Search PubMed⌕ Search

Biomedical subjects

G A Thompson

Publications and source records attributed to G A Thompson.

At least 127 records · Page 7Linked to original sources
PubMed1986

The influence of diazepam on the pharmacokinetics of intravenous and epidural bupivacaine in the rhesus monkey.

Pretreatment of patients with diazepam has been reported to reduce the plasma half-life of epidurally administered bupivacaine. The concentrations of bupivacaine used to estimate its plasma half-life may be influenced by input into the vascular system (rate and extent of absorption from the epidural space) and disposition (distribution and elimination). We conducted a study in Rhesus monkeys in which the input function was known and the influence of intravenous diazepam on the disposition of intravenous bupivacaine could be delineated. Results indicated no differences in the primary pharmacokinetic parameters (i.e., total clearance and volume of distribution) for the disposition of bupivacaine. To determine whether the apparent disparity between these results and a previous study might be due to a diazepam-induced alteration in the input function, the influence of intravenous diazepam or saline on the mean absorption time of epidurally administered bupivacaine was also studied in monkeys. Epidural bupivacaine was completely absorbed whether the animals received intravenous saline or intravenous diazepam. No significant differences in pharmacokinetic parameters were found between animals pretreated with intravenous saline or intravenous diazepam and receiving an epidural injection of bupivacaine. The mean residence time of bupivacaine in the body (P less than 0.01) and plasma elimination half-life (P less than 0.005) were significantly longer after epidural administration than after intravenous administration. Intravenous diazepam does not alter the pharmacokinetics of intravenously or epidurally administered bupivacaine.

Absorption↗
PubMed1985

Isolation and quantitative analysis of phosphatidylglycerol and glycolipid molecular species using reversed-phase high-performance liquid chromatography with flame ionization detection.

Conditions are described for the quantitative analysis of phosphatidylglycerol and plant glycolipid molecular species by reversed-phase high-performance liquid chromatography employing a commercially available flame ionization detector. Direct detection on a mass basis overcomes the problem of poor detectability found with most natural lipids. Effective mobile phases composed primarily of volatile solvents are described. Splitting of the column eluate stream allows a portion of each individual molecular species to be recovered for other types of analysis.

Chromatography, Gas↗
PubMed1985

The product-selective blot: a technique for measuring enzyme activities in large numbers of samples and in native electrophoresis gels.

A method termed "product-selective" blotting has been developed for screening large numbers of samples for enzyme activity. The technique is particularly well suited to detection of enzymes in native electrophoresis gels. The principle of the method was demonstrated by blotting samples from glutaminase (EC 3.5.1.2) or glutamate synthase (EC 1.4.7.1) reactions into an agarose gel embedded with ion-exchange resin under conditions favoring binding of product (glutamate) over substrates and other substances in the reaction mixture. After washes to remove these unbound substances, the product was measured using either fluorometric staining or radiometric techniques. Glutaminase activity in native electrophoresis gels was visualized by a related procedure in which substrates and products from reactions run in the electrophoresis gel were blotted directly into a resin-containing "image gel." Considering the selective-binding materials available for use in the image gel, along with the possible detection systems, this method has potentially broad application.

Chromatography, Ion Exchange↗
PubMed1985

Low-temperature-induced changes in intracellular fatty acid fluxes in Dunaliella salina.

Two-minute exposures to exogenous [14C]palmitic, [14C]oleic, or [14C]lauric acid differentially labeled the lipids of Dunaliella salina microsomes and chloroplasts. Changes in fatty acid desaturation and intracellular movement during a subsequent 16-h incubation in nonradioactive medium indicated a slow transfer of lipids into the chloroplast from other organelles. Since Dunaliella lacks the massive traffic of microsomally produced glycerolipids into chloroplast galactolipids that dominates chloroplast-microsome lipid relations in most plant cells, it affords a sensitive system for studying more subtle intracellular lipid fluxes. Lowering the culture temperature from 30 to 12 degrees C was more inhibitory toward glycerolipid biosynthesis in chloroplasts than in microsomes. The ability of Dunaliella chloroplasts to utilize microsomal lipids may be essential for their systematic acclimation to low temperature.

