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Biomedical subjects

J B Clark

Publications and source records attributed to J B Clark.

At least 217 records · Page 12Linked to original sources
PubMed1981

Rat brain 3-hydroxy-3-methylglutaryl-CoA reductase: subcellular distribution and cold lability.

Data are provided indicating that the rat brain 3-hydroxy-3-methylglutarhyl-CoA reductase is similar to the enzyme from other tissues as far as diurnal rythmicity, cold lability and half-life measurements of 0 degrees C are concerned. The enzyme activity in the brain decreased with age of the animals. Subcellular fractionation studies demonstrate that while 77% of the activity was associated with the microsomal fraction, 19% of the enzyme activity was recovered in the mitochondrial fraction. The possible function of such a mitochondrially located 3-hydroxy-3-methylglutaryl-CoA reductase in rat brain is discussed.

Animals↗
PubMed1981

Energy metabolism in rat brain: inhibition of pyruvate decarboxylation by 3-hydroxybutyrate in neonatal mitochondria.

The effect of 3-hydroxybutyrate on pyruvate decarboxylation by neonatal rat brain mitochondria and synaptosomes was investigated. The rate of [1-14C]pyruvate decarboxylation (1 mM final concentration) by brain synaptosomes derived from 8-day-old rats was inhibited by 10% in the presence of 2 mM-D,L-3-hydroxybutyrate and by more than 20% in the presence of 20 mM D,L-3-hydroxybutyrate. The presence of 2 mM-D,L-3-hydroxybutyrate did not affect the rate of [1-14C]pyruvate decarboxylation (1 mM final concentration) by brain mitochondria; however, at a concentration of 20 mM-D,L-3-hydroxybutyrate, a marked inhibition was seen in preparations from both 8-hydroxybutyrate, a marked inhibition was seen in preparations from both 8-day-old (35% inhibition) and 21-day-old (24% inhibition) but not in those from adult rats. Although the presence of 100 mM-K+ in the incubation medium stimulated the rate of pyruvate decarboxylation by approximately 50% compared with the rate in presence of 1 mM-K+, the presence of 20 mM-D,L-3-hydroxybutyrate still caused a marked inhibition in both media (1 and 100 mM-K+). The presence of 20 mM-D,L-3-hydroxybutyrate during the incubation caused an approximately 20% decrease in the level of the active form of the pyruvate dehydrogenase complex in brain mitochondria from 8-day-old rats. The concentrations of ATP, ADP, NAD+, NADH, acetyl CoA, and CoA were measured in brain mitochondria from 8-day-old rats incubated in the presence of 1 mM-pyruvate alone or 1 mM-pyruvate plus 20 mM-D,L-3-hydroxybutyrate. Neither the APT/ADP nor the NADH/NAD+ ratio showed significant changes. The acetyl CoA/CoA ratio was significantly increased by more than twofold in the presence of 3-hydroxybutyrate. The possible mechanisms and physiological significance of 3-hydroxybutyrate inhibition of pyruvate decarboxylation in neonatal rat brain rat mitochondria are discussed.

3-Hydroxybutyric Acid↗
PubMed1981

Energy-metabolizing enzymes in brain regions of adult and aging rats.

The regional enzyme activities of glucose metabolism in the rat brain were investigated. Hexokinase (EC 2.7.1.1) and pyruvate dehydrogenase (EC 1.2.4.1), key enzymes for glucose metabolism, showed no changes in activity in all the regions studied of the aging brain as compared with the adult brain. However, the activity of D-3-hydroxybutyrate dehydrogenase (EC 1.1.1.30) is low throughout the adult brain and, in contrast with hexokinase and pyruvate dehydrogenase, its activity decreases significantly during aging. Other enzymes that showed significant decreases during aging are aldolase (EC 4.1.2.13), lactate dehydrogenase (EC 1.1.1.27), citrate synthase (EC 4.1.3.7), and NAD+-linked isocitrate dehydrogenase (EC 1.1.1.41). The catabolic enzyme in cholinergic metabolism, acetylcholinesterase (EC 3.1.1.7), selected as an example of a non-energy-metabolising enzyme, also showed significant decreases in all regions of the brain in aging, although its highest activity remained in the striatum. These results are discussed with respect to the energy metabolism in various brain regions and their status with aging.

Acetylcholinesterase↗
PubMed1981

Blood pressure of alloxan diabetic rats at regular and high salt intake.

