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Biomedical subjects

J A Gilbert

Publications and source records attributed to J A Gilbert.

At least 73 records · Page 4Linked to original sources
PubMed1988

Desensitization of neurotensin receptor-mediated cyclic GMP formation in neuroblastoma clone N1E-115.

Murine neuroblastoma clone N1E-115 possesses receptors that specifically bind the tridecapeptide neurotensin, mediate the formation of intracellular cyclic GMP, and stimulate inositol phospholipid hydrolysis. These cells also rapidly degrade neurotensin in a sequential fashion. We studied the effect of prolonged exposure of cells to neurotensin on subsequent neurotensin receptor-mediated intracellular cyclic GMP formation under conditions that prevented degradation of this peptide [J. A. Gilbert and E. Richelson, Soc. Neurosci. Abstr. 12, 762 (1986)]. Neurotensin receptor-mediated cyclic GMP formation in neuroblastoma clone N1E-115 was decreased following prolonged exposure of intact cells to nondegraded neurotensin. The time course of this desensitization was very rapid; the maximal effect on cyclic GMP production (reduction to 10-30% of control values) occurred within 5 min of exposure of intact cells to neurotensin. This desensitization was homologous, as cells desensitized by neurotensin demonstrated no decrease in their cyclic GMP response to angiotensin II (1 microM) or bradykinin (10 nM). Neurotensin preincubation with intact N1E-115 cells for increasing lengths of time caused time-dependent shifts to the right of the dose-response curve and reductions in the maximum cyclic GMP response. Desensitization was reversible, but resensitization was a slower process than desensitization: full recovery of cyclic GMP production required incubation of the desensitized cells for at least 10 min at 37 degrees. From binding studies with [3H]neurotensin, we found that both the apparent equilibrium dissociation constant, KD, and the maximum number of receptor sites, Bmax, for this radioligand were decreased significantly (P less than 0.05) for completely desensitized cells from those values for control cells. These data suggest that desensitization of the neurotensin receptor involved an uncoupling of the pathway of events connecting receptor activation to intracellular cyclic GMP formation; complete desensitization involved both the apparent loss of neurotensin receptors on the cellular surface and the increase in affinity of the remaining receptors for the agonist. This decrease in Bmax is more likely to be a result of intracellular sequestration of recyclable NT receptors than of true down-regulation due to the rapid resensitization seen for the NT-mediated biological response.

Animals↗
PubMed1988

Avulsion of the flexor digitorum profundus: anatomic and biomechanical considerations.

Avulsion of the profundus insertion occurs most commonly in the ring finger. The exact reason for this predilection is unknown. Clinical observation of patients with this injury reveals that a common finding is that the ring fingertip is usually more prominent or "longer" than any other fingertip during grip. A laboratory investigation shows that during grip the ring fingertip becomes 5 mm more prominent than any other digit in 90% of subjects and that it absorbs more force than any other finger during pull-away testing. These factors contribute to the susceptibility of the ring finger to the profundus avulsion injury.

Adolescent↗
PubMed1988

Leg power characteristics of female firefighter applicants.

The primary purposes of this study were to characterize the anaerobic power of a large group of adult female subjects and to analyze the relationship of body composition, leg power, and leg strength tests to performance on the Wingate Anaerobic Test (WAT) in these women. A secondary purpose was to observe the relationship of the WAT to a stair-climbing test used to select firefighters. The subjects were the top 150 of the 1,090 women who took a firefighter applicant physical performance test. Predicted dependent variables from the WAT were mean power (MP), peak power (PP), and percent fatigue (%F). Among the nine independent variables entered into multiple regression analysis (age, height, weight, fat-free weight, percent fat, leg press strength, vertical jump, maximal physical work capacity (PWCmax) and stair climb) 45%, 40%, and 16% of the variance in MP, PP, and %F were accounted for. Fat-free weight accounted for the most variation in MP and PP, and PWCmax accounted for the most variation in %F. There was little relationship observed between MP, PP, or %F and the stair-climbing test.

Body Composition↗
PubMed1987

Rapid degradation of neurotensin by intact murine neuroblastoma cells (clone N1E-115).

Murine neuroblastoma clone N1E-115, which possesses receptors for neurotensin mediating the formation of intracellular cyclic GMP and the stimulation of inositol phospholipid hydrolysis, exhibited only partial desensitization to neurotensin. This result led to the observation that neurotensin was very rapidly degraded by intact N1E-115 cells. In experiments measuring the time course of [3H]neurotensin degradation, a minimum of six major tritiated products were found, with the breakdown peptides formed and the degree of proteolysis of [3H]neurotensin being dependent upon the length of incubation and the concentration of cells. Clone N1E-115 degraded [3H]neurotensin in an apparently sequential fashion; the primary initial cleavage of intact neurotensin was at the peptide bond between residues Arg8 and Arg9. Initial degradation peptides from the active carboxyl-terminal portion of neurotensin were more rapidly degraded, after formation, than were the peptides from the inactive amino-terminal half of neurotensin. The final two degradation products found were tyrosine, from the carboxyl-terminal portion of neurotensin, and an as yet unidentified peptide from the amino-terminal half of neurotensin. [3H]Neurotensin(8-13) was more rapidly hydrolyzed under identical conditions than was [3H]neurotensin itself. A combination of the protease inhibitors 1,10-phenanthroline and Z-Pro-Prolinal was able to inhibit almost completely the degradation of neurotensin by clone N1E-115.

