No description available.

The absorption and distribution of metals via the gut of fish is not well known. Consequently, the aim of the present study was to describe the movement of metals along the gut, their absorption and binding to gut tissues, and their distribution to the internal tissues following model dietary exposure. Two different approaches were employed, an in vivo gastric dosing procedure, and an in vitro gut bag protocol and two different metals were studied: an essential metal, zinc, and a non-essential (and more toxic) metal, cadmium. The dietary uptake and distribution of zinc and cadmium to 0.3 kg rainbow trout (Oncorhynchus mykiss) was examined at l5°C at 1, 2, 3, or 7 days following a single bolus dose to the stomach of 0.5 mM of radio labelled metaL After exposure, all internal organs and the remaining carcass were individually counted for radioactivity. Uptake, distribution and excretion of both zinc and cadmium was rapid, occurring largely within the first 24 h of exposure. By 24 h, fish exposed to Zn had absorbed 20.0% of the dose, 21.0% was bound in the gastrointestinal tissues and the remainder was either excreted (38.1 %) or was present in the gut lumen (20.9%). Cadmium showed a much different pattern of uptake, with only 2.9% of the dose absorbed after 24 h, and the remainder found either in the gut tissue (30.2%) and the lumen (19.0%) or excreted (47.9%). Over the following six days, very little uptake and internal metal redistribution occurred.When exposed to higher doses of metal in vivo (0.5 - 50 mM), there were distinct differences in the handling of the two metals. Zinc concentrations in the gut tissues continued to rise at higher doses until apparent saturation. In contrast, gut tissues were saturated with cadmium at the lowest dose employed (0.5 mM). Both metals bound most avidly to the distal intestine but all gut tissues had a higher binding capacity for zinc, as compared to cadmium. Target tissues (liver, gills, kidney) all saturated with zinc at high doses. In contrast, cadmium concentrations in these tissues continued to rise in a linear fashion with increasing dose. In vitro studies revealed that the most important region of the gut for metal uptake in rainbow trout was the mid-intestine. Studies using the metabolic uncoupler, 2,4-DNP, suggested that the transfer of both zinc and cadmium across intestinal cells was passive at the brush border membrane, but was at least partly dependent on A TP for movement across the basolateral membrane. Furthermore, this transport mechanism was not shared by calcium, as the presence of calcium had no inhibitory effect on the transport of either metal. Mucus within the intestinal lumen appears to have a higher binding affinity but lower capacity for cadmium than zinc. Calcium did not displace cadmium from the mucus layer. In contrast, zinc was displaced by an equimolar exposure to calcium in the medium. Gut mucus apparently impedes the movement of metals along the intestine with the extent of the delay likely being related to the binding affinity of the metal. The impediment was greatest for cadmium, as 10% of the metal remained in the lumen of fish exposed in vivo, after a period of7 days. In contrast, only 2% ofthe original dose of zinc remained in the gut lumen after only 3 days. / Thesis / Master of Science (MSc)

The main concern of this thesis is with desmoplasia - a process in which excessive connective tissue is deposited in a neoplasm. This is a common phenomenon in neoplasia but one whose mechanisms are poorly understood. To study the process, I used a human malignant melanoma cell line (UCT-Mel 7) that was established in this laboratory and that, when injected into athymic mice, gave rise to tumours that showed a number of interesting features. Firstly, the tumour induced a marked desmoplastic response as evidenced by a high content of hydroxyproline in tumour lysates, intense staining for reticulin in sections of the tumour and infiltration of the tumour by host mesenchymal cells. Secondly, the desmoplasia was associated in UCT-Mel 7-derived tumours with an unusual phasic pattern of growth that was related to the in vitro passage number of the melanoma cells. On occasions, murine tumours developed at the site of inoculation of human tumour cells. I have identified 2 possible mechanisms by which UCT-Mel 7 cells could have induced the desmoplastic response: either the tumour cells could have exerted their effect indirectly, i.e. via macrophages, or they could have stimulated the host's stromal cells directly. UCT-Mel 7 cells were shown to be chemotactic for mouse macrophages and human foreskin fibroblasts were stimulated, in a dose-dependent manner, to synthesize increased amounts of collagen when co-cultured with mouse peritoneal exudate cells. Stimulation could only be effected by direct cell:cell contact; medium conditioned by macrophages was not effective. The amount of stimulation was not dependent on the state of activation of the peritoneal cells nor on the strain of mouse used. Tumour cells were also found to act directly. Co-culture of UCT-Mel 7 cells and fibroblasts resulted in increased collagen synthesis by the fibroblasts. Increased synthesis of the protein was reflected in an increase in the amount of collagen mRNA. UCT-Mel 7 cell stimulated in a dose-dependent manner with an absolute requirement for intimate cell:cell contact with the fibroblasts. DNA synthesis was not required. Dexamethasone, retinoic acid and the tumour promoter, phorbol myristate acetate, had significant primary effects on fibroblast collagen synthesis but did not modify the response to melanoma cells. Indomethacin, however, had a minimal primary effect upon the fibroblasts but significantly augmented the melanoma cell effect. The nature of the stimulatory cell:cell contact is still uncertain. The gap junction inhibitor, α-glycyrrhetinic acid, did not diminish the melanoma cell effect. Preliminary findings suggested that cell-surface proteoglycans may be important. Removal of the proteoglycans with the inhibitor of proteoglycan assembly, 4-methylumbelliferyl-β-D-xyloside, abrogated the melanoma cell:fibroblast interaction. Recombinant basic fibroblast growth factor did. not seem to be involved in the desmoplastic response. It was of incidental interest to note that this compound inhibited fibroblast collagen synthesis in a manner that was augmented by the concomitant addition of heparin. A surprising finding was the production of a potent inhibitor of collagen synthesis by superinduced cells of the mouse macrophage cell line, P388D₁. This inhibitor has not been fully characterised.

Vita. / Digitized by Kansas Correctional Industries

Typescript (photocopy) / Digitized by Kansas Correctional Industries

Call number: LD2668 .T4 1957 C37 / Master of Science

No description available.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

published_or_final_version / abstract / Medicine / Master / Master of Philosophy

published_or_final_version / Medicine / Doctoral / Doctor of Philosophy