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Biomedical subjects

R M Collins

Publications and source records attributed to R M Collins.

At least 19 recordsLinked to original sources
PubMed1997

Effect of alpha-ketoisocaproate and leucine on the in vivo oxidation of glutamate and glutamine in the rat brain.

Leucine and alpha-ketoisocaproate (alpha-KIC) were perfused at increasing concentrations into rat brain hippocampus by microdialysis to mimic the conditions of maple syrup urine disease. The effects of elevated leucine or alpha-KIC on the oxidation of L-[U-14C]glutamate and L-[U-14C]glutamine in the brain were determined in the non-anesthetized rat. 14CO2 generated by the metabolic oxidation of [14C]glutamate and [14C]glutamine in brain was measured following its diffusion into the eluant during the microdialysis. Leucine and alpha-KIC exhibited differential effects on 14CO2 generation from radioactive glutamate on glutamine. Infusion of 0.5 mM alpha-KIC increased [14C]glutamate oxidation approximately 2-fold; higher concentrations of alpha-KIC did not further stimulate [14C]glutamate oxidation. The enhanced oxidation of [14C]glutamate may be attributed to the function of alpha-KIC as a nitrogen acceptor from [14C]glutamate yielding [14C]alpha-ketoglutarate, an intermediate of the tricarboxylic acid cycle. [14C]glutamine oxidation was not stimulated as much as [14C]glutamate oxidation and only increased at 10 mM alpha-KIC reflecting the extra metabolic step required for its oxidative metabolism. In contrast, leucine had no effect on the oxidation of either [14C]glutamate or [14C]glutamine. In maple syrup urine disease elevated alpha-KIC may play a significant role in altered energy metabolism in brain while leucine may contribute to clinical manifestations of this disease in other ways.

Animals↗
PubMed1997

Myocardial anaerobic metabolism occurs at a critical coronary venous PO2 in pigs.

We tested the hypothesis that the onset of myocardial anaerobic metabolism is fundamentally different from the whole body and other organs, where the onset of anaerobic metabolism occurs at a critical oxygen extraction ratio--not at a critical venous PO2. We measured oxygen saturation and PO2 of arterial and coronary venous blood at the onset of global myocardial anaerobic metabolism during progressive hypoxic hypoxia (n = 7) compared with carbon monoxide hypoxia (n = 7), which left-shifted the oxygen-hemoglobin dissociation curve. The onset of global myocardial anaerobic metabolism was defined by decreased myocardial lactate consumption and left ventricular contractility. Coronary venous PO2 was no different during hypoxic hypoxia and carbon monoxide hypoxia at equivalent arterial oxygen saturations, particularly at the onset of myocardial anaerobic metabolism (PO2 17.0 +/- 1.7 torr versus 15.9 +/- 2.2 torr, p = NS). However, the myocardial oxygen extraction ratio was significantly greater during hypoxic hypoxia than during carbon monoxide hypoxia at the onset of myocardial anaerobic metabolism (0.88 +/- 0.02 versus 0.65 +/- 0.04, p < 0.01). Thus, in contrast to the whole body where the onset of anaerobic metabolism occurs at a critical oxygen extraction ratio, the onset of myocardial anaerobic metabolism occurs at a critical coronary venous PO2.

Anaerobiosis↗
PubMed1997

A novel mutation adjacent to the switch III domain of G(S alpha) in a patient with pseudohypoparathyroidism.

