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Biomedical subjects

E C Chan

Publications and source records attributed to E C Chan.

At least 109 records · Page 6Linked to original sources
PubMed1988

Immunoreactive methionine-enkephalin in cerebrospinal fluid and blood plasma during acute stress in conscious sheep.

The opioid peptide methionine-enkephalin (Met-enkephalin) was measured in plasma and cerebrospinal fluid (CSF) of sheep in which the cisterna magna, carotid artery, and jugular vein were chronically cannulated. Venous blood plasma and CSF were collected before and after stress treatment and in control studies in conscious animals. Plasma and CSF were extracted with octadecylsilica and oxidized, and Met-enkephalin was measured as its Met-sulfoxide derivative by specific RIA. The molecular form of immunoreactive Met-enkephalin was characterized by peptide size exclusion chromatography of an octadecylsilica extract of sheep plasma through Bio-Gel P2, followed by reverse phase liquid chromatography, and was identical to Met-enkephalin and Met-sulfoxide-enkephalin. Insulin-induced hypoglycemia produced an elevation of plasma cortisol and an increase in the plasma concentration of Met-enkephalin. Acute hemorrhage led to an earlier and greater rise in plasma cortisol than that associated with insulin-induced hypoglycemia, but did not increase the concentration of Met-enkephalin in plasma. Neither form of acute stress increased the concentration of Met-enkephalin in CSF. These studies confirm that secretion of Met-enkephalin into blood can be dissociated from stimulation of the pituitary-adrenocortical system. They also show that circulating Met-enkephalin is elevated in conscious sheep during acute hypoglycemic stress, but plasma Met-enkephalin is unlikely to exert effects on the opiate receptors of periaqueductal or spinal nociceptive neurons under these conditions, since it does not enter cerebrospinal fluid in significant amounts.

Animals↗
PubMed1988

Secretion of beta-endorphin into the maternal circulation by uteroplacental tissues in response to hypoglycaemic stress.

The placenta has been shown to contain ACTH and beta-endorphin but the roles of these peptides are unknown. To investigate whether they are released into the maternal circulation from the placenta in response to physiological stimuli the effects of hypoglycaemic stress were investigated. Plasma samples were collected from the femoral artery (FA) and uterovarian (UV) vein of nine pregnant sheep before and during hypoglycaemia induced by intravenous insulin (100U). Plasma concentrations of ovine beta-endorphin (o beta-EP) were measured by radioimmunoassay. Concentrations of o beta-EP rose in both vessels by 60 min after insulin. The peak concentrations of o beta-EP (pmol/l) were 122 +/- 29 (mean +/- SEM, n = 8) in the UV and 96 +/- 24 (n = 9) fmol/ml in the FA 60 min after insulin injection. There was no difference between the concentrations of o beta-EP in the vessels before insulin injection but at 60 and 120 min after insulin the concentrations of o beta-EP were significantly higher in the UV than FA (P less than 0.02, analysis of variance). This indicates that the pregnant uterus or placenta can respond to hypoglycaemia by secreting beta-EP into the maternal circulation. It is therefore possible that placental pro-opiomelanocortin (POMC) peptides may have a role in maternal endocrinology and metabolism.

Animals↗
PubMed1988

Secretion of corticotropin-releasing hormone by superfused human placental fragments.

Corticotropin-releasing hormone (CRH) immunoreactivity (IR) is present in the blood of women in the 3rd trimester of pregnancy and in placental extracts. We have used a placental fragment superfusion system to investigate the release of CRH from fresh placental tissue. Fragments of normal term placenta were mixed with Biogel P2, packed into minicolumns and superfused with carbogen-gassed Earles buffer at 37 degrees C. The rheology of the superfusion system was determined and the oxygen consumption of the superfused placental fragments indicated viability of the tissue preparation over a 5-hour time span. CRH IR in the eluate was measured by radioimmunoassay (RIA) using the 41 residue synthetic peptide human, rat CRH-41 (h, r CRH-41) as the standard, 125I labelled Tyr- h, r CRH as the tracer and rabbit anti-ovine CRH as the antibody. The sensitivity of the assay is 2 pM. Size exclusion chromatography on Sephadex G-50 of the placental column eluate displayed one major peak of CRH IR which co-eluted with that of h, r CRH. Placental fragment superfusate displayed potent CRH bioactivity as assessed by beta-endorphin secretion from ovine pituitary cells. Replacing the superfusing medium of the placental fragments with 45 mM KCl resulted in a prompt increase in the release of CRH IR. These results indicate that placental cells in vitro secrete a molecule of similar molecular weight, immunoreactivity and bioactivity to h, r CRH and that the rate of secretion may be regulated.

