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Biomedical subjects

T Chen

Publications and source records attributed to T Chen.

At least 343 records · Page 19Linked to original sources
PubMed1991

Autoregulation of brain blood flow during hypotension and hypertension in infant lambs.

To determine the limits of aortic blood pressure in infant lambs for autoregulation of global and regional brain blood flow, we studied 10 unsedated lambs during hypotension and 10 unsedated lambs during hypertension. In lambs 6 to 13 d old, we produced graded changes in aortic blood pressure by inflating a balloon occluder placed around either the inferior vena cava or the descending aorta. Using radiolabeled microspheres, we measured global and regional brain blood flow at the baseline, and then with each graded change in aortic blood pressure. In an additional step, we administered atropine to determine if its antimuscarinic properties alter the fall in brain blood flow with severe hypotension, or alter the rise in brain blood flow with severe hypertension. We concluded that in the unsedated infant lamb, global brain blood flow remains stable between mean aortic blood pressures of 6.0 to 10.0 kPa (45 to 82 torr), a range from approximately 38% below to 12% above normal mean aortic blood pressure. We noted that this autoregulatory range is essentially unchanged from that described for the fetal lamb at 80% of term gestation--even though the mean aortic blood pressure rises during this period of maturation by more than 2.7 kPa (20 torr). We found that the lower limit of autoregulation varies among the different brain regions and is lowest in the thalamus, pons, and medulla. We saw little variation of the upper limit among the brain regions. Finally, we determined that atropine does not alter brain blood flow during severe hypotension or severe hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Sixth nerve schwannomas. Report of two cases.

Two cases of sixth cranial nerve schwannoma are presented with a review of four other cases from the literature. The clinical spectrum, neuroradiological findings, and surgical outcome of the six cases are discussed. There are two distinct clinical presentations for sixth cranial nerve schwannomas. Type I sixth nerve schwannomas present with sixth nerve palsy and diplopia and arise from the cavernous sinus. In contrast, type II sixth nerve schwannomas have a more severe presentation with obstructive hydrocephalus, raised intracranial pressure, sixth nerve palsy, and diplopia. This type arises along the course of the sixth cranial nerve in the prepontine area. Cavernous sinus involvement in either type may preclude total surgical excision and indicate an increase possibility for recurrence.

Abducens Nerve↗
PubMed1991

Prognostic factors in alcoholic liver disease. VA Cooperative Study Group.

Two hundred eighty-one alcoholic patients were prospectively evaluated by clinical, biochemical, and histologic parameters during a 4-yr period to assess their prognosis. They were stratified into four categories of injury: 1) fatty liver (26 patients), 2) acute alcoholic hepatitis (106), 3) cirrhosis (39), and 4) cirrhosis with superimposed alcoholic hepatitis (111). The rate of survival and variables correlating with survival varied according to the group. At 48 months, 70% of the patients with fatty liver were alive, 58% in the alcoholic hepatitis group, 49% in cirrhosis, and 35% in alcoholic hepatitis superimposed upon cirrhosis. Within group one, deaths were due to causes unrelated to liver disease. In the alcoholic hepatitis group, factors significantly correlating with survival were ascites, alanine amino-transferase levels, grams of alcohol consumed, continuation of alcohol intake, and clinical severity of disease. Survival in patients of group three correlated significantly with prothrombin time and histologic severity score. Patients with combined cirrhosis and alcoholic hepatitis exhibited the worst prognosis, with the most significant predictors of survival being age, grams of alcohol consumed, the ratio of serum aminotransferases (AST:ALT) and the histologic and clinical severity of the disease. Although a different pattern of correlates was observed for each pathologic level of injury, knowledge of the various correlates aids in prognostic assessment.

Acute Disease↗
PubMed1990

Metabolic stereoisomeric inversion of 2-arylpropionic acids. On the mechanism of ibuprofen epimerization in rats.

