This thesis is an account of studies made on the distribution and nature of acid mucopolysaccharides in the mammalian renal papilla. The papilla was found to be the only region of the kidney which has an appreciable extracellular space with acid mucopolysaccharide enmeshed in connective tissue fibres. Animals are unable to secrete urine which is either more concentrated or more dilute than plasma unless the tonicity of this region is greater than that of plasma. In the first part of this work (Chapter 2) the extent of extracellular acid mucopolysaccharide was correlated with the ability of the species to conserve water. It was found that the papilla could be sharply delineated by staining the acid mucopolysaccharide within it. This had the advantage over the less distinct cut surface appearances in that it was possible accurately to measure the length of the papilla in relation to that of the cortex and medulla in stained sections. An empirical relationship between the development of the papilla and the ability to secrete hypertonic urine was obtained for a number of species: U_max = 1.74 (Mandprime;/Candprime;) + 0.6, where U_max is the maximum concentration in Osmols/litre that can be achieved in the urine; Mandprime; is the length of the papilla, measured as the distance of the region containing extracellular acid mucopolysaccharide from the papillary tip towards the renal cortex; and Candprime; is the continuation of this line through the medulla and cortex. The correlation coefficient for the six species for which figures for maximum urinary concentration were known was 0.9. The significance of this expression is discussed in Chapter 2 in relation to a similar equation put forward by Black in 1965. The morphology of the connective tissue in the papilla of the guinea pig was examined by light and electron microscopy (Chapter 3) and by histochemistry (Chapter 4). The histological results were correlated with the electrophoretic and staining characteristics of acid mucopolysaccharides extracted from this region. There was very little collagen of the adult type to be found in the papilla. The main fibrillar component was reticulin which was well demonstrated by silver impregnation and the periodic acid - Schiff technique. Within the reticulin mesh another class of PAS positive fibril was found which, in addition, stained positively for anionic groups. These fibrils could not be impregnated with silver. In the electron microscope the second class of fibril was seen not to be banded and to be smaller than the reticulin fibrils. The histochemical results (Chapter 4) showed that the largest part of the amorphous extracellular acid mucopolysaccharide in the papilla was hyaluronic acid. In addition, two quantitatively small fractions were observed in the biochemical extracts which were associated with the extracellular acid mucopolysaccharide. Both these fractions stained metachromatically with thiazine dyes and were shown to incorporate radioactive sulphate. In sections metachromatic extracellular material was confined to the tip of the papilla: In this region of high in vivo osmotic pressures the interstitial cells also contained monochromatic granules. The exact nature of these two fractions was not elucidated, nor was an attempt made to identify the intracellular granules with its synthesis or destruction. The results from the morphometry of the kidneys of fourteen species (Table 2/1) showed that desert species have long papillae which contain a limited amount of connective tissue. The metachromatic staining of extracellular acid mucopolysaccharides extends further towards the cortex in those species which can secrete highly concentrated urine. On the other hand, the papillae of animals which habitually produce dilute urine were squat in outline and contained abundant connective tissue. The tip of the papilla in these species was not found to stain set metachromatically. The extent of metachromasia was thus found to be related to the development of high tonicity in vivo, and thus to be most prominent in that part of the papilla where the sodium concentration is greatest in life. It was observed histologically that acid mucopolysaccharide was associated with the lateral spaces between collecting tubule cells in the guinea pig. It had been suggested by Ginetzinsky in 1958 that the material found between these cells in the rat constituted the barrier between fluid in the collecting tubule lumen and the interstitium. He postulated that antidiuretic hormone released hyaluronidase from the apex of the collecting tubule cell and that the enzyme then digested the intercellular cement permitting tubular fluid to equilibrate osmotically with the interstitium. The material between collecting tubule cells the guinea pig was extracted and information about its nature was obtained from its behaviour in electrophoresis and from its staining characteristics. It was found to be a very soluble acid mucopolysaccharide which contained sulphate and PAS positive groups, both of which features distinguish it from hyaluronic acid. The histological technique had thus to be modified to preserve as much as possible of the material in the thin (3 andmu;) wax sections required for the optimal demonstration of this region in the light microscope. The fixative developed to give the most satisfactory retention of acid mucopolysaccharide at the same time as preserving cytological structure reasonably well was as follows:</p> <table> <tr> <td>Formol (40% CHO)</td> <td>100 ml</td> </tr> <tr> <td>Cellosolve</td> <td>225 ml</td> </tr> <tr> <td>Distilled water</td> <td>45 ml</td> </tr> <tr> <td>Aminoacridine hydrochloride</td> <td>1.6 gm.