Search PubMed⌕ Search

Biomedical subjects

K Shelton

Publications and source records attributed to K Shelton.

At least 19 recordsLinked to original sources
PubMed1999

Isolation and characterization of the mouse cytosolic phosphoenolpyruvate carboxykinase (GTP) gene: evidence for tissue-specific hypersensitive sites.

A 72 kilobase pair DNA fragment that contains the mouse phosphoenolpyruvate carboxykinase (PEPCK) gene locus, pck1, was isolated from a genomic bacterial artificial chromosome library. The region from approximately -5.5 to +6.6 kilobase pairs relative to the pck1 transcription start site was sequenced and exhibits a high degree of homology to the rat and human genes. Additionally, the chromatin structure of the PEPCK gene in mouse liver resembles that seen in rat. Backcross panel analysis of a microsatellite sequence confirms that the gene is located on chromosome 2. Hypersensitive site analysis was performed on nuclei isolated from the adipocyte cell line 3T3-F442A in the preadipose and adipose states. Several hypersensitive sites are present in the undifferentiated 3T3-F442A cells, before PEPCK mRNA is detected. The same sites are present after differentiation, however, the sensitivity of mHS 3 increases relative to the others. We conclude that the chromatin is open in 3T3-F442A cells and that factors are able to bind in the undifferentiated state but that something else is required for transcription.

3T3 Cells↗
PubMed1998

Glaucomatocyclitic crisis in a child.

PURPOSE: To report a case of glaucomatocyclitic crisis (Posner-Schlossman syndrome) in a child. METHOD: Case report. A 13-year-old boy presented with decreased vision, photophobia, halos, and pain in the right eye. RESULT: Findings in this child were consistent with a diagnosis of Posner-Schlossman syndrome. CONCLUSION: Glaucomatocyclitic crisis can occur in a child and must be included in the differential diagnosis of uveitis and glaucoma in pediatric patients.

Adolescent↗
PubMed1998

Histologic effect of diode laser sclerostomy in human cadaver eyes.

BACKGROUND AND OBJECTIVES: To study tissue effects and thresholds of efficacy in producing a full-thickness scleral fistula in human eyes obtained from cadavers. The effect of laser sclerostomies created with indocyanine green (ICG) was also evaluated. MATERIALS AND METHODS: Ab externo laser sclerostomies were produced in 12 fresh human eyes obtained from cadavers using a 200-micron diameter fiber optic connected to a diode laser system. Power settings were 500, 750, 1000, 1250, 1500, and 2000 mW with a constant duration of 100 and 200 ms. The same diode laser settings were repeated in the tissues injected with ICG. RESULTS: The laser sclerostomies were associated with heat coagulation damage adjacent to the burn margins, with disruption of stromal collagen. Tissue damage was greater at higher power and longer duration. Scleral injection of ICG prior to laser sclerostomy did not enhance laser penetration. CONCLUSION: The diode laser can create a sclerostomy in human sclera with an optimum level of 1500 mW and 100 ms. ICG did not significantly enhance the ease of penetration or reduce the association thermal damage to the sclera.

Coloring Agents↗
PubMed1996

Epidermal growth factor-binding protein in Mycobacterium avium and Mycobacterium tuberculosis: a possible role in the mechanism of infection.

Epidermal growth factor (EGF) is a potent mitogen for a variety of eukaryotic cells. EGF is found in a number of tissues and is prevalent in necrotic tissues and granulomata. The biological effect of EGF on mammalian cells is initiated by the binding to a specific receptor. Both Mycobacterium avium and Mycobacterium tuberculosis cause lung infections and localized or disseminated disease in both patients without AIDS and those with AIDS. Histopathologic studies show necrosis in the lung, liver, and splenic tissues of patients with disseminated mycobacterial infection. In the course of experiments to examine the effect of growth factors on macrophages, it was observed that M. avium and M. tuberculosis but not Mycobacterium smegmatis cultured in the presence of 5, 50, or 500 ng of EGF per ml grew significantly faster than mycobacteria cultured in the absence of EGF. 125I-EGF was found to bind to M. avium and M. tuberculosis, and the binding was competitively inhibited by unlabeled EGF. A receptor for EGF was identified on mycobacteria. Incubation of mycobacteria with EGF prior to infection of macrophage monolayers resulted in faster bacterial growth within macrophages compared with that of mycobacteria not incubated with EGF. EGF-binding protein was cloned and expressed in Escherichia coli, and subsequently the protein was purified and the N-terminal amino acids were sequenced. These results suggest that EGF is a growth factor for pathogenic mycobacteria in granulomatous tissues and within macrophages and might enhance growth rates of both intracellular and extracellular mycobacteria in the site of infection.