Kinetic and mechanistic studies are described for the metabolic stereoisomeric inversion of R-ibuprofen in rats. After oral administration of R-ibuprofen to rats, the plasma levels and enantiomeric compositions of ibuprofen and its major metabolite were monitored. Although individual animals exhibited great variations in metabolic rates, the concentration ratios of the S- and R-enantiomers of ibuprofen and also its metabolite remained roughly unchanged within 90 min. Even though it is generally believed that this bioconversion is strictly stereospecific in nature, chromatographic analysis revealed that S-ibuprofen also underwent metabolic inversion, however, at a much slower rate, than its R counterpart. The inversion mechanism was assessed by monitoring the loss of labeled deuterium from specifically deuterated ibuprofen. No significant isotope effect was observed for the metabolism of these deuterated derivatives. One deuterium atom was lost in the S-ibuprofen resulted from R-[2-2H]ibuprofen metabolism, whereas all the three deuterium atoms were retained when R-[3,3,3-2H3]ibuprofen was used as the substrate. These results reinforce the proposed mechanism that the inversion proceeds via a thioester carbanion intermediate. The pKa of the alpha-methine proton of ibuprofen N-acetylcysteamine thioester was shown to be 10.34 +/- 0.06, which excludes the possibility that ibuprofen may undergo inversion through the nonenzymatic isomerization of its acyl thioester.

Animals↗
PubMed1990

Characterization of a complete immunoglobulin heavy-chain variable region germ-line gene of rainbow trout.

A germ-line heavy-chain variable region (VH) gene (RTVH431) has been isolated from a rainbow trout (Salmo gairdneri) and characterized by complete nucleotide sequencing. It is characteristic of VH, as shown by the conserved octamer and TATA motif in the 5' region, the heptamernonamer recombination signal sequence in the 3' region, and the 18-amino-acid-long hydrophobic leader interrupted by an intron. The 98-amino-acid-long VH coding region has 50-70% nucleotide sequence homology and 40-60% amino acid sequence homology with VHS of various vertebrate species. We have also found unique or species-specific amino acid residues in the VHS of rainbow trout, amphibia (Xenopus), reptile (Caiman), and shark (Heterodontus) in our sequence analyses. The RTVH431 has an unusual amino acid in the conserved 34th position in complementarity-determining region 1 of VH. Southern hybridization results suggest the presence of a large gene family related to RTVH431 in the trout genome. The complex evolution of antibody V genes is discussed.

Amino Acid Sequence↗
PubMed1990

Effect of low-dose calcitriol and calcium therapy on bone histomorphometry and urinary calcium excretion in osteopenic women.

We evaluated low-dose calcitriol (0.25 microgram b.i.d.) in combination with 1 g of supplemental calcium therapy as treatment for osteopenic women over 60 years of age (n = 4). Control patients (n = 6) received ergocalciferol (50,000 units twice a week) and 1 g of supplemental calcium. Bone biopsies and CT-determined bone mineral density were done initially and after 1 year of therapy. Bone mineral density increased from 77 +/- 18 to 88 +/- 9 mg/ml (NS) in the calcitriol-treated group and from 87 +/- 13 to 112 +/- 30 mg/ml (NS) in the ergocalciferol-treated group. There was also no significant change in bone volume, as determined by bone biopsy in either group. No compression fractures occurred in either treatment group. After 1 year of therapy, urinary calcium excretion was increased significantly above that observed in age-matched untreated women. Creatinine clearance did not change significantly. Hypercalcemia was rare. In summary, we found calcitriol was not superior to ergocalciferol in preventing progressive bone loss and fractures. Both therapies were associated with significant hypercalciuria.

Bone Density↗
PubMed1989

Reversed phase high performance liquid chromatography of glycopeptides.

A practical procedure for isolating and purifying glycopeptides is described, viz. enzymatic hydrolysis-gel permeation chromatography-ion exchange chromatography-reversed phase HPLC. Using this procedure 28 glycopeptides from hen ovalbumin have been isolated some of which hitherto have not been identified. Water was a suitable mobile phase for preparing pure glycopeptides, and control of column temperature was important for good separations and reproducible retention times. Structural confirmation was by fast atom bombardment mass spectrometry.

Chromatography, High Pressure Liquid↗
PubMed1989

Elevated bone aluminum and suppressed parathyroid hormone levels in hypercalcemic dialysis patients.

