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M Timmerman

Publications and source records attributed to M Timmerman.

12 recordsLinked to original sources
PubMed2003

Induction of glutamate dehydrogenase in the ovine fetal liver by dexamethasone infusion during late gestation.

Glucocorticoids near term are known to upregulate many important enzyme systems prior to birth. Glutamate dehydrogenase (GDH) is a mitochondrial enzyme that catalyzes both the reversible conversion of ammonium nitrogen into organic nitrogen (glutamate production) and the oxidative deamination of glutamate resulting in 2-oxoglutarate. The activity of this enzyme is considered to be of major importance in the development of catabolic conditions leading to gluconeogenesis prior to birth. Ovine hepatic GDH mRNA expression and activity were determined in near-term (130 days of gestation, term 147 +/- 4 days) control and acutely dexamethasone-treated (0.07 mg(-1) hr(-1) for 26 hr) fetuses. Dexamethasone infusion had no effect on placental or fetal liver weights. Dexamethasone infusion for 26 hr significantly increased hepatic GDH mRNA expression. This increased GDH mRNA expression was accompanied by an increase in hepatic mitochondrial GDH activity, from 30.0 +/- 7.4 to 58.2 +/- 8.1 U GDH/U CS (citrate synthase), and there was a significant correlation between GDH mRNA expression and GDH activity. The generated ovine GDH sequence displayed significant similarity with published human, rat, and murine GDH sequence. These data are consistent with the in vivo studies that have shown a redirection of glutamine carbon away from net hepatic glutamate release and into the citric acid cycle through the forward reaction catalyzed by GDH, i.e., glutamate to oxoglutarate.

Animals↗
PubMed2001

Net amino acid flux across the fetal liver and placenta during spontaneous ovine parturition.

The uptake and/or release of amino acids across the fetal liver and the placenta were studied in 8 pregnant sheep during the 5 days preceding delivery of the lamb. During spontaneous parturition, there was a significant decrease in fetal hepatic glutamine uptake, in fetal hepatic glutamate release and in placental glutamate uptake. The fetal plasma concentrations of glutamate, leucine, isoleucine, valine, phenylalanine, serine and tyrosine also decreased significantly in the 5 days preceding delivery. There was no significant net output of glucose from the fetal liver nor any change in net lactate uptake by the liver. During this same time period there was a significant increase in the fetal plasma cortisol concentration and a decrease in progesterone output by the pregnant uterus. The results are compared to the previously reported amino acid changes during dexamethasone-induced parturition.

Amino Acids↗
PubMed2000

Effect of dexamethasone on fetal hepatic glutamine-glutamate exchange.

Intravenous infusion of dexamethasone (Dex) in the fetal lamb causes a two- to threefold increase in plasma glutamine and other glucogenic amino acids and a decrease of plasma glutamate to approximately one-third of normal. To explore the underlying mechanisms, hepatic amino acid uptake and conversion of L-[1-(13)C]glutamine to L-[1-(13)C]glutamate and (13)CO(2) were measured in six sheep fetuses before and in the last 2 h of a 26-h Dex infusion. Dex decreased hepatic glutamine and alanine uptakes (P < 0.01) and hepatic glutamate output (P < 0.001). Hepatic outputs of the glutamate (R(Glu,Gln)) and CO(2) formed from plasma glutamine decreased to 21 (P < 0.001) and 53% (P = 0.009) of control, respectively. R(Glu,Gln), expressed as a fraction of both outputs, decreased (P < 0.001) from 0.36 +/- 0.02 to 0.18 +/- 0.04. Hepatic glucose output remained virtually zero throughout the experiment. We conclude that Dex decreases fetal hepatic glutamate output by increasing the routing of glutamate carbon into the citric acid cycle and by decreasing the hepatic uptake of glucogenic amino acids.

Alanine↗
PubMed1998

Uptake and transport by the ovine placenta of neutral nonmetabolizable amino acids with different transport system affinities.

