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Biomedical subjects

D A Hood

Publications and source records attributed to D A Hood.

51 records · Page 3Linked to original sources
PubMed1990

Species-specific expression of cytochrome c oxidase subunit III mRNA.

1. A cDNA probe encoding cytochrome c oxidase subunit III cloned from rat liver mitochondria was used to quantify mRNA levels in rat, mouse and rabbit tissues. This was compared to its phenotypic expression, using enzyme activity. 2. Enzyme activities were highest in mouse, intermediate in rat, and lowest in rabbit tissues. 3. Subunit III mRNA levels were easily quantified in rat, but could not be accurately measured in rabbit or mouse tissues despite high cytochrome c oxidase activities. 4. Significant subunit III sequence divergence must exist, among these species. Caution should be exercised in quantifying the expression of this mitochondrial gene.

Animals↗
PubMed1990

Amino acid metabolism during exercise and following endurance training.

Exercise results in marked alterations in amino acid metabolism within the body. The branched-chain amino acids, especially leucine, are particularly important since they contribute as energy substrates and as nitrogen donors in the formation of alanine, glutamine and aspartate. Leucine oxidation increases during whole-body exercise. Nonetheless, leucine's contribution as a muscle energy substrate is amll, being 3 to 4% at rest, and even lower (1%) during exercise. Traditional energy substrates (carbohydrates, lipid) remain most important. These rates of leucine oxidation can be readily attributed to skeletal muscle. Following endurance training, whole-body leucine oxidation is increased at rest and during exercise. Since its oxidation by muscle is not augmented, this whole-body increase is not due to muscle. Thus, other tissues within the body (i.e. liver) must account for this. Comparisons of leucine oxidation in rats and humans indicate that species differences exist. Much larger increases in leucine oxidation are brought about by exercise in humans. Calculations based on steady-state rates of leucine oxidation at rest and during exercise indicate that the recommended dietary intake of leucine is inadequate, since it is lower than measured whole-body rates of leucine oxidation. This inadequacy is exacerbated in individuals who are physically active.

Amino Acids↗
PubMed1989

Chronic long-term electrostimulation creates a unique metabolic enzyme profile in rabbit fast-twitch muscle.

Long-term low-frequency stimulation (up to 120 days) of rabbit fast-twitch tibialis anterior muscle led, in a first-order-like time course, to changes in enzyme activities of energy metabolism which became stable with ongoing stimulation after 50 days. The glycolytic enzymes decreased to 30-40% of their normal values, but remained 2-3-fold higher than in heart or soleus muscle. The LDH isozyme pattern ultimately resembled that of the slow-twitch soleus muscle. Citrate synthase activity increased 3.7-fold which brought this enzyme to a value 45% above that of heart. These results indicate that chronic stimulation does not simply convert the fast-twitch muscle into a soleus-like slow-twitch muscle, but creates a tissue of unique metabolic properties.

Animals↗
PubMed1989

Meningococcal vaccine--do some children experience side effects?

In order to stop an outbreak of group A meningococcal meningitis, 130,000 Auckland children were immunised. During the month following vaccination there were 546 reports of unusual clinical events reported by parents and practitioners, together with 40 specialist paediatric assessments of children presenting with neurological symptoms. In 25 of these latter there was complete agreement between the history as presented by parents in the initial telephone report and the paediatrician's subsequent summarised history. Of the 546 reports, 217 either had too little detail for an assessment or the symptoms were clearly attributable to other causes. Of the remaining reports, there were 152 cases of fever with or without other symptoms; 85 were of rash and local reactions within 24h of vaccination; 63 reports were of headache, stiff neck and myalgia within 48h of vaccination. There were 92 reports of apparent peripheral nerve involvement, including 80 reports of unexplained weakness and 57 reports of paraesthesia or dysaesthesia. Both motor and sensory symptoms occurred in some children; none were permanent. The effects of adverse publicity during the campaign on the genesis of some symptoms is acknowledged, but the possibility that short term neurological symptoms occur after vaccination seems likely and has not been previously reported.

Bacterial Vaccines↗
PubMed1989

Chronic stimulation of rat skeletal muscle induces coordinate increases in mitochondrial and nuclear mRNAs of cytochrome-c-oxidase subunits.