Animals↗
PubMed1987

Postnatal disappearance of the pregnancy-associated reduced sensitivity of plasma cortisol to feedback inhibition.

We recently observed that the characteristic insensitivity of the pituitary-adrenal system in women to feedback inhibition during pregnancy persists for at least four days postnatally. We therefore examined women during the first five weeks after delivery to assess when the sensitivity of plasma cortisol to glucocorticoid inhibition returns to normal. Dexamethasone (DEXA, 1 mg) was ingested at 11 pm by normal healthy women, once between the 3rd and 27th postnatal days, and again on day 35. Blood plasma was collected at 4 pm on the following day for cortisol assay. Plasma cortisol levels (nmol/L, mean +/- sem [n]) after DEXA in the first two weeks (216 +/- 28, [47]) were higher (p less than 0.001) than in nonmedicated nonpregnant women (47.4 +/- 8.9 [12]) and were normal by the 35th day after delivery (41.7 +/- 4.8 [74]). A negative association was found between post-DEXA cortisol and time after delivery in the first 4 post-partum weeks (r = -0.46, p less than 0.001). The study confirms that insensitivity of plasma cortisol to feedback inhibition persists beyond normal pregnancy in a significant proportion of healthy women for two to three weeks, and is absent by the 5th postnatal week.

Dexamethasone↗
PubMed1987

Effects of extracellular products of a presumed gingival pathogen, the bacterium Peptostreptococcus 84H14S, on cultured human fibroblasts and HeLa cells.

Culture fluids from this microorganism, fibroblasts and HeLa cells contained potent factors which inhibited thymidine uptake in HeLa cells. The outcome of heating the culture fluid and fractionating it by gel filtration suggested that this was not due to bacterial hyaluronidase activity. Purified peptostreptococcal hyaluronidase and several commercially-available mucopolysaccharidases also did not inhibit thymidine uptake.

Cell Adhesion↗
PubMed1987

Reliability of attachment level measurements using the cementoenamel junction and a plastic stent.

Repeated measurements of attachment level appear to be important assessments in periodontal clinical trials, yet the lack of reliability for this assessment creates measurement error which in turn demands increased sample sizes or reduces the power of the test. A plastic occlusal stent has been developed as a fixed reference point to assess changes in probing depths over time and thus reflect differences in attachment levels. The advantages of this system over traditional methods have not been measured. The purpose of this study was to determine intra- and interexaminer reliability for probing depths from the stent and the CEJ. Paired measurements of attachment level using the stent produced correlation coefficients for inter- and intraexaminer readings of 0.84 and 0.76, respectively. For subgingival cementoenamel (CEJ) measurements, lower coefficients of 0.71 and 0.59 were found for inter- and intraexaminer paired readings, respectively. Thus, measurements using the stent appear to be more reliable than subgingival CEJ readings.

Dental Cementum↗
PubMed1987

The role of adjunctive Rodogyl therapy in the treatment of advanced periodontal disease. A longitudinal clinical and microbiologic study.

Several studies have indicated that the combination of metronidazole and spiramycin is synergistic against anaerobic bacteria and may be effective against oral infections. The present study sought to determine the efficacy and safety of a commercial preparation of these two antibiotics (Rodogyl) when used adjunctively in the treatment of advanced periodontal disease. In a double-blind parallel randomized trial, 56 patients (mean age = 44 years) with advanced periodontitis (50 of whom completed the study) were assigned to either the Rodogyl or placebo group. Both groups were thoroughly scaled and root planned for approximately 6 hours, with one group receiving Rodogyl for 2 weeks and the other a placebo. No other therapy was received during the study period. Two sites in each patient with probing depths of at least 7 mm were selected for study. Plaque level (P1I), gingival inflammation (GI), probing depth (PD), and attachment level (AL) were measured at baseline, 14 days, 1 month, and then at monthly intervals up to 6 months. Subgingival bacteria were monitored with dark-field microscopy. The development of resistant bacteria, as well as side effects to the medications, was also monitored. The Rodogyl group exhibited a greater gain in AL (0.67 mm) from the 2-month interval until the end of the study. Although this difference was statistically significant (P less than 0.05), it was not necessarily of biologic significance. There was a significantly greater decline in the proportion of spirochetes in the Rodogyl group at the 14-day interval, and this difference remained significant (P less than 0.05) at all study intervals. No difference in the proportion of motile organisms was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

Restriction endonuclease map of endogenous mouse mammary tumor virus loci in GR, DBA, and NFS mice.

