PubMed Health⌕ Search

Biomedical subjects

C Hwang

Publications and source records attributed to C Hwang.

68 records · Page 4Linked to original sources
PubMed1993

Age-related differences in gastric acid secretion and response of gastric inhibitory polypeptide after oral glucose in male rats.

Effects of aging on the secretion of gastric acid and the response of gastric inhibitory polypeptide (GIP) and insulin after oral glucose were studied. Male rats with the age of 3 and 20 months (mo) were fasted overnight before anesthetization with pentobarbital (25 mg/kg BW, ip). The right jugular vein was catheterized for pentagastrin infusion. A PE-320 cannula was introduced into the stomach through an incision in the duodenum and was ligated about 0.5 cm from the pylorus. The stomach was flushed through the esophagus cannula via a peristaltic pump with 10 ml saline at room temperature and then irrigated with saline. Acid output was determined by titration of the flushed perfusate with 0.01 N NaOH to pH 7.0. Basal secretions were collected for 45 min before intravenous infusion of pentagastrin (0.5 microgram/kg/min) for 90 min, then for an addition 45 min. In another experiment, rats were fasted for 4 hours before an oral glucose load (3.2 g/kg). Blood samples were collected from each animal via a jugular catheter at -10, 0, 10, 20, 30, 45, 60, and 90 min following glucose ingestion. The concentrations of plasma GIP, insulin and triiodothyronine (T3) were measured by specific radioimmunoassays. The plasma T3 concentration was decreased in male rats during aging. Pentagastrin infusion stimulated gastric acid secretion in both old and young rats. The spontaneous gastric acid secretion in 20 mo rats was not significantly different from that in 3 mo rats. However, the secretion of gastric acid in response to pentagastrin was greater in 20 mo rats than in 3 mo rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1992

Oxidized redox state of glutathione in the endoplasmic reticulum.

The redox state of the endoplasmic reticulum (ER) was measured with the peptide N-Acetyl-Asn-Tyr-Thr-Cys-NH2. The peptide diffused across cellular membranes; some became glycosylated and thus trapped within the secretory pathway, and its cysteine residue underwent reversible thiol-disulfide exchanges with the surrounding redox buffer. Glycosylated peptides from cells were disulfide-linked to glutathione, indicating that glutathione is the major redox buffer in the secretory pathway. The redox state of the secretory pathway was more oxidative than that of the cytosol; the ratio of reduced glutathione to the disulfide form (GSH/GSSG) within the secretory pathway ranged from 1:1 to 3:1, whereas the overall cellular GSH/GSSG ratio ranged from 30:1 to 100:1. Cytosolic glutathione was also transported into the lumen of microsomes in a cell-free system. Although how the ER maintains an oxidative environment is not known, these results suggest that the demonstrated preferential transport of GSSG compared to GSH into the ER lumen may contribute to this redox compartmentation.

Amino Acid Sequence↗
PubMed1990

Genetic and environmental influences on echocardiographically determined left ventricular mass in black twins.

Genetic and environmental influences on left ventricular mass were examined in normotensive black twins. Left ventricular mass was measured echocardiographically in 7 sets of monozygotic (MZ) and 15 sets of dizygotic (DZ) twins and adjusted for body surface area (LVMI). Regression analyses showed significant effects of gender (R2 = 0.48; P less than .01), systolic blood pressure (R2 = 0.21; P less than .01) and age (R2 = 0.10; P less than .05) on LVMI but did not show an effect for either diastolic blood pressure or caloric expenditure. Monozygotic twins showed smaller within-pair differences (7 +/- 5) than DZ twins (17 +/- 11) for LVMI following adjustment for gender, systolic blood pressure and age (P less than .03). The intraclass correlation for MZ twins was 0.90 (P less than .01) and 0.33 (P = NS) for DZ twins. These results indicate that both genetic and environmental factors are important determinants of left ventricular mass in blacks, independent of gender, blood pressure and age.

Adult↗
PubMed1990

Age-related differences in the release of luteinizing hormone and gonadotropin-releasing hormone in ovariectomized rats.

