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Biomedical subjects

T Tran

Publications and source records attributed to T Tran.

At least 127 records · Page 7Linked to original sources
PubMed1990

Acrosome reaction and concentration of prostaglandin E2 in semen of rams treated with flunixin meglumine (Banamine).

The objectives of this study were to determine 1) the effect of Banamine on the seminal concentration of PGE2 and 2) the ability of sperm cells from treated rams to undergo acrosome reaction in vitro as an indirect measure of their fertilizing capacity. Seven rams, approximately 55 kg bodyweight and 2 to 5 yr of age, were divided into two groups: Group 1, treated (n = 4) and Group 2, controls (n = 3). Treatment consisted of administration of 75 mg i.m. Banamine twice daily, 6 to 8 h apart, for 45 d. On Day 0 (first day of treatment) and on Days 2, 9, 11, 16, 23, 25, 28, 30, 36, 39, 43 and 46 semen samples were collected from both groups using an electroejaculator. Blood samples were obtained for determination of serum levels of Banamine using high-performance liquid chromatography. Semen samples were examined for motility and morphology. Highly motile (>/=85%), normal-appearing semen samples were pooled on each day of collection and 25 ul of the pooled sample (1x10(6)/ml) of each group were induced to undergo acrosome reaction in vitro using ionophore A23187. Acrosome reaction was demonstrated using a staining technique designed for demonstrating the process in bull sperm cells. The percentage of acrosome-reacted and non-acrosome-reacted sperm was determined by random microscopic examination of 100 sperm cells using a double-blind approach. The supernatants of the remainder of the semen samples were assayed for levels of PGE2 using RIA. Values for acrosome-reacted sperm cells and PGE2 levels on the first day of treatment from both groups were compared with corresponding values from each day of sampling using Wilcoxon Rank Sums test (P<0.05). In Group 1, the mean serum level of Banamine was 3.02+/-0.58ug/ml. There was a significant increase in the ability of sperm cells from rams in Group 1 to undergo acrosome reaction as treatment progressed compared with the sperm cells from rams in Group 2. However, there was a significant decrease in concentration of PGE2 in semen from rams in Group 1 compared with those from Group 2. The results of this study suggest an inverse relationship between the capacity of sperm cells to undergo acrosome reaction and concentration of PGE2 in semen of rams treated with a nonsteroidal anti-inflammatory drug.

Journal Article↗
PubMed1990

Incidence and treatment of abnormal postpartum ovarian function in dairy cows.

The objectives of this study were to determine 1) the incidence of abnormal postpartum ovarian function in a large dairy herd in North Central Florida and 2) the effectiveness of gonadotrophin releasing hormone (GnRH) in treating this condition. The study was conducted from April 1988 to June 1989. The internal genitalia of the cows were initially examined per rectum (Day 0) between 19 and 29 (23 +/- 0.25) d after calving and again 14 d later (Day 14) for evidence of uterine involution and ovarian activity. The presence of a palpable corpus luteum (CL) and retrospective determination of plasma progesterone (P4) concentrations > 1 ng/ml were the criteria used to assess ovarian activity. Cows possessing a palpable CL and P4 concentrations > 1 ng/ml on Day 0 were determined to be cycling normally. A total of 1356 cows was used in this study. On Day 0, two groups were formed: Group 1 consisted of normal, cyclic cows, Group 2 of noncyclic cows. On Day 0, alternate cows in Group 2 were treated with GnRH (100 microg i.m). On Day 14, the previously nontreated cows in Group 2 were further divided into two groups, forming Group 3, nontreated cows and Group 4, cows treated with GnRH at this time. Group 5 was comprised of cows from Group 2 that did not respond to treatment with GnRH on Day 0; these cows were treated on Day 14 with GnRH (100 microg i.m). Group 6 was comprised of nontreated cows from Group 2 that responded spontaneously (presence of a CL) by Day 14. Reproductive parameters evaluated were the percentage of cows pregnant within 180 d after calving and at the end of the study, the number of days open and the number of services per conception. Data were statistically analyzed using Chi square and survival analysis. The results of this study indicate that the incidence of abnormal postpartum ovarian function in this herd was 30.2% and that the nontreated cows experienced more days open and required more services per conception than the treated cows, those that were cycling normally on the initial examination, and those that responded spontaneously by Day 14.

