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Biomedical subjects

R A Wilson

Publications and source records attributed to R A Wilson.

At least 253 records · Page 14Linked to original sources
PubMed1983

Effect of glucose-insulin-potassium infusion on thallium myocardial clearance.

Factors influencing the rate of 201Tl clearance from the myocardium have not been clearly defined. This study determined the effect of an intravenous infusion of glucose-insulin-potassium (GIK) on the net 201Tl clearance rates from myocardium with and without initial 201Tl loading. Anesthetized open-chest dogs underwent 5 min of left anterior descending coronary artery occlusion and intravenous 201Tl was injected and the occlusion released 5 min later. Thirty minutes after 201Tl injection, 30 ml of either GIK (nine dogs) or saline (five dogs) was infused intravenously. The clearance rates of 201Tl from the anterior wall (without initial 201Tl loading) and from the posterior wall (with initial 201Tl loading) were monitored with miniaturized cadmium telluride detectors placed on the myocardium. Calculation of net myocardial clearance rates was performed by linear regression analysis from serial 1 min counts. Compared with saline infusion, GIK increased the net clearance of 201Tl from both myocardial regions with and without initial loading. The most marked change induced by GIK infusion was in the myocardial region without initial 201Tl loading; a net increase in 201Tl activity (72 +/- 42 cpm/30 min) was converted into a net loss (-594 +/- 228 cpm/30 min). There was no significant change in 201Tl clearance after the saline infusion. Heart rate, aortic and left atrial pressure, sonomicrometer-measured transmural myocardial wall thickness, microsphere-determined myocardial blood flow, and blood glucose and potassium concentrations did not change significantly during GIK or saline infusions. Thus, GIK infusion appears to increase net 201Tl clearance from myocardial zones with and without initial 201Tl loading.

Animals↗
PubMed1982

Transmission of Schistosoma mansoni from man to snail: experimental studies of miracidial survival and infectivity in relation to larval age, water temperature, host size and host age.

We report the results of experimental work on (a) the influence of temperature on the age-dependent survival and infectivity of the miracidia of Schistosoma mansoni and (b) the relationship between snail age, snail size and susceptibility to infection. The death rate of miracidia declined exponentially with age where life-expectancy was maximal (approximately 16 h) at 15 degrees C. Infectivity also declined rapidly with larval age but, in contrast to larval survival, the rate of infection was at a maximum at 25 degrees C. Snail susceptibility was shown to be more closely correlated with host size rather than host age. Susceptibility declined exponentially with increased host size. Size-dependent susceptibility was shown to generate concave age-prevalence curves for infection within snail populations, where the maximum prevalence is generated in snails of intermediary age. Simple mathematical models are developed to aid estimation of larval survival and infection rates and experimental results are discussed in relation to the overall transmission success of the parasite from man to snail.

Aging↗
PubMed1982

Transmission of Schistosoma mansoni from man to snail: laboratory studies on the influence of snail and miracidial densities on transmission success.

The relationship between infection success, the density of Schistosoma mansoni miracidia and the density of the snail host Biomphalaria glabrata was examined experimentally. Within laboratory infection arenas, the distribution of miracidial infections/snail was approximately uniform and the net rate of snail infection was directly positive binomial to miracidial density. In contrast, however, the rate of infection declined exponentially as snail density increased. Mathematical models are developed to aid in the estimation of infection rates and experimental results are discussed in the context of the transmission dynamics of schistosomiasis.

Animals↗
PubMed1981

Passive immunity of the G. I. tract.

The need for continued pursuit to identify all of the components necessary for effective passive immunity is obvious. With a focus upon natural phenomenon, we need to expand our understanding of antigenic modulation while determining the distribution of specific antibodies among the various isotypes available in lacteal secretions and capable of transfer to the intestinal tract of the neonate and broaden the scope of investigations to include the significance of cell mediated immune mechanisms present in lacteal secretions. Passively acquired immunocytes, plasma cells, macrophages and polymorphonuclear leucocytes may contribute to the immune status of suckling ruminants.

Animals↗
PubMed1980

The parasitic castration and gigantism of Lymnaea truncatula infected with the larval stages of Fasciola hepatica.

