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Biomedical subjects

D J Thornton

Publications and source records attributed to D J Thornton.

49 records · Page 3Linked to original sources
PubMed1989

Serum calcitriol and parathyroid hormone levels following prolonged infusion of calcitriol in vitamin D replete and depleted rabbits.

The objectives of this study are (1) to determine if serum calcitriol levels resulting from calcitriol infusion by subcutaneously implanted osmotic pumps are in proportion to dose, (2) to determine if such serum levels remain steady during the "pump-life" and (3) to determine if these increased calcitriol levels have an effect on serum parathyroid hormone (PTH) levels. A general objective of the study is to define a model whereby agents (calcitriol, and parathyroid hormone) suspected of enhancing absorption of metals other than calcium from the gastrointestinal tract could be evaluated individually by the levels of these hormones present in serum at a series of intervals during calcitriol infusion by osmotic pump. Calcitriol was infused into rabbits by subcutaneously implanted osmotic pumps at 3 different dosages (30, 60, and 100 IU/day) for 7 days and one dose (60 IU/day) for a 28 day period. The serum calcitriol levels initially rose markedly in all experimental rabbits in proportion to infused dosage and peaked at 3 days. The quantitative relationship between infused calcitriol and serum calcitriol at 3-5 days showed a correlation coefficient of 0.977 (P less than 0.005) for rabbits receiving the 7 day pumps with the 3 different dosages. There was subsequent decline of serum calcitriol which continued for the remainder of the pump-life, suggesting acceleration of degradation mechanisms. There was a sharp reduction in serum parathyroid hormone (PTH) levels 3-5 days after starting the calcitriol infusion, which was interpreted to result from direct suppression of PTH synthesis by calcitriol and/or the feedback effect of enhanced intestinal calcium absorption. Rabbits which had been depleted of vitamin D prior to implantation of the 28 day osmotic pumps showed a similar pattern of serum calcitriol and PTH. Multiple analyses within a single rabbit showed a reciprocal relationship between the serum calcitriol and PTH during the 28 days. There was a statistically significant negative correlation between these parameters (r = 0.635, P less than 0.05). The data indicate that despite a constant rate of infusion of calcitriol by osmotic pump, the levels of serum calcitriol and parathyroid hormone do not remain constant, but rather undergo marked changes. These findings demonstrate the necessity of monitoring blood levels, even in studies in which animals receive a constant infusion of calcitriol.

Animals↗
PubMed1987

A study of the interaction between cartilage proteoglycan and link protein.

The interaction between proteoglycan and link protein extracted from bovine articular cartilage (15-18-month-old animals) was investigated in 0.5 M-guanidinium chloride. The proteoglycans, radiolabelled as the aggregate (A1 fraction), were fractionated by two 'dissociative' density-gradient centrifugations (A1D1D1) followed by a rate-zonal centrifugation (S1) to yield an A1D1D1S1 preparation. At least 65% of these proteoglycans were able to bind to hyaluronate, but only 52% were able to bind to link protein as assessed by chromatography on Sepharose CL-2B. Over 80% of the [3H]link-protein preparation, radiolabelled as the aggregate, was able to interact with proteoglycan as assessed by chromatography on Sepharose CL-4B. Equilibrium-boundary-centrifugation studies performed at low link-protein concentrations (2.42 x 10(-9) M-5.93 x 10(-8) M) were analysed by Scatchard-type plots and indicated a Kd of 1.5 x 10(-8) M and a stoichiometry, n = 0.56, i.e. approx. 56% of those proteoglycans capable of binding to link protein had a strong site for link protein if a 1:1 stoichiometry were assumed. However, experiments performed at higher link-protein concentrations (3.5 x 10(-7) M and 8 x 10(-7) M) yielded stoichiometry values which were link-protein-concentration-dependent. Non-equilibrium binding studies using chromatography on Sepharose CL-2B and rate-zonal centrifugation yielded apparent stoichiometries between 0.6 and 7.5 link-protein molecules per proteoglycan monomer as a function of increasing link-protein concentration. It was concluded that a proportion of the proteoglycan molecules had a strong site for binding a single link protein (Kd 1.5 x 10(-8) M) and that at high link-protein concentrations a weaker, open-ended, process of link-protein self-association nucleated upon the strong link-protein-proteoglycan complex occurred. Hyaluronate oligosaccharides appeared to abolish a proportion of this self-association (as observed by Bonnet, Dunham & Hardingham [(1985) Biochem. J. 228, 77-85] in a study of link-protein-hyaluronate-oligosaccharide interactions) so as to leave a link protein:proteoglycan stoichiometry of 2. It is not clear whether this second link-protein molecule binds directly to the proteoglycan or to the first link protein.

