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G K Smith

Publications and source records attributed to G K Smith.

At least 73 records · Page 4Linked to original sources
PubMed1990

Activity of an NAD-dependent 5,10-methylenetetrahydrofolate dehydrogenase in normal tissue, neoplastic cells, and oncogene-transformed cells.

As an extension of the previously reported observation concerning the existence of NAD-dependent 5,10-methylenetrahydrofolate dehydrogenase in transformed cells a variety of tissues and cell lines have been assayed for this activity. This activity was found in all assayed transformed cells. Results with rat liver derived epithelial (RLE) cells transformed with a series of oncogenes (v-raf, v-raf/v-myc (J2), v-myc (J5), and v-Ha-ras (pRNR16)) indicated that expression of activity correlates with the extent of transformation and was independent of the oncogene used for transformation. Compared to previously reported values for normal tissue, surprisingly high levels of the NAD-dependent 5,10-methylenetetrahydrofolate dehydrogenase were found in the rat adrenal cortex. This activity was not seen in mouse or bovine adrenal. Enzymatic activity was also detected in mouse bone marrow and was strain dependent. The levels of activity in mouse bone marrow were lower than previously reported. The NAD-dependent 5,10-methylenetetrahydrofolate dehydrogenase activity in rat adrenal and RLE cells may represent tools for studying the regulation of expression of this activity.

Animals↗
PubMed1990

Synthesis and biological activity of an acyclic analogue of 5,6,7,8-tetrahydrofolic acid, N-[4-[[3-(2,4-diamino-1,6-dihydro-6-oxo-5- pyrimidinyl)propyl]amino]-benzoyl]-L-glutamic acid.

The synthesis and biological evaluation of N-[4-[[3-(2,4-diamino-1,6-dihydro-6-oxo-5-pyrimidinyl)propyl]amino]- benzoyl]-L-glutamic acid (1) (5-DACTHF, 543U76), an acyclic analogue of 5,6,7,8-tetrahydrofolic acid (THFA), are described. The key intermediate, hemiaminal 8, was prepared in four stages from 3-chloropropionaldehyde diethyl acetal. Reaction of 8 with dimethyl N-(4-aminobenzoyl)-L-glutamate gave the 2,4-bis(acetylamino) derivative 11, which was hydrolyzed with 1 N sodium hydroxide to give 1; the glycine analogue 16 was prepared in a similar manner. The N-methyl analogue 2 and N-formyl analogue 3 were prepared from 11 and 1, respectively. Compounds 1-3 inhibited growth of Detroit 98 and L cells in cell culture, with IC50s ranging from 2 to 0.018 microM. Cell culture toxicity reversal studies and enzyme inhibition tests showed that 1 was cytotoxic but not by the mechanism of the dihydrofolate reductase inhibitor aminopterin. Compound 1 and its polyglutamylated homologues inhibited glycinamide ribonucleotide transformylase (GAR-TFase) and aminoimidazole ribonucleotide transformylase (AICAR-TFase), the folate-dependent enzymes in de novo purine biosynthesis; and 1 was an effective substrate for mammalian folyl-polyglutamate synthetase. The compound inhibited (IC50 = 20 nM) the conversion of [14C]formate to [14C]-formylglycinamide ribonucleotide by MOLT-4 cells in culture. These data suggest that the site of action of 1 is inhibition of purine de novo biosynthesis. Moderate activity was observed against P388 leukemia in vivo.

Acyltransferases↗
PubMed1989

Radiobiological comparison of external beam irradiation and radioimmunotherapy in renal cell carcinoma xenografts.