A novel G(S alpha) mutation encoding the substitution of arginine for serine 250 (G[S alpha] S250R) was identified in a patient with pseudohypoparathyroidism type Ia. Both G(S) activity and G(S alpha) expression were decreased by about 50% in erythrocyte membranes from the affected patient. The cDNA of this G(S alpha) mutant, as well as one in which the S250 residue is deleted (G[S alpha]-deltaS250), was generated, and the biochemical properties of the products of in vitro transcription/translation were examined. Both mutants had a sedimentation coefficient similar to that of wild type G(S alpha) (approximately 3.7S) when kept at 0 C after synthesis. However when maintained for 1-2 h at 30-37 C, both mutants aggregated to a material sedimenting at approximately 6.3S or greater (G[S alpha]-S250R to a greater extent than G(S alpha]-deltaS250), while wild type G(S alpha) sedimented at approximately 3.7S, suggesting that the mutants were thermolabile. Incubation in the presence of high doses of guanine nucleotide partially prevented heat denaturation of G(S alpha) deltaS250 but had no protective effect on G(S alpha-S250R. Sucrose density gradient centrifugation at 0 C in the presence and absence of beta gamma-dimers demonstrated that, in contrast to wild type G(S alpha) neither mutant could interact with beta gamma. Trypsin protection assays revealed no protection of G(S alpha)-S250R by GTPgammaS or AIF4- at any temperature. GTPgammaS conferred modest protection of G(S alpha)-deltaS250 (approximately 50% of wild-type G[S alpha]) at 30 C but none at 37 C, while AIF4- conferred slight protection at 20 C but none at 30 C or above. Consistent with this result, G(S alpha)-deltaS250 was able to stimulate adenylyl cyclase at 30 C when reconstituted with cyc- membranes in the presence of GTPgammaS but not in the presence of AIF4-. G(S alpha)-S250R showed no ability to stimulate adenylyl cyclase in the presence of either agent. Stable transfection of mutant and wild-type G(S alpha) into cyc- S49 lymphoma cells revealed that the majority of wild type G(S alpha) localized to membranes, while little or no membrane localization occurred for either mutant. Modeling of G(S alpha) based upon the crystal structure of G(t alpha) or G(i alpha) suggests that Ser250 interacts with several residues within and around the conserved NKXD motif, which directly interacts with the guanine ring of bound GDP or GTP. It is therefore possible that substitution or deletion of this residue may alter guanine nucleotide binding, which could lead to thermolability and impaired function.

Animals↗
PubMed1995

Long-term prospective study of Helicobacter pylori in nonulcer dyspepsia.

Helicobacter pylori is present in up to 87% of patients with nonulcer dyspepsia. This study assessed the effect of eradicating Helicobacter pylori infection on the symptoms of nonulcer dyspepsia at four weeks and one year after treatment. Dyspepsia was assessed on the frequency and severity of six symptoms [epigastric pain (night and day), nausea and vomiting, upper abdominal discomfort, and regurgitation] where each symptom was scored from 0 to 4. Helicobacter pylori status was assessed before treatment and four weeks after treatment with histology and microbiology, and at one year with a carbon-13 urea breath test. Eighty-three patients (23 males, 60 females; mean age 56.3 years; mean symptom duration 3.6 months) with nonulcer dyspepsia and Helicobacter pylori infection entered the study. Seventy-five were available at one year follow-up. Four weeks after treatment, the mean symptom score improved in those with eradication (6.95-2.3, P = 0.01, N = 41) or persistent infection (6.69-3.0, P = 0.015, N = 42). At one year, those with persistent Helicobacter pylori infection (N = 38, score 5.24) had a higher score than those remaining clear of infection (N = 24, score 1.4, P < 0.0001) and those with reinfection (N = 13, score 2.2, P < 0.0001). In addition, persistent Helicobacter pylori infection was associated with more additional treatments than those with eradication (34/38 versus 4/37, P < 0.001). These results suggest that Helicobacter pylori plays an important role in the symptoms of nonulcer dyspepsia.

Adult↗
PubMed1994

Valproate increases glutaminase and decreases glutamine synthetase activities in primary cultures of rat brain astrocytes.

It has been proposed that hyperammonemia may be associated with valproate therapy. As astrocytes are the primary site of ammonia detoxification in brain, the effects of valproate on glutamate and glutamine metabolism in astrocytes were studied. It is well established that, because of compartmentation of glutamine synthetase, astrocytes are the site of synthesis of glutamine from glutamate and ammonia. The reverse reaction is catalyzed by the ubiquitous enzyme glutaminase, which is present in both neurons and astrocytes. In astrocytes exposed to 1.2 mM valproate, glutaminase activity increased 80% by day 2 and remained elevated at day 4; glutamine synthetase activity was decreased 30%. Direct addition of valproate to assay tubes with enzyme extracts from untreated astrocytes had significant effects only at concentrations of 10 and 20 mM. When astrocytes were exposed for 4 days to 0.3, 0.6, or 1.2 mM valproate and subsequently incubated with L-[U-14C]glutamate, label incorporation into [14C]glutamine was decreased by 11, 25, and 48%, respectively, and is consistent with a reduction in glutamine synthetase activity. Label incorporation from L-[U-14C]glutamate into [14C]aspartate also decreased with increasing concentrations of valproate. Following a 4-day exposure to 0.6 mM valproate, the glutamine levels increased 40% and the glutamate levels 100%. These effects were not directly proportional to valproate concentration, because exposure to 1.2 mM valproate resulted in a 15% decrease in glutamine levels and a 25% increase in glutamate levels compared with control cultures. Intracellular aspartate was inversely proportional to all concentrations of extracellular valproate, decreasing 60% with exposure to 1.2 mM valproate.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1992

Alternate day supplementation of corn stalk diets with soybean meal or corn gluten meal fed to ruminants.