To identify any relationship between diabetes mellitus and high salt intake in the production of hypertension, we studied the effect of a regular and high salt diet on blood pressure in rats made diabetic with alloxan. The diabetic animals developed marked hyperglycemia, glycosuria, and azotemia out of proportion to changes in glomerular filtration rate. Non-diabetic rats and diabetic rats on a high salt intake in excess of 14 mEq/day developed modest but significant increases in blood pressure, while diabetic rats on a regular diet did not. We conclude that diabetic rats have no greater susceptibility to salt-induced hypertension than rats receiving only salt. Although it is possible that dehydration may have served to attenuate blood pressure increases in our diabetic animals, the diabetic state per se does not appear to result in severe hypertension in the rat regardless of sodium intake.

Animals↗
PubMed1980

The distribution of glutamine synthetase in subcellular fractions of rat brain.

The subcellular localization of glutamine synthetase, an enzyme fundamental to the compartmentation of glutamate hypothesis, was investigated using brain tissue of adult rats. The distribution of this enzyme in relation to the distribution of glucose-6-phosphatase, glutamate dehydrogenase and acetycholine esterase was studied using a fractionation scheme which had been previously extensively characterized in terms of intramitochondrial enzyme complements. Glutamine synthetase was found to be predominantly localized at the nerve terminal and a number of results suggested a possibble association with the synaptic membrane. The observations are discussed in relation to the compartmentation of glutamate metabolism. Acetate and ammonia are precursors of the 'small' pool of glutamate from which most of the synthesis of glutamine occurs. Since one population of synaptic mitochondria has previously been shown to be enriched in glutamate dehydrogenase and acetyl CoA synthetase and in view of the current observtions that synaptosomes are probably in association with a large proportion of brain glutamine synthetase, it is tentatively suggested that the synaptic complex represents at least in part the site of the 'small' glutamate pool.

Animals↗
PubMed1980

Lipogenesis in the brain of suckling rats. Studies on the mechansim of mitochondrial-cytosolic carbon transfer.

1. Studies on the incorporation of [3-(14)C]pyruvate and d-3-hydroxy[3-(14)C]butyrate into the brain lipid fraction by brain homogenates of the suckling (7-day-old) rat have been carried out. 2. Whereas approximately twice as much CO(2) was evolved from pyruvate compared with 3-hydroxybutyrate metabolism, similar amounts of the radioactivity of these two precursors were incorporated into the lipid fraction. Furthermore, in both cases the incorporation into lipid was almost tripled when glucose (10mm) or NADPH (2.5mm) was added to the incubation media. 3. If 5mm-(-)-hydroxycitrate, an ATP-citrate lyase inhibitor, was added to the incubation the incorporation of carbon from pyruvate was inhibited to 39% of the control and from 3-hydroxybutyrate to 73% of the control, whereas CO(2) production from both precursors was not affected. 4. The incorporation from pyruvate or 3-hydroxybutyrate into lipids was not affected by the presence of 10mm-glutamate in the medium (to encourage N-acetylaspartate production). However, incorporation from pyruvate was inhibited by 21% in the presence of 5mm-amino-oxyacetate (a transaminase inhibitor) and by 83% in the presence of both hydroxycitrate (5mm) and amino-oxyacetate. 5. Incorporation from 3-hydroxybutyrate into brain lipids was inhibited by 20% by amino-oxyacetate alone, but by 55% in the presence of both hydroxycitrate and amino-oxyacetate. 6. It is concluded that the mechanism of carbon transfer from pyruvate into lipids across the mitochondrial membrane in the suckling rat brain is mainly via citrate and N-acetylaspartate. 3-Hydroxybutyrate, in addition to using these routes, may also be incorporated via acetoacetate formation and transport to the cytosol.

3-Hydroxybutyric Acid↗
PubMed1980

Studies of the fatty acid composition and membrane microviscosity in Salmonella typhimurium TA98.

When the mutagen tester bacterial strain Salmonella typhimurium TA 98 was grown at different temperatures, we found that the unsaturated fatty acid composition increased at the lower growth temperatures. Membrane microviscosity, as assessed with spin-probe fatty acids using electron spin resonance, decreased as the unsaturated fatty acid content increased. These findings are of importance in understanding our recent observation that the mutagenic response of these bacteria was increased when they were grown at 27 degrees C vs. 37 degrees C, and indicate that membrane properties may play an important role in the sequence of events leading to mutagenesis.

Cell Membrane↗
PubMed1980

Binding and mutagenicity studies with 2-nitrosofluorene on Salmonella typhimurium TA98 grown at different temperatures.

