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Biomedical subjects

P A Parsons

Publications and source records attributed to P A Parsons.

At least 19 recordsLinked to original sources
PubMed1995

Inherited stress resistance and longevity: a stress theory of ageing.

Ageing is considered in the context of the abiotic stresses to which free-living organisms are normally exposed. Assuming that the primary target of selection of stress is at the level of energy carriers, trade-offs under the rate-of-living theory of ageing predict increased longevity from selection for stress resistance. Changes in longevity then become incidental to selection for stress resistance. I therefore suggest the reformulation of the rate-of-living theory to become a stress theory of ageing. This directly incorporates the characteristics of habitats in nature. Under this theory, the primary trait inherited is resistance to stress. Consequently, at extreme ages those with inherited resistance to abiotic stress should dominate. Furthermore, the reduction in homeostasis manifested by deteriorating ability to adapt to abiotic stress as ageing proceeds, should be slowest in those surviving longest.

Aging↗
PubMed1992

Fluctuating asymmetry: a biological monitor of environmental and genomic stress.

Increased fluctuating asymmetry (FA) of morphological traits occurs under environmental and genomic stress. Such conditions will therefore lead to a reduction in developmental homeostasis. Based upon temperature extreme experiments, relatively severe stress is needed to increase FA under field conditions. Increasing asymmetry tends, therefore, to occur in stressed marginal habitats. Genetic perturbations implying genomic stress include certain specific genes, directional selection, inbreeding, and chromosome balance alterations. It is for these reasons that transgenic organisms may show increased FA. As there is evidence that the effects of genomic and environmental stress are cumulative, organisms in a state of genomic stress may provide sensitive biological monitors of environmental stress.

Animals↗
PubMed1991

Monoclonal immunofluorescence compared with silver stain for investigating Pneumocystis carinii pneumonia.

Two hundred and eighty two specimens from 220 patients positive for HIV with respiratory tract symptoms, or febrile illness, or both, were examined for the presence of Pneumocystis carinii. Specimens were either induced sputum samples or bronchoalveolar lavage fluids. To establish the optimal method for laboratory diagnosis a comparison was made of detection of the organism by use of monoclonal antibody and immunofluorescence with conventional silver staining methods. Three commercially available reagents for immunofluorescence were also compared. Immunofluorescence was significantly more sensitive than the silver stain and the best results for immunofluorescence were obtained using. Northumbria Biologicals Ltd reagents.

Bronchoalveolar Lavage Fluid↗
PubMed1990

Radiation hormesis: an evolutionary expectation and the evidence.

Fundamental to evolutionary biology is the tendency for organisms to become progressively adapted to those environments to which they are most frequently exposed. Since background radiation is a universal component of our environment, radiation hormesis is an evolutionary expectation. Whole-of-life experiments and more numerous (and evolutionarily more artificial) shorter duration and higher dose-rate experiments are consistent with this expectation. Additional research is needed especially at the molecular level to search for underlying mechanisms, and implications for radiation protection guidelines need to be analyzed.

Adaptation, Physiological↗
PubMed1990

Fluctuating asymmetry: an epigenetic measure of stress.

(1) Fluctuating asymmetry (FA) is a useful trait for monitoring stress in the laboratory and in natural environments. (2) Both genomic and environmental changes can increase FA which represents a deterioration in developmental homeostasis apparent in adult morphology. Genetic perturbations include intense directional selection and certain specific genes. Environmental perturbations include temperature extremes in particular, protein deprivation, audiogenic stress, and exposure to pollutants. (3) There is a negative association between FA and heterozygosity in a range of taxa especially fish, a result consistent with FA being a measure of fitness. (4) Scattered reports on non-experimental populations are consistent with experiments under controlled laboratory conditions. FA tends to increase as habitats become ecologically marginal; this includes exposure to environmental toxicants. (5) In our own species, FA of an increasing range of traits has been related to both environmental and genomic stress. (6) Domestication increases FA of the strength of homologous long bones of vertebrate species due to a relaxation of natural selection. (7) FA levels are paralleled by the incidence of skeletal abnormalities in stressful environments. (8) Increased FA is a reflection of poorer developmental homeostasis at the molecular, chromosomal and epigenetic levels.

Animals↗
PubMed1989

Selection for increased desiccation resistance in Drosophila melanogaster: additive genetic control and correlated responses for other stresses.