Animals↗
PubMed1987

An enzyme-linked immunosorbent assay (ELISA) of denatured cartilage link protein.

Antiserum (MB007) was raised in rabbits to SDS-denatured cartilage link protein in order to develop an enzyme-linked immunosorbent assay (ELISA) to quantify link protein in cartilage extracts. The antibodies were characterized by using native and denatured link protein, either as the immobilised or the inhibiting antigen in the assay, and shown to bind more effectively to denatured link protein. At low concentrations, neither hyaluronate (0-30 micrograms/ml), proteoglycan (0-50 micrograms/ml) nor hyaluronate-binding region (0-3 micrograms/ml) competitively inhibited the link protein assay. However, at higher concentrations of proteoglycan (50 micrograms/ml-4 mg/ml) and hyaluronate-binding region (3-40 micrograms/ml) inhibition was observed. A more highly purified proteoglycan and a further purified hyaluronate-binding region preparation showed identical behaviour. The inhibition produced by proteoglycan and hyaluronate-binding region occurred at approximately equivalent molar concentrations (assuming Mr of 10(6) and 7 X 10(4), respectively). These results suggest that a significant proportion of these polyclonal antibodies recognize an epitope common to link protein and hyaluronate-binding region. However, the possibility that these effects are due to contamination with covalently bound link protein cannot be excluded. Trypsinated aggregates (0-10 micrograms/ml) produced no inhibition in the link protein ELISA, but as higher concentrations the inhibition was approximately 2000-fold lower than might have been expected from the link protein concentration present. Thus, the accessibility and/or binding of the antibodies to link protein was substantially decreased, illustrating masking of the link protein antigenic sites, as found by A. Ratcliffe and T.E. Hardingham (Biochem. J. 213 (1983) 371-378). These studies indicate that link protein in tissue extracts may be quantified in the concentration range 30-200 ng/ml and in the presence of hyaluronate, proteoglycan and hyaluronate-binding region, provided that both the immobilised and extracted link proteins are denatured.

Animals↗
PubMed1986

Electron-microscopic and electrophoretic studies of bovine femoral-head cartilage proteoglycan fractions.

Proteoglycans (A1D1) extracted from bovine femoral-head cartilage were examined by electron microscopy using benzyldimethylammonium chloride as a spreading agent. The preparation contained a mixture of particles, some with a 'beaded' structure and a contiguous filamentous 'tail' at one end and others which appeared as round 'blobs', some of which also had filamentous tails. Previous electron-microscopic studies of proteoglycan monomers have indicated that their length distributions were apparently unimodal, a finding that contrasted with agarose/polyacrylamide-gel-electrophoresis results, which generally indicated two bands. In the present study proteoglycans isolated from the slowly migrating electrophoretic band were shown to be predominantly the larger molecules of beaded appearance, whereas the rapidly migrating proteoglycans were predominantly molecules with the 'blob-like' appearance. Gel-filtration, isopycnic-density-gradient-centrifugation and rate-zonal-centrifugation techniques were evaluated as means of proteoglycan fractionation by electron microscopy and agarose-gel electrophoresis. Rate-zonal centrifugation in mixed-salt gradients of caesium chloride/4 M-guanidinium chloride yielded the most effective fractionation.

Animals↗
PubMed1984

An outbreak of Cotyledon orbiculata L. poisoning in a flock of Angora goat rams.

An acute outbreak of C. orbiculata L. poisoning in a flock of 16 Angora Goat rams is described. Typical signs of acute bufadienolide cardiac glycoside toxicity were manifested and 6 animals died. In the 2 animals examined histopathologically multiple foci of myocardial degeneration and necrosis were present. Treatment consisted, inter alia, of drenching with a mixture of activated charcoal, potassium chloride and a commercial preparation, Universal Antidote (Centaur) and parenteral administration of atropine sulphate.