Fast-twitch tibialis anterior muscle of the rat was subjected to chronic low-frequency (10 Hz, 10 h daily) nerve stimulation in order to investigate the time course of changes in cytochrome-c-oxidase activity, as well as in tissue levels of specific mitochondrially and nuclear-encoded, cytochrome-c-oxidase-subunit mRNAs. Chronic stimulation induced a progressive increase in cytochrome-c-oxidase activity which was threefold elevated after 35 days. A similar increase was recorded for citrate-synthase activity. Glyceraldehyde-3-phosphate dehydrogenase, which was studied as a glycolytic reference enzyme, moderately decreased, as did the tissue level of its corresponding mRNA. There was a parallel increase in the tissue levels of the two cytochrome-c-oxidase-subunit mRNAs over the entire stimulation time course. The extent of increase (stimulated/control) was 2.4 +/- 0.3 and 1.8 +/- 0.2 (means +/- SEM) for the mitochondrial and nuclear subunit mRNAs, respectively. This parallel increase suggested a coordinate regulation of the two subunits. The increase in cytochrome-c-oxidase activity initially corresponded to the changes at the mRNA level. However, with longer stimulation times (beyond 14 days), the increase in cytochrome-c-oxidase activity clearly exceeded that of the two mRNAs. This divergence was progressive and was interpreted to indicate that the increase in cytochrome-c-oxidase content was brought about not only by changes in the levels of the specific mRNAs, but also by alterations at the level of translation.

Animals↗
PubMed1989

Rapid isolation of total RNA from small mammal and human skeletal muscle.

The present study was designed to assess the efficacy and reliability of a method (Anal. Biochem. 162: 156-59, 1987) of total RNA isolation from small muscle samples. The RNA content of skeletal muscles in mouse, rabbit, guinea pig, rat, and human was also investigated. Enough RNA was extractable from muscle samples as small as 25 mg in weight to provide material for the analysis of specific mRNA sequences using RNA blot hybridization with a cDNA probe for a mitochondrially encoded subunit of cytochrome-c oxidase. The RNA was free of detectable levels of protein or DNA. Gel electrophoresis and cDNA probe hybridization indicated that the RNA was relatively undegraded. Significant differences (P less than 0.05) in RNA content were found among fiber types (type I fibers greater than type II fibers) and among the soleus muscles of various species (guinea pig greater than rat = mouse greater than rabbit). Human muscle possessed the lowest RNA content (350 ng/mg) among the species investigated. The results indicate that intact RNA can be rapidly and reliably isolated from small skeletal muscle, including samples typically obtained from human muscle biopsies. This technique should permit the analysis of gene expression in muscle subject to a variety of physiological treatments.

Animals↗
PubMed1988

De novo synthesis of adenine nucleotides in different skeletal muscle fiber types.

Management of adenine nucleotide catabolism differs among skeletal muscle fiber types. This study evaluated whether there are corresponding differences in the rates of de novo synthesis of adenine nucleotide among fiber type sections of skeletal muscle using an isolated perfused rat hindquarter preparation. Label incorporation into adenine nucleotides from the [1-14C]glycine precursor was determined and used to calculate synthesis rates based on the intracellular glycine specific radioactivity. Results show that intracellular glycine is closely related to the direct precursor pool. Rates of de novo synthesis were highest in fast-twitch red muscle (57.0 +/- 4.0, 58.2 +/- 4.4 nmol.h-1.g-1; deep red gastrocnemius and vastus lateralis), relatively high in slow-twitch red muscle (47.0 +/- 3.1; soleus), and low in fast-twitch white muscle (26.1 +/- 2.0 and 21.6 +/- 2.3; superficial white gastrocnemius and vastus lateralis). Rates for four mixed muscles were intermediate, ranging between 32.3 and 37.3. Specific de novo synthesis rates exhibited a strong correlation (r = 0.986) with muscle section citrate synthase activity. Turnover rates (de novo synthesis rate/adenine nucleotide pool size) were highest in high oxidative muscle (0.82-1.06%/h), lowest in low oxidative muscle (0.30-0.35%/h), and intermediate in mixed muscle (0.44-0.55%/h). Our results demonstrate that differences in adenine nucleotide management among fiber types extends to the process of de novo adenine nucleotide synthesis.