Previously we found that Drosophila melanogaster lines selected for increased desiccation resistance have lowered metabolic rate and behavioral activity levels, and show correlated responses for resistance to starvation and a toxic ethanol level. These results were consistent with a prediction that increased resistance to many environmental stresses may be genetically correlated because of a reduction in metabolic energy expenditure. Here we present experiments on the genetic basis of the selection response and extend the study of correlated responses to other stresses. The response to selection was not sex-specific and involved X-linked and autosomal genes acting additively. Activity differences contributed little to differences in desiccation resistance between selected and control lines. Selected lines had lower metabolic rates than controls in darkness when activity was inhibited. Adults from selected lines showed increased resistance to a heat shock, 60Co-gamma-radiation, and acute ethanol and acetic acid stress. The desiccation, ethanol and starvation resistance of isofemale lines set up from the F2s of a cross between one of the selected and one of the control lines were correlated. Selected and control lines did not differ in ether-extractable lipid content or in resistance to acetone, ether or a cold shock.

Acetates↗
PubMed1989

Oesophageal symptoms, their causes, treatment, and prognosis in patients with the acquired immunodeficiency syndrome.

In a prospective study of 154 AIDS patients, 48 (31%) complained of pain on swallowing both liquids and solids and 32 (21%) of these also had dysphagia. While candidiasis was the most common cause of symptoms (26 patients), discrete ulceration of the oesophagus occurred in 12 instances in 10 patients (four cytomegalovirus, four herpes simplex virus, three aphthous ulcer, one peptic ulcer). One patient had a diffuse oesophagitis caused by Mycobacterium avium intracellulare. No cause was found for the oesophageal symptoms in four patients. Kaposi's sarcoma (KS) was found in seven patients associated with other pathology in four. All 26 patients with oesophageal candidiasis only, also had oral involvement. All the patients with herpes simplex virus (four) and aphthous ulcers (three) had obvious perioral involvement. Three of the four patients with cytomegalovirus ulceration had evidence of disease elsewhere (colon or retina). All patients with Kaposi's sarcoma lesions had skin and buccal cavity involvement. The cause of oesophageal disease was usually obvious at endoscopy. The appearance of candidiasis was typical and the various ulcerating lesions also had different macroscopic configurations. Cytomegalovirus infection produced deep linear ulcers in the distal oesophagus, herpes simplex oesophagitis is similar in appearance to the typical perioral lesions of fluid filled vesicles. Diagnostic radiology was not helpful in most patients. In nine of 17 patients with candidiasis, the barium swallow examination performed within 24 hours of presentation was normal. In only three of seven patients with oesophageal ulceration (three cytomegalovirus, two herpes simplex virus, one aphthous, one peptic) was there evidence of an abnormality. Treatment produces symptomatic relief. All patients with candidiasis responded to ketoconazole, the four with herpes simplex virus to acyclovir and one of three with aphthous ulceration had a dramatic response to thalidomide. The three patients with cytomegalovirus infection who were treated with foscarnet had a prolonged remission of symptoms. The overall prognosis of patients with oesophageal symptoms is poor, with an average survival time from a definitive diagnosis of five months (range one to 13).

Acquired Immunodeficiency Syndrome↗
PubMed1982

Permeability of canine submandibular glands to blood-borne horseradish peroxidase during parasympathetic secretion.

Potential permeability pathways exist between central acinar cells in submandibular glands of dogs and they are large enough to allow the passage of molecules of horseradish peroxidase (HRP) under certain conditions. During gentle submandibular secretion caused by parasympathetic nerve stimulation detectable amounts of HRP passed into the saliva as long as the concentration of HRP in the blood reaching the gland was high enough. Morphological results indicated that the passage was mainly via leaky junctions between acinar cells. It is likely that this movement was by passive permeation because it required a high concentration gradient, was slow to occur and gradually reached a peak; the actual amounts to reach the saliva under physiological conditions were small and depended on the effective concentration of HRP reaching the gland. A satisfactory reproducible secretory regime has been developed, using short periods of stimulation alternating with rest pauses. Using these conditions gradually increasing amounts of HRP reached the saliva and first samples of saliva during each stimulation period contained more HRP than subsequent samples from the same stimulation period. It is possible that contraction of myoepithelial cells, at the outset of each stimulation period, contributed to this increased movement by acting on HRP-containing fluid in spaces between themselves and the acinar cells, thereby causing an increased filtration pressure to be exerted on underlying tight junctions.

Animals↗
PubMed1982

Permeability of canine submandibular glands to blood-borne horseradish peroxidase: effects of transient ductal obstruction during secretion.