Animals↗
PubMed1983

The glycosaminoglycans of pig colonic wall connective tissue.

Colon wall from pig, stripped of most of the mucosal layer to leave material largely composed of muscle, basement membrane, and extracellular matrix, was subjected to procedures for isolation of glycosaminoglycans. A total ethanol precipitate from a papain digest was fractionated by selective ethanol precipitation in the presence of Ca2+. Glycosaminoglycan fractions, freed proteolytically from a high molecular weight glycoprotein component, were further purified by Sepharose CL-6B gel-filtration or DE-52 anion-exchange chromatography. Glycosaminoglycans were identified by chemical composition, 13C-NMR spectroscopy and response to chondroitinase and nitrous acid degradations. The content of glycosaminoglycan in the tissue is low (0.05% dry weight) being comprised of dermatan sulphate (38%), heparin (34%), heparan sulphate (18%) and chondroitin sulphates (10%) as a percentage of total glycosaminoglycan content. Hyaluronic acid and keratan sulphate have not been detected. The composition is generally typical of a high muscle content tissue.

Animals↗
PubMed1977

Ganskweek (Lasiospermum bipinnatum) poisoning in cattle.

An outbreak of ganskweek poisoning in a herd of 93 cattle on a farm in the Graaff-Reinet district of the Cape Province is described. Five animals died and at least 16 others were affected. Clinical signs included nervous symptoms (intractability, wildness, aggressiveness), icterus, melaena, abdominal pain and photosensitisation. The most prominent lesions present in the one animal autopsied were a severe hepatopathy and haemorrhagic tendencies.

Animals↗
PubMed1975

Cat bite transmission of Yersinia pestis infection to man.

The transmission of bubonic plague from the kitten of a domestic cat to a man by means of a bite on a finger is described. The human case was complicated by the development of a secondary meningitis, followed, after specific therapy, by protracted recovery. The kitten showed swollen lymph nodes of the head and neck, frothing at the mouth and nostrils, and signs of an acute infectious disease which had a fatal termination. Yersinia pestis was isolated on about the 8th day from the cerebrospinal fluid of the man. The foster mother of the kitten exhibited signs of spinal and cerebral meningitis but recovered following treatment; her serum contained plague antibody levels of 1:512 and 1:1024 on the 22nd and 34th days respectively after the first evidence of illness. Three litter mates of the kitten also died. The outbreak occurred on a farm in the Graaff-Reinet district of the eastern Cape Province, which is situated about 160 km from the nearest known natural plague focus.

Animals↗
PubMedDate not supplied

Interaction between mycobacteria and mucus on a human respiratory tissue organ culture model with an air interface.

Mycobacteria adhere specifically to extracellular matrix (ECM) and mucus with a fibrous, but not globular, appearance, in organ cultures of human respiratory mucosa examined by scanning electron microscopy. Previously, light microscopy sections made of tissue infected for 7 days demonstrated mycobacteria associated with mucus on the organ culture surface, and within submucosal glands in areas of damaged epithelium. The authors have now investigated the interactions between Mycobacterium avium complex (MAC), Mycobacterium tuberculosis (MTB), and Mycobacterium smegmatis (MS) and mucus by preincubating bacteria with purified mucins MUC5AC and MUC5B prior to inoculation onto the organ culture mucosal surface. They have also measured mucin production by the organ culture after mycobacterial infection. Mucus did not cause clumping of mycobacteria. There was a significant (P=.03) increase in the amount of fibrous mucus, but not globular mucus, observed on tissue inoculated with mucins compared to controls. The number of bacteria adhering to ECM was markedly reduced after incubation with mucins, which could indicate a protective effect. Mycobacterial infection did not increase mucin production by the organ culture. Mycobacterial adherence to mucins may play a role in the pathogenicity of mycobacteria in diseases such as cystic fibrosis, bronchiectasis, and chronic obstructive pulmonary disease (COPD), in which there are changes in mucus composition and clearance.

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