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Biomedical subjects

V Chapman

Publications and source records attributed to V Chapman.

At least 73 records · Page 4Linked to original sources
PubMed1994

Electrophysiologic analysis of preemptive effects of spinal opioids on N-methyl-D-aspartate receptor-mediated events.

BACKGROUND: Spinal N-methyl-D-aspartate (NMDA) receptor-mediated mechanisms may contribute to reduced opioid sensitivity in conditions of pain. The effectiveness of spinal opioids in inhibiting NMDA-mediated nociceptive events was assessed with two models. In addition, opioid dose-response curves with preemptive administration were compared with early and late postadministrations. METHODS: Dorsal horn nociceptive neuronal responses were recorded in the intact halothane anesthetized rat to acute repetitive C-fiber electrical stimulation (0.1 and 0.5 Hz) and to the peripheral injection of 5% formalin. At 0.5 Hz but not at 0.1 Hz, there was an enhanced C-fiber evoked response of dorsal horn neurons elicited by repetitive C-fiber stimulation (wind-up), which is mediated by the NMDA receptor. Formalin produced a biphasic response; the late protracted inflammatory phase was NMDA receptor-mediated. RESULTS: With 0.5-Hz stimulation a large degree of wind-up was elicited; it was less sensitive to 5 micrograms morphine compared with the effect of the same dose on the residual wind-up elicited at 0.1 Hz. Preadministration and early postadministration of morphine were equieffective at inhibiting the second-phase formalin response. In contrast, administration of the fast-acting mu opioid, D-Ala-Gly-MePHe-Gly-ol, given late postadministration (during the second phase) was less effective than preadministration. Increasing the dose of D-Ala-Gly-MePHe-Gly-ol produced complete inhibitions. CONCLUSIONS: NMDA receptor-mediated neuronal responses, such as wind-up and the established second phase of the formalin response, are poorly responsive to opioids. Dose increases and preemptive opioids effectively inhibit these NMDA receptor-mediated events.

Analgesics↗
PubMed1993

Deconjugation of bilirubin-IX alpha glucuronides: a physiologic role of hepatic microsomal beta-glucuronidase.

beta-Glucuronidase is an acid hydrolase located in both the lysosomal and microsomal compartments of the hepatocyte. The function of the latter remains undefined. We postulated that microsomal beta-glucuronidase may be responsible for the deconjugation of bilirubin-IX alpha glucuronides which are synthesized primarily in the hepatic microsomal compartment. We utilized two unique congenic strains of mice to characterize the role of hepatic beta-glucuronidase in the metabolism and disposition of bilirubin-IX alpha; the first exhibited less than 1% of total hepatic beta-glucuronidase activity (ATM), the second lacked only the microsomal enzyme activity (AT1). The biliary excretion of bilirubin-IX alpha conjugates was quantitated using reverse-phase high performance liquid chromatography. Under basal conditions, there was a 2-fold increase in the biliary excretion of bilirubin-IX alpha monoglucuronides and total glucuronides in the AT1 and ATM mutants compared to the normal controls. When the plasma bilirubin-IX alpha level was increased to approximately 7 mg/dl to simulate hyperbilirubinemia, by intravenous administration of [14C]bilirubin-IX alpha, mathematical modeling of the biliary excretion curves of bilirubin-IX alpha glucuronides revealed qualitative differences between control and mutant animals, whereas both mutant groups were similar. Collectively, these data demonstrate that microsomal beta-glucuronidase modulates the net rate of bilirubin-IX alpha glucuronidation and glucuronide excretion in bile, under both basal and hyperbilirubinemic conditions, and that lysosomal beta-glucuronidase has no such effects. Hepatic microsomal beta-glucuronidase appears likely to influence the biliary excretion and hence the hepatic elimination of endogenous and xenobiotic substrates (e.g. carcinogens) which undergo hepatic glucuronidation.

Animals↗
PubMed1993

The effect of intrathecal administration of RP67580, a potent neurokinin 1 antagonist on nociceptive transmission in the rat spinal cord.