Growth delay was measured in TK-82 renal cell carcinoma (RCC) xenografts implanted in nude mice receiving single fraction external beam irradiation (SF-XRT), multifraction external beam irradiation (MF-XRT), or radioimmunotherapy (RIT). Thermoluminescent dosimeter(s) (TLD) and autoradiography were used to ascertain the average absorbed dose delivered and the degree of heterogeneous uptake of radiolabeled antibody for the RIT irradiations. For intravenous administered activities of 100, 200, 400, and 600 microCi of I-131 labeled A6H antibody, volume doubling times (VDT) and TLD absorbed dose measurements for each administered activity were 7 days (341 cGy), 38 days (383 cGy), 85 days (886 cGy) and no regrowth (1034 cGy), respectively. For SF-XRT irradiations of 500, 1000, and 1500 cGy, VDT times were 11, 62, and 103 days, respectively. MF-XRT of 4 X 250 cGy over a 2-week period yielded a VDT of 25 days. Marked peripheral activity deposition was noted on most autoradiographs from multiple tumor samples. These data suggest that an equivalent to superior tumor growth delay is obtained for absorbed doses delivered by exponentially decaying low dose rate radioimmunotherapy RIT compared to similar doses of acute dose rate XRT as quantitated by the TLD method.

Animals↗
PubMed1988

Inhibition of chicken liver 5-aminoimidazole-4-carboxamide ribonucleotide transformylase by 5,8-dideaza analogues of folic acid.

A series of fourteen 5,8-dideaza analogues of folic and pteroic acids was evaluated for inhibition of 5-aminoimidazole-4-carboxamide ribonucleotide transformylase (AICAR TFase) from chicken liver. Of the 5,8-dideaza folate derivatives studies, 10-oxa-5,8-dideazafolic acid was the most potent inhibitor. The addition of one L-glutamate moiety to the gamma-carboxyl group caused a 6- to 7-fold reduction in Ki in three instances. Two compounds devoid of an L-glutamate were 4- to 6-fold less inhibitory than their parent counterparts possessing one L-glutamate residue.

Acyltransferases↗
PubMed1988

Spontaneous EEG spikes in the normal hippocampus. II. Relations to synchronous burst discharges.

Spontaneous EEG spikes (SPKs) were recorded from the CA1 region of the dorsal hippocampus in normal rats during awake immobility and slow wave sleep. These SPKs were accompanied by synchronous burst discharges in the pyramidal cell layer. These discharges are called 'population bursts (PBs)' in that they seem to require a population of synchronously bursting neurons. PBs were classified into 2 forms on the basis of their morphologies. One form (mixed burst or MB) consisted of a mixture or superimposition of action potential bursts from a relatively small number of neurons. The other form (ripple) was a series of 3-13 (typically 5-8) high frequency (125-250 Hz) waves, usually waxing and waning. Unit action potentials were superimposed mainly on negative portions of these high frequency waves. The ripple was considered to represent summed activity of highly synchronized complex spike bursts from a relatively large number of pyramidal cells. The similarity in wave structure between these non-pathological ripples and multipeaked, epileptiform (interictal) field potentials recorded from the penicillin-treated hippocampus suggests that they may share some common underlying mechanisms.

Action Potentials↗
PubMed1988

Spontaneous EEG spikes in the normal hippocampus. III. Relations to evoked potentials.

Spontaneous EEG spikes (SPKs) were recorded from the CA1 region of the dorsal hippocampus in normal rats during behavioral states not accompanied by rhythmical slow activity (RSA). SPKs were positive in stratum oriens, negative in stratum radiatum and accompanied by population bursts (PBs) in stratum pyramidale. In order to examine the origin of SPKs and PBs single pulse or brief high frequency electrical stimuli were applied to the Schaffer collateral/commissural pathway. Evoked potentials were recorded and compared with spontaneous SPKs and PBs. The results indicate the following: (1) the laminar amplitude profile of spontaneous SPKs was similar to that of population EPSPs evoked by stimulation of the Schaffer collateral/commissural pathway; (2) the population EPSP most similar to the spontaneous SPK was evoked by a brief (20-60 msec) train of high frequency (125-500 Hz) pulses; (3) the same pattern of stimulation was also found to be most efficient in evoking a series of multiple population spikes resembling a type of spontaneous PB (ripple). These observations suggest that SPKs and PBs in CA1 represent population EPSPs and multiple population spikes, respectively and that these CA1 events are triggered by brief, high frequency burst discharges of CA3 pyramidal cells via the Schaffer collateral and commissural pathway.

Action Potentials↗
PubMed1988

Spontaneous EEG spikes in the normal hippocampus. IV. Effects of medial septum and entorhinal cortex lesions.