Adenine Nucleotides↗
PubMed1987

Leucine metabolism in perfused rat skeletal muscle during contractions.

An isolated single rat hindlimb muscle preparation was used to examine leucine metabolism during steady-state conditions as a function of metabolic rate (VO2) and leucine concentration. The rates of muscle leucine uptake and leucine oxidation (measured as alpha-decarboxylation) were dependent on leucine delivery. At a physiological leucine concentration (0.1 mM), leucine uptake and alpha-ketoisocaproic acid (KIC) release during rest was 12.8 +/- 0.4 and 1.86 +/- 0.06 nmol.min-1.g-1 g, respectively. Leucine oxidation was 2.35 +/- 0.11 nmol.min-1.g-1 (n = 24) and if fully oxidized could account for only 3-4% of the resting VO2. This fraction was reduced to approximately 1% during contractions. The rate of leucine oxidation progressively increased, up to two to three times above rest (6-7 nmol.min-1.g-1), during contractions of graded frequency (7.5, 15, 30, 45, and 60 tetani/min) in a manner related to the eightfold increase in VO2 of the mixed fiber muscle. The fraction of muscle leucine uptake that was transaminated (i.e., leucine decarboxylation + KIC release) increased from 33% at rest to approximately 60% during contractions. The increase in leucine oxidation during contractions was probably primarily due to the high oxidative fast-twitch, red muscle mass, whose VO2 was estimated to increase up to 24-fold above rest. On the basis of our observed rates of muscle leucine alpha-decarboxylation, it is reasonable to attribute the rates of whole-body leucine oxidation of nontrained individuals during exercise to leucine oxidation by the working muscle.

Adenosine Triphosphate↗
PubMed1987

Effect of endurance training on leucine metabolism in perfused rat skeletal muscle.

An isolated single rat hindlimb muscle preparation was used to examine the influence of exercise training on leucine metabolism during steady-state conditions at rest and during isometric contractions. Treadmill training increased the activity of citrate synthase in the hindlimb muscle by 40-45%. Leucine oxidation, measured as the rate of alpha-decarboxylation, was not different between trained (2.28 +/- 0.15 nmol.min-1.g-1, n = 9) and control (2.57 +/- 0.20, n = 9) muscle at rest. In addition, successive 40-min contraction periods at 15 and 45 tetani/min induced similar increases (50 and 100%, respectively) in leucine oxidation in both groups. However, trained muscle maintained a greater tension output (P less than 0.05) during contractions and exhibited a greater oxygen consumption (VO2) (P less than 0.05) during 45 tetani/min. Thus the rate of leucine oxidation, relative to VO2, was less (P less than 0.05) in the trained group. This response was probably related to differences in intracellular factors modulating branched-chain alpha-keto acid dehydrogenase, the rate-limiting step in leucine oxidation. Although our observed rates of muscle leucine alpha-decarboxylation can reasonably account for the rates of whole-body leucine alpha-decarboxylation of nontrained individuals found during steady-state tracer studies in vivo, this is less reasonably the case for the trained group. This suggests that a greater rate of leucine oxidation by nonmuscle tissues (e.g., liver) may occur in trained compared with nontrained individuals.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1986

Blood flow distribution in tissues of perfused rat hindlimb preparations.

Aerobic muscle metabolism during concentrations requires adequate blood flow and oxygen delivery. Since the perfused rat hindquarter (HQ) has become widely used for muscle stimulation, we examined the blood flow distribution, using 15 microns radiolabeled microspheres, and oxygen consumption of the HQ, using different commonly used perfusion protocols. Perfusion via the abdominal aorta resulted in well-matched (r = 0.90) blood flows between tissues of both hindlimbs that were proportional to total perfusion inflow. Blood flows to the high-oxidative fast-twitch and slow-twitch red muscle sections were three- to fourfold greater than flows to sections of low-oxidative fast-twitch white muscle. However, a large fraction (28%) of the total inflow went to the trunk region, even though all apparent arterial branches to the trunk region were ligated. This trunk mass accounts for at least 40% of the total metabolic responses of the HQ and diverts a large blood flow that is often presumed to supply the hindlimbs. As a result, muscle performance of the distal hindlimb muscle during stimulation can be inordinately poor. Ligation of the iliac artery to the contralateral limb improves blood flow to the remaining hindlimb but does not eliminate trunk blood flow. In contrast, perfusion via the femoral artery restricted 95% of the inflow to the single hindlimb, thereby reducing the tissue mass perfused. Blood flow to the distal limb musculature was high, resulting in an enhanced muscle performance. Thus single hindlimb perfusion provides a preparation where the contracting muscle is a large fraction of the total tissue, and the venous effluent better reflects the metabolic events in the contracting muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Oxygen cost of twitch and tetanic isometric contractions of rat skeletal muscle.