Animals↗
PubMed1987

Displaced olecranon fractures in adults. Biomechanical analysis of fixation methods.

Four commonly used methods of internal fixation for displaced olecranon fractures were analyzed in a biomechanical model to determine strength of fixation. A transverse osteotomy in fresh cadaver specimens was internally fixed and was tested to failure by rapid loading. Screw plus wire in combination provided the greatest strength of fixation. Energy to failure averaged 31.0 Nm for cancellous screw, 32.0 Nm for figure-of-eight wire, 35.3 Nm for Arbeitsgemeinschaft fur Osteosynthesefragen (AO) tension band, and 39.4 Nm for screw-plus-wire combination. Comparison of screw and wire in combination to screw alone or to figure-of-eight wire demonstrated a significant difference (p less than 0.05). The difference between screw plus wire and AO tension-band fixation did not achieve statistical significance (0.2 greater than p greater than 0.1).

Biomechanical Phenomena↗
PubMed1987

An evaluation of the bending stiffness of various tibial fixation methods.

The relative stiffness of human tibial fixation by plaster casts, intramedullary rods, external fixators, and dynamic compression plates was compared to the stiffness of the intact tibia. Four-point bending was performed on each specimen, first intact, and then after sequential instrumentation, thus allowing each specimen to serve as its own control. The mean stiffnesses obtained for the bone-device complexes, as a percentage of the intact tibial stiffness, were 113 +/- 9% for the delta frame fixator, 57 +/- 14% for the dynamic compression plate, 28 +/- 2% for the unilateral external fixator (UEF) with stainless steel sidebar, 18 +/- 1% for the UEF with aluminum sidebar, 7 +/- 2% for the flexible intramedullary (IM) rods, and 6 +/- 2% for the cast. Even relatively flexible unilateral external fixators are much stiffer than cast or IM rod fixation, methods that usually lead to satisfactory union by secondary healing. If secondary union with callus formation is desirable, modifications of the external fixator may be necessary to provide more flexible fixation. This study may be one of the first attempts to quantitate the stiffness of tibial fixation in a standard cast and compare it with other devices.

Biomechanical Phenomena↗
PubMed1986

LANT-6, xenopsin and neuromedin N stimulate cyclic GMP at neurotensin receptors.

The naturally occurring analogs of neurotensin-(8-13), xenopsin, [Lys8,Asn9]neurotensin-(8-13) (LANT-6) and neuromedin N stimulated the production of intracellular cyclic GMP in murine neuroblastoma clone N1E-115, an adrenergic neuronal cell type. The order of potency was neurotensin-(8-13) greater than neurotensin greater than xenopsin greater than neuromedin N greater than LANT-6. Furthermore, xenopsin, LANT-6 and neuromedin N each inhibited the specific binding of [3H]neurotensin to intact N1E-115 cells in a dose-related fashion. The order of affinity of the peptides for the neurotensin receptor was neurotensin-(8-13) greater than xenopsin greater than neurotensin greater than neuromedin N greater than LANT-6.

Animals↗
PubMed1986

Neurotensin and its analogs--correlation of specific binding with stimulation of cyclic GMP formation in neuroblastoma clone N1E-115.

The receptors which mediate neurotensin-stimulated intracellular cyclic GMP formation in murine neuroblastoma clone N1E-115 [J. A. Gilbert and E. Richelson, Eur. J. Pharmac. 99, 245 (1984)] were further characterized. The binding of [3H]neurotensin to intact N1E-115 cells at 0 degree displayed specificity, saturability, reversibility, and tissue linearity. A single class of neurotensin receptors was demonstrated with an apparent KD of 9-11 nM and a Bmax of 180-250 fmoles/10(6) cells, determined by the type of serum employed in the cellular culture medium. A number of neurotensin analogs and fragments were compared for their ability to inhibit [3H]neurotensin binding and stimulate intracellular cyclic GMP formation with intact N1E-115 cells. A direct correlation was found to exist between the KD and EC50 for each peptide. The carboxyl-terminal portion of neurotensin proved to be responsible for the binding and biochemical activities of this peptide with clone N1E-115. Neurotensin(8-13) was, in fact, fifty times more potent than native neurotensin in stimulating intracellular cyclic GMP formation and had an 18-fold higher affinity for the neurotensin receptor on this neuronal cell type.

