Biomedical subjects

P Penfold

Publications and source records attributed to P Penfold.

23 records · Page 2Linked to original sources

PubMedDate not supplied

Mechanical and metabolic viability of a placental perfusion system in vitro under oxygenated and anoxic conditions.

In vitro dual circuit perfusion of the placenta with well-oxygenated medium results in the continuous and stable consumption of oxygen and glucose over a 2-h perfusion period. This is reflected in a stable production of lactate and an energy charge which is higher at the end of the perfusion period than that seen in fresh placental tissue immediately after vaginal delivery. Anoxic perfusion causes an increase in glucose consumption which is more than twofold higher than that seen in the oxygenated perfusion, resulting finally in placental uptake of glucose not only from the maternal but also from the fetal circulation. Lactate production is increased during the anoxic perfusion, while the final tissue energy charge value lies between the values observed for fresh tissue and for the oxygenated perfusion. The shift to anaerobic metabolism shown by placental tissue in anoxic conditions enables continued functioning of the tissue over the 2-h perfusion period but it appears that under anoxic conditions the tissue may incur an energy debt not observed in oxygenated perfusions.

Adenine Nucleotides↗

PubMedDate not supplied

Human placental ultrastructure after in vitro dual perfusion.

Unperfused term placental tissue maintained at 37 degrees C for two hours preserved a major part of its structure while displaying a number of signs of hypoxic damage. Most placentae perfused through maternal and fetal circulations with Krebs-Ringer medium retained their ultrastructural integrity after two or more hours of perfusion.

Female↗

PubMedDate not supplied

Lactate transfer across the perfused human placenta.

The transfer of lactate across the human placenta was investigated using an in vitro dually-perfused placental preparation. Using a novel technique, the unidirectional flux of L-lactate was found to be linearly dependent on L-lactate concentration. In addition, unidirectional transfer rates were found to be the same in both maternal-to-fetal and fetal-to-maternal directions at the same lactate concentration. Transfer of [14C]L-lactate was decreased by approximately 15 per cent in competition with unlabelled L-lactate. Stereospecificity and permeability experiments demonstrated the existence of a transfer mechanism which could distinguish between the L- and D-isomers of lactate. Our data suggest that, while a stereospecific carrier for lactate exists in the perfused placenta, the bulk of transplacental lactate transfer takes place by non-carrier-mediated diffusion.

Antipyrine↗

PubMedDate not supplied

Are neuronal transporters relevant in retinal glutamate homeostasis?

Exposure of isolated retinas to 30 microM D-aspartate, which is a substrate for all high affinity glutamate transporters, for 30 min, resulted in the accumulation of such D-aspartate into Müller glial cells but not glutamatergic neurons as evinced by immunocytochemistry for D-aspartate. Further incubation of such loaded retinas in physiological media, in the absence of D-aspartate, resulted in the slow release of accumulated D-aspartate from the Müller cells and its accumulation into populations of photoreceptors and bipolar cells. This result indicates that after initial transport into Müller cells, reversal of direction of transport of D-aspartate, and thus by inference glutamate, by GLAST, readily occurs. D-aspartate released by Müller cells was strongly accumulated into cone photoreceptors which are known to express GLT-1, and into rod photoreceptors which we demonstrate here to express the retina specific glutamate transporter EAAT5 (excitatory amino transporter 5). Populations of glutamatergic bipolar cells, which express GLT-1 also exhibited avid uptake of D-aspartate. We conclude that the Müller cell glutamate transporter GLAST is responsible for most of the initial glutamate clearance in the retina after its release from neurones. However, some glutamate is also returned from Müller cells, to neurons expressing GLT-1 and EAAT5, albeit at a slow rate. These data suggest that the role of neuronal glutamate transporters in the retina may be to facilitate a slow process of recycling glutamate back from Müller cells to neurons after its initial clearance from perisynaptic regions by GLAST.

ATP-Binding Cassette Transporters↗

PubMedDate not supplied

UTI in patients with urethral catheters: an audit tool.

This article presents an audit tool for the evaluation of practice relating to urinary tract infection in hospital patients with indwelling urethral catheters. It has been formulated primarily because urinary tract infection is a known complication of catheterization, and because studies have shown practitioners' knowledge in this area to be poor. Although health professionals have an obligation to ensure their practice is evidence based, this requires substantial time and skills in critical appraisal. The standard presented here is based on evidence from an extensive literature review on how best to minimize urinary tract infection during catheter insertion, meatal hygiene and management of the drainage system. The audit tool offers the potential for improved practice and demonstration of clinical effectiveness through measurable reduction in rates of urinary tract infection. Moreover, it provides an ideal opportunity for nurses to take the lead in clinical audit activity, which is so often medically led. The supplementary information will also provide a useful guide for nurses to undertake and initiate clinical audit activity in the future.

Catheters, Indwelling↗