The growth temperature of the histidine auxotroph Salmonella typhimurium TA98 influences the extent of binding of 2-nitrosofluorene (NOF) to this bacterium as well as the mutagenicity of this chemical carcinogen. Gas-liquid chromatography (GLC) of bacteria grown at 37, 27 and 17 degrees C revealed that the unsaturated (hexadecenoic plus octadecenoic) fatty-acid content increased from 15.0% at 37 degrees C to 20.5% at 27 degrees C and to 22.2% at 17 degrees C. It has been shown using both artificial and natural mammalian membranes that NOF adds to carbon-carbon double bonds in unsaturated fatty acids via an "Alder-ene" type reaction to produce a nitroxyl free radical adduct (N-O-LAF). The same adduct was formed when NOF was incubated with Salmonella typhimurium TA98. There was an increase in N-O-LAF formed in bacteria grown at 27 degrees C as compared to those grown at 37 degrees C, but very little formed in bacteria grown at 17 degrees C. Therefore the amount of N-O-LAF formed did not correlate with unsaturated fatty-acid content. 14C-labeled NOF uptake in bacteria grown at different temperatures showed a good correlation with mutagenicity data.

Carcinogens↗
PubMed1980

The development of enzymes of energy metabolism in the brain of a precocial (guinea pig) and non-precocial (rat) species.

Key enzymes of ketone body metabolism (3-hydroxybutyrate dehydrogenase, 3-oxo-acid:CoA transferase, acetoacetyl-CoA thiolase) and glucose metabolism (hexokinase, lactate dehydrogenase, pyruvate dehydrogenase, citrate synthase) have been measured in the brains of foetal, neonatal, and adult guinea pigs and compared to those in the brains of neonatal and adult rats. The activities of the guinea pig brain ketone-body-metabolising enzymes remain relatively low in activity throughout the foetal and neonatal periods, with only slight increases occurring at birth. This contrasts with the rat brain, where three- to fourfold increases in activity occur during the suckling period (0-21 days post partum), followed by a corresponding decrease in the adult. The activities of the hexokinase (mitochondrial and cytosolic), pyruvate dehydrogenase, lactate dehydrogenase, and citrate synthase of guinea pig brain show marked increases in the last 10-15 days before birth, so that at birth the guinea pig possesses activities of these enzymes similar to the adult state. This contrasts with the rat brain where these enzymes develop during the late suckling period (10-15 days after birth). The development of the enzymes of aerobic glycolytic metabolism correlate with the onset of neurological competence in the two species, the guinea pig being a "precocial" species born neurologically competent and the rat being a "non-precocial" species born neurologically immature. The results are discussed with respect to the enzymatic activities required for the energy metabolism of a fully developed, neurologically competent mammalian brain and its relative sensitivity to hypoxia.

Acetyl-CoA C-Acetyltransferase↗
PubMed1980

Comparison of the development of the fatty acid content and composition of the brain of a precocial species (guinea pig) and a non-precocial species (rat).

The fatty acid compositions of the brains of a precocial (guinea pig) and a non-precocial (rat) species have been studied as a function of development. In the rat brain the total fatty acid content expressed as mg g wet wt.-1 increased more than fourfold during the period from 5 days after birth to adulthood. However, the percentage composition of this total fatty acid content when expressed per individual fatty acid remained fairly constant, with the exception of nervonic acid (C24:1) which also increased fourfold on a percentage basis. In the guinea pig brain, however, at birth the total fatty acid content, expressed as mg g wet wt-1, is the same as that of the adult, the concentration doubling during the period from 25 days before birth until birth. Again, if the fatty acid content is analysed and expressed on a percentage basis, the relative concentrations of the individual fatty acids remain fairly constant over the period from 25 days before birth until adulthood, with the exception of nervonic (C24:1) acid which increases about fivefold from 25 days before birth to birth and only marginally (20%) from birth to adulthood. These results are discussed in relationship to the onset of neurological competence in the two species. It is concluded that the increase in fatty acid content (both total and individually) of the brains of these species as a function of the foetal and neonatal development follows a pattern which is similar to the pattern of development of certain key enzymes of energy metabolism and of neurological competence.

Aging↗
PubMed1980

Adenylyl cyclase responsiveness to guanyl nucleotides in the developing rat heart.

Guanyl nucleotides are effective activators of rat heart adenylyl cyclase activity from the earliest age studied, 16 fetal days, through adulthood. Both guanosine triphosphate and guanylyl-imidodiphosphate (GMP-PNP) significantly enhance epinephrine-stimulated adenylyl cyclase activity at all fetal and postnatal ages. The dose-response curves for epinephrine alone, GMP-PNP alone, or for the combination of epinephrine and GMP-PNP are similar for the newborn and adult heart preparations. Our results indicate that the epinephrine-guanyl nucleotide-adenylyl cyclase system is "mature" as a functional unit in the rat heart even prior to birth. The rat heart adenylyl cyclase system shows a dramatic increase in responsiveness to epinephrine and to guanyl nucleotides just before birth, a responsiveness which rapidly falls by 3 days of neonatal life. With increasing age, the absolute guanosine triphosphate or GMP-PNP activated rate rises in parallel with the basal rate of adenylyl cyclase activity in the rat heart. Speculation. The activation of adenylyl cyclalse systems by guanyl nucleotides may be a general feature of fetal as well as of adult tissues. This activation by guanyl nucleotides may magnify tissue hormonal responses at some stages of development.