Four experiments were conducted to determine the effect of adding corn gluten mean (CGM) or soybean meal (SBM) at 24- or 48-h intervals to diets based on corn stalks. In each experiment corn stalks was the primary diet ingredient fed to wethers or steers. Monensin was also fed to determine whether its effects on ruminal fermentation would improve the efficiency of N utilization under these conditions. Evaluation criteria included ruminal fermentation characteristics, DM intake and utilization, N balance in sheep, and steer feedlot performance. Ruminal ammonia nitrogen (NH3 N) concentrations measured over time were higher (P < .05) when diets contained SBM. Diet did not influence (P > .10) total VFA concentrations in ruminal fluid. Differences in diurnal shifts in ruminal NH3 N and total VFA due to protein source resulted in diet x hour interactions (P < .05). Dry matter intake response to protein source and frequency of supplement feeding was variable. Dry matter digestibility and nitrogen digestibility were not affected (P > .10) by protein source or feeding interval. The 48-h interval feeding of CGM was favorable compared with 24-h interval feeding (P < .05). The opposite response occurred with SBM, resulting in a diet x feeding interval interaction (P < .05). Nitrogen retention was greater (P < .05) when CGM was fed and with alternate day feeding. Diets that contained CGM supported higher (P < .05) ADG and gain/feed than diets that contained SBM when fed to steer calves. Alternate day feeding of supplements that contained monensin was detrimental to steer performance under the conditions of these experiments. Corn gluten meal is an effective substitute for SBM when alternate day protein supplementation is practiced.

Ammonia↗
PubMed1990

Mutations of the Gs alpha-subunit gene in Albright hereditary osteodystrophy detected by denaturing gradient gel electrophoresis.

Affected members of most kindreds with Albright hereditary osteodystrophy have a partial deficiency of functional Gs, the guanine nucleotide-binding protein that stimulates adenylyl cyclase. By use of the polymerase chain reaction to amplify genomic fragments with the attachment of a high-melting G + C-rich region (GC clamp) and analysis of these fragments by denaturing gradient gel electrophoresis, heterozygous mutations in the Gs alpha-subunit gene were found in two kindreds. These included a G----C substitution at the donor splice junction of intron 10 and a coding frameshift created by a single base deletion within exon 10. The findings illustrate the heterogeneity of genetic defects in Albright hereditary osteodystrophy and the usefulness of the polymerase chain reaction-denaturing gradient gel electrophoresis method to search rapidly for mutations in a large candidate gene.

Amino Acid Sequence↗
PubMed1989

Membrane attachment of recombinant G-protein alpha-subunits in excess of beta gamma subunits in a eukaryotic expression system.

Recombinant cDNAs encoding the alpha-subunits of Gi1, Gi2, Gi3, Go and Gs were transfected into COS cells with the pCD-PS mammalian expression vector. Expression of each G alpha was verified using subtype-specific peptide antisera on immunoblots. Quantitative immunoblotting of alpha and beta subunits indicated: i) that there was no change in expression of endogenous beta subunits, and ii) overexpression of alpha subunits could achieve a ratio of alpha:beta greater than 25:1. Despite the excess of alpha over beta, the G alpha subunits were found predominantly in the membrane fraction. The results demonstrate that G alpha subunits can attach to the membrane independently of beta gamma subunits.

Animals↗
PubMed1988

Growth studies in infants and children with Down's syndrome and elevated levels of thyrotropin.

A retrospective survey of 147 patients with Down's syndrome (age range, 4 months to 27 years) showed that 60% had a thyrotropin (TSH) level higher than 5.7 mU/L in the presence of high or normal thyroxine levels. The remaining 40% of the group had low to normal TSH values. High TSH levels were predominant in patients under 4 years of age (94 children), ie, during the phase of active growth, and showed a declining trend with increasing age. All 94 infants had delayed growth of all parameters including head circumference, height, and weight, as compared with normal infants, and growth was particularly retarded in patients with TSH levels greater than 5.7 mU/L. Thyroid dysfunction, expressed as a high TSH concentration, is associated with growth retardation in children with Down's syndrome who are younger than 4 years.

Adolescent↗
PubMed1988

Cloned muscarinic receptor subtypes expressed in A9 L cells differ in their coupling to electrical responses.