We studied 21 dialysis patients who became hypercalcemic without vitamin D or calcium therapy and compared them to 28 dialysis patients who were not hypercalcemic. In the hypercalcemic group, the mean ionized-calcium level was elevated compared to normal subjects (5.4 +/- 0.4 vs. 4.9 +/- 0.1; p less than 0.001), while the ionized-calcium level in the control dialysis patients was below normal (4.5 +/- 0.4 vs. 4.9 +/- 0.1; p less than 0.001). Bone biopsies were performed in all patients. Two thirds of the hypercalcemic patients had low-turnover osteodystrophy (LTO, predominantly osteomalacia), a fraction significantly higher than in the control dialysis patients (13/21 vs. 8/28, respectively; p less than 0.05). The hypercalcemic patients with LTO had markedly elevated surface bone aluminum (63 +/- 24% of all trabecular surfaces). In contrast, the nonhypercalcemic dialysis patients with LTO and all patients with osteitis fibrosa had minimal surface bone aluminum. Hypercalcemic patients with osteitis fibrosa had a significantly lower mean N-terminal parathyroid hormone (PTH) value than did nonhypercalcemic patients with osteitis fibrosa (149 +/- 81 vs. 278 +/- 135 pg/ml, respectively; p less than 0.005). Both mean values were markedly elevated in comparison with those obtained in normal subjects (16 +/- 5 pg/ml). In contrast, patients with LTO, irrespective of the calcium level, had mean PTH values that were not significantly different from those of normal subjects. A PTH level greater than 100 pg/ml was 95% sensitive and 87% specific for osteitis fibrosa, as demonstrated by histomorphometry in nonhypercalcemic dialysis patients. However, this level was only 62% sensitive and 77% specific for a diagnosis of osteitis fibrosa in hypercalcemic dialysis patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

[The tendencies of research on Chinese materia medica in Japan--establishment of morbid models in animals and their application to research on Chinese materia medica].

This paper presents a survey of some pathologic models on animals established to satisfy the needs of research on Chinese materia medica in Japan over the last several years, e.g., model of blood-stasis syndrome, model of "taiyang" syndrome, model of spleen deficiency syndrome, speeded aging model and two related models, i.e. chronic renal insufficiency and bronchitis. All these models can be used for reference in the experimental research on Chinese materia medica.

Animals↗
PubMed1989

[Effect of dexamethasone on the levels of plasma beta-endorphin-like-immunoreactivity in intestinal ischemia shock in the dog].

This paper observed the effect of Dexamethasone (Dex) on the levels of plasma Beta-endorphin-like-immunoreactivity (ir-beta-EP) and its correlation with hemodynamics during the shock. Ten adult mongrel dogs were randomized into two groups. Intestinal shock was created by occluding both superior mesenteric artery and vein in the two groups. After two hours of occlusion, the dogs in treated group were given Dex (5 mg/kg) and the dogs in control group were given normal saline. The intestinal vascular obstruction was released four hours later. It was shown that plasma levels of ir-beta-EP in control group were increased significantly during the shock and correlated significantly with deteriorated hemodynamics. In Dex treated group, the levels of plasma ir-beta-EP and ACTH were significantly lower than that in control group, hemodynamics were improved, and the survival times were much longer. Our results suggest that endogenous opiate beta-EP is involved in the cardiovascular pathophysiology of intestinal shock, and the beneficial effects of steroids (Dex) in the treatment of shock are correlated with its suppressing endogenous beta-EP secretion and release.

Animals↗
PubMed1989

Effect of vitamin D deficiency on amino acid excretion in the phosphate-depleted rat.