Amino Acid Sequence↗
PubMed1995

Comparison of the ability of Mycobacterium avium, M. smegmatis and M. tuberculosis to invade and replicate within HEp-2 epithelial cells.

OBJECTIVE: Previous studies have demonstrated that mycobacteria can interact with epithelial cells, a property which can be important for establishing infection. In this study we investigated comparatively the ability of Mycobacterium avium, M. tuberculosis and M. smegmatis to invade and multiply within HEp-2 epithelial cells. DESIGN: The ability to invade and to multiply intracellularly in HEp-2 cells was examined using a virulent strain of M. avium, a virulent (H37Rv) and an attenuated (H37Ra) strain of M. tuberculosis and a strain of M. smegmatis. The locus responsible for M. avium invasion was also cloned in Escherichia coli and M. smegmatis. RESULTS: It was observed that M. avium invaded HEp-2 cells with greater efficiency than M. tuberculosis and M. smegmatis, while the H37Rv strain of M. tuberculosis was more efficient in invading HEp-2 than H37Ra and M. smegmatis. Both M. avium and M. tuberculosis were capable of multiplying within HEp-2 cells, while M. smegmatis was not. E. coli K12 and M. smegmatis were transformed with M. avium DNA. The invasive locus of M. avium provided E. coli K12 and M. smegmatis strains S5M101-1 and S5M101-2 with the ability to invade HEp-2 epithelial cells. Transformed M. smegmatis strains were able to grow intracellularly. CONCLUSION: 'Virulent' strains of M. avium and M. tuberculosis were shown to invade and to multiply within HEp-2 epithelial cells. This property was transferred to E. coli K12 and M. smegmatis by transformation with the invasive locus of M. avium. The ability of certain strains of mycobacteria to invade epithelial cells (bronchial, alveolar, intestinal) may represent an important phenotypic characteristic and could be directly related to pathogenicity.

Animals↗
PubMed1994

Characterization of a cis-acting regulatory element which silences expression of the class II-A beta gene in epithelium.

Class II major histocompatibility complex (MHC) genes encode for alpha/beta chain pairs that are constitutively expressed principally on mature B cells and dendritic cells in mice. These gene products are easily induced on macrophages with cytokines, and may also aberrantly appear on the surface of epithelium during immune injury. The appearance of class II determinants in parenchymal tissue potentially renders these somatic cells capable of antigen presentation to circulating CD4+ T lymphocytes, and their absence may be protective for normal tissues expressing self-antigens. The low surface class II expression observed on parenchymal cells generally correlates with low levels of mRNA, suggesting that transcription rate is a major element in class II regulation. To understand the transcriptional mechanism maintaining low basal surface expression of class II in somatic cells, we transiently transfected mini-gene reporter constructs to study the regulation of the murine A beta promoter in a cultured renal epithelial cell line. We describe here a negative cis-acting regulatory region located between -552 and -489 bp upstream of the A beta cap site that silences the transcriptional activity of the A beta promoter in epithelial cells in an orientation-dependent manner, and is also able to silence a heterologous promoter. This region is not active in class II-expressing B cells (BAL-17) in culture, but is functional in two other murine class II-negative cell lines, fibroblasts and thymoma T cells. Using competition electrophoretic mobility shift assays, we have localized the core protein binding site within this region to an 8-10-bp response element, designated A beta NRE, at -543 to -534 bp. A nuclear extract from BAL-17 cells does not bind to this element. Mutation of this site abrogates the transcriptional silencing activity of the region. We conclude that the transcription of class II-A beta in parenchymal cells, and some lymphocytes, can be actively repressed by an upstream silencing element.