The effect of aging on the release of gonadotropin-releasing hormone (GnRH) in vitro and of luteinizing hormone (LH) both in vivo and in vitro in ovariectomized (Ovx) rats was studied. Old (21-24 months) and young (3-4 months) rats were Ovx before use. They were injected subcutaneously with estradiol benzoate (25 micrograms/kg) or sesame oil for 3 days and then challenged with GnRH (0.5, 2 or 10 micrograms/kg) via a jugular catheter. Blood samples were collected immediately before and at 5, 10, 20, 40 and 60 min following GnRH injection. For in vitro study, Ovx rats were decapitated. The anterior pituitary glands (APs) were incubated with GnRH (0.1 or 10 nM) and estradiol (0, 0.1, 1 or 10 nM) at 37 degrees C for 30 min. The mediobasal hypothalamus was superfused with Locke's solution at 37 degrees C for 210 min, and stimulated with 60 mM KCl at 90 and 150 min. The medium samples were collected at 10-min intervals. Concentrations of GnRH and LH in plasma and medium samples were measured by radioimmunoassay. In all rats, the basal and GnRH-stimulated levels of plasma LH were lower in old than in young rats. The spontaneous release of LH in vitro from APs of Ovx rats was increased by aging, whereas GnRH-stimulated release of LH in vitro was lower in old than in young animals. The potassium-stimulated, but not spontaneous, release of GnRH was lower in old than in young Ovx rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1990

Circadian variation of blood pressure in blacks: influence of age, gender and activity.

The purpose of the present study was to examine the circadian variation of blood pressure in black adults and determine the factors associated with this variation. Ambulatory blood pressure recordings were performed with a non-invasive recorder on 60 black subjects, 22 males and 38 females, with a mean age of 31 +/- 11 years and a mean causal blood pressure of 121/93 mm Hg. Only diastolic blood pressure exhibited a significant time of day effect (P less than 0.05). Age and gender were found to have both independent (r2 = 0.10 for each) and interactive effects (r2 = 0.26) on the level of systolic blood pressure during the day, but did not affect the diurnal pattern per se. Blood pressure at work (128/81 mm Hg) was higher (P less than 0.05) than blood pressure during miscellaneous activities (119/75 mm Hg) or sleep (119/73 mm Hg) but did not differ from blood pressure at home (123/77 mm Hg). Blood pressures at home while awake and during sleep were not different. These data show that blacks have a circadian rhythm of blood pressure which is characterized by a blunted nocturnal decline. In addition age, gender and activity are important determinants of the circadian variation. These results may help to explain racial differences in the prevalence of hypertension.

Activities of Daily Living↗
PubMed1989

Age-related differences in the spontaneous and thyrotropin-releasing hormone-stimulated release of prolactin and thyrotropin in ovariectomized rats.

Effect of estradiol on the spontaneous and thyrotropin-releasing hormone (TRH)-stimulated release of prolactin (PRL) and thyrotropin (TSH) in young and aged ovariectomized (Ovx) rats was investigated. Old (22-26 months) and young (3 months) female rats were Ovx 3 weeks before use. They were injected subcutaneously with estradiol benzoate (EB, 25 micrograms/kg) or sesame oil for 3 days and were catheterized via the right jugular vein. Twenty hours after the last administration of EB, rats were injected with TRH (10 micrograms/kg) through the catheter. Blood samples were collected before and 5, 10, 20, 40 and 60 min after TRH injection. On the day following blood sampling, all rats were decapitated. The anterior pituitary glands (APs) were excised, and incubated with or without TRH (10 ng/ml) at 37 degrees C for 30 min. The basal level of PRL concentration in plasma samples was 5-fold higher in old Ovx rats than in young Ovx rats. Five min after TRH injection, the increase in plasma PRL was greater in old animals than in young animals. Plasma PRL remained higher in old animals than in young animals at 10, 20, 40 and 60 min following TRH challenge. Administration of EB to old and to young Ovx rats produced increases in both basal and TRH-stimulated secretions of PRL, but did not affect the difference in plasma PRL patterns between old and young animals. The release of PRL from APs was increased significantly in all rats after a 30-min incubation with TRH. In Ovx rats injected with oil, the basal release of PRL in vitro was increased with age.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1988

A validation study of the Del Mar Avionics Pressurometer IV according to AAMI guidelines.