Spontaneous EEG spikes (SPKs) were recorded from the CA1 region of the dorsal hippocampus in normal rats during behavioral states not accompanied by rhythmical slow activity (RSA) such as awake immobility and slow wave sleep. The present experiment was designed to examine the effects of large electrolytic lesions of the 2 major hippocampo-petal systems, medial septum (MS) and entorhinal cortex (EC), on spontaneous SPK activity. MS lesions, while completely abolishing RSA, did not eliminate SPKs or change their behavioral correlates. SPKs were still suppressed during behaviors (walking, head movement, etc.) normally associated with RSA. However, SPK frequency was approximately halved after MS lesions. Total bilateral EC lesions did not, in general, change SPKs or RSA unless abnormal hippocampal activities persisted over the first post-lesion week during which most of the recordings were made. Laminar profiles of SPKs in both MS- and EC-lesioned rats showed a normal pattern; small positivity in stratum oriens, large negativity in stratum radiatum and polarity reversal around stratum pyramidale. These results suggest that (1) neither medial septal input nor entorhinal cortical input to the hippocampus is necessary for the generation of SPKs, and (2) SPK suppression still occurs in the absence of these inputs during behaviors normally associated with RSA. The possibility remains, however, that in intact animals these inputs do influence SPK activity in a behavior-dependent manner.

Animals↗
PubMed1988

Spontaneous EEG spikes in the normal hippocampus. V. Effects of ether, urethane, pentobarbital, atropine, diazepam and bicuculline.

Spontaneous EEG spikes (SPKs) were recorded from the CA1 region of the dorsal hippocampus in normal rats during behavioral states not accompanied by rhythmical slow activity (RSA) such as awake immobility and slow wave sleep. In the present study we examined the effects of various systemically administered drugs on hippocampal SPK activity. Three general anesthetics (ether, urethane and pentobarbital) all reduced SPK activity. At anesthetic doses both ether and pentobarbital completely abolished SPKs. This SPK abolition during anesthesia seemed qualitatively different from RSA-related SPK suppression in undrugged animals in that unlike the latter case RSA generation was not the cause of SPK abolition in the former case. Atropine (50-100 mg/kg, i.p.) did not change greatly SPK activity or its behavioral correlation. Diazepam (5-10 mg/kg, i.p.) increased amplitude and decreased frequency of hippocampal fast EEG activity, and reduced SPK activity. These effects may be based on the known action of diazepam to enhance GABA-mediated postsynaptic inhibition. At subepileptic doses (1-6 mg/kg, i.p.) the GABA antagonist bicuculline enhanced dramatically SPK-related activities. Particularly, SPK-concurrent population burst discharges in the pyramidal cell layer were greatly increased in amplitude and complexity after bicuculline. These results suggest that the SPK generation mechanism in the hippocampus is sensitive to the level of GABA-mediated inhibition.

Anesthetics↗
PubMed1988

Spinal decompressive procedures and dorsal compartment injuries: comparative biomechanical study in canine cadavers.

Effects of decompressive procedures or dorsal injuries on flexion-extension, 4-point bending properties of the L-3 and L-4 motion segment in dogs were quantitated and compared. Hemilaminectomy did not significantly (P less than 0.05) affect mechanical properties of the spine. Bilateral facetectomy caused a small increase in the range of motion and a 56% decrease in ultimate bending strength. Excision of the supraspinous and interspinous ligaments decreased the flexural stiffness of the spine, increased the range of motion of the interspace, and decreased ultimate flexion bending strength 62%. Dorsal laminectomy caused a marked decrease in spine stiffness in all phases of flexion and extension, increased the range of motion, and decreased ultimate flexion bending strength 75%. Seemingly, a hemilaminectomy was preferable to the dorsal laminectomy if adequate decompression and exploration were achieved with the hemilaminectomy.

Animals↗
PubMed1987

On the substrate specificity of bovine liver dihydrofolate reductase: new unconjugated dihydropterin substrates.