Animals↗
PubMed1993

Successful management of paraprotein-associated peripheral polyneuropathies by immunoadsorption of plasma with staphylococcal protein A.

Two patients with paraprotein-associated peripheral polyneuropathy were treated successfully using immunoadsorption of patient's plasma with staphylococcal protein A. Both had previously been treated with immunosuppressive agents or plasma exchange, and were rapidly relapsing at the time of their protein A immunoadsorption therapy. One patient was treated "on-line" with a blood cell separator, and one was treated "off-line." Both responded well to therapy with minimal toxicity. Serum levels of circulating immune complexes were elevated in one patient and remained so during and after therapy. Immunoadsorption with protein A should be investigated as a therapeutic option for patients with paraprotein-associated peripheral polyneuropathy. The therapy is relatively easy to administer, particularly "off-line," and was well tolerated by our patients. More experience, including formal clinical trials, will be required to properly define the indications for, and mechanism of response to, this therapy.

Aged↗
PubMed1991

Supersensitivity to the reinforcing effects of cocaine following 6-hydroxydopamine lesions to the medial prefrontal cortex in rats.

The effects of neurotoxic lesions to the medial prefrontal cortex on both the acquisition and maintenance of intravenous cocaine self-administration were examined. In one experiment, acquisition of intravenous cocaine self-administration (0.25, 0.5 or 1.0 mg/kg/infusion) was measured in separate groups of rats 14 days following either a sham or 6-hydroxydopamine lesion to the medial prefrontal cortex. For sham rats, the 1.0 and 0.5 mg/kg dose supported reliable self-administration as indicated by discriminative responding. These rats reliably chose a lever that resulted in the delivery of these doses of cocaine over an inactive lever. Reinforced response rates were reduced when 0.25 mg/kg was the available dose and there was a loss of discriminative responding for some of the rats suggesting that it was close to threshold for self-administration. For rats that sustained a 70% depletion of dopamine in the medial prefrontal cortex, the dose-response curve was an inverse function across the entire dose range tested. In contrast to the data from the control rats, lesioned rats had a high rate of reinforced responses and demonstrated good discrimination for all doses including 0.25 mg/kg/infusion, suggesting a supersensitive response to the initial reward effect of cocaine. Another group of rats was first screened for reliable cocaine self-administration (0.5 mg/kg/infusion) and then subjected to either the prefrontal cortical 6-hydroxydopamine or sham lesion. Dose-response curves for cocaine self-administration were compared 14 days following the infusions. The lesioned rats responded reliably for low doses of cocaine that were unable to maintain responding in sham rats. These data support the hypothesis that the medial prefrontal cortex plays an important role in cocaine self-administration.

Animals↗
PubMed1991

Analysis of the cDNA sequence encoding MHC-A beta in tubular epithelium from mouse kidney.

Class II gene products of the major histocompatibility complex (MHC) are not expressed usually in abundance on normal epithelium. The cell surface visibility of such proteins for the immune system is thought to be limited protectively in order to minimize inflammation consequent to the recognition of self-antigens in parenchymal structures by T lymphocytes. In the current experiments we investigated whether the previously recognized sparseness of A beta on the surface of tubular epithelial cells might be accounted for by a protein coding difference deduced from the primary structure of its transcript compared with sequence from lymphoid cells that normally express A beta in generous amounts. We demonstrate, however, using clones obtained from a cDNA library prepared from tubular epithelium harvested from H-2s (A beta/alpha+; E beta/alpha-) mice susceptible to autoimmune interstitial nephritis, that the nucleotide sequence encoding the class II A beta chain in cells from both compartments is essentially identical. Our findings suggest that there is no primary structural aberrancy in the coding region of parenchymal A beta that would contribute to its low expression. The protective tolerance afforded by reduced numbers of class II molecules in normal tissues is, therefore, more likely the result of repressive regulatory processes.

Animals↗
PubMed1991

Establishing pregnancies after follicular stimulation for IVF with clomiphene citrate and human menopausal gonadotrophin only.