Placental uptake and transport of three nonmetabolizable amino acids with different reactivities for transport systems were studied in sheep under normal physiologic conditions. Methylaminoisobutyric acid (MeAIB), which has specific affinity for the sodium-dependent A system transporters, demonstrated placental concentrative uptake from the uterine and the umbilical circulations, but virtually no transport from mother to fetus. By contrast, aminoisobutyric acid (AIB) and aminocyclopentane-1-carboxylic acid (ACP), which have affinity for both sodium-dependent and sodium-independent transporters, demonstrated both concentrative uptake and transport from mother to fetus. ACP transport rate to the fetus was approximately twice the AIB transport rate. It is concluded that a neutral amino acid which interacts almost exclusively with the weakly reversible system A transporters may be transported rapidly into the placenta and may attain high concentrations within this organ but cannot escape from placenta to fetus down its own concentration gradient because the exit route is controlled by reversible amino acid transporters at the fetal surface of the placenta. Conversely, high affinity for reversible Na-independent transporters may be a necessary condition for the rapid transport of an amino acid from placenta to fetus.

ATP-Binding Cassette Transporters↗
PubMed1998

Production and utilization of amino acids by ovine placenta in vivo.

Uterine and umbilical uptakes of plasma amino acids were measured simultaneously in eighteen singleton pregnant ewes at 130 +/- 1 days gestation for the purpose of establishing which amino acids are produced or used by the uteroplacenta under normal physiological conditions and at what rates. The branched-chain amino acids (BCAA) had uterine uptakes significantly greater than umbilical uptakes. Net uteroplacental BCAA utilization was 8.0 +/- 2.5 mumol.kg fetus-1.min-1 (P < 0.005) and represented 42% of the total BCAA utilization by fetus plus uteroplacenta. There was placental uptake of fetal glutamate (4.2 +/- 0.3 mumol.kg fetus-1.min-1, P < 0.001) and no uterine uptake of maternal glutamate. Umbilical uptake of glutamine was approximately 61% greater than uterine uptake, thus demonstrating net uteroplacental glutamine production of 2.2 +/- 0.9 mumol.kg fetus-1.min-1 (P < 0.021). In conjunction with other evidence, these data indicate rapid placental metabolism of glutamate, which is in part supplied by the fetus and in part produced locally via BCAA transamination. Most of the glutamate is oxidized, and some is used to synthesize glutamine, which is delivered to the fetus. There was net uteroplacental utilization of maternal serine and umbilical uptake of glycine produced by the placenta. Maternal serine utilization and glycine umbilical uptake were virtually equal (3.14 +/- 0.50 vs. 3.10 +/- 0.46 mumol.kg fetus-1.min-1). This evidence supports the conclusion that the ovine placenta converts large quantities of maternal serine into fetal glycine.

Amino Acids↗
PubMed1998

Relationship of fetal alanine uptake and placental alanine metabolism to maternal plasma alanine concentration.

Uterine and umbilical uptakes of alanine (Ala) were measured in 10 ewes before (control) and during intravenous infusion of Ala, which increased maternal arterial Ala concentration from 115 +/- 14 to 629 +/- 78 microM (P < 0.001). In 8 of these ewes, placental Ala fluxes were traced by constant intravenous infusion of L-[3,3,3-2H3]Ala in the mother and L-[1-13C]Ala in the fetus. Rates are reported as micromoles per minute per kilogram fetus. Ala infusion increased uterine uptake (2.5 +/- 0.6 to 15.6 +/- 3.1, P < 0.001), umbilical uptake (3.1 +/- 0.5 to 6.9 +/- 0.8, P < 0.001), and net uteroplacental utilization (-0.7 +/- 0.8 to 8.6 +/- 2.7, P < 0.01) of Ala. Control Ala flux to fetus from mother (Rf,m) was much less than the Ala flux to fetus from placenta (Rf,p) (0.17 +/- 0.04 vs. 5. 0 +/- 0.6). Two additional studies utilizing L-[U-13C]Ala as the maternal tracer confirmed the small relative contribution of Rf,m to Rf,p. During maternal Ala infusion, Rf,m increased significantly (P < 0.02) but remained a small fraction of Rf,p (0.71 +/- 0.2 vs. 7.3 +/- 1.3). We conclude that maternal Ala entering the placenta is metabolized and exchanged for placental Ala, so that most of the Ala delivered to the fetus is produced within the placenta. An increase in maternal Ala concentration increases placental Ala utilization and the fetal uptake of both maternal and placental Ala.