Journal Article↗
PubMed1990

Hepatic uptake of bilirubin diglucuronide: analysis by using sinusoidal plasma membrane vesicles.

In order to characterize the mechanism for bilirubin transport in the liver, the uptake of bilirubin diglucuronide (BDG) into purified sinusoidal plasma membrane vesicles was investigated. BDG uptake was saturable, and was inhibited by sulfobromophthalein and unconjugated bilirubin, but was not affected by sodium taurocholate. BDG uptake was sodium-independent and was stimulated by intravesicular bilirubin or BDG (trans-stimulation). BDG transport showed strong potential sensitivity; vesicle inside-negative membrane potential created by different anion gradients inhibited BDG uptake whereas vesicle inside-positive membrane potential generated by potassium gradients and valinomycin markedly stimulated BDG transport. These data suggest that BDG, sulfobromophthalein, and probably unconjugated bilirubin share a common transporter in liver cells which is sodium independent, membrane-potential-dependent and capable of exchange. The direction of transport in vivo may be governed by the intracellular concentration of BDG and of other yet unidentified organic anions sharing this transporter.

Animals↗
PubMed1990

Development of a sensitive and rapid chromogenic factor IX assay for clinical use.

A chromogenic factor IX assay is developed which requires only two time-dependent steps. Diluted plasma is mixed with a reagent containing factors VIII and X. The reaction is started by addition of a reagent containing factor XIa, thrombin, CaCl2, and phospholipids. Then factor XIa activates factor IX if present, thrombin activates factor VIII, and subsequently the complete factor X activating complex (factor IXa, factor VIIIa, Ca ions, and phospholipids) rapidly activates factor X. Finally, ethylenediaminetetraacetic acid plus a chromogenic substrate are added to stop the reaction and to measure formed factor Xa. Factor Xa formation is proportional to the plasma factor IX concentration (from 0 to 140%). The two reagents needed for the assay are stable at room temperature during a whole working day and for 3 h at 37 degrees C. A new isolation procedure for factor VIII is described. Factor VIII is purified from bovine plasma in a few steps with a yield of 20% and a 8,000-fold purification.

Animals↗
PubMed1990

Regulation of mouse T cell associated serine proteinase-1 (MTSP-1) by proteinase inhibitors and sulfated polysaccharides.

Mouse T cell associated serine proteinase-1 (MTSP-1) is expressed by activated T cells in vitro and in vivo, stored in cytoplasmic granules and secreted upon their specific restimulation. The aim of this study was to identify those structures which may control proteolysis by MTSP-1 in vivo in the vascular and extravascular systems. Here we show, that MTSP-1 was effectively inhibited by vascular and extravascular serpins such as antithrombin III and Cl-esterase inhibitor, as well as by aprotinin and alpha 2-macroglobulin. On the other hand, interaction of MTSP-1 with sulfated glycosaminoglycans, i.e., heparin and chondroitin sulfate, led to increased enzymatic activity and an altered fine specificity of MTSP-1 for peptide substrates. These results suggest that the level of MTSP-1 activity as well as its specificity can be regulated by constituents of the extracellular environments.

Animals↗
PubMed1989

Neonatal 6-hydroxydopa, but not DSP-4, elevates brainstem monoamines and impairs inhibitory avoidance learning in developing rats.

The involvement of brain monoamines in learning and memory in developing rats was studied by comparing the effects of 3 different noradrenergic neurotoxin treatments. Two experimental groups of male Sprague-Dawley rat pups were injected systemically with 50 micrograms/g of N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) either on the day of birth or on postnatal days 17-18. Rats in the third experimental group were injected systemically with 60 micrograms/g of 6-hydroxydopa (6-OHDOPA) on postnatal days 0 and 2. Control littermates received vehicle. The animals were trained on an inhibitory avoidance task on postnatal days 27-29 and tested for retention 24 h later. The drug treatments produced comparable depletion of norepinephrine in the hippocampus and frontal cortex. 6-OHDOPA, but neither DSP-4 treatment, significantly elevated brainstem concentrations of norepinephrine and serotonin. In addition, 6-OHDOPA, but not DSP-4, significantly impaired retention of the inhibitory avoidance task. The impairment did not reflect insensitivity to the footshock used in training: both neonatal drug treatments tended to lower, not raise, footshock thresholds, as measured by a flinch test. High affinity choline uptake was not affected by either neonatal drug treatment in any of the brain areas examined. Thus, the 6-OHDOPA-induced behavioral deficit did not involve altered acetylcholine function. The results implicate brainstem monoamines in the modulation of learning and memory during development.

