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Biomedical subjects

J Tai

Publications and source records attributed to J Tai.

At least 19 recordsLinked to original sources
PubMed2004

Active myogenic tone: a requisite for hemoglobin mediated vascular contraction?

Acellular free hemoglobin (Hb), when intravenously administered to animals and humans, elicits vascular contraction. A primary mechanism for the Hb mediated vasoconstriction is Hb scavenging of nitric oxide (NO), a potent relaxation factor, constitutively secreted by the vascular endothelium. However, in the isolated rat thoracic aorta in basal state, Hb does not elicit contraction. To investigate this apparent paradox, we assessed isolated rat aortic ring isometric contraction responses to Hb under different myogenic tone states: (1) following equilibration at a submaximal tension, (2) following agonist induced contraction, or (3) following a passive mechanical stretch. In vessel rings at basal state, Hb as high as 4 microM did not elicit any measurable contractions. In contrast, in vessel rings tone enhanced with norepinephrine, Hb as low as 0.1 microM Hb elicited a significant additional contraction. In vessel rings with passively induced tone, 4 microM Hb did not elicit a notable contraction. Similarly, in vessel rings in basal state, 0.17-1 mM acetylcholine, a NO dependent vasodilator, did not elicit relaxation. In these vessel rings, exogenous 8-Br-cGMP, a membrane permeable cGMP analog, did not elicit relaxation. In conclusion, in the isolated rat thoracic aorta, Hb mediated contraction may be contingent upon the state of myogenic tone.

Animals↗
PubMed2001

Nitric oxide scavenging modulates an experimental vasoplesia in-vitro.

Endogenous overproduction of nitric oxide (NO) is believed to be a primary cause of refractory hypotension in septic shock. Under this condition, effectiveness of vasopressors is diminished due to hyporeactivity of blood vessels, a condition termed as vasoplesia. Effective reduction of NO levels should alleviate the condition. In this study, we investigated whether NO scavenging could modulate the endotoxin mediated vasoplesia in-vitro. Further, we explored whether NO scavenging in combination with a moderate NO synthase (NOS) inhibition would also be effective in modulating NO mediated vasoplesia. Experimental vasoplesia was produced in-vitro by incubating isolated rat thoracic aortic rings with lipopolysaccharide (LPS). Vessel rings were then treated with N(omega)-nitro-L-arginine methyl ester (L-NAME; a NOS inhibitor), human hemoglobin (Hb; a NO scavenger), or both L-NAME and Hb. Vascular reactivity was assessed by measuring vessel ring isometric tension changes to norepinephrine (NE) doses; the median effective doses (logEC50) of NE before and after each experimental treatment were compared. Following a 6-hour LPS treatment, vascular reactivity logEC50 values for NE were significantly increased compared with control vessel rings incubated without LPS. Treatment with either L-NAME alone or Hb alone significantly improved the vessel ring reactivity to NE. When both L-NAME and Hb were used concomitantly, vascular reactivity was also significantly improved. These results indicate that NO scavenging with Hb is as effective as NO synthesis inhibition with NAME in modulating the endotoxin induced vasoplesia. In conclusion, NO scavenging, alone or in combination with a moderate NOS inhibition, may render an alternative therapeutic approach to NOS synthesis inhibition in modulating the vasoplesia in septic shock.

Animals↗
PubMed2001

Alpha adrenergic activation and hemoglobin mediated contraction in the isolated rat thoracic aorta.