</td> </tr> </table> <p>After fixation the tissue blocks were passed directly into pure cellosolve: Rinsing in aqueous solutions was avoided. Aminoacridine hydrochloride is soluble in cellosolve hence excess precipitant was removed during dehydration without running the risk that acid mucopolysaccharide might be leached out. The blocks were cleared in the usual way and then embedded in ester wax which was found to be superior to paraffin wax for a number of reasons discussed in Chapter 4. Radioactive sulphate was used to trace the synthesis of acid mucopolysaccharide by the collecting tubule cells. After injection of the label, radioactivity was first seen in sections to be associated with PAS positive, amylase resistant granules in the Golgi regions of the collecting tubule cells. After longer intervals radioactivity became associated with granules near the apical and lateral borders of the cells. The Golgi region as demonstrated morphologically (Chapter 3) was always seen to be between the nucleus and apical or lateral borders of the cell and never between the nucleus and the base. Similarly, material which had incorporated radioactive sulphate was never seen to pass across the base of a collecting tubule cell. The reasons for associating the development of an extensive Golgi region with the synthesis of acid mucopolysaccharide by these cells is discussed in connection with the results published by others working with embryonically similar gut cells. It proved possible by autoradiography to identify positively the material in the biochemical extract that had come from the collecting tubule cells. Autoradiography of tissue sections one hour after injection of the label showed that radioactivity was limited to the collecting tubule cells: Similarly only one band in the electrophoretic separation of acid mucopolysaccharides extracted from the papilla after this interval contained radioactivity.

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Fibroblast growth factors (FGFs) regulate a broad spectrum of biological processes and aberrant FGF signalling has been linked to many disorders and diseases. Heparan sulphate (HS) is a highly sulphated glycosaminoglycan, which regulates the activity of its protein ligands, mainly through anionic interactions. The interactions between HS, FGF and FGF receptors (FGFRs) depend on the size and the spatial distribution of the anionic moieties of the saccharides. To test the effects of these on FGF signalling, the activities of well-defined HS oligosaccharides were screened in bioassays. The aim of this thesis was to study the structural determinants which underpin the specificity/selectivity in HS-FGF-FGFR interactions. Two approaches were initially explored to generate suitable saccharides for screening. Firstly, the preparation of libraries of HS oligosaccharides was attempted by enzymatic digestion of porcine mucosal HS using heparinase III. This was followed by the sequential fractionation using size exclusion chromatography, strong anion-exchange and cetyltrimethylammonium strong anion-exchange chromatography. However, with regards to preparing saccharides of sufficient purity and amounts, this was found to be a limiting factor for bioassay screening. Secondly, the dimeric modular synthesis of HS octasaccharides was attempted by means of in-solution multi-step synthesis. The synthesis of a small oligosaccharide library was partially successful and resulted in novel synthetic routes for generation of pentasaccharide precursors, but not sulphated saccharides for screening. An alternative strategy was taken to exploit nineteen existing fully defined chemically and chemoenzymatically prepared oligosaccharides. Screening in bioassays of specific FGF ligands, using BaF3 cells expressing single receptors, showed that both general and specific structural changes, as subtle as a single additional sulphate moiety, significantly impact the ability of saccharides to support FGF signalling in a ligand-receptor complex-dependent manner. The size of the saccharides, the presence/absence of 2-O-, 6-O- and N-sulphate groups were shown to be crucial factors for functional activity. Most notably, the presence of a single 3-O-sulphate group towards the non-reducing end of the saccharides was related to high levels of activation for FGF1-FGFR1c, FGF1-FGFR2b and FGF7-FGFR2b and was demonstrated for the first time. Overall, this thesis provides new evidence concerning structural determinants in HS that modulate FGF signalling, using fully defined saccharides for the first time. The results support the view that significant selectivity is involved, and contribute to a better fundamental understanding of how HS modulates FGF-FGFR-HS complex formation. Ultimately, this information could be relevant for the development of better targeted HS saccharide-based therapeutics.

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