Alanine↗
PubMed1996

Luminometric measurement of subnanomole amounts of key metabolites in extracts from isolated heart muscle cells.

In principle, luminometry allows very sensitive metabolite measurements as shown with standards in aqueous solutions (e.g., buffers). However, components of complex biological samples may largely interfere with luminometric reactions. We now describe a procedure by which subnanomole amounts of intermediary metabolites (malate, glucose 6-phosphate) can be measured by luminometry in extracts from isolated mammalian cells, namely rat heart muscle cells. Basically, measurements occur in two steps: (i) Enzymatically catalyzed reactions involving the metabolite to be measured lead to the stoichiometric production of NAD(P)H; (ii) the oxidation of this NAD(P)H in a luciferase/reductase system results in light production which is proportional to the original concentration of the metabolite. The reaction scheme is thus as follows: (1) Metabolite (malate, glucose 6-phosphate) + NAD(P)+ --> X + NAD(P)H + H+; (2) NAD(P)H + O2 + RCOH --> NAD(P)+ + RCOOH + H2O + hnu. The cardiomyocytes used are previously subjected to an ethanolic extraction in which the cellular NAD(P)H is destroyed by acidification. Subsequent evaporation of the extracts allows to neutralize and to concentrate the samples. This contributes, along with other experimental maneuvers, to increasing the sensitivity of the method. With this procedure, we were able to detect amounts of approximately 70 pmol of malate and approximately 90 pmol of glucose 6-phosphate in cardiomyocyte samples. In addition, the calculated cellular concentrations of malate and glucose 6-phosphate (101.1 +/- 4.5, and 202.8 +/- 26.1 microM, respectively, in the absence of exogenous substrate) correspond to values previously reported for heart tissue. In principle, the procedure described could be applied to the measurement of any ethanol-extractable metabolite that can be converted in reactions involving NAD(P)+.

Animals↗
PubMed1996

Reported alcohol use and behavior in long-distance runners.

Because alcohol may impair sports performance, we hypothesized there would be less drinking in serious recreational runners. We used mailed questionnaires to examine drinking patterns (2-wk quantity/frequency), scores on modified versions of the Michigan Alcoholism Screening Test (brief MAST [BMAST], short MAST [SMAST]), and parental history of problem drinking in 397 men and 144 women runners participating in a 20-mile race, compared with a nonexercising control population of 138 men and 119 women. A subset of 188 pairs (104 men, 84 women) were matched for gender, age, educational level, and marital status. We used chi-square analysis, paired t-test, and ANOVA. Male gender, running, and a family history for problem drinking predicted increased total alcohol consumption. We found that male runners (vs male controls) drank more 14.2 +/- 19.6 vs 5.4 +/- 7.6 drinks.wk-2, P = 0.004) and felt guilty about their drinking (26.6% vs 13.8%, P < 0.01). Men and women runners reported more occasions of drinking than matched controls (2.8 +/- 2.7 vs 2.0 +/- 2.3.wk-2, P = 0.004). Runners with scores on the BMAST (> or = 6) or SMAST (> or = 3) suggestive of a history of problem drinking drank less than controls with a similar score. Contrary to our hypothesis, running is associated with increased alcohol consumption, except in those who report a history of problem alcohol behavior.