Animals↗
PubMed1989

Restriction fragment polymorphisms of the HLA-DR, HLA-DQ, and insulin gene regions in IDDM: the GAW5 data.

The primary aim of the insulin-dependent diabetes mellitus (IDDM) component of Genetic Analysis Workshop 5 (GAW5) was to collect and analyze new data on DNA polymorphisms closely linked to the HLA-D region and the insulin gene. The probes and restriction enzymes described here were used by all ten participating labs, and the data from Southern blotting were interpreted and reported according to conventions developed for the Workshop. These DNA data on members of 94 families with two or more IDDM sibs constitute the largest such sample available. The data were used in most of the analyses presented at the Workshop meeting, and are available on request.

Chromosome Mapping↗
PubMed1989

Inhibition of adenylate cyclase in bovine ciliary process and rabbit iris ciliary body to alpha 2-adrenergic agonists.

Alpha 2-adrenergic inhibition of adenylate cyclase in bovine ciliary processes and rabbit iris ciliary body (ICB) was studied. With bovine ciliary process membrane, it was found that cAMP production in the presence of 1 microM isoproterenol was increased with increasing NaCl concentrations from 0 to 200 mM. Clonidine, an alpha 2-adrenergic agonist, produced a NaCl concentration-dependent inhibition of cAMP production in the presence of isoproterenol with a maximum inhibition at 200 mM NaCl (P less than 0.05). NaCl concentrations had no effect on basal adenylate cyclase activities and activity in the presence of clonidine alone. The alpha 2-adrenergic agonists, lofexidine, clonidine and p-amino-clonidine were tested for their ability to inhibit isoproterenol-stimulated adenylate cyclase in bovine ciliary process membrane in the presence of 200 mM NaCl. Their dose-response curves showed that they had similar IC50's but the maximum inhibition differed among these agonists. Clonidine was found to be a partial agonists producing 55% of the inhibition obtained with lofexidine. The specificity of inhibition of isoproterenol-stimulated adenylate cyclase by alpha 2-agonists and blockade by pertussis toxin was examined by adenine labelling in rabbit ICB. The results demonstrate that alpha 2-adrenergic receptors exert specific inhibitory effects on adenylate cyclase activity in rabbit ICB, which are mediated by an inhibition guanine nucleotide regulatory protein, Gi.

Adenine↗
PubMed1988

Allosteric energy at the hemoglobin beta chain C terminus studied by hydrogen exchange.

When hemoglobin switches from the deoxy (T) to the liganded (R) form, several of its peptide group NH experience a great increase in their rate of exchange with water. Selective labeling and fragment isolation experiments identify some of the sensitive protons as three to four near-neighbor H-bonded peptide NH placed between Ala140 beta and the C-terminal His146 beta residue. These NH have differing solvent accessibilities, yet all exchange at about the same rate, and they maintain a common rate in the face of modifications that change their exchange rate over a 1000-fold range. This suggests that their exchange is mediated by a concerted transient unfolding reaction. The removal of allosterically important salt links at the distant alpha subunit N termini (des-Arg141 alpha hemoglobin) has little if any effect on the indicator NH at the beta C terminus. This demonstrates the restricted reach of the separate allosteric interactions in the T form as well as the localized nature of the H-exchange probe. Breakage of a salt link at the beta chain C terminus (His146 beta to Asp94 beta) by chemical modification (NES-Cys93 beta hemoglobin) speeds exchange of the indicator peptide NH in T-state hemoglobin by six-fold, which corresponds to an allosteric destabilization at the C-terminal segment of 1 kcal (pH 7.4, 0 degrees C), according to local unfolding theory. This is in quantitative agreement with energy values obtainable from other measurements. These NH exchange with an average halftime of five hours in deoxy hemoglobin and 15 seconds in oxy hemoglobin. According to the unfolding model for protein H-exchange, the 1200-fold increase in rate indicates a loss of 3.8 kcal in structural stabilization free energy at or near the C terminus of each beta chain in the T to R transition (pH 7.4, 0 degrees C, with 2,3-diphosphoglycerate). This result together with other available data places about 70% of hemoglobin's total allosterically significant structural energy change at the beta chain C termini.

