The first three studies in this thesis address the mechanism for the aberrant fall in serum 1,25-dihydroxyvitamin D$ sb3$ (1,25-(OH)$ sb2$D$ sb3 rbrack$ and increase in renal 1,25-(OH)$ sb2$D$ sb3$-24-hydroxylase(24-hydroxylase) activity in X-linked hypophosphatemic mice (Hyp). The 24-hydroxylase is the first enzyme in the C-24 oxidation pathway that degrades the vitamin D hormone to its final inactivation product, calcitroic acid. We demonstrated that: (i) the aberrant increase in 24-hydroxylase activity in Pi-deprived Hyp mice is specific to the kidney and is the result of an increase in enzyme Vmax, immunoreactive protein and mRNA abundance; (ii) the increase in 24-hydroxylase mRNA in both Pi-deprived Hyp mice and 1,25-(0H)$ sb2$D$ sb3$-treated normal littermates can be ascribed to an increase in the transcriptional activity of the 24-hydroxylase gene; (iii) 24-hydroxylase transcripts in normal mice, Pi-deprived Hyp and normal mice and 1,25-(OH)$ sb2$D$ sb3$-treated normal mice are localized to the proximal tubule by in situ hybridization; and (iv) recombinant human growth hormone administration normalizes the aberrant increase in 24-hydroxylase but that this response is not sufficient to correct serum 1,25-(OH)$ sb2$D$ sb3$ levels in Pi-deprived Hyp mice. / The fourth study addresses the mechanism whereby EB 1089, an analogue of 1,25-(OH)$ sb2$D$ sb3,$ is less calcemic than the vitamin D hormone, while being more potent in its antiproliferative action. We demonstrate that: (i) EB 1089 has a 50-fold lower affinity than 1,25-(OH)$ sb2$D$ sb3$ for the vitamin D catabolic enzyme, 24-hydroxylase; and (ii) EB 1089 and 1,25-(OH)$ sb2$D$ sb3$ exhibit tissue-specific differences in vitamin D receptor-mediated responses in vivo that may be ascribed, at least in part, to differences in binding affinities for the vitamin D receptor.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.34441 |
| Date | January 1997 |
| Creators | Roy, Stéphane. |
| Contributors | Tenenhouse, H. S. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Biology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001565587, proquestno: NQ30373, Theses scanned by UMI/ProQuest. |
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