Guidelines for the evaluation of automatic non-invasive blood pressure (BP) measurement devices have recently been established by the Association for the Advancement of Medical Instrumentation (AAMI). We evaluated the Del Mar Avionics Pressurometer IV (P4) in tests on 109 subjects, according to these guidelines. Three readings by two observers using a double stethoscope were first compared to each other to determine a standard and then averaged and compared to readings obtained using the P4. The two observers agreed within +/- 6 mmHg or 90% of the readings for both systolic and diastolic BP, with correlations of 0.99 and 0.98 for systolic and diastolic BP, respectively. The observers and the P4 in turn agreed to within +/- 6 mmHg for 85% of the readings for systolic BP, with a correlation of 0.98, and 65% of the readings for diastolic BP, with a correlation of 0.69. The correlations for both systolic and diastolic BP increased to 0.99 when readings were restricted to those obtained in individuals who fulfilled our previously defined calibration criterion of +/- 5 mmHg. In addition, we evaluated nine measurements of performance over 60 ambulatory recordings. The most serious problem was that of missing data which occurred in 85% of the recordings, primarily during sleep hours, and was generally attributed to either detection of Korotkoff sounds below 40 mmHg or a failure to detect Korotkoff sounds.

Adult↗
PubMed1983

Identification and visualization of the sexual agglutinin from the mating-type plus flagellar membrane of Chlamydomonas.

Sexual agglutinins located on the flagellar membranes of Chlamydomonas gametes mediate a mating-type-specific adhesion reaction that brings complementary gametes together for zygotic cell fusion. We identify the mating-type plus agglutinin, using a combination of biochemical and genetic analysis, as a glycopolypeptide with an apparent molecular weight of greater than 10(6) by SDS-polyacrylamide gel electrophoresis. Its core polypeptide migrates as a approximately 480-kd species, and it is estimated to be present in approximately 30 copies per gametic flagellum. The agglutinin is present in the wild type, in a mutant that agglutinates but cannot fuse, and in a complementing diploid, whereas it is absent from four nonagglutinating mutants and from a noncomplementing diploid. Electron microscopy shows the purified agglutinin to be a highly asymmetric molecule, 220 X 4 nm. To our knowledge, this is the first reported purification and visualization of a membrane-associated cell-cell recognition protein.

Agglutinins↗
PubMed1982

Sexual agglutinins from the Chlamydomonas flagellar membrane. Partial purification and characterization.

Chlamydomonas sexual agglutinins have been quantitatively extracted from isolated flagella in vitro using the dialyzable nonionic detergent octyl-D-glucopyranoside and from cells in vivo with 12.5 mM EDTA. Both preparations elicit normal sexual responses from gametes of complementary, but not like, mating types. Extracts of vegetative cells and several agglutination-deficient (imp) mutants are totally inactive. Agglutinin activity is sensitive to trypsin, mild periodate oxidation, and heating at 60 degrees C for 1 min. These findings, coupled with the size of the molecule (it is excluded from Sepharose 6B and sediments as a 12 S particle in sucrose gradients) lead us to propose that the Chlamydomonas sexual agglutinins are large glycoproteins or glycoprotein aggregates which associate with the flagellar membrane in an extrinsic fashion. Partial purification of in vivo 125I-surface labeled EDTA extracts rules out several surface polypeptides, including the bulk of material migrating in the region of the major membrane glycoprotein (Mr 350,000), as agglutinin candidates and indicates that the active molecule is a minor component of the flagellar membrane. In addition, in vitro assays suggest a mechanism for in vivo sexual agglutination whereby stable adhesion is achieved by the active redistribution of agglutinins to the flagellar tips.

Agglutinins↗
PubMed1982

Activation for cell fusion in Chlamydomonas: analysis of wild-type gametes and nonfusing mutants.

