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Biomedical subjects

D J Lewis

Publications and source records attributed to D J Lewis.

At least 73 records · Page 4Linked to original sources
PubMed1988

Studies on the mechanism by which tryptophan efflux from isolated synaptosomes is stimulated by depolarization.

1. The efflux and influx of tryptophan across the synaptosomal plasma membrane has been studied under a variety of experimental conditions, in order to examine the mechanism by which depolarization enhances the efflux of tryptophan from superfused synaptosomes. 2. Efflux of [3H]-tryptophan from preloaded superfused synaptosomes was found to be enhanced by K+ depolarization in a Ca2+ and dose-dependent manner. In contrast, [3H]-phenylalanine efflux was only poorly stimulated by depolarization and only by very high concentrations of K+. 3. Tryptophan efflux was also enhanced by decreasing the extracellular Na+ concentration, but this effect was not dependent on extracellular Ca2+. 4. Influx of [3H]-tryptophan into synaptosomes was stimulated by extracellular Na+ removal, but the uptake of [3H]-phenylalanine was unaffected by this procedure. 5. Both the induced influx and efflux of tryptophan observed under these experimental conditions was inhibited by immobilizing the plasma membrane carrier with parachlorophenylalanine. This implied that both the enhanced influx and efflux arose as a consequence of the activation of the membrane tryptophan carrier, the direction of the observed effect being dependent upon the manner in which the experiments were conducted. 6. The relationship between depolarization, the activation of the membrane tryptophan carrier and the significance of this to the in vivo situation is discussed.

Animals↗
PubMed1987

Malaria prophylaxis: postal questionnaire survey of general practitioners in south east Wales.

Postal questionnaires were sent to 494 general practitioners in south east Wales asking about their experience and understanding of antimalarial prophylaxis; 293 were returned, giving a response rate of 59%. Forty eight (16%) of the respondents reported being consulted by immigrants returning home for advice about malaria prophylaxis, of whom 13 (27%) overestimated the time for which their protective immunity might last after leaving the malarious area. Two hundred and eighty respondents (96%) considered that they were responsible for advising travellers and 195 (67%) would always consult a publication before giving chemoprophylactic advice (magazines were particularly popular), but only 18 (6%) would always consult a specialist centre--the Ross Institute in eight cases (3%), a local centre in 39 (13%). Only about half of the doctors were aware of chloroquine resistance in Kenya and Thailand. Over half would withhold chloroquine in pregnancy, and many chose pyrimethamine alone or sulfadoxine-pyrimethamine as suitable chemoprophylactic drugs, though neither is still recommended by the World Health Organisation. One hundred and ninety two respondents (66%) would give advice about protective measures other than chemoprophylaxis. More must be done to encourage general practitioners to contact specialist centres and to educate them in the use of antimalarial chemoprophylactic drugs.

Adult↗
PubMed1987

Reproduction of epigastric pain of duodenal ulceration by adenosine.

Intravenous boluses of adenosine produced transient epigastric discomfort indistinguishable from spontaneous pain in five of six patients with endoscopically confirmed duodenal ulcer, an effect which was slightly but significantly antagonised by aminophylline. These findings may be relevant to the pathophysiology of peptic ulcer pain.

Adenosine↗
PubMed1987

Depth of penetration of vertebrate skin by phlebotomine sandflies (Diptera: Psychodidae).

The limited knowledge of penetration depth and its relation to Leishmania transmission is reviewed. Labrum length and maxillary dentition of a number of species of phlebotomines are compared. It appears that the labrum of Phlebotomus argentipes, the vector of kala-azar in eastern India, is only just long enough for obtaining a blood meal in normal human skin. More information on penetration depth is needed, and it might possibly be estimated from the length of the labium when it remains outside the skin and contracts. It would be necessary, however, to note the position of the labium which changes in relation to the labrum.

Animals↗
PubMed1987

Ovarian choriocarcinoma in the mouse.

Choriocarcinoma is one of the rarest ovarian tumors in any animal species. This paper describes the gross and microscopic appearance of seven such neoplasms in B6C3F1 mice. Mean age at death was 47 weeks. Tumors were described at necropsy as dark or hemorrhagic cystic lesions. On microscopic examination tumors were composed of hematocysts, intercellular hemorrhage, and cytotrophoblasts, syncytiotrophoblasts, and/or trophoblastic giant cells. Cytotrophoblasts, syncytiotrophoblasts, and occasional giant cells were present in three cases while the other four tumors contained only trophoblastic giant cells.

Animals↗
PubMed1987

Ovarian neoplasia in the Sprague-Dawley rat.

Macroscopic and microscopic characteristics of 210 spontaneous ovarian tumors from 7748 Sprague-Dawley rats are described. The tumors were classified as tubular adenoma, anaplastic adenocarcinoma, papillary cystadenoma, papillary cystadenocarcinoma, mesothelioma, sertoliform tubular adenoma, Sertoli's cell tumor, granulosa cell tumor, thecal cell tumor, polycystic sex cord/stromal tumor, and lipoid cell tumor. The histogenesis of the tumor types is discussed.

Adenocarcinoma↗
PubMed1987

Susceptibility of Aedes aegypti and Anopheles quadrimaculatus larvae to infection with the cercariae of Plagiorchis noblei (Trematoda: Plagiorchiidae).

The impact of interspecific behavioral differences on the relative susceptibility of third instar Aedes aegypti and Anopheles quadrimaculatus larvae to infection with cercariae of Plagiorchis noblei was determined. When permitted to move freely in a column of water, larvae of Ae. aegypti were significantly more susceptible to infection with the parasite than were An. quadrimaculatus larvae. This difference is ascribed to the significantly greater activity of Ae. aegypti larvae in the water column. Since cercariae are suspended in the column, particularly near the bottom, contact with larvae of Ae. aegypti may be enhanced, whereas contact with An. quadrimaculatus larvae, which tend to remain near the surface, may be reduced. Interspecific differences other than behavior are not thought to play a major role, since immobilized larvae of the two species did not differ significantly in their susceptibility to this parasite.

Aedes↗
PubMed1986

The effects of Plagiorchis noblei metacercariae on the development and survival of Aedes aegypti larvae in the laboratory.

Plagiorchis noblei infections impair the survival and development of fourth instar Aedes aegypti larvae. Mortality during the larval and pupal stages reached 92%, and 60% of the emerging adults were malformed. The metacercariae interfere with pupation and the emergence of adults. Larvae and pupae that fail to transform to the next developmental stage within the normal time characteristically persist for extended periods, but invariably die without transforming. Whereas 82% of the control larvae gave rise to functional adults, only 4% of infected larvae managed to do so. Such effects may facilitate the transmission of the parasite.

Aedes↗