The substrate specificity of dihydrofolate reductase from cells of different origin has been thought to be quite narrow, and unconjugated dihydropterins such as 6-methyl-dihydropterin are known to be very poor substrates. We have reinvestigated the substrate specificity of several dihydropterins and, in addition, have observed that in a new series of unconjugated dihydropterins of the general structure 6-CH2O(CH2)nCH3 several compounds are excellent substrates for the bovine liver enzyme, but none of them bind as well as dihydrofolate. The substrate activity (apparent Vmax) of these compounds increases from 17 to 110% that of the natural substrate, dihydrofolate, as n is increased from 0 to 3. In contrast, these unconjugated dihydropterins are very poor substrates for the Escherichia coli enzyme.

Animals↗
PubMed1987

The effects of maternal isolation and light and feeding cycles on the growth of rat pups.

Rat pups were implanted with intragastric catheters and reared in isolation from their dams and siblings from 3 to 18 days postnatally. They were kept in 12:12 LD or DL, constant light, or constant darkness and were fed with one of three feeding schedules: equal amounts of food delivered during the light and dark periods, 65.3% of the food delivered during the light period, or 65.3% of the food delivered during the dark period. At 18 days postnatally the body, spleen, and kidney weights of all isolated pups did not differ from those of their mother-reared littermates. The isolated pups had smaller cerebellums and forebrains and heavier livers than mother-reared pups. Heavier body and spleen weights and smaller livers were observed in pups with cyclic feeding. Heavier body and forebrain weights were associated with a predominantly diurnal feeding schedule--the schedule which most closely approximated the natural nursing rhythm. Isolated pups opened their eyes sooner than mother-reared littermates. These results suggest that interactions between feeding and light cycles may influence growth and development.

Animals↗
PubMed1987

On the role of sepiapterin reductase in the biosynthesis of tetrahydrobiopterin.

Rat erythrocyte sepiapterin reductase can catalyze the NADPH-dependent reduction of tetrahydropterin substrates with relative velocities of sepiapterin greater than lactoyltetrahydropterin greater than or equal to pyruvoyltetrahydropterin greater than 1'-hydroxy-2'-oxopropyltetrahydropterin; L-erythrotetrahydrobiopterin is the product of the reduction of all three tetrahydropterins. The 1' position of the 1',2'-diketone, pyruvoyltetrahydropterin, is reduced first; the product of this first reduction is 1'-hydroxy-2'-oxopropyltetrahydropterin. Both steps are inhibited by N-acetylserotonin. An antibody to sepiapterin reductase purified from rat erythrocytes was produced in rabbits, and the purified antibody is highly specific for sepiapterin reductase. This antibody is an inhibitor of both sepiapterin reductase activity and tetrahydrobiopterin biosynthesis in crude extracts of rat adrenal and brain. The antibody inhibits the production of both the biosynthetic intermediate, 1'-hydroxy-2'-oxopropyltetrahydropterin, and tetrahydrobiopterin. The results indicate that sepiapterin reductase is on the biosynthetic pathway to tetrahydrobiopterin, and catalyzes the complete reduction of pyruvoyltetrahydropterin to tetrahydrobiopterin. In contrast, homogenates of whole rat adrenal also produce large quantities of lactoyltetrahydropterin which suggests that in some tissues this compound may also be an intermediate in tetrahydrobiopterin biosynthesis. The synthesis of lactoyltetrahydropterin is not inhibited by the antibody to sepiapterin reductase and therefore does not appear to be catalyzed by sepiapterin reductase. However, sepiapterin reductase is responsible for the conversion of lactoyltetrahydropterin to tetrahydrobiopterin. The source of sepiapterin in biosynthetic reactions was found to be oxidative decomposition of lactoyltetrahydropterin.

Alcohol Oxidoreductases↗
PubMed1987

Spontaneous EEG spikes in the normal hippocampus. I. Behavioral correlates, laminar profiles and bilateral synchrony.