The electrophysiological responses to cholinergic stimulation of four cloned muscarinic receptor subtypes (m1-m4) were studied in A9 L cells transfected with the expression plasmids of each of the different subtypes, using the tight-seal whole-cell recording technique. Cells transfected with m1 and m3 muscarinic receptor subtypes were hyperpolarized by acetylcholine (ACh), whereas m2- and m4-transfected cells did not respond to ACh concentrations of up to 1 mM. Stimulation of both m1 and m3 muscarinic receptor subtypes evoked outward currents in cells voltage-clamped at -50 mV, associated with an increase in membrane conductance. These outward currents were blocked by atropine but not by tubocurarine. The ACh-induced currents of m1- and m3-transfected cells primarily involved potassium ions, although chloride ions also contributed to a minor extent. The potassium and chloride conductances were blocked by barium or cobalt and by buffering the intracellular calcium to low levels with 5 mM 1,2-bis(2-aminophenoxy)ethane-N,N,N'N'-tetraacetic acid, showing a dependence of these conductances on calcium. Thus, m1- and m3-transfected cells respond to ACh in a manner that is qualitatively similar, evoking calcium-dependent potassium and chloride conductances, whereas m2- and m4-transfected cells are not coupled to electrically detectable responses in A9 L cells.

Acetylcholine↗
PubMed1987

Localization of mRNAs encoding the alpha-subunits of signal-transducing G-proteins within rat brain and among peripheral tissues.

The sequence of the mRNAs which encode the alpha-subunits of the signal-transducing G-proteins Gs, Go and two forms of Gi (termed Gi1 and Gi2) have recently been reported. Based on rat sequences we prepared oligodeoxynucleotide probes for measurement of these mRNAs in rat brain and peripheral tissues. The relative abundance of these mRNA species in brain was Gs greater than Go approximately Gi2 greater than Gi1. The Gs and Gi2 mRNAs had somewhat lower levels in heart, kidney and liver than in brain, and Go and Gi1 mRNAs were not detected in the peripheral tissues. Using in situ hybridization we localized each of these mRNAs within slices of the rat brain. The patterns of distribution of Gs and Gi2 mRNA were very similar, but very different from that of Go and Gi1 mRNA. These data illustrate that receptor-effector coupling G-proteins are regionally specialized in their expression. This regional specialization may reflect a selective coupling of individual G-proteins with the various neurotransmitter receptors and effector pathways.

Animals↗
PubMed1984

Neurochemical changes in murine trisomy 16: delay in cholinergic and catecholaminergic systems.

Two strains of Mus musculus musculus, C57BL/6J and CD-1, and Mus musculus poschiavinus, the tobacco mouse, were used to study the effects of increased gene dosage of mouse chromosome 16 (MMU 16). A developmental delay has been found in the brains of murine trisomy 16 (Ts16) fetuses. Both the brain weight (in all three strains) and DNA content (in CD-1) were reduced, while protein content was unchanged in Ts16 compared to normal littermates. The daily increments of weight and protein (except in M. m. poschiavinus) were significantly greater in Ts16. The activities of choline acetyltransferase and acetylcholinesterase and muscarinic receptor binding were reduced. Their daily increments were also reduced to less than 56% that of littermates in Ts16 brains. The rate limiting enzymes of catecholaminergic neurons, tyrosine hydroxylase and dopamine beta-hydroxylase, and the concentration of catecholamines in the brains of Ts16 animals were lower. The activities of three other catecholaminergic enzymes, DOPA decarboxylase, catechol O-methyltransferase, and monoamine oxidase, were generally elevated in Ts16 brain, as were their daily increments. These observations indicate a significant developmental alteration in the maturation of the trisomic brain and suggest future avenues for defining the effect of increased gene dosage of MMU 16 in the CNS.

Acetylcholine↗
PubMed1980

The effect of somatostatin (SRIF) on the release of amino acids from skeletal muscle.

1. Somatostatin (SRIF, somatotropin release inhibiting factor), at a concentration of 2 x 10(-8) M (32 ng/ml) decreased the rat of alanine release (approximately 45%) and increased glutamine release (approximately 30%) in in vitro preprations of m. extensor digitorum longus (EDL) muscle from 35--40 day old Wistar rats. These effects of SRIF were observed under both aerobic and anaerobic conditions. 2. SRIF increased the formation of 14CO2 from alanine but not from glutamine, glutamate, leucine, isoleucine or valine. 3. The incorporation of alanine, glutamine, glutamate, leucine, isoleucine and valine into muscle protein was unaffected by the presence of SRIF.

Alanine↗