The shells of Lymnaea truncatula infected with the larval stages of Fasciola hepatica were significantly longer than those of comparable uninfected controls. The dry mass (tissue, shell + parasite) of the same infected snails, 56 days after infection, was approximately twice that of the controls (tissue + shell). The increased mass of infected snails was not due to a disproportionate increase in shell weight relative to tissues. Infected snails maintained at 20 degrees C had virtually ceased egg production by 21 days post-infection whereas control snails continued to lay eggs steadily for the duration of the experiment. The dry mass of snail tissue plus the cumulative dry weight of eggs produced was taken as an indication of the ability of control snails to generate biomass. Similarly the tissue mass plus cumulative egg weight and parasite weight was taken as an indication of the ability of the infected snails to generate biomass. The control and infected snails were not significantly different in this respect indicating that the gigantism of infected snails could be the result of a switch in nutrient supply from reproduction to somatic tissue growth and parasite growth. Castration was brought about 17-21 days after infection as a result of the direct consumption of the ovotestis by a proportion of the redial population. In a separate experiment it was demonstrated that a population of infected snails maintained at 20 degrees C survived as long as a similar group of control snails. The findings with this host-parasite system are discussed in relation to possible mechanisms causing castration and gigantism in other digene-snail interactions, and in relation to parasitic castration in other groups. It is concluded that the observed gigantism of infected snails is more likely to have a nutritional rather than endocrine origin.

Animals↗
PubMed1980

An examination of the skin phase of schistosome migration using a hamster cheek pouch preparation.

A living hamster cheek pouch preparation has been used to study the skin phase of schistosomulum migration. Between 0 and 16 h post-exposure schistosomula become increasingly difficult to see and lateral movement in the skin ceases. Up to 50 h post-exposure they remain poorly visible. They lie in fluid-filled lacunae within the epidermis, external to the basement membrane. The first schistosomula enter the dermis from 40 h post-exposure, approximately half having done so by 52.5 h. Coincidentally, they can be more easily distinguished from surrounding tissue. Up to 91% of original penetrants have been observed alive in pouch tissue at 65 h post-exposure. Since only 26% eventually mature in the hepatic portal system there would appear to be considerable attrition subsequent to the skin phase of migration. The mean diameter of venules penetrated was 22.7 micrometers and the mean time taken to penetrate was 8.01 h. The majority of schistosomula left the pouch between 60 and 80 h post-exposure.

Animals↗
PubMed1980

Metabolic changes associated with the migration of the schistosomulum of Schistosoma mansoni in the mammal host.

A variety of measurements was made on small samples of schistosomula recovered from the skin, lungs and hepatic portal system of percutaneously infected mice, on the basis of which development could be divided into a migration and a growth phase. The density of schistosomula, estimated using a Ficoll gradient, was found not to vary significantly between Day 0 and Day 24 post-infection, having a mean value of 1.077. The reduced weight was measured by means of a Cartesian diver balance and used in conjunction with density to estimate the change in wet weight of schistosomula. Wet weight was found to decline slightly during the migration phase and to increase exponentially following arrival of schistosomula in the hepatic portal system. No change in nitrogen content was detected during migration but there was a rapid increase after arrival in the hepatic portal system. The rate of oxygen consumption, measured by Cartesian diver respirometer, declined significantly during migration and then increased exponentially after arrival of worms in the hepatic portal system. No change was detected in the lactic dehydrogenase activity of migrating worms but again, an exponential increase occurred after entry into the hepatic portal system. It was concluded that the migrating schistosomulum is in a semi-quiescent metabolic state, although it possesses the ability to take up nutrients and undergoes morphological changes. Growth is triggered by an unknown mechanism after arrival in the hepatic portal system. Examination of the various sets of data suggests that it is initiated between 10 and 11 days post-infection in the most advanced schistosomula.

Animals↗
PubMed1980

The survival of the cercariae of Schistosoma mansoni in relation to water temperature and glycogen utilization.

Survival curves for cercariae of Schistosoma mansoni maintained at different temperatures were determined. Between 15 and 35 degrees C the curves were of reverse sigmoid form and the probit transformation gave a statistically good fit. The slope of the regression lines fitted to the probit transformation increased exponentially as the temperature rose. Above 35 degrees C heat intolerance became important and increased exponentially as the temperature rose. Below 15 degrees C, cold intolerance caused an initial high level of mortality followed by an extended period with insignificant mortality. The glycogen content of whole cercariae and separated cercarial bodies and tails was measured during ageing. The glycogen content of whole cercariae declined exponentially during ageing. This was a product of exponential decreases in the glycogen content of both the body and the tail of the organism. The cercarial tail was shown to contain slightly over half of the total glycogen content. The rate of glycogen use was higher in the tail than in the body. A computer simulation model was used to demonstrate that the observed exponential use of glycogen could generate survival curves similar to those observed experimentally.

Aging↗
PubMed1980

Schistosoma mansoni: a scanning electron microscope study of the developing schistosomulum.