Allosteric Site↗
PubMed1985

Daunomycin in the treatment of experimental proliferative vitreoretinopathy. Effective doses in vitro and in vivo.

In previous studies the authors have shown that daunomycin, an anthracycline antibiotic, when injected into the vitreous effectively controls experimental proliferative vitreoretinopathy. Here we show that by administering daunomycin intravitreally it is possible to achieve in vivo concentrations that prevent fibroblast proliferation in vitro. The authors have also determined that the half-life of daunomycin in the vitreous is 131 min, indicating that a critical concentration is maintained in the eye for longer than 4 hr after a single injection. Using 3H-daunomycin, the authors have found that the drug is eliminated across the retina; no significant binding of the drug to vitreous components occurs. These studies demonstrate that it is possible to define the kinetics of drugs injected into the vitreous; and a knowledge of the distribution of any drug in ocular tissues is necessary to effectively determine whether such drug is of therapeutic value.

Animals↗
PubMed1984

Glutathione transport across hepatocyte plasma membranes. Analysis using isolated rat-liver sinusoidal-membrane vesicles.

Transport of reduced glutathione (GSH) and its derivatives was studied in rat-liver sinusoidal plasma-membrane vesicles by a rapid filtration technique. The membrane vesicles exhibited transport of GSH into an osmotically active intravesicular space. Equilibrium uptake of vesicle-associated GSH was similar to that of free ligands which can be trapped by the intravesicular space of sinusoidal membrane samples. Kinetic analysis of the transport process revealed that the sinusoidal membrane vesicles have high-affinity and low-affinity GSH transport systems; the former has an apparent Km of 0.34 mM for GSH and V of 1.4 nmol X mg protein-1 X 20 s-1, and the latter has an apparent Km of 3.3 mM and V of 3.9 nmol X mg protein-1 X 20 s-1. Both Km values are lower than intrahepatic GSH levels, indicating that GSH transport across the sinusoidal membrane occurs via carrier-mediated mechanism and argues simple diffusion mechanism. The presence of oxidized glutathione (GSSG) or S-benzylglutathione inhibited GSH transport by the vesicles; the low-affinity transport system was inhibited more markedly than the high-affinity transport system. This suggests that these glutathione derivatives interacted preferentially with the low-affinity transport system for GSH. S-Dinitrophenylglutathione was also transported by the vesicles by a process which was inhibited by GSH and GSSG. The vesicles also transported GSSG, and this transport was markedly inhibited by S-benzylglutathione or GSH. The transport systems in sinusoidal plasma membranes may function in vivo in translocating GSH and its derivatives from hepatocytes into plasma and play an important role in inter-organ metabolism of these compounds.

Animals↗
PubMed1984

Taurocholate transport by rat liver canalicular membrane vesicles. Evidence for the presence of an Na+-independent transport system.

To elucidate the mechanism of vectorial translocation of bile acids in the liver, taurocholate transport was studied in isolated liver canalicular membrane vesicles by a rapid filtration method. The membrane vesicles revealed temperature-dependent, Na+-independent transport of taurocholate into an osmotically reactive intravesicular space. In the absence of sodium, taurocholate uptake followed saturation kinetics (apparent Km for taurocholate = 43 microM and Vmax = 0.22 nmol/mg protein X 20 s at 37 degrees C) and was inhibited by cholate and probenecid. Transstimulation by unlabeled taurocholate was also demonstrated. When the electrical potential difference across the membranes was altered by anion replacement, a more positive intravesicular potential stimulated, and a more negative potential inhibited, transport of taurocholate by the vesicles. Valinomycin-induced K+-diffusion potential (vesicle inside-positive) enhanced the rate of taurocholate uptake that was not altered by imposed pH gradients. These results indicate that rat liver canalicular plasma membrane contains a sodium-independent taurocholate transport system that translocates the bile acid as an anion across the membrane. In intact hepatocytes, the electrical potential difference across the canalicular membrane probably provides the driving force for taurocholate secretion. The contribution of nonionic diffusion to taurocholate secretion appears to be minimal.