Animals↗
PubMed1986

Biomechanical studies of an anterior pelvic external fixation frame intended for control of vertical shear fractures.

Biomechanical testing of an experimental pelvic external fixation frame incorporating a large tubular horizontal member was carried out on formalin-fixed cadaver pelves with simulated vertical shear injuries. The device was tested with 5 mm standard and 6 mm experimental pins, and was compared to a Pittsburgh triangular (PT) frame constructed of standard Hoffmann components. Tested by vertical loading, the experimental frame with 5 mm standard pins was 1.9 times as stiff as the PT frame, and with the 6 mm experimental pins it was 2.4 times as stiff as the PT frame. Clinical trials are needed to determine efficacy in vivo.

Aged↗
PubMed1985

Influence of delta-opioid receptors on production of labeled methionine5-enkephalin in murine neuroblastoma cells.

Synthesis of methionine5-enkephalin by intact cells of murine neuroblastoma clone N1E-115 has been demonstrated both immunocytochemically and biochemically. In addition, N1E-115 cells possess homogeneous enkephalin (delta) receptors which inhibit prostaglandin E1-induced intracellular cyclic AMP formation. An assay was developed for measuring de novo synthesis of methionine5-enkephalin by pulsing cells in culture with radioactive methionine and isolating this pentapeptide to radiochemical purity by a procedure that included immunoaffinity chromatography specific for oxidized methionine5-enkephalin. This assay indicated that production of radiolabeled-methionine5-enkephalin was increased upon lengthy exposure of intact N1E-115 cells in the late logarithmic phase of growth to a nonproteolyzable analog of methionine5-enkephalin. This increase in synthesis of intracellular methionine5-enkephalin relative to control cells was prevented by prior incubation of the clone with naloxone, indicating that the response was mediated by the delta receptor.

Animals↗
PubMed1984

A system to measure the forces and moments at the knee and hip during level walking.

The forces and moments in the sagittal plane at the knee and hip were calculated using gait data collected during level walking. Accelerations were measured by accelerometers attached to the legs, and the force reactions at the foot were measured by a force plate. The recorded accelerations and the foot forces were used to determine the joint reactions through a Newtonian formulation modeling the leg as articulated, rigid links. Twelve normal subjects were included in this study along with nine lower limb amputees. Obvious differences were observed when comparing amputee data to normal data both at the knee and hip. Gait data obtained by this system can be readily used to form criteria for objective gait analysis and improved prosthesis design.

Acceleration↗
PubMed1984

The effect of steam sterilization on plaster casting material.

Plaster-impregnated gauze was autoclaved as a preventative measure against infection. The mechanical properties and the hardening time of casts made with autoclaved plaster were investigated by measuring flexural yield stress and flexural modulus of elasticity. A cantilever bending test was used to determine the time required to harden. The average yield stress in bending was reduced by an average of 8% and the modulus of elasticity was unchanged by the steam sterilization. The time required for the plaster splint to harden was increased by a factor of 5.6 after steam sterilization. Although the reduction in the yield strength was not prohibitive, the increase in hardening time was unacceptable. The use of gas sterilization is recommended when a sterile cast is necessary because gas sterilization does not increase hardening time.

Casts, Surgical↗
PubMed1982

Function and regulation of methionine5-enkephalin and its receptors in murine neuroblastoma cells.

A homogeneous class of enkephalin receptors found in murine neuroblastoma clone N1E-115 (Chang, K.-J., and Cuatrecasas, P. (1979) J. Biol. Chem. 254, 2610-2618) has been confirmed using a centrifugation assay employing cellular membranes. In intact N1E-115 cells, synthetic methionine5-enkephalin inhibited prostaglandin E1-induced intracellular cyclic AMP formation in a naloxone-sensitive manner. Upon demonstrating intracellular methionine5-enkephalin immunocytochemically (Knodel, E., and Richelson, E. (1980) Brain Res. 197, 565-570), analyses of crude N1E-115 extract were made by radioimmunoassay or opiate receptor binding assay following fractionation by molecular sieve chromatography and high pressure liquid chromatography on a mu-Bondapak C18 column. Extracted methionine5-enkephalin immunoreactive material behaved similarly to synthetic methionie5-enkephalin in these analyses. Growth curve studies of the N1E-115 cells indicated that the quantity of methionine5-enkephalin immunoreactive material synthesized per milligram of cellular protein and the maximum number of enkephalin receptor sites per milligram of membrane protein increased as the cells progressed from logarithmic to stationary phase, with no change in the apparent affinity of the enkephalin receptors for [3H]methionine5-enkephalin. These data suggest that adrenergic clone N1E-115 has functional methionine5-enkephalin membrane receptors, that this clone synthesizes methionine5-enkephalin, and that both the enkephalin receptor number and the content of stored methionine5-enkephalin are regulated with respect to cell division.

Alprostadil↗