A primary mechanism for Hb mediated vascular contraction appears to be Hb scavenging of endothelium derive nitric oxide (NO), a potent vasodilator. In isolated rat thoracic aorta, however, Hb elicits contraction only after precontraction. The present study investigated a possible role of the alpha adrenergic activation in the Hb mediated contraction. Thoracic aortic rings harvested from normal male SD rats were prepared in a tissue bath and isometric tension changes were evaluated. In vessel rings precontracted with 50nM norepinephrine (NE), 1 microM Hb produced an additional 21.8+/-13.2% increase in tension. Pretreatment with 70nM phentolamine, an alpha adrenergic antagonist, prevented the 50nM NE induced contraction. In these vessels, subsequent treatment with 2-4 microM Hb did not elicit contraction. In vessel rings precontracted with 37mM KCl, 2 microM Hb produced an additional 21.8+/-20.1% tension increase (P<0.05). Pretreatment with phentolamine did neither prevent KCl induced contraction nor affect subsequent Hb mediated additional contraction. To test whether there is a threshold level of basal tension for Hb to trigger contraction, a group of vessel rings were passively stretched to match the tension generated by NE before Hb treatment. In these passively stretched vessel rings, Hb did not produce a significant contraction. Pretreatment with 10mM EGTA, a Ca++ chelator, significantly reduced NE induced contraction (9.7+/-5.9 vs 137.7+/-60.0%, P<0.01) but did not prevent it. EGTA also significantly reduced 2 microM Hb induced contraction (27.2+/-29.3% vs 8.9+/-7.7%, P<0.05). In contrast, pretreatment with verapamil, a Ca++ channel blocker, did not completely block NE and Hb induced contractions. In conclusion, alpha adrenergic activation is not a requisite for the Hb mediated contraction in isolated rat aortic rings. The mechanism how prior tone enhancement allows Hb mediated contraction remains unclear but results from this study suggest a factor that controls cytosolic Ca++ levels may be involved.

Adrenergic alpha-Agonists↗
PubMed2001

Melatonin replacement therapy in a child with a pineal tumor.

The case report of a child with the diagnosis of a pineal tumor and severe, chronic sleep disorder is reported. Due to treatment of her lesion, the nighttime melatonin secretion was markedly suppressed. For 4(1/2) years, she has been receiving oral melatonin, which has greatly improved her sleep, without any adverse effects. Sleep difficulties should be considered in the management of pineal lesions. Melatonin replacement therapy is beneficial for those patients who have deficient melatonin synthesis.

Adolescent↗
PubMed2001

Letter detection in very familiar texts.

In the present study, we investigated whether patterns of letter detection for function and content words in texts are affected by the familiarity of the material being read. In Experiment 1, subjects searched for target letters in sentences that had been rehearsed prior to performing the letter detection on them as well as on unfamiliar sentences. In Experiment 2, subjects searched for target letters in highly familiar verses (e.g., nursery rhymes) and in unfamiliar sentences that were matched to the familiar verses. A disadvantage in letter detection for function as compared with content words consistently found with unfamiliar passages was reduced significantly with the familiar material in both experiments. Specifically, letter detection for content words grew worse in familiar text, but letter detection for function words showed a contrasting modest, though nonsignificant, improvement. The results are consistent with the proposition that in very familiar texts, parafoveal analysis permits the identification of generally less familiar content words. Simultaneously, the normal pattern of weighing the structure and content elements of text changes so that more fixations on function words occur than when one is reading unfamiliar texts.

Cognition↗
PubMed1999

Alterations of the actin polymerization status as an apoptotic morphological effector in HL-60 cells.

The alterations of the cytoskeletal actin network have been implicated as a morphological effector in apoptosis. However, studies directly linking actin change to the morphological events in apoptosis are lacking. This study quantitatively examined the effect of actin alteration on the camptothecin (CPT)-induced apoptotic process in HL-60 cells. Actin alteration was induced by two distinctive types of agent: the polymerization-stimulating agent, Jasplakinolide (Jas), and the polymerization-blocking agent, cytochalasin B (CB). The actin polymerization status was measured by two complementary methods: the cell pellet-based DNase I inhibition method, and the individual cell-based quantitative fluorescence image analysis (QFIA) assay. Actin polymerization induced by Jas caused apoptosis directly. By contrast, CB, an actin polymerization-blocking agent, partially inhibited CPT-induced apoptosis. A similar inhibition of the CPT-induced apoptosis response was observed with a more specific actin depolymerization agent, cytochalasin E. The alterations of the actin polymerization status occurred in three sequential steps during the apoptotic process: first polymerization, followed by depolymerization, and finally degradation. However, compared with CPT-induced apoptosis, Jas-induced apoptosis was characterized by pronounced actin polymerization that corresponded morphologically with prominent membrane blebbing, but less apoptotic body formation. Furthermore, DNase I activity, which is normally inhibited by G-actin, was specifically detected in Jas-treated cells. These results show that the regulation of actin polymerization is an important apoptotic morphological effector, whereas the alterations of the actin polymerization status by chemicals have profound effects not only on altering the morphology of apoptotic cells, but on apoptosis induction in HL-60 cells as well.