The effect of intrathecal application of the selective neurokinin 1 (NK1) receptor antagonist RP67580 and its enantiomer RP68651 was studied on the responses of dorsal horn nociceptive neurones to formalin in the rat. The first and second phases of the formalin response were inhibited by RP67580 in a dose-related manner (1-10 micrograms), whereas RP68651 (5 micrograms) facilitated the second phase of the response. The same doses of RP67580 had minimal effects on the acute C-fibre responses. The NK1 receptor appears to play a role in prolonged nociceptive transmission in the spinal cord.

Animals↗
PubMed1993

Colocalization of X-linked agammaglobulinemia and X-linked immunodeficiency genes.

Mice that bear the X-linked immunodeficiency (xid) mutation have a B lymphocyte-specific defect resulting in an inability to make antibody responses to polysaccharide antigens. A backcross of 1114 progeny revealed the colocalization of xid with Bruton's agammaglobulinemia tyrosine kinase (btk) gene, which is implicated in the human immune deficiency, X-linked agammaglobulinemia. Mice that carry xid have a missense mutation that alters a highly conserved arginine near the amino-terminus of the btk protein, Btk. Because this region of Btk lies outside any obvious kinase domain, the xid mutation may define another aspect of tyrosine kinase function.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed1993

Improving diabetes care for American Indians.

In 1986, a diabetes control program was implemented in the Billings area of the IHS. Baseline health-care practices in the program were described using a structured audit. The program included adoption of the IHS Minimum Standards of Care for diabetes, technical assistance, and professional and patient education. A second audit was performed in 1988. Care practices improved significantly for all facilities in 7 of 10 parameters measured. Facilities that implemented key program activities showed more overall improvement in screening practices, education, and immunization than those that did not organize diabetes care. Factors associated with improved care practices include establishment of a coordinated, multidisciplinary diabetes team with regular meetings, acceptance of standards of care by the medical staff, use of flow sheets by multiple providers, and diabetes-related professional and patient education sessions.

Diabetes Mellitus↗
PubMed1992

Parental imprinting studied by allele-specific primer extension after PCR: paternal X chromosome-linked genes are transcribed prior to preferential paternal X chromosome inactivation.

The preferential inactivation of the paternal X chromosome in extraembryonic cells during early mouse development is an example of parental imprinting, but it has not been studied at the transcriptional level because standard methods of measuring RNA levels do not allow detection of allele-specific RNAs in individual early embryos. We sought to determine whether the paternal allele of the X chromosome-linked gene for 3-phosphoglycerate kinase 1 (Pgk-1), which is located very near the center of X chromosome inactivation, is transcribed prior to differentiation of extraembryonic lineages. Previous reports indicated that in heterozygous embryos there is a delay in the appearance of the phosphoglycerate kinase 1 allozyme encoded by the paternal X chromosome until 2 days after the appearance of the corresponding maternal allozyme. We report results obtained by use of a reverse transcription/PCR-based method which allows the quantitative measurement of allele-specific RNA. The assay is sensitive enough for the quantitative analysis in single embryos of allele-specific transcripts differing by only one nucleotide. We have used this assay to analyze mouse embryos heterozygous at the Pgk-1 and Hprt [hypoxanthine (guanine) phosphoribosyltransferase] loci, and we find that individual 8-cell and blastocyst embryos express both Hprt and Pgk-1 paternal transcripts, as do pooled 2- to 4-cell embryos. These results are discussed in view of the apparent temporal delay in paternal expression of the Pgk-1 gene at the enzyme level.

Alleles↗
PubMed1992

The spinal and peripheral roles of bradykinin and prostaglandins in nociceptive processing in the rat.