Chloroplasts↗
PubMed1985

Effects of low-temperature stress on the metabolism of phosphatidylglycerol molecular species in Dunaliella salina.

A detailed analysis was made of individual phosphatidylglycerol (PG) molecular species isolated from microsomes and chloroplasts at various times after labeling Dunaliella salina cells with [14C]palmitic, [14C]oleic, or [14C]lauric acid. The patterns of [14C]fatty acid incorporation were in agreement with PG being formed by the "eucaryotic" type pathway in microsomes and the "procaryotic" type pathway in chloroplasts. In Dunaliella, which lacks a quantitatively significant flux of eucaryotic-type lipids from microsomes into chloroplast glycolipids, indications were found for a more subtle movement of microsomally synthesized PG into the chloroplasts. This transfer was more evident in cells stressed by exposure to 12 degrees C than it was at 30 degrees C, and may afford a mechanism for recruiting key microsomal PG molecular species toward low-temperature acclimation in chloroplasts.

Chloroplasts↗
PubMed1985

Further studies of dopamine metabolism and function in Tetrahymena.

The large amounts of dopamine accumulated by cells of Tetrahymena pyriformis strain NT-1 and secreted into their growth medium were found to depend primarily upon an extracellular, non-enzymatic conversion of tyrosine to L-dihydroxyphenylalanine (L-DOPA); L-DOPA was then rapidly taken into the cells and transformed into dopamine enzymatically. Efforts to find physiologically significant dopamine binding sites on the cell surface or dopamine-sensitive adenylate cyclase activity were unsuccessful, suggesting that the catecholamine does not function in Tetrahymena as it does in higher animals.

Adenylyl Cyclases↗
PubMed1984

The mechanism of membrane response to chilling. Effect of temperature on phospholipid deacylation and reacylation reactions in the cell surface membrane.

The ciliary membrane of Tetrahymena pyriformis is physically and metabolically remote from the main centers of lipid metabolism. Nevertheless, it possesses an independent capacity to modify its phospholipid molecular species composition rapidly under stress. The role of ciliary phospholipid deacylating and reacylating enzymes in this phenomenon has been evaluated. Isolated cilia showed substantial phospholipase A (combined A1 and A2), acyl-CoA synthetase and acyltransferase activities. Activities of all the three enzymes of cilia from 39 degrees C-grown cells were greatly reduced when the cilia were incubated at 15 degrees C. In contrast, the phospholipase A and acyltransferase activities in cilia from 15 degrees C-grown cells were surprisingly high at 15 degrees C and twice as high at 37 degrees C as were the equivalent activities in preparations from 39 degrees C-grown cells. While the in vivo substrate specificity of phospholipase A could not be meaningfully assessed, the acyltransferases exhibited a temperature-dependent substrate specificity in vivo. Growth temperature also affected the positional distribution of fatty acids incorporated into ciliary phospholipids in vivo. The ability of acyltransferases to utilize added [14C] acyl-CoA could be markedly stimulated, and their lipid class specificity could be significantly altered in vitro by supplementing the incubation mixture with exogenous lysophospholipid acceptors. These findings suggest that the rate-limiting factor in acyl chain turnover is not the activity of acyltransferases per se but rather the availability of suitable substrates and acceptors. Therefore, we postulate that temperature alters the rate and specificity of ciliary membrane phospholipid retailoring primarily by controlling the in situ phospholipase A activity.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1984

On the formation of alpha-hydroxy fatty acids. Evidence for a direct hydroxylation of nonhydroxy fatty acid-containing sphingolipids.