Gametes of Chlamydomonas reinhardi become activated for cell fusion as the consequence of sexual adhesion between membranes of mating-type plus and minus flagella. By using tannic acid plus en bloc uranyl acetate staining, and by fixing at very early stages in the mating reaction, we have demonstrated the following. (a) Activation of the minus mating structure entails major modifications in the structure of the organelle, causing it to double in size and to concentrate surface coat material, termed fringe, into a central zone. (b) The unactivated plus mating structure is endowed with fringe that moves with the tip of the actin-filled fertilization tubule during activation. Pre-fusion images suggest the occurrence of a specific recognition event between the plus and minus fringes. (c) Gametes carrying the imp-1 mutation fail to form a fringe and are unable to fuse. The imp-1 mutation is linked to the mating-type plus (mt+) locus, suggesting that the gene specifying the synthesis or insertion of fringe is encoded in this sector of the genome. (d) Gametes carrying the imp-11 mutation fail to form both a normal fringe and a normal submembranous density beneath the fringe, and are also unable to fuse. The imp-11 mutation converted a wild-type minus cell into a pseudo-plus strain; a model to explain this conversion proposes that the normal imp-11 gene product represses plus-specific genes concerned with Chlamydomonas gametogenesis.

Agglutinins↗
PubMed1976

Isolation and genetic analysis of mutant strains of Chlamydomonas reinhardi defective in gametic differentiation.

Impotent mutant strains of Chlamydomonas reinhardi, mating-type (mt) plus, are described that have normal growth and motility but fail to differentiate into normal gametes. Procedures for their isolation and their genetic analysis are described. Five of the imp strains (imp-2, imp-5, imp-l, imp-7, and imp-8) exhibit no flagellar agglutination when mixed with mt- or mt+ gametes and the mutations are shown to be unlinked to the mt locus (with the possible exception of imp-7). Two of the strains (imp-3 and imp-4) carry leaky mutations that affect cell fusion; neither mutation is found by tetrad analysis to be linked to mt or to the other. Cells of the imp-1 strain agglutinate well with mt- gametes and active agglutination continues for up to 48 hours, but cell fusion occurs only very rarely. Analysis of these rare zygotes indicates that imp-1 is closely linked to the mt+ locus, and fine-structural studies reveal that imp-1 gametes produce a mutant mating structure involved in zygotic cell fusion. The development of sexuality in C. reinhardi therefore appears amenable to genetic dissection.

Acetates↗
PubMedDate not supplied

Measurement and control of dissolved carbon dioxide in mammalian cell culture processes using an in situ fiber optic chemical sensor.

At high viable cell concentrations in large-scale mammalian cell culture processes, the accumulation of dissolved carbon dioxide (dCO(2), typically quantified as an equilibrium gas-phase concentration) becomes problematic as a result of low CO(2) removal rates at reduced surface-to-volume ratios. High dCO(2) concentrations have previously been shown to inhibit cell growth and product formation in mammalian cells and to alter the glycosylation pattern of recombinant proteins. Therefore, reliable monitoring and control of dCO(2) are important for successful large-scale operation. Off-line measurements by instruments such as blood gas analyzers (BGA) are constrained by the low frequency of data collection and cannot be used for on-line control. In a preliminary evaluation of the YSI 8500 in situ sensor, a response time (t(90%)) of 6 min, sensitivity of 0.5% CO(2) (3.6 mmHg), and linearity of measurement (R(2) = 0.9997) between the equivalent gas-phase partial pressure of 0-180 mmHg (0% and 25% CO(2)) were established. Measurements were found to be unaffected by culture pH and typical mammalian cell culture concentrations of glucose, glutamine, glutamate, lactate, and ammonium. The sensor withstood repeated sterilization and cleaning cycles. The reliability of this sensor was demonstrated in microcarrier-based Chinese hamster ovary (CHO) cell perfusion cultures at reactor scales of 30, 40, 340, and 2000 L and was successfully implemented in a dCO(2) control strategy using N(2) sparging.

Animals↗