Actins↗
PubMed1999

Direct selection for mutators in Escherichia coli.

We have constructed strains that allow a direct selection for mutators of Escherichia coli on a single plate medium. The plate selection is based on using two different markers whose reversion is enhanced by a given mutator. Plates containing limiting amounts of each respective nutrient allow the growth of ghost colonies or microcolonies that give rise to full-size colonies only if a reversion event occurs. Because two successive mutational events are required, mutator cells are favored to generate full-size colonies. Reversion of a third marker allows direct visualization of the mutator phenotype by the large number of blue papillae in the full-size colonies. We also describe plate selections involving three successive nutrient markers followed by a fourth papillation step. Different frameshift or base substitution mutations are used to select for mismatch-repair-defective strains (mutHLS and uvrD). We can detect and monitor mutator cells arising spontaneously, at frequencies lower than 10(-5) in the population. Also, we can measure a mutator cascade, in which one type of mutator (mutT) generates a second mutator (mutHLS) that then allows stepwise frameshift mutations. We discuss the relevance of mutators arising on a single medium as a result of cells overcoming successive growth barriers to the development and progression of cancerous tumors, some of which are mutator cell lines.

2-Aminopurine↗
PubMed1998

Xenotransplantation of adult porcine islets in diabetic mice. A study of UVB irradiation, cryopreservation and immunosuppression on graft survival time.

The major obstacle for successful xenotransplantation of islets to large animals and human diabetics is the host rejection. To address the rejection problem, we studied the efficacy of UV-B irradiation, cryopreservation and immunosuppression on the in vivo functional time and immunogenicity of adult porcine islets (PI) in outbred CD1 mice. Exposure of PI to UV-B irradiation between 300-1800J/M2 did not affect the cellular viability as assessed by fluorescein diacetate or their daily insulin secretion in vitro. Fresh PI normalized the blood glucose (BG) of diabetic CD1 mice for 3.1+/-0.6 (n = 8, mean+/-SEM) days. Islets treated with 600J/M2 UV-B irradiation or cryopreservation had similar graft functional times to fresh islets upon transplantation in diabetic CD1 mice. Immunosuppression with cyclosporin A (CsA), antilymphocyte serum (ALS) and FK506 prolonged the functional time of fresh pig islets to 7.9+/-0.9 (n = 9), 6.2+/-1.3 (n = 5) and 24.2+/-10.4 (n = 12) days, respectively. However, additional pretransplant treatment with either UV-B irradiation or cryopreservation did not further increase the functional time of pig islets in mice immunosuppressed with CsA. Furthermore, there was no apparent difference in the frequency of appearance of cytotoxic antibodies and antibody titers in the recipients of UV-B irradiated or cryopreserved pig islet compared with non-treated islets. The UV-B irradiation and cryopreservation of PI before transplantation with the present protocols did not appear to have significant effect on the islet immunogenicity when assessed by in vivo survival duration and anti-donor antibody titer production.