The distal muscles of a rat single hindlimb preparation, perfused at 14-15 ml/min, were stimulated sequentially for 10-min intervals at 12, 24, 36, 48, 60, 75, and 120 twitch/min (8 V, 0.05 ms) or at 7.5, 15, 30, 45, 60, 75, and 90 tetani/min (100-ms train, 100 Hz). Oxygen consumption (VO2) of the whole muscle increased up to 6- and 10-fold over rest during twitch and tetanic conditions, respectively. Tension development during each stimulation interval decreased sequentially at the higher contraction frequencies. VO2, corrected for this loss in tension development, increased linearly with contraction frequency with a slope of 0.037 +/- 0.003 mumol O2 X g-1 X twitch contraction-1 and 0.260 +/- 0.034 mumol O2 X g-1 X tetanic contraction-1. This sevenfold difference in slopes, which represent the O2 cost of a single contraction without fatigue, corresponds to the difference in developed tension between twitch and tetanic contractions. Anaerobic metabolism was negligible during tetanic contractions, but was significant during some twitch conditions. These values probably represent the O2 cost for fast-twitch muscle, since this is the predominant type (greater than 90%) in the rat hindlimb. However, an approximate fourfold difference in blood flow (determined with microspheres) between the white and red gastrocnemius sections (predominantly fast-twitch white and fast-twitch red, respectively) suggested a disparity in metabolic response. Estimates of the peak VO2 for each fiber type, for our perfusion conditions, are 6- and 30-fold above rest, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Incorporation of 15N-leucine amine into ATP of fast-twitch muscle following stimulation.

During intense contraction conditions, ATP content in fast-twitch muscle rapidly decreases (approx. 50%) by the deamination of AMP to IMP and NH3. During recovery, the ATP content returns to normal by the reamination of IMP from aspartate. We evaluated whether the donor amine may be obtained from branched chain amino acid uptake by perfusing muscle in situ with 1.0 mM [15N]-leucine during a 1 hr recovery. [15N]-enriched adenine nucleotide accounted for 14% to 24% of the IMP reaminated, depending on whether [15N]-leucine was provided only during the recovery period or, in addition, 30 min prior to stimulation. Thus, the uptake of leucine by fast-twitch muscle may provide an important source of amine for adenine nucleotide resynthesis following contractions.

Adenosine Triphosphate↗
PubMed1984

Insulin binding in human skeletal muscle.

Insulin binding to crude plasma membranes derived from human skeletal muscle was characterized. Incubations were performed for 22 h at 4 degrees C. Typical insulin binding characteristics were found, i.e., (a) specificity for insulin, (b) pH sensitivity, (c) dissociation of insulin by the addition of excess insulin and (d) concave Scatchard curves. Half-maximal inhibition of 125I-labeled-insulin binding occurred at 1 X 10(-8) M. Affinity constants were 0.76 X 10(9) and 0.02 X 10(9) M-1 for the high- and low-affinity receptor (2-site model), respectively, and the corresponding receptor numbers were 89 and 1450 fmol/mg protein, respectively. The procedures employed permit the determination of insulin binding to small quantities of human muscle (approx. 250 mg).

Adult↗
PubMed1975

A comparative study of the health of elite Maori and Caucasian children in Auckland.

A group of socially elite Maori and part-Maori parents kept a 10 month record (February to November 1972) of their children's health. The majority of a Caucasian control group were matched for socio-economic status by the Maori parents. The majority of both parent groups were of professional or skilled tradesman status whose income exceeded the then current New Zealand average. The results show no overall difference between the morbidity of the two racial groups studied.

Child↗