incubated in Krebs-Henseleit bicarbonate buffer with different pH values (7.2-7.5). No significant difference was found in muscle AIB uptake. In summary, since muscle amino acid uptake remained relatively stable during this period, it is suggested that the alteration of amino acid transport across muscle cells may not be a contributing factor to the alteration of amino acid flux during the early phase of stress.

Aminoisobutyric Acids↗

PubMed1992

Recombinant human bone morphogenetic protein 2B stimulates PC12 cell differentiation: potentiation and binding to type IV collagen.

Bone morphogenetic protein 2B (BMP 2B, also known as BMP 4) induces cartilage and bone morphogenesis in ectopic extraskeletal sites. BMP 2B is one of several bone morphogenetic proteins which along with activins and inhibins are members of the transforming growth factor-beta (TGF-beta) family. Both BMP 2B and activin A, but not TGF-beta 1, induce rat pheochromocytoma PC12 neuronal cell differentiation and expression of VGF, a nervous system-specific mRNA. PC12 cells exhibited approximately 2,500 receptors per cell for BMP 2B with an apparent dissociation constant of 19 pM. Extracellular matrix components, including fibronectin, laminin, and collagen type IV potentiated the activity of BMP and activin A, with the latter being the most active. Direct experiments demonstrated that radioiodinated BMP 2B bound to collagen type IV better than to either laminin or fibronectin. These data demonstrate a common neurotrophic activity of both BMP 2B and activin A, and suggest that these regulatory molecules alone and in conjunction with extracellular matrix components may play a role in both the development and repair of nervous tissue.

Activins↗