Animals↗
PubMed1983

The mechanism of biliary secretion of reduced glutathione. Analysis of transport process in isolated rat-liver canalicular membrane vesicles.

Transport of reduced glutathione (GSH) was studied in isolated rat liver canalicular membrane vesicles by a rapid filtration technique. The membrane vesicles exhibit uptake of [2-3H]glycine--labeled GSH into an osmotically reactive intravesicular space. Although the canalicular membrane vesicles possess gamma-glutamyltransferase and aminopeptidase M, enzymes that hydrolyze glutathione into component amino acids, inactivation of the vesicle-associated transferase by affinity labeling with L-(alpha S,5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid (AT-125) had no effect on the initial rate of GSH transport. Chemical analysis revealed that intact GSH accounted for most of vesicle-associated radioactivity. The initial rate of transport followed saturation kinetics with respect to GSH concentration; an apparent Km of 0.33 mM and V of 1.47 nmol/mg protein in 20 s were calculated. These results indicate that transport of GSH across the canalicular membranes is a carrier-mediated process. Replacement of NaCl in the transport medium by KCl, LiCl or choline chloride had no effect on the transport activity of the vesicles. The rate of GSH uptake by the vesicles was enhanced by valinomycin-induced K+-diffusion potential (vesicle inside-positive) and was inhibited by probenecid, indicating that GSH transport across the canalicular membranes is electrogenic and involves the transfer of negative charge. The transport of GSH was inhibited by oxidized glutathione or S-benzyl-glutathione. This transport system in canalicular plasma membranes may function in biliary secretion of GSH and its derivatives which are synthesized in hepatocytes by oxidative processes or glutathione S-transferase.

Animals↗
PubMed1983

Rat liver canalicular membrane vesicles. Isolation and topological characterization.

Canalicular plasma membranes were isolated from rat liver homogenates using nitrogen cavitation and calcium precipitation methods. Compared with homogenates, the membranes were enriched 55- to 56-fold in gamma-glutamyltransferase, aminopeptidase M, and alkaline phosphatase activities and showed very low enrichment in markers of other membranes. By electron microscopy, the membrane preparation contained neither junctional complexes nor contaminating organelles and consisted exclusively of vesicles. The presence of vesicles was also evident from the osmotic sensitivity of D-[6-3H]glucose uptake into the membrane preparation. Antisera obtained from rabbits immunized with highly purified rat kidney gamma-glutamyltransferase inhibited the transferase activity of intact or Triton X-100-solubilized membranes by 45-55%. Treatment of vesicles with anti-gamma-glutamyltransferase antisera and anti-rabbit IgG antisera increased the apparent density of the membranes during sucrose density gradient centrifugation. gamma-Glutamyltransferase and aminopeptidase M activities were selectively removed from the vesicles by limited proteolysis with papain without changing the intravesicular space or alkaline phosphatase activity of the membranes. Specific binding of anti-gamma-glutamyltransferase antibody to the outer surface of isolated hepatocytes was observed as measured by the antisera and 125I-labeled protein A; binding followed saturation kinetics with respect to antibody concentration. These data indicate that the isolated canalicular membrane vesicles are exclusively oriented right-side-out and that gamma-glutamyltransferase and aminopeptidase M are located on the luminal side of rat liver canalicular plasma membranes.

Animals↗
PubMed1977

Influence of hydrogen bonding on the rotamer distribution of the histidine side chain in peptides: 1H NMR and CD studies.

Both 1H NMR and circular dichroism pH titration studies on histidine, His-Gly, Gly-His and Gly-His-Gly indicate that the side-chain spatial orientation depends strongly on the vicinal charges. The arrangement of the imidazole side-chain (rotamer population) is shown by the histidine beta and beta' and the glycine methylene proton chemical shifts as well as the vicinal 1H-1H coupling constants 3JCalpha-H-beta-H, beta'-H. For His-Gly and Gly-His-Gly a good correlation can be found between the ionization of the glycine COOH group and the increase of rotamer III (g-g) which is also visualized by circular dichroism through an enhancement of the ellipticity at 212 nm. In these two peptides a hydrogen bond between the imidazolium and the carboxylate group is supposed to stabilize rotamer III at pH 4-5.

Circular Dichroism↗