The effect of peripheral and intrathecal administration of the bradykinin B2 receptor antagonist HOE140 and the non-steroidal anti-inflammatory drug indomethacin were studied on the response of dorsal horn nociceptive neurones to formalin in the anaesthetized rat. Peripheral pretreatment with HOE140 reduced both phases of the formalin response whereas subcutaneous administration of indomethacin (5 mg/kg) reduced only the second phase. Pre-treatment with intrathecal HOE140 resulted in a dose-dependent reduction of the second phase whereas a high dose (500 micrograms) intrathecal indomethacin reduced both phases of the response. Bradykinin plays a role in peripheral nociception during the first and second phase of the response whereas the prostaglandins are only involved during the second phase. The converse is true centrally, the prostaglandins appear to be involved in both phases of the formalin response whereas bradykinin only plays a central role during the second phase of the response.

Animals↗
PubMed1992

Freeze-thaw effects on the detection of blood group substances in detergent extracts by enzyme-linked immunosorbent assays (ELISA).

The sensitivity of an enzyme-linked immunosorbent assay (ELISA) for human blood group antigens extracted from blood stains with the surfactant, n-octyl-beta-D-glucopyranoside (OBG), at concentrations below the critical micelle concentration can be increased by the introduction of a single freeze-thaw step. The ELISA signals increase from 3- to 4-fold for OBG extracts of 80 nl bloodstains. The ELISA signal enhancement occurs irrespective of the age of the bloodstains, at least for bloodstains up to 1 year old. The origin of the effect has been investigated and its is demonstrated that the freeze-thawing cycle increases the extent of adsorption of the blood group determinants in OBG-solubilized complexes onto microtitre plates. Gel filtration has been used to analyse the composition of OBG extracts of bloodstains in terms of the carriers of the blood group substances, protein and phospholipid in fresh and freeze-thawed extracts. It was found that freeze-thawing alters the distribution of blood group active material in the lipid-protein OBG complexes leading to a greater proportion of blood group active material in higher molecular weight complexes. The freeze-thaw effect is eliminated on the addition of a cryoprotectant, such as glycerol, and the factors which contribute to changes in the microstructure of OBG extracts on freeze-thawing are discussed.

Blood Group Antigens↗
PubMed1992

The combination of NMDA antagonism and morphine produces profound antinociception in the rat dorsal horn.

Dorsal horn nociceptive neurones exhibit wind up, a frequency dependent potentiation of their responses to repeated C-fibre stimulation. Intrathecal morphine (5 micrograms) significantly reduces the initial responses of the neurones but not wind up whereas the reverse is true for N-methyl-D-aspartate (NMDA) antagonists. The combination of intrathecal morphine (5 micrograms) and 7-chlorokynurenate (2.5 micrograms), an antagonist at the glycine site of the NMDA receptor, abolishes both the input and wind up of these neurones.

Afferent Pathways↗
PubMed1992

The effects of sandostatin and somatostatin on nociceptive transmission in the dorsal horn of the rat spinal cord.

The role of somatostatin and a stable analogue, sandostatin (Octreotide), on the responses of spinal cord neurones in vivo was investigated in the rat. Electrical C-fibre stimulation was used as a model of acute nociception and the response to subcutaneous formalin was used as a model of longer term events. Intrathecal pre-treatment with sandostatin and somatostatin did not alter the C-fibre response, wind up or A beta responses of the cells. However, intrathecal pre-treatment with sandostatin and somatostatin inhibited both the first and second phases of the formalin response dose dependently. Thus, sandostatin (20 micrograms) and somatostatin (150 micrograms) inhibited the first phase (66 +/- 12% inhibition and 52 +/- 13% respectively) and second phase (91 +/- 2% inhibition and 39 +/- 16% inhibition respectively). The second phase of the formalin response was more sensitive to somatostatin and sandostatin than the first. Sandostatin was approximately 400 times more potent than somatostatin on the second phase of the response. Subcutaneous sandostatin (100 mg/kg) significantly inhibited both the first and second phase of the formalin response whereas the local peripheral administration of sandostatin (20 micrograms) only inhibited the second phase of the formalin response.