Mouse mammary tumor virus (MMTV) is integrated in the genome of most mice as an endogenous provirus. Two of these MMTV proviral loci (Mtv-1 and Mtv-2) are associated with virus expression and tumorigenicity. We prepared restriction endonuclease maps of the endogenous MMTV proviruses in two strains, DBA and GR, which contain the Mtv-1 and Mtv-2 loci, plus a third strain, NFS, which has a low mammary tumor incidence. We find that all these mouse strains have certain MMTV loci in common even though their origins are widely divergent. We also find that some integrated MMTV proviruses appear to have undergone alterations or deletions when compared with MMTV exogenous proviral DNA. We have thus made a comprehensive characterization of MMTV loci in these mouse strains which could serve as a basis for the study of their differences in expression.

Animals↗
PubMed1986

Acute hemorrhagic stress in conscious sheep elevates immunoreactive beta-endorphin in plasma but not in cerebrospinal fluid.

The effects of acute hemorrhagic stress on the concentrations of immunoreactive beta-endorphin (IR beta EP) in cerebrospinal fluid (CSF) and blood plasma were investigated in conscious sheep in which the cisterna magna, a carotid artery, and a jugular vein were chronically cannulated. Serial samples of CSF and jugular venous blood were collected before and after acute arterial hemorrhage and in control experiments. Basal concentrations of IR beta EP were higher in plasma than in CSF. Plasma concentrations of cortisol and IR beta EP increased within 45 min of the commencement of hemorrhage and returned to near baseline levels within 2.25 h. The concentrations of cortisol and IR beta EP in plasma observed after hemorrhage were significantly different from those observed in controls (analysis of variance). Neither the molar nor the relative changes from initial concentrations of IR beta EP in CSF were significantly different between hemorrhage-stressed and controls by analysis of variance. These results show that hemorrhagic stress in conscious sheep elevates concentrations of IR beta EP in plasma but not in CSF, indicating that pituitary beta EP secreted into blood does not enter CSF in significant amounts.

Animals↗
PubMed1985

Secretion of N-terminal pro-opiomelanocortin-derived peptides in response to acute haemorrhagic stress in conscious sheep.

To determine whether peptides derived from the N-terminus of the corticotropin/melanotropin/endorphin precursor, pro-opiomelanocortin, are released into blood in response to acute haemorrhagic stress, we examined the effect of haemorrhage on plasma concentrations of immunoreactive gamma 3-melanotropin, beta-endorphin and cortisol. Plasma concentrations of immunoreactive gamma 3-melanotropin (mean +/- SEM) increased within 30 min of haemorrhage from 71.1 +/- 10.4 to 106.8 +/- 6.3 fmol/mL (p less than 0.01) and plasma cortisol increased from 16.2 +/- 3.8 to 85.9 +/- 22.4 pmol/mL (p less than 0.025). The changes in plasma immunoreactive gamma 3-melanotropin and beta-endorphin were positively correlated (p less than 0.025). This study shows that peptides derived from the N-terminus of pro-opiomelanocortin are co-secreted with the C-terminal peptide beta-endorphin during acute haemorrhagic stress in sheep.

Animals↗
PubMed1985

Purification and characterization of hyaluronidase from oral Peptostreptococcus species.

Hyaluronidase was purified to apparent homogeneity from the spent medium of Peptostreptococcus sp. strain 84H14S. The enzyme was purified 310-fold by ethanol precipitation, gel chromatography, and cation-exchange chromatography with a recovery of 42% of the original activity in the culture medium. The molecular weight of the purified enzyme was estimated to be 160,000 by gel filtration with Sephacryl S-300. Like bacterial mucopolysaccharidases of other sources, the enzyme carried out an eliminative reaction with the substrate, producing 4,5-unsaturated disaccharides as the final end products. Its optimum temperature of activity is 46 degrees C. The purified peptostreptococcal hyaluronidase was different from previously reported bacterial hyaluronidases in several respects. It degraded hyaluronic acid rapidly and also exhibited some activity against chondroitin sulfate A and chondroitin sulfate C. The KmS for hyaluronic acid, chondroitin sulfate A, and chondroitin sulfate C were 0.14, 1.4, and 2.6 mg/ml, respectively. The specific activity of hyaluronidase was much higher than that of any previously purified mucopolysaccharidases. The Vmax against hyaluronic acid reached 400 mmol of product per min per mg of protein at 22 degrees C. The peptostreptococcal hyaluronidase was also unique in that its optimum pH of activity was around neutrality, whereas other bacterial hyaluronidases were most active at acidic pHs.

Bacterial Proteins↗