Adult↗
PubMed1987

Effect of noradrenergic denervation on task-related visual evoked potentials in rats.

The present study examines whether destruction of the noradrenergic innervation of the forebrain interferes with the processing of sensory information in a manner that results in impaired selective attention. Electro-cortical responses to task-relevant and irrelevant stimuli were found to be sensitive indicators of the rat's attention to the stimuli. The amplitude of the response to the task-relevant stimulus increased as the rat's performance improved. The response to irrelevant flashes of light depended on the predictability of the flashes and on the rat's level of arousal. Noradrenergic denervation (with the selective neurotoxin DSP4) did not affect either the behavioural response to a visual stimulus which the rat had been trained to respond to for a food reward, or the late positive potential evoked by this stimulus. Neither did it affect the response to continuous (temporally predictable) flashes of light that were irrelevant to the task. Although the response to unpredictable flashes was also largely unaffected, we did find an additional late component in this response after DSP4 treatment. These results show that the noradrenergic innervation of the occipital cortex does not always regulate the extent to which visual stimuli are processed, but that noradrenergic neurotransmission may be activated in order to diminish excessive processing of unexpected stimuli.

Animals↗
PubMed1986

Training community developmental disabilities associates: a collaborative model.

Direct care staff play critical roles in contributing to the successful community adjustment of individuals with developmental disabilities. The current shortage of qualified personnel for these positions, however, will hinder future community integration efforts, particularly as individuals with more intensive needs attempt to live in the community. Improvements, both in the training of staff and in the pay and other incentives they receive, are needed. One response to this growing need is associate degree training that is being provided by a few community colleges and technical schools throughout the country. This article briefly describes the implementation and major components of such a program now being offered through Wisconsin's Vocational, Technical, and Adult Education System. Developed in response to local needs and representing an ongoing collaborative effort among the academic, advocacy, and service communities, the program also illustrates an important role the University Affiliated Facility can play in promoting exemplary training.

Allied Health Personnel↗
PubMedDate not supplied

Amino acid solutions for premature neonates during the first week of life: the role of N-acetyl-L-cysteine and N-acetyl-L-tyrosine.

Tyrosine and cyst(e)ine are amino acids that are thought to be essential for preterm neonates. These amino acids have low stability (cyst(e)ine) or low solubility (tyrosine) and are therefore usually present only in small amounts in amino acid solutions. Acetylation improves the stability and solubility of amino acids, facilitating a higher concentration in the solution. We compared three commercially available amino acid solutions, Aminovenös-N-päd 10%, Vaminolact 6.5%, and Primène 10%, administered to 20 low-birth-weight neonates on total parenteral nutrition from postnatal day 2 onward. Aminovenös-N-päd 10% contains acetylated tyrosine and acetylated cysteine; the other solutions do not contain acetylated amino acids and differ in the amount of tyrosine and cysteine added. On postnatal day 7, plasma amino acids were measured together with urinary excretion of amino acids and the total nitrogen excretion; 38% of the intake of N-acetyl-L-tyrosine and 53% of the intake of N-acetyl-L-cysteine were excreted in urine. Plasma levels of N-acetyl-L-tyrosine (331 +/- 74 mumol/L) and N-acetyl-L-cysteine (18 +/- 29 mumol/L) were higher than those of tyrosine (105 +/- 108 mumol/L) and cystine (11 +/- 9 mumol/L), respectively. Plasma tyrosine levels in the groups receiving small amounts of tyrosine remained just below the reference range. We show a linear correlation of plasma cystine with the intake of cysteine (r = .75, p = 0.01), but not with N-acetyl-L-cysteine. The estimated intake of cysteine should be 500 mumol.kg-1.d-1 in order to obtain levels comparable with those shown in normal term, breast-fed neonates. Nitrogen retention did not differ among the three groups (247 to 273 mg.kg-1.d-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcysteine↗