Adenylyl Cyclases↗
PubMed1980

A comparison of the association of Neisseria gonorrhoeae with human and guinea-pig genital mucosa maintained in organ culture.

Organ cultures of human and guinea-pig genital mucosa were inoculated with Neisseria gonorrhoeae, and the association of the bacteria with the epithelial surface of each tissue was studied by light microscopy and by scanning electron microscopy. Gonococci attached to the mucosa of human fallopian tube, adhering specifically to the surface of non-ciliated epithelial cells. In contrast, gonococci rarely attached to the mucosal surface of guinea-pig uterine horn, vagina or bladder, although organisms were occasionally seen associated with the submucosal tissue in areas where the epithelium had sloughed, and in extracellular mucus secretions. There is no evidence from this study that gonococci adhere to guinea-pig tissue in a manner analogous to that seen with human genital tissue.

Animals↗
PubMed1979

Synthesis of N-acetyl-L-aspartate by rat brain mitochondria and its involvement in mitochondrial/cytosolic carbon transport.

1. The synthesis and efflux of N-acetyl-l-aspartate from brain mitochondria of rats of different ages has been studied. 2. Brain mitochondrial State 3 (+ADP) respiration rate, using 10mm-glutamate and 2.5mm-malate as substrates, increases during the suckling period and reaches approx. 50% of the adult value at 17 days after birth [adult State 3 respiration rate=160+/-7ng-atoms of O/min per mg of mitochondrial protein(mean+/-s.d.; n=3)]. 3. The influence of 5mm-pyruvate or 10mm-dl-3-hydroxybutyrate on aspartate efflux from brain mitochondira from rats of different ages oxidizing glutamate and malate was studied. In all cases the aspartate efflux in State 3 was greater than in State 4, but, whereas the aspartate efflux in State 3 increased as the animals developed, that of State 4 showed only a small increase. However, the rate of aspartate efflux in the presence of pyruvate or 3-hydroxybutyrate as well as glutamate and malate was approx. 60-65% of that in the presence of glutamate and malate alone. 4. An inverse relationship between aspartate efflux and N-acetylaspartate efflux was observed with adult rat brain mitochondria oxidizing 10mm-glutamate and 2.5mm-malate in the presence of various pyruvate concentrations (0-5mm). 5. N-Acetylaspartate efflux by brain mitochondria of rats of different ages was studied in States 3 and 4, utilizing 5mm-pyruvate or 10mm-dl-3-hydroxybutyrate as acetyl-CoA sources. A similar pattern of increase during development was seen in State 3 for N-acetylaspartate efflux as for aspartate efflux (see point 3 above). Also only very small increases in N-acetylaspartate efflux occurred during development in State 4.6. Rat brain mitochondria in the presence of iso-osmotic N-acetylaspartate showed some swelling which was markedly increased in the presence of malate. 7. It is concluded that N-acetylaspartate may be synthesized and exported from both neonatal and adult rat brain mitochondria. It is proposed that the N-acetylaspartate is transported by the dicarboxylic acid translocase and may be an additional mechanism for mitochondrial/cytosolic carbon transport to that of citrate.

Animals↗
PubMed1979

A mitochondrial myopathy with a deficiency of respiratory chain NADH-CoQ reductase activity.

This paper presents data on two sisters with a mitochondrial myopathy characterised by weakness, marked exercise intolerance and a fluctuating lactic acidaemia. Both patients also experienced episodes of increased weakness which could be brought on by unaccustomed activity, going without food or by taking small quantities of alcohol. Metabolic studies during exercise showed a marked and sudden rise in blood lactate and pyruvate levels. Biochemical studies in one case showed that mitochondrial respiratory rates were markedly decreased with all NAD-linked substrates tested but were normal with succinate and with TMPD + ascorbate. The mitochondrial cytochrome components were normal as determined by low temperature spectroscopy and the addition of uncoupler did not enhance state 3 respiratory rates utilising NAD-linked substrates. It was concluded, therefore, that the mitochondrial lesion was located at the level of the NADH-CoQ reductase complex.

Adult↗
PubMed1979

The development of tuberculosis in Afro-Asian immigrants.

Tuberculin testing and a chest x-ray have been carried out on 1492 Asian immigrants. Analysis has shown that the percentage tuberculin positive reactions does not increase with increasing length of stay in this country. Few arrive with active disease but after 3 months residence there is a steady incidence of tuberculosis morbidity. Apparently immigrants in the Harrow area arrive with past tuberculous infection, manifest only by a positive tuberculin test, and subsequently suffer endogenous exacerbation.

Adolescent↗