Vitamin D deficiency is associated with a generalized aminoaciduria which has been shown to be independent of parathyroid hormone (PTH) and urinary cyclic AMP excretion. To further characterize the mechanism underlying the tubulopathy, weanling rats were placed on one of the following diets for 5 weeks: (1) control [0.7% phosphorus (P), 5.5 micrograms % vitamin D]; (2) D-P- (0.1% P, 0 vitamin D); (3) D+P- (0.1% P, 5.5 micrograms % vitamin D); (4) D-P+ (0.3% P, 0 vitamin D); (5) D-P++ (0.7% P, 0 vitamin D). All diets contained 1.2% calcium (Ca). A group of rats raised on D-P++ for 4 weeks were fed D-P- for 7 days after which they received 500 pmol of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3; SUPP] or an equal volume of the vehicle (ETH). The above diets resulted in partial vitamin D depletion in that 1,25(OH)2D levels were 50.25-79 pg/ml in the presence of very low 25(OH)D concentrations. Augmentation in the urinary excretion of 6 out of 8 amino acids measured was observed in P depletion irrespective of vitamin D status. For the most part, acute supplementation with 1,25(OH)2D3 did not ameliorate the tubulopathy. Plasma PTH and Ca concentrations remained normal in all diets, except D+P-, where plasma Ca was 15.88 +/- 0.54 mg/dl. P depletion was associated with hypercalciuria, hypophosphatemia, avid reabsorption of P and growth retardation, irrespective of vitamin D status. Using taurine as a representative of the amino affected, there was a strong correlation between urinary taurine on the one hand and dietary P content (r = 0.613), plasma P (r = 0.399) and 1,25(OH)2D levels (r = -0.576) on the other. The present study suggests that the aminoaciduria of vitamin D deficiency is not related to elevated levels of PTH. A similar defect may be produced by P depletion, suggesting the possibility of a common pathway for the effect.

Amino Acids↗
PubMed1989

Blood glutathione: a biochemical index of life span enhancement in the diet restricted Lobund-Wistar rat.

These experimental results demonstrate that dietary restriction in both conventional and germfree rats results in enhanced longevity compared to fullfed animals. This increase in median survival age was due to a delay of 8 months in the onset of mortality in the restricted rats. Thereafter the aging rates of the short-lived subpopulations were the same for both groups. However, the aging rate of the long-lived restricted subpopulation was greater. The blood glutathione profiles demonstrated that a GSH deficiency of aging occurred in both the restricted and the long-lived groups. These data confirmed in the rat the findings observed previously in mosquito, mouse and man and verified the generality of the GSH and longevity relationship. Of special interest is that the blood glutathione levels were consistently higher at all ages of the restricted compared to fullfed rats and decreased more slowly during senescence. These findings indicate a direct relationship between enhanced GSH status and increased longevity due to dietary restriction. Further this suggests that glutathione may be a molecular mechanism for the diet restriction and longevity phenomenon.

Aging↗
PubMed1988

Effects of early antigen exposure through lactation on later specific antibody responses in mice.

This study characterized totally the effects of early Ag exposure by the suckling route on later specific antibody responses. When mother mice of BALB/c or C57BL/6 strains were injected with deaggregated human gamma-globulin (HGG) immediately after delivery, total amounts of HGG in sera of offspring increased until 2 wk of age. The catabolism of transferred HGG was extremely slow and the half-life was about 3 wk in both strains. Hence, small amounts of Ag in mothers, 0.5 micrograms in C57BL/6 and 50 micrograms in BALB/c, could tolerize their offspring effectively. As these were minimum tolerogenic doses, the strain difference in ease of tolerance induction is apparent already during suckling. The study on timing dependent effects of HGG-specific antiserum on tolerance induction by mothers given 50 micrograms HGG demonstrated that the tolerance is achieved within the 1st wk of lactation in C57BL/6 offspring, but not in BALB/c offspring, and the restoration from the tolerance needs more than 6 wk under circumstances, supposedly, without free Ag. Whereas the tolerance was induced in a dose-dependent manner in each class of antibody, the dissociation of tolerant states between IgM, IgG, and IgE antibody classes was found in C57BL/6 offspring. It is interesting that C57BL/6 offspring were sensitized weakly, but significantly, by mothers given subtolerogenic doses. However, this was not apparent in BALB/c. Thus, the Ag dose and the animal strain are related closely to the consequences of this Ag exposure. The aging of suckling mice within the first 2 wk of life or immunomodulators administered early in life did not seriously affect the consequences. Studies on a cellular basis showed that the tolerance is caused by the selective defect in helper T cell function and the suppressor cell activity is not associated with the mechanisms. This contrasts with other models of oral tolerance.

Adjuvants, Immunologic↗