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Biomedical subjects

N Harrison

Publications and source records attributed to N Harrison.

At least 19 recordsLinked to original sources
PubMed1999

In vivo pH and metabolite changes during a single contraction in rat uterine smooth muscle.

1. We have used 31P NMR spectroscopy to measure metabolites and pHi at three periods during a phasic contraction of the uterus, in vivo, to determine whether they change as a consequence of contraction. The regular uterine contractions were recorded via a balloon catheter in the uterine lumen. Each phasic contraction was divided into three parts: the period between contractions (rest), the development of force (up) and the relaxation of force (down). The NMR data were summed separately from each of these three periods over 20-40 successive contractions. 2. Significant changes in ATP, phosphocreatine (PCr) and inorganic phosphate (Pi) occurred during the contraction. [ATP] fell from 2.0 to 1.6 mM and [PCr] from 2.6 to 2.0 mM during the up period, while [Pi] increased from 2.2 to 2.8 mM. Recovery of ATP and PCr occurred during the relaxation part of the contraction, whereas Pi did not fully recover until the contraction was complete. 3. Significant acidification from pH 7.28 +/- 0.02 at rest to 7.16 +/- 0.02, occurred with contraction. This acidification is greater than that previously reported for in vitro uterine preparations. Measurements of uterine blood flow show that it decreased with contraction. Therefore, ischaemia, in addition to the metabolic consequences of contraction, may account for the larger acidification observed in vivo. 4. Lowering pHi in an in vitro uterine preparation by a similar level to that found in vivo produced a significant reduction of the phasic contractions. Thus we propose that these changes, especially the fall in pHi during force development, feed back negatively on the contraction to limit its strength, and may help prevent uterine ischaemia and fetal hypoxia during labour.

Adenosine Triphosphate↗
PubMed1999

Dietary exposures to nitrate in the UK.

Dietary exposures to nitrate have been estimated for two different groups of UK consumers. The daily dietary exposure of the general population was estimated from the UK 1997 Total Diet study to be 52 mg/day. Vegetables contributed approximately 70% to this total dietary exposure. Dietary exposure estimates for adult consumers of vegetables commonly eaten in the UK were 93 mg/day and 140 mg/day for mean and 97.5th percentile consumers, respectively. Dietary exposures to nitrate of UK consumers are similar to those in other European countries and are less than the Acceptable Daily Intake (ADI) for nitrate set by the European Commission's Scientific Committee for Food.

Adult↗
PubMed1999

Dietary exposure estimates of 30 elements from the UK Total Diet Study.

Dietary exposures of consumers to 30 elements (aluminium, antimony, arsenic, barium, bismuth, boron, cadmium, calcium, chromium, cobalt, copper, germanium, gold, iridium, iron, lead, lithium, manganese, mercury, molybdenum, nickel, palladium, platinum, rhodium, ruthenium, selenium, strontium, thallium, tin and zinc) estimated from the UK 1994 Total Diet Study are reported, and compared with those from previous UK Total Diet Studies and those from other countries. Dietary exposure estimates were generally low and, where comparisons are possible, similar to those from other countries and below the relevant Provisional Tolerable Weekly Intakes and Provisional Maximum Tolerable Daily Intakes. For most of those elements included in previous UK Total Diet Studies, dietary exposures have declined.

Diet↗
PubMed1999

Monitoring for nitrate in UK-grown lettuce and spinach.

To comply with European Commission requirements, the UK is carrying out a monitoring programme on nitrate concentrations in lettuce and spinach. This paper reports the results obtained between June 1996 and April 1998. A total of 182 samples of protected lettuce, 131 samples of outdoor-grown lettuce and 34 samples of fresh spinach were taken from the main growing areas of the UK. Nitrate concentrations in protected lettuce were influenced by the season with summer-grown crops (mean of 2382 mg/kg) having lower levels than those grown in the winter (mean of 3124 mg/kg). Weather conditions also affected concentrations in protected lettuces with long hours of sunshine and low rainfall associated with low nitrate levels. Nitrate concentrations in outdoor-grown lettuces were lower (mean of 1085 mg/kg) than those in protected lettuces but there were insufficient data to determine if they were affected by the weather conditions or season. Similarly there were insufficient data to determine if weather conditions or season influenced nitrate concentrations in spinach (mean of 1900 mg/kg) but regional differences were observed.