Data are presented on establishing pregnancies by IVF during 1987 using only clomiphene citrate and human menopausal gonadotrophin for follicular stimulation. Of the 562 patients undergoing follicular stimulation, 80% reached oocyte recovery and 70% had at least one conceptus replaced. Patients having one or more (up to a maximum of four) conceptuses replaced demonstrated a significant increase in the establishment of pregnancies from one to two (14-29%: P = 0.035) and from two to three conceptuses (29-42%: P = 0.037). There was a significant decline in pregnancies when four conceptuses were replaced compared with three (P = 0.004). The data were also analysed according to the cause of infertility, specifically tubal, endometriosis, unexplained infertility and male factors only. After the replacement of conceptuses, the incidence of implantation and abortion was not significantly different. The incidence of pregnancy declined significantly after 35 years (26%) compared with women under 31 years (43%; P = 0.043). Of 129 women having three conceptuses replaced, in those greater than 35 years (63 patients) 23 (37%) became pregnant whereas in those less than 31 years (65 patients), 34 (52%; P = 0.05) became pregnant. Twenty-two per cent of stimulated cycles resulted in an endogenous LH surge and the incidence of patients having three conceptuses replaced in this group was lower than those in the HCG group (P = 0.007). Fertilization per oocyte was also significantly reduced (P less than 0.001) in patients with an LH surge. In total, 2824 oocytes were recovered and 57% fertilized with 54% of patients having three conceptuses replaced.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

The use of the GnRH analogue buserelin for IVF--does it improve fertility?

OBJECTIVE: To determine the effect of a short course of the GnRH analogue buserelin and human menopausal gonadotrophin (hMG), for ovarian stimulation in our IVF programme, on reproductive endocrinology and pregnancy rates compared with conventional clomiphene citrate and hMG treatment. DESIGN: Prospective randomized allocation to one of two ovulation stimulation regimens. SETTING: Fertility clinic. SUBJECTS: 373 infertile couples with various factors associated with their subfertility. All the women were less than 46 years of age and had normal menstrual cycles. INTERVENTION: The first group (n = 151) was given clomiphene citrate (CC) from days 2-6 of the menstrual cycle and hMG from day 5 onwards (CC/hMG). The second group (n = 222) was given buserelin from days 1-3 and hMG from day 2 (buserelin/hMG). MAIN OUTCOME MEASURES: Concentration of plasma luteinizing hormone (LH), oestradiol (E2) and progesterone, number of ovulatory follicles induced and the occurrence of pregnancy. RESULTS: Plasma LH, E2 and progesterone concentrations were reduced in the late follicular phase after buserelin/hMG compared with CC/hMG. Buserelin/hMG promoted the development of more follicles than CC/hMG. The overall pregnancy rate after buserelin/hMG was not significantly different from that following CC/hMG treatment. CONCLUSION: The chance of pregnancy is not improved by the short-term use of buserelin with hMG, provided adequate follicular phase management is maintained.

Adult↗
PubMed1990

Ready and able.

Explore the source record for details and available documents.

Contract Services↗
PubMed1990

Preexposure sensitizes rats to the rewarding effects of cocaine.

During a preexposure period rats were injected once daily with either cocaine HCI (10 mg/kg, IP) or the saline vehicle for 12 consecutive days. Rats that were chronically exposed to cocaine during the pretreatment phase were more responsive to the motor activating effects of a subsequent injection of cocaine than were rats chronically treated with saline. In self-administration testing, saline-pretreated groups did not exhibit a significant preference for a lever producing a cocaine infusion relative to an inactive lever, suggesting that the doses tested (0.225 and 0.45 mg/kg/infusion) were subthreshold for cocaine reward. In contrast, subjects preexposed to cocaine had a higher rate of reinforced responses and exhibited a preference for a lever that resulted in a cocaine infusion. It was unlikely that the higher response rate was due to an elevation in nonspecific activity since inactive lever responding remained low and relatively invariant over the 9 days of testing. Thus the enhanced responding in the cocaine-preexposed rats suggests that the reinforcing effectiveness of the drug had increased. These data indicate that sensitivity to cocaine's behavioral effects can be enhanced and that predisposing factors to cocaine abuse can be manipulated.