When Tetrahymena pyriformis, strain NT-1, was warmed from a growth temperature of 15 degrees C to 39 degrees C, there was a rapid conversion of its sphingolipids from the nonhydroxy fatty acid-containing ceramide aminoethylphosphonate (NCAEP) predominant at low temperature to the alpha-hydroxy fatty acid-containing analog (HCAEP). The fatty acid composition of the freshly formed HCAEP strongly resembled that of the original NCAEP pool. An extensive utilization of NCAEP long chain bases for HCAEP formation was shown by prelabeling the NCAEP bases with [14C]serine. The specific radioactivities of both fatty acids and long chain bases of the two sphingolipid classes of cells prelabeled with [3H]palmitic acid at 15 degrees C and then warmed to 39 degrees C were compatible with a direct hydroxylation of the intact ceramide aminoethylphosphonate or free ceramide formed from it. Exogenously added alpha-hydroxypalmitic acid was not incorporated into the sphingolipids intact, but there was an active alpha-oxidation of alpha-hydroxy fatty acids, yielding nonhydroxy fatty acids one carbon atom shorter in length. In vitro experiments failed to demonstrate a direct hydroxylation of NCAEP, and nonhydroxy fatty acid-containing free ceramides were hydroxylated only sparingly. This inefficient hydroxylation is attributed to the rapid enzymatic hydrolysis of these substrates in vitro and to a limited availability of the added ceramides to the hydroxylating enzymes. The weight of the evidence from this study strongly favors the alpha-hydroxylation of fatty acids only when they are bound as elements of sphingolipids.

Animals↗
PubMed1984

Basal and squamous cell carcinoma of the eyelids and their treatment by radiotherapy.

We report 1,166 tumors of the eyelids that were treated by single or fractionated exposures to doses of 20-60 Gy. The five year tumor control rate was 95% for basal cell and 93.3% for squamous cell carcinoma. Irradiation was equally successful in primary cases and in those recurrent following surgery. Recurrence following irradiation was managed by surgery or further irradiation. The cosmetic and functional results were generally excellent and readily accepted by most patients. The overall complication rate was 9.6% with fewer than one-half rated as serious; these problems mainly occurred with large tumors that had destroyed normal tissues. In only 14 (1.2%) patients was death related to the tumor. Approximately one-half of the patients received a dose of 35 Gy in five daily fractions, one-quarter, 20 to 22.5 Gy in a single exposure and the others with larger tumors 42.5-60 Gy in 10 to 30 exposures in two to six weeks. Radiotherapy is a safe and cost effective treatment for eyelid tumors.

Adult↗
PubMed1984

Bupivacaine protein binding in the term parturient: effects of lactic acidosis.

The effects of lactic acidosis on bupivacaine serum protein binding was studied in a group of term parturients and a group of nonpregnant female control subjects. Groups were matched in age and health. Distribution characteristics of bupivacaine in pregnancy were determined. Bupivacaine protein binding was best characterized by the model for two classes of binding sites in all studies. The parturients exhibited a lower capacity for the high-affinity, low-capacity (alpha 1-acid glycoprotein) site and higher affinity for the low-affinity, high-capacity (albumin) site. Lactic acidosis decreased the affinity constant for the high-affinity, low-capacity site in the control group but did not change binding characteristics in the parturients. Free concentration of bupivacaine (Cu) was elevated at low total bupivacaine concentrations (Ct) (less than 10 micrograms/ml). No differences in Cu were detected at concentrations in the cardiotoxic range (greater than 20 micrograms/ml). The Cu values predicted by the estimated binding parameters from in vitro experiments were compared with actual Cu measured in nine parturients at delivery; they correlated significantly (r = 0.94). Distribution changes for bupivacaine in the parturients were consistent with known physiologic changes in body composition associated with pregnancy. Alterations that occur in serum protein binding during pregnancy should not result in increased risk of central nervous system or cardiovascular system toxicity since these alterations do not increase free tissue concentration.

Absorption↗
PubMed1984

The influence of lactic acid on the serum protein binding of bupivacaine: species differences.

Various animal models have been used for studies of bupivacaine cardiovascular toxicity. These studies are difficult to relate to the clinical situation, since the disposition of bupivacaine in the various species is unknown. The serum protein binding of bupivacaine, therefore, was determined in human, sheep, monkey, dog, and rat at physiologic pH using ultrafiltration. Since a mixed acidosis results during a systemic toxicity reaction to bupivacaine, the influences of an acidic pH, resulting from the addition of lactic acid, also was examined. All sera exhibited two classes of binding sites, a high-affinity, low-capacity class (class 1) and a low-affinity, high-capacity class (class 2). When compared to human serum at physiologic pH, a significantly higher (P less than 0.05) affinity constant for the class 1 sites was observed for all species studied, with the exception of the rat. All species studied exhibited a significantly lower (P less than 0.05) capacity for the class 1 sites. The binding parameters of the class 2 sites displayed no significant difference. An acid pH resulted in a decrease in bupivacaine protein binding over the entire concentration range studied for all species, with the exception of the monkey. Monkey serum exhibited no change in bupivacaine binding with a decrease in pH. Since protein binding explains only a portion of the total disposition of bupivacaine, further delineation of each animal model under both acidotic and physiologic conditions needs to be accomplished before the animal studies currently under investigation can be extrapolated to the clinical situation.