The surface morphology of schistosomula extracted from the skin, lungs and hepatic portal system (hps) of mice was investigated from Days 0 to 18 post-infection. Skin schistosomula and newly arrived schistosomula from the hps were of similar dimensions but were morphologically distinct. Lung schistosomula were considerably elongated with an estimated 53% increase in surface area compared to skin schistosomula. The pitted tegument of lung schistosomula was formed into ridges and troughs. These were compressed together in contracted individuals recovered from the hps on Day 10. The annular ridges were cross-linked by longitudinal septae which possibly prevent further elongation of the body. A regression of the spines between the mouth and the ventral sucker was observed in Day 2 skin schistosomula. In lung schistosomula only the spines at the anterior and posterior of the body remained. New spines were formed after the schistosomula reached the hps. It is suggested that the spines in the mid-region of the body are selectively disassembled and that their loss facilities migration along the lumina of capillaries with the residual spines acting as anterior and posterior anchors. The mouth opening was enlarged in schistosomula from the hps recovered from Day 10 onwards. Skin schistosomula lost the cercarial apical tegumentary ridges between 24 and 48 h after penetration but a spineless protrusible area remained. After arrival in the hps this area became integrated into the anterior surface as the oral sucker developed around the sub-terminal mouth. The cercarial ciliated papillae were lost on penetration. The migrating schistosomulum had few visible sensory papillae but following arrival in the hps new papillae were observed.

Animals↗
PubMed1979

Synthesis of macromolecules by the epithelial surfaces of Schistosoma mansoni: an autoradiographic study.

The use of tritiated leucine as a marker for protein synthesis and of tritiated glucosamine as a marker for polysaccharide/glycoprotein synthesis, is described. Adult worms were pulse-labelled by incubation in medium containing the substrate. Labelled worms were then incubated in chase medium, without labelled substrate, for varying lengths of time before fixation. The distribution of label which had been incorporated into macromolecules in the worm tissues, was examined by light and electron microscope autoradiography. It was estimated that the tegument and tegument cell bodies were the source of 67--80%, and the gut epithelium of 20--30%, of exportable leucine-containing protein. Conversely, the gut epithelium was the source of 72%, and the tegument cells 28%, of exportable glucosamine-containing polysaccharide. The specific activity of labelled protein reached a peak in the tegument cytoplasm after 1.5 h of chase incubation. Half of the labelled protein was secreted into the worm's environment by 3 h of chase incubation. The half-life of secretory protein in gut cells appears to be around 2 h. Labelled protein disappears from the gut lumen relatively rapidly but labelled polysaccharide remains in the lumen at high specific activity for at least 24 h. The major carbohydrate labelled may be the glycocalyx on the luminal surface of the gut epithelial cells. The results suggest that the bulk of worm secretions have a rapid turnover with a half-life of a few hours. Against this background of rapid mass secretion a slower process of membrane turnover would be difficult to detect and quantitatively small.

Animals↗
PubMed1979

Schistosoma mansoni: a histological study of migration in the laboratory mouse.

Quantitative histological methods were applied in a study of the migratory route of schistosomula within the definitive mammal host. The observations are consistent with an entirely intravascular mode of migration in the direction of blood flow. They do not support a trans-diaphragm route. Schistosomula can be identified in low numbers in systemic organs, in the left side of the heart and in the venous compartment of the pulmonary circulation. They were not observed penetrating the diaphragm or the capsule of the liver. No histopathological evidence was found to suggest that the tissue responses of previously unexposed hosts affect migrating schistosomula at any stage during migration. These non-specific tissue responses were marked only in the skin phase of migration.

Animals↗
PubMed1978

A comparative study of 14 cases of familial and nonfamilial pheochromocytomas.

A comparison is made between epidemiological features found in a group of 14 patients with familial and nonfamilial pheochromocytomas at M. D. Anderson Hospital and Tumor Institute. The Sipple syndrome (familial) group comprised eitht patients from three different families, and the nonfamilial group consisted of six nonrelated patients. The main differences were noted in the age of onset, sex ratio, bilaterality, malignant behavior, and occurrence of a second nonendocrine primary tumor. An attempt was made by light microscopy to define features that would indicate malignant behavior. No such features could be delineated. Survival time was unrelated to the presence of pheochromocytoma except in operative and investigative procedures.

Adrenal Gland Neoplasms↗
PubMed1978

The effect of variations in host and parasite density on the level of parasitization of Lymnaea truncatula by Fasciola hepatica.

Groups of the snail Lymnaea truncatula, maintained at a range of spatial densities, were exposed to different densities of miracidia of Fasiola hepatica. The resulting degree of parasitization was measured 3--4 weeks after infection. The relationship between parasite densities and parasitization appeared to be curvilinear. The lower than expected parasitization at high parasite densities could be explained by the multiple infection of some snails by two or more miracidia. The level of parasitization was not related exponentially to the temperature at which infection was carried out. This was thought to be due to the inverse relationship between miracidial longevity and swimming speed, with respect to temperature. A depth of free water overlying a mud surface was an absolute requirement for miracidia to successfully infect snails.

Animals↗