Animals↗
PubMed1990

Luteal inadequacy during the early luteal phase of subfertile cows.

A study was made of early luteal function (up to Day 6) in cyclic and pregnant heifers and also in older, subfertile cows. There were no differences in vivo or in vitro between cyclic and pregnant heifers, indicating no luteotrophic effect of the embryo at this stage, but the increase in postovulatory peripheral progesterone concentrations was delayed (P less than 0.01) and occurred more slowly (P less than 0.001) in the subfertile cows than in the heifers. The corpora lutea of the subfertile cows were heavier (P less than 0.001) than those of the heifers on Day 6. Basal progesterone production by dispersed luteal cells was similar between heifers and subfertile cows, but there was a difference (P less than 0.001) in the pattern of response to exogenous LH and PGE-2. Cells from subfertile cows were less sensitive to the stimulatory effects of PGE-2 and although LH increased (P less than 0.001) progesterone production by all cells, this stimulation by a low dose of LH was inhibited by PGE-2 in luteal cells from subfertile cows. This effect did not occur in the luteal cells from heifers. These results indicate the possibility that luteal inadequacy, due to a diminished response to circulating luteotrophic hormones, may contribute to embryo mortality in subfertile cows.

Animals↗
PubMed1990

Prostaglandin E-2 as a potential luteotrophic agent during early pregnancy in cattle.

Heifers slaughtered on Day 18/19 of pregnancy had significantly higher (P less than 0.001) concentrations of PGE-2 (measured as its methyl oxime) in uterine flushings than did animals slaughtered on Days 6 or 12 of pregnancy, or on Days 6 or 12 of the oestrous cycle. In addition, concentrations were higher in the uterine horn ipsilateral to the corpus lueum on Days 12 (P less than 0.05) and 18/19 (P less than 0.01) than in the contralateral horn. Incubation of dispersed luteal cells for 3 h with LH (0.1 or 100 ng/ml) and/or PGE-2 (0.01-1000 ng/ml) in vitro showed no differences in basal progesterone production or in the responses to exogenous hormones between pregnant and non-pregnant cattle. However, low doses of PGE-2 (0.01-10 ng/ml) inhibited the stimulation of progesterone secretion by the lower dose of LH. These findings indicate that although PGE-2 can stimulate progesterone synthesis by luteal cells it may also have inhibitory effects, and therefore its role in pregnancy requires further definition.

Animals↗
PubMed1989

Self-administration of phenylpropanolamine (PPA) by rats previously trained to self-administer amphetamine.

Central nervous system stimulation, similar to that observed for amphetamine, has been attributed to phenylpropanolamine (PPA). However, formal tests, using evaluation of locomotion or of self-administration, fail to reveal that PPA is a stimulant. Self-administration studies have trained rats to self-administer cocaine and then have attempted to switch rats to PPA with no success of transfer. The present study further examined the reinforcing properties of PPA (0.08, 0.16, and 0.32 mg/infusion, IV) in rats that were initially trained to self-administer d-amphetamine (0.005-0.08 mg/infusion) in a two-lever paradigm. Self-administration of amphetamine was a function of dose with 0.01 mg/infusion producing reliably high responding on the active lever. The proportion of active/inactive lever presses remained constant (0.60-0.80) across the amphetamine dose range. PPA was dose-dependently self-administered during the first hour of each session with rats responding at approximately 70% on the active lever. In contrast, responding on the active lever dropped off to approximately 48% when saline was substituted for amphetamine. These data document that rats with prior exposure to amphetamine will self-administer PPA during the initial portion of a three-hour test.

Amphetamine↗
PubMed1980

Ovum retention in the human.

Two cases of ovum retention occurring in postovulatory follicles are described. The ova were recovered at laparoscopy by aspiration of decompressed ovulatory follicles, one during a natural cycle and the other following a programmed clomiphene/human chorionic gonadotropin cycle. Each patient had a normal luteal phase with an increased progesterone level indicative of ovulation. The implications of these findings and their relevance to human fertility studies are discussed.

Adult↗