Acidosis↗
PubMed1984

Serum bupivacaine concentrations in term parturients following continuous epidural analgesia for labor and delivery.

This study was undertaken to measure the blood concentrations of bupivacaine associated with a single loading dose followed by continuous epidural infusion for the management of the pain of labor and delivery with special reference to the potential for accumulation and toxicity. Four-milliliter venous blood samples were obtained every 15 min following the loading dose until delivery. If inadequate analgesia was observed just prior to delivery, an additional dose of bupivacaine was administered. Bupivacaine concentrations were measured using a double extraction technique followed by gas chromatographic analysis using a nitrogen-specific detector. Clearance, volume of distribution, and rate of absorption were estimated from the blood concentration time data and were 43.39 +/- 11.46 L/h, 67.56 +/- 17.66 L, and 8.97 +/- 3.69 h-1, respectively. Peak serum bupivacaine concentrations were 0.68 +/- 0.14 microgram/ml and occurred 0.58 +/- 0.25 h following administration of the loading dose. The duration of bupivacaine infusion was 3.42 +/- 0.80 h. Serum bupivacaine concentrations at delivery or just prior to administration of a supplemental delivery dose were significantly lower than the peak concentration in all patients (p less than 0.001). Fetal-to-maternal serum concentration ratios were found to be 0.44 +/- 0.16 for the six patients requiring a supplemental delivery dose and 0.44 +/- 0.13 for the six patients receiving bupivacaine only by infusion. The data reported here illustrate that epidural analgesia for labor and delivery achieved using a single 50-mg loading dose followed by a continuous infusion of 12.5 mg/h of bupivacaine will not result in maternal or fetal accumulation or toxicity.

Adult↗
PubMed1984

Microsomal Phospholipid Molecular Species Alterations during Low Temperature Acclimation in Dunaliella.

A detailed analysis of the low temperature-induced alterations of Dunaliella salina (UTEX 1644) microsomal membrane lipids was carried out. Microsomal membranes were isolated from cells grown at 30 degrees C, from cells shifted to 12 degrees C for 12 hours, and from cells acclimated to 12 degrees C. Fatty acid analyses of the major lipid classes demonstrated significant changes in the fatty acid composition of phosphatidylcholinemine (PE) and phosphatidylglycerol (PG) but not phosphatidylcholine (PC) during the initial 12 hours at low temperature. These changes did not entail enhanced desaturation of linoleic acid. Subsequent to 12 hours, the proportions of linolenic acid increased in all phospholipids.Molecular species analyses of the phospholipids demonstrated that the most immediate changes following a shift to low temperature were limited to several molecular species of PE and PG. The changes observed in PE included a decrease in C(30) species and concomitant increases in C(34) and C(36) species. Compositional changes associated with PG entailed the emergence of a new molecular species (18:1/18:1) not found at 30 degrees C. The retailoring of molecular species resulted in an increase in the number of species having two unsaturated acyl chains and did not reflect a simple enhancement of desaturase activity as suggested by the fatty acid analysis. We conclude that the initial alterations in response to low temperature stress involve discrete changes in certain molecular species. These and further alterations of molecular species following acclimation to low temperature would appear to augment increases in acyl chain desaturation as a means of modifying membrane properties in response to low temperature stress.

Journal Article↗
PubMed1984

Chloroplast Phospholipid Molecular Species Alterations during Low Temperature Acclimation in Dunaliella.

