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Biomedical subjects

M Fraser

Publications and source records attributed to M Fraser.

At least 109 records · Page 6Linked to original sources
PubMed1979

Isolation and genetic analysis of nuclease halo (nuh) mutants of Neurospora crassa.

Nuclease halo (nuh) mutants of the ascomycete Neurospora crassa have been isolated which are characterized reduced release of deoxyribonuclease (DNase) activities from colonies grown on sorbose-containing agar media. To identify nuh mutants, mutagenized isolates were transferred to commercial DNase test agar, or grown on minimal medium and then overlayed with agar that contained heat-denatured DNA. DNase activity was visualized by acid precipitation which produced clear rings of digestion (haloes) around the colonies. To identify the number of genes in which mutations lead to reduced release of nuclease activity, eleven nuh mutants were checked for close linkage and linked pairs were tested for complementation. These mutants were assigned to eight genes, and all except one were mapped in six small regions of the Neurospora linkage maps. In addition, among a large number of existing mutants which were tested for nuclease haloes, two mutants were found that showed the Nuh phenotype, namely uvs-3 and uvs-6. One of the isolated nuh mutants was also found to be sensitive to UV and was mapped close to uvs-3; it may represent a new allele of this gene. As a first step towards identification of genuine nuclease mutants, extensively backcrossed strains of mutants from different genes have been assayed for nuclease activity with denatured DNA in extracts. A pronounced reduction, compared to wild type at the same stage of growth, was found in uvs-3 and also in nuh-3, a mutant that is not UV-sensitive.

Chromosome Mapping↗
PubMedDate not supplied

Placental release of corticotrophin-releasing hormone across the umbilical circulation of the human newborn.

This study attempted to determine the placental release of corticotrophin-releasing hormone (CRH) into the umbilical circulation, and the factors which affect it, by measuring venous and arterial levels for CRH across the umbilical circulation in labouring as well as non-labouring elective caesarean section patients. The relationship with measures of fetal oxygenation and acid-base status at birth was investigated also. Forty-eight patients were studied (term labour n = 30, term elective caesarean section n = 12, and preterm labour n = 6) with blood sampling from a clamped segment of cord after delivery of the fetus and from the cord at its insertion into the placenta after delivery of the placenta, with subsequent measurement of blood gases, pH, base excess, and CRH. For all patients, mean plasma CRH levels in the umbilical and placental vein (115+/-13 and 145+/-18 pg/ml) were higher than those from the corresponding artery (85+/-7 and 102+/-8 pg/ml, P<0.01 and P<0.05, respectively), indicating placental release of CRH into the fetal compartment. In addition, placental venous and arterial cord CRH levels were higher than those from the corresponding umbilical levels (P<0.01 and P<0.02, respectively) indicating continued placental release of CRH into blood within the placenta after clamping of the umbilical circulation and delivery of the fetus. While plasma CRH levels from respective cord vessels were all significantly higher in labouring patients at term versus elective caesarean section patients, there were no differences compared with preterm labouring patients. For all patients, CRH as measured in both the umbilical and placental vein showed a modest inverse correlation to base excess as measured in the umbilical artery, -0.31 and -0.33, respectively, both P<0.05. It is concluded that CRH is released by the placenta into the fetal compartment and is increased with both term and preterm labour, and with metabolic acidosis during labour, supporting a role in the endocrine events of labour and/or compensatory changes in uteroplacental blood flow.

Acid-Base Equilibrium↗
PubMedDate not supplied

Activation of the hypothalamic-pituitary-adrenal axis with repetitive umbilical cord occlusion in the preterm ovine fetus.

OBJECTIVE: To determine whether repeated hypoxic insults with umbilical cord occlusion over 4 days will lead to activation of the hypothalamic-pituitary-adrenal (HPA) axis altered adrenocortical responsiveness in the preterm ovine fetus. METHODS: Umbilical cord occlusions of 90 seconds duration were performed every 30 minutes for 3 to 5 hours each day (experimental group n = 7, control group n = 7; at 112-116 days' gestation, term = 147 days). Arterial blood was sampled at predetermined times for blood gases and pH, plasma ACTH, and cortisol. Pituitary proopiomelanocortin (POMC) and glucocorticoid receptor (GR) mRNA also were localized and quantified by in situ hybridization. RESULTS: During umbilical cord occlusions fetal arterial oxygen pressure (approximately 17 mmHg) and pH (approximately 0.05) decreased, and carbon dioxide pressure increased (approximately 8 mmHg) as measured on days 1 and 4, but with no cumulative blood gas or pH change over successive occlusions for any of the 4 study days. Plasma ACTH increased, as measured after cord occlusion and over the course of successive cord occlusions on days 1 and 4, and returned to control values by the next day. The cumulative increase in ACTH was much less on day 4 than day 1 (15 +/- 3 compared with 101 +/- 25 pg/mL, P <.05). Plasma cortisol increased, as measured after cord occlusion and over the course of successive cord occlusions on day 4 only (2.7 +/- 0.4 to 4. 7 +/- 0.3 ng/mL, P <.05). POMC mRNA increased 2.5-fold in the pars distalis of the pituitaries from cord occlusion compared to control fetuses, but was unchanged in the pars intermedia. GR mRNA, which was detected in the pars distalis only, was unaltered. CONCLUSION: Repetitive umbilical cord occlusion in the preterm ovine fetus resulted in the activation of the HPA axis, with increased adrenocortical responsiveness over time, and involved differential regulation of POMC mRNA expression in the pars distalis and pars intermedia of the pituitary, but with no change in GR.

Adrenal Glands↗
PubMedDate not supplied

Rice as a vehicle for dietary fluoride uptake.

The objective of this study was to analyze aspects of the metabolism and bio-availability of fluoride after consumption of a sample of polished white rice containing 5.6 ppm fluoride ion. Up to 400 g of fluoridated rice was consumed by three volunteer adult subjects over specific time periods on two separate occasions. Saliva concentrations were elevated immediately and remained so 90 minutes following ingestion, among other indications. It was concluded that polished rice has the potential to be a useful vehicle for dietary fluoride transport.

Adult↗