Food Contamination↗
PubMed1998

The in vivo relationship between blood flow, contractions, pH and metabolites in the rat uterus.

Little is known about the relationship between smooth muscle contractile activity and its blood supply. We have therefore investigated this in the rat uterus, using laser-Doppler flow measurement and intra-uterine pressure recordings. We found an inverse linear relationship between flow and contractile activity. There was no evidence for a critical level of flow, above which function is maintained and below which it declines; even small reductions in blood flow decreased uterine force. Force was rapidly restored upon reperfusion. Reactive hyperaemia was absent from all but 6 of the 41 preparations studied. We used 31P nuclear magnetic resonance (NMR) spectroscopy to measure concentrations of adenosine triphosphate (ATP), phosphocreatine (PCr), inorganic phosphate (Pi) and intracellular pH (pHi) simultaneously with force and flow. Reductions in flow were associated with significant reductions in [ATP], [PCr] and pHi, and an increase in [Pi]. These changes were related to flow significantly and linearly and their effects on force may be additive. These data show that uterine smooth muscle is closely dependent upon its blood supply for maintaining both normal force production and metabolite levels. Consequently, even small decrements in flow may have deleterious functional effects.

Adenosine Triphosphate↗
PubMed1996

PCDDS and PCDFS in milk from farms in Derbyshire, U.K.

As part of a programme to establish the background levels of PCDD/Fs in milk in the U.K., samples of cows' milk were collected from farms in Derbyshire in 1990 and 1991. The concentrations of PCDD/Fs in the samples from two farms in the Bolsover area of Derbyshire were found to be significantly elevated compared with the normal range for PCDD/Fs in milk in the U.K. Details of the findings and the actions taken as a result are given. The concentrations of PCDD/Fs in milk from those farms previously supplying milk for human consumption are now below the Maximum Tolerable Concentration of 17.5 ng TEQ/kg fat.

Animals↗
PubMed1996

Carbon monoxide within circle systems.

After reports of carbon monoxide toxicity from the United States, the Medicines Control Agency issued a warning which recommended that soda lime used in circle breathing systems should not be allowed to dry out. We have measured carbon monoxide levels within a circle system in vitro (under a variety of conditions) and in vivo. Carbon monoxide was detected only when a patient was connected to the circle system. As levels in the expiratory limb of the circle system were significantly higher than those in the inspiratory limb, we conclude that the patient acts as the source of carbon monoxide.

Anesthesiology↗
PubMed1995

A 31P NMR investigation into the effects of repeated vascular occlusion on uterine metabolites, intracellular pH and force, in vivo.

Little is known about the metabolic effects of ischaemia on high energy phosphates in vivo in smooth muscle. We have developed a method for reversibly occluding the uterine artery, which allows simultaneous measurement of uterine metabolites using 31P NMR spectroscopy, and intra-uterine pressure, in vivo during ischaemia. We have investigated the effects of repeated ischaemia on metabolites, intracellular pH and contractions in anaesthetized rats. Occlusion produced an immediate drop in uterine blood flow and decreased contractions. Although contractions recovered upon reperfusion after both occlusions, the contractile activity was less after the second period of occlusion, suggesting less resistance after a prior ischaemic period. Significant falls in [ATP] and [phosphocreatine] and an increase in [P(i)] occurred during both occlusions. These were all reversed within 30 min of reperfusion. There was a large drop in intracellular pH produced by occlusion, which was rapidly reversed upon reperfusion. The changes in metabolites and intracellular pH were similar during the repeated ischaemic period, to those occurring during the first ischaemic period suggesting no alteration in energy production or utilization had occurred, with prior exposure to ischaemia. The significance of these results to the functioning of the uterus in labour is briefly discussed.

Adenosine Triphosphate↗
PubMed1995

Using humour as an educational technique.

Humour can be constructive or destructive, so needs to be used selectively and sensitively. Teachers require training to acquire the appropriate level of self-awareness, knowledge and skills. Educational humour needs monitoring and evaluation.

Education, Nursing↗