Animals↗
PubMed1992

Sequence of the human factor VIII-associated gene is conserved in mouse.

cDNA and genomic clones corresponding to the human factor VIII-associated gene (F8A) were isolated from mouse cDNA and F8A-enriched genomic libraries. The sequences of these clones revealed an intronless gene coding for 380 amino acids, with 85% identity to the predicted human sequence. The single murine gene copy is genetically linked to factor VIII, but appears to lie outside the factor VIII gene by physical mapping. Like the human gene, the mouse F8A gene is highly expressed in a wide variety of tissues. This evolutionary comparison has helped to clarify the derived amino acid sequence in the human and strongly supports the hypothesis that the F8A gene encodes a protein.

Amino Acid Sequence↗
PubMed1992

The frequency of revertants in mdx mouse genetic models for Duchenne muscular dystrophy.

The mdx mouse has been used for the development of cellular and gene therapies for Duchenne muscular dystrophy. The relatively frequent occurrence of dystrophin-positive muscle cells called revertants has hampered these efforts by interfering with data interpretation. The mdx4cv and mdx5cv dystrophin mouse mutants have approximately 10-fold fewer revertants than the mdx mutant at both 2 and 6 mo. The mdx3cv dystrophin mouse mutant may be a useful model for some types of human dystrophin deficiencies in which the levels of dystrophin are low but not completely absent.

Animals↗
PubMed1992

An X-linked human collagen transgene escapes X inactivation in a subset of cells.

Transgenic mice carrying one complete copy of the human alpha 1(I) collagen gene on the X chromosome (HucII mice) were used to study the effect of X inactivation on transgene expression. By chromosomal in situ hybridization, the transgene was mapped to the D/E region close to the Xce locus, which is the controlling element. Quantitative RNA analyses indicated that transgene expression in homozygous and heterozygous females was about 125% and 62%, respectively, of the level found in hemizygous males. Also, females with Searle's translocation carrying the transgene on the inactive X chromosome (Xi) expressed about 18% transgene RNA when compared to hemizygous males. These results were consistent with the transgene being subject to but partially escaping from X inactivation. Two lines of evidence indicated that the transgene escaped X inactivation or was reactivated in a small subset of cells rather than being expressed at a lower level from the Xi in all cells, (i) None of nine single cell clones carrying the transgene on the Xi transcribed transgene RNA. In these clones the transgene was highly methylated in contrast to clones carrying the transgene on the Xa. (ii) In situ hybridization to RNA of cultured cells revealed that about 3% of uncloned cells with the transgene on the Xi expressed transgene RNA at a level comparable to that on the Xa. Our results indicate that the autosomal human collagen gene integrated on the mouse X chromosome is susceptible to X inactivation. Inactivation is, however, not complete as a subset of cells carrying the transgene on Xi expresses the transgene at a level comparable to that when carried on Xa.

Animals↗
PubMed1990

The propeptide of beta-glucuronidase. Further evidence of its involvement in compartmentalization of beta-glucuronidase and sequence similarity with portions of the reactive site region of the serpin superfamily.

A significant portion of murine hepatocyte beta-glucuronidase is maintained within the endoplasmic reticulum (ER) by complex formation with the esterase active site of the protein egasyn. The carboxyl-terminal propeptide of the precursor form of glucuronidase appears important in localization of glucuronidase to the ER since a naturally occurring mutation in it is associated with decreased levels of ER glucuronidase. A sequence similarity was noted between the carboxyl-terminal propeptide and portions of the conserved sequences of the reactive site region of members of the serpin (serine proteinase inhibitor) superfamily. Also, previous studies had shown that a synthetic peptide, corresponding to the propeptide region, was a specific and potent inhibitor of the esterase activity of purified egasyn. Taken together, these results suggest that (a) the egasyn-glucuronidase system may use a novel mechanism related to that of serine proteinases and their inhibitors in complex formation and in subsequent localization of glucuronidase within the ER and that (b) a possible function of ER glucuronidase is to modulate the esterase activity of egasyn.

Amino Acid Sequence↗