The alterations in chloroplast phospholipid acyl chain composition and phospholipid molecular species composition of Dunaliella salina (UTEX 1644) were monitored during acclimation to low temperature. Chlorophyll fluorescence yield, an indicator of chloroplast membrane stability, was used as a physical means of following the acclimation process.Minor alterations in phospholipid acyl chain composition were evident within 36 hours of shifting the cells from 30 to 12 degrees C. Between 36 and 60 hours, pronounced changes in the acyl chain composition of phosphatidylglycerol (PG) were observed. Changes in the acyl chain composition of phosphatidylcholine (PC) did not occur until sometime after 60 hours.Alterations in the phospholipid molecular species during acclimation were also examined. The pattern of change observed in PC molecular species, namely a decrease in species having one saturated chain (16:0) paired with a C(18) acyl chain and a concomitant increase in species having two unsaturated C(18) acyl chains, suggests that molecular species changes augment fatty acid compositional changes as a mean of adapting to low temperature. The molecular species of PG were found to change abruptly between 36 and 60 hours following a shift to low temperature. During this time, a dramatic alteration in the threshold temperature of thermal denaturation of the photosynthetic apparatus, as measured by chlorophyll fluorescence, also occurred. Lipid compositional changes other than those associated with PG were negligible during this time. This strongly suggests that a correlation exists between the molecular species composition of PG and the thermal stability of the photosynthetic membrane.

Journal Article↗
PubMed1984

Threonine Synthase of Lemna paucicostata Hegelm. 6746.

Threonine synthase (TS) was purified approximately 40-fold from Lemna paucicostata, and some of its properties determined by use of a sensitive and specific assay. During the course of its purification, TS was separated from cystathionine gamma-synthase, establishing the separate identity of these enzymes. Compared to cystathionine gamma-synthase, TS is relatively insensitive to irreversible inhibition by propargylglycine (both in vitro and in vivo) and to gabaculine, vinylglycine, or cysteine in vitro. TS is highly specific for O-phospho-l-homoserine (OPH) and water (hydroxyl ion). Nucleophilic attack by hydroxyl ion is restricted to carbon-3 of OPH and proceeds sterospecifically to form threonine rather than allo-threonine. The K(m) for OPH, determined at saturating S-adenosylmethionine (AdoMet), is 2.2 to 6.9 micromolar, two orders of magnitude less than values reported for TS from other plant tissues. AdoMet markedly stimulates the enzyme in a reversible and cooperative manner, consistent with its proposed role in regulation of methionine biosynthesis. Cysteine (1 millimolar) caused a slight (26%) reversible inhibition of the enzyme. Activities of TS isolated from Lemna were inversely related to the methionine nutrition of the plants. Down-regulation of TS by methionine may help to limit the overproduction of threonine that could result from allosteric stimulation of the enzyme by AdoMet.No evidence was obtained for feedback inhibition, repression, or covalent modification of TS by threonine and/or isoleucine.

Journal Article↗
PubMed1984

Temperature-induced changes in the hydroxy and non-hydroxy fatty acid-containing sphingolipids abundant in the surface membrane of Tetrahymena pyriformis NT-1.

Sphingolipids make up 30 to 40 mole % of the phospholipids found in the surface membrane of Tetrahymena pyriformis NT-1. We have identified the two major classes as non-hydroxy fatty acid-containing ceramide-2-aminoethylphosphonate (NCAEP) and alpha-hydroxy fatty acid-containing ceramide-2-aminoethylphosphonate (HCAEP). Both classes were well represented in cells grown at 39 degrees C. At this temperature their principal long chain bases were n-hexadeca-4-sphingenine and n-nonadeca-4-sphingenine. The major fatty acid of NCAEP from 39 degrees C-grown cells was palmitic acid and that of HCAEP was alpha-hydroxypalmitic acid. Cells grown at 15 degrees C contained NCAEP, but only traces of HCAEP. By analyzing the incorporation of [1-14C]palmitic acid into cells growing isothermally or shifted from 15 degrees C to 39 degrees C, we obtained evidence favoring a direct conversion of NCAEP to HCAEP. This conversion was blocked in cells grown at 15 degrees C, causing an accumulation of NCAEP. Tetrahymena is a useful model system for studying the poorly understood alpha-hydroxylation process that is of critical importance in myelination of animal nervous tissues.

Animals↗