Biomedical subjects
Publications and source records attributed to R W Mason.
Lesions typical of congenital toxoplasmosis were found in 5 aborted and stillborn kids. Serological findings in 2 of these kids and all their dams supported the diagnosis of congenital toxoplasmosis. In additon. Toxoplasma gondii was isolated from twin kids.
A cat fed commercially prepared cat food and free-living rats (Rattus rattus and R. norvegicus) passed coccidian oocysts which were morphologically similar to Toxoplasma gondii. Mice dosed with these oocysts did not develop toxoplasmosis, but instead developed small, thin-walled parasitic cysts containing small bradyzoites in their striated muscles. These cysts measured 35 to 90 micron by 9 to 40 micron and they resembled cysts of Hammondia hammondi. Unlike T. gondii this coccidian parasite was shown to have an obligatory two-host cycle and consequently it is considered to be H. hammondi. This represents the first recorded detection of H. hammondi in Australia. The source of the H. hammondi infection was a Rattus rattus. This represents the first record of a natural intermediate host for H. hammondi.
Plasma thyroxine concentrations were measured by radioimmunoassay in plasma samples from 691 lactating ewes in 26 areas of New South Wales, Queensland, Western Australia and Tasmania. Sheep sampled in New South Wales and Tasmania had significantly lower plasma thyroxine values (4.0 and 4.3 microgram/100 ml respectively) than those sampled in Queensland and Western Australia (5.4 and 5.3 microgram/100 ml respectively). However, sheep in some districts in southern Queensland also had low plasma thyroxine values. The areas where sheep had low plasma thyroxine values correlate well with areas where goitre has been previously reported, both in man and in domestic animals. This suggests that measurement of plasma thyroxine is probably a valid empirical method of assessing the relative iodine deficiency of grazing sheep and further that sheep grazing substantial areas of New South Wales, Tasmania and to a lesser extent Queensland may have thyroid dysfunction of varying degrees of severity. These findings could have implications for animal production in these areas.
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The physicochemical factors responsible for the aurothiomalate-albumin interaction were studied by a thermodynamic analysis of the binding of the anion to bovine albumin. The binding process was entropically driven and it was concluded that electrostatic bonding formed the basis of the aurothiomalate-albumin interaction. The binding of aurothiomalate to human plasma proteins at 37 degrees C and pH 7.45 and the modification of its binding by indomethacin and phenylbutazone was studied by ultrafiltration. Aurothiomalate was bound to human plasma albumin at a single site with an affinity constant of 6.1 X 10(3) M-1 and also at several sites of lower affinity. The plasma protein binding of the anion was increased in the presence of indomethacin and phenylbutazone. At therapeutic concentrations in vitro phenylbutazone significantly increased the plasma protein binding of aurothiomalate.
Five central nervous diseases are described and their relationships to previously recorded conditions are discussed. The conditions are congenital inclusion-body encephalopathy probably caused by a paramyxovirus infection, idiopathic neuraxial oedema of a newborn calf, focal symmetrical encephalomalacia of a young calf, yacca (Xanthorrhoea spp) poisoning of adult cattle leading to spinal demyelination, and focal demyelination and neuropathy in an adult cow.
The phenoxyalkanoix acids are bound to bovine serum albumin at a single site of high affinity, where the interaction is most importantly influenced by strong hydrophobic bonding, with ionic bonding being of lesser importance, and also at several sites of lower affinity. The hydrophobic binding site has almost equal affinity for the phenoxy groups of 2,4-dichlorophenoxyacetic acid, 4-(2,4-dichlorophenoxy)butyric acid and 2-(2,4,5-trichlorophenoxy)propionic acid and greater affinity for the phenoxy group of 2,4,5-trichlorophenoxyacetic acid. The properties of the high affinity binding site bear some resemblance to the properties of the amino acid sequence adjoining the tryptophan residue of human serum albumin, and evidence is presented for the presence of tryptophan at the high affinity binding site of bovine serum albumin.
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