Outflow obstruction of the submandibular duct, for a short period during parasympathetic secretion, caused an increase in glandular permeability to horseradish peroxidase. Higher frequencies of parasympathetic nerve stimulation during the obstructive period induced greater increases in the permeability. It is likely that the intraluminal distensions had disrupted some tight junctions and so permitted a greater paracellular leakiness. The damage tended to induce ballooning between striated ductal cells, similar to the appearances observed by Emmelin, Garrett & Gjörstrup (1977 a) when sympathetic secretion was accompanied by myoepithelial contraction against a raised outflow pressure. The present results have been compared with experimental data from other workers and give support to the idea that tight junctions can behave in a sieve-like manner towards the back-diffusion of molecules across them. This work indicates that there is a great need for care in permeability studies. It is possible that some permeability changes observed by other workers may have been the consequences of physical damage between cells. Our findings reinforce the need for morphological assessment of the glands after permeability experiments. In man it is likely that naturally occurring or artificially induced obstructive events may at times create similar permeability changes and these may enable protective substances to pass from the blood to the saliva. This affords possible explanation for such phenomena as the therapeutic value that often accrues from sialography and the efficacy of many different antibiotics in obstructive sialadenitis, despite the fact that most antibiotics do not normally permeate to the saliva.

Animals↗
PubMed1981

Permeability of submandibular salivary glands in dogs to blood-borne horseradish peroxidase (HRP). I. Perarterial bolus injection in "resting" glands.

Horseradish peroxidase (HRP) was administered to the submandibular glands of dogs by close-arterial bolus-type injections, and its localisation was examined histochemically by light and electron microscopy. The HRP became widespread in the interstices of the glands and reached many central acinar lumina via scattered localised parts of their "tight" junctional complexes. Reaction product was less often found in the lumina of demilunes, which suggested that the intercellular junctions there were less "leaky". HRP was often found in sizeable spaces between myoepithelial cells and the underlying parenchymal cells; such large spaces have not been observed in this situation in other species. The possibility that permeability pathways may arise intermittently at different sites in the adhering mechanisms between the acinar cells is discussed. It is concluded that potential paracellular permeability pathways for macromolecules exist in these glands and, if the concentration gradient is sufficiently high, molecules even as large as those of HRP can to some extent permeate passively from the interstices to the saliva. In "resting" glands the principal permeability site is between the central acinar cells.

Animals↗
PubMed1981

Sexual isolation among isofemale strains within a population of Drosophila immigrans.

Eight isofemale strains of the cosmopolitan species Drosophila immigrans derived from single location in Melbourne, Australia, were crossed in all combinations to test for sexual isolation. Statistically significant sexual isolation occurred in 12 of 28 crosses, with one strain showing significant isolation from the other seven. There were significantly unequal male mating propensities (relative rates of mating) in 7 of the 28 crosses.

Animals↗
PubMed1980

Acetic acid vapour as a resource: threshold differences among three Drosophila species.

Acetic acid vapour is utilized as an energy source up to a threshold where it becomes a stress in 3 Drosophila species. The threshold ranking is D. melanogaster much greater than D. simulans greater than D. immigrans, which qualitatively parallels that for ethanol. The capacity to use nutritive vapours appears to be very important in Drosophila ecology.

Acetates↗
PubMed1980

Genetic variability of alcohol dehydrogenase among Australian Drosophila species: correlation of ADH biochemical phenotype with ethanol resource utilization.

Alcohol dehydrogenase (ADH) activities, electrophoretic phenotypes, and the extent of ethanol resource utilization are compared for three groups of species distinguishable on ecological criteria: 1) the cosmopolitan species D. melanogaster, a frequent inhabitant of wineries; 2) fruit-baited species of the typically Australian subgenus Scaptodrosophila: D. lativittata, D. nitidithorax and D. howensis; and 3) Scaptodrosophila species not attracted to fermented-fruit baits being collected by sweeping in temperate rain forests (D. inornata, D. collessi) or from Hibiscus flowers (D. hibisci). D. melanogaster showed the highest levels of ADH activity and an electrophoretic polymorphism with two active allelic forms, while group 2) species showed intermediate ADH activities and polymorphisms, which were consistent with "high activity" and "low activity" allelic forms in natural populations of these species, and group 3) species showed only "low activity" forms. Ethanol resource utilization follows the same sequence, being 1 greater than 2 greater than 3 (D. howensis and D. collessi were not tested). Therefore the species considered show an association of ADH biochemical phenotype, laboratory ethanol utilization, and resources utilized.

Alcohol Oxidoreductases↗