Spontaneous EEG and unit activities were recorded from the CA1 region of the dorsal hippocampus by means of a movable microelectrode in normal behaving rats. Large amplitude (less than 4 mV) negative EEG spikes (SPKs) of 40-100 msec duration with frequencies in the range of 0.2-5/sec were consistently recorded from the middle apical dendritic layer (stratum radiatum) during awake immobility, grooming and slow-wave sleep. SPKs were replaced by rhythmical slow activity (RSA) during walking and paradoxical sleep. Laminar analysis indicated that SPKs were positive in stratum oriens, negative in stratum radiatum and polarity reversal just below stratum pyramidale. Peak positivity (about 1 mV on average) and peak negativity (2 mV) occurred some 80 micron above and 200 micron below the reversal point, respectively. The SPKs were invariably accompanied by synchronous burst discharges in stratum pyramidale. Bilateral recordings demonstrated the SPKs occurred synchronously in large areas of the CA1 field of the two hippocampi. These results suggest that the SPK represents a massive synaptic excitation of middle apical dendrites triggering synchronous burst discharges in a population of pyramidal cell bodies. A possibility was discussed that these non-pathological SPKs and interictal spikes share some common underlying mechanisms.

Action Potentials↗
PubMed1987

Effects of feeding and light cycles on activity rhythms of maternally isolated rat pups.

Motor activity of infant rat pups was measured continuously between days 3 and 18 of postnatal age. Mother-reared rats on a 12:12 LD cycle exhibited significant rhythmic activity in the circadian range as early as day 5 of postnatal age. Some of the pups reared in isolation from maternal and sibling contact and kept on 12:12 LD cycles, feeding cycles, or combinations of feeding, temperature, and LD cycles also showed rhythmic activity but it was less persistent and of a lower amplitude than the rhythms of the mother-reared group. In the isolated rat pups nocturnal partitioning of activity was strengthened in the presence of both a light-dark cycle and a feeding cycle but only when the feeding resembled more natural nursing rhythms. In animals kept on constant light and a feeding cycle, activity occurred slightly more often during the 12-hr interval of decreased food intake. The addition of a temperature cycle--cooler nocturnal temperature--decreased the proportions of nocturnal motor activity. These results indicate that feeding and light-dark cycles may contribute to the synchronization of activity rhythms during the early postnatal period.

Activity Cycles↗
PubMed1987

Synthetic analogues of tetrahydrobiopterin with cofactor activity for aromatic amino acid hydroxylases.

Tetrahydrobiopterin (THB) analogues with 6-alkoxymethyl substituents, 3a-j, where the substituents were straight- and branched-chain alkyl ranging from methyl to octyl, have been synthesized by the Taylor method from pyrazine ortho amino nitriles by guanidine cyclization, hydrolysis in aqueous NaOH, and catalytic hydrogenation over Pt in trifluoroacetic acid (TFA). The best of these compounds, 3b, is an excellent cofactor for phenylalanine hydroxylase, tyrosine hydroxylase (V = 154% of THB), and tryptophan hydroxylase, does not destablize the binding of substrate (Kmtyr = 23 microM), and is recycled by dihydropteridine reductase (V = 419% of THB). The compounds are being evaluated as cofactor replacements in biopterin-deficiency diseases.

Adrenal Medulla↗
PubMed1986

A rapid and sensitive assay for tyrosine-3-monooxygenase based upon the release of 3H2O and adsorption of [3H]-tyrosine by charcoal.

A rapid, simple and sensitive assay has been developed for tyrosine-3-monooxygenase, the enzyme catalyzing the rate-limiting step in catecholamine biosynthesis. The assay is based upon the release of 3H2O from 3H-[3,5]-L-tyrosine with adsorption of the isotopic substrate (and its metabolites) by an aqueous slurry of activated charcoal. This method routinely yields low blank values and is simpler than the procedure requiring the use of cation exchange columns to separate the isotopic substrate from the 3H2O formed during the hydroxylation reaction.

Adsorption↗
PubMed1986

Treatment of severely comminuted diaphyseal fractures in the dog, using standard bone plates and autogenous cancellous bone graft to span fracture gaps: 11 cases (1979-1983).

Severely comminuted diaphyseal fractures in 11 dogs were repaired with standard bone plates that spanned a fracture gap filled with autogenous cancellous bone graft. Five dogs had closed injuries, 4 dogs had open fractures, and 2 dogs had infected nonunion fractures for which previous attempts at internal pin fixation had failed. A second autogenous cancellous bone graft was performed in 3 of the dogs during the healing period. The technique was successful in all dogs. The technique was considered a versatile and relatively simple alternative, compared with meticulous small fragment reconstruction and cortical bone allografts.

Animals↗