Animals↗
PubMed1998

Rate-limiting steps in selenium assimilation and volatilization by indian mustard

Se can be accumulated by plants and volatilized to dimethylselenide, providing an attractive technology for Se phytoremediation. To determine the rate-limiting steps in Se volatilization from selenate and selenite, time- and concentration-dependent kinetics of Se accumulation and volatilization were studied in Indian mustard (Brassica juncea). Time-dependent kinetic studies showed that selenate was taken up 2-fold faster than selenite. Selenate was rapidly translocated to the shoot, away from the root, the site of volatilization, whereas only approximately 10% of the selenite was translocated. For both selenate- and selenite-supplied plants, Se accumulation and volatilization increased linearly with external Se concentration up to 20 &mgr;M; volatilization rates were also linearly correlated with root Se concentrations. Se-volatilization rates were 2- to 3-fold higher from plants supplied with selenite compared with selenate. Se speciation by x-ray absorption spectroscopy revealed that selenite-supplied plants accumulated organic Se, most likely selenomethionine, whereas selenate-supplied plants accumulated selenate. Our data suggest that Se volatilization from selenate is limited by the rate of selenate reduction, as well as by the availability of Se in roots, as influenced by uptake and translocation. Se volatilization from selenite may be limited by selenite uptake and by the conversion of selenomethionine to dimethylselenide.

Journal Article↗
PubMed1997

Prolongation of pig islet xenograft survival in rats immunosuppressed with FK506.

FK506 a new and potent immunosuppressive agent has been shown to be effective in prolonging pancreatic islet allograft survival. The present study was to determine its efficacy in prolonging pig islet xenotransplantation in two different strains of rat recipients. A total of two dosages of FK506 at 1 or 2 mg/kg per day for 2 weeks and then at weekly intervals were tested as monotherapy for their effect on the survival of renal subcapsular xenografts of purified or impure adult pig islets in inbred ACI and outbred Wistar rats. Histological assessment indicated that FK506 at 2 mg/kg per day significantly prolonged purified pig islet xenograft survival and to 7.5 months in two of three ACI recipients. Monotherapy with a lower dosage of FK506 or transplantation with impure pig islets resulted in increased graft survival time over controls, but less than that with the 2 mg/kg per day FK506. The viable pig islet xenografts showed a normal appearance and were readily identified by immunohistochemical staining for insulin and glucagon and further confirmed by immunohistochemical staining with anti-pig islet specific monoclonal antibody clone P44, developed in our laboratory. Mononuclear cell infiltration, mainly of the CD8-positive T-cell subset, increased with the duration of the graft in the recipient. By 7.5 months the majority of the xenografted islet cells were enclosed by the cellular infiltrate. The in vitro perfusion study of pig islets that had survived for 1 or 2 months in vivo showed that they were responsive to glucose stimulation with increase in insulin secretion into the perfusate. The results demonstrated that FK506 significantly prolonged pig islet survival in two rat strains and suggested that it is an effective immunosuppressant for the xenotransplantation model.

Animals↗
PubMed1996

Enzymatic synthesis of S-adenosyl-L-methionine on the preparative scale.

The problems inherent in the enzymatic and chemical synthesis of S-adenosyl-L-methionine (SAM) led us to develop an efficient, simple method for the synthesis of large amounts of labeled SAM. Previously, we reported that the problem of product inhibition of E. coli SAM synthetase encoded by the metK gene was successfully overcome in the presence of sodium p-toluenesulfonate (pTsONa). This research has now been expanded to demonstrate that product inhibition of this enzyme can also be overcome by adding a high concentration of beta-mercaptoethanol (beta ME), acetonitrile, or urea. In addition a recombinant strain of E. coli has been constructed that expresses the yeast SAM synthetase encoded by the sam2 gene. The yeast enzyme does not have the problem of product inhibition seen with the E. coli enzyme. Complete conversion of 10 mM methionine to SAM was achieved in incubations with either the recombinant yeast enzyme and 1 molar potassium ion or the E. coli enzyme in the presence of additives such as beta ME, acetonitrile, urea, or pTsONa. The recombinant yeast SAM synthetase was used to generate SAM in situ for use in the multi-enzymatic synthesis of precorrin 2.

Escherichia coli↗